tor-browser

hb-ot-layout-gsubgpos.hh (158834B)

---

/*
* Copyright © 2007,2008,2009,2010  Red Hat, Inc.
* Copyright © 2010,2012  Google, Inc.
*
*  This is part of HarfBuzz, a text shaping library.
*
* Permission is hereby granted, without written agreement and without
* license or royalty fees, to use, copy, modify, and distribute this
* software and its documentation for any purpose, provided that the
* above copyright notice and the following two paragraphs appear in
* all copies of this software.
*
* IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
* DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
* ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
* IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
* DAMAGE.
*
* THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
* BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
* FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
* ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
* PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
*
* Red Hat Author(s): Behdad Esfahbod
* Google Author(s): Behdad Esfahbod
*/

#ifndef HB_OT_LAYOUT_GSUBGPOS_HH
#define HB_OT_LAYOUT_GSUBGPOS_HH

#include "hb.hh"
#include "hb-buffer.hh"
#include "hb-map.hh"
#include "hb-set.hh"
#include "hb-ot-map.hh"
#include "hb-ot-layout-common.hh"
#include "hb-ot-layout-gdef-table.hh"


namespace OT {


struct hb_intersects_context_t :
      hb_dispatch_context_t<hb_intersects_context_t, bool>
{
 template <typename T>
 return_t dispatch (const T &obj) { return obj.intersects (this->glyphs); }
 static return_t default_return_value () { return false; }
 bool stop_sublookup_iteration (return_t r) const { return r; }

 const hb_set_t *glyphs;

 hb_intersects_context_t (const hb_set_t *glyphs_) :
                           glyphs (glyphs_) {}
};

struct hb_have_non_1to1_context_t :
      hb_dispatch_context_t<hb_have_non_1to1_context_t, bool>
{
 template <typename T>
 return_t dispatch (const T &obj) { return obj.may_have_non_1to1 (); }
 static return_t default_return_value () { return false; }
 bool stop_sublookup_iteration (return_t r) const { return r; }
};

struct hb_closure_context_t :
      hb_dispatch_context_t<hb_closure_context_t>
{
 typedef return_t (*recurse_func_t) (hb_closure_context_t *c, unsigned lookup_index, hb_set_t *covered_seq_indicies, unsigned seq_index, unsigned end_index);
 template <typename T>
 return_t dispatch (const T &obj) { obj.closure (this); return hb_empty_t (); }
 static return_t default_return_value () { return hb_empty_t (); }
 void recurse (unsigned lookup_index, hb_set_t *covered_seq_indicies, unsigned seq_index, unsigned end_index)
 {
   if (unlikely (nesting_level_left == 0 || !recurse_func))
     return;

   nesting_level_left--;
   recurse_func (this, lookup_index, covered_seq_indicies, seq_index, end_index);
   nesting_level_left++;
 }

 void reset_lookup_visit_count ()
 { lookup_count = 0; }

 bool lookup_limit_exceeded ()
 { return lookup_count > HB_MAX_LOOKUP_VISIT_COUNT; }

 bool should_visit_lookup (unsigned int lookup_index)
 {
   if (lookup_count++ > HB_MAX_LOOKUP_VISIT_COUNT)
     return false;

   if (is_lookup_done (lookup_index))
     return false;

   return true;
 }

 bool is_lookup_done (unsigned int lookup_index)
 {
   if (unlikely (done_lookups_glyph_count->in_error () ||
	  done_lookups_glyph_set->in_error ()))
     return true;

   /* Have we visited this lookup with the current set of glyphs? */
   if (done_lookups_glyph_count->get (lookup_index) != glyphs->get_population ())
   {
     done_lookups_glyph_count->set (lookup_index, glyphs->get_population ());

     if (!done_lookups_glyph_set->has (lookup_index))
     {
if (unlikely (!done_lookups_glyph_set->set (lookup_index, hb::unique_ptr<hb_set_t> {hb_set_create ()})))
  return true;
     }

     done_lookups_glyph_set->get (lookup_index)->clear ();
   }

   hb_set_t *covered_glyph_set = done_lookups_glyph_set->get (lookup_index);
   if (unlikely (covered_glyph_set->in_error ()))
     return true;
   if (parent_active_glyphs ().is_subset (*covered_glyph_set))
     return true;

   covered_glyph_set->union_ (parent_active_glyphs ());
   return false;
 }

 const hb_set_t& previous_parent_active_glyphs () {
   if (active_glyphs_stack.length <= 1)
     return *glyphs;

   return active_glyphs_stack[active_glyphs_stack.length - 2];
 }

 const hb_set_t& parent_active_glyphs ()
 {
   if (!active_glyphs_stack)
     return *glyphs;

   return active_glyphs_stack.tail ();
 }

 hb_set_t* push_cur_active_glyphs ()
 {
   hb_set_t *s = active_glyphs_stack.push ();
   if (unlikely (active_glyphs_stack.in_error ()))
     return nullptr;
   return s;
 }

 bool pop_cur_done_glyphs ()
 {
   if (!active_glyphs_stack)
     return false;

   active_glyphs_stack.pop ();
   return true;
 }

 hb_face_t *face;
 hb_set_t *glyphs;
 hb_set_t output[1];
 hb_vector_t<hb_set_t> active_glyphs_stack;
 recurse_func_t recurse_func = nullptr;
 unsigned int nesting_level_left;

 hb_closure_context_t (hb_face_t *face_,
		hb_set_t *glyphs_,
		hb_map_t *done_lookups_glyph_count_,
		hb_hashmap_t<unsigned, hb::unique_ptr<hb_set_t>> *done_lookups_glyph_set_,
		unsigned int nesting_level_left_ = HB_MAX_NESTING_LEVEL) :
		  face (face_),
		  glyphs (glyphs_),
		  nesting_level_left (nesting_level_left_),
		  done_lookups_glyph_count (done_lookups_glyph_count_),
		  done_lookups_glyph_set (done_lookups_glyph_set_)
 {}

 ~hb_closure_context_t () { flush (); }

 void set_recurse_func (recurse_func_t func) { recurse_func = func; }

 void flush ()
 {
   output->del_range (face->get_num_glyphs (), HB_SET_VALUE_INVALID);	/* Remove invalid glyphs. */
   glyphs->union_ (*output);
   output->clear ();
   active_glyphs_stack.pop ();
   active_glyphs_stack.reset ();
 }

 private:
 hb_map_t *done_lookups_glyph_count;
 hb_hashmap_t<unsigned, hb::unique_ptr<hb_set_t>> *done_lookups_glyph_set;
 unsigned int lookup_count = 0;
};



struct hb_closure_lookups_context_t :
      hb_dispatch_context_t<hb_closure_lookups_context_t>
{
 typedef return_t (*recurse_func_t) (hb_closure_lookups_context_t *c, unsigned lookup_index);
 template <typename T>
 return_t dispatch (const T &obj) { obj.closure_lookups (this); return hb_empty_t (); }
 static return_t default_return_value () { return hb_empty_t (); }
 void recurse (unsigned lookup_index)
 {
   if (unlikely (nesting_level_left == 0 || !recurse_func))
     return;

   /* Return if new lookup was recursed to before. */
   if (lookup_limit_exceeded ()
       || visited_lookups->in_error ()
       || visited_lookups->has (lookup_index))
     // Don't increment lookup count here, that will be done in the call to closure_lookups()
     // made by recurse_func.
     return;

   nesting_level_left--;
   recurse_func (this, lookup_index);
   nesting_level_left++;
 }

 void set_lookup_visited (unsigned lookup_index)
 { visited_lookups->add (lookup_index); }

 void set_lookup_inactive (unsigned lookup_index)
 { inactive_lookups->add (lookup_index); }

 bool lookup_limit_exceeded ()
 {
   bool ret = lookup_count > HB_MAX_LOOKUP_VISIT_COUNT;
   if (ret)
     DEBUG_MSG (SUBSET, nullptr, "lookup visit count limit exceeded in lookup closure!");
   return ret; }

 bool is_lookup_visited (unsigned lookup_index)
 {
   if (unlikely (lookup_count++ > HB_MAX_LOOKUP_VISIT_COUNT))
   {
     DEBUG_MSG (SUBSET, nullptr, "total visited lookup count %u exceeds max limit, lookup %u is dropped.",
                lookup_count, lookup_index);
     return true;
   }

   if (unlikely (visited_lookups->in_error ()))
     return true;

   return visited_lookups->has (lookup_index);
 }

 hb_face_t *face;
 const hb_set_t *glyphs;
 recurse_func_t recurse_func;
 unsigned int nesting_level_left;

 hb_closure_lookups_context_t (hb_face_t *face_,
			const hb_set_t *glyphs_,
			hb_set_t *visited_lookups_,
			hb_set_t *inactive_lookups_,
			unsigned nesting_level_left_ = HB_MAX_NESTING_LEVEL) :
			face (face_),
			glyphs (glyphs_),
			recurse_func (nullptr),
			nesting_level_left (nesting_level_left_),
			visited_lookups (visited_lookups_),
			inactive_lookups (inactive_lookups_),
			lookup_count (0) {}

 void set_recurse_func (recurse_func_t func) { recurse_func = func; }

 private:
 hb_set_t *visited_lookups;
 hb_set_t *inactive_lookups;
 unsigned int lookup_count;
};

struct hb_would_apply_context_t :
      hb_dispatch_context_t<hb_would_apply_context_t, bool>
{
 template <typename T>
 return_t dispatch (const T &obj) { return obj.would_apply (this); }
 static return_t default_return_value () { return false; }
 bool stop_sublookup_iteration (return_t r) const { return r; }

 hb_face_t *face;
 const hb_codepoint_t *glyphs;
 unsigned int len;
 bool zero_context;

 hb_would_apply_context_t (hb_face_t *face_,
		    const hb_codepoint_t *glyphs_,
		    unsigned int len_,
		    bool zero_context_) :
		      face (face_),
		      glyphs (glyphs_),
		      len (len_),
		      zero_context (zero_context_) {}
};

struct hb_collect_glyphs_context_t :
      hb_dispatch_context_t<hb_collect_glyphs_context_t>
{
 typedef return_t (*recurse_func_t) (hb_collect_glyphs_context_t *c, unsigned int lookup_index);
 template <typename T>
 return_t dispatch (const T &obj) { obj.collect_glyphs (this); return hb_empty_t (); }
 static return_t default_return_value () { return hb_empty_t (); }
 void recurse (unsigned int lookup_index)
 {
   if (unlikely (nesting_level_left == 0 || !recurse_func))
     return;

   /* Note that GPOS sets recurse_func to nullptr already, so it doesn't get
    * past the previous check.  For GSUB, we only want to collect the output
    * glyphs in the recursion.  If output is not requested, we can go home now.
    *
    * Note further, that the above is not exactly correct.  A recursed lookup
    * is allowed to match input that is not matched in the context, but that's
    * not how most fonts are built.  It's possible to relax that and recurse
    * with all sets here if it proves to be an issue.
    */

   if (output == hb_set_get_empty ())
     return;

   /* Return if new lookup was recursed to before. */
   if (recursed_lookups->has (lookup_index))
     return;

   hb_set_t *old_before = before;
   hb_set_t *old_input  = input;
   hb_set_t *old_after  = after;
   before = input = after = hb_set_get_empty ();

   nesting_level_left--;
   recurse_func (this, lookup_index);
   nesting_level_left++;

   before = old_before;
   input  = old_input;
   after  = old_after;

   recursed_lookups->add (lookup_index);
 }

 hb_face_t *face;
 hb_set_t *before;
 hb_set_t *input;
 hb_set_t *after;
 hb_set_t *output;
 recurse_func_t recurse_func;
 hb_set_t *recursed_lookups;
 unsigned int nesting_level_left;

 hb_collect_glyphs_context_t (hb_face_t *face_,
		       hb_set_t  *glyphs_before, /* OUT.  May be NULL */
		       hb_set_t  *glyphs_input,  /* OUT.  May be NULL */
		       hb_set_t  *glyphs_after,  /* OUT.  May be NULL */
		       hb_set_t  *glyphs_output, /* OUT.  May be NULL */
		       unsigned int nesting_level_left_ = HB_MAX_NESTING_LEVEL) :
		      face (face_),
		      before (glyphs_before ? glyphs_before : hb_set_get_empty ()),
		      input  (glyphs_input  ? glyphs_input  : hb_set_get_empty ()),
		      after  (glyphs_after  ? glyphs_after  : hb_set_get_empty ()),
		      output (glyphs_output ? glyphs_output : hb_set_get_empty ()),
		      recurse_func (nullptr),
		      recursed_lookups (hb_set_create ()),
		      nesting_level_left (nesting_level_left_) {}
 ~hb_collect_glyphs_context_t () { hb_set_destroy (recursed_lookups); }

 void set_recurse_func (recurse_func_t func) { recurse_func = func; }
};



template <typename set_t>
struct hb_collect_coverage_context_t :
      hb_dispatch_context_t<hb_collect_coverage_context_t<set_t>, const Coverage &>
{
 typedef const Coverage &return_t; // Stoopid that we have to dupe this here.
 template <typename T>
 return_t dispatch (const T &obj) { return obj.get_coverage (); }
 static return_t default_return_value () { return Null (Coverage); }
 bool stop_sublookup_iteration (return_t r) const
 {
   r.collect_coverage (set);
   return false;
 }

 hb_collect_coverage_context_t (set_t *set_) :
			   set (set_) {}

 set_t *set;
};

struct matcher_t
{
 typedef bool (*match_func_t) (hb_glyph_info_t &info, unsigned value, const void *data);

 template <typename context_t>
 void init (const context_t *c, bool context_match = false)
 {
   set_match_func (nullptr, nullptr);
   lookup_props = c->lookup_props;
   /* Ignore ZWNJ if we are matching GPOS, or matching GSUB context and asked to. */
   ignore_zwnj = c->table_index == 1 || (context_match && c->auto_zwnj);
   /* Ignore ZWJ if we are matching context, or asked to. */
   ignore_zwj = context_match || c->auto_zwj;
   /* Ignore hidden glyphs (like CGJ) during GPOS. */
   ignore_hidden = c->table_index == 1;
   mask = context_match ? -1 : c->lookup_mask;
   /* Per syllable matching is only for GSUB. */
   per_syllable = c->table_index == 0 && c->per_syllable;
   syllable = 0;
 }

 void set_match_func (match_func_t match_func_,
	       const void *match_data_)
 { match_func = match_func_; match_data = match_data_; }

 enum may_match_t {
   MATCH_NO,
   MATCH_YES,
   MATCH_MAYBE
 };

#ifndef HB_OPTIMIZE_SIZE
 HB_ALWAYS_INLINE
#endif
 may_match_t may_match (hb_glyph_info_t &info,
		 hb_codepoint_t glyph_data) const
 {
   if (!(info.mask & mask) ||
(per_syllable && syllable && syllable != info.syllable ()))
     return MATCH_NO;

   if (match_func)
     return match_func (info, glyph_data, match_data) ? MATCH_YES : MATCH_NO;

   return MATCH_MAYBE;
 }

 enum may_skip_t {
   SKIP_NO,
   SKIP_YES,
   SKIP_MAYBE
 };

 template <typename context_t>
#ifndef HB_OPTIMIZE_SIZE
 HB_ALWAYS_INLINE
#endif
 may_skip_t may_skip (const context_t *c,
	       const hb_glyph_info_t &info) const
 {
   if (!c->check_glyph_property (&info, lookup_props))
     return SKIP_YES;

   if (unlikely (_hb_glyph_info_is_default_ignorable (&info) &&
	  (ignore_zwnj || !_hb_glyph_info_is_zwnj (&info)) &&
	  (ignore_zwj || !_hb_glyph_info_is_zwj (&info)) &&
	  (ignore_hidden || !_hb_glyph_info_is_hidden (&info))))
     return SKIP_MAYBE;

   return SKIP_NO;
 }

 public:
 unsigned int lookup_props = 0;
 hb_mask_t mask = -1;
 bool ignore_zwnj = false;
 bool ignore_zwj = false;
 bool ignore_hidden = false;
 bool per_syllable = false;
 uint8_t syllable = 0;
 match_func_t match_func = nullptr;
 const void *match_data = nullptr;
};

template <typename context_t>
struct skipping_iterator_t
{
 void init (context_t *c_, bool context_match = false)
 {
   c = c_;
   end = c->buffer->len;
   match_glyph_data16 = nullptr;
#ifndef HB_NO_BEYOND_64K
   match_glyph_data24 = nullptr;
#endif
   matcher.init (c, context_match);
 }
 void set_lookup_props (unsigned int lookup_props)
 {
   matcher.lookup_props = lookup_props;
 }
 void set_match_func (matcher_t::match_func_t match_func_,
	       const void *match_data_)
 {
   matcher.set_match_func (match_func_, match_data_);
 }
 void set_glyph_data (const HBUINT16 glyph_data[])
 {
   match_glyph_data16 = glyph_data;
#ifndef HB_NO_BEYOND_64K
   match_glyph_data24 = nullptr;
#endif
 }
#ifndef HB_NO_BEYOND_64K
 void set_glyph_data (const HBUINT24 glyph_data[])
 {
   match_glyph_data16 = nullptr;
   match_glyph_data24 = glyph_data;
 }
#endif

#ifndef HB_OPTIMIZE_SIZE
 HB_ALWAYS_INLINE
#endif
 void reset (unsigned int start_index_)
 {
   // For GSUB forward iterator
   idx = start_index_;
   end = c->buffer->len;
   matcher.syllable = c->buffer->cur().syllable();
 }
 void reset_back (unsigned int start_index_, bool from_out_buffer = false)
 {
   // For GSUB backward iterator
   idx = start_index_;
   matcher.syllable = c->buffer->cur().syllable();
 }

#ifndef HB_OPTIMIZE_SIZE
 HB_ALWAYS_INLINE
#endif
 void reset_fast (unsigned int start_index_)
 {
   // Doesn't set end or syllable. Used by GPOS which doesn't care / change.
   idx = start_index_;
 }

#ifndef HB_OPTIMIZE_SIZE
 HB_ALWAYS_INLINE
#endif
 matcher_t::may_skip_t may_skip (const hb_glyph_info_t &info) const
 { return matcher.may_skip (c, info); }

 enum match_t {
   MATCH,
   NOT_MATCH,
   SKIP
 };

#ifndef HB_OPTIMIZE_SIZE
 HB_ALWAYS_INLINE
#endif
 match_t match (hb_glyph_info_t &info)
 {
   matcher_t::may_skip_t skip = matcher.may_skip (c, info);
   if (unlikely (skip == matcher_t::SKIP_YES))
     return SKIP;

   matcher_t::may_match_t match = matcher.may_match (info, get_glyph_data ());
   if (match == matcher_t::MATCH_YES ||
(match == matcher_t::MATCH_MAYBE &&
 skip == matcher_t::SKIP_NO))
     return MATCH;

   if (skip == matcher_t::SKIP_NO)
     return NOT_MATCH;

   return SKIP;
 }

#ifndef HB_OPTIMIZE_SIZE
 HB_ALWAYS_INLINE
#endif
 bool next (unsigned *unsafe_to = nullptr)
 {
   const signed stop = (signed) end - 1;
   while ((signed) idx < stop)
   {
     idx++;
     switch (match (c->buffer->info[idx]))
     {
case MATCH:
{
  advance_glyph_data ();
  return true;
}
case NOT_MATCH:
{
  if (unsafe_to)
    *unsafe_to = idx + 1;
  return false;
}
case SKIP:
  continue;
     }
   }
   if (unsafe_to)
     *unsafe_to = end;
   return false;
 }
#ifndef HB_OPTIMIZE_SIZE
 HB_ALWAYS_INLINE
#endif
 bool prev (unsigned *unsafe_from = nullptr)
 {
   const unsigned stop = 0;
   while (idx > stop)
   {
     idx--;
     switch (match (c->buffer->out_info[idx]))
     {
case MATCH:
{
  advance_glyph_data ();
  return true;
}
case NOT_MATCH:
{
  if (unsafe_from)
    *unsafe_from = hb_max (1u, idx) - 1u;
  return false;
}
case SKIP:
  continue;
     }
   }
   if (unsafe_from)
     *unsafe_from = 0;
   return false;
 }

 HB_ALWAYS_INLINE
 hb_codepoint_t
 get_glyph_data ()
 {
   if (match_glyph_data16) return *match_glyph_data16;
#ifndef HB_NO_BEYOND_64K
   else
   if (match_glyph_data24) return *match_glyph_data24;
#endif
   return 0;
 }
 HB_ALWAYS_INLINE
 void
 advance_glyph_data ()
 {
   if (match_glyph_data16) match_glyph_data16++;
#ifndef HB_NO_BEYOND_64K
   else
   if (match_glyph_data24) match_glyph_data24++;
#endif
 }

 unsigned int idx;
 protected:
 context_t *c;
 matcher_t matcher;
 const HBUINT16 *match_glyph_data16;
#ifndef HB_NO_BEYOND_64K
 const HBUINT24 *match_glyph_data24;
#endif

 unsigned int end;
};

struct hb_ot_apply_context_t :
      hb_dispatch_context_t<hb_ot_apply_context_t, bool, HB_DEBUG_APPLY>
{
 const char *get_name () { return "APPLY"; }
 typedef return_t (*recurse_func_t) (hb_ot_apply_context_t *c, unsigned int lookup_index);

 template <typename T>
 static inline auto apply_ (const T &obj, hb_ot_apply_context_t *c, hb_priority<1>) HB_RETURN (return_t, obj.apply (c, nullptr) )
 template <typename T>
 static inline auto apply_ (const T &obj, hb_ot_apply_context_t *c, hb_priority<0>) HB_RETURN (return_t, obj.apply (c) )
 template <typename T>
 return_t dispatch (const T &obj) { return apply_(obj, this, hb_prioritize); }

 static return_t default_return_value () { return false; }
 bool stop_sublookup_iteration (return_t r) const { return r; }
 return_t recurse (unsigned int sub_lookup_index)
 {
   assert (recurse_func);
   if (unlikely (nesting_level_left == 0))
   {
     buffer->successful = false;
     return default_return_value ();
   }

   buffer->max_ops--;
   if (unlikely (buffer->max_ops < 0))
   {
     buffer->successful = false;
     return default_return_value ();
   }

   nesting_level_left--;
   bool ret = recurse_func (this, sub_lookup_index);
   nesting_level_left++;
   return ret;
 }

 skipping_iterator_t<hb_ot_apply_context_t> iter_input, iter_context;

 unsigned int table_index; /* GSUB/GPOS */
 hb_font_t *font;
 hb_face_t *face;
 hb_buffer_t *buffer;
 hb_sanitize_context_t sanitizer;
 recurse_func_t recurse_func = nullptr;
 const GDEF &gdef;
 const GDEF::accelerator_t &gdef_accel;
 const hb_ot_layout_lookup_accelerator_t *lookup_accel = nullptr;
 const ItemVariationStore &var_store;
 hb_scalar_cache_t *var_store_cache;

 hb_direction_t direction;
 hb_mask_t lookup_mask = 1;
 unsigned int lookup_index = (unsigned) -1;
 unsigned int lookup_props = 0;
 unsigned int nesting_level_left = HB_MAX_NESTING_LEVEL;

 bool has_glyph_classes;
 bool auto_zwnj = true;
 bool auto_zwj = true;
 bool per_syllable = false;
 bool random = false;
 unsigned new_syllables = (unsigned) -1;

 signed last_base = -1; // GPOS uses
 unsigned last_base_until = 0; // GPOS uses

 hb_vector_t<uint32_t> match_positions;
 uint32_t stack_match_positions[8];

 hb_ot_apply_context_t (unsigned int table_index_,
		 hb_font_t *font_,
		 hb_buffer_t *buffer_,
		 hb_blob_t *table_blob_,
		 hb_scalar_cache_t *var_store_cache_ = nullptr) :
		table_index (table_index_),
		font (font_), face (font->face), buffer (buffer_),
		sanitizer (table_blob_),
		gdef (
#ifndef HB_NO_OT_LAYOUT
		      *face->table.GDEF->table
#else
		      Null (GDEF)
#endif
		     ),
		gdef_accel (
#ifndef HB_NO_OT_LAYOUT
		      *face->table.GDEF
#else
		      Null (GDEF::accelerator_t)
#endif
		     ),
		var_store (gdef.get_var_store ()),
		var_store_cache (var_store_cache_),
		direction (buffer_->props.direction),
		has_glyph_classes (gdef.has_glyph_classes ())
 {
   init_iters ();
   match_positions.set_storage (stack_match_positions);
 }

 void init_iters ()
 {
   iter_input.init (this, false);
   iter_context.init (this, true);
 }

 void set_lookup_mask (hb_mask_t mask, bool init = true) { lookup_mask = mask; last_base = -1; last_base_until = 0; if (init) init_iters (); }
 void set_auto_zwj (bool auto_zwj_, bool init = true) { auto_zwj = auto_zwj_; if (init) init_iters (); }
 void set_auto_zwnj (bool auto_zwnj_, bool init = true) { auto_zwnj = auto_zwnj_; if (init) init_iters (); }
 void set_per_syllable (bool per_syllable_, bool init = true) { per_syllable = per_syllable_; if (init) init_iters (); }
 void set_random (bool random_) { random = random_; }
 void set_recurse_func (recurse_func_t func) { recurse_func = func; }
 void set_lookup_index (unsigned int lookup_index_) { lookup_index = lookup_index_; }
 void set_lookup_props (unsigned int lookup_props_) { lookup_props = lookup_props_; init_iters (); }

 uint32_t random_number ()
 {
   /* http://www.cplusplus.com/reference/random/minstd_rand/ */
   buffer->random_state = buffer->random_state * 48271 % 2147483647;
   return buffer->random_state;
 }

 HB_ALWAYS_INLINE
 HB_HOT
 bool match_properties_mark (const hb_glyph_info_t *info,
		      unsigned int    glyph_props,
		      unsigned int    match_props) const
 {
   /* If using mark filtering sets, the high short of
    * match_props has the set index.
    */
   if (match_props & LookupFlag::UseMarkFilteringSet)
     return gdef_accel.mark_set_covers (match_props >> 16, info->codepoint);

   /* The second byte of match_props has the meaning
    * "ignore marks of attachment type different than
    * the attachment type specified."
    */
   if (match_props & LookupFlag::MarkAttachmentType)
     return (match_props & LookupFlag::MarkAttachmentType) == (glyph_props & LookupFlag::MarkAttachmentType);

   return true;
 }

#ifndef HB_OPTIMIZE_SIZE
 HB_ALWAYS_INLINE
#endif
 bool check_glyph_property (const hb_glyph_info_t *info,
		     unsigned match_props) const
 {
   unsigned int glyph_props = _hb_glyph_info_get_glyph_props (info);

   /* Not covered, if, for example, glyph class is ligature and
    * match_props includes LookupFlags::IgnoreLigatures
    */
   if (glyph_props & match_props & LookupFlag::IgnoreFlags)
     return false;

   if (unlikely (glyph_props & HB_OT_LAYOUT_GLYPH_PROPS_MARK))
     return match_properties_mark (info, glyph_props, match_props);

   return true;
 }

 void _set_glyph_class (hb_codepoint_t glyph_index,
		  unsigned int class_guess = 0,
		  bool ligature = false,
		  bool component = false)
 {
   buffer->digest.add (glyph_index);

   if (new_syllables != (unsigned) -1)
     buffer->cur().syllable() = new_syllables;

   unsigned int props = _hb_glyph_info_get_glyph_props (&buffer->cur());
   props |= HB_OT_LAYOUT_GLYPH_PROPS_SUBSTITUTED;
   if (ligature)
   {
     props |= HB_OT_LAYOUT_GLYPH_PROPS_LIGATED;
     /* In the only place that the MULTIPLIED bit is used, Uniscribe
      * seems to only care about the "last" transformation between
      * Ligature and Multiple substitutions.  Ie. if you ligate, expand,
      * and ligate again, it forgives the multiplication and acts as
      * if only ligation happened.  As such, clear MULTIPLIED bit.
      */
     props &= ~HB_OT_LAYOUT_GLYPH_PROPS_MULTIPLIED;
   }
   if (component)
     props |= HB_OT_LAYOUT_GLYPH_PROPS_MULTIPLIED;
   if (likely (has_glyph_classes))
   {
     props &= HB_OT_LAYOUT_GLYPH_PROPS_PRESERVE;
     _hb_glyph_info_set_glyph_props (&buffer->cur(), props | gdef_accel.get_glyph_props (glyph_index));
   }
   else if (class_guess)
   {
     props &= HB_OT_LAYOUT_GLYPH_PROPS_PRESERVE;
     _hb_glyph_info_set_glyph_props (&buffer->cur(), props | class_guess);
   }
   else
     _hb_glyph_info_set_glyph_props (&buffer->cur(), props);
 }

 void replace_glyph (hb_codepoint_t glyph_index)
 {
   _set_glyph_class (glyph_index);
   (void) buffer->replace_glyph (glyph_index);
 }
 void replace_glyph_inplace (hb_codepoint_t glyph_index)
 {
   _set_glyph_class (glyph_index);
   buffer->cur().codepoint = glyph_index;
 }
 void replace_glyph_with_ligature (hb_codepoint_t glyph_index,
			    unsigned int class_guess)
 {
   _set_glyph_class (glyph_index, class_guess, true);
   (void) buffer->replace_glyph (glyph_index);
 }
 void output_glyph_for_component (hb_codepoint_t glyph_index,
			   unsigned int class_guess)
 {
   _set_glyph_class (glyph_index, class_guess, false, true);
   (void) buffer->output_glyph (glyph_index);
 }
};

enum class hb_ot_subtable_cache_op_t
{
 ENTER,
 LEAVE,
};

struct hb_accelerate_subtables_context_t :
      hb_dispatch_context_t<hb_accelerate_subtables_context_t>
{
 template <typename T>
 static inline auto apply_ (const T *obj, hb_ot_apply_context_t *c, void *external_cache, hb_priority<1>) HB_RETURN (bool, obj->apply (c, external_cache) )
 template <typename T>
 static inline auto apply_ (const T *obj, hb_ot_apply_context_t *c, void *external_cache, hb_priority<0>) HB_RETURN (bool, obj->apply (c) )
 template <typename T>
 static inline bool apply_to (const void *obj, hb_ot_apply_context_t *c, void *external_cache)
 {
   const T *typed_obj = (const T *) obj;
   return apply_ (typed_obj, c, external_cache, hb_prioritize);
 }

#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
 template <typename T>
 static inline auto apply_cached_ (const T *obj, hb_ot_apply_context_t *c, void *external_cache, hb_priority<2>) HB_RETURN (bool, obj->apply_cached (c, external_cache) )
 template <typename T>
 static inline auto apply_cached_ (const T *obj, hb_ot_apply_context_t *c, void *external_cache, hb_priority<1>) HB_RETURN (bool, obj->apply (c, external_cache) )
 template <typename T>
 static inline auto apply_cached_ (const T *obj, hb_ot_apply_context_t *c, void *external_cache, hb_priority<0>) HB_RETURN (bool, obj->apply (c) )
 template <typename T>
 static inline bool apply_cached_to (const void *obj, hb_ot_apply_context_t *c, void *external_cache)
 {
   const T *typed_obj = (const T *) obj;
   return apply_cached_ (typed_obj, c, external_cache, hb_prioritize);
 }

 template <typename T>
 static inline auto cache_func_ (hb_ot_apply_context_t *c,
			  hb_ot_subtable_cache_op_t op,
			  hb_priority<1>) HB_RETURN (bool, T::cache_func (c, op) )
 template <typename T=void>
 static inline bool cache_func_ (hb_ot_apply_context_t *c,
			  hb_ot_subtable_cache_op_t op HB_UNUSED,
			  hb_priority<0>) { return false; }
 template <typename Type>
 static inline bool cache_func_to (hb_ot_apply_context_t *c,
			    hb_ot_subtable_cache_op_t op)
 {
   return cache_func_<Type> (c, op, hb_prioritize);
 }
#endif

 typedef bool (*hb_apply_func_t) (const void *obj, hb_ot_apply_context_t *c, void *external_cache);
 typedef bool (*hb_cache_func_t) (hb_ot_apply_context_t *c, hb_ot_subtable_cache_op_t op);

 struct hb_applicable_t
 {
   friend struct hb_accelerate_subtables_context_t;
   friend struct hb_ot_layout_lookup_accelerator_t;

   template <typename T>
   void init (const T &obj_,
       hb_apply_func_t apply_func_
#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
       , hb_apply_func_t apply_cached_func_
       , hb_cache_func_t cache_func_
       , void *external_cache_
#endif
	)
   {
     obj = &obj_;
     apply_func = apply_func_;
#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
     apply_cached_func = apply_cached_func_;
     cache_func = cache_func_;
     external_cache = external_cache_;
#endif
     digest.init ();
     obj_.get_coverage ().collect_coverage (&digest);
   }

#ifdef HB_NO_OT_LAYOUT_LOOKUP_CACHE
   bool apply (hb_ot_apply_context_t *c) const
   {
     return digest.may_have (c->buffer->cur().codepoint) && apply_func (obj, c, nullptr);
   }
#else
   bool apply (hb_ot_apply_context_t *c) const
   {
     return digest.may_have (c->buffer->cur().codepoint) && apply_func (obj, c, external_cache);
   }
   bool apply_cached (hb_ot_apply_context_t *c) const
   {
     return digest.may_have (c->buffer->cur().codepoint) &&  apply_cached_func (obj, c, external_cache);
   }

   bool cache_enter (hb_ot_apply_context_t *c) const
   {
     return cache_func (c, hb_ot_subtable_cache_op_t::ENTER);
   }
   void cache_leave (hb_ot_apply_context_t *c) const
   {
     cache_func (c, hb_ot_subtable_cache_op_t::LEAVE);
   }
#endif

   private:
   const void *obj;
   hb_apply_func_t apply_func;
#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
   hb_apply_func_t apply_cached_func;
   hb_cache_func_t cache_func;
   void *external_cache;
#endif
   hb_set_digest_t digest;
 };

#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
 template <typename T>
 auto cache_cost (const T &obj, hb_priority<1>) HB_AUTO_RETURN ( obj.cache_cost () )
 template <typename T>
 auto cache_cost (const T &obj, hb_priority<0>) HB_AUTO_RETURN ( 0u )

 template <typename T>
 auto external_cache_create (const T &obj, hb_priority<1>) HB_AUTO_RETURN ( obj.external_cache_create () )
 template <typename T>
 auto external_cache_create (const T &obj, hb_priority<0>) HB_AUTO_RETURN ( nullptr )
#endif

 /* Dispatch interface. */
 template <typename T>
 return_t dispatch (const T &obj)
 {
#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
   void *external_cache = nullptr;
   if (i < 8)
     external_cache = external_cache_create (obj, hb_prioritize);
#endif

   hb_applicable_t *entry = &array[i++];

   entry->init (obj,
	 apply_to<T>
#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
	 , apply_cached_to<T>
	 , cache_func_to<T>
	 , external_cache
#endif
	 );

#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
   /* Cache handling
    *
    * We allow one subtable from each lookup to use a cache. The assumption
    * being that multiple subtables of the same lookup cannot use a cache
    * because the resources they would use will collide.  As such, we ask
    * each subtable to tell us how much it costs (which a cache would avoid),
    * and we allocate the cache opportunity to the costliest subtable.
    */
   unsigned cost = cache_cost (obj, hb_prioritize);
   if (cost > subtable_cache_user_cost)
   {
     subtable_cache_user_idx = i - 1;
     subtable_cache_user_cost = cost;
   }
#endif

   return hb_empty_t ();
 }
 static return_t default_return_value () { return hb_empty_t (); }

 hb_accelerate_subtables_context_t (hb_applicable_t *array_) :
			     array (array_) {}

 hb_applicable_t *array;
 unsigned i = 0;

#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
 unsigned subtable_cache_user_idx = (unsigned) -1;
 unsigned subtable_cache_user_cost = 0;
#endif
};


typedef bool (*intersects_func_t) (const hb_set_t *glyphs, unsigned value, const void *data, void *cache);
typedef void (*intersected_glyphs_func_t) (const hb_set_t *glyphs, const void *data, unsigned value, hb_set_t *intersected_glyphs, void *cache);
typedef void (*collect_glyphs_func_t) (hb_set_t *glyphs, unsigned value, const void *data);
typedef bool (*match_func_t) (hb_glyph_info_t &info, unsigned value, const void *data);

struct ContextClosureFuncs
{
 intersects_func_t intersects;
 intersected_glyphs_func_t intersected_glyphs;
};
struct ContextCollectGlyphsFuncs
{
 collect_glyphs_func_t collect;
};
struct ContextApplyFuncs
{
 match_func_t match;
};
struct ChainContextApplyFuncs
{
 match_func_t match[3];
};


static inline bool intersects_glyph (const hb_set_t *glyphs, unsigned value, const void *data HB_UNUSED, void *cache HB_UNUSED)
{
 return glyphs->has (value);
}
static inline bool intersects_class (const hb_set_t *glyphs, unsigned value, const void *data, void *cache)
{
 const ClassDef &class_def = *reinterpret_cast<const ClassDef *>(data);
 hb_map_t *map = (hb_map_t *) cache;

 hb_codepoint_t *cached_v;
 if (map->has (value, &cached_v))
   return *cached_v;

 bool v = class_def.intersects_class (glyphs, value);
 map->set (value, v);

 return v;
}
static inline bool intersects_coverage (const hb_set_t *glyphs, unsigned value, const void *data, void *cache HB_UNUSED)
{
 Offset16To<Coverage> coverage;
 coverage = value;
 return (data+coverage).intersects (glyphs);
}


static inline void intersected_glyph (const hb_set_t *glyphs HB_UNUSED, const void *data, unsigned value, hb_set_t *intersected_glyphs, HB_UNUSED void *cache)
{
 unsigned g = reinterpret_cast<const HBUINT16 *>(data)[value];
 intersected_glyphs->add (g);
}

using intersected_class_cache_t = hb_hashmap_t<unsigned, hb_set_t>;

static inline void intersected_class_glyphs (const hb_set_t *glyphs, const void *data, unsigned value, hb_set_t *intersected_glyphs, void *cache)
{
 const ClassDef &class_def = *reinterpret_cast<const ClassDef *>(data);

 intersected_class_cache_t *map = (intersected_class_cache_t *) cache;

 hb_set_t *cached_v;
 if (map->has (value, &cached_v))
 {
   intersected_glyphs->union_ (*cached_v);
   return;
 }

 hb_set_t v;
 class_def.intersected_class_glyphs (glyphs, value, &v);

 intersected_glyphs->union_ (v);

 map->set (value, std::move (v));
}

static inline void intersected_coverage_glyphs (const hb_set_t *glyphs, const void *data, unsigned value, hb_set_t *intersected_glyphs, HB_UNUSED void *cache)
{
 Offset16To<Coverage> coverage;
 coverage = value;
 (data+coverage).intersect_set (*glyphs, *intersected_glyphs);
}


template <typename HBUINT>
static inline bool array_is_subset_of (const hb_set_t *glyphs,
			       unsigned int count,
			       const HBUINT values[],
			       intersects_func_t intersects_func,
			       const void *intersects_data,
			       void *cache)
{
 for (const auto &_ : + hb_iter (values, count))
   if (!intersects_func (glyphs, _, intersects_data, cache)) return false;
 return true;
}


static inline void collect_glyph (hb_set_t *glyphs, unsigned value, const void *data HB_UNUSED)
{
 glyphs->add (value);
}
static inline void collect_class (hb_set_t *glyphs, unsigned value, const void *data)
{
 const ClassDef &class_def = *reinterpret_cast<const ClassDef *>(data);
 class_def.collect_class (glyphs, value);
}
static inline void collect_coverage (hb_set_t *glyphs, unsigned value, const void *data)
{
 Offset16To<Coverage> coverage;
 coverage = value;
 (data+coverage).collect_coverage (glyphs);
}
template <typename HBUINT>
static inline void collect_array (hb_collect_glyphs_context_t *c HB_UNUSED,
			  hb_set_t *glyphs,
			  unsigned int count,
			  const HBUINT values[],
			  collect_glyphs_func_t collect_func,
			  const void *collect_data)
{
 return
 + hb_iter (values, count)
 | hb_apply ([&] (const HBUINT &_) { collect_func (glyphs, _, collect_data); })
 ;
}


static inline bool match_always (hb_glyph_info_t &info HB_UNUSED, unsigned value HB_UNUSED, const void *data HB_UNUSED)
{
 return true;
}
static inline bool match_glyph (hb_glyph_info_t &info, unsigned value, const void *data HB_UNUSED)
{
 return info.codepoint == value;
}
static inline bool match_class (hb_glyph_info_t &info, unsigned value, const void *data)
{
 const ClassDef &class_def = *reinterpret_cast<const ClassDef *>(data);
 return class_def.get_class (info.codepoint) == value;
}
static inline unsigned get_class_cached (const ClassDef &class_def, hb_glyph_info_t &info)
{
 unsigned klass = info.syllable();
 if (klass < 255)
   return klass;
 klass = class_def.get_class (info.codepoint);
 if (likely (klass < 255))
   info.syllable() = klass;
 return klass;
}
static inline bool match_class_cached (hb_glyph_info_t &info, unsigned value, const void *data)
{
 const ClassDef &class_def = *reinterpret_cast<const ClassDef *>(data);
 return get_class_cached (class_def, info) == value;
}
static inline unsigned get_class_cached1 (const ClassDef &class_def, hb_glyph_info_t &info)
{
 unsigned klass = info.syllable() & 0x0F;
 if (klass < 15)
   return klass;
 klass = class_def.get_class (info.codepoint);
 if (likely (klass < 15))
   info.syllable() = (info.syllable() & 0xF0) | klass;
 return klass;
}
static inline bool match_class_cached1 (hb_glyph_info_t &info, unsigned value, const void *data)
{
 const ClassDef &class_def = *reinterpret_cast<const ClassDef *>(data);
 return get_class_cached1 (class_def, info) == value;
}
static inline unsigned get_class_cached2 (const ClassDef &class_def, hb_glyph_info_t &info)
{
 unsigned klass = (info.syllable() & 0xF0) >> 4;
 if (klass < 15)
   return klass;
 klass = class_def.get_class (info.codepoint);
 if (likely (klass < 15))
   info.syllable() = (info.syllable() & 0x0F) | (klass << 4);
 return klass;
}
static inline bool match_class_cached2 (hb_glyph_info_t &info, unsigned value, const void *data)
{
 const ClassDef &class_def = *reinterpret_cast<const ClassDef *>(data);
 return get_class_cached2 (class_def, info) == value;
}
static inline bool match_coverage (hb_glyph_info_t &info, unsigned value, const void *data)
{
 Offset16To<Coverage> coverage;
 coverage = value;
 return (data+coverage).get_coverage (info.codepoint) != NOT_COVERED;
}

template <typename HBUINT>
static inline bool would_match_input (hb_would_apply_context_t *c,
			      unsigned int count, /* Including the first glyph (not matched) */
			      const HBUINT input[], /* Array of input values--start with second glyph */
			      match_func_t match_func,
			      const void *match_data)
{
 if (count != c->len)
   return false;

 for (unsigned int i = 1; i < count; i++)
 {
   hb_glyph_info_t info;
   info.codepoint = c->glyphs[i];
   if (likely (!match_func (info, input[i - 1], match_data)))
     return false;
 }

 return true;
}
template <typename HBUINT>
#ifndef HB_OPTIMIZE_SIZE
HB_ALWAYS_INLINE
#endif
static bool match_input (hb_ot_apply_context_t *c,
		 unsigned int count, /* Including the first glyph (not matched) */
		 const HBUINT input[], /* Array of input values--start with second glyph */
		 match_func_t match_func,
		 const void *match_data,
		 unsigned int *end_position,
		 unsigned int *p_total_component_count = nullptr)
{
 TRACE_APPLY (nullptr);

 hb_buffer_t *buffer = c->buffer;

 if (count == 1)
 {
   *end_position = buffer->idx + 1;
   c->match_positions[0] = buffer->idx;
   if (p_total_component_count)
     *p_total_component_count = _hb_glyph_info_get_lig_num_comps (&buffer->cur());
   return_trace (true);
 }

 if (unlikely (count > HB_MAX_CONTEXT_LENGTH)) return_trace (false);

 auto &skippy_iter = c->iter_input;
 skippy_iter.reset (buffer->idx);
 skippy_iter.set_match_func (match_func, match_data);
 skippy_iter.set_glyph_data (input);

 /*
  * This is perhaps the trickiest part of OpenType...  Remarks:
  *
  * - If all components of the ligature were marks, we call this a mark ligature.
  *
  * - If there is no GDEF, and the ligature is NOT a mark ligature, we categorize
  *   it as a ligature glyph.
  *
  * - Ligatures cannot be formed across glyphs attached to different components
  *   of previous ligatures.  Eg. the sequence is LAM,SHADDA,LAM,FATHA,HEH, and
  *   LAM,LAM,HEH form a ligature, leaving SHADDA,FATHA next to eachother.
  *   However, it would be wrong to ligate that SHADDA,FATHA sequence.
  *   There are a couple of exceptions to this:
  *
  *   o If a ligature tries ligating with marks that belong to it itself, go ahead,
  *     assuming that the font designer knows what they are doing (otherwise it can
  *     break Indic stuff when a matra wants to ligate with a conjunct,
  *
  *   o If two marks want to ligate and they belong to different components of the
  *     same ligature glyph, and said ligature glyph is to be ignored according to
  *     mark-filtering rules, then allow.
  *     https://github.com/harfbuzz/harfbuzz/issues/545
  */

 unsigned int total_component_count = 0;

 unsigned int first_lig_id = _hb_glyph_info_get_lig_id (&buffer->cur());
 unsigned int first_lig_comp = _hb_glyph_info_get_lig_comp (&buffer->cur());

 enum {
   LIGBASE_NOT_CHECKED,
   LIGBASE_MAY_NOT_SKIP,
   LIGBASE_MAY_SKIP
 } ligbase = LIGBASE_NOT_CHECKED;

 for (unsigned int i = 1; i < count; i++)
 {
   unsigned unsafe_to;
   if (!skippy_iter.next (&unsafe_to))
   {
     *end_position = unsafe_to;
     return_trace (false);
   }

   if (unlikely (i + 1 > c->match_positions.length &&
	  !c->match_positions.resize_dirty  (i + 1)))
     return_trace (false);
   c->match_positions.arrayZ[i] = skippy_iter.idx;

   unsigned int this_lig_id = _hb_glyph_info_get_lig_id (&buffer->info[skippy_iter.idx]);
   unsigned int this_lig_comp = _hb_glyph_info_get_lig_comp (&buffer->info[skippy_iter.idx]);

   if (first_lig_id && first_lig_comp)
   {
     /* If first component was attached to a previous ligature component,
      * all subsequent components should be attached to the same ligature
      * component, otherwise we shouldn't ligate them... */
     if (first_lig_id != this_lig_id || first_lig_comp != this_lig_comp)
     {
/* ...unless, we are attached to a base ligature and that base
 * ligature is ignorable. */
if (ligbase == LIGBASE_NOT_CHECKED)
{
  bool found = false;
  const auto *out = buffer->out_info;
  unsigned int j = buffer->out_len;
  while (j && _hb_glyph_info_get_lig_id (&out[j - 1]) == first_lig_id)
  {
    if (_hb_glyph_info_get_lig_comp (&out[j - 1]) == 0)
    {
      j--;
      found = true;
      break;
    }
    j--;
  }

  if (found && skippy_iter.may_skip (out[j]) == matcher_t::SKIP_YES)
    ligbase = LIGBASE_MAY_SKIP;
  else
    ligbase = LIGBASE_MAY_NOT_SKIP;
}

if (ligbase == LIGBASE_MAY_NOT_SKIP)
  return_trace (false);
     }
   }
   else
   {
     /* If first component was NOT attached to a previous ligature component,
      * all subsequent components should also NOT be attached to any ligature
      * component, unless they are attached to the first component itself! */
     if (this_lig_id && this_lig_comp && (this_lig_id != first_lig_id))
return_trace (false);
   }

   total_component_count += _hb_glyph_info_get_lig_num_comps (&buffer->info[skippy_iter.idx]);
 }

 *end_position = skippy_iter.idx + 1;

 if (p_total_component_count)
 {
   total_component_count += _hb_glyph_info_get_lig_num_comps (&buffer->cur());
   *p_total_component_count = total_component_count;
 }

 c->match_positions.arrayZ[0] = buffer->idx;

 return_trace (true);
}
static inline bool ligate_input (hb_ot_apply_context_t *c,
			 unsigned int count, /* Including the first glyph */
			 unsigned int match_end,
			 hb_codepoint_t lig_glyph,
			 unsigned int total_component_count)
{
 TRACE_APPLY (nullptr);

 hb_buffer_t *buffer = c->buffer;

 buffer->merge_clusters (buffer->idx, match_end);

 /* - If a base and one or more marks ligate, consider that as a base, NOT
  *   ligature, such that all following marks can still attach to it.
  *   https://github.com/harfbuzz/harfbuzz/issues/1109
  *
  * - If all components of the ligature were marks, we call this a mark ligature.
  *   If it *is* a mark ligature, we don't allocate a new ligature id, and leave
  *   the ligature to keep its old ligature id.  This will allow it to attach to
  *   a base ligature in GPOS.  Eg. if the sequence is: LAM,LAM,SHADDA,FATHA,HEH,
  *   and LAM,LAM,HEH for a ligature, they will leave SHADDA and FATHA with a
  *   ligature id and component value of 2.  Then if SHADDA,FATHA form a ligature
  *   later, we don't want them to lose their ligature id/component, otherwise
  *   GPOS will fail to correctly position the mark ligature on top of the
  *   LAM,LAM,HEH ligature.  See:
  *     https://bugzilla.gnome.org/show_bug.cgi?id=676343
  *
  * - If a ligature is formed of components that some of which are also ligatures
  *   themselves, and those ligature components had marks attached to *their*
  *   components, we have to attach the marks to the new ligature component
  *   positions!  Now *that*'s tricky!  And these marks may be following the
  *   last component of the whole sequence, so we should loop forward looking
  *   for them and update them.
  *
  *   Eg. the sequence is LAM,LAM,SHADDA,FATHA,HEH, and the font first forms a
  *   'calt' ligature of LAM,HEH, leaving the SHADDA and FATHA with a ligature
  *   id and component == 1.  Now, during 'liga', the LAM and the LAM-HEH ligature
  *   form a LAM-LAM-HEH ligature.  We need to reassign the SHADDA and FATHA to
  *   the new ligature with a component value of 2.
  *
  *   This in fact happened to a font...  See:
  *   https://bugzilla.gnome.org/show_bug.cgi?id=437633
  */

 bool is_base_ligature = _hb_glyph_info_is_base_glyph (&buffer->info[c->match_positions.arrayZ[0]]);
 bool is_mark_ligature = _hb_glyph_info_is_mark (&buffer->info[c->match_positions.arrayZ[0]]);
 for (unsigned int i = 1; i < count; i++)
   if (!_hb_glyph_info_is_mark (&buffer->info[c->match_positions.arrayZ[i]]))
   {
     is_base_ligature = false;
     is_mark_ligature = false;
     break;
   }
 bool is_ligature = !is_base_ligature && !is_mark_ligature;

 unsigned int klass = is_ligature ? HB_OT_LAYOUT_GLYPH_PROPS_LIGATURE : 0;
 unsigned int lig_id = is_ligature ? _hb_allocate_lig_id (buffer) : 0;
 unsigned int last_lig_id = _hb_glyph_info_get_lig_id (&buffer->cur());
 unsigned int last_num_components = _hb_glyph_info_get_lig_num_comps (&buffer->cur());
 unsigned int components_so_far = last_num_components;

 if (is_ligature)
 {
   _hb_glyph_info_set_lig_props_for_ligature (&buffer->cur(), lig_id, total_component_count);
   if (_hb_glyph_info_get_general_category (&buffer->cur()) == HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK)
   {
     _hb_glyph_info_set_general_category (&buffer->cur(), HB_UNICODE_GENERAL_CATEGORY_OTHER_LETTER);
   }
 }
 c->replace_glyph_with_ligature (lig_glyph, klass);

 for (unsigned int i = 1; i < count; i++)
 {
   while (buffer->idx < c->match_positions.arrayZ[i] && buffer->successful)
   {
     if (is_ligature)
     {
unsigned int this_comp = _hb_glyph_info_get_lig_comp (&buffer->cur());
if (this_comp == 0)
  this_comp = last_num_components;
assert (components_so_far >= last_num_components);
unsigned int new_lig_comp = components_so_far - last_num_components +
			    hb_min (this_comp, last_num_components);
  _hb_glyph_info_set_lig_props_for_mark (&buffer->cur(), lig_id, new_lig_comp);
     }
     (void) buffer->next_glyph ();
   }

   last_lig_id = _hb_glyph_info_get_lig_id (&buffer->cur());
   last_num_components = _hb_glyph_info_get_lig_num_comps (&buffer->cur());
   components_so_far += last_num_components;

   /* Skip the base glyph */
   buffer->idx++;
 }

 if (!is_mark_ligature && last_lig_id)
 {
   /* Re-adjust components for any marks following. */
   for (unsigned i = buffer->idx; i < buffer->len; ++i)
   {
     if (last_lig_id != _hb_glyph_info_get_lig_id (&buffer->info[i])) break;

     unsigned this_comp = _hb_glyph_info_get_lig_comp (&buffer->info[i]);
     if (!this_comp) break;

     assert (components_so_far >= last_num_components);
     unsigned new_lig_comp = components_so_far - last_num_components +
		      hb_min (this_comp, last_num_components);
     _hb_glyph_info_set_lig_props_for_mark (&buffer->info[i], lig_id, new_lig_comp);
   }
 }
 return_trace (true);
}

template <typename HBUINT>
#ifndef HB_OPTIMIZE_SIZE
HB_ALWAYS_INLINE
#endif
static bool match_backtrack (hb_ot_apply_context_t *c,
		     unsigned int count,
		     const HBUINT backtrack[],
		     match_func_t match_func,
		     const void *match_data,
		     unsigned int *match_start)
{
 TRACE_APPLY (nullptr);

 if (!count)
 {
   *match_start = c->buffer->backtrack_len ();
   return_trace (true);
 }

 auto &skippy_iter = c->iter_context;
 skippy_iter.reset_back (c->buffer->backtrack_len ());
 skippy_iter.set_match_func (match_func, match_data);
 skippy_iter.set_glyph_data (backtrack);

 for (unsigned int i = 0; i < count; i++)
 {
   unsigned unsafe_from;
   if (!skippy_iter.prev (&unsafe_from))
   {
     *match_start = unsafe_from;
     return_trace (false);
   }
 }

 *match_start = skippy_iter.idx;
 return_trace (true);
}

template <typename HBUINT>
#ifndef HB_OPTIMIZE_SIZE
HB_ALWAYS_INLINE
#endif
static bool match_lookahead (hb_ot_apply_context_t *c,
		     unsigned int count,
		     const HBUINT lookahead[],
		     match_func_t match_func,
		     const void *match_data,
		     unsigned int start_index,
		     unsigned int *end_index)
{
 TRACE_APPLY (nullptr);

 if (!count)
 {
   *end_index = start_index;
   return_trace (true);
 }

 auto &skippy_iter = c->iter_context;
 assert (start_index >= 1);
 skippy_iter.reset (start_index - 1);
 skippy_iter.set_match_func (match_func, match_data);
 skippy_iter.set_glyph_data (lookahead);

 for (unsigned int i = 0; i < count; i++)
 {
   unsigned unsafe_to;
   if (!skippy_iter.next (&unsafe_to))
   {
     *end_index = unsafe_to;
     return_trace (false);
   }
 }

 *end_index = skippy_iter.idx + 1;
 return_trace (true);
}



struct LookupRecord
{
 bool serialize (hb_serialize_context_t *c,
	  const hb_map_t         *lookup_map) const
 {
   TRACE_SERIALIZE (this);
   auto *out = c->embed (*this);
   if (unlikely (!out)) return_trace (false);

   return_trace (c->check_assign (out->lookupListIndex, lookup_map->get (lookupListIndex), HB_SERIALIZE_ERROR_INT_OVERFLOW));
 }

 bool sanitize (hb_sanitize_context_t *c) const
 {
   TRACE_SANITIZE (this);
   return_trace (c->check_struct (this));
 }

 HBUINT16	sequenceIndex;		/* Index into current glyph
				 * sequence--first glyph = 0 */
 HBUINT16	lookupListIndex;	/* Lookup to apply to that
				 * position--zero--based */
 public:
 DEFINE_SIZE_STATIC (4);
};

static unsigned serialize_lookuprecord_array (hb_serialize_context_t *c,
				      const hb_array_t<const LookupRecord> lookupRecords,
				      const hb_map_t *lookup_map)
{
 unsigned count = 0;
 for (const LookupRecord& r : lookupRecords)
 {
   if (!lookup_map->has (r.lookupListIndex))
     continue;

   if (!r.serialize (c, lookup_map))
     return 0;

   count++;
 }
 return count;
}

enum ContextFormat { SimpleContext = 1, ClassBasedContext = 2, CoverageBasedContext = 3 };

template <typename HBUINT>
static void context_closure_recurse_lookups (hb_closure_context_t *c,
				     unsigned inputCount, const HBUINT input[],
				     unsigned lookupCount,
				     const LookupRecord lookupRecord[] /* Array of LookupRecords--in design order */,
				     unsigned value,
				     ContextFormat context_format,
				     const void *data,
				     intersected_glyphs_func_t intersected_glyphs_func,
				     void *cache)
{
 hb_set_t covered_seq_indicies;
 hb_set_t pos_glyphs;
 for (unsigned int i = 0; i < lookupCount; i++)
 {
   unsigned seqIndex = lookupRecord[i].sequenceIndex;
   if (seqIndex >= inputCount) continue;

   bool has_pos_glyphs = false;

   if (!covered_seq_indicies.has (seqIndex))
   {
     has_pos_glyphs = true;
     pos_glyphs.clear ();
     if (seqIndex == 0)
     {
       switch (context_format) {
       case ContextFormat::SimpleContext:
         pos_glyphs.add (value);
         break;
       case ContextFormat::ClassBasedContext:
         intersected_glyphs_func (&c->parent_active_glyphs (), data, value, &pos_glyphs, cache);
         break;
       case ContextFormat::CoverageBasedContext:
         pos_glyphs.set (c->parent_active_glyphs ());
         break;
       }
     }
     else
     {
       const void *input_data = input;
       unsigned input_value = seqIndex - 1;
       if (context_format != ContextFormat::SimpleContext)
       {
         input_data = data;
         input_value = input[seqIndex - 1];
       }

       intersected_glyphs_func (c->glyphs, input_data, input_value, &pos_glyphs, cache);
     }
   }

   covered_seq_indicies.add (seqIndex);
   hb_set_t *cur_active_glyphs = c->push_cur_active_glyphs ();
   if (unlikely (!cur_active_glyphs))
     return;
   if (has_pos_glyphs) {
     *cur_active_glyphs = std::move (pos_glyphs);
   } else {
     *cur_active_glyphs = *c->glyphs;
   }

   unsigned endIndex = inputCount;
   if (context_format == ContextFormat::CoverageBasedContext)
     endIndex += 1;

   c->recurse (lookupRecord[i].lookupListIndex, &covered_seq_indicies, seqIndex, endIndex);

   c->pop_cur_done_glyphs ();
 }
}

template <typename context_t>
static inline void recurse_lookups (context_t *c,
                                   unsigned int lookupCount,
                                   const LookupRecord lookupRecord[] /* Array of LookupRecords--in design order */)
{
 for (unsigned int i = 0; i < lookupCount; i++)
   c->recurse (lookupRecord[i].lookupListIndex);
}

static inline void apply_lookup (hb_ot_apply_context_t *c,
			 unsigned int count, /* Including the first glyph */
			 unsigned int lookupCount,
			 const LookupRecord lookupRecord[], /* Array of LookupRecords--in design order */
			 unsigned int match_end)
{
 hb_buffer_t *buffer = c->buffer;
 int end;

 /* All positions are distance from beginning of *output* buffer.
  * Adjust. */
 {
   unsigned int bl = buffer->backtrack_len ();
   end = bl + match_end - buffer->idx;

   int delta = bl - buffer->idx;
   /* Convert positions to new indexing. */
   for (unsigned int j = 0; j < count; j++)
     c->match_positions.arrayZ[j] += delta;
 }

 for (unsigned int i = 0; i < lookupCount && buffer->successful; i++)
 {
   unsigned int idx = lookupRecord[i].sequenceIndex;
   if (idx >= count)
     continue;

   unsigned int orig_len = buffer->backtrack_len () + buffer->lookahead_len ();

   /* This can happen if earlier recursed lookups deleted many entries. */
   if (unlikely (c->match_positions.arrayZ[idx] >= orig_len))
     continue;

   if (unlikely (!buffer->move_to (c->match_positions.arrayZ[idx])))
     break;

   if (unlikely (buffer->max_ops <= 0))
     break;

   if (HB_BUFFER_MESSAGE_MORE && c->buffer->messaging ())
   {
     if (buffer->have_output)
       c->buffer->sync_so_far ();
     c->buffer->message (c->font,
		  "recursing to lookup %u at %u",
		  (unsigned) lookupRecord[i].lookupListIndex,
		  buffer->idx);
   }

   if (!c->recurse (lookupRecord[i].lookupListIndex))
     continue;

   if (HB_BUFFER_MESSAGE_MORE && c->buffer->messaging ())
   {
     if (buffer->have_output)
       c->buffer->sync_so_far ();
     c->buffer->message (c->font,
		  "recursed to lookup %u",
		  (unsigned) lookupRecord[i].lookupListIndex);
   }

   unsigned int new_len = buffer->backtrack_len () + buffer->lookahead_len ();
   int delta = new_len - orig_len;

   if (!delta)
     continue;

   /* Recursed lookup changed buffer len.  Adjust.
    *
    * TODO:
    *
    * Right now, if buffer length increased by n, we assume n new glyphs
    * were added right after the current position, and if buffer length
    * was decreased by n, we assume n match positions after the current
    * one where removed.  The former (buffer length increased) case is
    * fine, but the decrease case can be improved in at least two ways,
    * both of which are significant:
    *
    *   - If recursed-to lookup is MultipleSubst and buffer length
    *     decreased, then it's current match position that was deleted,
    *     NOT the one after it.
    *
    *   - If buffer length was decreased by n, it does not necessarily
    *     mean that n match positions where removed, as there recursed-to
    *     lookup might had a different LookupFlag.  Here's a constructed
    *     case of that:
    *     https://github.com/harfbuzz/harfbuzz/discussions/3538
    *
    * It should be possible to construct tests for both of these cases.
    */

   end += delta;
   if (end < int (c->match_positions.arrayZ[idx]))
   {
     /* End might end up being smaller than match_positions.arrayZ[idx] if the recursed
      * lookup ended up removing many items.
      * Just never rewind end beyond start of current position, since that is
      * not possible in the recursed lookup.  Also adjust delta as such.
      *
      * https://bugs.chromium.org/p/chromium/issues/detail?id=659496
      * https://github.com/harfbuzz/harfbuzz/issues/1611
      */
     delta += c->match_positions.arrayZ[idx] - end;
     end = c->match_positions.arrayZ[idx];
   }

   unsigned int next = idx + 1; /* next now is the position after the recursed lookup. */

   if (delta > 0)
   {
     if (unlikely (delta + count > HB_MAX_CONTEXT_LENGTH))
break;
     if (unlikely (count + delta > c->match_positions.length &&
	    !c->match_positions.resize_dirty  (count + delta)))
       return;
   }
   else
   {
     /* NOTE: delta is non-positive. */
     delta = hb_max (delta, (int) next - (int) count);
     next -= delta;
   }

   /* Shift! */
   memmove (c->match_positions + next + delta, c->match_positions + next,
     (count - next) * sizeof (c->match_positions.arrayZ[0]));
   next += delta;
   count += delta;

   /* Fill in new entries. */
   for (unsigned int j = idx + 1; j < next; j++)
     c->match_positions.arrayZ[j] = c->match_positions.arrayZ[j - 1] + 1;

   /* And fixup the rest. */
   for (; next < count; next++)
     c->match_positions.arrayZ[next] += delta;
 }

 assert (end >= 0);
 (void) buffer->move_to (end);
}



/* Contextual lookups */

struct ContextClosureLookupContext
{
 ContextClosureFuncs funcs;
 ContextFormat context_format;
 const void *intersects_data;
 void *intersects_cache;
 void *intersected_glyphs_cache;
};

struct ContextCollectGlyphsLookupContext
{
 ContextCollectGlyphsFuncs funcs;
 const void *collect_data;
};

struct ContextApplyLookupContext
{
 ContextApplyFuncs funcs;
 const void *match_data;
};

template <typename HBUINT>
static inline bool context_intersects (const hb_set_t *glyphs,
			       unsigned int inputCount, /* Including the first glyph (not matched) */
			       const HBUINT input[], /* Array of input values--start with second glyph */
			       ContextClosureLookupContext &lookup_context)
{
 return array_is_subset_of (glyphs,
		     inputCount ? inputCount - 1 : 0, input,
		     lookup_context.funcs.intersects,
		     lookup_context.intersects_data,
		     lookup_context.intersects_cache);
}

template <typename HBUINT>
static inline void context_closure_lookup (hb_closure_context_t *c,
				   unsigned int inputCount, /* Including the first glyph (not matched) */
				   const HBUINT input[], /* Array of input values--start with second glyph */
				   unsigned int lookupCount,
				   const LookupRecord lookupRecord[],
				   unsigned value, /* Index of first glyph in Coverage or Class value in ClassDef table */
				   ContextClosureLookupContext &lookup_context)
{
 if (context_intersects (c->glyphs,
		  inputCount, input,
		  lookup_context))
   context_closure_recurse_lookups (c,
			     inputCount, input,
			     lookupCount, lookupRecord,
			     value,
			     lookup_context.context_format,
			     lookup_context.intersects_data,
			     lookup_context.funcs.intersected_glyphs,
			     lookup_context.intersected_glyphs_cache);
}

template <typename HBUINT>
static inline void context_collect_glyphs_lookup (hb_collect_glyphs_context_t *c,
					  unsigned int inputCount, /* Including the first glyph (not matched) */
					  const HBUINT input[], /* Array of input values--start with second glyph */
					  unsigned int lookupCount,
					  const LookupRecord lookupRecord[],
					  ContextCollectGlyphsLookupContext &lookup_context)
{
 collect_array (c, c->input,
	 inputCount ? inputCount - 1 : 0, input,
	 lookup_context.funcs.collect, lookup_context.collect_data);
 recurse_lookups (c,
	   lookupCount, lookupRecord);
}

template <typename HBUINT>
static inline bool context_would_apply_lookup (hb_would_apply_context_t *c,
				       unsigned int inputCount, /* Including the first glyph (not matched) */
				       const HBUINT input[], /* Array of input values--start with second glyph */
				       unsigned int lookupCount HB_UNUSED,
				       const LookupRecord lookupRecord[] HB_UNUSED,
				       const ContextApplyLookupContext &lookup_context)
{
 return would_match_input (c,
		    inputCount, input,
		    lookup_context.funcs.match, lookup_context.match_data);
}

template <typename HBUINT>
HB_ALWAYS_INLINE
static bool context_apply_lookup (hb_ot_apply_context_t *c,
			  unsigned int inputCount, /* Including the first glyph (not matched) */
			  const HBUINT input[], /* Array of input values--start with second glyph */
			  unsigned int lookupCount,
			  const LookupRecord lookupRecord[],
			  const ContextApplyLookupContext &lookup_context)
{
 if (unlikely (inputCount > HB_MAX_CONTEXT_LENGTH)) return false;

 unsigned match_end = 0;
 bool ret = false;
 if (match_input (c,
	   inputCount, input,
	   lookup_context.funcs.match, lookup_context.match_data,
	   &match_end))
 {
   c->buffer->unsafe_to_break (c->buffer->idx, match_end);
   apply_lookup (c,
	  inputCount,
	  lookupCount, lookupRecord,
	  match_end);
   ret = true;
 }
 else
 {
   c->buffer->unsafe_to_concat (c->buffer->idx, match_end);
   ret = false;
 }

 return ret;
}

static inline bool context_cache_func (hb_ot_apply_context_t *c, hb_ot_subtable_cache_op_t op)
{
 switch (op)
 {
   case hb_ot_subtable_cache_op_t::ENTER:
   {
     if (!HB_BUFFER_TRY_ALLOCATE_VAR (c->buffer, syllable))
return false;
     auto &info = c->buffer->info;
     unsigned count = c->buffer->len;
     for (unsigned i = 0; i < count; i++)
info[i].syllable() = 255;
     c->new_syllables = 255;
     return true;
   }
   case hb_ot_subtable_cache_op_t::LEAVE:
   {
     c->new_syllables = (unsigned) -1;
     HB_BUFFER_DEALLOCATE_VAR (c->buffer, syllable);
     break;
   }
 }
 return false;
}

template <typename Types>
struct Rule
{
 template <typename T>
 friend struct RuleSet;

 bool intersects (const hb_set_t *glyphs, ContextClosureLookupContext &lookup_context) const
 {
   return context_intersects (glyphs,
		       inputCount, inputZ.arrayZ,
		       lookup_context);
 }

 void closure (hb_closure_context_t *c, unsigned value, ContextClosureLookupContext &lookup_context) const
 {
   if (unlikely (c->lookup_limit_exceeded ())) return;

   const auto &lookupRecord = StructAfter<UnsizedArrayOf<LookupRecord>>
				   (inputZ.as_array ((inputCount ? inputCount - 1 : 0)));
   context_closure_lookup (c,
		    inputCount, inputZ.arrayZ,
		    lookupCount, lookupRecord.arrayZ,
		    value, lookup_context);
 }

 void closure_lookups (hb_closure_lookups_context_t *c,
                       ContextClosureLookupContext &lookup_context) const
 {
   if (unlikely (c->lookup_limit_exceeded ())) return;
   if (!intersects (c->glyphs, lookup_context)) return;

   const auto &lookupRecord = StructAfter<UnsizedArrayOf<LookupRecord>>
				   (inputZ.as_array (inputCount ? inputCount - 1 : 0));
   recurse_lookups (c, lookupCount, lookupRecord.arrayZ);
 }

 void collect_glyphs (hb_collect_glyphs_context_t *c,
	       ContextCollectGlyphsLookupContext &lookup_context) const
 {
   const auto &lookupRecord = StructAfter<UnsizedArrayOf<LookupRecord>>
				   (inputZ.as_array (inputCount ? inputCount - 1 : 0));
   context_collect_glyphs_lookup (c,
			   inputCount, inputZ.arrayZ,
			   lookupCount, lookupRecord.arrayZ,
			   lookup_context);
 }

 bool would_apply (hb_would_apply_context_t *c,
	    const ContextApplyLookupContext &lookup_context) const
 {
   const auto &lookupRecord = StructAfter<UnsizedArrayOf<LookupRecord>>
				   (inputZ.as_array (inputCount ? inputCount - 1 : 0));
   return context_would_apply_lookup (c,
			       inputCount, inputZ.arrayZ,
			       lookupCount, lookupRecord.arrayZ,
			       lookup_context);
 }

 bool apply (hb_ot_apply_context_t *c,
      const ContextApplyLookupContext &lookup_context) const
 {
   TRACE_APPLY (this);
   const auto &lookupRecord = StructAfter<UnsizedArrayOf<LookupRecord>>
				   (inputZ.as_array (inputCount ? inputCount - 1 : 0));
   return_trace (context_apply_lookup (c, inputCount, inputZ.arrayZ, lookupCount, lookupRecord.arrayZ, lookup_context));
 }

 bool serialize (hb_serialize_context_t *c,
	  const hb_map_t *input_mapping, /* old->new glyphid or class mapping */
	  const hb_map_t *lookup_map) const
 {
   TRACE_SERIALIZE (this);
   auto *out = c->start_embed (this);
   if (unlikely (!c->extend_min (out))) return_trace (false);

   out->inputCount = inputCount;
   const auto input = inputZ.as_array (inputCount - 1);
   for (const auto org : input)
   {
     HBUINT16 d;
     d = input_mapping->get (org);
     c->copy (d);
   }

   const auto &lookupRecord = StructAfter<UnsizedArrayOf<LookupRecord>>
				   (inputZ.as_array ((inputCount ? inputCount - 1 : 0)));

   unsigned count = serialize_lookuprecord_array (c, lookupRecord.as_array (lookupCount), lookup_map);
   return_trace (c->check_assign (out->lookupCount, count, HB_SERIALIZE_ERROR_INT_OVERFLOW));
 }

 bool subset (hb_subset_context_t *c,
       const hb_map_t *lookup_map,
       const hb_map_t *klass_map = nullptr) const
 {
   TRACE_SUBSET (this);
   if (unlikely (!inputCount)) return_trace (false);
   const auto input = inputZ.as_array (inputCount - 1);

   const hb_map_t *mapping = klass_map == nullptr ? c->plan->glyph_map : klass_map;
   if (!hb_all (input, mapping)) return_trace (false);
   return_trace (serialize (c->serializer, mapping, lookup_map));
 }

 public:
 bool sanitize (hb_sanitize_context_t *c) const
 {
   TRACE_SANITIZE (this);
   return_trace (c->check_struct (this) &&
	  hb_barrier () &&
	  c->check_range (inputZ.arrayZ,
			  inputZ.item_size * (inputCount ? inputCount - 1 : 0) +
			  LookupRecord::static_size * lookupCount));
 }

 protected:
 HBUINT16	inputCount;		/* Total number of glyphs in input
				 * glyph sequence--includes the first
				 * glyph */
 HBUINT16	lookupCount;		/* Number of LookupRecords */
 UnsizedArrayOf<typename Types::HBUINT>
	inputZ;			/* Array of match inputs--start with
				 * second glyph */
/*UnsizedArrayOf<LookupRecord>
	lookupRecordX;*/	/* Array of LookupRecords--in
				 * design order */
 public:
 DEFINE_SIZE_ARRAY (4, inputZ);
};

template <typename Types>
struct RuleSet
{
 using Rule = OT::Rule<Types>;

 bool intersects (const hb_set_t *glyphs,
	   ContextClosureLookupContext &lookup_context) const
 {
   return
   + hb_iter (rule)
   | hb_map (hb_add (this))
   | hb_map ([&] (const Rule &_) { return _.intersects (glyphs, lookup_context); })
   | hb_any
   ;
 }

 void closure (hb_closure_context_t *c, unsigned value,
	ContextClosureLookupContext &lookup_context) const
 {
   if (unlikely (c->lookup_limit_exceeded ())) return;

   return
   + hb_iter (rule)
   | hb_map (hb_add (this))
   | hb_apply ([&] (const Rule &_) { _.closure (c, value, lookup_context); })
   ;
 }

 void closure_lookups (hb_closure_lookups_context_t *c,
                       ContextClosureLookupContext &lookup_context) const
 {
   if (unlikely (c->lookup_limit_exceeded ())) return;
   + hb_iter (rule)
   | hb_map (hb_add (this))
   | hb_apply ([&] (const Rule &_) { _.closure_lookups (c, lookup_context); })
   ;
 }

 void collect_glyphs (hb_collect_glyphs_context_t *c,
	       ContextCollectGlyphsLookupContext &lookup_context) const
 {
   return
   + hb_iter (rule)
   | hb_map (hb_add (this))
   | hb_apply ([&] (const Rule &_) { _.collect_glyphs (c, lookup_context); })
   ;
 }

 bool would_apply (hb_would_apply_context_t *c,
	    const ContextApplyLookupContext &lookup_context) const
 {
   return
   + hb_iter (rule)
   | hb_map (hb_add (this))
   | hb_map ([&] (const Rule &_) { return _.would_apply (c, lookup_context); })
   | hb_any
   ;
 }

 bool apply (hb_ot_apply_context_t *c,
      const ContextApplyLookupContext &lookup_context) const
 {
   TRACE_APPLY (this);

   unsigned num_rules = rule.len;

#ifndef HB_NO_OT_RULESETS_FAST_PATH
   if (HB_OPTIMIZE_SIZE_VAL || num_rules <= 4)
#endif
   {
   slow:
     return_trace (
     + hb_iter (rule)
     | hb_map (hb_add (this))
     | hb_map ([&] (const Rule &_) { return _.apply (c, lookup_context); })
     | hb_any
     )
     ;
   }

   /* This version is optimized for speed by matching the first & second
    * components of the rule here, instead of calling into the matching code.
    *
    * Replicated from LigatureSet::apply(). */

   /* We use the iter_context instead of iter_input, to avoid skipping
    * default-ignorables and such.
    *
    * Related: https://github.com/harfbuzz/harfbuzz/issues/4813
    */
   auto &skippy_iter = c->iter_context;
   skippy_iter.reset (c->buffer->idx);
   skippy_iter.set_match_func (match_always, nullptr);
   skippy_iter.set_glyph_data ((HBUINT16 *) nullptr);
   unsigned unsafe_to = (unsigned) -1, unsafe_to1 = 0, unsafe_to2 = 0;
   hb_glyph_info_t *first = nullptr, *second = nullptr;
   bool matched = skippy_iter.next ();
   if (likely (matched))
   {
     if (skippy_iter.may_skip (c->buffer->info[skippy_iter.idx]))
     {
/* Can't use the fast path if eg. the next char is a default-ignorable
 * or other skippable. */
       goto slow;
     }

     first = &c->buffer->info[skippy_iter.idx];
     unsafe_to = skippy_iter.idx + 1;
   }
   else
   {
     /* Failed to match a next glyph. Only try applying rules that have
      * no further input. */
     return_trace (
     + hb_iter (rule)
     | hb_map (hb_add (this))
     | hb_filter ([&] (const Rule &_) { return _.inputCount <= 1; })
     | hb_map ([&] (const Rule &_) { return _.apply (c, lookup_context); })
     | hb_any
     )
     ;
   }
   matched = skippy_iter.next ();
   if (likely (matched))
   {
     if (skippy_iter.may_skip (c->buffer->info[skippy_iter.idx]))
     {
/* Can't use the fast path if eg. the next char is a default-ignorable
 * or other skippable. */
       goto slow;
     }

     second = &c->buffer->info[skippy_iter.idx];
     unsafe_to2 = skippy_iter.idx + 1;
   }

   auto match_input = lookup_context.funcs.match;
   auto *input_data = lookup_context.match_data;
   for (unsigned int i = 0; i < num_rules; i++)
   {
     const auto &r = this+rule.arrayZ[i];

     const auto &input = r.inputZ;

     if (r.inputCount <= 1 ||
  (!match_input ||
   match_input (*first, input.arrayZ[0], input_data)))
     {
       if (!second ||
    (r.inputCount <= 2 ||
     (!match_input ||
      match_input (*second, input.arrayZ[1], input_data)))
   )
{
  if (r.apply (c, lookup_context))
  {
    if (unsafe_to != (unsigned) -1)
      c->buffer->unsafe_to_concat (c->buffer->idx, unsafe_to);
    return_trace (true);
  }
}
else
  unsafe_to = unsafe_to2;
     }
     else
     {
if (unsafe_to == (unsigned) -1)
  unsafe_to = unsafe_to1;

// Skip ahead to next possible first glyph match.
for (; i + 1 < num_rules; i++)
{
  const auto &r2 = this+rule.arrayZ[i + 1];
  const auto &input2 = r2.inputZ;
  if (r2.inputCount <= 1 || input2.arrayZ[0] != input.arrayZ[0])
    break;
}
     }
   }
   if (likely (unsafe_to != (unsigned) -1))
     c->buffer->unsafe_to_concat (c->buffer->idx, unsafe_to);

   return_trace (false);
 }

 bool subset (hb_subset_context_t *c,
       const hb_map_t *lookup_map,
       const hb_map_t *klass_map = nullptr) const
 {
   TRACE_SUBSET (this);

   auto snap = c->serializer->snapshot ();
   auto *out = c->serializer->start_embed (*this);
   if (unlikely (!c->serializer->extend_min (out))) return_trace (false);

   for (const Offset16To<Rule>& _ : rule)
   {
     if (!_) continue;
     auto o_snap = c->serializer->snapshot ();
     auto *o = out->rule.serialize_append (c->serializer);
     if (unlikely (!o)) continue;

     if (!o->serialize_subset (c, _, this, lookup_map, klass_map))
     {
out->rule.pop ();
c->serializer->revert (o_snap);
     }
   }

   bool ret = bool (out->rule);
   if (!ret) c->serializer->revert (snap);

   return_trace (ret);
 }

 bool sanitize (hb_sanitize_context_t *c) const
 {
   TRACE_SANITIZE (this);
   return_trace (rule.sanitize (c, this));
 }

 protected:
 Array16OfOffset16To<Rule>
	rule;			/* Array of Rule tables
				 * ordered by preference */
 public:
 DEFINE_SIZE_ARRAY (2, rule);
};


template <typename Types>
struct ContextFormat1_4
{
 using RuleSet = OT::RuleSet<Types>;

 bool intersects (const hb_set_t *glyphs) const
 {
   struct ContextClosureLookupContext lookup_context = {
     {intersects_glyph, intersected_glyph},
     ContextFormat::SimpleContext,
     nullptr
   };

   return
   + hb_zip (this+coverage, ruleSet)
   | hb_filter (*glyphs, hb_first)
   | hb_map (hb_second)
   | hb_map (hb_add (this))
   | hb_map ([&] (const RuleSet &_) { return _.intersects (glyphs, lookup_context); })
   | hb_any
   ;
 }

 bool may_have_non_1to1 () const
 { return true; }

 void closure (hb_closure_context_t *c) const
 {
   hb_set_t* cur_active_glyphs = c->push_cur_active_glyphs ();
   if (unlikely (!cur_active_glyphs)) return;
   get_coverage ().intersect_set (c->previous_parent_active_glyphs (), *cur_active_glyphs);

   struct ContextClosureLookupContext lookup_context = {
     {intersects_glyph, intersected_glyph},
     ContextFormat::SimpleContext,
     nullptr
   };

   + hb_zip (this+coverage, hb_range ((unsigned) ruleSet.len))
   | hb_filter ([&] (hb_codepoint_t _) {
     return c->previous_parent_active_glyphs ().has (_);
   }, hb_first)
   | hb_map ([&](const hb_pair_t<hb_codepoint_t, unsigned> _) { return hb_pair_t<unsigned, const RuleSet&> (_.first, this+ruleSet[_.second]); })
   | hb_apply ([&] (const hb_pair_t<unsigned, const RuleSet&>& _) { _.second.closure (c, _.first, lookup_context); })
   ;

   c->pop_cur_done_glyphs ();
 }

 void closure_lookups (hb_closure_lookups_context_t *c) const
 {
   struct ContextClosureLookupContext lookup_context = {
     {intersects_glyph, nullptr},
     ContextFormat::SimpleContext,
     nullptr
   };

   + hb_zip (this+coverage, ruleSet)
   | hb_filter (*c->glyphs, hb_first)
   | hb_map (hb_second)
   | hb_map (hb_add (this))
   | hb_apply ([&] (const RuleSet &_) { _.closure_lookups (c, lookup_context); })
   ;
 }

 void collect_variation_indices (hb_collect_variation_indices_context_t *c) const {}

 void collect_glyphs (hb_collect_glyphs_context_t *c) const
 {
   (this+coverage).collect_coverage (c->input);

   struct ContextCollectGlyphsLookupContext lookup_context = {
     {collect_glyph},
     nullptr
   };

   + hb_iter (ruleSet)
   | hb_map (hb_add (this))
   | hb_apply ([&] (const RuleSet &_) { _.collect_glyphs (c, lookup_context); })
   ;
 }

 bool would_apply (hb_would_apply_context_t *c) const
 {
   const RuleSet &rule_set = this+ruleSet[(this+coverage).get_coverage (c->glyphs[0])];
   struct ContextApplyLookupContext lookup_context = {
     {match_glyph},
     nullptr
   };
   return rule_set.would_apply (c, lookup_context);
 }

 const Coverage &get_coverage () const { return this+coverage; }

 bool apply (hb_ot_apply_context_t *c) const
 {
   TRACE_APPLY (this);
   unsigned int index = (this+coverage).get_coverage (c->buffer->cur().codepoint);
   if (likely (index == NOT_COVERED))
     return_trace (false);

   const RuleSet &rule_set = this+ruleSet[index];
   struct ContextApplyLookupContext lookup_context = {
     {match_glyph},
     nullptr
   };
   return_trace (rule_set.apply (c, lookup_context));
 }

 bool subset (hb_subset_context_t *c) const
 {
   TRACE_SUBSET (this);
   const hb_set_t &glyphset = *c->plan->glyphset_gsub ();
   const hb_map_t &glyph_map = *c->plan->glyph_map;

   auto *out = c->serializer->start_embed (*this);
   if (unlikely (!c->serializer->extend_min (out))) return_trace (false);
   out->format = format;

   const hb_map_t *lookup_map = c->table_tag == HB_OT_TAG_GSUB ? &c->plan->gsub_lookups : &c->plan->gpos_lookups;
   hb_sorted_vector_t<hb_codepoint_t> new_coverage;
   + hb_zip (this+coverage, ruleSet)
   | hb_filter (glyphset, hb_first)
   | hb_filter (subset_offset_array (c, out->ruleSet, this, lookup_map), hb_second)
   | hb_map (hb_first)
   | hb_map (glyph_map)
   | hb_sink (new_coverage)
   ;

   out->coverage.serialize_serialize (c->serializer, new_coverage.iter ());
   return_trace (bool (new_coverage));
 }

 bool sanitize (hb_sanitize_context_t *c) const
 {
   TRACE_SANITIZE (this);
   return_trace (coverage.sanitize (c, this) && ruleSet.sanitize (c, this));
 }

 protected:
 HBUINT16	format;			/* Format identifier--format = 1 */
 typename Types::template OffsetTo<Coverage>
	coverage;		/* Offset to Coverage table--from
				 * beginning of table */
 Array16Of<typename Types::template OffsetTo<RuleSet>>
	ruleSet;		/* Array of RuleSet tables
				 * ordered by Coverage Index */
 public:
 DEFINE_SIZE_ARRAY (2 + 2 * Types::size, ruleSet);
};


template <typename Types>
struct ContextFormat2_5
{
 using RuleSet = OT::RuleSet<SmallTypes>;

 bool intersects (const hb_set_t *glyphs) const
 {
   if (!(this+coverage).intersects (glyphs))
     return false;

   const ClassDef &class_def = this+classDef;

   hb_map_t cache;
   struct ContextClosureLookupContext lookup_context = {
     {intersects_class, nullptr},
     ContextFormat::ClassBasedContext,
     &class_def,
     &cache
   };

   hb_set_t retained_coverage_glyphs;
   (this+coverage).intersect_set (*glyphs, retained_coverage_glyphs);

   hb_set_t coverage_glyph_classes;
   class_def.intersected_classes (&retained_coverage_glyphs, &coverage_glyph_classes);


   return
   + hb_iter (ruleSet)
   | hb_map (hb_add (this))
   | hb_enumerate
   | hb_map ([&] (const hb_pair_t<unsigned, const RuleSet &> p)
      { return class_def.intersects_class (glyphs, p.first) &&
	       coverage_glyph_classes.has (p.first) &&
	       p.second.intersects (glyphs, lookup_context); })
   | hb_any
   ;
 }

 bool may_have_non_1to1 () const
 { return true; }

 void closure (hb_closure_context_t *c) const
 {
   if (!(this+coverage).intersects (c->glyphs))
     return;

   hb_set_t* cur_active_glyphs = c->push_cur_active_glyphs ();
   if (unlikely (!cur_active_glyphs)) return;
   get_coverage ().intersect_set (c->previous_parent_active_glyphs (),
			   *cur_active_glyphs);

   const ClassDef &class_def = this+classDef;

   hb_map_t cache;
   intersected_class_cache_t intersected_cache;
   struct ContextClosureLookupContext lookup_context = {
     {intersects_class, intersected_class_glyphs},
     ContextFormat::ClassBasedContext,
     &class_def,
     &cache,
     &intersected_cache
   };

   + hb_enumerate (ruleSet)
   | hb_filter ([&] (unsigned _)
   { return class_def.intersects_class (&c->parent_active_glyphs (), _); },
	 hb_first)
   | hb_apply ([&] (const hb_pair_t<unsigned, const typename Types::template OffsetTo<RuleSet>&> _)
               {
                 const RuleSet& rule_set = this+_.second;
                 rule_set.closure (c, _.first, lookup_context);
               })
   ;

   c->pop_cur_done_glyphs ();
 }

 void closure_lookups (hb_closure_lookups_context_t *c) const
 {
   if (!(this+coverage).intersects (c->glyphs))
     return;

   const ClassDef &class_def = this+classDef;

   hb_map_t cache;
   struct ContextClosureLookupContext lookup_context = {
     {intersects_class, nullptr},
     ContextFormat::ClassBasedContext,
     &class_def,
     &cache
   };

   + hb_iter (ruleSet)
   | hb_map (hb_add (this))
   | hb_enumerate
   | hb_filter ([&] (const hb_pair_t<unsigned, const RuleSet &> p)
   { return class_def.intersects_class (c->glyphs, p.first); })
   | hb_map (hb_second)
   | hb_apply ([&] (const RuleSet & _)
   { _.closure_lookups (c, lookup_context); });
 }

 void collect_variation_indices (hb_collect_variation_indices_context_t *c) const {}

 void collect_glyphs (hb_collect_glyphs_context_t *c) const
 {
   (this+coverage).collect_coverage (c->input);

   const ClassDef &class_def = this+classDef;
   struct ContextCollectGlyphsLookupContext lookup_context = {
     {collect_class},
     &class_def
   };

   + hb_iter (ruleSet)
   | hb_map (hb_add (this))
   | hb_apply ([&] (const RuleSet &_) { _.collect_glyphs (c, lookup_context); })
   ;
 }

 bool would_apply (hb_would_apply_context_t *c) const
 {
   const ClassDef &class_def = this+classDef;
   unsigned int index = class_def.get_class (c->glyphs[0]);
   const RuleSet &rule_set = this+ruleSet[index];
   struct ContextApplyLookupContext lookup_context = {
     {match_class},
     &class_def
   };
   return rule_set.would_apply (c, lookup_context);
 }

 const Coverage &get_coverage () const { return this+coverage; }

 unsigned cache_cost () const
 {
   return (this+classDef).cost ();
 }
 static bool cache_func (hb_ot_apply_context_t *c, hb_ot_subtable_cache_op_t op)
 {
   return context_cache_func (c, op);
 }

 struct external_cache_t
 {
   hb_ot_layout_binary_cache_t coverage;
 };
 void *external_cache_create () const
 {
   external_cache_t *cache = (external_cache_t *) hb_malloc (sizeof (external_cache_t));
   if (likely (cache))
   {
     cache->coverage.clear ();
   }
   return cache;
 }
 bool apply_cached (hb_ot_apply_context_t *c, void *external_cache) const { return _apply (c, true, external_cache); }
 bool apply (hb_ot_apply_context_t *c, void *external_cache) const { return _apply (c, false, external_cache); }
 bool _apply (hb_ot_apply_context_t *c, bool cached, void *external_cache) const
 {
   TRACE_APPLY (this);
#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
   external_cache_t *cache = (external_cache_t *) external_cache;
   unsigned int index = (this+coverage).get_coverage_binary (c->buffer->cur().codepoint, cache ? &cache->coverage : nullptr);
#else
   unsigned int index = (this+coverage).get_coverage (c->buffer->cur().codepoint);
#endif
   if (index == NOT_COVERED) return_trace (false);

   const ClassDef &class_def = this+classDef;

   struct ContextApplyLookupContext lookup_context = {
     {cached ? match_class_cached : match_class},
     &class_def
   };

   index = cached ? get_class_cached (class_def, c->buffer->cur()) : class_def.get_class (c->buffer->cur().codepoint);
   const RuleSet &rule_set = this+ruleSet[index];
   return_trace (rule_set.apply (c, lookup_context));
 }

 bool subset (hb_subset_context_t *c) const
 {
   TRACE_SUBSET (this);
   auto *out = c->serializer->start_embed (*this);
   if (unlikely (!c->serializer->extend_min (out))) return_trace (false);
   out->format = format;
   if (unlikely (!out->coverage.serialize_subset (c, coverage, this)))
     return_trace (false);

   hb_map_t klass_map;
   out->classDef.serialize_subset (c, classDef, this, &klass_map);

   const hb_set_t* glyphset = c->plan->glyphset_gsub ();
   hb_set_t retained_coverage_glyphs;
   (this+coverage).intersect_set (*glyphset, retained_coverage_glyphs);

   hb_set_t coverage_glyph_classes;
   (this+classDef).intersected_classes (&retained_coverage_glyphs, &coverage_glyph_classes);

   const hb_map_t *lookup_map = c->table_tag == HB_OT_TAG_GSUB ? &c->plan->gsub_lookups : &c->plan->gpos_lookups;
   bool ret = true;
   int non_zero_index = -1, index = 0;
   auto snapshot = c->serializer->snapshot();
   for (const auto& _ : + hb_enumerate (ruleSet)
		 | hb_filter (klass_map, hb_first))
   {
     auto *o = out->ruleSet.serialize_append (c->serializer);
     if (unlikely (!o))
     {
ret = false;
break;
     }

     if (coverage_glyph_classes.has (_.first) &&
  o->serialize_subset (c, _.second, this, lookup_map, &klass_map)) {
non_zero_index = index;
       snapshot = c->serializer->snapshot();
     }

     index++;
   }

   if (!ret || non_zero_index == -1) return_trace (false);

   //prune empty trailing ruleSets
   --index;
   while (index > non_zero_index)
   {
     out->ruleSet.pop ();
     index--;
   }
   c->serializer->revert (snapshot);

   return_trace (bool (out->ruleSet));
 }

 bool sanitize (hb_sanitize_context_t *c) const
 {
   TRACE_SANITIZE (this);
   return_trace (coverage.sanitize (c, this) && classDef.sanitize (c, this) && ruleSet.sanitize (c, this));
 }

 protected:
 HBUINT16	format;			/* Format identifier--format = 2 */
 typename Types::template OffsetTo<Coverage>
	coverage;		/* Offset to Coverage table--from
				 * beginning of table */
 typename Types::template OffsetTo<ClassDef>
	classDef;		/* Offset to glyph ClassDef table--from
				 * beginning of table */
 Array16Of<typename Types::template OffsetTo<RuleSet>>
	ruleSet;		/* Array of RuleSet tables
				 * ordered by class */
 public:
 DEFINE_SIZE_ARRAY (4 + 2 * Types::size, ruleSet);
};


struct ContextFormat3
{
 using RuleSet = OT::RuleSet<SmallTypes>;

 bool intersects (const hb_set_t *glyphs) const
 {
   if (!(this+coverageZ[0]).intersects (glyphs))
     return false;

   struct ContextClosureLookupContext lookup_context = {
     {intersects_coverage, nullptr},
     ContextFormat::CoverageBasedContext,
     this
   };
   return context_intersects (glyphs,
		       glyphCount, (const HBUINT16 *) (coverageZ.arrayZ + 1),
		       lookup_context);
 }

 bool may_have_non_1to1 () const
 { return true; }

 void closure (hb_closure_context_t *c) const
 {
   if (!(this+coverageZ[0]).intersects (c->glyphs))
     return;

   hb_set_t* cur_active_glyphs = c->push_cur_active_glyphs ();
   if (unlikely (!cur_active_glyphs)) return;
   get_coverage ().intersect_set (c->previous_parent_active_glyphs (),
			   *cur_active_glyphs);

   const LookupRecord *lookupRecord = &StructAfter<LookupRecord> (coverageZ.as_array (glyphCount));
   struct ContextClosureLookupContext lookup_context = {
     {intersects_coverage, intersected_coverage_glyphs},
     ContextFormat::CoverageBasedContext,
     this
   };
   context_closure_lookup (c,
		    glyphCount, (const HBUINT16 *) (coverageZ.arrayZ + 1),
		    lookupCount, lookupRecord,
		    0, lookup_context);

   c->pop_cur_done_glyphs ();
 }

 void closure_lookups (hb_closure_lookups_context_t *c) const
 {
   if (!intersects (c->glyphs))
     return;
   const LookupRecord *lookupRecord = &StructAfter<LookupRecord> (coverageZ.as_array (glyphCount));
   recurse_lookups (c, lookupCount, lookupRecord);
 }

 void collect_variation_indices (hb_collect_variation_indices_context_t *c) const {}

 void collect_glyphs (hb_collect_glyphs_context_t *c) const
 {
   (this+coverageZ[0]).collect_coverage (c->input);

   const LookupRecord *lookupRecord = &StructAfter<LookupRecord> (coverageZ.as_array (glyphCount));
   struct ContextCollectGlyphsLookupContext lookup_context = {
     {collect_coverage},
     this
   };

   context_collect_glyphs_lookup (c,
			   glyphCount, (const HBUINT16 *) (coverageZ.arrayZ + 1),
			   lookupCount, lookupRecord,
			   lookup_context);
 }

 bool would_apply (hb_would_apply_context_t *c) const
 {
   const LookupRecord *lookupRecord = &StructAfter<LookupRecord> (coverageZ.as_array (glyphCount));
   struct ContextApplyLookupContext lookup_context = {
     {match_coverage},
     this
   };
   return context_would_apply_lookup (c,
			       glyphCount, (const HBUINT16 *) (coverageZ.arrayZ + 1),
			       lookupCount, lookupRecord,
			       lookup_context);
 }

 const Coverage &get_coverage () const { return this+coverageZ[0]; }

 bool apply (hb_ot_apply_context_t *c) const
 {
   TRACE_APPLY (this);
   unsigned int index = (this+coverageZ[0]).get_coverage (c->buffer->cur().codepoint);
   if (index == NOT_COVERED) return_trace (false);

   const LookupRecord *lookupRecord = &StructAfter<LookupRecord> (coverageZ.as_array (glyphCount));
   struct ContextApplyLookupContext lookup_context = {
     {match_coverage},
     this
   };
   return_trace (context_apply_lookup (c, glyphCount, (const HBUINT16 *) (coverageZ.arrayZ + 1), lookupCount, lookupRecord, lookup_context));
 }

 bool subset (hb_subset_context_t *c) const
 {
   TRACE_SUBSET (this);
   auto *out = c->serializer->start_embed (this);
   if (unlikely (!c->serializer->extend_min (out))) return_trace (false);

   out->format = format;
   out->glyphCount = glyphCount;

   auto coverages = coverageZ.as_array (glyphCount);

   for (const Offset16To<Coverage>& offset : coverages)
   {
     /* TODO(subset) This looks like should not be necessary to write this way. */
     auto *o = c->serializer->allocate_size<Offset16To<Coverage>> (Offset16To<Coverage>::static_size);
     if (unlikely (!o)) return_trace (false);
     if (!o->serialize_subset (c, offset, this)) return_trace (false);
   }

   const auto& lookupRecord = StructAfter<UnsizedArrayOf<LookupRecord>> (coverageZ.as_array (glyphCount));
   const hb_map_t *lookup_map = c->table_tag == HB_OT_TAG_GSUB ? &c->plan->gsub_lookups : &c->plan->gpos_lookups;


   unsigned count = serialize_lookuprecord_array (c->serializer, lookupRecord.as_array (lookupCount), lookup_map);
   return_trace (c->serializer->check_assign (out->lookupCount, count, HB_SERIALIZE_ERROR_INT_OVERFLOW));
 }

 bool sanitize (hb_sanitize_context_t *c) const
 {
   TRACE_SANITIZE (this);
   if (unlikely (!c->check_struct (this))) return_trace (false);
   hb_barrier ();
   unsigned int count = glyphCount;
   if (unlikely (!count)) return_trace (false); /* We want to access coverageZ[0] freely. */
   if (unlikely (!c->check_array (coverageZ.arrayZ, count))) return_trace (false);
   for (unsigned int i = 0; i < count; i++)
     if (unlikely (!coverageZ[i].sanitize (c, this))) return_trace (false);
   const LookupRecord *lookupRecord = &StructAfter<LookupRecord> (coverageZ.as_array (glyphCount));
   return_trace (likely (c->check_array (lookupRecord, lookupCount)));
 }

 protected:
 HBUINT16	format;			/* Format identifier--format = 3 */
 HBUINT16	glyphCount;		/* Number of glyphs in the input glyph
				 * sequence */
 HBUINT16	lookupCount;		/* Number of LookupRecords */
 UnsizedArrayOf<Offset16To<Coverage>>
	coverageZ;		/* Array of offsets to Coverage
				 * table in glyph sequence order */
/*UnsizedArrayOf<LookupRecord>
	lookupRecordX;*/	/* Array of LookupRecords--in
				 * design order */
 public:
 DEFINE_SIZE_ARRAY (6, coverageZ);
};

struct Context
{
 template <typename context_t, typename ...Ts>
 typename context_t::return_t dispatch (context_t *c, Ts&&... ds) const
 {
   if (unlikely (!c->may_dispatch (this, &u.format.v))) return c->no_dispatch_return_value ();
   TRACE_DISPATCH (this, u.format.v);
   switch (u.format.v) {
   case 1: hb_barrier (); return_trace (c->dispatch (u.format1, std::forward<Ts> (ds)...));
   case 2: hb_barrier (); return_trace (c->dispatch (u.format2, std::forward<Ts> (ds)...));
   case 3: hb_barrier (); return_trace (c->dispatch (u.format3, std::forward<Ts> (ds)...));
#ifndef HB_NO_BEYOND_64K
   case 4: hb_barrier (); return_trace (c->dispatch (u.format4, std::forward<Ts> (ds)...));
   case 5: hb_barrier (); return_trace (c->dispatch (u.format5, std::forward<Ts> (ds)...));
#endif
   default:return_trace (c->default_return_value ());
   }
 }

 protected:
 union {
 struct { HBUINT16 v; }	format;		/* Format identifier */
 ContextFormat1_4<SmallTypes>	format1;
 ContextFormat2_5<SmallTypes>	format2;
 ContextFormat3		format3;
#ifndef HB_NO_BEYOND_64K
 ContextFormat1_4<MediumTypes>	format4;
 ContextFormat2_5<MediumTypes>	format5;
#endif
 } u;
};


/* Chaining Contextual lookups */

struct ChainContextClosureLookupContext
{
 ContextClosureFuncs funcs;
 ContextFormat context_format;
 const void *intersects_data[3];
 void *intersects_cache[3];
 void *intersected_glyphs_cache;
};

struct ChainContextCollectGlyphsLookupContext
{
 ContextCollectGlyphsFuncs funcs;
 const void *collect_data[3];
};

struct ChainContextApplyLookupContext
{
 ChainContextApplyFuncs funcs;
 const void *match_data[3];
};

template <typename HBUINT>
static inline bool chain_context_intersects (const hb_set_t *glyphs,
				     unsigned int backtrackCount,
				     const HBUINT backtrack[],
				     unsigned int inputCount, /* Including the first glyph (not matched) */
				     const HBUINT input[], /* Array of input values--start with second glyph */
				     unsigned int lookaheadCount,
				     const HBUINT lookahead[],
				     ChainContextClosureLookupContext &lookup_context)
{
 return array_is_subset_of (glyphs,
		     backtrackCount, backtrack,
		     lookup_context.funcs.intersects,
		     lookup_context.intersects_data[0],
		     lookup_context.intersects_cache[0])
     && array_is_subset_of (glyphs,
		     inputCount ? inputCount - 1 : 0, input,
		     lookup_context.funcs.intersects,
		     lookup_context.intersects_data[1],
		     lookup_context.intersects_cache[1])
     && array_is_subset_of (glyphs,
		     lookaheadCount, lookahead,
		     lookup_context.funcs.intersects,
		     lookup_context.intersects_data[2],
		     lookup_context.intersects_cache[2]);
}

template <typename HBUINT>
static inline void chain_context_closure_lookup (hb_closure_context_t *c,
					 unsigned int backtrackCount,
					 const HBUINT backtrack[],
					 unsigned int inputCount, /* Including the first glyph (not matched) */
					 const HBUINT input[], /* Array of input values--start with second glyph */
					 unsigned int lookaheadCount,
					 const HBUINT lookahead[],
					 unsigned int lookupCount,
					 const LookupRecord lookupRecord[],
					 unsigned value,
					 ChainContextClosureLookupContext &lookup_context)
{
 if (chain_context_intersects (c->glyphs,
			backtrackCount, backtrack,
			inputCount, input,
			lookaheadCount, lookahead,
			lookup_context))
   context_closure_recurse_lookups (c,
	     inputCount, input,
	     lookupCount, lookupRecord,
	     value,
	     lookup_context.context_format,
	     lookup_context.intersects_data[1],
	     lookup_context.funcs.intersected_glyphs,
	     lookup_context.intersected_glyphs_cache);
}

template <typename HBUINT>
static inline void chain_context_collect_glyphs_lookup (hb_collect_glyphs_context_t *c,
						unsigned int backtrackCount,
						const HBUINT backtrack[],
						unsigned int inputCount, /* Including the first glyph (not matched) */
						const HBUINT input[], /* Array of input values--start with second glyph */
						unsigned int lookaheadCount,
						const HBUINT lookahead[],
						unsigned int lookupCount,
						const LookupRecord lookupRecord[],
						ChainContextCollectGlyphsLookupContext &lookup_context)
{
 collect_array (c, c->before,
	 backtrackCount, backtrack,
	 lookup_context.funcs.collect, lookup_context.collect_data[0]);
 collect_array (c, c->input,
	 inputCount ? inputCount - 1 : 0, input,
	 lookup_context.funcs.collect, lookup_context.collect_data[1]);
 collect_array (c, c->after,
	 lookaheadCount, lookahead,
	 lookup_context.funcs.collect, lookup_context.collect_data[2]);
 recurse_lookups (c,
	   lookupCount, lookupRecord);
}

template <typename HBUINT>
static inline bool chain_context_would_apply_lookup (hb_would_apply_context_t *c,
					     unsigned int backtrackCount,
					     const HBUINT backtrack[] HB_UNUSED,
					     unsigned int inputCount, /* Including the first glyph (not matched) */
					     const HBUINT input[], /* Array of input values--start with second glyph */
					     unsigned int lookaheadCount,
					     const HBUINT lookahead[] HB_UNUSED,
					     unsigned int lookupCount HB_UNUSED,
					     const LookupRecord lookupRecord[] HB_UNUSED,
					     const ChainContextApplyLookupContext &lookup_context)
{
 return (c->zero_context ? !backtrackCount && !lookaheadCount : true)
     && would_match_input (c,
		    inputCount, input,
		    lookup_context.funcs.match[1], lookup_context.match_data[1]);
}

template <typename HBUINT>
HB_ALWAYS_INLINE
static bool chain_context_apply_lookup (hb_ot_apply_context_t *c,
				unsigned int backtrackCount,
				const HBUINT backtrack[],
				unsigned int inputCount, /* Including the first glyph (not matched) */
				const HBUINT input[], /* Array of input values--start with second glyph */
				unsigned int lookaheadCount,
				const HBUINT lookahead[],
				unsigned int lookupCount,
				const LookupRecord lookupRecord[],
				const ChainContextApplyLookupContext &lookup_context)
{
 if (unlikely (inputCount > HB_MAX_CONTEXT_LENGTH)) return false;

 unsigned start_index = c->buffer->out_len;
 unsigned end_index = c->buffer->idx;
 unsigned match_end = 0;
 bool ret = true;
 if (!(match_input (c,
	     inputCount, input,
	     lookup_context.funcs.match[1], lookup_context.match_data[1],
	     &match_end) && (end_index = match_end)
      && match_lookahead (c,
		   lookaheadCount, lookahead,
		   lookup_context.funcs.match[2], lookup_context.match_data[2],
		   match_end, &end_index)))
 {
   c->buffer->unsafe_to_concat (c->buffer->idx, end_index);
   return false;
 }

 if (!match_backtrack (c,
		backtrackCount, backtrack,
		lookup_context.funcs.match[0], lookup_context.match_data[0],
		&start_index))
 {
   c->buffer->unsafe_to_concat_from_outbuffer (start_index, end_index);
   return false;
 }

 c->buffer->unsafe_to_break_from_outbuffer (start_index, end_index);
 apply_lookup (c,
	inputCount,
	lookupCount, lookupRecord,
	match_end);

 return ret;
}

template <typename Types>
struct ChainRule
{
 template <typename T>
 friend struct ChainRuleSet;

 bool intersects (const hb_set_t *glyphs, ChainContextClosureLookupContext &lookup_context) const
 {
   const auto &input = StructAfter<decltype (inputX)> (backtrack);
   const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
   return chain_context_intersects (glyphs,
			     backtrack.len, backtrack.arrayZ,
			     input.lenP1, input.arrayZ,
			     lookahead.len, lookahead.arrayZ,
			     lookup_context);
 }

 void closure (hb_closure_context_t *c, unsigned value,
	ChainContextClosureLookupContext &lookup_context) const
 {
   if (unlikely (c->lookup_limit_exceeded ())) return;

   const auto &input = StructAfter<decltype (inputX)> (backtrack);
   const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
   const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
   chain_context_closure_lookup (c,
			  backtrack.len, backtrack.arrayZ,
			  input.lenP1, input.arrayZ,
			  lookahead.len, lookahead.arrayZ,
			  lookup.len, lookup.arrayZ,
			  value,
			  lookup_context);
 }

 void closure_lookups (hb_closure_lookups_context_t *c,
                       ChainContextClosureLookupContext &lookup_context) const
 {
   if (unlikely (c->lookup_limit_exceeded ())) return;
   if (!intersects (c->glyphs, lookup_context)) return;

   const auto &input = StructAfter<decltype (inputX)> (backtrack);
   const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
   const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
   recurse_lookups (c, lookup.len, lookup.arrayZ);
 }

 void collect_glyphs (hb_collect_glyphs_context_t *c,
	       ChainContextCollectGlyphsLookupContext &lookup_context) const
 {
   const auto &input = StructAfter<decltype (inputX)> (backtrack);
   const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
   const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
   chain_context_collect_glyphs_lookup (c,
				 backtrack.len, backtrack.arrayZ,
				 input.lenP1, input.arrayZ,
				 lookahead.len, lookahead.arrayZ,
				 lookup.len, lookup.arrayZ,
				 lookup_context);
 }

 bool would_apply (hb_would_apply_context_t *c,
	    const ChainContextApplyLookupContext &lookup_context) const
 {
   const auto &input = StructAfter<decltype (inputX)> (backtrack);
   const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
   const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
   return chain_context_would_apply_lookup (c,
				     backtrack.len, backtrack.arrayZ,
				     input.lenP1, input.arrayZ,
				     lookahead.len, lookahead.arrayZ, lookup.len,
				     lookup.arrayZ, lookup_context);
 }

 bool apply (hb_ot_apply_context_t *c,
      const ChainContextApplyLookupContext &lookup_context) const
 {
   TRACE_APPLY (this);
   const auto &input = StructAfter<decltype (inputX)> (backtrack);
   const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
   const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
   return_trace (chain_context_apply_lookup (c,
				      backtrack.len, backtrack.arrayZ,
				      input.lenP1, input.arrayZ,
				      lookahead.len, lookahead.arrayZ, lookup.len,
				      lookup.arrayZ, lookup_context));
 }

 template<typename Iterator,
   hb_requires (hb_is_iterator (Iterator))>
 void serialize_array (hb_serialize_context_t *c,
		HBUINT16 len,
		Iterator it) const
 {
   c->copy (len);
   for (const auto g : it)
     c->copy ((HBUINT16) g);
 }

 bool serialize (hb_serialize_context_t *c,
	  const hb_map_t *lookup_map,
	  const hb_map_t *backtrack_map,
	  const hb_map_t *input_map = nullptr,
	  const hb_map_t *lookahead_map = nullptr) const
 {
   TRACE_SERIALIZE (this);

   const hb_map_t *mapping = backtrack_map;
   serialize_array (c, backtrack.len, + backtrack.iter ()
			       | hb_map (mapping));

   const auto &input = StructAfter<decltype (inputX)> (backtrack);
   if (input_map) mapping = input_map;
   serialize_array (c, input.lenP1, + input.iter ()
			     | hb_map (mapping));

   const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
   if (lookahead_map) mapping = lookahead_map;
   serialize_array (c, lookahead.len, + lookahead.iter ()
			       | hb_map (mapping));

   const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);

   HBUINT16* lookupCount = c->embed (&(lookup.len));
   if (!lookupCount) return_trace (false);

   unsigned count = serialize_lookuprecord_array (c, lookup.as_array (), lookup_map);
   return_trace (c->check_assign (*lookupCount, count, HB_SERIALIZE_ERROR_INT_OVERFLOW));
 }

 bool subset (hb_subset_context_t *c,
       const hb_map_t *lookup_map,
       const hb_map_t *backtrack_map = nullptr,
       const hb_map_t *input_map = nullptr,
       const hb_map_t *lookahead_map = nullptr) const
 {
   TRACE_SUBSET (this);

   const auto &input = StructAfter<decltype (inputX)> (backtrack);
   const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);

   if (!backtrack_map)
   {
     const hb_set_t &glyphset = *c->plan->glyphset_gsub ();
     if (!hb_all (backtrack, glyphset) ||
  !hb_all (input, glyphset) ||
  !hb_all (lookahead, glyphset))
return_trace (false);

     serialize (c->serializer, lookup_map, c->plan->glyph_map);
   }
   else
   {
     if (!hb_all (backtrack, backtrack_map) ||
  !hb_all (input, input_map) ||
  !hb_all (lookahead, lookahead_map))
return_trace (false);

     serialize (c->serializer, lookup_map, backtrack_map, input_map, lookahead_map);
   }

   return_trace (true);
 }

 bool sanitize (hb_sanitize_context_t *c) const
 {
   TRACE_SANITIZE (this);
   /* Hyper-optimized sanitized because this is really hot. */
   if (unlikely (!backtrack.len.sanitize (c))) return_trace (false);
   hb_barrier ();
   const auto &input = StructAfter<decltype (inputX)> (backtrack);
   if (unlikely (!input.lenP1.sanitize (c))) return_trace (false);
   hb_barrier ();
   const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
   if (unlikely (!lookahead.len.sanitize (c))) return_trace (false);
   hb_barrier ();
   const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
   return_trace (likely (lookup.sanitize (c)));
 }

 protected:
 Array16Of<typename Types::HBUINT>
	backtrack;		/* Array of backtracking values
				 * (to be matched before the input
				 * sequence) */
 HeadlessArray16Of<typename Types::HBUINT>
	inputX;			/* Array of input values (start with
				 * second glyph) */
 Array16Of<typename Types::HBUINT>
	lookaheadX;		/* Array of lookahead values's (to be
				 * matched after the input sequence) */
 Array16Of<LookupRecord>
	lookupX;		/* Array of LookupRecords--in
				 * design order) */
 public:
 DEFINE_SIZE_MIN (8);
};

template <typename Types>
struct ChainRuleSet
{
 using ChainRule = OT::ChainRule<Types>;

 bool intersects (const hb_set_t *glyphs, ChainContextClosureLookupContext &lookup_context) const
 {
   return
   + hb_iter (rule)
   | hb_map (hb_add (this))
   | hb_map ([&] (const ChainRule &_) { return _.intersects (glyphs, lookup_context); })
   | hb_any
   ;
 }
 void closure (hb_closure_context_t *c, unsigned value, ChainContextClosureLookupContext &lookup_context) const
 {
   if (unlikely (c->lookup_limit_exceeded ())) return;

   return
   + hb_iter (rule)
   | hb_map (hb_add (this))
   | hb_apply ([&] (const ChainRule &_) { _.closure (c, value, lookup_context); })
   ;
 }

 void closure_lookups (hb_closure_lookups_context_t *c,
                       ChainContextClosureLookupContext &lookup_context) const
 {
   if (unlikely (c->lookup_limit_exceeded ())) return;

   + hb_iter (rule)
   | hb_map (hb_add (this))
   | hb_apply ([&] (const ChainRule &_) { _.closure_lookups (c, lookup_context); })
   ;
 }

 void collect_glyphs (hb_collect_glyphs_context_t *c, ChainContextCollectGlyphsLookupContext &lookup_context) const
 {
   return
   + hb_iter (rule)
   | hb_map (hb_add (this))
   | hb_apply ([&] (const ChainRule &_) { _.collect_glyphs (c, lookup_context); })
   ;
 }

 bool would_apply (hb_would_apply_context_t *c,
	    const ChainContextApplyLookupContext &lookup_context) const
 {
   return
   + hb_iter (rule)
   | hb_map (hb_add (this))
   | hb_map ([&] (const ChainRule &_) { return _.would_apply (c, lookup_context); })
   | hb_any
   ;
 }

 bool apply (hb_ot_apply_context_t *c,
      const ChainContextApplyLookupContext &lookup_context) const
 {
   TRACE_APPLY (this);

   unsigned num_rules = rule.len;

#ifndef HB_NO_OT_RULESETS_FAST_PATH
   if (HB_OPTIMIZE_SIZE_VAL || num_rules <= 4)
#endif
   {
   slow:
     return_trace (
     + hb_iter (rule)
     | hb_map (hb_add (this))
     | hb_map ([&] (const ChainRule &_) { return _.apply (c, lookup_context); })
     | hb_any
     )
     ;
   }

   /* This version is optimized for speed by matching the first & second
    * components of the rule here, instead of calling into the matching code.
    *
    * Replicated from LigatureSet::apply(). */

   /* We use the iter_context instead of iter_input, to avoid skipping
    * default-ignorables and such.
    *
    * Related: https://github.com/harfbuzz/harfbuzz/issues/4813
    */
   auto &skippy_iter = c->iter_context;
   skippy_iter.reset (c->buffer->idx);
   skippy_iter.set_match_func (match_always, nullptr);
   skippy_iter.set_glyph_data ((HBUINT16 *) nullptr);
   unsigned unsafe_to = (unsigned) -1, unsafe_to1 = 0, unsafe_to2 = 0;
   hb_glyph_info_t *first = nullptr, *second = nullptr;
   bool matched = skippy_iter.next ();
   if (likely (matched))
   {
     if (skippy_iter.may_skip (c->buffer->info[skippy_iter.idx]))
     {
/* Can't use the fast path if eg. the next char is a default-ignorable
 * or other skippable. */
       goto slow;
     }

     first = &c->buffer->info[skippy_iter.idx];
     unsafe_to1 = skippy_iter.idx + 1;
   }
   else
   {
     /* Failed to match a next glyph. Only try applying rules that have
      * no further input and lookahead. */
     return_trace (
     + hb_iter (rule)
     | hb_map (hb_add (this))
     | hb_filter ([&] (const ChainRule &_)
	   {
	     const auto &input = StructAfter<decltype (_.inputX)> (_.backtrack);
	     const auto &lookahead = StructAfter<decltype (_.lookaheadX)> (input);
	     return input.lenP1 <= 1 && lookahead.len == 0;
	   })
     | hb_map ([&] (const ChainRule &_) { return _.apply (c, lookup_context); })
     | hb_any
     )
     ;
   }
   matched = skippy_iter.next ();
   if (likely (matched))
   {
     if (skippy_iter.may_skip (c->buffer->info[skippy_iter.idx]))
     {
/* Can't use the fast path if eg. the next char is a default-ignorable
 * or other skippable. */
       goto slow;
     }

     second = &c->buffer->info[skippy_iter.idx];
     unsafe_to2 = skippy_iter.idx + 1;
   }

   auto match_input = lookup_context.funcs.match[1];
   auto match_lookahead = lookup_context.funcs.match[2];
   auto *input_data = lookup_context.match_data[1];
   auto *lookahead_data = lookup_context.match_data[2];
   for (unsigned int i = 0; i < num_rules; i++)
   {
     const auto &r = this+rule.arrayZ[i];

     const auto &input = StructAfter<decltype (r.inputX)> (r.backtrack);
     const auto &lookahead = StructAfter<decltype (r.lookaheadX)> (input);

     unsigned lenP1 = input.lenP1;
     if (lenP1 > 1 ?
   (!match_input ||
    match_input (*first, input.arrayZ[0], input_data))
  :
   (!lookahead.len || !match_lookahead ||
    match_lookahead (*first, lookahead.arrayZ[0], lookahead_data)))
     {
lenP1 = hb_max (lenP1, 1u);
       if (!second ||
    (lenP1 > 2 ?
     (!match_input ||
      match_input (*second, input.arrayZ[1], input_data))
     :
     (lookahead.len <= 2 - lenP1 || !match_lookahead ||
      match_lookahead (*second, lookahead.arrayZ[2 - lenP1], lookahead_data))))
{
  if (r.apply (c, lookup_context))
  {
    if (unsafe_to != (unsigned) -1)
      c->buffer->unsafe_to_concat (c->buffer->idx, unsafe_to);
    return_trace (true);
  }
}
else
  unsafe_to = unsafe_to2;
     }
     else
     {
if (unsafe_to == (unsigned) -1)
  unsafe_to = unsafe_to1;

if (lenP1 > 1)
{
  // Skip ahead to next possible first glyph match.
  for (; i + 1 < num_rules; i++)
  {
    const auto &r2 = this+rule.arrayZ[i + 1];
    const auto &input2 = StructAfter<decltype (r2.inputX)> (r2.backtrack);
    if (input2.lenP1 <= 1 || input2.arrayZ[0] != input.arrayZ[0])
      break;
  }
}
     }
   }
   if (likely (unsafe_to != (unsigned) -1))
     c->buffer->unsafe_to_concat (c->buffer->idx, unsafe_to);

   return_trace (false);
 }

 bool subset (hb_subset_context_t *c,
       const hb_map_t *lookup_map,
       const hb_map_t *backtrack_klass_map = nullptr,
       const hb_map_t *input_klass_map = nullptr,
       const hb_map_t *lookahead_klass_map = nullptr) const
 {
   TRACE_SUBSET (this);

   auto snap = c->serializer->snapshot ();
   auto *out = c->serializer->start_embed (*this);
   if (unlikely (!c->serializer->extend_min (out))) return_trace (false);

   for (const Offset16To<ChainRule>& _ : rule)
   {
     if (!_) continue;
     auto o_snap = c->serializer->snapshot ();
     auto *o = out->rule.serialize_append (c->serializer);
     if (unlikely (!o)) continue;

     if (!o->serialize_subset (c, _, this,
			lookup_map,
			backtrack_klass_map,
			input_klass_map,
			lookahead_klass_map))
     {
out->rule.pop ();
c->serializer->revert (o_snap);
     }
   }

   bool ret = bool (out->rule);
   if (!ret) c->serializer->revert (snap);

   return_trace (ret);
 }

 bool sanitize (hb_sanitize_context_t *c) const
 {
   TRACE_SANITIZE (this);
   return_trace (rule.sanitize (c, this));
 }

 protected:
 Array16OfOffset16To<ChainRule>
	rule;			/* Array of ChainRule tables
				 * ordered by preference */
 public:
 DEFINE_SIZE_ARRAY (2, rule);
};

template <typename Types>
struct ChainContextFormat1_4
{
 using ChainRuleSet = OT::ChainRuleSet<Types>;

 bool intersects (const hb_set_t *glyphs) const
 {
   struct ChainContextClosureLookupContext lookup_context = {
     {intersects_glyph, intersected_glyph},
     ContextFormat::SimpleContext,
     {nullptr, nullptr, nullptr}
   };

   return
   + hb_zip (this+coverage, ruleSet)
   | hb_filter (*glyphs, hb_first)
   | hb_map (hb_second)
   | hb_map (hb_add (this))
   | hb_map ([&] (const ChainRuleSet &_) { return _.intersects (glyphs, lookup_context); })
   | hb_any
   ;
 }

 bool may_have_non_1to1 () const
 { return true; }

 void closure (hb_closure_context_t *c) const
 {
   hb_set_t* cur_active_glyphs = c->push_cur_active_glyphs ();
   if (unlikely (!cur_active_glyphs)) return;
   get_coverage ().intersect_set (c->previous_parent_active_glyphs (),
			   *cur_active_glyphs);

   struct ChainContextClosureLookupContext lookup_context = {
     {intersects_glyph, intersected_glyph},
     ContextFormat::SimpleContext,
     {nullptr, nullptr, nullptr}
   };

   + hb_zip (this+coverage, hb_range ((unsigned) ruleSet.len))
   | hb_filter ([&] (hb_codepoint_t _) {
     return c->previous_parent_active_glyphs ().has (_);
   }, hb_first)
   | hb_map ([&](const hb_pair_t<hb_codepoint_t, unsigned> _) { return hb_pair_t<unsigned, const ChainRuleSet&> (_.first, this+ruleSet[_.second]); })
   | hb_apply ([&] (const hb_pair_t<unsigned, const ChainRuleSet&>& _) { _.second.closure (c, _.first, lookup_context); })
   ;

   c->pop_cur_done_glyphs ();
 }

 void closure_lookups (hb_closure_lookups_context_t *c) const
 {
   struct ChainContextClosureLookupContext lookup_context = {
     {intersects_glyph, nullptr},
     ContextFormat::SimpleContext,
     {nullptr, nullptr, nullptr}
   };

   + hb_zip (this+coverage, ruleSet)
   | hb_filter (*c->glyphs, hb_first)
   | hb_map (hb_second)
   | hb_map (hb_add (this))
   | hb_apply ([&] (const ChainRuleSet &_) { _.closure_lookups (c, lookup_context); })
   ;
 }

 void collect_variation_indices (hb_collect_variation_indices_context_t *c) const {}

 void collect_glyphs (hb_collect_glyphs_context_t *c) const
 {
   (this+coverage).collect_coverage (c->input);

   struct ChainContextCollectGlyphsLookupContext lookup_context = {
     {collect_glyph},
     {nullptr, nullptr, nullptr}
   };

   + hb_iter (ruleSet)
   | hb_map (hb_add (this))
   | hb_apply ([&] (const ChainRuleSet &_) { _.collect_glyphs (c, lookup_context); })
   ;
 }

 bool would_apply (hb_would_apply_context_t *c) const
 {
   const ChainRuleSet &rule_set = this+ruleSet[(this+coverage).get_coverage (c->glyphs[0])];
   struct ChainContextApplyLookupContext lookup_context = {
     {{match_glyph, match_glyph, match_glyph}},
     {nullptr, nullptr, nullptr}
   };
   return rule_set.would_apply (c, lookup_context);
 }

 const Coverage &get_coverage () const { return this+coverage; }

 bool apply (hb_ot_apply_context_t *c) const
 {
   TRACE_APPLY (this);
   unsigned int index = (this+coverage).get_coverage (c->buffer->cur().codepoint);
   if (index == NOT_COVERED) return_trace (false);

   const ChainRuleSet &rule_set = this+ruleSet[index];
   struct ChainContextApplyLookupContext lookup_context = {
     {{match_glyph, match_glyph, match_glyph}},
     {nullptr, nullptr, nullptr}
   };
   return_trace (rule_set.apply (c, lookup_context));
 }

 bool subset (hb_subset_context_t *c) const
 {
   TRACE_SUBSET (this);
   const hb_set_t &glyphset = *c->plan->glyphset_gsub ();
   const hb_map_t &glyph_map = *c->plan->glyph_map;

   auto *out = c->serializer->start_embed (*this);
   if (unlikely (!c->serializer->extend_min (out))) return_trace (false);
   out->format = format;

   const hb_map_t *lookup_map = c->table_tag == HB_OT_TAG_GSUB ? &c->plan->gsub_lookups : &c->plan->gpos_lookups;
   hb_sorted_vector_t<hb_codepoint_t> new_coverage;
   + hb_zip (this+coverage, ruleSet)
   | hb_filter (glyphset, hb_first)
   | hb_filter (subset_offset_array (c, out->ruleSet, this, lookup_map), hb_second)
   | hb_map (hb_first)
   | hb_map (glyph_map)
   | hb_sink (new_coverage)
   ;

   out->coverage.serialize_serialize (c->serializer, new_coverage.iter ());
   return_trace (bool (new_coverage));
 }

 bool sanitize (hb_sanitize_context_t *c) const
 {
   TRACE_SANITIZE (this);
   return_trace (coverage.sanitize (c, this) && ruleSet.sanitize (c, this));
 }

 protected:
 HBUINT16	format;			/* Format identifier--format = 1 */
 typename Types::template OffsetTo<Coverage>
	coverage;		/* Offset to Coverage table--from
				 * beginning of table */
 Array16Of<typename Types::template OffsetTo<ChainRuleSet>>
	ruleSet;		/* Array of ChainRuleSet tables
				 * ordered by Coverage Index */
 public:
 DEFINE_SIZE_ARRAY (2 + 2 * Types::size, ruleSet);
};

template <typename Types>
struct ChainContextFormat2_5
{
 using ChainRuleSet = OT::ChainRuleSet<SmallTypes>;

 bool intersects (const hb_set_t *glyphs) const
 {
   if (!(this+coverage).intersects (glyphs))
     return false;

   const ClassDef &backtrack_class_def = this+backtrackClassDef;
   const ClassDef &input_class_def = this+inputClassDef;
   const ClassDef &lookahead_class_def = this+lookaheadClassDef;

   hb_map_t caches[3] = {};
   struct ChainContextClosureLookupContext lookup_context = {
     {intersects_class, nullptr},
     ContextFormat::ClassBasedContext,
     {&backtrack_class_def,
      &input_class_def,
      &lookahead_class_def},
     {&caches[0], &caches[1], &caches[2]}
   };

   hb_set_t retained_coverage_glyphs;
   (this+coverage).intersect_set (*glyphs, retained_coverage_glyphs);

   hb_set_t coverage_glyph_classes;
   input_class_def.intersected_classes (&retained_coverage_glyphs, &coverage_glyph_classes);

   return
   + hb_iter (ruleSet)
   | hb_map (hb_add (this))
   | hb_enumerate
   | hb_map ([&] (const hb_pair_t<unsigned, const ChainRuleSet &> p)
      { return input_class_def.intersects_class (glyphs, p.first) &&
	       coverage_glyph_classes.has (p.first) &&
	       p.second.intersects (glyphs, lookup_context); })
   | hb_any
   ;
 }

 bool may_have_non_1to1 () const
 { return true; }

 void closure (hb_closure_context_t *c) const
 {
   if (!(this+coverage).intersects (c->glyphs))
     return;

   hb_set_t* cur_active_glyphs = c->push_cur_active_glyphs ();
   if (unlikely (!cur_active_glyphs)) return;
   get_coverage ().intersect_set (c->previous_parent_active_glyphs (),
			   *cur_active_glyphs);

   const ClassDef &backtrack_class_def = this+backtrackClassDef;
   const ClassDef &input_class_def = this+inputClassDef;
   const ClassDef &lookahead_class_def = this+lookaheadClassDef;

   hb_map_t caches[3] = {};
   intersected_class_cache_t intersected_cache;
   struct ChainContextClosureLookupContext lookup_context = {
     {intersects_class, intersected_class_glyphs},
     ContextFormat::ClassBasedContext,
     {&backtrack_class_def,
      &input_class_def,
      &lookahead_class_def},
     {&caches[0], &caches[1], &caches[2]},
     &intersected_cache
   };

   + hb_enumerate (ruleSet)
   | hb_filter ([&] (unsigned _)
   { return input_class_def.intersects_class (&c->parent_active_glyphs (), _); },
	 hb_first)
   | hb_apply ([&] (const hb_pair_t<unsigned, const typename Types::template OffsetTo<ChainRuleSet>&> _)
               {
                 const ChainRuleSet& chainrule_set = this+_.second;
                 chainrule_set.closure (c, _.first, lookup_context);
               })
   ;

   c->pop_cur_done_glyphs ();
 }

 void closure_lookups (hb_closure_lookups_context_t *c) const
 {
   if (!(this+coverage).intersects (c->glyphs))
     return;

   const ClassDef &backtrack_class_def = this+backtrackClassDef;
   const ClassDef &input_class_def = this+inputClassDef;
   const ClassDef &lookahead_class_def = this+lookaheadClassDef;

   hb_map_t caches[3] = {};
   struct ChainContextClosureLookupContext lookup_context = {
     {intersects_class, nullptr},
     ContextFormat::ClassBasedContext,
     {&backtrack_class_def,
      &input_class_def,
      &lookahead_class_def},
     {&caches[0], &caches[1], &caches[2]}
   };

   + hb_iter (ruleSet)
   | hb_map (hb_add (this))
   | hb_enumerate
   | hb_filter([&] (unsigned klass)
   { return input_class_def.intersects_class (c->glyphs, klass); }, hb_first)
   | hb_map (hb_second)
   | hb_apply ([&] (const ChainRuleSet &_)
   { _.closure_lookups (c, lookup_context); })
   ;
 }

 void collect_variation_indices (hb_collect_variation_indices_context_t *c) const {}

 void collect_glyphs (hb_collect_glyphs_context_t *c) const
 {
   (this+coverage).collect_coverage (c->input);

   const ClassDef &backtrack_class_def = this+backtrackClassDef;
   const ClassDef &input_class_def = this+inputClassDef;
   const ClassDef &lookahead_class_def = this+lookaheadClassDef;

   struct ChainContextCollectGlyphsLookupContext lookup_context = {
     {collect_class},
     {&backtrack_class_def,
      &input_class_def,
      &lookahead_class_def}
   };

   + hb_iter (ruleSet)
   | hb_map (hb_add (this))
   | hb_apply ([&] (const ChainRuleSet &_) { _.collect_glyphs (c, lookup_context); })
   ;
 }

 bool would_apply (hb_would_apply_context_t *c) const
 {
   const ClassDef &backtrack_class_def = this+backtrackClassDef;
   const ClassDef &input_class_def = this+inputClassDef;
   const ClassDef &lookahead_class_def = this+lookaheadClassDef;

   unsigned int index = input_class_def.get_class (c->glyphs[0]);
   const ChainRuleSet &rule_set = this+ruleSet[index];
   struct ChainContextApplyLookupContext lookup_context = {
     {{match_class, match_class, match_class}},
     {&backtrack_class_def,
      &input_class_def,
      &lookahead_class_def}
   };
   return rule_set.would_apply (c, lookup_context);
 }

 const Coverage &get_coverage () const { return this+coverage; }

 unsigned cache_cost () const
 {
   return (this+inputClassDef).cost () + (this+lookaheadClassDef).cost ();
 }
 static bool cache_func (hb_ot_apply_context_t *c, hb_ot_subtable_cache_op_t op)
 {
   return context_cache_func (c, op);
 }

 struct external_cache_t
 {
   hb_ot_layout_binary_cache_t coverage;
 };
 void *external_cache_create () const
 {
   external_cache_t *cache = (external_cache_t *) hb_malloc (sizeof (external_cache_t));
   if (likely (cache))
   {
     cache->coverage.clear ();
   }
   return cache;
 }
 bool apply_cached (hb_ot_apply_context_t *c, void *external_cache) const { return _apply (c, true, external_cache); }
 bool apply (hb_ot_apply_context_t *c, void *external_cache) const { return _apply (c, false, external_cache); }
 bool _apply (hb_ot_apply_context_t *c, bool cached, void *external_cache) const
 {
   TRACE_APPLY (this);
#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
   external_cache_t *cache = (external_cache_t *) external_cache;
   unsigned int index = (this+coverage).get_coverage_binary (c->buffer->cur().codepoint, cache ? &cache->coverage : nullptr);
#else
   unsigned int index = (this+coverage).get_coverage (c->buffer->cur().codepoint);
#endif
   if (index == NOT_COVERED) return_trace (false);

   const ClassDef &backtrack_class_def = this+backtrackClassDef;
   const ClassDef &input_class_def = this+inputClassDef;
   const ClassDef &lookahead_class_def = this+lookaheadClassDef;

   /* match_class_caches1 is slightly faster. Use it for lookahead,
    * which is typically longer. */
   struct ChainContextApplyLookupContext lookup_context = {
     {{cached && &backtrack_class_def == &lookahead_class_def ? match_class_cached1 : match_class,
       cached ? match_class_cached2 : match_class,
       cached ? match_class_cached1 : match_class}},
     {&backtrack_class_def,
      &input_class_def,
      &lookahead_class_def}
   };

   index = cached
        ? get_class_cached2 (input_class_def, c->buffer->cur())
         : input_class_def.get_class (c->buffer->cur().codepoint);
   const ChainRuleSet &rule_set = this+ruleSet[index];
   return_trace (rule_set.apply (c, lookup_context));
 }

 bool subset (hb_subset_context_t *c) const
 {
   TRACE_SUBSET (this);
   auto *out = c->serializer->start_embed (*this);
   if (unlikely (!c->serializer->extend_min (out))) return_trace (false);
   out->format = format;
   out->coverage.serialize_subset (c, coverage, this);

   hb_map_t backtrack_klass_map;
   hb_map_t input_klass_map;
   hb_map_t lookahead_klass_map;

   out->backtrackClassDef.serialize_subset (c, backtrackClassDef, this, &backtrack_klass_map);
   // TODO: subset inputClassDef based on glyphs survived in Coverage subsetting
   out->inputClassDef.serialize_subset (c, inputClassDef, this, &input_klass_map);
   out->lookaheadClassDef.serialize_subset (c, lookaheadClassDef, this, &lookahead_klass_map);

   if (unlikely (!c->serializer->propagate_error (backtrack_klass_map,
					   input_klass_map,
					   lookahead_klass_map)))
     return_trace (false);

   const hb_set_t* glyphset = c->plan->glyphset_gsub ();
   hb_set_t retained_coverage_glyphs;
   (this+coverage).intersect_set (*glyphset, retained_coverage_glyphs);

   hb_set_t coverage_glyph_classes;
   (this+inputClassDef).intersected_classes (&retained_coverage_glyphs, &coverage_glyph_classes);

   int non_zero_index = -1, index = 0;
   bool ret = true;
   const hb_map_t *lookup_map = c->table_tag == HB_OT_TAG_GSUB ? &c->plan->gsub_lookups : &c->plan->gpos_lookups;
   auto last_non_zero = c->serializer->snapshot ();
   for (const auto& _ : + hb_enumerate (ruleSet)
		 | hb_filter (input_klass_map, hb_first))
   {
     auto *o = out->ruleSet.serialize_append (c->serializer);
     if (unlikely (!o))
     {
ret = false;
break;
     }
     if (coverage_glyph_classes.has (_.first) &&
         o->serialize_subset (c, _.second, this,
		       lookup_map,
		       &backtrack_klass_map,
		       &input_klass_map,
		       &lookahead_klass_map))
     {
       last_non_zero = c->serializer->snapshot ();
non_zero_index = index;
     }

     index++;
   }

   if (!ret || non_zero_index == -1) return_trace (false);

   // prune empty trailing ruleSets
   if (index > non_zero_index) {
     c->serializer->revert (last_non_zero);
     out->ruleSet.len = non_zero_index + 1;
   }

   return_trace (bool (out->ruleSet));
 }

 bool sanitize (hb_sanitize_context_t *c) const
 {
   TRACE_SANITIZE (this);
   return_trace (coverage.sanitize (c, this) &&
	  backtrackClassDef.sanitize (c, this) &&
	  inputClassDef.sanitize (c, this) &&
	  lookaheadClassDef.sanitize (c, this) &&
	  ruleSet.sanitize (c, this));
 }

 protected:
 HBUINT16	format;			/* Format identifier--format = 2 */
 typename Types::template OffsetTo<Coverage>
	coverage;		/* Offset to Coverage table--from
				 * beginning of table */
 typename Types::template OffsetTo<ClassDef>
	backtrackClassDef;	/* Offset to glyph ClassDef table
				 * containing backtrack sequence
				 * data--from beginning of table */
 typename Types::template OffsetTo<ClassDef>
	inputClassDef;		/* Offset to glyph ClassDef
				 * table containing input sequence
				 * data--from beginning of table */
 typename Types::template OffsetTo<ClassDef>
	lookaheadClassDef;	/* Offset to glyph ClassDef table
				 * containing lookahead sequence
				 * data--from beginning of table */
 Array16Of<typename Types::template OffsetTo<ChainRuleSet>>
	ruleSet;		/* Array of ChainRuleSet tables
				 * ordered by class */
 public:
 DEFINE_SIZE_ARRAY (4 + 4 * Types::size, ruleSet);
};

struct ChainContextFormat3
{
 using RuleSet = OT::RuleSet<SmallTypes>;

 bool intersects (const hb_set_t *glyphs) const
 {
   const auto &input = StructAfter<decltype (inputX)> (backtrack);

   if (!(this+input[0]).intersects (glyphs))
     return false;

   const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
   struct ChainContextClosureLookupContext lookup_context = {
     {intersects_coverage, nullptr},
     ContextFormat::CoverageBasedContext,
     {this, this, this}
   };
   return chain_context_intersects (glyphs,
			     backtrack.len, (const HBUINT16 *) backtrack.arrayZ,
			     input.len, (const HBUINT16 *) input.arrayZ + 1,
			     lookahead.len, (const HBUINT16 *) lookahead.arrayZ,
			     lookup_context);
 }

 bool may_have_non_1to1 () const
 { return true; }

 void closure (hb_closure_context_t *c) const
 {
   const auto &input = StructAfter<decltype (inputX)> (backtrack);

   if (!(this+input[0]).intersects (c->glyphs))
     return;

   hb_set_t* cur_active_glyphs = c->push_cur_active_glyphs ();
   if (unlikely (!cur_active_glyphs))
     return;
   get_coverage ().intersect_set (c->previous_parent_active_glyphs (),
			   *cur_active_glyphs);

   const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
   const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
   struct ChainContextClosureLookupContext lookup_context = {
     {intersects_coverage, intersected_coverage_glyphs},
     ContextFormat::CoverageBasedContext,
     {this, this, this}
   };
   chain_context_closure_lookup (c,
			  backtrack.len, (const HBUINT16 *) backtrack.arrayZ,
			  input.len, (const HBUINT16 *) input.arrayZ + 1,
			  lookahead.len, (const HBUINT16 *) lookahead.arrayZ,
			  lookup.len, lookup.arrayZ,
			  0, lookup_context);

   c->pop_cur_done_glyphs ();
 }

 void closure_lookups (hb_closure_lookups_context_t *c) const
 {
   if (!intersects (c->glyphs))
     return;

   const auto &input = StructAfter<decltype (inputX)> (backtrack);
   const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
   const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
   recurse_lookups (c, lookup.len, lookup.arrayZ);
 }

 void collect_variation_indices (hb_collect_variation_indices_context_t *c) const {}

 void collect_glyphs (hb_collect_glyphs_context_t *c) const
 {
   const auto &input = StructAfter<decltype (inputX)> (backtrack);

   (this+input[0]).collect_coverage (c->input);

   const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
   const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);

   struct ChainContextCollectGlyphsLookupContext lookup_context = {
     {collect_coverage},
     {this, this, this}
   };
   chain_context_collect_glyphs_lookup (c,
				 backtrack.len, (const HBUINT16 *) backtrack.arrayZ,
				 input.len, (const HBUINT16 *) input.arrayZ + 1,
				 lookahead.len, (const HBUINT16 *) lookahead.arrayZ,
				 lookup.len, lookup.arrayZ,
				 lookup_context);
 }

 bool would_apply (hb_would_apply_context_t *c) const
 {
   const auto &input = StructAfter<decltype (inputX)> (backtrack);
   const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
   const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
   struct ChainContextApplyLookupContext lookup_context = {
     {{match_coverage, match_coverage, match_coverage}},
     {this, this, this}
   };
   return chain_context_would_apply_lookup (c,
				     backtrack.len, (const HBUINT16 *) backtrack.arrayZ,
				     input.len, (const HBUINT16 *) input.arrayZ + 1,
				     lookahead.len, (const HBUINT16 *) lookahead.arrayZ,
				     lookup.len, lookup.arrayZ, lookup_context);
 }

 const Coverage &get_coverage () const
 {
   const auto &input = StructAfter<decltype (inputX)> (backtrack);
   return this+input[0];
 }

 bool apply (hb_ot_apply_context_t *c) const
 {
   TRACE_APPLY (this);
   const auto &input = StructAfter<decltype (inputX)> (backtrack);

   unsigned int index = (this+input[0]).get_coverage (c->buffer->cur().codepoint);
   if (index == NOT_COVERED) return_trace (false);

   const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
   const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
   struct ChainContextApplyLookupContext lookup_context = {
     {{match_coverage, match_coverage, match_coverage}},
     {this, this, this}
   };
   return_trace (chain_context_apply_lookup (c,
				      backtrack.len, (const HBUINT16 *) backtrack.arrayZ,
				      input.len, (const HBUINT16 *) input.arrayZ + 1,
				      lookahead.len, (const HBUINT16 *) lookahead.arrayZ,
				      lookup.len, lookup.arrayZ, lookup_context));
 }

 template<typename Iterator,
   hb_requires (hb_is_iterator (Iterator))>
 bool serialize_coverage_offsets (hb_subset_context_t *c, Iterator it, const void* base) const
 {
   TRACE_SERIALIZE (this);
   auto *out = c->serializer->start_embed<Array16OfOffset16To<Coverage>> ();

   if (unlikely (!c->serializer->allocate_size<HBUINT16> (HBUINT16::static_size)))
     return_trace (false);

   for (auto& offset : it) {
     auto *o = out->serialize_append (c->serializer);
     if (unlikely (!o) || !o->serialize_subset (c, offset, base))
       return_trace (false);
   }

   return_trace (true);
 }

 bool subset (hb_subset_context_t *c) const
 {
   TRACE_SUBSET (this);

   if (unlikely (!c->serializer->embed (this->format))) return_trace (false);

   if (!serialize_coverage_offsets (c, backtrack.iter (), this))
     return_trace (false);

   const auto &input = StructAfter<decltype (inputX)> (backtrack);
   if (!serialize_coverage_offsets (c, input.iter (), this))
     return_trace (false);

   const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
   if (!serialize_coverage_offsets (c, lookahead.iter (), this))
     return_trace (false);

   const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
   const hb_map_t *lookup_map = c->table_tag == HB_OT_TAG_GSUB ? &c->plan->gsub_lookups : &c->plan->gpos_lookups;

   HBUINT16 *lookupCount = c->serializer->copy<HBUINT16> (lookup.len);
   if (!lookupCount) return_trace (false);

   unsigned count = serialize_lookuprecord_array (c->serializer, lookup.as_array (), lookup_map);
   return_trace (c->serializer->check_assign (*lookupCount, count, HB_SERIALIZE_ERROR_INT_OVERFLOW));
 }

 bool sanitize (hb_sanitize_context_t *c) const
 {
   TRACE_SANITIZE (this);
   if (unlikely (!backtrack.sanitize (c, this))) return_trace (false);
   hb_barrier ();
   const auto &input = StructAfter<decltype (inputX)> (backtrack);
   if (unlikely (!input.sanitize (c, this))) return_trace (false);
   hb_barrier ();
   if (unlikely (!input.len)) return_trace (false); /* To be consistent with Context. */
   const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
   if (unlikely (!lookahead.sanitize (c, this))) return_trace (false);
   hb_barrier ();
   const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
   return_trace (likely (lookup.sanitize (c)));
 }

 protected:
 HBUINT16	format;			/* Format identifier--format = 3 */
 Array16OfOffset16To<Coverage>
	backtrack;		/* Array of coverage tables
				 * in backtracking sequence, in  glyph
				 * sequence order */
 Array16OfOffset16To<Coverage>
	inputX		;	/* Array of coverage
				 * tables in input sequence, in glyph
				 * sequence order */
 Array16OfOffset16To<Coverage>
	lookaheadX;		/* Array of coverage tables
				 * in lookahead sequence, in glyph
				 * sequence order */
 Array16Of<LookupRecord>
	lookupX;		/* Array of LookupRecords--in
				 * design order) */
 public:
 DEFINE_SIZE_MIN (10);
};

struct ChainContext
{
 template <typename context_t, typename ...Ts>
 typename context_t::return_t dispatch (context_t *c, Ts&&... ds) const
 {
   if (unlikely (!c->may_dispatch (this, &u.format.v))) return c->no_dispatch_return_value ();
   TRACE_DISPATCH (this, u.format.v);
   switch (u.format.v) {
   case 1: hb_barrier (); return_trace (c->dispatch (u.format1, std::forward<Ts> (ds)...));
   case 2: hb_barrier (); return_trace (c->dispatch (u.format2, std::forward<Ts> (ds)...));
   case 3: hb_barrier (); return_trace (c->dispatch (u.format3, std::forward<Ts> (ds)...));
#ifndef HB_NO_BEYOND_64K
   case 4: hb_barrier (); return_trace (c->dispatch (u.format4, std::forward<Ts> (ds)...));
   case 5: hb_barrier (); return_trace (c->dispatch (u.format5, std::forward<Ts> (ds)...));
#endif
   default:return_trace (c->default_return_value ());
   }
 }

 protected:
 union {
 struct { HBUINT16 v; }		format;	/* Format identifier */
 ChainContextFormat1_4<SmallTypes>	format1;
 ChainContextFormat2_5<SmallTypes>	format2;
 ChainContextFormat3			format3;
#ifndef HB_NO_BEYOND_64K
 ChainContextFormat1_4<MediumTypes>	format4;
 ChainContextFormat2_5<MediumTypes>	format5;
#endif
 } u;
};


template <typename T>
struct ExtensionFormat1
{
 unsigned int get_type () const { return extensionLookupType; }

 template <typename X>
 const X& get_subtable () const
 { return this + reinterpret_cast<const Offset32To<typename T::SubTable> &> (extensionOffset); }

 template <typename context_t, typename ...Ts>
 typename context_t::return_t dispatch (context_t *c, Ts&&... ds) const
 {
   if (unlikely (!c->may_dispatch (this, this))) return c->no_dispatch_return_value ();
   TRACE_DISPATCH (this, format);
   return_trace (get_subtable<typename T::SubTable> ().dispatch (c, get_type (), std::forward<Ts> (ds)...));
 }

 void collect_variation_indices (hb_collect_variation_indices_context_t *c) const
 { dispatch (c); }

 /* This is called from may_dispatch() above with hb_sanitize_context_t. */
 bool sanitize (hb_sanitize_context_t *c) const
 {
   TRACE_SANITIZE (this);
   return_trace (c->check_struct (this) &&
	  hb_barrier () &&
	  extensionLookupType != T::SubTable::Extension);
 }

 bool subset (hb_subset_context_t *c) const
 {
   TRACE_SUBSET (this);

   auto *out = c->serializer->start_embed (this);
   if (unlikely (!c->serializer->extend_min (out))) return_trace (false);

   out->format = format;
   out->extensionLookupType = extensionLookupType;

   const auto& src_offset =
       reinterpret_cast<const Offset32To<typename T::SubTable> &> (extensionOffset);
   auto& dest_offset =
       reinterpret_cast<Offset32To<typename T::SubTable> &> (out->extensionOffset);

   return_trace (dest_offset.serialize_subset (c, src_offset, this, get_type ()));
 }

 protected:
 HBUINT16	format;			/* Format identifier. Set to 1. */
 HBUINT16	extensionLookupType;	/* Lookup type of subtable referenced
				 * by ExtensionOffset (i.e. the
				 * extension subtable). */
 Offset32	extensionOffset;	/* Offset to the extension subtable,
				 * of lookup type subtable. */
 public:
 DEFINE_SIZE_STATIC (8);
};

template <typename T>
struct Extension
{
 unsigned int get_type () const
 {
   switch (u.format.v) {
   case 1: hb_barrier (); return u.format1.get_type ();
   default:return 0;
   }
 }
 template <typename X>
 const X& get_subtable () const
 {
   switch (u.format.v) {
   case 1: hb_barrier (); return u.format1.template get_subtable<typename T::SubTable> ();
   default:return Null (typename T::SubTable);
   }
 }

 // Specialization of dispatch for subset. dispatch() normally just
 // dispatches to the sub table this points too, but for subset
 // we need to run subset on this subtable too.
 template <typename ...Ts>
 typename hb_subset_context_t::return_t dispatch (hb_subset_context_t *c, Ts&&... ds) const
 {
   switch (u.format.v) {
   case 1: hb_barrier (); return u.format1.subset (c);
   default: return c->default_return_value ();
   }
 }

 template <typename context_t, typename ...Ts>
 typename context_t::return_t dispatch (context_t *c, Ts&&... ds) const
 {
   if (unlikely (!c->may_dispatch (this, &u.format.v))) return c->no_dispatch_return_value ();
   TRACE_DISPATCH (this, u.format.v);
   switch (u.format.v) {
   case 1: hb_barrier (); return_trace (u.format1.dispatch (c, std::forward<Ts> (ds)...));
   default:return_trace (c->default_return_value ());
   }
 }

 protected:
 union {
 struct { HBUINT16 v; }	format;		/* Format identifier */
 ExtensionFormat1<T>	format1;
 } u;
};


/*
* GSUB/GPOS Common
*/

struct hb_ot_layout_lookup_accelerator_t
{
 template <typename TLookup>
 static hb_ot_layout_lookup_accelerator_t *create (const TLookup &lookup)
 {
   unsigned count = lookup.get_subtable_count ();

   unsigned size = sizeof (hb_ot_layout_lookup_accelerator_t) -
	    HB_VAR_ARRAY * sizeof (hb_accelerate_subtables_context_t::hb_applicable_t) +
	    count * sizeof (hb_accelerate_subtables_context_t::hb_applicable_t);

   /* The following is a calloc because when we are collecting subtables,
    * some of them might be invalid and hence not collect; as a result,
    * we might not fill in all the count entries of the subtables array.
    * Zeroing it allows the set digest to gatekeep it without having to
    * initialize it further. */
   auto *thiz = (hb_ot_layout_lookup_accelerator_t *) hb_calloc (1, size);
   if (unlikely (!thiz))
     return nullptr;

   hb_accelerate_subtables_context_t c_accelerate_subtables (thiz->subtables);
   lookup.dispatch (&c_accelerate_subtables);

   thiz->digest.init ();
   for (auto& subtable : hb_iter (thiz->subtables, count))
     thiz->digest.union_ (subtable.digest);

   thiz->count = count;

#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
   thiz->subtable_cache_user_idx = c_accelerate_subtables.subtable_cache_user_idx;

   for (unsigned i = 0; i < count; i++)
     if (i != thiz->subtable_cache_user_idx)
      thiz->subtables[i].apply_cached_func = thiz->subtables[i].apply_func;
#endif

   return thiz;
 }

 void fini ()
 {
#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
   for (unsigned i = 0; i < count; i++)
     hb_free (subtables[i].external_cache);
#endif
 }

 bool may_have (hb_codepoint_t g) const
 { return digest.may_have (g); }

#ifndef HB_OPTIMIZE_SIZE
 HB_ALWAYS_INLINE
#endif
 bool apply (hb_ot_apply_context_t *c, bool use_cache) const
 {
   c->lookup_accel = this;
#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
   if (use_cache)
   {
     return
     + hb_iter (hb_iter (subtables, count))
     | hb_map ([&c] (const hb_accelerate_subtables_context_t::hb_applicable_t &_) { return _.apply_cached (c); })
     | hb_any
     ;
   }
   else
#endif
   {
     return
     + hb_iter (hb_iter (subtables, count))
     | hb_map ([&c] (const hb_accelerate_subtables_context_t::hb_applicable_t &_) { return _.apply (c); })
     | hb_any
     ;
   }
   return false;
 }

 bool cache_enter (hb_ot_apply_context_t *c) const
 {
#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
   return subtable_cache_user_idx != (unsigned) -1 &&
   subtables[subtable_cache_user_idx].cache_enter (c);
#else
   return false;
#endif
 }
 void cache_leave (hb_ot_apply_context_t *c) const
 {
#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
   subtables[subtable_cache_user_idx].cache_leave (c);
#endif
 }


 hb_set_digest_t digest;
 private:
 unsigned count = 0; /* Number of subtables in the array. */
#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
 unsigned subtable_cache_user_idx = (unsigned) -1;
#endif
 hb_accelerate_subtables_context_t::hb_applicable_t subtables[HB_VAR_ARRAY];
};

template <typename Types>
struct GSUBGPOSVersion1_2
{
 friend struct GSUBGPOS;

 protected:
 FixedVersion<>version;	/* Version of the GSUB/GPOS table--initially set
			 * to 0x00010000u */
 typename Types:: template OffsetTo<ScriptList>
	scriptList;	/* ScriptList table */
 typename Types::template OffsetTo<FeatureList>
	featureList;	/* FeatureList table */
 typename Types::template OffsetTo<LookupList<Types>>
	lookupList;	/* LookupList table */
 Offset32To<FeatureVariations>
	featureVars;	/* Offset to Feature Variations
			   table--from beginning of table
			 * (may be NULL).  Introduced
			 * in version 0x00010001. */
 public:
 DEFINE_SIZE_MIN (4 + 3 * Types::size);

 unsigned int get_size () const
 {
   return min_size +
   (version.to_int () >= 0x00010001u ? featureVars.static_size : 0);
 }

 const typename Types::template OffsetTo<LookupList<Types>>* get_lookup_list_offset () const
 {
   return &lookupList;
 }

 template <typename TLookup>
 bool sanitize (hb_sanitize_context_t *c) const
 {
   TRACE_SANITIZE (this);
   typedef List16OfOffsetTo<TLookup, typename Types::HBUINT> TLookupList;
   if (unlikely (!(scriptList.sanitize (c, this) &&
	    featureList.sanitize (c, this) &&
	    reinterpret_cast<const typename Types::template OffsetTo<TLookupList> &> (lookupList).sanitize (c, this))))
     return_trace (false);

#ifndef HB_NO_VAR
   if (unlikely (!(version.to_int () < 0x00010001u || featureVars.sanitize (c, this))))
     return_trace (false);
#endif

   return_trace (true);
 }

 template <typename TLookup>
 bool subset (hb_subset_layout_context_t *c) const
 {
   TRACE_SUBSET (this);

   auto *out = c->subset_context->serializer->start_embed (this);
   if (unlikely (!c->subset_context->serializer->extend_min (out))) return_trace (false);

   out->version = version;

   typedef LookupOffsetList<TLookup, typename Types::HBUINT> TLookupList;
   reinterpret_cast<typename Types::template OffsetTo<TLookupList> &> (out->lookupList)
.serialize_subset (c->subset_context,
		   reinterpret_cast<const typename Types::template OffsetTo<TLookupList> &> (lookupList),
		   this,
		   c);

   reinterpret_cast<typename Types::template OffsetTo<RecordListOfFeature> &> (out->featureList)
.serialize_subset (c->subset_context,
		   reinterpret_cast<const typename Types::template OffsetTo<RecordListOfFeature> &> (featureList),
		   this,
		   c);

   out->scriptList.serialize_subset (c->subset_context,
			      scriptList,
			      this,
			      c);

#ifndef HB_NO_VAR
   if (version.to_int () >= 0x00010001u)
   {
     auto snapshot = c->subset_context->serializer->snapshot ();
     if (!c->subset_context->serializer->extend_min (&out->featureVars))
       return_trace (false);

     // if all axes are pinned all feature vars are dropped.
     bool ret = !c->subset_context->plan->all_axes_pinned
                && out->featureVars.serialize_subset (c->subset_context, featureVars, this, c);
     if (!ret && version.major == 1)
     {
       c->subset_context->serializer->revert (snapshot);
out->version.major = 1;
out->version.minor = 0;
     }
   }
#endif

   return_trace (true);
 }
};

struct GSUBGPOS
{
 unsigned int get_size () const
 {
   switch (u.version.major) {
   case 1: hb_barrier (); return u.version1.get_size ();
#ifndef HB_NO_BEYOND_64K
   case 2: hb_barrier (); return u.version2.get_size ();
#endif
   default: return u.version.static_size;
   }
 }

 template <typename TLookup>
 bool sanitize (hb_sanitize_context_t *c) const
 {
   TRACE_SANITIZE (this);
   if (unlikely (!u.version.sanitize (c))) return_trace (false);
   hb_barrier ();
   switch (u.version.major) {
   case 1: hb_barrier (); return_trace (u.version1.sanitize<TLookup> (c));
#ifndef HB_NO_BEYOND_64K
   case 2: hb_barrier (); return_trace (u.version2.sanitize<TLookup> (c));
#endif
   default: return_trace (true);
   }
 }

 template <typename TLookup>
 bool subset (hb_subset_layout_context_t *c) const
 {
   switch (u.version.major) {
   case 1: hb_barrier (); return u.version1.subset<TLookup> (c);
#ifndef HB_NO_BEYOND_64K
   case 2: hb_barrier (); return u.version2.subset<TLookup> (c);
#endif
   default: return false;
   }
 }

 const ScriptList &get_script_list () const
 {
   switch (u.version.major) {
   case 1: hb_barrier (); return this+u.version1.scriptList;
#ifndef HB_NO_BEYOND_64K
   case 2: hb_barrier (); return this+u.version2.scriptList;
#endif
   default: return Null (ScriptList);
   }
 }
 const FeatureList &get_feature_list () const
 {
   switch (u.version.major) {
   case 1: hb_barrier (); return this+u.version1.featureList;
#ifndef HB_NO_BEYOND_64K
   case 2: hb_barrier (); return this+u.version2.featureList;
#endif
   default: return Null (FeatureList);
   }
 }
 unsigned int get_lookup_count () const
 {
   switch (u.version.major) {
   case 1: hb_barrier (); return (this+u.version1.lookupList).len;
#ifndef HB_NO_BEYOND_64K
   case 2: hb_barrier (); return (this+u.version2.lookupList).len;
#endif
   default: return 0;
   }
 }
 const Lookup& get_lookup (unsigned int i) const
 {
   switch (u.version.major) {
   case 1: hb_barrier (); return (this+u.version1.lookupList)[i];
#ifndef HB_NO_BEYOND_64K
   case 2: hb_barrier (); return (this+u.version2.lookupList)[i];
#endif
   default: return Null (Lookup);
   }
 }
 const FeatureVariations &get_feature_variations () const
 {
   switch (u.version.major) {
   case 1: hb_barrier (); return (u.version.to_int () >= 0x00010001u && hb_barrier () ? this+u.version1.featureVars : Null (FeatureVariations));
#ifndef HB_NO_BEYOND_64K
   case 2: hb_barrier (); return this+u.version2.featureVars;
#endif
   default: return Null (FeatureVariations);
   }
 }

 bool has_data () const { return u.version.to_int (); }
 unsigned int get_script_count () const
 { return get_script_list ().len; }
 const Tag& get_script_tag (unsigned int i) const
 { return get_script_list ().get_tag (i); }
 unsigned int get_script_tags (unsigned int start_offset,
			unsigned int *script_count /* IN/OUT */,
			hb_tag_t     *script_tags /* OUT */) const
 { return get_script_list ().get_tags (start_offset, script_count, script_tags); }
 const Script& get_script (unsigned int i) const
 { return get_script_list ()[i]; }
 bool find_script_index (hb_tag_t tag, unsigned int *index) const
 { return get_script_list ().find_index (tag, index); }

 unsigned int get_feature_count () const
 { return get_feature_list ().len; }
 hb_tag_t get_feature_tag (unsigned int i) const
 { return i == Index::NOT_FOUND_INDEX ? HB_TAG_NONE : get_feature_list ().get_tag (i); }
 unsigned int get_feature_tags (unsigned int start_offset,
			 unsigned int *feature_count /* IN/OUT */,
			 hb_tag_t     *feature_tags /* OUT */) const
 { return get_feature_list ().get_tags (start_offset, feature_count, feature_tags); }
 const Feature& get_feature (unsigned int i) const
 { return get_feature_list ()[i]; }
 bool find_feature_index (hb_tag_t tag, unsigned int *index) const
 { return get_feature_list ().find_index (tag, index); }

 bool find_variations_index (const int *coords, unsigned int num_coords,
		      unsigned int *index,
		      ItemVarStoreInstancer *instancer) const
 {
#ifdef HB_NO_VAR
   *index = FeatureVariations::NOT_FOUND_INDEX;
   return false;
#endif
   return get_feature_variations ().find_index (coords, num_coords, index, instancer);
 }
 const Feature& get_feature_variation (unsigned int feature_index,
				unsigned int variations_index) const
 {
#ifndef HB_NO_VAR
   if (FeatureVariations::NOT_FOUND_INDEX != variations_index &&
u.version.to_int () >= 0x00010001u)
   {
     const Feature *feature = get_feature_variations ().find_substitute (variations_index,
								  feature_index);
     if (feature)
return *feature;
   }
#endif
   return get_feature (feature_index);
 }

 void feature_variation_collect_lookups (const hb_set_t *feature_indexes,
				  const hb_hashmap_t<unsigned, hb::shared_ptr<hb_set_t>> *feature_record_cond_idx_map,
				  hb_set_t       *lookup_indexes /* OUT */) const
 {
#ifndef HB_NO_VAR
   get_feature_variations ().collect_lookups (feature_indexes, feature_record_cond_idx_map, lookup_indexes);
#endif
 }

#ifndef HB_NO_VAR
 void collect_feature_substitutes_with_variations (hb_collect_feature_substitutes_with_var_context_t *c) const
 { get_feature_variations ().collect_feature_substitutes_with_variations (c); }
#endif

 template <typename TLookup>
 void closure_lookups (hb_face_t      *face,
		const hb_set_t *glyphs,
		hb_set_t       *lookup_indexes /* IN/OUT */) const
 {
   hb_set_t visited_lookups, inactive_lookups;
   hb_closure_lookups_context_t c (face, glyphs, &visited_lookups, &inactive_lookups);

   c.set_recurse_func (TLookup::template dispatch_recurse_func<hb_closure_lookups_context_t>);

   for (unsigned lookup_index : *lookup_indexes)
     reinterpret_cast<const TLookup &> (get_lookup (lookup_index)).closure_lookups (&c, lookup_index);

   hb_set_union (lookup_indexes, &visited_lookups);
   hb_set_subtract (lookup_indexes, &inactive_lookups);
 }

 void prune_langsys (const hb_map_t *duplicate_feature_map,
                     const hb_set_t *layout_scripts,
                     hb_hashmap_t<unsigned, hb::unique_ptr<hb_set_t>> *script_langsys_map,
                     hb_set_t       *new_feature_indexes /* OUT */) const
 {
   hb_prune_langsys_context_t c (this, script_langsys_map, duplicate_feature_map, new_feature_indexes);

   unsigned count = get_script_count ();
   for (unsigned script_index = 0; script_index < count; script_index++)
   {
     const Tag& tag = get_script_tag (script_index);
     if (!layout_scripts->has (tag)) continue;
     const Script& s = get_script (script_index);
     s.prune_langsys (&c, script_index);
   }
 }

 void prune_features (const hb_map_t *lookup_indices, /* IN */
	       const hb_hashmap_t<unsigned, hb::shared_ptr<hb_set_t>> *feature_record_cond_idx_map, /* IN */
	       const hb_hashmap_t<unsigned, const Feature*> *feature_substitutes_map, /* IN */
	       hb_set_t       *feature_indices /* IN/OUT */) const
 {
#ifndef HB_NO_VAR
   // This is the set of feature indices which have alternate versions defined
   // if the FeatureVariation's table and the alternate version(s) intersect the
   // set of lookup indices.
   hb_set_t alternate_feature_indices;
   get_feature_variations ().closure_features (lookup_indices, feature_record_cond_idx_map, &alternate_feature_indices);
   if (unlikely (alternate_feature_indices.in_error()))
   {
     feature_indices->err ();
     return;
   }
#endif

   for (unsigned i : hb_iter (feature_indices))
   {
     hb_tag_t tag =  get_feature_tag (i);
     if (tag == HB_TAG ('p', 'r', 'e', 'f'))
       // Note: Never ever drop feature 'pref', even if it's empty.
       // HarfBuzz chooses shaper for Khmer based on presence of this
       // feature.	See thread at:
// http://lists.freedesktop.org/archives/harfbuzz/2012-November/002660.html
       continue;


     const Feature *f = &(get_feature (i));
     const Feature** p = nullptr;
     if (feature_substitutes_map->has (i, &p))
       f = *p;

     if (!f->featureParams.is_null () &&
         tag == HB_TAG ('s', 'i', 'z', 'e'))
       continue;

     if (!f->intersects_lookup_indexes (lookup_indices)
#ifndef HB_NO_VAR
         && !alternate_feature_indices.has (i)
#endif
  )
feature_indices->del (i);
   }
 }

 void collect_name_ids (const hb_map_t *feature_index_map,
                        hb_set_t *nameids_to_retain /* OUT */) const
 {
   unsigned count = get_feature_count ();
   for (unsigned i = 0 ; i < count; i++)
   {
     if (!feature_index_map->has (i)) continue;
     hb_tag_t tag = get_feature_tag (i);
     get_feature (i).collect_name_ids (tag, nameids_to_retain);
   }
 }

 template <typename T>
 struct accelerator_t
 {
   accelerator_t (hb_face_t *face)
   {
     hb_sanitize_context_t sc;
     sc.lazy_some_gpos = true;
     this->table = sc.reference_table<T> (face);

     if (unlikely (this->table->is_blocklisted (this->table.get_blob (), face)))
     {
hb_blob_destroy (this->table.get_blob ());
this->table = hb_blob_get_empty ();
     }

     this->lookup_count = table->get_lookup_count ();

     this->accels = (hb_atomic_t<hb_ot_layout_lookup_accelerator_t *> *) hb_calloc (this->lookup_count, sizeof (*accels));
     if (unlikely (!this->accels))
     {
this->lookup_count = 0;
this->table.destroy ();
this->table = hb_blob_get_empty ();
     }
   }
   ~accelerator_t ()
   {
     for (unsigned int i = 0; i < this->lookup_count; i++)
     {
auto *accel = this->accels[i].get_relaxed ();
if (accel)
  accel->fini ();
hb_free (accel);
     }
     hb_free (this->accels);
     this->table.destroy ();
   }

   hb_blob_t *get_blob () const { return table.get_blob (); }

   hb_ot_layout_lookup_accelerator_t *get_accel (unsigned lookup_index) const
   {
     if (unlikely (lookup_index >= lookup_count)) return nullptr;

   retry:
     auto *accel = accels[lookup_index].get_acquire ();
     if (unlikely (!accel))
     {
accel = hb_ot_layout_lookup_accelerator_t::create (table->get_lookup (lookup_index));
if (unlikely (!accel))
  return nullptr;

if (unlikely (!accels[lookup_index].cmpexch (nullptr, accel)))
{
  accel->fini ();
  hb_free (accel);
  goto retry;
}
     }

     return accel;
   }

   hb_blob_ptr_t<T> table;
   unsigned int lookup_count;
   hb_atomic_t<hb_ot_layout_lookup_accelerator_t *> *accels;
 };

 protected:
 union {
 FixedVersion<>			version;	/* Version identifier */
 GSUBGPOSVersion1_2<SmallTypes>	version1;
#ifndef HB_NO_BEYOND_64K
 GSUBGPOSVersion1_2<MediumTypes>	version2;
#endif
 } u;
 public:
 DEFINE_SIZE_MIN (4);
};


} /* namespace OT */


#endif /* HB_OT_LAYOUT_GSUBGPOS_HH */