harfbuzz/src/hb-ot-layout-gsubgpos-private.hh

/*
 * 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_PRIVATE_HH
#define HB_OT_LAYOUT_GSUBGPOS_PRIVATE_HH

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


namespace OT {



#define TRACE_PROCESS(this) \
	hb_auto_trace_t<context_t::max_debug_depth, typename context_t::return_t> trace \
	(&c->debug_depth, c->get_name (), this, HB_FUNC, \
	 "");


#ifndef HB_DEBUG_CLOSURE
#define HB_DEBUG_CLOSURE (HB_DEBUG+0)
#endif

#define TRACE_CLOSURE(this) \
	hb_auto_trace_t<HB_DEBUG_CLOSURE, void_t> trace \
	(&c->debug_depth, c->get_name (), this, HB_FUNC, \
	 "");

struct hb_closure_context_t
{
  inline const char *get_name (void) { return "CLOSURE"; }
  static const unsigned int max_debug_depth = HB_DEBUG_CLOSURE;
  typedef void_t return_t;
  typedef return_t (*recurse_func_t) (hb_closure_context_t *c, unsigned int lookup_index);
  template <typename T>
  inline return_t process (const T &obj) { obj.closure (this); return VOID; }
  static return_t default_return_value (void) { return VOID; }
  bool stop_sublookup_iteration (const return_t r) const { return false; }
  return_t recurse (unsigned int lookup_index)
  {
    if (unlikely (nesting_level_left == 0 || !recurse_func))
      return default_return_value ();

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

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

  hb_closure_context_t (hb_face_t *face_,
			hb_set_t *glyphs_,
		        unsigned int nesting_level_left_ = MAX_NESTING_LEVEL) :
			  face (face_),
			  glyphs (glyphs_),
			  recurse_func (NULL),
			  nesting_level_left (nesting_level_left_),
			  debug_depth (0) {}

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



#ifndef HB_DEBUG_WOULD_APPLY
#define HB_DEBUG_WOULD_APPLY (HB_DEBUG+0)
#endif

#define TRACE_WOULD_APPLY(this) \
	hb_auto_trace_t<HB_DEBUG_WOULD_APPLY, bool> trace \
	(&c->debug_depth, c->get_name (), this, HB_FUNC, \
	 "%d glyphs", c->len);

struct hb_would_apply_context_t
{
  inline const char *get_name (void) { return "WOULD_APPLY"; }
  static const unsigned int max_debug_depth = HB_DEBUG_WOULD_APPLY;
  typedef bool return_t;
  template <typename T>
  inline return_t process (const T &obj) { return obj.would_apply (this); }
  static return_t default_return_value (void) { return false; }
  bool stop_sublookup_iteration (const return_t r) const { return r; }
  return_t recurse (unsigned int lookup_index) { return true; }

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

  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_),
			      debug_depth (0) {}
};



#ifndef HB_DEBUG_COLLECT_GLYPHS
#define HB_DEBUG_COLLECT_GLYPHS (HB_DEBUG+0)
#endif

#define TRACE_COLLECT_GLYPHS(this) \
	hb_auto_trace_t<HB_DEBUG_COLLECT_GLYPHS, void_t> trace \
	(&c->debug_depth, c->get_name (), this, HB_FUNC, \
	 "");

struct hb_collect_glyphs_context_t
{
  inline const char *get_name (void) { return "COLLECT_GLYPHS"; }
  static const unsigned int max_debug_depth = HB_DEBUG_COLLECT_GLYPHS;
  typedef void_t return_t;
  typedef return_t (*recurse_func_t) (hb_collect_glyphs_context_t *c, unsigned int lookup_index);
  template <typename T>
  inline return_t process (const T &obj) { obj.collect_glyphs (this); return VOID; }
  static return_t default_return_value (void) { return VOID; }
  bool stop_sublookup_iteration (const return_t r) const { return false; }
  return_t recurse (unsigned int lookup_index)
  {
    if (unlikely (nesting_level_left == 0 || !recurse_func))
      return default_return_value ();

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

  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;
  unsigned int nesting_level_left;
  unsigned int debug_depth;

  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_ = 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 (NULL),
			      nesting_level_left (nesting_level_left_),
			      debug_depth (0) {}

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



struct hb_get_coverage_context_t
{
  inline const char *get_name (void) { return "GET_COVERAGE"; }
  static const unsigned int max_debug_depth = 0;
  typedef const Coverage &return_t;
  template <typename T>
  inline return_t process (const T &obj) { return obj.get_coverage (); }
  static return_t default_return_value (void) { return Null(Coverage); }

  hb_get_coverage_context_t (void) :
			    debug_depth (0) {}

  unsigned int debug_depth;
};



#ifndef HB_DEBUG_APPLY
#define HB_DEBUG_APPLY (HB_DEBUG+0)
#endif

#define TRACE_APPLY(this) \
	hb_auto_trace_t<HB_DEBUG_APPLY, bool> trace \
	(&c->debug_depth, c->get_name (), this, HB_FUNC, \
	 "idx %d codepoint %u", c->buffer->idx, c->buffer->cur().codepoint);

struct hb_apply_context_t
{
  inline const char *get_name (void) { return "APPLY"; }
  static const unsigned int max_debug_depth = HB_DEBUG_APPLY;
  typedef bool return_t;
  typedef return_t (*recurse_func_t) (hb_apply_context_t *c, unsigned int lookup_index);
  template <typename T>
  inline return_t process (const T &obj) { return obj.apply (this); }
  static return_t default_return_value (void) { return false; }
  bool stop_sublookup_iteration (const return_t r) const { return r; }
  return_t recurse (unsigned int lookup_index)
  {
    if (unlikely (nesting_level_left == 0 || !recurse_func))
      return default_return_value ();

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

  hb_font_t *font;
  hb_face_t *face;
  hb_buffer_t *buffer;
  hb_direction_t direction;
  hb_mask_t lookup_mask;
  recurse_func_t recurse_func;
  unsigned int nesting_level_left;
  unsigned int lookup_props;
  unsigned int property; /* propety of first glyph */
  const GDEF &gdef;
  bool has_glyph_classes;
  unsigned int debug_depth;


  hb_apply_context_t (hb_font_t *font_,
		      hb_buffer_t *buffer_,
		      hb_mask_t lookup_mask_) :
			font (font_), face (font->face), buffer (buffer_),
			direction (buffer_->props.direction),
			lookup_mask (lookup_mask_),
			recurse_func (NULL),
			nesting_level_left (MAX_NESTING_LEVEL),
			lookup_props (0), property (0),
			gdef (*hb_ot_layout_from_face (face)->gdef),
			has_glyph_classes (gdef.has_glyph_classes ()),
			debug_depth (0) {}

  void set_recurse_func (recurse_func_t func) { recurse_func = func; }
  void set_lookup_props (unsigned int lookup_props_) { lookup_props = lookup_props_; }
  void set_lookup (const Lookup &l) { lookup_props = l.get_props (); }

  struct mark_skipping_forward_iterator_t
  {
    inline mark_skipping_forward_iterator_t (hb_apply_context_t *c_,
					     unsigned int start_index_,
					     unsigned int num_items_,
					     bool context_match = false)
    {
      c = c_;
      idx = start_index_;
      num_items = num_items_;
      mask = context_match ? -1 : c->lookup_mask;
      syllable = context_match ? 0 : c->buffer->cur().syllable ();
      end = c->buffer->len;
    }
    inline bool has_no_chance (void) const
    {
      return unlikely (num_items && idx + num_items >= end);
    }
    inline void reject (void)
    {
      num_items++;
    }
    inline bool next (unsigned int *property_out,
		      unsigned int  lookup_props)
    {
      assert (num_items > 0);
      do
      {
	if (has_no_chance ())
	  return false;
	idx++;
      } while (c->should_skip_mark (&c->buffer->info[idx], lookup_props, property_out));
      num_items--;
      return (c->buffer->info[idx].mask & mask) && (!syllable || syllable == c->buffer->info[idx].syllable ());
    }
    inline bool next (unsigned int *property_out = NULL)
    {
      return next (property_out, c->lookup_props);
    }

    unsigned int idx;
    protected:
    hb_apply_context_t *c;
    unsigned int num_items;
    hb_mask_t mask;
    uint8_t syllable;
    unsigned int end;
  };

  struct mark_skipping_backward_iterator_t
  {
    inline mark_skipping_backward_iterator_t (hb_apply_context_t *c_,
					      unsigned int start_index_,
					      unsigned int num_items_,
					      hb_mask_t mask_ = 0,
					      bool match_syllable_ = true)
    {
      c = c_;
      idx = start_index_;
      num_items = num_items_;
      mask = mask_ ? mask_ : c->lookup_mask;
      syllable = match_syllable_ ? c->buffer->cur().syllable () : 0;
    }
    inline bool has_no_chance (void) const
    {
      return unlikely (idx < num_items);
    }
    inline void reject (void)
    {
      num_items++;
    }
    inline bool prev (unsigned int *property_out,
		      unsigned int  lookup_props)
    {
      assert (num_items > 0);
      do
      {
	if (has_no_chance ())
	  return false;
	idx--;
      } while (c->should_skip_mark (&c->buffer->out_info[idx], lookup_props, property_out));
      num_items--;
      return (c->buffer->out_info[idx].mask & mask) && (!syllable || syllable == c->buffer->out_info[idx].syllable ());
    }
    inline bool prev (unsigned int *property_out = NULL)
    {
      return prev (property_out, c->lookup_props);
    }

    unsigned int idx;
    protected:
    hb_apply_context_t *c;
    unsigned int num_items;
    hb_mask_t mask;
    uint8_t syllable;
  };

  inline bool
  match_properties_mark (hb_codepoint_t  glyph,
			 unsigned int    glyph_props,
			 unsigned int    lookup_props) const
  {
    /* If using mark filtering sets, the high short of
     * lookup_props has the set index.
     */
    if (lookup_props & LookupFlag::UseMarkFilteringSet)
      return gdef.mark_set_covers (lookup_props >> 16, glyph);

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

    return true;
  }

  inline bool
  match_properties (hb_codepoint_t  glyph,
		    unsigned int    glyph_props,
		    unsigned int    lookup_props) const
  {
    /* Not covered, if, for example, glyph class is ligature and
     * lookup_props includes LookupFlags::IgnoreLigatures
     */
    if (glyph_props & lookup_props & LookupFlag::IgnoreFlags)
      return false;

    if (unlikely (glyph_props & HB_OT_LAYOUT_GLYPH_PROPS_MARK))
      return match_properties_mark (glyph, glyph_props, lookup_props);

    return true;
  }

  inline bool
  check_glyph_property (hb_glyph_info_t *info,
			unsigned int  lookup_props,
			unsigned int *property_out) const
  {
    unsigned int property;

    property = info->glyph_props();
    *property_out = property;

    return match_properties (info->codepoint, property, lookup_props);
  }

  inline bool
  should_skip_mark (hb_glyph_info_t *info,
		   unsigned int  lookup_props,
		   unsigned int *property_out) const
  {
    unsigned int property;

    property = info->glyph_props();
    if (property_out)
      *property_out = property;

    /* If it's a mark, skip it if we don't accept it. */
    if (unlikely (property & HB_OT_LAYOUT_GLYPH_PROPS_MARK))
      return !match_properties (info->codepoint, property, lookup_props);

    /* If not a mark, don't skip. */
    return false;
  }


  inline bool should_mark_skip_current_glyph (void) const
  {
    return should_skip_mark (&buffer->cur(), lookup_props, NULL);
  }

  inline void set_class (hb_codepoint_t glyph_index, unsigned int class_guess) const
  {
    if (likely (has_glyph_classes))
      buffer->cur().glyph_props() = gdef.get_glyph_props (glyph_index);
    else if (class_guess)
      buffer->cur().glyph_props() = class_guess;
  }

  inline void output_glyph (hb_codepoint_t glyph_index,
			    unsigned int class_guess = 0) const
  {
    set_class (glyph_index, class_guess);
    buffer->output_glyph (glyph_index);
  }
  inline void replace_glyph (hb_codepoint_t glyph_index,
			     unsigned int class_guess = 0) const
  {
    set_class (glyph_index, class_guess);
    buffer->replace_glyph (glyph_index);
  }
  inline void replace_glyph_inplace (hb_codepoint_t glyph_index,
				     unsigned int class_guess = 0) const
  {
    set_class (glyph_index, class_guess);
    buffer->cur().codepoint = glyph_index;
  }
};



typedef bool (*intersects_func_t) (hb_set_t *glyphs, const USHORT &value, const void *data);
typedef void (*collect_glyphs_func_t) (hb_set_t *glyphs, const USHORT &value, const void *data);
typedef bool (*match_func_t) (hb_codepoint_t glyph_id, const USHORT &value, const void *data);

struct ContextClosureFuncs
{
  intersects_func_t intersects;
};
struct ContextCollectGlyphsFuncs
{
  collect_glyphs_func_t collect;
};
struct ContextApplyFuncs
{
  match_func_t match;
};


static inline bool intersects_glyph (hb_set_t *glyphs, const USHORT &value, const void *data HB_UNUSED)
{
  return glyphs->has (value);
}
static inline bool intersects_class (hb_set_t *glyphs, const USHORT &value, const void *data)
{
  const ClassDef &class_def = *reinterpret_cast<const ClassDef *>(data);
  return class_def.intersects_class (glyphs, value);
}
static inline bool intersects_coverage (hb_set_t *glyphs, const USHORT &value, const void *data)
{
  const OffsetTo<Coverage> &coverage = (const OffsetTo<Coverage>&)value;
  return (data+coverage).intersects (glyphs);
}

static inline bool intersects_array (hb_closure_context_t *c,
				     unsigned int count,
				     const USHORT values[],
				     intersects_func_t intersects_func,
				     const void *intersects_data)
{
  for (unsigned int i = 0; i < count; i++)
    if (likely (!intersects_func (c->glyphs, values[i], intersects_data)))
      return false;
  return true;
}


static inline void collect_glyph (hb_set_t *glyphs, const USHORT &value, const void *data HB_UNUSED)
{
  glyphs->add (value);
}
static inline void collect_class (hb_set_t *glyphs, const USHORT &value, const void *data)
{
  const ClassDef &class_def = *reinterpret_cast<const ClassDef *>(data);
  class_def.add_class (glyphs, value);
}
static inline void collect_coverage (hb_set_t *glyphs, const USHORT &value, const void *data)
{
  const OffsetTo<Coverage> &coverage = (const OffsetTo<Coverage>&)value;
  (data+coverage).add_coverage (glyphs);
}
static inline void collect_array (hb_collect_glyphs_context_t *c,
				  unsigned int count,
				  const USHORT values[],
				  collect_glyphs_func_t collect_func,
				  const void *collect_data)
{
  for (unsigned int i = 0; i < count; i++)
    collect_func (&c->input, values[i], collect_data);
}


static inline bool match_glyph (hb_codepoint_t glyph_id, const USHORT &value, const void *data HB_UNUSED)
{
  return glyph_id == value;
}
static inline bool match_class (hb_codepoint_t glyph_id, const USHORT &value, const void *data)
{
  const ClassDef &class_def = *reinterpret_cast<const ClassDef *>(data);
  return class_def.get_class (glyph_id) == value;
}
static inline bool match_coverage (hb_codepoint_t glyph_id, const USHORT &value, const void *data)
{
  const OffsetTo<Coverage> &coverage = (const OffsetTo<Coverage>&)value;
  return (data+coverage).get_coverage (glyph_id) != NOT_COVERED;
}

static inline bool would_match_input (hb_would_apply_context_t *c,
				      unsigned int count, /* Including the first glyph (not matched) */
				      const USHORT 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++)
    if (likely (!match_func (c->glyphs[i], input[i - 1], match_data)))
      return false;

  return true;
}
static inline bool match_input (hb_apply_context_t *c,
				unsigned int count, /* Including the first glyph (not matched) */
				const USHORT input[], /* Array of input values--start with second glyph */
				match_func_t match_func,
				const void *match_data,
				unsigned int *end_offset = NULL,
				bool *p_is_mark_ligature = NULL,
				unsigned int *p_total_component_count = NULL)
{
  TRACE_APPLY (NULL);

  hb_apply_context_t::mark_skipping_forward_iterator_t skippy_iter (c, c->buffer->idx, count - 1);
  if (skippy_iter.has_no_chance ()) return TRACE_RETURN (false);

  /*
   * 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.o
   *   There is an exception to this: 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...)
   */

  bool is_mark_ligature = !!(c->property & HB_OT_LAYOUT_GLYPH_PROPS_MARK);

  unsigned int total_component_count = 0;
  total_component_count += get_lig_num_comps (c->buffer->cur());

  unsigned int first_lig_id = get_lig_id (c->buffer->cur());
  unsigned int first_lig_comp = get_lig_comp (c->buffer->cur());

  for (unsigned int i = 1; i < count; i++)
  {
    unsigned int property;

    if (!skippy_iter.next (&property)) return TRACE_RETURN (false);

    if (likely (!match_func (c->buffer->info[skippy_iter.idx].codepoint, input[i - 1], match_data))) return TRACE_RETURN (false);

    unsigned int this_lig_id = get_lig_id (c->buffer->info[skippy_iter.idx]);
    unsigned int this_lig_comp = get_lig_comp (c->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)
	return TRACE_RETURN (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_RETURN (false);
    }

    is_mark_ligature = is_mark_ligature && (property & HB_OT_LAYOUT_GLYPH_PROPS_MARK);
    total_component_count += get_lig_num_comps (c->buffer->info[skippy_iter.idx]);
  }

  if (end_offset)
    *end_offset = skippy_iter.idx - c->buffer->idx + 1;

  if (p_is_mark_ligature)
    *p_is_mark_ligature = is_mark_ligature;

  if (p_total_component_count)
    *p_total_component_count = total_component_count;

  return TRACE_RETURN (true);
}
static inline void ligate_input (hb_apply_context_t *c,
				 unsigned int count, /* Including the first glyph (not matched) */
				 const USHORT input[], /* Array of input values--start with second glyph */
				 hb_codepoint_t lig_glyph,
				 match_func_t match_func,
				 const void *match_data,
				 bool is_mark_ligature,
				 unsigned int total_component_count)
{
  /*
   * - 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 wit 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
   */

  unsigned int klass = is_mark_ligature ? 0 : HB_OT_LAYOUT_GLYPH_PROPS_LIGATURE;
  unsigned int lig_id = is_mark_ligature ? 0 : allocate_lig_id (c->buffer);
  unsigned int last_lig_id = get_lig_id (c->buffer->cur());
  unsigned int last_num_components = get_lig_num_comps (c->buffer->cur());
  unsigned int components_so_far = last_num_components;

  if (!is_mark_ligature)
    set_lig_props_for_ligature (c->buffer->cur(), lig_id, total_component_count);
  c->replace_glyph (lig_glyph, klass);

  for (unsigned int i = 1; i < count; i++)
  {
    while (c->should_mark_skip_current_glyph ())
    {
      if (!is_mark_ligature) {
	unsigned int new_lig_comp = components_so_far - last_num_components +
				    MIN (MAX (get_lig_comp (c->buffer->cur()), 1u), last_num_components);
	set_lig_props_for_mark (c->buffer->cur(), lig_id, new_lig_comp);
      }
      c->buffer->next_glyph ();
    }

    last_lig_id = get_lig_id (c->buffer->cur());
    last_num_components = get_lig_num_comps (c->buffer->cur());
    components_so_far += last_num_components;

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

  if (!is_mark_ligature && last_lig_id) {
    /* Re-adjust components for any marks following. */
    for (unsigned int i = c->buffer->idx; i < c->buffer->len; i++) {
      if (last_lig_id == get_lig_id (c->buffer->info[i])) {
	unsigned int new_lig_comp = components_so_far - last_num_components +
				    MIN (MAX (get_lig_comp (c->buffer->info[i]), 1u), last_num_components);
	set_lig_props_for_mark (c->buffer->info[i], lig_id, new_lig_comp);
      } else
	break;
    }
  }
}

static inline bool match_backtrack (hb_apply_context_t *c,
				    unsigned int count,
				    const USHORT backtrack[],
				    match_func_t match_func,
				    const void *match_data)
{
  TRACE_APPLY (NULL);

  hb_apply_context_t::mark_skipping_backward_iterator_t skippy_iter (c, c->buffer->backtrack_len (), count, true);
  if (skippy_iter.has_no_chance ())
    return TRACE_RETURN (false);

  for (unsigned int i = 0; i < count; i++)
  {
    if (!skippy_iter.prev ())
      return TRACE_RETURN (false);

    if (likely (!match_func (c->buffer->out_info[skippy_iter.idx].codepoint, backtrack[i], match_data)))
      return TRACE_RETURN (false);
  }

  return TRACE_RETURN (true);
}

static inline bool match_lookahead (hb_apply_context_t *c,
				    unsigned int count,
				    const USHORT lookahead[],
				    match_func_t match_func,
				    const void *match_data,
				    unsigned int offset)
{
  TRACE_APPLY (NULL);

  hb_apply_context_t::mark_skipping_forward_iterator_t skippy_iter (c, c->buffer->idx + offset - 1, count, true);
  if (skippy_iter.has_no_chance ())
    return TRACE_RETURN (false);

  for (unsigned int i = 0; i < count; i++)
  {
    if (!skippy_iter.next ())
      return TRACE_RETURN (false);

    if (likely (!match_func (c->buffer->info[skippy_iter.idx].codepoint, lookahead[i], match_data)))
      return TRACE_RETURN (false);
  }

  return TRACE_RETURN (true);
}



struct LookupRecord
{
  inline bool sanitize (hb_sanitize_context_t *c) {
    TRACE_SANITIZE (this);
    return TRACE_RETURN (c->check_struct (this));
  }

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


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->lookupListIndex);
}

static inline bool apply_lookup (hb_apply_context_t *c,
				 unsigned int count, /* Including the first glyph */
				 unsigned int lookupCount,
				 const LookupRecord lookupRecord[] /* Array of LookupRecords--in design order */)
{
  TRACE_APPLY (NULL);

  unsigned int end = c->buffer->len;
  if (unlikely (count == 0 || c->buffer->idx + count > end))
    return TRACE_RETURN (false);

  /* TODO We don't support lookupRecord arrays that are not increasing:
   *      Should be easy for in_place ones at least. */

  /* Note: If sublookup is reverse, it will underflow after the first loop
   * and we jump out of it.  Not entirely disastrous.  So we don't check
   * for reverse lookup here.
   */
  for (unsigned int i = 0; i < count; /* NOP */)
  {
    if (unlikely (c->buffer->idx == end))
      return TRACE_RETURN (true);
    while (c->should_mark_skip_current_glyph ())
    {
      /* No lookup applied for this index */
      c->buffer->next_glyph ();
      if (unlikely (c->buffer->idx == end))
	return TRACE_RETURN (true);
    }

    if (lookupCount && i == lookupRecord->sequenceIndex)
    {
      unsigned int old_pos = c->buffer->idx;

      /* Apply a lookup */
      bool done = c->recurse (lookupRecord->lookupListIndex);

      lookupRecord++;
      lookupCount--;
      /* Err, this is wrong if the lookup jumped over some glyphs */
      i += c->buffer->idx - old_pos;
      if (unlikely (c->buffer->idx == end))
	return TRACE_RETURN (true);

      if (!done)
	goto not_applied;
    }
    else
    {
    not_applied:
      /* No lookup applied for this index */
      c->buffer->next_glyph ();
      i++;
    }
  }

  return TRACE_RETURN (true);
}



/* Contextual lookups */

struct ContextClosureLookupContext
{
  ContextClosureFuncs funcs;
  const void *intersects_data;
};

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

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

static inline void context_closure_lookup (hb_closure_context_t *c,
					   unsigned int inputCount, /* Including the first glyph (not matched) */
					   const USHORT input[], /* Array of input values--start with second glyph */
					   unsigned int lookupCount,
					   const LookupRecord lookupRecord[],
					   ContextClosureLookupContext &lookup_context)
{
  if (intersects_array (c,
			inputCount ? inputCount - 1 : 0, input,
			lookup_context.funcs.intersects, lookup_context.intersects_data))
    recurse_lookups (c,
		     lookupCount, lookupRecord);
}

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

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

struct Rule
{
  inline void closure (hb_closure_context_t *c, ContextClosureLookupContext &lookup_context) const
  {
    TRACE_CLOSURE (this);
    const LookupRecord *lookupRecord = &StructAtOffset<LookupRecord> (input, input[0].static_size * (inputCount ? inputCount - 1 : 0));
    context_closure_lookup (c,
			    inputCount, input,
			    lookupCount, lookupRecord,
			    lookup_context);
  }

  inline void collect_glyphs (hb_collect_glyphs_context_t *c, ContextCollectGlyphsLookupContext &lookup_context) const
  {
    TRACE_COLLECT_GLYPHS (this);
    const LookupRecord *lookupRecord = &StructAtOffset<LookupRecord> (input, input[0].static_size * (inputCount ? inputCount - 1 : 0));
    context_collect_glyphs_lookup (c,
				   inputCount, input,
				   lookupCount, lookupRecord,
				   lookup_context);
  }

  inline bool would_apply (hb_would_apply_context_t *c, ContextApplyLookupContext &lookup_context) const
  {
    TRACE_WOULD_APPLY (this);
    const LookupRecord *lookupRecord = &StructAtOffset<LookupRecord> (input, input[0].static_size * (inputCount ? inputCount - 1 : 0));
    return TRACE_RETURN (context_would_apply_lookup (c, inputCount, input, lookupCount, lookupRecord, lookup_context));
  }

  inline bool apply (hb_apply_context_t *c, ContextApplyLookupContext &lookup_context) const
  {
    TRACE_APPLY (this);
    const LookupRecord *lookupRecord = &StructAtOffset<LookupRecord> (input, input[0].static_size * (inputCount ? inputCount - 1 : 0));
    return TRACE_RETURN (context_apply_lookup (c, inputCount, input, lookupCount, lookupRecord, lookup_context));
  }

  public:
  inline bool sanitize (hb_sanitize_context_t *c) {
    TRACE_SANITIZE (this);
    return inputCount.sanitize (c)
	&& lookupCount.sanitize (c)
	&& c->check_range (input,
			   input[0].static_size * inputCount
			   + lookupRecordX[0].static_size * lookupCount);
  }

  protected:
  USHORT	inputCount;		/* Total number of glyphs in input
					 * glyph sequence--includes the first
					 * glyph */
  USHORT	lookupCount;		/* Number of LookupRecords */
  USHORT	input[VAR];		/* Array of match inputs--start with
					 * second glyph */
  LookupRecord	lookupRecordX[VAR];	/* Array of LookupRecords--in
					 * design order */
  public:
  DEFINE_SIZE_ARRAY2 (4, input, lookupRecordX);
};

struct RuleSet
{
  inline void closure (hb_closure_context_t *c, ContextClosureLookupContext &lookup_context) const
  {
    TRACE_CLOSURE (this);
    unsigned int num_rules = rule.len;
    for (unsigned int i = 0; i < num_rules; i++)
      (this+rule[i]).closure (c, lookup_context);
  }

  inline void collect_glyphs (hb_collect_glyphs_context_t *c, ContextCollectGlyphsLookupContext &lookup_context) const
  {
    TRACE_COLLECT_GLYPHS (this);
    unsigned int num_rules = rule.len;
    for (unsigned int i = 0; i < num_rules; i++)
      (this+rule[i]).collect_glyphs (c, lookup_context);
  }

  inline bool would_apply (hb_would_apply_context_t *c, ContextApplyLookupContext &lookup_context) const
  {
    TRACE_WOULD_APPLY (this);
    unsigned int num_rules = rule.len;
    for (unsigned int i = 0; i < num_rules; i++)
    {
      if ((this+rule[i]).would_apply (c, lookup_context))
        return TRACE_RETURN (true);
    }
    return TRACE_RETURN (false);
  }

  inline bool apply (hb_apply_context_t *c, ContextApplyLookupContext &lookup_context) const
  {
    TRACE_APPLY (this);
    unsigned int num_rules = rule.len;
    for (unsigned int i = 0; i < num_rules; i++)
    {
      if ((this+rule[i]).apply (c, lookup_context))
        return TRACE_RETURN (true);
    }
    return TRACE_RETURN (false);
  }

  inline bool sanitize (hb_sanitize_context_t *c) {
    TRACE_SANITIZE (this);
    return TRACE_RETURN (rule.sanitize (c, this));
  }

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


struct ContextFormat1
{
  inline void closure (hb_closure_context_t *c) const
  {
    TRACE_CLOSURE (this);

    const Coverage &cov = (this+coverage);

    struct ContextClosureLookupContext lookup_context = {
      {intersects_glyph},
      NULL
    };

    unsigned int count = ruleSet.len;
    for (unsigned int i = 0; i < count; i++)
      if (cov.intersects_coverage (c->glyphs, i)) {
	const RuleSet &rule_set = this+ruleSet[i];
	rule_set.closure (c, lookup_context);
      }
  }

  inline void collect_glyphs (hb_collect_glyphs_context_t *c) const
  {
    TRACE_COLLECT_GLYPHS (this);
    (this+coverage).add_coverage (&c->input);

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

    unsigned int count = ruleSet.len;
    for (unsigned int i = 0; i < count; i++)
	(this+ruleSet[i]).collect_glyphs (c, lookup_context);
  }

  inline bool would_apply (hb_would_apply_context_t *c) const
  {
    TRACE_WOULD_APPLY (this);

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

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

  inline bool apply (hb_apply_context_t *c) const
  {
    TRACE_APPLY (this);
    unsigned int index = (this+coverage) (c->buffer->cur().codepoint);
    if (likely (index == NOT_COVERED))
      return TRACE_RETURN (false);

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

  inline bool sanitize (hb_sanitize_context_t *c) {
    TRACE_SANITIZE (this);
    return TRACE_RETURN (coverage.sanitize (c, this) && ruleSet.sanitize (c, this));
  }

  protected:
  USHORT	format;			/* Format identifier--format = 1 */
  OffsetTo<Coverage>
		coverage;		/* Offset to Coverage table--from
					 * beginning of table */
  OffsetArrayOf<RuleSet>
		ruleSet;		/* Array of RuleSet tables
					 * ordered by Coverage Index */
  public:
  DEFINE_SIZE_ARRAY (6, ruleSet);
};


struct ContextFormat2
{
  inline void closure (hb_closure_context_t *c) const
  {
    TRACE_CLOSURE (this);
    if (!(this+coverage).intersects (c->glyphs))
      return;

    const ClassDef &class_def = this+classDef;

    struct ContextClosureLookupContext lookup_context = {
      {intersects_class},
      NULL
    };

    unsigned int count = ruleSet.len;
    for (unsigned int i = 0; i < count; i++)
      if (class_def.intersects_class (c->glyphs, i)) {
	const RuleSet &rule_set = this+ruleSet[i];
	rule_set.closure (c, lookup_context);
      }
  }

  inline void collect_glyphs (hb_collect_glyphs_context_t *c) const
  {
    TRACE_COLLECT_GLYPHS (this);
    (this+coverage).add_coverage (&c->input);

    struct ContextCollectGlyphsLookupContext lookup_context = {
      {collect_class},
      NULL
    };

    unsigned int count = ruleSet.len;
    for (unsigned int i = 0; i < count; i++)
	(this+ruleSet[i]).collect_glyphs (c, lookup_context);
  }

  inline bool would_apply (hb_would_apply_context_t *c) const
  {
    TRACE_WOULD_APPLY (this);

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

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

  inline bool apply (hb_apply_context_t *c) const
  {
    TRACE_APPLY (this);
    unsigned int index = (this+coverage) (c->buffer->cur().codepoint);
    if (likely (index == NOT_COVERED)) return TRACE_RETURN (false);

    const ClassDef &class_def = this+classDef;
    index = class_def (c->buffer->cur().codepoint);
    const RuleSet &rule_set = this+ruleSet[index];
    struct ContextApplyLookupContext lookup_context = {
      {match_class},
      &class_def
    };
    return TRACE_RETURN (rule_set.apply (c, lookup_context));
  }

  inline bool sanitize (hb_sanitize_context_t *c) {
    TRACE_SANITIZE (this);
    return TRACE_RETURN (coverage.sanitize (c, this) && classDef.sanitize (c, this) && ruleSet.sanitize (c, this));
  }

  protected:
  USHORT	format;			/* Format identifier--format = 2 */
  OffsetTo<Coverage>
		coverage;		/* Offset to Coverage table--from
					 * beginning of table */
  OffsetTo<ClassDef>
		classDef;		/* Offset to glyph ClassDef table--from
					 * beginning of table */
  OffsetArrayOf<RuleSet>
		ruleSet;		/* Array of RuleSet tables
					 * ordered by class */
  public:
  DEFINE_SIZE_ARRAY (8, ruleSet);
};


struct ContextFormat3
{
  inline void closure (hb_closure_context_t *c) const
  {
    TRACE_CLOSURE (this);
    if (!(this+coverage[0]).intersects (c->glyphs))
      return;

    const LookupRecord *lookupRecord = &StructAtOffset<LookupRecord> (coverage, coverage[0].static_size * glyphCount);
    struct ContextClosureLookupContext lookup_context = {
      {intersects_coverage},
      this
    };
    context_closure_lookup (c,
			    glyphCount, (const USHORT *) (coverage + 1),
			    lookupCount, lookupRecord,
			    lookup_context);
  }

  inline void collect_glyphs (hb_collect_glyphs_context_t *c) const
  {
    TRACE_COLLECT_GLYPHS (this);
    (this+coverage[0]).add_coverage (&c->input);

    const LookupRecord *lookupRecord = &StructAtOffset<LookupRecord> (coverage, coverage[0].static_size * glyphCount);
    struct ContextCollectGlyphsLookupContext lookup_context = {
      {collect_coverage},
      NULL
    };

    context_collect_glyphs_lookup (c,
				   glyphCount, (const USHORT *) (coverage + 1),
				   lookupCount, lookupRecord,
				   lookup_context);
  }

  inline bool would_apply (hb_would_apply_context_t *c) const
  {
    TRACE_WOULD_APPLY (this);

    const LookupRecord *lookupRecord = &StructAtOffset<LookupRecord> (coverage, coverage[0].static_size * glyphCount);
    struct ContextApplyLookupContext lookup_context = {
      {match_coverage},
      this
    };
    return TRACE_RETURN (context_would_apply_lookup (c, glyphCount, (const USHORT *) (coverage + 1), lookupCount, lookupRecord, lookup_context));
  }

  inline const Coverage &get_coverage (void) const
  {
    return this+coverage[0];
  }

  inline bool apply (hb_apply_context_t *c) const
  {
    TRACE_APPLY (this);
    unsigned int index = (this+coverage[0]) (c->buffer->cur().codepoint);
    if (likely (index == NOT_COVERED)) return TRACE_RETURN (false);

    const LookupRecord *lookupRecord = &StructAtOffset<LookupRecord> (coverage, coverage[0].static_size * glyphCount);
    struct ContextApplyLookupContext lookup_context = {
      {match_coverage},
      this
    };
    return TRACE_RETURN (context_apply_lookup (c, glyphCount, (const USHORT *) (coverage + 1), lookupCount, lookupRecord, lookup_context));
  }

  inline bool sanitize (hb_sanitize_context_t *c) {
    TRACE_SANITIZE (this);
    if (!c->check_struct (this)) return TRACE_RETURN (false);
    unsigned int count = glyphCount;
    if (!c->check_array (coverage, coverage[0].static_size, count)) return TRACE_RETURN (false);
    for (unsigned int i = 0; i < count; i++)
      if (!coverage[i].sanitize (c, this)) return TRACE_RETURN (false);
    LookupRecord *lookupRecord = &StructAtOffset<LookupRecord> (coverage, coverage[0].static_size * count);
    return TRACE_RETURN (c->check_array (lookupRecord, lookupRecord[0].static_size, lookupCount));
  }

  protected:
  USHORT	format;			/* Format identifier--format = 3 */
  USHORT	glyphCount;		/* Number of glyphs in the input glyph
					 * sequence */
  USHORT	lookupCount;		/* Number of LookupRecords */
  OffsetTo<Coverage>
		coverage[VAR];		/* Array of offsets to Coverage
					 * table in glyph sequence order */
  LookupRecord	lookupRecordX[VAR];	/* Array of LookupRecords--in
					 * design order */
  public:
  DEFINE_SIZE_ARRAY2 (6, coverage, lookupRecordX);
};

struct Context
{
  template <typename context_t>
  inline typename context_t::return_t process (context_t *c) const
  {
    TRACE_PROCESS (this);
    switch (u.format) {
    case 1: return TRACE_RETURN (c->process (u.format1));
    case 2: return TRACE_RETURN (c->process (u.format2));
    case 3: return TRACE_RETURN (c->process (u.format3));
    default:return TRACE_RETURN (c->default_return_value ());
    }
  }

  inline bool sanitize (hb_sanitize_context_t *c) {
    TRACE_SANITIZE (this);
    if (!u.format.sanitize (c)) return TRACE_RETURN (false);
    switch (u.format) {
    case 1: return TRACE_RETURN (u.format1.sanitize (c));
    case 2: return TRACE_RETURN (u.format2.sanitize (c));
    case 3: return TRACE_RETURN (u.format3.sanitize (c));
    default:return TRACE_RETURN (true);
    }
  }

  protected:
  union {
  USHORT		format;		/* Format identifier */
  ContextFormat1	format1;
  ContextFormat2	format2;
  ContextFormat3	format3;
  } u;
};


/* Chaining Contextual lookups */

struct ChainContextClosureLookupContext
{
  ContextClosureFuncs funcs;
  const void *intersects_data[3];
};

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

static inline void chain_context_closure_lookup (hb_closure_context_t *c,
						 unsigned int backtrackCount,
						 const USHORT backtrack[],
						 unsigned int inputCount, /* Including the first glyph (not matched) */
						 const USHORT input[], /* Array of input values--start with second glyph */
						 unsigned int lookaheadCount,
						 const USHORT lookahead[],
						 unsigned int lookupCount,
						 const LookupRecord lookupRecord[],
						 ChainContextClosureLookupContext &lookup_context)
{
  if (intersects_array (c,
			backtrackCount, backtrack,
			lookup_context.funcs.intersects, lookup_context.intersects_data[0])
   && intersects_array (c,
			inputCount ? inputCount - 1 : 0, input,
			lookup_context.funcs.intersects, lookup_context.intersects_data[1])
  && intersects_array (c,
		       lookaheadCount, lookahead,
		       lookup_context.funcs.intersects, lookup_context.intersects_data[2]))
    recurse_lookups (c,
		     lookupCount, lookupRecord);
}

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

static inline bool chain_context_apply_lookup (hb_apply_context_t *c,
					       unsigned int backtrackCount,
					       const USHORT backtrack[],
					       unsigned int inputCount, /* Including the first glyph (not matched) */
					       const USHORT input[], /* Array of input values--start with second glyph */
					       unsigned int lookaheadCount,
					       const USHORT lookahead[],
					       unsigned int lookupCount,
					       const LookupRecord lookupRecord[],
					       ChainContextApplyLookupContext &lookup_context)
{
  unsigned int lookahead_offset = 0;
  return match_input (c,
		      inputCount, input,
		      lookup_context.funcs.match, lookup_context.match_data[1],
		      &lookahead_offset)
      && match_backtrack (c,
			  backtrackCount, backtrack,
			  lookup_context.funcs.match, lookup_context.match_data[0])
      && match_lookahead (c,
			  lookaheadCount, lookahead,
			  lookup_context.funcs.match, lookup_context.match_data[2],
			  lookahead_offset)
      && apply_lookup (c,
		       inputCount,
		       lookupCount, lookupRecord);
}

struct ChainRule
{
  inline void closure (hb_closure_context_t *c, ChainContextClosureLookupContext &lookup_context) const
  {
    TRACE_CLOSURE (this);
    const HeadlessArrayOf<USHORT> &input = StructAfter<HeadlessArrayOf<USHORT> > (backtrack);
    const ArrayOf<USHORT> &lookahead = StructAfter<ArrayOf<USHORT> > (input);
    const ArrayOf<LookupRecord> &lookup = StructAfter<ArrayOf<LookupRecord> > (lookahead);
    chain_context_closure_lookup (c,
				  backtrack.len, backtrack.array,
				  input.len, input.array,
				  lookahead.len, lookahead.array,
				  lookup.len, lookup.array,
				  lookup_context);
  }

  inline bool would_apply (hb_would_apply_context_t *c, ChainContextApplyLookupContext &lookup_context) const
  {
    TRACE_WOULD_APPLY (this);
    const HeadlessArrayOf<USHORT> &input = StructAfter<HeadlessArrayOf<USHORT> > (backtrack);
    const ArrayOf<USHORT> &lookahead = StructAfter<ArrayOf<USHORT> > (input);
    const ArrayOf<LookupRecord> &lookup = StructAfter<ArrayOf<LookupRecord> > (lookahead);
    return TRACE_RETURN (chain_context_would_apply_lookup (c,
							   backtrack.len, backtrack.array,
							   input.len, input.array,
							   lookahead.len, lookahead.array, lookup.len,
							   lookup.array, lookup_context));
  }

  inline bool apply (hb_apply_context_t *c, ChainContextApplyLookupContext &lookup_context) const
  {
    TRACE_APPLY (this);
    const HeadlessArrayOf<USHORT> &input = StructAfter<HeadlessArrayOf<USHORT> > (backtrack);
    const ArrayOf<USHORT> &lookahead = StructAfter<ArrayOf<USHORT> > (input);
    const ArrayOf<LookupRecord> &lookup = StructAfter<ArrayOf<LookupRecord> > (lookahead);
    return TRACE_RETURN (chain_context_apply_lookup (c,
						     backtrack.len, backtrack.array,
						     input.len, input.array,
						     lookahead.len, lookahead.array, lookup.len,
						     lookup.array, lookup_context));
  }

  inline bool sanitize (hb_sanitize_context_t *c) {
    TRACE_SANITIZE (this);
    if (!backtrack.sanitize (c)) return TRACE_RETURN (false);
    HeadlessArrayOf<USHORT> &input = StructAfter<HeadlessArrayOf<USHORT> > (backtrack);
    if (!input.sanitize (c)) return TRACE_RETURN (false);
    ArrayOf<USHORT> &lookahead = StructAfter<ArrayOf<USHORT> > (input);
    if (!lookahead.sanitize (c)) return TRACE_RETURN (false);
    ArrayOf<LookupRecord> &lookup = StructAfter<ArrayOf<LookupRecord> > (lookahead);
    return TRACE_RETURN (lookup.sanitize (c));
  }

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

struct ChainRuleSet
{
  inline void closure (hb_closure_context_t *c, ChainContextClosureLookupContext &lookup_context) const
  {
    TRACE_CLOSURE (this);
    unsigned int num_rules = rule.len;
    for (unsigned int i = 0; i < num_rules; i++)
      (this+rule[i]).closure (c, lookup_context);
  }

  inline bool would_apply (hb_would_apply_context_t *c, ChainContextApplyLookupContext &lookup_context) const
  {
    TRACE_WOULD_APPLY (this);
    unsigned int num_rules = rule.len;
    for (unsigned int i = 0; i < num_rules; i++)
      if ((this+rule[i]).would_apply (c, lookup_context))
        return TRACE_RETURN (true);

    return TRACE_RETURN (false);
  }

  inline bool apply (hb_apply_context_t *c, ChainContextApplyLookupContext &lookup_context) const
  {
    TRACE_APPLY (this);
    unsigned int num_rules = rule.len;
    for (unsigned int i = 0; i < num_rules; i++)
      if ((this+rule[i]).apply (c, lookup_context))
        return TRACE_RETURN (true);

    return TRACE_RETURN (false);
  }

  inline bool sanitize (hb_sanitize_context_t *c) {
    TRACE_SANITIZE (this);
    return TRACE_RETURN (rule.sanitize (c, this));
  }

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

struct ChainContextFormat1
{
  inline void closure (hb_closure_context_t *c) const
  {
    TRACE_CLOSURE (this);
    const Coverage &cov = (this+coverage);

    struct ChainContextClosureLookupContext lookup_context = {
      {intersects_glyph},
      {NULL, NULL, NULL}
    };

    unsigned int count = ruleSet.len;
    for (unsigned int i = 0; i < count; i++)
      if (cov.intersects_coverage (c->glyphs, i)) {
	const ChainRuleSet &rule_set = this+ruleSet[i];
	rule_set.closure (c, lookup_context);
      }
  }

  inline void collect_glyphs (hb_collect_glyphs_context_t *c) const
  {
    /* XXXXXXXXXX */
  }

  inline bool would_apply (hb_would_apply_context_t *c) const
  {
    TRACE_WOULD_APPLY (this);

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

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

  inline bool apply (hb_apply_context_t *c) const
  {
    TRACE_APPLY (this);
    unsigned int index = (this+coverage) (c->buffer->cur().codepoint);
    if (likely (index == NOT_COVERED)) return TRACE_RETURN (false);

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

  inline bool sanitize (hb_sanitize_context_t *c) {
    TRACE_SANITIZE (this);
    return TRACE_RETURN (coverage.sanitize (c, this) && ruleSet.sanitize (c, this));
  }

  protected:
  USHORT	format;			/* Format identifier--format = 1 */
  OffsetTo<Coverage>
		coverage;		/* Offset to Coverage table--from
					 * beginning of table */
  OffsetArrayOf<ChainRuleSet>
		ruleSet;		/* Array of ChainRuleSet tables
					 * ordered by Coverage Index */
  public:
  DEFINE_SIZE_ARRAY (6, ruleSet);
};

struct ChainContextFormat2
{
  inline void closure (hb_closure_context_t *c) const
  {
    TRACE_CLOSURE (this);
    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;

    struct ChainContextClosureLookupContext lookup_context = {
      {intersects_class},
      {&backtrack_class_def,
       &input_class_def,
       &lookahead_class_def}
    };

    unsigned int count = ruleSet.len;
    for (unsigned int i = 0; i < count; i++)
      if (input_class_def.intersects_class (c->glyphs, i)) {
	const ChainRuleSet &rule_set = this+ruleSet[i];
	rule_set.closure (c, lookup_context);
      }
  }

  inline void collect_glyphs (hb_collect_glyphs_context_t *c) const
  {
    /* XXXXXXXXXX */
  }

  inline bool would_apply (hb_would_apply_context_t *c) const
  {
    TRACE_WOULD_APPLY (this);

    const ClassDef &input_class_def = this+inputClassDef;

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

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

  inline bool apply (hb_apply_context_t *c) const
  {
    TRACE_APPLY (this);
    unsigned int index = (this+coverage) (c->buffer->cur().codepoint);
    if (likely (index == NOT_COVERED)) return TRACE_RETURN (false);

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

    index = input_class_def (c->buffer->cur().codepoint);
    const ChainRuleSet &rule_set = this+ruleSet[index];
    struct ChainContextApplyLookupContext lookup_context = {
      {match_class},
      {&backtrack_class_def,
       &input_class_def,
       &lookahead_class_def}
    };
    return TRACE_RETURN (rule_set.apply (c, lookup_context));
  }

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

  protected:
  USHORT	format;			/* Format identifier--format = 2 */
  OffsetTo<Coverage>
		coverage;		/* Offset to Coverage table--from
					 * beginning of table */
  OffsetTo<ClassDef>
		backtrackClassDef;	/* Offset to glyph ClassDef table
					 * containing backtrack sequence
					 * data--from beginning of table */
  OffsetTo<ClassDef>
		inputClassDef;		/* Offset to glyph ClassDef
					 * table containing input sequence
					 * data--from beginning of table */
  OffsetTo<ClassDef>
		lookaheadClassDef;	/* Offset to glyph ClassDef table
					 * containing lookahead sequence
					 * data--from beginning of table */
  OffsetArrayOf<ChainRuleSet>
		ruleSet;		/* Array of ChainRuleSet tables
					 * ordered by class */
  public:
  DEFINE_SIZE_ARRAY (12, ruleSet);
};

struct ChainContextFormat3
{
  inline void closure (hb_closure_context_t *c) const
  {
    TRACE_CLOSURE (this);
    const OffsetArrayOf<Coverage> &input = StructAfter<OffsetArrayOf<Coverage> > (backtrack);

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

    const OffsetArrayOf<Coverage> &lookahead = StructAfter<OffsetArrayOf<Coverage> > (input);
    const ArrayOf<LookupRecord> &lookup = StructAfter<ArrayOf<LookupRecord> > (lookahead);
    struct ChainContextClosureLookupContext lookup_context = {
      {intersects_coverage},
      {this, this, this}
    };
    chain_context_closure_lookup (c,
				  backtrack.len, (const USHORT *) backtrack.array,
				  input.len, (const USHORT *) input.array + 1,
				  lookahead.len, (const USHORT *) lookahead.array,
				  lookup.len, lookup.array,
				  lookup_context);
  }

  inline void collect_glyphs (hb_collect_glyphs_context_t *c) const
  {
    /* XXXXXXXXXX */
  }

  inline bool would_apply (hb_would_apply_context_t *c) const
  {
    TRACE_WOULD_APPLY (this);

    const OffsetArrayOf<Coverage> &input = StructAfter<OffsetArrayOf<Coverage> > (backtrack);
    const OffsetArrayOf<Coverage> &lookahead = StructAfter<OffsetArrayOf<Coverage> > (input);
    const ArrayOf<LookupRecord> &lookup = StructAfter<ArrayOf<LookupRecord> > (lookahead);
    struct ChainContextApplyLookupContext lookup_context = {
      {match_coverage},
      {this, this, this}
    };
    return TRACE_RETURN (chain_context_would_apply_lookup (c,
							   backtrack.len, (const USHORT *) backtrack.array,
							   input.len, (const USHORT *) input.array + 1,
							   lookahead.len, (const USHORT *) lookahead.array,
							   lookup.len, lookup.array, lookup_context));
  }

  inline const Coverage &get_coverage (void) const
  {
    const OffsetArrayOf<Coverage> &input = StructAfter<OffsetArrayOf<Coverage> > (backtrack);
    return this+input[0];
  }

  inline bool apply (hb_apply_context_t *c) const
  {
    TRACE_APPLY (this);
    const OffsetArrayOf<Coverage> &input = StructAfter<OffsetArrayOf<Coverage> > (backtrack);

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

    const OffsetArrayOf<Coverage> &lookahead = StructAfter<OffsetArrayOf<Coverage> > (input);
    const ArrayOf<LookupRecord> &lookup = StructAfter<ArrayOf<LookupRecord> > (lookahead);
    struct ChainContextApplyLookupContext lookup_context = {
      {match_coverage},
      {this, this, this}
    };
    return TRACE_RETURN (chain_context_apply_lookup (c,
						     backtrack.len, (const USHORT *) backtrack.array,
						     input.len, (const USHORT *) input.array + 1,
						     lookahead.len, (const USHORT *) lookahead.array,
						     lookup.len, lookup.array, lookup_context));
  }

  inline bool sanitize (hb_sanitize_context_t *c) {
    TRACE_SANITIZE (this);
    if (!backtrack.sanitize (c, this)) return TRACE_RETURN (false);
    OffsetArrayOf<Coverage> &input = StructAfter<OffsetArrayOf<Coverage> > (backtrack);
    if (!input.sanitize (c, this)) return TRACE_RETURN (false);
    OffsetArrayOf<Coverage> &lookahead = StructAfter<OffsetArrayOf<Coverage> > (input);
    if (!lookahead.sanitize (c, this)) return TRACE_RETURN (false);
    ArrayOf<LookupRecord> &lookup = StructAfter<ArrayOf<LookupRecord> > (lookahead);
    return TRACE_RETURN (lookup.sanitize (c));
  }

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

struct ChainContext
{
  template <typename context_t>
  inline typename context_t::return_t process (context_t *c) const
  {
    TRACE_PROCESS (this);
    switch (u.format) {
    case 1: return TRACE_RETURN (c->process (u.format1));
    case 2: return TRACE_RETURN (c->process (u.format2));
    case 3: return TRACE_RETURN (c->process (u.format3));
    default:return TRACE_RETURN (c->default_return_value ());
    }
  }

  inline bool sanitize (hb_sanitize_context_t *c) {
    TRACE_SANITIZE (this);
    if (!u.format.sanitize (c)) return TRACE_RETURN (false);
    switch (u.format) {
    case 1: return TRACE_RETURN (u.format1.sanitize (c));
    case 2: return TRACE_RETURN (u.format2.sanitize (c));
    case 3: return TRACE_RETURN (u.format3.sanitize (c));
    default:return TRACE_RETURN (true);
    }
  }

  protected:
  union {
  USHORT		format;	/* Format identifier */
  ChainContextFormat1	format1;
  ChainContextFormat2	format2;
  ChainContextFormat3	format3;
  } u;
};


struct ExtensionFormat1
{
  inline unsigned int get_type (void) const { return extensionLookupType; }
  inline unsigned int get_offset (void) const { return extensionOffset; }

  inline bool sanitize (hb_sanitize_context_t *c) {
    TRACE_SANITIZE (this);
    return TRACE_RETURN (c->check_struct (this));
  }

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

template <typename T>
struct Extension
{
  inline unsigned int get_type (void) const
  {
    switch (u.format) {
    case 1: return u.format1.get_type ();
    default:return 0;
    }
  }
  inline unsigned int get_offset (void) const
  {
    switch (u.format) {
    case 1: return u.format1.get_offset ();
    default:return 0;
    }
  }

  template <typename X>
  inline const X& get_subtable (void) const
  {
    unsigned int offset = get_offset ();
    if (unlikely (!offset)) return Null(typename T::LookupSubTable);
    return StructAtOffset<typename T::LookupSubTable> (this, offset);
  }

  template <typename context_t>
  inline typename context_t::return_t process (context_t *c) const
  {
    return get_subtable<typename T::LookupSubTable> ().process (c, get_type ());
  }

  inline bool sanitize_self (hb_sanitize_context_t *c) {
    TRACE_SANITIZE (this);
    if (!u.format.sanitize (c)) return TRACE_RETURN (false);
    switch (u.format) {
    case 1: return TRACE_RETURN (u.format1.sanitize (c));
    default:return TRACE_RETURN (true);
    }
  }

  inline bool sanitize (hb_sanitize_context_t *c) {
    TRACE_SANITIZE (this);
    if (!sanitize_self (c)) return TRACE_RETURN (false);
    unsigned int offset = get_offset ();
    if (unlikely (!offset)) return TRACE_RETURN (true);
    return TRACE_RETURN (StructAtOffset<typename T::LookupSubTable> (this, offset).sanitize (c, get_type ()));
  }

  protected:
  union {
  USHORT		format;		/* Format identifier */
  ExtensionFormat1	format1;
  } u;
};


/*
 * GSUB/GPOS Common
 */

struct GSUBGPOS
{
  static const hb_tag_t GSUBTag	= HB_OT_TAG_GSUB;
  static const hb_tag_t GPOSTag	= HB_OT_TAG_GPOS;

  inline unsigned int get_script_count (void) const
  { return (this+scriptList).len; }
  inline const Tag& get_script_tag (unsigned int i) const
  { return (this+scriptList).get_tag (i); }
  inline unsigned int get_script_tags (unsigned int start_offset,
				       unsigned int *script_count /* IN/OUT */,
				       hb_tag_t     *script_tags /* OUT */) const
  { return (this+scriptList).get_tags (start_offset, script_count, script_tags); }
  inline const Script& get_script (unsigned int i) const
  { return (this+scriptList)[i]; }
  inline bool find_script_index (hb_tag_t tag, unsigned int *index) const
  { return (this+scriptList).find_index (tag, index); }

  inline unsigned int get_feature_count (void) const
  { return (this+featureList).len; }
  inline const Tag& get_feature_tag (unsigned int i) const
  { return (this+featureList).get_tag (i); }
  inline unsigned int get_feature_tags (unsigned int start_offset,
					unsigned int *feature_count /* IN/OUT */,
					hb_tag_t     *feature_tags /* OUT */) const
  { return (this+featureList).get_tags (start_offset, feature_count, feature_tags); }
  inline const Feature& get_feature (unsigned int i) const
  { return (this+featureList)[i]; }
  inline bool find_feature_index (hb_tag_t tag, unsigned int *index) const
  { return (this+featureList).find_index (tag, index); }

  inline unsigned int get_lookup_count (void) const
  { return (this+lookupList).len; }
  inline const Lookup& get_lookup (unsigned int i) const
  { return (this+lookupList)[i]; }

  inline bool sanitize (hb_sanitize_context_t *c) {
    TRACE_SANITIZE (this);
    return TRACE_RETURN (version.sanitize (c) && likely (version.major == 1) &&
			 scriptList.sanitize (c, this) &&
			 featureList.sanitize (c, this) &&
			 lookupList.sanitize (c, this));
  }

  protected:
  FixedVersion	version;	/* Version of the GSUB/GPOS table--initially set
				 * to 0x00010000 */
  OffsetTo<ScriptList>
		scriptList;  	/* ScriptList table */
  OffsetTo<FeatureList>
		featureList; 	/* FeatureList table */
  OffsetTo<LookupList>
		lookupList; 	/* LookupList table */
  public:
  DEFINE_SIZE_STATIC (10);
};


} /* namespace OT */


#endif /* HB_OT_LAYOUT_GSUBGPOS_PRIVATE_HH */