tor-browser

trees.c (40937B)

---

/* trees.c -- output deflated data using Huffman coding
* Copyright (C) 1995-2024 Jean-loup Gailly
* detect_data_type() function provided freely by Cosmin Truta, 2006
* For conditions of distribution and use, see copyright notice in zlib.h
*/

/*
*  ALGORITHM
*
*      The "deflation" process uses several Huffman trees. The more
*      common source values are represented by shorter bit sequences.
*
*      Each code tree is stored in a compressed form which is itself
* a Huffman encoding of the lengths of all the code strings (in
* ascending order by source values).  The actual code strings are
* reconstructed from the lengths in the inflate process, as described
* in the deflate specification.
*
*  REFERENCES
*
*      Deutsch, L.P.,"'Deflate' Compressed Data Format Specification".
*      Available in ftp.uu.net:/pub/archiving/zip/doc/deflate-1.1.doc
*
*      Storer, James A.
*          Data Compression:  Methods and Theory, pp. 49-50.
*          Computer Science Press, 1988.  ISBN 0-7167-8156-5.
*
*      Sedgewick, R.
*          Algorithms, p290.
*          Addison-Wesley, 1983. ISBN 0-201-06672-6.
*/

/* @(#) $Id$ */

/* #define GEN_TREES_H */

#include "deflate.h"

#ifdef ZLIB_DEBUG
#  include <ctype.h>
#endif

/* ===========================================================================
* Constants
*/

#define MAX_BL_BITS 7
/* Bit length codes must not exceed MAX_BL_BITS bits */

#define END_BLOCK 256
/* end of block literal code */

#define REP_3_6      16
/* repeat previous bit length 3-6 times (2 bits of repeat count) */

#define REPZ_3_10    17
/* repeat a zero length 3-10 times  (3 bits of repeat count) */

#define REPZ_11_138  18
/* repeat a zero length 11-138 times  (7 bits of repeat count) */

local const int extra_lbits[LENGTH_CODES] /* extra bits for each length code */
  = {0,0,0,0,0,0,0,0,1,1,1,1,2,2,2,2,3,3,3,3,4,4,4,4,5,5,5,5,0};

local const int extra_dbits[D_CODES] /* extra bits for each distance code */
  = {0,0,0,0,1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13};

local const int extra_blbits[BL_CODES]/* extra bits for each bit length code */
  = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,2,3,7};

local const uch bl_order[BL_CODES]
  = {16,17,18,0,8,7,9,6,10,5,11,4,12,3,13,2,14,1,15};
/* The lengths of the bit length codes are sent in order of decreasing
* probability, to avoid transmitting the lengths for unused bit length codes.
*/

/* ===========================================================================
* Local data. These are initialized only once.
*/

#define DIST_CODE_LEN  512 /* see definition of array dist_code below */

#if defined(GEN_TREES_H) || !defined(STDC)
/* non ANSI compilers may not accept trees.h */

local ct_data static_ltree[L_CODES+2];
/* The static literal tree. Since the bit lengths are imposed, there is no
* need for the L_CODES extra codes used during heap construction. However
* The codes 286 and 287 are needed to build a canonical tree (see _tr_init
* below).
*/

local ct_data static_dtree[D_CODES];
/* The static distance tree. (Actually a trivial tree since all codes use
* 5 bits.)
*/

uch _dist_code[DIST_CODE_LEN];
/* Distance codes. The first 256 values correspond to the distances
* 3 .. 258, the last 256 values correspond to the top 8 bits of
* the 15 bit distances.
*/

uch _length_code[MAX_MATCH-MIN_MATCH+1];
/* length code for each normalized match length (0 == MIN_MATCH) */

local int base_length[LENGTH_CODES];
/* First normalized length for each code (0 = MIN_MATCH) */

local int base_dist[D_CODES];
/* First normalized distance for each code (0 = distance of 1) */

#else
#  include "trees.h"
#endif /* GEN_TREES_H */

struct static_tree_desc_s {
   const ct_data *static_tree;  /* static tree or NULL */
   const intf *extra_bits;      /* extra bits for each code or NULL */
   int     extra_base;          /* base index for extra_bits */
   int     elems;               /* max number of elements in the tree */
   int     max_length;          /* max bit length for the codes */
};

#ifdef NO_INIT_GLOBAL_POINTERS
#  define TCONST
#else
#  define TCONST const
#endif

local TCONST static_tree_desc static_l_desc =
{static_ltree, extra_lbits, LITERALS+1, L_CODES, MAX_BITS};

local TCONST static_tree_desc static_d_desc =
{static_dtree, extra_dbits, 0,          D_CODES, MAX_BITS};

local TCONST static_tree_desc static_bl_desc =
{(const ct_data *)0, extra_blbits, 0,   BL_CODES, MAX_BL_BITS};

/* ===========================================================================
* Output a short LSB first on the stream.
* IN assertion: there is enough room in pendingBuf.
*/
#define put_short(s, w) { \
   put_byte(s, (uch)((w) & 0xff)); \
   put_byte(s, (uch)((ush)(w) >> 8)); \
}

/* ===========================================================================
* Reverse the first len bits of a code, using straightforward code (a faster
* method would use a table)
* IN assertion: 1 <= len <= 15
*/
local unsigned bi_reverse(unsigned code, int len) {
   register unsigned res = 0;
   do {
       res |= code & 1;
       code >>= 1, res <<= 1;
   } while (--len > 0);
   return res >> 1;
}

/* ===========================================================================
* Flush the bit buffer, keeping at most 7 bits in it.
*/
local void bi_flush(deflate_state *s) {
   if (s->bi_valid == 16) {
       put_short(s, s->bi_buf);
       s->bi_buf = 0;
       s->bi_valid = 0;
   } else if (s->bi_valid >= 8) {
       put_byte(s, (Byte)s->bi_buf);
       s->bi_buf >>= 8;
       s->bi_valid -= 8;
   }
}

/* ===========================================================================
* Flush the bit buffer and align the output on a byte boundary
*/
local void bi_windup(deflate_state *s) {
   if (s->bi_valid > 8) {
       put_short(s, s->bi_buf);
   } else if (s->bi_valid > 0) {
       put_byte(s, (Byte)s->bi_buf);
   }
   s->bi_buf = 0;
   s->bi_valid = 0;
#ifdef ZLIB_DEBUG
   s->bits_sent = (s->bits_sent + 7) & ~7;
#endif
}

/* ===========================================================================
* Generate the codes for a given tree and bit counts (which need not be
* optimal).
* IN assertion: the array bl_count contains the bit length statistics for
* the given tree and the field len is set for all tree elements.
* OUT assertion: the field code is set for all tree elements of non
*     zero code length.
*/
local void gen_codes(ct_data *tree, int max_code, ushf *bl_count) {
   ush next_code[MAX_BITS+1]; /* next code value for each bit length */
   unsigned code = 0;         /* running code value */
   int bits;                  /* bit index */
   int n;                     /* code index */

   /* The distribution counts are first used to generate the code values
    * without bit reversal.
    */
   for (bits = 1; bits <= MAX_BITS; bits++) {
       code = (code + bl_count[bits - 1]) << 1;
       next_code[bits] = (ush)code;
   }
   /* Check that the bit counts in bl_count are consistent. The last code
    * must be all ones.
    */
   Assert (code + bl_count[MAX_BITS] - 1 == (1 << MAX_BITS) - 1,
           "inconsistent bit counts");
   Tracev((stderr,"\ngen_codes: max_code %d ", max_code));

   for (n = 0;  n <= max_code; n++) {
       int len = tree[n].Len;
       if (len == 0) continue;
       /* Now reverse the bits */
       tree[n].Code = (ush)bi_reverse(next_code[len]++, len);

       Tracecv(tree != static_ltree, (stderr,"\nn %3d %c l %2d c %4x (%x) ",
           n, (isgraph(n) ? n : ' '), len, tree[n].Code, next_code[len] - 1));
   }
}

#ifdef GEN_TREES_H
local void gen_trees_header(void);
#endif

#ifndef ZLIB_DEBUG
#  define send_code(s, c, tree) send_bits(s, tree[c].Code, tree[c].Len)
  /* Send a code of the given tree. c and tree must not have side effects */

#else /* !ZLIB_DEBUG */
#  define send_code(s, c, tree) \
    { if (z_verbose>2) fprintf(stderr,"\ncd %3d ",(c)); \
      send_bits(s, tree[c].Code, tree[c].Len); }
#endif

/* ===========================================================================
* Send a value on a given number of bits.
* IN assertion: length <= 16 and value fits in length bits.
*/
#ifdef ZLIB_DEBUG
local void send_bits(deflate_state *s, int value, int length) {
   Tracevv((stderr," l %2d v %4x ", length, value));
   Assert(length > 0 && length <= 15, "invalid length");
   s->bits_sent += (ulg)length;

   /* If not enough room in bi_buf, use (valid) bits from bi_buf and
    * (16 - bi_valid) bits from value, leaving (width - (16 - bi_valid))
    * unused bits in value.
    */
   if (s->bi_valid > (int)Buf_size - length) {
       s->bi_buf |= (ush)value << s->bi_valid;
       put_short(s, s->bi_buf);
       s->bi_buf = (ush)value >> (Buf_size - s->bi_valid);
       s->bi_valid += length - Buf_size;
   } else {
       s->bi_buf |= (ush)value << s->bi_valid;
       s->bi_valid += length;
   }
}
#else /* !ZLIB_DEBUG */

#define send_bits(s, value, length) \
{ int len = length;\
 if (s->bi_valid > (int)Buf_size - len) {\
   int val = (int)value;\
   s->bi_buf |= (ush)val << s->bi_valid;\
   put_short(s, s->bi_buf);\
   s->bi_buf = (ush)val >> (Buf_size - s->bi_valid);\
   s->bi_valid += len - Buf_size;\
 } else {\
   s->bi_buf |= (ush)(value) << s->bi_valid;\
   s->bi_valid += len;\
 }\
}
#endif /* ZLIB_DEBUG */


/* the arguments must not have side effects */

/* ===========================================================================
* Initialize the various 'constant' tables.
*/
local void tr_static_init(void) {
#if defined(GEN_TREES_H) || !defined(STDC)
   static int static_init_done = 0;
   int n;        /* iterates over tree elements */
   int bits;     /* bit counter */
   int length;   /* length value */
   int code;     /* code value */
   int dist;     /* distance index */
   ush bl_count[MAX_BITS+1];
   /* number of codes at each bit length for an optimal tree */

   if (static_init_done) return;

   /* For some embedded targets, global variables are not initialized: */
#ifdef NO_INIT_GLOBAL_POINTERS
   static_l_desc.static_tree = static_ltree;
   static_l_desc.extra_bits = extra_lbits;
   static_d_desc.static_tree = static_dtree;
   static_d_desc.extra_bits = extra_dbits;
   static_bl_desc.extra_bits = extra_blbits;
#endif

   /* Initialize the mapping length (0..255) -> length code (0..28) */
   length = 0;
   for (code = 0; code < LENGTH_CODES-1; code++) {
       base_length[code] = length;
       for (n = 0; n < (1 << extra_lbits[code]); n++) {
           _length_code[length++] = (uch)code;
       }
   }
   Assert (length == 256, "tr_static_init: length != 256");
   /* Note that the length 255 (match length 258) can be represented
    * in two different ways: code 284 + 5 bits or code 285, so we
    * overwrite length_code[255] to use the best encoding:
    */
   _length_code[length - 1] = (uch)code;

   /* Initialize the mapping dist (0..32K) -> dist code (0..29) */
   dist = 0;
   for (code = 0 ; code < 16; code++) {
       base_dist[code] = dist;
       for (n = 0; n < (1 << extra_dbits[code]); n++) {
           _dist_code[dist++] = (uch)code;
       }
   }
   Assert (dist == 256, "tr_static_init: dist != 256");
   dist >>= 7; /* from now on, all distances are divided by 128 */
   for ( ; code < D_CODES; code++) {
       base_dist[code] = dist << 7;
       for (n = 0; n < (1 << (extra_dbits[code] - 7)); n++) {
           _dist_code[256 + dist++] = (uch)code;
       }
   }
   Assert (dist == 256, "tr_static_init: 256 + dist != 512");

   /* Construct the codes of the static literal tree */
   for (bits = 0; bits <= MAX_BITS; bits++) bl_count[bits] = 0;
   n = 0;
   while (n <= 143) static_ltree[n++].Len = 8, bl_count[8]++;
   while (n <= 255) static_ltree[n++].Len = 9, bl_count[9]++;
   while (n <= 279) static_ltree[n++].Len = 7, bl_count[7]++;
   while (n <= 287) static_ltree[n++].Len = 8, bl_count[8]++;
   /* Codes 286 and 287 do not exist, but we must include them in the
    * tree construction to get a canonical Huffman tree (longest code
    * all ones)
    */
   gen_codes((ct_data *)static_ltree, L_CODES+1, bl_count);

   /* The static distance tree is trivial: */
   for (n = 0; n < D_CODES; n++) {
       static_dtree[n].Len = 5;
       static_dtree[n].Code = bi_reverse((unsigned)n, 5);
   }
   static_init_done = 1;

#  ifdef GEN_TREES_H
   gen_trees_header();
#  endif
#endif /* defined(GEN_TREES_H) || !defined(STDC) */
}

/* ===========================================================================
* Generate the file trees.h describing the static trees.
*/
#ifdef GEN_TREES_H
#  ifndef ZLIB_DEBUG
#    include <stdio.h>
#  endif

#  define SEPARATOR(i, last, width) \
     ((i) == (last)? "\n};\n\n" :    \
      ((i) % (width) == (width) - 1 ? ",\n" : ", "))

void gen_trees_header(void) {
   FILE *header = fopen("trees.h", "w");
   int i;

   Assert (header != NULL, "Can't open trees.h");
   fprintf(header,
           "/* header created automatically with -DGEN_TREES_H */\n\n");

   fprintf(header, "local const ct_data static_ltree[L_CODES+2] = {\n");
   for (i = 0; i < L_CODES+2; i++) {
       fprintf(header, "{{%3u},{%3u}}%s", static_ltree[i].Code,
               static_ltree[i].Len, SEPARATOR(i, L_CODES+1, 5));
   }

   fprintf(header, "local const ct_data static_dtree[D_CODES] = {\n");
   for (i = 0; i < D_CODES; i++) {
       fprintf(header, "{{%2u},{%2u}}%s", static_dtree[i].Code,
               static_dtree[i].Len, SEPARATOR(i, D_CODES-1, 5));
   }

   fprintf(header, "const uch ZLIB_INTERNAL _dist_code[DIST_CODE_LEN] = {\n");
   for (i = 0; i < DIST_CODE_LEN; i++) {
       fprintf(header, "%2u%s", _dist_code[i],
               SEPARATOR(i, DIST_CODE_LEN-1, 20));
   }

   fprintf(header,
       "const uch ZLIB_INTERNAL _length_code[MAX_MATCH-MIN_MATCH+1]= {\n");
   for (i = 0; i < MAX_MATCH-MIN_MATCH+1; i++) {
       fprintf(header, "%2u%s", _length_code[i],
               SEPARATOR(i, MAX_MATCH-MIN_MATCH, 20));
   }

   fprintf(header, "local const int base_length[LENGTH_CODES] = {\n");
   for (i = 0; i < LENGTH_CODES; i++) {
       fprintf(header, "%1u%s", base_length[i],
               SEPARATOR(i, LENGTH_CODES-1, 20));
   }

   fprintf(header, "local const int base_dist[D_CODES] = {\n");
   for (i = 0; i < D_CODES; i++) {
       fprintf(header, "%5u%s", base_dist[i],
               SEPARATOR(i, D_CODES-1, 10));
   }

   fclose(header);
}
#endif /* GEN_TREES_H */

/* ===========================================================================
* Initialize a new block.
*/
local void init_block(deflate_state *s) {
   int n; /* iterates over tree elements */

   /* Initialize the trees. */
   for (n = 0; n < L_CODES;  n++) s->dyn_ltree[n].Freq = 0;
   for (n = 0; n < D_CODES;  n++) s->dyn_dtree[n].Freq = 0;
   for (n = 0; n < BL_CODES; n++) s->bl_tree[n].Freq = 0;

   s->dyn_ltree[END_BLOCK].Freq = 1;
   s->opt_len = s->static_len = 0L;
   s->sym_next = s->matches = 0;
}

/* ===========================================================================
* Initialize the tree data structures for a new zlib stream.
*/
void ZLIB_INTERNAL _tr_init(deflate_state *s) {
   tr_static_init();

   s->l_desc.dyn_tree = s->dyn_ltree;
   s->l_desc.stat_desc = &static_l_desc;

   s->d_desc.dyn_tree = s->dyn_dtree;
   s->d_desc.stat_desc = &static_d_desc;

   s->bl_desc.dyn_tree = s->bl_tree;
   s->bl_desc.stat_desc = &static_bl_desc;

   s->bi_buf = 0;
   s->bi_valid = 0;
#ifdef ZLIB_DEBUG
   s->compressed_len = 0L;
   s->bits_sent = 0L;
#endif

   /* Initialize the first block of the first file: */
   init_block(s);
}

#define SMALLEST 1
/* Index within the heap array of least frequent node in the Huffman tree */


/* ===========================================================================
* Remove the smallest element from the heap and recreate the heap with
* one less element. Updates heap and heap_len.
*/
#define pqremove(s, tree, top) \
{\
   top = s->heap[SMALLEST]; \
   s->heap[SMALLEST] = s->heap[s->heap_len--]; \
   pqdownheap(s, tree, SMALLEST); \
}

/* ===========================================================================
* Compares to subtrees, using the tree depth as tie breaker when
* the subtrees have equal frequency. This minimizes the worst case length.
*/
#define smaller(tree, n, m, depth) \
  (tree[n].Freq < tree[m].Freq || \
  (tree[n].Freq == tree[m].Freq && depth[n] <= depth[m]))

/* ===========================================================================
* Restore the heap property by moving down the tree starting at node k,
* exchanging a node with the smallest of its two sons if necessary, stopping
* when the heap property is re-established (each father smaller than its
* two sons).
*/
local void pqdownheap(deflate_state *s, ct_data *tree, int k) {
   int v = s->heap[k];
   int j = k << 1;  /* left son of k */
   while (j <= s->heap_len) {
       /* Set j to the smallest of the two sons: */
       if (j < s->heap_len &&
           smaller(tree, s->heap[j + 1], s->heap[j], s->depth)) {
           j++;
       }
       /* Exit if v is smaller than both sons */
       if (smaller(tree, v, s->heap[j], s->depth)) break;

       /* Exchange v with the smallest son */
       s->heap[k] = s->heap[j];  k = j;

       /* And continue down the tree, setting j to the left son of k */
       j <<= 1;
   }
   s->heap[k] = v;
}

/* ===========================================================================
* Compute the optimal bit lengths for a tree and update the total bit length
* for the current block.
* IN assertion: the fields freq and dad are set, heap[heap_max] and
*    above are the tree nodes sorted by increasing frequency.
* OUT assertions: the field len is set to the optimal bit length, the
*     array bl_count contains the frequencies for each bit length.
*     The length opt_len is updated; static_len is also updated if stree is
*     not null.
*/
local void gen_bitlen(deflate_state *s, tree_desc *desc) {
   ct_data *tree        = desc->dyn_tree;
   int max_code         = desc->max_code;
   const ct_data *stree = desc->stat_desc->static_tree;
   const intf *extra    = desc->stat_desc->extra_bits;
   int base             = desc->stat_desc->extra_base;
   int max_length       = desc->stat_desc->max_length;
   int h;              /* heap index */
   int n, m;           /* iterate over the tree elements */
   int bits;           /* bit length */
   int xbits;          /* extra bits */
   ush f;              /* frequency */
   int overflow = 0;   /* number of elements with bit length too large */

   for (bits = 0; bits <= MAX_BITS; bits++) s->bl_count[bits] = 0;

   /* In a first pass, compute the optimal bit lengths (which may
    * overflow in the case of the bit length tree).
    */
   tree[s->heap[s->heap_max]].Len = 0; /* root of the heap */

   for (h = s->heap_max + 1; h < HEAP_SIZE; h++) {
       n = s->heap[h];
       bits = tree[tree[n].Dad].Len + 1;
       if (bits > max_length) bits = max_length, overflow++;
       tree[n].Len = (ush)bits;
       /* We overwrite tree[n].Dad which is no longer needed */

       if (n > max_code) continue; /* not a leaf node */

       s->bl_count[bits]++;
       xbits = 0;
       if (n >= base) xbits = extra[n - base];
       f = tree[n].Freq;
       s->opt_len += (ulg)f * (unsigned)(bits + xbits);
       if (stree) s->static_len += (ulg)f * (unsigned)(stree[n].Len + xbits);
   }
   if (overflow == 0) return;

   Tracev((stderr,"\nbit length overflow\n"));
   /* This happens for example on obj2 and pic of the Calgary corpus */

   /* Find the first bit length which could increase: */
   do {
       bits = max_length - 1;
       while (s->bl_count[bits] == 0) bits--;
       s->bl_count[bits]--;        /* move one leaf down the tree */
       s->bl_count[bits + 1] += 2; /* move one overflow item as its brother */
       s->bl_count[max_length]--;
       /* The brother of the overflow item also moves one step up,
        * but this does not affect bl_count[max_length]
        */
       overflow -= 2;
   } while (overflow > 0);

   /* Now recompute all bit lengths, scanning in increasing frequency.
    * h is still equal to HEAP_SIZE. (It is simpler to reconstruct all
    * lengths instead of fixing only the wrong ones. This idea is taken
    * from 'ar' written by Haruhiko Okumura.)
    */
   for (bits = max_length; bits != 0; bits--) {
       n = s->bl_count[bits];
       while (n != 0) {
           m = s->heap[--h];
           if (m > max_code) continue;
           if ((unsigned) tree[m].Len != (unsigned) bits) {
               Tracev((stderr,"code %d bits %d->%d\n", m, tree[m].Len, bits));
               s->opt_len += ((ulg)bits - tree[m].Len) * tree[m].Freq;
               tree[m].Len = (ush)bits;
           }
           n--;
       }
   }
}

#ifdef DUMP_BL_TREE
#  include <stdio.h>
#endif

/* ===========================================================================
* Construct one Huffman tree and assigns the code bit strings and lengths.
* Update the total bit length for the current block.
* IN assertion: the field freq is set for all tree elements.
* OUT assertions: the fields len and code are set to the optimal bit length
*     and corresponding code. The length opt_len is updated; static_len is
*     also updated if stree is not null. The field max_code is set.
*/
local void build_tree(deflate_state *s, tree_desc *desc) {
   ct_data *tree         = desc->dyn_tree;
   const ct_data *stree  = desc->stat_desc->static_tree;
   int elems             = desc->stat_desc->elems;
   int n, m;          /* iterate over heap elements */
   int max_code = -1; /* largest code with non zero frequency */
   int node;          /* new node being created */

   /* Construct the initial heap, with least frequent element in
    * heap[SMALLEST]. The sons of heap[n] are heap[2*n] and heap[2*n + 1].
    * heap[0] is not used.
    */
   s->heap_len = 0, s->heap_max = HEAP_SIZE;

   for (n = 0; n < elems; n++) {
       if (tree[n].Freq != 0) {
           s->heap[++(s->heap_len)] = max_code = n;
           s->depth[n] = 0;
       } else {
           tree[n].Len = 0;
       }
   }

   /* The pkzip format requires that at least one distance code exists,
    * and that at least one bit should be sent even if there is only one
    * possible code. So to avoid special checks later on we force at least
    * two codes of non zero frequency.
    */
   while (s->heap_len < 2) {
       node = s->heap[++(s->heap_len)] = (max_code < 2 ? ++max_code : 0);
       tree[node].Freq = 1;
       s->depth[node] = 0;
       s->opt_len--; if (stree) s->static_len -= stree[node].Len;
       /* node is 0 or 1 so it does not have extra bits */
   }
   desc->max_code = max_code;

   /* The elements heap[heap_len/2 + 1 .. heap_len] are leaves of the tree,
    * establish sub-heaps of increasing lengths:
    */
   for (n = s->heap_len/2; n >= 1; n--) pqdownheap(s, tree, n);

   /* Construct the Huffman tree by repeatedly combining the least two
    * frequent nodes.
    */
   node = elems;              /* next internal node of the tree */
   do {
       pqremove(s, tree, n);  /* n = node of least frequency */
       m = s->heap[SMALLEST]; /* m = node of next least frequency */

       s->heap[--(s->heap_max)] = n; /* keep the nodes sorted by frequency */
       s->heap[--(s->heap_max)] = m;

       /* Create a new node father of n and m */
       tree[node].Freq = tree[n].Freq + tree[m].Freq;
       s->depth[node] = (uch)((s->depth[n] >= s->depth[m] ?
                               s->depth[n] : s->depth[m]) + 1);
       tree[n].Dad = tree[m].Dad = (ush)node;
#ifdef DUMP_BL_TREE
       if (tree == s->bl_tree) {
           fprintf(stderr,"\nnode %d(%d), sons %d(%d) %d(%d)",
                   node, tree[node].Freq, n, tree[n].Freq, m, tree[m].Freq);
       }
#endif
       /* and insert the new node in the heap */
       s->heap[SMALLEST] = node++;
       pqdownheap(s, tree, SMALLEST);

   } while (s->heap_len >= 2);

   s->heap[--(s->heap_max)] = s->heap[SMALLEST];

   /* At this point, the fields freq and dad are set. We can now
    * generate the bit lengths.
    */
   gen_bitlen(s, (tree_desc *)desc);

   /* The field len is now set, we can generate the bit codes */
   gen_codes ((ct_data *)tree, max_code, s->bl_count);
}

/* ===========================================================================
* Scan a literal or distance tree to determine the frequencies of the codes
* in the bit length tree.
*/
local void scan_tree(deflate_state *s, ct_data *tree, int max_code) {
   int n;                     /* iterates over all tree elements */
   int prevlen = -1;          /* last emitted length */
   int curlen;                /* length of current code */
   int nextlen = tree[0].Len; /* length of next code */
   int count = 0;             /* repeat count of the current code */
   int max_count = 7;         /* max repeat count */
   int min_count = 4;         /* min repeat count */

   if (nextlen == 0) max_count = 138, min_count = 3;
   tree[max_code + 1].Len = (ush)0xffff; /* guard */

   for (n = 0; n <= max_code; n++) {
       curlen = nextlen; nextlen = tree[n + 1].Len;
       if (++count < max_count && curlen == nextlen) {
           continue;
       } else if (count < min_count) {
           s->bl_tree[curlen].Freq += count;
       } else if (curlen != 0) {
           if (curlen != prevlen) s->bl_tree[curlen].Freq++;
           s->bl_tree[REP_3_6].Freq++;
       } else if (count <= 10) {
           s->bl_tree[REPZ_3_10].Freq++;
       } else {
           s->bl_tree[REPZ_11_138].Freq++;
       }
       count = 0; prevlen = curlen;
       if (nextlen == 0) {
           max_count = 138, min_count = 3;
       } else if (curlen == nextlen) {
           max_count = 6, min_count = 3;
       } else {
           max_count = 7, min_count = 4;
       }
   }
}

/* ===========================================================================
* Send a literal or distance tree in compressed form, using the codes in
* bl_tree.
*/
local void send_tree(deflate_state *s, ct_data *tree, int max_code) {
   int n;                     /* iterates over all tree elements */
   int prevlen = -1;          /* last emitted length */
   int curlen;                /* length of current code */
   int nextlen = tree[0].Len; /* length of next code */
   int count = 0;             /* repeat count of the current code */
   int max_count = 7;         /* max repeat count */
   int min_count = 4;         /* min repeat count */

   /* tree[max_code + 1].Len = -1; */  /* guard already set */
   if (nextlen == 0) max_count = 138, min_count = 3;

   for (n = 0; n <= max_code; n++) {
       curlen = nextlen; nextlen = tree[n + 1].Len;
       if (++count < max_count && curlen == nextlen) {
           continue;
       } else if (count < min_count) {
           do { send_code(s, curlen, s->bl_tree); } while (--count != 0);

       } else if (curlen != 0) {
           if (curlen != prevlen) {
               send_code(s, curlen, s->bl_tree); count--;
           }
           Assert(count >= 3 && count <= 6, " 3_6?");
           send_code(s, REP_3_6, s->bl_tree); send_bits(s, count - 3, 2);

       } else if (count <= 10) {
           send_code(s, REPZ_3_10, s->bl_tree); send_bits(s, count - 3, 3);

       } else {
           send_code(s, REPZ_11_138, s->bl_tree); send_bits(s, count - 11, 7);
       }
       count = 0; prevlen = curlen;
       if (nextlen == 0) {
           max_count = 138, min_count = 3;
       } else if (curlen == nextlen) {
           max_count = 6, min_count = 3;
       } else {
           max_count = 7, min_count = 4;
       }
   }
}

/* ===========================================================================
* Construct the Huffman tree for the bit lengths and return the index in
* bl_order of the last bit length code to send.
*/
local int build_bl_tree(deflate_state *s) {
   int max_blindex;  /* index of last bit length code of non zero freq */

   /* Determine the bit length frequencies for literal and distance trees */
   scan_tree(s, (ct_data *)s->dyn_ltree, s->l_desc.max_code);
   scan_tree(s, (ct_data *)s->dyn_dtree, s->d_desc.max_code);

   /* Build the bit length tree: */
   build_tree(s, (tree_desc *)(&(s->bl_desc)));
   /* opt_len now includes the length of the tree representations, except the
    * lengths of the bit lengths codes and the 5 + 5 + 4 bits for the counts.
    */

   /* Determine the number of bit length codes to send. The pkzip format
    * requires that at least 4 bit length codes be sent. (appnote.txt says
    * 3 but the actual value used is 4.)
    */
   for (max_blindex = BL_CODES-1; max_blindex >= 3; max_blindex--) {
       if (s->bl_tree[bl_order[max_blindex]].Len != 0) break;
   }
   /* Update opt_len to include the bit length tree and counts */
   s->opt_len += 3*((ulg)max_blindex + 1) + 5 + 5 + 4;
   Tracev((stderr, "\ndyn trees: dyn %ld, stat %ld",
           s->opt_len, s->static_len));

   return max_blindex;
}

/* ===========================================================================
* Send the header for a block using dynamic Huffman trees: the counts, the
* lengths of the bit length codes, the literal tree and the distance tree.
* IN assertion: lcodes >= 257, dcodes >= 1, blcodes >= 4.
*/
local void send_all_trees(deflate_state *s, int lcodes, int dcodes,
                         int blcodes) {
   int rank;                    /* index in bl_order */

   Assert (lcodes >= 257 && dcodes >= 1 && blcodes >= 4, "not enough codes");
   Assert (lcodes <= L_CODES && dcodes <= D_CODES && blcodes <= BL_CODES,
           "too many codes");
   Tracev((stderr, "\nbl counts: "));
   send_bits(s, lcodes - 257, 5);  /* not +255 as stated in appnote.txt */
   send_bits(s, dcodes - 1,   5);
   send_bits(s, blcodes - 4,  4);  /* not -3 as stated in appnote.txt */
   for (rank = 0; rank < blcodes; rank++) {
       Tracev((stderr, "\nbl code %2d ", bl_order[rank]));
       send_bits(s, s->bl_tree[bl_order[rank]].Len, 3);
   }
   Tracev((stderr, "\nbl tree: sent %ld", s->bits_sent));

   send_tree(s, (ct_data *)s->dyn_ltree, lcodes - 1);  /* literal tree */
   Tracev((stderr, "\nlit tree: sent %ld", s->bits_sent));

   send_tree(s, (ct_data *)s->dyn_dtree, dcodes - 1);  /* distance tree */
   Tracev((stderr, "\ndist tree: sent %ld", s->bits_sent));
}

/* ===========================================================================
* Send a stored block
*/
void ZLIB_INTERNAL _tr_stored_block(deflate_state *s, charf *buf,
                                   ulg stored_len, int last) {
   send_bits(s, (STORED_BLOCK<<1) + last, 3);  /* send block type */
   bi_windup(s);        /* align on byte boundary */
   put_short(s, (ush)stored_len);
   put_short(s, (ush)~stored_len);
   if (stored_len)
       zmemcpy(s->pending_buf + s->pending, (Bytef *)buf, stored_len);
   s->pending += stored_len;
#ifdef ZLIB_DEBUG
   s->compressed_len = (s->compressed_len + 3 + 7) & (ulg)~7L;
   s->compressed_len += (stored_len + 4) << 3;
   s->bits_sent += 2*16;
   s->bits_sent += stored_len << 3;
#endif
}

/* ===========================================================================
* Flush the bits in the bit buffer to pending output (leaves at most 7 bits)
*/
void ZLIB_INTERNAL _tr_flush_bits(deflate_state *s) {
   bi_flush(s);
}

/* ===========================================================================
* Send one empty static block to give enough lookahead for inflate.
* This takes 10 bits, of which 7 may remain in the bit buffer.
*/
void ZLIB_INTERNAL _tr_align(deflate_state *s) {
   send_bits(s, STATIC_TREES<<1, 3);
   send_code(s, END_BLOCK, static_ltree);
#ifdef ZLIB_DEBUG
   s->compressed_len += 10L; /* 3 for block type, 7 for EOB */
#endif
   bi_flush(s);
}

/* ===========================================================================
* Send the block data compressed using the given Huffman trees
*/
local void compress_block(deflate_state *s, const ct_data *ltree,
                         const ct_data *dtree) {
   unsigned dist;      /* distance of matched string */
   int lc;             /* match length or unmatched char (if dist == 0) */
   unsigned sx = 0;    /* running index in symbol buffers */
   unsigned code;      /* the code to send */
   int extra;          /* number of extra bits to send */

   if (s->sym_next != 0) do {
#ifdef LIT_MEM
       dist = s->d_buf[sx];
       lc = s->l_buf[sx++];
#else
       dist = s->sym_buf[sx++] & 0xff;
       dist += (unsigned)(s->sym_buf[sx++] & 0xff) << 8;
       lc = s->sym_buf[sx++];
#endif
       if (dist == 0) {
           send_code(s, lc, ltree); /* send a literal byte */
           Tracecv(isgraph(lc), (stderr," '%c' ", lc));
       } else {
           /* Here, lc is the match length - MIN_MATCH */
           code = _length_code[lc];
           send_code(s, code + LITERALS + 1, ltree);   /* send length code */
           extra = extra_lbits[code];
           if (extra != 0) {
               lc -= base_length[code];
               send_bits(s, lc, extra);       /* send the extra length bits */
           }
           dist--; /* dist is now the match distance - 1 */
           code = d_code(dist);
           Assert (code < D_CODES, "bad d_code");

           send_code(s, code, dtree);       /* send the distance code */
           extra = extra_dbits[code];
           if (extra != 0) {
               dist -= (unsigned)base_dist[code];
               send_bits(s, dist, extra);   /* send the extra distance bits */
           }
       } /* literal or match pair ? */

       /* Check for no overlay of pending_buf on needed symbols */
#ifdef LIT_MEM
       Assert(s->pending < 2 * (s->lit_bufsize + sx), "pendingBuf overflow");
#else
       Assert(s->pending < s->lit_bufsize + sx, "pendingBuf overflow");
#endif

   } while (sx < s->sym_next);

   send_code(s, END_BLOCK, ltree);
}

/* ===========================================================================
* Check if the data type is TEXT or BINARY, using the following algorithm:
* - TEXT if the two conditions below are satisfied:
*    a) There are no non-portable control characters belonging to the
*       "block list" (0..6, 14..25, 28..31).
*    b) There is at least one printable character belonging to the
*       "allow list" (9 {TAB}, 10 {LF}, 13 {CR}, 32..255).
* - BINARY otherwise.
* - The following partially-portable control characters form a
*   "gray list" that is ignored in this detection algorithm:
*   (7 {BEL}, 8 {BS}, 11 {VT}, 12 {FF}, 26 {SUB}, 27 {ESC}).
* IN assertion: the fields Freq of dyn_ltree are set.
*/
local int detect_data_type(deflate_state *s) {
   /* block_mask is the bit mask of block-listed bytes
    * set bits 0..6, 14..25, and 28..31
    * 0xf3ffc07f = binary 11110011111111111100000001111111
    */
   unsigned long block_mask = 0xf3ffc07fUL;
   int n;

   /* Check for non-textual ("block-listed") bytes. */
   for (n = 0; n <= 31; n++, block_mask >>= 1)
       if ((block_mask & 1) && (s->dyn_ltree[n].Freq != 0))
           return Z_BINARY;

   /* Check for textual ("allow-listed") bytes. */
   if (s->dyn_ltree[9].Freq != 0 || s->dyn_ltree[10].Freq != 0
           || s->dyn_ltree[13].Freq != 0)
       return Z_TEXT;
   for (n = 32; n < LITERALS; n++)
       if (s->dyn_ltree[n].Freq != 0)
           return Z_TEXT;

   /* There are no "block-listed" or "allow-listed" bytes:
    * this stream either is empty or has tolerated ("gray-listed") bytes only.
    */
   return Z_BINARY;
}

/* ===========================================================================
* Determine the best encoding for the current block: dynamic trees, static
* trees or store, and write out the encoded block.
*/
void ZLIB_INTERNAL _tr_flush_block(deflate_state *s, charf *buf,
                                  ulg stored_len, int last) {
   ulg opt_lenb, static_lenb; /* opt_len and static_len in bytes */
   int max_blindex = 0;  /* index of last bit length code of non zero freq */

   /* Build the Huffman trees unless a stored block is forced */
   if (s->level > 0) {

       /* Check if the file is binary or text */
       if (s->strm->data_type == Z_UNKNOWN)
           s->strm->data_type = detect_data_type(s);

       /* Construct the literal and distance trees */
       build_tree(s, (tree_desc *)(&(s->l_desc)));
       Tracev((stderr, "\nlit data: dyn %ld, stat %ld", s->opt_len,
               s->static_len));

       build_tree(s, (tree_desc *)(&(s->d_desc)));
       Tracev((stderr, "\ndist data: dyn %ld, stat %ld", s->opt_len,
               s->static_len));
       /* At this point, opt_len and static_len are the total bit lengths of
        * the compressed block data, excluding the tree representations.
        */

       /* Build the bit length tree for the above two trees, and get the index
        * in bl_order of the last bit length code to send.
        */
       max_blindex = build_bl_tree(s);

       /* Determine the best encoding. Compute the block lengths in bytes. */
       opt_lenb = (s->opt_len + 3 + 7) >> 3;
       static_lenb = (s->static_len + 3 + 7) >> 3;

       Tracev((stderr, "\nopt %lu(%lu) stat %lu(%lu) stored %lu lit %u ",
               opt_lenb, s->opt_len, static_lenb, s->static_len, stored_len,
               s->sym_next / 3));

#ifndef FORCE_STATIC
       if (static_lenb <= opt_lenb || s->strategy == Z_FIXED)
#endif
           opt_lenb = static_lenb;

   } else {
       Assert(buf != (char*)0, "lost buf");
       opt_lenb = static_lenb = stored_len + 5; /* force a stored block */
   }

#ifdef FORCE_STORED
   if (buf != (char*)0) { /* force stored block */
#else
   if (stored_len + 4 <= opt_lenb && buf != (char*)0) {
                      /* 4: two words for the lengths */
#endif
       /* The test buf != NULL is only necessary if LIT_BUFSIZE > WSIZE.
        * Otherwise we can't have processed more than WSIZE input bytes since
        * the last block flush, because compression would have been
        * successful. If LIT_BUFSIZE <= WSIZE, it is never too late to
        * transform a block into a stored block.
        */
       _tr_stored_block(s, buf, stored_len, last);

   } else if (static_lenb == opt_lenb) {
       send_bits(s, (STATIC_TREES<<1) + last, 3);
       compress_block(s, (const ct_data *)static_ltree,
                      (const ct_data *)static_dtree);
#ifdef ZLIB_DEBUG
       s->compressed_len += 3 + s->static_len;
#endif
   } else {
       send_bits(s, (DYN_TREES<<1) + last, 3);
       send_all_trees(s, s->l_desc.max_code + 1, s->d_desc.max_code + 1,
                      max_blindex + 1);
       compress_block(s, (const ct_data *)s->dyn_ltree,
                      (const ct_data *)s->dyn_dtree);
#ifdef ZLIB_DEBUG
       s->compressed_len += 3 + s->opt_len;
#endif
   }
   Assert (s->compressed_len == s->bits_sent, "bad compressed size");
   /* The above check is made mod 2^32, for files larger than 512 MB
    * and uLong implemented on 32 bits.
    */
   init_block(s);

   if (last) {
       bi_windup(s);
#ifdef ZLIB_DEBUG
       s->compressed_len += 7;  /* align on byte boundary */
#endif
   }
   Tracev((stderr,"\ncomprlen %lu(%lu) ", s->compressed_len >> 3,
          s->compressed_len - 7*last));
}

/* ===========================================================================
* Save the match info and tally the frequency counts. Return true if
* the current block must be flushed.
*/
int ZLIB_INTERNAL _tr_tally(deflate_state *s, unsigned dist, unsigned lc) {
#ifdef LIT_MEM
   s->d_buf[s->sym_next] = (ush)dist;
   s->l_buf[s->sym_next++] = (uch)lc;
#else
   s->sym_buf[s->sym_next++] = (uch)dist;
   s->sym_buf[s->sym_next++] = (uch)(dist >> 8);
   s->sym_buf[s->sym_next++] = (uch)lc;
#endif
   if (dist == 0) {
       /* lc is the unmatched char */
       s->dyn_ltree[lc].Freq++;
   } else {
       s->matches++;
       /* Here, lc is the match length - MIN_MATCH */
       dist--;             /* dist = match distance - 1 */
       Assert((ush)dist < (ush)MAX_DIST(s) &&
              (ush)lc <= (ush)(MAX_MATCH-MIN_MATCH) &&
              (ush)d_code(dist) < (ush)D_CODES,  "_tr_tally: bad match");

       s->dyn_ltree[_length_code[lc] + LITERALS + 1].Freq++;
       s->dyn_dtree[d_code(dist)].Freq++;
   }
   return (s->sym_next == s->sym_end);
}