bit_reader.h

// 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.
 
#ifndef PACKAGER_MEDIA_BASE_BIT_READER_H_
#define PACKAGER_MEDIA_BASE_BIT_READER_H_
 
#include <cstddef>
#include <cstdint>
 
#include <absl/log/check.h>
 
#include <packager/macros/classes.h>
 
namespace shaka {
namespace media {
 
class BitReader {
 public:
  BitReader(const uint8_t* data, size_t size);
  ~BitReader();
 
  template <typename T>
  bool ReadBits(size_t num_bits, T* out) {
    DCHECK_LE(num_bits, sizeof(T) * 8);
    uint64_t temp;
    bool ret = ReadBitsInternal(num_bits, &temp);
    *out = static_cast<T>(temp);
    return ret;
  }
 
  // Explicit T=bool overload to make MSVC happy.
  bool ReadBits(size_t num_bits, bool* out) {
    DCHECK_EQ(num_bits, 1u);
    uint64_t temp;
    bool ret = ReadBitsInternal(num_bits, &temp);
    *out = temp != 0;
    return ret;
  }
 
  bool SkipBits(size_t num_bits);
 
  bool SkipBitsConditional(bool condition, size_t num_bits) {
    bool condition_read = true;
    if (!ReadBits(1, &condition_read))
      return false;
    return condition_read == condition ? SkipBits(num_bits) : true;
  }
 
  void SkipToNextByte();
 
  bool SkipBytes(size_t num_bytes);
 
  size_t bits_available() const {
    return 8 * bytes_left_ + num_remaining_bits_in_curr_byte_;
  }
 
  size_t bit_position() const { return 8 * initial_size_ - bits_available(); }
 
  const uint8_t* current_byte_ptr() const { return data_ - 1; }
 
 private:
  // Help function used by ReadBits to avoid inlining the bit reading logic.
  bool ReadBitsInternal(size_t num_bits, uint64_t* out);
 
  // Advance to the next byte, loading it into curr_byte_.
  // If the num_remaining_bits_in_curr_byte_ is 0 after this function returns,
  // the stream has reached the end.
  void UpdateCurrByte();
 
  // Pointer to the next unread (not in curr_byte_) byte in the stream.
  const uint8_t* data_;
 
  // Initial size of the input data.
  size_t initial_size_;
 
  // Bytes left in the stream (without the curr_byte_).
  size_t bytes_left_;
 
  // Contents of the current byte; first unread bit starting at position
  // 8 - num_remaining_bits_in_curr_byte_ from MSB.
  uint8_t curr_byte_;
 
  // Number of bits remaining in curr_byte_
  size_t num_remaining_bits_in_curr_byte_;
 
 private:
  DISALLOW_COPY_AND_ASSIGN(BitReader);
};
 
}  // namespace media
}  // namespace shaka
 
#endif  // PACKAGER_MEDIA_BASE_BIT_READER_H_