chrome/browser/net/bit_stream_reader.cc

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "chrome/browser/net/bit_stream_reader.h"
   6
   7 #include "base/big_endian.h"
   8 #include "base/logging.h"
   9 #include "base/numerics/safe_conversions.h"
  10
  11 namespace internal {
  12
  13 BitStreamReader::BitStreamReader(const base::StringPiece& source)
  14     : source_(source), current_byte_(0), current_bit_(7) {
  15   DCHECK_LT(source_.length(), UINT32_MAX);
  16 }
  17
  18 bool BitStreamReader::ReadUnaryEncoding(uint64_t* out) {
  19   if (BitsLeft() == 0)
  20     return false;
  21
  22   *out = 0;
  23   while ((BitsLeft() > 0) && ReadBit())
  24     ++(*out);
  25
  26   return true;
  27 }
  28
  29 bool BitStreamReader::ReadBits(uint8_t num_bits, uint64_t* out) {
  30   DCHECK_LE(num_bits, 64);
  31
  32   if (BitsLeft() < num_bits)
  33     return false;
  34
  35   *out = 0;
  36   for (uint8_t i = 0; i < num_bits; ++i)
  37     (*out) |= (static_cast<uint64_t>(ReadBit()) << (num_bits - (i + 1)));
  38
  39   return true;
  40 }
  41
  42 uint64_t BitStreamReader::BitsLeft() const {
  43   if (current_byte_ == source_.length())
  44     return 0;
  45   DCHECK_GT(source_.length(), current_byte_);
  46   return (source_.length() - (current_byte_ + 1)) * 8 + current_bit_ + 1;
  47 }
  48
  49 uint8_t BitStreamReader::ReadBit() {
  50   DCHECK_GT(BitsLeft(), 0u);
  51   DCHECK(current_bit_ < 8 && current_bit_ >= 0);
  52   uint8_t res =
  53       (source_.data()[current_byte_] & (1 << current_bit_)) >> current_bit_;
  54   current_bit_--;
  55   if (current_bit_ < 0) {
  56     current_byte_++;
  57     current_bit_ = 7;
  58   }
  59
  60   return res;
  61 }
  62
  63 }  // namespace internal