Update from https://crrev.com/317530

third_party/ots/src/gsub.cc

Index: third_party/ots/src/gsub.cc
diff --git a/third_party/ots/src/gsub.cc b/third_party/ots/src/gsub.cc
new file mode 100644
index 0000000000000000000000000000000000000000..af31144635f6ae9596881833097b17b9d44f99fe
--- /dev/null
+++ b/third_party/ots/src/gsub.cc
@@ -0,0 +1,685 @@
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "gsub.h"
+
+#include <limits>
+#include <vector>
+
+#include "layout.h"
+#include "maxp.h"
+
+// GSUB - The Glyph Substitution Table
+// http://www.microsoft.com/typography/otspec/gsub.htm
+
+#define TABLE_NAME "GSUB"
+
+namespace {
+
+// The GSUB header size
+const size_t kGsubHeaderSize = 4 + 3 * 2;
+
+enum GSUB_TYPE {
+  GSUB_TYPE_SINGLE = 1,
+  GSUB_TYPE_MULTIPLE = 2,
+  GSUB_TYPE_ALTERNATE = 3,
+  GSUB_TYPE_LIGATURE = 4,
+  GSUB_TYPE_CONTEXT = 5,
+  GSUB_TYPE_CHANGING_CONTEXT = 6,
+  GSUB_TYPE_EXTENSION_SUBSTITUTION = 7,
+  GSUB_TYPE_REVERSE_CHAINING_CONTEXT_SINGLE = 8,
+  GSUB_TYPE_RESERVED = 9
+};
+
+// Lookup type parsers.
+bool ParseSingleSubstitution(const ots::OpenTypeFile *file,
+                             const uint8_t *data, const size_t length);
+bool ParseMutipleSubstitution(const ots::OpenTypeFile *file,
+                              const uint8_t *data, const size_t length);
+bool ParseAlternateSubstitution(const ots::OpenTypeFile *file,
+                                const uint8_t *data, const size_t length);
+bool ParseLigatureSubstitution(const ots::OpenTypeFile *file,
+      const uint8_t *data, const size_t length);
+bool ParseContextSubstitution(const ots::OpenTypeFile *file,
+                              const uint8_t *data, const size_t length);
+bool ParseChainingContextSubstitution(const ots::OpenTypeFile *file,
+                                      const uint8_t *data,
+                                      const size_t length);
+bool ParseExtensionSubstitution(const ots::OpenTypeFile *file,
+                                const uint8_t *data, const size_t length);
+bool ParseReverseChainingContextSingleSubstitution(
+    const ots::OpenTypeFile *file, const uint8_t *data, const size_t length);
+
+const ots::LookupSubtableParser::TypeParser kGsubTypeParsers[] = {
+  {GSUB_TYPE_SINGLE, ParseSingleSubstitution},
+  {GSUB_TYPE_MULTIPLE, ParseMutipleSubstitution},
+  {GSUB_TYPE_ALTERNATE, ParseAlternateSubstitution},
+  {GSUB_TYPE_LIGATURE, ParseLigatureSubstitution},
+  {GSUB_TYPE_CONTEXT, ParseContextSubstitution},
+  {GSUB_TYPE_CHANGING_CONTEXT, ParseChainingContextSubstitution},
+  {GSUB_TYPE_EXTENSION_SUBSTITUTION, ParseExtensionSubstitution},
+  {GSUB_TYPE_REVERSE_CHAINING_CONTEXT_SINGLE,
+    ParseReverseChainingContextSingleSubstitution}
+};
+
+const ots::LookupSubtableParser kGsubLookupSubtableParser = {
+  arraysize(kGsubTypeParsers),
+  GSUB_TYPE_EXTENSION_SUBSTITUTION, kGsubTypeParsers
+};
+
+// Lookup Type 1:
+// Single Substitution Subtable
+bool ParseSingleSubstitution(const ots::OpenTypeFile *file,
+                             const uint8_t *data, const size_t length) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t format = 0;
+  uint16_t offset_coverage = 0;
+
+  if (!subtable.ReadU16(&format) ||
+      !subtable.ReadU16(&offset_coverage)) {
+    return OTS_FAILURE_MSG("Failed to read single subst table header");
+  }
+
+  const uint16_t num_glyphs = file->maxp->num_glyphs;
+  if (format == 1) {
+    // Parse SingleSubstFormat1
+    int16_t delta_glyph_id = 0;
+    if (!subtable.ReadS16(&delta_glyph_id)) {
+      return OTS_FAILURE_MSG("Failed to read glyph shift from format 1 single subst table");
+    }
+    if (std::abs(delta_glyph_id) >= num_glyphs) {
+      return OTS_FAILURE_MSG("bad glyph shift of %d in format 1 single subst table", delta_glyph_id);
+    }
+  } else if (format == 2) {
+    // Parse SingleSubstFormat2
+    uint16_t glyph_count = 0;
+    if (!subtable.ReadU16(&glyph_count)) {
+      return OTS_FAILURE_MSG("Failed to read glyph cound in format 2 single subst table");
+    }
+    if (glyph_count > num_glyphs) {
+      return OTS_FAILURE_MSG("Bad glyph count %d > %d in format 2 single subst table", glyph_count, num_glyphs);
+    }
+    for (unsigned i = 0; i < glyph_count; ++i) {
+      uint16_t substitute = 0;
+      if (!subtable.ReadU16(&substitute)) {
+        return OTS_FAILURE_MSG("Failed to read substitution %d in format 2 single subst table", i);
+      }
+      if (substitute >= num_glyphs) {
+        return OTS_FAILURE_MSG("too large substitute: %u", substitute);
+      }
+    }
+  } else {
+    return OTS_FAILURE_MSG("Bad single subst table format %d", format);
+  }
+
+  if (offset_coverage < subtable.offset() || offset_coverage >= length) {
+    return OTS_FAILURE_MSG("Bad coverage offset %x", offset_coverage);
+  }
+  if (!ots::ParseCoverageTable(file, data + offset_coverage,
+                               length - offset_coverage, num_glyphs)) {
+    return OTS_FAILURE_MSG("Failed to parse coverage table");
+  }
+
+  return true;
+}
+
+bool ParseSequenceTable(const ots::OpenTypeFile *file,
+                        const uint8_t *data, const size_t length,
+                        const uint16_t num_glyphs) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t glyph_count = 0;
+  if (!subtable.ReadU16(&glyph_count)) {
+    return OTS_FAILURE_MSG("Failed to read glyph count in sequence table");
+  }
+  if (glyph_count > num_glyphs) {
+    return OTS_FAILURE_MSG("bad glyph count %d > %d", glyph_count, num_glyphs);
+  }
+  for (unsigned i = 0; i < glyph_count; ++i) {
+    uint16_t substitute = 0;
+    if (!subtable.ReadU16(&substitute)) {
+      return OTS_FAILURE_MSG("Failedt o read substitution %d in sequence table", i);
+    }
+    if (substitute >= num_glyphs) {
+      return OTS_FAILURE_MSG("Bad subsitution (%d) %d > %d", i, substitute, num_glyphs);
+    }
+  }
+
+  return true;
+}
+
+// Lookup Type 2:
+// Multiple Substitution Subtable
+bool ParseMutipleSubstitution(const ots::OpenTypeFile *file,
+                              const uint8_t *data, const size_t length) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t format = 0;
+  uint16_t offset_coverage = 0;
+  uint16_t sequence_count = 0;
+
+  if (!subtable.ReadU16(&format) ||
+      !subtable.ReadU16(&offset_coverage) ||
+      !subtable.ReadU16(&sequence_count)) {
+    return OTS_FAILURE_MSG("Can't read header of multiple subst table");
+  }
+
+  if (format != 1) {
+    return OTS_FAILURE_MSG("Bad multiple subst table format %d", format);
+  }
+
+  const uint16_t num_glyphs = file->maxp->num_glyphs;
+  const unsigned sequence_end = static_cast<unsigned>(6) +
+      sequence_count * 2;
+  if (sequence_end > std::numeric_limits<uint16_t>::max()) {
+    return OTS_FAILURE_MSG("Bad segence end %d, in multiple subst", sequence_end);
+  }
+  for (unsigned i = 0; i < sequence_count; ++i) {
+    uint16_t offset_sequence = 0;
+    if (!subtable.ReadU16(&offset_sequence)) {
+      return OTS_FAILURE_MSG("Failed to read sequence offset for sequence %d", i);
+    }
+    if (offset_sequence < sequence_end || offset_sequence >= length) {
+      return OTS_FAILURE_MSG("Bad sequence offset %d for sequence %d", offset_sequence, i);
+    }
+    if (!ParseSequenceTable(file, data + offset_sequence, length - offset_sequence,
+                            num_glyphs)) {
+      return OTS_FAILURE_MSG("Failed to parse sequence table %d", i);
+    }
+  }
+
+  if (offset_coverage < sequence_end || offset_coverage >= length) {
+    return OTS_FAILURE_MSG("Bad coverage offset %d", offset_coverage);
+  }
+  if (!ots::ParseCoverageTable(file, data + offset_coverage,
+                               length - offset_coverage, num_glyphs)) {
+    return OTS_FAILURE_MSG("Failed to parse coverage table");
+  }
+
+  return true;
+}
+
+bool ParseAlternateSetTable(const ots::OpenTypeFile *file,
+                            const uint8_t *data, const size_t length,
+                            const uint16_t num_glyphs) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t glyph_count = 0;
+  if (!subtable.ReadU16(&glyph_count)) {
+    return OTS_FAILURE_MSG("Failed to read alternate set header");
+  }
+  if (glyph_count > num_glyphs) {
+    return OTS_FAILURE_MSG("Bad glyph count %d > %d in alternate set table", glyph_count, num_glyphs);
+  }
+  for (unsigned i = 0; i < glyph_count; ++i) {
+    uint16_t alternate = 0;
+    if (!subtable.ReadU16(&alternate)) {
+      return OTS_FAILURE_MSG("Can't read alternate %d", i);
+    }
+    if (alternate >= num_glyphs) {
+      return OTS_FAILURE_MSG("Too large alternate: %u", alternate);
+    }
+  }
+  return true;
+}
+
+// Lookup Type 3:
+// Alternate Substitution Subtable
+bool ParseAlternateSubstitution(const ots::OpenTypeFile *file,
+                                const uint8_t *data, const size_t length) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t format = 0;
+  uint16_t offset_coverage = 0;
+  uint16_t alternate_set_count = 0;
+
+  if (!subtable.ReadU16(&format) ||
+      !subtable.ReadU16(&offset_coverage) ||
+      !subtable.ReadU16(&alternate_set_count)) {
+    return OTS_FAILURE_MSG("Can't read alternate subst header");
+  }
+
+  if (format != 1) {
+    return OTS_FAILURE_MSG("Bad alternate subst table format %d", format);
+  }
+
+  const uint16_t num_glyphs = file->maxp->num_glyphs;
+  const unsigned alternate_set_end = static_cast<unsigned>(6) +
+      alternate_set_count * 2;
+  if (alternate_set_end > std::numeric_limits<uint16_t>::max()) {
+    return OTS_FAILURE_MSG("Bad end of alternate set %d", alternate_set_end);
+  }
+  for (unsigned i = 0; i < alternate_set_count; ++i) {
+    uint16_t offset_alternate_set = 0;
+    if (!subtable.ReadU16(&offset_alternate_set)) {
+      return OTS_FAILURE_MSG("Can't read alternate set offset for set %d", i);
+    }
+    if (offset_alternate_set < alternate_set_end ||
+        offset_alternate_set >= length) {
+      return OTS_FAILURE_MSG("Bad alternate set offset %d for set %d", offset_alternate_set, i);
+    }
+    if (!ParseAlternateSetTable(file, data + offset_alternate_set,
+                                length - offset_alternate_set,
+                                num_glyphs)) {
+      return OTS_FAILURE_MSG("Failed to parse alternate set");
+    }
+  }
+
+  if (offset_coverage < alternate_set_end || offset_coverage >= length) {
+    return OTS_FAILURE_MSG("Bad coverage offset %d", offset_coverage);
+  }
+  if (!ots::ParseCoverageTable(file, data + offset_coverage,
+                               length - offset_coverage, num_glyphs)) {
+    return OTS_FAILURE_MSG("Failed to parse coverage table");
+  }
+
+  return true;
+}
+
+bool ParseLigatureTable(const ots::OpenTypeFile *file,
+                        const uint8_t *data, const size_t length,
+                        const uint16_t num_glyphs) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t lig_glyph = 0;
+  uint16_t comp_count = 0;
+
+  if (!subtable.ReadU16(&lig_glyph) ||
+      !subtable.ReadU16(&comp_count)) {
+    return OTS_FAILURE_MSG("Failed to read ligatuer table header");
+  }
+
+  if (lig_glyph >= num_glyphs) {
+    return OTS_FAILURE_MSG("too large lig_glyph: %u", lig_glyph);
+  }
+  if (comp_count == 0 || comp_count > num_glyphs) {
+    return OTS_FAILURE_MSG("Bad component count of %d", comp_count);
+  }
+  for (unsigned i = 0; i < comp_count - static_cast<unsigned>(1); ++i) {
+    uint16_t component = 0;
+    if (!subtable.ReadU16(&component)) {
+      return OTS_FAILURE_MSG("Can't read ligature component %d", i);
+    }
+    if (component >= num_glyphs) {
+      return OTS_FAILURE_MSG("Bad ligature component %d of %d", i, component);
+    }
+  }
+
+  return true;
+}
+
+bool ParseLigatureSetTable(const ots::OpenTypeFile *file,
+                           const uint8_t *data, const size_t length,
+                           const uint16_t num_glyphs) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t ligature_count = 0;
+
+  if (!subtable.ReadU16(&ligature_count)) {
+    return OTS_FAILURE_MSG("Can't read ligature count in ligature set");
+  }
+
+  const unsigned ligature_end = static_cast<unsigned>(2) + ligature_count * 2;
+  if (ligature_end > std::numeric_limits<uint16_t>::max()) {
+    return OTS_FAILURE_MSG("Bad end of ligature %d in ligature set", ligature_end);
+  }
+  for (unsigned i = 0; i < ligature_count; ++i) {
+    uint16_t offset_ligature = 0;
+    if (!subtable.ReadU16(&offset_ligature)) {
+      return OTS_FAILURE_MSG("Failed to read ligature offset %d", i);
+    }
+    if (offset_ligature < ligature_end || offset_ligature >= length) {
+      return OTS_FAILURE_MSG("Bad ligature offset %d for ligature %d", offset_ligature, i);
+    }
+    if (!ParseLigatureTable(file, data + offset_ligature, length - offset_ligature,
+                            num_glyphs)) {
+      return OTS_FAILURE_MSG("Failed to parse ligature %d", i);
+    }
+  }
+
+  return true;
+}
+
+// Lookup Type 4:
+// Ligature Substitution Subtable
+bool ParseLigatureSubstitution(const ots::OpenTypeFile *file,
+                               const uint8_t *data, const size_t length) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t format = 0;
+  uint16_t offset_coverage = 0;
+  uint16_t lig_set_count = 0;
+
+  if (!subtable.ReadU16(&format) ||
+      !subtable.ReadU16(&offset_coverage) ||
+      !subtable.ReadU16(&lig_set_count)) {
+    return OTS_FAILURE_MSG("Failed to read ligature substitution header");
+  }
+
+  if (format != 1) {
+    return OTS_FAILURE_MSG("Bad ligature substitution table format %d", format);
+  }
+
+  const uint16_t num_glyphs = file->maxp->num_glyphs;
+  const unsigned ligature_set_end = static_cast<unsigned>(6) +
+      lig_set_count * 2;
+  if (ligature_set_end > std::numeric_limits<uint16_t>::max()) {
+    return OTS_FAILURE_MSG("Bad end of ligature set %d in ligature substitution table", ligature_set_end);
+  }
+  for (unsigned i = 0; i < lig_set_count; ++i) {
+    uint16_t offset_ligature_set = 0;
+    if (!subtable.ReadU16(&offset_ligature_set)) {
+      return OTS_FAILURE_MSG("Can't read ligature set offset %d", i);
+    }
+    if (offset_ligature_set < ligature_set_end ||
+        offset_ligature_set >= length) {
+      return OTS_FAILURE_MSG("Bad ligature set offset %d for set %d", offset_ligature_set, i);
+    }
+    if (!ParseLigatureSetTable(file, data + offset_ligature_set,
+                               length - offset_ligature_set, num_glyphs)) {
+      return OTS_FAILURE_MSG("Failed to parse ligature set %d", i);
+    }
+  }
+
+  if (offset_coverage < ligature_set_end || offset_coverage >= length) {
+    return OTS_FAILURE_MSG("Bad coverage offset %d", offset_coverage);
+  }
+  if (!ots::ParseCoverageTable(file, data + offset_coverage,
+                               length - offset_coverage, num_glyphs)) {
+    return OTS_FAILURE_MSG("Failed to parse coverage table");
+  }
+
+  return true;
+}
+
+// Lookup Type 5:
+// Contextual Substitution Subtable
+bool ParseContextSubstitution(const ots::OpenTypeFile *file,
+                              const uint8_t *data, const size_t length) {
+  return ots::ParseContextSubtable(file, data, length, file->maxp->num_glyphs,
+                                   file->gsub->num_lookups);
+}
+
+// Lookup Type 6:
+// Chaining Contextual Substitution Subtable
+bool ParseChainingContextSubstitution(const ots::OpenTypeFile *file,
+                                      const uint8_t *data,
+                                      const size_t length) {
+  return ots::ParseChainingContextSubtable(file, data, length,
+                                           file->maxp->num_glyphs,
+                                           file->gsub->num_lookups);
+}
+
+// Lookup Type 7:
+// Extension Substition
+bool ParseExtensionSubstitution(const ots::OpenTypeFile *file,
+                                const uint8_t *data, const size_t length) {
+  return ots::ParseExtensionSubtable(file, data, length,
+                                     &kGsubLookupSubtableParser);
+}
+
+// Lookup Type 8:
+// Reverse Chaining Contexual Single Substitution Subtable
+bool ParseReverseChainingContextSingleSubstitution(
+    const ots::OpenTypeFile *file, const uint8_t *data, const size_t length) {
+  ots::Buffer subtable(data, length);
+
+  uint16_t format = 0;
+  uint16_t offset_coverage = 0;
+
+  if (!subtable.ReadU16(&format) ||
+      !subtable.ReadU16(&offset_coverage)) {
+    return OTS_FAILURE_MSG("Failed to read reverse chaining header");
+  }
+
+  const uint16_t num_glyphs = file->maxp->num_glyphs;
+
+  uint16_t backtrack_glyph_count = 0;
+  if (!subtable.ReadU16(&backtrack_glyph_count)) {
+    return OTS_FAILURE_MSG("Failed to read backtrack glyph count in reverse chaining table");
+  }
+  if (backtrack_glyph_count > num_glyphs) {
+    return OTS_FAILURE_MSG("Bad backtrack glyph count of %d", backtrack_glyph_count);
+  }
+  std::vector<uint16_t> offsets_backtrack;
+  offsets_backtrack.reserve(backtrack_glyph_count);
+  for (unsigned i = 0; i < backtrack_glyph_count; ++i) {
+    uint16_t offset = 0;
+    if (!subtable.ReadU16(&offset)) {
+      return OTS_FAILURE_MSG("Failed to read backtrack offset %d", i);
+    }
+    offsets_backtrack.push_back(offset);
+  }
+
+  uint16_t lookahead_glyph_count = 0;
+  if (!subtable.ReadU16(&lookahead_glyph_count)) {
+    return OTS_FAILURE_MSG("Failed to read look ahead glyph count");
+  }
+  if (lookahead_glyph_count > num_glyphs) {
+    return OTS_FAILURE_MSG("Bad look ahead glyph count %d", lookahead_glyph_count);
+  }
+  std::vector<uint16_t> offsets_lookahead;
+  offsets_lookahead.reserve(lookahead_glyph_count);
+  for (unsigned i = 0; i < lookahead_glyph_count; ++i) {
+    uint16_t offset = 0;
+    if (!subtable.ReadU16(&offset)) {
+      return OTS_FAILURE_MSG("Can't read look ahead offset %d", i);
+    }
+    offsets_lookahead.push_back(offset);
+  }
+
+  uint16_t glyph_count = 0;
+  if (!subtable.ReadU16(&glyph_count)) {
+    return OTS_FAILURE_MSG("Can't read glyph count in reverse chaining table");
+  }
+  if (glyph_count > num_glyphs) {
+    return OTS_FAILURE_MSG("Bad glyph count of %d", glyph_count);
+  }
+  for (unsigned i = 0; i < glyph_count; ++i) {
+    uint16_t substitute = 0;
+    if (!subtable.ReadU16(&substitute)) {
+      return OTS_FAILURE_MSG("Failed to read substitution %d reverse chaining table", i);
+    }
+    if (substitute >= num_glyphs) {
+      return OTS_FAILURE_MSG("Bad substitute glyph %d in reverse chaining table substitution %d", substitute, i);
+    }
+  }
+
+  const unsigned substitute_end = static_cast<unsigned>(10) +
+      (backtrack_glyph_count + lookahead_glyph_count + glyph_count) * 2;
+  if (substitute_end > std::numeric_limits<uint16_t>::max()) {
+    return OTS_FAILURE_MSG("Bad substitute end offset in reverse chaining table");
+  }
+
+  if (offset_coverage < substitute_end || offset_coverage >= length) {
+    return OTS_FAILURE_MSG("Bad coverage offset %d in reverse chaining table", offset_coverage);
+  }
+  if (!ots::ParseCoverageTable(file, data + offset_coverage,
+                               length - offset_coverage, num_glyphs)) {
+    return OTS_FAILURE_MSG("Failed to parse coverage table in reverse chaining table");
+  }
+
+  for (unsigned i = 0; i < backtrack_glyph_count; ++i) {
+    if (offsets_backtrack[i] < substitute_end ||
+        offsets_backtrack[i] >= length) {
+      return OTS_FAILURE_MSG("Bad backtrack offset %d for backtrack %d in reverse chaining table", offsets_backtrack[i], i);
+    }
+    if (!ots::ParseCoverageTable(file, data + offsets_backtrack[i],
+                                 length - offsets_backtrack[i], num_glyphs)) {
+      return OTS_FAILURE_MSG("Failed to parse coverage table for backtrack %d in reverse chaining table", i);
+    }
+  }
+
+  for (unsigned i = 0; i < lookahead_glyph_count; ++i) {
+    if (offsets_lookahead[i] < substitute_end ||
+        offsets_lookahead[i] >= length) {
+      return OTS_FAILURE_MSG("Bad lookahead offset %d for lookahead %d in reverse chaining table", offsets_lookahead[i], i);
+    }
+    if (!ots::ParseCoverageTable(file, data + offsets_lookahead[i],
+                                 length - offsets_lookahead[i], num_glyphs)) {
+      return OTS_FAILURE_MSG("Failed to parse lookahead coverage table %d in reverse chaining table", i);
+    }
+  }
+
+  return true;
+}
+
+}  // namespace
+
+#define DROP_THIS_TABLE(msg_) \
+  do { \
+    OTS_FAILURE_MSG(msg_ ", table discarded"); \
+    file->gsub->data = 0; \
+    file->gsub->length = 0; \
+  } while (0)
+
+namespace ots {
+
+// As far as I checked, following fonts contain invalid values in GSUB table.
+// OTS will drop their GSUB table.
+//
+// # too large substitute (value is 0xFFFF)
+// kaiu.ttf
+// mingliub2.ttf
+// mingliub1.ttf
+// mingliub0.ttf
+// GraublauWeb.otf
+// GraublauWebBold.otf
+//
+// # too large alternate (value is 0xFFFF)
+// ManchuFont.ttf
+//
+// # bad offset to lang sys table (NULL offset)
+// DejaVuMonoSansBold.ttf
+// DejaVuMonoSansBoldOblique.ttf
+// DejaVuMonoSansOblique.ttf
+// DejaVuSansMono-BoldOblique.ttf
+// DejaVuSansMono-Oblique.ttf
+// DejaVuSansMono-Bold.ttf
+//
+// # bad start coverage index
+// GenBasBI.ttf
+// GenBasI.ttf
+// AndBasR.ttf
+// GenBkBasI.ttf
+// CharisSILR.ttf
+// CharisSILBI.ttf
+// CharisSILI.ttf
+// CharisSILB.ttf
+// DoulosSILR.ttf
+// CharisSILBI.ttf
+// GenBkBasB.ttf
+// GenBkBasR.ttf
+// GenBkBasBI.ttf
+// GenBasB.ttf
+// GenBasR.ttf
+//
+// # glyph range is overlapping
+// KacstTitleL.ttf
+// KacstDecorative.ttf
+// KacstTitle.ttf
+// KacstArt.ttf
+// KacstPoster.ttf
+// KacstQurn.ttf
+// KacstDigital.ttf
+// KacstBook.ttf
+// KacstFarsi.ttf
+
+bool ots_gsub_parse(OpenTypeFile *file, const uint8_t *data, size_t length) {
+  // Parsing gsub table requires |file->maxp->num_glyphs|
+  if (!file->maxp) {
+    return OTS_FAILURE_MSG("Missing maxp table in font, needed by GSUB");
+  }
+
+  Buffer table(data, length);
+
+  OpenTypeGSUB *gsub = new OpenTypeGSUB;
+  file->gsub = gsub;
+
+  uint32_t version = 0;
+  uint16_t offset_script_list = 0;
+  uint16_t offset_feature_list = 0;
+  uint16_t offset_lookup_list = 0;
+  if (!table.ReadU32(&version) ||
+      !table.ReadU16(&offset_script_list) ||
+      !table.ReadU16(&offset_feature_list) ||
+      !table.ReadU16(&offset_lookup_list)) {
+    DROP_THIS_TABLE("Incomplete table");
+    return true;
+  }
+
+  if (version != 0x00010000) {
+    DROP_THIS_TABLE("Bad version");
+    return true;
+  }
+
+  if (offset_lookup_list) {
+    if (offset_lookup_list < kGsubHeaderSize || offset_lookup_list >= length) {
+      DROP_THIS_TABLE("Bad lookup list offset in table header");
+      return true;
+    }
+
+    if (!ParseLookupListTable(file, data + offset_lookup_list,
+                              length - offset_lookup_list,
+                              &kGsubLookupSubtableParser,
+                              &gsub->num_lookups)) {
+      DROP_THIS_TABLE("Failed to parse lookup list table");
+      return true;
+    }
+  }
+
+  uint16_t num_features = 0;
+  if (offset_feature_list) {
+    if (offset_feature_list < kGsubHeaderSize || offset_feature_list >= length) {
+      DROP_THIS_TABLE("Bad feature list offset in table header");
+      return true;
+    }
+
+    if (!ParseFeatureListTable(file, data + offset_feature_list,
+                               length - offset_feature_list, gsub->num_lookups,
+                               &num_features)) {
+      DROP_THIS_TABLE("Failed to parse feature list table");
+      return true;
+    }
+  }
+
+  if (offset_script_list) {
+    if (offset_script_list < kGsubHeaderSize || offset_script_list >= length) {
+      DROP_THIS_TABLE("Bad script list offset in table header");
+      return true;
+    }
+
+    if (!ParseScriptListTable(file, data + offset_script_list,
+                              length - offset_script_list, num_features)) {
+      DROP_THIS_TABLE("Failed to parse script list table");
+      return true;
+    }
+  }
+
+  gsub->data = data;
+  gsub->length = length;
+  return true;
+}
+
+bool ots_gsub_should_serialise(OpenTypeFile *file) {
+  return file->gsub != NULL && file->gsub->data != NULL;
+}
+
+bool ots_gsub_serialise(OTSStream *out, OpenTypeFile *file) {
+  if (!out->Write(file->gsub->data, file->gsub->length)) {
+    return OTS_FAILURE_MSG("Failed to write GSUB table");
+  }
+
+  return true;
+}
+
+void ots_gsub_free(OpenTypeFile *file) {
+  delete file->gsub;
+}
+
+}  // namespace ots
+
+#undef TABLE_NAME
+#undef DROP_THIS_TABLE