neovim

regexp.c (454742B)

---

// Handling of regular expressions: vim_regcomp(), vim_regexec(), vim_regsub()

// By default: do not create debugging logs or files related to regular
// expressions, even when compiling with -DDEBUG.
// Uncomment the second line to get the regexp debugging.
// #undef REGEXP_DEBUG
// #define REGEXP_DEBUG

#include <assert.h>
#include <ctype.h>
#include <inttypes.h>
#include <limits.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdlib.h>
#include <string.h>
#include <uv.h>

#include "nvim/ascii_defs.h"
#include "nvim/buffer_defs.h"
#include "nvim/charset.h"
#include "nvim/errors.h"
#include "nvim/eval.h"
#include "nvim/eval/typval.h"
#include "nvim/eval/userfunc.h"
#include "nvim/garray.h"
#include "nvim/garray_defs.h"
#include "nvim/gettext_defs.h"
#include "nvim/globals.h"
#include "nvim/keycodes.h"
#include "nvim/macros_defs.h"
#include "nvim/mark.h"
#include "nvim/mark_defs.h"
#include "nvim/mbyte.h"
#include "nvim/mbyte_defs.h"
#include "nvim/memline.h"
#include "nvim/memory.h"
#include "nvim/message.h"
#include "nvim/option_vars.h"
#include "nvim/os/input.h"
#include "nvim/plines.h"
#include "nvim/pos_defs.h"
#include "nvim/profile.h"
#include "nvim/regexp.h"
#include "nvim/regexp_defs.h"
#include "nvim/strings.h"
#include "nvim/types_defs.h"
#include "nvim/vim_defs.h"

typedef enum {
 RGLF_LINE = 0x01,
 RGLF_LENGTH = 0x02,
 RGLF_SUBMATCH = 0x04,
} reg_getline_flags_T;

enum {
 /// In the NFA engine: how many braces are allowed.
 /// TODO(RE): Use dynamic memory allocation instead of static, like here
 NFA_MAX_BRACES = 20,
};

enum {
 /// In the NFA engine: how many states are allowed.
 NFA_MAX_STATES = 100000,
 NFA_TOO_EXPENSIVE = -1,
};

/// Which regexp engine to use? Needed for vim_regcomp().
/// Must match with 'regexpengine'.
enum {
 AUTOMATIC_ENGINE    = 0,
 BACKTRACKING_ENGINE = 1,
 NFA_ENGINE          = 2,
};

/// Structure returned by vim_regcomp() to pass on to vim_regexec().
/// This is the general structure. For the actual matcher, two specific
/// structures are used. See code below.
struct regprog {
 regengine_T *engine;
 unsigned regflags;
 unsigned re_engine;  ///< Automatic, backtracking or NFA engine.
 unsigned re_flags;   ///< Second argument for vim_regcomp().
 bool re_in_use;      ///< prog is being executed
};

/// Structure used by the back track matcher.
/// These fields are only to be used in regexp.c!
/// See regexp.c for an explanation.
typedef struct {
 // These four members implement regprog_T.
 regengine_T *engine;
 unsigned regflags;
 unsigned re_engine;
 unsigned re_flags;
 bool re_in_use;

 int regstart;
 uint8_t reganch;
 uint8_t *regmust;
 int regmlen;
 uint8_t reghasz;
 uint8_t program[];
} bt_regprog_T;

/// Structure representing a NFA state.
/// An NFA state may have no outgoing edge, when it is a NFA_MATCH state.
typedef struct nfa_state nfa_state_T;
struct nfa_state {
 int c;
 nfa_state_T *out;
 nfa_state_T *out1;
 int id;
 int lastlist[2];  ///< 0: normal, 1: recursive
 int val;
};

/// Structure used by the NFA matcher.
typedef struct {
 // These four members implement regprog_T.
 regengine_T *engine;
 unsigned regflags;
 unsigned re_engine;
 unsigned re_flags;
 bool re_in_use;

 nfa_state_T *start;   ///< points into state[]

 int reganch;          ///< pattern starts with ^
 int regstart;         ///< char at start of pattern
 uint8_t *match_text;  ///< plain text to match with

 int has_zend;         ///< pattern contains \ze
 int has_backref;      ///< pattern contains \1 .. \9
 int reghasz;
 char *pattern;
 int nsubexp;          ///< number of ()
 int nstate;
 nfa_state_T state[];
} nfa_regprog_T;

struct regengine {
 /// bt_regcomp or nfa_regcomp
 regprog_T *(*regcomp)(uint8_t *, int);
 /// bt_regfree or nfa_regfree
 void (*regfree)(regprog_T *);
 /// bt_regexec_nl or nfa_regexec_nl
 int (*regexec_nl)(regmatch_T *, uint8_t *, colnr_T, bool);
 /// bt_regexec_mult or nfa_regexec_mult
 int (*regexec_multi)(regmmatch_T *, win_T *, buf_T *, linenr_T, colnr_T, proftime_T *, int *);
#ifdef REGEXP_DEBUG
 uint8_t *expr;
#endif
};

// Structure used to save the current input state, when it needs to be
// restored after trying a match.  Used by reg_save() and reg_restore().
// Also stores the length of "backpos".
typedef struct {
 union {
   uint8_t *ptr;       // rex.input pointer, for single-line regexp
   lpos_T pos;        // rex.input pos, for multi-line regexp
 } rs_u;
 int rs_len;
} regsave_T;

// struct to save start/end pointer/position in for \(\)
typedef struct {
 union {
   uint8_t *ptr;
   lpos_T pos;
 } se_u;
} save_se_T;

// Values for rs_state in regitem_T.
typedef enum regstate_E {
 RS_NOPEN = 0,         // NOPEN and NCLOSE
 RS_MOPEN,             // MOPEN + [0-9]
 RS_MCLOSE,            // MCLOSE + [0-9]
 RS_ZOPEN,             // ZOPEN + [0-9]
 RS_ZCLOSE,            // ZCLOSE + [0-9]
 RS_BRANCH,            // BRANCH
 RS_BRCPLX_MORE,       // BRACE_COMPLEX and trying one more match
 RS_BRCPLX_LONG,       // BRACE_COMPLEX and trying longest match
 RS_BRCPLX_SHORT,      // BRACE_COMPLEX and trying shortest match
 RS_NOMATCH,           // NOMATCH
 RS_BEHIND1,           // BEHIND / NOBEHIND matching rest
 RS_BEHIND2,           // BEHIND / NOBEHIND matching behind part
 RS_STAR_LONG,         // STAR/PLUS/BRACE_SIMPLE longest match
 RS_STAR_SHORT,  // STAR/PLUS/BRACE_SIMPLE shortest match
} regstate_T;

// When there are alternatives a regstate_T is put on the regstack to remember
// what we are doing.
// Before it may be another type of item, depending on rs_state, to remember
// more things.
typedef struct regitem_S {
 regstate_T rs_state;         // what we are doing, one of RS_ above
 int16_t rs_no;            // submatch nr or BEHIND/NOBEHIND
 uint8_t *rs_scan;         // current node in program
 union {
   save_se_T sesave;
   regsave_T regsave;
 } rs_un;                      // room for saving rex.input
} regitem_T;

// used for BEHIND and NOBEHIND matching
typedef struct regbehind_S {
 regsave_T save_after;
 regsave_T save_behind;
 int save_need_clear_subexpr;
 save_se_T save_start[NSUBEXP];
 save_se_T save_end[NSUBEXP];
} regbehind_T;

// Since the out pointers in the list are always
// uninitialized, we use the pointers themselves
// as storage for the Ptrlists.
typedef union Ptrlist Ptrlist;
union Ptrlist {
 Ptrlist *next;
 nfa_state_T *s;
};

struct Frag {
 nfa_state_T *start;
 Ptrlist *out;
};
typedef struct Frag Frag_T;

typedef struct {
 int in_use;       ///< number of subexpr with useful info

 // When REG_MULTI is true list.multi is used, otherwise list.line.
 union {
   struct multipos {
     linenr_T start_lnum;
     linenr_T end_lnum;
     colnr_T start_col;
     colnr_T end_col;
   } multi[NSUBEXP];
   struct linepos {
     uint8_t *start;
     uint8_t *end;
   } line[NSUBEXP];
 } list;
 colnr_T orig_start_col;  // list.multi[0].start_col without \zs
} regsub_T;

typedef struct {
 regsub_T norm;      // \( .. \) matches
 regsub_T synt;      // \z( .. \) matches
} regsubs_T;

// nfa_pim_T stores a Postponed Invisible Match.
typedef struct nfa_pim_S nfa_pim_T;
struct nfa_pim_S {
 int result;                   // NFA_PIM_*, see below
 nfa_state_T *state;           // the invisible match start state
 regsubs_T subs;               // submatch info, only party used
 union {
   lpos_T pos;
   uint8_t *ptr;
 } end;                        // where the match must end
};

// nfa_thread_T contains execution information of a NFA state
typedef struct {
 nfa_state_T *state;
 int count;
 nfa_pim_T pim;                // if pim.result != NFA_PIM_UNUSED: postponed
                               // invisible match
 regsubs_T subs;               // submatch info, only party used
} nfa_thread_T;

// nfa_list_T contains the alternative NFA execution states.
typedef struct {
 nfa_thread_T *t;           ///< allocated array of states
 int n;                        ///< nr of states currently in "t"
 int len;                      ///< max nr of states in "t"
 int id;                       ///< ID of the list
 int has_pim;                  ///< true when any state has a PIM
} nfa_list_T;

#ifdef REGEXP_DEBUG
// show/save debugging data when BT engine is used
# define BT_REGEXP_DUMP
// save the debugging data to a file instead of displaying it
# define BT_REGEXP_LOG
# define BT_REGEXP_DEBUG_LOG
# define BT_REGEXP_DEBUG_LOG_NAME       "bt_regexp_debug.log"
#endif

// Magic characters have a special meaning, they don't match literally.
// Magic characters are negative.  This separates them from literal characters
// (possibly multi-byte).  Only ASCII characters can be Magic.
#define Magic(x)        ((int)(x) - 256)
#define un_Magic(x)     ((x) + 256)
#define is_Magic(x)     ((x) < 0)

typedef void (*fptr_T)(int *, int);

static int no_Magic(int x)
{
 if (is_Magic(x)) {
   return un_Magic(x);
 }
 return x;
}

static int toggle_Magic(int x)
{
 if (is_Magic(x)) {
   return un_Magic(x);
 }
 return Magic(x);
}

// The first byte of the BT regexp internal "program" is actually this magic
// number; the start node begins in the second byte.  It's used to catch the
// most severe mutilation of the program by the caller.
#define REGMAGIC        0234

// Utility definitions.
#define UCHARAT(p)      ((int)(*(uint8_t *)(p)))

// Used for an error (down from) vim_regcomp(): give the error message, set
// rc_did_emsg and return NULL
#define EMSG_RET_NULL(m) return (emsg(m), rc_did_emsg = true, (void *)NULL)
#define IEMSG_RET_NULL(m) return (iemsg(m), rc_did_emsg = true, (void *)NULL)
#define EMSG_RET_FAIL(m) return (emsg(m), rc_did_emsg = true, FAIL)
#define EMSG2_RET_NULL(m, c) \
 return (semsg((m), (c) ? "" : "\\"), rc_did_emsg = true, (void *)NULL)
#define EMSG3_RET_NULL(m, c, a) \
 return (semsg((m), (c) ? "" : "\\", (a)), rc_did_emsg = true, (void *)NULL)
#define EMSG2_RET_FAIL(m, c) \
 return (semsg((m), (c) ? "" : "\\"), rc_did_emsg = true, FAIL)
#define EMSG_ONE_RET_NULL EMSG2_RET_NULL(_(e_invalid_item_in_str_brackets), reg_magic == MAGIC_ALL)

#define MAX_LIMIT       (32767 << 16)

static const char e_invalid_character_after_str_at[]
 = N_("E59: Invalid character after %s@");
static const char e_invalid_use_of_underscore[]
 = N_("E63: Invalid use of \\_");
static const char e_pattern_uses_more_memory_than_maxmempattern[]
 = N_("E363: Pattern uses more memory than 'maxmempattern'");
static const char e_invalid_item_in_str_brackets[]
 = N_("E369: Invalid item in %s%%[]");
static const char e_missing_delimiter_after_search_pattern_str[]
 = N_("E654: Missing delimiter after search pattern: %s");
static const char e_missingbracket[] = N_("E769: Missing ] after %s[");
static const char e_reverse_range[] = N_("E944: Reverse range in character class");
static const char e_large_class[] = N_("E945: Range too large in character class");
static const char e_unmatchedpp[] = N_("E53: Unmatched %s%%(");
static const char e_unmatchedp[] = N_("E54: Unmatched %s(");
static const char e_unmatchedpar[] = N_("E55: Unmatched %s)");
static const char e_z_not_allowed[] = N_("E66: \\z( not allowed here");
static const char e_z1_not_allowed[] = N_("E67: \\z1 - \\z9 not allowed here");
static const char e_missing_sb[] = N_("E69: Missing ] after %s%%[");
static const char e_empty_sb[] = N_("E70: Empty %s%%[]");
static const char e_recursive[] = N_("E956: Cannot use pattern recursively");
static const char e_regexp_number_after_dot_pos_search_chr[]
 = N_("E1204: No Number allowed after .: '\\%%%c'");
static const char e_nfa_regexp_missing_value_in_chr[]
 = N_("E1273: (NFA regexp) missing value in '\\%%%c'");
static const char e_atom_engine_must_be_at_start_of_pattern[]
 = N_("E1281: Atom '\\%%#=%c' must be at the start of the pattern");
static const char e_substitute_nesting_too_deep[] = N_("E1290: substitute nesting too deep");
static const char e_unicode_val_too_large[]
 = N_("E1541: Value too large, max Unicode codepoint is U+10FFFF");

#define NOT_MULTI       0
#define MULTI_ONE       1
#define MULTI_MULT      2

// return values for regmatch()
#define RA_FAIL         1       // something failed, abort
#define RA_CONT         2       // continue in inner loop
#define RA_BREAK        3       // break inner loop
#define RA_MATCH        4       // successful match
#define RA_NOMATCH      5       // didn't match

/// Return NOT_MULTI if c is not a "multi" operator.
/// Return MULTI_ONE if c is a single "multi" operator.
/// Return MULTI_MULT if c is a multi "multi" operator.
static int re_multi_type(int c)
{
 if (c == Magic('@') || c == Magic('=') || c == Magic('?')) {
   return MULTI_ONE;
 }
 if (c == Magic('*') || c == Magic('+') || c == Magic('{')) {
   return MULTI_MULT;
 }
 return NOT_MULTI;
}

static char *reg_prev_sub = NULL;
static size_t reg_prev_sublen = 0;

// REGEXP_INRANGE contains all characters which are always special in a []
// range after '\'.
// REGEXP_ABBR contains all characters which act as abbreviations after '\'.
// These are:
//  \n  - New line (NL).
//  \r  - Carriage Return (CR).
//  \t  - Tab (TAB).
//  \e  - Escape (ESC).
//  \b  - Backspace (Ctrl_H).
//  \d  - Character code in decimal, eg \d123
//  \o  - Character code in octal, eg \o80
//  \x  - Character code in hex, eg \x4a
//  \u  - Multibyte character code, eg \u20ac
//  \U  - Long multibyte character code, eg \U12345678
static char REGEXP_INRANGE[] = "]^-n\\";
static char REGEXP_ABBR[] = "nrtebdoxuU";

// Translate '\x' to its control character, except "\n", which is Magic.
static int backslash_trans(int c)
{
 switch (c) {
 case 'r':
   return CAR;
 case 't':
   return TAB;
 case 'e':
   return ESC;
 case 'b':
   return BS;
 }
 return c;
}

enum {
 CLASS_ALNUM = 0,
 CLASS_ALPHA,
 CLASS_BLANK,
 CLASS_CNTRL,
 CLASS_DIGIT,
 CLASS_GRAPH,
 CLASS_LOWER,
 CLASS_PRINT,
 CLASS_PUNCT,
 CLASS_SPACE,
 CLASS_UPPER,
 CLASS_XDIGIT,
 CLASS_TAB,
 CLASS_RETURN,
 CLASS_BACKSPACE,
 CLASS_ESCAPE,
 CLASS_IDENT,
 CLASS_KEYWORD,
 CLASS_FNAME,
 CLASS_NONE = 99,
};

/// Check for a character class name "[:name:]".  "pp" points to the '['.
/// Returns one of the CLASS_ items. CLASS_NONE means that no item was
/// recognized.  Otherwise "pp" is advanced to after the item.
static int get_char_class(char **pp)
{
 // must be sorted by the 'value' field because it is used by bsearch()!
 static keyvalue_T char_class_tab[] = {
   KEYVALUE_ENTRY(CLASS_ALNUM, "alnum:]"),
   KEYVALUE_ENTRY(CLASS_ALPHA, "alpha:]"),
   KEYVALUE_ENTRY(CLASS_BACKSPACE, "backspace:]"),
   KEYVALUE_ENTRY(CLASS_BLANK, "blank:]"),
   KEYVALUE_ENTRY(CLASS_CNTRL, "cntrl:]"),
   KEYVALUE_ENTRY(CLASS_DIGIT, "digit:]"),
   KEYVALUE_ENTRY(CLASS_ESCAPE, "escape:]"),
   KEYVALUE_ENTRY(CLASS_FNAME, "fname:]"),
   KEYVALUE_ENTRY(CLASS_GRAPH, "graph:]"),
   KEYVALUE_ENTRY(CLASS_IDENT, "ident:]"),
   KEYVALUE_ENTRY(CLASS_KEYWORD, "keyword:]"),
   KEYVALUE_ENTRY(CLASS_LOWER, "lower:]"),
   KEYVALUE_ENTRY(CLASS_PRINT, "print:]"),
   KEYVALUE_ENTRY(CLASS_PUNCT, "punct:]"),
   KEYVALUE_ENTRY(CLASS_RETURN, "return:]"),
   KEYVALUE_ENTRY(CLASS_SPACE, "space:]"),
   KEYVALUE_ENTRY(CLASS_TAB, "tab:]"),
   KEYVALUE_ENTRY(CLASS_UPPER, "upper:]"),
   KEYVALUE_ENTRY(CLASS_XDIGIT, "xdigit:]")
 };

 // check that the value of "pp" has a chance of matching
 if ((*pp)[1] == ':' && ASCII_ISLOWER((*pp)[2])
     && ASCII_ISLOWER((*pp)[3]) && ASCII_ISLOWER((*pp)[4])) {
   // this function can be called repeatedly with the same value for "pp"
   // so we cache the last found entry.
   static keyvalue_T *last_entry = NULL;

   keyvalue_T target = {
     .key = 0,
     .value = *pp + 2,
     .length = 0,  // not used, see cmp_keyvalue_value_n()
   };

   keyvalue_T *entry;
   if (last_entry != NULL && cmp_keyvalue_value_n(&target, last_entry) == 0) {
     entry = last_entry;
   } else {
     entry = (keyvalue_T *)bsearch(&target, &char_class_tab,
                                   ARRAY_SIZE(char_class_tab),
                                   sizeof(char_class_tab[0]), cmp_keyvalue_value_n);
   }
   if (entry != NULL) {
     last_entry = entry;
     *pp += entry->length + 2;
     return entry->key;
   }
 }
 return CLASS_NONE;
}

// Specific version of character class functions.
// Using a table to keep this fast.
static int16_t class_tab[256];

#define     RI_DIGIT    0x01
#define     RI_HEX      0x02
#define     RI_OCTAL    0x04
#define     RI_WORD     0x08
#define     RI_HEAD     0x10
#define     RI_ALPHA    0x20
#define     RI_LOWER    0x40
#define     RI_UPPER    0x80
#define     RI_WHITE    0x100

static void init_class_tab(void)
{
 int i;
 static int done = false;

 if (done) {
   return;
 }

 for (i = 0; i < 256; i++) {
   if (i >= '0' && i <= '7') {
     class_tab[i] = RI_DIGIT + RI_HEX + RI_OCTAL + RI_WORD;
   } else if (i >= '8' && i <= '9') {
     class_tab[i] = RI_DIGIT + RI_HEX + RI_WORD;
   } else if (i >= 'a' && i <= 'f') {
     class_tab[i] = RI_HEX + RI_WORD + RI_HEAD + RI_ALPHA + RI_LOWER;
   } else if (i >= 'g' && i <= 'z') {
     class_tab[i] = RI_WORD + RI_HEAD + RI_ALPHA + RI_LOWER;
   } else if (i >= 'A' && i <= 'F') {
     class_tab[i] = RI_HEX + RI_WORD + RI_HEAD + RI_ALPHA + RI_UPPER;
   } else if (i >= 'G' && i <= 'Z') {
     class_tab[i] = RI_WORD + RI_HEAD + RI_ALPHA + RI_UPPER;
   } else if (i == '_') {
     class_tab[i] = RI_WORD + RI_HEAD;
   } else {
     class_tab[i] = 0;
   }
 }
 class_tab[' '] |= RI_WHITE;
 class_tab['\t'] |= RI_WHITE;
 done = true;
}

#define ri_digit(c)    ((c) < 0x100 && (class_tab[c] & RI_DIGIT))
#define ri_hex(c)      ((c) < 0x100 && (class_tab[c] & RI_HEX))
#define ri_octal(c)    ((c) < 0x100 && (class_tab[c] & RI_OCTAL))
#define ri_word(c)     ((c) < 0x100 && (class_tab[c] & RI_WORD))
#define ri_head(c)     ((c) < 0x100 && (class_tab[c] & RI_HEAD))
#define ri_alpha(c)    ((c) < 0x100 && (class_tab[c] & RI_ALPHA))
#define ri_lower(c)    ((c) < 0x100 && (class_tab[c] & RI_LOWER))
#define ri_upper(c)    ((c) < 0x100 && (class_tab[c] & RI_UPPER))
#define ri_white(c)    ((c) < 0x100 && (class_tab[c] & RI_WHITE))

// flags for regflags
#define RF_ICASE    1   // ignore case
#define RF_NOICASE  2   // don't ignore case
#define RF_HASNL    4   // can match a NL
#define RF_ICOMBINE 8   // ignore combining characters
#define RF_LOOKBH   16  // uses "\@<=" or "\@<!"

// Global work variables for vim_regcomp().

static char *regparse;          ///< Input-scan pointer.
static int regnpar;             ///< () count.
static bool wants_nfa;          ///< regex should use NFA engine
static int regnzpar;            ///< \z() count.
static int re_has_z;            ///< \z item detected
static unsigned regflags;       ///< RF_ flags for prog
static int had_eol;             ///< true when EOL found by vim_regcomp()

static magic_T reg_magic;       ///< magicness of the pattern

static int reg_string;          // matching with a string instead of a buffer
                               // line
static int reg_strict;          // "[abc" is illegal

// META contains all characters that may be magic, except '^' and '$'.

// uncrustify:off

// META[] is used often enough to justify turning it into a table.
static uint8_t META_flags[] = {
   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
//                 %  &     (  )  *  +        .
   0, 0, 0, 0, 0, 1, 1, 0, 1, 1, 1, 1, 0, 0, 1, 0,
//     1  2  3  4  5  6  7  8  9        <  =  >  ?
   0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1,
//  @  A     C  D     F     H  I     K  L  M     O
   1, 1, 0, 1, 1, 0, 1, 0, 1, 1, 0, 1, 1, 1, 0, 1,
//  P        S     U  V  W  X     Z  [           _
   1, 0, 0, 1, 0, 1, 1, 1, 1, 0, 1, 1, 0, 0, 0, 1,
//     a     c  d     f     h  i     k  l  m  n  o
   0, 1, 0, 1, 1, 0, 1, 0, 1, 1, 0, 1, 1, 1, 1, 1,
//  p        s     u  v  w  x     z  {  |     ~
   1, 0, 0, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1
};

// uncrustify:on

static int curchr;              // currently parsed character
// Previous character.  Note: prevchr is sometimes -1 when we are not at the
// start, eg in /[ ^I]^ the pattern was never found even if it existed,
// because ^ was taken to be magic -- webb
static int prevchr;
static int prevprevchr;         // previous-previous character
static int nextchr;             // used for ungetchr()

// arguments for reg()
#define REG_NOPAREN     0       // toplevel reg()
#define REG_PAREN       1       // \(\)
#define REG_ZPAREN      2       // \z(\)
#define REG_NPAREN      3       // \%(\)

typedef struct {
 char *regparse;
 int prevchr_len;
 int curchr;
 int prevchr;
 int prevprevchr;
 int nextchr;
 int at_start;
 int prev_at_start;
 int regnpar;
} parse_state_T;

static regengine_T bt_regengine;
static regengine_T nfa_regengine;

#include "regexp.c.generated.h"

// Return true if compiled regular expression "prog" can match a line break.
int re_multiline(const regprog_T *prog)
 FUNC_ATTR_NONNULL_ALL
{
 return prog->regflags & RF_HASNL;
}

// Check for an equivalence class name "[=a=]".  "pp" points to the '['.
// Returns a character representing the class. Zero means that no item was
// recognized.  Otherwise "pp" is advanced to after the item.
static int get_equi_class(char **pp)
{
 int c;
 int l = 1;
 char *p = *pp;

 if (p[1] == '=' && p[2] != NUL) {
   l = utfc_ptr2len(p + 2);
   if (p[l + 2] == '=' && p[l + 3] == ']') {
     c = utf_ptr2char(p + 2);
     *pp += l + 4;
     return c;
   }
 }
 return 0;
}

// Check for a collating element "[.a.]".  "pp" points to the '['.
// Returns a character. Zero means that no item was recognized.  Otherwise
// "pp" is advanced to after the item.
// Currently only single characters are recognized!
static int get_coll_element(char **pp)
{
 int c;
 int l = 1;
 char *p = *pp;

 if (p[0] != NUL && p[1] == '.' && p[2] != NUL) {
   l = utfc_ptr2len(p + 2);
   if (p[l + 2] == '.' && p[l + 3] == ']') {
     c = utf_ptr2char(p + 2);
     *pp += l + 4;
     return c;
   }
 }
 return 0;
}

static int reg_cpo_lit;  // 'cpoptions' contains 'l' flag

static void get_cpo_flags(void)
{
 reg_cpo_lit = vim_strchr(p_cpo, CPO_LITERAL) != NULL;
}

/// Skip over a "[]" range.
/// "p" must point to the character after the '['.
/// The returned pointer is on the matching ']', or the terminating NUL.
static char *skip_anyof(char *p)
{
 int l;

 if (*p == '^') {  // Complement of range.
   p++;
 }
 if (*p == ']' || *p == '-') {
   p++;
 }
 while (*p != NUL && *p != ']') {
   if ((l = utfc_ptr2len(p)) > 1) {
     p += l;
   } else if (*p == '-') {
     p++;
     if (*p != ']' && *p != NUL) {
       MB_PTR_ADV(p);
     }
   } else if (*p == '\\'
              && (vim_strchr(REGEXP_INRANGE, (uint8_t)p[1]) != NULL
                  || (!reg_cpo_lit
                      && vim_strchr(REGEXP_ABBR, (uint8_t)p[1]) != NULL))) {
     p += 2;
   } else if (*p == '[') {
     if (get_char_class(&p) == CLASS_NONE
         && get_equi_class(&p) == 0
         && get_coll_element(&p) == 0
         && *p != NUL) {
       p++;          // It is not a class name and not NUL
     }
   } else {
     p++;
   }
 }

 return p;
}

/// Skip past regular expression.
/// Stop at end of "startp" or where "delim" is found ('/', '?', etc).
/// Take care of characters with a backslash in front of it.
/// Skip strings inside [ and ].
char *skip_regexp(char *startp, int delim, int magic)
{
 return skip_regexp_ex(startp, delim, magic, NULL, NULL, NULL);
}

/// Call skip_regexp() and when the delimiter does not match give an error and
/// return NULL.
char *skip_regexp_err(char *startp, int delim, int magic)
{
 char *p = skip_regexp(startp, delim, magic);

 if (*p != delim) {
   semsg(_(e_missing_delimiter_after_search_pattern_str), startp);
   return NULL;
 }
 return p;
}

/// skip_regexp() with extra arguments:
/// When "newp" is not NULL and "dirc" is '?', make an allocated copy of the
/// expression and change "\?" to "?".  If "*newp" is not NULL the expression
/// is changed in-place.
/// If a "\?" is changed to "?" then "dropped" is incremented, unless NULL.
/// If "magic_val" is not NULL, returns the effective magicness of the pattern
char *skip_regexp_ex(char *startp, int dirc, int magic, char **newp, int *dropped,
                    magic_T *magic_val)
{
 magic_T mymagic;
 char *p = startp;
 size_t startplen = 0;

 if (magic) {
   mymagic = MAGIC_ON;
 } else {
   mymagic = MAGIC_OFF;
 }
 get_cpo_flags();

 for (; p[0] != NUL; MB_PTR_ADV(p)) {
   if (p[0] == dirc) {         // found end of regexp
     break;
   }
   if ((p[0] == '[' && mymagic >= MAGIC_ON)
       || (p[0] == '\\' && p[1] == '[' && mymagic <= MAGIC_OFF)) {
     p = skip_anyof(p + 1);
     if (p[0] == NUL) {
       break;
     }
   } else if (p[0] == '\\' && p[1] != NUL) {
     if (dirc == '?' && newp != NULL && p[1] == '?') {
       // change "\?" to "?", make a copy first.
       if (startplen == 0) {
         startplen = strlen(startp);
       }
       if (*newp == NULL) {
         *newp = xstrnsave(startp, startplen);
         p = *newp + (p - startp);
         startp = *newp;
       }
       if (dropped != NULL) {
         (*dropped)++;
       }
       memmove(p, p + 1, startplen - (size_t)((p + 1) - startp) + 1);
     } else {
       p++;            // skip next character
     }
     if (*p == 'v') {
       mymagic = MAGIC_ALL;
     } else if (*p == 'V') {
       mymagic = MAGIC_NONE;
     }
   }
 }
 if (magic_val != NULL) {
   *magic_val = mymagic;
 }
 return p;
}

// variables used for parsing
static int prevchr_len;    // byte length of previous char
static int at_start;       // True when on the first character
static int prev_at_start;  // True when on the second character

// Start parsing at "str".
static void initchr(char *str)
{
 regparse = str;
 prevchr_len = 0;
 curchr = prevprevchr = prevchr = nextchr = -1;
 at_start = true;
 prev_at_start = false;
}

// Save the current parse state, so that it can be restored and parsing
// starts in the same state again.
static void save_parse_state(parse_state_T *ps)
{
 ps->regparse = regparse;
 ps->prevchr_len = prevchr_len;
 ps->curchr = curchr;
 ps->prevchr = prevchr;
 ps->prevprevchr = prevprevchr;
 ps->nextchr = nextchr;
 ps->at_start = at_start;
 ps->prev_at_start = prev_at_start;
 ps->regnpar = regnpar;
}

// Restore a previously saved parse state.
static void restore_parse_state(parse_state_T *ps)
{
 regparse = ps->regparse;
 prevchr_len = ps->prevchr_len;
 curchr = ps->curchr;
 prevchr = ps->prevchr;
 prevprevchr = ps->prevprevchr;
 nextchr = ps->nextchr;
 at_start = ps->at_start;
 prev_at_start = ps->prev_at_start;
 regnpar = ps->regnpar;
}

// Get the next character without advancing.
static int peekchr(void)
{
 static int after_slash = false;

 if (curchr != -1) {
   return curchr;
 }

 switch (curchr = (uint8_t)regparse[0]) {
 case '.':
 case '[':
 case '~':
   // magic when 'magic' is on
   if (reg_magic >= MAGIC_ON) {
     curchr = Magic(curchr);
   }
   break;
 case '(':
 case ')':
 case '{':
 case '%':
 case '+':
 case '=':
 case '?':
 case '@':
 case '!':
 case '&':
 case '|':
 case '<':
 case '>':
 case '#':           // future ext.
 case '"':           // future ext.
 case '\'':          // future ext.
 case ',':           // future ext.
 case '-':           // future ext.
 case ':':           // future ext.
 case ';':           // future ext.
 case '`':           // future ext.
 case '/':           // Can't be used in / command
   // magic only after "\v"
   if (reg_magic == MAGIC_ALL) {
     curchr = Magic(curchr);
   }
   break;
 case '*':
   // * is not magic as the very first character, eg "?*ptr", when
   // after '^', eg "/^*ptr" and when after "\(", "\|", "\&".  But
   // "\(\*" is not magic, thus must be magic if "after_slash"
   if (reg_magic >= MAGIC_ON
       && !at_start
       && !(prev_at_start && prevchr == Magic('^'))
       && (after_slash
           || (prevchr != Magic('(')
               && prevchr != Magic('&')
               && prevchr != Magic('|')))) {
     curchr = Magic('*');
   }
   break;
 case '^':
   // '^' is only magic as the very first character and if it's after
   // "\(", "\|", "\&' or "\n"
   if (reg_magic >= MAGIC_OFF
       && (at_start
           || reg_magic == MAGIC_ALL
           || prevchr == Magic('(')
           || prevchr == Magic('|')
           || prevchr == Magic('&')
           || prevchr == Magic('n')
           || (no_Magic(prevchr) == '('
               && prevprevchr == Magic('%')))) {
     curchr = Magic('^');
     at_start = true;
     prev_at_start = false;
   }
   break;
 case '$':
   // '$' is only magic as the very last char and if it's in front of
   // either "\|", "\)", "\&", or "\n"
   if (reg_magic >= MAGIC_OFF) {
     uint8_t *p = (uint8_t *)regparse + 1;
     bool is_magic_all = (reg_magic == MAGIC_ALL);

     // ignore \c \C \m \M \v \V and \Z after '$'
     while (p[0] == '\\' && (p[1] == 'c' || p[1] == 'C'
                             || p[1] == 'm' || p[1] == 'M'
                             || p[1] == 'v' || p[1] == 'V'
                             || p[1] == 'Z')) {
       if (p[1] == 'v') {
         is_magic_all = true;
       } else if (p[1] == 'm' || p[1] == 'M' || p[1] == 'V') {
         is_magic_all = false;
       }
       p += 2;
     }
     if (p[0] == NUL
         || (p[0] == '\\'
             && (p[1] == '|' || p[1] == '&' || p[1] == ')'
                 || p[1] == 'n'))
         || (is_magic_all
             && (p[0] == '|' || p[0] == '&' || p[0] == ')'))
         || reg_magic == MAGIC_ALL) {
       curchr = Magic('$');
     }
   }
   break;
 case '\\': {
   int c = (uint8_t)regparse[1];

   if (c == NUL) {
     curchr = '\\';  // trailing '\'
   } else if (c <= '~' && META_flags[c]) {
     // META contains everything that may be magic sometimes,
     // except ^ and $ ("\^" and "\$" are only magic after
     // "\V").  We now fetch the next character and toggle its
     // magicness.  Therefore, \ is so meta-magic that it is
     // not in META.
     curchr = -1;
     prev_at_start = at_start;
     at_start = false;  // be able to say "/\*ptr"
     regparse++;
     after_slash++;
     (void)peekchr();
     regparse--;
     after_slash--;
     curchr = toggle_Magic(curchr);
   } else if (vim_strchr(REGEXP_ABBR, c)) {
     // Handle abbreviations, like "\t" for TAB -- webb
     curchr = backslash_trans(c);
   } else if (reg_magic == MAGIC_NONE && (c == '$' || c == '^')) {
     curchr = toggle_Magic(c);
   } else {
     // Next character can never be (made) magic?
     // Then backslashing it won't do anything.
     curchr = utf_ptr2char(regparse + 1);
   }
   break;
 }

 default:
   curchr = utf_ptr2char(regparse);
 }

 return curchr;
}

// Eat one lexed character.  Do this in a way that we can undo it.
static void skipchr(void)
{
 // peekchr() eats a backslash, do the same here
 if (*regparse == '\\') {
   prevchr_len = 1;
 } else {
   prevchr_len = 0;
 }
 if (regparse[prevchr_len] != NUL) {
   // Exclude composing chars that utfc_ptr2len does include.
   prevchr_len += utf_ptr2len(regparse + prevchr_len);
 }
 regparse += prevchr_len;
 prev_at_start = at_start;
 at_start = false;
 prevprevchr = prevchr;
 prevchr = curchr;
 curchr = nextchr;         // use previously unget char, or -1
 nextchr = -1;
}

// Skip a character while keeping the value of prev_at_start for at_start.
// prevchr and prevprevchr are also kept.
static void skipchr_keepstart(void)
{
 int as = prev_at_start;
 int pr = prevchr;
 int prpr = prevprevchr;

 skipchr();
 at_start = as;
 prevchr = pr;
 prevprevchr = prpr;
}

// Get the next character from the pattern. We know about magic and such, so
// therefore we need a lexical analyzer.
static int getchr(void)
{
 int chr = peekchr();

 skipchr();
 return chr;
}

// put character back.  Works only once!
static void ungetchr(void)
{
 nextchr = curchr;
 curchr = prevchr;
 prevchr = prevprevchr;
 at_start = prev_at_start;
 prev_at_start = false;

 // Backup regparse, so that it's at the same position as before the
 // getchr().
 regparse -= prevchr_len;
}

// Get and return the value of the hex string at the current position.
// Return -1 if there is no valid hex number.
// The position is updated:
//     blahblah\%x20asdf
//         before-^ ^-after
// The parameter controls the maximum number of input characters. This will be
// 2 when reading a \%x20 sequence and 4 when reading a \%u20AC sequence.
static int64_t gethexchrs(int maxinputlen)
{
 int64_t nr = 0;
 int c;
 int i;

 for (i = 0; i < maxinputlen; i++) {
   c = (uint8_t)regparse[0];
   if (!ascii_isxdigit(c)) {
     break;
   }
   nr <<= 4;
   nr |= hex2nr(c);
   regparse++;
 }

 if (i == 0) {
   return -1;
 }
 return nr;
}

// Get and return the value of the decimal string immediately after the
// current position. Return -1 for invalid.  Consumes all digits.
static int64_t getdecchrs(void)
{
 int64_t nr = 0;
 int c;
 int i;

 for (i = 0;; i++) {
   c = (uint8_t)regparse[0];
   if (c < '0' || c > '9') {
     break;
   }
   nr *= 10;
   nr += c - '0';
   regparse++;
   curchr = -1;     // no longer valid
 }

 if (i == 0) {
   return -1;
 }
 return nr;
}

// get and return the value of the octal string immediately after the current
// position. Return -1 for invalid, or 0-255 for valid. Smart enough to handle
// numbers > 377 correctly (for example, 400 is treated as 40) and doesn't
// treat 8 or 9 as recognised characters. Position is updated:
//     blahblah\%o210asdf
//         before-^  ^-after
static int64_t getoctchrs(void)
{
 int64_t nr = 0;
 int c;
 int i;

 for (i = 0; i < 3 && nr < 040; i++) {
   c = (uint8_t)regparse[0];
   if (c < '0' || c > '7') {
     break;
   }
   nr <<= 3;
   nr |= hex2nr(c);
   regparse++;
 }

 if (i == 0) {
   return -1;
 }
 return nr;
}

// read_limits - Read two integers to be taken as a minimum and maximum.
// If the first character is '-', then the range is reversed.
// Should end with 'end'.  If minval is missing, zero is default, if maxval is
// missing, a very big number is the default.
static int read_limits(int *minval, int *maxval)
{
 int reverse = false;
 char *first_char;
 int tmp;

 if (*regparse == '-') {
   // Starts with '-', so reverse the range later.
   regparse++;
   reverse = true;
 }
 first_char = regparse;
 *minval = getdigits_int(&regparse, false, 0);
 if (*regparse == ',') {           // There is a comma.
   if (ascii_isdigit(*++regparse)) {
     *maxval = getdigits_int(&regparse, false, MAX_LIMIT);
   } else {
     *maxval = MAX_LIMIT;
   }
 } else if (ascii_isdigit(*first_char)) {
   *maxval = *minval;              // It was \{n} or \{-n}
 } else {
   *maxval = MAX_LIMIT;            // It was \{} or \{-}
 }
 if (*regparse == '\\') {
   regparse++;         // Allow either \{...} or \{...\}
 }
 if (*regparse != '}') {
   EMSG2_RET_FAIL(_("E554: Syntax error in %s{...}"), reg_magic == MAGIC_ALL);
 }

 // Reverse the range if there was a '-', or make sure it is in the right
 // order otherwise.
 if ((!reverse && *minval > *maxval) || (reverse && *minval < *maxval)) {
   tmp = *minval;
   *minval = *maxval;
   *maxval = tmp;
 }
 skipchr();            // let's be friends with the lexer again
 return OK;
}

// vim_regexec and friends

// Global work variables for vim_regexec().

// Sometimes need to save a copy of a line.  Since alloc()/free() is very
// slow, we keep one allocated piece of memory and only re-allocate it when
// it's too small.  It's freed in bt_regexec_both() when finished.
static uint8_t *reg_tofree = NULL;
static unsigned reg_tofreelen;

// Structure used to store the execution state of the regex engine.
// Which ones are set depends on whether a single-line or multi-line match is
// done:
//                      single-line             multi-line
// reg_match            &regmatch_T             NULL
// reg_mmatch           NULL                    &regmmatch_T
// reg_startp           reg_match->startp       <invalid>
// reg_endp             reg_match->endp         <invalid>
// reg_startpos         <invalid>               reg_mmatch->startpos
// reg_endpos           <invalid>               reg_mmatch->endpos
// reg_win              NULL                    window in which to search
// reg_buf              curbuf                  buffer in which to search
// reg_firstlnum        <invalid>               first line in which to search
// reg_maxline          0                       last line nr
// reg_line_lbr         false or true           false
typedef struct {
 regmatch_T *reg_match;
 regmmatch_T *reg_mmatch;

 uint8_t **reg_startp;
 uint8_t **reg_endp;
 lpos_T *reg_startpos;
 lpos_T *reg_endpos;

 win_T *reg_win;
 buf_T *reg_buf;
 linenr_T reg_firstlnum;
 linenr_T reg_maxline;
 bool reg_line_lbr;  // "\n" in string is line break

 // The current match-position is remembered with these variables:
 linenr_T lnum;  ///< line number, relative to first line
 uint8_t *line;   ///< start of current line
 uint8_t *input;  ///< current input, points into "line"

 int need_clear_subexpr;   ///< subexpressions still need to be cleared
 int need_clear_zsubexpr;  ///< extmatch subexpressions still need to be
                           ///< cleared

 // Internal copy of 'ignorecase'.  It is set at each call to vim_regexec().
 // Normally it gets the value of "rm_ic" or "rmm_ic", but when the pattern
 // contains '\c' or '\C' the value is overruled.
 bool reg_ic;

 // Similar to "reg_ic", but only for 'combining' characters.  Set with \Z
 // flag in the regexp.  Defaults to false, always.
 bool reg_icombine;

 bool reg_nobreak;

 // Copy of "rmm_maxcol": maximum column to search for a match.  Zero when
 // there is no maximum.
 colnr_T reg_maxcol;

 // State for the NFA engine regexec.
 int nfa_has_zend;     ///< NFA regexp \ze operator encountered.
 int nfa_has_backref;  ///< NFA regexp \1 .. \9 encountered.
 int nfa_nsubexpr;     ///< Number of sub expressions actually being used
                       ///< during execution. 1 if only the whole match
                       ///< (subexpr 0) is used.
 // listid is global, so that it increases on recursive calls to
 // nfa_regmatch(), which means we don't have to clear the lastlist field of
 // all the states.
 int nfa_listid;
 int nfa_alt_listid;

 int nfa_has_zsubexpr;  ///< NFA regexp has \z( ), set zsubexpr.
} regexec_T;

static regexec_T rex;
static bool rex_in_use = false;

static void reg_breakcheck(void)
{
 if (!rex.reg_nobreak) {
   fast_breakcheck();
 }
}

// Return true if character 'c' is included in 'iskeyword' option for
// "reg_buf" buffer.
static bool reg_iswordc(int c)
{
 return vim_iswordc_buf(c, rex.reg_buf);
}

static bool can_f_submatch = false;  ///< true when submatch() can be used

/// These pointers are used for reg_submatch().  Needed for when the
/// substitution string is an expression that contains a call to substitute()
/// and submatch().
typedef struct {
 regmatch_T *sm_match;
 regmmatch_T *sm_mmatch;
 linenr_T sm_firstlnum;
 linenr_T sm_maxline;
 int sm_line_lbr;
} regsubmatch_T;

static regsubmatch_T rsm;  ///< can only be used when can_f_submatch is true

/// Common code for reg_getline(), reg_getline_len(), reg_getline_submatch() and
/// reg_getline_submatch_len().
///
/// @param flags  a bitmask that controls what info is to be returned
///               and whether or not submatch is in effect.
static void reg_getline_common(linenr_T lnum, reg_getline_flags_T flags, char **line,
                              colnr_T *length)
{
 bool get_line = flags & RGLF_LINE;
 bool get_length = flags & RGLF_LENGTH;
 linenr_T firstlnum;
 linenr_T maxline;

 if (flags & RGLF_SUBMATCH) {
   firstlnum = rsm.sm_firstlnum + lnum;
   maxline = rsm.sm_maxline;
 } else {
   firstlnum = rex.reg_firstlnum + lnum;
   maxline = rex.reg_maxline;
 }

 // when looking behind for a match/no-match lnum is negative. but we
 // can't go before line 1.
 if (firstlnum < 1) {
   if (get_line) {
     *line = NULL;
   }
   if (get_length) {
     *length = 0;
   }

   return;
 }

 if (lnum > maxline) {
   // must have matched the "\n" in the last line.
   if (get_line) {
     *line = "";
   }
   if (get_length) {
     *length = 0;
   }

   return;
 }

 if (get_line) {
   *line = ml_get_buf(rex.reg_buf, firstlnum);
 }
 if (get_length) {
   *length = ml_get_buf_len(rex.reg_buf, firstlnum);
 }
}

/// Get pointer to the line "lnum", which is relative to "reg_firstlnum".
static char *reg_getline(linenr_T lnum)
{
 char *line;
 reg_getline_common(lnum, RGLF_LINE, &line, NULL);
 return line;
}

/// Get length of line "lnum", which is relative to "reg_firstlnum".
static colnr_T reg_getline_len(linenr_T lnum)
{
 colnr_T length;
 reg_getline_common(lnum, RGLF_LENGTH, NULL, &length);
 return length;
}

static uint8_t *reg_startzp[NSUBEXP];  // Workspace to mark beginning
static uint8_t *reg_endzp[NSUBEXP];    //   and end of \z(...\) matches
static lpos_T reg_startzpos[NSUBEXP];   // idem, beginning pos
static lpos_T reg_endzpos[NSUBEXP];     // idem, end pos

// true if using multi-line regexp.
#define REG_MULTI       (rex.reg_match == NULL)

// Create a new extmatch and mark it as referenced once.
static reg_extmatch_T *make_extmatch(void)
 FUNC_ATTR_NONNULL_RET
{
 reg_extmatch_T *em = xcalloc(1, sizeof(reg_extmatch_T));
 em->refcnt = 1;
 return em;
}

// Add a reference to an extmatch.
reg_extmatch_T *ref_extmatch(reg_extmatch_T *em)
{
 if (em != NULL) {
   em->refcnt++;
 }
 return em;
}

// Remove a reference to an extmatch.  If there are no references left, free
// the info.
void unref_extmatch(reg_extmatch_T *em)
{
 int i;

 if (em != NULL && --em->refcnt <= 0) {
   for (i = 0; i < NSUBEXP; i++) {
     xfree(em->matches[i]);
   }
   xfree(em);
 }
}

// Get class of previous character.
static int reg_prev_class(void)
{
 if (rex.input > rex.line) {
   return mb_get_class_tab((char *)rex.input - 1 -
                           utf_head_off((char *)rex.line, (char *)rex.input - 1),
                           rex.reg_buf->b_chartab);
 }
 return -1;
}

// Return true if the current rex.input position matches the Visual area.
static bool reg_match_visual(void)
{
 pos_T top, bot;
 linenr_T lnum;
 colnr_T col;
 win_T *wp = rex.reg_win == NULL ? curwin : rex.reg_win;
 int mode;
 colnr_T start, end;
 colnr_T start2, end2;
 colnr_T curswant;

 // Check if the buffer is the current buffer and not using a string.
 if (rex.reg_buf != curbuf || VIsual.lnum == 0 || !REG_MULTI) {
   return false;
 }

 if (VIsual_active) {
   if (lt(VIsual, wp->w_cursor)) {
     top = VIsual;
     bot = wp->w_cursor;
   } else {
     top = wp->w_cursor;
     bot = VIsual;
   }
   mode = VIsual_mode;
   curswant = wp->w_curswant;
 } else {
   if (lt(curbuf->b_visual.vi_start, curbuf->b_visual.vi_end)) {
     top = curbuf->b_visual.vi_start;
     bot = curbuf->b_visual.vi_end;
   } else {
     top = curbuf->b_visual.vi_end;
     bot = curbuf->b_visual.vi_start;
   }
   // a substitute command may have removed some lines
   if (bot.lnum > curbuf->b_ml.ml_line_count) {
     bot.lnum = curbuf->b_ml.ml_line_count;
   }
   mode = curbuf->b_visual.vi_mode;
   curswant = curbuf->b_visual.vi_curswant;
 }
 lnum = rex.lnum + rex.reg_firstlnum;
 if (lnum < top.lnum || lnum > bot.lnum) {
   return false;
 }

 col = (colnr_T)(rex.input - rex.line);
 if (mode == 'v') {
   if ((lnum == top.lnum && col < top.col)
       || (lnum == bot.lnum && col >= bot.col + (*p_sel != 'e'))) {
     return false;
   }
 } else if (mode == Ctrl_V) {
   getvvcol(wp, &top, &start, NULL, &end);
   getvvcol(wp, &bot, &start2, NULL, &end2);
   if (start2 < start) {
     start = start2;
   }
   if (end2 > end) {
     end = end2;
   }
   if (top.col == MAXCOL || bot.col == MAXCOL || curswant == MAXCOL) {
     end = MAXCOL;
   }

   // getvvcol() flushes rex.line, need to get it again
   rex.line = (uint8_t *)reg_getline(rex.lnum);
   rex.input = rex.line + col;

   colnr_T cols = win_linetabsize(wp, rex.reg_firstlnum + rex.lnum, (char *)rex.line, col);
   if (cols < start || cols > end - (*p_sel == 'e')) {
     return false;
   }
 }
 return true;
}

// Check the regexp program for its magic number.
// Return true if it's wrong.
static int prog_magic_wrong(void)
{
 regprog_T *prog;

 prog = REG_MULTI ? rex.reg_mmatch->regprog : rex.reg_match->regprog;
 if (prog->engine == &nfa_regengine) {
   // For NFA matcher we don't check the magic
   return false;
 }

 if (UCHARAT(((bt_regprog_T *)prog)->program) != REGMAGIC) {
   emsg(_(e_re_corr));
   return true;
 }
 return false;
}

// Cleanup the subexpressions, if this wasn't done yet.
// This construction is used to clear the subexpressions only when they are
// used (to increase speed).
static void cleanup_subexpr(void)
{
 if (!rex.need_clear_subexpr) {
   return;
 }

 if (REG_MULTI) {
   // Use 0xff to set lnum to -1
   memset(rex.reg_startpos, 0xff, sizeof(lpos_T) * NSUBEXP);
   memset(rex.reg_endpos, 0xff, sizeof(lpos_T) * NSUBEXP);
 } else {
   memset(rex.reg_startp, 0, sizeof(char *) * NSUBEXP);
   memset(rex.reg_endp, 0, sizeof(char *) * NSUBEXP);
 }
 rex.need_clear_subexpr = false;
}

static void cleanup_zsubexpr(void)
{
 if (!rex.need_clear_zsubexpr) {
   return;
 }

 if (REG_MULTI) {
   // Use 0xff to set lnum to -1
   memset(reg_startzpos, 0xff, sizeof(lpos_T) * NSUBEXP);
   memset(reg_endzpos, 0xff, sizeof(lpos_T) * NSUBEXP);
 } else {
   memset(reg_startzp, 0, sizeof(char *) * NSUBEXP);
   memset(reg_endzp, 0, sizeof(char *) * NSUBEXP);
 }
 rex.need_clear_zsubexpr = false;
}

// Advance rex.lnum, rex.line and rex.input to the next line.
static void reg_nextline(void)
{
 rex.line = (uint8_t *)reg_getline(++rex.lnum);
 rex.input = rex.line;
 reg_breakcheck();
}

// Check whether a backreference matches.
// Returns RA_FAIL, RA_NOMATCH or RA_MATCH.
// If "bytelen" is not NULL, it is set to the byte length of the match in the
// last line.
// Optional: ignore case if rex.reg_ic is set.
static int match_with_backref(linenr_T start_lnum, colnr_T start_col, linenr_T end_lnum,
                             colnr_T end_col, int *bytelen)
{
 linenr_T clnum = start_lnum;
 colnr_T ccol = start_col;
 int len;
 char *p;

 if (bytelen != NULL) {
   *bytelen = 0;
 }
 while (true) {
   // Since getting one line may invalidate the other, need to make copy.
   // Slow!
   if (rex.line != reg_tofree) {
     len = (int)strlen((char *)rex.line);
     if (reg_tofree == NULL || len >= (int)reg_tofreelen) {
       len += 50;              // get some extra
       xfree(reg_tofree);
       reg_tofree = xmalloc((size_t)len);
       reg_tofreelen = (unsigned)len;
     }
     STRCPY(reg_tofree, rex.line);
     rex.input = reg_tofree + (rex.input - rex.line);
     rex.line = reg_tofree;
   }

   // Get the line to compare with.
   p = reg_getline(clnum);
   assert(p);

   if (clnum == end_lnum) {
     len = end_col - ccol;
   } else {
     len = reg_getline_len(clnum) - ccol;
   }

   if ((!rex.reg_ic && cstrncmp(p + ccol, (char *)rex.input, &len) != 0)
       || (rex.reg_ic && mb_strnicmp(p + ccol, (char *)rex.input, (size_t)len) != 0)) {
     return RA_NOMATCH;  // doesn't match
   }
   if (bytelen != NULL) {
     *bytelen += len;
   }
   if (clnum == end_lnum) {
     break;  // match and at end!
   }
   if (rex.lnum >= rex.reg_maxline) {
     return RA_NOMATCH;  // text too short
   }

   // Advance to next line.
   reg_nextline();
   if (bytelen != NULL) {
     *bytelen = 0;
   }
   clnum++;
   ccol = 0;
   if (got_int) {
     return RA_FAIL;
   }
 }

 // found a match!  Note that rex.line may now point to a copy of the line,
 // that should not matter.
 return RA_MATCH;
}

/// Used in a place where no * or \+ can follow.
static bool re_mult_next(char *what)
{
 if (re_multi_type(peekchr()) == MULTI_MULT) {
   semsg(_("E888: (NFA regexp) cannot repeat %s"), what);
   rc_did_emsg = true;
   return false;
 }
 return true;
}

typedef struct {
 int a, b, c;
} decomp_T;

// 0xfb20 - 0xfb4f
static decomp_T decomp_table[0xfb4f - 0xfb20 + 1] = {
 { 0x5e2, 0, 0 },          // 0xfb20       alt ayin
 { 0x5d0, 0, 0 },          // 0xfb21       alt alef
 { 0x5d3, 0, 0 },          // 0xfb22       alt dalet
 { 0x5d4, 0, 0 },          // 0xfb23       alt he
 { 0x5db, 0, 0 },          // 0xfb24       alt kaf
 { 0x5dc, 0, 0 },          // 0xfb25       alt lamed
 { 0x5dd, 0, 0 },          // 0xfb26       alt mem-sofit
 { 0x5e8, 0, 0 },          // 0xfb27       alt resh
 { 0x5ea, 0, 0 },          // 0xfb28       alt tav
 { '+', 0, 0 },            // 0xfb29       alt plus
 { 0x5e9, 0x5c1, 0 },      // 0xfb2a       shin+shin-dot
 { 0x5e9, 0x5c2, 0 },      // 0xfb2b       shin+sin-dot
 { 0x5e9, 0x5c1, 0x5bc },  // 0xfb2c       shin+shin-dot+dagesh
 { 0x5e9, 0x5c2, 0x5bc },  // 0xfb2d       shin+sin-dot+dagesh
 { 0x5d0, 0x5b7, 0 },      // 0xfb2e       alef+patah
 { 0x5d0, 0x5b8, 0 },      // 0xfb2f       alef+qamats
 { 0x5d0, 0x5b4, 0 },      // 0xfb30       alef+hiriq
 { 0x5d1, 0x5bc, 0 },      // 0xfb31       bet+dagesh
 { 0x5d2, 0x5bc, 0 },      // 0xfb32       gimel+dagesh
 { 0x5d3, 0x5bc, 0 },      // 0xfb33       dalet+dagesh
 { 0x5d4, 0x5bc, 0 },      // 0xfb34       he+dagesh
 { 0x5d5, 0x5bc, 0 },      // 0xfb35       vav+dagesh
 { 0x5d6, 0x5bc, 0 },      // 0xfb36       zayin+dagesh
 { 0xfb37, 0, 0 },         // 0xfb37 -- UNUSED
 { 0x5d8, 0x5bc, 0 },      // 0xfb38       tet+dagesh
 { 0x5d9, 0x5bc, 0 },      // 0xfb39       yud+dagesh
 { 0x5da, 0x5bc, 0 },      // 0xfb3a       kaf sofit+dagesh
 { 0x5db, 0x5bc, 0 },      // 0xfb3b       kaf+dagesh
 { 0x5dc, 0x5bc, 0 },      // 0xfb3c       lamed+dagesh
 { 0xfb3d, 0, 0 },         // 0xfb3d -- UNUSED
 { 0x5de, 0x5bc, 0 },      // 0xfb3e       mem+dagesh
 { 0xfb3f, 0, 0 },         // 0xfb3f -- UNUSED
 { 0x5e0, 0x5bc, 0 },      // 0xfb40       nun+dagesh
 { 0x5e1, 0x5bc, 0 },      // 0xfb41       samech+dagesh
 { 0xfb42, 0, 0 },         // 0xfb42 -- UNUSED
 { 0x5e3, 0x5bc, 0 },      // 0xfb43       pe sofit+dagesh
 { 0x5e4, 0x5bc, 0 },      // 0xfb44       pe+dagesh
 { 0xfb45, 0, 0 },         // 0xfb45 -- UNUSED
 { 0x5e6, 0x5bc, 0 },      // 0xfb46       tsadi+dagesh
 { 0x5e7, 0x5bc, 0 },      // 0xfb47       qof+dagesh
 { 0x5e8, 0x5bc, 0 },      // 0xfb48       resh+dagesh
 { 0x5e9, 0x5bc, 0 },      // 0xfb49       shin+dagesh
 { 0x5ea, 0x5bc, 0 },      // 0xfb4a       tav+dagesh
 { 0x5d5, 0x5b9, 0 },      // 0xfb4b       vav+holam
 { 0x5d1, 0x5bf, 0 },      // 0xfb4c       bet+rafe
 { 0x5db, 0x5bf, 0 },      // 0xfb4d       kaf+rafe
 { 0x5e4, 0x5bf, 0 },      // 0xfb4e       pe+rafe
 { 0x5d0, 0x5dc, 0 }       // 0xfb4f       alef-lamed
};

static void mb_decompose(int c, int *c1, int *c2, int *c3)
{
 decomp_T d;

 if (c >= 0xfb20 && c <= 0xfb4f) {
   d = decomp_table[c - 0xfb20];
   *c1 = d.a;
   *c2 = d.b;
   *c3 = d.c;
 } else {
   *c1 = c;
   *c2 = 0;
   *c3 = 0;
 }
}

/// Compare two strings, ignore case if rex.reg_ic set.
/// Return 0 if strings match, non-zero otherwise.
/// Correct the length "*n" when composing characters are ignored
/// or when both utf codepoints are considered equal because of
/// case-folding but have different length (e.g. 's' and 'ſ')
static int cstrncmp(char *s1, char *s2, int *n)
{
 int result;

 if (!rex.reg_ic) {
   result = strncmp(s1, s2, (size_t)(*n));
 } else {
   char *p = s1;
   int n2 = 0;
   int n1 = *n;
   // count the number of characters for byte-length of s1
   while (n1 > 0 && *p != NUL) {
     n1 -= utfc_ptr2len(s1);
     MB_PTR_ADV(p);
     n2++;
   }
   // count the number of bytes to advance the same number of chars for s2
   p = s2;
   while (n2-- > 0 && *p != NUL) {
     MB_PTR_ADV(p);
   }

   n2 = (int)(p - s2);

   result = utf_strnicmp(s1, s2, (size_t)(*n), (size_t)n2);
   if (result == 0 && n2 < *n) {
     *n = n2;
   }
 }

 // if it failed and it's utf8 and we want to combineignore:
 if (result != 0 && rex.reg_icombine) {
   const char *str1, *str2;
   int c1, c2, c11, c12;
   int junk;

   // we have to handle the strcmp ourselves, since it is necessary to
   // deal with the composing characters by ignoring them:
   str1 = s1;
   str2 = s2;
   c1 = c2 = 0;
   while ((int)(str1 - s1) < *n) {
     c1 = mb_ptr2char_adv(&str1);
     c2 = mb_ptr2char_adv(&str2);

     // decompose the character if necessary, into 'base' characters
     // because I don't care about Arabic, I will hard-code the Hebrew
     // which I *do* care about!  So sue me...
     if (c1 != c2 && (!rex.reg_ic || utf_fold(c1) != utf_fold(c2))) {
       // decomposition necessary?
       mb_decompose(c1, &c11, &junk, &junk);
       mb_decompose(c2, &c12, &junk, &junk);
       c1 = c11;
       c2 = c12;
       if (c11 != c12 && (!rex.reg_ic || utf_fold(c11) != utf_fold(c12))) {
         break;
       }
     }
   }
   result = c2 - c1;
   if (result == 0) {
     *n = (int)(str2 - s2);
   }
 }

 return result;
}

/// Wrapper around strchr which accounts for case-insensitive searches and
/// non-ASCII characters.
///
/// This function is used a lot for simple searches, keep it fast!
///
/// @param  s  string to search
/// @param  c  character to find in @a s
///
/// @return  NULL if no match, otherwise pointer to the position in @a s
static inline char *cstrchr(const char *const s, const int c)
 FUNC_ATTR_PURE FUNC_ATTR_WARN_UNUSED_RESULT FUNC_ATTR_NONNULL_ALL
 FUNC_ATTR_ALWAYS_INLINE
{
 if (!rex.reg_ic) {
   return vim_strchr(s, c);
 }

 int cc, lc;
 if (c > 0x80) {
   cc = utf_fold(c);
   lc = cc;
 } else if (ASCII_ISUPPER(c)) {
   cc = TOLOWER_ASC(c);
   lc = cc;
 } else if (ASCII_ISLOWER(c)) {
   cc = TOUPPER_ASC(c);
   lc = c;
 } else {
   return vim_strchr(s, c);
 }

 for (const char *p = s; *p != NUL; p += utfc_ptr2len(p)) {
   const int uc = utf_ptr2char(p);
   if (c > 0x80 || uc > 0x80) {
     // Do not match an illegal byte.  E.g. 0xff matches 0xc3 0xbf, not 0xff.
     // Compare with lower case of the character.
     if ((uc < 0x80 || uc != (uint8_t)(*p)) && utf_fold(uc) == lc) {
       return (char *)p;
     }
   } else if ((uint8_t)(*p) == c || (uint8_t)(*p) == cc) {
     return (char *)p;
   }
 }

 return NULL;
}

////////////////////////////////////////////////////////////////
//                    regsub stuff                            //
////////////////////////////////////////////////////////////////

static void do_upper(int *d, int c)
{
 *d = mb_toupper(c);
}

static void do_lower(int *d, int c)
{
 *d = mb_tolower(c);
}

/// regtilde(): Replace tildes in the pattern by the old pattern.
///
/// Short explanation of the tilde: It stands for the previous replacement
/// pattern.  If that previous pattern also contains a ~ we should go back a
/// step further...  But we insert the previous pattern into the current one
/// and remember that.
/// This still does not handle the case where "magic" changes.  So require the
/// user to keep his hands off of "magic".
///
/// The tildes are parsed once before the first call to vim_regsub().
char *regtilde(char *source, int magic, bool preview)
{
 char *newsub = source;
 size_t newsublen = 0;
 char tilde[3] = { '~', NUL, NUL };
 size_t tildelen = 1;
 bool error = false;

 if (!magic) {
   tilde[0] = '\\';
   tilde[1] = '~';
   tilde[2] = NUL;
   tildelen = 2;
 }

 char *p;
 for (p = newsub; *p; p++) {
   if (strncmp(p, tilde, tildelen) == 0) {
     size_t prefixlen = (size_t)(p - newsub);  // not including the tilde
     char *postfix = p + tildelen;
     size_t postfixlen;
     size_t tmpsublen;

     if (newsublen == 0) {
       newsublen = strlen(newsub);
     }
     newsublen -= tildelen;
     postfixlen = newsublen - prefixlen;
     tmpsublen = prefixlen + reg_prev_sublen + postfixlen;

     if (tmpsublen > 0 && reg_prev_sub != NULL) {
       // Avoid making the text longer than MAXCOL, it will cause
       // trouble at some point.
       if (tmpsublen > MAXCOL) {
         emsg(_(e_resulting_text_too_long));
         error = true;
         break;
       }

       char *tmpsub = xmalloc(tmpsublen + 1);
       // copy prefix
       memmove(tmpsub, newsub, prefixlen);
       // interpret tilde
       memmove(tmpsub + prefixlen, reg_prev_sub, reg_prev_sublen);
       // copy postfix
       STRCPY(tmpsub + prefixlen + reg_prev_sublen, postfix);

       if (newsub != source) {  // allocated newsub before
         xfree(newsub);
       }
       newsub = tmpsub;
       newsublen = tmpsublen;
       p = newsub + prefixlen + reg_prev_sublen;
     } else {
       memmove(p, postfix, postfixlen + 1);  // remove the tilde (+1 for the NUL)
     }
     p--;
   } else {
     if (*p == '\\' && p[1]) {  // skip escaped characters
       p++;
     }
     p += utfc_ptr2len(p) - 1;
   }
 }

 if (error) {
   if (newsub != source) {
     xfree(newsub);
   }
   return source;
 }

 // Only change reg_prev_sub when not previewing.
 if (!preview) {
   // Store a copy of newsub  in reg_prev_sub.  It is always allocated,
   // because recursive calls may make the returned string invalid.
   // Only store it if there something to store.
   newsublen = (size_t)(p - newsub);
   if (newsublen == 0) {
     XFREE_CLEAR(reg_prev_sub);
   } else {
     xfree(reg_prev_sub);
     reg_prev_sub = xstrnsave(newsub, newsublen);
   }
   reg_prev_sublen = newsublen;
 }

 return newsub;
}

/// Put the submatches in "argv[argskip]" which is a list passed into
/// call_func() by vim_regsub_both().
static int fill_submatch_list(int argc FUNC_ATTR_UNUSED, typval_T *argv, int argskip, ufunc_T *fp)
 FUNC_ATTR_NONNULL_ALL
{
 typval_T *listarg = argv + argskip;

 if (!fp->uf_varargs && fp->uf_args.ga_len <= argskip) {
   // called function doesn't take a submatches argument
   return argskip;
 }

 // Relies on sl_list to be the first item in staticList10_T.
 tv_list_init_static10((staticList10_T *)listarg->vval.v_list);

 // There are always 10 list items in staticList10_T.
 listitem_T *li = tv_list_first(listarg->vval.v_list);
 for (int i = 0; i < 10; i++) {
   char *s = rsm.sm_match->startp[i];
   if (s == NULL || rsm.sm_match->endp[i] == NULL) {
     s = NULL;
   } else {
     s = xstrnsave(s, (size_t)(rsm.sm_match->endp[i] - s));
   }
   TV_LIST_ITEM_TV(li)->v_type = VAR_STRING;
   TV_LIST_ITEM_TV(li)->vval.v_string = s;
   li = TV_LIST_ITEM_NEXT(argv->vval.v_list, li);
 }
 return argskip + 1;
}

static void clear_submatch_list(staticList10_T *sl)
{
 TV_LIST_ITER(&sl->sl_list, li, {
   xfree(TV_LIST_ITEM_TV(li)->vval.v_string);
 });
}

/// vim_regsub() - perform substitutions after a vim_regexec() or
/// vim_regexec_multi() match.
///
/// If "flags" has REGSUB_COPY really copy into "dest[destlen]".
/// Otherwise nothing is copied, only compute the length of the result.
///
/// If "flags" has REGSUB_MAGIC then behave like 'magic' is set.
///
/// If "flags" has REGSUB_BACKSLASH a backslash will be removed later, need to
/// double them to keep them, and insert a backslash before a CR to avoid it
/// being replaced with a line break later.
///
/// Note: The matched text must not change between the call of
/// vim_regexec()/vim_regexec_multi() and vim_regsub()!  It would make the back
/// references invalid!
///
/// Returns the size of the replacement, including terminating NUL.
int vim_regsub(regmatch_T *rmp, char *source, typval_T *expr, char *dest, int destlen, int flags)
{
 regexec_T rex_save;
 bool rex_in_use_save = rex_in_use;

 if (rex_in_use) {
   // Being called recursively, save the state.
   rex_save = rex;
 }
 rex_in_use = true;

 rex.reg_match = rmp;
 rex.reg_mmatch = NULL;
 rex.reg_maxline = 0;
 rex.reg_buf = curbuf;
 rex.reg_line_lbr = true;
 int result = vim_regsub_both(source, expr, dest, destlen, flags);

 rex_in_use = rex_in_use_save;
 if (rex_in_use) {
   rex = rex_save;
 }

 return result;
}

int vim_regsub_multi(regmmatch_T *rmp, linenr_T lnum, char *source, char *dest, int destlen,
                    int flags)
{
 regexec_T rex_save;
 bool rex_in_use_save = rex_in_use;

 if (rex_in_use) {
   // Being called recursively, save the state.
   rex_save = rex;
 }
 rex_in_use = true;

 rex.reg_match = NULL;
 rex.reg_mmatch = rmp;
 rex.reg_buf = curbuf;  // always works on the current buffer!
 rex.reg_firstlnum = lnum;
 rex.reg_maxline = curbuf->b_ml.ml_line_count - lnum;
 rex.reg_line_lbr = false;
 int result = vim_regsub_both(source, NULL, dest, destlen, flags);

 rex_in_use = rex_in_use_save;
 if (rex_in_use) {
   rex = rex_save;
 }

 return result;
}

// When nesting more than a couple levels it's probably a mistake.
#define MAX_REGSUB_NESTING 4
static char *eval_result[MAX_REGSUB_NESTING] = { NULL, NULL, NULL, NULL };

#if defined(EXITFREE)
void free_resub_eval_result(void)
{
 for (int i = 0; i < MAX_REGSUB_NESTING; i++) {
   XFREE_CLEAR(eval_result[i]);
 }
}
#endif

static int vim_regsub_both(char *source, typval_T *expr, char *dest, int destlen, int flags)
{
 char *src;
 char *dst;
 char *s;
 int c;
 int cc;
 int no = -1;
 fptr_T func_all = (fptr_T)NULL;
 fptr_T func_one = (fptr_T)NULL;
 linenr_T clnum = 0;           // init for GCC
 int len = 0;                  // init for GCC
 static int nesting = 0;
 bool copy = flags & REGSUB_COPY;

 // Be paranoid...
 if ((source == NULL && expr == NULL) || dest == NULL) {
   emsg(_(e_null));
   return 0;
 }
 if (prog_magic_wrong()) {
   return 0;
 }
 if (nesting == MAX_REGSUB_NESTING) {
   emsg(_(e_substitute_nesting_too_deep));
   return 0;
 }
 int nested = nesting;
 src = source;
 dst = dest;

 // When the substitute part starts with "\=" evaluate it as an expression.
 if (expr != NULL || (source[0] == '\\' && source[1] == '=')) {
   // To make sure that the length doesn't change between checking the
   // length and copying the string, and to speed up things, the
   // resulting string is saved from the call with
   // "flags & REGSUB_COPY" == 0 to the call with
   // "flags & REGSUB_COPY" != 0.
   if (copy) {
     if (eval_result[nested] != NULL) {
       size_t eval_len = strlen(eval_result[nested]);
       if (eval_len < (size_t)destlen) {
         STRCPY(dest, eval_result[nested]);
         dst += eval_len;
         XFREE_CLEAR(eval_result[nested]);
       }
     }
   } else {
     const bool prev_can_f_submatch = can_f_submatch;
     regsubmatch_T rsm_save;

     XFREE_CLEAR(eval_result[nested]);

     // The expression may contain substitute(), which calls us
     // recursively.  Make sure submatch() gets the text from the first
     // level.
     if (can_f_submatch) {
       rsm_save = rsm;
     }
     can_f_submatch = true;
     rsm.sm_match = rex.reg_match;
     rsm.sm_mmatch = rex.reg_mmatch;
     rsm.sm_firstlnum = rex.reg_firstlnum;
     rsm.sm_maxline = rex.reg_maxline;
     rsm.sm_line_lbr = rex.reg_line_lbr;

     // Although unlikely, it is possible that the expression invokes a
     // substitute command (it might fail, but still).  Therefore keep
     // an array of eval results.
     nesting++;

     if (expr != NULL) {
       typval_T argv[2];
       typval_T rettv;
       staticList10_T matchList = TV_LIST_STATIC10_INIT;
       rettv.v_type = VAR_STRING;
       rettv.vval.v_string = NULL;
       argv[0].v_type = VAR_LIST;
       argv[0].vval.v_list = &matchList.sl_list;
       funcexe_T funcexe = FUNCEXE_INIT;
       funcexe.fe_argv_func = fill_submatch_list;
       funcexe.fe_evaluate = true;
       if (expr->v_type == VAR_FUNC) {
         s = expr->vval.v_string;
         call_func(s, -1, &rettv, 1, argv, &funcexe);
       } else if (expr->v_type == VAR_PARTIAL) {
         partial_T *partial = expr->vval.v_partial;

         s = partial_name(partial);
         funcexe.fe_partial = partial;
         call_func(s, -1, &rettv, 1, argv, &funcexe);
       }
       if (tv_list_len(&matchList.sl_list) > 0) {
         // fill_submatch_list() was called.
         clear_submatch_list(&matchList);
       }
       if (rettv.v_type == VAR_UNKNOWN) {
         // something failed, no need to report another error
         eval_result[nested] = NULL;
       } else {
         char buf[NUMBUFLEN];
         eval_result[nested] = (char *)tv_get_string_buf_chk(&rettv, buf);
         if (eval_result[nested] != NULL) {
           eval_result[nested] = xstrdup(eval_result[nested]);
         }
       }
       tv_clear(&rettv);
     } else {
       eval_result[nested] = eval_to_string(source + 2, true, false);
     }
     nesting--;

     if (eval_result[nested] != NULL) {
       int had_backslash = false;

       for (s = eval_result[nested]; *s != NUL; MB_PTR_ADV(s)) {
         // Change NL to CR, so that it becomes a line break,
         // unless called from vim_regexec_nl().
         // Skip over a backslashed character.
         if (*s == NL && !rsm.sm_line_lbr) {
           *s = CAR;
         } else if (*s == '\\' && s[1] != NUL) {
           s++;
           // Change NL to CR here too, so that this works:
           // :s/abc\\\ndef/\="aaa\\\nbbb"/  on text:
           //   abc{backslash}
           //   def
           // Not when called from vim_regexec_nl().
           if (*s == NL && !rsm.sm_line_lbr) {
             *s = CAR;
           }
           had_backslash = true;
         }
       }
       if (had_backslash && (flags & REGSUB_BACKSLASH)) {
         // Backslashes will be consumed, need to double them.
         s = vim_strsave_escaped(eval_result[nested], "\\");
         xfree(eval_result[nested]);
         eval_result[nested] = s;
       }

       dst += strlen(eval_result[nested]);
     }

     can_f_submatch = prev_can_f_submatch;
     if (can_f_submatch) {
       rsm = rsm_save;
     }
   }
 } else {
   while ((c = (uint8_t)(*src++)) != NUL) {
     if (c == '&' && (flags & REGSUB_MAGIC)) {
       no = 0;
     } else if (c == '\\' && *src != NUL) {
       if (*src == '&' && !(flags & REGSUB_MAGIC)) {
         src++;
         no = 0;
       } else if ('0' <= *src && *src <= '9') {
         no = *src++ - '0';
       } else if (vim_strchr("uUlLeE", (uint8_t)(*src))) {
         switch (*src++) {
         case 'u':
           func_one = do_upper;
           continue;
         case 'U':
           func_all = do_upper;
           continue;
         case 'l':
           func_one = do_lower;
           continue;
         case 'L':
           func_all = do_lower;
           continue;
         case 'e':
         case 'E':
           func_one = func_all = (fptr_T)NULL;
           continue;
         }
       }
     }
     if (no < 0) {           // Ordinary character.
       if (c == K_SPECIAL && src[0] != NUL && src[1] != NUL) {
         // Copy a special key as-is.
         if (copy) {
           if (dst + 3 > dest + destlen) {
             iemsg("vim_regsub_both(): not enough space");
             return 0;
           }
           *dst++ = (char)c;
           *dst++ = *src++;
           *dst++ = *src++;
         } else {
           dst += 3;
           src += 2;
         }
         continue;
       }

       if (c == '\\' && *src != NUL) {
         // Check for abbreviations -- webb
         switch (*src) {
         case 'r':
           c = CAR;        ++src;  break;
         case 'n':
           c = NL;         ++src;  break;
         case 't':
           c = TAB;        ++src;  break;
         // Oh no!  \e already has meaning in subst pat :-(
         // case 'e':   c = ESC;        ++src;  break;
         case 'b':
           c = Ctrl_H;     ++src;  break;

         // If "backslash" is true the backslash will be removed
         // later.  Used to insert a literal CR.
         default:
           if (flags & REGSUB_BACKSLASH) {
             if (copy) {
               if (dst + 1 > dest + destlen) {
                 iemsg("vim_regsub_both(): not enough space");
                 return 0;
               }
               *dst = '\\';
             }
             dst++;
           }
           c = (uint8_t)(*src++);
         }
       } else {
         c = utf_ptr2char(src - 1);
       }

       // Write to buffer, if copy is set.
       if (func_one != NULL) {
         func_one(&cc, c);
         func_one = NULL;
       } else if (func_all != NULL) {
         func_all(&cc, c);
       } else {
         // just copy
         cc = c;
       }

       int totlen = utfc_ptr2len(src - 1);
       int charlen = utf_char2len(cc);

       if (copy) {
         if (dst + charlen > dest + destlen) {
           iemsg("vim_regsub_both(): not enough space");
           return 0;
         }
         utf_char2bytes(cc, dst);
       }
       dst += charlen - 1;
       int clen = utf_ptr2len(src - 1);

       // If the character length is shorter than "totlen", there
       // are composing characters; copy them as-is.
       if (clen < totlen) {
         if (copy) {
           if (dst + totlen - clen > dest + destlen) {
             iemsg("vim_regsub_both(): not enough space");
             return 0;
           }
           memmove(dst + 1, src - 1 + clen, (size_t)(totlen - clen));
         }
         dst += totlen - clen;
       }
       src += totlen - 1;
       dst++;
     } else {
       if (REG_MULTI) {
         clnum = rex.reg_mmatch->startpos[no].lnum;
         if (clnum < 0 || rex.reg_mmatch->endpos[no].lnum < 0) {
           s = NULL;
         } else {
           s = reg_getline(clnum) + rex.reg_mmatch->startpos[no].col;
           if (rex.reg_mmatch->endpos[no].lnum == clnum) {
             len = rex.reg_mmatch->endpos[no].col
                   - rex.reg_mmatch->startpos[no].col;
           } else {
             len = reg_getline_len(clnum) - rex.reg_mmatch->startpos[no].col;
           }
         }
       } else {
         s = rex.reg_match->startp[no];
         if (rex.reg_match->endp[no] == NULL) {
           s = NULL;
         } else {
           len = (int)(rex.reg_match->endp[no] - s);
         }
       }
       if (s != NULL) {
         while (true) {
           if (len == 0) {
             if (REG_MULTI) {
               if (rex.reg_mmatch->endpos[no].lnum == clnum) {
                 break;
               }
               if (copy) {
                 if (dst + 1 > dest + destlen) {
                   iemsg("vim_regsub_both(): not enough space");
                   return 0;
                 }
                 *dst = CAR;
               }
               dst++;
               s = reg_getline(++clnum);
               if (rex.reg_mmatch->endpos[no].lnum == clnum) {
                 len = rex.reg_mmatch->endpos[no].col;
               } else {
                 len = reg_getline_len(clnum);
               }
             } else {
               break;
             }
           } else if (*s == NUL) {  // we hit NUL.
             if (copy) {
               iemsg(_(e_re_damg));
             }
             goto exit;
           } else {
             if ((flags & REGSUB_BACKSLASH) && (*s == CAR || *s == '\\')) {
               // Insert a backslash in front of a CR, otherwise
               // it will be replaced by a line break.
               // Number of backslashes will be halved later,
               // double them here.
               if (copy) {
                 if (dst + 2 > dest + destlen) {
                   iemsg("vim_regsub_both(): not enough space");
                   return 0;
                 }
                 dst[0] = '\\';
                 dst[1] = *s;
               }
               dst += 2;
             } else {
               c = utf_ptr2char(s);

               if (func_one != (fptr_T)NULL) {
                 func_one(&cc, c);
                 func_one = NULL;
               } else if (func_all != (fptr_T)NULL) {
                 func_all(&cc, c);
               } else {  // just copy
                 cc = c;
               }

               {
                 int l;
                 int charlen;

                 // Copy composing characters separately, one
                 // at a time.
                 l = utf_ptr2len(s) - 1;

                 s += l;
                 len -= l;
                 charlen = utf_char2len(cc);
                 if (copy) {
                   if (dst + charlen > dest + destlen) {
                     iemsg("vim_regsub_both(): not enough space");
                     return 0;
                   }
                   utf_char2bytes(cc, dst);
                 }
                 dst += charlen - 1;
               }
               dst++;
             }

             s++;
             len--;
           }
         }
       }
       no = -1;
     }
   }
 }
 if (copy) {
   *dst = NUL;
 }

exit:
 return (int)((dst - dest) + 1);
}

static char *reg_getline_submatch(linenr_T lnum)
{
 char *line;
 reg_getline_common(lnum, RGLF_LINE | RGLF_SUBMATCH, &line, NULL);
 return line;
}

static colnr_T reg_getline_submatch_len(linenr_T lnum)
{
 colnr_T length;
 reg_getline_common(lnum, RGLF_LENGTH | RGLF_SUBMATCH, NULL, &length);
 return length;
}

/// Used for the submatch() function: get the string from the n'th submatch in
/// allocated memory.
///
/// @return  NULL when not in a ":s" command and for a non-existing submatch.
char *reg_submatch(int no)
{
 char *retval = NULL;
 char *s;
 int round;
 linenr_T lnum;

 if (!can_f_submatch || no < 0) {
   return NULL;
 }

 if (rsm.sm_match == NULL) {
   ssize_t len;

   // First round: compute the length and allocate memory.
   // Second round: copy the text.
   for (round = 1; round <= 2; round++) {
     lnum = rsm.sm_mmatch->startpos[no].lnum;
     if (lnum < 0 || rsm.sm_mmatch->endpos[no].lnum < 0) {
       return NULL;
     }

     s = reg_getline_submatch(lnum);
     if (s == NULL) {  // anti-crash check, cannot happen?
       break;
     }
     s += rsm.sm_mmatch->startpos[no].col;
     if (rsm.sm_mmatch->endpos[no].lnum == lnum) {
       // Within one line: take form start to end col.
       len = rsm.sm_mmatch->endpos[no].col - rsm.sm_mmatch->startpos[no].col;
       if (round == 2) {
         xmemcpyz(retval, s, (size_t)len);
       }
       len++;
     } else {
       // Multiple lines: take start line from start col, middle
       // lines completely and end line up to end col.
       len = reg_getline_submatch_len(lnum) - rsm.sm_mmatch->startpos[no].col;
       if (round == 2) {
         STRCPY(retval, s);
         retval[len] = '\n';
       }
       len++;
       lnum++;
       while (lnum < rsm.sm_mmatch->endpos[no].lnum) {
         s = reg_getline_submatch(lnum);
         if (round == 2) {
           STRCPY(retval + len, s);
         }
         len += reg_getline_submatch_len(lnum);
         if (round == 2) {
           retval[len] = '\n';
         }
         len++;
         lnum++;
       }
       if (round == 2) {
         strncpy(retval + len,  // NOLINT(runtime/printf)
                 reg_getline_submatch(lnum),
                 (size_t)rsm.sm_mmatch->endpos[no].col);
       }
       len += rsm.sm_mmatch->endpos[no].col;
       if (round == 2) {
         retval[len] = NUL;
       }
       len++;
     }

     if (retval == NULL) {
       retval = xmalloc((size_t)len);
     }
   }
 } else {
   s = rsm.sm_match->startp[no];
   if (s == NULL || rsm.sm_match->endp[no] == NULL) {
     retval = NULL;
   } else {
     retval = xstrnsave(s, (size_t)(rsm.sm_match->endp[no] - s));
   }
 }

 return retval;
}

// Used for the submatch() function with the optional non-zero argument: get
// the list of strings from the n'th submatch in allocated memory with NULs
// represented in NLs.
// Returns a list of allocated strings.  Returns NULL when not in a ":s"
// command, for a non-existing submatch and for any error.
list_T *reg_submatch_list(int no)
{
 if (!can_f_submatch || no < 0) {
   return NULL;
 }

 linenr_T slnum;
 linenr_T elnum;
 list_T *list;
 const char *s;

 if (rsm.sm_match == NULL) {
   slnum = rsm.sm_mmatch->startpos[no].lnum;
   elnum = rsm.sm_mmatch->endpos[no].lnum;
   if (slnum < 0 || elnum < 0) {
     return NULL;
   }

   colnr_T scol = rsm.sm_mmatch->startpos[no].col;
   colnr_T ecol = rsm.sm_mmatch->endpos[no].col;

   list = tv_list_alloc(elnum - slnum + 1);

   s = reg_getline_submatch(slnum) + scol;
   if (slnum == elnum) {
     tv_list_append_string(list, s, ecol - scol);
   } else {
     int max_lnum = elnum - slnum;
     tv_list_append_string(list, s, -1);
     for (int i = 1; i < max_lnum; i++) {
       s = reg_getline_submatch(slnum + i);
       tv_list_append_string(list, s, -1);
     }
     s = reg_getline_submatch(elnum);
     tv_list_append_string(list, s, ecol);
   }
 } else {
   s = rsm.sm_match->startp[no];
   if (s == NULL || rsm.sm_match->endp[no] == NULL) {
     return NULL;
   }
   list = tv_list_alloc(1);
   tv_list_append_string(list, s, rsm.sm_match->endp[no] - s);
 }

 tv_list_ref(list);
 return list;
}

/// Initialize the values used for matching against multiple lines
///
/// @param win   window in which to search or NULL
/// @param buf   buffer in which to search
/// @param lnum  nr of line to start looking for match
static void init_regexec_multi(regmmatch_T *rmp, win_T *win, buf_T *buf, linenr_T lnum)
{
 rex.reg_match = NULL;
 rex.reg_mmatch = rmp;
 rex.reg_buf = buf;
 rex.reg_win = win;
 rex.reg_firstlnum = lnum;
 rex.reg_maxline = rex.reg_buf->b_ml.ml_line_count - lnum;
 rex.reg_line_lbr = false;
 rex.reg_ic = rmp->rmm_ic;
 rex.reg_icombine = false;
 rex.reg_nobreak = rmp->regprog->re_flags & RE_NOBREAK;
 rex.reg_maxcol = rmp->rmm_maxcol;
}

// regexp_bt.c {{{1

// Backtracking regular expression implementation.
//
// NOTICE:
//
// This is NOT the original regular expression code as written by Henry
// Spencer.  This code has been modified specifically for use with the VIM
// editor, and should not be used separately from Vim.  If you want a good
// regular expression library, get the original code.  The copyright notice
// that follows is from the original.
//
// END NOTICE
//
//      Copyright (c) 1986 by University of Toronto.
//      Written by Henry Spencer.  Not derived from licensed software.
//
//      Permission is granted to anyone to use this software for any
//      purpose on any computer system, and to redistribute it freely,
//      subject to the following restrictions:
//
//      1. The author is not responsible for the consequences of use of
//              this software, no matter how awful, even if they arise
//              from defects in it.
//
//      2. The origin of this software must not be misrepresented, either
//              by explicit claim or by omission.
//
//      3. Altered versions must be plainly marked as such, and must not
//              be misrepresented as being the original software.
//
// Beware that some of this code is subtly aware of the way operator
// precedence is structured in regular expressions.  Serious changes in
// regular-expression syntax might require a total rethink.
//
// Changes have been made by Tony Andrews, Olaf 'Rhialto' Seibert, Robert
// Webb, Ciaran McCreesh and Bram Moolenaar.
// Named character class support added by Walter Briscoe (1998 Jul 01)

// The "internal use only" fields in regexp_defs.h are present to pass info from
// compile to execute that permits the execute phase to run lots faster on
// simple cases.  They are:
//
// regstart     char that must begin a match; NUL if none obvious; Can be a
//              multi-byte character.
// reganch      is the match anchored (at beginning-of-line only)?
// regmust      string (pointer into program) that match must include, or NULL
// regmlen      length of regmust string
// regflags     RF_ values or'ed together
//
// Regstart and reganch permit very fast decisions on suitable starting points
// for a match, cutting down the work a lot.  Regmust permits fast rejection
// of lines that cannot possibly match.  The regmust tests are costly enough
// that vim_regcomp() supplies a regmust only if the r.e. contains something
// potentially expensive (at present, the only such thing detected is * or +
// at the start of the r.e., which can involve a lot of backup).  Regmlen is
// supplied because the test in vim_regexec() needs it and vim_regcomp() is
// computing it anyway.

// Structure for regexp "program".  This is essentially a linear encoding
// of a nondeterministic finite-state machine (aka syntax charts or
// "railroad normal form" in parsing technology).  Each node is an opcode
// plus a "next" pointer, possibly plus an operand.  "Next" pointers of
// all nodes except BRANCH and BRACES_COMPLEX implement concatenation; a "next"
// pointer with a BRANCH on both ends of it is connecting two alternatives.
// (Here we have one of the subtle syntax dependencies: an individual BRANCH
// (as opposed to a collection of them) is never concatenated with anything
// because of operator precedence).  The "next" pointer of a BRACES_COMPLEX
// node points to the node after the stuff to be repeated.
// The operand of some types of node is a literal string; for others, it is a
// node leading into a sub-FSM.  In particular, the operand of a BRANCH node
// is the first node of the branch.
// (NB this is *not* a tree structure: the tail of the branch connects to the
// thing following the set of BRANCHes.)
//
// pattern      is coded like:
//
//                        +-----------------+
//                        |                 V
// <aa>\|<bb>   BRANCH <aa> BRANCH <bb> --> END
//                   |      ^    |          ^
//                   +------+    +----------+
//
//
//                     +------------------+
//                     V                  |
// <aa>*        BRANCH BRANCH <aa> --> BACK BRANCH --> NOTHING --> END
//                   |      |               ^                      ^
//                   |      +---------------+                      |
//                   +---------------------------------------------+
//
//
//                     +----------------------+
//                     V                      |
// <aa>\+       BRANCH <aa> --> BRANCH --> BACK  BRANCH --> NOTHING --> END
//                   |               |           ^                      ^
//                   |               +-----------+                      |
//                   +--------------------------------------------------+
//
//
//                                      +-------------------------+
//                                      V                         |
// <aa>\{}      BRANCH BRACE_LIMITS --> BRACE_COMPLEX <aa> --> BACK  END
//                   |                              |                ^
//                   |                              +----------------+
//                   +-----------------------------------------------+
//
//
// <aa>\@!<bb>  BRANCH NOMATCH <aa> --> END  <bb> --> END
//                   |       |                ^       ^
//                   |       +----------------+       |
//                   +--------------------------------+
//
//                                                    +---------+
//                                                    |         V
// \z[abc]      BRANCH BRANCH  a  BRANCH  b  BRANCH  c  BRANCH  NOTHING --> END
//                   |      |          |          |     ^                   ^
//                   |      |          |          +-----+                   |
//                   |      |          +----------------+                   |
//                   |      +---------------------------+                   |
//                   +------------------------------------------------------+
//
// They all start with a BRANCH for "\|" alternatives, even when there is only
// one alternative.

// The opcodes are:

// definition   number             opnd?    meaning
#define END             0       //      End of program or NOMATCH operand.
#define BOL             1       //      Match "" at beginning of line.
#define EOL             2       //      Match "" at end of line.
#define BRANCH          3       // node Match this alternative, or the
                               //      next...
#define BACK            4       //      Match "", "next" ptr points backward.
#define EXACTLY         5       // str  Match this string.
#define NOTHING         6       //      Match empty string.
#define STAR            7       // node Match this (simple) thing 0 or more
                               //      times.
#define PLUS            8       // node Match this (simple) thing 1 or more
                               //      times.
#define MATCH           9       // node match the operand zero-width
#define NOMATCH         10      // node check for no match with operand
#define BEHIND          11      // node look behind for a match with operand
#define NOBEHIND        12      // node look behind for no match with operand
#define SUBPAT          13      // node match the operand here
#define BRACE_SIMPLE    14      // node Match this (simple) thing between m and
                               //      n times (\{m,n\}).
#define BOW             15      //      Match "" after [^a-zA-Z0-9_]
#define EOW             16      //      Match "" at    [^a-zA-Z0-9_]
#define BRACE_LIMITS    17      // nr nr  define the min & max for BRACE_SIMPLE
                               //      and BRACE_COMPLEX.
#define NEWL            18      //      Match line-break
#define BHPOS           19      //      End position for BEHIND or NOBEHIND

// character classes: 20-48 normal, 50-78 include a line-break
#define ADD_NL          30
#define FIRST_NL        ANY + ADD_NL
#define ANY             20      //      Match any one character.
#define ANYOF           21      // str  Match any character in this string.
#define ANYBUT          22      // str  Match any character not in this
                               //      string.
#define IDENT           23      //      Match identifier char
#define SIDENT          24      //      Match identifier char but no digit
#define KWORD           25      //      Match keyword char
#define SKWORD          26      //      Match word char but no digit
#define FNAME           27      //      Match file name char
#define SFNAME          28      //      Match file name char but no digit
#define PRINT           29      //      Match printable char
#define SPRINT          30      //      Match printable char but no digit
#define WHITE           31      //      Match whitespace char
#define NWHITE          32      //      Match non-whitespace char
#define DIGIT           33      //      Match digit char
#define NDIGIT          34      //      Match non-digit char
#define HEX             35      //      Match hex char
#define NHEX            36      //      Match non-hex char
#define OCTAL           37      //      Match octal char
#define NOCTAL          38      //      Match non-octal char
#define WORD            39      //      Match word char
#define NWORD           40      //      Match non-word char
#define HEAD            41      //      Match head char
#define NHEAD           42      //      Match non-head char
#define ALPHA           43      //      Match alpha char
#define NALPHA          44      //      Match non-alpha char
#define LOWER           45      //      Match lowercase char
#define NLOWER          46      //      Match non-lowercase char
#define UPPER           47      //      Match uppercase char
#define NUPPER          48      //      Match non-uppercase char
#define LAST_NL         NUPPER + ADD_NL
#define WITH_NL(op)     ((op) >= FIRST_NL && (op) <= LAST_NL)

#define MOPEN           80   // -89 Mark this point in input as start of
                            //     \( … \) subexpr.  MOPEN + 0 marks start of
                            //     match.
#define MCLOSE          90   // -99 Analogous to MOPEN.  MCLOSE + 0 marks
                            //     end of match.
#define BACKREF         100  // -109 node Match same string again \1-\9.

#define ZOPEN          110  // -119 Mark this point in input as start of
                           //  \z( … \) subexpr.
#define ZCLOSE         120  // -129 Analogous to ZOPEN.
#define ZREF           130  // -139 node Match external submatch \z1-\z9

#define BRACE_COMPLEX   140  // -149 node Match nodes between m & n times

#define NOPEN           150     // Mark this point in input as start of
                               // \%( subexpr.
#define NCLOSE          151     // Analogous to NOPEN.

#define MULTIBYTECODE   200     // mbc  Match one multi-byte character
#define RE_BOF          201     //      Match "" at beginning of file.
#define RE_EOF          202     //      Match "" at end of file.
#define CURSOR          203     //      Match location of cursor.

#define RE_LNUM         204     // nr cmp  Match line number
#define RE_COL          205     // nr cmp  Match column number
#define RE_VCOL         206     // nr cmp  Match virtual column number

#define RE_MARK         207     // mark cmp  Match mark position
#define RE_VISUAL       208     //      Match Visual area
#define RE_COMPOSING    209     // any composing characters

// Flags to be passed up and down.
#define HASWIDTH        0x1     // Known never to match null string.
#define SIMPLE          0x2     // Simple enough to be STAR/PLUS operand.
#define SPSTART         0x4     // Starts with * or +.
#define HASNL           0x8     // Contains some \n.
#define HASLOOKBH       0x10    // Contains "\@<=" or "\@<!".
#define WORST           0       // Worst case.

static int prevchr_len;         ///< byte length of previous char
static int num_complex_braces;  ///< Complex \{...} count
static uint8_t *regcode;         ///< Code-emit pointer, or JUST_CALC_SIZE
static int64_t regsize;            ///< Code size.
static int reg_toolong;         ///< true when offset out of range
static uint8_t had_endbrace[NSUBEXP];  ///< flags, true if end of () found
static int64_t brace_min[10];        ///< Minimums for complex brace repeats
static int64_t brace_max[10];        ///< Maximums for complex brace repeats
static int brace_count[10];       ///< Current counts for complex brace repeats
static int one_exactly = false;   ///< only do one char for EXACTLY

// When making changes to classchars also change nfa_classcodes.
static uint8_t *classchars = (uint8_t *)".iIkKfFpPsSdDxXoOwWhHaAlLuU";
static int classcodes[] = {
 ANY, IDENT, SIDENT, KWORD, SKWORD,
 FNAME, SFNAME, PRINT, SPRINT,
 WHITE, NWHITE, DIGIT, NDIGIT,
 HEX, NHEX, OCTAL, NOCTAL,
 WORD, NWORD, HEAD, NHEAD,
 ALPHA, NALPHA, LOWER, NLOWER,
 UPPER, NUPPER
};

// When regcode is set to this value, code is not emitted and size is computed
// instead.
#define JUST_CALC_SIZE  ((uint8_t *)-1)

// used for STAR, PLUS and BRACE_SIMPLE matching
typedef struct regstar_S {
 int nextb;            // next byte
 int nextb_ic;         // next byte reverse case
 int64_t count;
 int64_t minval;
 int64_t maxval;
} regstar_T;

// used to store input position when a BACK was encountered, so that we now if
// we made any progress since the last time.
typedef struct backpos_S {
 uint8_t *bp_scan;         // "scan" where BACK was encountered
 regsave_T bp_pos;           // last input position
} backpos_T;

// "regstack" and "backpos" are used by regmatch().  They are kept over calls
// to avoid invoking malloc() and free() often.
// "regstack" is a stack with regitem_T items, sometimes preceded by regstar_T
// or regbehind_T.
// "backpos_T" is a table with backpos_T for BACK
static garray_T regstack = GA_EMPTY_INIT_VALUE;
static garray_T backpos = GA_EMPTY_INIT_VALUE;

static regsave_T behind_pos;

// Both for regstack and backpos tables we use the following strategy of
// allocation (to reduce malloc/free calls):
// - Initial size is fairly small.
// - When needed, the tables are grown bigger (8 times at first, double after
//   that).
// - After executing the match we free the memory only if the array has grown.
//   Thus the memory is kept allocated when it's at the initial size.
// This makes it fast while not keeping a lot of memory allocated.
// A three times speed increase was observed when using many simple patterns.
#define REGSTACK_INITIAL        2048
#define BACKPOS_INITIAL         64

// Opcode notes:
//
// BRANCH       The set of branches constituting a single choice are hooked
//              together with their "next" pointers, since precedence prevents
//              anything being concatenated to any individual branch.  The
//              "next" pointer of the last BRANCH in a choice points to the
//              thing following the whole choice.  This is also where the
//              final "next" pointer of each individual branch points; each
//              branch starts with the operand node of a BRANCH node.
//
// BACK         Normal "next" pointers all implicitly point forward; BACK
//              exists to make loop structures possible.
//
// STAR,PLUS    '=', and complex '*' and '+', are implemented as circular
//              BRANCH structures using BACK.  Simple cases (one character
//              per match) are implemented with STAR and PLUS for speed
//              and to minimize recursive plunges.
//
// BRACE_LIMITS This is always followed by a BRACE_SIMPLE or BRACE_COMPLEX
//              node, and defines the min and max limits to be used for that
//              node.
//
// MOPEN,MCLOSE ...are numbered at compile time.
// ZOPEN,ZCLOSE ...ditto
///
//
//
// A node is one char of opcode followed by two chars of "next" pointer.
// "Next" pointers are stored as two 8-bit bytes, high order first.  The
// value is a positive offset from the opcode of the node containing it.
// An operand, if any, simply follows the node.  (Note that much of the
// code generation knows about this implicit relationship.)
//
// Using two bytes for the "next" pointer is vast overkill for most things,
// but allows patterns to get big without disasters.
#define OP(p)           ((int)(*(p)))
#define NEXT(p)         (((*((p) + 1) & 0377) << 8) + (*((p) + 2) & 0377))
#define OPERAND(p)      ((p) + 3)
// Obtain an operand that was stored as four bytes, MSB first.
#define OPERAND_MIN(p)  (((int64_t)(p)[3] << 24) + ((int64_t)(p)[4] << 16) \
                        + ((int64_t)(p)[5] << 8) + (int64_t)(p)[6])
// Obtain a second operand stored as four bytes.
#define OPERAND_MAX(p)  OPERAND_MIN((p) + 4)
// Obtain a second single-byte operand stored after a four bytes operand.
#define OPERAND_CMP(p)  (p)[7]

static uint8_t *reg(int paren, int *flagp);

#ifdef BT_REGEXP_DUMP
static void     regdump(uint8_t *, bt_regprog_T *);
#endif

#ifdef REGEXP_DEBUG
static uint8_t *regprop(uint8_t *);

static int regnarrate = 0;
#endif

// Setup to parse the regexp.  Used once to get the length and once to do it.
static void regcomp_start(uint8_t *expr, int re_flags)                        // see vim_regcomp()
{
 initchr((char *)expr);
 if (re_flags & RE_MAGIC) {
   reg_magic = MAGIC_ON;
 } else {
   reg_magic = MAGIC_OFF;
 }
 reg_string = (re_flags & RE_STRING);
 reg_strict = (re_flags & RE_STRICT);
 get_cpo_flags();

 num_complex_braces = 0;
 regnpar = 1;
 CLEAR_FIELD(had_endbrace);
 regnzpar = 1;
 re_has_z = 0;
 regsize = 0L;
 reg_toolong = false;
 regflags = 0;
 had_eol = false;
}

// Return true if MULTIBYTECODE should be used instead of EXACTLY for
// character "c".
static bool use_multibytecode(int c)
{
 return utf_char2len(c) > 1
        && (re_multi_type(peekchr()) != NOT_MULTI
            || utf_iscomposing_legacy(c));
}

// Emit (if appropriate) a byte of code
static void regc(int b)
{
 if (regcode == JUST_CALC_SIZE) {
   regsize++;
 } else {
   *regcode++ = (uint8_t)b;
 }
}

// Emit (if appropriate) a multi-byte character of code
static void regmbc(int c)
{
 if (regcode == JUST_CALC_SIZE) {
   regsize += utf_char2len(c);
 } else {
   regcode += utf_char2bytes(c, (char *)regcode);
 }
}

// Produce the bytes for equivalence class "c".
// Currently only handles latin1, latin9 and utf-8.
// NOTE: When changing this function, also change nfa_emit_equi_class()
static void reg_equi_class(int c)
{
 {
   switch (c) {
   // Do not use '\300' style, it results in a negative number.
   case 'A':
   case 0xc0:
   case 0xc1:
   case 0xc2:
   case 0xc3:
   case 0xc4:
   case 0xc5:
   case 0x100:
   case 0x102:
   case 0x104:
   case 0x1cd:
   case 0x1de:
   case 0x1e0:
   case 0x1fa:
   case 0x202:
   case 0x226:
   case 0x23a:
   case 0x1e00:
   case 0x1ea0:
   case 0x1ea2:
   case 0x1ea4:
   case 0x1ea6:
   case 0x1ea8:
   case 0x1eaa:
   case 0x1eac:
   case 0x1eae:
   case 0x1eb0:
   case 0x1eb2:
   case 0x1eb4:
   case 0x1eb6:
     regmbc('A'); regmbc(0xc0); regmbc(0xc1); regmbc(0xc2);
     regmbc(0xc3); regmbc(0xc4); regmbc(0xc5);
     regmbc(0x100); regmbc(0x102); regmbc(0x104);
     regmbc(0x1cd); regmbc(0x1de); regmbc(0x1e0);
     regmbc(0x1fa); regmbc(0x202); regmbc(0x226);
     regmbc(0x23a); regmbc(0x1e00); regmbc(0x1ea0);
     regmbc(0x1ea2); regmbc(0x1ea4); regmbc(0x1ea6);
     regmbc(0x1ea8); regmbc(0x1eaa); regmbc(0x1eac);
     regmbc(0x1eae); regmbc(0x1eb0); regmbc(0x1eb2);
     regmbc(0x1eb4); regmbc(0x1eb6);
     return;
   case 'B':
   case 0x181:
   case 0x243:
   case 0x1e02:
   case 0x1e04:
   case 0x1e06:
     regmbc('B');
     regmbc(0x181); regmbc(0x243); regmbc(0x1e02);
     regmbc(0x1e04); regmbc(0x1e06);
     return;
   case 'C':
   case 0xc7:
   case 0x106:
   case 0x108:
   case 0x10a:
   case 0x10c:
   case 0x187:
   case 0x23b:
   case 0x1e08:
   case 0xa792:
     regmbc('C'); regmbc(0xc7);
     regmbc(0x106); regmbc(0x108); regmbc(0x10a);
     regmbc(0x10c); regmbc(0x187); regmbc(0x23b);
     regmbc(0x1e08); regmbc(0xa792);
     return;
   case 'D':
   case 0x10e:
   case 0x110:
   case 0x18a:
   case 0x1e0a:
   case 0x1e0c:
   case 0x1e0e:
   case 0x1e10:
   case 0x1e12:
     regmbc('D'); regmbc(0x10e); regmbc(0x110);
     regmbc(0x18a); regmbc(0x1e0a); regmbc(0x1e0c);
     regmbc(0x1e0e); regmbc(0x1e10); regmbc(0x1e12);
     return;
   case 'E':
   case 0xc8:
   case 0xc9:
   case 0xca:
   case 0xcb:
   case 0x112:
   case 0x114:
   case 0x116:
   case 0x118:
   case 0x11a:
   case 0x204:
   case 0x206:
   case 0x228:
   case 0x246:
   case 0x1e14:
   case 0x1e16:
   case 0x1e18:
   case 0x1e1a:
   case 0x1e1c:
   case 0x1eb8:
   case 0x1eba:
   case 0x1ebc:
   case 0x1ebe:
   case 0x1ec0:
   case 0x1ec2:
   case 0x1ec4:
   case 0x1ec6:
     regmbc('E'); regmbc(0xc8); regmbc(0xc9);
     regmbc(0xca); regmbc(0xcb); regmbc(0x112);
     regmbc(0x114); regmbc(0x116); regmbc(0x118);
     regmbc(0x11a); regmbc(0x204); regmbc(0x206);
     regmbc(0x228); regmbc(0x246); regmbc(0x1e14);
     regmbc(0x1e16); regmbc(0x1e18); regmbc(0x1e1a);
     regmbc(0x1e1c); regmbc(0x1eb8); regmbc(0x1eba);
     regmbc(0x1ebc); regmbc(0x1ebe); regmbc(0x1ec0);
     regmbc(0x1ec2); regmbc(0x1ec4); regmbc(0x1ec6);
     return;
   case 'F':
   case 0x191:
   case 0x1e1e:
   case 0xa798:
     regmbc('F'); regmbc(0x191); regmbc(0x1e1e);
     regmbc(0xa798);
     return;
   case 'G':
   case 0x11c:
   case 0x11e:
   case 0x120:
   case 0x122:
   case 0x193:
   case 0x1e4:
   case 0x1e6:
   case 0x1f4:
   case 0x1e20:
   case 0xa7a0:
     regmbc('G'); regmbc(0x11c); regmbc(0x11e);
     regmbc(0x120); regmbc(0x122); regmbc(0x193);
     regmbc(0x1e4); regmbc(0x1e6); regmbc(0x1f4);
     regmbc(0x1e20); regmbc(0xa7a0);
     return;
   case 'H':
   case 0x124:
   case 0x126:
   case 0x21e:
   case 0x1e22:
   case 0x1e24:
   case 0x1e26:
   case 0x1e28:
   case 0x1e2a:
   case 0x2c67:
     regmbc('H'); regmbc(0x124); regmbc(0x126);
     regmbc(0x21e); regmbc(0x1e22); regmbc(0x1e24);
     regmbc(0x1e26); regmbc(0x1e28); regmbc(0x1e2a);
     regmbc(0x2c67);
     return;
   case 'I':
   case 0xcc:
   case 0xcd:
   case 0xce:
   case 0xcf:
   case 0x128:
   case 0x12a:
   case 0x12c:
   case 0x12e:
   case 0x130:
   case 0x197:
   case 0x1cf:
   case 0x208:
   case 0x20a:
   case 0x1e2c:
   case 0x1e2e:
   case 0x1ec8:
   case 0x1eca:
     regmbc('I'); regmbc(0xcc); regmbc(0xcd);
     regmbc(0xce); regmbc(0xcf); regmbc(0x128);
     regmbc(0x12a); regmbc(0x12c); regmbc(0x12e);
     regmbc(0x130); regmbc(0x197); regmbc(0x1cf);
     regmbc(0x208); regmbc(0x20a); regmbc(0x1e2c);
     regmbc(0x1e2e); regmbc(0x1ec8); regmbc(0x1eca);
     return;
   case 'J':
   case 0x134:
   case 0x248:
     regmbc('J'); regmbc(0x134); regmbc(0x248);
     return;
   case 'K':
   case 0x136:
   case 0x198:
   case 0x1e8:
   case 0x1e30:
   case 0x1e32:
   case 0x1e34:
   case 0x2c69:
   case 0xa740:
     regmbc('K'); regmbc(0x136); regmbc(0x198);
     regmbc(0x1e8); regmbc(0x1e30); regmbc(0x1e32);
     regmbc(0x1e34); regmbc(0x2c69); regmbc(0xa740);
     return;
   case 'L':
   case 0x139:
   case 0x13b:
   case 0x13d:
   case 0x13f:
   case 0x141:
   case 0x23d:
   case 0x1e36:
   case 0x1e38:
   case 0x1e3a:
   case 0x1e3c:
   case 0x2c60:
     regmbc('L'); regmbc(0x139); regmbc(0x13b);
     regmbc(0x13d); regmbc(0x13f); regmbc(0x141);
     regmbc(0x23d); regmbc(0x1e36); regmbc(0x1e38);
     regmbc(0x1e3a); regmbc(0x1e3c); regmbc(0x2c60);
     return;
   case 'M':
   case 0x1e3e:
   case 0x1e40:
   case 0x1e42:
     regmbc('M'); regmbc(0x1e3e); regmbc(0x1e40);
     regmbc(0x1e42);
     return;
   case 'N':
   case 0xd1:
   case 0x143:
   case 0x145:
   case 0x147:
   case 0x1f8:
   case 0x1e44:
   case 0x1e46:
   case 0x1e48:
   case 0x1e4a:
   case 0xa7a4:
     regmbc('N'); regmbc(0xd1);
     regmbc(0x143); regmbc(0x145); regmbc(0x147);
     regmbc(0x1f8); regmbc(0x1e44); regmbc(0x1e46);
     regmbc(0x1e48); regmbc(0x1e4a); regmbc(0xa7a4);
     return;
   case 'O':
   case 0xd2:
   case 0xd3:
   case 0xd4:
   case 0xd5:
   case 0xd6:
   case 0xd8:
   case 0x14c:
   case 0x14e:
   case 0x150:
   case 0x19f:
   case 0x1a0:
   case 0x1d1:
   case 0x1ea:
   case 0x1ec:
   case 0x1fe:
   case 0x20c:
   case 0x20e:
   case 0x22a:
   case 0x22c:
   case 0x22e:
   case 0x230:
   case 0x1e4c:
   case 0x1e4e:
   case 0x1e50:
   case 0x1e52:
   case 0x1ecc:
   case 0x1ece:
   case 0x1ed0:
   case 0x1ed2:
   case 0x1ed4:
   case 0x1ed6:
   case 0x1ed8:
   case 0x1eda:
   case 0x1edc:
   case 0x1ede:
   case 0x1ee0:
   case 0x1ee2:
     regmbc('O'); regmbc(0xd2); regmbc(0xd3); regmbc(0xd4);
     regmbc(0xd5); regmbc(0xd6); regmbc(0xd8);
     regmbc(0x14c); regmbc(0x14e); regmbc(0x150);
     regmbc(0x19f); regmbc(0x1a0); regmbc(0x1d1);
     regmbc(0x1ea); regmbc(0x1ec); regmbc(0x1fe);
     regmbc(0x20c); regmbc(0x20e); regmbc(0x22a);
     regmbc(0x22c); regmbc(0x22e); regmbc(0x230);
     regmbc(0x1e4c); regmbc(0x1e4e); regmbc(0x1e50);
     regmbc(0x1e52); regmbc(0x1ecc); regmbc(0x1ece);
     regmbc(0x1ed0); regmbc(0x1ed2); regmbc(0x1ed4);
     regmbc(0x1ed6); regmbc(0x1ed8); regmbc(0x1eda);
     regmbc(0x1edc); regmbc(0x1ede); regmbc(0x1ee0);
     regmbc(0x1ee2);
     return;
   case 'P':
   case 0x1a4:
   case 0x1e54:
   case 0x1e56:
   case 0x2c63:
     regmbc('P'); regmbc(0x1a4); regmbc(0x1e54);
     regmbc(0x1e56); regmbc(0x2c63);
     return;
   case 'Q':
   case 0x24a:
     regmbc('Q'); regmbc(0x24a);
     return;
   case 'R':
   case 0x154:
   case 0x156:
   case 0x158:
   case 0x210:
   case 0x212:
   case 0x24c:
   case 0x1e58:
   case 0x1e5a:
   case 0x1e5c:
   case 0x1e5e:
   case 0x2c64:
   case 0xa7a6:
     regmbc('R'); regmbc(0x154); regmbc(0x156);
     regmbc(0x210); regmbc(0x212); regmbc(0x158);
     regmbc(0x24c); regmbc(0x1e58); regmbc(0x1e5a);
     regmbc(0x1e5c); regmbc(0x1e5e); regmbc(0x2c64);
     regmbc(0xa7a6);
     return;
   case 'S':
   case 0x15a:
   case 0x15c:
   case 0x15e:
   case 0x160:
   case 0x218:
   case 0x1e60:
   case 0x1e62:
   case 0x1e64:
   case 0x1e66:
   case 0x1e68:
   case 0x2c7e:
   case 0xa7a8:
     regmbc('S'); regmbc(0x15a); regmbc(0x15c);
     regmbc(0x15e); regmbc(0x160); regmbc(0x218);
     regmbc(0x1e60); regmbc(0x1e62); regmbc(0x1e64);
     regmbc(0x1e66); regmbc(0x1e68); regmbc(0x2c7e);
     regmbc(0xa7a8);
     return;
   case 'T':
   case 0x162:
   case 0x164:
   case 0x166:
   case 0x1ac:
   case 0x1ae:
   case 0x21a:
   case 0x23e:
   case 0x1e6a:
   case 0x1e6c:
   case 0x1e6e:
   case 0x1e70:
     regmbc('T'); regmbc(0x162); regmbc(0x164);
     regmbc(0x166); regmbc(0x1ac); regmbc(0x23e);
     regmbc(0x1ae); regmbc(0x21a); regmbc(0x1e6a);
     regmbc(0x1e6c); regmbc(0x1e6e); regmbc(0x1e70);
     return;
   case 'U':
   case 0xd9:
   case 0xda:
   case 0xdb:
   case 0xdc:
   case 0x168:
   case 0x16a:
   case 0x16c:
   case 0x16e:
   case 0x170:
   case 0x172:
   case 0x1af:
   case 0x1d3:
   case 0x1d5:
   case 0x1d7:
   case 0x1d9:
   case 0x1db:
   case 0x214:
   case 0x216:
   case 0x244:
   case 0x1e72:
   case 0x1e74:
   case 0x1e76:
   case 0x1e78:
   case 0x1e7a:
   case 0x1ee4:
   case 0x1ee6:
   case 0x1ee8:
   case 0x1eea:
   case 0x1eec:
   case 0x1eee:
   case 0x1ef0:
     regmbc('U'); regmbc(0xd9); regmbc(0xda);
     regmbc(0xdb); regmbc(0xdc); regmbc(0x168);
     regmbc(0x16a); regmbc(0x16c); regmbc(0x16e);
     regmbc(0x170); regmbc(0x172); regmbc(0x1af);
     regmbc(0x1d3); regmbc(0x1d5); regmbc(0x1d7);
     regmbc(0x1d9); regmbc(0x1db); regmbc(0x214);
     regmbc(0x216); regmbc(0x244); regmbc(0x1e72);
     regmbc(0x1e74); regmbc(0x1e76); regmbc(0x1e78);
     regmbc(0x1e7a); regmbc(0x1ee4); regmbc(0x1ee6);
     regmbc(0x1ee8); regmbc(0x1eea); regmbc(0x1eec);
     regmbc(0x1eee); regmbc(0x1ef0);
     return;
   case 'V':
   case 0x1b2:
   case 0x1e7c:
   case 0x1e7e:
     regmbc('V'); regmbc(0x1b2); regmbc(0x1e7c);
     regmbc(0x1e7e);
     return;
   case 'W':
   case 0x174:
   case 0x1e80:
   case 0x1e82:
   case 0x1e84:
   case 0x1e86:
   case 0x1e88:
     regmbc('W'); regmbc(0x174); regmbc(0x1e80);
     regmbc(0x1e82); regmbc(0x1e84); regmbc(0x1e86);
     regmbc(0x1e88);
     return;
   case 'X':
   case 0x1e8a:
   case 0x1e8c:
     regmbc('X'); regmbc(0x1e8a); regmbc(0x1e8c);
     return;
   case 'Y':
   case 0xdd:
   case 0x176:
   case 0x178:
   case 0x1b3:
   case 0x232:
   case 0x24e:
   case 0x1e8e:
   case 0x1ef2:
   case 0x1ef6:
   case 0x1ef4:
   case 0x1ef8:
     regmbc('Y'); regmbc(0xdd); regmbc(0x176);
     regmbc(0x178); regmbc(0x1b3); regmbc(0x232);
     regmbc(0x24e); regmbc(0x1e8e); regmbc(0x1ef2);
     regmbc(0x1ef4); regmbc(0x1ef6); regmbc(0x1ef8);
     return;
   case 'Z':
   case 0x179:
   case 0x17b:
   case 0x17d:
   case 0x1b5:
   case 0x1e90:
   case 0x1e92:
   case 0x1e94:
   case 0x2c6b:
     regmbc('Z'); regmbc(0x179); regmbc(0x17b);
     regmbc(0x17d); regmbc(0x1b5); regmbc(0x1e90);
     regmbc(0x1e92); regmbc(0x1e94); regmbc(0x2c6b);
     return;
   case 'a':
   case 0xe0:
   case 0xe1:
   case 0xe2:
   case 0xe3:
   case 0xe4:
   case 0xe5:
   case 0x101:
   case 0x103:
   case 0x105:
   case 0x1ce:
   case 0x1df:
   case 0x1e1:
   case 0x1fb:
   case 0x201:
   case 0x203:
   case 0x227:
   case 0x1d8f:
   case 0x1e01:
   case 0x1e9a:
   case 0x1ea1:
   case 0x1ea3:
   case 0x1ea5:
   case 0x1ea7:
   case 0x1ea9:
   case 0x1eab:
   case 0x1ead:
   case 0x1eaf:
   case 0x1eb1:
   case 0x1eb3:
   case 0x1eb5:
   case 0x1eb7:
   case 0x2c65:
     regmbc('a'); regmbc(0xe0); regmbc(0xe1);
     regmbc(0xe2); regmbc(0xe3); regmbc(0xe4);
     regmbc(0xe5); regmbc(0x101); regmbc(0x103);
     regmbc(0x105); regmbc(0x1ce); regmbc(0x1df);
     regmbc(0x1e1); regmbc(0x1fb); regmbc(0x201);
     regmbc(0x203); regmbc(0x227); regmbc(0x1d8f);
     regmbc(0x1e01); regmbc(0x1e9a); regmbc(0x1ea1);
     regmbc(0x1ea3); regmbc(0x1ea5); regmbc(0x1ea7);
     regmbc(0x1ea9); regmbc(0x1eab); regmbc(0x1ead);
     regmbc(0x1eaf); regmbc(0x1eb1); regmbc(0x1eb3);
     regmbc(0x1eb5); regmbc(0x1eb7); regmbc(0x2c65);
     return;
   case 'b':
   case 0x180:
   case 0x253:
   case 0x1d6c:
   case 0x1d80:
   case 0x1e03:
   case 0x1e05:
   case 0x1e07:
     regmbc('b');
     regmbc(0x180); regmbc(0x253); regmbc(0x1d6c);
     regmbc(0x1d80); regmbc(0x1e03); regmbc(0x1e05);
     regmbc(0x1e07);
     return;
   case 'c':
   case 0xe7:
   case 0x107:
   case 0x109:
   case 0x10b:
   case 0x10d:
   case 0x188:
   case 0x23c:
   case 0x1e09:
   case 0xa793:
   case 0xa794:
     regmbc('c'); regmbc(0xe7); regmbc(0x107);
     regmbc(0x109); regmbc(0x10b); regmbc(0x10d);
     regmbc(0x188); regmbc(0x23c); regmbc(0x1e09);
     regmbc(0xa793); regmbc(0xa794);
     return;
   case 'd':
   case 0x10f:
   case 0x111:
   case 0x257:
   case 0x1d6d:
   case 0x1d81:
   case 0x1d91:
   case 0x1e0b:
   case 0x1e0d:
   case 0x1e0f:
   case 0x1e11:
   case 0x1e13:
     regmbc('d'); regmbc(0x10f); regmbc(0x111);
     regmbc(0x257); regmbc(0x1d6d); regmbc(0x1d81);
     regmbc(0x1d91); regmbc(0x1e0b); regmbc(0x1e0d);
     regmbc(0x1e0f); regmbc(0x1e11); regmbc(0x1e13);
     return;
   case 'e':
   case 0xe8:
   case 0xe9:
   case 0xea:
   case 0xeb:
   case 0x113:
   case 0x115:
   case 0x117:
   case 0x119:
   case 0x11b:
   case 0x205:
   case 0x207:
   case 0x229:
   case 0x247:
   case 0x1d92:
   case 0x1e15:
   case 0x1e17:
   case 0x1e19:
   case 0x1e1b:
   case 0x1eb9:
   case 0x1ebb:
   case 0x1e1d:
   case 0x1ebd:
   case 0x1ebf:
   case 0x1ec1:
   case 0x1ec3:
   case 0x1ec5:
   case 0x1ec7:
     regmbc('e'); regmbc(0xe8); regmbc(0xe9);
     regmbc(0xea); regmbc(0xeb); regmbc(0x113);
     regmbc(0x115); regmbc(0x117); regmbc(0x119);
     regmbc(0x11b); regmbc(0x205); regmbc(0x207);
     regmbc(0x229); regmbc(0x247); regmbc(0x1d92);
     regmbc(0x1e15); regmbc(0x1e17); regmbc(0x1e19);
     regmbc(0x1e1b); regmbc(0x1e1d); regmbc(0x1eb9);
     regmbc(0x1ebb); regmbc(0x1ebd); regmbc(0x1ebf);
     regmbc(0x1ec1); regmbc(0x1ec3); regmbc(0x1ec5);
     regmbc(0x1ec7);
     return;
   case 'f':
   case 0x192:
   case 0x1d6e:
   case 0x1d82:
   case 0x1e1f:
   case 0xa799:
     regmbc('f'); regmbc(0x192); regmbc(0x1d6e);
     regmbc(0x1d82); regmbc(0x1e1f); regmbc(0xa799);
     return;
   case 'g':
   case 0x11d:
   case 0x11f:
   case 0x121:
   case 0x123:
   case 0x1e5:
   case 0x1e7:
   case 0x260:
   case 0x1f5:
   case 0x1d83:
   case 0x1e21:
   case 0xa7a1:
     regmbc('g'); regmbc(0x11d); regmbc(0x11f);
     regmbc(0x121); regmbc(0x123); regmbc(0x1e5);
     regmbc(0x1e7); regmbc(0x1f5); regmbc(0x260);
     regmbc(0x1d83); regmbc(0x1e21); regmbc(0xa7a1);
     return;
   case 'h':
   case 0x125:
   case 0x127:
   case 0x21f:
   case 0x1e23:
   case 0x1e25:
   case 0x1e27:
   case 0x1e29:
   case 0x1e2b:
   case 0x1e96:
   case 0x2c68:
   case 0xa795:
     regmbc('h'); regmbc(0x125); regmbc(0x127);
     regmbc(0x21f); regmbc(0x1e23); regmbc(0x1e25);
     regmbc(0x1e27); regmbc(0x1e29); regmbc(0x1e2b);
     regmbc(0x1e96); regmbc(0x2c68); regmbc(0xa795);
     return;
   case 'i':
   case 0xec:
   case 0xed:
   case 0xee:
   case 0xef:
   case 0x129:
   case 0x12b:
   case 0x12d:
   case 0x12f:
   case 0x1d0:
   case 0x209:
   case 0x20b:
   case 0x268:
   case 0x1d96:
   case 0x1e2d:
   case 0x1e2f:
   case 0x1ec9:
   case 0x1ecb:
     regmbc('i'); regmbc(0xec); regmbc(0xed);
     regmbc(0xee); regmbc(0xef); regmbc(0x129);
     regmbc(0x12b); regmbc(0x12d); regmbc(0x12f);
     regmbc(0x1d0); regmbc(0x209); regmbc(0x20b);
     regmbc(0x268); regmbc(0x1d96); regmbc(0x1e2d);
     regmbc(0x1e2f); regmbc(0x1ec9); regmbc(0x1ecb);
     return;
   case 'j':
   case 0x135:
   case 0x1f0:
   case 0x249:
     regmbc('j'); regmbc(0x135); regmbc(0x1f0);
     regmbc(0x249);
     return;
   case 'k':
   case 0x137:
   case 0x199:
   case 0x1e9:
   case 0x1d84:
   case 0x1e31:
   case 0x1e33:
   case 0x1e35:
   case 0x2c6a:
   case 0xa741:
     regmbc('k'); regmbc(0x137); regmbc(0x199);
     regmbc(0x1e9); regmbc(0x1d84); regmbc(0x1e31);
     regmbc(0x1e33); regmbc(0x1e35); regmbc(0x2c6a);
     regmbc(0xa741);
     return;
   case 'l':
   case 0x13a:
   case 0x13c:
   case 0x13e:
   case 0x140:
   case 0x142:
   case 0x19a:
   case 0x1e37:
   case 0x1e39:
   case 0x1e3b:
   case 0x1e3d:
   case 0x2c61:
     regmbc('l'); regmbc(0x13a); regmbc(0x13c);
     regmbc(0x13e); regmbc(0x140); regmbc(0x142);
     regmbc(0x19a); regmbc(0x1e37); regmbc(0x1e39);
     regmbc(0x1e3b); regmbc(0x1e3d); regmbc(0x2c61);
     return;
   case 'm':
   case 0x1d6f:
   case 0x1e3f:
   case 0x1e41:
   case 0x1e43:
     regmbc('m'); regmbc(0x1d6f); regmbc(0x1e3f);
     regmbc(0x1e41); regmbc(0x1e43);
     return;
   case 'n':
   case 0xf1:
   case 0x144:
   case 0x146:
   case 0x148:
   case 0x149:
   case 0x1f9:
   case 0x1d70:
   case 0x1d87:
   case 0x1e45:
   case 0x1e47:
   case 0x1e49:
   case 0x1e4b:
   case 0xa7a5:
     regmbc('n'); regmbc(0xf1); regmbc(0x144);
     regmbc(0x146); regmbc(0x148); regmbc(0x149);
     regmbc(0x1f9); regmbc(0x1d70); regmbc(0x1d87);
     regmbc(0x1e45); regmbc(0x1e47); regmbc(0x1e49);
     regmbc(0x1e4b); regmbc(0xa7a5);
     return;
   case 'o':
   case 0xf2:
   case 0xf3:
   case 0xf4:
   case 0xf5:
   case 0xf6:
   case 0xf8:
   case 0x14d:
   case 0x14f:
   case 0x151:
   case 0x1a1:
   case 0x1d2:
   case 0x1eb:
   case 0x1ed:
   case 0x1ff:
   case 0x20d:
   case 0x20f:
   case 0x22b:
   case 0x22d:
   case 0x22f:
   case 0x231:
   case 0x275:
   case 0x1e4d:
   case 0x1e4f:
   case 0x1e51:
   case 0x1e53:
   case 0x1ecd:
   case 0x1ecf:
   case 0x1ed1:
   case 0x1ed3:
   case 0x1ed5:
   case 0x1ed7:
   case 0x1ed9:
   case 0x1edb:
   case 0x1edd:
   case 0x1edf:
   case 0x1ee1:
   case 0x1ee3:
     regmbc('o'); regmbc(0xf2); regmbc(0xf3);
     regmbc(0xf4); regmbc(0xf5); regmbc(0xf6);
     regmbc(0xf8); regmbc(0x14d); regmbc(0x14f);
     regmbc(0x151); regmbc(0x1a1); regmbc(0x1d2);
     regmbc(0x1eb); regmbc(0x1ed); regmbc(0x1ff);
     regmbc(0x20d); regmbc(0x20f); regmbc(0x22b);
     regmbc(0x22d); regmbc(0x22f); regmbc(0x231);
     regmbc(0x275); regmbc(0x1e4d); regmbc(0x1e4f);
     regmbc(0x1e51); regmbc(0x1e53); regmbc(0x1ecd);
     regmbc(0x1ecf); regmbc(0x1ed1); regmbc(0x1ed3);
     regmbc(0x1ed5); regmbc(0x1ed7); regmbc(0x1ed9);
     regmbc(0x1edb); regmbc(0x1edd); regmbc(0x1edf);
     regmbc(0x1ee1); regmbc(0x1ee3);
     return;
   case 'p':
   case 0x1a5:
   case 0x1d71:
   case 0x1d88:
   case 0x1d7d:
   case 0x1e55:
   case 0x1e57:
     regmbc('p'); regmbc(0x1a5); regmbc(0x1d71);
     regmbc(0x1d7d); regmbc(0x1d88); regmbc(0x1e55);
     regmbc(0x1e57);
     return;
   case 'q':
   case 0x24b:
   case 0x2a0:
     regmbc('q'); regmbc(0x24b); regmbc(0x2a0);
     return;
   case 'r':
   case 0x155:
   case 0x157:
   case 0x159:
   case 0x211:
   case 0x213:
   case 0x24d:
   case 0x27d:
   case 0x1d72:
   case 0x1d73:
   case 0x1d89:
   case 0x1e59:
   case 0x1e5b:
   case 0x1e5d:
   case 0x1e5f:
   case 0xa7a7:
     regmbc('r'); regmbc(0x155); regmbc(0x157);
     regmbc(0x159); regmbc(0x211); regmbc(0x213);
     regmbc(0x24d); regmbc(0x1d72); regmbc(0x1d73);
     regmbc(0x1d89); regmbc(0x1e59); regmbc(0x27d);
     regmbc(0x1e5b); regmbc(0x1e5d); regmbc(0x1e5f);
     regmbc(0xa7a7);
     return;
   case 's':
   case 0x15b:
   case 0x15d:
   case 0x15f:
   case 0x161:
   case 0x1e61:
   case 0x219:
   case 0x23f:
   case 0x1d74:
   case 0x1d8a:
   case 0x1e63:
   case 0x1e65:
   case 0x1e67:
   case 0x1e69:
   case 0xa7a9:
     regmbc('s'); regmbc(0x15b); regmbc(0x15d);
     regmbc(0x15f); regmbc(0x161); regmbc(0x23f);
     regmbc(0x219); regmbc(0x1d74); regmbc(0x1d8a);
     regmbc(0x1e61); regmbc(0x1e63); regmbc(0x1e65);
     regmbc(0x1e67); regmbc(0x1e69); regmbc(0xa7a9);
     return;
   case 't':
   case 0x163:
   case 0x165:
   case 0x167:
   case 0x1ab:
   case 0x1ad:
   case 0x21b:
   case 0x288:
   case 0x1d75:
   case 0x1e6b:
   case 0x1e6d:
   case 0x1e6f:
   case 0x1e71:
   case 0x1e97:
   case 0x2c66:
     regmbc('t'); regmbc(0x163); regmbc(0x165);
     regmbc(0x167); regmbc(0x1ab); regmbc(0x21b);
     regmbc(0x1ad); regmbc(0x288); regmbc(0x1d75);
     regmbc(0x1e6b); regmbc(0x1e6d); regmbc(0x1e6f);
     regmbc(0x1e71); regmbc(0x1e97); regmbc(0x2c66);
     return;
   case 'u':
   case 0xf9:
   case 0xfa:
   case 0xfb:
   case 0xfc:
   case 0x169:
   case 0x16b:
   case 0x16d:
   case 0x16f:
   case 0x171:
   case 0x173:
   case 0x1b0:
   case 0x1d4:
   case 0x1d6:
   case 0x1d8:
   case 0x1da:
   case 0x1dc:
   case 0x215:
   case 0x217:
   case 0x289:
   case 0x1e73:
   case 0x1d7e:
   case 0x1d99:
   case 0x1e75:
   case 0x1e77:
   case 0x1e79:
   case 0x1e7b:
   case 0x1ee5:
   case 0x1ee7:
   case 0x1ee9:
   case 0x1eeb:
   case 0x1eed:
   case 0x1eef:
   case 0x1ef1:
     regmbc('u'); regmbc(0xf9); regmbc(0xfa);
     regmbc(0xfb); regmbc(0xfc); regmbc(0x169);
     regmbc(0x16b); regmbc(0x16d); regmbc(0x16f);
     regmbc(0x171); regmbc(0x173); regmbc(0x1d6);
     regmbc(0x1d8); regmbc(0x1da); regmbc(0x1dc);
     regmbc(0x215); regmbc(0x217); regmbc(0x1b0);
     regmbc(0x1d4); regmbc(0x289); regmbc(0x1d7e);
     regmbc(0x1d99); regmbc(0x1e73); regmbc(0x1e75);
     regmbc(0x1e77); regmbc(0x1e79); regmbc(0x1e7b);
     regmbc(0x1ee5); regmbc(0x1ee7); regmbc(0x1ee9);
     regmbc(0x1eeb); regmbc(0x1eed); regmbc(0x1eef);
     regmbc(0x1ef1);
     return;
   case 'v':
   case 0x28b:
   case 0x1d8c:
   case 0x1e7d:
   case 0x1e7f:
     regmbc('v'); regmbc(0x28b); regmbc(0x1d8c);
     regmbc(0x1e7d); regmbc(0x1e7f);
     return;
   case 'w':
   case 0x175:
   case 0x1e81:
   case 0x1e83:
   case 0x1e85:
   case 0x1e87:
   case 0x1e89:
   case 0x1e98:
     regmbc('w'); regmbc(0x175); regmbc(0x1e81);
     regmbc(0x1e83); regmbc(0x1e85); regmbc(0x1e87);
     regmbc(0x1e89); regmbc(0x1e98);
     return;
   case 'x':
   case 0x1e8b:
   case 0x1e8d:
     regmbc('x'); regmbc(0x1e8b); regmbc(0x1e8d);
     return;
   case 'y':
   case 0xfd:
   case 0xff:
   case 0x177:
   case 0x1b4:
   case 0x233:
   case 0x24f:
   case 0x1e8f:
   case 0x1e99:
   case 0x1ef3:
   case 0x1ef5:
   case 0x1ef7:
   case 0x1ef9:
     regmbc('y'); regmbc(0xfd); regmbc(0xff);
     regmbc(0x177); regmbc(0x1b4); regmbc(0x233);
     regmbc(0x24f); regmbc(0x1e8f); regmbc(0x1e99);
     regmbc(0x1ef3); regmbc(0x1ef5); regmbc(0x1ef7);
     regmbc(0x1ef9);
     return;
   case 'z':
   case 0x17a:
   case 0x17c:
   case 0x17e:
   case 0x1b6:
   case 0x1d76:
   case 0x1d8e:
   case 0x1e91:
   case 0x1e93:
   case 0x1e95:
   case 0x2c6c:
     regmbc('z'); regmbc(0x17a); regmbc(0x17c);
     regmbc(0x17e); regmbc(0x1b6); regmbc(0x1d76);
     regmbc(0x1d8e); regmbc(0x1e91); regmbc(0x1e93);
     regmbc(0x1e95); regmbc(0x2c6c);
     return;
   }
 }
 regmbc(c);
}

// Emit a node.
// Return pointer to generated code.
static uint8_t *regnode(int op)
{
 uint8_t *ret;

 ret = regcode;
 if (ret == JUST_CALC_SIZE) {
   regsize += 3;
 } else {
   *regcode++ = (uint8_t)op;
   *regcode++ = NUL;                   // Null "next" pointer.
   *regcode++ = NUL;
 }
 return ret;
}

// Write a four bytes number at "p" and return pointer to the next char.
static uint8_t *re_put_uint32(uint8_t *p, uint32_t val)
{
 *p++ = (uint8_t)((val >> 24) & 0377);
 *p++ = (uint8_t)((val >> 16) & 0377);
 *p++ = (uint8_t)((val >> 8) & 0377);
 *p++ = (uint8_t)(val & 0377);
 return p;
}

// regnext - dig the "next" pointer out of a node
// Returns NULL when calculating size, when there is no next item and when
// there is an error.
static uint8_t *regnext(uint8_t *p)
 FUNC_ATTR_NONNULL_ALL
{
 int offset;

 if (p == JUST_CALC_SIZE || reg_toolong) {
   return NULL;
 }

 offset = NEXT(p);
 if (offset == 0) {
   return NULL;
 }

 if (OP(p) == BACK) {
   return p - offset;
 } else {
   return p + offset;
 }
}

// Set the next-pointer at the end of a node chain.
static void regtail(uint8_t *p, const uint8_t *val)
{
 int offset;

 if (p == JUST_CALC_SIZE) {
   return;
 }

 // Find last node.
 uint8_t *scan = p;
 while (true) {
   uint8_t *temp = regnext(scan);
   if (temp == NULL) {
     break;
   }
   scan = temp;
 }

 if (OP(scan) == BACK) {
   offset = (int)(scan - val);
 } else {
   offset = (int)(val - scan);
 }
 // When the offset uses more than 16 bits it can no longer fit in the two
 // bytes available.  Use a global flag to avoid having to check return
 // values in too many places.
 if (offset > 0xffff) {
   reg_toolong = true;
 } else {
   *(scan + 1) = (uint8_t)(((unsigned)offset >> 8) & 0377);
   *(scan + 2) = (uint8_t)(offset & 0377);
 }
}

// Like regtail, on item after a BRANCH; nop if none.
static void regoptail(uint8_t *p, uint8_t *val)
{
 // When op is neither BRANCH nor BRACE_COMPLEX0-9, it is "operandless"
 if (p == NULL || p == JUST_CALC_SIZE
     || (OP(p) != BRANCH
         && (OP(p) < BRACE_COMPLEX || OP(p) > BRACE_COMPLEX + 9))) {
   return;
 }
 regtail(OPERAND(p), val);
}

// Insert an operator in front of already-emitted operand
//
// Means relocating the operand.
static void reginsert(int op, uint8_t *opnd)
{
 uint8_t *src;
 uint8_t *dst;
 uint8_t *place;

 if (regcode == JUST_CALC_SIZE) {
   regsize += 3;
   return;
 }
 src = regcode;
 regcode += 3;
 dst = regcode;
 while (src > opnd) {
   *--dst = *--src;
 }

 place = opnd;                 // Op node, where operand used to be.
 *place++ = (uint8_t)op;
 *place++ = NUL;
 *place = NUL;
}

// Insert an operator in front of already-emitted operand.
// Add a number to the operator.
static void reginsert_nr(int op, int64_t val, uint8_t *opnd)
{
 uint8_t *src;
 uint8_t *dst;
 uint8_t *place;

 if (regcode == JUST_CALC_SIZE) {
   regsize += 7;
   return;
 }
 src = regcode;
 regcode += 7;
 dst = regcode;
 while (src > opnd) {
   *--dst = *--src;
 }

 place = opnd;                 // Op node, where operand used to be.
 *place++ = (uint8_t)op;
 *place++ = NUL;
 *place++ = NUL;
 assert(val >= 0 && (uintmax_t)val <= UINT32_MAX);
 re_put_uint32(place, (uint32_t)val);
}

// Insert an operator in front of already-emitted operand.
// The operator has the given limit values as operands.  Also set next pointer.
//
// Means relocating the operand.
static void reginsert_limits(int op, int64_t minval, int64_t maxval, uint8_t *opnd)
{
 uint8_t *src;
 uint8_t *dst;
 uint8_t *place;

 if (regcode == JUST_CALC_SIZE) {
   regsize += 11;
   return;
 }
 src = regcode;
 regcode += 11;
 dst = regcode;
 while (src > opnd) {
   *--dst = *--src;
 }

 place = opnd;                 // Op node, where operand used to be.
 *place++ = (uint8_t)op;
 *place++ = NUL;
 *place++ = NUL;
 assert(minval >= 0 && (uintmax_t)minval <= UINT32_MAX);
 place = re_put_uint32(place, (uint32_t)minval);
 assert(maxval >= 0 && (uintmax_t)maxval <= UINT32_MAX);
 place = re_put_uint32(place, (uint32_t)maxval);
 regtail(opnd, place);
}

/// Return true if the back reference is legal. We must have seen the close
/// brace.
/// TODO(vim): Should also check that we don't refer to something repeated
/// (+*=): what instance of the repetition should we match?
static int seen_endbrace(int refnum)
{
 if (!had_endbrace[refnum]) {
   uint8_t *p;

   // Trick: check if "@<=" or "@<!" follows, in which case
   // the \1 can appear before the referenced match.
   for (p = (uint8_t *)regparse; *p != NUL; p++) {
     if (p[0] == '@' && p[1] == '<' && (p[2] == '!' || p[2] == '=')) {
       break;
     }
   }

   if (*p == NUL) {
     emsg(_("E65: Illegal back reference"));
     rc_did_emsg = true;
     return false;
   }
 }
 return true;
}

// Parse the lowest level.
//
// Optimization:  gobbles an entire sequence of ordinary characters so that
// it can turn them into a single node, which is smaller to store and
// faster to run.  Don't do this when one_exactly is set.
static uint8_t *regatom(int *flagp)
{
 uint8_t *ret;
 int flags;
 int c;
 uint8_t *p;
 int extra = 0;
 int save_prev_at_start = prev_at_start;

 *flagp = WORST;               // Tentatively.

 c = getchr();
 switch (c) {
 case Magic('^'):
   ret = regnode(BOL);
   break;

 case Magic('$'):
   ret = regnode(EOL);
   had_eol = true;
   break;

 case Magic('<'):
   ret = regnode(BOW);
   break;

 case Magic('>'):
   ret = regnode(EOW);
   break;

 case Magic('_'):
   c = no_Magic(getchr());
   if (c == '^') {             // "\_^" is start-of-line
     ret = regnode(BOL);
     break;
   }
   if (c == '$') {             // "\_$" is end-of-line
     ret = regnode(EOL);
     had_eol = true;
     break;
   }

   extra = ADD_NL;
   *flagp |= HASNL;

   // "\_[" is character range plus newline
   if (c == '[') {
     goto collection;
   }

   // "\_x" is character class plus newline
   FALLTHROUGH;

 // Character classes.
 case Magic('.'):
 case Magic('i'):
 case Magic('I'):
 case Magic('k'):
 case Magic('K'):
 case Magic('f'):
 case Magic('F'):
 case Magic('p'):
 case Magic('P'):
 case Magic('s'):
 case Magic('S'):
 case Magic('d'):
 case Magic('D'):
 case Magic('x'):
 case Magic('X'):
 case Magic('o'):
 case Magic('O'):
 case Magic('w'):
 case Magic('W'):
 case Magic('h'):
 case Magic('H'):
 case Magic('a'):
 case Magic('A'):
 case Magic('l'):
 case Magic('L'):
 case Magic('u'):
 case Magic('U'):
   p = (uint8_t *)vim_strchr((char *)classchars, no_Magic(c));
   if (p == NULL) {
     EMSG_RET_NULL(_(e_invalid_use_of_underscore));
   }
   // When '.' is followed by a composing char ignore the dot, so that
   // the composing char is matched here.
   if (c == Magic('.') && utf_iscomposing_legacy(peekchr())) {
     c = getchr();
     goto do_multibyte;
   }
   ret = regnode(classcodes[p - classchars] + extra);
   *flagp |= HASWIDTH | SIMPLE;
   break;

 case Magic('n'):
   if (reg_string) {
     // In a string "\n" matches a newline character.
     ret = regnode(EXACTLY);
     regc(NL);
     regc(NUL);
     *flagp |= HASWIDTH | SIMPLE;
   } else {
     // In buffer text "\n" matches the end of a line.
     ret = regnode(NEWL);
     *flagp |= HASWIDTH | HASNL;
   }
   break;

 case Magic('('):
   if (one_exactly) {
     EMSG_ONE_RET_NULL;
   }
   ret = reg(REG_PAREN, &flags);
   if (ret == NULL) {
     return NULL;
   }
   *flagp |= flags & (HASWIDTH | SPSTART | HASNL | HASLOOKBH);
   break;

 case NUL:
 case Magic('|'):
 case Magic('&'):
 case Magic(')'):
   if (one_exactly) {
     EMSG_ONE_RET_NULL;
   }
   // Supposed to be caught earlier.
   IEMSG_RET_NULL(_(e_internal_error_in_regexp));
 // NOTREACHED

 case Magic('='):
 case Magic('?'):
 case Magic('+'):
 case Magic('@'):
 case Magic('{'):
 case Magic('*'):
   c = no_Magic(c);
   EMSG3_RET_NULL(_("E64: %s%c follows nothing"),
                  (c == '*' ? reg_magic >= MAGIC_ON : reg_magic == MAGIC_ALL), c);
 // NOTREACHED

 case Magic('~'):              // previous substitute pattern
   if (reg_prev_sub != NULL) {
     uint8_t *lp;

     ret = regnode(EXACTLY);
     lp = (uint8_t *)reg_prev_sub;
     while (*lp != NUL) {
       regc(*lp++);
     }
     regc(NUL);
     if (*reg_prev_sub != NUL) {
       *flagp |= HASWIDTH;
       if ((lp - (uint8_t *)reg_prev_sub) == 1) {
         *flagp |= SIMPLE;
       }
     }
   } else {
     EMSG_RET_NULL(_(e_nopresub));
   }
   break;

 case Magic('1'):
 case Magic('2'):
 case Magic('3'):
 case Magic('4'):
 case Magic('5'):
 case Magic('6'):
 case Magic('7'):
 case Magic('8'):
 case Magic('9'): {
   int refnum;

   refnum = c - Magic('0');
   if (!seen_endbrace(refnum)) {
     return NULL;
   }
   ret = regnode(BACKREF + refnum);
 }
 break;

 case Magic('z'):
   c = no_Magic(getchr());
   switch (c) {
   case '(':
     if ((reg_do_extmatch & REX_SET) == 0) {
       EMSG_RET_NULL(_(e_z_not_allowed));
     }
     if (one_exactly) {
       EMSG_ONE_RET_NULL;
     }
     ret = reg(REG_ZPAREN, &flags);
     if (ret == NULL) {
       return NULL;
     }
     *flagp |= flags & (HASWIDTH|SPSTART|HASNL|HASLOOKBH);
     re_has_z = REX_SET;
     break;

   case '1':
   case '2':
   case '3':
   case '4':
   case '5':
   case '6':
   case '7':
   case '8':
   case '9':
     if ((reg_do_extmatch & REX_USE) == 0) {
       EMSG_RET_NULL(_(e_z1_not_allowed));
     }
     ret = regnode(ZREF + c - '0');
     re_has_z = REX_USE;
     break;

   case 's':
     ret = regnode(MOPEN + 0);
     if (!re_mult_next("\\zs")) {
       return NULL;
     }
     break;

   case 'e':
     ret = regnode(MCLOSE + 0);
     if (!re_mult_next("\\ze")) {
       return NULL;
     }
     break;

   default:
     EMSG_RET_NULL(_("E68: Invalid character after \\z"));
   }
   break;

 case Magic('%'):
   c = no_Magic(getchr());
   switch (c) {
   // () without a back reference
   case '(':
     if (one_exactly) {
       EMSG_ONE_RET_NULL;
     }
     ret = reg(REG_NPAREN, &flags);
     if (ret == NULL) {
       return NULL;
     }
     *flagp |= flags & (HASWIDTH | SPSTART | HASNL | HASLOOKBH);
     break;

   // Catch \%^ and \%$ regardless of where they appear in the
   // pattern -- regardless of whether or not it makes sense.
   case '^':
     ret = regnode(RE_BOF);
     break;

   case '$':
     ret = regnode(RE_EOF);
     break;

   case '#':
     if (regparse[0] == '=' && regparse[1] >= 48 && regparse[1] <= 50) {
       // misplaced \%#=1
       semsg(_(e_atom_engine_must_be_at_start_of_pattern), regparse[1]);
       return FAIL;
     }
     ret = regnode(CURSOR);
     break;

   case 'V':
     ret = regnode(RE_VISUAL);
     break;

   case 'C':
     ret = regnode(RE_COMPOSING);
     break;

   // \%[abc]: Emit as a list of branches, all ending at the last
   // branch which matches nothing.
   case '[':
     if (one_exactly) {                        // doesn't nest
       EMSG_ONE_RET_NULL;
     }
     {
       uint8_t *lastbranch;
       uint8_t *lastnode = NULL;
       uint8_t *br;

       ret = NULL;
       while ((c = getchr()) != ']') {
         if (c == NUL) {
           EMSG2_RET_NULL(_(e_missing_sb),
                          reg_magic == MAGIC_ALL);
         }
         br = regnode(BRANCH);
         if (ret == NULL) {
           ret = br;
         } else {
           regtail(lastnode, br);
           if (reg_toolong) {
             return NULL;
           }
         }

         ungetchr();
         one_exactly = true;
         lastnode = regatom(flagp);
         one_exactly = false;
         if (lastnode == NULL) {
           return NULL;
         }
       }
       if (ret == NULL) {
         EMSG2_RET_NULL(_(e_empty_sb),
                        reg_magic == MAGIC_ALL);
       }
       lastbranch = regnode(BRANCH);
       br = regnode(NOTHING);
       if (ret != JUST_CALC_SIZE) {
         regtail(lastnode, br);
         regtail(lastbranch, br);
         // connect all branches to the NOTHING
         // branch at the end
         for (br = ret; br != lastnode;) {
           if (OP(br) == BRANCH) {
             regtail(br, lastbranch);
             if (reg_toolong) {
               return NULL;
             }
             br = OPERAND(br);
           } else {
             br = regnext(br);
           }
         }
       }
       *flagp &= ~(HASWIDTH | SIMPLE);
       break;
     }

   case 'd':               // %d123 decimal
   case 'o':               // %o123 octal
   case 'x':               // %xab hex 2
   case 'u':               // %uabcd hex 4
   case 'U':               // %U1234abcd hex 8
   {
     int64_t i;

     switch (c) {
     case 'd':
       i = getdecchrs(); break;
     case 'o':
       i = getoctchrs(); break;
     case 'x':
       i = gethexchrs(2); break;
     case 'u':
       i = gethexchrs(4); break;
     case 'U':
       i = gethexchrs(8); break;
     default:
       i = -1; break;
     }

     if (i < 0 || i > INT_MAX) {
       EMSG2_RET_NULL(_("E678: Invalid character after %s%%[dxouU]"),
                      reg_magic == MAGIC_ALL);
     }
     if (use_multibytecode((int)i)) {
       ret = regnode(MULTIBYTECODE);
     } else {
       ret = regnode(EXACTLY);
     }
     if (i == 0) {
       regc(0x0a);
     } else {
       regmbc((int)i);
     }
     regc(NUL);
     *flagp |= HASWIDTH;
     break;
   }

   default:
     if (ascii_isdigit(c) || c == '<' || c == '>' || c == '\'' || c == '.') {
       uint32_t n = 0;
       int cmp;
       bool cur = false;
       bool got_digit = false;

       cmp = c;
       if (cmp == '<' || cmp == '>') {
         c = getchr();
       }
       if (no_Magic(c) == '.') {
         cur = true;
         c = getchr();
       }
       while (ascii_isdigit(c)) {
         got_digit = true;
         n = n * 10 + (uint32_t)(c - '0');
         c = getchr();
       }
       if (no_Magic(c) == '\'' && n == 0) {
         // "\%'m", "\%<'m" and "\%>'m": Mark
         c = getchr();
         ret = regnode(RE_MARK);
         if (ret == JUST_CALC_SIZE) {
           regsize += 2;
         } else {
           *regcode++ = (uint8_t)c;
           *regcode++ = (uint8_t)cmp;
         }
         break;
       } else if ((c == 'l' || c == 'c' || c == 'v') && (cur || got_digit)) {
         if (cur && n) {
           semsg(_(e_regexp_number_after_dot_pos_search_chr), no_Magic(c));
           rc_did_emsg = true;
           return NULL;
         }
         if (c == 'l') {
           if (cur) {
             n = (uint32_t)curwin->w_cursor.lnum;
           }
           ret = regnode(RE_LNUM);
           if (save_prev_at_start) {
             at_start = true;
           }
         } else if (c == 'c') {
           if (cur) {
             n = (uint32_t)curwin->w_cursor.col;
             n++;
           }
           ret = regnode(RE_COL);
         } else {
           if (cur) {
             colnr_T vcol = 0;
             getvvcol(curwin, &curwin->w_cursor, NULL, NULL, &vcol);
             n = (uint32_t)(++vcol);
           }
           ret = regnode(RE_VCOL);
         }
         if (ret == JUST_CALC_SIZE) {
           regsize += 5;
         } else {
           // put the number and the optional
           // comparator after the opcode
           regcode = re_put_uint32(regcode, n);
           *regcode++ = (uint8_t)cmp;
         }
         break;
       }
     }

     EMSG2_RET_NULL(_("E71: Invalid character after %s%%"),
                    reg_magic == MAGIC_ALL);
   }
   break;

 case Magic('['):
collection:
   {
     uint8_t *lp;

     // If there is no matching ']', we assume the '[' is a normal
     // character.  This makes 'incsearch' and ":help [" work.
     lp = (uint8_t *)skip_anyof(regparse);
     if (*lp == ']') {         // there is a matching ']'
       int startc = -1;                // > 0 when next '-' is a range
       int endc;

       // In a character class, different parsing rules apply.
       // Not even \ is special anymore, nothing is.
       if (*regparse == '^') {             // Complement of range.
         ret = regnode(ANYBUT + extra);
         regparse++;
       } else {
         ret = regnode(ANYOF + extra);
       }

       // At the start ']' and '-' mean the literal character.
       if (*regparse == ']' || *regparse == '-') {
         startc = (uint8_t)(*regparse);
         regc(*regparse++);
       }

       while (*regparse != NUL && *regparse != ']') {
         if (*regparse == '-') {
           regparse++;
           // The '-' is not used for a range at the end and
           // after or before a '\n'.
           if (*regparse == ']' || *regparse == NUL
               || startc == -1
               || (regparse[0] == '\\' && regparse[1] == 'n')) {
             regc('-');
             startc = '-';                     // [--x] is a range
           } else {
             // Also accept "a-[.z.]"
             endc = 0;
             if (*regparse == '[') {
               endc = get_coll_element(&regparse);
             }
             if (endc == 0) {
               endc = mb_ptr2char_adv((const char **)&regparse);
             }

             // Handle \o40, \x20 and \u20AC style sequences
             if (endc == '\\' && !reg_cpo_lit) {
               endc = coll_get_char();
             }

             if (startc > endc) {
               EMSG_RET_NULL(_(e_reverse_range));
             }
             if (utf_char2len(startc) > 1
                 || utf_char2len(endc) > 1) {
               // Limit to a range of 256 chars
               if (endc > startc + 256) {
                 EMSG_RET_NULL(_(e_large_class));
               }
               while (++startc <= endc) {
                 regmbc(startc);
               }
             } else {
               while (++startc <= endc) {
                 regc(startc);
               }
             }
             startc = -1;
           }
         }
         // Only "\]", "\^", "\]" and "\\" are special in Vi.  Vim
         // accepts "\t", "\e", etc., but only when the 'l' flag in
         // 'cpoptions' is not included.
         else if (*regparse == '\\'
                  && (vim_strchr(REGEXP_INRANGE, (uint8_t)regparse[1]) != NULL
                      || (!reg_cpo_lit
                          && vim_strchr(REGEXP_ABBR,
                                        (uint8_t)regparse[1]) != NULL))) {
           regparse++;
           if (*regparse == 'n') {
             // '\n' in range: also match NL
             if (ret != JUST_CALC_SIZE) {
               // Using \n inside [^] does not change what
               // matches. "[^\n]" is the same as ".".
               if (*ret == ANYOF) {
                 *ret = ANYOF + ADD_NL;
                 *flagp |= HASNL;
               }
               // else: must have had a \n already
             }
             regparse++;
             startc = -1;
           } else if (*regparse == 'd'
                      || *regparse == 'o'
                      || *regparse == 'x'
                      || *regparse == 'u'
                      || *regparse == 'U') {
             startc = coll_get_char();
             // max UTF-8 Codepoint is U+10FFFF,
             // but allow values until INT_MAX
             if (startc == INT_MAX) {
               EMSG_RET_NULL(_(e_unicode_val_too_large));
             }
             if (startc == 0) {
               regc(0x0a);
             } else {
               regmbc(startc);
             }
           } else {
             startc = backslash_trans(*regparse++);
             regc(startc);
           }
         } else if (*regparse == '[') {
           int c_class;
           int cu;

           c_class = get_char_class(&regparse);
           startc = -1;
           // Characters assumed to be 8 bits!
           switch (c_class) {
           case CLASS_NONE:
             c_class = get_equi_class(&regparse);
             if (c_class != 0) {
               // produce equivalence class
               reg_equi_class(c_class);
             } else if ((c_class = get_coll_element(&regparse)) != 0) {
               // produce a collating element
               regmbc(c_class);
             } else {
               // literal '[', allow [[-x] as a range
               startc = (uint8_t)(*regparse++);
               regc(startc);
             }
             break;
           case CLASS_ALNUM:
             for (cu = 1; cu < 128; cu++) {
               if (isalnum(cu)) {
                 regmbc(cu);
               }
             }
             break;
           case CLASS_ALPHA:
             for (cu = 1; cu < 128; cu++) {
               if (isalpha(cu)) {
                 regmbc(cu);
               }
             }
             break;
           case CLASS_BLANK:
             regc(' ');
             regc('\t');
             break;
           case CLASS_CNTRL:
             for (cu = 1; cu <= 127; cu++) {
               if (iscntrl(cu)) {
                 regmbc(cu);
               }
             }
             break;
           case CLASS_DIGIT:
             for (cu = 1; cu <= 127; cu++) {
               if (ascii_isdigit(cu)) {
                 regmbc(cu);
               }
             }
             break;
           case CLASS_GRAPH:
             for (cu = 1; cu <= 127; cu++) {
               if (isgraph(cu)) {
                 regmbc(cu);
               }
             }
             break;
           case CLASS_LOWER:
             for (cu = 1; cu <= 255; cu++) {
               if (mb_islower(cu) && cu != 170 && cu != 186) {
                 regmbc(cu);
               }
             }
             break;
           case CLASS_PRINT:
             for (cu = 1; cu <= 255; cu++) {
               if (vim_isprintc(cu)) {
                 regmbc(cu);
               }
             }
             break;
           case CLASS_PUNCT:
             for (cu = 1; cu < 128; cu++) {
               if (ispunct(cu)) {
                 regmbc(cu);
               }
             }
             break;
           case CLASS_SPACE:
             for (cu = 9; cu <= 13; cu++) {
               regc(cu);
             }
             regc(' ');
             break;
           case CLASS_UPPER:
             for (cu = 1; cu <= 255; cu++) {
               if (mb_isupper(cu)) {
                 regmbc(cu);
               }
             }
             break;
           case CLASS_XDIGIT:
             for (cu = 1; cu <= 255; cu++) {
               if (ascii_isxdigit(cu)) {
                 regmbc(cu);
               }
             }
             break;
           case CLASS_TAB:
             regc('\t');
             break;
           case CLASS_RETURN:
             regc('\r');
             break;
           case CLASS_BACKSPACE:
             regc('\b');
             break;
           case CLASS_ESCAPE:
             regc(ESC);
             break;
           case CLASS_IDENT:
             for (cu = 1; cu <= 255; cu++) {
               if (vim_isIDc(cu)) {
                 regmbc(cu);
               }
             }
             break;
           case CLASS_KEYWORD:
             for (cu = 1; cu <= 255; cu++) {
               if (reg_iswordc(cu)) {
                 regmbc(cu);
               }
             }
             break;
           case CLASS_FNAME:
             for (cu = 1; cu <= 255; cu++) {
               if (vim_isfilec(cu)) {
                 regmbc(cu);
               }
             }
             break;
           }
         } else {
           // produce a multibyte character, including any
           // following composing characters.
           startc = utf_ptr2char(regparse);
           int len = utfc_ptr2len(regparse);
           if (utf_char2len(startc) != len) {
             // composing chars
             startc = -1;
           }
           while (--len >= 0) {
             regc(*regparse++);
           }
         }
       }
       regc(NUL);
       prevchr_len = 1;                // last char was the ']'
       if (*regparse != ']') {
         EMSG_RET_NULL(_(e_toomsbra));                 // Cannot happen?
       }
       skipchr();                  // let's be friends with the lexer again
       *flagp |= HASWIDTH | SIMPLE;
       break;
     } else if (reg_strict) {
       EMSG2_RET_NULL(_(e_missingbracket), reg_magic > MAGIC_OFF);
     }
   }
   FALLTHROUGH;

 default: {
   int len;

   // A multi-byte character is handled as a separate atom if it's
   // before a multi and when it's a composing char.
   if (use_multibytecode(c)) {
do_multibyte:
     ret = regnode(MULTIBYTECODE);
     regmbc(c);
     *flagp |= HASWIDTH | SIMPLE;
     break;
   }

   ret = regnode(EXACTLY);

   // Append characters as long as:
   // - there is no following multi, we then need the character in
   //   front of it as a single character operand
   // - not running into a Magic character
   // - "one_exactly" is not set
   // But always emit at least one character.  Might be a Multi,
   // e.g., a "[" without matching "]".
   for (len = 0; c != NUL && (len == 0
                              || (re_multi_type(peekchr()) == NOT_MULTI
                                  && !one_exactly
                                  && !is_Magic(c))); len++) {
     c = no_Magic(c);
     {
       regmbc(c);
       {
         int l;

         // Need to get composing character too.
         GraphemeState state = GRAPHEME_STATE_INIT;
         while (true) {
           l = utf_ptr2len(regparse);
           if (!utf_composinglike(regparse, regparse + l, &state)) {
             break;
           }
           regmbc(utf_ptr2char(regparse));
           skipchr();
         }
       }
     }
     c = getchr();
   }
   ungetchr();

   regc(NUL);
   *flagp |= HASWIDTH;
   if (len == 1) {
     *flagp |= SIMPLE;
   }
 }
 break;
 }

 return ret;
}

// Parse something followed by possible [*+=].
//
// Note that the branching code sequences used for = and the general cases
// of * and + are somewhat optimized:  they use the same NOTHING node as
// both the endmarker for their branch list and the body of the last branch.
// It might seem that this node could be dispensed with entirely, but the
// endmarker role is not redundant.
static uint8_t *regpiece(int *flagp)
{
 uint8_t *ret;
 int op;
 uint8_t *next;
 int flags;
 int minval;
 int maxval;

 ret = regatom(&flags);
 if (ret == NULL) {
   return NULL;
 }

 op = peekchr();
 if (re_multi_type(op) == NOT_MULTI) {
   *flagp = flags;
   return ret;
 }
 // default flags
 *flagp = (WORST | SPSTART | (flags & (HASNL | HASLOOKBH)));

 skipchr();
 switch (op) {
 case Magic('*'):
   if (flags & SIMPLE) {
     reginsert(STAR, ret);
   } else {
     // Emit x* as (x&|), where & means "self".
     reginsert(BRANCH, ret);           // Either x
     regoptail(ret, regnode(BACK));            // and loop
     regoptail(ret, ret);              // back
     regtail(ret, regnode(BRANCH));            // or
     regtail(ret, regnode(NOTHING));           // null.
   }
   break;

 case Magic('+'):
   if (flags & SIMPLE) {
     reginsert(PLUS, ret);
   } else {
     // Emit x+ as x(&|), where & means "self".
     next = regnode(BRANCH);           // Either
     regtail(ret, next);
     regtail(regnode(BACK), ret);              // loop back
     regtail(next, regnode(BRANCH));           // or
     regtail(ret, regnode(NOTHING));           // null.
   }
   *flagp = (WORST | HASWIDTH | (flags & (HASNL | HASLOOKBH)));
   break;

 case Magic('@'): {
   int lop = END;
   int64_t nr = getdecchrs();

   switch (no_Magic(getchr())) {
   case '=':
     lop = MATCH; break;                                 // \@=
   case '!':
     lop = NOMATCH; break;                               // \@!
   case '>':
     lop = SUBPAT; break;                                // \@>
   case '<':
     switch (no_Magic(getchr())) {
     case '=':
       lop = BEHIND; break;                               // \@<=
     case '!':
       lop = NOBEHIND; break;                             // \@<!
     }
   }
   if (lop == END) {
     EMSG2_RET_NULL(_(e_invalid_character_after_str_at),
                    reg_magic == MAGIC_ALL);
   }
   // Look behind must match with behind_pos.
   if (lop == BEHIND || lop == NOBEHIND) {
     regtail(ret, regnode(BHPOS));
     *flagp |= HASLOOKBH;
   }
   regtail(ret, regnode(END));             // operand ends
   if (lop == BEHIND || lop == NOBEHIND) {
     if (nr < 0) {
       nr = 0;                 // no limit is same as zero limit
     }
     reginsert_nr(lop, (uint32_t)nr, ret);
   } else {
     reginsert(lop, ret);
   }
   break;
 }

 case Magic('?'):
 case Magic('='):
   // Emit x= as (x|)
   reginsert(BRANCH, ret);                     // Either x
   regtail(ret, regnode(BRANCH));              // or
   next = regnode(NOTHING);                    // null.
   regtail(ret, next);
   regoptail(ret, next);
   break;

 case Magic('{'):
   if (!read_limits(&minval, &maxval)) {
     return NULL;
   }
   if (flags & SIMPLE) {
     reginsert(BRACE_SIMPLE, ret);
     reginsert_limits(BRACE_LIMITS, minval, maxval, ret);
   } else {
     if (num_complex_braces >= 10) {
       EMSG2_RET_NULL(_("E60: Too many complex %s{...}s"),
                      reg_magic == MAGIC_ALL);
     }
     reginsert(BRACE_COMPLEX + num_complex_braces, ret);
     regoptail(ret, regnode(BACK));
     regoptail(ret, ret);
     reginsert_limits(BRACE_LIMITS, minval, maxval, ret);
     num_complex_braces++;
   }
   if (minval > 0 && maxval > 0) {
     *flagp = (HASWIDTH | (flags & (HASNL | HASLOOKBH)));
   }
   break;
 }
 if (re_multi_type(peekchr()) != NOT_MULTI) {
   // Can't have a multi follow a multi.
   if (peekchr() == Magic('*')) {
     EMSG2_RET_NULL(_("E61: Nested %s*"), reg_magic >= MAGIC_ON);
   }
   EMSG3_RET_NULL(_("E62: Nested %s%c"), reg_magic == MAGIC_ALL, no_Magic(peekchr()));
 }

 return ret;
}

// Parse one alternative of an | or & operator.
// Implements the concatenation operator.
static uint8_t *regconcat(int *flagp)
{
 uint8_t *first = NULL;
 uint8_t *chain = NULL;
 uint8_t *latest;
 int flags;
 int cont = true;

 *flagp = WORST;               // Tentatively.

 while (cont) {
   switch (peekchr()) {
   case NUL:
   case Magic('|'):
   case Magic('&'):
   case Magic(')'):
     cont = false;
     break;
   case Magic('Z'):
     regflags |= RF_ICOMBINE;
     skipchr_keepstart();
     break;
   case Magic('c'):
     regflags |= RF_ICASE;
     skipchr_keepstart();
     break;
   case Magic('C'):
     regflags |= RF_NOICASE;
     skipchr_keepstart();
     break;
   case Magic('v'):
     reg_magic = MAGIC_ALL;
     skipchr_keepstart();
     curchr = -1;
     break;
   case Magic('m'):
     reg_magic = MAGIC_ON;
     skipchr_keepstart();
     curchr = -1;
     break;
   case Magic('M'):
     reg_magic = MAGIC_OFF;
     skipchr_keepstart();
     curchr = -1;
     break;
   case Magic('V'):
     reg_magic = MAGIC_NONE;
     skipchr_keepstart();
     curchr = -1;
     break;
   default:
     latest = regpiece(&flags);
     if (latest == NULL || reg_toolong) {
       return NULL;
     }
     *flagp |= flags & (HASWIDTH | HASNL | HASLOOKBH);
     if (chain == NULL) {                      // First piece.
       *flagp |= flags & SPSTART;
     } else {
       regtail(chain, latest);
     }
     chain = latest;
     if (first == NULL) {
       first = latest;
     }
     break;
   }
 }
 if (first == NULL) {          // Loop ran zero times.
   first = regnode(NOTHING);
 }
 return first;
}

// Parse one alternative of an | operator.
// Implements the & operator.
static uint8_t *regbranch(int *flagp)
{
 uint8_t *ret;
 uint8_t *chain = NULL;
 uint8_t *latest;
 int flags;

 *flagp = WORST | HASNL;               // Tentatively.

 ret = regnode(BRANCH);
 while (true) {
   latest = regconcat(&flags);
   if (latest == NULL) {
     return NULL;
   }
   // If one of the branches has width, the whole thing has.  If one of
   // the branches anchors at start-of-line, the whole thing does.
   // If one of the branches uses look-behind, the whole thing does.
   *flagp |= flags & (HASWIDTH | SPSTART | HASLOOKBH);
   // If one of the branches doesn't match a line-break, the whole thing
   // doesn't.
   *flagp &= ~HASNL | (flags & HASNL);
   if (chain != NULL) {
     regtail(chain, latest);
   }
   if (peekchr() != Magic('&')) {
     break;
   }
   skipchr();
   regtail(latest, regnode(END));     // operand ends
   if (reg_toolong) {
     break;
   }
   reginsert(MATCH, latest);
   chain = latest;
 }

 return ret;
}

/// Parse regular expression, i.e. main body or parenthesized thing.
///
/// Caller must absorb opening parenthesis.
///
/// Combining parenthesis handling with the base level of regular expression
/// is a trifle forced, but the need to tie the tails of the branches to what
/// follows makes it hard to avoid.
///
/// @param paren  REG_NOPAREN, REG_PAREN, REG_NPAREN or REG_ZPAREN
static uint8_t *reg(int paren, int *flagp)
{
 uint8_t *ret;
 uint8_t *br;
 uint8_t *ender;
 int parno = 0;
 int flags;

 *flagp = HASWIDTH;            // Tentatively.

 if (paren == REG_ZPAREN) {
   // Make a ZOPEN node.
   if (regnzpar >= NSUBEXP) {
     EMSG_RET_NULL(_("E50: Too many \\z("));
   }
   parno = regnzpar;
   regnzpar++;
   ret = regnode(ZOPEN + parno);
 } else if (paren == REG_PAREN) {
   // Make a MOPEN node.
   if (regnpar >= NSUBEXP) {
     EMSG2_RET_NULL(_("E51: Too many %s("), reg_magic == MAGIC_ALL);
   }
   parno = regnpar;
   regnpar++;
   ret = regnode(MOPEN + parno);
 } else if (paren == REG_NPAREN) {
   // Make a NOPEN node.
   ret = regnode(NOPEN);
 } else {
   ret = NULL;
 }

 // Pick up the branches, linking them together.
 br = regbranch(&flags);
 if (br == NULL) {
   return NULL;
 }
 if (ret != NULL) {
   regtail(ret, br);           // [MZ]OPEN -> first.
 } else {
   ret = br;
 }
 // If one of the branches can be zero-width, the whole thing can.
 // If one of the branches has * at start or matches a line-break, the
 // whole thing can.
 if (!(flags & HASWIDTH)) {
   *flagp &= ~HASWIDTH;
 }
 *flagp |= flags & (SPSTART | HASNL | HASLOOKBH);
 while (peekchr() == Magic('|')) {
   skipchr();
   br = regbranch(&flags);
   if (br == NULL || reg_toolong) {
     return NULL;
   }
   regtail(ret, br);           // BRANCH -> BRANCH.
   if (!(flags & HASWIDTH)) {
     *flagp &= ~HASWIDTH;
   }
   *flagp |= flags & (SPSTART | HASNL | HASLOOKBH);
 }

 // Make a closing node, and hook it on the end.
 ender = regnode(paren == REG_ZPAREN ? ZCLOSE + parno
                                     : paren == REG_PAREN ? MCLOSE + parno
                                                          : paren == REG_NPAREN ? NCLOSE : END);
 regtail(ret, ender);

 // Hook the tails of the branches to the closing node.
 for (br = ret; br != NULL; br = regnext(br)) {
   regoptail(br, ender);
 }

 // Check for proper termination.
 if (paren != REG_NOPAREN && getchr() != Magic(')')) {
   if (paren == REG_ZPAREN) {
     EMSG_RET_NULL(_("E52: Unmatched \\z("));
   } else if (paren == REG_NPAREN) {
     EMSG2_RET_NULL(_(e_unmatchedpp), reg_magic == MAGIC_ALL);
   } else {
     EMSG2_RET_NULL(_(e_unmatchedp), reg_magic == MAGIC_ALL);
   }
 } else if (paren == REG_NOPAREN && peekchr() != NUL) {
   if (curchr == Magic(')')) {
     EMSG2_RET_NULL(_(e_unmatchedpar), reg_magic == MAGIC_ALL);
   } else {
     EMSG_RET_NULL(_(e_trailing));             // "Can't happen".
   }
   // NOTREACHED
 }
 // Here we set the flag allowing back references to this set of
 // parentheses.
 if (paren == REG_PAREN) {
   had_endbrace[parno] = true;  // have seen the close paren
 }
 return ret;
}

// bt_regcomp() - compile a regular expression into internal code for the
// traditional back track matcher.
// Returns the program in allocated space.  Returns NULL for an error.
//
// We can't allocate space until we know how big the compiled form will be,
// but we can't compile it (and thus know how big it is) until we've got a
// place to put the code.  So we cheat:  we compile it twice, once with code
// generation turned off and size counting turned on, and once "for real".
// This also means that we don't allocate space until we are sure that the
// thing really will compile successfully, and we never have to move the
// code and thus invalidate pointers into it.  (Note that it has to be in
// one piece because free() must be able to free it all.)
//
// Whether upper/lower case is to be ignored is decided when executing the
// program, it does not matter here.
//
// Beware that the optimization-preparation code in here knows about some
// of the structure of the compiled regexp.
// "re_flags": RE_MAGIC and/or RE_STRING.
static regprog_T *bt_regcomp(uint8_t *expr, int re_flags)
{
 uint8_t *scan;
 uint8_t *longest;
 int len;
 int flags;

 if (expr == NULL) {
   IEMSG_RET_NULL(_(e_null));
 }

 init_class_tab();

 // First pass: determine size, legality.
 regcomp_start(expr, re_flags);
 regcode = JUST_CALC_SIZE;
 regc(REGMAGIC);
 if (reg(REG_NOPAREN, &flags) == NULL) {
   return NULL;
 }

 // Allocate space.
 bt_regprog_T *r = xmalloc(offsetof(bt_regprog_T, program) + (size_t)regsize);
 r->re_in_use = false;

 // Second pass: emit code.
 regcomp_start(expr, re_flags);
 regcode = r->program;
 regc(REGMAGIC);
 if (reg(REG_NOPAREN, &flags) == NULL || reg_toolong) {
   xfree(r);
   if (reg_toolong) {
     EMSG_RET_NULL(_("E339: Pattern too long"));
   }
   return NULL;
 }

 // Dig out information for optimizations.
 r->regstart = NUL;            // Worst-case defaults.
 r->reganch = 0;
 r->regmust = NULL;
 r->regmlen = 0;
 r->regflags = regflags;
 if (flags & HASNL) {
   r->regflags |= RF_HASNL;
 }
 if (flags & HASLOOKBH) {
   r->regflags |= RF_LOOKBH;
 }
 // Remember whether this pattern has any \z specials in it.
 r->reghasz = (uint8_t)re_has_z;
 scan = &r->program[1];  // First BRANCH.
 if (OP(regnext(scan)) == END) {   // Only one top-level choice.
   scan = OPERAND(scan);

   // Starting-point info.
   if (OP(scan) == BOL || OP(scan) == RE_BOF) {
     r->reganch++;
     scan = regnext(scan);
   }

   if (OP(scan) == EXACTLY) {
     r->regstart = utf_ptr2char((char *)OPERAND(scan));
   } else if (OP(scan) == BOW
              || OP(scan) == EOW
              || OP(scan) == NOTHING
              || OP(scan) == MOPEN + 0 || OP(scan) == NOPEN
              || OP(scan) == MCLOSE + 0 || OP(scan) == NCLOSE) {
     uint8_t *regnext_scan = regnext(scan);
     if (OP(regnext_scan) == EXACTLY) {
       r->regstart = utf_ptr2char((char *)OPERAND(regnext_scan));
     }
   }

   // If there's something expensive in the r.e., find the longest
   // literal string that must appear and make it the regmust.  Resolve
   // ties in favor of later strings, since the regstart check works
   // with the beginning of the r.e. and avoiding duplication
   // strengthens checking.  Not a strong reason, but sufficient in the
   // absence of others.

   // When the r.e. starts with BOW, it is faster to look for a regmust
   // first. Used a lot for "#" and "*" commands. (Added by mool).
   if ((flags & SPSTART || OP(scan) == BOW || OP(scan) == EOW)
       && !(flags & HASNL)) {
     longest = NULL;
     len = 0;
     for (; scan != NULL; scan = regnext(scan)) {
       if (OP(scan) == EXACTLY) {
         size_t scanlen = strlen((char *)OPERAND(scan));
         if (scanlen >= (size_t)len) {
           longest = OPERAND(scan);
           len = (int)scanlen;
         }
       }
     }
     r->regmust = longest;
     r->regmlen = len;
   }
 }
#ifdef BT_REGEXP_DUMP
 regdump(expr, r);
#endif
 r->engine = &bt_regengine;
 return (regprog_T *)r;
}

// Check if during the previous call to vim_regcomp the EOL item "$" has been
// found.  This is messy, but it works fine.
int vim_regcomp_had_eol(void)
{
 return had_eol;
}

// Get a number after a backslash that is inside [].
// When nothing is recognized return a backslash.
static int coll_get_char(void)
{
 int64_t nr = -1;

 switch (*regparse++) {
 case 'd':
   nr = getdecchrs(); break;
 case 'o':
   nr = getoctchrs(); break;
 case 'x':
   nr = gethexchrs(2); break;
 case 'u':
   nr = gethexchrs(4); break;
 case 'U':
   nr = gethexchrs(8); break;
 }
 if (nr < 0) {
   // If getting the number fails be backwards compatible: the character
   // is a backslash.
   regparse--;
   nr = '\\';
 }
 if (nr > INT_MAX) {
   nr = INT_MAX;
 }
 return (int)nr;
}

// Free a compiled regexp program, returned by bt_regcomp().
static void bt_regfree(regprog_T *prog)
{
 xfree(prog);
}

#define ADVANCE_REGINPUT() MB_PTR_ADV(rex.input)

// The arguments from BRACE_LIMITS are stored here.  They are actually local
// to regmatch(), but they are here to reduce the amount of stack space used
// (it can be called recursively many times).
static int64_t bl_minval;
static int64_t bl_maxval;

// Save the input line and position in a regsave_T.
static void reg_save(regsave_T *save, garray_T *gap)
 FUNC_ATTR_NONNULL_ALL
{
 if (REG_MULTI) {
   save->rs_u.pos.col = (colnr_T)(rex.input - rex.line);
   save->rs_u.pos.lnum = rex.lnum;
 } else {
   save->rs_u.ptr = rex.input;
 }
 save->rs_len = gap->ga_len;
}

// Restore the input line and position from a regsave_T.
static void reg_restore(regsave_T *save, garray_T *gap)
 FUNC_ATTR_NONNULL_ALL
{
 if (REG_MULTI) {
   if (rex.lnum != save->rs_u.pos.lnum) {
     // only call reg_getline() when the line number changed to save
     // a bit of time
     rex.lnum = save->rs_u.pos.lnum;
     rex.line = (uint8_t *)reg_getline(rex.lnum);
   }
   rex.input = rex.line + save->rs_u.pos.col;
 } else {
   rex.input = save->rs_u.ptr;
 }
 gap->ga_len = save->rs_len;
}

// Return true if current position is equal to saved position.
static bool reg_save_equal(const regsave_T *save)
 FUNC_ATTR_NONNULL_ALL
{
 if (REG_MULTI) {
   return rex.lnum == save->rs_u.pos.lnum
          && rex.input == rex.line + save->rs_u.pos.col;
 }
 return rex.input == save->rs_u.ptr;
}

// Save the sub-expressions before attempting a match.
#define save_se(savep, posp, pp) \
 REG_MULTI ? save_se_multi((savep), (posp)) : save_se_one((savep), (pp))

// After a failed match restore the sub-expressions.
#define restore_se(savep, posp, pp) { \
 if (REG_MULTI) \
 *(posp) = (savep)->se_u.pos; \
 else \
 *(pp) = (savep)->se_u.ptr; }

// Tentatively set the sub-expression start to the current position (after
// calling regmatch() they will have changed).  Need to save the existing
// values for when there is no match.
// Use se_save() to use pointer (save_se_multi()) or position (save_se_one()),
// depending on REG_MULTI.
static void save_se_multi(save_se_T *savep, lpos_T *posp)
{
 savep->se_u.pos = *posp;
 posp->lnum = rex.lnum;
 posp->col = (colnr_T)(rex.input - rex.line);
}

static void save_se_one(save_se_T *savep, uint8_t **pp)
{
 savep->se_u.ptr = *pp;
 *pp = rex.input;
}

/// regrepeat - repeatedly match something simple, return how many.
/// Advances rex.input (and rex.lnum) to just after the matched chars.
///
/// @param maxcount  maximum number of matches allowed
static int regrepeat(uint8_t *p, int64_t maxcount)
{
 int64_t count = 0;
 uint8_t *opnd;
 int mask;
 int testval = 0;

 uint8_t *scan = rex.input;  // Make local copy of rex.input for speed.
 opnd = OPERAND(p);
 switch (OP(p)) {
 case ANY:
 case ANY + ADD_NL:
   while (count < maxcount) {
     // Matching anything means we continue until end-of-line (or
     // end-of-file for ANY + ADD_NL), only limited by maxcount.
     while (*scan != NUL && count < maxcount) {
       count++;
       MB_PTR_ADV(scan);
     }
     if (!REG_MULTI || !WITH_NL(OP(p)) || rex.lnum > rex.reg_maxline
         || rex.reg_line_lbr || count == maxcount) {
       break;
     }
     count++;  // count the line-break
     reg_nextline();
     scan = rex.input;
     if (got_int) {
       break;
     }
   }
   break;

 case IDENT:
 case IDENT + ADD_NL:
   testval = 1;
   FALLTHROUGH;
 case SIDENT:
 case SIDENT + ADD_NL:
   while (count < maxcount) {
     if (vim_isIDc(utf_ptr2char((char *)scan)) && (testval || !ascii_isdigit(*scan))) {
       MB_PTR_ADV(scan);
     } else if (*scan == NUL) {
       if (!REG_MULTI || !WITH_NL(OP(p)) || rex.lnum > rex.reg_maxline
           || rex.reg_line_lbr) {
         break;
       }
       reg_nextline();
       scan = rex.input;
       if (got_int) {
         break;
       }
     } else if (rex.reg_line_lbr && *scan == '\n' && WITH_NL(OP(p))) {
       scan++;
     } else {
       break;
     }
     count++;
   }
   break;

 case KWORD:
 case KWORD + ADD_NL:
   testval = 1;
   FALLTHROUGH;
 case SKWORD:
 case SKWORD + ADD_NL:
   while (count < maxcount) {
     if (vim_iswordp_buf((char *)scan, rex.reg_buf)
         && (testval || !ascii_isdigit(*scan))) {
       MB_PTR_ADV(scan);
     } else if (*scan == NUL) {
       if (!REG_MULTI || !WITH_NL(OP(p)) || rex.lnum > rex.reg_maxline
           || rex.reg_line_lbr) {
         break;
       }
       reg_nextline();
       scan = rex.input;
       if (got_int) {
         break;
       }
     } else if (rex.reg_line_lbr && *scan == '\n' && WITH_NL(OP(p))) {
       scan++;
     } else {
       break;
     }
     count++;
   }
   break;

 case FNAME:
 case FNAME + ADD_NL:
   testval = 1;
   FALLTHROUGH;
 case SFNAME:
 case SFNAME + ADD_NL:
   while (count < maxcount) {
     if (vim_isfilec(utf_ptr2char((char *)scan)) && (testval || !ascii_isdigit(*scan))) {
       MB_PTR_ADV(scan);
     } else if (*scan == NUL) {
       if (!REG_MULTI || !WITH_NL(OP(p)) || rex.lnum > rex.reg_maxline
           || rex.reg_line_lbr) {
         break;
       }
       reg_nextline();
       scan = rex.input;
       if (got_int) {
         break;
       }
     } else if (rex.reg_line_lbr && *scan == '\n' && WITH_NL(OP(p))) {
       scan++;
     } else {
       break;
     }
     count++;
   }
   break;

 case PRINT:
 case PRINT + ADD_NL:
   testval = 1;
   FALLTHROUGH;
 case SPRINT:
 case SPRINT + ADD_NL:
   while (count < maxcount) {
     if (*scan == NUL) {
       if (!REG_MULTI || !WITH_NL(OP(p)) || rex.lnum > rex.reg_maxline
           || rex.reg_line_lbr) {
         break;
       }
       reg_nextline();
       scan = rex.input;
       if (got_int) {
         break;
       }
     } else if (vim_isprintc(utf_ptr2char((char *)scan)) == 1
                && (testval || !ascii_isdigit(*scan))) {
       MB_PTR_ADV(scan);
     } else if (rex.reg_line_lbr && *scan == '\n' && WITH_NL(OP(p))) {
       scan++;
     } else {
       break;
     }
     count++;
   }
   break;

 case WHITE:
 case WHITE + ADD_NL:
   testval = mask = RI_WHITE;
do_class:
   while (count < maxcount) {
     int l;
     if (*scan == NUL) {
       if (!REG_MULTI || !WITH_NL(OP(p)) || rex.lnum > rex.reg_maxline
           || rex.reg_line_lbr) {
         break;
       }
       reg_nextline();
       scan = rex.input;
       if (got_int) {
         break;
       }
     } else if ((l = utfc_ptr2len((char *)scan)) > 1) {
       if (testval != 0) {
         break;
       }
       scan += l;
     } else if ((class_tab[*scan] & mask) == testval) {
       scan++;
     } else if (rex.reg_line_lbr && *scan == '\n' && WITH_NL(OP(p))) {
       scan++;
     } else {
       break;
     }
     count++;
   }
   break;

 case NWHITE:
 case NWHITE + ADD_NL:
   mask = RI_WHITE;
   goto do_class;
 case DIGIT:
 case DIGIT + ADD_NL:
   testval = mask = RI_DIGIT;
   goto do_class;
 case NDIGIT:
 case NDIGIT + ADD_NL:
   mask = RI_DIGIT;
   goto do_class;
 case HEX:
 case HEX + ADD_NL:
   testval = mask = RI_HEX;
   goto do_class;
 case NHEX:
 case NHEX + ADD_NL:
   mask = RI_HEX;
   goto do_class;
 case OCTAL:
 case OCTAL + ADD_NL:
   testval = mask = RI_OCTAL;
   goto do_class;
 case NOCTAL:
 case NOCTAL + ADD_NL:
   mask = RI_OCTAL;
   goto do_class;
 case WORD:
 case WORD + ADD_NL:
   testval = mask = RI_WORD;
   goto do_class;
 case NWORD:
 case NWORD + ADD_NL:
   mask = RI_WORD;
   goto do_class;
 case HEAD:
 case HEAD + ADD_NL:
   testval = mask = RI_HEAD;
   goto do_class;
 case NHEAD:
 case NHEAD + ADD_NL:
   mask = RI_HEAD;
   goto do_class;
 case ALPHA:
 case ALPHA + ADD_NL:
   testval = mask = RI_ALPHA;
   goto do_class;
 case NALPHA:
 case NALPHA + ADD_NL:
   mask = RI_ALPHA;
   goto do_class;
 case LOWER:
 case LOWER + ADD_NL:
   testval = mask = RI_LOWER;
   goto do_class;
 case NLOWER:
 case NLOWER + ADD_NL:
   mask = RI_LOWER;
   goto do_class;
 case UPPER:
 case UPPER + ADD_NL:
   testval = mask = RI_UPPER;
   goto do_class;
 case NUPPER:
 case NUPPER + ADD_NL:
   mask = RI_UPPER;
   goto do_class;

 case EXACTLY: {
   int cu, cl;

   // This doesn't do a multi-byte character, because a MULTIBYTECODE
   // would have been used for it.  It does handle single-byte
   // characters, such as latin1.
   if (rex.reg_ic) {
     cu = mb_toupper(*opnd);
     cl = mb_tolower(*opnd);
     while (count < maxcount && (*scan == cu || *scan == cl)) {
       count++;
       scan++;
     }
   } else {
     cu = *opnd;
     while (count < maxcount && *scan == cu) {
       count++;
       scan++;
     }
   }
   break;
 }

 case MULTIBYTECODE: {
   int i, len, cf = 0;

   // Safety check (just in case 'encoding' was changed since
   // compiling the program).
   if ((len = utfc_ptr2len((char *)opnd)) > 1) {
     if (rex.reg_ic) {
       cf = utf_fold(utf_ptr2char((char *)opnd));
     }
     while (count < maxcount && utfc_ptr2len((char *)scan) >= len) {
       for (i = 0; i < len; i++) {
         if (opnd[i] != scan[i]) {
           break;
         }
       }
       if (i < len && (!rex.reg_ic
                       || utf_fold(utf_ptr2char((char *)scan)) != cf)) {
         break;
       }
       scan += len;
       count++;
     }
   }
 }
 break;

 case ANYOF:
 case ANYOF + ADD_NL:
   testval = 1;
   FALLTHROUGH;

 case ANYBUT:
 case ANYBUT + ADD_NL:
   while (count < maxcount) {
     int len;
     if (*scan == NUL) {
       if (!REG_MULTI || !WITH_NL(OP(p)) || rex.lnum > rex.reg_maxline
           || rex.reg_line_lbr) {
         break;
       }
       reg_nextline();
       scan = rex.input;
       if (got_int) {
         break;
       }
     } else if (rex.reg_line_lbr && *scan == '\n' && WITH_NL(OP(p))) {
       scan++;
     } else if ((len = utfc_ptr2len((char *)scan)) > 1) {
       if ((cstrchr((char *)opnd, utf_ptr2char((char *)scan)) == NULL) == testval) {
         break;
       }
       scan += len;
     } else {
       if ((cstrchr((char *)opnd, *scan) == NULL) == testval) {
         break;
       }
       scan++;
     }
     count++;
   }
   break;

 case NEWL:
   while (count < maxcount
          && ((*scan == NUL && rex.lnum <= rex.reg_maxline && !rex.reg_line_lbr
               && REG_MULTI) || (*scan == '\n' && rex.reg_line_lbr))) {
     count++;
     if (rex.reg_line_lbr) {
       ADVANCE_REGINPUT();
     } else {
       reg_nextline();
     }
     scan = rex.input;
     if (got_int) {
       break;
     }
   }
   break;

 default:  // Oh dear.  Called inappropriately.
   iemsg(_(e_re_corr));
#ifdef REGEXP_DEBUG
   printf("Called regrepeat with op code %d\n", OP(p));
#endif
   break;
 }

 rex.input = scan;

 return (int)count;
}

// Push an item onto the regstack.
// Returns pointer to new item.  Returns NULL when out of memory.
static regitem_T *regstack_push(regstate_T state, uint8_t *scan)
{
 regitem_T *rp;

 if ((int64_t)((unsigned)regstack.ga_len >> 10) >= p_mmp) {
   emsg(_(e_pattern_uses_more_memory_than_maxmempattern));
   return NULL;
 }
 ga_grow(&regstack, sizeof(regitem_T));

 rp = (regitem_T *)((char *)regstack.ga_data + regstack.ga_len);
 rp->rs_state = state;
 rp->rs_scan = scan;

 regstack.ga_len += (int)sizeof(regitem_T);
 return rp;
}

// Pop an item from the regstack.
static void regstack_pop(uint8_t **scan)
{
 regitem_T *rp;

 rp = (regitem_T *)((char *)regstack.ga_data + regstack.ga_len) - 1;
 *scan = rp->rs_scan;

 regstack.ga_len -= (int)sizeof(regitem_T);
}

// Save the current subexpr to "bp", so that they can be restored
// later by restore_subexpr().
static void save_subexpr(regbehind_T *bp)
 FUNC_ATTR_NONNULL_ALL
{
 // When "rex.need_clear_subexpr" is set we don't need to save the values, only
 // remember that this flag needs to be set again when restoring.
 bp->save_need_clear_subexpr = rex.need_clear_subexpr;
 if (rex.need_clear_subexpr) {
   return;
 }

 for (int i = 0; i < NSUBEXP; i++) {
   if (REG_MULTI) {
     bp->save_start[i].se_u.pos = rex.reg_startpos[i];
     bp->save_end[i].se_u.pos = rex.reg_endpos[i];
   } else {
     bp->save_start[i].se_u.ptr = rex.reg_startp[i];
     bp->save_end[i].se_u.ptr = rex.reg_endp[i];
   }
 }
}

// Restore the subexpr from "bp".
static void restore_subexpr(regbehind_T *bp)
 FUNC_ATTR_NONNULL_ALL
{
 // Only need to restore saved values when they are not to be cleared.
 rex.need_clear_subexpr = bp->save_need_clear_subexpr;
 if (rex.need_clear_subexpr) {
   return;
 }

 for (int i = 0; i < NSUBEXP; i++) {
   if (REG_MULTI) {
     rex.reg_startpos[i] = bp->save_start[i].se_u.pos;
     rex.reg_endpos[i] = bp->save_end[i].se_u.pos;
   } else {
     rex.reg_startp[i] = bp->save_start[i].se_u.ptr;
     rex.reg_endp[i] = bp->save_end[i].se_u.ptr;
   }
 }
}
/// Main matching routine
///
/// Conceptually the strategy is simple: Check to see whether the current node
/// matches, push an item onto the regstack and loop to see whether the rest
/// matches, and then act accordingly.  In practice we make some effort to
/// avoid using the regstack, in particular by going through "ordinary" nodes
/// (that don't need to know whether the rest of the match failed) by a nested
/// loop.
///
/// @param scan       Current node.
/// @param tm         timeout limit or NULL
/// @param timed_out  flag set on timeout or NULL
///
/// @return - true when there is a match.  Leaves rex.input and rex.lnum
///         just after the last matched character.
///         - false when there is no match.  Leaves rex.input and rex.lnum in an
///         undefined state!
static bool regmatch(uint8_t *scan, const proftime_T *tm, int *timed_out)
{
 uint8_t *next;          // Next node.
 int op;
 int c;
 regitem_T *rp;
 int no;
 int status;                   // one of the RA_ values:
 int tm_count = 0;

 // Make "regstack" and "backpos" empty.  They are allocated and freed in
 // bt_regexec_both() to reduce malloc()/free() calls.
 regstack.ga_len = 0;
 backpos.ga_len = 0;

 // Repeat until "regstack" is empty.
 while (true) {
   // Some patterns may take a long time to match, e.g., "\([a-z]\+\)\+Q".
   // Allow interrupting them with CTRL-C.
   reg_breakcheck();

#ifdef REGEXP_DEBUG
   if (scan != NULL && regnarrate) {
     fprintf(stderr, "%s", (char *)regprop(scan));
     fprintf(stderr, "%s", "(\n");
   }
#endif

   // Repeat for items that can be matched sequentially, without using the
   // regstack.
   while (true) {
     if (got_int || scan == NULL) {
       status = RA_FAIL;
       break;
     }
     // Check for timeout once in a 100 times to avoid overhead.
     if (tm != NULL && ++tm_count == 100) {
       tm_count = 0;
       if (profile_passed_limit(*tm)) {
         if (timed_out != NULL) {
           *timed_out = true;
         }
         status = RA_FAIL;
         break;
       }
     }
     status = RA_CONT;

#ifdef REGEXP_DEBUG
     if (regnarrate) {
       fprintf(stderr, "%s", (char *)regprop(scan));
       fprintf(stderr, "%s", "...\n");
       if (re_extmatch_in != NULL) {
         int i;

         fprintf(stderr, _("External submatches:\n"));
         for (i = 0; i < NSUBEXP; i++) {
           fprintf(stderr, "%s", "    \"");
           if (re_extmatch_in->matches[i] != NULL) {
             fprintf(stderr, "%s", (char *)re_extmatch_in->matches[i]);
           }
           fprintf(stderr, "%s", "\"\n");
         }
       }
     }
#endif
     next = regnext(scan);

     op = OP(scan);
     // Check for character class with NL added.
     if (!rex.reg_line_lbr && WITH_NL(op) && REG_MULTI
         && *rex.input == NUL && rex.lnum <= rex.reg_maxline) {
       reg_nextline();
     } else if (rex.reg_line_lbr && WITH_NL(op) && *rex.input == '\n') {
       ADVANCE_REGINPUT();
     } else {
       if (WITH_NL(op)) {
         op -= ADD_NL;
       }
       c = utf_ptr2char((char *)rex.input);
       switch (op) {
       case BOL:
         if (rex.input != rex.line) {
           status = RA_NOMATCH;
         }
         break;

       case EOL:
         if (c != NUL) {
           status = RA_NOMATCH;
         }
         break;

       case RE_BOF:
         // We're not at the beginning of the file when below the first
         // line where we started, not at the start of the line or we
         // didn't start at the first line of the buffer.
         if (rex.lnum != 0 || rex.input != rex.line
             || (REG_MULTI && rex.reg_firstlnum > 1)) {
           status = RA_NOMATCH;
         }
         break;

       case RE_EOF:
         if (rex.lnum != rex.reg_maxline || c != NUL) {
           status = RA_NOMATCH;
         }
         break;

       case CURSOR:
         // Check if the buffer is in a window and compare the
         // rex.reg_win->w_cursor position to the match position.
         if (rex.reg_win == NULL
             || (rex.lnum + rex.reg_firstlnum != rex.reg_win->w_cursor.lnum)
             || ((colnr_T)(rex.input - rex.line) !=
                 rex.reg_win->w_cursor.col)) {
           status = RA_NOMATCH;
         }
         break;

       case RE_MARK:
         // Compare the mark position to the match position.
       {
         int mark = OPERAND(scan)[0];
         int cmp = OPERAND(scan)[1];
         pos_T *pos;
         size_t col = REG_MULTI ? (size_t)(rex.input - rex.line) : 0;
         fmark_T *fm = mark_get(rex.reg_buf, curwin, NULL, kMarkBufLocal, mark);

         // Line may have been freed, get it again.
         if (REG_MULTI) {
           rex.line = (uint8_t *)reg_getline(rex.lnum);
           rex.input = rex.line + col;
         }

         if (fm == NULL                    // mark doesn't exist
             || fm->mark.lnum <= 0) {           // mark isn't set in reg_buf
           status = RA_NOMATCH;
         } else {
           pos = &fm->mark;
           const colnr_T pos_col = pos->lnum == rex.lnum + rex.reg_firstlnum
                                   && pos->col == MAXCOL
                                   ? reg_getline_len(pos->lnum - rex.reg_firstlnum)
                                   : pos->col;

           if (pos->lnum == rex.lnum + rex.reg_firstlnum
               ? (pos_col == (colnr_T)(rex.input - rex.line)
                  ? (cmp == '<' || cmp == '>')
                  : (pos_col < (colnr_T)(rex.input - rex.line)
                     ? cmp != '>'
                     : cmp != '<'))
               : (pos->lnum < rex.lnum + rex.reg_firstlnum
                  ? cmp != '>'
                  : cmp != '<')) {
             status = RA_NOMATCH;
           }
         }
       }
       break;

       case RE_VISUAL:
         if (!reg_match_visual()) {
           status = RA_NOMATCH;
         }
         break;

       case RE_LNUM:
         assert(rex.lnum + rex.reg_firstlnum >= 0
                && (uintmax_t)(rex.lnum + rex.reg_firstlnum) <= UINT32_MAX);
         if (!REG_MULTI
             || !re_num_cmp((uint32_t)(rex.lnum + rex.reg_firstlnum), scan)) {
           status = RA_NOMATCH;
         }
         break;

       case RE_COL:
         assert(rex.input - rex.line + 1 >= 0
                && (uintmax_t)(rex.input - rex.line + 1) <= UINT32_MAX);
         if (!re_num_cmp((uint32_t)(rex.input - rex.line + 1), scan)) {
           status = RA_NOMATCH;
         }
         break;

       case RE_VCOL: {
         win_T *wp = rex.reg_win == NULL ? curwin : rex.reg_win;
         linenr_T lnum = REG_MULTI ? rex.reg_firstlnum + rex.lnum : 1;
         if (REG_MULTI && (lnum <= 0 || lnum > wp->w_buffer->b_ml.ml_line_count)) {
           lnum = 1;
         }
         int vcol = win_linetabsize(wp, lnum, (char *)rex.line,
                                    (colnr_T)(rex.input - rex.line));
         if (!re_num_cmp((uint32_t)vcol + 1, scan)) {
           status = RA_NOMATCH;
         }
         break;
       }
       break;

       case BOW:  // \<word; rex.input points to w
         if (c == NUL) {  // Can't match at end of line
           status = RA_NOMATCH;
         } else {
           // Get class of current and previous char (if it exists).
           const int this_class =
             mb_get_class_tab((char *)rex.input, rex.reg_buf->b_chartab);
           if (this_class <= 1) {
             status = RA_NOMATCH;  // Not on a word at all.
           } else if (reg_prev_class() == this_class) {
             status = RA_NOMATCH;  // Previous char is in same word.
           }
         }
         break;

       case EOW:  // word\>; rex.input points after d
         if (rex.input == rex.line) {  // Can't match at start of line
           status = RA_NOMATCH;
         } else {
           int this_class, prev_class;

           // Get class of current and previous char (if it exists).
           this_class = mb_get_class_tab((char *)rex.input, rex.reg_buf->b_chartab);
           prev_class = reg_prev_class();
           if (this_class == prev_class
               || prev_class == 0 || prev_class == 1) {
             status = RA_NOMATCH;
           }
         }
         break;  // Matched with EOW

       case ANY:
         // ANY does not match new lines.
         if (c == NUL) {
           status = RA_NOMATCH;
         } else {
           ADVANCE_REGINPUT();
         }
         break;

       case IDENT:
         if (!vim_isIDc(c)) {
           status = RA_NOMATCH;
         } else {
           ADVANCE_REGINPUT();
         }
         break;

       case SIDENT:
         if (ascii_isdigit(*rex.input) || !vim_isIDc(c)) {
           status = RA_NOMATCH;
         } else {
           ADVANCE_REGINPUT();
         }
         break;

       case KWORD:
         if (!vim_iswordp_buf((char *)rex.input, rex.reg_buf)) {
           status = RA_NOMATCH;
         } else {
           ADVANCE_REGINPUT();
         }
         break;

       case SKWORD:
         if (ascii_isdigit(*rex.input)
             || !vim_iswordp_buf((char *)rex.input, rex.reg_buf)) {
           status = RA_NOMATCH;
         } else {
           ADVANCE_REGINPUT();
         }
         break;

       case FNAME:
         if (!vim_isfilec(c)) {
           status = RA_NOMATCH;
         } else {
           ADVANCE_REGINPUT();
         }
         break;

       case SFNAME:
         if (ascii_isdigit(*rex.input) || !vim_isfilec(c)) {
           status = RA_NOMATCH;
         } else {
           ADVANCE_REGINPUT();
         }
         break;

       case PRINT:
         if (!vim_isprintc(utf_ptr2char((char *)rex.input))) {
           status = RA_NOMATCH;
         } else {
           ADVANCE_REGINPUT();
         }
         break;

       case SPRINT:
         if (ascii_isdigit(*rex.input) || !vim_isprintc(utf_ptr2char((char *)rex.input))) {
           status = RA_NOMATCH;
         } else {
           ADVANCE_REGINPUT();
         }
         break;

       case WHITE:
         if (!ascii_iswhite(c)) {
           status = RA_NOMATCH;
         } else {
           ADVANCE_REGINPUT();
         }
         break;

       case NWHITE:
         if (c == NUL || ascii_iswhite(c)) {
           status = RA_NOMATCH;
         } else {
           ADVANCE_REGINPUT();
         }
         break;

       case DIGIT:
         if (!ri_digit(c)) {
           status = RA_NOMATCH;
         } else {
           ADVANCE_REGINPUT();
         }
         break;

       case NDIGIT:
         if (c == NUL || ri_digit(c)) {
           status = RA_NOMATCH;
         } else {
           ADVANCE_REGINPUT();
         }
         break;

       case HEX:
         if (!ri_hex(c)) {
           status = RA_NOMATCH;
         } else {
           ADVANCE_REGINPUT();
         }
         break;

       case NHEX:
         if (c == NUL || ri_hex(c)) {
           status = RA_NOMATCH;
         } else {
           ADVANCE_REGINPUT();
         }
         break;

       case OCTAL:
         if (!ri_octal(c)) {
           status = RA_NOMATCH;
         } else {
           ADVANCE_REGINPUT();
         }
         break;

       case NOCTAL:
         if (c == NUL || ri_octal(c)) {
           status = RA_NOMATCH;
         } else {
           ADVANCE_REGINPUT();
         }
         break;

       case WORD:
         if (!ri_word(c)) {
           status = RA_NOMATCH;
         } else {
           ADVANCE_REGINPUT();
         }
         break;

       case NWORD:
         if (c == NUL || ri_word(c)) {
           status = RA_NOMATCH;
         } else {
           ADVANCE_REGINPUT();
         }
         break;

       case HEAD:
         if (!ri_head(c)) {
           status = RA_NOMATCH;
         } else {
           ADVANCE_REGINPUT();
         }
         break;

       case NHEAD:
         if (c == NUL || ri_head(c)) {
           status = RA_NOMATCH;
         } else {
           ADVANCE_REGINPUT();
         }
         break;

       case ALPHA:
         if (!ri_alpha(c)) {
           status = RA_NOMATCH;
         } else {
           ADVANCE_REGINPUT();
         }
         break;

       case NALPHA:
         if (c == NUL || ri_alpha(c)) {
           status = RA_NOMATCH;
         } else {
           ADVANCE_REGINPUT();
         }
         break;

       case LOWER:
         if (!ri_lower(c)) {
           status = RA_NOMATCH;
         } else {
           ADVANCE_REGINPUT();
         }
         break;

       case NLOWER:
         if (c == NUL || ri_lower(c)) {
           status = RA_NOMATCH;
         } else {
           ADVANCE_REGINPUT();
         }
         break;

       case UPPER:
         if (!ri_upper(c)) {
           status = RA_NOMATCH;
         } else {
           ADVANCE_REGINPUT();
         }
         break;

       case NUPPER:
         if (c == NUL || ri_upper(c)) {
           status = RA_NOMATCH;
         } else {
           ADVANCE_REGINPUT();
         }
         break;

       case EXACTLY: {
         int len;
         uint8_t *opnd;

         opnd = OPERAND(scan);
         // Inline the first byte, for speed.
         if (*opnd != *rex.input
             && (!rex.reg_ic)) {
           status = RA_NOMATCH;
         } else if (*opnd == NUL) {
           // match empty string always works; happens when "~" is
           // empty.
         } else {
           if (opnd[1] == NUL && !rex.reg_ic) {
             len = 1;  // matched a single byte above
           } else {
             // Need to match first byte again for multi-byte.
             len = (int)strlen((char *)opnd);
             if (cstrncmp((char *)opnd, (char *)rex.input, &len) != 0) {
               status = RA_NOMATCH;
             }
           }
           // Check for following composing character, unless %C
           // follows (skips over all composing chars).
           if (status != RA_NOMATCH
               && utf_composinglike((char *)rex.input, (char *)rex.input + len, NULL)
               && !rex.reg_icombine
               && OP(next) != RE_COMPOSING) {
             // raaron: This code makes a composing character get
             // ignored, which is the correct behavior (sometimes)
             // for voweled Hebrew texts.
             status = RA_NOMATCH;
           }
           if (status != RA_NOMATCH) {
             rex.input += len;
           }
         }
       }
       break;

       case ANYOF:
       case ANYBUT: {
         uint8_t *q = OPERAND(scan);

         if (c == NUL) {
           status = RA_NOMATCH;
         } else if ((cstrchr((char *)q, c) == NULL) == (op == ANYOF)) {
           status = RA_NOMATCH;
         } else {  // Check following combining characters
           int len = utfc_ptr2len((char *)q) - utf_ptr2len((char *)q);

           rex.input += utf_ptr2len((char *)rex.input);
           q += utf_ptr2len((char *)q);

           if (len == 0) {
             break;
           }

           for (int i = 0; i < len; i++) {
             if (q[i] != rex.input[i]) {
               status = RA_NOMATCH;
               break;
             }
           }
           rex.input += len;
         }
         break;
       }

       case MULTIBYTECODE: {
         int i, len;

         const uint8_t *opnd = OPERAND(scan);
         // Safety check (just in case 'encoding' was changed since
         // compiling the program).
         if ((len = utfc_ptr2len((char *)opnd)) < 2) {
           status = RA_NOMATCH;
           break;
         }
         const int opndc = utf_ptr2char((char *)opnd);
         if (utf_iscomposing_legacy(opndc)) {
           // When only a composing char is given match at any
           // position where that composing char appears.
           status = RA_NOMATCH;
           for (i = 0; rex.input[i] != NUL;
                i += utf_ptr2len((char *)rex.input + i)) {
             const int inpc = utf_ptr2char((char *)rex.input + i);
             if (!utf_iscomposing_legacy(inpc)) {
               if (i > 0) {
                 break;
               }
             } else if (opndc == inpc) {
               // Include all following composing chars.
               len = i + utfc_ptr2len((char *)rex.input + i);
               status = RA_MATCH;
               break;
             }
           }
         } else {
           if (cstrncmp((char *)opnd, (char *)rex.input, &len) != 0) {
             status = RA_NOMATCH;
             break;
           }
         }
         rex.input += len;
       }
       break;

       case RE_COMPOSING:
         // Skip composing characters.
         while (utf_iscomposing_legacy(utf_ptr2char((char *)rex.input))) {
           rex.input += utf_ptr2len((char *)rex.input);
         }
         break;

       case NOTHING:
         break;

       case BACK: {
         int i;

         // When we run into BACK we need to check if we don't keep
         // looping without matching any input.  The second and later
         // times a BACK is encountered it fails if the input is still
         // at the same position as the previous time.
         // The positions are stored in "backpos" and found by the
         // current value of "scan", the position in the RE program.
         backpos_T *bp = (backpos_T *)backpos.ga_data;
         for (i = 0; i < backpos.ga_len; i++) {
           if (bp[i].bp_scan == scan) {
             break;
           }
         }
         if (i == backpos.ga_len) {
           backpos_T *p = GA_APPEND_VIA_PTR(backpos_T, &backpos);
           p->bp_scan = scan;
         } else if (reg_save_equal(&bp[i].bp_pos)) {
           // Still at same position as last time, fail.
           status = RA_NOMATCH;
         }

         assert(status != RA_FAIL);
         if (status != RA_NOMATCH) {
           reg_save(&bp[i].bp_pos, &backpos);
         }
       }
       break;

       case MOPEN + 0:     // Match start: \zs
       case MOPEN + 1:     // \(
       case MOPEN + 2:
       case MOPEN + 3:
       case MOPEN + 4:
       case MOPEN + 5:
       case MOPEN + 6:
       case MOPEN + 7:
       case MOPEN + 8:
       case MOPEN + 9:
         no = op - MOPEN;
         cleanup_subexpr();
         rp = regstack_push(RS_MOPEN, scan);
         if (rp == NULL) {
           status = RA_FAIL;
         } else {
           rp->rs_no = (int16_t)no;
           save_se(&rp->rs_un.sesave, &rex.reg_startpos[no],
                   &rex.reg_startp[no]);
           // We simply continue and handle the result when done.
         }
         break;

       case NOPEN:         // \%(
       case NCLOSE:        // \) after \%(
         if (regstack_push(RS_NOPEN, scan) == NULL) {
           status = RA_FAIL;
         }
         // We simply continue and handle the result when done.
         break;

       case ZOPEN + 1:
       case ZOPEN + 2:
       case ZOPEN + 3:
       case ZOPEN + 4:
       case ZOPEN + 5:
       case ZOPEN + 6:
       case ZOPEN + 7:
       case ZOPEN + 8:
       case ZOPEN + 9:
         no = op - ZOPEN;
         cleanup_zsubexpr();
         rp = regstack_push(RS_ZOPEN, scan);
         if (rp == NULL) {
           status = RA_FAIL;
         } else {
           rp->rs_no = (int16_t)no;
           save_se(&rp->rs_un.sesave, &reg_startzpos[no],
                   &reg_startzp[no]);
           // We simply continue and handle the result when done.
         }
         break;

       case MCLOSE + 0:    // Match end: \ze
       case MCLOSE + 1:    // \)
       case MCLOSE + 2:
       case MCLOSE + 3:
       case MCLOSE + 4:
       case MCLOSE + 5:
       case MCLOSE + 6:
       case MCLOSE + 7:
       case MCLOSE + 8:
       case MCLOSE + 9:
         no = op - MCLOSE;
         cleanup_subexpr();
         rp = regstack_push(RS_MCLOSE, scan);
         if (rp == NULL) {
           status = RA_FAIL;
         } else {
           rp->rs_no = (int16_t)no;
           save_se(&rp->rs_un.sesave, &rex.reg_endpos[no], &rex.reg_endp[no]);
           // We simply continue and handle the result when done.
         }
         break;

       case ZCLOSE + 1:    // \) after \z(
       case ZCLOSE + 2:
       case ZCLOSE + 3:
       case ZCLOSE + 4:
       case ZCLOSE + 5:
       case ZCLOSE + 6:
       case ZCLOSE + 7:
       case ZCLOSE + 8:
       case ZCLOSE + 9:
         no = op - ZCLOSE;
         cleanup_zsubexpr();
         rp = regstack_push(RS_ZCLOSE, scan);
         if (rp == NULL) {
           status = RA_FAIL;
         } else {
           rp->rs_no = (int16_t)no;
           save_se(&rp->rs_un.sesave, &reg_endzpos[no],
                   &reg_endzp[no]);
           // We simply continue and handle the result when done.
         }
         break;

       case BACKREF + 1:
       case BACKREF + 2:
       case BACKREF + 3:
       case BACKREF + 4:
       case BACKREF + 5:
       case BACKREF + 6:
       case BACKREF + 7:
       case BACKREF + 8:
       case BACKREF + 9: {
         int len;

         no = op - BACKREF;
         cleanup_subexpr();
         if (!REG_MULTI) {  // Single-line regexp
           if (rex.reg_startp[no] == NULL || rex.reg_endp[no] == NULL) {
             // Backref was not set: Match an empty string.
             len = 0;
           } else {
             // Compare current input with back-ref in the same line.
             len = (int)(rex.reg_endp[no] - rex.reg_startp[no]);
             if (cstrncmp((char *)rex.reg_startp[no], (char *)rex.input, &len) != 0) {
               status = RA_NOMATCH;
             }
           }
         } else {  // Multi-line regexp
           if (rex.reg_startpos[no].lnum < 0 || rex.reg_endpos[no].lnum < 0) {
             // Backref was not set: Match an empty string.
             len = 0;
           } else {
             if (rex.reg_startpos[no].lnum == rex.lnum
                 && rex.reg_endpos[no].lnum == rex.lnum) {
               // Compare back-ref within the current line.
               len = rex.reg_endpos[no].col - rex.reg_startpos[no].col;
               if (cstrncmp((char *)rex.line + rex.reg_startpos[no].col,
                            (char *)rex.input, &len) != 0) {
                 status = RA_NOMATCH;
               }
             } else {
               // Messy situation: Need to compare between two lines.
               int r = match_with_backref(rex.reg_startpos[no].lnum,
                                          rex.reg_startpos[no].col,
                                          rex.reg_endpos[no].lnum,
                                          rex.reg_endpos[no].col,
                                          &len);
               if (r != RA_MATCH) {
                 status = r;
               }
             }
           }
         }

         // Matched the backref, skip over it.
         rex.input += len;
       }
       break;

       case ZREF + 1:
       case ZREF + 2:
       case ZREF + 3:
       case ZREF + 4:
       case ZREF + 5:
       case ZREF + 6:
       case ZREF + 7:
       case ZREF + 8:
       case ZREF + 9:
         cleanup_zsubexpr();
         no = op - ZREF;
         if (re_extmatch_in != NULL
             && re_extmatch_in->matches[no] != NULL) {
           int len = (int)strlen((char *)re_extmatch_in->matches[no]);
           if (cstrncmp((char *)re_extmatch_in->matches[no], (char *)rex.input, &len) != 0) {
             status = RA_NOMATCH;
           } else {
             rex.input += len;
           }
         } else {
           // Backref was not set: Match an empty string.
         }
         break;

       case BRANCH:
         if (OP(next) != BRANCH) {     // No choice.
           next = OPERAND(scan);               // Avoid recursion.
         } else {
           rp = regstack_push(RS_BRANCH, scan);
           if (rp == NULL) {
             status = RA_FAIL;
           } else {
             status = RA_BREAK;                // rest is below
           }
         }
         break;

       case BRACE_LIMITS:
         if (OP(next) == BRACE_SIMPLE) {
           bl_minval = OPERAND_MIN(scan);
           bl_maxval = OPERAND_MAX(scan);
         } else if (OP(next) >= BRACE_COMPLEX
                    && OP(next) < BRACE_COMPLEX + 10) {
           no = OP(next) - BRACE_COMPLEX;
           brace_min[no] = OPERAND_MIN(scan);
           brace_max[no] = OPERAND_MAX(scan);
           brace_count[no] = 0;
         } else {
           internal_error("BRACE_LIMITS");
           status = RA_FAIL;
         }
         break;

       case BRACE_COMPLEX + 0:
       case BRACE_COMPLEX + 1:
       case BRACE_COMPLEX + 2:
       case BRACE_COMPLEX + 3:
       case BRACE_COMPLEX + 4:
       case BRACE_COMPLEX + 5:
       case BRACE_COMPLEX + 6:
       case BRACE_COMPLEX + 7:
       case BRACE_COMPLEX + 8:
       case BRACE_COMPLEX + 9:
         no = op - BRACE_COMPLEX;
         brace_count[no]++;

         // If not matched enough times yet, try one more
         if (brace_count[no] <= (brace_min[no] <= brace_max[no]
                                 ? brace_min[no] : brace_max[no])) {
           rp = regstack_push(RS_BRCPLX_MORE, scan);
           if (rp == NULL) {
             status = RA_FAIL;
           } else {
             rp->rs_no = (int16_t)no;
             reg_save(&rp->rs_un.regsave, &backpos);
             next = OPERAND(scan);
             // We continue and handle the result when done.
           }
           break;
         }

         // If matched enough times, may try matching some more
         if (brace_min[no] <= brace_max[no]) {
           // Range is the normal way around, use longest match
           if (brace_count[no] <= brace_max[no]) {
             rp = regstack_push(RS_BRCPLX_LONG, scan);
             if (rp == NULL) {
               status = RA_FAIL;
             } else {
               rp->rs_no = (int16_t)no;
               reg_save(&rp->rs_un.regsave, &backpos);
               next = OPERAND(scan);
               // We continue and handle the result when done.
             }
           }
         } else {
           // Range is backwards, use shortest match first
           if (brace_count[no] <= brace_min[no]) {
             rp = regstack_push(RS_BRCPLX_SHORT, scan);
             if (rp == NULL) {
               status = RA_FAIL;
             } else {
               reg_save(&rp->rs_un.regsave, &backpos);
               // We continue and handle the result when done.
             }
           }
         }
         break;

       case BRACE_SIMPLE:
       case STAR:
       case PLUS: {
         regstar_T rst;

         // Lookahead to avoid useless match attempts when we know
         // what character comes next.
         if (OP(next) == EXACTLY) {
           rst.nextb = *OPERAND(next);
           if (rex.reg_ic) {
             if (mb_isupper(rst.nextb)) {
               rst.nextb_ic = mb_tolower(rst.nextb);
             } else {
               rst.nextb_ic = mb_toupper(rst.nextb);
             }
           } else {
             rst.nextb_ic = rst.nextb;
           }
         } else {
           rst.nextb = NUL;
           rst.nextb_ic = NUL;
         }
         if (op != BRACE_SIMPLE) {
           rst.minval = (op == STAR) ? 0 : 1;
           rst.maxval = MAX_LIMIT;
         } else {
           rst.minval = bl_minval;
           rst.maxval = bl_maxval;
         }

         // When maxval > minval, try matching as much as possible, up
         // to maxval.  When maxval < minval, try matching at least the
         // minimal number (since the range is backwards, that's also
         // maxval!).
         rst.count = regrepeat(OPERAND(scan), rst.maxval);
         if (got_int) {
           status = RA_FAIL;
           break;
         }
         if (rst.minval <= rst.maxval
             ? rst.count >= rst.minval : rst.count >= rst.maxval) {
           // It could match.  Prepare for trying to match what
           // follows.  The code is below.  Parameters are stored in
           // a regstar_T on the regstack.
           if ((int64_t)((unsigned)regstack.ga_len >> 10) >= p_mmp) {
             emsg(_(e_pattern_uses_more_memory_than_maxmempattern));
             status = RA_FAIL;
           } else {
             ga_grow(&regstack, sizeof(regstar_T));
             regstack.ga_len += (int)sizeof(regstar_T);
             rp = regstack_push(rst.minval <= rst.maxval ? RS_STAR_LONG : RS_STAR_SHORT, scan);
             if (rp == NULL) {
               status = RA_FAIL;
             } else {
               *(((regstar_T *)rp) - 1) = rst;
               status = RA_BREAK;                  // skip the restore bits
             }
           }
         } else {
           status = RA_NOMATCH;
         }
       }
       break;

       case NOMATCH:
       case MATCH:
       case SUBPAT:
         rp = regstack_push(RS_NOMATCH, scan);
         if (rp == NULL) {
           status = RA_FAIL;
         } else {
           rp->rs_no = (int16_t)op;
           reg_save(&rp->rs_un.regsave, &backpos);
           next = OPERAND(scan);
           // We continue and handle the result when done.
         }
         break;

       case BEHIND:
       case NOBEHIND:
         // Need a bit of room to store extra positions.
         if ((int64_t)((unsigned)regstack.ga_len >> 10) >= p_mmp) {
           emsg(_(e_pattern_uses_more_memory_than_maxmempattern));
           status = RA_FAIL;
         } else {
           ga_grow(&regstack, sizeof(regbehind_T));
           regstack.ga_len += (int)sizeof(regbehind_T);
           rp = regstack_push(RS_BEHIND1, scan);
           if (rp == NULL) {
             status = RA_FAIL;
           } else {
             // Need to save the subexpr to be able to restore them
             // when there is a match but we don't use it.
             save_subexpr(((regbehind_T *)rp) - 1);

             rp->rs_no = (int16_t)op;
             reg_save(&rp->rs_un.regsave, &backpos);
             // First try if what follows matches.  If it does then we
             // check the behind match by looping.
           }
         }
         break;

       case BHPOS:
         if (REG_MULTI) {
           if (behind_pos.rs_u.pos.col != (colnr_T)(rex.input - rex.line)
               || behind_pos.rs_u.pos.lnum != rex.lnum) {
             status = RA_NOMATCH;
           }
         } else if (behind_pos.rs_u.ptr != rex.input) {
           status = RA_NOMATCH;
         }
         break;

       case NEWL:
         if ((c != NUL || !REG_MULTI || rex.lnum > rex.reg_maxline
              || rex.reg_line_lbr) && (c != '\n' || !rex.reg_line_lbr)) {
           status = RA_NOMATCH;
         } else if (rex.reg_line_lbr) {
           ADVANCE_REGINPUT();
         } else {
           reg_nextline();
         }
         break;

       case END:
         status = RA_MATCH;    // Success!
         break;

       default:
         iemsg(_(e_re_corr));
#ifdef REGEXP_DEBUG
         printf("Illegal op code %d\n", op);
#endif
         status = RA_FAIL;
         break;
       }
     }

     // If we can't continue sequentially, break the inner loop.
     if (status != RA_CONT) {
       break;
     }

     // Continue in inner loop, advance to next item.
     scan = next;
   }  // end of inner loop

   // If there is something on the regstack execute the code for the state.
   // If the state is popped then loop and use the older state.
   while (!GA_EMPTY(&regstack) && status != RA_FAIL) {
     rp = (regitem_T *)((char *)regstack.ga_data + regstack.ga_len) - 1;
     switch (rp->rs_state) {
     case RS_NOPEN:
       // Result is passed on as-is, simply pop the state.
       regstack_pop(&scan);
       break;

     case RS_MOPEN:
       // Pop the state.  Restore pointers when there is no match.
       if (status == RA_NOMATCH) {
         restore_se(&rp->rs_un.sesave, &rex.reg_startpos[rp->rs_no],
                    &rex.reg_startp[rp->rs_no]);
       }
       regstack_pop(&scan);
       break;

     case RS_ZOPEN:
       // Pop the state.  Restore pointers when there is no match.
       if (status == RA_NOMATCH) {
         restore_se(&rp->rs_un.sesave, &reg_startzpos[rp->rs_no],
                    &reg_startzp[rp->rs_no]);
       }
       regstack_pop(&scan);
       break;

     case RS_MCLOSE:
       // Pop the state.  Restore pointers when there is no match.
       if (status == RA_NOMATCH) {
         restore_se(&rp->rs_un.sesave, &rex.reg_endpos[rp->rs_no],
                    &rex.reg_endp[rp->rs_no]);
       }
       regstack_pop(&scan);
       break;

     case RS_ZCLOSE:
       // Pop the state.  Restore pointers when there is no match.
       if (status == RA_NOMATCH) {
         restore_se(&rp->rs_un.sesave, &reg_endzpos[rp->rs_no],
                    &reg_endzp[rp->rs_no]);
       }
       regstack_pop(&scan);
       break;

     case RS_BRANCH:
       if (status == RA_MATCH) {
         // this branch matched, use it
         regstack_pop(&scan);
       } else {
         if (status != RA_BREAK) {
           // After a non-matching branch: try next one.
           reg_restore(&rp->rs_un.regsave, &backpos);
           scan = rp->rs_scan;
         }
         if (scan == NULL || OP(scan) != BRANCH) {
           // no more branches, didn't find a match
           status = RA_NOMATCH;
           regstack_pop(&scan);
         } else {
           // Prepare to try a branch.
           rp->rs_scan = regnext(scan);
           reg_save(&rp->rs_un.regsave, &backpos);
           scan = OPERAND(scan);
         }
       }
       break;

     case RS_BRCPLX_MORE:
       // Pop the state.  Restore pointers when there is no match.
       if (status == RA_NOMATCH) {
         reg_restore(&rp->rs_un.regsave, &backpos);
         brace_count[rp->rs_no]--;             // decrement match count
       }
       regstack_pop(&scan);
       break;

     case RS_BRCPLX_LONG:
       // Pop the state.  Restore pointers when there is no match.
       if (status == RA_NOMATCH) {
         // There was no match, but we did find enough matches.
         reg_restore(&rp->rs_un.regsave, &backpos);
         brace_count[rp->rs_no]--;
         // continue with the items after "\{}"
         status = RA_CONT;
       }
       regstack_pop(&scan);
       if (status == RA_CONT) {
         scan = regnext(scan);
       }
       break;

     case RS_BRCPLX_SHORT:
       // Pop the state.  Restore pointers when there is no match.
       if (status == RA_NOMATCH) {
         // There was no match, try to match one more item.
         reg_restore(&rp->rs_un.regsave, &backpos);
       }
       regstack_pop(&scan);
       if (status == RA_NOMATCH) {
         scan = OPERAND(scan);
         status = RA_CONT;
       }
       break;

     case RS_NOMATCH:
       // Pop the state.  If the operand matches for NOMATCH or
       // doesn't match for MATCH/SUBPAT, we fail.  Otherwise backup,
       // except for SUBPAT, and continue with the next item.
       if (status == (rp->rs_no == NOMATCH ? RA_MATCH : RA_NOMATCH)) {
         status = RA_NOMATCH;
       } else {
         status = RA_CONT;
         if (rp->rs_no != SUBPAT) {            // zero-width
           reg_restore(&rp->rs_un.regsave, &backpos);
         }
       }
       regstack_pop(&scan);
       if (status == RA_CONT) {
         scan = regnext(scan);
       }
       break;

     case RS_BEHIND1:
       if (status == RA_NOMATCH) {
         regstack_pop(&scan);
         regstack.ga_len -= (int)sizeof(regbehind_T);
       } else {
         // The stuff after BEHIND/NOBEHIND matches.  Now try if
         // the behind part does (not) match before the current
         // position in the input.  This must be done at every
         // position in the input and checking if the match ends at
         // the current position.

         // save the position after the found match for next
         reg_save(&(((regbehind_T *)rp) - 1)->save_after, &backpos);

         // Start looking for a match with operand at the current
         // position.  Go back one character until we find the
         // result, hitting the start of the line or the previous
         // line (for multi-line matching).
         // Set behind_pos to where the match should end, BHPOS
         // will match it.  Save the current value.
         (((regbehind_T *)rp) - 1)->save_behind = behind_pos;
         behind_pos = rp->rs_un.regsave;

         rp->rs_state = RS_BEHIND2;

         reg_restore(&rp->rs_un.regsave, &backpos);
         scan = OPERAND(rp->rs_scan) + 4;
       }
       break;

     case RS_BEHIND2:
       // Looping for BEHIND / NOBEHIND match.
       if (status == RA_MATCH && reg_save_equal(&behind_pos)) {
         // found a match that ends where "next" started
         behind_pos = (((regbehind_T *)rp) - 1)->save_behind;
         if (rp->rs_no == BEHIND) {
           reg_restore(&(((regbehind_T *)rp) - 1)->save_after,
                       &backpos);
         } else {
           // But we didn't want a match.  Need to restore the
           // subexpr, because what follows matched, so they have
           // been set.
           status = RA_NOMATCH;
           restore_subexpr(((regbehind_T *)rp) - 1);
         }
         regstack_pop(&scan);
         regstack.ga_len -= (int)sizeof(regbehind_T);
       } else {
         int64_t limit;

         // No match or a match that doesn't end where we want it: Go
         // back one character.  May go to previous line once.
         no = OK;
         limit = OPERAND_MIN(rp->rs_scan);
         if (REG_MULTI) {
           if (limit > 0
               && ((rp->rs_un.regsave.rs_u.pos.lnum
                    < behind_pos.rs_u.pos.lnum
                    ? (colnr_T)strlen((char *)rex.line)
                    : behind_pos.rs_u.pos.col)
                   - rp->rs_un.regsave.rs_u.pos.col >= limit)) {
             no = FAIL;
           } else if (rp->rs_un.regsave.rs_u.pos.col == 0) {
             if (rp->rs_un.regsave.rs_u.pos.lnum
                 < behind_pos.rs_u.pos.lnum
                 || reg_getline(--rp->rs_un.regsave.rs_u.pos.lnum)
                 == NULL) {
               no = FAIL;
             } else {
               reg_restore(&rp->rs_un.regsave, &backpos);
               rp->rs_un.regsave.rs_u.pos.col =
                 (colnr_T)strlen((char *)rex.line);
             }
           } else {
             const uint8_t *const line =
               (uint8_t *)reg_getline(rp->rs_un.regsave.rs_u.pos.lnum);

             rp->rs_un.regsave.rs_u.pos.col -=
               utf_head_off((char *)line,
                            (char *)line + rp->rs_un.regsave.rs_u.pos.col - 1)
               + 1;
           }
         } else {
           if (rp->rs_un.regsave.rs_u.ptr == rex.line) {
             no = FAIL;
           } else {
             MB_PTR_BACK(rex.line, rp->rs_un.regsave.rs_u.ptr);
             if (limit > 0
                 && (behind_pos.rs_u.ptr - rp->rs_un.regsave.rs_u.ptr) > (ptrdiff_t)limit) {
               no = FAIL;
             }
           }
         }
         if (no == OK) {
           // Advanced, prepare for finding match again.
           reg_restore(&rp->rs_un.regsave, &backpos);
           scan = OPERAND(rp->rs_scan) + 4;
           if (status == RA_MATCH) {
             // We did match, so subexpr may have been changed,
             // need to restore them for the next try.
             status = RA_NOMATCH;
             restore_subexpr(((regbehind_T *)rp) - 1);
           }
         } else {
           // Can't advance.  For NOBEHIND that's a match.
           behind_pos = (((regbehind_T *)rp) - 1)->save_behind;
           if (rp->rs_no == NOBEHIND) {
             reg_restore(&(((regbehind_T *)rp) - 1)->save_after,
                         &backpos);
             status = RA_MATCH;
           } else {
             // We do want a proper match.  Need to restore the
             // subexpr if we had a match, because they may have
             // been set.
             if (status == RA_MATCH) {
               status = RA_NOMATCH;
               restore_subexpr(((regbehind_T *)rp) - 1);
             }
           }
           regstack_pop(&scan);
           regstack.ga_len -= (int)sizeof(regbehind_T);
         }
       }
       break;

     case RS_STAR_LONG:
     case RS_STAR_SHORT: {
       regstar_T *rst = ((regstar_T *)rp) - 1;

       if (status == RA_MATCH) {
         regstack_pop(&scan);
         regstack.ga_len -= (int)sizeof(regstar_T);
         break;
       }

       // Tried once already, restore input pointers.
       if (status != RA_BREAK) {
         reg_restore(&rp->rs_un.regsave, &backpos);
       }

       // Repeat until we found a position where it could match.
       while (true) {
         if (status != RA_BREAK) {
           // Tried first position already, advance.
           if (rp->rs_state == RS_STAR_LONG) {
             // Trying for longest match, but couldn't or
             // didn't match -- back up one char.
             if (--rst->count < rst->minval) {
               break;
             }
             if (rex.input == rex.line) {
               // backup to last char of previous line
               if (rex.lnum == 0) {
                 status = RA_NOMATCH;
                 break;
               }
               rex.lnum--;
               rex.line = (uint8_t *)reg_getline(rex.lnum);
               // Just in case regrepeat() didn't count right.
               if (rex.line == NULL) {
                 break;
               }
               rex.input = rex.line + reg_getline_len(rex.lnum);
               reg_breakcheck();
             } else {
               MB_PTR_BACK(rex.line, rex.input);
             }
           } else {
             // Range is backwards, use shortest match first.
             // Careful: maxval and minval are exchanged!
             // Couldn't or didn't match: try advancing one
             // char.
             if (rst->count == rst->minval
                 || regrepeat(OPERAND(rp->rs_scan), 1L) == 0) {
               break;
             }
             rst->count++;
           }
           if (got_int) {
             break;
           }
         } else {
           status = RA_NOMATCH;
         }

         // If it could match, try it.
         if (rst->nextb == NUL || *rex.input == rst->nextb
             || *rex.input == rst->nextb_ic) {
           reg_save(&rp->rs_un.regsave, &backpos);
           scan = regnext(rp->rs_scan);
           status = RA_CONT;
           break;
         }
       }
       if (status != RA_CONT) {
         // Failed.
         regstack_pop(&scan);
         regstack.ga_len -= (int)sizeof(regstar_T);
         status = RA_NOMATCH;
       }
     }
     break;
     }

     // If we want to continue the inner loop or didn't pop a state
     // continue matching loop
     if (status == RA_CONT || rp == (regitem_T *)
         ((char *)regstack.ga_data + regstack.ga_len) - 1) {
       break;
     }
   }

   // May need to continue with the inner loop, starting at "scan".
   if (status == RA_CONT) {
     continue;
   }

   // If the regstack is empty or something failed we are done.
   if (GA_EMPTY(&regstack) || status == RA_FAIL) {
     if (scan == NULL) {
       // We get here only if there's trouble -- normally "case END" is
       // the terminating point.
       iemsg(_(e_re_corr));
#ifdef REGEXP_DEBUG
       printf("Premature EOL\n");
#endif
     }
     return status == RA_MATCH;
   }
 }  // End of loop until the regstack is empty.

 // NOTREACHED
}

/// Try match of "prog" with at rex.line["col"].
///
/// @param tm         timeout limit or NULL
/// @param timed_out  flag set on timeout or NULL
///
/// @return  0 for failure, or number of lines contained in the match.
static int regtry(bt_regprog_T *prog, colnr_T col, proftime_T *tm, int *timed_out)
{
 rex.input = rex.line + col;
 rex.need_clear_subexpr = true;
 // Clear the external match subpointers if necessaey.
 rex.need_clear_zsubexpr = (prog->reghasz == REX_SET);

 if (regmatch(&prog->program[1], tm, timed_out) == 0) {
   return 0;
 }

 cleanup_subexpr();
 if (REG_MULTI) {
   if (rex.reg_startpos[0].lnum < 0) {
     rex.reg_startpos[0].lnum = 0;
     rex.reg_startpos[0].col = col;
   }
   if (rex.reg_endpos[0].lnum < 0) {
     rex.reg_endpos[0].lnum = rex.lnum;
     rex.reg_endpos[0].col = (int)(rex.input - rex.line);
   } else {
     // Use line number of "\ze".
     rex.lnum = rex.reg_endpos[0].lnum;
   }
 } else {
   if (rex.reg_startp[0] == NULL) {
     rex.reg_startp[0] = rex.line + col;
   }
   if (rex.reg_endp[0] == NULL) {
     rex.reg_endp[0] = rex.input;
   }
 }
 // Package any found \z(...\) matches for export. Default is none.
 unref_extmatch(re_extmatch_out);
 re_extmatch_out = NULL;

 if (prog->reghasz == REX_SET) {
   int i;

   cleanup_zsubexpr();
   re_extmatch_out = make_extmatch();
   for (i = 0; i < NSUBEXP; i++) {
     if (REG_MULTI) {
       // Only accept single line matches.
       if (reg_startzpos[i].lnum >= 0
           && reg_endzpos[i].lnum == reg_startzpos[i].lnum
           && reg_endzpos[i].col >= reg_startzpos[i].col) {
         re_extmatch_out->matches[i] =
           (uint8_t *)xstrnsave(reg_getline(reg_startzpos[i].lnum) + reg_startzpos[i].col,
                                (size_t)(reg_endzpos[i].col - reg_startzpos[i].col));
       }
     } else {
       if (reg_startzp[i] != NULL && reg_endzp[i] != NULL) {
         re_extmatch_out->matches[i] =
           (uint8_t *)xstrnsave((char *)reg_startzp[i], (size_t)(reg_endzp[i] - reg_startzp[i]));
       }
     }
   }
 }
 return 1 + rex.lnum;
}

/// Match a regexp against a string ("line" points to the string) or multiple
/// lines (if "line" is NULL, use reg_getline()).
///
/// @param startcol   column to start looking for match
/// @param tm         timeout limit or NULL
/// @param timed_out  flag set on timeout or NULL
///
/// @return  0 for failure, or number of lines contained in the match.
static int bt_regexec_both(uint8_t *line, colnr_T startcol, proftime_T *tm, int *timed_out)
{
 bt_regprog_T *prog;
 uint8_t *s;
 colnr_T col = startcol;
 int retval = 0;

 // Create "regstack" and "backpos" if they are not allocated yet.
 // We allocate *_INITIAL amount of bytes first and then set the grow size
 // to much bigger value to avoid many malloc calls in case of deep regular
 // expressions.
 if (regstack.ga_data == NULL) {
   // Use an item size of 1 byte, since we push different things
   // onto the regstack.
   ga_init(&regstack, 1, REGSTACK_INITIAL);
   ga_grow(&regstack, REGSTACK_INITIAL);
   ga_set_growsize(&regstack, REGSTACK_INITIAL * 8);
 }

 if (backpos.ga_data == NULL) {
   ga_init(&backpos, sizeof(backpos_T), BACKPOS_INITIAL);
   ga_grow(&backpos, BACKPOS_INITIAL);
   ga_set_growsize(&backpos, BACKPOS_INITIAL * 8);
 }

 if (REG_MULTI) {
   prog = (bt_regprog_T *)rex.reg_mmatch->regprog;
   line = (uint8_t *)reg_getline(0);
   rex.reg_startpos = rex.reg_mmatch->startpos;
   rex.reg_endpos = rex.reg_mmatch->endpos;
 } else {
   prog = (bt_regprog_T *)rex.reg_match->regprog;
   rex.reg_startp = (uint8_t **)rex.reg_match->startp;
   rex.reg_endp = (uint8_t **)rex.reg_match->endp;
 }

 // Be paranoid...
 if (prog == NULL || line == NULL) {
   iemsg(_(e_null));
   goto theend;
 }

 // Check validity of program.
 if (prog_magic_wrong()) {
   goto theend;
 }

 // If the start column is past the maximum column: no need to try.
 if (rex.reg_maxcol > 0 && col >= rex.reg_maxcol) {
   goto theend;
 }

 // If pattern contains "\c" or "\C": overrule value of rex.reg_ic
 if (prog->regflags & RF_ICASE) {
   rex.reg_ic = true;
 } else if (prog->regflags & RF_NOICASE) {
   rex.reg_ic = false;
 }

 // If pattern contains "\Z" overrule value of rex.reg_icombine
 if (prog->regflags & RF_ICOMBINE) {
   rex.reg_icombine = true;
 }

 // If there is a "must appear" string, look for it.
 if (prog->regmust != NULL) {
   int c = utf_ptr2char((char *)prog->regmust);
   s = line + col;

   // This is used very often, esp. for ":global".  Use two versions of
   // the loop to avoid overhead of conditions.
   if (!rex.reg_ic) {
     while ((s = (uint8_t *)vim_strchr((char *)s, c)) != NULL) {
       if (cstrncmp((char *)s, (char *)prog->regmust, &prog->regmlen) == 0) {
         break;  // Found it.
       }
       MB_PTR_ADV(s);
     }
   } else {
     while ((s = (uint8_t *)cstrchr((char *)s, c)) != NULL) {
       if (cstrncmp((char *)s, (char *)prog->regmust, &prog->regmlen) == 0) {
         break;  // Found it.
       }
       MB_PTR_ADV(s);
     }
   }
   if (s == NULL) {  // Not present.
     goto theend;
   }
 }

 rex.line = line;
 rex.lnum = 0;
 reg_toolong = false;

 // Simplest case: Anchored match need be tried only once.
 if (prog->reganch) {
   int c = utf_ptr2char((char *)rex.line + col);
   if (prog->regstart == NUL
       || prog->regstart == c
       || (rex.reg_ic
           && (utf_fold(prog->regstart) == utf_fold(c)
               || (c < 255 && prog->regstart < 255
                   && mb_tolower(prog->regstart) == mb_tolower(c))))) {
     retval = regtry(prog, col, tm, timed_out);
   } else {
     retval = 0;
   }
 } else {
   int tm_count = 0;
   // Messy cases:  unanchored match.
   while (!got_int) {
     if (prog->regstart != NUL) {
       // Skip until the char we know it must start with.
       s = (uint8_t *)cstrchr((char *)rex.line + col, prog->regstart);
       if (s == NULL) {
         retval = 0;
         break;
       }
       col = (int)(s - rex.line);
     }

     // Check for maximum column to try.
     if (rex.reg_maxcol > 0 && col >= rex.reg_maxcol) {
       retval = 0;
       break;
     }

     retval = regtry(prog, col, tm, timed_out);
     if (retval > 0) {
       break;
     }

     // if not currently on the first line, get it again
     if (rex.lnum != 0) {
       rex.lnum = 0;
       rex.line = (uint8_t *)reg_getline(0);
     }
     if (rex.line[col] == NUL) {
       break;
     }
     col += utfc_ptr2len((char *)rex.line + col);
     // Check for timeout once in a twenty times to avoid overhead.
     if (tm != NULL && ++tm_count == 20) {
       tm_count = 0;
       if (profile_passed_limit(*tm)) {
         if (timed_out != NULL) {
           *timed_out = true;
         }
         break;
       }
     }
   }
 }

theend:
 // Free "reg_tofree" when it's a bit big.
 // Free regstack and backpos if they are bigger than their initial size.
 if (reg_tofreelen > 400) {
   XFREE_CLEAR(reg_tofree);
 }
 if (regstack.ga_maxlen > REGSTACK_INITIAL) {
   ga_clear(&regstack);
 }
 if (backpos.ga_maxlen > BACKPOS_INITIAL) {
   ga_clear(&backpos);
 }

 if (retval > 0) {
   // Make sure the end is never before the start.  Can happen when \zs
   // and \ze are used.
   if (REG_MULTI) {
     const lpos_T *const start = &rex.reg_mmatch->startpos[0];
     const lpos_T *const end = &rex.reg_mmatch->endpos[0];

     if (end->lnum < start->lnum
         || (end->lnum == start->lnum && end->col < start->col)) {
       rex.reg_mmatch->endpos[0] = rex.reg_mmatch->startpos[0];
     }

     // startpos[0] may be set by "\zs", also return the column where
     // the whole pattern matched.
     rex.reg_mmatch->rmm_matchcol = col;
   } else {
     if (rex.reg_match->endp[0] < rex.reg_match->startp[0]) {
       rex.reg_match->endp[0] = rex.reg_match->startp[0];
     }

     // startpos[0] may be set by "\zs", also return the column where
     // the whole pattern matched.
     rex.reg_match->rm_matchcol = col;
   }
 }

 return retval;
}

/// Match a regexp against a string.
/// "rmp->regprog" is a compiled regexp as returned by vim_regcomp().
/// Uses curbuf for line count and 'iskeyword'.
/// If "line_lbr" is true, consider a "\n" in "line" to be a line break.
///
/// @param line  string to match against
/// @param col   column to start looking for match
///
/// @return  0 for failure, number of lines contained in the match otherwise.
static int bt_regexec_nl(regmatch_T *rmp, uint8_t *line, colnr_T col, bool line_lbr)
{
 rex.reg_match = rmp;
 rex.reg_mmatch = NULL;
 rex.reg_maxline = 0;
 rex.reg_line_lbr = line_lbr;
 rex.reg_buf = curbuf;
 rex.reg_win = NULL;
 rex.reg_ic = rmp->rm_ic;
 rex.reg_icombine = false;
 rex.reg_nobreak = rmp->regprog->re_flags & RE_NOBREAK;
 rex.reg_maxcol = 0;

 int64_t r = bt_regexec_both(line, col, NULL, NULL);
 assert(r <= INT_MAX);
 return (int)r;
}

/// Matches a regexp against multiple lines.
/// "rmp->regprog" is a compiled regexp as returned by vim_regcomp().
/// Uses curbuf for line count and 'iskeyword'.
///
/// @param win Window in which to search or NULL
/// @param buf Buffer in which to search
/// @param lnum Number of line to start looking for match
/// @param col Column to start looking for match
/// @param tm Timeout limit or NULL
///
/// @return zero if there is no match and number of lines contained in the match
///         otherwise.
static int bt_regexec_multi(regmmatch_T *rmp, win_T *win, buf_T *buf, linenr_T lnum, colnr_T col,
                           proftime_T *tm, int *timed_out)
{
 init_regexec_multi(rmp, win, buf, lnum);
 return bt_regexec_both(NULL, col, tm, timed_out);
}

// Compare a number with the operand of RE_LNUM, RE_COL or RE_VCOL.
static int re_num_cmp(uint32_t val, const uint8_t *scan)
{
 uint32_t n = (uint32_t)OPERAND_MIN(scan);

 if (OPERAND_CMP(scan) == '>') {
   return val > n;
 }
 if (OPERAND_CMP(scan) == '<') {
   return val < n;
 }
 return val == n;
}

#ifdef BT_REGEXP_DUMP

// regdump - dump a regexp onto stdout in vaguely comprehensible form
static void regdump(uint8_t *pattern, bt_regprog_T *r)
{
 uint8_t *s;
 int op = EXACTLY;             // Arbitrary non-END op.
 uint8_t *next;
 uint8_t *end = NULL;
 FILE *f;

# ifdef BT_REGEXP_LOG
 f = fopen("bt_regexp_log.log", "a");
# else
 f = stdout;
# endif
 if (f == NULL) {
   return;
 }
 fprintf(f, "-------------------------------------\n\r\nregcomp(%s):\r\n",
         pattern);

 s = &r->program[1];
 // Loop until we find the END that isn't before a referred next (an END
 // can also appear in a NOMATCH operand).
 while (op != END || s <= end) {
   op = OP(s);
   fprintf(f, "%2d%s", (int)(s - r->program), regprop(s));     // Where, what.
   next = regnext(s);
   if (next == NULL) {         // Next ptr.
     fprintf(f, "(0)");
   } else {
     fprintf(f, "(%d)", (int)((s - r->program) + (next - s)));
   }
   if (end < next) {
     end = next;
   }
   if (op == BRACE_LIMITS) {
     // Two ints
     fprintf(f, " minval %" PRId64 ", maxval %" PRId64,
             (int64_t)OPERAND_MIN(s), (int64_t)OPERAND_MAX(s));
     s += 8;
   } else if (op == BEHIND || op == NOBEHIND) {
     // one int
     fprintf(f, " count %" PRId64, (int64_t)OPERAND_MIN(s));
     s += 4;
   } else if (op == RE_LNUM || op == RE_COL || op == RE_VCOL) {
     // one int plus comparator
     fprintf(f, " count %" PRId64, (int64_t)OPERAND_MIN(s));
     s += 5;
   }
   s += 3;
   if (op == ANYOF || op == ANYOF + ADD_NL
       || op == ANYBUT || op == ANYBUT + ADD_NL
       || op == EXACTLY) {
     // Literal string, where present.
     fprintf(f, "\nxxxxxxxxx\n");
     while (*s != NUL) {
       fprintf(f, "%c", *s++);
     }
     fprintf(f, "\nxxxxxxxxx\n");
     s++;
   }
   fprintf(f, "\r\n");
 }

 // Header fields of interest.
 if (r->regstart != NUL) {
   fprintf(f, "start `%s' 0x%x; ", r->regstart < 256
           ? (char *)transchar(r->regstart)
           : "multibyte", r->regstart);
 }
 if (r->reganch) {
   fprintf(f, "anchored; ");
 }
 if (r->regmust != NULL) {
   fprintf(f, "must have \"%s\"", r->regmust);
 }
 fprintf(f, "\r\n");

# ifdef BT_REGEXP_LOG
 fclose(f);
# endif
}
#endif      // BT_REGEXP_DUMP

#ifdef REGEXP_DEBUG

// regprop - printable representation of opcode
static uint8_t *regprop(uint8_t *op)
{
 char *p;
 static char buf[50];
 static size_t buflen = 0;

 STRCPY(buf, ":");
 buflen = 1;

 switch ((int)OP(op)) {
 case BOL:
   p = "BOL";
   break;
 case EOL:
   p = "EOL";
   break;
 case RE_BOF:
   p = "BOF";
   break;
 case RE_EOF:
   p = "EOF";
   break;
 case CURSOR:
   p = "CURSOR";
   break;
 case RE_VISUAL:
   p = "RE_VISUAL";
   break;
 case RE_LNUM:
   p = "RE_LNUM";
   break;
 case RE_MARK:
   p = "RE_MARK";
   break;
 case RE_COL:
   p = "RE_COL";
   break;
 case RE_VCOL:
   p = "RE_VCOL";
   break;
 case BOW:
   p = "BOW";
   break;
 case EOW:
   p = "EOW";
   break;
 case ANY:
   p = "ANY";
   break;
 case ANY + ADD_NL:
   p = "ANY+NL";
   break;
 case ANYOF:
   p = "ANYOF";
   break;
 case ANYOF + ADD_NL:
   p = "ANYOF+NL";
   break;
 case ANYBUT:
   p = "ANYBUT";
   break;
 case ANYBUT + ADD_NL:
   p = "ANYBUT+NL";
   break;
 case IDENT:
   p = "IDENT";
   break;
 case IDENT + ADD_NL:
   p = "IDENT+NL";
   break;
 case SIDENT:
   p = "SIDENT";
   break;
 case SIDENT + ADD_NL:
   p = "SIDENT+NL";
   break;
 case KWORD:
   p = "KWORD";
   break;
 case KWORD + ADD_NL:
   p = "KWORD+NL";
   break;
 case SKWORD:
   p = "SKWORD";
   break;
 case SKWORD + ADD_NL:
   p = "SKWORD+NL";
   break;
 case FNAME:
   p = "FNAME";
   break;
 case FNAME + ADD_NL:
   p = "FNAME+NL";
   break;
 case SFNAME:
   p = "SFNAME";
   break;
 case SFNAME + ADD_NL:
   p = "SFNAME+NL";
   break;
 case PRINT:
   p = "PRINT";
   break;
 case PRINT + ADD_NL:
   p = "PRINT+NL";
   break;
 case SPRINT:
   p = "SPRINT";
   break;
 case SPRINT + ADD_NL:
   p = "SPRINT+NL";
   break;
 case WHITE:
   p = "WHITE";
   break;
 case WHITE + ADD_NL:
   p = "WHITE+NL";
   break;
 case NWHITE:
   p = "NWHITE";
   break;
 case NWHITE + ADD_NL:
   p = "NWHITE+NL";
   break;
 case DIGIT:
   p = "DIGIT";
   break;
 case DIGIT + ADD_NL:
   p = "DIGIT+NL";
   break;
 case NDIGIT:
   p = "NDIGIT";
   break;
 case NDIGIT + ADD_NL:
   p = "NDIGIT+NL";
   break;
 case HEX:
   p = "HEX";
   break;
 case HEX + ADD_NL:
   p = "HEX+NL";
   break;
 case NHEX:
   p = "NHEX";
   break;
 case NHEX + ADD_NL:
   p = "NHEX+NL";
   break;
 case OCTAL:
   p = "OCTAL";
   break;
 case OCTAL + ADD_NL:
   p = "OCTAL+NL";
   break;
 case NOCTAL:
   p = "NOCTAL";
   break;
 case NOCTAL + ADD_NL:
   p = "NOCTAL+NL";
   break;
 case WORD:
   p = "WORD";
   break;
 case WORD + ADD_NL:
   p = "WORD+NL";
   break;
 case NWORD:
   p = "NWORD";
   break;
 case NWORD + ADD_NL:
   p = "NWORD+NL";
   break;
 case HEAD:
   p = "HEAD";
   break;
 case HEAD + ADD_NL:
   p = "HEAD+NL";
   break;
 case NHEAD:
   p = "NHEAD";
   break;
 case NHEAD + ADD_NL:
   p = "NHEAD+NL";
   break;
 case ALPHA:
   p = "ALPHA";
   break;
 case ALPHA + ADD_NL:
   p = "ALPHA+NL";
   break;
 case NALPHA:
   p = "NALPHA";
   break;
 case NALPHA + ADD_NL:
   p = "NALPHA+NL";
   break;
 case LOWER:
   p = "LOWER";
   break;
 case LOWER + ADD_NL:
   p = "LOWER+NL";
   break;
 case NLOWER:
   p = "NLOWER";
   break;
 case NLOWER + ADD_NL:
   p = "NLOWER+NL";
   break;
 case UPPER:
   p = "UPPER";
   break;
 case UPPER + ADD_NL:
   p = "UPPER+NL";
   break;
 case NUPPER:
   p = "NUPPER";
   break;
 case NUPPER + ADD_NL:
   p = "NUPPER+NL";
   break;
 case BRANCH:
   p = "BRANCH";
   break;
 case EXACTLY:
   p = "EXACTLY";
   break;
 case NOTHING:
   p = "NOTHING";
   break;
 case BACK:
   p = "BACK";
   break;
 case END:
   p = "END";
   break;
 case MOPEN + 0:
   p = "MATCH START";
   break;
 case MOPEN + 1:
 case MOPEN + 2:
 case MOPEN + 3:
 case MOPEN + 4:
 case MOPEN + 5:
 case MOPEN + 6:
 case MOPEN + 7:
 case MOPEN + 8:
 case MOPEN + 9:
   buflen += (size_t)snprintf(buf + buflen, sizeof(buf) - buflen,
                              "MOPEN%d", OP(op) - MOPEN);
   p = NULL;
   break;
 case MCLOSE + 0:
   p = "MATCH END";
   break;
 case MCLOSE + 1:
 case MCLOSE + 2:
 case MCLOSE + 3:
 case MCLOSE + 4:
 case MCLOSE + 5:
 case MCLOSE + 6:
 case MCLOSE + 7:
 case MCLOSE + 8:
 case MCLOSE + 9:
   buflen += (size_t)snprintf(buf + buflen, sizeof(buf) - buflen,
                              "MCLOSE%d", OP(op) - MCLOSE);
   p = NULL;
   break;
 case BACKREF + 1:
 case BACKREF + 2:
 case BACKREF + 3:
 case BACKREF + 4:
 case BACKREF + 5:
 case BACKREF + 6:
 case BACKREF + 7:
 case BACKREF + 8:
 case BACKREF + 9:
   buflen += (size_t)snprintf(buf + buflen, sizeof(buf) - buflen,
                              "BACKREF%d", OP(op) - BACKREF);
   p = NULL;
   break;
 case NOPEN:
   p = "NOPEN";
   break;
 case NCLOSE:
   p = "NCLOSE";
   break;
 case ZOPEN + 1:
 case ZOPEN + 2:
 case ZOPEN + 3:
 case ZOPEN + 4:
 case ZOPEN + 5:
 case ZOPEN + 6:
 case ZOPEN + 7:
 case ZOPEN + 8:
 case ZOPEN + 9:
   buflen += (size_t)snprintf(buf + buflen, sizeof(buf) - buflen,
                              "ZOPEN%d", OP(op) - ZOPEN);
   p = NULL;
   break;
 case ZCLOSE + 1:
 case ZCLOSE + 2:
 case ZCLOSE + 3:
 case ZCLOSE + 4:
 case ZCLOSE + 5:
 case ZCLOSE + 6:
 case ZCLOSE + 7:
 case ZCLOSE + 8:
 case ZCLOSE + 9:
   buflen += (size_t)snprintf(buf + buflen, sizeof(buf) - buflen,
                              "ZCLOSE%d", OP(op) - ZCLOSE);
   p = NULL;
   break;
 case ZREF + 1:
 case ZREF + 2:
 case ZREF + 3:
 case ZREF + 4:
 case ZREF + 5:
 case ZREF + 6:
 case ZREF + 7:
 case ZREF + 8:
 case ZREF + 9:
   buflen += (size_t)snprintf(buf + buflen, sizeof(buf) - buflen,
                              "ZREF%d", OP(op) - ZREF);
   p = NULL;
   break;
 case STAR:
   p = "STAR";
   break;
 case PLUS:
   p = "PLUS";
   break;
 case NOMATCH:
   p = "NOMATCH";
   break;
 case MATCH:
   p = "MATCH";
   break;
 case BEHIND:
   p = "BEHIND";
   break;
 case NOBEHIND:
   p = "NOBEHIND";
   break;
 case SUBPAT:
   p = "SUBPAT";
   break;
 case BRACE_LIMITS:
   p = "BRACE_LIMITS";
   break;
 case BRACE_SIMPLE:
   p = "BRACE_SIMPLE";
   break;
 case BRACE_COMPLEX + 0:
 case BRACE_COMPLEX + 1:
 case BRACE_COMPLEX + 2:
 case BRACE_COMPLEX + 3:
 case BRACE_COMPLEX + 4:
 case BRACE_COMPLEX + 5:
 case BRACE_COMPLEX + 6:
 case BRACE_COMPLEX + 7:
 case BRACE_COMPLEX + 8:
 case BRACE_COMPLEX + 9:
   buflen += (size_t)snprintf(buf + buflen, sizeof(buf) - buflen,
                              "BRACE_COMPLEX%d", OP(op) - BRACE_COMPLEX);
   p = NULL;
   break;
 case MULTIBYTECODE:
   p = "MULTIBYTECODE";
   break;
 case NEWL:
   p = "NEWL";
   break;
 default:
   buflen += (size_t)snprintf(buf + buflen, sizeof(buf) - buflen,
                              "corrupt %d", OP(op));
   p = NULL;
   break;
 }
 if (p != NULL) {
   STRCPY(buf + buflen, p);
 }
 return (uint8_t *)buf;
}
#endif      // REGEXP_DEBUG

// }}}1

// regexp_nfa.c {{{1
// NFA regular expression implementation.

// Logging of NFA engine.
//
// The NFA engine can write four log files:
// - Error log: Contains NFA engine's fatal errors.
// - Dump log: Contains compiled NFA state machine's information.
// - Run log: Contains information of matching procedure.
// - Debug log: Contains detailed information of matching procedure. Can be
//   disabled by undefining NFA_REGEXP_DEBUG_LOG.
// The first one can also be used without debug mode.
// The last three are enabled when compiled as debug mode and individually
// disabled by commenting them out.
// The log files can get quite big!
// To disable all of this when compiling Vim for debugging, undefine REGEXP_DEBUG in
// regexp.c
#ifdef REGEXP_DEBUG
# define NFA_REGEXP_ERROR_LOG   "nfa_regexp_error.log"
# define NFA_REGEXP_DUMP_LOG    "nfa_regexp_dump.log"
# define NFA_REGEXP_RUN_LOG     "nfa_regexp_run.log"
# define NFA_REGEXP_DEBUG_LOG   "nfa_regexp_debug.log"
#endif

// Added to NFA_ANY - NFA_NUPPER_IC to include a NL.
#define NFA_ADD_NL              31

enum {
 NFA_SPLIT = -1024,
 NFA_MATCH,
 NFA_EMPTY,                        // matches 0-length

 NFA_START_COLL,                   // [abc] start
 NFA_END_COLL,                     // [abc] end
 NFA_START_NEG_COLL,               // [^abc] start
 NFA_END_NEG_COLL,                 // [^abc] end (postfix only)
 NFA_RANGE,                        // range of the two previous items
                                   // (postfix only)
 NFA_RANGE_MIN,                    // low end of a range
 NFA_RANGE_MAX,                    // high end of a range

 NFA_CONCAT,                       // concatenate two previous items (postfix
                                   // only)
 NFA_OR,                           // \| (postfix only)
 NFA_STAR,                         // greedy * (postfix only)
 NFA_STAR_NONGREEDY,               // non-greedy * (postfix only)
 NFA_QUEST,                        // greedy \? (postfix only)
 NFA_QUEST_NONGREEDY,              // non-greedy \? (postfix only)

 NFA_BOL,                          // ^    Begin line
 NFA_EOL,                          // $    End line
 NFA_BOW,                          // \<   Begin word
 NFA_EOW,                          // \>   End word
 NFA_BOF,                          // \%^  Begin file
 NFA_EOF,                          // \%$  End file
 NFA_NEWL,
 NFA_ZSTART,                       // Used for \zs
 NFA_ZEND,                         // Used for \ze
 NFA_NOPEN,                        // Start of subexpression marked with \%(
 NFA_NCLOSE,                       // End of subexpr. marked with \%( ... \)
 NFA_START_INVISIBLE,
 NFA_START_INVISIBLE_FIRST,
 NFA_START_INVISIBLE_NEG,
 NFA_START_INVISIBLE_NEG_FIRST,
 NFA_START_INVISIBLE_BEFORE,
 NFA_START_INVISIBLE_BEFORE_FIRST,
 NFA_START_INVISIBLE_BEFORE_NEG,
 NFA_START_INVISIBLE_BEFORE_NEG_FIRST,
 NFA_START_PATTERN,
 NFA_END_INVISIBLE,
 NFA_END_INVISIBLE_NEG,
 NFA_END_PATTERN,
 NFA_COMPOSING,                    // Next nodes in NFA are part of the
                                   // composing multibyte char
 NFA_END_COMPOSING,                // End of a composing char in the NFA
 NFA_ANY_COMPOSING,                // \%C: Any composing characters.
 NFA_OPT_CHARS,                    // \%[abc]

 // The following are used only in the postfix form, not in the NFA
 NFA_PREV_ATOM_NO_WIDTH,           // Used for \@=
 NFA_PREV_ATOM_NO_WIDTH_NEG,       // Used for \@!
 NFA_PREV_ATOM_JUST_BEFORE,        // Used for \@<=
 NFA_PREV_ATOM_JUST_BEFORE_NEG,    // Used for \@<!
 NFA_PREV_ATOM_LIKE_PATTERN,       // Used for \@>

 NFA_BACKREF1,                     // \1
 NFA_BACKREF2,                     // \2
 NFA_BACKREF3,                     // \3
 NFA_BACKREF4,                     // \4
 NFA_BACKREF5,                     // \5
 NFA_BACKREF6,                     // \6
 NFA_BACKREF7,                     // \7
 NFA_BACKREF8,                     // \8
 NFA_BACKREF9,                     // \9
 NFA_ZREF1,                        // \z1
 NFA_ZREF2,                        // \z2
 NFA_ZREF3,                        // \z3
 NFA_ZREF4,                        // \z4
 NFA_ZREF5,                        // \z5
 NFA_ZREF6,                        // \z6
 NFA_ZREF7,                        // \z7
 NFA_ZREF8,                        // \z8
 NFA_ZREF9,                        // \z9
 NFA_SKIP,                         // Skip characters

 NFA_MOPEN,
 NFA_MOPEN1,
 NFA_MOPEN2,
 NFA_MOPEN3,
 NFA_MOPEN4,
 NFA_MOPEN5,
 NFA_MOPEN6,
 NFA_MOPEN7,
 NFA_MOPEN8,
 NFA_MOPEN9,

 NFA_MCLOSE,
 NFA_MCLOSE1,
 NFA_MCLOSE2,
 NFA_MCLOSE3,
 NFA_MCLOSE4,
 NFA_MCLOSE5,
 NFA_MCLOSE6,
 NFA_MCLOSE7,
 NFA_MCLOSE8,
 NFA_MCLOSE9,

 NFA_ZOPEN,
 NFA_ZOPEN1,
 NFA_ZOPEN2,
 NFA_ZOPEN3,
 NFA_ZOPEN4,
 NFA_ZOPEN5,
 NFA_ZOPEN6,
 NFA_ZOPEN7,
 NFA_ZOPEN8,
 NFA_ZOPEN9,

 NFA_ZCLOSE,
 NFA_ZCLOSE1,
 NFA_ZCLOSE2,
 NFA_ZCLOSE3,
 NFA_ZCLOSE4,
 NFA_ZCLOSE5,
 NFA_ZCLOSE6,
 NFA_ZCLOSE7,
 NFA_ZCLOSE8,
 NFA_ZCLOSE9,

 // NFA_FIRST_NL
 NFA_ANY,              //      Match any one character.
 NFA_IDENT,            //      Match identifier char
 NFA_SIDENT,           //      Match identifier char but no digit
 NFA_KWORD,            //      Match keyword char
 NFA_SKWORD,           //      Match word char but no digit
 NFA_FNAME,            //      Match file name char
 NFA_SFNAME,           //      Match file name char but no digit
 NFA_PRINT,            //      Match printable char
 NFA_SPRINT,           //      Match printable char but no digit
 NFA_WHITE,            //      Match whitespace char
 NFA_NWHITE,           //      Match non-whitespace char
 NFA_DIGIT,            //      Match digit char
 NFA_NDIGIT,           //      Match non-digit char
 NFA_HEX,              //      Match hex char
 NFA_NHEX,             //      Match non-hex char
 NFA_OCTAL,            //      Match octal char
 NFA_NOCTAL,           //      Match non-octal char
 NFA_WORD,             //      Match word char
 NFA_NWORD,            //      Match non-word char
 NFA_HEAD,             //      Match head char
 NFA_NHEAD,            //      Match non-head char
 NFA_ALPHA,            //      Match alpha char
 NFA_NALPHA,           //      Match non-alpha char
 NFA_LOWER,            //      Match lowercase char
 NFA_NLOWER,           //      Match non-lowercase char
 NFA_UPPER,            //      Match uppercase char
 NFA_NUPPER,           //      Match non-uppercase char
 NFA_LOWER_IC,         //      Match [a-z]
 NFA_NLOWER_IC,        //      Match [^a-z]
 NFA_UPPER_IC,         //      Match [A-Z]
 NFA_NUPPER_IC,        //      Match [^A-Z]

 NFA_FIRST_NL = NFA_ANY + NFA_ADD_NL,
 NFA_LAST_NL = NFA_NUPPER_IC + NFA_ADD_NL,

 NFA_CURSOR,           //      Match cursor pos
 NFA_LNUM,             //      Match line number
 NFA_LNUM_GT,          //      Match > line number
 NFA_LNUM_LT,          //      Match < line number
 NFA_COL,              //      Match cursor column
 NFA_COL_GT,           //      Match > cursor column
 NFA_COL_LT,           //      Match < cursor column
 NFA_VCOL,             //      Match cursor virtual column
 NFA_VCOL_GT,          //      Match > cursor virtual column
 NFA_VCOL_LT,          //      Match < cursor virtual column
 NFA_MARK,             //      Match mark
 NFA_MARK_GT,          //      Match > mark
 NFA_MARK_LT,          //      Match < mark
 NFA_VISUAL,           //      Match Visual area

 // Character classes [:alnum:] etc
 NFA_CLASS_ALNUM,
 NFA_CLASS_ALPHA,
 NFA_CLASS_BLANK,
 NFA_CLASS_CNTRL,
 NFA_CLASS_DIGIT,
 NFA_CLASS_GRAPH,
 NFA_CLASS_LOWER,
 NFA_CLASS_PRINT,
 NFA_CLASS_PUNCT,
 NFA_CLASS_SPACE,
 NFA_CLASS_UPPER,
 NFA_CLASS_XDIGIT,
 NFA_CLASS_TAB,
 NFA_CLASS_RETURN,
 NFA_CLASS_BACKSPACE,
 NFA_CLASS_ESCAPE,
 NFA_CLASS_IDENT,
 NFA_CLASS_KEYWORD,
 NFA_CLASS_FNAME,
};

// Keep in sync with classchars.
static int nfa_classcodes[] = {
 NFA_ANY, NFA_IDENT, NFA_SIDENT, NFA_KWORD, NFA_SKWORD,
 NFA_FNAME, NFA_SFNAME, NFA_PRINT, NFA_SPRINT,
 NFA_WHITE, NFA_NWHITE, NFA_DIGIT, NFA_NDIGIT,
 NFA_HEX, NFA_NHEX, NFA_OCTAL, NFA_NOCTAL,
 NFA_WORD, NFA_NWORD, NFA_HEAD, NFA_NHEAD,
 NFA_ALPHA, NFA_NALPHA, NFA_LOWER, NFA_NLOWER,
 NFA_UPPER, NFA_NUPPER
};

static const char e_nul_found[] = N_("E865: (NFA) Regexp end encountered prematurely");
static const char e_misplaced[] = N_("E866: (NFA regexp) Misplaced %c");
static const char e_ill_char_class[] = N_("E877: (NFA regexp) Invalid character class: %" PRId64);
static const char e_value_too_large[] = N_("E951: \\% value too large");

// Variables only used in nfa_regcomp() and descendants.
static int nfa_re_flags;  ///< re_flags passed to nfa_regcomp().
static int *post_start;   ///< holds the postfix form of r.e.
static int *post_end;
static int *post_ptr;

// Set when the pattern should use the NFA engine.
// E.g. [[:upper:]] only allows 8bit characters for BT engine,
// while NFA engine handles multibyte characters correctly.
static bool wants_nfa;

static int nstate;  ///< Number of states in the NFA. Also used when executing.
static int istate;  ///< Index in the state vector, used in alloc_state()

// If not NULL match must end at this position
static save_se_T *nfa_endp = NULL;

// 0 for first call to nfa_regmatch(), 1 for recursive call.
static int nfa_ll_index = 0;

// Helper functions used when doing re2post() ... regatom() parsing
#define EMIT(c) \
 do { \
   if (post_ptr >= post_end) { \
     realloc_post_list(); \
   } \
   *post_ptr++ = c; \
 } while (0)

/// Initialize internal variables before NFA compilation.
///
/// @param re_flags  @see vim_regcomp()
static void nfa_regcomp_start(uint8_t *expr, int re_flags)
{
 size_t postfix_size;
 size_t nstate_max;

 nstate = 0;
 istate = 0;
 // A reasonable estimation for maximum size
 nstate_max = (strlen((char *)expr) + 1) * 25;

 // Some items blow up in size, such as [A-z].  Add more space for that.
 // When it is still not enough realloc_post_list() will be used.
 nstate_max += 1000;

 // Size for postfix representation of expr.
 postfix_size = sizeof(int) * nstate_max;

 post_start = (int *)xmalloc(postfix_size);
 post_ptr = post_start;
 post_end = post_start + nstate_max;
 wants_nfa = false;
 rex.nfa_has_zend = false;
 rex.nfa_has_backref = false;

 // shared with BT engine
 regcomp_start(expr, re_flags);
}

// Figure out if the NFA state list starts with an anchor, must match at start
// of the line.
static int nfa_get_reganch(nfa_state_T *start, int depth)
{
 nfa_state_T *p = start;

 if (depth > 4) {
   return 0;
 }

 while (p != NULL) {
   switch (p->c) {
   case NFA_BOL:
   case NFA_BOF:
     return 1;           // yes!

   case NFA_ZSTART:
   case NFA_ZEND:
   case NFA_CURSOR:
   case NFA_VISUAL:

   case NFA_MOPEN:
   case NFA_MOPEN1:
   case NFA_MOPEN2:
   case NFA_MOPEN3:
   case NFA_MOPEN4:
   case NFA_MOPEN5:
   case NFA_MOPEN6:
   case NFA_MOPEN7:
   case NFA_MOPEN8:
   case NFA_MOPEN9:
   case NFA_NOPEN:
   case NFA_ZOPEN:
   case NFA_ZOPEN1:
   case NFA_ZOPEN2:
   case NFA_ZOPEN3:
   case NFA_ZOPEN4:
   case NFA_ZOPEN5:
   case NFA_ZOPEN6:
   case NFA_ZOPEN7:
   case NFA_ZOPEN8:
   case NFA_ZOPEN9:
     p = p->out;
     break;

   case NFA_SPLIT:
     return nfa_get_reganch(p->out, depth + 1)
            && nfa_get_reganch(p->out1, depth + 1);

   default:
     return 0;           // noooo
   }
 }
 return 0;
}

// Figure out if the NFA state list starts with a character which must match
// at start of the match.
static int nfa_get_regstart(nfa_state_T *start, int depth)
{
 nfa_state_T *p = start;

 if (depth > 4) {
   return 0;
 }

 while (p != NULL) {
   switch (p->c) {
   // all kinds of zero-width matches
   case NFA_BOL:
   case NFA_BOF:
   case NFA_BOW:
   case NFA_EOW:
   case NFA_ZSTART:
   case NFA_ZEND:
   case NFA_CURSOR:
   case NFA_VISUAL:
   case NFA_LNUM:
   case NFA_LNUM_GT:
   case NFA_LNUM_LT:
   case NFA_COL:
   case NFA_COL_GT:
   case NFA_COL_LT:
   case NFA_VCOL:
   case NFA_VCOL_GT:
   case NFA_VCOL_LT:
   case NFA_MARK:
   case NFA_MARK_GT:
   case NFA_MARK_LT:

   case NFA_MOPEN:
   case NFA_MOPEN1:
   case NFA_MOPEN2:
   case NFA_MOPEN3:
   case NFA_MOPEN4:
   case NFA_MOPEN5:
   case NFA_MOPEN6:
   case NFA_MOPEN7:
   case NFA_MOPEN8:
   case NFA_MOPEN9:
   case NFA_NOPEN:
   case NFA_ZOPEN:
   case NFA_ZOPEN1:
   case NFA_ZOPEN2:
   case NFA_ZOPEN3:
   case NFA_ZOPEN4:
   case NFA_ZOPEN5:
   case NFA_ZOPEN6:
   case NFA_ZOPEN7:
   case NFA_ZOPEN8:
   case NFA_ZOPEN9:
     p = p->out;
     break;

   case NFA_SPLIT: {
     int c1 = nfa_get_regstart(p->out, depth + 1);
     int c2 = nfa_get_regstart(p->out1, depth + 1);

     if (c1 == c2) {
       return c1;             // yes!
     }
     return 0;
   }

   default:
     if (p->c > 0) {
       return p->c;             // yes!
     }
     return 0;
   }
 }
 return 0;
}

// Figure out if the NFA state list contains just literal text and nothing
// else.  If so return a string in allocated memory with what must match after
// regstart.  Otherwise return NULL.
static uint8_t *nfa_get_match_text(nfa_state_T *start)
{
 nfa_state_T *p = start;
 int len = 0;
 uint8_t *ret;
 uint8_t *s;

 if (p->c != NFA_MOPEN) {
   return NULL;     // just in case
 }
 p = p->out;
 while (p->c > 0) {
   len += utf_char2len(p->c);
   p = p->out;
 }
 if (p->c != NFA_MCLOSE || p->out->c != NFA_MATCH) {
   return NULL;
 }

 ret = xmalloc((size_t)len);
 p = start->out->out;     // skip first char, it goes into regstart
 s = ret;
 while (p->c > 0) {
   s += utf_char2bytes(p->c, (char *)s);
   p = p->out;
 }
 *s = NUL;

 return ret;
}

// Allocate more space for post_start.  Called when
// running above the estimated number of states.
static void realloc_post_list(void)
{
 // For weird patterns the number of states can be very high. Increasing by
 // 50% seems a reasonable compromise between memory use and speed.
 const size_t new_max = (size_t)(post_end - post_start) * 3 / 2;
 int *new_start = xrealloc(post_start, new_max * sizeof(int));
 post_ptr = new_start + (post_ptr - post_start);
 post_end = new_start + new_max;
 post_start = new_start;
}

// Search between "start" and "end" and try to recognize a
// character class in expanded form. For example [0-9].
// On success, return the id the character class to be emitted.
// On failure, return 0 (=FAIL)
// Start points to the first char of the range, while end should point
// to the closing brace.
// Keep in mind that 'ignorecase' applies at execution time, thus [a-z] may
// need to be interpreted as [a-zA-Z].
static int nfa_recognize_char_class(uint8_t *start, const uint8_t *end, int extra_newl)
{
#define CLASS_not            0x80
#define CLASS_af             0x40
#define CLASS_AF             0x20
#define CLASS_az             0x10
#define CLASS_AZ             0x08
#define CLASS_o7             0x04
#define CLASS_o9             0x02
#define CLASS_underscore     0x01

 uint8_t *p;
 int config = 0;

 bool newl = extra_newl == true;

 if (*end != ']') {
   return FAIL;
 }
 p = start;
 if (*p == '^') {
   config |= CLASS_not;
   p++;
 }

 while (p < end) {
   if (p + 2 < end && *(p + 1) == '-') {
     switch (*p) {
     case '0':
       if (*(p + 2) == '9') {
         config |= CLASS_o9;
         break;
       } else if (*(p + 2) == '7') {
         config |= CLASS_o7;
         break;
       }
       return FAIL;
     case 'a':
       if (*(p + 2) == 'z') {
         config |= CLASS_az;
         break;
       } else if (*(p + 2) == 'f') {
         config |= CLASS_af;
         break;
       }
       return FAIL;
     case 'A':
       if (*(p + 2) == 'Z') {
         config |= CLASS_AZ;
         break;
       } else if (*(p + 2) == 'F') {
         config |= CLASS_AF;
         break;
       }
       return FAIL;
     default:
       return FAIL;
     }
     p += 3;
   } else if (p + 1 < end && *p == '\\' && *(p + 1) == 'n') {
     newl = true;
     p += 2;
   } else if (*p == '_') {
     config |= CLASS_underscore;
     p++;
   } else if (*p == '\n') {
     newl = true;
     p++;
   } else {
     return FAIL;
   }
 }   // while (p < end)

 if (p != end) {
   return FAIL;
 }

 if (newl == true) {
   extra_newl = NFA_ADD_NL;
 }

 switch (config) {
 case CLASS_o9:
   return extra_newl + NFA_DIGIT;
 case CLASS_not |  CLASS_o9:
   return extra_newl + NFA_NDIGIT;
 case CLASS_af | CLASS_AF | CLASS_o9:
   return extra_newl + NFA_HEX;
 case CLASS_not | CLASS_af | CLASS_AF | CLASS_o9:
   return extra_newl + NFA_NHEX;
 case CLASS_o7:
   return extra_newl + NFA_OCTAL;
 case CLASS_not | CLASS_o7:
   return extra_newl + NFA_NOCTAL;
 case CLASS_az | CLASS_AZ | CLASS_o9 | CLASS_underscore:
   return extra_newl + NFA_WORD;
 case CLASS_not | CLASS_az | CLASS_AZ | CLASS_o9 | CLASS_underscore:
   return extra_newl + NFA_NWORD;
 case CLASS_az | CLASS_AZ | CLASS_underscore:
   return extra_newl + NFA_HEAD;
 case CLASS_not | CLASS_az | CLASS_AZ | CLASS_underscore:
   return extra_newl + NFA_NHEAD;
 case CLASS_az | CLASS_AZ:
   return extra_newl + NFA_ALPHA;
 case CLASS_not | CLASS_az | CLASS_AZ:
   return extra_newl + NFA_NALPHA;
 case CLASS_az:
   return extra_newl + NFA_LOWER_IC;
 case CLASS_not | CLASS_az:
   return extra_newl + NFA_NLOWER_IC;
 case CLASS_AZ:
   return extra_newl + NFA_UPPER_IC;
 case CLASS_not | CLASS_AZ:
   return extra_newl + NFA_NUPPER_IC;
 }
 return FAIL;
}

// Produce the bytes for equivalence class "c".
// Currently only handles latin1, latin9 and utf-8.
// Emits bytes in postfix notation: 'a,b,NFA_OR,c,NFA_OR' is
// equivalent to 'a OR b OR c'
//
// NOTE! When changing this function, also update reg_equi_class()
static void nfa_emit_equi_class(int c)
{
#define EMIT2(c)   EMIT(c); EMIT(NFA_CONCAT);

 {
#define A_grave 0xc0
#define A_acute 0xc1
#define A_circumflex 0xc2
#define A_virguilla 0xc3
#define A_diaeresis 0xc4
#define A_ring 0xc5
#define C_cedilla 0xc7
#define E_grave 0xc8
#define E_acute 0xc9
#define E_circumflex 0xca
#define E_diaeresis 0xcb
#define I_grave 0xcc
#define I_acute 0xcd
#define I_circumflex 0xce
#define I_diaeresis 0xcf
#define N_virguilla 0xd1
#define O_grave 0xd2
#define O_acute 0xd3
#define O_circumflex 0xd4
#define O_virguilla 0xd5
#define O_diaeresis 0xd6
#define O_slash 0xd8
#define U_grave 0xd9
#define U_acute 0xda
#define U_circumflex 0xdb
#define U_diaeresis 0xdc
#define Y_acute 0xdd
#define a_grave 0xe0
#define a_acute 0xe1
#define a_circumflex 0xe2
#define a_virguilla 0xe3
#define a_diaeresis 0xe4
#define a_ring 0xe5
#define c_cedilla 0xe7
#define e_grave 0xe8
#define e_acute 0xe9
#define e_circumflex 0xea
#define e_diaeresis 0xeb
#define i_grave 0xec
#define i_acute 0xed
#define i_circumflex 0xee
#define i_diaeresis 0xef
#define n_virguilla 0xf1
#define o_grave 0xf2
#define o_acute 0xf3
#define o_circumflex 0xf4
#define o_virguilla 0xf5
#define o_diaeresis 0xf6
#define o_slash 0xf8
#define u_grave 0xf9
#define u_acute 0xfa
#define u_circumflex 0xfb
#define u_diaeresis 0xfc
#define y_acute 0xfd
#define y_diaeresis 0xff
   switch (c) {
   case 'A':
   case A_grave:
   case A_acute:
   case A_circumflex:
   case A_virguilla:
   case A_diaeresis:
   case A_ring:
   case 0x100:
   case 0x102:
   case 0x104:
   case 0x1cd:
   case 0x1de:
   case 0x1e0:
   case 0x1fa:
   case 0x200:
   case 0x202:
   case 0x226:
   case 0x23a:
   case 0x1e00:
   case 0x1ea0:
   case 0x1ea2:
   case 0x1ea4:
   case 0x1ea6:
   case 0x1ea8:
   case 0x1eaa:
   case 0x1eac:
   case 0x1eae:
   case 0x1eb0:
   case 0x1eb2:
   case 0x1eb4:
   case 0x1eb6:
     EMIT2('A') EMIT2(A_grave) EMIT2(A_acute)
     EMIT2(A_circumflex) EMIT2(A_virguilla)
     EMIT2(A_diaeresis) EMIT2(A_ring)
     EMIT2(0x100) EMIT2(0x102) EMIT2(0x104)
     EMIT2(0x1cd) EMIT2(0x1de) EMIT2(0x1e0)
     EMIT2(0x1fa) EMIT2(0x200) EMIT2(0x202)
     EMIT2(0x226) EMIT2(0x23a) EMIT2(0x1e00)
     EMIT2(0x1ea0) EMIT2(0x1ea2) EMIT2(0x1ea4)
     EMIT2(0x1ea6) EMIT2(0x1ea8) EMIT2(0x1eaa)
     EMIT2(0x1eac) EMIT2(0x1eae) EMIT2(0x1eb0)
     EMIT2(0x1eb2) EMIT2(0x1eb6) EMIT2(0x1eb4)
     return;

   case 'B':
   case 0x181:
   case 0x243:
   case 0x1e02:
   case 0x1e04:
   case 0x1e06:
     EMIT2('B')
     EMIT2(0x181) EMIT2(0x243) EMIT2(0x1e02)
     EMIT2(0x1e04) EMIT2(0x1e06)
     return;

   case 'C':
   case C_cedilla:
   case 0x106:
   case 0x108:
   case 0x10a:
   case 0x10c:
   case 0x187:
   case 0x23b:
   case 0x1e08:
   case 0xa792:
     EMIT2('C') EMIT2(C_cedilla)
     EMIT2(0x106) EMIT2(0x108) EMIT2(0x10a)
     EMIT2(0x10c) EMIT2(0x187) EMIT2(0x23b)
     EMIT2(0x1e08) EMIT2(0xa792)
     return;

   case 'D':
   case 0x10e:
   case 0x110:
   case 0x18a:
   case 0x1e0a:
   case 0x1e0c:
   case 0x1e0e:
   case 0x1e10:
   case 0x1e12:
     EMIT2('D') EMIT2(0x10e) EMIT2(0x110) EMIT2(0x18a)
     EMIT2(0x1e0a) EMIT2(0x1e0c) EMIT2(0x1e0e)
     EMIT2(0x1e10) EMIT2(0x1e12)
     return;

   case 'E':
   case E_grave:
   case E_acute:
   case E_circumflex:
   case E_diaeresis:
   case 0x112:
   case 0x114:
   case 0x116:
   case 0x118:
   case 0x11a:
   case 0x204:
   case 0x206:
   case 0x228:
   case 0x246:
   case 0x1e14:
   case 0x1e16:
   case 0x1e18:
   case 0x1e1a:
   case 0x1e1c:
   case 0x1eb8:
   case 0x1eba:
   case 0x1ebc:
   case 0x1ebe:
   case 0x1ec0:
   case 0x1ec2:
   case 0x1ec4:
   case 0x1ec6:
     EMIT2('E') EMIT2(E_grave) EMIT2(E_acute)
     EMIT2(E_circumflex) EMIT2(E_diaeresis)
     EMIT2(0x112) EMIT2(0x114) EMIT2(0x116)
     EMIT2(0x118) EMIT2(0x11a) EMIT2(0x204)
     EMIT2(0x206) EMIT2(0x228) EMIT2(0x246)
     EMIT2(0x1e14) EMIT2(0x1e16) EMIT2(0x1e18)
     EMIT2(0x1e1a) EMIT2(0x1e1c) EMIT2(0x1eb8)
     EMIT2(0x1eba) EMIT2(0x1ebc) EMIT2(0x1ebe)
     EMIT2(0x1ec0) EMIT2(0x1ec2) EMIT2(0x1ec4)
     EMIT2(0x1ec6)
     return;

   case 'F':
   case 0x191:
   case 0x1e1e:
   case 0xa798:
     EMIT2('F') EMIT2(0x191) EMIT2(0x1e1e) EMIT2(0xa798)
     return;

   case 'G':
   case 0x11c:
   case 0x11e:
   case 0x120:
   case 0x122:
   case 0x193:
   case 0x1e4:
   case 0x1e6:
   case 0x1f4:
   case 0x1e20:
   case 0xa7a0:
     EMIT2('G') EMIT2(0x11c) EMIT2(0x11e) EMIT2(0x120)
     EMIT2(0x122) EMIT2(0x193) EMIT2(0x1e4)
     EMIT2(0x1e6) EMIT2(0x1f4) EMIT2(0x1e20)
     EMIT2(0xa7a0)
     return;

   case 'H':
   case 0x124:
   case 0x126:
   case 0x21e:
   case 0x1e22:
   case 0x1e24:
   case 0x1e26:
   case 0x1e28:
   case 0x1e2a:
   case 0x2c67:
     EMIT2('H') EMIT2(0x124) EMIT2(0x126) EMIT2(0x21e)
     EMIT2(0x1e22) EMIT2(0x1e24) EMIT2(0x1e26)
     EMIT2(0x1e28) EMIT2(0x1e2a) EMIT2(0x2c67)
     return;

   case 'I':
   case I_grave:
   case I_acute:
   case I_circumflex:
   case I_diaeresis:
   case 0x128:
   case 0x12a:
   case 0x12c:
   case 0x12e:
   case 0x130:
   case 0x197:
   case 0x1cf:
   case 0x208:
   case 0x20a:
   case 0x1e2c:
   case 0x1e2e:
   case 0x1ec8:
   case 0x1eca:
     EMIT2('I') EMIT2(I_grave) EMIT2(I_acute)
     EMIT2(I_circumflex) EMIT2(I_diaeresis)
     EMIT2(0x128) EMIT2(0x12a) EMIT2(0x12c)
     EMIT2(0x12e) EMIT2(0x130) EMIT2(0x197)
     EMIT2(0x1cf) EMIT2(0x208) EMIT2(0x20a)
     EMIT2(0x1e2c) EMIT2(0x1e2e) EMIT2(0x1ec8)
     EMIT2(0x1eca)
     return;

   case 'J':
   case 0x134:
   case 0x248:
     EMIT2('J') EMIT2(0x134) EMIT2(0x248)
     return;

   case 'K':
   case 0x136:
   case 0x198:
   case 0x1e8:
   case 0x1e30:
   case 0x1e32:
   case 0x1e34:
   case 0x2c69:
   case 0xa740:
     EMIT2('K') EMIT2(0x136) EMIT2(0x198) EMIT2(0x1e8)
     EMIT2(0x1e30) EMIT2(0x1e32) EMIT2(0x1e34)
     EMIT2(0x2c69) EMIT2(0xa740)
     return;

   case 'L':
   case 0x139:
   case 0x13b:
   case 0x13d:
   case 0x13f:
   case 0x141:
   case 0x23d:
   case 0x1e36:
   case 0x1e38:
   case 0x1e3a:
   case 0x1e3c:
   case 0x2c60:
     EMIT2('L') EMIT2(0x139) EMIT2(0x13b)
     EMIT2(0x13d) EMIT2(0x13f) EMIT2(0x141)
     EMIT2(0x23d) EMIT2(0x1e36) EMIT2(0x1e38)
     EMIT2(0x1e3a) EMIT2(0x1e3c) EMIT2(0x2c60)
     return;

   case 'M':
   case 0x1e3e:
   case 0x1e40:
   case 0x1e42:
     EMIT2('M') EMIT2(0x1e3e) EMIT2(0x1e40)
     EMIT2(0x1e42)
     return;

   case 'N':
   case N_virguilla:
   case 0x143:
   case 0x145:
   case 0x147:
   case 0x1f8:
   case 0x1e44:
   case 0x1e46:
   case 0x1e48:
   case 0x1e4a:
   case 0xa7a4:
     EMIT2('N') EMIT2(N_virguilla)
     EMIT2(0x143) EMIT2(0x145) EMIT2(0x147)
     EMIT2(0x1f8) EMIT2(0x1e44) EMIT2(0x1e46)
     EMIT2(0x1e48) EMIT2(0x1e4a) EMIT2(0xa7a4)
     return;

   case 'O':
   case O_grave:
   case O_acute:
   case O_circumflex:
   case O_virguilla:
   case O_diaeresis:
   case O_slash:
   case 0x14c:
   case 0x14e:
   case 0x150:
   case 0x19f:
   case 0x1a0:
   case 0x1d1:
   case 0x1ea:
   case 0x1ec:
   case 0x1fe:
   case 0x20c:
   case 0x20e:
   case 0x22a:
   case 0x22c:
   case 0x22e:
   case 0x230:
   case 0x1e4c:
   case 0x1e4e:
   case 0x1e50:
   case 0x1e52:
   case 0x1ecc:
   case 0x1ece:
   case 0x1ed0:
   case 0x1ed2:
   case 0x1ed4:
   case 0x1ed6:
   case 0x1ed8:
   case 0x1eda:
   case 0x1edc:
   case 0x1ede:
   case 0x1ee0:
   case 0x1ee2:
     EMIT2('O') EMIT2(O_grave) EMIT2(O_acute)
     EMIT2(O_circumflex) EMIT2(O_virguilla)
     EMIT2(O_diaeresis) EMIT2(O_slash)
     EMIT2(0x14c) EMIT2(0x14e) EMIT2(0x150)
     EMIT2(0x19f) EMIT2(0x1a0) EMIT2(0x1d1)
     EMIT2(0x1ea) EMIT2(0x1ec) EMIT2(0x1fe)
     EMIT2(0x20c) EMIT2(0x20e) EMIT2(0x22a)
     EMIT2(0x22c) EMIT2(0x22e) EMIT2(0x230)
     EMIT2(0x1e4c) EMIT2(0x1e4e) EMIT2(0x1e50)
     EMIT2(0x1e52) EMIT2(0x1ecc) EMIT2(0x1ece)
     EMIT2(0x1ed0) EMIT2(0x1ed2) EMIT2(0x1ed4)
     EMIT2(0x1ed6) EMIT2(0x1ed8) EMIT2(0x1eda)
     EMIT2(0x1edc) EMIT2(0x1ede) EMIT2(0x1ee0)
     EMIT2(0x1ee2)
     return;

   case 'P':
   case 0x1a4:
   case 0x1e54:
   case 0x1e56:
   case 0x2c63:
     EMIT2('P') EMIT2(0x1a4) EMIT2(0x1e54) EMIT2(0x1e56)
     EMIT2(0x2c63)
     return;

   case 'Q':
   case 0x24a:
     EMIT2('Q') EMIT2(0x24a)
     return;

   case 'R':
   case 0x154:
   case 0x156:
   case 0x158:
   case 0x210:
   case 0x212:
   case 0x24c:
   case 0x1e58:
   case 0x1e5a:
   case 0x1e5c:
   case 0x1e5e:
   case 0x2c64:
   case 0xa7a6:
     EMIT2('R') EMIT2(0x154) EMIT2(0x156) EMIT2(0x158)
     EMIT2(0x210) EMIT2(0x212) EMIT2(0x24c) EMIT2(0x1e58)
     EMIT2(0x1e5a) EMIT2(0x1e5c) EMIT2(0x1e5e) EMIT2(0x2c64)
     EMIT2(0xa7a6)
     return;

   case 'S':
   case 0x15a:
   case 0x15c:
   case 0x15e:
   case 0x160:
   case 0x218:
   case 0x1e60:
   case 0x1e62:
   case 0x1e64:
   case 0x1e66:
   case 0x1e68:
   case 0x2c7e:
   case 0xa7a8:
     EMIT2('S') EMIT2(0x15a) EMIT2(0x15c) EMIT2(0x15e)
     EMIT2(0x160) EMIT2(0x218) EMIT2(0x1e60) EMIT2(0x1e62)
     EMIT2(0x1e64) EMIT2(0x1e66) EMIT2(0x1e68) EMIT2(0x2c7e)
     EMIT2(0xa7a8)
     return;

   case 'T':
   case 0x162:
   case 0x164:
   case 0x166:
   case 0x1ac:
   case 0x1ae:
   case 0x21a:
   case 0x23e:
   case 0x1e6a:
   case 0x1e6c:
   case 0x1e6e:
   case 0x1e70:
     EMIT2('T') EMIT2(0x162) EMIT2(0x164) EMIT2(0x166)
     EMIT2(0x1ac) EMIT2(0x1ae) EMIT2(0x23e) EMIT2(0x21a)
     EMIT2(0x1e6a) EMIT2(0x1e6c) EMIT2(0x1e6e) EMIT2(0x1e70)
     return;

   case 'U':
   case U_grave:
   case U_acute:
   case U_diaeresis:
   case U_circumflex:
   case 0x168:
   case 0x16a:
   case 0x16c:
   case 0x16e:
   case 0x170:
   case 0x172:
   case 0x1af:
   case 0x1d3:
   case 0x1d5:
   case 0x1d7:
   case 0x1d9:
   case 0x1db:
   case 0x214:
   case 0x216:
   case 0x244:
   case 0x1e72:
   case 0x1e74:
   case 0x1e76:
   case 0x1e78:
   case 0x1e7a:
   case 0x1ee4:
   case 0x1ee6:
   case 0x1ee8:
   case 0x1eea:
   case 0x1eec:
   case 0x1eee:
   case 0x1ef0:
     EMIT2('U') EMIT2(U_grave) EMIT2(U_acute)
     EMIT2(U_diaeresis) EMIT2(U_circumflex)
     EMIT2(0x168) EMIT2(0x16a)
     EMIT2(0x16c) EMIT2(0x16e) EMIT2(0x170)
     EMIT2(0x172) EMIT2(0x1af) EMIT2(0x1d3)
     EMIT2(0x1d5) EMIT2(0x1d7) EMIT2(0x1d9)
     EMIT2(0x1db) EMIT2(0x214) EMIT2(0x216)
     EMIT2(0x244) EMIT2(0x1e72) EMIT2(0x1e74)
     EMIT2(0x1e76) EMIT2(0x1e78) EMIT2(0x1e7a)
     EMIT2(0x1ee4) EMIT2(0x1ee6) EMIT2(0x1ee8)
     EMIT2(0x1eea) EMIT2(0x1eec) EMIT2(0x1eee)
     EMIT2(0x1ef0)
     return;

   case 'V':
   case 0x1b2:
   case 0x1e7c:
   case 0x1e7e:
     EMIT2('V') EMIT2(0x1b2) EMIT2(0x1e7c) EMIT2(0x1e7e)
     return;

   case 'W':
   case 0x174:
   case 0x1e80:
   case 0x1e82:
   case 0x1e84:
   case 0x1e86:
   case 0x1e88:
     EMIT2('W') EMIT2(0x174) EMIT2(0x1e80) EMIT2(0x1e82)
     EMIT2(0x1e84) EMIT2(0x1e86) EMIT2(0x1e88)
     return;

   case 'X':
   case 0x1e8a:
   case 0x1e8c:
     EMIT2('X') EMIT2(0x1e8a) EMIT2(0x1e8c)
     return;

   case 'Y':
   case Y_acute:
   case 0x176:
   case 0x178:
   case 0x1b3:
   case 0x232:
   case 0x24e:
   case 0x1e8e:
   case 0x1ef2:
   case 0x1ef4:
   case 0x1ef6:
   case 0x1ef8:
     EMIT2('Y') EMIT2(Y_acute)
     EMIT2(0x176) EMIT2(0x178) EMIT2(0x1b3)
     EMIT2(0x232) EMIT2(0x24e) EMIT2(0x1e8e)
     EMIT2(0x1ef2) EMIT2(0x1ef4) EMIT2(0x1ef6)
     EMIT2(0x1ef8)
     return;

   case 'Z':
   case 0x179:
   case 0x17b:
   case 0x17d:
   case 0x1b5:
   case 0x1e90:
   case 0x1e92:
   case 0x1e94:
   case 0x2c6b:
     EMIT2('Z') EMIT2(0x179) EMIT2(0x17b) EMIT2(0x17d)
     EMIT2(0x1b5) EMIT2(0x1e90) EMIT2(0x1e92)
     EMIT2(0x1e94) EMIT2(0x2c6b)
     return;

   case 'a':
   case a_grave:
   case a_acute:
   case a_circumflex:
   case a_virguilla:
   case a_diaeresis:
   case a_ring:
   case 0x101:
   case 0x103:
   case 0x105:
   case 0x1ce:
   case 0x1df:
   case 0x1e1:
   case 0x1fb:
   case 0x201:
   case 0x203:
   case 0x227:
   case 0x1d8f:
   case 0x1e01:
   case 0x1e9a:
   case 0x1ea1:
   case 0x1ea3:
   case 0x1ea5:
   case 0x1ea7:
   case 0x1ea9:
   case 0x1eab:
   case 0x1ead:
   case 0x1eaf:
   case 0x1eb1:
   case 0x1eb3:
   case 0x1eb5:
   case 0x1eb7:
   case 0x2c65:
     EMIT2('a') EMIT2(a_grave) EMIT2(a_acute)
     EMIT2(a_circumflex) EMIT2(a_virguilla)
     EMIT2(a_diaeresis) EMIT2(a_ring)
     EMIT2(0x101) EMIT2(0x103) EMIT2(0x105)
     EMIT2(0x1ce) EMIT2(0x1df) EMIT2(0x1e1)
     EMIT2(0x1fb) EMIT2(0x201) EMIT2(0x203)
     EMIT2(0x227) EMIT2(0x1d8f) EMIT2(0x1e01)
     EMIT2(0x1e9a) EMIT2(0x1ea1) EMIT2(0x1ea3)
     EMIT2(0x1ea5) EMIT2(0x1ea7) EMIT2(0x1ea9)
     EMIT2(0x1eab) EMIT2(0x1ead) EMIT2(0x1eaf)
     EMIT2(0x1eb1) EMIT2(0x1eb3) EMIT2(0x1eb5)
     EMIT2(0x1eb7) EMIT2(0x2c65)
     return;

   case 'b':
   case 0x180:
   case 0x253:
   case 0x1d6c:
   case 0x1d80:
   case 0x1e03:
   case 0x1e05:
   case 0x1e07:
     EMIT2('b') EMIT2(0x180) EMIT2(0x253) EMIT2(0x1d6c)
     EMIT2(0x1d80) EMIT2(0x1e03) EMIT2(0x1e05) EMIT2(0x1e07)
     return;

   case 'c':
   case c_cedilla:
   case 0x107:
   case 0x109:
   case 0x10b:
   case 0x10d:
   case 0x188:
   case 0x23c:
   case 0x1e09:
   case 0xa793:
   case 0xa794:
     EMIT2('c') EMIT2(c_cedilla)
     EMIT2(0x107) EMIT2(0x109) EMIT2(0x10b)
     EMIT2(0x10d) EMIT2(0x188) EMIT2(0x23c)
     EMIT2(0x1e09) EMIT2(0xa793) EMIT2(0xa794)
     return;

   case 'd':
   case 0x10f:
   case 0x111:
   case 0x257:
   case 0x1d6d:
   case 0x1d81:
   case 0x1d91:
   case 0x1e0b:
   case 0x1e0d:
   case 0x1e0f:
   case 0x1e11:
   case 0x1e13:
     EMIT2('d') EMIT2(0x10f) EMIT2(0x111)
     EMIT2(0x257) EMIT2(0x1d6d) EMIT2(0x1d81)
     EMIT2(0x1d91) EMIT2(0x1e0b) EMIT2(0x1e0d)
     EMIT2(0x1e0f) EMIT2(0x1e11) EMIT2(0x1e13)
     return;

   case 'e':
   case e_grave:
   case e_acute:
   case e_circumflex:
   case e_diaeresis:
   case 0x113:
   case 0x115:
   case 0x117:
   case 0x119:
   case 0x11b:
   case 0x205:
   case 0x207:
   case 0x229:
   case 0x247:
   case 0x1d92:
   case 0x1e15:
   case 0x1e17:
   case 0x1e19:
   case 0x1e1b:
   case 0x1e1d:
   case 0x1eb9:
   case 0x1ebb:
   case 0x1ebd:
   case 0x1ebf:
   case 0x1ec1:
   case 0x1ec3:
   case 0x1ec5:
   case 0x1ec7:
     EMIT2('e') EMIT2(e_grave) EMIT2(e_acute)
     EMIT2(e_circumflex) EMIT2(e_diaeresis)
     EMIT2(0x113) EMIT2(0x115)
     EMIT2(0x117) EMIT2(0x119) EMIT2(0x11b)
     EMIT2(0x205) EMIT2(0x207) EMIT2(0x229)
     EMIT2(0x247) EMIT2(0x1d92) EMIT2(0x1e15)
     EMIT2(0x1e17) EMIT2(0x1e19) EMIT2(0x1e1b)
     EMIT2(0x1e1d) EMIT2(0x1eb9) EMIT2(0x1ebb)
     EMIT2(0x1ebd) EMIT2(0x1ebf) EMIT2(0x1ec1)
     EMIT2(0x1ec3) EMIT2(0x1ec5) EMIT2(0x1ec7)
     return;

   case 'f':
   case 0x192:
   case 0x1d6e:
   case 0x1d82:
   case 0x1e1f:
   case 0xa799:
     EMIT2('f') EMIT2(0x192) EMIT2(0x1d6e) EMIT2(0x1d82)
     EMIT2(0x1e1f) EMIT2(0xa799)
     return;

   case 'g':
   case 0x11d:
   case 0x11f:
   case 0x121:
   case 0x123:
   case 0x1e5:
   case 0x1e7:
   case 0x1f5:
   case 0x260:
   case 0x1d83:
   case 0x1e21:
   case 0xa7a1:
     EMIT2('g') EMIT2(0x11d) EMIT2(0x11f) EMIT2(0x121)
     EMIT2(0x123) EMIT2(0x1e5) EMIT2(0x1e7)
     EMIT2(0x1f5) EMIT2(0x260) EMIT2(0x1d83)
     EMIT2(0x1e21) EMIT2(0xa7a1)
     return;

   case 'h':
   case 0x125:
   case 0x127:
   case 0x21f:
   case 0x1e23:
   case 0x1e25:
   case 0x1e27:
   case 0x1e29:
   case 0x1e2b:
   case 0x1e96:
   case 0x2c68:
   case 0xa795:
     EMIT2('h') EMIT2(0x125) EMIT2(0x127) EMIT2(0x21f)
     EMIT2(0x1e23) EMIT2(0x1e25) EMIT2(0x1e27)
     EMIT2(0x1e29) EMIT2(0x1e2b) EMIT2(0x1e96)
     EMIT2(0x2c68) EMIT2(0xa795)
     return;

   case 'i':
   case i_grave:
   case i_acute:
   case i_circumflex:
   case i_diaeresis:
   case 0x129:
   case 0x12b:
   case 0x12d:
   case 0x12f:
   case 0x1d0:
   case 0x209:
   case 0x20b:
   case 0x268:
   case 0x1d96:
   case 0x1e2d:
   case 0x1e2f:
   case 0x1ec9:
   case 0x1ecb:
     EMIT2('i') EMIT2(i_grave) EMIT2(i_acute)
     EMIT2(i_circumflex) EMIT2(i_diaeresis)
     EMIT2(0x129) EMIT2(0x12b) EMIT2(0x12d)
     EMIT2(0x12f) EMIT2(0x1d0) EMIT2(0x209)
     EMIT2(0x20b) EMIT2(0x268) EMIT2(0x1d96)
     EMIT2(0x1e2d) EMIT2(0x1e2f) EMIT2(0x1ec9)
     EMIT2(0x1ecb) EMIT2(0x1ecb)
     return;

   case 'j':
   case 0x135:
   case 0x1f0:
   case 0x249:
     EMIT2('j') EMIT2(0x135) EMIT2(0x1f0) EMIT2(0x249)
     return;

   case 'k':
   case 0x137:
   case 0x199:
   case 0x1e9:
   case 0x1d84:
   case 0x1e31:
   case 0x1e33:
   case 0x1e35:
   case 0x2c6a:
   case 0xa741:
     EMIT2('k') EMIT2(0x137) EMIT2(0x199) EMIT2(0x1e9)
     EMIT2(0x1d84) EMIT2(0x1e31) EMIT2(0x1e33)
     EMIT2(0x1e35) EMIT2(0x2c6a) EMIT2(0xa741)
     return;

   case 'l':
   case 0x13a:
   case 0x13c:
   case 0x13e:
   case 0x140:
   case 0x142:
   case 0x19a:
   case 0x1e37:
   case 0x1e39:
   case 0x1e3b:
   case 0x1e3d:
   case 0x2c61:
     EMIT2('l') EMIT2(0x13a) EMIT2(0x13c)
     EMIT2(0x13e) EMIT2(0x140) EMIT2(0x142)
     EMIT2(0x19a) EMIT2(0x1e37) EMIT2(0x1e39)
     EMIT2(0x1e3b) EMIT2(0x1e3d) EMIT2(0x2c61)
     return;

   case 'm':
   case 0x1d6f:
   case 0x1e3f:
   case 0x1e41:
   case 0x1e43:
     EMIT2('m') EMIT2(0x1d6f) EMIT2(0x1e3f)
     EMIT2(0x1e41) EMIT2(0x1e43)
     return;

   case 'n':
   case n_virguilla:
   case 0x144:
   case 0x146:
   case 0x148:
   case 0x149:
   case 0x1f9:
   case 0x1d70:
   case 0x1d87:
   case 0x1e45:
   case 0x1e47:
   case 0x1e49:
   case 0x1e4b:
   case 0xa7a5:
     EMIT2('n') EMIT2(n_virguilla)
     EMIT2(0x144) EMIT2(0x146) EMIT2(0x148)
     EMIT2(0x149) EMIT2(0x1f9) EMIT2(0x1d70)
     EMIT2(0x1d87) EMIT2(0x1e45) EMIT2(0x1e47)
     EMIT2(0x1e49) EMIT2(0x1e4b) EMIT2(0xa7a5)
     return;

   case 'o':
   case o_grave:
   case o_acute:
   case o_circumflex:
   case o_virguilla:
   case o_diaeresis:
   case o_slash:
   case 0x14d:
   case 0x14f:
   case 0x151:
   case 0x1a1:
   case 0x1d2:
   case 0x1eb:
   case 0x1ed:
   case 0x1ff:
   case 0x20d:
   case 0x20f:
   case 0x22b:
   case 0x22d:
   case 0x22f:
   case 0x231:
   case 0x275:
   case 0x1e4d:
   case 0x1e4f:
   case 0x1e51:
   case 0x1e53:
   case 0x1ecd:
   case 0x1ecf:
   case 0x1ed1:
   case 0x1ed3:
   case 0x1ed5:
   case 0x1ed7:
   case 0x1ed9:
   case 0x1edb:
   case 0x1edd:
   case 0x1edf:
   case 0x1ee1:
   case 0x1ee3:
     EMIT2('o') EMIT2(o_grave) EMIT2(o_acute)
     EMIT2(o_circumflex) EMIT2(o_virguilla)
     EMIT2(o_diaeresis) EMIT2(o_slash)
     EMIT2(0x14d) EMIT2(0x14f) EMIT2(0x151)
     EMIT2(0x1a1) EMIT2(0x1d2) EMIT2(0x1eb)
     EMIT2(0x1ed) EMIT2(0x1ff) EMIT2(0x20d)
     EMIT2(0x20f) EMIT2(0x22b) EMIT2(0x22d)
     EMIT2(0x22f) EMIT2(0x231) EMIT2(0x275)
     EMIT2(0x1e4d) EMIT2(0x1e4f) EMIT2(0x1e51)
     EMIT2(0x1e53) EMIT2(0x1ecd) EMIT2(0x1ecf)
     EMIT2(0x1ed1) EMIT2(0x1ed3) EMIT2(0x1ed5)
     EMIT2(0x1ed7) EMIT2(0x1ed9) EMIT2(0x1edb)
     EMIT2(0x1edd) EMIT2(0x1edf) EMIT2(0x1ee1)
     EMIT2(0x1ee3)
     return;

   case 'p':
   case 0x1a5:
   case 0x1d71:
   case 0x1d7d:
   case 0x1d88:
   case 0x1e55:
   case 0x1e57:
     EMIT2('p') EMIT2(0x1a5) EMIT2(0x1d71) EMIT2(0x1d7d)
     EMIT2(0x1d88) EMIT2(0x1e55) EMIT2(0x1e57)
     return;

   case 'q':
   case 0x24b:
   case 0x2a0:
     EMIT2('q') EMIT2(0x24b) EMIT2(0x2a0)
     return;

   case 'r':
   case 0x155:
   case 0x157:
   case 0x159:
   case 0x211:
   case 0x213:
   case 0x24d:
   case 0x27d:
   case 0x1d72:
   case 0x1d73:
   case 0x1d89:
   case 0x1e59:
   case 0x1e5b:
   case 0x1e5d:
   case 0x1e5f:
   case 0xa7a7:
     EMIT2('r') EMIT2(0x155) EMIT2(0x157) EMIT2(0x159)
     EMIT2(0x211) EMIT2(0x213) EMIT2(0x24d) EMIT2(0x27d)
     EMIT2(0x1d72) EMIT2(0x1d73) EMIT2(0x1d89) EMIT2(0x1e59)
     EMIT2(0x1e5b) EMIT2(0x1e5d) EMIT2(0x1e5f) EMIT2(0xa7a7)
     return;

   case 's':
   case 0x15b:
   case 0x15d:
   case 0x15f:
   case 0x161:
   case 0x219:
   case 0x23f:
   case 0x1d74:
   case 0x1d8a:
   case 0x1e61:
   case 0x1e63:
   case 0x1e65:
   case 0x1e67:
   case 0x1e69:
   case 0xa7a9:
     EMIT2('s') EMIT2(0x15b) EMIT2(0x15d) EMIT2(0x15f)
     EMIT2(0x161) EMIT2(0x219) EMIT2(0x23f) EMIT2(0x1d74)
     EMIT2(0x1d8a) EMIT2(0x1e61) EMIT2(0x1e63) EMIT2(0x1e65)
     EMIT2(0x1e67) EMIT2(0x1e69) EMIT2(0xa7a9)
     return;

   case 't':
   case 0x163:
   case 0x165:
   case 0x167:
   case 0x1ab:
   case 0x1ad:
   case 0x21b:
   case 0x288:
   case 0x1d75:
   case 0x1e6b:
   case 0x1e6d:
   case 0x1e6f:
   case 0x1e71:
   case 0x1e97:
   case 0x2c66:
     EMIT2('t') EMIT2(0x163) EMIT2(0x165) EMIT2(0x167)
     EMIT2(0x1ab) EMIT2(0x1ad) EMIT2(0x21b) EMIT2(0x288)
     EMIT2(0x1d75) EMIT2(0x1e6b) EMIT2(0x1e6d) EMIT2(0x1e6f)
     EMIT2(0x1e71) EMIT2(0x1e97) EMIT2(0x2c66)
     return;

   case 'u':
   case u_grave:
   case u_acute:
   case u_circumflex:
   case u_diaeresis:
   case 0x169:
   case 0x16b:
   case 0x16d:
   case 0x16f:
   case 0x171:
   case 0x173:
   case 0x1b0:
   case 0x1d4:
   case 0x1d6:
   case 0x1d8:
   case 0x1da:
   case 0x1dc:
   case 0x215:
   case 0x217:
   case 0x289:
   case 0x1d7e:
   case 0x1d99:
   case 0x1e73:
   case 0x1e75:
   case 0x1e77:
   case 0x1e79:
   case 0x1e7b:
   case 0x1ee5:
   case 0x1ee7:
   case 0x1ee9:
   case 0x1eeb:
   case 0x1eed:
   case 0x1eef:
   case 0x1ef1:
     EMIT2('u') EMIT2(u_grave) EMIT2(u_acute)
     EMIT2(u_circumflex) EMIT2(u_diaeresis)
     EMIT2(0x169) EMIT2(0x16b)
     EMIT2(0x16d) EMIT2(0x16f) EMIT2(0x171)
     EMIT2(0x173) EMIT2(0x1d6) EMIT2(0x1d8)
     EMIT2(0x215) EMIT2(0x217) EMIT2(0x1b0)
     EMIT2(0x1d4) EMIT2(0x1da) EMIT2(0x1dc)
     EMIT2(0x289) EMIT2(0x1e73) EMIT2(0x1d7e)
     EMIT2(0x1d99) EMIT2(0x1e75) EMIT2(0x1e77)
     EMIT2(0x1e79) EMIT2(0x1e7b) EMIT2(0x1ee5)
     EMIT2(0x1ee7) EMIT2(0x1ee9) EMIT2(0x1eeb)
     EMIT2(0x1eed) EMIT2(0x1eef) EMIT2(0x1ef1)
     return;

   case 'v':
   case 0x28b:
   case 0x1d8c:
   case 0x1e7d:
   case 0x1e7f:
     EMIT2('v') EMIT2(0x28b) EMIT2(0x1d8c) EMIT2(0x1e7d)
     EMIT2(0x1e7f)
     return;

   case 'w':
   case 0x175:
   case 0x1e81:
   case 0x1e83:
   case 0x1e85:
   case 0x1e87:
   case 0x1e89:
   case 0x1e98:
     EMIT2('w') EMIT2(0x175) EMIT2(0x1e81) EMIT2(0x1e83)
     EMIT2(0x1e85) EMIT2(0x1e87) EMIT2(0x1e89) EMIT2(0x1e98)
     return;

   case 'x':
   case 0x1e8b:
   case 0x1e8d:
     EMIT2('x') EMIT2(0x1e8b) EMIT2(0x1e8d)
     return;

   case 'y':
   case y_acute:
   case y_diaeresis:
   case 0x177:
   case 0x1b4:
   case 0x233:
   case 0x24f:
   case 0x1e8f:
   case 0x1e99:
   case 0x1ef3:
   case 0x1ef5:
   case 0x1ef7:
   case 0x1ef9:
     EMIT2('y') EMIT2(y_acute) EMIT2(y_diaeresis)
     EMIT2(0x177) EMIT2(0x1b4) EMIT2(0x233) EMIT2(0x24f)
     EMIT2(0x1e8f) EMIT2(0x1e99) EMIT2(0x1ef3)
     EMIT2(0x1ef5) EMIT2(0x1ef7) EMIT2(0x1ef9)
     return;

   case 'z':
   case 0x17a:
   case 0x17c:
   case 0x17e:
   case 0x1b6:
   case 0x1d76:
   case 0x1d8e:
   case 0x1e91:
   case 0x1e93:
   case 0x1e95:
   case 0x2c6c:
     EMIT2('z') EMIT2(0x17a) EMIT2(0x17c) EMIT2(0x17e)
     EMIT2(0x1b6) EMIT2(0x1d76) EMIT2(0x1d8e) EMIT2(0x1e91)
     EMIT2(0x1e93) EMIT2(0x1e95) EMIT2(0x2c6c)
     return;

     // default: character itself
   }
 }

 EMIT2(c);
#undef EMIT2
}

// Code to parse regular expression.
//
// We try to reuse parsing functions in regexp.c to
// minimize surprise and keep the syntax consistent.

// Parse the lowest level.
//
// An atom can be one of a long list of items.  Many atoms match one character
// in the text.  It is often an ordinary character or a character class.
// Braces can be used to make a pattern into an atom.  The "\z(\)" construct
// is only for syntax highlighting.
//
// atom    ::=     ordinary-atom
//     or  \( pattern \)
//     or  \%( pattern \)
//     or  \z( pattern \)
static int nfa_regatom(void)
{
 int c;
 int charclass;
 int equiclass;
 int collclass;
 int got_coll_char;
 uint8_t *p;
 uint8_t *endp;
 uint8_t *old_regparse = (uint8_t *)regparse;
 int extra = 0;
 int emit_range;
 int negated;
 int startc = -1;
 int save_prev_at_start = prev_at_start;

 c = getchr();
 switch (c) {
 case NUL:
   EMSG_RET_FAIL(_(e_nul_found));

 case Magic('^'):
   EMIT(NFA_BOL);
   break;

 case Magic('$'):
   EMIT(NFA_EOL);
   had_eol = true;
   break;

 case Magic('<'):
   EMIT(NFA_BOW);
   break;

 case Magic('>'):
   EMIT(NFA_EOW);
   break;

 case Magic('_'):
   c = no_Magic(getchr());
   if (c == NUL) {
     EMSG_RET_FAIL(_(e_nul_found));
   }

   if (c == '^') {             // "\_^" is start-of-line
     EMIT(NFA_BOL);
     break;
   }
   if (c == '$') {             // "\_$" is end-of-line
     EMIT(NFA_EOL);
     had_eol = true;
     break;
   }

   extra = NFA_ADD_NL;

   // "\_[" is collection plus newline
   if (c == '[') {
     goto collection;
   }

   // "\_x" is character class plus newline
   FALLTHROUGH;

 // Character classes.
 case Magic('.'):
 case Magic('i'):
 case Magic('I'):
 case Magic('k'):
 case Magic('K'):
 case Magic('f'):
 case Magic('F'):
 case Magic('p'):
 case Magic('P'):
 case Magic('s'):
 case Magic('S'):
 case Magic('d'):
 case Magic('D'):
 case Magic('x'):
 case Magic('X'):
 case Magic('o'):
 case Magic('O'):
 case Magic('w'):
 case Magic('W'):
 case Magic('h'):
 case Magic('H'):
 case Magic('a'):
 case Magic('A'):
 case Magic('l'):
 case Magic('L'):
 case Magic('u'):
 case Magic('U'):
   p = (uint8_t *)vim_strchr((char *)classchars, no_Magic(c));
   if (p == NULL) {
     if (extra == NFA_ADD_NL) {
       semsg(_(e_ill_char_class), (int64_t)c);
       rc_did_emsg = true;
       return FAIL;
     }
     siemsg("INTERNAL: Unknown character class char: %d", c);
     return FAIL;
   }
   // When '.' is followed by a composing char ignore the dot, so that
   // the composing char is matched here.
   if (c == Magic('.') && utf_iscomposing_legacy(peekchr())) {
     old_regparse = (uint8_t *)regparse;
     c = getchr();
     goto nfa_do_multibyte;
   }
   EMIT(nfa_classcodes[p - classchars]);
   if (extra == NFA_ADD_NL) {
     EMIT(NFA_NEWL);
     EMIT(NFA_OR);
     regflags |= RF_HASNL;
   }
   break;

 case Magic('n'):
   if (reg_string) {
     // In a string "\n" matches a newline character.
     EMIT(NL);
   } else {
     // In buffer text "\n" matches the end of a line.
     EMIT(NFA_NEWL);
     regflags |= RF_HASNL;
   }
   break;

 case Magic('('):
   if (nfa_reg(REG_PAREN) == FAIL) {
     return FAIL;                  // cascaded error
   }
   break;

 case Magic('|'):
 case Magic('&'):
 case Magic(')'):
   semsg(_(e_misplaced), (char)no_Magic(c));
   return FAIL;

 case Magic('='):
 case Magic('?'):
 case Magic('+'):
 case Magic('@'):
 case Magic('*'):
 case Magic('{'):
   // these should follow an atom, not form an atom
   semsg(_(e_misplaced), (char)no_Magic(c));
   return FAIL;

 case Magic('~'): {
   uint8_t *lp;

   // Previous substitute pattern.
   // Generated as "\%(pattern\)".
   if (reg_prev_sub == NULL) {
     emsg(_(e_nopresub));
     return FAIL;
   }
   for (lp = (uint8_t *)reg_prev_sub; *lp != NUL; lp += utf_ptr2len((char *)lp)) {
     EMIT(utf_ptr2char((char *)lp));
     if (lp != (uint8_t *)reg_prev_sub) {
       EMIT(NFA_CONCAT);
     }
   }
   EMIT(NFA_NOPEN);
   break;
 }

 case Magic('1'):
 case Magic('2'):
 case Magic('3'):
 case Magic('4'):
 case Magic('5'):
 case Magic('6'):
 case Magic('7'):
 case Magic('8'):
 case Magic('9'): {
   int refnum = no_Magic(c) - '1';

   if (!seen_endbrace(refnum + 1)) {
     return FAIL;
   }
   EMIT(NFA_BACKREF1 + refnum);
   rex.nfa_has_backref = true;
 }
 break;

 case Magic('z'):
   c = no_Magic(getchr());
   switch (c) {
   case 's':
     EMIT(NFA_ZSTART);
     if (!re_mult_next("\\zs")) {
       return false;
     }
     break;
   case 'e':
     EMIT(NFA_ZEND);
     rex.nfa_has_zend = true;
     if (!re_mult_next("\\ze")) {
       return false;
     }
     break;
   case '1':
   case '2':
   case '3':
   case '4':
   case '5':
   case '6':
   case '7':
   case '8':
   case '9':
     // \z1...\z9
     if ((reg_do_extmatch & REX_USE) == 0) {
       EMSG_RET_FAIL(_(e_z1_not_allowed));
     }
     EMIT(NFA_ZREF1 + (no_Magic(c) - '1'));
     // No need to set rex.nfa_has_backref, the sub-matches don't
     // change when \z1 .. \z9 matches or not.
     re_has_z = REX_USE;
     break;
   case '(':
     // \z(
     if (reg_do_extmatch != REX_SET) {
       EMSG_RET_FAIL(_(e_z_not_allowed));
     }
     if (nfa_reg(REG_ZPAREN) == FAIL) {
       return FAIL;                        // cascaded error
     }
     re_has_z = REX_SET;
     break;
   default:
     semsg(_("E867: (NFA) Unknown operator '\\z%c'"),
           no_Magic(c));
     return FAIL;
   }
   break;

 case Magic('%'):
   c = no_Magic(getchr());
   switch (c) {
   // () without a back reference
   case '(':
     if (nfa_reg(REG_NPAREN) == FAIL) {
       return FAIL;
     }
     EMIT(NFA_NOPEN);
     break;

   case 'd':               // %d123 decimal
   case 'o':               // %o123 octal
   case 'x':               // %xab hex 2
   case 'u':               // %uabcd hex 4
   case 'U':               // %U1234abcd hex 8
   {
     int64_t nr;

     switch (c) {
     case 'd':
       nr = getdecchrs(); break;
     case 'o':
       nr = getoctchrs(); break;
     case 'x':
       nr = gethexchrs(2); break;
     case 'u':
       nr = gethexchrs(4); break;
     case 'U':
       nr = gethexchrs(8); break;
     default:
       nr = -1; break;
     }

     if (nr < 0 || nr > INT_MAX) {
       EMSG2_RET_FAIL(_("E678: Invalid character after %s%%[dxouU]"),
                      reg_magic == MAGIC_ALL);
     }
     // A NUL is stored in the text as NL
     // TODO(vim): what if a composing character follows?
     EMIT(nr == 0 ? 0x0a : (int)nr);
   }
   break;

   // Catch \%^ and \%$ regardless of where they appear in the
   // pattern -- regardless of whether or not it makes sense.
   case '^':
     EMIT(NFA_BOF);
     break;

   case '$':
     EMIT(NFA_EOF);
     break;

   case '#':
     if (regparse[0] == '=' && regparse[1] >= 48
         && regparse[1] <= 50) {
       // misplaced \%#=1
       semsg(_(e_atom_engine_must_be_at_start_of_pattern), regparse[1]);
       return FAIL;
     }
     EMIT(NFA_CURSOR);
     break;

   case 'V':
     EMIT(NFA_VISUAL);
     break;

   case 'C':
     EMIT(NFA_ANY_COMPOSING);
     break;

   case '[': {
     int n;

     // \%[abc]
     for (n = 0; (c = peekchr()) != ']'; n++) {
       if (c == NUL) {
         EMSG2_RET_FAIL(_(e_missing_sb),
                        reg_magic == MAGIC_ALL);
       }
       // recursive call!
       if (nfa_regatom() == FAIL) {
         return FAIL;
       }
     }
     (void)getchr();  // get the ]
     if (n == 0) {
       EMSG2_RET_FAIL(_(e_empty_sb), reg_magic == MAGIC_ALL);
     }
     EMIT(NFA_OPT_CHARS);
     EMIT(n);

     // Emit as "\%(\%[abc]\)" to be able to handle
     // "\%[abc]*" which would cause the empty string to be
     // matched an unlimited number of times. NFA_NOPEN is
     // added only once at a position, while NFA_SPLIT is
     // added multiple times.  This is more efficient than
     // not allowing NFA_SPLIT multiple times, it is used
     // a lot.
     EMIT(NFA_NOPEN);
     break;
   }

   default: {
     int64_t n = 0;
     const int cmp = c;
     bool cur = false;
     bool got_digit = false;

     if (c == '<' || c == '>') {
       c = getchr();
     }
     if (no_Magic(c) == '.') {
       cur = true;
       c = getchr();
     }
     while (ascii_isdigit(c)) {
       if (cur) {
         semsg(_(e_regexp_number_after_dot_pos_search_chr), no_Magic(c));
         return FAIL;
       }
       if (n > (INT32_MAX - (c - '0')) / 10) {
         // overflow.
         emsg(_(e_value_too_large));
         return FAIL;
       }
       n = n * 10 + (c - '0');
       c = getchr();
       got_digit = true;
     }
     if (c == 'l' || c == 'c' || c == 'v') {
       int32_t limit = INT32_MAX;

       if (!cur && !got_digit) {
         semsg(_(e_nfa_regexp_missing_value_in_chr), no_Magic(c));
         return FAIL;
       }
       if (c == 'l') {
         if (cur) {
           n = curwin->w_cursor.lnum;
         }
         // \%{n}l  \%{n}<l  \%{n}>l
         EMIT(cmp == '<' ? NFA_LNUM_LT
                         : cmp == '>' ? NFA_LNUM_GT : NFA_LNUM);
         if (save_prev_at_start) {
           at_start = true;
         }
       } else if (c == 'c') {
         if (cur) {
           n = curwin->w_cursor.col;
           n++;
         }
         // \%{n}c  \%{n}<c  \%{n}>c
         EMIT(cmp == '<' ? NFA_COL_LT
                         : cmp == '>' ? NFA_COL_GT : NFA_COL);
       } else {
         if (cur) {
           colnr_T vcol = 0;
           getvvcol(curwin, &curwin->w_cursor, NULL, NULL, &vcol);
           n = ++vcol;
         }
         // \%{n}v  \%{n}<v  \%{n}>v
         EMIT(cmp == '<' ? NFA_VCOL_LT
                         : cmp == '>' ? NFA_VCOL_GT : NFA_VCOL);
         limit = INT32_MAX / MB_MAXBYTES;
       }
       if (n >= limit) {
         emsg(_(e_value_too_large));
         return FAIL;
       }
       EMIT((int)n);
       break;
     } else if (no_Magic(c) == '\'' && n == 0) {
       // \%'m  \%<'m  \%>'m
       EMIT(cmp == '<' ? NFA_MARK_LT
                       : cmp == '>' ? NFA_MARK_GT : NFA_MARK);
       EMIT(getchr());
       break;
     }
   }
     semsg(_("E867: (NFA) Unknown operator '\\%%%c'"),
           no_Magic(c));
     return FAIL;
   }
   break;

 case Magic('['):
collection:
   // [abc]  uses NFA_START_COLL - NFA_END_COLL
   // [^abc] uses NFA_START_NEG_COLL - NFA_END_NEG_COLL
   // Each character is produced as a regular state, using
   // NFA_CONCAT to bind them together.
   // Besides normal characters there can be:
   // - character classes  NFA_CLASS_*
   // - ranges, two characters followed by NFA_RANGE.

   p = (uint8_t *)regparse;
   endp = (uint8_t *)skip_anyof((char *)p);
   if (*endp == ']') {
     // Try to reverse engineer character classes. For example,
     // recognize that [0-9] stands for \d and [A-Za-z_] for \h,
     // and perform the necessary substitutions in the NFA.
     int result = nfa_recognize_char_class((uint8_t *)regparse, endp, extra == NFA_ADD_NL);
     if (result != FAIL) {
       if (result >= NFA_FIRST_NL && result <= NFA_LAST_NL) {
         EMIT(result - NFA_ADD_NL);
         EMIT(NFA_NEWL);
         EMIT(NFA_OR);
       } else {
         EMIT(result);
       }
       regparse = (char *)endp;
       MB_PTR_ADV(regparse);
       return OK;
     }
     // Failed to recognize a character class. Use the simple
     // version that turns [abc] into 'a' OR 'b' OR 'c'
     negated = false;
     if (*regparse == '^') {                           // negated range
       negated = true;
       MB_PTR_ADV(regparse);
       EMIT(NFA_START_NEG_COLL);
     } else {
       EMIT(NFA_START_COLL);
     }
     if (*regparse == '-') {
       startc = '-';
       EMIT(startc);
       EMIT(NFA_CONCAT);
       MB_PTR_ADV(regparse);
     }
     // Emit the OR branches for each character in the []
     emit_range = false;
     while ((uint8_t *)regparse < endp) {
       int oldstartc = startc;
       startc = -1;
       got_coll_char = false;
       if (*regparse == '[') {
         // Check for [: :], [= =], [. .]
         equiclass = collclass = 0;
         charclass = get_char_class(&regparse);
         if (charclass == CLASS_NONE) {
           equiclass = get_equi_class(&regparse);
           if (equiclass == 0) {
             collclass = get_coll_element(&regparse);
           }
         }

         // Character class like [:alpha:]
         if (charclass != CLASS_NONE) {
           switch (charclass) {
           case CLASS_ALNUM:
             EMIT(NFA_CLASS_ALNUM);
             break;
           case CLASS_ALPHA:
             EMIT(NFA_CLASS_ALPHA);
             break;
           case CLASS_BLANK:
             EMIT(NFA_CLASS_BLANK);
             break;
           case CLASS_CNTRL:
             EMIT(NFA_CLASS_CNTRL);
             break;
           case CLASS_DIGIT:
             EMIT(NFA_CLASS_DIGIT);
             break;
           case CLASS_GRAPH:
             EMIT(NFA_CLASS_GRAPH);
             break;
           case CLASS_LOWER:
             wants_nfa = true;
             EMIT(NFA_CLASS_LOWER);
             break;
           case CLASS_PRINT:
             EMIT(NFA_CLASS_PRINT);
             break;
           case CLASS_PUNCT:
             EMIT(NFA_CLASS_PUNCT);
             break;
           case CLASS_SPACE:
             EMIT(NFA_CLASS_SPACE);
             break;
           case CLASS_UPPER:
             wants_nfa = true;
             EMIT(NFA_CLASS_UPPER);
             break;
           case CLASS_XDIGIT:
             EMIT(NFA_CLASS_XDIGIT);
             break;
           case CLASS_TAB:
             EMIT(NFA_CLASS_TAB);
             break;
           case CLASS_RETURN:
             EMIT(NFA_CLASS_RETURN);
             break;
           case CLASS_BACKSPACE:
             EMIT(NFA_CLASS_BACKSPACE);
             break;
           case CLASS_ESCAPE:
             EMIT(NFA_CLASS_ESCAPE);
             break;
           case CLASS_IDENT:
             EMIT(NFA_CLASS_IDENT);
             break;
           case CLASS_KEYWORD:
             EMIT(NFA_CLASS_KEYWORD);
             break;
           case CLASS_FNAME:
             EMIT(NFA_CLASS_FNAME);
             break;
           }
           EMIT(NFA_CONCAT);
           continue;
         }
         // Try equivalence class [=a=] and the like
         if (equiclass != 0) {
           nfa_emit_equi_class(equiclass);
           continue;
         }
         // Try collating class like [. .]
         if (collclass != 0) {
           startc = collclass;                  // allow [.a.]-x as a range
           // Will emit the proper atom at the end of the
           // while loop.
         }
       }
       // Try a range like 'a-x' or '\t-z'. Also allows '-' as a
       // start character.
       if (*regparse == '-' && oldstartc != -1) {
         emit_range = true;
         startc = oldstartc;
         MB_PTR_ADV(regparse);
         continue;                         // reading the end of the range
       }

       // Now handle simple and escaped characters.
       // Only "\]", "\^", "\]" and "\\" are special in Vi.  Vim
       // accepts "\t", "\e", etc., but only when the 'l' flag in
       // 'cpoptions' is not included.
       if (*regparse == '\\'
           && (uint8_t *)regparse + 1 <= endp
           && (vim_strchr(REGEXP_INRANGE, (uint8_t)regparse[1]) != NULL
               || (!reg_cpo_lit
                   && vim_strchr(REGEXP_ABBR, (uint8_t)regparse[1])
                   != NULL))) {
         MB_PTR_ADV(regparse);

         if (*regparse == 'n') {
           startc = (reg_string || emit_range || regparse[1] == '-')
                    ? NL : NFA_NEWL;
         } else if (*regparse == 'd'
                    || *regparse == 'o'
                    || *regparse == 'x'
                    || *regparse == 'u'
                    || *regparse == 'U') {
           // TODO(RE): This needs more testing
           startc = coll_get_char();
           // max UTF-8 Codepoint is U+10FFFF,
           // but allow values until INT_MAX
           if (startc == INT_MAX) {
             EMSG_RET_FAIL(_(e_unicode_val_too_large));
           }
           got_coll_char = true;
           MB_PTR_BACK(old_regparse, regparse);
         } else {
           // \r,\t,\e,\b
           startc = backslash_trans(*regparse);
         }
       }

       // Normal printable char
       if (startc == -1) {
         startc = utf_ptr2char(regparse);
       }

       // Previous char was '-', so this char is end of range.
       if (emit_range) {
         int endc = startc;
         startc = oldstartc;
         if (startc > endc) {
           EMSG_RET_FAIL(_(e_reverse_range));
         }

         if (endc > startc + 2) {
           // Emit a range instead of the sequence of
           // individual characters.
           if (startc == 0) {
             // \x00 is translated to \x0a, start at \x01.
             EMIT(1);
           } else {
             post_ptr--;                   // remove NFA_CONCAT
           }
           EMIT(endc);
           EMIT(NFA_RANGE);
           EMIT(NFA_CONCAT);
         } else if (utf_char2len(startc) > 1
                    || utf_char2len(endc) > 1) {
           // Emit the characters in the range.
           // "startc" was already emitted, so skip it.
           for (c = startc + 1; c <= endc; c++) {
             EMIT(c);
             EMIT(NFA_CONCAT);
           }
         } else {
           // Emit the range. "startc" was already emitted, so
           // skip it.
           for (c = startc + 1; c <= endc; c++) {
             EMIT(c);
             EMIT(NFA_CONCAT);
           }
         }
         emit_range = false;
         startc = -1;
       } else {
         // This char (startc) is not part of a range. Just
         // emit it.
         // Normally, simply emit startc. But if we get char
         // code=0 from a collating char, then replace it with
         // 0x0a.
         // This is needed to completely mimic the behaviour of
         // the backtracking engine.
         if (startc == NFA_NEWL) {
           // Line break can't be matched as part of the
           // collection, add an OR below. But not for negated
           // range.
           if (!negated) {
             extra = NFA_ADD_NL;
           }
         } else {
           if (got_coll_char == true && startc == 0) {
             EMIT(0x0a);
             EMIT(NFA_CONCAT);
           } else {
             EMIT(startc);
             if (utf_ptr2len(regparse) == utfc_ptr2len(regparse)) {
               EMIT(NFA_CONCAT);
             }
           }
         }
       }

       int plen;
       if (utf_ptr2len(regparse) != (plen = utfc_ptr2len(regparse))) {
         int i = utf_ptr2len(regparse);

         c = utf_ptr2char(regparse + i);

         // Add composing characters
         while (true) {
           if (c == 0) {
             // \x00 is translated to \x0a, start at \x01.
             EMIT(1);
           } else {
             EMIT(c);
           }
           EMIT(NFA_CONCAT);
           if ((i += utf_char2len(c)) >= plen) {
             break;
           }
           c = utf_ptr2char(regparse + i);
         }
         EMIT(NFA_COMPOSING);
         EMIT(NFA_CONCAT);
       }
       MB_PTR_ADV(regparse);
     }           // while (p < endp)

     MB_PTR_BACK(old_regparse, regparse);
     if (*regparse == '-') {               // if last, '-' is just a char
       EMIT('-');
       EMIT(NFA_CONCAT);
     }

     // skip the trailing ]
     regparse = (char *)endp;
     MB_PTR_ADV(regparse);

     // Mark end of the collection.
     if (negated == true) {
       EMIT(NFA_END_NEG_COLL);
     } else {
       EMIT(NFA_END_COLL);
     }

     // \_[] also matches \n but it's not negated
     if (extra == NFA_ADD_NL) {
       EMIT(reg_string ? NL : NFA_NEWL);
       EMIT(NFA_OR);
     }

     return OK;
   }         // if exists closing ]

   if (reg_strict) {
     EMSG_RET_FAIL(_(e_missingbracket));
   }
   FALLTHROUGH;

 default: {
   int plen;

nfa_do_multibyte:
   // plen is length of current char with composing chars
   if (utf_char2len(c) != (plen = utfc_ptr2len((char *)old_regparse))
       || utf_iscomposing_legacy(c)) {
     int i = 0;

     // A base character plus composing characters, or just one
     // or more composing characters.
     // This requires creating a separate atom as if enclosing
     // the characters in (), where NFA_COMPOSING is the ( and
     // NFA_END_COMPOSING is the ). Note that right now we are
     // building the postfix form, not the NFA itself;
     // a composing char could be: a, b, c, NFA_COMPOSING
     // where 'b' and 'c' are chars with codes > 256.
     while (true) {
       EMIT(c);
       if (i > 0) {
         EMIT(NFA_CONCAT);
       }
       if ((i += utf_char2len(c)) >= plen) {
         break;
       }
       c = utf_ptr2char((char *)old_regparse + i);
     }
     EMIT(NFA_COMPOSING);
     regparse = (char *)old_regparse + plen;
   } else {
     c = no_Magic(c);
     EMIT(c);
   }
   return OK;
 }
 }

 return OK;
}

// Parse something followed by possible [*+=].
//
// A piece is an atom, possibly followed by a multi, an indication of how many
// times the atom can be matched.  Example: "a*" matches any sequence of "a"
// characters: "", "a", "aa", etc.
//
// piece   ::=      atom
//      or  atom  multi
static int nfa_regpiece(void)
{
 int i;
 int op;
 int ret;
 int minval, maxval;
 bool greedy = true;  // Braces are prefixed with '-' ?
 parse_state_T old_state;
 parse_state_T new_state;
 int64_t c2;
 int old_post_pos;
 int my_post_start;
 int quest;

 // Save the current parse state, so that we can use it if <atom>{m,n} is
 // next.
 save_parse_state(&old_state);

 // store current pos in the postfix form, for \{m,n} involving 0s
 my_post_start = (int)(post_ptr - post_start);

 ret = nfa_regatom();
 if (ret == FAIL) {
   return FAIL;            // cascaded error
 }
 op = peekchr();
 if (re_multi_type(op) == NOT_MULTI) {
   return OK;
 }

 skipchr();
 switch (op) {
 case Magic('*'):
   EMIT(NFA_STAR);
   break;

 case Magic('+'):
   // Trick: Normally, (a*)\+ would match the whole input "aaa".  The
   // first and only submatch would be "aaa". But the backtracking
   // engine interprets the plus as "try matching one more time", and
   // a* matches a second time at the end of the input, the empty
   // string.
   // The submatch will be the empty string.
   //
   // In order to be consistent with the old engine, we replace
   // <atom>+ with <atom><atom>*
   restore_parse_state(&old_state);
   curchr = -1;
   if (nfa_regatom() == FAIL) {
     return FAIL;
   }
   EMIT(NFA_STAR);
   EMIT(NFA_CONCAT);
   skipchr();                  // skip the \+
   break;

 case Magic('@'):
   c2 = getdecchrs();
   op = no_Magic(getchr());
   i = 0;
   switch (op) {
   case '=':
     // \@=
     i = NFA_PREV_ATOM_NO_WIDTH;
     break;
   case '!':
     // \@!
     i = NFA_PREV_ATOM_NO_WIDTH_NEG;
     break;
   case '<':
     op = no_Magic(getchr());
     if (op == '=') {
       // \@<=
       i = NFA_PREV_ATOM_JUST_BEFORE;
     } else if (op == '!') {
       // \@<!
       i = NFA_PREV_ATOM_JUST_BEFORE_NEG;
     }
     break;
   case '>':
     // \@>
     i = NFA_PREV_ATOM_LIKE_PATTERN;
     break;
   }
   if (i == 0) {
     semsg(_("E869: (NFA) Unknown operator '\\@%c'"), op);
     return FAIL;
   }
   EMIT(i);
   if (i == NFA_PREV_ATOM_JUST_BEFORE
       || i == NFA_PREV_ATOM_JUST_BEFORE_NEG) {
     EMIT((int)c2);
   }
   break;

 case Magic('?'):
 case Magic('='):
   EMIT(NFA_QUEST);
   break;

 case Magic('{'):
   // a{2,5} will expand to 'aaa?a?a?'
   // a{-1,3} will expand to 'aa??a??', where ?? is the nongreedy
   // version of '?'
   // \v(ab){2,3} will expand to '(ab)(ab)(ab)?', where all the
   // parenthesis have the same id

   greedy = true;
   c2 = peekchr();
   if (c2 == '-' || c2 == Magic('-')) {
     skipchr();
     greedy = false;
   }
   if (!read_limits(&minval, &maxval)) {
     EMSG_RET_FAIL(_("E870: (NFA regexp) Error reading repetition limits"));
   }

   //  <atom>{0,inf}, <atom>{0,} and <atom>{}  are equivalent to
   //  <atom>*
   if (minval == 0 && maxval == MAX_LIMIT) {
     if (greedy) {
       // \{}, \{0,}
       EMIT(NFA_STAR);
     } else {
       // \{-}, \{-0,}
       EMIT(NFA_STAR_NONGREEDY);
     }
     break;
   }

   // Special case: x{0} or x{-0}
   if (maxval == 0) {
     // Ignore result of previous call to nfa_regatom()
     post_ptr = post_start + my_post_start;
     // NFA_EMPTY is 0-length and works everywhere
     EMIT(NFA_EMPTY);
     return OK;
   }

   // The engine is very inefficient (uses too many states) when the
   // maximum is much larger than the minimum and when the maximum is
   // large.  However, when maxval is MAX_LIMIT, it is okay, as this
   // will emit NFA_STAR.
   // Bail out if we can use the other engine, but only, when the
   // pattern does not need the NFA engine like (e.g. [[:upper:]]\{2,\}
   // does not work with characters > 8 bit with the BT engine)
   if ((nfa_re_flags & RE_AUTO)
       && (maxval > 500 || maxval > minval + 200)
       && (maxval != MAX_LIMIT && minval < 200)
       && !wants_nfa) {
     return FAIL;
   }

   // Ignore previous call to nfa_regatom()
   post_ptr = post_start + my_post_start;
   // Save parse state after the repeated atom and the \{}
   save_parse_state(&new_state);

   quest = (greedy == true ? NFA_QUEST : NFA_QUEST_NONGREEDY);
   for (i = 0; i < maxval; i++) {
     // Goto beginning of the repeated atom
     restore_parse_state(&old_state);
     old_post_pos = (int)(post_ptr - post_start);
     if (nfa_regatom() == FAIL) {
       return FAIL;
     }
     // after "minval" times, atoms are optional
     if (i + 1 > minval) {
       if (maxval == MAX_LIMIT) {
         if (greedy) {
           EMIT(NFA_STAR);
         } else {
           EMIT(NFA_STAR_NONGREEDY);
         }
       } else {
         EMIT(quest);
       }
     }
     if (old_post_pos != my_post_start) {
       EMIT(NFA_CONCAT);
     }
     if (i + 1 > minval && maxval == MAX_LIMIT) {
       break;
     }
   }

   // Go to just after the repeated atom and the \{}
   restore_parse_state(&new_state);
   curchr = -1;

   break;

 default:
   break;
 }     // end switch

 if (re_multi_type(peekchr()) != NOT_MULTI) {
   // Can't have a multi follow a multi.
   EMSG_RET_FAIL(_("E871: (NFA regexp) Can't have a multi follow a multi"));
 }

 return OK;
}

// Parse one or more pieces, concatenated.  It matches a match for the
// first piece, followed by a match for the second piece, etc.  Example:
// "f[0-9]b", first matches "f", then a digit and then "b".
//
// concat  ::=      piece
//      or  piece piece
//      or  piece piece piece
//      etc.
static int nfa_regconcat(void)
{
 bool cont = true;
 bool first = true;

 while (cont) {
   switch (peekchr()) {
   case NUL:
   case Magic('|'):
   case Magic('&'):
   case Magic(')'):
     cont = false;
     break;

   case Magic('Z'):
     regflags |= RF_ICOMBINE;
     skipchr_keepstart();
     break;
   case Magic('c'):
     regflags |= RF_ICASE;
     skipchr_keepstart();
     break;
   case Magic('C'):
     regflags |= RF_NOICASE;
     skipchr_keepstart();
     break;
   case Magic('v'):
     reg_magic = MAGIC_ALL;
     skipchr_keepstart();
     curchr = -1;
     break;
   case Magic('m'):
     reg_magic = MAGIC_ON;
     skipchr_keepstart();
     curchr = -1;
     break;
   case Magic('M'):
     reg_magic = MAGIC_OFF;
     skipchr_keepstart();
     curchr = -1;
     break;
   case Magic('V'):
     reg_magic = MAGIC_NONE;
     skipchr_keepstart();
     curchr = -1;
     break;

   default:
     if (nfa_regpiece() == FAIL) {
       return FAIL;
     }
     if (first == false) {
       EMIT(NFA_CONCAT);
     } else {
       first = false;
     }
     break;
   }
 }

 return OK;
}

// Parse a branch, one or more concats, separated by "\&".  It matches the
// last concat, but only if all the preceding concats also match at the same
// position.  Examples:
//      "foobeep\&..." matches "foo" in "foobeep".
//      ".*Peter\&.*Bob" matches in a line containing both "Peter" and "Bob"
//
// branch ::=       concat
//              or  concat \& concat
//              or  concat \& concat \& concat
//              etc.
static int nfa_regbranch(void)
{
 int old_post_pos;

 old_post_pos = (int)(post_ptr - post_start);

 // First branch, possibly the only one
 if (nfa_regconcat() == FAIL) {
   return FAIL;
 }

 // Try next concats
 while (peekchr() == Magic('&')) {
   skipchr();
   // if concat is empty do emit a node
   if (old_post_pos == (int)(post_ptr - post_start)) {
     EMIT(NFA_EMPTY);
   }
   EMIT(NFA_NOPEN);
   EMIT(NFA_PREV_ATOM_NO_WIDTH);
   old_post_pos = (int)(post_ptr - post_start);
   if (nfa_regconcat() == FAIL) {
     return FAIL;
   }
   // if concat is empty do emit a node
   if (old_post_pos == (int)(post_ptr - post_start)) {
     EMIT(NFA_EMPTY);
   }
   EMIT(NFA_CONCAT);
 }

 // if a branch is empty, emit one node for it
 if (old_post_pos == (int)(post_ptr - post_start)) {
   EMIT(NFA_EMPTY);
 }

 return OK;
}

///  Parse a pattern, one or more branches, separated by "\|".  It matches
///  anything that matches one of the branches.  Example: "foo\|beep" matches
///  "foo" and matches "beep".  If more than one branch matches, the first one
///  is used.
///
///  pattern ::=     branch
///      or  branch \| branch
///      or  branch \| branch \| branch
///      etc.
///
/// @param paren  REG_NOPAREN, REG_PAREN, REG_NPAREN or REG_ZPAREN
static int nfa_reg(int paren)
{
 int parno = 0;

 if (paren == REG_PAREN) {
   if (regnpar >= NSUBEXP) {   // Too many `('
     EMSG_RET_FAIL(_("E872: (NFA regexp) Too many '('"));
   }
   parno = regnpar++;
 } else if (paren == REG_ZPAREN) {
   // Make a ZOPEN node.
   if (regnzpar >= NSUBEXP) {
     EMSG_RET_FAIL(_("E879: (NFA regexp) Too many \\z("));
   }
   parno = regnzpar++;
 }

 if (nfa_regbranch() == FAIL) {
   return FAIL;            // cascaded error
 }
 while (peekchr() == Magic('|')) {
   skipchr();
   if (nfa_regbranch() == FAIL) {
     return FAIL;          // cascaded error
   }
   EMIT(NFA_OR);
 }

 // Check for proper termination.
 if (paren != REG_NOPAREN && getchr() != Magic(')')) {
   if (paren == REG_NPAREN) {
     EMSG2_RET_FAIL(_(e_unmatchedpp), reg_magic == MAGIC_ALL);
   } else {
     EMSG2_RET_FAIL(_(e_unmatchedp), reg_magic == MAGIC_ALL);
   }
 } else if (paren == REG_NOPAREN && peekchr() != NUL) {
   if (peekchr() == Magic(')')) {
     EMSG2_RET_FAIL(_(e_unmatchedpar), reg_magic == MAGIC_ALL);
   } else {
     EMSG_RET_FAIL(_("E873: (NFA regexp) proper termination error"));
   }
 }
 // Here we set the flag allowing back references to this set of
 // parentheses.
 if (paren == REG_PAREN) {
   had_endbrace[parno] = true;  // have seen the close paren
   EMIT(NFA_MOPEN + parno);
 } else if (paren == REG_ZPAREN) {
   EMIT(NFA_ZOPEN + parno);
 }

 return OK;
}

#ifdef REGEXP_DEBUG
static uint8_t code[50];

static void nfa_set_code(int c)
{
 int addnl = false;

 if (c >= NFA_FIRST_NL && c <= NFA_LAST_NL) {
   addnl = true;
   c -= NFA_ADD_NL;
 }

 STRCPY(code, "");
 switch (c) {
 case NFA_MATCH:
   STRCPY(code, "NFA_MATCH "); break;
 case NFA_SPLIT:
   STRCPY(code, "NFA_SPLIT "); break;
 case NFA_CONCAT:
   STRCPY(code, "NFA_CONCAT "); break;
 case NFA_NEWL:
   STRCPY(code, "NFA_NEWL "); break;
 case NFA_ZSTART:
   STRCPY(code, "NFA_ZSTART"); break;
 case NFA_ZEND:
   STRCPY(code, "NFA_ZEND"); break;

 case NFA_BACKREF1:
   STRCPY(code, "NFA_BACKREF1"); break;
 case NFA_BACKREF2:
   STRCPY(code, "NFA_BACKREF2"); break;
 case NFA_BACKREF3:
   STRCPY(code, "NFA_BACKREF3"); break;
 case NFA_BACKREF4:
   STRCPY(code, "NFA_BACKREF4"); break;
 case NFA_BACKREF5:
   STRCPY(code, "NFA_BACKREF5"); break;
 case NFA_BACKREF6:
   STRCPY(code, "NFA_BACKREF6"); break;
 case NFA_BACKREF7:
   STRCPY(code, "NFA_BACKREF7"); break;
 case NFA_BACKREF8:
   STRCPY(code, "NFA_BACKREF8"); break;
 case NFA_BACKREF9:
   STRCPY(code, "NFA_BACKREF9"); break;
 case NFA_ZREF1:
   STRCPY(code, "NFA_ZREF1"); break;
 case NFA_ZREF2:
   STRCPY(code, "NFA_ZREF2"); break;
 case NFA_ZREF3:
   STRCPY(code, "NFA_ZREF3"); break;
 case NFA_ZREF4:
   STRCPY(code, "NFA_ZREF4"); break;
 case NFA_ZREF5:
   STRCPY(code, "NFA_ZREF5"); break;
 case NFA_ZREF6:
   STRCPY(code, "NFA_ZREF6"); break;
 case NFA_ZREF7:
   STRCPY(code, "NFA_ZREF7"); break;
 case NFA_ZREF8:
   STRCPY(code, "NFA_ZREF8"); break;
 case NFA_ZREF9:
   STRCPY(code, "NFA_ZREF9"); break;
 case NFA_SKIP:
   STRCPY(code, "NFA_SKIP"); break;

 case NFA_PREV_ATOM_NO_WIDTH:
   STRCPY(code, "NFA_PREV_ATOM_NO_WIDTH"); break;
 case NFA_PREV_ATOM_NO_WIDTH_NEG:
   STRCPY(code, "NFA_PREV_ATOM_NO_WIDTH_NEG"); break;
 case NFA_PREV_ATOM_JUST_BEFORE:
   STRCPY(code, "NFA_PREV_ATOM_JUST_BEFORE"); break;
 case NFA_PREV_ATOM_JUST_BEFORE_NEG:
   STRCPY(code, "NFA_PREV_ATOM_JUST_BEFORE_NEG"); break;
 case NFA_PREV_ATOM_LIKE_PATTERN:
   STRCPY(code, "NFA_PREV_ATOM_LIKE_PATTERN"); break;

 case NFA_NOPEN:
   STRCPY(code, "NFA_NOPEN"); break;
 case NFA_NCLOSE:
   STRCPY(code, "NFA_NCLOSE"); break;
 case NFA_START_INVISIBLE:
   STRCPY(code, "NFA_START_INVISIBLE"); break;
 case NFA_START_INVISIBLE_FIRST:
   STRCPY(code, "NFA_START_INVISIBLE_FIRST"); break;
 case NFA_START_INVISIBLE_NEG:
   STRCPY(code, "NFA_START_INVISIBLE_NEG"); break;
 case NFA_START_INVISIBLE_NEG_FIRST:
   STRCPY(code, "NFA_START_INVISIBLE_NEG_FIRST"); break;
 case NFA_START_INVISIBLE_BEFORE:
   STRCPY(code, "NFA_START_INVISIBLE_BEFORE"); break;
 case NFA_START_INVISIBLE_BEFORE_FIRST:
   STRCPY(code, "NFA_START_INVISIBLE_BEFORE_FIRST"); break;
 case NFA_START_INVISIBLE_BEFORE_NEG:
   STRCPY(code, "NFA_START_INVISIBLE_BEFORE_NEG"); break;
 case NFA_START_INVISIBLE_BEFORE_NEG_FIRST:
   STRCPY(code, "NFA_START_INVISIBLE_BEFORE_NEG_FIRST"); break;
 case NFA_START_PATTERN:
   STRCPY(code, "NFA_START_PATTERN"); break;
 case NFA_END_INVISIBLE:
   STRCPY(code, "NFA_END_INVISIBLE"); break;
 case NFA_END_INVISIBLE_NEG:
   STRCPY(code, "NFA_END_INVISIBLE_NEG"); break;
 case NFA_END_PATTERN:
   STRCPY(code, "NFA_END_PATTERN"); break;

 case NFA_COMPOSING:
   STRCPY(code, "NFA_COMPOSING"); break;
 case NFA_END_COMPOSING:
   STRCPY(code, "NFA_END_COMPOSING"); break;
 case NFA_OPT_CHARS:
   STRCPY(code, "NFA_OPT_CHARS"); break;

 case NFA_MOPEN:
 case NFA_MOPEN1:
 case NFA_MOPEN2:
 case NFA_MOPEN3:
 case NFA_MOPEN4:
 case NFA_MOPEN5:
 case NFA_MOPEN6:
 case NFA_MOPEN7:
 case NFA_MOPEN8:
 case NFA_MOPEN9:
   STRCPY(code, "NFA_MOPEN(x)");
   code[10] = c - NFA_MOPEN + '0';
   break;
 case NFA_MCLOSE:
 case NFA_MCLOSE1:
 case NFA_MCLOSE2:
 case NFA_MCLOSE3:
 case NFA_MCLOSE4:
 case NFA_MCLOSE5:
 case NFA_MCLOSE6:
 case NFA_MCLOSE7:
 case NFA_MCLOSE8:
 case NFA_MCLOSE9:
   STRCPY(code, "NFA_MCLOSE(x)");
   code[11] = c - NFA_MCLOSE + '0';
   break;
 case NFA_ZOPEN:
 case NFA_ZOPEN1:
 case NFA_ZOPEN2:
 case NFA_ZOPEN3:
 case NFA_ZOPEN4:
 case NFA_ZOPEN5:
 case NFA_ZOPEN6:
 case NFA_ZOPEN7:
 case NFA_ZOPEN8:
 case NFA_ZOPEN9:
   STRCPY(code, "NFA_ZOPEN(x)");
   code[10] = c - NFA_ZOPEN + '0';
   break;
 case NFA_ZCLOSE:
 case NFA_ZCLOSE1:
 case NFA_ZCLOSE2:
 case NFA_ZCLOSE3:
 case NFA_ZCLOSE4:
 case NFA_ZCLOSE5:
 case NFA_ZCLOSE6:
 case NFA_ZCLOSE7:
 case NFA_ZCLOSE8:
 case NFA_ZCLOSE9:
   STRCPY(code, "NFA_ZCLOSE(x)");
   code[11] = c - NFA_ZCLOSE + '0';
   break;
 case NFA_EOL:
   STRCPY(code, "NFA_EOL "); break;
 case NFA_BOL:
   STRCPY(code, "NFA_BOL "); break;
 case NFA_EOW:
   STRCPY(code, "NFA_EOW "); break;
 case NFA_BOW:
   STRCPY(code, "NFA_BOW "); break;
 case NFA_EOF:
   STRCPY(code, "NFA_EOF "); break;
 case NFA_BOF:
   STRCPY(code, "NFA_BOF "); break;
 case NFA_LNUM:
   STRCPY(code, "NFA_LNUM "); break;
 case NFA_LNUM_GT:
   STRCPY(code, "NFA_LNUM_GT "); break;
 case NFA_LNUM_LT:
   STRCPY(code, "NFA_LNUM_LT "); break;
 case NFA_COL:
   STRCPY(code, "NFA_COL "); break;
 case NFA_COL_GT:
   STRCPY(code, "NFA_COL_GT "); break;
 case NFA_COL_LT:
   STRCPY(code, "NFA_COL_LT "); break;
 case NFA_VCOL:
   STRCPY(code, "NFA_VCOL "); break;
 case NFA_VCOL_GT:
   STRCPY(code, "NFA_VCOL_GT "); break;
 case NFA_VCOL_LT:
   STRCPY(code, "NFA_VCOL_LT "); break;
 case NFA_MARK:
   STRCPY(code, "NFA_MARK "); break;
 case NFA_MARK_GT:
   STRCPY(code, "NFA_MARK_GT "); break;
 case NFA_MARK_LT:
   STRCPY(code, "NFA_MARK_LT "); break;
 case NFA_CURSOR:
   STRCPY(code, "NFA_CURSOR "); break;
 case NFA_VISUAL:
   STRCPY(code, "NFA_VISUAL "); break;
 case NFA_ANY_COMPOSING:
   STRCPY(code, "NFA_ANY_COMPOSING "); break;

 case NFA_STAR:
   STRCPY(code, "NFA_STAR "); break;
 case NFA_STAR_NONGREEDY:
   STRCPY(code, "NFA_STAR_NONGREEDY "); break;
 case NFA_QUEST:
   STRCPY(code, "NFA_QUEST"); break;
 case NFA_QUEST_NONGREEDY:
   STRCPY(code, "NFA_QUEST_NON_GREEDY"); break;
 case NFA_EMPTY:
   STRCPY(code, "NFA_EMPTY"); break;
 case NFA_OR:
   STRCPY(code, "NFA_OR"); break;

 case NFA_START_COLL:
   STRCPY(code, "NFA_START_COLL"); break;
 case NFA_END_COLL:
   STRCPY(code, "NFA_END_COLL"); break;
 case NFA_START_NEG_COLL:
   STRCPY(code, "NFA_START_NEG_COLL"); break;
 case NFA_END_NEG_COLL:
   STRCPY(code, "NFA_END_NEG_COLL"); break;
 case NFA_RANGE:
   STRCPY(code, "NFA_RANGE"); break;
 case NFA_RANGE_MIN:
   STRCPY(code, "NFA_RANGE_MIN"); break;
 case NFA_RANGE_MAX:
   STRCPY(code, "NFA_RANGE_MAX"); break;

 case NFA_CLASS_ALNUM:
   STRCPY(code, "NFA_CLASS_ALNUM"); break;
 case NFA_CLASS_ALPHA:
   STRCPY(code, "NFA_CLASS_ALPHA"); break;
 case NFA_CLASS_BLANK:
   STRCPY(code, "NFA_CLASS_BLANK"); break;
 case NFA_CLASS_CNTRL:
   STRCPY(code, "NFA_CLASS_CNTRL"); break;
 case NFA_CLASS_DIGIT:
   STRCPY(code, "NFA_CLASS_DIGIT"); break;
 case NFA_CLASS_GRAPH:
   STRCPY(code, "NFA_CLASS_GRAPH"); break;
 case NFA_CLASS_LOWER:
   STRCPY(code, "NFA_CLASS_LOWER"); break;
 case NFA_CLASS_PRINT:
   STRCPY(code, "NFA_CLASS_PRINT"); break;
 case NFA_CLASS_PUNCT:
   STRCPY(code, "NFA_CLASS_PUNCT"); break;
 case NFA_CLASS_SPACE:
   STRCPY(code, "NFA_CLASS_SPACE"); break;
 case NFA_CLASS_UPPER:
   STRCPY(code, "NFA_CLASS_UPPER"); break;
 case NFA_CLASS_XDIGIT:
   STRCPY(code, "NFA_CLASS_XDIGIT"); break;
 case NFA_CLASS_TAB:
   STRCPY(code, "NFA_CLASS_TAB"); break;
 case NFA_CLASS_RETURN:
   STRCPY(code, "NFA_CLASS_RETURN"); break;
 case NFA_CLASS_BACKSPACE:
   STRCPY(code, "NFA_CLASS_BACKSPACE"); break;
 case NFA_CLASS_ESCAPE:
   STRCPY(code, "NFA_CLASS_ESCAPE"); break;
 case NFA_CLASS_IDENT:
   STRCPY(code, "NFA_CLASS_IDENT"); break;
 case NFA_CLASS_KEYWORD:
   STRCPY(code, "NFA_CLASS_KEYWORD"); break;
 case NFA_CLASS_FNAME:
   STRCPY(code, "NFA_CLASS_FNAME"); break;

 case NFA_ANY:
   STRCPY(code, "NFA_ANY"); break;
 case NFA_IDENT:
   STRCPY(code, "NFA_IDENT"); break;
 case NFA_SIDENT:
   STRCPY(code, "NFA_SIDENT"); break;
 case NFA_KWORD:
   STRCPY(code, "NFA_KWORD"); break;
 case NFA_SKWORD:
   STRCPY(code, "NFA_SKWORD"); break;
 case NFA_FNAME:
   STRCPY(code, "NFA_FNAME"); break;
 case NFA_SFNAME:
   STRCPY(code, "NFA_SFNAME"); break;
 case NFA_PRINT:
   STRCPY(code, "NFA_PRINT"); break;
 case NFA_SPRINT:
   STRCPY(code, "NFA_SPRINT"); break;
 case NFA_WHITE:
   STRCPY(code, "NFA_WHITE"); break;
 case NFA_NWHITE:
   STRCPY(code, "NFA_NWHITE"); break;
 case NFA_DIGIT:
   STRCPY(code, "NFA_DIGIT"); break;
 case NFA_NDIGIT:
   STRCPY(code, "NFA_NDIGIT"); break;
 case NFA_HEX:
   STRCPY(code, "NFA_HEX"); break;
 case NFA_NHEX:
   STRCPY(code, "NFA_NHEX"); break;
 case NFA_OCTAL:
   STRCPY(code, "NFA_OCTAL"); break;
 case NFA_NOCTAL:
   STRCPY(code, "NFA_NOCTAL"); break;
 case NFA_WORD:
   STRCPY(code, "NFA_WORD"); break;
 case NFA_NWORD:
   STRCPY(code, "NFA_NWORD"); break;
 case NFA_HEAD:
   STRCPY(code, "NFA_HEAD"); break;
 case NFA_NHEAD:
   STRCPY(code, "NFA_NHEAD"); break;
 case NFA_ALPHA:
   STRCPY(code, "NFA_ALPHA"); break;
 case NFA_NALPHA:
   STRCPY(code, "NFA_NALPHA"); break;
 case NFA_LOWER:
   STRCPY(code, "NFA_LOWER"); break;
 case NFA_NLOWER:
   STRCPY(code, "NFA_NLOWER"); break;
 case NFA_UPPER:
   STRCPY(code, "NFA_UPPER"); break;
 case NFA_NUPPER:
   STRCPY(code, "NFA_NUPPER"); break;
 case NFA_LOWER_IC:
   STRCPY(code, "NFA_LOWER_IC"); break;
 case NFA_NLOWER_IC:
   STRCPY(code, "NFA_NLOWER_IC"); break;
 case NFA_UPPER_IC:
   STRCPY(code, "NFA_UPPER_IC"); break;
 case NFA_NUPPER_IC:
   STRCPY(code, "NFA_NUPPER_IC"); break;

 default:
   STRCPY(code, "CHAR(x)");
   code[5] = c;
 }

 if (addnl == true) {
   strcat(code, " + NEWLINE ");
 }
}

static FILE *log_fd;
static const uint8_t e_log_open_failed[] =
 N_("Could not open temporary log file for writing, displaying on stderr... ");

// Print the postfix notation of the current regexp.
static void nfa_postfix_dump(uint8_t *expr, int retval)
{
 int *p;
 FILE *f;

 f = fopen(NFA_REGEXP_DUMP_LOG, "a");
 if (f == NULL) {
   return;
 }

 fprintf(f, "\n-------------------------\n");
 if (retval == FAIL) {
   fprintf(f, ">>> NFA engine failed... \n");
 } else if (retval == OK) {
   fprintf(f, ">>> NFA engine succeeded !\n");
 }
 fprintf(f, "Regexp: \"%s\"\nPostfix notation (char): \"", expr);
 for (p = post_start; *p && p < post_ptr; p++) {
   nfa_set_code(*p);
   fprintf(f, "%s, ", code);
 }
 fprintf(f, "\"\nPostfix notation (int): ");
 for (p = post_start; *p && p < post_ptr; p++) {
   fprintf(f, "%d ", *p);
 }
 fprintf(f, "\n\n");
 fclose(f);
}

// Print the NFA starting with a root node "state".
static void nfa_print_state(FILE *debugf, nfa_state_T *state)
{
 garray_T indent;

 ga_init(&indent, 1, 64);
 ga_append(&indent, NUL);
 nfa_print_state2(debugf, state, &indent);
 ga_clear(&indent);
}

static void nfa_print_state2(FILE *debugf, nfa_state_T *state, garray_T *indent)
{
 uint8_t *p;

 if (state == NULL) {
   return;
 }

 fprintf(debugf, "(%2d)", abs(state->id));

 // Output indent
 p = (uint8_t *)indent->ga_data;
 if (indent->ga_len >= 3) {
   int last = indent->ga_len - 3;
   uint8_t save[2];

   strncpy(save, &p[last], 2);  // NOLINT(runtime/printf)
   memcpy(&p[last], "+-", 2);
   fprintf(debugf, " %s", p);
   strncpy(&p[last], save, 2);  // NOLINT(runtime/printf)
 } else {
   fprintf(debugf, " %s", p);
 }

 nfa_set_code(state->c);
 fprintf(debugf, "%s (%d) (id=%d) val=%d\n",
         code,
         state->c,
         abs(state->id),
         state->val);
 if (state->id < 0) {
   return;
 }

 state->id = abs(state->id) * -1;

 // grow indent for state->out
 indent->ga_len -= 1;
 if (state->out1) {
   GA_CONCAT_LITERAL(indent, "| ");
 } else {
   GA_CONCAT_LITERAL(indent, "  ");
 }
 ga_append(indent, NUL);

 nfa_print_state2(debugf, state->out, indent);

 // replace last part of indent for state->out1
 indent->ga_len -= 3;
 GA_CONCAT_LITERAL(indent, "  ");
 ga_append(indent, NUL);

 nfa_print_state2(debugf, state->out1, indent);

 // shrink indent
 indent->ga_len -= 3;
 ga_append(indent, NUL);
}

// Print the NFA state machine.
static void nfa_dump(nfa_regprog_T *prog)
{
 FILE *debugf = fopen(NFA_REGEXP_DUMP_LOG, "a");

 if (debugf == NULL) {
   return;
 }

 nfa_print_state(debugf, prog->start);

 if (prog->reganch) {
   fprintf(debugf, "reganch: %d\n", prog->reganch);
 }
 if (prog->regstart != NUL) {
   fprintf(debugf, "regstart: %c (decimal: %d)\n",
           prog->regstart, prog->regstart);
 }
 if (prog->match_text != NULL) {
   fprintf(debugf, "match_text: \"%s\"\n", prog->match_text);
 }

 fclose(debugf);
}
#endif  // REGEXP_DEBUG

// Parse r.e. @expr and convert it into postfix form.
// Return the postfix string on success, NULL otherwise.
static int *re2post(void)
{
 if (nfa_reg(REG_NOPAREN) == FAIL) {
   return NULL;
 }
 EMIT(NFA_MOPEN);
 return post_start;
}

// NB. Some of the code below is inspired by Russ's.

// Represents an NFA state plus zero or one or two arrows exiting.
// if c == MATCH, no arrows out; matching state.
// If c == SPLIT, unlabeled arrows to out and out1 (if != NULL).
// If c < 256, labeled arrow with character c to out.

static nfa_state_T *state_ptr;  // points to nfa_prog->state

// Allocate and initialize nfa_state_T.
static nfa_state_T *alloc_state(int c, nfa_state_T *out, nfa_state_T *out1)
{
 nfa_state_T *s;

 if (istate >= nstate) {
   return NULL;
 }

 s = &state_ptr[istate++];

 s->c = c;
 s->out = out;
 s->out1 = out1;
 s->val = 0;

 s->id = istate;
 s->lastlist[0] = 0;
 s->lastlist[1] = 0;

 return s;
}

// A partially built NFA without the matching state filled in.
// Frag_T.start points at the start state.
// Frag_T.out is a list of places that need to be set to the
// next state for this fragment.

// Initialize a Frag_T struct and return it.
static Frag_T frag(nfa_state_T *start, Ptrlist *out)
{
 Frag_T n;

 n.start = start;
 n.out = out;
 return n;
}

// Create singleton list containing just outp.
static Ptrlist *list1(nfa_state_T **outp)
{
 Ptrlist *l;

 l = (Ptrlist *)outp;
 l->next = NULL;
 return l;
}

// Patch the list of states at out to point to start.
static void patch(Ptrlist *l, nfa_state_T *s)
{
 Ptrlist *next;

 for (; l; l = next) {
   next = l->next;
   l->s = s;
 }
}

// Join the two lists l1 and l2, returning the combination.
static Ptrlist *append(Ptrlist *l1, Ptrlist *l2)
{
 Ptrlist *oldl1;

 oldl1 = l1;
 while (l1->next) {
   l1 = l1->next;
 }
 l1->next = l2;
 return oldl1;
}

// Stack used for transforming postfix form into NFA.
static Frag_T empty;

static void st_error(int *postfix, int *end, int *p)
{
#ifdef NFA_REGEXP_ERROR_LOG
 FILE *df;
 int *p2;

 df = fopen(NFA_REGEXP_ERROR_LOG, "a");
 if (df) {
   fprintf(df, "Error popping the stack!\n");
# ifdef REGEXP_DEBUG
   fprintf(df, "Current regexp is \"%s\"\n", nfa_regengine.expr);
# endif
   fprintf(df, "Postfix form is: ");
# ifdef REGEXP_DEBUG
   for (p2 = postfix; p2 < end; p2++) {
     nfa_set_code(*p2);
     fprintf(df, "%s, ", code);
   }
   nfa_set_code(*p);
   fprintf(df, "\nCurrent position is: ");
   for (p2 = postfix; p2 <= p; p2++) {
     nfa_set_code(*p2);
     fprintf(df, "%s, ", code);
   }
# else
   for (p2 = postfix; p2 < end; p2++) {
     fprintf(df, "%d, ", *p2);
   }
   fprintf(df, "\nCurrent position is: ");
   for (p2 = postfix; p2 <= p; p2++) {
     fprintf(df, "%d, ", *p2);
   }
# endif
   fprintf(df, "\n--------------------------\n");
   fclose(df);
 }
#endif
 emsg(_("E874: (NFA) Could not pop the stack!"));
}

// Push an item onto the stack.
static void st_push(Frag_T s, Frag_T **p, Frag_T *stack_end)
{
 Frag_T *stackp = *p;

 if (stackp >= stack_end) {
   return;
 }
 *stackp = s;
 *p = *p + 1;
}

// Pop an item from the stack.
static Frag_T st_pop(Frag_T **p, Frag_T *stack)
{
 Frag_T *stackp;

 *p = *p - 1;
 stackp = *p;
 if (stackp < stack) {
   return empty;
 }
 return **p;
}

// Estimate the maximum byte length of anything matching "state".
// When unknown or unlimited return -1.
static int nfa_max_width(nfa_state_T *startstate, int depth)
{
 int l, r;
 nfa_state_T *state = startstate;
 int len = 0;

 // detect looping in a NFA_SPLIT
 if (depth > 4) {
   return -1;
 }

 while (state != NULL) {
   switch (state->c) {
   case NFA_END_INVISIBLE:
   case NFA_END_INVISIBLE_NEG:
     // the end, return what we have
     return len;

   case NFA_SPLIT:
     // two alternatives, use the maximum
     l = nfa_max_width(state->out, depth + 1);
     r = nfa_max_width(state->out1, depth + 1);
     if (l < 0 || r < 0) {
       return -1;
     }
     return len + (l > r ? l : r);

   case NFA_ANY:
   case NFA_START_COLL:
   case NFA_START_NEG_COLL:
     // Matches some character, including composing chars.
     len += MB_MAXBYTES;
     if (state->c != NFA_ANY) {
       // Skip over the characters.
       state = state->out1->out;
       continue;
     }
     break;

   case NFA_DIGIT:
   case NFA_WHITE:
   case NFA_HEX:
   case NFA_OCTAL:
     // ascii
     len++;
     break;

   case NFA_IDENT:
   case NFA_SIDENT:
   case NFA_KWORD:
   case NFA_SKWORD:
   case NFA_FNAME:
   case NFA_SFNAME:
   case NFA_PRINT:
   case NFA_SPRINT:
   case NFA_NWHITE:
   case NFA_NDIGIT:
   case NFA_NHEX:
   case NFA_NOCTAL:
   case NFA_WORD:
   case NFA_NWORD:
   case NFA_HEAD:
   case NFA_NHEAD:
   case NFA_ALPHA:
   case NFA_NALPHA:
   case NFA_LOWER:
   case NFA_NLOWER:
   case NFA_UPPER:
   case NFA_NUPPER:
   case NFA_LOWER_IC:
   case NFA_NLOWER_IC:
   case NFA_UPPER_IC:
   case NFA_NUPPER_IC:
   case NFA_ANY_COMPOSING:
     // possibly non-ascii
     len += 3;
     break;

   case NFA_START_INVISIBLE:
   case NFA_START_INVISIBLE_NEG:
   case NFA_START_INVISIBLE_BEFORE:
   case NFA_START_INVISIBLE_BEFORE_NEG:
     // zero-width, out1 points to the END state
     state = state->out1->out;
     continue;

   case NFA_BACKREF1:
   case NFA_BACKREF2:
   case NFA_BACKREF3:
   case NFA_BACKREF4:
   case NFA_BACKREF5:
   case NFA_BACKREF6:
   case NFA_BACKREF7:
   case NFA_BACKREF8:
   case NFA_BACKREF9:
   case NFA_ZREF1:
   case NFA_ZREF2:
   case NFA_ZREF3:
   case NFA_ZREF4:
   case NFA_ZREF5:
   case NFA_ZREF6:
   case NFA_ZREF7:
   case NFA_ZREF8:
   case NFA_ZREF9:
   case NFA_NEWL:
   case NFA_SKIP:
     // unknown width
     return -1;

   case NFA_BOL:
   case NFA_EOL:
   case NFA_BOF:
   case NFA_EOF:
   case NFA_BOW:
   case NFA_EOW:
   case NFA_MOPEN:
   case NFA_MOPEN1:
   case NFA_MOPEN2:
   case NFA_MOPEN3:
   case NFA_MOPEN4:
   case NFA_MOPEN5:
   case NFA_MOPEN6:
   case NFA_MOPEN7:
   case NFA_MOPEN8:
   case NFA_MOPEN9:
   case NFA_ZOPEN:
   case NFA_ZOPEN1:
   case NFA_ZOPEN2:
   case NFA_ZOPEN3:
   case NFA_ZOPEN4:
   case NFA_ZOPEN5:
   case NFA_ZOPEN6:
   case NFA_ZOPEN7:
   case NFA_ZOPEN8:
   case NFA_ZOPEN9:
   case NFA_ZCLOSE:
   case NFA_ZCLOSE1:
   case NFA_ZCLOSE2:
   case NFA_ZCLOSE3:
   case NFA_ZCLOSE4:
   case NFA_ZCLOSE5:
   case NFA_ZCLOSE6:
   case NFA_ZCLOSE7:
   case NFA_ZCLOSE8:
   case NFA_ZCLOSE9:
   case NFA_MCLOSE:
   case NFA_MCLOSE1:
   case NFA_MCLOSE2:
   case NFA_MCLOSE3:
   case NFA_MCLOSE4:
   case NFA_MCLOSE5:
   case NFA_MCLOSE6:
   case NFA_MCLOSE7:
   case NFA_MCLOSE8:
   case NFA_MCLOSE9:
   case NFA_NOPEN:
   case NFA_NCLOSE:

   case NFA_LNUM_GT:
   case NFA_LNUM_LT:
   case NFA_COL_GT:
   case NFA_COL_LT:
   case NFA_VCOL_GT:
   case NFA_VCOL_LT:
   case NFA_MARK_GT:
   case NFA_MARK_LT:
   case NFA_VISUAL:
   case NFA_LNUM:
   case NFA_CURSOR:
   case NFA_COL:
   case NFA_VCOL:
   case NFA_MARK:

   case NFA_ZSTART:
   case NFA_ZEND:
   case NFA_OPT_CHARS:
   case NFA_EMPTY:
   case NFA_START_PATTERN:
   case NFA_END_PATTERN:
   case NFA_COMPOSING:
   case NFA_END_COMPOSING:
     // zero-width
     break;

   default:
     if (state->c < 0) {
       // don't know what this is
       return -1;
     }
     // normal character
     len += utf_char2len(state->c);
     break;
   }

   // normal way to continue
   state = state->out;
 }

 // unrecognized, "cannot happen"
 return -1;
}

// Convert a postfix form into its equivalent NFA.
// Return the NFA start state on success, NULL otherwise.
static nfa_state_T *post2nfa(int *postfix, int *end, int nfa_calc_size)
{
 int *p;
 int mopen;
 int mclose;
 Frag_T *stack = NULL;
 Frag_T *stackp = NULL;
 Frag_T *stack_end = NULL;
 Frag_T e1;
 Frag_T e2;
 Frag_T e;
 nfa_state_T *s;
 nfa_state_T *s1;
 nfa_state_T *matchstate;
 nfa_state_T *ret = NULL;

 if (postfix == NULL) {
   return NULL;
 }

#define PUSH(s)     st_push((s), &stackp, stack_end)
#define POP()       st_pop(&stackp, stack); \
 if (stackp < stack) { \
   st_error(postfix, end, p); \
   xfree(stack); \
   return NULL; \
 }

 if (nfa_calc_size == false) {
   // Allocate space for the stack. Max states on the stack: "nstate".
   stack = xmalloc((size_t)(nstate + 1) * sizeof(Frag_T));
   stackp = stack;
   stack_end = stack + (nstate + 1);
 }

 for (p = postfix; p < end; p++) {
   switch (*p) {
   case NFA_CONCAT:
     // Concatenation.
     // Pay attention: this operator does not exist in the r.e. itself
     // (it is implicit, really).  It is added when r.e. is translated
     // to postfix form in re2post().
     if (nfa_calc_size == true) {
       // nstate += 0;
       break;
     }
     e2 = POP();
     e1 = POP();
     patch(e1.out, e2.start);
     PUSH(frag(e1.start, e2.out));
     break;

   case NFA_OR:
     // Alternation
     if (nfa_calc_size == true) {
       nstate++;
       break;
     }
     e2 = POP();
     e1 = POP();
     s = alloc_state(NFA_SPLIT, e1.start, e2.start);
     if (s == NULL) {
       goto theend;
     }
     PUSH(frag(s, append(e1.out, e2.out)));
     break;

   case NFA_STAR:
     // Zero or more, prefer more
     if (nfa_calc_size == true) {
       nstate++;
       break;
     }
     e = POP();
     s = alloc_state(NFA_SPLIT, e.start, NULL);
     if (s == NULL) {
       goto theend;
     }
     patch(e.out, s);
     PUSH(frag(s, list1(&s->out1)));
     break;

   case NFA_STAR_NONGREEDY:
     // Zero or more, prefer zero
     if (nfa_calc_size == true) {
       nstate++;
       break;
     }
     e = POP();
     s = alloc_state(NFA_SPLIT, NULL, e.start);
     if (s == NULL) {
       goto theend;
     }
     patch(e.out, s);
     PUSH(frag(s, list1(&s->out)));
     break;

   case NFA_QUEST:
     // one or zero atoms=> greedy match
     if (nfa_calc_size == true) {
       nstate++;
       break;
     }
     e = POP();
     s = alloc_state(NFA_SPLIT, e.start, NULL);
     if (s == NULL) {
       goto theend;
     }
     PUSH(frag(s, append(e.out, list1(&s->out1))));
     break;

   case NFA_QUEST_NONGREEDY:
     // zero or one atoms => non-greedy match
     if (nfa_calc_size == true) {
       nstate++;
       break;
     }
     e = POP();
     s = alloc_state(NFA_SPLIT, NULL, e.start);
     if (s == NULL) {
       goto theend;
     }
     PUSH(frag(s, append(e.out, list1(&s->out))));
     break;

   case NFA_END_COLL:
   case NFA_END_NEG_COLL:
     // On the stack is the sequence starting with NFA_START_COLL or
     // NFA_START_NEG_COLL and all possible characters. Patch it to
     // add the output to the start.
     if (nfa_calc_size == true) {
       nstate++;
       break;
     }
     e = POP();
     s = alloc_state(NFA_END_COLL, NULL, NULL);
     if (s == NULL) {
       goto theend;
     }
     patch(e.out, s);
     e.start->out1 = s;
     PUSH(frag(e.start, list1(&s->out)));
     break;

   case NFA_RANGE:
     // Before this are two characters, the low and high end of a
     // range.  Turn them into two states with MIN and MAX.
     if (nfa_calc_size == true) {
       // nstate += 0;
       break;
     }
     e2 = POP();
     e1 = POP();
     e2.start->val = e2.start->c;
     e2.start->c = NFA_RANGE_MAX;
     e1.start->val = e1.start->c;
     e1.start->c = NFA_RANGE_MIN;
     patch(e1.out, e2.start);
     PUSH(frag(e1.start, e2.out));
     break;

   case NFA_EMPTY:
     // 0-length, used in a repetition with max/min count of 0
     if (nfa_calc_size == true) {
       nstate++;
       break;
     }
     s = alloc_state(NFA_EMPTY, NULL, NULL);
     if (s == NULL) {
       goto theend;
     }
     PUSH(frag(s, list1(&s->out)));
     break;

   case NFA_OPT_CHARS: {
     int n;

     // \%[abc] implemented as:
     //    NFA_SPLIT
     //    +-CHAR(a)
     //    | +-NFA_SPLIT
     //    |   +-CHAR(b)
     //    |   | +-NFA_SPLIT
     //    |   |   +-CHAR(c)
     //    |   |   | +-next
     //    |   |   +- next
     //    |   +- next
     //    +- next
     n = *++p;  // get number of characters
     if (nfa_calc_size == true) {
       nstate += n;
       break;
     }
     s = NULL;       // avoid compiler warning
     e1.out = NULL;       // stores list with out1's
     s1 = NULL;       // previous NFA_SPLIT to connect to
     while (n-- > 0) {
       e = POP();         // get character
       s = alloc_state(NFA_SPLIT, e.start, NULL);
       if (s == NULL) {
         goto theend;
       }
       if (e1.out == NULL) {
         e1 = e;
       }
       patch(e.out, s1);
       append(e1.out, list1(&s->out1));
       s1 = s;
     }
     PUSH(frag(s, e1.out));
     break;
   }

   case NFA_PREV_ATOM_NO_WIDTH:
   case NFA_PREV_ATOM_NO_WIDTH_NEG:
   case NFA_PREV_ATOM_JUST_BEFORE:
   case NFA_PREV_ATOM_JUST_BEFORE_NEG:
   case NFA_PREV_ATOM_LIKE_PATTERN: {
     int before = (*p == NFA_PREV_ATOM_JUST_BEFORE
                   || *p == NFA_PREV_ATOM_JUST_BEFORE_NEG);
     int pattern = (*p == NFA_PREV_ATOM_LIKE_PATTERN);
     int start_state;
     int end_state;
     int n = 0;
     nfa_state_T *zend;
     nfa_state_T *skip;

     switch (*p) {
     case NFA_PREV_ATOM_NO_WIDTH:
       start_state = NFA_START_INVISIBLE;
       end_state = NFA_END_INVISIBLE;
       break;
     case NFA_PREV_ATOM_NO_WIDTH_NEG:
       start_state = NFA_START_INVISIBLE_NEG;
       end_state = NFA_END_INVISIBLE_NEG;
       break;
     case NFA_PREV_ATOM_JUST_BEFORE:
       start_state = NFA_START_INVISIBLE_BEFORE;
       end_state = NFA_END_INVISIBLE;
       break;
     case NFA_PREV_ATOM_JUST_BEFORE_NEG:
       start_state = NFA_START_INVISIBLE_BEFORE_NEG;
       end_state = NFA_END_INVISIBLE_NEG;
       break;
     default:           // NFA_PREV_ATOM_LIKE_PATTERN:
       start_state = NFA_START_PATTERN;
       end_state = NFA_END_PATTERN;
       break;
     }

     if (before) {
       n = *++p;         // get the count
     }
     // The \@= operator: match the preceding atom with zero width.
     // The \@! operator: no match for the preceding atom.
     // The \@<= operator: match for the preceding atom.
     // The \@<! operator: no match for the preceding atom.
     // Surrounds the preceding atom with START_INVISIBLE and
     // END_INVISIBLE, similarly to MOPEN.

     if (nfa_calc_size == true) {
       nstate += pattern ? 4 : 2;
       break;
     }
     e = POP();
     s1 = alloc_state(end_state, NULL, NULL);
     if (s1 == NULL) {
       goto theend;
     }

     s = alloc_state(start_state, e.start, s1);
     if (s == NULL) {
       goto theend;
     }
     if (pattern) {
       // NFA_ZEND -> NFA_END_PATTERN -> NFA_SKIP -> what follows.
       skip = alloc_state(NFA_SKIP, NULL, NULL);
       if (skip == NULL) {
         goto theend;
       }
       zend = alloc_state(NFA_ZEND, s1, NULL);
       if (zend == NULL) {
         goto theend;
       }
       s1->out = skip;
       patch(e.out, zend);
       PUSH(frag(s, list1(&skip->out)));
     } else {
       patch(e.out, s1);
       PUSH(frag(s, list1(&s1->out)));
       if (before) {
         if (n <= 0) {
           // See if we can guess the maximum width, it avoids a
           // lot of pointless tries.
           n = nfa_max_width(e.start, 0);
         }
         s->val = n;           // store the count
       }
     }
     break;
   }

   case NFA_COMPOSING:         // char with composing char
     FALLTHROUGH;

   case NFA_MOPEN:     // \( \) Submatch
   case NFA_MOPEN1:
   case NFA_MOPEN2:
   case NFA_MOPEN3:
   case NFA_MOPEN4:
   case NFA_MOPEN5:
   case NFA_MOPEN6:
   case NFA_MOPEN7:
   case NFA_MOPEN8:
   case NFA_MOPEN9:
   case NFA_ZOPEN:     // \z( \) Submatch
   case NFA_ZOPEN1:
   case NFA_ZOPEN2:
   case NFA_ZOPEN3:
   case NFA_ZOPEN4:
   case NFA_ZOPEN5:
   case NFA_ZOPEN6:
   case NFA_ZOPEN7:
   case NFA_ZOPEN8:
   case NFA_ZOPEN9:
   case NFA_NOPEN:     // \%( \) "Invisible Submatch"
     if (nfa_calc_size == true) {
       nstate += 2;
       break;
     }

     mopen = *p;
     switch (*p) {
     case NFA_NOPEN:
       mclose = NFA_NCLOSE; break;
     case NFA_ZOPEN:
       mclose = NFA_ZCLOSE; break;
     case NFA_ZOPEN1:
       mclose = NFA_ZCLOSE1; break;
     case NFA_ZOPEN2:
       mclose = NFA_ZCLOSE2; break;
     case NFA_ZOPEN3:
       mclose = NFA_ZCLOSE3; break;
     case NFA_ZOPEN4:
       mclose = NFA_ZCLOSE4; break;
     case NFA_ZOPEN5:
       mclose = NFA_ZCLOSE5; break;
     case NFA_ZOPEN6:
       mclose = NFA_ZCLOSE6; break;
     case NFA_ZOPEN7:
       mclose = NFA_ZCLOSE7; break;
     case NFA_ZOPEN8:
       mclose = NFA_ZCLOSE8; break;
     case NFA_ZOPEN9:
       mclose = NFA_ZCLOSE9; break;
     case NFA_COMPOSING:
       mclose = NFA_END_COMPOSING; break;
     default:
       // NFA_MOPEN, NFA_MOPEN1 .. NFA_MOPEN9
       mclose = *p + NSUBEXP;
       break;
     }

     // Allow "NFA_MOPEN" as a valid postfix representation for
     // the empty regexp "". In this case, the NFA will be
     // NFA_MOPEN -> NFA_MCLOSE. Note that this also allows
     // empty groups of parenthesis, and empty mbyte chars
     if (stackp == stack) {
       s = alloc_state(mopen, NULL, NULL);
       if (s == NULL) {
         goto theend;
       }
       s1 = alloc_state(mclose, NULL, NULL);
       if (s1 == NULL) {
         goto theend;
       }
       patch(list1(&s->out), s1);
       PUSH(frag(s, list1(&s1->out)));
       break;
     }

     // At least one node was emitted before NFA_MOPEN, so
     // at least one node will be between NFA_MOPEN and NFA_MCLOSE
     e = POP();
     s = alloc_state(mopen, e.start, NULL);         // `('
     if (s == NULL) {
       goto theend;
     }

     s1 = alloc_state(mclose, NULL, NULL);         // `)'
     if (s1 == NULL) {
       goto theend;
     }
     patch(e.out, s1);

     if (mopen == NFA_COMPOSING) {
       // COMPOSING->out1 = END_COMPOSING
       patch(list1(&s->out1), s1);
     }

     PUSH(frag(s, list1(&s1->out)));
     break;

   case NFA_BACKREF1:
   case NFA_BACKREF2:
   case NFA_BACKREF3:
   case NFA_BACKREF4:
   case NFA_BACKREF5:
   case NFA_BACKREF6:
   case NFA_BACKREF7:
   case NFA_BACKREF8:
   case NFA_BACKREF9:
   case NFA_ZREF1:
   case NFA_ZREF2:
   case NFA_ZREF3:
   case NFA_ZREF4:
   case NFA_ZREF5:
   case NFA_ZREF6:
   case NFA_ZREF7:
   case NFA_ZREF8:
   case NFA_ZREF9:
     if (nfa_calc_size == true) {
       nstate += 2;
       break;
     }
     s = alloc_state(*p, NULL, NULL);
     if (s == NULL) {
       goto theend;
     }
     s1 = alloc_state(NFA_SKIP, NULL, NULL);
     if (s1 == NULL) {
       goto theend;
     }
     patch(list1(&s->out), s1);
     PUSH(frag(s, list1(&s1->out)));
     break;

   case NFA_LNUM:
   case NFA_LNUM_GT:
   case NFA_LNUM_LT:
   case NFA_VCOL:
   case NFA_VCOL_GT:
   case NFA_VCOL_LT:
   case NFA_COL:
   case NFA_COL_GT:
   case NFA_COL_LT:
   case NFA_MARK:
   case NFA_MARK_GT:
   case NFA_MARK_LT: {
     int n = *++p;       // lnum, col or mark name

     if (nfa_calc_size == true) {
       nstate += 1;
       break;
     }
     s = alloc_state(p[-1], NULL, NULL);
     if (s == NULL) {
       goto theend;
     }
     s->val = n;
     PUSH(frag(s, list1(&s->out)));
     break;
   }

   case NFA_ZSTART:
   case NFA_ZEND:
   default:
     // Operands
     if (nfa_calc_size == true) {
       nstate++;
       break;
     }
     s = alloc_state(*p, NULL, NULL);
     if (s == NULL) {
       goto theend;
     }
     PUSH(frag(s, list1(&s->out)));
     break;
   }     // switch(*p)
 }   // for(p = postfix; *p; ++p)

 if (nfa_calc_size == true) {
   nstate++;
   goto theend;        // Return value when counting size is ignored anyway
 }

 e = POP();
 if (stackp != stack) {
   xfree(stack);
   EMSG_RET_NULL(_("E875: (NFA regexp) (While converting from postfix to NFA),"
                   "too many states left on stack"));
 }

 if (istate >= nstate) {
   xfree(stack);
   EMSG_RET_NULL(_("E876: (NFA regexp) "
                   "Not enough space to store the whole NFA "));
 }

 matchstate = &state_ptr[istate++];   // the match state
 matchstate->c = NFA_MATCH;
 matchstate->out = matchstate->out1 = NULL;
 matchstate->id = 0;

 patch(e.out, matchstate);
 ret = e.start;

theend:
 xfree(stack);
 return ret;

#undef POP1
#undef PUSH1
#undef POP2
#undef PUSH2
#undef POP
#undef PUSH
}

// After building the NFA program, inspect it to add optimization hints.
static void nfa_postprocess(nfa_regprog_T *prog)
{
 int i;
 int c;

 for (i = 0; i < prog->nstate; i++) {
   c = prog->state[i].c;
   if (c == NFA_START_INVISIBLE
       || c == NFA_START_INVISIBLE_NEG
       || c == NFA_START_INVISIBLE_BEFORE
       || c == NFA_START_INVISIBLE_BEFORE_NEG) {
     int directly;

     // Do it directly when what follows is possibly the end of the
     // match.
     if (match_follows(prog->state[i].out1->out, 0)) {
       directly = true;
     } else {
       int ch_invisible = failure_chance(prog->state[i].out, 0);
       int ch_follows = failure_chance(prog->state[i].out1->out, 0);

       // Postpone when the invisible match is expensive or has a
       // lower chance of failing.
       if (c == NFA_START_INVISIBLE_BEFORE
           || c == NFA_START_INVISIBLE_BEFORE_NEG) {
         // "before" matches are very expensive when
         // unbounded, always prefer what follows then,
         // unless what follows will always match.
         // Otherwise strongly prefer what follows.
         if (prog->state[i].val <= 0 && ch_follows > 0) {
           directly = false;
         } else {
           directly = ch_follows * 10 < ch_invisible;
         }
       } else {
         // normal invisible, first do the one with the
         // highest failure chance
         directly = ch_follows < ch_invisible;
       }
     }
     if (directly) {
       // switch to the _FIRST state
       prog->state[i].c++;
     }
   }
 }
}

/////////////////////////////////////////////////////////////////
// NFA execution code.
/////////////////////////////////////////////////////////////////

// Values for done in nfa_pim_T.
#define NFA_PIM_UNUSED   0      // pim not used
#define NFA_PIM_TODO     1      // pim not done yet
#define NFA_PIM_MATCH    2      // pim executed, matches
#define NFA_PIM_NOMATCH  3      // pim executed, no match

#ifdef REGEXP_DEBUG
static void log_subsexpr(regsubs_T *subs)
{
 log_subexpr(&subs->norm);
 if (rex.nfa_has_zsubexpr) {
   log_subexpr(&subs->synt);
 }
}

static void log_subexpr(regsub_T *sub)
{
 int j;

 for (j = 0; j < sub->in_use; j++) {
   if (REG_MULTI) {
     fprintf(log_fd, "*** group %d, start: c=%d, l=%d, end: c=%d, l=%d\n",
             j,
             sub->list.multi[j].start_col,
             (int)sub->list.multi[j].start_lnum,
             sub->list.multi[j].end_col,
             (int)sub->list.multi[j].end_lnum);
   } else {
     char *s = (char *)sub->list.line[j].start;
     char *e = (char *)sub->list.line[j].end;

     fprintf(log_fd, "*** group %d, start: \"%s\", end: \"%s\"\n",
             j,
             s == NULL ? "NULL" : s,
             e == NULL ? "NULL" : e);
   }
 }
}

static char *pim_info(const nfa_pim_T *pim)
{
 static char buf[30];

 if (pim == NULL || pim->result == NFA_PIM_UNUSED) {
   buf[0] = NUL;
 } else {
   snprintf(buf, sizeof(buf), " PIM col %d",
            REG_MULTI
            ? (int)pim->end.pos.col
            : (int)(pim->end.ptr - rex.input));
 }
 return buf;
}

#endif

// Used during execution: whether a match has been found.
static int nfa_match;
static proftime_T *nfa_time_limit;
static int *nfa_timed_out;
static int nfa_time_count;

// Copy postponed invisible match info from "from" to "to".
static void copy_pim(nfa_pim_T *to, nfa_pim_T *from)
{
 to->result = from->result;
 to->state = from->state;
 copy_sub(&to->subs.norm, &from->subs.norm);
 if (rex.nfa_has_zsubexpr) {
   copy_sub(&to->subs.synt, &from->subs.synt);
 }
 to->end = from->end;
}

static void clear_sub(regsub_T *sub)
{
 if (REG_MULTI) {
   // Use 0xff to set lnum to -1
   memset(sub->list.multi, 0xff, sizeof(struct multipos) * (size_t)rex.nfa_nsubexpr);
 } else {
   memset(sub->list.line, 0, sizeof(struct linepos) * (size_t)rex.nfa_nsubexpr);
 }
 sub->in_use = 0;
}

// Copy the submatches from "from" to "to".
static void copy_sub(regsub_T *to, regsub_T *from)
{
 to->in_use = from->in_use;
 if (from->in_use <= 0) {
   return;
 }

 // Copy the match start and end positions.
 if (REG_MULTI) {
   memmove(&to->list.multi[0], &from->list.multi[0],
           sizeof(struct multipos) * (size_t)from->in_use);
   to->orig_start_col = from->orig_start_col;
 } else {
   memmove(&to->list.line[0], &from->list.line[0],
           sizeof(struct linepos) * (size_t)from->in_use);
 }
}

// Like copy_sub() but exclude the main match.
static void copy_sub_off(regsub_T *to, regsub_T *from)
{
 if (to->in_use < from->in_use) {
   to->in_use = from->in_use;
 }
 if (from->in_use <= 1) {
   return;
 }

 // Copy the match start and end positions.
 if (REG_MULTI) {
   memmove(&to->list.multi[1], &from->list.multi[1],
           sizeof(struct multipos) * (size_t)(from->in_use - 1));
 } else {
   memmove(&to->list.line[1], &from->list.line[1],
           sizeof(struct linepos) * (size_t)(from->in_use - 1));
 }
}

// Like copy_sub() but only do the end of the main match if \ze is present.
static void copy_ze_off(regsub_T *to, regsub_T *from)
{
 if (!rex.nfa_has_zend) {
   return;
 }

 if (REG_MULTI) {
   if (from->list.multi[0].end_lnum >= 0) {
     to->list.multi[0].end_lnum = from->list.multi[0].end_lnum;
     to->list.multi[0].end_col = from->list.multi[0].end_col;
   }
 } else {
   if (from->list.line[0].end != NULL) {
     to->list.line[0].end = from->list.line[0].end;
   }
 }
}

// Return true if "sub1" and "sub2" have the same start positions.
// When using back-references also check the end position.
static bool sub_equal(regsub_T *sub1, regsub_T *sub2)
{
 int i;
 int todo;
 linenr_T s1;
 linenr_T s2;
 uint8_t *sp1;
 uint8_t *sp2;

 todo = sub1->in_use > sub2->in_use ? sub1->in_use : sub2->in_use;
 if (REG_MULTI) {
   for (i = 0; i < todo; i++) {
     if (i < sub1->in_use) {
       s1 = sub1->list.multi[i].start_lnum;
     } else {
       s1 = -1;
     }
     if (i < sub2->in_use) {
       s2 = sub2->list.multi[i].start_lnum;
     } else {
       s2 = -1;
     }
     if (s1 != s2) {
       return false;
     }
     if (s1 != -1 && sub1->list.multi[i].start_col
         != sub2->list.multi[i].start_col) {
       return false;
     }
     if (rex.nfa_has_backref) {
       if (i < sub1->in_use) {
         s1 = sub1->list.multi[i].end_lnum;
       } else {
         s1 = -1;
       }
       if (i < sub2->in_use) {
         s2 = sub2->list.multi[i].end_lnum;
       } else {
         s2 = -1;
       }
       if (s1 != s2) {
         return false;
       }
       if (s1 != -1
           && sub1->list.multi[i].end_col != sub2->list.multi[i].end_col) {
         return false;
       }
     }
   }
 } else {
   for (i = 0; i < todo; i++) {
     if (i < sub1->in_use) {
       sp1 = sub1->list.line[i].start;
     } else {
       sp1 = NULL;
     }
     if (i < sub2->in_use) {
       sp2 = sub2->list.line[i].start;
     } else {
       sp2 = NULL;
     }
     if (sp1 != sp2) {
       return false;
     }
     if (rex.nfa_has_backref) {
       if (i < sub1->in_use) {
         sp1 = sub1->list.line[i].end;
       } else {
         sp1 = NULL;
       }
       if (i < sub2->in_use) {
         sp2 = sub2->list.line[i].end;
       } else {
         sp2 = NULL;
       }
       if (sp1 != sp2) {
         return false;
       }
     }
   }
 }

 return true;
}

#ifdef REGEXP_DEBUG
static void open_debug_log(TriState result)
{
 log_fd = fopen(NFA_REGEXP_RUN_LOG, "a");
 if (log_fd == NULL) {
   emsg(_(e_log_open_failed));
   log_fd = stderr;
 }

 fprintf(log_fd, "****************************\n");
 fprintf(log_fd, "FINISHED RUNNING nfa_regmatch() recursively\n");
 fprintf(log_fd, "MATCH = %s\n", result == kTrue ? "OK" : result == kNone ? "MAYBE" : "FALSE");
 fprintf(log_fd, "****************************\n");
}

static void report_state(char *action, regsub_T *sub, nfa_state_T *state, int lid, nfa_pim_T *pim)
{
 int col;

 if (sub->in_use <= 0) {
   col = -1;
 } else if (REG_MULTI) {
   col = sub->list.multi[0].start_col;
 } else {
   col = (int)(sub->list.line[0].start - rex.line);
 }
 nfa_set_code(state->c);
 if (log_fd == NULL) {
   open_debug_log(kNone);
 }
 fprintf(log_fd, "> %s state %d to list %d. char %d: %s (start col %d)%s\n",
         action, abs(state->id), lid, state->c, code, col,
         pim_info(pim));
}

#endif

/// @param l      runtime state list
/// @param state  state to update
/// @param subs   pointers to subexpressions
/// @param pim    postponed match or NULL
///
/// @return  true if the same state is already in list "l" with the same
///          positions as "subs".
static bool has_state_with_pos(nfa_list_T *l, nfa_state_T *state, regsubs_T *subs, nfa_pim_T *pim)
 FUNC_ATTR_NONNULL_ARG(1, 2, 3)
{
 for (int i = 0; i < l->n; i++) {
   nfa_thread_T *thread = &l->t[i];
   if (thread->state->id == state->id
       && sub_equal(&thread->subs.norm, &subs->norm)
       && (!rex.nfa_has_zsubexpr
           || sub_equal(&thread->subs.synt, &subs->synt))
       && pim_equal(&thread->pim, pim)) {
     return true;
   }
 }
 return false;
}

// Return true if "one" and "two" are equal.  That includes when both are not
// set.
static bool pim_equal(const nfa_pim_T *one, const nfa_pim_T *two)
{
 const bool one_unused = (one == NULL || one->result == NFA_PIM_UNUSED);
 const bool two_unused = (two == NULL || two->result == NFA_PIM_UNUSED);

 if (one_unused) {
   // one is unused: equal when two is also unused
   return two_unused;
 }
 if (two_unused) {
   // one is used and two is not: not equal
   return false;
 }
 // compare the state id
 if (one->state->id != two->state->id) {
   return false;
 }
 // compare the position
 if (REG_MULTI) {
   return one->end.pos.lnum == two->end.pos.lnum
          && one->end.pos.col == two->end.pos.col;
 }
 return one->end.ptr == two->end.ptr;
}

// Return true if "state" leads to a NFA_MATCH without advancing the input.
static bool match_follows(const nfa_state_T *startstate, int depth)
 FUNC_ATTR_NONNULL_ALL
{
 const nfa_state_T *state = startstate;

 // avoid too much recursion
 if (depth > 10) {
   return false;
 }
 while (state != NULL) {
   switch (state->c) {
   case NFA_MATCH:
   case NFA_MCLOSE:
   case NFA_END_INVISIBLE:
   case NFA_END_INVISIBLE_NEG:
   case NFA_END_PATTERN:
     return true;

   case NFA_SPLIT:
     return match_follows(state->out, depth + 1)
            || match_follows(state->out1, depth + 1);

   case NFA_START_INVISIBLE:
   case NFA_START_INVISIBLE_FIRST:
   case NFA_START_INVISIBLE_BEFORE:
   case NFA_START_INVISIBLE_BEFORE_FIRST:
   case NFA_START_INVISIBLE_NEG:
   case NFA_START_INVISIBLE_NEG_FIRST:
   case NFA_START_INVISIBLE_BEFORE_NEG:
   case NFA_START_INVISIBLE_BEFORE_NEG_FIRST:
   case NFA_COMPOSING:
     // skip ahead to next state
     state = state->out1->out;
     continue;

   case NFA_ANY:
   case NFA_ANY_COMPOSING:
   case NFA_IDENT:
   case NFA_SIDENT:
   case NFA_KWORD:
   case NFA_SKWORD:
   case NFA_FNAME:
   case NFA_SFNAME:
   case NFA_PRINT:
   case NFA_SPRINT:
   case NFA_WHITE:
   case NFA_NWHITE:
   case NFA_DIGIT:
   case NFA_NDIGIT:
   case NFA_HEX:
   case NFA_NHEX:
   case NFA_OCTAL:
   case NFA_NOCTAL:
   case NFA_WORD:
   case NFA_NWORD:
   case NFA_HEAD:
   case NFA_NHEAD:
   case NFA_ALPHA:
   case NFA_NALPHA:
   case NFA_LOWER:
   case NFA_NLOWER:
   case NFA_UPPER:
   case NFA_NUPPER:
   case NFA_LOWER_IC:
   case NFA_NLOWER_IC:
   case NFA_UPPER_IC:
   case NFA_NUPPER_IC:
   case NFA_START_COLL:
   case NFA_START_NEG_COLL:
   case NFA_NEWL:
     // state will advance input
     return false;

   default:
     if (state->c > 0) {
       // state will advance input
       return false;
     }
     // Others: zero-width or possibly zero-width, might still find
     // a match at the same position, keep looking.
     break;
   }
   state = state->out;
 }
 return false;
}

/// @param l      runtime state list
/// @param state  state to update
/// @param subs   pointers to subexpressions
///
/// @return  true if "state" is already in list "l".
static bool state_in_list(nfa_list_T *l, nfa_state_T *state, regsubs_T *subs)
 FUNC_ATTR_NONNULL_ALL
{
 if (state->lastlist[nfa_ll_index] == l->id) {
   if (!rex.nfa_has_backref || has_state_with_pos(l, state, subs, NULL)) {
     return true;
   }
 }
 return false;
}

// Offset used for "off" by addstate_here().
#define ADDSTATE_HERE_OFFSET 10

/// Add "state" and possibly what follows to state list ".".
///
/// @param l         runtime state list
/// @param state     state to update
/// @param subs_arg  pointers to subexpressions
/// @param pim       postponed look-behind match
/// @param off_arg   byte offset, when -1 go to next line
///
/// @return  "subs_arg", possibly copied into temp_subs.
///          NULL when recursiveness is too deep.
static regsubs_T *addstate(nfa_list_T *l, nfa_state_T *state, regsubs_T *subs_arg, nfa_pim_T *pim,
                          int off_arg)
 FUNC_ATTR_NONNULL_ARG(1, 2) FUNC_ATTR_WARN_UNUSED_RESULT
{
 int subidx;
 int off = off_arg;
 int add_here = false;
 int listindex = 0;
 int k;
 int found = false;
 nfa_thread_T *thread;
 struct multipos save_multipos;
 int save_in_use;
 uint8_t *save_ptr;
 int i;
 regsub_T *sub;
 regsubs_T *subs = subs_arg;
 static regsubs_T temp_subs;
#ifdef REGEXP_DEBUG
 int did_print = false;
#endif
 static int depth = 0;

 // This function is called recursively.  When the depth is too much we run
 // out of stack and crash, limit recursiveness here.
 if (++depth >= 5000 || subs == NULL) {
   depth--;
   return NULL;
 }

 if (off_arg <= -ADDSTATE_HERE_OFFSET) {
   add_here = true;
   off = 0;
   listindex = -(off_arg + ADDSTATE_HERE_OFFSET);
 }

 switch (state->c) {
 case NFA_NCLOSE:
 case NFA_MCLOSE:
 case NFA_MCLOSE1:
 case NFA_MCLOSE2:
 case NFA_MCLOSE3:
 case NFA_MCLOSE4:
 case NFA_MCLOSE5:
 case NFA_MCLOSE6:
 case NFA_MCLOSE7:
 case NFA_MCLOSE8:
 case NFA_MCLOSE9:
 case NFA_ZCLOSE:
 case NFA_ZCLOSE1:
 case NFA_ZCLOSE2:
 case NFA_ZCLOSE3:
 case NFA_ZCLOSE4:
 case NFA_ZCLOSE5:
 case NFA_ZCLOSE6:
 case NFA_ZCLOSE7:
 case NFA_ZCLOSE8:
 case NFA_ZCLOSE9:
 case NFA_MOPEN:
 case NFA_ZEND:
 case NFA_SPLIT:
 case NFA_EMPTY:
   // These nodes are not added themselves but their "out" and/or
   // "out1" may be added below.
   break;

 case NFA_BOL:
 case NFA_BOF:
   // "^" won't match past end-of-line, don't bother trying.
   // Except when at the end of the line, or when we are going to the
   // next line for a look-behind match.
   if (rex.input > rex.line
       && *rex.input != NUL
       && (nfa_endp == NULL
           || !REG_MULTI
           || rex.lnum == nfa_endp->se_u.pos.lnum)) {
     goto skip_add;
   }
   FALLTHROUGH;

 case NFA_MOPEN1:
 case NFA_MOPEN2:
 case NFA_MOPEN3:
 case NFA_MOPEN4:
 case NFA_MOPEN5:
 case NFA_MOPEN6:
 case NFA_MOPEN7:
 case NFA_MOPEN8:
 case NFA_MOPEN9:
 case NFA_ZOPEN:
 case NFA_ZOPEN1:
 case NFA_ZOPEN2:
 case NFA_ZOPEN3:
 case NFA_ZOPEN4:
 case NFA_ZOPEN5:
 case NFA_ZOPEN6:
 case NFA_ZOPEN7:
 case NFA_ZOPEN8:
 case NFA_ZOPEN9:
 case NFA_NOPEN:
 case NFA_ZSTART:
 // These nodes need to be added so that we can bail out when it
 // was added to this list before at the same position to avoid an
 // endless loop for "\(\)*"

 default:
   if (state->lastlist[nfa_ll_index] == l->id && state->c != NFA_SKIP) {
     // This state is already in the list, don't add it again,
     // unless it is an MOPEN that is used for a backreference or
     // when there is a PIM. For NFA_MATCH check the position,
     // lower position is preferred.
     if (!rex.nfa_has_backref && pim == NULL && !l->has_pim
         && state->c != NFA_MATCH) {
       // When called from addstate_here() do insert before
       // existing states.
       if (add_here) {
         for (k = 0; k < l->n && k < listindex; k++) {
           if (l->t[k].state->id == state->id) {
             found = true;
             break;
           }
         }
       }

       if (!add_here || found) {
skip_add:
#ifdef REGEXP_DEBUG
         nfa_set_code(state->c);
         fprintf(log_fd,
                 "> Not adding state %d to list %d. char %d: %s pim: %s has_pim: %d found: %d\n",
                 abs(state->id), l->id, state->c, code,
                 pim == NULL ? "NULL" : "yes", l->has_pim, found);
#endif
         depth--;
         return subs;
       }
     }

     // Do not add the state again when it exists with the same
     // positions.
     if (has_state_with_pos(l, state, subs, pim)) {
       goto skip_add;
     }
   }

   // When there are backreferences or PIMs the number of states may
   // be (a lot) bigger than anticipated.
   if (l->n == l->len) {
     const int newlen = l->len * 3 / 2 + 50;
     const size_t newsize = (size_t)newlen * sizeof(nfa_thread_T);

     if ((int64_t)(newsize >> 10) >= p_mmp) {
       emsg(_(e_pattern_uses_more_memory_than_maxmempattern));
       depth--;
       return NULL;
     }
     if (subs != &temp_subs) {
       // "subs" may point into the current array, need to make a
       // copy before it becomes invalid.
       copy_sub(&temp_subs.norm, &subs->norm);
       if (rex.nfa_has_zsubexpr) {
         copy_sub(&temp_subs.synt, &subs->synt);
       }
       subs = &temp_subs;
     }

     nfa_thread_T *const newt = xrealloc(l->t, newsize);
     l->t = newt;
     l->len = newlen;
   }

   // add the state to the list
   state->lastlist[nfa_ll_index] = l->id;
   thread = &l->t[l->n++];
   thread->state = state;
   if (pim == NULL) {
     thread->pim.result = NFA_PIM_UNUSED;
   } else {
     copy_pim(&thread->pim, pim);
     l->has_pim = true;
   }
   copy_sub(&thread->subs.norm, &subs->norm);
   if (rex.nfa_has_zsubexpr) {
     copy_sub(&thread->subs.synt, &subs->synt);
   }
#ifdef REGEXP_DEBUG
   report_state("Adding", &thread->subs.norm, state, l->id, pim);
   did_print = true;
#endif
 }

#ifdef REGEXP_DEBUG
 if (!did_print) {
   report_state("Processing", &subs->norm, state, l->id, pim);
 }
#endif
 switch (state->c) {
 case NFA_MATCH:
   break;

 case NFA_SPLIT:
   // order matters here
   subs = addstate(l, state->out, subs, pim, off_arg);
   subs = addstate(l, state->out1, subs, pim, off_arg);
   break;

 case NFA_EMPTY:
 case NFA_NOPEN:
 case NFA_NCLOSE:
   subs = addstate(l, state->out, subs, pim, off_arg);
   break;

 case NFA_MOPEN:
 case NFA_MOPEN1:
 case NFA_MOPEN2:
 case NFA_MOPEN3:
 case NFA_MOPEN4:
 case NFA_MOPEN5:
 case NFA_MOPEN6:
 case NFA_MOPEN7:
 case NFA_MOPEN8:
 case NFA_MOPEN9:
 case NFA_ZOPEN:
 case NFA_ZOPEN1:
 case NFA_ZOPEN2:
 case NFA_ZOPEN3:
 case NFA_ZOPEN4:
 case NFA_ZOPEN5:
 case NFA_ZOPEN6:
 case NFA_ZOPEN7:
 case NFA_ZOPEN8:
 case NFA_ZOPEN9:
 case NFA_ZSTART:
   if (state->c == NFA_ZSTART) {
     subidx = 0;
     sub = &subs->norm;
   } else if (state->c >= NFA_ZOPEN && state->c <= NFA_ZOPEN9) {
     subidx = state->c - NFA_ZOPEN;
     sub = &subs->synt;
   } else {
     subidx = state->c - NFA_MOPEN;
     sub = &subs->norm;
   }

   // avoid compiler warnings
   save_ptr = NULL;
   CLEAR_FIELD(save_multipos);

   // Set the position (with "off" added) in the subexpression.  Save
   // and restore it when it was in use.  Otherwise fill any gap.
   if (REG_MULTI) {
     if (subidx < sub->in_use) {
       save_multipos = sub->list.multi[subidx];
       save_in_use = -1;
     } else {
       save_in_use = sub->in_use;
       for (i = sub->in_use; i < subidx; i++) {
         sub->list.multi[i].start_lnum = -1;
         sub->list.multi[i].end_lnum = -1;
       }
       sub->in_use = subidx + 1;
     }
     if (off == -1) {
       sub->list.multi[subidx].start_lnum = rex.lnum + 1;
       sub->list.multi[subidx].start_col = 0;
     } else {
       sub->list.multi[subidx].start_lnum = rex.lnum;
       sub->list.multi[subidx].start_col =
         (colnr_T)(rex.input - rex.line + off);
     }
     sub->list.multi[subidx].end_lnum = -1;
   } else {
     if (subidx < sub->in_use) {
       save_ptr = sub->list.line[subidx].start;
       save_in_use = -1;
     } else {
       save_in_use = sub->in_use;
       for (i = sub->in_use; i < subidx; i++) {
         sub->list.line[i].start = NULL;
         sub->list.line[i].end = NULL;
       }
       sub->in_use = subidx + 1;
     }
     sub->list.line[subidx].start = rex.input + off;
   }

   subs = addstate(l, state->out, subs, pim, off_arg);
   if (subs == NULL) {
     break;
   }
   // "subs" may have changed, need to set "sub" again.
   if (state->c >= NFA_ZOPEN && state->c <= NFA_ZOPEN9) {
     sub = &subs->synt;
   } else {
     sub = &subs->norm;
   }

   if (save_in_use == -1) {
     if (REG_MULTI) {
       sub->list.multi[subidx] = save_multipos;
     } else {
       sub->list.line[subidx].start = save_ptr;
     }
   } else {
     sub->in_use = save_in_use;
   }
   break;

 case NFA_MCLOSE:
   if (rex.nfa_has_zend
       && (REG_MULTI
           ? subs->norm.list.multi[0].end_lnum >= 0
           : subs->norm.list.line[0].end != NULL)) {
     // Do not overwrite the position set by \ze.
     subs = addstate(l, state->out, subs, pim, off_arg);
     break;
   }
   FALLTHROUGH;
 case NFA_MCLOSE1:
 case NFA_MCLOSE2:
 case NFA_MCLOSE3:
 case NFA_MCLOSE4:
 case NFA_MCLOSE5:
 case NFA_MCLOSE6:
 case NFA_MCLOSE7:
 case NFA_MCLOSE8:
 case NFA_MCLOSE9:
 case NFA_ZCLOSE:
 case NFA_ZCLOSE1:
 case NFA_ZCLOSE2:
 case NFA_ZCLOSE3:
 case NFA_ZCLOSE4:
 case NFA_ZCLOSE5:
 case NFA_ZCLOSE6:
 case NFA_ZCLOSE7:
 case NFA_ZCLOSE8:
 case NFA_ZCLOSE9:
 case NFA_ZEND:
   if (state->c == NFA_ZEND) {
     subidx = 0;
     sub = &subs->norm;
   } else if (state->c >= NFA_ZCLOSE && state->c <= NFA_ZCLOSE9) {
     subidx = state->c - NFA_ZCLOSE;
     sub = &subs->synt;
   } else {
     subidx = state->c - NFA_MCLOSE;
     sub = &subs->norm;
   }

   // We don't fill in gaps here, there must have been an MOPEN that
   // has done that.
   save_in_use = sub->in_use;
   if (sub->in_use <= subidx) {
     sub->in_use = subidx + 1;
   }
   if (REG_MULTI) {
     save_multipos = sub->list.multi[subidx];
     if (off == -1) {
       sub->list.multi[subidx].end_lnum = rex.lnum + 1;
       sub->list.multi[subidx].end_col = 0;
     } else {
       sub->list.multi[subidx].end_lnum = rex.lnum;
       sub->list.multi[subidx].end_col =
         (colnr_T)(rex.input - rex.line + off);
     }
     // avoid compiler warnings
     save_ptr = NULL;
   } else {
     save_ptr = sub->list.line[subidx].end;
     sub->list.line[subidx].end = rex.input + off;
     // avoid compiler warnings
     CLEAR_FIELD(save_multipos);
   }

   subs = addstate(l, state->out, subs, pim, off_arg);
   if (subs == NULL) {
     break;
   }
   // "subs" may have changed, need to set "sub" again.
   if (state->c >= NFA_ZCLOSE && state->c <= NFA_ZCLOSE9) {
     sub = &subs->synt;
   } else {
     sub = &subs->norm;
   }

   if (REG_MULTI) {
     sub->list.multi[subidx] = save_multipos;
   } else {
     sub->list.line[subidx].end = save_ptr;
   }
   sub->in_use = save_in_use;
   break;
 }
 depth--;
 return subs;
}

/// Like addstate(), but the new state(s) are put at position "*ip".
/// Used for zero-width matches, next state to use is the added one.
/// This makes sure the order of states to be tried does not change, which
/// matters for alternatives.
///
/// @param l      runtime state list
/// @param state  state to update
/// @param subs   pointers to subexpressions
/// @param pim    postponed look-behind match
static regsubs_T *addstate_here(nfa_list_T *l, nfa_state_T *state, regsubs_T *subs, nfa_pim_T *pim,
                               int *ip)
 FUNC_ATTR_NONNULL_ARG(1, 2, 5) FUNC_ATTR_WARN_UNUSED_RESULT
{
 int tlen = l->n;
 int count;
 int listidx = *ip;

 // First add the state(s) at the end, so that we know how many there are.
 // Pass the listidx as offset (avoids adding another argument to
 // addstate()).
 regsubs_T *r = addstate(l, state, subs, pim, -listidx - ADDSTATE_HERE_OFFSET);
 if (r == NULL) {
   return NULL;
 }

 // when "*ip" was at the end of the list, nothing to do
 if (listidx + 1 == tlen) {
   return r;
 }

 // re-order to put the new state at the current position
 count = l->n - tlen;
 if (count == 0) {
   return r;  // no state got added
 }
 if (count == 1) {
   // overwrite the current state
   l->t[listidx] = l->t[l->n - 1];
 } else if (count > 1) {
   if (l->n + count - 1 >= l->len) {
     // not enough space to move the new states, reallocate the list
     // and move the states to the right position
     const int newlen = l->len * 3 / 2 + 50;
     const size_t newsize = (size_t)newlen * sizeof(nfa_thread_T);

     if ((int64_t)(newsize >> 10) >= p_mmp) {
       emsg(_(e_pattern_uses_more_memory_than_maxmempattern));
       return NULL;
     }
     nfa_thread_T *const newl = xmalloc(newsize);
     l->len = newlen;
     memmove(&(newl[0]),
             &(l->t[0]),
             sizeof(nfa_thread_T) * (size_t)listidx);
     memmove(&(newl[listidx]),
             &(l->t[l->n - count]),
             sizeof(nfa_thread_T) * (size_t)count);
     memmove(&(newl[listidx + count]),
             &(l->t[listidx + 1]),
             sizeof(nfa_thread_T) * (size_t)(l->n - count - listidx - 1));
     xfree(l->t);
     l->t = newl;
   } else {
     // make space for new states, then move them from the
     // end to the current position
     memmove(&(l->t[listidx + count]),
             &(l->t[listidx + 1]),
             sizeof(nfa_thread_T) * (size_t)(l->n - listidx - 1));
     memmove(&(l->t[listidx]),
             &(l->t[l->n - 1]),
             sizeof(nfa_thread_T) * (size_t)count);
   }
 }
 l->n--;
 *ip = listidx - 1;

 return r;
}

// Check character class "class" against current character c.
static int check_char_class(int cls, int c)
{
 switch (cls) {
 case NFA_CLASS_ALNUM:
   if (c >= 1 && c < 128 && isalnum(c)) {
     return OK;
   }
   break;
 case NFA_CLASS_ALPHA:
   if (c >= 1 && c < 128 && isalpha(c)) {
     return OK;
   }
   break;
 case NFA_CLASS_BLANK:
   if (c == ' ' || c == '\t') {
     return OK;
   }
   break;
 case NFA_CLASS_CNTRL:
   if (c >= 1 && c <= 127 && iscntrl(c)) {
     return OK;
   }
   break;
 case NFA_CLASS_DIGIT:
   if (ascii_isdigit(c)) {
     return OK;
   }
   break;
 case NFA_CLASS_GRAPH:
   if (c >= 1 && c <= 127 && isgraph(c)) {
     return OK;
   }
   break;
 case NFA_CLASS_LOWER:
   if (mb_islower(c) && c != 170 && c != 186) {
     return OK;
   }
   break;
 case NFA_CLASS_PRINT:
   if (vim_isprintc(c)) {
     return OK;
   }
   break;
 case NFA_CLASS_PUNCT:
   if (c >= 1 && c < 128 && ispunct(c)) {
     return OK;
   }
   break;
 case NFA_CLASS_SPACE:
   if ((c >= 9 && c <= 13) || (c == ' ')) {
     return OK;
   }
   break;
 case NFA_CLASS_UPPER:
   if (mb_isupper(c)) {
     return OK;
   }
   break;
 case NFA_CLASS_XDIGIT:
   if (ascii_isxdigit(c)) {
     return OK;
   }
   break;
 case NFA_CLASS_TAB:
   if (c == '\t') {
     return OK;
   }
   break;
 case NFA_CLASS_RETURN:
   if (c == '\r') {
     return OK;
   }
   break;
 case NFA_CLASS_BACKSPACE:
   if (c == '\b') {
     return OK;
   }
   break;
 case NFA_CLASS_ESCAPE:
   if (c == ESC) {
     return OK;
   }
   break;
 case NFA_CLASS_IDENT:
   if (vim_isIDc(c)) {
     return OK;
   }
   break;
 case NFA_CLASS_KEYWORD:
   if (reg_iswordc(c)) {
     return OK;
   }
   break;
 case NFA_CLASS_FNAME:
   if (vim_isfilec(c)) {
     return OK;
   }
   break;

 default:
   // should not be here :P
   siemsg(_(e_ill_char_class), (int64_t)cls);
   return FAIL;
 }
 return FAIL;
}

/// Check for a match with subexpression "subidx".
///
/// @param sub      pointers to subexpressions
/// @param bytelen  out: length of match in bytes
///
/// @return  true if it matches.
static int match_backref(regsub_T *sub, int subidx, int *bytelen)
{
 int len;

 if (sub->in_use <= subidx) {
retempty:
   // backref was not set, match an empty string
   *bytelen = 0;
   return true;
 }

 if (REG_MULTI) {
   if (sub->list.multi[subidx].start_lnum < 0
       || sub->list.multi[subidx].end_lnum < 0) {
     goto retempty;
   }
   if (sub->list.multi[subidx].start_lnum == rex.lnum
       && sub->list.multi[subidx].end_lnum == rex.lnum) {
     len = sub->list.multi[subidx].end_col
           - sub->list.multi[subidx].start_col;
     if (cstrncmp((char *)rex.line + sub->list.multi[subidx].start_col,
                  (char *)rex.input, &len) == 0) {
       *bytelen = len;
       return true;
     }
   } else {
     if (match_with_backref(sub->list.multi[subidx].start_lnum,
                            sub->list.multi[subidx].start_col,
                            sub->list.multi[subidx].end_lnum,
                            sub->list.multi[subidx].end_col,
                            bytelen) == RA_MATCH) {
       return true;
     }
   }
 } else {
   if (sub->list.line[subidx].start == NULL
       || sub->list.line[subidx].end == NULL) {
     goto retempty;
   }
   len = (int)(sub->list.line[subidx].end - sub->list.line[subidx].start);
   if (cstrncmp((char *)sub->list.line[subidx].start, (char *)rex.input, &len) == 0) {
     *bytelen = len;
     return true;
   }
 }
 return false;
}

/// Check for a match with \z subexpression "subidx".
///
/// @param bytelen  out: length of match in bytes
///
/// @return  true if it matches.
static int match_zref(int subidx, int *bytelen)
{
 int len;

 cleanup_zsubexpr();
 if (re_extmatch_in == NULL || re_extmatch_in->matches[subidx] == NULL) {
   // backref was not set, match an empty string
   *bytelen = 0;
   return true;
 }

 len = (int)strlen((char *)re_extmatch_in->matches[subidx]);
 if (cstrncmp((char *)re_extmatch_in->matches[subidx], (char *)rex.input, &len) == 0) {
   *bytelen = len;
   return true;
 }
 return false;
}

// Save list IDs for all NFA states of "prog" into "list".
// Also reset the IDs to zero.
// Only used for the recursive value lastlist[1].
static void nfa_save_listids(nfa_regprog_T *prog, int *list)
{
 int i;
 nfa_state_T *p;

 // Order in the list is reverse, it's a bit faster that way.
 p = &prog->state[0];
 for (i = prog->nstate; --i >= 0;) {
   list[i] = p->lastlist[1];
   p->lastlist[1] = 0;
   p++;
 }
}

// Restore list IDs from "list" to all NFA states.
static void nfa_restore_listids(nfa_regprog_T *prog, const int *list)
{
 int i;
 nfa_state_T *p;

 p = &prog->state[0];
 for (i = prog->nstate; --i >= 0;) {
   p->lastlist[1] = list[i];
   p++;
 }
}

static bool nfa_re_num_cmp(uintmax_t val, int op, uintmax_t pos)
{
 if (op == 1) {
   return pos > val;
 }
 if (op == 2) {
   return pos < val;
 }
 return val == pos;
}

// Recursively call nfa_regmatch()
// "pim" is NULL or contains info about a Postponed Invisible Match (start
// position).
static int recursive_regmatch(nfa_state_T *state, nfa_pim_T *pim, nfa_regprog_T *prog,
                             regsubs_T *submatch, regsubs_T *m, int **listids, int *listids_len)
 FUNC_ATTR_NONNULL_ARG(1, 3, 5, 6, 7)
{
 const int save_reginput_col = (int)(rex.input - rex.line);
 const int save_reglnum = rex.lnum;
 const int save_nfa_match = nfa_match;
 const int save_nfa_listid = rex.nfa_listid;
 save_se_T *const save_nfa_endp = nfa_endp;
 save_se_T endpos;
 save_se_T *endposp = NULL;
 int need_restore = false;

 if (pim != NULL) {
   // start at the position where the postponed match was
   if (REG_MULTI) {
     rex.input = rex.line + pim->end.pos.col;
   } else {
     rex.input = pim->end.ptr;
   }
 }

 if (state->c == NFA_START_INVISIBLE_BEFORE
     || state->c == NFA_START_INVISIBLE_BEFORE_FIRST
     || state->c == NFA_START_INVISIBLE_BEFORE_NEG
     || state->c == NFA_START_INVISIBLE_BEFORE_NEG_FIRST) {
   // The recursive match must end at the current position. When "pim" is
   // not NULL it specifies the current position.
   endposp = &endpos;
   if (REG_MULTI) {
     if (pim == NULL) {
       endpos.se_u.pos.col = (int)(rex.input - rex.line);
       endpos.se_u.pos.lnum = rex.lnum;
     } else {
       endpos.se_u.pos = pim->end.pos;
     }
   } else {
     if (pim == NULL) {
       endpos.se_u.ptr = rex.input;
     } else {
       endpos.se_u.ptr = pim->end.ptr;
     }
   }

   // Go back the specified number of bytes, or as far as the
   // start of the previous line, to try matching "\@<=" or
   // not matching "\@<!". This is very inefficient, limit the number of
   // bytes if possible.
   if (state->val <= 0) {
     if (REG_MULTI) {
       rex.line = (uint8_t *)reg_getline(--rex.lnum);
       if (rex.line == NULL) {
         // can't go before the first line
         rex.line = (uint8_t *)reg_getline(++rex.lnum);
       }
     }
     rex.input = rex.line;
   } else {
     if (REG_MULTI && (int)(rex.input - rex.line) < state->val) {
       // Not enough bytes in this line, go to end of
       // previous line.
       rex.line = (uint8_t *)reg_getline(--rex.lnum);
       if (rex.line == NULL) {
         // can't go before the first line
         rex.line = (uint8_t *)reg_getline(++rex.lnum);
         rex.input = rex.line;
       } else {
         rex.input = rex.line + reg_getline_len(rex.lnum);
       }
     }
     if ((int)(rex.input - rex.line) >= state->val) {
       rex.input -= state->val;
       rex.input -= utf_head_off((char *)rex.line, (char *)rex.input);
     } else {
       rex.input = rex.line;
     }
   }
 }

#ifdef REGEXP_DEBUG
 if (log_fd != stderr) {
   fclose(log_fd);
 }
 log_fd = NULL;
#endif
 // Have to clear the lastlist field of the NFA nodes, so that
 // nfa_regmatch() and addstate() can run properly after recursion.
 if (nfa_ll_index == 1) {
   // Already calling nfa_regmatch() recursively.  Save the lastlist[1]
   // values and clear them.
   if (*listids == NULL || *listids_len < prog->nstate) {
     xfree(*listids);
     *listids = xmalloc(sizeof(**listids) * (size_t)prog->nstate);
     *listids_len = prog->nstate;
   }
   nfa_save_listids(prog, *listids);
   need_restore = true;
   // any value of rex.nfa_listid will do
 } else {
   // First recursive nfa_regmatch() call, switch to the second lastlist
   // entry.  Make sure rex.nfa_listid is different from a previous
   // recursive call, because some states may still have this ID.
   nfa_ll_index++;
   if (rex.nfa_listid <= rex.nfa_alt_listid) {
     rex.nfa_listid = rex.nfa_alt_listid;
   }
 }

 // Call nfa_regmatch() to check if the current concat matches at this
 // position. The concat ends with the node NFA_END_INVISIBLE
 nfa_endp = endposp;
 const int result = nfa_regmatch(prog, state->out, submatch, m);

 if (need_restore) {
   nfa_restore_listids(prog, *listids);
 } else {
   nfa_ll_index--;
   rex.nfa_alt_listid = rex.nfa_listid;
 }

 // restore position in input text
 rex.lnum = save_reglnum;
 if (REG_MULTI) {
   rex.line = (uint8_t *)reg_getline(rex.lnum);
 }
 rex.input = rex.line + save_reginput_col;
 if (result != NFA_TOO_EXPENSIVE) {
   nfa_match = save_nfa_match;
   rex.nfa_listid = save_nfa_listid;
 }
 nfa_endp = save_nfa_endp;

#ifdef REGEXP_DEBUG
 open_debug_log(result);
#endif

 return result;
}

// Estimate the chance of a match with "state" failing.
// empty match: 0
// NFA_ANY: 1
// specific character: 99
static int failure_chance(nfa_state_T *state, int depth)
{
 int c = state->c;
 int l, r;

 // detect looping
 if (depth > 4) {
   return 1;
 }

 switch (c) {
 case NFA_SPLIT:
   if (state->out->c == NFA_SPLIT || state->out1->c == NFA_SPLIT) {
     // avoid recursive stuff
     return 1;
   }
   // two alternatives, use the lowest failure chance
   l = failure_chance(state->out, depth + 1);
   r = failure_chance(state->out1, depth + 1);
   return l < r ? l : r;

 case NFA_ANY:
   // matches anything, unlikely to fail
   return 1;

 case NFA_MATCH:
 case NFA_MCLOSE:
 case NFA_ANY_COMPOSING:
   // empty match works always
   return 0;

 case NFA_START_INVISIBLE:
 case NFA_START_INVISIBLE_FIRST:
 case NFA_START_INVISIBLE_NEG:
 case NFA_START_INVISIBLE_NEG_FIRST:
 case NFA_START_INVISIBLE_BEFORE:
 case NFA_START_INVISIBLE_BEFORE_FIRST:
 case NFA_START_INVISIBLE_BEFORE_NEG:
 case NFA_START_INVISIBLE_BEFORE_NEG_FIRST:
 case NFA_START_PATTERN:
   // recursive regmatch is expensive, use low failure chance
   return 5;

 case NFA_BOL:
 case NFA_EOL:
 case NFA_BOF:
 case NFA_EOF:
 case NFA_NEWL:
   return 99;

 case NFA_BOW:
 case NFA_EOW:
   return 90;

 case NFA_MOPEN:
 case NFA_MOPEN1:
 case NFA_MOPEN2:
 case NFA_MOPEN3:
 case NFA_MOPEN4:
 case NFA_MOPEN5:
 case NFA_MOPEN6:
 case NFA_MOPEN7:
 case NFA_MOPEN8:
 case NFA_MOPEN9:
 case NFA_ZOPEN:
 case NFA_ZOPEN1:
 case NFA_ZOPEN2:
 case NFA_ZOPEN3:
 case NFA_ZOPEN4:
 case NFA_ZOPEN5:
 case NFA_ZOPEN6:
 case NFA_ZOPEN7:
 case NFA_ZOPEN8:
 case NFA_ZOPEN9:
 case NFA_ZCLOSE:
 case NFA_ZCLOSE1:
 case NFA_ZCLOSE2:
 case NFA_ZCLOSE3:
 case NFA_ZCLOSE4:
 case NFA_ZCLOSE5:
 case NFA_ZCLOSE6:
 case NFA_ZCLOSE7:
 case NFA_ZCLOSE8:
 case NFA_ZCLOSE9:
 case NFA_NOPEN:
 case NFA_MCLOSE1:
 case NFA_MCLOSE2:
 case NFA_MCLOSE3:
 case NFA_MCLOSE4:
 case NFA_MCLOSE5:
 case NFA_MCLOSE6:
 case NFA_MCLOSE7:
 case NFA_MCLOSE8:
 case NFA_MCLOSE9:
 case NFA_NCLOSE:
   return failure_chance(state->out, depth + 1);

 case NFA_BACKREF1:
 case NFA_BACKREF2:
 case NFA_BACKREF3:
 case NFA_BACKREF4:
 case NFA_BACKREF5:
 case NFA_BACKREF6:
 case NFA_BACKREF7:
 case NFA_BACKREF8:
 case NFA_BACKREF9:
 case NFA_ZREF1:
 case NFA_ZREF2:
 case NFA_ZREF3:
 case NFA_ZREF4:
 case NFA_ZREF5:
 case NFA_ZREF6:
 case NFA_ZREF7:
 case NFA_ZREF8:
 case NFA_ZREF9:
   // backreferences don't match in many places
   return 94;

 case NFA_LNUM_GT:
 case NFA_LNUM_LT:
 case NFA_COL_GT:
 case NFA_COL_LT:
 case NFA_VCOL_GT:
 case NFA_VCOL_LT:
 case NFA_MARK_GT:
 case NFA_MARK_LT:
 case NFA_VISUAL:
   // before/after positions don't match very often
   return 85;

 case NFA_LNUM:
   return 90;

 case NFA_CURSOR:
 case NFA_COL:
 case NFA_VCOL:
 case NFA_MARK:
   // specific positions rarely match
   return 98;

 case NFA_COMPOSING:
   return 95;

 default:
   if (c > 0) {
     // character match fails often
     return 95;
   }
 }

 // something else, includes character classes
 return 50;
}

// Skip until the char "c" we know a match must start with.
static int skip_to_start(int c, colnr_T *colp)
{
 const uint8_t *const s = (uint8_t *)cstrchr((char *)rex.line + *colp, c);
 if (s == NULL) {
   return FAIL;
 }
 *colp = (int)(s - rex.line);
 return OK;
}

// Check for a match with match_text.
// Called after skip_to_start() has found regstart.
// Returns zero for no match, 1 for a match.
static int find_match_text(colnr_T *startcol, int regstart, uint8_t *match_text)
{
 colnr_T col = *startcol;
 const int regstart_len = utf_char2len(regstart);

 while (true) {
   bool match = true;
   uint8_t *s1 = match_text;
   // skip regstart
   int regstart_len2 = regstart_len;
   if (regstart_len2 > 1 && utf_ptr2len((char *)rex.line + col) != regstart_len2) {
     // because of case-folding of the previously matched text, we may need
     // to skip fewer bytes than utf_char2len(regstart)
     regstart_len2 = utf_char2len(utf_fold(regstart));
   }
   uint8_t *s2 = rex.line + col + regstart_len2;
   while (*s1) {
     int c1_len = utf_ptr2len((char *)s1);
     int c1 = utf_ptr2char((char *)s1);
     int c2_len = utf_ptr2len((char *)s2);
     int c2 = utf_ptr2char((char *)s2);
     if (c1 != c2 && (!rex.reg_ic || utf_fold(c1) != utf_fold(c2))) {
       match = false;
       break;
     }
     s1 += c1_len;
     s2 += c2_len;
   }
   if (match
       // check that no composing char follows
       && !utf_iscomposing_legacy(utf_ptr2char((char *)s2))) {
     cleanup_subexpr();
     if (REG_MULTI) {
       rex.reg_startpos[0].lnum = rex.lnum;
       rex.reg_startpos[0].col = col;
       rex.reg_endpos[0].lnum = rex.lnum;
       rex.reg_endpos[0].col = (colnr_T)(s2 - rex.line);
     } else {
       rex.reg_startp[0] = rex.line + col;
       rex.reg_endp[0] = s2;
     }
     *startcol = col;
     return 1L;
   }

   // Try finding regstart after the current match.
   col += regstart_len;  // skip regstart
   if (skip_to_start(regstart, &col) == FAIL) {
     break;
   }
 }

 *startcol = col;
 return 0L;
}

static int nfa_did_time_out(void)
{
 if (nfa_time_limit != NULL && profile_passed_limit(*nfa_time_limit)) {
   if (nfa_timed_out != NULL) {
     *nfa_timed_out = true;
   }
   return true;
 }
 return false;
}

/// Main matching routine.
///
/// Run NFA to determine whether it matches rex.input.
///
/// When "nfa_endp" is not NULL it is a required end-of-match position.
///
/// Return true if there is a match, false if there is no match,
/// NFA_TOO_EXPENSIVE if we end up with too many states.
/// When there is a match "submatch" contains the positions.
///
/// Note: Caller must ensure that: start != NULL.
static int nfa_regmatch(nfa_regprog_T *prog, nfa_state_T *start, regsubs_T *submatch, regsubs_T *m)
 FUNC_ATTR_NONNULL_ARG(1, 2, 4)
{
 int result = false;
 int flag = 0;
 bool go_to_nextline = false;
 nfa_thread_T *t;
 nfa_list_T list[2];
 int listidx;
 nfa_list_T *thislist;
 nfa_list_T *nextlist;
 int *listids = NULL;
 int listids_len = 0;
 nfa_state_T *add_state;
 bool add_here;
 int add_count;
 int add_off = 0;
 int toplevel = start->c == NFA_MOPEN;
 regsubs_T *r;
 // Some patterns may take a long time to match, especially when using
 // recursive_regmatch(). Allow interrupting them with CTRL-C.
 reg_breakcheck();
 if (got_int) {
   return false;
 }
 if (nfa_did_time_out()) {
   return false;
 }

#ifdef NFA_REGEXP_DEBUG_LOG
 FILE *debug = fopen(NFA_REGEXP_DEBUG_LOG, "a");

 if (debug == NULL) {
   semsg("(NFA) COULD NOT OPEN %s!", NFA_REGEXP_DEBUG_LOG);
   return false;
 }
#endif
 nfa_match = false;

 // Allocate memory for the lists of nodes.
 size_t size = (size_t)(prog->nstate + 1) * sizeof(nfa_thread_T);
 list[0].t = xmalloc(size);
 list[0].len = prog->nstate + 1;
 list[1].t = xmalloc(size);
 list[1].len = prog->nstate + 1;

#ifdef REGEXP_DEBUG
 log_fd = fopen(NFA_REGEXP_RUN_LOG, "a");
 if (log_fd == NULL) {
   emsg(_(e_log_open_failed));
   log_fd = stderr;
 }
 fprintf(log_fd, "**********************************\n");
 nfa_set_code(start->c);
 fprintf(log_fd, " RUNNING nfa_regmatch() starting with state %d, code %s\n",
         abs(start->id), code);
 fprintf(log_fd, "**********************************\n");
#endif

 thislist = &list[0];
 thislist->n = 0;
 thislist->has_pim = false;
 nextlist = &list[1];
 nextlist->n = 0;
 nextlist->has_pim = false;
#ifdef REGEXP_DEBUG
 fprintf(log_fd, "(---) STARTSTATE first\n");
#endif
 thislist->id = rex.nfa_listid + 1;

 // Inline optimized code for addstate(thislist, start, m, 0) if we know
 // it's the first MOPEN.
 if (toplevel) {
   if (REG_MULTI) {
     m->norm.list.multi[0].start_lnum = rex.lnum;
     m->norm.list.multi[0].start_col = (colnr_T)(rex.input - rex.line);
     m->norm.orig_start_col = m->norm.list.multi[0].start_col;
   } else {
     m->norm.list.line[0].start = rex.input;
   }
   m->norm.in_use = 1;
   r = addstate(thislist, start->out, m, NULL, 0);
 } else {
   r = addstate(thislist, start, m, NULL, 0);
 }
 if (r == NULL) {
   nfa_match = NFA_TOO_EXPENSIVE;
   goto theend;
 }

#define ADD_STATE_IF_MATCH(state) \
 if (result) { \
   add_state = (state)->out; \
   add_off = clen; \
 }

 // Run for each character.
 while (true) {
   int curc = utf_ptr2char((char *)rex.input);
   int clen = utfc_ptr2len((char *)rex.input);
   if (curc == NUL) {
     clen = 0;
     go_to_nextline = false;
   }

   // swap lists
   thislist = &list[flag];
   nextlist = &list[flag ^= 1];
   nextlist->n = 0;                // clear nextlist
   nextlist->has_pim = false;
   rex.nfa_listid++;
   if (prog->re_engine == AUTOMATIC_ENGINE
       && (rex.nfa_listid >= NFA_MAX_STATES)) {
     // Too many states, retry with old engine.
     nfa_match = NFA_TOO_EXPENSIVE;
     goto theend;
   }

   thislist->id = rex.nfa_listid;
   nextlist->id = rex.nfa_listid + 1;

#ifdef REGEXP_DEBUG
   fprintf(log_fd, "------------------------------------------\n");
   fprintf(log_fd, ">>> Reginput is \"%s\"\n", rex.input);
   fprintf(log_fd,
           ">>> Advanced one character... Current char is %c (code %d) \n",
           curc,
           (int)curc);
   fprintf(log_fd, ">>> Thislist has %d states available: ", thislist->n);
   {
     int i;

     for (i = 0; i < thislist->n; i++) {
       fprintf(log_fd, "%d  ", abs(thislist->t[i].state->id));
     }
   }
   fprintf(log_fd, "\n");
#endif

#ifdef NFA_REGEXP_DEBUG_LOG
   fprintf(debug, "\n-------------------\n");
#endif
   // If the state lists are empty we can stop.
   if (thislist->n == 0) {
     break;
   }

   // compute nextlist
   for (listidx = 0; listidx < thislist->n; listidx++) {
     // If the list gets very long there probably is something wrong.
     // At least allow interrupting with CTRL-C.
     reg_breakcheck();
     if (got_int) {
       break;
     }
     if (nfa_time_limit != NULL && ++nfa_time_count == 20) {
       nfa_time_count = 0;
       if (nfa_did_time_out()) {
         break;
       }
     }
     t = &thislist->t[listidx];

#ifdef NFA_REGEXP_DEBUG_LOG
     nfa_set_code(t->state->c);
     fprintf(debug, "%s, ", code);
#endif
#ifdef REGEXP_DEBUG
     {
       int col;

       if (t->subs.norm.in_use <= 0) {
         col = -1;
       } else if (REG_MULTI) {
         col = t->subs.norm.list.multi[0].start_col;
       } else {
         col = (int)(t->subs.norm.list.line[0].start - rex.line);
       }
       nfa_set_code(t->state->c);
       fprintf(log_fd, "(%d) char %d %s (start col %d)%s... \n",
               abs(t->state->id), (int)t->state->c, code, col,
               pim_info(&t->pim));
     }
#endif

     // Handle the possible codes of the current state.
     // The most important is NFA_MATCH.
     add_state = NULL;
     add_here = false;
     add_count = 0;
     switch (t->state->c) {
     case NFA_MATCH:
       // If the match is not at the start of the line, ends before a
       // composing characters and rex.reg_icombine is not set, that
       // is not really a match.
       if (!rex.reg_icombine
           && rex.input != rex.line
           && utf_iscomposing_legacy(curc)) {
         break;
       }
       nfa_match = true;
       copy_sub(&submatch->norm, &t->subs.norm);
       if (rex.nfa_has_zsubexpr) {
         copy_sub(&submatch->synt, &t->subs.synt);
       }
#ifdef REGEXP_DEBUG
       log_subsexpr(&t->subs);
#endif
       // Found the left-most longest match, do not look at any other
       // states at this position.  When the list of states is going
       // to be empty quit without advancing, so that "rex.input" is
       // correct.
       if (nextlist->n == 0) {
         clen = 0;
       }
       goto nextchar;

     case NFA_END_INVISIBLE:
     case NFA_END_INVISIBLE_NEG:
     case NFA_END_PATTERN:
       // This is only encountered after a NFA_START_INVISIBLE or
       // NFA_START_INVISIBLE_BEFORE node.
       // They surround a zero-width group, used with "\@=", "\&",
       // "\@!", "\@<=" and "\@<!".
       // If we got here, it means that the current "invisible" group
       // finished successfully, so return control to the parent
       // nfa_regmatch().  For a look-behind match only when it ends
       // in the position in "nfa_endp".
       // Submatches are stored in *m, and used in the parent call.
#ifdef REGEXP_DEBUG
       if (nfa_endp != NULL) {
         if (REG_MULTI) {
           fprintf(log_fd,
                   "Current lnum: %d, endp lnum: %d;"
                   " current col: %d, endp col: %d\n",
                   (int)rex.lnum,
                   (int)nfa_endp->se_u.pos.lnum,
                   (int)(rex.input - rex.line),
                   nfa_endp->se_u.pos.col);
         } else {
           fprintf(log_fd, "Current col: %d, endp col: %d\n",
                   (int)(rex.input - rex.line),
                   (int)(nfa_endp->se_u.ptr - rex.input));
         }
       }
#endif
       // If "nfa_endp" is set it's only a match if it ends at
       // "nfa_endp"
       if (nfa_endp != NULL
           && (REG_MULTI
               ? (rex.lnum != nfa_endp->se_u.pos.lnum
                  || (int)(rex.input - rex.line) != nfa_endp->se_u.pos.col)
               : rex.input != nfa_endp->se_u.ptr)) {
         break;
       }
       // do not set submatches for \@!
       if (t->state->c != NFA_END_INVISIBLE_NEG) {
         copy_sub(&m->norm, &t->subs.norm);
         if (rex.nfa_has_zsubexpr) {
           copy_sub(&m->synt, &t->subs.synt);
         }
       }
#ifdef REGEXP_DEBUG
       fprintf(log_fd, "Match found:\n");
       log_subsexpr(m);
#endif
       nfa_match = true;
       // See comment above at "goto nextchar".
       if (nextlist->n == 0) {
         clen = 0;
       }
       goto nextchar;

     case NFA_START_INVISIBLE:
     case NFA_START_INVISIBLE_FIRST:
     case NFA_START_INVISIBLE_NEG:
     case NFA_START_INVISIBLE_NEG_FIRST:
     case NFA_START_INVISIBLE_BEFORE:
     case NFA_START_INVISIBLE_BEFORE_FIRST:
     case NFA_START_INVISIBLE_BEFORE_NEG:
     case NFA_START_INVISIBLE_BEFORE_NEG_FIRST:
#ifdef REGEXP_DEBUG
       fprintf(log_fd, "Failure chance invisible: %d, what follows: %d\n",
               failure_chance(t->state->out, 0),
               failure_chance(t->state->out1->out, 0));
#endif
       // Do it directly if there already is a PIM or when
       // nfa_postprocess() detected it will work better.
       if (t->pim.result != NFA_PIM_UNUSED
           || t->state->c == NFA_START_INVISIBLE_FIRST
           || t->state->c == NFA_START_INVISIBLE_NEG_FIRST
           || t->state->c == NFA_START_INVISIBLE_BEFORE_FIRST
           || t->state->c == NFA_START_INVISIBLE_BEFORE_NEG_FIRST) {
         int in_use = m->norm.in_use;

         // Copy submatch info for the recursive call, opposite
         // of what happens on success below.
         copy_sub_off(&m->norm, &t->subs.norm);
         if (rex.nfa_has_zsubexpr) {
           copy_sub_off(&m->synt, &t->subs.synt);
         }
         // First try matching the invisible match, then what
         // follows.
         result = recursive_regmatch(t->state, NULL, prog, submatch, m,
                                     &listids, &listids_len);
         if (result == NFA_TOO_EXPENSIVE) {
           nfa_match = result;
           goto theend;
         }

         // for \@! and \@<! it is a match when the result is
         // false
         if (result != (t->state->c == NFA_START_INVISIBLE_NEG
                        || t->state->c == NFA_START_INVISIBLE_NEG_FIRST
                        || t->state->c
                        == NFA_START_INVISIBLE_BEFORE_NEG
                        || t->state->c
                        == NFA_START_INVISIBLE_BEFORE_NEG_FIRST)) {
           // Copy submatch info from the recursive call
           copy_sub_off(&t->subs.norm, &m->norm);
           if (rex.nfa_has_zsubexpr) {
             copy_sub_off(&t->subs.synt, &m->synt);
           }
           // If the pattern has \ze and it matched in the
           // sub pattern, use it.
           copy_ze_off(&t->subs.norm, &m->norm);

           // t->state->out1 is the corresponding
           // END_INVISIBLE node; Add its out to the current
           // list (zero-width match).
           add_here = true;
           add_state = t->state->out1->out;
         }
         m->norm.in_use = in_use;
       } else {
         nfa_pim_T pim;

         // First try matching what follows.  Only if a match
         // is found verify the invisible match matches.  Add a
         // nfa_pim_T to the following states, it contains info
         // about the invisible match.
         pim.state = t->state;
         pim.result = NFA_PIM_TODO;
         pim.subs.norm.in_use = 0;
         pim.subs.synt.in_use = 0;
         if (REG_MULTI) {
           pim.end.pos.col = (int)(rex.input - rex.line);
           pim.end.pos.lnum = rex.lnum;
         } else {
           pim.end.ptr = rex.input;
         }
         // t->state->out1 is the corresponding END_INVISIBLE
         // node; Add its out to the current list (zero-width
         // match).
         if (addstate_here(thislist, t->state->out1->out, &t->subs,
                           &pim, &listidx) == NULL) {
           nfa_match = NFA_TOO_EXPENSIVE;
           goto theend;
         }
       }
       break;

     case NFA_START_PATTERN: {
       nfa_state_T *skip = NULL;
#ifdef REGEXP_DEBUG
       int skip_lid = 0;
#endif

       // There is no point in trying to match the pattern if the
       // output state is not going to be added to the list.
       if (state_in_list(nextlist, t->state->out1->out, &t->subs)) {
         skip = t->state->out1->out;
#ifdef REGEXP_DEBUG
         skip_lid = nextlist->id;
#endif
       } else if (state_in_list(nextlist,
                                t->state->out1->out->out, &t->subs)) {
         skip = t->state->out1->out->out;
#ifdef REGEXP_DEBUG
         skip_lid = nextlist->id;
#endif
       } else if (state_in_list(thislist,
                                t->state->out1->out->out, &t->subs)) {
         skip = t->state->out1->out->out;
#ifdef REGEXP_DEBUG
         skip_lid = thislist->id;
#endif
       }
       if (skip != NULL) {
#ifdef REGEXP_DEBUG
         nfa_set_code(skip->c);
         fprintf(log_fd,
                 "> Not trying to match pattern, output state %d is already in list %d. char %d: %s\n",
                 abs(skip->id), skip_lid, skip->c, code);
#endif
         break;
       }
       // Copy submatch info to the recursive call, opposite of what
       // happens afterwards.
       copy_sub_off(&m->norm, &t->subs.norm);
       if (rex.nfa_has_zsubexpr) {
         copy_sub_off(&m->synt, &t->subs.synt);
       }

       // First try matching the pattern.
       result = recursive_regmatch(t->state, NULL, prog, submatch, m,
                                   &listids, &listids_len);
       if (result == NFA_TOO_EXPENSIVE) {
         nfa_match = result;
         goto theend;
       }
       if (result) {
         int bytelen;

#ifdef REGEXP_DEBUG
         fprintf(log_fd, "NFA_START_PATTERN matches:\n");
         log_subsexpr(m);
#endif
         // Copy submatch info from the recursive call
         copy_sub_off(&t->subs.norm, &m->norm);
         if (rex.nfa_has_zsubexpr) {
           copy_sub_off(&t->subs.synt, &m->synt);
         }
         // Now we need to skip over the matched text and then
         // continue with what follows.
         if (REG_MULTI) {
           // TODO(RE): multi-line match
           bytelen = m->norm.list.multi[0].end_col
                     - (int)(rex.input - rex.line);
         } else {
           bytelen = (int)(m->norm.list.line[0].end - rex.input);
         }

#ifdef REGEXP_DEBUG
         fprintf(log_fd, "NFA_START_PATTERN length: %d\n", bytelen);
#endif
         if (bytelen == 0) {
           // empty match, output of corresponding
           // NFA_END_PATTERN/NFA_SKIP to be used at current
           // position
           add_here = true;
           add_state = t->state->out1->out->out;
         } else if (bytelen <= clen) {
           // match current character, output of corresponding
           // NFA_END_PATTERN to be used at next position.
           add_state = t->state->out1->out->out;
           add_off = clen;
         } else {
           // skip over the matched characters, set character
           // count in NFA_SKIP
           add_state = t->state->out1->out;
           add_off = bytelen;
           add_count = bytelen - clen;
         }
       }
       break;
     }

     case NFA_BOL:
       if (rex.input == rex.line) {
         add_here = true;
         add_state = t->state->out;
       }
       break;

     case NFA_EOL:
       if (curc == NUL) {
         add_here = true;
         add_state = t->state->out;
       }
       break;

     case NFA_BOW:
       result = true;

       if (curc == NUL) {
         result = false;
       } else {
         int this_class;

         // Get class of current and previous char (if it exists).
         this_class = mb_get_class_tab((char *)rex.input, rex.reg_buf->b_chartab);
         if (this_class <= 1) {
           result = false;
         } else if (reg_prev_class() == this_class) {
           result = false;
         }
       }
       if (result) {
         add_here = true;
         add_state = t->state->out;
       }
       break;

     case NFA_EOW:
       result = true;
       if (rex.input == rex.line) {
         result = false;
       } else {
         int this_class, prev_class;

         // Get class of current and previous char (if it exists).
         this_class = mb_get_class_tab((char *)rex.input, rex.reg_buf->b_chartab);
         prev_class = reg_prev_class();
         if (this_class == prev_class
             || prev_class == 0 || prev_class == 1) {
           result = false;
         }
       }
       if (result) {
         add_here = true;
         add_state = t->state->out;
       }
       break;

     case NFA_BOF:
       if (rex.lnum == 0 && rex.input == rex.line
           && (!REG_MULTI || rex.reg_firstlnum == 1)) {
         add_here = true;
         add_state = t->state->out;
       }
       break;

     case NFA_EOF:
       if (rex.lnum == rex.reg_maxline && curc == NUL) {
         add_here = true;
         add_state = t->state->out;
       }
       break;

     case NFA_COMPOSING: {
       int mc = curc;
       int len = 0;
       nfa_state_T *end;
       nfa_state_T *sta;
       int cchars[MAX_MCO];
       int ccount = 0;
       int j;

       sta = t->state->out;
       len = 0;
       if (utf_iscomposing_legacy(sta->c)) {
         // Only match composing character(s), ignore base
         // character.  Used for ".{composing}" and "{composing}"
         // (no preceding character).
         len += utf_char2len(mc);
       }
       if (rex.reg_icombine && len == 0) {
         // If \Z was present, then ignore composing characters.
         // When ignoring the base character this always matches.
         if (sta->c != curc) {
           result = FAIL;
         } else {
           result = OK;
         }
         while (sta->c != NFA_END_COMPOSING) {
           sta = sta->out;
         }
       } else if (len > 0 || mc == sta->c) {
         // Check base character matches first, unless ignored.
         if (len == 0) {
           len += utf_char2len(mc);
           sta = sta->out;
         }

         // We don't care about the order of composing characters.
         // Get them into cchars[] first.
         while (len < clen) {
           mc = utf_ptr2char((char *)rex.input + len);
           cchars[ccount++] = mc;
           len += utf_char2len(mc);
           if (ccount == MAX_MCO) {
             break;
           }
         }

         // Check that each composing char in the pattern matches a
         // composing char in the text.  We do not check if all
         // composing chars are matched.
         result = OK;
         while (sta->c != NFA_END_COMPOSING) {
           for (j = 0; j < ccount; j++) {
             if (cchars[j] == sta->c) {
               break;
             }
           }
           if (j == ccount) {
             result = FAIL;
             break;
           }
           sta = sta->out;
         }
       } else {
         result = FAIL;
       }

       end = t->state->out1;               // NFA_END_COMPOSING
       ADD_STATE_IF_MATCH(end);
       break;
     }

     case NFA_NEWL:
       if (curc == NUL && !rex.reg_line_lbr && REG_MULTI
           && rex.lnum <= rex.reg_maxline) {
         go_to_nextline = true;
         // Pass -1 for the offset, which means taking the position
         // at the start of the next line.
         add_state = t->state->out;
         add_off = -1;
       } else if (curc == '\n' && rex.reg_line_lbr) {
         // match \n as if it is an ordinary character
         add_state = t->state->out;
         add_off = 1;
       }
       break;

     case NFA_START_COLL:
     case NFA_START_NEG_COLL: {
       // What follows is a list of characters, until NFA_END_COLL.
       // One of them must match or none of them must match.
       nfa_state_T *state;
       int result_if_matched;
       int c1, c2;

       // Never match EOL. If it's part of the collection it is added
       // as a separate state with an OR.
       if (curc == NUL) {
         break;
       }

       state = t->state->out;
       result_if_matched = (t->state->c == NFA_START_COLL);
       while (true) {
         if (state->c == NFA_COMPOSING) {
           int mc = curc;
           int len = 0;
           nfa_state_T *end;
           nfa_state_T *sta;
           int cchars[MAX_MCO];
           int ccount = 0;
           int j;

           sta = t->state->out->out;
           if (utf_iscomposing_legacy(sta->c)) {
             // Only match composing character(s), ignore base
             // character.  Used for ".{composing}" and "{composing}"
             // (no preceding character).
             len += utf_char2len(mc);
           }
           if (rex.reg_icombine && len == 0) {
             // If \Z was present, then ignore composing characters.
             // When ignoring the base character this always matches.
             if (sta->c != curc) {
               result = FAIL;
             } else {
               result = OK;
             }
             while (sta->c != NFA_END_COMPOSING) {
               sta = sta->out;
             }
           }
           // Check base character matches first, unless ignored.
           else if (len > 0 || mc == sta->c) {
             if (len == 0) {
               len += utf_char2len(mc);
               sta = sta->out;
             }

             // We don't care about the order of composing characters.
             // Get them into cchars[] first.
             while (len < clen) {
               mc = utf_ptr2char((char *)rex.input + len);
               cchars[ccount++] = mc;
               len += utf_char2len(mc);
               if (ccount == MAX_MCO) {
                 break;
               }
             }

             // Check that each composing char in the pattern matches a
             // composing char in the text.  We do not check if all
             // composing chars are matched.
             result = OK;
             while (sta->c != NFA_END_COMPOSING) {
               for (j = 0; j < ccount; j++) {
                 if (cchars[j] == sta->c) {
                   break;
                 }
               }
               if (j == ccount) {
                 result = FAIL;
                 break;
               }
               sta = sta->out;
             }
           } else {
             result = FAIL;
           }

           if (t->state->out->out1 != NULL
               && t->state->out->out1->c == NFA_END_COMPOSING) {
             end = t->state->out->out1;
             ADD_STATE_IF_MATCH(end);
           }
           break;
         }
         if (state->c == NFA_END_COLL) {
           result = !result_if_matched;
           break;
         }
         if (state->c == NFA_RANGE_MIN) {
           c1 = state->val;
           state = state->out;             // advance to NFA_RANGE_MAX
           c2 = state->val;
#ifdef REGEXP_DEBUG
           fprintf(log_fd, "NFA_RANGE_MIN curc=%d c1=%d c2=%d\n",
                   curc, c1, c2);
#endif
           if (curc >= c1 && curc <= c2) {
             result = result_if_matched;
             break;
           }
           if (rex.reg_ic) {
             int curc_low = utf_fold(curc);
             int done = false;

             for (; c1 <= c2; c1++) {
               if (utf_fold(c1) == curc_low) {
                 result = result_if_matched;
                 done = true;
                 break;
               }
             }
             if (done) {
               break;
             }
           }
         } else if (state->c < 0 ? check_char_class(state->c, curc)
                                 : (curc == state->c
                                    || (rex.reg_ic
                                        && utf_fold(curc) == utf_fold(state->c)))) {
           result = result_if_matched;
           break;
         }
         state = state->out;
       }
       if (result) {
         // next state is in out of the NFA_END_COLL, out1 of
         // START points to the END state
         add_state = t->state->out1->out;
         add_off = clen;
       }
       break;
     }

     case NFA_ANY:
       // Any char except NUL, (end of input) does not match.
       if (curc > 0) {
         add_state = t->state->out;
         add_off = clen;
       }
       break;

     case NFA_ANY_COMPOSING:
       // On a composing character skip over it.  Otherwise do
       // nothing.  Always matches.
       if (utf_iscomposing_legacy(curc)) {
         add_off = clen;
       } else {
         add_here = true;
         add_off = 0;
       }
       add_state = t->state->out;
       break;

     // Character classes like \a for alpha, \d for digit etc.
     case NFA_IDENT:           //  \i
       result = vim_isIDc(curc);
       ADD_STATE_IF_MATCH(t->state);
       break;

     case NFA_SIDENT:          //  \I
       result = !ascii_isdigit(curc) && vim_isIDc(curc);
       ADD_STATE_IF_MATCH(t->state);
       break;

     case NFA_KWORD:           //  \k
       result = vim_iswordp_buf((char *)rex.input, rex.reg_buf);
       ADD_STATE_IF_MATCH(t->state);
       break;

     case NFA_SKWORD:          //  \K
       result = !ascii_isdigit(curc)
                && vim_iswordp_buf((char *)rex.input, rex.reg_buf);
       ADD_STATE_IF_MATCH(t->state);
       break;

     case NFA_FNAME:           //  \f
       result = vim_isfilec(curc);
       ADD_STATE_IF_MATCH(t->state);
       break;

     case NFA_SFNAME:          //  \F
       result = !ascii_isdigit(curc) && vim_isfilec(curc);
       ADD_STATE_IF_MATCH(t->state);
       break;

     case NFA_PRINT:           //  \p
       result = vim_isprintc(utf_ptr2char((char *)rex.input));
       ADD_STATE_IF_MATCH(t->state);
       break;

     case NFA_SPRINT:          //  \P
       result = !ascii_isdigit(curc) && vim_isprintc(utf_ptr2char((char *)rex.input));
       ADD_STATE_IF_MATCH(t->state);
       break;

     case NFA_WHITE:           //  \s
       result = ascii_iswhite(curc);
       ADD_STATE_IF_MATCH(t->state);
       break;

     case NFA_NWHITE:          //  \S
       result = curc != NUL && !ascii_iswhite(curc);
       ADD_STATE_IF_MATCH(t->state);
       break;

     case NFA_DIGIT:           //  \d
       result = ri_digit(curc);
       ADD_STATE_IF_MATCH(t->state);
       break;

     case NFA_NDIGIT:          //  \D
       result = curc != NUL && !ri_digit(curc);
       ADD_STATE_IF_MATCH(t->state);
       break;

     case NFA_HEX:             //  \x
       result = ri_hex(curc);
       ADD_STATE_IF_MATCH(t->state);
       break;

     case NFA_NHEX:            //  \X
       result = curc != NUL && !ri_hex(curc);
       ADD_STATE_IF_MATCH(t->state);
       break;

     case NFA_OCTAL:           //  \o
       result = ri_octal(curc);
       ADD_STATE_IF_MATCH(t->state);
       break;

     case NFA_NOCTAL:          //  \O
       result = curc != NUL && !ri_octal(curc);
       ADD_STATE_IF_MATCH(t->state);
       break;

     case NFA_WORD:            //  \w
       result = ri_word(curc);
       ADD_STATE_IF_MATCH(t->state);
       break;

     case NFA_NWORD:           //  \W
       result = curc != NUL && !ri_word(curc);
       ADD_STATE_IF_MATCH(t->state);
       break;

     case NFA_HEAD:            //  \h
       result = ri_head(curc);
       ADD_STATE_IF_MATCH(t->state);
       break;

     case NFA_NHEAD:           //  \H
       result = curc != NUL && !ri_head(curc);
       ADD_STATE_IF_MATCH(t->state);
       break;

     case NFA_ALPHA:           //  \a
       result = ri_alpha(curc);
       ADD_STATE_IF_MATCH(t->state);
       break;

     case NFA_NALPHA:          //  \A
       result = curc != NUL && !ri_alpha(curc);
       ADD_STATE_IF_MATCH(t->state);
       break;

     case NFA_LOWER:           //  \l
       result = ri_lower(curc);
       ADD_STATE_IF_MATCH(t->state);
       break;

     case NFA_NLOWER:          //  \L
       result = curc != NUL && !ri_lower(curc);
       ADD_STATE_IF_MATCH(t->state);
       break;

     case NFA_UPPER:           //  \u
       result = ri_upper(curc);
       ADD_STATE_IF_MATCH(t->state);
       break;

     case NFA_NUPPER:          // \U
       result = curc != NUL && !ri_upper(curc);
       ADD_STATE_IF_MATCH(t->state);
       break;

     case NFA_LOWER_IC:        // [a-z]
       result = ri_lower(curc) || (rex.reg_ic && ri_upper(curc));
       ADD_STATE_IF_MATCH(t->state);
       break;

     case NFA_NLOWER_IC:       // [^a-z]
       result = curc != NUL
                && !(ri_lower(curc) || (rex.reg_ic && ri_upper(curc)));
       ADD_STATE_IF_MATCH(t->state);
       break;

     case NFA_UPPER_IC:        // [A-Z]
       result = ri_upper(curc) || (rex.reg_ic && ri_lower(curc));
       ADD_STATE_IF_MATCH(t->state);
       break;

     case NFA_NUPPER_IC:       // [^A-Z]
       result = curc != NUL
                && !(ri_upper(curc) || (rex.reg_ic && ri_lower(curc)));
       ADD_STATE_IF_MATCH(t->state);
       break;

     case NFA_BACKREF1:
     case NFA_BACKREF2:
     case NFA_BACKREF3:
     case NFA_BACKREF4:
     case NFA_BACKREF5:
     case NFA_BACKREF6:
     case NFA_BACKREF7:
     case NFA_BACKREF8:
     case NFA_BACKREF9:
     case NFA_ZREF1:
     case NFA_ZREF2:
     case NFA_ZREF3:
     case NFA_ZREF4:
     case NFA_ZREF5:
     case NFA_ZREF6:
     case NFA_ZREF7:
     case NFA_ZREF8:
     case NFA_ZREF9:
       // \1 .. \9  \z1 .. \z9
     {
       int subidx;
       int bytelen;

       if (t->state->c >= NFA_BACKREF1 && t->state->c <= NFA_BACKREF9) {
         subidx = t->state->c - NFA_BACKREF1 + 1;
         result = match_backref(&t->subs.norm, subidx, &bytelen);
       } else {
         subidx = t->state->c - NFA_ZREF1 + 1;
         result = match_zref(subidx, &bytelen);
       }

       if (result) {
         if (bytelen == 0) {
           // empty match always works, output of NFA_SKIP to be
           // used next
           add_here = true;
           add_state = t->state->out->out;
         } else if (bytelen <= clen) {
           // match current character, jump ahead to out of
           // NFA_SKIP
           add_state = t->state->out->out;
           add_off = clen;
         } else {
           // skip over the matched characters, set character
           // count in NFA_SKIP
           add_state = t->state->out;
           add_off = bytelen;
           add_count = bytelen - clen;
         }
       }
       break;
     }
     case NFA_SKIP:
       // character of previous matching \1 .. \9  or \@>
       if (t->count - clen <= 0) {
         // end of match, go to what follows
         add_state = t->state->out;
         add_off = clen;
       } else {
         // add state again with decremented count
         add_state = t->state;
         add_off = 0;
         add_count = t->count - clen;
       }
       break;

     case NFA_LNUM:
     case NFA_LNUM_GT:
     case NFA_LNUM_LT:
       assert(t->state->val >= 0
              && !((rex.reg_firstlnum > 0
                    && rex.lnum > LONG_MAX - rex.reg_firstlnum)
                   || (rex.reg_firstlnum < 0
                       && rex.lnum < LONG_MIN + rex.reg_firstlnum))
              && rex.lnum + rex.reg_firstlnum >= 0);
       result = (REG_MULTI
                 && nfa_re_num_cmp((uintmax_t)t->state->val,
                                   t->state->c - NFA_LNUM,
                                   (uintmax_t)rex.lnum + (uintmax_t)rex.reg_firstlnum));
       if (result) {
         add_here = true;
         add_state = t->state->out;
       }
       break;

     case NFA_COL:
     case NFA_COL_GT:
     case NFA_COL_LT:
       assert(t->state->val >= 0
              && rex.input >= rex.line
              && (uintmax_t)(rex.input - rex.line) <= UINTMAX_MAX - 1);
       result = nfa_re_num_cmp((uintmax_t)t->state->val,
                               t->state->c - NFA_COL,
                               (uintmax_t)(rex.input - rex.line + 1));
       if (result) {
         add_here = true;
         add_state = t->state->out;
       }
       break;

     case NFA_VCOL:
     case NFA_VCOL_GT:
     case NFA_VCOL_LT: {
       int op = t->state->c - NFA_VCOL;
       colnr_T col = (colnr_T)(rex.input - rex.line);

       // Bail out quickly when there can't be a match, avoid the overhead of
       // win_linetabsize() on long lines.
       if (op != 1 && col > t->state->val * MB_MAXBYTES) {
         break;
       }

       result = false;
       win_T *wp = rex.reg_win == NULL ? curwin : rex.reg_win;
       if (op == 1 && col - 1 > t->state->val && col > 100) {
         int64_t ts = (int64_t)wp->w_buffer->b_p_ts;

         // Guess that a character won't use more columns than 'tabstop',
         // with a minimum of 4.
         if (ts < 4) {
           ts = 4;
         }
         result = col > t->state->val * ts;
       }
       if (!result) {
         linenr_T lnum = REG_MULTI ? rex.reg_firstlnum + rex.lnum : 1;
         if (REG_MULTI && (lnum <= 0 || lnum > wp->w_buffer->b_ml.ml_line_count)) {
           lnum = 1;
         }
         int vcol = win_linetabsize(wp, lnum, (char *)rex.line, col);
         assert(t->state->val >= 0);
         result = nfa_re_num_cmp((uintmax_t)t->state->val, op, (uintmax_t)vcol + 1);
       }
       if (result) {
         add_here = true;
         add_state = t->state->out;
       }
     }
     break;

     case NFA_MARK:
     case NFA_MARK_GT:
     case NFA_MARK_LT: {
       size_t col = REG_MULTI ? (size_t)(rex.input - rex.line) : 0;
       fmark_T *fm = mark_get(rex.reg_buf, curwin, NULL, kMarkBufLocal, t->state->val);

       // Line may have been freed, get it again.
       if (REG_MULTI) {
         rex.line = (uint8_t *)reg_getline(rex.lnum);
         rex.input = rex.line + col;
       }

       // Compare the mark position to the match position, if the mark
       // exists and mark is set in reg_buf.
       if (fm != NULL && fm->mark.lnum > 0) {
         pos_T *pos = &fm->mark;
         const colnr_T pos_col = pos->lnum == rex.lnum + rex.reg_firstlnum
                                 && pos->col == MAXCOL
                                 ? reg_getline_len(pos->lnum - rex.reg_firstlnum)
                                 : pos->col;

         result = pos->lnum == rex.lnum + rex.reg_firstlnum
                  ? (pos_col == (colnr_T)(rex.input - rex.line)
                     ? t->state->c == NFA_MARK
                     : (pos_col < (colnr_T)(rex.input - rex.line)
                        ? t->state->c == NFA_MARK_GT
                        : t->state->c == NFA_MARK_LT))
                  : (pos->lnum < rex.lnum + rex.reg_firstlnum
                     ? t->state->c == NFA_MARK_GT
                     : t->state->c == NFA_MARK_LT);
         if (result) {
           add_here = true;
           add_state = t->state->out;
         }
       }
       break;
     }

     case NFA_CURSOR:
       result = rex.reg_win != NULL
                && (rex.lnum + rex.reg_firstlnum == rex.reg_win->w_cursor.lnum)
                && ((colnr_T)(rex.input - rex.line) == rex.reg_win->w_cursor.col);
       if (result) {
         add_here = true;
         add_state = t->state->out;
       }
       break;

     case NFA_VISUAL:
       result = reg_match_visual();
       if (result) {
         add_here = true;
         add_state = t->state->out;
       }
       break;

     case NFA_MOPEN1:
     case NFA_MOPEN2:
     case NFA_MOPEN3:
     case NFA_MOPEN4:
     case NFA_MOPEN5:
     case NFA_MOPEN6:
     case NFA_MOPEN7:
     case NFA_MOPEN8:
     case NFA_MOPEN9:
     case NFA_ZOPEN:
     case NFA_ZOPEN1:
     case NFA_ZOPEN2:
     case NFA_ZOPEN3:
     case NFA_ZOPEN4:
     case NFA_ZOPEN5:
     case NFA_ZOPEN6:
     case NFA_ZOPEN7:
     case NFA_ZOPEN8:
     case NFA_ZOPEN9:
     case NFA_NOPEN:
     case NFA_ZSTART:
       // These states are only added to be able to bail out when
       // they are added again, nothing is to be done.
       break;

     default:          // regular character
     {
       int c = t->state->c;

#ifdef REGEXP_DEBUG
       if (c < 0) {
         siemsg("INTERNAL: Negative state char: %" PRId64, (int64_t)c);
       }
#endif
       result = (c == curc);

       if (!result && rex.reg_ic) {
         result = utf_fold(c) == utf_fold(curc);
       }

       // If rex.reg_icombine is not set only skip over the character
       // itself.  When it is set skip over composing characters.
       if (result && !rex.reg_icombine) {
         clen = utf_ptr2len((char *)rex.input);
       }

       ADD_STATE_IF_MATCH(t->state);
       break;
     }
     }       // switch (t->state->c)

     if (add_state != NULL) {
       nfa_pim_T *pim;
       nfa_pim_T pim_copy;

       if (t->pim.result == NFA_PIM_UNUSED) {
         pim = NULL;
       } else {
         pim = &t->pim;
       }

       // Handle the postponed invisible match if the match might end
       // without advancing and before the end of the line.
       if (pim != NULL && (clen == 0 || match_follows(add_state, 0))) {
         if (pim->result == NFA_PIM_TODO) {
#ifdef REGEXP_DEBUG
           fprintf(log_fd, "\n");
           fprintf(log_fd, "==================================\n");
           fprintf(log_fd, "Postponed recursive nfa_regmatch()\n");
           fprintf(log_fd, "\n");
#endif
           result = recursive_regmatch(pim->state, pim, prog, submatch, m,
                                       &listids, &listids_len);
           pim->result = result ? NFA_PIM_MATCH : NFA_PIM_NOMATCH;
           // for \@! and \@<! it is a match when the result is
           // false
           if (result != (pim->state->c == NFA_START_INVISIBLE_NEG
                          || pim->state->c == NFA_START_INVISIBLE_NEG_FIRST
                          || pim->state->c
                          == NFA_START_INVISIBLE_BEFORE_NEG
                          || pim->state->c
                          == NFA_START_INVISIBLE_BEFORE_NEG_FIRST)) {
             // Copy submatch info from the recursive call
             copy_sub_off(&pim->subs.norm, &m->norm);
             if (rex.nfa_has_zsubexpr) {
               copy_sub_off(&pim->subs.synt, &m->synt);
             }
           }
         } else {
           result = (pim->result == NFA_PIM_MATCH);
#ifdef REGEXP_DEBUG
           fprintf(log_fd, "\n");
           fprintf(log_fd,
                   "Using previous recursive nfa_regmatch() result, result == %d\n",
                   pim->result);
           fprintf(log_fd, "MATCH = %s\n", result ? "OK" : "false");
           fprintf(log_fd, "\n");
#endif
         }

         // for \@! and \@<! it is a match when result is false
         if (result != (pim->state->c == NFA_START_INVISIBLE_NEG
                        || pim->state->c == NFA_START_INVISIBLE_NEG_FIRST
                        || pim->state->c
                        == NFA_START_INVISIBLE_BEFORE_NEG
                        || pim->state->c
                        == NFA_START_INVISIBLE_BEFORE_NEG_FIRST)) {
           // Copy submatch info from the recursive call
           copy_sub_off(&t->subs.norm, &pim->subs.norm);
           if (rex.nfa_has_zsubexpr) {
             copy_sub_off(&t->subs.synt, &pim->subs.synt);
           }
         } else {
           // look-behind match failed, don't add the state
           continue;
         }

         // Postponed invisible match was handled, don't add it to
         // following states.
         pim = NULL;
       }

       // If "pim" points into l->t it will become invalid when
       // adding the state causes the list to be reallocated.  Make a
       // local copy to avoid that.
       if (pim == &t->pim) {
         copy_pim(&pim_copy, pim);
         pim = &pim_copy;
       }

       if (add_here) {
         r = addstate_here(thislist, add_state, &t->subs, pim, &listidx);
       } else {
         r = addstate(nextlist, add_state, &t->subs, pim, add_off);
         if (add_count > 0) {
           nextlist->t[nextlist->n - 1].count = add_count;
         }
       }
       if (r == NULL) {
         nfa_match = NFA_TOO_EXPENSIVE;
         goto theend;
       }
     }
   }     // for (thislist = thislist; thislist->state; thislist++)

   // Look for the start of a match in the current position by adding the
   // start state to the list of states.
   // The first found match is the leftmost one, thus the order of states
   // matters!
   // Do not add the start state in recursive calls of nfa_regmatch(),
   // because recursive calls should only start in the first position.
   // Unless "nfa_endp" is not NULL, then we match the end position.
   // Also don't start a match past the first line.
   if (!nfa_match
       && ((toplevel
            && rex.lnum == 0
            && clen != 0
            && (rex.reg_maxcol == 0
                || (colnr_T)(rex.input - rex.line) < rex.reg_maxcol))
           || (nfa_endp != NULL
               && (REG_MULTI
                   ? (rex.lnum < nfa_endp->se_u.pos.lnum
                      || (rex.lnum == nfa_endp->se_u.pos.lnum
                          && (int)(rex.input - rex.line)
                          < nfa_endp->se_u.pos.col))
                   : rex.input < nfa_endp->se_u.ptr)))) {
#ifdef REGEXP_DEBUG
     fprintf(log_fd, "(---) STARTSTATE\n");
#endif
     // Inline optimized code for addstate() if we know the state is
     // the first MOPEN.
     if (toplevel) {
       int add = true;

       if (prog->regstart != NUL && clen != 0) {
         if (nextlist->n == 0) {
           colnr_T col = (colnr_T)(rex.input - rex.line) + clen;

           // Nextlist is empty, we can skip ahead to the
           // character that must appear at the start.
           if (skip_to_start(prog->regstart, &col) == FAIL) {
             break;
           }
#ifdef REGEXP_DEBUG
           fprintf(log_fd, "  Skipping ahead %d bytes to regstart\n",
                   col - ((colnr_T)(rex.input - rex.line) + clen));
#endif
           rex.input = rex.line + col - clen;
         } else {
           // Checking if the required start character matches is
           // cheaper than adding a state that won't match.
           const int c = utf_ptr2char((char *)rex.input + clen);
           if (c != prog->regstart
               && (!rex.reg_ic
                   || utf_fold(c) != utf_fold(prog->regstart))) {
#ifdef REGEXP_DEBUG
             fprintf(log_fd,
                     "  Skipping start state, regstart does not match\n");
#endif
             add = false;
           }
         }
       }

       if (add) {
         if (REG_MULTI) {
           m->norm.list.multi[0].start_col =
             (colnr_T)(rex.input - rex.line) + clen;
           m->norm.orig_start_col =
             m->norm.list.multi[0].start_col;
         } else {
           m->norm.list.line[0].start = rex.input + clen;
         }
         if (addstate(nextlist, start->out, m, NULL, clen) == NULL) {
           nfa_match = NFA_TOO_EXPENSIVE;
           goto theend;
         }
       }
     } else {
       if (addstate(nextlist, start, m, NULL, clen) == NULL) {
         nfa_match = NFA_TOO_EXPENSIVE;
         goto theend;
       }
     }
   }

#ifdef REGEXP_DEBUG
   fprintf(log_fd, ">>> Thislist had %d states available: ", thislist->n);
   {
     int i;

     for (i = 0; i < thislist->n; i++) {
       fprintf(log_fd, "%d  ", abs(thislist->t[i].state->id));
     }
   }
   fprintf(log_fd, "\n");
#endif

nextchar:
   // Advance to the next character, or advance to the next line, or
   // finish.
   if (clen != 0) {
     rex.input += clen;
   } else if (go_to_nextline || (nfa_endp != NULL && REG_MULTI
                                 && rex.lnum < nfa_endp->se_u.pos.lnum)) {
     reg_nextline();
   } else {
     break;
   }

   // Allow interrupting with CTRL-C.
   reg_breakcheck();
   if (got_int) {
     break;
   }
   // Check for timeout once every twenty times to avoid overhead.
   if (nfa_time_limit != NULL && ++nfa_time_count == 20) {
     nfa_time_count = 0;
     if (nfa_did_time_out()) {
       break;
     }
   }
 }

#ifdef REGEXP_DEBUG
 if (log_fd != stderr) {
   fclose(log_fd);
 }
 log_fd = NULL;
#endif

theend:
 // Free memory
 xfree(list[0].t);
 xfree(list[1].t);
 xfree(listids);
#undef ADD_STATE_IF_MATCH
#ifdef NFA_REGEXP_DEBUG_LOG
 fclose(debug);
#endif

 return nfa_match;
}

/// Try match of "prog" with at rex.line["col"].
///
/// @param tm         timeout limit or NULL
/// @param timed_out  flag set on timeout or NULL
///
/// @return  <= 0 for failure, number of lines contained in the match otherwise.
static int nfa_regtry(nfa_regprog_T *prog, colnr_T col, proftime_T *tm, int *timed_out)
{
 int i;
 regsubs_T subs, m;
 nfa_state_T *start = prog->start;
#ifdef REGEXP_DEBUG
 FILE *f;
#endif

 rex.input = rex.line + col;
 nfa_time_limit = tm;
 nfa_timed_out = timed_out;
 nfa_time_count = 0;

#ifdef REGEXP_DEBUG
 f = fopen(NFA_REGEXP_RUN_LOG, "a");
 if (f != NULL) {
   fprintf(f,
           "\n\n\t=======================================================\n");
# ifdef REGEXP_DEBUG
   fprintf(f, "\tRegexp is \"%s\"\n", nfa_regengine.expr);
# endif
   fprintf(f, "\tInput text is \"%s\" \n", rex.input);
   fprintf(f, "\t=======================================================\n\n");
   nfa_print_state(f, start);
   fprintf(f, "\n\n");
   fclose(f);
 } else {
   emsg("Could not open temporary log file for writing");
 }
#endif

 clear_sub(&subs.norm);
 clear_sub(&m.norm);
 clear_sub(&subs.synt);
 clear_sub(&m.synt);

 int result = nfa_regmatch(prog, start, &subs, &m);
 if (!result) {
   return 0;
 } else if (result == NFA_TOO_EXPENSIVE) {
   return result;
 }

 cleanup_subexpr();
 if (REG_MULTI) {
   for (i = 0; i < subs.norm.in_use; i++) {
     rex.reg_startpos[i].lnum = subs.norm.list.multi[i].start_lnum;
     rex.reg_startpos[i].col = subs.norm.list.multi[i].start_col;

     rex.reg_endpos[i].lnum = subs.norm.list.multi[i].end_lnum;
     rex.reg_endpos[i].col = subs.norm.list.multi[i].end_col;
   }
   if (rex.reg_mmatch != NULL) {
     rex.reg_mmatch->rmm_matchcol = subs.norm.orig_start_col;
   }

   if (rex.reg_startpos[0].lnum < 0) {
     rex.reg_startpos[0].lnum = 0;
     rex.reg_startpos[0].col = col;
   }
   if (rex.reg_endpos[0].lnum < 0) {
     // pattern has a \ze but it didn't match, use current end
     rex.reg_endpos[0].lnum = rex.lnum;
     rex.reg_endpos[0].col = (int)(rex.input - rex.line);
   } else {
     // Use line number of "\ze".
     rex.lnum = rex.reg_endpos[0].lnum;
   }
 } else {
   for (i = 0; i < subs.norm.in_use; i++) {
     rex.reg_startp[i] = subs.norm.list.line[i].start;
     rex.reg_endp[i] = subs.norm.list.line[i].end;
   }

   if (rex.reg_startp[0] == NULL) {
     rex.reg_startp[0] = rex.line + col;
   }
   if (rex.reg_endp[0] == NULL) {
     rex.reg_endp[0] = rex.input;
   }
 }

 // Package any found \z(...\) matches for export. Default is none.
 unref_extmatch(re_extmatch_out);
 re_extmatch_out = NULL;

 if (prog->reghasz == REX_SET) {
   cleanup_zsubexpr();
   re_extmatch_out = make_extmatch();
   // Loop over \z1, \z2, etc.  There is no \z0.
   for (i = 1; i < subs.synt.in_use; i++) {
     if (REG_MULTI) {
       struct multipos *mpos = &subs.synt.list.multi[i];

       // Only accept single line matches that are valid.
       if (mpos->start_lnum >= 0
           && mpos->start_lnum == mpos->end_lnum
           && mpos->end_col >= mpos->start_col) {
         re_extmatch_out->matches[i] =
           (uint8_t *)xstrnsave(reg_getline(mpos->start_lnum) + mpos->start_col,
                                (size_t)(mpos->end_col - mpos->start_col));
       }
     } else {
       struct linepos *lpos = &subs.synt.list.line[i];

       if (lpos->start != NULL && lpos->end != NULL) {
         re_extmatch_out->matches[i] =
           (uint8_t *)xstrnsave((char *)lpos->start, (size_t)(lpos->end - lpos->start));
       }
     }
   }
 }

 return 1 + rex.lnum;
}

/// Match a regexp against a string ("line" points to the string) or multiple
/// lines (if "line" is NULL, use reg_getline()).
///
/// @param line String in which to search or NULL
/// @param startcol Column to start looking for match
/// @param tm Timeout limit or NULL
/// @param timed_out Flag set on timeout or NULL
///
/// @return <= 0 if there is no match and number of lines contained in the
/// match otherwise.
static int nfa_regexec_both(uint8_t *line, colnr_T startcol, proftime_T *tm, int *timed_out)
{
 nfa_regprog_T *prog;
 int retval = 0;
 colnr_T col = startcol;

 if (REG_MULTI) {
   prog = (nfa_regprog_T *)rex.reg_mmatch->regprog;
   line = (uint8_t *)reg_getline(0);  // relative to the cursor
   rex.reg_startpos = rex.reg_mmatch->startpos;
   rex.reg_endpos = rex.reg_mmatch->endpos;
 } else {
   prog = (nfa_regprog_T *)rex.reg_match->regprog;
   rex.reg_startp = (uint8_t **)rex.reg_match->startp;
   rex.reg_endp = (uint8_t **)rex.reg_match->endp;
 }

 // Be paranoid...
 if (prog == NULL || line == NULL) {
   iemsg(_(e_null));
   goto theend;
 }

 // If pattern contains "\c" or "\C": overrule value of rex.reg_ic
 if (prog->regflags & RF_ICASE) {
   rex.reg_ic = true;
 } else if (prog->regflags & RF_NOICASE) {
   rex.reg_ic = false;
 }

 // If pattern contains "\Z" overrule value of rex.reg_icombine
 if (prog->regflags & RF_ICOMBINE) {
   rex.reg_icombine = true;
 }

 rex.line = line;
 rex.lnum = 0;  // relative to line

 rex.nfa_has_zend = prog->has_zend;
 rex.nfa_has_backref = prog->has_backref;
 rex.nfa_nsubexpr = prog->nsubexp;
 rex.nfa_listid = 1;
 rex.nfa_alt_listid = 2;
#ifdef REGEXP_DEBUG
 nfa_regengine.expr = prog->pattern;
#endif

 if (prog->reganch && col > 0) {
   return 0L;
 }

 rex.need_clear_subexpr = true;
 // Clear the external match subpointers if necessary.
 if (prog->reghasz == REX_SET) {
   rex.nfa_has_zsubexpr = true;
   rex.need_clear_zsubexpr = true;
 } else {
   rex.nfa_has_zsubexpr = false;
   rex.need_clear_zsubexpr = false;
 }

 if (prog->regstart != NUL) {
   // Skip ahead until a character we know the match must start with.
   // When there is none there is no match.
   if (skip_to_start(prog->regstart, &col) == FAIL) {
     return 0L;
   }

   // If match_text is set it contains the full text that must match.
   // Nothing else to try. Doesn't handle combining chars well.
   if (prog->match_text != NULL && *prog->match_text != NUL && !rex.reg_icombine) {
     retval = find_match_text(&col, prog->regstart, prog->match_text);
     if (REG_MULTI) {
       rex.reg_mmatch->rmm_matchcol = col;
     } else {
       rex.reg_match->rm_matchcol = col;
     }
     return retval;
   }
 }

 // If the start column is past the maximum column: no need to try.
 if (rex.reg_maxcol > 0 && col >= rex.reg_maxcol) {
   goto theend;
 }

 // Set the "nstate" used by nfa_regcomp() to zero to trigger an error when
 // it's accidentally used during execution.
 nstate = 0;
 for (int i = 0; i < prog->nstate; i++) {
   prog->state[i].id = i;
   prog->state[i].lastlist[0] = 0;
   prog->state[i].lastlist[1] = 0;
 }

 retval = nfa_regtry(prog, col, tm, timed_out);

#ifdef REGEXP_DEBUG
 nfa_regengine.expr = NULL;
#endif

theend:
 if (retval > 0) {
   // Make sure the end is never before the start.  Can happen when \zs and
   // \ze are used.
   if (REG_MULTI) {
     const lpos_T *const start = &rex.reg_mmatch->startpos[0];
     const lpos_T *const end = &rex.reg_mmatch->endpos[0];

     if (end->lnum < start->lnum
         || (end->lnum == start->lnum && end->col < start->col)) {
       rex.reg_mmatch->endpos[0] = rex.reg_mmatch->startpos[0];
     }
   } else {
     if (rex.reg_match->endp[0] < rex.reg_match->startp[0]) {
       rex.reg_match->endp[0] = rex.reg_match->startp[0];
     }

     // startpos[0] may be set by "\zs", also return the column where
     // the whole pattern matched.
     rex.reg_match->rm_matchcol = col;
   }
 }

 return retval;
}

// Compile a regular expression into internal code for the NFA matcher.
// Returns the program in allocated space.  Returns NULL for an error.
static regprog_T *nfa_regcomp(uint8_t *expr, int re_flags)
{
 nfa_regprog_T *prog = NULL;
 int *postfix;

 if (expr == NULL) {
   return NULL;
 }

#ifdef REGEXP_DEBUG
 nfa_regengine.expr = expr;
#endif
 nfa_re_flags = re_flags;

 init_class_tab();

 nfa_regcomp_start(expr, re_flags);

 // Build postfix form of the regexp. Needed to build the NFA
 // (and count its size).
 postfix = re2post();
 if (postfix == NULL) {
   goto fail;              // Cascaded (syntax?) error
 }

 // In order to build the NFA, we parse the input regexp twice:
 // 1. first pass to count size (so we can allocate space)
 // 2. second to emit code
#ifdef REGEXP_DEBUG
 {
   FILE *f = fopen(NFA_REGEXP_RUN_LOG, "a");

   if (f != NULL) {
     fprintf(f,
             "\n*****************************\n\n\n\n\t"
             "Compiling regexp \"%s\"... hold on !\n",
             expr);
     fclose(f);
   }
 }
#endif

 // PASS 1
 // Count number of NFA states in "nstate". Do not build the NFA.
 post2nfa(postfix, post_ptr, true);

 // allocate the regprog with space for the compiled regexp
 size_t prog_size = offsetof(nfa_regprog_T, state) + sizeof(nfa_state_T) * (size_t)nstate;
 prog = xmalloc(prog_size);
 state_ptr = prog->state;
 prog->re_in_use = false;

 // PASS 2
 // Build the NFA
 prog->start = post2nfa(postfix, post_ptr, false);
 if (prog->start == NULL) {
   goto fail;
 }
 prog->regflags = regflags;
 prog->engine = &nfa_regengine;
 prog->nstate = nstate;
 prog->has_zend = rex.nfa_has_zend;
 prog->has_backref = rex.nfa_has_backref;
 prog->nsubexp = regnpar;

 nfa_postprocess(prog);

 prog->reganch = nfa_get_reganch(prog->start, 0);
 prog->regstart = nfa_get_regstart(prog->start, 0);
 prog->match_text = nfa_get_match_text(prog->start);

#ifdef REGEXP_DEBUG
 nfa_postfix_dump(expr, OK);
 nfa_dump(prog);
#endif
 // Remember whether this pattern has any \z specials in it.
 prog->reghasz = re_has_z;
 prog->pattern = xstrdup((char *)expr);
#ifdef REGEXP_DEBUG
 nfa_regengine.expr = NULL;
#endif

out:
 xfree(post_start);
 post_start = post_ptr = post_end = NULL;
 state_ptr = NULL;
 return (regprog_T *)prog;

fail:
 XFREE_CLEAR(prog);
#ifdef REGEXP_DEBUG
 nfa_postfix_dump(expr, FAIL);
 nfa_regengine.expr = NULL;
#endif
 goto out;
}

// Free a compiled regexp program, returned by nfa_regcomp().
static void nfa_regfree(regprog_T *prog)
{
 if (prog == NULL) {
   return;
 }

 xfree(((nfa_regprog_T *)prog)->match_text);
 xfree(((nfa_regprog_T *)prog)->pattern);
 xfree(prog);
}

/// Match a regexp against a string.
/// "rmp->regprog" is a compiled regexp as returned by nfa_regcomp().
/// Uses curbuf for line count and 'iskeyword'.
/// If "line_lbr" is true, consider a "\n" in "line" to be a line break.
///
/// @param line  string to match against
/// @param col   column to start looking for match
///
/// @return  <= 0 for failure, number of lines contained in the match otherwise.
static int nfa_regexec_nl(regmatch_T *rmp, uint8_t *line, colnr_T col, bool line_lbr)
{
 rex.reg_match = rmp;
 rex.reg_mmatch = NULL;
 rex.reg_maxline = 0;
 rex.reg_line_lbr = line_lbr;
 rex.reg_buf = curbuf;
 rex.reg_win = NULL;
 rex.reg_ic = rmp->rm_ic;
 rex.reg_icombine = false;
 rex.reg_nobreak = rmp->regprog->re_flags & RE_NOBREAK;
 rex.reg_maxcol = 0;
 return nfa_regexec_both(line, col, NULL, NULL);
}

/// Matches a regexp against multiple lines.
/// "rmp->regprog" is a compiled regexp as returned by vim_regcomp().
/// Uses curbuf for line count and 'iskeyword'.
///
/// @param win Window in which to search or NULL
/// @param buf Buffer in which to search
/// @param lnum Number of line to start looking for match
/// @param col Column to start looking for match
/// @param tm Timeout limit or NULL
/// @param timed_out Flag set on timeout or NULL
///
/// @return <= 0 if there is no match and number of lines contained in the match
/// otherwise.
///
/// @note The body is the same as bt_regexec() except for nfa_regexec_both()
///
/// @warning
/// Match may actually be in another line. e.g.:
/// when r.e. is \nc, cursor is at 'a' and the text buffer looks like
///
/// @par
///
///     +-------------------------+
///     |a                        |
///     |b                        |
///     |c                        |
///     |                         |
///     +-------------------------+
///
/// @par
/// then nfa_regexec_multi() returns 3. while the original vim_regexec_multi()
/// returns 0 and a second call at line 2 will return 2.
///
/// @par
/// FIXME if this behavior is not compatible.
static int nfa_regexec_multi(regmmatch_T *rmp, win_T *win, buf_T *buf, linenr_T lnum, colnr_T col,
                            proftime_T *tm, int *timed_out)
{
 init_regexec_multi(rmp, win, buf, lnum);
 return nfa_regexec_both(NULL, col, tm, timed_out);
}
// }}}1

static regengine_T bt_regengine = {
 bt_regcomp,
 bt_regfree,
 bt_regexec_nl,
 bt_regexec_multi,
#ifdef REGEXP_DEBUG
 "",
#endif
};

static regengine_T nfa_regengine = {
 nfa_regcomp,
 nfa_regfree,
 nfa_regexec_nl,
 nfa_regexec_multi,
#ifdef REGEXP_DEBUG
 "",
#endif
};

// Which regexp engine to use? Needed for vim_regcomp().
// Must match with 'regexpengine'.
static int regexp_engine = 0;

#ifdef REGEXP_DEBUG
static uint8_t regname[][30] = {
 "AUTOMATIC Regexp Engine",
 "BACKTRACKING Regexp Engine",
 "NFA Regexp Engine"
};
#endif

// Compile a regular expression into internal code.
// Returns the program in allocated memory.
// Use vim_regfree() to free the memory.
// Returns NULL for an error.
regprog_T *vim_regcomp(const char *expr_arg, int re_flags)
{
 regprog_T *prog = NULL;
 const char *expr = expr_arg;

 regexp_engine = (int)p_re;

 // Check for prefix "\%#=", that sets the regexp engine
 if (strncmp(expr, "\\%#=", 4) == 0) {
   int newengine = expr[4] - '0';

   if (newengine == AUTOMATIC_ENGINE
       || newengine == BACKTRACKING_ENGINE
       || newengine == NFA_ENGINE) {
     regexp_engine = expr[4] - '0';
     expr += 5;
#ifdef REGEXP_DEBUG
     smsg(0, "New regexp mode selected (%d): %s",
          regexp_engine,
          regname[newengine]);
#endif
   } else {
     emsg(_("E864: \\%#= can only be followed by 0, 1, or 2. The automatic engine will be used "));
     regexp_engine = AUTOMATIC_ENGINE;
   }
 }
#ifdef REGEXP_DEBUG
 bt_regengine.expr = expr;
 nfa_regengine.expr = expr;
#endif
 // reg_iswordc() uses rex.reg_buf
 rex.reg_buf = curbuf;

 //
 // First try the NFA engine, unless backtracking was requested.
 //
 const int called_emsg_before = called_emsg;
 if (regexp_engine != BACKTRACKING_ENGINE) {
   prog = nfa_regengine.regcomp((uint8_t *)expr,
                                re_flags + (regexp_engine == AUTOMATIC_ENGINE ? RE_AUTO : 0));
 } else {
   prog = bt_regengine.regcomp((uint8_t *)expr, re_flags);
 }

 // Check for error compiling regexp with initial engine.
 if (prog == NULL) {
#ifdef BT_REGEXP_DEBUG_LOG
   // Debugging log for BT engine.
   if (regexp_engine != BACKTRACKING_ENGINE) {
     FILE *f = fopen(BT_REGEXP_DEBUG_LOG_NAME, "a");
     if (f) {
       fprintf(f, "Syntax error in \"%s\"\n", expr);
       fclose(f);
     } else {
       semsg("(NFA) Could not open \"%s\" to write !!!",
             BT_REGEXP_DEBUG_LOG_NAME);
     }
   }
#endif
   // If the NFA engine failed, try the backtracking engine. The NFA engine
   // also fails for patterns that it can't handle well but are still valid
   // patterns, thus a retry should work.
   // But don't try if an error message was given.
   if (regexp_engine == AUTOMATIC_ENGINE && called_emsg == called_emsg_before) {
     regexp_engine = BACKTRACKING_ENGINE;
     report_re_switch(expr);
     prog = bt_regengine.regcomp((uint8_t *)expr, re_flags);
   }
 }

 if (prog != NULL) {
   // Store the info needed to call regcomp() again when the engine turns out
   // to be very slow when executing it.
   prog->re_engine = (unsigned)regexp_engine;
   prog->re_flags = (unsigned)re_flags;
 }

 return prog;
}

// Free a compiled regexp program, returned by vim_regcomp().
void vim_regfree(regprog_T *prog)
{
 if (prog != NULL) {
   prog->engine->regfree(prog);
 }
}

#if defined(EXITFREE)
void free_regexp_stuff(void)
{
 ga_clear(&regstack);
 ga_clear(&backpos);
 xfree(reg_tofree);
 xfree(reg_prev_sub);
}

#endif

static void report_re_switch(const char *pat)
{
 if (p_verbose > 0) {
   verbose_enter();
   msg_puts(_("Switching to backtracking RE engine for pattern: "));
   msg_puts(pat);
   verbose_leave();
 }
}

/// Match a regexp against a string.
/// "rmp->regprog" must be a compiled regexp as returned by vim_regcomp().
/// Note: "rmp->regprog" may be freed and changed.
/// Uses curbuf for line count and 'iskeyword'.
/// When "nl" is true consider a "\n" in "line" to be a line break.
///
/// @param rmp
/// @param line the string to match against
/// @param col  the column to start looking for match
/// @param nl
///
/// @return true if there is a match, false if not.
static bool vim_regexec_string(regmatch_T *rmp, const char *line, colnr_T col, bool nl)
{
 regexec_T rex_save;
 bool rex_in_use_save = rex_in_use;

 // Cannot use the same prog recursively, it contains state.
 if (rmp->regprog->re_in_use) {
   emsg(_(e_recursive));
   return false;
 }
 rmp->regprog->re_in_use = true;

 if (rex_in_use) {
   // Being called recursively, save the state.
   rex_save = rex;
 }
 rex_in_use = true;

 rex.reg_startp = NULL;
 rex.reg_endp = NULL;
 rex.reg_startpos = NULL;
 rex.reg_endpos = NULL;

 int result = rmp->regprog->engine->regexec_nl(rmp, (uint8_t *)line, col, nl);
 rmp->regprog->re_in_use = false;

 // NFA engine aborted because it's very slow, use backtracking engine instead.
 if (rmp->regprog->re_engine == AUTOMATIC_ENGINE
     && result == NFA_TOO_EXPENSIVE) {
   int save_p_re = (int)p_re;
   int re_flags = (int)rmp->regprog->re_flags;
   char *pat = xstrdup(((nfa_regprog_T *)rmp->regprog)->pattern);

   p_re = BACKTRACKING_ENGINE;
   vim_regfree(rmp->regprog);
   report_re_switch(pat);
   rmp->regprog = vim_regcomp(pat, re_flags);
   if (rmp->regprog != NULL) {
     rmp->regprog->re_in_use = true;
     result = rmp->regprog->engine->regexec_nl(rmp, (uint8_t *)line, col, nl);
     rmp->regprog->re_in_use = false;
   }

   xfree(pat);
   p_re = save_p_re;
 }

 rex_in_use = rex_in_use_save;
 if (rex_in_use) {
   rex = rex_save;
 }

 return result > 0;
}

// Note: "*prog" may be freed and changed.
// Return true if there is a match, false if not.
bool vim_regexec_prog(regprog_T **prog, bool ignore_case, const char *line, colnr_T col)
{
 regmatch_T regmatch = { .regprog = *prog, .rm_ic = ignore_case };
 bool r = vim_regexec_string(&regmatch, line, col, false);
 *prog = regmatch.regprog;
 return r;
}

// Note: "rmp->regprog" may be freed and changed.
// Return true if there is a match, false if not.
bool vim_regexec(regmatch_T *rmp, const char *line, colnr_T col)
{
 return vim_regexec_string(rmp, line, col, false);
}

// Like vim_regexec(), but consider a "\n" in "line" to be a line break.
// Note: "rmp->regprog" may be freed and changed.
// Return true if there is a match, false if not.
bool vim_regexec_nl(regmatch_T *rmp, const char *line, colnr_T col)
{
 return vim_regexec_string(rmp, line, col, true);
}

/// Match a regexp against multiple lines.
/// "rmp->regprog" must be a compiled regexp as returned by vim_regcomp().
/// Note: "rmp->regprog" may be freed and changed, even set to NULL.
/// Uses curbuf for line count and 'iskeyword'.
///
/// @param win        window in which to search or NULL
/// @param buf        buffer in which to search
/// @param lnum       nr of line to start looking for match
/// @param col        column to start looking for match
/// @param tm         timeout limit or NULL
/// @param timed_out  flag is set when timeout limit reached
///
/// @return  zero if there is no match.  Return number of lines contained in the
///          match otherwise.
int vim_regexec_multi(regmmatch_T *rmp, win_T *win, buf_T *buf, linenr_T lnum, colnr_T col,
                     proftime_T *tm, int *timed_out)
 FUNC_ATTR_NONNULL_ARG(1)
{
 regexec_T rex_save;
 bool rex_in_use_save = rex_in_use;

 // Cannot use the same prog recursively, it contains state.
 if (rmp->regprog->re_in_use) {
   emsg(_(e_recursive));
   return false;
 }
 rmp->regprog->re_in_use = true;

 if (rex_in_use) {
   // Being called recursively, save the state.
   rex_save = rex;
 }
 rex_in_use = true;

 int result = rmp->regprog->engine->regexec_multi(rmp, win, buf, lnum, col, tm, timed_out);
 rmp->regprog->re_in_use = false;

 // NFA engine aborted because it's very slow, use backtracking engine instead.
 if (rmp->regprog->re_engine == AUTOMATIC_ENGINE
     && result == NFA_TOO_EXPENSIVE) {
   int save_p_re = (int)p_re;
   int re_flags = (int)rmp->regprog->re_flags;
   char *pat = xstrdup(((nfa_regprog_T *)rmp->regprog)->pattern);

   p_re = BACKTRACKING_ENGINE;
   regprog_T *prev_prog = rmp->regprog;

   report_re_switch(pat);
   // checking for \z misuse was already done when compiling for NFA,
   // allow all here
   reg_do_extmatch = REX_ALL;
   rmp->regprog = vim_regcomp(pat, re_flags);
   reg_do_extmatch = 0;

   if (rmp->regprog == NULL) {
     // Somehow compiling the pattern failed now, put back the
     // previous one to avoid "regprog" becoming NULL.
     rmp->regprog = prev_prog;
   } else {
     vim_regfree(prev_prog);

     rmp->regprog->re_in_use = true;
     result = rmp->regprog->engine->regexec_multi(rmp, win, buf, lnum, col, tm, timed_out);
     rmp->regprog->re_in_use = false;
   }

   xfree(pat);
   p_re = save_p_re;
 }

 rex_in_use = rex_in_use_save;
 if (rex_in_use) {
   rex = rex_save;
 }

 return result <= 0 ? 0 : result;
}