Add m-esr52 at 52.6.0

1 files changed, 2329 insertions, 0 deletions

diff --git a/gfx/harfbuzz/src/hb-ot-layout-gsubgpos-private.hh b/gfx/harfbuzz/src/hb-ot-layout-gsubgpos-private.hh
new file mode 100644
index 000000000..c4de40386
--- /dev/null
+++ b/gfx/harfbuzz/src/hb-ot-layout-gsubgpos-private.hh
@@ -0,0 +1,2329 @@
+/*
+ * 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 {
+
+
+#ifndef HB_DEBUG_CLOSURE
+#define HB_DEBUG_CLOSURE (HB_DEBUG+0)
+#endif
+
+#define TRACE_CLOSURE(this) \
+	hb_auto_trace_t<HB_DEBUG_CLOSURE, hb_void_t> trace \
+	(&c->debug_depth, c->get_name (), this, HB_FUNC, \
+	 "");
+
+struct hb_closure_context_t :
+       hb_dispatch_context_t<hb_closure_context_t, hb_void_t, HB_DEBUG_CLOSURE>
+{
+  inline const char *get_name (void) { return "CLOSURE"; }
+  typedef return_t (*recurse_func_t) (hb_closure_context_t *c, unsigned int lookup_index);
+  template <typename T>
+  inline return_t dispatch (const T &obj) { obj.closure (this); return HB_VOID; }
+  static return_t default_return_value (void) { return HB_VOID; }
+  bool stop_sublookup_iteration (return_t r HB_UNUSED) 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 HB_VOID;
+  }
+
+  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_ = HB_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 :
+       hb_dispatch_context_t<hb_would_apply_context_t, bool, HB_DEBUG_WOULD_APPLY>
+{
+  inline const char *get_name (void) { return "WOULD_APPLY"; }
+  template <typename T>
+  inline return_t dispatch (const T &obj) { return obj.would_apply (this); }
+  static return_t default_return_value (void) { return false; }
+  bool stop_sublookup_iteration (return_t r) const { return r; }
+
+  hb_face_t *face;
+  const hb_codepoint_t *glyphs;
+  unsigned int len;
+  bool zero_context;
+  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, hb_void_t> trace \
+	(&c->debug_depth, c->get_name (), this, HB_FUNC, \
+	 "");
+
+struct hb_collect_glyphs_context_t :
+       hb_dispatch_context_t<hb_collect_glyphs_context_t, hb_void_t, HB_DEBUG_COLLECT_GLYPHS>
+{
+  inline const char *get_name (void) { return "COLLECT_GLYPHS"; }
+  typedef return_t (*recurse_func_t) (hb_collect_glyphs_context_t *c, unsigned int lookup_index);
+  template <typename T>
+  inline return_t dispatch (const T &obj) { obj.collect_glyphs (this); return HB_VOID; }
+  static return_t default_return_value (void) { return HB_VOID; }
+  bool stop_sublookup_iteration (return_t r HB_UNUSED) const { return false; }
+  return_t recurse (unsigned int lookup_index)
+  {
+    if (unlikely (nesting_level_left == 0 || !recurse_func))
+      return default_return_value ();
+
+    /* Note that GPOS sets recurse_func to NULL already, so it doesn't get
+     * past the previous check.  For GSUB, we only want to collect the output
+     * glyphs in the recursion.  If output is not requested, we can go home now.
+     *
+     * Note further, that the above is not exactly correct.  A recursed lookup
+     * is allowed to match input that is not matched in the context, but that's
+     * not how most fonts are built.  It's possible to relax that and recurse
+     * with all sets here if it proves to be an issue.
+     */
+
+    if (output == hb_set_get_empty ())
+      return HB_VOID;
+
+    /* Return if new lookup was recursed to before. */
+    if (recursed_lookups.has (lookup_index))
+      return HB_VOID;
+
+    hb_set_t *old_before = before;
+    hb_set_t *old_input  = input;
+    hb_set_t *old_after  = after;
+    before = input = after = hb_set_get_empty ();
+
+    nesting_level_left--;
+    recurse_func (this, lookup_index);
+    nesting_level_left++;
+
+    before = old_before;
+    input  = old_input;
+    after  = old_after;
+
+    recursed_lookups.add (lookup_index);
+
+    return HB_VOID;
+  }
+
+  hb_face_t *face;
+  hb_set_t *before;
+  hb_set_t *input;
+  hb_set_t *after;
+  hb_set_t *output;
+  recurse_func_t recurse_func;
+  hb_set_t recursed_lookups;
+  unsigned int nesting_level_left;
+  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_ = HB_MAX_NESTING_LEVEL) :
+			      face (face_),
+			      before (glyphs_before ? glyphs_before : hb_set_get_empty ()),
+			      input  (glyphs_input  ? glyphs_input  : hb_set_get_empty ()),
+			      after  (glyphs_after  ? glyphs_after  : hb_set_get_empty ()),
+			      output (glyphs_output ? glyphs_output : hb_set_get_empty ()),
+			      recurse_func (NULL),
+			      recursed_lookups (),
+			      nesting_level_left (nesting_level_left_),
+			      debug_depth (0)
+  {
+    recursed_lookups.init ();
+  }
+  ~hb_collect_glyphs_context_t (void)
+  {
+    recursed_lookups.fini ();
+  }
+
+  void set_recurse_func (recurse_func_t func) { recurse_func = func; }
+};
+
+
+
+#ifndef HB_DEBUG_GET_COVERAGE
+#define HB_DEBUG_GET_COVERAGE (HB_DEBUG+0)
+#endif
+
+/* XXX Can we remove this? */
+
+template <typename set_t>
+struct hb_add_coverage_context_t :
+       hb_dispatch_context_t<hb_add_coverage_context_t<set_t>, const Coverage &, HB_DEBUG_GET_COVERAGE>
+{
+  inline const char *get_name (void) { return "GET_COVERAGE"; }
+  typedef const Coverage &return_t;
+  template <typename T>
+  inline return_t dispatch (const T &obj) { return obj.get_coverage (); }
+  static return_t default_return_value (void) { return Null(Coverage); }
+  bool stop_sublookup_iteration (return_t r) const
+  {
+    r.add_coverage (set);
+    return false;
+  }
+
+  hb_add_coverage_context_t (set_t *set_) :
+			    set (set_),
+			    debug_depth (0) {}
+
+  set_t *set;
+  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 gid %u lookup %d", \
+	 c->buffer->idx, c->buffer->cur().codepoint, (int) c->lookup_index);
+
+struct hb_apply_context_t :
+       hb_dispatch_context_t<hb_apply_context_t, bool, HB_DEBUG_APPLY>
+{
+  struct matcher_t
+  {
+    inline matcher_t (void) :
+	     lookup_props (0),
+	     ignore_zwnj (false),
+	     ignore_zwj (false),
+	     mask (-1),
+#define arg1(arg) (arg) /* Remove the macro to see why it's needed! */
+	     syllable arg1(0),
+#undef arg1
+	     match_func (NULL),
+	     match_data (NULL) {};
+
+    typedef bool (*match_func_t) (hb_codepoint_t glyph_id, const USHORT &value, const void *data);
+
+    inline void set_ignore_zwnj (bool ignore_zwnj_) { ignore_zwnj = ignore_zwnj_; }
+    inline void set_ignore_zwj (bool ignore_zwj_) { ignore_zwj = ignore_zwj_; }
+    inline void set_lookup_props (unsigned int lookup_props_) { lookup_props = lookup_props_; }
+    inline void set_mask (hb_mask_t mask_) { mask = mask_; }
+    inline void set_syllable (uint8_t syllable_)  { syllable = syllable_; }
+    inline void set_match_func (match_func_t match_func_,
+				const void *match_data_)
+    { match_func = match_func_; match_data = match_data_; }
+
+    enum may_match_t {
+      MATCH_NO,
+      MATCH_YES,
+      MATCH_MAYBE
+    };
+
+    inline may_match_t may_match (const hb_glyph_info_t &info,
+				  const USHORT          *glyph_data) const
+    {
+      if (!(info.mask & mask) ||
+	  (syllable && syllable != info.syllable ()))
+	return MATCH_NO;
+
+      if (match_func)
+        return match_func (info.codepoint, *glyph_data, match_data) ? MATCH_YES : MATCH_NO;
+
+      return MATCH_MAYBE;
+    }
+
+    enum may_skip_t {
+      SKIP_NO,
+      SKIP_YES,
+      SKIP_MAYBE
+    };
+
+    inline may_skip_t
+    may_skip (const hb_apply_context_t *c,
+	      const hb_glyph_info_t    &info) const
+    {
+      if (!c->check_glyph_property (&info, lookup_props))
+	return SKIP_YES;
+
+      if (unlikely (_hb_glyph_info_is_default_ignorable_and_not_fvs (&info) &&
+		    (ignore_zwnj || !_hb_glyph_info_is_zwnj (&info)) &&
+		    (ignore_zwj || !_hb_glyph_info_is_zwj (&info))))
+	return SKIP_MAYBE;
+
+      return SKIP_NO;
+    }
+
+    protected:
+    unsigned int lookup_props;
+    bool ignore_zwnj;
+    bool ignore_zwj;
+    hb_mask_t mask;
+    uint8_t syllable;
+    match_func_t match_func;
+    const void *match_data;
+  };
+
+  struct skipping_iterator_t
+  {
+    inline void init (hb_apply_context_t *c_, bool context_match = false)
+    {
+      c = c_;
+      match_glyph_data = NULL,
+      matcher.set_match_func (NULL, NULL);
+      matcher.set_lookup_props (c->lookup_props);
+      /* Ignore ZWNJ if we are matching GSUB context, or matching GPOS. */
+      matcher.set_ignore_zwnj (context_match || c->table_index == 1);
+      /* Ignore ZWJ if we are matching GSUB context, or matching GPOS, or if asked to. */
+      matcher.set_ignore_zwj (context_match || c->table_index == 1 || c->auto_zwj);
+      matcher.set_mask (context_match ? -1 : c->lookup_mask);
+    }
+    inline void set_lookup_props (unsigned int lookup_props)
+    {
+      matcher.set_lookup_props (lookup_props);
+    }
+    inline void set_match_func (matcher_t::match_func_t match_func_,
+				const void *match_data_,
+				const USHORT glyph_data[])
+    {
+      matcher.set_match_func (match_func_, match_data_);
+      match_glyph_data = glyph_data;
+    }
+
+    inline void reset (unsigned int start_index_,
+		       unsigned int num_items_)
+    {
+      idx = start_index_;
+      num_items = num_items_;
+      end = c->buffer->len;
+      matcher.set_syllable (start_index_ == c->buffer->idx ? c->buffer->cur().syllable () : 0);
+    }
+
+    inline void reject (void) { num_items++; match_glyph_data--; }
+
+    inline bool next (void)
+    {
+      assert (num_items > 0);
+      while (idx + num_items < end)
+      {
+	idx++;
+	const hb_glyph_info_t &info = c->buffer->info[idx];
+
+	matcher_t::may_skip_t skip = matcher.may_skip (c, info);
+	if (unlikely (skip == matcher_t::SKIP_YES))
+	  continue;
+
+	matcher_t::may_match_t match = matcher.may_match (info, match_glyph_data);
+	if (match == matcher_t::MATCH_YES ||
+	    (match == matcher_t::MATCH_MAYBE &&
+	     skip == matcher_t::SKIP_NO))
+	{
+	  num_items--;
+	  match_glyph_data++;
+	  return true;
+	}
+
+	if (skip == matcher_t::SKIP_NO)
+	  return false;
+      }
+      return false;
+    }
+    inline bool prev (void)
+    {
+      assert (num_items > 0);
+      while (idx >= num_items)
+      {
+	idx--;
+	const hb_glyph_info_t &info = c->buffer->out_info[idx];
+
+	matcher_t::may_skip_t skip = matcher.may_skip (c, info);
+	if (unlikely (skip == matcher_t::SKIP_YES))
+	  continue;
+
+	matcher_t::may_match_t match = matcher.may_match (info, match_glyph_data);
+	if (match == matcher_t::MATCH_YES ||
+	    (match == matcher_t::MATCH_MAYBE &&
+	     skip == matcher_t::SKIP_NO))
+	{
+	  num_items--;
+	  match_glyph_data++;
+	  return true;
+	}
+
+	if (skip == matcher_t::SKIP_NO)
+	  return false;
+      }
+      return false;
+    }
+
+    unsigned int idx;
+    protected:
+    hb_apply_context_t *c;
+    matcher_t matcher;
+    const USHORT *match_glyph_data;
+
+    unsigned int num_items;
+    unsigned int end;
+  };
+
+
+  inline const char *get_name (void) { return "APPLY"; }
+  typedef return_t (*recurse_func_t) (hb_apply_context_t *c, unsigned int lookup_index);
+  template <typename T>
+  inline return_t dispatch (const T &obj) { return obj.apply (this); }
+  static return_t default_return_value (void) { return false; }
+  bool stop_sublookup_iteration (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--;
+    bool ret = recurse_func (this, lookup_index);
+    nesting_level_left++;
+    return ret;
+  }
+
+  unsigned int table_index; /* GSUB/GPOS */
+  hb_font_t *font;
+  hb_face_t *face;
+  hb_buffer_t *buffer;
+  hb_direction_t direction;
+  hb_mask_t lookup_mask;
+  bool auto_zwj;
+  recurse_func_t recurse_func;
+  unsigned int nesting_level_left;
+  unsigned int lookup_props;
+  const GDEF &gdef;
+  bool has_glyph_classes;
+  const VariationStore &var_store;
+  skipping_iterator_t iter_input, iter_context;
+  unsigned int lookup_index;
+  unsigned int debug_depth;
+
+
+  hb_apply_context_t (unsigned int table_index_,
+		      hb_font_t *font_,
+		      hb_buffer_t *buffer_) :
+			table_index (table_index_),
+			font (font_), face (font->face), buffer (buffer_),
+			direction (buffer_->props.direction),
+			lookup_mask (1),
+			auto_zwj (true),
+			recurse_func (NULL),
+			nesting_level_left (HB_MAX_NESTING_LEVEL),
+			lookup_props (0),
+			gdef (*hb_ot_layout_from_face (face)->gdef),
+			has_glyph_classes (gdef.has_glyph_classes ()),
+			var_store (gdef.get_var_store ()),
+			iter_input (),
+			iter_context (),
+			lookup_index ((unsigned int) -1),
+			debug_depth (0) {}
+
+  inline void set_lookup_mask (hb_mask_t mask) { lookup_mask = mask; }
+  inline void set_auto_zwj (bool auto_zwj_) { auto_zwj = auto_zwj_; }
+  inline void set_recurse_func (recurse_func_t func) { recurse_func = func; }
+  inline void set_lookup_index (unsigned int lookup_index_) { lookup_index = lookup_index_; }
+  inline void set_lookup_props (unsigned int lookup_props_)
+  {
+    lookup_props = lookup_props_;
+    iter_input.init (this, false);
+    iter_context.init (this, true);
+  }
+
+  inline bool
+  match_properties_mark (hb_codepoint_t  glyph,
+			 unsigned int    glyph_props,
+			 unsigned int    match_props) const
+  {
+    /* If using mark filtering sets, the high short of
+     * match_props has the set index.
+     */
+    if (match_props & LookupFlag::UseMarkFilteringSet)
+      return gdef.mark_set_covers (match_props >> 16, glyph);
+
+    /* The second byte of match_props has the meaning
+     * "ignore marks of attachment type different than
+     * the attachment type specified."
+     */
+    if (match_props & LookupFlag::MarkAttachmentType)
+      return (match_props & LookupFlag::MarkAttachmentType) == (glyph_props & LookupFlag::MarkAttachmentType);
+
+    return true;
+  }
+
+  inline bool
+  check_glyph_property (const hb_glyph_info_t *info,
+			unsigned int  match_props) const
+  {
+    hb_codepoint_t glyph = info->codepoint;
+    unsigned int glyph_props = _hb_glyph_info_get_glyph_props (info);
+
+    /* Not covered, if, for example, glyph class is ligature and
+     * match_props includes LookupFlags::IgnoreLigatures
+     */
+    if (glyph_props & match_props & LookupFlag::IgnoreFlags)
+      return false;
+
+    if (unlikely (glyph_props & HB_OT_LAYOUT_GLYPH_PROPS_MARK))
+      return match_properties_mark (glyph, glyph_props, match_props);
+
+    return true;
+  }
+
+  inline void _set_glyph_props (hb_codepoint_t glyph_index,
+			  unsigned int class_guess = 0,
+			  bool ligature = false,
+			  bool component = false) const
+  {
+    unsigned int add_in = _hb_glyph_info_get_glyph_props (&buffer->cur()) &
+			  HB_OT_LAYOUT_GLYPH_PROPS_PRESERVE;
+    add_in |= HB_OT_LAYOUT_GLYPH_PROPS_SUBSTITUTED;
+    if (ligature)
+    {
+      add_in |= HB_OT_LAYOUT_GLYPH_PROPS_LIGATED;
+      /* In the only place that the MULTIPLIED bit is used, Uniscribe
+       * seems to only care about the "last" transformation between
+       * Ligature and Multiple substitions.  Ie. if you ligate, expand,
+       * and ligate again, it forgives the multiplication and acts as
+       * if only ligation happened.  As such, clear MULTIPLIED bit.
+       */
+      add_in &= ~HB_OT_LAYOUT_GLYPH_PROPS_MULTIPLIED;
+    }
+    if (component)
+      add_in |= HB_OT_LAYOUT_GLYPH_PROPS_MULTIPLIED;
+    if (likely (has_glyph_classes))
+      _hb_glyph_info_set_glyph_props (&buffer->cur(), add_in | gdef.get_glyph_props (glyph_index));
+    else if (class_guess)
+      _hb_glyph_info_set_glyph_props (&buffer->cur(), add_in | class_guess);
+  }
+
+  inline void replace_glyph (hb_codepoint_t glyph_index) const
+  {
+    _set_glyph_props (glyph_index);
+    buffer->replace_glyph (glyph_index);
+  }
+  inline void replace_glyph_inplace (hb_codepoint_t glyph_index) const
+  {
+    _set_glyph_props (glyph_index);
+    buffer->cur().codepoint = glyph_index;
+  }
+  inline void replace_glyph_with_ligature (hb_codepoint_t glyph_index,
+					   unsigned int class_guess) const
+  {
+    _set_glyph_props (glyph_index, class_guess, true);
+    buffer->replace_glyph (glyph_index);
+  }
+  inline void output_glyph_for_component (hb_codepoint_t glyph_index,
+					  unsigned int class_guess) const
+  {
+    _set_glyph_props (glyph_index, class_guess, false, true);
+    buffer->output_glyph (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 HB_UNUSED,
+				  hb_set_t *glyphs,
+				  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 (glyphs, 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,
+				unsigned int match_positions[HB_MAX_CONTEXT_LENGTH],
+				bool *p_is_mark_ligature = NULL,
+				unsigned int *p_total_component_count = NULL)
+{
+  TRACE_APPLY (NULL);
+
+  if (unlikely (count > HB_MAX_CONTEXT_LENGTH)) return_trace (false);
+
+  hb_buffer_t *buffer = c->buffer;
+
+  hb_apply_context_t::skipping_iterator_t &skippy_iter = c->iter_input;
+  skippy_iter.reset (buffer->idx, count - 1);
+  skippy_iter.set_match_func (match_func, match_data, input);
+
+  /*
+   * This is perhaps the trickiest part of OpenType...  Remarks:
+   *
+   * - If all components of the ligature were marks, we call this a mark ligature.
+   *
+   * - If there is no GDEF, and the ligature is NOT a mark ligature, we categorize
+   *   it as a ligature glyph.
+   *
+   * - Ligatures cannot be formed across glyphs attached to different components
+   *   of previous ligatures.  Eg. the sequence is LAM,SHADDA,LAM,FATHA,HEH, and
+   *   LAM,LAM,HEH form a ligature, leaving SHADDA,FATHA next to eachother.
+   *   However, it would be wrong to ligate that SHADDA,FATHA sequence.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 = _hb_glyph_info_is_mark (&buffer->cur());
+
+  unsigned int total_component_count = 0;
+  total_component_count += _hb_glyph_info_get_lig_num_comps (&buffer->cur());
+
+  unsigned int first_lig_id = _hb_glyph_info_get_lig_id (&buffer->cur());
+  unsigned int first_lig_comp = _hb_glyph_info_get_lig_comp (&buffer->cur());
+
+  match_positions[0] = buffer->idx;
+  for (unsigned int i = 1; i < count; i++)
+  {
+    if (!skippy_iter.next ()) return_trace (false);
+
+    match_positions[i] = skippy_iter.idx;
+
+    unsigned int this_lig_id = _hb_glyph_info_get_lig_id (&buffer->info[skippy_iter.idx]);
+    unsigned int this_lig_comp = _hb_glyph_info_get_lig_comp (&buffer->info[skippy_iter.idx]);
+
+    if (first_lig_id && first_lig_comp) {
+      /* If first component was attached to a previous ligature component,
+       * all subsequent components should be attached to the same ligature
+       * component, otherwise we shouldn't ligate them. */
+      if (first_lig_id != this_lig_id || first_lig_comp != this_lig_comp)
+	return_trace (false);
+    } else {
+      /* If first component was NOT attached to a previous ligature component,
+       * all subsequent components should also NOT be attached to any ligature
+       * component, unless they are attached to the first component itself! */
+      if (this_lig_id && this_lig_comp && (this_lig_id != first_lig_id))
+	return_trace (false);
+    }
+
+    is_mark_ligature = is_mark_ligature && _hb_glyph_info_is_mark (&buffer->info[skippy_iter.idx]);
+    total_component_count += _hb_glyph_info_get_lig_num_comps (&buffer->info[skippy_iter.idx]);
+  }
+
+  *end_offset = skippy_iter.idx - 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 (true);
+}
+static inline bool ligate_input (hb_apply_context_t *c,
+				 unsigned int count, /* Including the first glyph */
+				 unsigned int match_positions[HB_MAX_CONTEXT_LENGTH], /* Including the first glyph */
+				 unsigned int match_length,
+				 hb_codepoint_t lig_glyph,
+				 bool is_mark_ligature,
+				 unsigned int total_component_count)
+{
+  TRACE_APPLY (NULL);
+
+  hb_buffer_t *buffer = c->buffer;
+
+  buffer->merge_clusters (buffer->idx, buffer->idx + match_length);
+
+  /*
+   * - 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 : _hb_allocate_lig_id (buffer);
+  unsigned int last_lig_id = _hb_glyph_info_get_lig_id (&buffer->cur());
+  unsigned int last_num_components = _hb_glyph_info_get_lig_num_comps (&buffer->cur());
+  unsigned int components_so_far = last_num_components;
+
+  if (!is_mark_ligature)
+  {
+    _hb_glyph_info_set_lig_props_for_ligature (&buffer->cur(), lig_id, total_component_count);
+    if (_hb_glyph_info_get_general_category (&buffer->cur()) == HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK)
+    {
+      _hb_glyph_info_set_general_category (&buffer->cur(), HB_UNICODE_GENERAL_CATEGORY_OTHER_LETTER);
+    }
+  }
+  c->replace_glyph_with_ligature (lig_glyph, klass);
+
+  for (unsigned int i = 1; i < count; i++)
+  {
+    while (buffer->idx < match_positions[i] && !buffer->in_error)
+    {
+      if (!is_mark_ligature) {
+        unsigned int this_comp = _hb_glyph_info_get_lig_comp (&buffer->cur());
+	if (this_comp == 0)
+	  this_comp = last_num_components;
+	unsigned int new_lig_comp = components_so_far - last_num_components +
+				    MIN (this_comp, last_num_components);
+	  _hb_glyph_info_set_lig_props_for_mark (&buffer->cur(), lig_id, new_lig_comp);
+      }
+      buffer->next_glyph ();
+    }
+
+    last_lig_id = _hb_glyph_info_get_lig_id (&buffer->cur());
+    last_num_components = _hb_glyph_info_get_lig_num_comps (&buffer->cur());
+    components_so_far += last_num_components;
+
+    /* Skip the base glyph */
+    buffer->idx++;
+  }
+
+  if (!is_mark_ligature && last_lig_id) {
+    /* Re-adjust components for any marks following. */
+    for (unsigned int i = buffer->idx; i < buffer->len; i++) {
+      if (last_lig_id == _hb_glyph_info_get_lig_id (&buffer->info[i])) {
+        unsigned int this_comp = _hb_glyph_info_get_lig_comp (&buffer->info[i]);
+	if (!this_comp)
+	  break;
+	unsigned int new_lig_comp = components_so_far - last_num_components +
+				    MIN (this_comp, last_num_components);
+	_hb_glyph_info_set_lig_props_for_mark (&buffer->info[i], lig_id, new_lig_comp);
+      } else
+	break;
+    }
+  }
+  return_trace (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)
+{
+  TRACE_APPLY (NULL);
+
+  hb_apply_context_t::skipping_iterator_t &skippy_iter = c->iter_context;
+  skippy_iter.reset (c->buffer->backtrack_len (), count);
+  skippy_iter.set_match_func (match_func, match_data, backtrack);
+
+  for (unsigned int i = 0; i < count; i++)
+    if (!skippy_iter.prev ())
+      return_trace (false);
+
+  return_trace (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::skipping_iterator_t &skippy_iter = c->iter_context;
+  skippy_iter.reset (c->buffer->idx + offset - 1, count);
+  skippy_iter.set_match_func (match_func, match_data, lookahead);
+
+  for (unsigned int i = 0; i < count; i++)
+    if (!skippy_iter.next ())
+      return_trace (false);
+
+  return_trace (true);
+}
+
+
+
+struct LookupRecord
+{
+  inline bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    return_trace (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[i].lookupListIndex);
+}
+
+static inline bool apply_lookup (hb_apply_context_t *c,
+				 unsigned int count, /* Including the first glyph */
+				 unsigned int match_positions[HB_MAX_CONTEXT_LENGTH], /* Including the first glyph */
+				 unsigned int lookupCount,
+				 const LookupRecord lookupRecord[], /* Array of LookupRecords--in design order */
+				 unsigned int match_length)
+{
+  TRACE_APPLY (NULL);
+
+  hb_buffer_t *buffer = c->buffer;
+  int end;
+
+  /* All positions are distance from beginning of *output* buffer.
+   * Adjust. */
+  {
+    unsigned int bl = buffer->backtrack_len ();
+    end = bl + match_length;
+
+    int delta = bl - buffer->idx;
+    /* Convert positions to new indexing. */
+    for (unsigned int j = 0; j < count; j++)
+      match_positions[j] += delta;
+  }
+
+  for (unsigned int i = 0; i < lookupCount && !buffer->in_error; i++)
+  {
+    unsigned int idx = lookupRecord[i].sequenceIndex;
+    if (idx >= count)
+      continue;
+
+    /* Don't recurse to ourself at same position.
+     * Note that this test is too naive, it doesn't catch longer loops. */
+    if (idx == 0 && lookupRecord[i].lookupListIndex == c->lookup_index)
+      continue;
+
+    buffer->move_to (match_positions[idx]);
+
+    unsigned int orig_len = buffer->backtrack_len () + buffer->lookahead_len ();
+    if (!c->recurse (lookupRecord[i].lookupListIndex))
+      continue;
+
+    unsigned int new_len = buffer->backtrack_len () + buffer->lookahead_len ();
+    int delta = new_len - orig_len;
+
+    if (!delta)
+        continue;
+
+    /* Recursed lookup changed buffer len.  Adjust. */
+
+    end += delta;
+    if (end <= int (match_positions[idx]))
+    {
+      /* End might end up being smaller than match_positions[idx] if the recursed
+       * lookup ended up removing many items, more than we have had matched.
+       * Just never rewind end back and get out of here.
+       * https://bugs.chromium.org/p/chromium/issues/detail?id=659496 */
+      end = match_positions[idx];
+      /* There can't be any further changes. */
+      break;
+    }
+
+    unsigned int next = idx + 1; /* next now is the position after the recursed lookup. */
+
+    if (delta > 0)
+    {
+      if (unlikely (delta + count > HB_MAX_CONTEXT_LENGTH))
+	break;
+    }
+    else
+    {
+      /* NOTE: delta is negative. */
+      delta = MAX (delta, (int) next - (int) count);
+      next -= delta;
+    }
+
+    /* Shift! */
+    memmove (match_positions + next + delta, match_positions + next,
+	     (count - next) * sizeof (match_positions[0]));
+    next += delta;
+    count += delta;
+
+    /* Fill in new entries. */
+    for (unsigned int j = idx + 1; j < next; j++)
+      match_positions[j] = match_positions[j - 1] + 1;
+
+    /* And fixup the rest. */
+    for (; next < count; next++)
+      match_positions[next] += delta;
+  }
+
+  buffer->move_to (end);
+
+  return_trace (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, c->input,
+		 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 HB_UNUSED,
+					       const LookupRecord lookupRecord[] HB_UNUSED,
+					       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)
+{
+  unsigned int match_length = 0;
+  unsigned int match_positions[HB_MAX_CONTEXT_LENGTH];
+  return match_input (c,
+		      inputCount, input,
+		      lookup_context.funcs.match, lookup_context.match_data,
+		      &match_length, match_positions)
+      && apply_lookup (c,
+		       inputCount, match_positions,
+		       lookupCount, lookupRecord,
+		       match_length);
+}
+
+struct Rule
+{
+  inline void closure (hb_closure_context_t *c, ContextClosureLookupContext &lookup_context) const
+  {
+    TRACE_CLOSURE (this);
+    const LookupRecord *lookupRecord = &StructAtOffset<LookupRecord> (inputZ, inputZ[0].static_size * (inputCount ? inputCount - 1 : 0));
+    context_closure_lookup (c,
+			    inputCount, inputZ,
+			    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> (inputZ, inputZ[0].static_size * (inputCount ? inputCount - 1 : 0));
+    context_collect_glyphs_lookup (c,
+				   inputCount, inputZ,
+				   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> (inputZ, inputZ[0].static_size * (inputCount ? inputCount - 1 : 0));
+    return_trace (context_would_apply_lookup (c, inputCount, inputZ, lookupCount, lookupRecord, lookup_context));
+  }
+
+  inline bool apply (hb_apply_context_t *c, ContextApplyLookupContext &lookup_context) const
+  {
+    TRACE_APPLY (this);
+    const LookupRecord *lookupRecord = &StructAtOffset<LookupRecord> (inputZ, inputZ[0].static_size * (inputCount ? inputCount - 1 : 0));
+    return_trace (context_apply_lookup (c, inputCount, inputZ, lookupCount, lookupRecord, lookup_context));
+  }
+
+  public:
+  inline bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    return inputCount.sanitize (c)
+	&& lookupCount.sanitize (c)
+	&& c->check_range (inputZ,
+			   inputZ[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	inputZ[VAR];		/* Array of match inputs--start with
+					 * second glyph */
+  LookupRecord	lookupRecordX[VAR];	/* Array of LookupRecords--in
+					 * design order */
+  public:
+  DEFINE_SIZE_ARRAY2 (4, inputZ, 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 (true);
+    }
+    return_trace (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 (true);
+    }
+    return_trace (false);
+  }
+
+  inline bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    return_trace (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).get_coverage (c->glyphs[0])];
+    struct ContextApplyLookupContext lookup_context = {
+      {match_glyph},
+      NULL
+    };
+    return_trace (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).get_coverage (c->buffer->cur().codepoint);
+    if (likely (index == NOT_COVERED))
+      return_trace (false);
+
+    const RuleSet &rule_set = this+ruleSet[index];
+    struct ContextApplyLookupContext lookup_context = {
+      {match_glyph},
+      NULL
+    };
+    return_trace (rule_set.apply (c, lookup_context));
+  }
+
+  inline bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    return_trace (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},
+      &class_def
+    };
+
+    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);
+
+    const ClassDef &class_def = this+classDef;
+    struct ContextCollectGlyphsLookupContext lookup_context = {
+      {collect_class},
+      &class_def
+    };
+
+    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.get_class (c->glyphs[0]);
+    const RuleSet &rule_set = this+ruleSet[index];
+    struct ContextApplyLookupContext lookup_context = {
+      {match_class},
+      &class_def
+    };
+    return_trace (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).get_coverage (c->buffer->cur().codepoint);
+    if (likely (index == NOT_COVERED)) return_trace (false);
+
+    const ClassDef &class_def = this+classDef;
+    index = class_def.get_class (c->buffer->cur().codepoint);
+    const RuleSet &rule_set = this+ruleSet[index];
+    struct ContextApplyLookupContext lookup_context = {
+      {match_class},
+      &class_def
+    };
+    return_trace (rule_set.apply (c, lookup_context));
+  }
+
+  inline bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    return_trace (coverage.sanitize (c, this) && classDef.sanitize (c, this) && ruleSet.sanitize (c, this));
+  }
+
+  protected:
+  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+coverageZ[0]).intersects (c->glyphs))
+      return;
+
+    const LookupRecord *lookupRecord = &StructAtOffset<LookupRecord> (coverageZ, coverageZ[0].static_size * glyphCount);
+    struct ContextClosureLookupContext lookup_context = {
+      {intersects_coverage},
+      this
+    };
+    context_closure_lookup (c,
+			    glyphCount, (const USHORT *) (coverageZ + 1),
+			    lookupCount, lookupRecord,
+			    lookup_context);
+  }
+
+  inline void collect_glyphs (hb_collect_glyphs_context_t *c) const
+  {
+    TRACE_COLLECT_GLYPHS (this);
+    (this+coverageZ[0]).add_coverage (c->input);
+
+    const LookupRecord *lookupRecord = &StructAtOffset<LookupRecord> (coverageZ, coverageZ[0].static_size * glyphCount);
+    struct ContextCollectGlyphsLookupContext lookup_context = {
+      {collect_coverage},
+      this
+    };
+
+    context_collect_glyphs_lookup (c,
+				   glyphCount, (const USHORT *) (coverageZ + 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> (coverageZ, coverageZ[0].static_size * glyphCount);
+    struct ContextApplyLookupContext lookup_context = {
+      {match_coverage},
+      this
+    };
+    return_trace (context_would_apply_lookup (c, glyphCount, (const USHORT *) (coverageZ + 1), lookupCount, lookupRecord, lookup_context));
+  }
+
+  inline const Coverage &get_coverage (void) const
+  {
+    return this+coverageZ[0];
+  }
+
+  inline bool apply (hb_apply_context_t *c) const
+  {
+    TRACE_APPLY (this);
+    unsigned int index = (this+coverageZ[0]).get_coverage (c->buffer->cur().codepoint);
+    if (likely (index == NOT_COVERED)) return_trace (false);
+
+    const LookupRecord *lookupRecord = &StructAtOffset<LookupRecord> (coverageZ, coverageZ[0].static_size * glyphCount);
+    struct ContextApplyLookupContext lookup_context = {
+      {match_coverage},
+      this
+    };
+    return_trace (context_apply_lookup (c, glyphCount, (const USHORT *) (coverageZ + 1), lookupCount, lookupRecord, lookup_context));
+  }
+
+  inline bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    if (!c->check_struct (this)) return_trace (false);
+    unsigned int count = glyphCount;
+    if (!count) return_trace (false); /* We want to access coverageZ[0] freely. */
+    if (!c->check_array (coverageZ, coverageZ[0].static_size, count)) return_trace (false);
+    for (unsigned int i = 0; i < count; i++)
+      if (!coverageZ[i].sanitize (c, this)) return_trace (false);
+    const LookupRecord *lookupRecord = &StructAtOffset<LookupRecord> (coverageZ, coverageZ[0].static_size * count);
+    return_trace (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>
+		coverageZ[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, coverageZ, lookupRecordX);
+};
+
+struct Context
+{
+  template <typename context_t>
+  inline typename context_t::return_t dispatch (context_t *c) const
+  {
+    TRACE_DISPATCH (this, u.format);
+    if (unlikely (!c->may_dispatch (this, &u.format))) return_trace (c->no_dispatch_return_value ());
+    switch (u.format) {
+    case 1: return_trace (c->dispatch (u.format1));
+    case 2: return_trace (c->dispatch (u.format2));
+    case 3: return_trace (c->dispatch (u.format3));
+    default:return_trace (c->default_return_value ());
+    }
+  }
+
+  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 ChainContextCollectGlyphsLookupContext
+{
+  ContextCollectGlyphsFuncs funcs;
+  const void *collect_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 void chain_context_collect_glyphs_lookup (hb_collect_glyphs_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[],
+						        ChainContextCollectGlyphsLookupContext &lookup_context)
+{
+  collect_array (c, c->before,
+		 backtrackCount, backtrack,
+		 lookup_context.funcs.collect, lookup_context.collect_data[0]);
+  collect_array (c, c->input,
+		 inputCount ? inputCount - 1 : 0, input,
+		 lookup_context.funcs.collect, lookup_context.collect_data[1]);
+  collect_array (c, c->after,
+		 lookaheadCount, lookahead,
+		 lookup_context.funcs.collect, lookup_context.collect_data[2]);
+  recurse_lookups (c,
+		   lookupCount, lookupRecord);
+}
+
+static inline bool chain_context_would_apply_lookup (hb_would_apply_context_t *c,
+						     unsigned int backtrackCount,
+						     const USHORT backtrack[] HB_UNUSED,
+						     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[] HB_UNUSED,
+						     unsigned int lookupCount HB_UNUSED,
+						     const LookupRecord lookupRecord[] HB_UNUSED,
+						     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 match_length = 0;
+  unsigned int match_positions[HB_MAX_CONTEXT_LENGTH];
+  return match_input (c,
+		      inputCount, input,
+		      lookup_context.funcs.match, lookup_context.match_data[1],
+		      &match_length, match_positions)
+      && 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],
+			  match_length)
+      && apply_lookup (c,
+		       inputCount, match_positions,
+		       lookupCount, lookupRecord,
+		       match_length);
+}
+
+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 void collect_glyphs (hb_collect_glyphs_context_t *c, ChainContextCollectGlyphsLookupContext &lookup_context) const
+  {
+    TRACE_COLLECT_GLYPHS (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_collect_glyphs_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 (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 (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) const
+  {
+    TRACE_SANITIZE (this);
+    if (!backtrack.sanitize (c)) return_trace (false);
+    const HeadlessArrayOf<USHORT> &input = StructAfter<HeadlessArrayOf<USHORT> > (backtrack);
+    if (!input.sanitize (c)) return_trace (false);
+    const ArrayOf<USHORT> &lookahead = StructAfter<ArrayOf<USHORT> > (input);
+    if (!lookahead.sanitize (c)) return_trace (false);
+    const ArrayOf<LookupRecord> &lookup = StructAfter<ArrayOf<LookupRecord> > (lookahead);
+    return_trace (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 void collect_glyphs (hb_collect_glyphs_context_t *c, ChainContextCollectGlyphsLookupContext &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, 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 (true);
+
+    return_trace (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 (true);
+
+    return_trace (false);
+  }
+
+  inline bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    return_trace (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
+  {
+    TRACE_COLLECT_GLYPHS (this);
+    (this+coverage).add_coverage (c->input);
+
+    struct ChainContextCollectGlyphsLookupContext lookup_context = {
+      {collect_glyph},
+      {NULL, NULL, 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 ChainRuleSet &rule_set = this+ruleSet[(this+coverage).get_coverage (c->glyphs[0])];
+    struct ChainContextApplyLookupContext lookup_context = {
+      {match_glyph},
+      {NULL, NULL, NULL}
+    };
+    return_trace (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).get_coverage (c->buffer->cur().codepoint);
+    if (likely (index == NOT_COVERED)) return_trace (false);
+
+    const ChainRuleSet &rule_set = this+ruleSet[index];
+    struct ChainContextApplyLookupContext lookup_context = {
+      {match_glyph},
+      {NULL, NULL, NULL}
+    };
+    return_trace (rule_set.apply (c, lookup_context));
+  }
+
+  inline bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    return_trace (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
+  {
+    TRACE_COLLECT_GLYPHS (this);
+    (this+coverage).add_coverage (c->input);
+
+    const ClassDef &backtrack_class_def = this+backtrackClassDef;
+    const ClassDef &input_class_def = this+inputClassDef;
+    const ClassDef &lookahead_class_def = this+lookaheadClassDef;
+
+    struct ChainContextCollectGlyphsLookupContext lookup_context = {
+      {collect_class},
+      {&backtrack_class_def,
+       &input_class_def,
+       &lookahead_class_def}
+    };
+
+    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 &backtrack_class_def = this+backtrackClassDef;
+    const ClassDef &input_class_def = this+inputClassDef;
+    const ClassDef &lookahead_class_def = this+lookaheadClassDef;
+
+    unsigned int index = input_class_def.get_class (c->glyphs[0]);
+    const ChainRuleSet &rule_set = this+ruleSet[index];
+    struct ChainContextApplyLookupContext lookup_context = {
+      {match_class},
+      {&backtrack_class_def,
+       &input_class_def,
+       &lookahead_class_def}
+    };
+    return_trace (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).get_coverage (c->buffer->cur().codepoint);
+    if (likely (index == NOT_COVERED)) return_trace (false);
+
+    const ClassDef &backtrack_class_def = this+backtrackClassDef;
+    const ClassDef &input_class_def = this+inputClassDef;
+    const ClassDef &lookahead_class_def = this+lookaheadClassDef;
+
+    index = input_class_def.get_class (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 (rule_set.apply (c, lookup_context));
+  }
+
+  inline bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    return_trace (coverage.sanitize (c, this) &&
+		  backtrackClassDef.sanitize (c, this) &&
+		  inputClassDef.sanitize (c, this) &&
+		  lookaheadClassDef.sanitize (c, this) &&
+		  ruleSet.sanitize (c, this));
+  }
+
+  protected:
+  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
+  {
+    TRACE_COLLECT_GLYPHS (this);
+    const OffsetArrayOf<Coverage> &input = StructAfter<OffsetArrayOf<Coverage> > (backtrack);
+
+    (this+input[0]).add_coverage (c->input);
+
+    const OffsetArrayOf<Coverage> &lookahead = StructAfter<OffsetArrayOf<Coverage> > (input);
+    const ArrayOf<LookupRecord> &lookup = StructAfter<ArrayOf<LookupRecord> > (lookahead);
+    struct ChainContextCollectGlyphsLookupContext lookup_context = {
+      {collect_coverage},
+      {this, this, this}
+    };
+    chain_context_collect_glyphs_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 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 (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]).get_coverage (c->buffer->cur().codepoint);
+    if (likely (index == NOT_COVERED)) return_trace (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 (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) const
+  {
+    TRACE_SANITIZE (this);
+    if (!backtrack.sanitize (c, this)) return_trace (false);
+    const OffsetArrayOf<Coverage> &input = StructAfter<OffsetArrayOf<Coverage> > (backtrack);
+    if (!input.sanitize (c, this)) return_trace (false);
+    if (!input.len) return_trace (false); /* To be consistent with Context. */
+    const OffsetArrayOf<Coverage> &lookahead = StructAfter<OffsetArrayOf<Coverage> > (input);
+    if (!lookahead.sanitize (c, this)) return_trace (false);
+    const ArrayOf<LookupRecord> &lookup = StructAfter<ArrayOf<LookupRecord> > (lookahead);
+    return_trace (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 dispatch (context_t *c) const
+  {
+    TRACE_DISPATCH (this, u.format);
+    if (unlikely (!c->may_dispatch (this, &u.format))) return_trace (c->no_dispatch_return_value ());
+    switch (u.format) {
+    case 1: return_trace (c->dispatch (u.format1));
+    case 2: return_trace (c->dispatch (u.format2));
+    case 3: return_trace (c->dispatch (u.format3));
+    default:return_trace (c->default_return_value ());
+    }
+  }
+
+  protected:
+  union {
+  USHORT		format;	/* Format identifier */
+  ChainContextFormat1	format1;
+  ChainContextFormat2	format2;
+  ChainContextFormat3	format3;
+  } u;
+};
+
+
+template <typename T>
+struct ExtensionFormat1
+{
+  inline unsigned int get_type (void) const { return extensionLookupType; }
+
+  template <typename X>
+  inline const X& get_subtable (void) const
+  {
+    unsigned int offset = extensionOffset;
+    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 dispatch (context_t *c) const
+  {
+    TRACE_DISPATCH (this, format);
+    if (unlikely (!c->may_dispatch (this, this))) return_trace (c->no_dispatch_return_value ());
+    return_trace (get_subtable<typename T::LookupSubTable> ().dispatch (c, get_type ()));
+  }
+
+  /* This is called from may_dispatch() above with hb_sanitize_context_t. */
+  inline bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    return_trace (c->check_struct (this) && extensionOffset != 0);
+  }
+
+  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;
+    }
+  }
+  template <typename X>
+  inline const X& get_subtable (void) const
+  {
+    switch (u.format) {
+    case 1: return u.format1.template get_subtable<typename T::LookupSubTable> ();
+    default:return Null(typename T::LookupSubTable);
+    }
+  }
+
+  template <typename context_t>
+  inline typename context_t::return_t dispatch (context_t *c) const
+  {
+    TRACE_DISPATCH (this, u.format);
+    if (unlikely (!c->may_dispatch (this, &u.format))) return_trace (c->no_dispatch_return_value ());
+    switch (u.format) {
+    case 1: return_trace (u.format1.dispatch (c));
+    default:return_trace (c->default_return_value ());
+    }
+  }
+
+  protected:
+  union {
+  USHORT		format;		/* Format identifier */
+  ExtensionFormat1<T>	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 hb_tag_t get_feature_tag (unsigned int i) const
+  { return i == Index::NOT_FOUND_INDEX ? HB_TAG_NONE : (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 find_variations_index (const int *coords, unsigned int num_coords,
+				     unsigned int *index) const
+  { return (version.to_int () >= 0x00010001u ? this+featureVars : Null(FeatureVariations))
+	   .find_index (coords, num_coords, index); }
+  inline const Feature& get_feature_variation (unsigned int feature_index,
+					       unsigned int variations_index) const
+  {
+    if (FeatureVariations::NOT_FOUND_INDEX != variations_index &&
+	version.to_int () >= 0x00010001u)
+    {
+      const Feature *feature = (this+featureVars).find_substitute (variations_index,
+								   feature_index);
+      if (feature)
+        return *feature;
+    }
+    return get_feature (feature_index);
+  }
+
+  inline bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    return_trace (version.sanitize (c) &&
+		  likely (version.major == 1) &&
+		  scriptList.sanitize (c, this) &&
+		  featureList.sanitize (c, this) &&
+		  lookupList.sanitize (c, this) &&
+		  (version.to_int () < 0x00010001u || featureVars.sanitize (c, this)));
+  }
+
+  protected:
+  FixedVersion<>version;	/* Version of the GSUB/GPOS table--initially set
+				 * to 0x00010000u */
+  OffsetTo<ScriptList>
+		scriptList;  	/* ScriptList table */
+  OffsetTo<FeatureList>
+		featureList; 	/* FeatureList table */
+  OffsetTo<LookupList>
+		lookupList; 	/* LookupList table */
+  OffsetTo<FeatureVariations, ULONG>
+		featureVars;	/* Offset to Feature Variations
+				   table--from beginning of table
+				 * (may be NULL).  Introduced
+				 * in version 0x00010001. */
+  public:
+  DEFINE_SIZE_MIN (10);
+};
+
+
+} /* namespace OT */
+
+
+#endif /* HB_OT_LAYOUT_GSUBGPOS_PRIVATE_HH */