blob: 1becf916d9eee92155c61fafe89dd444c56706b2 [file] [log] [blame]
// 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 <sys/types.h>
#include "base/basictypes.h"
#include "base/logging.h"
#include "media/base/media_export.h"
namespace media {
// A class to read bit streams.
class MEDIA_EXPORT BitReader {
// Initialize the reader to start reading at |data|, |size| being size
// of |data| in bytes.
BitReader(const uint8* data, off_t size);
// Read |num_bits| next bits from stream and return in |*out|, first bit
// from the stream starting at |num_bits| position in |*out|.
// |num_bits| cannot be larger than the bits the type can hold.
// Return false if the given number of bits cannot be read (not enough
// bits in the stream), true otherwise. When return false, the stream will
// enter a state where further ReadBits/SkipBits operations will always
// return false unless |num_bits| is 0. The type |T| has to be a primitive
// integer type.
template<typename T> bool ReadBits(int num_bits, T *out) {
DCHECK_LE(num_bits, static_cast<int>(sizeof(T) * 8));
uint64 temp;
bool ret = ReadBitsInternal(num_bits, &temp);
*out = static_cast<T>(temp);
return ret;
// Help function used by ReadBits to avoid inlining the bit reading logic.
bool ReadBitsInternal(int num_bits, uint64* 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* data_;
// Bytes left in the stream (without the curr_byte_).
off_t bytes_left_;
// Contents of the current byte; first unread bit starting at position
// 8 - num_remaining_bits_in_curr_byte_ from MSB.
uint8 curr_byte_;
// Number of bits remaining in curr_byte_
int num_remaining_bits_in_curr_byte_;
} // namespace media