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