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

third_party/harfbuzz-ng/src/hb-ot-layout-gsub-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_GSUB_PRIVATE_HH
+#define HB_OT_LAYOUT_GSUB_PRIVATE_HH
+
+#include "hb-ot-layout-gsubgpos-private.hh"
+
+HB_BEGIN_DECLS
+
+
+struct SingleSubstFormat1
+{
+  friend struct SingleSubst;
+
+  private:
+
+  inline bool apply (hb_apply_context_t *c) const
+  {
+    TRACE_APPLY ();
+    hb_codepoint_t glyph_id = c->buffer->info[c->buffer->i].codepoint;
+    unsigned int index = (this+coverage) (glyph_id);
+    if (likely (index == NOT_COVERED))
+      return false;
+
+    glyph_id += deltaGlyphID;
+    c->replace_glyph (glyph_id);
+
+    return true;
+  }
+
+  inline bool sanitize (hb_sanitize_context_t *c) {
+    TRACE_SANITIZE ();
+    return coverage.sanitize (c, this)
+        && deltaGlyphID.sanitize (c);
+  }
+
+  private:
+  USHORT        format;                 /* Format identifier--format = 1 */
+  OffsetTo<Coverage>
+                coverage;               /* Offset to Coverage table--from
+                                         * beginning of Substitution table */
+  SHORT         deltaGlyphID;           /* Add to original GlyphID to get
+                                         * substitute GlyphID */
+  public:
+  DEFINE_SIZE_STATIC (6);
+};
+
+struct SingleSubstFormat2
+{
+  friend struct SingleSubst;
+
+  private:
+
+  inline bool apply (hb_apply_context_t *c) const
+  {
+    TRACE_APPLY ();
+    hb_codepoint_t glyph_id = c->buffer->info[c->buffer->i].codepoint;
+    unsigned int index = (this+coverage) (glyph_id);
+    if (likely (index == NOT_COVERED))
+      return false;
+
+    if (unlikely (index >= substitute.len))
+      return false;
+
+    glyph_id = substitute[index];
+    c->replace_glyph (glyph_id);
+
+    return true;
+  }
+
+  inline bool sanitize (hb_sanitize_context_t *c) {
+    TRACE_SANITIZE ();
+    return coverage.sanitize (c, this)
+        && substitute.sanitize (c);
+  }
+
+  private:
+  USHORT        format;                 /* Format identifier--format = 2 */
+  OffsetTo<Coverage>
+                coverage;               /* Offset to Coverage table--from
+                                         * beginning of Substitution table */
+  ArrayOf<GlyphID>
+                substitute;             /* Array of substitute
+                                         * GlyphIDs--ordered by Coverage Index */
+  public:
+  DEFINE_SIZE_ARRAY (6, substitute);
+};
+
+struct SingleSubst
+{
+  friend struct SubstLookupSubTable;
+
+  private:
+
+  inline bool apply (hb_apply_context_t *c) const
+  {
+    TRACE_APPLY ();
+    switch (u.format) {
+    case 1: return u.format1.apply (c);
+    case 2: return u.format2.apply (c);
+    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);
+    default:return true;
+    }
+  }
+
+  private:
+  union {
+  USHORT                format;         /* Format identifier */
+  SingleSubstFormat1    format1;
+  SingleSubstFormat2    format2;
+  } u;
+};
+
+
+struct Sequence
+{
+  friend struct MultipleSubstFormat1;
+
+  private:
+  inline bool apply (hb_apply_context_t *c) const
+  {
+    TRACE_APPLY ();
+    if (unlikely (!substitute.len))
+      return false;
+
+    if (c->property & HB_OT_LAYOUT_GLYPH_CLASS_LIGATURE)
+      c->guess_glyph_class (HB_OT_LAYOUT_GLYPH_CLASS_BASE_GLYPH);
+    c->replace_glyphs_be16 (1, substitute.len, (const uint16_t *) substitute.array);
+
+    return true;
+  }
+
+  public:
+  inline bool sanitize (hb_sanitize_context_t *c) {
+    TRACE_SANITIZE ();
+    return substitute.sanitize (c);
+  }
+
+  private:
+  ArrayOf<GlyphID>
+                substitute;             /* String of GlyphIDs to substitute */
+  public:
+  DEFINE_SIZE_ARRAY (2, substitute);
+};
+
+struct MultipleSubstFormat1
+{
+  friend struct MultipleSubst;
+
+  private:
+
+  inline bool apply (hb_apply_context_t *c) const
+  {
+    TRACE_APPLY ();
+
+    unsigned int index = (this+coverage) (c->buffer->info[c->buffer->i].codepoint);
+    if (likely (index == NOT_COVERED))
+      return false;
+
+    return (this+sequence[index]).apply (c);
+  }
+
+  inline bool sanitize (hb_sanitize_context_t *c) {
+    TRACE_SANITIZE ();
+    return coverage.sanitize (c, this)
+        && sequence.sanitize (c, this);
+  }
+
+  private:
+  USHORT        format;                 /* Format identifier--format = 1 */
+  OffsetTo<Coverage>
+                coverage;               /* Offset to Coverage table--from
+                                         * beginning of Substitution table */
+  OffsetArrayOf<Sequence>
+                sequence;               /* Array of Sequence tables
+                                         * ordered by Coverage Index */
+  public:
+  DEFINE_SIZE_ARRAY (6, sequence);
+};
+
+struct MultipleSubst
+{
+  friend struct SubstLookupSubTable;
+
+  private:
+
+  inline bool apply (hb_apply_context_t *c) const
+  {
+    TRACE_APPLY ();
+    switch (u.format) {
+    case 1: return u.format1.apply (c);
+    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);
+    default:return true;
+    }
+  }
+
+  private:
+  union {
+  USHORT                format;         /* Format identifier */
+  MultipleSubstFormat1  format1;
+  } u;
+};
+
+
+typedef ArrayOf<GlyphID> AlternateSet;  /* Array of alternate GlyphIDs--in
+                                         * arbitrary order */
+
+struct AlternateSubstFormat1
+{
+  friend struct AlternateSubst;
+
+  private:
+
+  inline bool apply (hb_apply_context_t *c) const
+  {
+    TRACE_APPLY ();
+    hb_codepoint_t glyph_id = c->buffer->info[c->buffer->i].codepoint;
+    hb_mask_t glyph_mask = c->buffer->info[c->buffer->i].mask;
+    hb_mask_t lookup_mask = c->lookup_mask;
+
+    unsigned int index = (this+coverage) (glyph_id);
+    if (likely (index == NOT_COVERED))
+      return false;
+
+    const AlternateSet &alt_set = this+alternateSet[index];
+
+    if (unlikely (!alt_set.len))
+      return false;
+
+    /* Note: This breaks badly if two features enabled this lookup together. */
+    unsigned int shift = _hb_ctz (lookup_mask);
+    unsigned int alt_index = ((lookup_mask & glyph_mask) >> shift);
+
+    if (unlikely (alt_index > alt_set.len || alt_index == 0))
+      return false;
+
+    glyph_id = alt_set[alt_index - 1];
+
+    c->replace_glyph (glyph_id);
+
+    return true;
+  }
+
+  inline bool sanitize (hb_sanitize_context_t *c) {
+    TRACE_SANITIZE ();
+    return coverage.sanitize (c, this)
+        && alternateSet.sanitize (c, this);
+  }
+
+  private:
+  USHORT        format;                 /* Format identifier--format = 1 */
+  OffsetTo<Coverage>
+                coverage;               /* Offset to Coverage table--from
+                                         * beginning of Substitution table */
+  OffsetArrayOf<AlternateSet>
+                alternateSet;           /* Array of AlternateSet tables
+                                         * ordered by Coverage Index */
+  public:
+  DEFINE_SIZE_ARRAY (6, alternateSet);
+};
+
+struct AlternateSubst
+{
+  friend struct SubstLookupSubTable;
+
+  private:
+
+  inline bool apply (hb_apply_context_t *c) const
+  {
+    TRACE_APPLY ();
+    switch (u.format) {
+    case 1: return u.format1.apply (c);
+    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);
+    default:return true;
+    }
+  }
+
+  private:
+  union {
+  USHORT                format;         /* Format identifier */
+  AlternateSubstFormat1 format1;
+  } u;
+};
+
+
+struct Ligature
+{
+  friend struct LigatureSet;
+
+  private:
+  inline bool apply (hb_apply_context_t *c) const
+  {
+    TRACE_APPLY ();
+    unsigned int i, j;
+    unsigned int count = component.len;
+    unsigned int end = MIN (c->buffer->len, c->buffer->i + c->context_length);
+    if (unlikely (count < 2 || c->buffer->i + count > end))
+      return false;
+
+    bool first_was_mark = (c->property & HB_OT_LAYOUT_GLYPH_CLASS_MARK);
+    bool found_non_mark = false;
+
+    for (i = 1, j = c->buffer->i + 1; i < count; i++, j++)
+    {
+      unsigned int property;
+      while (_hb_ot_layout_skip_mark (c->layout->face, &c->buffer->info[j], c->lookup_props, &property))
+      {
+        if (unlikely (j + count - i == end))
+          return false;
+        j++;
+      }
+
+      found_non_mark |= !(property & HB_OT_LAYOUT_GLYPH_CLASS_MARK);
+
+      if (likely (c->buffer->info[j].codepoint != component[i]))
+        return false;
+    }
+
+    if (first_was_mark && found_non_mark)
+      c->guess_glyph_class (HB_OT_LAYOUT_GLYPH_CLASS_LIGATURE);
+
+    /* Allocate new ligature id */
+    unsigned int lig_id = allocate_lig_id (c->buffer);
+    c->buffer->info[c->buffer->i].lig_comp() = 0;
+    c->buffer->info[c->buffer->i].lig_id() = lig_id;
+
+    if (j == c->buffer->i + i) /* No input glyphs skipped */
+    {
+      c->replace_glyphs_be16 (i, 1, (const uint16_t *) &ligGlyph);
+    }
+    else
+    {
+      c->replace_glyph (ligGlyph);
+
+      /* Now we must do a second loop to copy the skipped glyphs to
+         `out' and assign component values to it.  We start with the
+         glyph after the first component.  Glyphs between component
+         i and i+1 belong to component i.  Together with the lig_id
+         value it is later possible to check whether a specific
+         component value really belongs to a given ligature. */
+
+      for (i = 1; i < count; i++)
+      {
+        while (_hb_ot_layout_skip_mark (c->layout->face, &c->buffer->info[c->buffer->i], c->lookup_props, NULL))
+        {
+          c->buffer->info[c->buffer->i].lig_comp() = i;
+          c->buffer->info[c->buffer->i].lig_id() = lig_id;
+          c->replace_glyph (c->buffer->info[c->buffer->i].codepoint);
+        }
+
+        /* Skip the base glyph */
+        c->buffer->i++;
+      }
+    }
+
+    return true;
+  }
+
+  inline uint16_t allocate_lig_id (hb_buffer_t *buffer) const {
+    uint16_t lig_id = buffer->next_serial ();
+    if (unlikely (!lig_id)) lig_id = buffer->next_serial (); /* in case of overflows */
+    return lig_id;
+  }
+
+  public:
+  inline bool sanitize (hb_sanitize_context_t *c) {
+    TRACE_SANITIZE ();
+    return ligGlyph.sanitize (c)
+        && component.sanitize (c);
+  }
+
+  private:
+  GlyphID       ligGlyph;               /* GlyphID of ligature to substitute */
+  HeadlessArrayOf<GlyphID>
+                component;              /* Array of component GlyphIDs--start
+                                         * with the second  component--ordered
+                                         * in writing direction */
+  public:
+  DEFINE_SIZE_ARRAY (4, component);
+};
+
+struct LigatureSet
+{
+  friend struct LigatureSubstFormat1;
+
+  private:
+  inline bool apply (hb_apply_context_t *c) const
+  {
+    TRACE_APPLY ();
+    unsigned int num_ligs = ligature.len;
+    for (unsigned int i = 0; i < num_ligs; i++)
+    {
+      const Ligature &lig = this+ligature[i];
+      if (lig.apply (c))
+        return true;
+    }
+
+    return false;
+  }
+
+  public:
+  inline bool sanitize (hb_sanitize_context_t *c) {
+    TRACE_SANITIZE ();
+    return ligature.sanitize (c, this);
+  }
+
+  private:
+  OffsetArrayOf<Ligature>
+                ligature;               /* Array LigatureSet tables
+                                         * ordered by preference */
+  public:
+  DEFINE_SIZE_ARRAY (2, ligature);
+};
+
+struct LigatureSubstFormat1
+{
+  friend struct LigatureSubst;
+
+  private:
+  inline bool apply (hb_apply_context_t *c) const
+  {
+    TRACE_APPLY ();
+    hb_codepoint_t glyph_id = c->buffer->info[c->buffer->i].codepoint;
+
+    unsigned int index = (this+coverage) (glyph_id);
+    if (likely (index == NOT_COVERED))
+      return false;
+
+    const LigatureSet &lig_set = this+ligatureSet[index];
+    return lig_set.apply (c);
+  }
+
+  inline bool sanitize (hb_sanitize_context_t *c) {
+    TRACE_SANITIZE ();
+    return coverage.sanitize (c, this)
+        && ligatureSet.sanitize (c, this);
+  }
+
+  private:
+  USHORT        format;                 /* Format identifier--format = 1 */
+  OffsetTo<Coverage>
+                coverage;               /* Offset to Coverage table--from
+                                         * beginning of Substitution table */
+  OffsetArrayOf<LigatureSet>
+                ligatureSet;            /* Array LigatureSet tables
+                                         * ordered by Coverage Index */
+  public:
+  DEFINE_SIZE_ARRAY (6, ligatureSet);
+};
+
+struct LigatureSubst
+{
+  friend struct SubstLookupSubTable;
+
+  private:
+  inline bool apply (hb_apply_context_t *c) const
+  {
+    TRACE_APPLY ();
+    switch (u.format) {
+    case 1: return u.format1.apply (c);
+    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);
+    default:return true;
+    }
+  }
+
+  private:
+  union {
+  USHORT                format;         /* Format identifier */
+  LigatureSubstFormat1  format1;
+  } u;
+};
+
+
+HB_BEGIN_DECLS
+static inline bool substitute_lookup (hb_apply_context_t *c, unsigned int lookup_index);
+HB_END_DECLS
+
+struct ContextSubst : Context
+{
+  friend struct SubstLookupSubTable;
+
+  private:
+  inline bool apply (hb_apply_context_t *c) const
+  {
+    TRACE_APPLY ();
+    return Context::apply (c, substitute_lookup);
+  }
+};
+
+struct ChainContextSubst : ChainContext
+{
+  friend struct SubstLookupSubTable;
+
+  private:
+  inline bool apply (hb_apply_context_t *c) const
+  {
+    TRACE_APPLY ();
+    return ChainContext::apply (c, substitute_lookup);
+  }
+};
+
+
+struct ExtensionSubst : Extension
+{
+  friend struct SubstLookupSubTable;
+  friend struct SubstLookup;
+
+  private:
+  inline const struct SubstLookupSubTable& get_subtable (void) const
+  {
+    unsigned int offset = get_offset ();
+    if (unlikely (!offset)) return Null(SubstLookupSubTable);
+    return StructAtOffset<SubstLookupSubTable> (this, offset);
+  }
+
+  inline bool apply (hb_apply_context_t *c) const;
+
+  inline bool sanitize (hb_sanitize_context_t *c);
+
+  inline bool is_reverse (void) const;
+};
+
+
+struct ReverseChainSingleSubstFormat1
+{
+  friend struct ReverseChainSingleSubst;
+
+  private:
+  inline bool apply (hb_apply_context_t *c) const
+  {
+    TRACE_APPLY ();
+    if (unlikely (c->context_length != NO_CONTEXT))
+      return false; /* No chaining to this type */
+
+    unsigned int index = (this+coverage) (c->buffer->info[c->buffer->i].codepoint);
+    if (likely (index == NOT_COVERED))
+      return false;
+
+    const OffsetArrayOf<Coverage> &lookahead = StructAfter<OffsetArrayOf<Coverage> > (backtrack);
+    const ArrayOf<GlyphID> &substitute = StructAfter<ArrayOf<GlyphID> > (lookahead);
+
+    if (match_backtrack (c,
+                         backtrack.len, (USHORT *) backtrack.array,
+                         match_coverage, this) &&
+        match_lookahead (c,
+                         lookahead.len, (USHORT *) lookahead.array,
+                         match_coverage, this,
+                         1))
+    {
+      c->buffer->info[c->buffer->i].codepoint = substitute[index];
+      c->buffer->i--; /* Reverse! */
+      return true;
+    }
+
+    return false;
+  }
+
+  inline bool sanitize (hb_sanitize_context_t *c) {
+    TRACE_SANITIZE ();
+    if (!(coverage.sanitize (c, this)
+       && backtrack.sanitize (c, this)))
+      return false;
+    OffsetArrayOf<Coverage> &lookahead = StructAfter<OffsetArrayOf<Coverage> > (backtrack);
+    if (!lookahead.sanitize (c, this))
+      return false;
+    ArrayOf<GlyphID> &substitute = StructAfter<ArrayOf<GlyphID> > (lookahead);
+    return substitute.sanitize (c);
+  }
+
+  private:
+  USHORT        format;                 /* Format identifier--format = 1 */
+  OffsetTo<Coverage>
+                coverage;               /* Offset to Coverage table--from
+                                         * beginning of table */
+  OffsetArrayOf<Coverage>
+                backtrack;              /* Array of coverage tables
+                                         * in backtracking sequence, in  glyph
+                                         * sequence order */
+  OffsetArrayOf<Coverage>
+                lookaheadX;             /* Array of coverage tables
+                                         * in lookahead sequence, in glyph
+                                         * sequence order */
+  ArrayOf<GlyphID>
+                substituteX;            /* Array of substitute
+                                         * GlyphIDs--ordered by Coverage Index */
+  public:
+  DEFINE_SIZE_MIN (10);
+};
+
+struct ReverseChainSingleSubst
+{
+  friend struct SubstLookupSubTable;
+
+  private:
+  inline bool apply (hb_apply_context_t *c) const
+  {
+    TRACE_APPLY ();
+    switch (u.format) {
+    case 1: return u.format1.apply (c);
+    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);
+    default:return true;
+    }
+  }
+
+  private:
+  union {
+  USHORT                                format;         /* Format identifier */
+  ReverseChainSingleSubstFormat1        format1;
+  } u;
+};
+
+
+
+/*
+ * SubstLookup
+ */
+
+struct SubstLookupSubTable
+{
+  friend struct SubstLookup;
+
+  enum {
+    Single              = 1,
+    Multiple            = 2,
+    Alternate           = 3,
+    Ligature            = 4,
+    Context             = 5,
+    ChainContext        = 6,
+    Extension           = 7,
+    ReverseChainSingle  = 8
+  };
+
+  inline bool apply (hb_apply_context_t *c, unsigned int lookup_type) const
+  {
+    TRACE_APPLY ();
+    switch (lookup_type) {
+    case Single:                return u.single.apply (c);
+    case Multiple:              return u.multiple.apply (c);
+    case Alternate:             return u.alternate.apply (c);
+    case Ligature:              return u.ligature.apply (c);
+    case Context:               return u.c.apply (c);
+    case ChainContext:          return u.chainContext.apply (c);
+    case Extension:             return u.extension.apply (c);
+    case ReverseChainSingle:    return u.reverseChainContextSingle.apply (c);
+    default:return false;
+    }
+  }
+
+  inline bool sanitize (hb_sanitize_context_t *c, unsigned int lookup_type) {
+    TRACE_SANITIZE ();
+    switch (lookup_type) {
+    case Single:                return u.single.sanitize (c);
+    case Multiple:              return u.multiple.sanitize (c);
+    case Alternate:             return u.alternate.sanitize (c);
+    case Ligature:              return u.ligature.sanitize (c);
+    case Context:               return u.c.sanitize (c);
+    case ChainContext:          return u.chainContext.sanitize (c);
+    case Extension:             return u.extension.sanitize (c);
+    case ReverseChainSingle:    return u.reverseChainContextSingle.sanitize (c);
+    default:return true;
+    }
+  }
+
+  private:
+  union {
+  USHORT                        sub_format;
+  SingleSubst                   single;
+  MultipleSubst                 multiple;
+  AlternateSubst                alternate;
+  LigatureSubst                 ligature;
+  ContextSubst                  c;
+  ChainContextSubst             chainContext;
+  ExtensionSubst                extension;
+  ReverseChainSingleSubst       reverseChainContextSingle;
+  } u;
+  public:
+  DEFINE_SIZE_UNION (2, sub_format);
+};
+
+
+struct SubstLookup : Lookup
+{
+  inline const SubstLookupSubTable& get_subtable (unsigned int i) const
+  { return this+CastR<OffsetArrayOf<SubstLookupSubTable> > (subTable)[i]; }
+
+  inline static bool lookup_type_is_reverse (unsigned int lookup_type)
+  { return lookup_type == SubstLookupSubTable::ReverseChainSingle; }
+
+  inline bool is_reverse (void) const
+  {
+    unsigned int type = get_type ();
+    if (unlikely (type == SubstLookupSubTable::Extension))
+      return CastR<ExtensionSubst> (get_subtable(0)).is_reverse ();
+    return lookup_type_is_reverse (type);
+  }
+
+
+  inline bool apply_once (hb_ot_layout_context_t *layout,
+                          hb_buffer_t *buffer,
+                          hb_mask_t lookup_mask,
+                          unsigned int context_length,
+                          unsigned int nesting_level_left) const
+  {
+    unsigned int lookup_type = get_type ();
+    hb_apply_context_t c[1] = {{0}};
+
+    c->layout = layout;
+    c->buffer = buffer;
+    c->lookup_mask = lookup_mask;
+    c->context_length = context_length;
+    c->nesting_level_left = nesting_level_left;
+    c->lookup_props = get_props ();
+
+    if (!_hb_ot_layout_check_glyph_property (c->layout->face, &c->buffer->info[c->buffer->i], c->lookup_props, &c->property))
+      return false;
+
+    if (unlikely (lookup_type == SubstLookupSubTable::Extension))
+    {
+      /* The spec says all subtables should have the same type.
+       * This is specially important if one has a reverse type!
+       *
+       * This is rather slow to do this here for every glyph,
+       * but it's easiest, and who uses extension lookups anyway?!*/
+      unsigned int count = get_subtable_count ();
+      unsigned int type = get_subtable(0).u.extension.get_type ();
+      for (unsigned int i = 1; i < count; i++)
+        if (get_subtable(i).u.extension.get_type () != type)
+          return false;
+    }
+
+    unsigned int count = get_subtable_count ();
+    for (unsigned int i = 0; i < count; i++)
+      if (get_subtable (i).apply (c, lookup_type))
+        return true;
+
+    return false;
+  }
+
+  inline bool apply_string (hb_ot_layout_context_t *layout,
+                            hb_buffer_t *buffer,
+                            hb_mask_t    mask) const
+  {
+    bool ret = false;
+
+    if (unlikely (!buffer->len))
+      return false;
+
+    if (likely (!is_reverse ()))
+    {
+        /* in/out forward substitution */
+        buffer->clear_output ();
+        buffer->i = 0;
+        while (buffer->i < buffer->len)
+        {
+          if ((buffer->info[buffer->i].mask & mask) &&
+              apply_once (layout, buffer, mask, NO_CONTEXT, MAX_NESTING_LEVEL))
+            ret = true;
+          else
+            buffer->next_glyph ();
+
+        }
+        if (ret)
+          buffer->swap ();
+    }
+    else
+    {
+        /* in-place backward substitution */
+        buffer->i = buffer->len - 1;
+        do
+        {
+          if ((buffer->info[buffer->i].mask & mask) &&
+              apply_once (layout, buffer, mask, NO_CONTEXT, MAX_NESTING_LEVEL))
+            ret = true;
+          else
+            buffer->i--;
+
+        }
+        while ((int) buffer->i >= 0);
+    }
+
+    return ret;
+  }
+
+  inline bool sanitize (hb_sanitize_context_t *c) {
+    TRACE_SANITIZE ();
+    if (unlikely (!Lookup::sanitize (c))) return false;
+    OffsetArrayOf<SubstLookupSubTable> &list = CastR<OffsetArrayOf<SubstLookupSubTable> > (subTable);
+    return list.sanitize (c, this, get_type ());
+  }
+};
+
+typedef OffsetListOf<SubstLookup> SubstLookupList;
+
+/*
+ * GSUB
+ */
+
+struct GSUB : GSUBGPOS
+{
+  static const hb_tag_t Tag     = HB_OT_TAG_GSUB;
+
+  inline const SubstLookup& get_lookup (unsigned int i) const
+  { return CastR<SubstLookup> (GSUBGPOS::get_lookup (i)); }
+
+  inline bool substitute_lookup (hb_ot_layout_context_t *layout,
+                                 hb_buffer_t  *buffer,
+                                 unsigned int  lookup_index,
+                                 hb_mask_t     mask) const
+  { return get_lookup (lookup_index).apply_string (layout, buffer, mask); }
+
+  inline bool sanitize (hb_sanitize_context_t *c) {
+    TRACE_SANITIZE ();
+    if (unlikely (!GSUBGPOS::sanitize (c))) return false;
+    OffsetTo<SubstLookupList> &list = CastR<OffsetTo<SubstLookupList> > (lookupList);
+    return list.sanitize (c, this);
+  }
+  public:
+  DEFINE_SIZE_STATIC (10);
+};
+
+
+/* Out-of-class implementation for methods recursing */
+
+inline bool ExtensionSubst::apply (hb_apply_context_t *c) const
+{
+  TRACE_APPLY ();
+  return get_subtable ().apply (c, get_type ());
+}
+
+inline bool ExtensionSubst::sanitize (hb_sanitize_context_t *c)
+{
+  TRACE_SANITIZE ();
+  if (unlikely (!Extension::sanitize (c))) return false;
+  unsigned int offset = get_offset ();
+  if (unlikely (!offset)) return true;
+  return StructAtOffset<SubstLookupSubTable> (this, offset).sanitize (c, get_type ());
+}
+
+inline bool ExtensionSubst::is_reverse (void) const
+{
+  unsigned int type = get_type ();
+  if (unlikely (type == SubstLookupSubTable::Extension))
+    return CastR<ExtensionSubst> (get_subtable()).is_reverse ();
+  return SubstLookup::lookup_type_is_reverse (type);
+}
+
+static inline bool substitute_lookup (hb_apply_context_t *c, unsigned int lookup_index)
+{
+  const GSUB &gsub = *(c->layout->face->ot_layout->gsub);
+  const SubstLookup &l = gsub.get_lookup (lookup_index);
+
+  if (unlikely (c->nesting_level_left == 0))
+    return false;
+
+  if (unlikely (c->context_length < 1))
+    return false;
+
+  return l.apply_once (c->layout, c->buffer, c->lookup_mask, c->context_length, c->nesting_level_left - 1);
+}
+
+
+HB_END_DECLS
+
+#endif /* HB_OT_LAYOUT_GSUB_PRIVATE_HH */