tor-browser

layout.cc (65426B)

---

// Copyright (c) 2011-2017 The OTS 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 "layout.h"

#include <limits>
#include <vector>

#include "fvar.h"
#include "gdef.h"
#include "maxp.h"

// OpenType Layout Common Table Formats
// http://www.microsoft.com/typography/otspec/chapter2.htm

#define TABLE_NAME "Layout" // XXX: use individual table names

namespace {

// The 'DFLT' tag of script table.
const uint32_t kScriptTableTagDflt = 0x44464c54;
// The value which represents there is no required feature index.
const uint16_t kNoRequiredFeatureIndexDefined = 0xFFFF;
// The lookup flag bit which indicates existence of MarkFilteringSet.
const uint16_t kUseMarkFilteringSetBit = 0x0010;
// The maximum type number of format for device tables.
const uint16_t kMaxDeltaFormatType = 3;
// In variation fonts, Device Tables are replaced by VariationIndex tables,
// indicated by this flag in the deltaFormat field.
const uint16_t kVariationIndex = 0x8000;

struct ScriptRecord {
 uint32_t tag;
 uint16_t offset;
};

struct LangSysRecord {
 uint32_t tag;
 uint16_t offset;
};

struct FeatureRecord {
 uint32_t tag;
 uint16_t offset;
};

bool ParseLangSysTable(const ots::Font *font,
                      ots::Buffer *subtable, const uint32_t tag,
                      const uint16_t num_features) {
 uint16_t offset_lookup_order = 0;
 uint16_t req_feature_index = 0;
 uint16_t feature_count = 0;
 if (!subtable->ReadU16(&offset_lookup_order) ||
     !subtable->ReadU16(&req_feature_index) ||
     !subtable->ReadU16(&feature_count)) {
   return OTS_FAILURE_MSG("Failed to read langsys header for tag %c%c%c%c", OTS_UNTAG(tag));
 }
 // |offset_lookup_order| is reserved and should be NULL.
 if (offset_lookup_order != 0) {
   return OTS_FAILURE_MSG("Bad lookup offset order %d for langsys tag %c%c%c%c", offset_lookup_order, OTS_UNTAG(tag));
 }
 if (req_feature_index != kNoRequiredFeatureIndexDefined &&
     req_feature_index >= num_features) {
   return OTS_FAILURE_MSG("Bad required features index %d for langsys tag %c%c%c%c", req_feature_index, OTS_UNTAG(tag));
 }
 if (feature_count > num_features) {
   return OTS_FAILURE_MSG("Bad feature count %d for langsys tag %c%c%c%c", feature_count, OTS_UNTAG(tag));
 }

 for (unsigned i = 0; i < feature_count; ++i) {
   uint16_t feature_index = 0;
   if (!subtable->ReadU16(&feature_index)) {
     return OTS_FAILURE_MSG("Failed to read feature index %d for langsys tag %c%c%c%c", i, OTS_UNTAG(tag));
   }
   if (feature_index >= num_features) {
     return OTS_FAILURE_MSG("Bad feature index %d for feature %d for langsys tag %c%c%c%c", feature_index, i, OTS_UNTAG(tag));
   }
 }
 return true;
}

bool ParseScriptTable(const ots::Font *font,
                     const uint8_t *data, const size_t length,
                     const uint32_t tag, const uint16_t num_features) {
 ots::Buffer subtable(data, length);

 uint16_t offset_default_lang_sys = 0;
 uint16_t lang_sys_count = 0;
 if (!subtable.ReadU16(&offset_default_lang_sys) ||
     !subtable.ReadU16(&lang_sys_count)) {
   return OTS_FAILURE_MSG("Failed to read script header for script tag %c%c%c%c", OTS_UNTAG(tag));
 }

 // The spec requires a script table for 'DFLT' tag must contain non-NULL
 // |offset_default_lang_sys|.
 // https://www.microsoft.com/typography/otspec/chapter2.htm
 if (tag == kScriptTableTagDflt) {
   if (offset_default_lang_sys == 0) {
     return OTS_FAILURE_MSG("DFLT script doesn't satisfy the spec. DefaultLangSys is NULL");
   }
 }

 const unsigned lang_sys_record_end =
     6 * static_cast<unsigned>(lang_sys_count) + 4;
 if (lang_sys_record_end > std::numeric_limits<uint16_t>::max()) {
   return OTS_FAILURE_MSG("Bad end of langsys record %d for script tag %c%c%c%c", lang_sys_record_end, OTS_UNTAG(tag));
 }

 std::vector<LangSysRecord> lang_sys_records;
 lang_sys_records.resize(lang_sys_count);
 uint32_t last_tag = 0;
 for (unsigned i = 0; i < lang_sys_count; ++i) {
   if (!subtable.ReadU32(&lang_sys_records[i].tag) ||
       !subtable.ReadU16(&lang_sys_records[i].offset)) {
     return OTS_FAILURE_MSG("Failed to read langsys record header %d for script tag %c%c%c%c", i, OTS_UNTAG(tag));
   }
   // The record array must store the records alphabetically by tag
   if (last_tag != 0 && last_tag > lang_sys_records[i].tag) {
     return OTS_FAILURE_MSG("Bad last tag %d for langsys record %d for script tag %c%c%c%c", last_tag, i, OTS_UNTAG(tag));
   }
   if (lang_sys_records[i].offset < lang_sys_record_end ||
       lang_sys_records[i].offset >= length) {
     return OTS_FAILURE_MSG("bad offset to lang sys table: %x",
                 lang_sys_records[i].offset);
   }
   last_tag = lang_sys_records[i].tag;
 }

 // Check lang sys tables
 for (unsigned i = 0; i < lang_sys_count; ++i) {
   subtable.set_offset(lang_sys_records[i].offset);
   if (!ParseLangSysTable(font, &subtable, lang_sys_records[i].tag, num_features)) {
     return OTS_FAILURE_MSG("Failed to parse langsys table %d (%c%c%c%c) for script tag %c%c%c%c", i, OTS_UNTAG(lang_sys_records[i].tag), OTS_UNTAG(tag));
   }
 }

 return true;
}

bool ParseFeatureTable(const ots::Font *font,
                      const uint8_t *data, const size_t length,
                      const uint16_t num_lookups) {
 ots::Buffer subtable(data, length);

 uint16_t offset_feature_params = 0;
 uint16_t lookup_count = 0;
 if (!subtable.ReadU16(&offset_feature_params) ||
     !subtable.ReadU16(&lookup_count)) {
   return OTS_FAILURE_MSG("Failed to read feature table header");
 }

 const unsigned feature_table_end =
     2 * static_cast<unsigned>(lookup_count) + 4;
 if (feature_table_end > std::numeric_limits<uint16_t>::max()) {
   return OTS_FAILURE_MSG("Bad end of feature table %d", feature_table_end);
 }
 // |offset_feature_params| is generally set to NULL.
 if (offset_feature_params != 0 &&
     (offset_feature_params < feature_table_end ||
      offset_feature_params >= length)) {
   return OTS_FAILURE_MSG("Bad feature params offset %d", offset_feature_params);
 }

 for (unsigned i = 0; i < lookup_count; ++i) {
   uint16_t lookup_index = 0;
   if (!subtable.ReadU16(&lookup_index)) {
     return OTS_FAILURE_MSG("Failed to read lookup index for lookup %d", i);
   }
   // lookup index starts with 0.
   if (lookup_index >= num_lookups) {
     return OTS_FAILURE_MSG("Bad lookup index %d for lookup %d", lookup_index, i);
   }
 }
 return true;
}

bool ParseClassDefFormat1(const ots::Font *font,
                         const uint8_t *data, size_t length,
                         const uint16_t num_glyphs,
                         const uint16_t num_classes) {
 ots::Buffer subtable(data, length);

 // Skip format field.
 if (!subtable.Skip(2)) {
   return OTS_FAILURE_MSG("Failed to skip class definition header");
 }

 uint16_t start_glyph = 0;
 if (!subtable.ReadU16(&start_glyph)) {
   return OTS_FAILURE_MSG("Failed to read starting glyph of class definition");
 }
 if (start_glyph > num_glyphs) {
   return OTS_FAILURE_MSG("Bad starting glyph %d in class definition", start_glyph);
 }

 uint16_t glyph_count = 0;
 if (!subtable.ReadU16(&glyph_count)) {
   return OTS_FAILURE_MSG("Failed to read glyph count in class definition");
 }
 if (glyph_count > num_glyphs) {
   return OTS_FAILURE_MSG("bad glyph count: %u", glyph_count);
 }
 for (unsigned i = 0; i < glyph_count; ++i) {
   uint16_t class_value = 0;
   if (!subtable.ReadU16(&class_value)) {
     return OTS_FAILURE_MSG("Failed to read class value for glyph %d in class definition", i);
   }
   if (class_value > num_classes) {
     return OTS_FAILURE_MSG("Bad class value %d for glyph %d in class definition", class_value, i);
   }
 }

 return true;
}

bool ParseClassDefFormat2(const ots::Font *font,
                         const uint8_t *data, size_t length,
                         const uint16_t num_glyphs,
                         const uint16_t num_classes) {
 ots::Buffer subtable(data, length);

 // Skip format field.
 if (!subtable.Skip(2)) {
   return OTS_FAILURE_MSG("Failed to read class definition format");
 }

 uint16_t range_count = 0;
 if (!subtable.ReadU16(&range_count)) {
   return OTS_FAILURE_MSG("Failed to read classRangeCount");
 }
 if (range_count > num_glyphs) {
   return OTS_FAILURE_MSG("classRangeCount > glyph count: %u > %u", range_count, num_glyphs);
 }

 uint16_t last_end = 0;
 for (unsigned i = 0; i < range_count; ++i) {
   uint16_t start = 0;
   uint16_t end = 0;
   uint16_t class_value = 0;
   if (!subtable.ReadU16(&start) ||
       !subtable.ReadU16(&end) ||
       !subtable.ReadU16(&class_value)) {
     return OTS_FAILURE_MSG("Failed to read ClassRangeRecord %d", i);
   }
   if (start > end) {
     return OTS_FAILURE_MSG("ClassRangeRecord %d, start > end: %u > %u", i, start, end);
   }
   if (last_end && start <= last_end) {
     return OTS_FAILURE_MSG("ClassRangeRecord %d start overlaps with end of the previous one: %u <= %u", i, start, last_end);
   }
   if (class_value > num_classes) {
     return OTS_FAILURE_MSG("ClassRangeRecord %d class > number of classes: %u > %u", i, class_value, num_classes);
   }
   last_end = end;
 }

 return true;
}

bool ParseCoverageFormat1(const ots::Font *font,
                         const uint8_t *data, size_t length,
                         const uint16_t num_glyphs,
                         const uint16_t expected_num_glyphs) {
 ots::Buffer subtable(data, length);

 // Skip format field.
 if (!subtable.Skip(2)) {
   return OTS_FAILURE_MSG("Failed to skip coverage format");
 }

 uint16_t glyph_count = 0;
 if (!subtable.ReadU16(&glyph_count)) {
   return OTS_FAILURE_MSG("Failed to read glyph count in coverage");
 }
 if (glyph_count > num_glyphs) {
   return OTS_FAILURE_MSG("bad glyph count: %u", glyph_count);
 }
 for (unsigned i = 0; i < glyph_count; ++i) {
   uint16_t glyph = 0;
   if (!subtable.ReadU16(&glyph)) {
     return OTS_FAILURE_MSG("Failed to read glyph %d in coverage", i);
   }
   if (glyph > num_glyphs) {
     return OTS_FAILURE_MSG("bad glyph ID: %u", glyph);
   }
 }

 if (expected_num_glyphs && expected_num_glyphs != glyph_count) {
     return OTS_FAILURE_MSG("unexpected number of glyphs: %u", glyph_count);
 }

 return true;
}

bool ParseCoverageFormat2(const ots::Font *font,
                         const uint8_t *data, size_t length,
                         const uint16_t num_glyphs,
                         const uint16_t expected_num_glyphs) {
 ots::Buffer subtable(data, length);

 // Skip format field.
 if (!subtable.Skip(2)) {
   return OTS_FAILURE_MSG("Failed to skip format of coverage type 2");
 }

 uint16_t range_count = 0;
 if (!subtable.ReadU16(&range_count)) {
   return OTS_FAILURE_MSG("Failed to read range count in coverage");
 }
 if (range_count > num_glyphs) {
   return OTS_FAILURE_MSG("bad range count: %u", range_count);
 }
 uint16_t last_end = 0;
 uint16_t last_start_coverage_index = 0;
 for (unsigned i = 0; i < range_count; ++i) {
   uint16_t start = 0;
   uint16_t end = 0;
   uint16_t start_coverage_index = 0;
   if (!subtable.ReadU16(&start) ||
       !subtable.ReadU16(&end) ||
       !subtable.ReadU16(&start_coverage_index)) {
     return OTS_FAILURE_MSG("Failed to read range %d in coverage", i);
   }

   // Some of the Adobe Pro fonts have ranges that overlap by one element: the
   // start of one range is equal to the end of the previous range. Therefore
   // the < in the following condition should be <= were it not for this.
   // See crbug.com/134135.
   if (start > end || (last_end && start < last_end)) {
     return OTS_FAILURE_MSG("glyph range is overlapping.");
   }
   if (start_coverage_index != last_start_coverage_index) {
     return OTS_FAILURE_MSG("bad start coverage index.");
   }
   last_end = end;
   last_start_coverage_index += end - start + 1;
 }

 if (expected_num_glyphs &&
     expected_num_glyphs != last_start_coverage_index) {
     return OTS_FAILURE_MSG("unexpected number of glyphs: %u", last_start_coverage_index);
 }

 return true;
}

// Parsers for Contextual subtables in GSUB/GPOS tables.

bool ParseLookupRecord(const ots::Font *font,
                      ots::Buffer *subtable, const uint16_t num_glyphs,
                      const uint16_t num_lookups) {
 uint16_t sequence_index = 0;
 uint16_t lookup_list_index = 0;
 if (!subtable->ReadU16(&sequence_index) ||
     !subtable->ReadU16(&lookup_list_index)) {
   return OTS_FAILURE_MSG("Failed to read header for lookup record");
 }
 if (sequence_index >= num_glyphs) {
   return OTS_FAILURE_MSG("Bad sequence index %d in lookup record", sequence_index);
 }
 if (lookup_list_index >= num_lookups) {
   return OTS_FAILURE_MSG("Bad lookup list index %d in lookup record", lookup_list_index);
 }
 return true;
}

bool ParseRuleSubtable(const ots::Font *font,
                      const uint8_t *data, const size_t length,
                      const uint16_t num_glyphs,
                      const uint16_t num_lookups) {
 ots::Buffer subtable(data, length);

 uint16_t glyph_count = 0;
 uint16_t lookup_count = 0;
 if (!subtable.ReadU16(&glyph_count) ||
     !subtable.ReadU16(&lookup_count)) {
   return OTS_FAILURE_MSG("Failed to read rule subtable header");
 }

 if (glyph_count == 0) {
   return OTS_FAILURE_MSG("Bad glyph count %d in rule subtable", glyph_count);
 }
 for (unsigned i = 0; i < glyph_count - static_cast<unsigned>(1); ++i) {
   uint16_t glyph_id = 0;
   if (!subtable.ReadU16(&glyph_id)) {
     return OTS_FAILURE_MSG("Failed to read glyph %d", i);
   }
   if (glyph_id > num_glyphs) {
     return OTS_FAILURE_MSG("Bad glyph %d for entry %d", glyph_id, i);
   }
 }

 for (unsigned i = 0; i < lookup_count; ++i) {
   if (!ParseLookupRecord(font, &subtable, num_glyphs, num_lookups)) {
     return OTS_FAILURE_MSG("Failed to parse lookup record %d", i);
   }
 }
 return true;
}

bool ParseRuleSetTable(const ots::Font *font,
                      const uint8_t *data, const size_t length,
                      const uint16_t num_glyphs,
                      const uint16_t num_lookups) {
 ots::Buffer subtable(data, length);

 uint16_t rule_count = 0;
 if (!subtable.ReadU16(&rule_count)) {
   return OTS_FAILURE_MSG("Failed to read rule count in rule set");
 }
 const unsigned rule_end = 2 * static_cast<unsigned>(rule_count) + 2;
 if (rule_end > std::numeric_limits<uint16_t>::max()) {
   return OTS_FAILURE_MSG("Bad end of rule %d in rule set", rule_end);
 }

 for (unsigned i = 0; i < rule_count; ++i) {
   uint16_t offset_rule = 0;
   if (!subtable.ReadU16(&offset_rule)) {
     return OTS_FAILURE_MSG("Failed to read rule offset for rule set %d", i);
   }
   if (offset_rule < rule_end || offset_rule >= length) {
     return OTS_FAILURE_MSG("Bad rule offset %d in set %d", offset_rule, i);
   }
   if (!ParseRuleSubtable(font, data + offset_rule, length - offset_rule,
                          num_glyphs, num_lookups)) {
     return OTS_FAILURE_MSG("Failed to parse rule set %d", i);
   }
 }

 return true;
}

bool ParseContextFormat1(const ots::Font *font,
                        const uint8_t *data, const size_t length,
                        const uint16_t num_glyphs,
                        const uint16_t num_lookups) {
 ots::Buffer subtable(data, length);

 uint16_t offset_coverage = 0;
 uint16_t rule_set_count = 0;
 // Skip format field.
 if (!subtable.Skip(2) ||
     !subtable.ReadU16(&offset_coverage) ||
     !subtable.ReadU16(&rule_set_count)) {
   return OTS_FAILURE_MSG("Failed to read header of context format 1");
 }

 const unsigned rule_set_end = static_cast<unsigned>(6) +
     rule_set_count * 2;
 if (rule_set_end > std::numeric_limits<uint16_t>::max()) {
   return OTS_FAILURE_MSG("Bad end of rule set %d of context format 1", rule_set_end);
 }
 if (offset_coverage < rule_set_end || offset_coverage >= length) {
   return OTS_FAILURE_MSG("Bad coverage offset %d in context format 1", offset_coverage);
 }
 if (!ots::ParseCoverageTable(font, data + offset_coverage,
                              length - offset_coverage, num_glyphs)) {
   return OTS_FAILURE_MSG("Failed to parse coverage table in context format 1");
 }

 for (unsigned i = 0; i < rule_set_count; ++i) {
   uint16_t offset_rule = 0;
   if (!subtable.ReadU16(&offset_rule)) {
     return OTS_FAILURE_MSG("Failed to read rule offset %d in context format 1", i);
   }
   if (offset_rule < rule_set_end || offset_rule >= length) {
     return OTS_FAILURE_MSG("Bad rule offset %d in rule %d in context format 1", offset_rule, i);
   }
   if (!ParseRuleSetTable(font, data + offset_rule, length - offset_rule,
                          num_glyphs, num_lookups)) {
     return OTS_FAILURE_MSG("Failed to parse rule set %d in context format 1", i);
   }
 }

 return true;
}

bool ParseClassRuleTable(const ots::Font *font,
                        const uint8_t *data, const size_t length,
                        const uint16_t num_glyphs,
                        const uint16_t num_lookups) {
 ots::Buffer subtable(data, length);

 uint16_t glyph_count = 0;
 uint16_t lookup_count = 0;
 if (!subtable.ReadU16(&glyph_count) ||
     !subtable.ReadU16(&lookup_count)) {
   return OTS_FAILURE_MSG("Failed to read header of class rule table");
 }

 if (glyph_count == 0 || glyph_count >= num_glyphs) {
   return OTS_FAILURE_MSG("Bad glyph count %d in class rule table", glyph_count);
 }

 // ClassRule table contains an array of classes. Each value of classes
 // could take arbitrary values including zero so we don't check these value.
 const unsigned num_classes = glyph_count - static_cast<unsigned>(1);
 if (!subtable.Skip(2 * num_classes)) {
   return OTS_FAILURE_MSG("Failed to skip classes in class rule table");
 }

 for (unsigned i = 0; i < lookup_count; ++i) {
   if (!ParseLookupRecord(font, &subtable, num_glyphs, num_lookups)) {
     return OTS_FAILURE_MSG("Failed to parse lookup record %d in class rule table", i);
   }
 }
 return true;
}

bool ParseClassSetTable(const ots::Font *font,
                       const uint8_t *data, const size_t length,
                       const uint16_t num_glyphs,
                       const uint16_t num_lookups) {
 ots::Buffer subtable(data, length);

 uint16_t class_rule_count = 0;
 if (!subtable.ReadU16(&class_rule_count)) {
   return OTS_FAILURE_MSG("Failed to read class rule count in class set table");
 }
 const unsigned class_rule_end =
     2 * static_cast<unsigned>(class_rule_count) + 2;
 if (class_rule_end > std::numeric_limits<uint16_t>::max()) {
   return OTS_FAILURE_MSG("bad class rule end %d in class set table", class_rule_end);
 }
 for (unsigned i = 0; i < class_rule_count; ++i) {
   uint16_t offset_class_rule = 0;
   if (!subtable.ReadU16(&offset_class_rule)) {
     return OTS_FAILURE_MSG("Failed to read class rule offset %d in class set table", i);
   }
   if (offset_class_rule < class_rule_end || offset_class_rule >= length) {
     return OTS_FAILURE_MSG("Bad class rule offset %d in class %d", offset_class_rule, i);
   }
   if (!ParseClassRuleTable(font, data + offset_class_rule,
                            length - offset_class_rule, num_glyphs,
                            num_lookups)) {
     return OTS_FAILURE_MSG("Failed to parse class rule table %d", i);
   }
 }

 return true;
}

bool ParseContextFormat2(const ots::Font *font,
                        const uint8_t *data, const size_t length,
                        const uint16_t num_glyphs,
                        const uint16_t num_lookups) {
 ots::Buffer subtable(data, length);

 uint16_t offset_coverage = 0;
 uint16_t offset_class_def = 0;
 uint16_t class_set_cnt = 0;
 // Skip format field.
 if (!subtable.Skip(2) ||
     !subtable.ReadU16(&offset_coverage) ||
     !subtable.ReadU16(&offset_class_def) ||
     !subtable.ReadU16(&class_set_cnt)) {
   return OTS_FAILURE_MSG("Failed to read header for context format 2");
 }

 const unsigned class_set_end = 2 * static_cast<unsigned>(class_set_cnt) + 8;
 if (class_set_end > std::numeric_limits<uint16_t>::max()) {
   return OTS_FAILURE_MSG("Bad end of class set %d for context format 2", class_set_end);
 }
 if (offset_coverage < class_set_end || offset_coverage >= length) {
   return OTS_FAILURE_MSG("Bad coverage offset %d in context format 2", offset_coverage);
 }
 if (!ots::ParseCoverageTable(font, data + offset_coverage,
                              length - offset_coverage, num_glyphs)) {
   return OTS_FAILURE_MSG("Failed to parse coverage table in context format 2");
 }

 if (offset_class_def < class_set_end || offset_class_def >= length) {
   return OTS_FAILURE_MSG("bad class definition offset %d in context format 2", offset_class_def);
 }
 if (!ots::ParseClassDefTable(font, data + offset_class_def,
                              length - offset_class_def,
                              num_glyphs, ots::kMaxClassDefValue)) {
   return OTS_FAILURE_MSG("Failed to parse class definition table in context format 2");
 }

 for (unsigned i = 0; i < class_set_cnt; ++i) {
   uint16_t offset_class_rule = 0;
   if (!subtable.ReadU16(&offset_class_rule)) {
     return OTS_FAILURE_MSG("Failed to read class rule offset %d in context format 2", i);
   }
   if (offset_class_rule) {
     if (offset_class_rule < class_set_end || offset_class_rule >= length) {
       return OTS_FAILURE_MSG("Bad class rule offset %d for rule %d in context format 2", offset_class_rule, i);
     }
     if (!ParseClassSetTable(font, data + offset_class_rule,
                             length - offset_class_rule, num_glyphs,
                             num_lookups)) {
       return OTS_FAILURE_MSG("Failed to parse class set %d in context format 2", i);
     }
   }
 }

 return true;
}

bool ParseContextFormat3(const ots::Font *font,
                        const uint8_t *data, const size_t length,
                        const uint16_t num_glyphs,
                        const uint16_t num_lookups) {
 ots::Buffer subtable(data, length);

 uint16_t glyph_count = 0;
 uint16_t lookup_count = 0;
 // Skip format field.
 if (!subtable.Skip(2) ||
     !subtable.ReadU16(&glyph_count) ||
     !subtable.ReadU16(&lookup_count)) {
   return OTS_FAILURE_MSG("Failed to read header in context format 3");
 }

 if (glyph_count >= num_glyphs) {
   return OTS_FAILURE_MSG("Bad glyph count %d in context format 3", glyph_count);
 }
 const unsigned lookup_record_end = 2 * static_cast<unsigned>(glyph_count) +
     4 * static_cast<unsigned>(lookup_count) + 6;
 if (lookup_record_end > std::numeric_limits<uint16_t>::max()) {
   return OTS_FAILURE_MSG("Bad end of lookup %d in context format 3", lookup_record_end);
 }
 for (unsigned i = 0; i < glyph_count; ++i) {
   uint16_t offset_coverage = 0;
   if (!subtable.ReadU16(&offset_coverage)) {
     return OTS_FAILURE_MSG("Failed to read coverage offset %d in conxtext format 3", i);
   }
   if (offset_coverage < lookup_record_end || offset_coverage >= length) {
     return OTS_FAILURE_MSG("Bad coverage offset %d for glyph %d in context format 3", offset_coverage, i);
   }
   if (!ots::ParseCoverageTable(font, data + offset_coverage,
                                length - offset_coverage, num_glyphs)) {
     return OTS_FAILURE_MSG("Failed to parse coverage table for glyph %d in context format 3", i);
   }
 }

 for (unsigned i = 0; i < lookup_count; ++i) {
   if (!ParseLookupRecord(font, &subtable, num_glyphs, num_lookups)) {
     return OTS_FAILURE_MSG("Failed to parse lookup record %d in context format 3", i);
   }
 }

 return true;
}

// Parsers for Chaning Contextual subtables in GSUB/GPOS tables.

bool ParseChainRuleSubtable(const ots::Font *font,
                           const uint8_t *data, const size_t length,
                           const uint16_t num_glyphs,
                           const uint16_t num_lookups) {
 ots::Buffer subtable(data, length);

 uint16_t backtrack_count = 0;
 if (!subtable.ReadU16(&backtrack_count)) {
   return OTS_FAILURE_MSG("Failed to read backtrack count in chain rule subtable");
 }
 for (unsigned i = 0; i < backtrack_count; ++i) {
   uint16_t glyph_id = 0;
   if (!subtable.ReadU16(&glyph_id)) {
     return OTS_FAILURE_MSG("Failed to read backtrack glyph %d in chain rule subtable", i);
   }
   if (glyph_id > num_glyphs) {
     return OTS_FAILURE_MSG("Bad glyph id %d for bactrack glyph %d in chain rule subtable", glyph_id, i);
   }
 }

 uint16_t input_count = 0;
 if (!subtable.ReadU16(&input_count)) {
   return OTS_FAILURE_MSG("Failed to read input count in chain rule subtable");
 }
 if (input_count == 0) {
   return OTS_FAILURE_MSG("Bad input count %d in chain rule subtable", input_count);
 }
 for (unsigned i = 0; i < input_count - static_cast<unsigned>(1); ++i) {
   uint16_t glyph_id = 0;
   if (!subtable.ReadU16(&glyph_id)) {
     return OTS_FAILURE_MSG("Failed to read input glyph %d in chain rule subtable", i);
   }
   if (glyph_id > num_glyphs) {
     return OTS_FAILURE_MSG("Bad glyph id %d for input glyph %d in chain rule subtable", glyph_id, i);
   }
 }

 uint16_t lookahead_count = 0;
 if (!subtable.ReadU16(&lookahead_count)) {
   return OTS_FAILURE_MSG("Failed to read lookahead count in chain rule subtable");
 }
 for (unsigned i = 0; i < lookahead_count; ++i) {
   uint16_t glyph_id = 0;
   if (!subtable.ReadU16(&glyph_id)) {
     return OTS_FAILURE_MSG("Failed to read lookahead glyph %d in chain rule subtable", i);
   }
   if (glyph_id > num_glyphs) {
     return OTS_FAILURE_MSG("Bad glyph id %d for lookadhead glyph %d in chain rule subtable", glyph_id, i);
   }
 }

 uint16_t lookup_count = 0;
 if (!subtable.ReadU16(&lookup_count)) {
   return OTS_FAILURE_MSG("Failed to read lookup count in chain rule subtable");
 }
 for (unsigned i = 0; i < lookup_count; ++i) {
   if (!ParseLookupRecord(font, &subtable, num_glyphs, num_lookups)) {
     return OTS_FAILURE_MSG("Failed to parse lookup record %d in chain rule subtable", i);
   }
 }

 return true;
}

bool ParseChainRuleSetTable(const ots::Font *font,
                           const uint8_t *data, const size_t length,
                           const uint16_t num_glyphs,
                           const uint16_t num_lookups) {
 ots::Buffer subtable(data, length);

 uint16_t chain_rule_count = 0;
 if (!subtable.ReadU16(&chain_rule_count)) {
   return OTS_FAILURE_MSG("Failed to read rule count in chain rule set");
 }
 const unsigned chain_rule_end =
     2 * static_cast<unsigned>(chain_rule_count) + 2;
 if (chain_rule_end > std::numeric_limits<uint16_t>::max()) {
   return OTS_FAILURE_MSG("Bad end of chain rule %d in chain rule set", chain_rule_end);
 }
 for (unsigned i = 0; i < chain_rule_count; ++i) {
   uint16_t offset_chain_rule = 0;
   if (!subtable.ReadU16(&offset_chain_rule)) {
     return OTS_FAILURE_MSG("Failed to read chain rule offset %d in chain rule set", i);
   }
   if (offset_chain_rule < chain_rule_end || offset_chain_rule >= length) {
     return OTS_FAILURE_MSG("Bad chain rule offset %d for chain rule %d in chain rule set", offset_chain_rule, i);
   }
   if (!ParseChainRuleSubtable(font, data + offset_chain_rule,
                               length - offset_chain_rule,
                               num_glyphs, num_lookups)) {
     return OTS_FAILURE_MSG("Failed to parse chain rule %d in chain rule set", i);
   }
 }

 return true;
}

bool ParseChainContextFormat1(const ots::Font *font,
                             const uint8_t *data, const size_t length,
                             const uint16_t num_glyphs,
                             const uint16_t num_lookups) {
 ots::Buffer subtable(data, length);

 uint16_t offset_coverage = 0;
 uint16_t chain_rule_set_count = 0;
 // Skip format field.
 if (!subtable.Skip(2) ||
     !subtable.ReadU16(&offset_coverage) ||
     !subtable.ReadU16(&chain_rule_set_count)) {
   return OTS_FAILURE_MSG("Failed to read header of chain context format 1");
 }

 const unsigned chain_rule_set_end =
     2 * static_cast<unsigned>(chain_rule_set_count) + 6;
 if (chain_rule_set_end > std::numeric_limits<uint16_t>::max()) {
   return OTS_FAILURE_MSG("Bad chain rule end %d in chain context format 1", chain_rule_set_end);
 }
 if (offset_coverage < chain_rule_set_end || offset_coverage >= length) {
   return OTS_FAILURE_MSG("Bad coverage offset %d in chain context format 1", chain_rule_set_end);
 }
 if (!ots::ParseCoverageTable(font, data + offset_coverage,
                              length - offset_coverage, num_glyphs)) {
   return OTS_FAILURE_MSG("Failed to parse coverage table for chain context format 1");
 }

 for (unsigned i = 0; i < chain_rule_set_count; ++i) {
   uint16_t offset_chain_rule_set = 0;
   if (!subtable.ReadU16(&offset_chain_rule_set)) {
     return OTS_FAILURE_MSG("Failed to read chain rule offset %d in chain context format 1", i);
   }
   if (offset_chain_rule_set < chain_rule_set_end ||
       offset_chain_rule_set >= length) {
     return OTS_FAILURE_MSG("Bad chain rule set offset %d for chain rule set %d in chain context format 1", offset_chain_rule_set, i);
   }
   if (!ParseChainRuleSetTable(font, data + offset_chain_rule_set,
                                  length - offset_chain_rule_set,
                                  num_glyphs, num_lookups)) {
     return OTS_FAILURE_MSG("Failed to parse chain rule set %d in chain context format 1", i);
   }
 }

 return true;
}

bool ParseChainClassRuleSubtable(const ots::Font *font,
                                const uint8_t *data, const size_t length,
                                const uint16_t num_glyphs,
                                const uint16_t num_lookups) {
 ots::Buffer subtable(data, length);

 // In this subtable, we don't check the value of classes for now since
 // these could take arbitrary values.

 uint16_t backtrack_count = 0;
 if (!subtable.ReadU16(&backtrack_count)) {
   return OTS_FAILURE_MSG("Failed to read backtrack count in chain class rule subtable");
 }
 if (!subtable.Skip(2 * backtrack_count)) {
   return OTS_FAILURE_MSG("Failed to skip backtrack offsets in chain class rule subtable");
 }

 uint16_t input_count = 0;
 if (!subtable.ReadU16(&input_count)) {
   return OTS_FAILURE_MSG("Failed to read input count in chain class rule subtable");
 }
 if (input_count == 0) {
   return OTS_FAILURE_MSG("Bad input count %d in chain class rule subtable", input_count);
 }
 if (!subtable.Skip(2 * (input_count - 1))) {
   return OTS_FAILURE_MSG("Failed to skip input offsets in chain class rule subtable");
 }

 uint16_t lookahead_count = 0;
 if (!subtable.ReadU16(&lookahead_count)) {
   return OTS_FAILURE_MSG("Failed to read lookahead count in chain class rule subtable");
 }
 if (!subtable.Skip(2 * lookahead_count)) {
   return OTS_FAILURE_MSG("Failed to skip lookahead offsets in chain class rule subtable");
 }

 uint16_t lookup_count = 0;
 if (!subtable.ReadU16(&lookup_count)) {
   return OTS_FAILURE_MSG("Failed to read lookup count in chain class rule subtable");
 }
 for (unsigned i = 0; i < lookup_count; ++i) {
   if (!ParseLookupRecord(font, &subtable, num_glyphs, num_lookups)) {
     return OTS_FAILURE_MSG("Failed to parse lookup record %d in chain class rule subtable", i);
   }
 }

 return true;
}

bool ParseChainClassSetTable(const ots::Font *font,
                            const uint8_t *data, const size_t length,
                            const uint16_t num_glyphs,
                            const uint16_t num_lookups) {
 ots::Buffer subtable(data, length);

 uint16_t chain_class_rule_count = 0;
 if (!subtable.ReadU16(&chain_class_rule_count)) {
   return OTS_FAILURE_MSG("Failed to read rule count in chain class set");
 }
 const unsigned chain_class_rule_end =
     2 * static_cast<unsigned>(chain_class_rule_count) + 2;
 if (chain_class_rule_end > std::numeric_limits<uint16_t>::max()) {
   return OTS_FAILURE_MSG("Bad end of chain class set %d in chain class set", chain_class_rule_end);
 }
 for (unsigned i = 0; i < chain_class_rule_count; ++i) {
   uint16_t offset_chain_class_rule = 0;
   if (!subtable.ReadU16(&offset_chain_class_rule)) {
     return OTS_FAILURE_MSG("Failed to read chain class rule offset %d in chain class set", i);
   }
   if (offset_chain_class_rule < chain_class_rule_end ||
       offset_chain_class_rule >= length) {
     return OTS_FAILURE_MSG("Bad chain class rule offset %d for chain class %d in chain class set", offset_chain_class_rule, i);
   }
   if (!ParseChainClassRuleSubtable(font, data + offset_chain_class_rule,
                                    length - offset_chain_class_rule,
                                    num_glyphs, num_lookups)) {
     return OTS_FAILURE_MSG("Failed to parse chain class rule %d in chain class set", i);
   }
 }

 return true;
}

bool ParseChainContextFormat2(const ots::Font *font,
                             const uint8_t *data, const size_t length,
                             const uint16_t num_glyphs,
                             const uint16_t num_lookups) {
 ots::Buffer subtable(data, length);

 uint16_t offset_coverage = 0;
 uint16_t offset_backtrack_class_def = 0;
 uint16_t offset_input_class_def = 0;
 uint16_t offset_lookahead_class_def = 0;
 uint16_t chain_class_set_count = 0;
 // Skip format field.
 if (!subtable.Skip(2) ||
     !subtable.ReadU16(&offset_coverage) ||
     !subtable.ReadU16(&offset_backtrack_class_def) ||
     !subtable.ReadU16(&offset_input_class_def) ||
     !subtable.ReadU16(&offset_lookahead_class_def) ||
     !subtable.ReadU16(&chain_class_set_count)) {
   return OTS_FAILURE_MSG("Failed to read header of chain context format 2");
 }

 const unsigned chain_class_set_end =
     2 * static_cast<unsigned>(chain_class_set_count) + 12;
 if (chain_class_set_end > std::numeric_limits<uint16_t>::max()) {
   return OTS_FAILURE_MSG("Bad chain class set end %d in chain context format 2", chain_class_set_end);
 }
 if (offset_coverage < chain_class_set_end || offset_coverage >= length) {
   return OTS_FAILURE_MSG("Bad coverage offset %d in chain context format 2", offset_coverage);
 }
 if (!ots::ParseCoverageTable(font, data + offset_coverage,
                              length - offset_coverage, num_glyphs)) {
   return OTS_FAILURE_MSG("Failed to parse coverage table in chain context format 2");
 }

 // Classes for backtrack/lookahead sequences might not be defined.
 if (offset_backtrack_class_def) {
   if (offset_backtrack_class_def < chain_class_set_end ||
       offset_backtrack_class_def >= length) {
     return OTS_FAILURE_MSG("Bad backtrack class offset %d in chain context format 2", offset_backtrack_class_def);
   }
   if (!ots::ParseClassDefTable(font, data + offset_backtrack_class_def,
                                length - offset_backtrack_class_def,
                                num_glyphs, ots::kMaxClassDefValue)) {
     return OTS_FAILURE_MSG("Failed to parse backtrack class defn table in chain context format 2");
   }
 }

 if (offset_input_class_def < chain_class_set_end ||
     offset_input_class_def >= length) {
   return OTS_FAILURE_MSG("Bad input class defn offset %d in chain context format 2", offset_input_class_def);
 }
 if (!ots::ParseClassDefTable(font, data + offset_input_class_def,
                              length - offset_input_class_def,
                              num_glyphs, ots::kMaxClassDefValue)) {
   return OTS_FAILURE_MSG("Failed to parse input class defn in chain context format 2");
 }

 if (offset_lookahead_class_def) {
   if (offset_lookahead_class_def < chain_class_set_end ||
       offset_lookahead_class_def >= length) {
     return OTS_FAILURE_MSG("Bad lookahead class defn offset %d in chain context format 2", offset_lookahead_class_def);
   }
   if (!ots::ParseClassDefTable(font, data + offset_lookahead_class_def,
                                length - offset_lookahead_class_def,
                                num_glyphs, ots::kMaxClassDefValue)) {
     return OTS_FAILURE_MSG("Failed to parse lookahead class defn in chain context format 2");
   }
 }

 for (unsigned i = 0; i < chain_class_set_count; ++i) {
   uint16_t offset_chain_class_set = 0;
   if (!subtable.ReadU16(&offset_chain_class_set)) {
     return OTS_FAILURE_MSG("Failed to read chain class set offset %d", i);
   }
   // |offset_chain_class_set| could be NULL.
   if (offset_chain_class_set) {
     if (offset_chain_class_set < chain_class_set_end ||
         offset_chain_class_set >= length) {
       return OTS_FAILURE_MSG("Bad chain set class offset %d for chain set %d in chain context format 2", offset_chain_class_set, i);
     }
     if (!ParseChainClassSetTable(font, data + offset_chain_class_set,
                                  length - offset_chain_class_set,
                                  num_glyphs, num_lookups)) {
       return OTS_FAILURE_MSG("Failed to parse chain class set table %d in chain context format 2", i);
     }
   }
 }

 return true;
}

bool ParseChainContextFormat3(const ots::Font *font,
                             const uint8_t *data, const size_t length,
                             const uint16_t num_glyphs,
                             const uint16_t num_lookups) {
 ots::Buffer subtable(data, length);

 uint16_t backtrack_count = 0;
 // Skip format field.
 if (!subtable.Skip(2) ||
     !subtable.ReadU16(&backtrack_count)) {
   return OTS_FAILURE_MSG("Failed to read backtrack count in chain context format 3");
 }

 std::vector<uint16_t> offsets_backtrack;
 offsets_backtrack.reserve(backtrack_count);
 for (unsigned i = 0; i < backtrack_count; ++i) {
   uint16_t offset = 0;
   if (!subtable.ReadU16(&offset)) {
     return OTS_FAILURE_MSG("Failed to read backtrack offset %d in chain context format 3", i);
   }
   offsets_backtrack.push_back(offset);
 }
 if (offsets_backtrack.size() != backtrack_count) {
   return OTS_FAILURE_MSG("Bad backtrack offsets size %ld in chain context format 3", offsets_backtrack.size());
 }

 uint16_t input_count = 0;
 if (!subtable.ReadU16(&input_count)) {
   return OTS_FAILURE_MSG("Failed to read input count in chain context format 3");
 }
 std::vector<uint16_t> offsets_input;
 offsets_input.reserve(input_count);
 for (unsigned i = 0; i < input_count; ++i) {
   uint16_t offset = 0;
   if (!subtable.ReadU16(&offset)) {
     return OTS_FAILURE_MSG("Failed to read input offset %d in chain context format 3", i);
   }
   offsets_input.push_back(offset);
 }
 if (offsets_input.size() != input_count) {
   return OTS_FAILURE_MSG("Bad input offsets size %ld in chain context format 3", offsets_input.size());
 }

 uint16_t lookahead_count = 0;
 if (!subtable.ReadU16(&lookahead_count)) {
   return OTS_FAILURE_MSG("Failed ot read lookahead count in chain context format 3");
 }
 std::vector<uint16_t> offsets_lookahead;
 offsets_lookahead.reserve(lookahead_count);
 for (unsigned i = 0; i < lookahead_count; ++i) {
   uint16_t offset = 0;
   if (!subtable.ReadU16(&offset)) {
     return OTS_FAILURE_MSG("Failed to read lookahead offset %d in chain context format 3", i);
   }
   offsets_lookahead.push_back(offset);
 }
 if (offsets_lookahead.size() != lookahead_count) {
   return OTS_FAILURE_MSG("Bad lookahead offsets size %ld in chain context format 3", offsets_lookahead.size());
 }

 uint16_t lookup_count = 0;
 if (!subtable.ReadU16(&lookup_count)) {
   return OTS_FAILURE_MSG("Failed to read lookup count in chain context format 3");
 }
 for (unsigned i = 0; i < lookup_count; ++i) {
   if (!ParseLookupRecord(font, &subtable, num_glyphs, num_lookups)) {
     return OTS_FAILURE_MSG("Failed to parse lookup %d in chain context format 3", i);
   }
 }

 const unsigned lookup_record_end =
     2 * (static_cast<unsigned>(backtrack_count) +
          static_cast<unsigned>(input_count) +
          static_cast<unsigned>(lookahead_count)) +
     4 * static_cast<unsigned>(lookup_count) + 10;
 if (lookup_record_end > std::numeric_limits<uint16_t>::max()) {
   return OTS_FAILURE_MSG("Bad end of lookup record %d in chain context format 3", lookup_record_end);
 }
 for (unsigned i = 0; i < backtrack_count; ++i) {
   if (offsets_backtrack[i] < lookup_record_end ||
       offsets_backtrack[i] >= length) {
     return OTS_FAILURE_MSG("Bad backtrack offset of %d for backtrack %d in chain context format 3", offsets_backtrack[i], i);
   }
   if (!ots::ParseCoverageTable(font, data + offsets_backtrack[i],
                                length - offsets_backtrack[i], num_glyphs)) {
     return OTS_FAILURE_MSG("Failed to parse backtrack coverage %d in chain context format 3", i);
   }
 }
 for (unsigned i = 0; i < input_count; ++i) {
   if (offsets_input[i] < lookup_record_end || offsets_input[i] >= length) {
     return OTS_FAILURE_MSG("Bad input offset %d for input %d in chain context format 3", offsets_input[i], i);
   }
   if (!ots::ParseCoverageTable(font, data + offsets_input[i],
                                length - offsets_input[i], num_glyphs)) {
     return OTS_FAILURE_MSG("Failed to parse input coverage table %d in chain context format 3", i);
   }
 }
 for (unsigned i = 0; i < lookahead_count; ++i) {
   if (offsets_lookahead[i] < lookup_record_end ||
       offsets_lookahead[i] >= length) {
     return OTS_FAILURE_MSG("Bad lookadhead offset %d for lookahead %d in chain context format 3", offsets_lookahead[i], i);
   }
   if (!ots::ParseCoverageTable(font, data + offsets_lookahead[i],
                                length - offsets_lookahead[i], num_glyphs)) {
     return OTS_FAILURE_MSG("Failed to parse lookahead coverage table %d in chain context format 3", i);
   }
 }

 return true;
}

bool ParseFeatureTableSubstitutionTable(const ots::Font *font,
                                       const uint8_t *data, const size_t length,
                                       const uint16_t num_lookups) {
 ots::Buffer subtable(data, length);

 uint16_t version_major = 0;
 uint16_t version_minor = 0;
 uint16_t substitution_count = 0;
 const size_t kFeatureTableSubstitutionHeaderSize = 3 * sizeof(uint16_t);

 if (!subtable.ReadU16(&version_major) ||
     !subtable.ReadU16(&version_minor) ||
     !subtable.ReadU16(&substitution_count)) {
   return OTS_FAILURE_MSG("Failed to read feature table substitution table header");
 }

 for (uint16_t i = 0; i < substitution_count; i++) {
   uint16_t feature_index = 0;
   uint32_t alternate_feature_table_offset = 0;
   const size_t kFeatureTableSubstitutionRecordSize = sizeof(uint16_t) + sizeof(uint32_t);

   if (!subtable.ReadU16(&feature_index) ||
       !subtable.ReadU32(&alternate_feature_table_offset)) {
     return OTS_FAILURE_MSG("Failed to read feature table substitution record");
   }

   if (alternate_feature_table_offset < kFeatureTableSubstitutionHeaderSize +
                                        kFeatureTableSubstitutionRecordSize * substitution_count ||
       alternate_feature_table_offset >= length) {
     return OTS_FAILURE_MSG("Invalid alternate feature table offset");
   }

   if (!ParseFeatureTable(font, data + alternate_feature_table_offset,
                          length - alternate_feature_table_offset, num_lookups)) {
     return OTS_FAILURE_MSG("Failed to parse alternate feature table");
   }
 }

 return true;
}

bool ParseConditionTable(const ots::Font *font,
                        const uint8_t *data, const size_t length,
                        const uint16_t axis_count) {
 ots::Buffer subtable(data, length);

 uint16_t format = 0;
 if (!subtable.ReadU16(&format)) {
   return OTS_FAILURE_MSG("Failed to read condition table format");
 }

 if (format != 1) {
   // An unknown format is not an error, but should be ignored per spec.
   return true;
 }

 uint16_t axis_index = 0;
 int16_t filter_range_min_value = 0;
 int16_t filter_range_max_value = 0;
 if (!subtable.ReadU16(&axis_index) ||
     !subtable.ReadS16(&filter_range_min_value) ||
     !subtable.ReadS16(&filter_range_max_value)) {
   return OTS_FAILURE_MSG("Failed to read condition table (format 1)");
 }

 if (axis_index >= axis_count) {
   return OTS_FAILURE_MSG("Axis index out of range in condition");
 }

 // Check min/max values are within range -1.0 .. 1.0.
 if (filter_range_min_value < -0x4000 || // -1.0 in F2DOT14 format
     filter_range_max_value > 0x4000) { // +1.0 in F2DOT14 format
   return OTS_FAILURE_MSG("Invalid filter range in condition");
 }

 // Warn if range is improperly ordered (and therefore useless).
 if (filter_range_min_value > filter_range_max_value) {
   OTS_WARNING("Misordered filter range in condition table");
 }

 return true;
}

bool ParseConditionSetTable(const ots::Font *font,
                           const uint8_t *data, const size_t length,
                           const uint16_t axis_count) {
 ots::Buffer subtable(data, length);

 uint16_t condition_count = 0;
 if (!subtable.ReadU16(&condition_count)) {
   return OTS_FAILURE_MSG("Failed to read condition count");
 }

 for (uint16_t i = 0; i < condition_count; i++) {
   uint32_t condition_offset = 0;
   if (!subtable.ReadU32(&condition_offset)) {
     return OTS_FAILURE_MSG("Failed to read condition offset");
   }
   if (condition_offset < subtable.offset() || condition_offset >= length) {
     return OTS_FAILURE_MSG("Offset out of range");
   }
   if (!ParseConditionTable(font, data + condition_offset, length - condition_offset,
                            axis_count)) {
     return OTS_FAILURE_MSG("Failed to parse condition table");
   }
 }

 return true;
}

}  // namespace

namespace ots {

// Parsing ScriptListTable requires number of features so we need to
// parse FeatureListTable before calling this function.
bool OpenTypeLayoutTable::ParseScriptListTable(const uint8_t *data, const size_t length) {
 Font* font = GetFont();
 Buffer subtable(data, length);

 uint16_t script_count = 0;
 if (!subtable.ReadU16(&script_count)) {
   return Error("Failed to read script count in script list table");
 }

 const unsigned script_record_end =
     6 * static_cast<unsigned>(script_count) + 2;
 if (script_record_end > std::numeric_limits<uint16_t>::max()) {
   return Error("Bad end of script record %d in script list table", script_record_end);
 }
 std::vector<ScriptRecord> script_list;
 script_list.reserve(script_count);
 uint32_t last_tag = 0;
 for (unsigned i = 0; i < script_count; ++i) {
   ScriptRecord record;
   if (!subtable.ReadU32(&record.tag) ||
       !subtable.ReadU16(&record.offset)) {
     return Error("Failed to read script record %d in script list table", i);
   }
   // Script tags should be arranged alphabetically by tag
   if (last_tag != 0 && last_tag > record.tag) {
     // Several fonts don't arrange tags alphabetically.
     // It seems that the order of tags might not be a security issue
     // so we just warn it.
     OTS_WARNING("tags aren't arranged alphabetically.");
   }
   last_tag = record.tag;
   if (record.offset < script_record_end || record.offset >= length) {
     return Error("Bad record offset %d for script %c%c%c%c entry %d in script list table", record.offset, OTS_UNTAG(record.tag), i);
   }
   script_list.push_back(record);
 }
 if (script_list.size() != script_count) {
   return Error("Bad script list size %ld in script list table", script_list.size());
 }

 // Check script records.
 for (unsigned i = 0; i < script_count; ++i) {
   if (!ParseScriptTable(font, data + script_list[i].offset,
                         length - script_list[i].offset,
                         script_list[i].tag, m_num_features)) {
     return Error("Failed to parse script table %d", i);
   }
 }

 return true;
}

// Parsing FeatureListTable requires number of lookups so we need to parse
// LookupListTable before calling this function.
bool OpenTypeLayoutTable::ParseFeatureListTable(const uint8_t *data, const size_t length) {
 Font *font = GetFont();
 Buffer subtable(data, length);

 uint16_t feature_count = 0;
 if (!subtable.ReadU16(&feature_count)) {
   return Error("Failed to read feature count");
 }

 std::vector<FeatureRecord> feature_records;
 feature_records.resize(feature_count);
 const unsigned feature_record_end =
     6 * static_cast<unsigned>(feature_count) + 2;
 if (feature_record_end > std::numeric_limits<uint16_t>::max()) {
   return Error("Bad end of feature record %d", feature_record_end);
 }
 uint32_t last_tag = 0;
 for (unsigned i = 0; i < feature_count; ++i) {
   if (!subtable.ReadU32(&feature_records[i].tag) ||
       !subtable.ReadU16(&feature_records[i].offset)) {
     return Error("Failed to read feature header %d", i);
   }
   // Feature record array should be arranged alphabetically by tag
   if (last_tag != 0 && last_tag > feature_records[i].tag) {
     // Several fonts don't arrange tags alphabetically.
     // It seems that the order of tags might not be a security issue
     // so we just warn it.
     OTS_WARNING("tags aren't arranged alphabetically.");
   }
   last_tag = feature_records[i].tag;
   if (feature_records[i].offset < feature_record_end ||
       feature_records[i].offset >= length) {
     return Error("Bad feature offset %d for feature %d %c%c%c%c", feature_records[i].offset, i, OTS_UNTAG(feature_records[i].tag));
   }
 }

 for (unsigned i = 0; i < feature_count; ++i) {
   if (!ParseFeatureTable(font, data + feature_records[i].offset,
                          length - feature_records[i].offset, m_num_lookups)) {
     return Error("Failed to parse feature table %d", i);
   }
 }
 m_num_features = feature_count;
 return true;
}

bool OpenTypeLayoutTable::ParseLookupTable(const uint8_t *data,
                                          const size_t length) {
 Font* font = GetFont(); 
 Buffer subtable(data, length);

 uint16_t lookup_type = 0;
 uint16_t lookup_flag = 0;
 uint16_t subtable_count = 0;
 if (!subtable.ReadU16(&lookup_type) ||
     !subtable.ReadU16(&lookup_flag) ||
     !subtable.ReadU16(&subtable_count)) {
   return Error("Failed to read lookup table header");
 }

 if (!ValidLookupSubtableType(lookup_type)) {
   return Error("Bad lookup type %d", lookup_type);
 }

 bool use_mark_filtering_set = lookup_flag & kUseMarkFilteringSetBit;

 std::vector<uint16_t> subtables;
 subtables.reserve(subtable_count);
 // If the |kUseMarkFilteringSetBit| of |lookup_flag| is set,
 // extra 2 bytes will follow after subtable offset array.
 const unsigned lookup_table_end = 2 * static_cast<unsigned>(subtable_count) +
     (use_mark_filtering_set ? 8 : 6);
 if (lookup_table_end > std::numeric_limits<uint16_t>::max()) {
   return Error("Bad end of lookup %d", lookup_table_end);
 }
 for (unsigned i = 0; i < subtable_count; ++i) {
   uint16_t offset_subtable = 0;
   if (!subtable.ReadU16(&offset_subtable)) {
     return Error("Failed to read subtable offset %d", i);
   }
   if (offset_subtable < lookup_table_end ||
       offset_subtable >= length) {
     return Error("Bad subtable offset %d for subtable %d", offset_subtable, i);
   }
   subtables.push_back(offset_subtable);
 }
 if (subtables.size() != subtable_count) {
   return Error("Bad subtable size %ld", subtables.size());
 }

 if (use_mark_filtering_set) {
   uint16_t mark_filtering_set = 0;
   if (!subtable.ReadU16(&mark_filtering_set)) {
     return Error("Failed to read mark filtering set");
   }

   OpenTypeGDEF *gdef = static_cast<OpenTypeGDEF*>(
       font->GetTypedTable(OTS_TAG_GDEF));

   if (gdef && (gdef->num_mark_glyph_sets == 0 ||
       mark_filtering_set >= gdef->num_mark_glyph_sets)) {
     return Error("Bad mark filtering set %d", mark_filtering_set);
   }
 }

 // Parse lookup subtables for this lookup type.
 for (unsigned i = 0; i < subtable_count; ++i) {
   if (!ParseLookupSubtable(data + subtables[i], length - subtables[i],
                            lookup_type)) {
     return Error("Failed to parse subtable %d", i);
   }
 }
 return true;
}

// For parsing GPOS/GSUB tables, this function should be called at first to
// obtain the number of lookups because parsing FeatureTableList requires
// the number.
bool OpenTypeLayoutTable::ParseLookupListTable(const uint8_t *data,
                                              const size_t length) {
 Buffer subtable(data, length);

 if (!subtable.ReadU16(&m_num_lookups)) {
   return Error("Failed to read number of lookups");
 }

 std::vector<uint16_t> lookups;
 lookups.reserve(m_num_lookups);
 const unsigned lookup_end =
     2 * static_cast<unsigned>(m_num_lookups) + 2;
 if (lookup_end > std::numeric_limits<uint16_t>::max()) {
   return Error("Bad end of lookups %d", lookup_end);
 }
 for (unsigned i = 0; i < m_num_lookups; ++i) {
   uint16_t offset = 0;
   if (!subtable.ReadU16(&offset)) {
     return Error("Failed to read lookup offset %d", i);
   }
   if (offset < lookup_end || offset >= length) {
     return Error("Bad lookup offset %d for lookup %d", offset, i);
   }
   lookups.push_back(offset);
 }
 if (lookups.size() != m_num_lookups) {
   return Error("Bad lookup offsets list size %ld", lookups.size());
 }

 for (unsigned i = 0; i < m_num_lookups; ++i) {
   if (!ParseLookupTable(data + lookups[i], length - lookups[i])) {
     return Error("Failed to parse lookup %d", i);
   }
 }

 return true;
}

bool ParseClassDefTable(const ots::Font *font,
                       const uint8_t *data, size_t length,
                       const uint16_t num_glyphs,
                       const uint16_t num_classes) {
 Buffer subtable(data, length);

 uint16_t format = 0;
 if (!subtable.ReadU16(&format)) {
   return OTS_FAILURE_MSG("Failed to read class defn format");
 }
 if (format == 1) {
   return ParseClassDefFormat1(font, data, length, num_glyphs, num_classes);
 } else if (format == 2) {
   return ParseClassDefFormat2(font, data, length, num_glyphs, num_classes);
 }

 return OTS_FAILURE_MSG("Bad class defn format %d", format);
}

bool ParseCoverageTable(const ots::Font *font,
                       const uint8_t *data, size_t length,
                       const uint16_t num_glyphs,
                       const uint16_t expected_num_glyphs) {
 Buffer subtable(data, length);

 uint16_t format = 0;
 if (!subtable.ReadU16(&format)) {
   return OTS_FAILURE_MSG("Failed to read coverage table format");
 }
 if (format == 1) {
   return ParseCoverageFormat1(font, data, length, num_glyphs, expected_num_glyphs);
 } else if (format == 2) {
   return ParseCoverageFormat2(font, data, length, num_glyphs, expected_num_glyphs);
 }

 return OTS_FAILURE_MSG("Bad coverage table format %d", format);
}

bool ParseDeviceTable(const ots::Font *font,
                     const uint8_t *data, size_t length) {
 Buffer subtable(data, length);

 uint16_t start_size = 0;
 uint16_t end_size = 0;
 uint16_t delta_format = 0;
 if (!subtable.ReadU16(&start_size) ||
     !subtable.ReadU16(&end_size) ||
     !subtable.ReadU16(&delta_format)) {
   return OTS_FAILURE_MSG("Failed to read device table header");
 }
 if (delta_format == kVariationIndex) {
   // start_size and end_size are replaced by deltaSetOuterIndex
   // and deltaSetInnerIndex respectively, but we don't attempt to
   // check them here, so nothing more to do.
   return true;
 }
 if (start_size > end_size) {
   return OTS_FAILURE_MSG("Bad device table size range: %u > %u", start_size, end_size);
 }
 if (delta_format == 0 || delta_format > kMaxDeltaFormatType) {
   return OTS_FAILURE_MSG("Bad device table delta format: 0x%x", delta_format);
 }
 // The number of delta values per uint16. The device table should contain
 // at least |num_units| * 2 bytes compressed data.
 const unsigned num_units = (end_size - start_size) /
     (1 << (4 - delta_format)) + 1;
 // Just skip |num_units| * 2 bytes since the compressed data could take
 // arbitrary values.
 if (!subtable.Skip(num_units * 2)) {
   return OTS_FAILURE_MSG("Failed to skip data in device table");
 }
 return true;
}

bool OpenTypeLayoutTable::ParseContextSubtable(const uint8_t *data,
                                              const size_t length) {
 Font *font = GetFont();
 Buffer subtable(data, length);

 uint16_t format = 0;
 if (!subtable.ReadU16(&format)) {
   return Error("Failed to read context subtable format");
 }

 OpenTypeMAXP *maxp = static_cast<OpenTypeMAXP*>(
     font->GetTypedTable(OTS_TAG_MAXP));
 if (!maxp) {
   return Error("Required maxp table missing");
 }

 if (format == 1) {
   if (!ParseContextFormat1(font, data, length, maxp->num_glyphs, m_num_lookups)) {
     return Error("Failed to parse context format 1 subtable");
   }
 } else if (format == 2) {
   if (!ParseContextFormat2(font, data, length, maxp->num_glyphs, m_num_lookups)) {
     return Error("Failed to parse context format 2 subtable");
   }
 } else if (format == 3) {
   if (!ParseContextFormat3(font, data, length, maxp->num_glyphs, m_num_lookups)) {
     return Error("Failed to parse context format 3 subtable");
   }
 } else {
   return Error("Bad context subtable format %d", format);
 }

 return true;
}

bool OpenTypeLayoutTable::ParseChainingContextSubtable(const uint8_t *data,
                                                      const size_t length) {
 Font *font = GetFont();
 Buffer subtable(data, length);

 uint16_t format = 0;
 if (!subtable.ReadU16(&format)) {
   return Error("Failed to read chaining context subtable format");
 }

 OpenTypeMAXP *maxp = static_cast<OpenTypeMAXP*>(
     font->GetTypedTable(OTS_TAG_MAXP));
 if (!maxp) {
   return Error("Required maxp table missing");
 }

 if (format == 1) {
   if (!ParseChainContextFormat1(font, data, length, maxp->num_glyphs, m_num_lookups)) {
     return Error("Failed to parse chaining context format 1 subtable");
   }
 } else if (format == 2) {
   if (!ParseChainContextFormat2(font, data, length, maxp->num_glyphs, m_num_lookups)) {
     return Error("Failed to parse chaining context format 2 subtable");
   }
 } else if (format == 3) {
   if (!ParseChainContextFormat3(font, data, length, maxp->num_glyphs, m_num_lookups)) {
     return Error("Failed to parse chaining context format 3 subtable");
   }
 } else {
   return Error("Bad chaining context subtable format %d", format);
 }

 return true;
}

bool OpenTypeLayoutTable::ParseExtensionSubtable(const uint8_t *data,
                                                const size_t length) {
 Buffer subtable(data, length);

 uint16_t format = 0;
 uint16_t lookup_type = 0;
 uint32_t offset_extension = 0;
 if (!subtable.ReadU16(&format) ||
     !subtable.ReadU16(&lookup_type) ||
     !subtable.ReadU32(&offset_extension)) {
   return Error("Failed to read extension table header");
 }

 if (format != 1) {
   return Error("Bad extension table format %d", format);
 }
 // |lookup_type| should be other than |parser->extension_type|.
 if (!ValidLookupSubtableType(lookup_type, true)) {
   return Error("Bad lookup type %d in extension table", lookup_type);
 }

 const unsigned format_end = static_cast<unsigned>(8);
 if (offset_extension < format_end ||
     offset_extension >= length) {
   return Error("Bad extension offset %d", offset_extension);
 }

 // Parse the extension subtable of |lookup_type|.
 if (!ParseLookupSubtable(data + offset_extension, length - offset_extension,
                          lookup_type)) {
   return Error("Failed to parse lookup from extension lookup");
 }

 return true;
}

// Parsing feature variations table (in GSUB/GPOS v1.1)
bool OpenTypeLayoutTable::ParseFeatureVariationsTable(const uint8_t *data, const size_t length) {
 Font *font = GetFont();
 Buffer subtable(data, length);

 uint16_t version_major = 0;
 uint16_t version_minor = 0;
 uint32_t feature_variation_record_count = 0;

 if (!subtable.ReadU16(&version_major) ||
     !subtable.ReadU16(&version_minor) ||
     !subtable.ReadU32(&feature_variation_record_count)) {
   return Error("Failed to read feature variations table header");
 }

 OpenTypeFVAR* fvar = static_cast<OpenTypeFVAR*>(font->GetTypedTable(OTS_TAG_FVAR));
 if (!fvar) {
   return Error("Not a variation font");
 }
 const uint16_t axis_count = fvar->AxisCount();

 const size_t kEndOfFeatureVariationRecords =
   2 * sizeof(uint16_t) + sizeof(uint32_t) +
   feature_variation_record_count * 2 * sizeof(uint32_t);

 for (uint32_t i = 0; i < feature_variation_record_count; i++) {
   uint32_t condition_set_offset = 0;
   uint32_t feature_table_substitution_offset = 0;
   if (!subtable.ReadU32(&condition_set_offset) ||
       !subtable.ReadU32(&feature_table_substitution_offset)) {
     return Error("Failed to read feature variation record");
   }

   if (condition_set_offset) {
     if (condition_set_offset < kEndOfFeatureVariationRecords ||
         condition_set_offset >= length) {
       return Error("Condition set offset out of range");
     }
     if (!ParseConditionSetTable(font, data + condition_set_offset,
                                 length - condition_set_offset,
                                 axis_count)) {
       return Error("Failed to parse condition set table");
     }
   }

   if (feature_table_substitution_offset) {
     if (feature_table_substitution_offset < kEndOfFeatureVariationRecords ||
         feature_table_substitution_offset >= length) {
       return Error("Feature table substitution offset out of range");
     }
     if (!ParseFeatureTableSubstitutionTable(font, data + feature_table_substitution_offset,
                                             length - feature_table_substitution_offset,
                                             m_num_lookups)) {
       return Error("Failed to parse feature table substitution table");
     }
   }
 }

 return true;
}

// GSUB/GPOS header size for table version 1.0
const size_t kHeaderSize_1_0 = 4 + 3 * 2;
// GSUB/GPOS header size for table versio 1.1
const size_t kHeaderSize_1_1 = 4 + 3 * 2 + 4;

bool OpenTypeLayoutTable::Parse(const uint8_t *data, size_t length) {
 Buffer table(data, length);

 uint16_t version_major = 0, version_minor = 0;
 uint16_t offset_script_list = 0;
 uint16_t offset_feature_list = 0;
 uint16_t offset_lookup_list = 0;
 uint32_t offset_feature_variations = 0;
 if (!table.ReadU16(&version_major) ||
     !table.ReadU16(&version_minor) ||
     !table.ReadU16(&offset_script_list) ||
     !table.ReadU16(&offset_feature_list) ||
     !table.ReadU16(&offset_lookup_list)) {
   return Error("Incomplete table");
 }

 if (version_major != 1 || version_minor > 1) {
   return Error("Bad version");
 }

 if (version_minor > 0) {
   if (!table.ReadU32(&offset_feature_variations)) {
     return Error("Incomplete table");
   }
 }

 const size_t header_size =
   (version_minor == 0) ? kHeaderSize_1_0 : kHeaderSize_1_1;

 if (offset_lookup_list) {
   if (offset_lookup_list < header_size || offset_lookup_list >= length) {
     return Error("Bad lookup list offset in table header");
   }

   if (!ParseLookupListTable(data + offset_lookup_list,
                             length - offset_lookup_list)) {
     return Error("Failed to parse lookup list table");
   }
 }

 if (offset_feature_list) {
   if (offset_feature_list < header_size || offset_feature_list >= length) {
     return Error("Bad feature list offset in table header");
   }

   if (!ParseFeatureListTable(data + offset_feature_list,
                              length - offset_feature_list)) {
     return Error("Failed to parse feature list table");
   }
 }

 if (offset_script_list) {
   if (offset_script_list < header_size || offset_script_list >= length) {
     return Error("Bad script list offset in table header");
   }

   if (!ParseScriptListTable(data + offset_script_list,
                             length - offset_script_list)) {
     return Error("Failed to parse script list table");
   }
 }

 if (offset_feature_variations) {
   if (offset_feature_variations < header_size || offset_feature_variations >= length) {
     return Error("Bad feature variations offset in table header");
   }

   if (!ParseFeatureVariationsTable(data + offset_feature_variations,
                                    length - offset_feature_variations)) {
     return Error("Failed to parse feature variations table");
   }
 }

 this->m_data = data;
 this->m_length = length;
 return true;
}

bool OpenTypeLayoutTable::Serialize(OTSStream *out) {
 if (!out->Write(this->m_data, this->m_length)) {
   return Error("Failed to write table");
 }

 return true;
}

}  // namespace ots

#undef TABLE_NAME