text: // Copyright (c) 2012 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 "media/base/bit_reader.h"
  
  namespace media {
  
  BitReader::BitReader(const uint8* data, off_t size)
      : data_(data), bytes_left_(size), num_remaining_bits_in_curr_byte_(0) {
    DCHECK(data_ != NULL && bytes_left_ > 0);
  
    UpdateCurrByte();
  }
  
  BitReader::~BitReader() {}
  
  bool BitReader::ReadBitsInternal(int num_bits, uint64* out) {
    DCHECK_LE(num_bits, 64);
  
    *out = 0;
  
    while (num_remaining_bits_in_curr_byte_ != 0 && num_bits != 0) {
      int bits_to_take = std::min(num_remaining_bits_in_curr_byte_, num_bits);
  
      *out <<= bits_to_take;
      *out += curr_byte_ >> (num_remaining_bits_in_curr_byte_ - bits_to_take);
      num_bits -= bits_to_take;
      num_remaining_bits_in_curr_byte_ -= bits_to_take;
      curr_byte_ &= (1 << num_remaining_bits_in_curr_byte_) - 1;
  
      if (num_remaining_bits_in_curr_byte_ == 0)
        UpdateCurrByte();
    }
  
    return num_bits == 0;
  }
  
  void BitReader::UpdateCurrByte() {
    DCHECK_EQ(num_remaining_bits_in_curr_byte_, 0);
  
    if (bytes_left_ == 0)
      return;
  
    // Load a new byte and advance pointers.
    curr_byte_ = *data_;
    ++data_;
    --bytes_left_;
    num_remaining_bits_in_curr_byte_ = 8;
  }
  
  }  // namespace media
  