tor-browser

The Tor Browser
git clone https://git.dasho.dev/tor-browser.git
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variable_length.cc (3176B)

      1 /* Copyright 2015 Google Inc. All Rights Reserved.
      2 
      3   Distributed under MIT license.
      4   See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
      5 */
      6 
      7 /* Helper functions for woff2 variable length types: 255UInt16 and UIntBase128 */
      8 
      9 #include "./variable_length.h"
     10 
     11 namespace woff2 {
     12 
     13 size_t Size255UShort(uint16_t value) {
     14  size_t result = 3;
     15  if (value < 253) {
     16    result = 1;
     17  } else if (value < 762) {
     18    result = 2;
     19  } else {
     20    result = 3;
     21  }
     22  return result;
     23 }
     24 
     25 void Write255UShort(std::vector<uint8_t>* out, int value) {
     26  if (value < 253) {
     27    out->push_back(value);
     28  } else if (value < 506) {
     29    out->push_back(255);
     30    out->push_back(value - 253);
     31  } else if (value < 762) {
     32    out->push_back(254);
     33    out->push_back(value - 506);
     34  } else {
     35    out->push_back(253);
     36    out->push_back(value >> 8);
     37    out->push_back(value & 0xff);
     38  }
     39 }
     40 
     41 void Store255UShort(int val, size_t* offset, uint8_t* dst) {
     42  std::vector<uint8_t> packed;
     43  Write255UShort(&packed, val);
     44  for (uint8_t packed_byte : packed) {
     45    dst[(*offset)++] = packed_byte;
     46  }
     47 }
     48 
     49 // Based on section 6.1.1 of MicroType Express draft spec
     50 bool Read255UShort(Buffer* buf, unsigned int* value) {
     51  static const int kWordCode = 253;
     52  static const int kOneMoreByteCode2 = 254;
     53  static const int kOneMoreByteCode1 = 255;
     54  static const int kLowestUCode = 253;
     55  uint8_t code = 0;
     56  if (!buf->ReadU8(&code)) {
     57    return FONT_COMPRESSION_FAILURE();
     58  }
     59  if (code == kWordCode) {
     60    uint16_t result = 0;
     61    if (!buf->ReadU16(&result)) {
     62      return FONT_COMPRESSION_FAILURE();
     63    }
     64    *value = result;
     65    return true;
     66  } else if (code == kOneMoreByteCode1) {
     67    uint8_t result = 0;
     68    if (!buf->ReadU8(&result)) {
     69      return FONT_COMPRESSION_FAILURE();
     70    }
     71    *value = result + kLowestUCode;
     72    return true;
     73  } else if (code == kOneMoreByteCode2) {
     74    uint8_t result = 0;
     75    if (!buf->ReadU8(&result)) {
     76      return FONT_COMPRESSION_FAILURE();
     77    }
     78    *value = result + kLowestUCode * 2;
     79    return true;
     80  } else {
     81    *value = code;
     82    return true;
     83  }
     84 }
     85 
     86 bool ReadBase128(Buffer* buf, uint32_t* value) {
     87  uint32_t result = 0;
     88  for (size_t i = 0; i < 5; ++i) {
     89    uint8_t code = 0;
     90    if (!buf->ReadU8(&code)) {
     91      return FONT_COMPRESSION_FAILURE();
     92    }
     93    // Leading zeros are invalid.
     94    if (i == 0 && code == 0x80) {
     95      return FONT_COMPRESSION_FAILURE();
     96    }
     97    // If any of the top seven bits are set then we're about to overflow.
     98    if (result & 0xfe000000) {
     99      return FONT_COMPRESSION_FAILURE();
    100    }
    101    result = (result << 7) | (code & 0x7f);
    102    if ((code & 0x80) == 0) {
    103      *value = result;
    104      return true;
    105    }
    106  }
    107  // Make sure not to exceed the size bound
    108  return FONT_COMPRESSION_FAILURE();
    109 }
    110 
    111 size_t Base128Size(size_t n) {
    112  size_t size = 1;
    113  for (; n >= 128; n >>= 7) ++size;
    114  return size;
    115 }
    116 
    117 void StoreBase128(size_t len, size_t* offset, uint8_t* dst) {
    118  size_t size = Base128Size(len);
    119  for (size_t i = 0; i < size; ++i) {
    120    int b = static_cast<int>((len >> (7 * (size - i - 1))) & 0x7f);
    121    if (i < size - 1) {
    122      b |= 0x80;
    123    }
    124    dst[(*offset)++] = b;
    125  }
    126 }
    127 
    128 } // namespace woff2