tor-browser

kern.cc (5924B)

---

// Copyright (c) 2009-2017 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 "kern.h"

// kern - Kerning
// http://www.microsoft.com/typography/otspec/kern.htm

namespace ots {

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

 uint16_t num_tables = 0;
 if (!table.ReadU16(&this->version) ||
     !table.ReadU16(&num_tables)) {
   return Error("Failed to read table header");
 }

 if (this->version > 0) {
   return Drop("Unsupported table version: %d", this->version);
 }

 if (num_tables == 0) {
   return Drop("nTables is zero");
 }

 this->subtables.reserve(num_tables);
 for (unsigned i = 0; i < num_tables; ++i) {
   OpenTypeKERNFormat0 subtable;
   uint16_t sub_length = 0;

   if (!table.ReadU16(&subtable.version) ||
       !table.ReadU16(&sub_length)) {
     return Error("Failed to read subtable %d header", i);
   }

   if (subtable.version > 0) {
     Warning("Ignoring subtable %d with unsupported version: %d",
             i, subtable.version);
     continue;
   }

   const size_t current_offset = table.offset();
   if (current_offset - 4 + sub_length > length) {
     return Error("Bad subtable %d offset %ld", i, current_offset);
   }

   if (!table.ReadU16(&subtable.coverage)) {
     return Error("Failed to read subtable %d coverage", i);
   }

   if (!(subtable.coverage & 0x1)) {
     Warning(
         "We don't support vertical data as the renderer doesn't support it.");
     continue;
   }
   if (subtable.coverage & 0xF0) {
     return Drop("Reserved fields should be zero");
   }
   const uint32_t format = (subtable.coverage & 0xFF00) >> 8;
   if (format != 0) {
     Warning("Ignoring subtable %d with unsupported format: %d", i, format);
     continue;
   }

   // Parse the format 0 field.
   uint16_t num_pairs = 0;
   if (!table.ReadU16(&num_pairs) ||
       !table.ReadU16(&subtable.search_range) ||
       !table.ReadU16(&subtable.entry_selector) ||
       !table.ReadU16(&subtable.range_shift)) {
     return Error("Failed to read subtable %d format 0 fields", i);
   }

   if (!num_pairs) {
     return Drop("Zero length subtable is found");
   }

   // Sanity checks for search_range, entry_selector, and range_shift. See the
   // comment in ots.cc for details.
   const size_t kFormat0PairSize = 6;  // left, right, and value. 2 bytes each.
   if (num_pairs > (65536 / kFormat0PairSize)) {
     // Some fonts (e.g. calibri.ttf, pykes_peak_zero.ttf) have pairs >= 10923.
     return Drop("Too large subtable");
   }
   unsigned max_pow2 = 0;
   while (1u << (max_pow2 + 1) <= num_pairs) {
     ++max_pow2;
   }
   const uint16_t expected_search_range = (1u << max_pow2) * kFormat0PairSize;
   if (subtable.search_range != expected_search_range) {
     Warning("bad search range");
     subtable.search_range = expected_search_range;
   }
   if (subtable.entry_selector != max_pow2) {
     return Error("Bad subtable %d entry selector %d", i, subtable.entry_selector);
   }
   const uint16_t expected_range_shift =
       kFormat0PairSize * num_pairs - subtable.search_range;
   if (subtable.range_shift != expected_range_shift) {
     Warning("bad range shift");
     subtable.range_shift = expected_range_shift;
   }

   // Read kerning pairs.
   subtable.pairs.reserve(num_pairs);
   uint32_t last_pair = 0;
   for (unsigned j = 0; j < num_pairs; ++j) {
     OpenTypeKERNFormat0Pair kerning_pair;
     if (!table.ReadU16(&kerning_pair.left) ||
         !table.ReadU16(&kerning_pair.right) ||
         !table.ReadS16(&kerning_pair.value)) {
       return Error("Failed to read subtable %d kerning pair %d", i, j);
     }
     const uint32_t current_pair
         = (kerning_pair.left << 16) + kerning_pair.right;
     if (j != 0 && current_pair <= last_pair) {
       // Many free fonts don't follow this rule, so we don't call OTS_FAILURE
       // in order to support these fonts.
       return Drop("Kerning pairs are not sorted");
     }
     last_pair = current_pair;
     subtable.pairs.push_back(kerning_pair);
   }

   this->subtables.push_back(subtable);
 }

 if (!this->subtables.size()) {
   return Drop("All subtables were removed");
 }

 return true;
}

bool OpenTypeKERN::Serialize(OTSStream *out) {
 const uint16_t num_subtables = static_cast<uint16_t>(this->subtables.size());
 if (num_subtables != this->subtables.size() ||
     !out->WriteU16(this->version) ||
     !out->WriteU16(num_subtables)) {
   return Error("Failed to write kern table header");
 }

 for (uint16_t i = 0; i < num_subtables; ++i) {
   const size_t length = 14 + (6 * this->subtables[i].pairs.size());
   if (length > std::numeric_limits<uint16_t>::max() ||
       !out->WriteU16(this->subtables[i].version) ||
       !out->WriteU16(static_cast<uint16_t>(length)) ||
       !out->WriteU16(this->subtables[i].coverage) ||
       !out->WriteU16(
           static_cast<uint16_t>(this->subtables[i].pairs.size())) ||
       !out->WriteU16(this->subtables[i].search_range) ||
       !out->WriteU16(this->subtables[i].entry_selector) ||
       !out->WriteU16(this->subtables[i].range_shift)) {
     return Error("Failed to write kern subtable %d", i);
   }
   for (unsigned j = 0; j < this->subtables[i].pairs.size(); ++j) {
     if (!out->WriteU16(this->subtables[i].pairs[j].left) ||
         !out->WriteU16(this->subtables[i].pairs[j].right) ||
         !out->WriteS16(this->subtables[i].pairs[j].value)) {
       return Error("Failed to write kern pair %d for subtable %d", j, i);
     }
   }
 }

 return true;
}

bool OpenTypeKERN::ShouldSerialize() {
 return Table::ShouldSerialize() &&
        // this table is not for CFF fonts.
        GetFont()->GetTable(OTS_TAG_GLYF) != NULL;
}

}  // namespace ots