harfbuzz: check in harfbuzz-ng, add gyp define to use it

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

+/*
+ * Copyright (C) 2007,2008,2009,2010  Red Hat, Inc.
+ * Copyright (C) 2010  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-private.hh"
+
+HB_BEGIN_DECLS
+
+
+/* buffer var allocations */
+#define lig_id() var2.u16[0] /* unique ligature id */
+#define lig_comp() var2.u16[1] /* component number in the ligature (0 = base) */
+
+
+#ifndef HB_DEBUG_APPLY
+#define HB_DEBUG_APPLY (HB_DEBUG+0)
+#endif
+
+#define TRACE_APPLY() \
+        hb_trace_t<HB_DEBUG_APPLY> trace (&c->debug_depth, "APPLY", HB_FUNC, this); \
+
+
+HB_BEGIN_DECLS
+
+struct hb_apply_context_t
+{
+  unsigned int debug_depth;
+  hb_ot_layout_context_t *layout;
+  hb_buffer_t *buffer;
+  hb_mask_t lookup_mask;
+  unsigned int context_length;
+  unsigned int nesting_level_left;
+  unsigned int lookup_props;
+  unsigned int property; /* propety of first glyph */
+
+
+  inline void replace_glyph (hb_codepoint_t glyph_index) const
+  {
+    clear_property ();
+    buffer->replace_glyph (glyph_index);
+  }
+  inline void replace_glyphs_be16 (unsigned int num_in,
+                                   unsigned int num_out,
+                                   const uint16_t *glyph_data_be) const
+  {
+    clear_property ();
+    buffer->replace_glyphs_be16 (num_in, num_out, glyph_data_be);
+  }
+
+  inline void guess_glyph_class (unsigned int klass)
+  {
+    /* XXX if ! has gdef */
+    buffer->info[buffer->i].props_cache() = klass;
+  }
+
+  private:
+  inline void clear_property (void) const
+  {
+    /* XXX if has gdef */
+    buffer->info[buffer->i].props_cache() = 0;
+  }
+};
+
+
+
+typedef bool (*match_func_t) (hb_codepoint_t glyph_id, const USHORT &value, const void *data);
+typedef bool (*apply_lookup_func_t) (hb_apply_context_t *c, unsigned int lookup_index);
+
+struct ContextFuncs
+{
+  match_func_t match;
+  apply_lookup_func_t apply;
+};
+
+
+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) (glyph_id) != NOT_COVERED;
+}
+
+
+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 *context_length_out)
+{
+  unsigned int i, j;
+  unsigned int end = MIN (c->buffer->len, c->buffer->i + c->context_length);
+  if (unlikely (c->buffer->i + count > end))
+    return false;
+
+  for (i = 1, j = c->buffer->i + 1; i < count; i++, j++)
+  {
+    while (_hb_ot_layout_skip_mark (c->layout->face, &c->buffer->info[j], c->lookup_props, NULL))
+    {
+      if (unlikely (j + count - i == end))
+        return false;
+      j++;
+    }
+
+    if (likely (!match_func (c->buffer->info[j].codepoint, input[i - 1], match_data)))
+      return false;
+  }
+
+  *context_length_out = j - c->buffer->i;
+
+  return true;
+}
+
+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)
+{
+  if (unlikely (c->buffer->out_len < count))
+    return false;
+
+  for (unsigned int i = 0, j = c->buffer->out_len - 1; i < count; i++, j--)
+  {
+    while (_hb_ot_layout_skip_mark (c->layout->face, &c->buffer->out_info[j], c->lookup_props, NULL))
+    {
+      if (unlikely (j + 1 == count - i))
+        return false;
+      j--;
+    }
+
+    if (likely (!match_func (c->buffer->out_info[j].codepoint, backtrack[i], match_data)))
+      return false;
+  }
+
+  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)
+{
+  unsigned int i, j;
+  unsigned int end = MIN (c->buffer->len, c->buffer->i + c->context_length);
+  if (unlikely (c->buffer->i + offset + count > end))
+    return false;
+
+  for (i = 0, j = c->buffer->i + offset; i < count; i++, j++)
+  {
+    while (_hb_ot_layout_skip_mark (c->layout->face, &c->buffer->info[j], c->lookup_props, NULL))
+    {
+      if (unlikely (j + count - i == end))
+        return false;
+      j++;
+    }
+
+    if (likely (!match_func (c->buffer->info[j].codepoint, lookahead[i], match_data)))
+      return false;
+  }
+
+  return true;
+}
+
+HB_END_DECLS
+
+
+struct LookupRecord
+{
+  inline bool sanitize (hb_sanitize_context_t *c) {
+    TRACE_SANITIZE ();
+    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);
+};
+
+
+HB_BEGIN_DECLS
+
+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 */
+                                 apply_lookup_func_t apply_func)
+{
+  unsigned int end = MIN (c->buffer->len, c->buffer->i + c->context_length);
+  if (unlikely (count == 0 || c->buffer->i + count > end))
+    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 */)
+  {
+    while (_hb_ot_layout_skip_mark (c->layout->face, &c->buffer->info[c->buffer->i], c->lookup_props, NULL))
+    {
+      if (unlikely (c->buffer->i == end))
+        return true;
+      /* No lookup applied for this index */
+      c->buffer->next_glyph ();
+    }
+
+    if (lookupCount && i == lookupRecord->sequenceIndex)
+    {
+      unsigned int old_pos = c->buffer->i;
+
+      /* Apply a lookup */
+      bool done = apply_func (c, lookupRecord->lookupListIndex);
+
+      lookupRecord++;
+      lookupCount--;
+      /* Err, this is wrong if the lookup jumped over some glyphs */
+      i += c->buffer->i - old_pos;
+      if (unlikely (c->buffer->i == end))
+        return true;
+
+      if (!done)
+        goto not_applied;
+    }
+    else
+    {
+    not_applied:
+      /* No lookup applied for this index */
+      c->buffer->next_glyph ();
+      i++;
+    }
+  }
+
+  return true;
+}
+
+HB_END_DECLS
+
+
+/* Contextual lookups */
+
+struct ContextLookupContext
+{
+  ContextFuncs funcs;
+  const void *match_data;
+};
+
+static inline bool context_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[],
+                                   ContextLookupContext &lookup_context)
+{
+  hb_apply_context_t new_context = *c;
+  return match_input (c,
+                      inputCount, input,
+                      lookup_context.funcs.match, lookup_context.match_data,
+                      &new_context.context_length)
+      && apply_lookup (&new_context,
+                       inputCount,
+                       lookupCount, lookupRecord,
+                       lookup_context.funcs.apply);
+}
+
+struct Rule
+{
+  friend struct RuleSet;
+
+  private:
+  inline bool apply (hb_apply_context_t *c, ContextLookupContext &lookup_context) const
+  {
+    TRACE_APPLY ();
+    const LookupRecord *lookupRecord = &StructAtOffset<LookupRecord> (input, input[0].static_size * (inputCount ? inputCount - 1 : 0));
+    return context_lookup (c,
+                           inputCount, input,
+                           lookupCount, lookupRecord,
+                           lookup_context);
+  }
+
+  public:
+  inline bool sanitize (hb_sanitize_context_t *c) {
+    TRACE_SANITIZE ();
+    return inputCount.sanitize (c)
+        && lookupCount.sanitize (c)
+        && c->check_range (input,
+                                 input[0].static_size * inputCount
+                                 + lookupRecordX[0].static_size * lookupCount);
+  }
+
+  private:
+  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 bool apply (hb_apply_context_t *c, ContextLookupContext &lookup_context) const
+  {
+    TRACE_APPLY ();
+    unsigned int num_rules = rule.len;
+    for (unsigned int i = 0; i < num_rules; i++)
+    {
+      if ((this+rule[i]).apply (c, lookup_context))
+        return true;
+    }
+
+    return false;
+  }
+
+  inline bool sanitize (hb_sanitize_context_t *c) {
+    TRACE_SANITIZE ();
+    return rule.sanitize (c, this);
+  }
+
+  private:
+  OffsetArrayOf<Rule>
+                rule;                   /* Array of Rule tables
+                                         * ordered by preference */
+  public:
+  DEFINE_SIZE_ARRAY (2, rule);
+};
+
+
+struct ContextFormat1
+{
+  friend struct Context;
+
+  private:
+  inline bool apply (hb_apply_context_t *c, apply_lookup_func_t apply_func) const
+  {
+    TRACE_APPLY ();
+    unsigned int index = (this+coverage) (c->buffer->info[c->buffer->i].codepoint);
+    if (likely (index == NOT_COVERED))
+      return false;
+
+    const RuleSet &rule_set = this+ruleSet[index];
+    struct ContextLookupContext lookup_context = {
+      {match_glyph, apply_func},
+      NULL
+    };
+    return rule_set.apply (c, lookup_context);
+  }
+
+  inline bool sanitize (hb_sanitize_context_t *c) {
+    TRACE_SANITIZE ();
+    return coverage.sanitize (c, this)
+        && ruleSet.sanitize (c, this);
+  }
+
+  private:
+  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
+{
+  friend struct Context;
+
+  private:
+  inline bool apply (hb_apply_context_t *c, apply_lookup_func_t apply_func) const
+  {
+    TRACE_APPLY ();
+    unsigned int index = (this+coverage) (c->buffer->info[c->buffer->i].codepoint);
+    if (likely (index == NOT_COVERED))
+      return false;
+
+    const ClassDef &class_def = this+classDef;
+    index = class_def (c->buffer->info[c->buffer->i].codepoint);
+    const RuleSet &rule_set = this+ruleSet[index];
+    struct ContextLookupContext lookup_context = {
+      {match_class, apply_func},
+      &class_def
+    };
+    return rule_set.apply (c, lookup_context);
+  }
+
+  inline bool sanitize (hb_sanitize_context_t *c) {
+    TRACE_SANITIZE ();
+    return coverage.sanitize (c, this)
+        && classDef.sanitize (c, this)
+        && ruleSet.sanitize (c, this);
+  }
+
+  private:
+  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
+{
+  friend struct Context;
+
+  private:
+  inline bool apply (hb_apply_context_t *c, apply_lookup_func_t apply_func) const
+  {
+    TRACE_APPLY ();
+    unsigned int index = (this+coverage[0]) (c->buffer->info[c->buffer->i].codepoint);
+    if (likely (index == NOT_COVERED))
+      return false;
+
+    const LookupRecord *lookupRecord = &StructAtOffset<LookupRecord> (coverage, coverage[0].static_size * glyphCount);
+    struct ContextLookupContext lookup_context = {
+      {match_coverage, apply_func},
+      this
+    };
+    return context_lookup (c,
+                           glyphCount, (const USHORT *) (coverage + 1),
+                           lookupCount, lookupRecord,
+                           lookup_context);
+  }
+
+  inline bool sanitize (hb_sanitize_context_t *c) {
+    TRACE_SANITIZE ();
+    if (!c->check_struct (this)) return false;
+    unsigned int count = glyphCount;
+    if (!c->check_array (coverage, coverage[0].static_size, count)) return false;
+    for (unsigned int i = 0; i < count; i++)
+      if (!coverage[i].sanitize (c, this)) return false;
+    LookupRecord *lookupRecord = &StructAtOffset<LookupRecord> (coverage, coverage[0].static_size * count);
+    return c->check_array (lookupRecord, lookupRecord[0].static_size, lookupCount);
+  }
+
+  private:
+  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
+{
+  protected:
+  inline bool apply (hb_apply_context_t *c, apply_lookup_func_t apply_func) const
+  {
+    TRACE_APPLY ();
+    switch (u.format) {
+    case 1: return u.format1.apply (c, apply_func);
+    case 2: return u.format2.apply (c, apply_func);
+    case 3: return u.format3.apply (c, apply_func);
+    default:return false;
+    }
+  }
+
+  inline bool sanitize (hb_sanitize_context_t *c) {
+    TRACE_SANITIZE ();
+    if (!u.format.sanitize (c)) return false;
+    switch (u.format) {
+    case 1: return u.format1.sanitize (c);
+    case 2: return u.format2.sanitize (c);
+    case 3: return u.format3.sanitize (c);
+    default:return true;
+    }
+  }
+
+  private:
+  union {
+  USHORT                format;         /* Format identifier */
+  ContextFormat1        format1;
+  ContextFormat2        format2;
+  ContextFormat3        format3;
+  } u;
+};
+
+
+/* Chaining Contextual lookups */
+
+struct ChainContextLookupContext
+{
+  ContextFuncs funcs;
+  const void *match_data[3];
+};
+
+static inline bool chain_context_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[],
+                                         ChainContextLookupContext &lookup_context)
+{
+  /* First guess */
+  if (unlikely (c->buffer->out_len < backtrackCount ||
+                c->buffer->i + inputCount + lookaheadCount > c->buffer->len ||
+                inputCount + lookaheadCount > c->context_length))
+    return false;
+
+  hb_apply_context_t new_context = *c;
+  return match_backtrack (c,
+                          backtrackCount, backtrack,
+                          lookup_context.funcs.match, lookup_context.match_data[0])
+      && match_input (c,
+                      inputCount, input,
+                      lookup_context.funcs.match, lookup_context.match_data[1],
+                      &new_context.context_length)
+      && match_lookahead (c,
+                          lookaheadCount, lookahead,
+                          lookup_context.funcs.match, lookup_context.match_data[2],
+                          new_context.context_length)
+      && apply_lookup (&new_context,
+                       inputCount,
+                       lookupCount, lookupRecord,
+                       lookup_context.funcs.apply);
+}
+
+struct ChainRule
+{
+  friend struct ChainRuleSet;
+
+  private:
+  inline bool apply (hb_apply_context_t *c, ChainContextLookupContext &lookup_context) const
+  {
+    TRACE_APPLY ();
+    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 chain_context_lookup (c,
+                                 backtrack.len, backtrack.array,
+                                 input.len, input.array,
+                                 lookahead.len, lookahead.array,
+                                 lookup.len, lookup.array,
+                                 lookup_context);
+  }
+
+  public:
+  inline bool sanitize (hb_sanitize_context_t *c) {
+    TRACE_SANITIZE ();
+    if (!backtrack.sanitize (c)) return false;
+    HeadlessArrayOf<USHORT> &input = StructAfter<HeadlessArrayOf<USHORT> > (backtrack);
+    if (!input.sanitize (c)) return false;
+    ArrayOf<USHORT> &lookahead = StructAfter<ArrayOf<USHORT> > (input);
+    if (!lookahead.sanitize (c)) return false;
+    ArrayOf<LookupRecord> &lookup = StructAfter<ArrayOf<LookupRecord> > (lookahead);
+    return lookup.sanitize (c);
+  }
+
+  private:
+  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 bool apply (hb_apply_context_t *c, ChainContextLookupContext &lookup_context) const
+  {
+    TRACE_APPLY ();
+    unsigned int num_rules = rule.len;
+    for (unsigned int i = 0; i < num_rules; i++)
+    {
+      if ((this+rule[i]).apply (c, lookup_context))
+        return true;
+    }
+
+    return false;
+  }
+
+  inline bool sanitize (hb_sanitize_context_t *c) {
+    TRACE_SANITIZE ();
+    return rule.sanitize (c, this);
+  }
+
+  private:
+  OffsetArrayOf<ChainRule>
+                rule;                   /* Array of ChainRule tables
+                                         * ordered by preference */
+  public:
+  DEFINE_SIZE_ARRAY (2, rule);
+};
+
+struct ChainContextFormat1
+{
+  friend struct ChainContext;
+
+  private:
+  inline bool apply (hb_apply_context_t *c, apply_lookup_func_t apply_func) const
+  {
+    TRACE_APPLY ();
+    unsigned int index = (this+coverage) (c->buffer->info[c->buffer->i].codepoint);
+    if (likely (index == NOT_COVERED))
+      return false;
+
+    const ChainRuleSet &rule_set = this+ruleSet[index];
+    struct ChainContextLookupContext lookup_context = {
+      {match_glyph, apply_func},
+      {NULL, NULL, NULL}
+    };
+    return rule_set.apply (c, lookup_context);
+  }
+
+  inline bool sanitize (hb_sanitize_context_t *c) {
+    TRACE_SANITIZE ();
+    return coverage.sanitize (c, this)
+        && ruleSet.sanitize (c, this);
+  }
+
+  private:
+  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
+{
+  friend struct ChainContext;
+
+  private:
+  inline bool apply (hb_apply_context_t *c, apply_lookup_func_t apply_func) const
+  {
+    TRACE_APPLY ();
+    unsigned int index = (this+coverage) (c->buffer->info[c->buffer->i].codepoint);
+    if (likely (index == NOT_COVERED))
+      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->info[c->buffer->i].codepoint);
+    const ChainRuleSet &rule_set = this+ruleSet[index];
+    struct ChainContextLookupContext lookup_context = {
+      {match_class, apply_func},
+      {&backtrack_class_def,
+       &input_class_def,
+       &lookahead_class_def}
+    };
+    return rule_set.apply (c, lookup_context);
+  }
+
+  inline bool sanitize (hb_sanitize_context_t *c) {
+    TRACE_SANITIZE ();
+    return coverage.sanitize (c, this)
+        && backtrackClassDef.sanitize (c, this)
+        && inputClassDef.sanitize (c, this)
+        && lookaheadClassDef.sanitize (c, this)
+        && ruleSet.sanitize (c, this);
+  }
+
+  private:
+  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
+{
+  friend struct ChainContext;
+
+  private:
+
+  inline bool apply (hb_apply_context_t *c, apply_lookup_func_t apply_func) const
+  {
+    TRACE_APPLY ();
+    const OffsetArrayOf<Coverage> &input = StructAfter<OffsetArrayOf<Coverage> > (backtrack);
+
+    unsigned int index = (this+input[0]) (c->buffer->info[c->buffer->i].codepoint);
+    if (likely (index == NOT_COVERED))
+      return false;
+
+    const OffsetArrayOf<Coverage> &lookahead = StructAfter<OffsetArrayOf<Coverage> > (input);
+    const ArrayOf<LookupRecord> &lookup = StructAfter<ArrayOf<LookupRecord> > (lookahead);
+    struct ChainContextLookupContext lookup_context = {
+      {match_coverage, apply_func},
+      {this, this, this}
+    };
+    return chain_context_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 ();
+    if (!backtrack.sanitize (c, this)) return false;
+    OffsetArrayOf<Coverage> &input = StructAfter<OffsetArrayOf<Coverage> > (backtrack);
+    if (!input.sanitize (c, this)) return false;
+    OffsetArrayOf<Coverage> &lookahead = StructAfter<OffsetArrayOf<Coverage> > (input);
+    if (!lookahead.sanitize (c, this)) return false;
+    ArrayOf<LookupRecord> &lookup = StructAfter<ArrayOf<LookupRecord> > (lookahead);
+    return lookup.sanitize (c);
+  }
+
+  private:
+  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
+{
+  protected:
+  inline bool apply (hb_apply_context_t *c, apply_lookup_func_t apply_func) const
+  {
+    TRACE_APPLY ();
+    switch (u.format) {
+    case 1: return u.format1.apply (c, apply_func);
+    case 2: return u.format2.apply (c, apply_func);
+    case 3: return u.format3.apply (c, apply_func);
+    default:return false;
+    }
+  }
+
+  inline bool sanitize (hb_sanitize_context_t *c) {
+    TRACE_SANITIZE ();
+    if (!u.format.sanitize (c)) return false;
+    switch (u.format) {
+    case 1: return u.format1.sanitize (c);
+    case 2: return u.format2.sanitize (c);
+    case 3: return u.format3.sanitize (c);
+    default:return true;
+    }
+  }
+
+  private:
+  union {
+  USHORT                format; /* Format identifier */
+  ChainContextFormat1   format1;
+  ChainContextFormat2   format2;
+  ChainContextFormat3   format3;
+  } u;
+};
+
+
+struct ExtensionFormat1
+{
+  friend struct Extension;
+
+  protected:
+  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 ();
+    return c->check_struct (this);
+  }
+
+  private:
+  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);
+};
+
+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;
+    }
+  }
+
+  inline bool sanitize (hb_sanitize_context_t *c) {
+    TRACE_SANITIZE ();
+    if (!u.format.sanitize (c)) return false;
+    switch (u.format) {
+    case 1: return u.format1.sanitize (c);
+    default:return true;
+    }
+  }
+
+  private:
+  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 ();
+    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);
+};
+
+
+HB_END_DECLS
+
+#endif /* HB_OT_LAYOUT_GSUBGPOS_PRIVATE_HH */