text: // Copyright (c) 2009 The Chromium Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  
  #include "kern.h"
  
  // kern - Kerning
  // http://www.microsoft.com/typography/otspec/kern.htm
  
  #define TABLE_NAME "kern"
  
  #define DROP_THIS_TABLE(msg_) \
    do { \
      OTS_FAILURE_MSG(msg_ ", table discarded"); \
      delete font->kern; \
      font->kern = 0; \
    } while (0)
  
  namespace ots {
  
  bool ots_kern_parse(Font *font, const uint8_t *data, size_t length) {
    Buffer table(data, length);
  
    OpenTypeKERN *kern = new OpenTypeKERN;
    font->kern = kern;
  
    uint16_t num_tables = 0;
    if (!table.ReadU16(&kern->version) ||
        !table.ReadU16(&num_tables)) {
      return OTS_FAILURE_MSG("Failed to read kern header");
    }
  
    if (kern->version > 0) {
      DROP_THIS_TABLE("bad table version");
      return true;
    }
  
    if (num_tables == 0) {
      DROP_THIS_TABLE("num_tables is zero");
      return true;
    }
  
    kern->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 OTS_FAILURE_MSG("Failed to read kern subtable %d header", i);
      }
  
      if (subtable.version > 0) {
        OTS_WARNING("Bad subtable version: %d", subtable.version);
        continue;
      }
  
      const size_t current_offset = table.offset();
      if (current_offset - 4 + sub_length > length) {
        return OTS_FAILURE_MSG("Bad kern subtable %d offset %ld", i, current_offset);
      }
  
      if (!table.ReadU16(&subtable.coverage)) {
        return OTS_FAILURE_MSG("Cailed to read kern subtable %d coverage", i);
      }
  
      if (!(subtable.coverage & 0x1)) {
        OTS_WARNING(
            "We don't support vertical data as the renderer doesn't support it.");
        continue;
      }
      if (subtable.coverage & 0xF0) {
        DROP_THIS_TABLE("Reserved fields should zero-filled");
        return true;
      }
      const uint32_t format = (subtable.coverage & 0xFF00) >> 8;
      if (format != 0) {
        OTS_WARNING("Format %d is not supported.", 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 OTS_FAILURE_MSG("Failed to read kern subtable %d format 0 fields", i);
      }
  
      if (!num_pairs) {
        DROP_THIS_TABLE("Zero length subtable is found");
        return true;
      }
  
      // 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.
        DROP_THIS_TABLE("Too large subtable");
        return true;
      }
      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) {
        OTS_WARNING("bad search range");
        subtable.search_range = expected_search_range;
      }
      if (subtable.entry_selector != max_pow2) {
        return OTS_FAILURE_MSG("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) {
        OTS_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 OTS_FAILURE_MSG("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.
          DROP_THIS_TABLE("Kerning pairs are not sorted");
          return true;
        }
        last_pair = current_pair;
        subtable.pairs.push_back(kerning_pair);
      }
  
      kern->subtables.push_back(subtable);
    }
  
    if (!kern->subtables.size()) {
      DROP_THIS_TABLE("All subtables are removed");
      return true;
    }
  
    return true;
  }
  
  bool ots_kern_should_serialise(Font *font) {
    if (!font->glyf) return false;  // this table is not for CFF fonts.
    return font->kern != NULL;
  }
  
  bool ots_kern_serialise(OTSStream *out, Font *font) {
    const OpenTypeKERN *kern = font->kern;
  
    const uint16_t num_subtables = static_cast<uint16_t>(kern->subtables.size());
    if (num_subtables != kern->subtables.size() ||
        !out->WriteU16(kern->version) ||
        !out->WriteU16(num_subtables)) {
      return OTS_FAILURE_MSG("Can't write kern table header");
    }
  
    for (uint16_t i = 0; i < num_subtables; ++i) {
      const size_t length = 14 + (6 * kern->subtables[i].pairs.size());
      if (length > std::numeric_limits<uint16_t>::max() ||
          !out->WriteU16(kern->subtables[i].version) ||
          !out->WriteU16(static_cast<uint16_t>(length)) ||
          !out->WriteU16(kern->subtables[i].coverage) ||
          !out->WriteU16(
              static_cast<uint16_t>(kern->subtables[i].pairs.size())) ||
          !out->WriteU16(kern->subtables[i].search_range) ||
          !out->WriteU16(kern->subtables[i].entry_selector) ||
          !out->WriteU16(kern->subtables[i].range_shift)) {
        return OTS_FAILURE_MSG("Failed to write kern subtable %d", i);
      }
      for (unsigned j = 0; j < kern->subtables[i].pairs.size(); ++j) {
        if (!out->WriteU16(kern->subtables[i].pairs[j].left) ||
            !out->WriteU16(kern->subtables[i].pairs[j].right) ||
            !out->WriteS16(kern->subtables[i].pairs[j].value)) {
          return OTS_FAILURE_MSG("Failed to write kern pair %d for subtable %d", j, i);
        }
      }
    }
  
    return true;
  }
  
  void ots_kern_reuse(Font *font, Font *other) {
    font->kern = other->kern;
    font->kern_reused = true;
  }
  
  void ots_kern_free(Font *font) {
    delete font->kern;
  }
  
  }  // namespace ots
  
  #undef TABLE_NAME
  #undef DROP_THIS_TABLE
  