Adding upstream version 115.7.0esr.upstream/115.7.0esr

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1001 insertions, 0 deletions

diff --git a/gfx/harfbuzz/src/hb-aat-layout-kerx-table.hh b/gfx/harfbuzz/src/hb-aat-layout-kerx-table.hh
new file mode 100644
index 0000000000..35d7c84c2b
--- /dev/null
+++ b/gfx/harfbuzz/src/hb-aat-layout-kerx-table.hh
@@ -0,0 +1,1001 @@
+/*
+ * Copyright © 2018  Ebrahim Byagowi
+ * Copyright © 2018  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.
+ *
+ * Google Author(s): Behdad Esfahbod
+ */
+
+#ifndef HB_AAT_LAYOUT_KERX_TABLE_HH
+#define HB_AAT_LAYOUT_KERX_TABLE_HH
+
+#include "hb-kern.hh"
+#include "hb-aat-layout-ankr-table.hh"
+
+/*
+ * kerx -- Extended Kerning
+ * https://developer.apple.com/fonts/TrueType-Reference-Manual/RM06/Chap6kerx.html
+ */
+#define HB_AAT_TAG_kerx HB_TAG('k','e','r','x')
+
+
+namespace AAT {
+
+using namespace OT;
+
+
+static inline int
+kerxTupleKern (int value,
+	       unsigned int tupleCount,
+	       const void *base,
+	       hb_aat_apply_context_t *c)
+{
+  if (likely (!tupleCount || !c)) return value;
+
+  unsigned int offset = value;
+  const FWORD *pv = &StructAtOffset<FWORD> (base, offset);
+  if (unlikely (!c->sanitizer.check_array (pv, tupleCount))) return 0;
+  return *pv;
+}
+
+
+struct hb_glyph_pair_t
+{
+  hb_codepoint_t left;
+  hb_codepoint_t right;
+};
+
+struct KernPair
+{
+  int get_kerning () const { return value; }
+
+  int cmp (const hb_glyph_pair_t &o) const
+  {
+    int ret = left.cmp (o.left);
+    if (ret) return ret;
+    return right.cmp (o.right);
+  }
+
+  bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    return_trace (c->check_struct (this));
+  }
+
+  protected:
+  HBGlyphID16	left;
+  HBGlyphID16	right;
+  FWORD		value;
+  public:
+  DEFINE_SIZE_STATIC (6);
+};
+
+template <typename KernSubTableHeader>
+struct KerxSubTableFormat0
+{
+  int get_kerning (hb_codepoint_t left, hb_codepoint_t right,
+		   hb_aat_apply_context_t *c = nullptr) const
+  {
+    hb_glyph_pair_t pair = {left, right};
+    int v = pairs.bsearch (pair).get_kerning ();
+    return kerxTupleKern (v, header.tuple_count (), this, c);
+  }
+
+  bool apply (hb_aat_apply_context_t *c) const
+  {
+    TRACE_APPLY (this);
+
+    if (!c->plan->requested_kerning)
+      return false;
+
+    if (header.coverage & header.Backwards)
+      return false;
+
+    accelerator_t accel (*this, c);
+    hb_kern_machine_t<accelerator_t> machine (accel, header.coverage & header.CrossStream);
+    machine.kern (c->font, c->buffer, c->plan->kern_mask);
+
+    return_trace (true);
+  }
+
+  struct accelerator_t
+  {
+    const KerxSubTableFormat0 &table;
+    hb_aat_apply_context_t *c;
+
+    accelerator_t (const KerxSubTableFormat0 &table_,
+		   hb_aat_apply_context_t *c_) :
+		     table (table_), c (c_) {}
+
+    int get_kerning (hb_codepoint_t left, hb_codepoint_t right) const
+    { return table.get_kerning (left, right, c); }
+  };
+
+
+  bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    return_trace (likely (pairs.sanitize (c)));
+  }
+
+  protected:
+  KernSubTableHeader	header;
+  BinSearchArrayOf<KernPair, typename KernSubTableHeader::Types::HBUINT>
+			pairs;	/* Sorted kern records. */
+  public:
+  DEFINE_SIZE_ARRAY (KernSubTableHeader::static_size + 16, pairs);
+};
+
+
+template <bool extended>
+struct Format1Entry;
+
+template <>
+struct Format1Entry<true>
+{
+  enum Flags
+  {
+    Push		= 0x8000,	/* If set, push this glyph on the kerning stack. */
+    DontAdvance		= 0x4000,	/* If set, don't advance to the next glyph
+					 * before going to the new state. */
+    Reset		= 0x2000,	/* If set, reset the kerning data (clear the stack) */
+    Reserved		= 0x1FFF,	/* Not used; set to 0. */
+  };
+
+  struct EntryData
+  {
+    HBUINT16	kernActionIndex;/* Index into the kerning value array. If
+				 * this index is 0xFFFF, then no kerning
+				 * is to be performed. */
+    public:
+    DEFINE_SIZE_STATIC (2);
+  };
+
+  static bool performAction (const Entry<EntryData> &entry)
+  { return entry.data.kernActionIndex != 0xFFFF; }
+
+  static unsigned int kernActionIndex (const Entry<EntryData> &entry)
+  { return entry.data.kernActionIndex; }
+};
+template <>
+struct Format1Entry<false>
+{
+  enum Flags
+  {
+    Push		= 0x8000,	/* If set, push this glyph on the kerning stack. */
+    DontAdvance		= 0x4000,	/* If set, don't advance to the next glyph
+					 * before going to the new state. */
+    Offset		= 0x3FFF,	/* Byte offset from beginning of subtable to the
+					 * value table for the glyphs on the kerning stack. */
+
+    Reset		= 0x0000,	/* Not supported? */
+  };
+
+  typedef void EntryData;
+
+  static bool performAction (const Entry<EntryData> &entry)
+  { return entry.flags & Offset; }
+
+  static unsigned int kernActionIndex (const Entry<EntryData> &entry)
+  { return entry.flags & Offset; }
+};
+
+template <typename KernSubTableHeader>
+struct KerxSubTableFormat1
+{
+  typedef typename KernSubTableHeader::Types Types;
+  typedef typename Types::HBUINT HBUINT;
+
+  typedef Format1Entry<Types::extended> Format1EntryT;
+  typedef typename Format1EntryT::EntryData EntryData;
+
+  struct driver_context_t
+  {
+    static constexpr bool in_place = true;
+    enum
+    {
+      DontAdvance	= Format1EntryT::DontAdvance,
+    };
+
+    driver_context_t (const KerxSubTableFormat1 *table_,
+		      hb_aat_apply_context_t *c_) :
+	c (c_),
+	table (table_),
+	/* Apparently the offset kernAction is from the beginning of the state-machine,
+	 * similar to offsets in morx table, NOT from beginning of this table, like
+	 * other subtables in kerx.  Discovered via testing. */
+	kernAction (&table->machine + table->kernAction),
+	depth (0),
+	crossStream (table->header.coverage & table->header.CrossStream) {}
+
+    bool is_actionable (StateTableDriver<Types, EntryData> *driver HB_UNUSED,
+			const Entry<EntryData> &entry)
+    { return Format1EntryT::performAction (entry); }
+    void transition (StateTableDriver<Types, EntryData> *driver,
+		     const Entry<EntryData> &entry)
+    {
+      hb_buffer_t *buffer = driver->buffer;
+      unsigned int flags = entry.flags;
+
+      if (flags & Format1EntryT::Reset)
+	depth = 0;
+
+      if (flags & Format1EntryT::Push)
+      {
+	if (likely (depth < ARRAY_LENGTH (stack)))
+	  stack[depth++] = buffer->idx;
+	else
+	  depth = 0; /* Probably not what CoreText does, but better? */
+      }
+
+      if (Format1EntryT::performAction (entry) && depth)
+      {
+	unsigned int tuple_count = hb_max (1u, table->header.tuple_count ());
+
+	unsigned int kern_idx = Format1EntryT::kernActionIndex (entry);
+	kern_idx = Types::byteOffsetToIndex (kern_idx, &table->machine, kernAction.arrayZ);
+	const FWORD *actions = &kernAction[kern_idx];
+	if (!c->sanitizer.check_array (actions, depth, tuple_count))
+	{
+	  depth = 0;
+	  return;
+	}
+
+	hb_mask_t kern_mask = c->plan->kern_mask;
+
+	/* From Apple 'kern' spec:
+	 * "Each pops one glyph from the kerning stack and applies the kerning value to it.
+	 * The end of the list is marked by an odd value... */
+	bool last = false;
+	while (!last && depth)
+	{
+	  unsigned int idx = stack[--depth];
+	  int v = *actions;
+	  actions += tuple_count;
+	  if (idx >= buffer->len) continue;
+
+	  /* "The end of the list is marked by an odd value..." */
+	  last = v & 1;
+	  v &= ~1;
+
+	  hb_glyph_position_t &o = buffer->pos[idx];
+
+	  if (HB_DIRECTION_IS_HORIZONTAL (buffer->props.direction))
+	  {
+	    if (crossStream)
+	    {
+	      /* The following flag is undocumented in the spec, but described
+	       * in the 'kern' table example. */
+	      if (v == -0x8000)
+	      {
+		o.attach_type() = OT::Layout::GPOS_impl::ATTACH_TYPE_NONE;
+		o.attach_chain() = 0;
+		o.y_offset = 0;
+	      }
+	      else if (o.attach_type())
+	      {
+		o.y_offset += c->font->em_scale_y (v);
+		buffer->scratch_flags |= HB_BUFFER_SCRATCH_FLAG_HAS_GPOS_ATTACHMENT;
+	      }
+	    }
+	    else if (buffer->info[idx].mask & kern_mask)
+	    {
+	      o.x_advance += c->font->em_scale_x (v);
+	      o.x_offset += c->font->em_scale_x (v);
+	    }
+	  }
+	  else
+	  {
+	    if (crossStream)
+	    {
+	      /* CoreText doesn't do crossStream kerning in vertical.  We do. */
+	      if (v == -0x8000)
+	      {
+		o.attach_type() = OT::Layout::GPOS_impl::ATTACH_TYPE_NONE;
+		o.attach_chain() = 0;
+		o.x_offset = 0;
+	      }
+	      else if (o.attach_type())
+	      {
+		o.x_offset += c->font->em_scale_x (v);
+		buffer->scratch_flags |= HB_BUFFER_SCRATCH_FLAG_HAS_GPOS_ATTACHMENT;
+	      }
+	    }
+	    else if (buffer->info[idx].mask & kern_mask)
+	    {
+	      o.y_advance += c->font->em_scale_y (v);
+	      o.y_offset += c->font->em_scale_y (v);
+	    }
+	  }
+	}
+      }
+    }
+
+    private:
+    hb_aat_apply_context_t *c;
+    const KerxSubTableFormat1 *table;
+    const UnsizedArrayOf<FWORD> &kernAction;
+    unsigned int stack[8];
+    unsigned int depth;
+    bool crossStream;
+  };
+
+  bool apply (hb_aat_apply_context_t *c) const
+  {
+    TRACE_APPLY (this);
+
+    if (!c->plan->requested_kerning &&
+	!(header.coverage & header.CrossStream))
+      return false;
+
+    driver_context_t dc (this, c);
+
+    StateTableDriver<Types, EntryData> driver (machine, c->buffer, c->font->face);
+    driver.drive (&dc, c);
+
+    return_trace (true);
+  }
+
+  bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    /* The rest of array sanitizations are done at run-time. */
+    return_trace (likely (c->check_struct (this) &&
+			  machine.sanitize (c)));
+  }
+
+  protected:
+  KernSubTableHeader				header;
+  StateTable<Types, EntryData>			machine;
+  NNOffsetTo<UnsizedArrayOf<FWORD>, HBUINT>	kernAction;
+  public:
+  DEFINE_SIZE_STATIC (KernSubTableHeader::static_size + 5 * sizeof (HBUINT));
+};
+
+template <typename KernSubTableHeader>
+struct KerxSubTableFormat2
+{
+  typedef typename KernSubTableHeader::Types Types;
+  typedef typename Types::HBUINT HBUINT;
+
+  int get_kerning (hb_codepoint_t left, hb_codepoint_t right,
+		   hb_aat_apply_context_t *c) const
+  {
+    unsigned int num_glyphs = c->sanitizer.get_num_glyphs ();
+    unsigned int l = (this+leftClassTable).get_class (left, num_glyphs, 0);
+    unsigned int r = (this+rightClassTable).get_class (right, num_glyphs, 0);
+
+    const UnsizedArrayOf<FWORD> &arrayZ = this+array;
+    unsigned int kern_idx = l + r;
+    kern_idx = Types::offsetToIndex (kern_idx, this, arrayZ.arrayZ);
+    const FWORD *v = &arrayZ[kern_idx];
+    if (unlikely (!v->sanitize (&c->sanitizer))) return 0;
+
+    return kerxTupleKern (*v, header.tuple_count (), this, c);
+  }
+
+  bool apply (hb_aat_apply_context_t *c) const
+  {
+    TRACE_APPLY (this);
+
+    if (!c->plan->requested_kerning)
+      return false;
+
+    if (header.coverage & header.Backwards)
+      return false;
+
+    accelerator_t accel (*this, c);
+    hb_kern_machine_t<accelerator_t> machine (accel, header.coverage & header.CrossStream);
+    machine.kern (c->font, c->buffer, c->plan->kern_mask);
+
+    return_trace (true);
+  }
+
+  struct accelerator_t
+  {
+    const KerxSubTableFormat2 &table;
+    hb_aat_apply_context_t *c;
+
+    accelerator_t (const KerxSubTableFormat2 &table_,
+		   hb_aat_apply_context_t *c_) :
+		     table (table_), c (c_) {}
+
+    int get_kerning (hb_codepoint_t left, hb_codepoint_t right) const
+    { return table.get_kerning (left, right, c); }
+  };
+
+  bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    return_trace (likely (c->check_struct (this) &&
+			  leftClassTable.sanitize (c, this) &&
+			  rightClassTable.sanitize (c, this) &&
+			  c->check_range (this, array)));
+  }
+
+  protected:
+  KernSubTableHeader	header;
+  HBUINT		rowWidth;	/* The width, in bytes, of a row in the table. */
+  NNOffsetTo<typename Types::ClassTypeWide, HBUINT>
+			leftClassTable;	/* Offset from beginning of this subtable to
+					 * left-hand class table. */
+  NNOffsetTo<typename Types::ClassTypeWide, HBUINT>
+			rightClassTable;/* Offset from beginning of this subtable to
+					 * right-hand class table. */
+  NNOffsetTo<UnsizedArrayOf<FWORD>, HBUINT>
+			 array;		/* Offset from beginning of this subtable to
+					 * the start of the kerning array. */
+  public:
+  DEFINE_SIZE_STATIC (KernSubTableHeader::static_size + 4 * sizeof (HBUINT));
+};
+
+template <typename KernSubTableHeader>
+struct KerxSubTableFormat4
+{
+  typedef ExtendedTypes Types;
+
+  struct EntryData
+  {
+    HBUINT16	ankrActionIndex;/* Either 0xFFFF (for no action) or the index of
+				 * the action to perform. */
+    public:
+    DEFINE_SIZE_STATIC (2);
+  };
+
+  struct driver_context_t
+  {
+    static constexpr bool in_place = true;
+    enum Flags
+    {
+      Mark		= 0x8000,	/* If set, remember this glyph as the marked glyph. */
+      DontAdvance	= 0x4000,	/* If set, don't advance to the next glyph before
+					 * going to the new state. */
+      Reserved		= 0x3FFF,	/* Not used; set to 0. */
+    };
+
+    enum SubTableFlags
+    {
+      ActionType	= 0xC0000000,	/* A two-bit field containing the action type. */
+      Unused		= 0x3F000000,	/* Unused - must be zero. */
+      Offset		= 0x00FFFFFF,	/* Masks the offset in bytes from the beginning
+					 * of the subtable to the beginning of the control
+					 * point table. */
+    };
+
+    driver_context_t (const KerxSubTableFormat4 *table,
+		      hb_aat_apply_context_t *c_) :
+	c (c_),
+	action_type ((table->flags & ActionType) >> 30),
+	ankrData ((HBUINT16 *) ((const char *) &table->machine + (table->flags & Offset))),
+	mark_set (false),
+	mark (0) {}
+
+    bool is_actionable (StateTableDriver<Types, EntryData> *driver HB_UNUSED,
+			const Entry<EntryData> &entry)
+    { return entry.data.ankrActionIndex != 0xFFFF; }
+    void transition (StateTableDriver<Types, EntryData> *driver,
+		     const Entry<EntryData> &entry)
+    {
+      hb_buffer_t *buffer = driver->buffer;
+
+      if (mark_set && entry.data.ankrActionIndex != 0xFFFF && buffer->idx < buffer->len)
+      {
+	hb_glyph_position_t &o = buffer->cur_pos();
+	switch (action_type)
+	{
+	  case 0: /* Control Point Actions.*/
+	  {
+	    /* Indexed into glyph outline. */
+	    /* Each action (record in ankrData) contains two 16-bit fields, so we must
+	       double the ankrActionIndex to get the correct offset here. */
+	    const HBUINT16 *data = &ankrData[entry.data.ankrActionIndex * 2];
+	    if (!c->sanitizer.check_array (data, 2)) return;
+	    unsigned int markControlPoint = *data++;
+	    unsigned int currControlPoint = *data++;
+	    hb_position_t markX = 0;
+	    hb_position_t markY = 0;
+	    hb_position_t currX = 0;
+	    hb_position_t currY = 0;
+	    if (!c->font->get_glyph_contour_point_for_origin (c->buffer->info[mark].codepoint,
+							      markControlPoint,
+							      HB_DIRECTION_LTR /*XXX*/,
+							      &markX, &markY) ||
+		!c->font->get_glyph_contour_point_for_origin (c->buffer->cur ().codepoint,
+							      currControlPoint,
+							      HB_DIRECTION_LTR /*XXX*/,
+							      &currX, &currY))
+	      return;
+
+	    o.x_offset = markX - currX;
+	    o.y_offset = markY - currY;
+	  }
+	  break;
+
+	  case 1: /* Anchor Point Actions. */
+	  {
+	    /* Indexed into 'ankr' table. */
+	    /* Each action (record in ankrData) contains two 16-bit fields, so we must
+	       double the ankrActionIndex to get the correct offset here. */
+	    const HBUINT16 *data = &ankrData[entry.data.ankrActionIndex * 2];
+	    if (!c->sanitizer.check_array (data, 2)) return;
+	    unsigned int markAnchorPoint = *data++;
+	    unsigned int currAnchorPoint = *data++;
+	    const Anchor &markAnchor = c->ankr_table->get_anchor (c->buffer->info[mark].codepoint,
+								  markAnchorPoint,
+								  c->sanitizer.get_num_glyphs ());
+	    const Anchor &currAnchor = c->ankr_table->get_anchor (c->buffer->cur ().codepoint,
+								  currAnchorPoint,
+								  c->sanitizer.get_num_glyphs ());
+
+	    o.x_offset = c->font->em_scale_x (markAnchor.xCoordinate) - c->font->em_scale_x (currAnchor.xCoordinate);
+	    o.y_offset = c->font->em_scale_y (markAnchor.yCoordinate) - c->font->em_scale_y (currAnchor.yCoordinate);
+	  }
+	  break;
+
+	  case 2: /* Control Point Coordinate Actions. */
+	  {
+	    /* Each action contains four 16-bit fields, so we multiply the ankrActionIndex
+	       by 4 to get the correct offset for the given action. */
+	    const FWORD *data = (const FWORD *) &ankrData[entry.data.ankrActionIndex * 4];
+	    if (!c->sanitizer.check_array (data, 4)) return;
+	    int markX = *data++;
+	    int markY = *data++;
+	    int currX = *data++;
+	    int currY = *data++;
+
+	    o.x_offset = c->font->em_scale_x (markX) - c->font->em_scale_x (currX);
+	    o.y_offset = c->font->em_scale_y (markY) - c->font->em_scale_y (currY);
+	  }
+	  break;
+	}
+	o.attach_type() = OT::Layout::GPOS_impl::ATTACH_TYPE_MARK;
+	o.attach_chain() = (int) mark - (int) buffer->idx;
+	buffer->scratch_flags |= HB_BUFFER_SCRATCH_FLAG_HAS_GPOS_ATTACHMENT;
+      }
+
+      if (entry.flags & Mark)
+      {
+	mark_set = true;
+	mark = buffer->idx;
+      }
+    }
+
+    private:
+    hb_aat_apply_context_t *c;
+    unsigned int action_type;
+    const HBUINT16 *ankrData;
+    bool mark_set;
+    unsigned int mark;
+  };
+
+  bool apply (hb_aat_apply_context_t *c) const
+  {
+    TRACE_APPLY (this);
+
+    driver_context_t dc (this, c);
+
+    StateTableDriver<Types, EntryData> driver (machine, c->buffer, c->font->face);
+    driver.drive (&dc, c);
+
+    return_trace (true);
+  }
+
+  bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    /* The rest of array sanitizations are done at run-time. */
+    return_trace (likely (c->check_struct (this) &&
+			  machine.sanitize (c)));
+  }
+
+  protected:
+  KernSubTableHeader		header;
+  StateTable<Types, EntryData>	machine;
+  HBUINT32			flags;
+  public:
+  DEFINE_SIZE_STATIC (KernSubTableHeader::static_size + 20);
+};
+
+template <typename KernSubTableHeader>
+struct KerxSubTableFormat6
+{
+  enum Flags
+  {
+    ValuesAreLong	= 0x00000001,
+  };
+
+  bool is_long () const { return flags & ValuesAreLong; }
+
+  int get_kerning (hb_codepoint_t left, hb_codepoint_t right,
+		   hb_aat_apply_context_t *c) const
+  {
+    unsigned int num_glyphs = c->sanitizer.get_num_glyphs ();
+    if (is_long ())
+    {
+      const typename U::Long &t = u.l;
+      unsigned int l = (this+t.rowIndexTable).get_value_or_null (left, num_glyphs);
+      unsigned int r = (this+t.columnIndexTable).get_value_or_null (right, num_glyphs);
+      unsigned int offset = l + r;
+      if (unlikely (offset < l)) return 0; /* Addition overflow. */
+      if (unlikely (hb_unsigned_mul_overflows (offset, sizeof (FWORD32)))) return 0;
+      const FWORD32 *v = &StructAtOffset<FWORD32> (&(this+t.array), offset * sizeof (FWORD32));
+      if (unlikely (!v->sanitize (&c->sanitizer))) return 0;
+      return kerxTupleKern (*v, header.tuple_count (), &(this+vector), c);
+    }
+    else
+    {
+      const typename U::Short &t = u.s;
+      unsigned int l = (this+t.rowIndexTable).get_value_or_null (left, num_glyphs);
+      unsigned int r = (this+t.columnIndexTable).get_value_or_null (right, num_glyphs);
+      unsigned int offset = l + r;
+      const FWORD *v = &StructAtOffset<FWORD> (&(this+t.array), offset * sizeof (FWORD));
+      if (unlikely (!v->sanitize (&c->sanitizer))) return 0;
+      return kerxTupleKern (*v, header.tuple_count (), &(this+vector), c);
+    }
+  }
+
+  bool apply (hb_aat_apply_context_t *c) const
+  {
+    TRACE_APPLY (this);
+
+    if (!c->plan->requested_kerning)
+      return false;
+
+    if (header.coverage & header.Backwards)
+      return false;
+
+    accelerator_t accel (*this, c);
+    hb_kern_machine_t<accelerator_t> machine (accel, header.coverage & header.CrossStream);
+    machine.kern (c->font, c->buffer, c->plan->kern_mask);
+
+    return_trace (true);
+  }
+
+  bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    return_trace (likely (c->check_struct (this) &&
+			  (is_long () ?
+			   (
+			     u.l.rowIndexTable.sanitize (c, this) &&
+			     u.l.columnIndexTable.sanitize (c, this) &&
+			     c->check_range (this, u.l.array)
+			   ) : (
+			     u.s.rowIndexTable.sanitize (c, this) &&
+			     u.s.columnIndexTable.sanitize (c, this) &&
+			     c->check_range (this, u.s.array)
+			   )) &&
+			  (header.tuple_count () == 0 ||
+			   c->check_range (this, vector))));
+  }
+
+  struct accelerator_t
+  {
+    const KerxSubTableFormat6 &table;
+    hb_aat_apply_context_t *c;
+
+    accelerator_t (const KerxSubTableFormat6 &table_,
+		   hb_aat_apply_context_t *c_) :
+		     table (table_), c (c_) {}
+
+    int get_kerning (hb_codepoint_t left, hb_codepoint_t right) const
+    { return table.get_kerning (left, right, c); }
+  };
+
+  protected:
+  KernSubTableHeader		header;
+  HBUINT32			flags;
+  HBUINT16			rowCount;
+  HBUINT16			columnCount;
+  union U
+  {
+    struct Long
+    {
+      NNOffset32To<Lookup<HBUINT32>>		rowIndexTable;
+      NNOffset32To<Lookup<HBUINT32>>		columnIndexTable;
+      NNOffset32To<UnsizedArrayOf<FWORD32>>	array;
+    } l;
+    struct Short
+    {
+      NNOffset32To<Lookup<HBUINT16>>		rowIndexTable;
+      NNOffset32To<Lookup<HBUINT16>>		columnIndexTable;
+      NNOffset32To<UnsizedArrayOf<FWORD>>	array;
+    } s;
+  } u;
+  NNOffset32To<UnsizedArrayOf<FWORD>>	vector;
+  public:
+  DEFINE_SIZE_STATIC (KernSubTableHeader::static_size + 24);
+};
+
+
+struct KerxSubTableHeader
+{
+  typedef ExtendedTypes Types;
+
+  unsigned   tuple_count () const { return tupleCount; }
+  bool     is_horizontal () const { return !(coverage & Vertical); }
+
+  enum Coverage
+  {
+    Vertical	= 0x80000000u,	/* Set if table has vertical kerning values. */
+    CrossStream	= 0x40000000u,	/* Set if table has cross-stream kerning values. */
+    Variation	= 0x20000000u,	/* Set if table has variation kerning values. */
+    Backwards	= 0x10000000u,	/* If clear, process the glyphs forwards, that
+				 * is, from first to last in the glyph stream.
+				 * If we, process them from last to first.
+				 * This flag only applies to state-table based
+				 * 'kerx' subtables (types 1 and 4). */
+    Reserved	= 0x0FFFFF00u,	/* Reserved, set to zero. */
+    SubtableType= 0x000000FFu,	/* Subtable type. */
+  };
+
+  bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    return_trace (c->check_struct (this));
+  }
+
+  public:
+  HBUINT32	length;
+  HBUINT32	coverage;
+  HBUINT32	tupleCount;
+  public:
+  DEFINE_SIZE_STATIC (12);
+};
+
+struct KerxSubTable
+{
+  friend struct kerx;
+
+  unsigned int get_size () const { return u.header.length; }
+  unsigned int get_type () const { return u.header.coverage & u.header.SubtableType; }
+
+  template <typename context_t, typename ...Ts>
+  typename context_t::return_t dispatch (context_t *c, Ts&&... ds) const
+  {
+    unsigned int subtable_type = get_type ();
+    TRACE_DISPATCH (this, subtable_type);
+    switch (subtable_type) {
+    case 0:	return_trace (c->dispatch (u.format0, std::forward<Ts> (ds)...));
+    case 1:	return_trace (c->dispatch (u.format1, std::forward<Ts> (ds)...));
+    case 2:	return_trace (c->dispatch (u.format2, std::forward<Ts> (ds)...));
+    case 4:	return_trace (c->dispatch (u.format4, std::forward<Ts> (ds)...));
+    case 6:	return_trace (c->dispatch (u.format6, std::forward<Ts> (ds)...));
+    default:	return_trace (c->default_return_value ());
+    }
+  }
+
+  bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    if (!u.header.sanitize (c) ||
+	u.header.length <= u.header.static_size ||
+	!c->check_range (this, u.header.length))
+      return_trace (false);
+
+    return_trace (dispatch (c));
+  }
+
+  public:
+  union {
+  KerxSubTableHeader				header;
+  KerxSubTableFormat0<KerxSubTableHeader>	format0;
+  KerxSubTableFormat1<KerxSubTableHeader>	format1;
+  KerxSubTableFormat2<KerxSubTableHeader>	format2;
+  KerxSubTableFormat4<KerxSubTableHeader>	format4;
+  KerxSubTableFormat6<KerxSubTableHeader>	format6;
+  } u;
+  public:
+  DEFINE_SIZE_MIN (12);
+};
+
+
+/*
+ * The 'kerx' Table
+ */
+
+template <typename T>
+struct KerxTable
+{
+  /* https://en.wikipedia.org/wiki/Curiously_recurring_template_pattern */
+  const T* thiz () const { return static_cast<const T *> (this); }
+
+  bool has_state_machine () const
+  {
+    typedef typename T::SubTable SubTable;
+
+    const SubTable *st = &thiz()->firstSubTable;
+    unsigned int count = thiz()->tableCount;
+    for (unsigned int i = 0; i < count; i++)
+    {
+      if (st->get_type () == 1)
+	return true;
+      st = &StructAfter<SubTable> (*st);
+    }
+    return false;
+  }
+
+  bool has_cross_stream () const
+  {
+    typedef typename T::SubTable SubTable;
+
+    const SubTable *st = &thiz()->firstSubTable;
+    unsigned int count = thiz()->tableCount;
+    for (unsigned int i = 0; i < count; i++)
+    {
+      if (st->u.header.coverage & st->u.header.CrossStream)
+	return true;
+      st = &StructAfter<SubTable> (*st);
+    }
+    return false;
+  }
+
+  int get_h_kerning (hb_codepoint_t left, hb_codepoint_t right) const
+  {
+    typedef typename T::SubTable SubTable;
+
+    int v = 0;
+    const SubTable *st = &thiz()->firstSubTable;
+    unsigned int count = thiz()->tableCount;
+    for (unsigned int i = 0; i < count; i++)
+    {
+      if ((st->u.header.coverage & (st->u.header.Variation | st->u.header.CrossStream)) ||
+	  !st->u.header.is_horizontal ())
+	continue;
+      v += st->get_kerning (left, right);
+      st = &StructAfter<SubTable> (*st);
+    }
+    return v;
+  }
+
+  bool apply (AAT::hb_aat_apply_context_t *c) const
+  {
+    c->buffer->unsafe_to_concat ();
+
+    typedef typename T::SubTable SubTable;
+
+    bool ret = false;
+    bool seenCrossStream = false;
+    c->set_lookup_index (0);
+    const SubTable *st = &thiz()->firstSubTable;
+    unsigned int count = thiz()->tableCount;
+    for (unsigned int i = 0; i < count; i++)
+    {
+      bool reverse;
+
+      if (!T::Types::extended && (st->u.header.coverage & st->u.header.Variation))
+	goto skip;
+
+      if (HB_DIRECTION_IS_HORIZONTAL (c->buffer->props.direction) != st->u.header.is_horizontal ())
+	goto skip;
+
+      reverse = bool (st->u.header.coverage & st->u.header.Backwards) !=
+		HB_DIRECTION_IS_BACKWARD (c->buffer->props.direction);
+
+      if (!c->buffer->message (c->font, "start subtable %u", c->lookup_index))
+	goto skip;
+
+      if (!seenCrossStream &&
+	  (st->u.header.coverage & st->u.header.CrossStream))
+      {
+	/* Attach all glyphs into a chain. */
+	seenCrossStream = true;
+	hb_glyph_position_t *pos = c->buffer->pos;
+	unsigned int count = c->buffer->len;
+	for (unsigned int i = 0; i < count; i++)
+	{
+	  pos[i].attach_type() = OT::Layout::GPOS_impl::ATTACH_TYPE_CURSIVE;
+	  pos[i].attach_chain() = HB_DIRECTION_IS_FORWARD (c->buffer->props.direction) ? -1 : +1;
+	  /* We intentionally don't set HB_BUFFER_SCRATCH_FLAG_HAS_GPOS_ATTACHMENT,
+	   * since there needs to be a non-zero attachment for post-positioning to
+	   * be needed. */
+	}
+      }
+
+      if (reverse)
+	c->buffer->reverse ();
+
+      {
+	/* See comment in sanitize() for conditional here. */
+	hb_sanitize_with_object_t with (&c->sanitizer, i < count - 1 ? st : (const SubTable *) nullptr);
+	ret |= st->dispatch (c);
+      }
+
+      if (reverse)
+	c->buffer->reverse ();
+
+      (void) c->buffer->message (c->font, "end subtable %u", c->lookup_index);
+
+    skip:
+      st = &StructAfter<SubTable> (*st);
+      c->set_lookup_index (c->lookup_index + 1);
+    }
+
+    return ret;
+  }
+
+  bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    if (unlikely (!thiz()->version.sanitize (c) ||
+		  (unsigned) thiz()->version < (unsigned) T::minVersion ||
+		  !thiz()->tableCount.sanitize (c)))
+      return_trace (false);
+
+    typedef typename T::SubTable SubTable;
+
+    const SubTable *st = &thiz()->firstSubTable;
+    unsigned int count = thiz()->tableCount;
+    for (unsigned int i = 0; i < count; i++)
+    {
+      if (unlikely (!st->u.header.sanitize (c)))
+	return_trace (false);
+      /* OpenType kern table has 2-byte subtable lengths.  That's limiting.
+       * MS implementation also only supports one subtable, of format 0,
+       * anyway.  Certain versions of some fonts, like Calibry, contain
+       * kern subtable that exceeds 64kb.  Looks like, the subtable length
+       * is simply ignored.  Which makes sense.  It's only needed if you
+       * have multiple subtables.  To handle such fonts, we just ignore
+       * the length for the last subtable. */
+      hb_sanitize_with_object_t with (c, i < count - 1 ? st : (const SubTable *) nullptr);
+
+      if (unlikely (!st->sanitize (c)))
+	return_trace (false);
+
+      st = &StructAfter<SubTable> (*st);
+    }
+
+    return_trace (true);
+  }
+};
+
+struct kerx : KerxTable<kerx>
+{
+  friend struct KerxTable<kerx>;
+
+  static constexpr hb_tag_t tableTag = HB_AAT_TAG_kerx;
+  static constexpr unsigned minVersion = 2u;
+
+  typedef KerxSubTableHeader SubTableHeader;
+  typedef SubTableHeader::Types Types;
+  typedef KerxSubTable SubTable;
+
+  bool has_data () const { return version; }
+
+  protected:
+  HBUINT16	version;	/* The version number of the extended kerning table
+				 * (currently 2, 3, or 4). */
+  HBUINT16	unused;		/* Set to 0. */
+  HBUINT32	tableCount;	/* The number of subtables included in the extended kerning
+				 * table. */
+  SubTable	firstSubTable;	/* Subtables. */
+/*subtableGlyphCoverageArray*/	/* Only if version >= 3. We don't use. */
+
+  public:
+  DEFINE_SIZE_MIN (8);
+};
+
+
+} /* namespace AAT */
+
+
+#endif /* HB_AAT_LAYOUT_KERX_TABLE_HH */