1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/content/media/fmp4/demuxer/bit_reader.h Wed Dec 31 06:09:35 2014 +0100
1.3 @@ -0,0 +1,69 @@
1.4 +// Copyright (c) 2012 The Chromium Authors. All rights reserved.
1.5 +// Use of this source code is governed by a BSD-style license that can be
1.6 +// found in the LICENSE file.
1.7 +
1.8 +#ifndef MEDIA_BASE_BIT_READER_H_
1.9 +#define MEDIA_BASE_BIT_READER_H_
1.10 +
1.11 +#include <sys/types.h>
1.12 +
1.13 +#include "mp4_demuxer/basictypes.h"
1.14 +
1.15 +namespace mp4_demuxer {
1.16 +
1.17 +// A class to read bit streams.
1.18 +class BitReader {
1.19 + public:
1.20 + // Initialize the reader to start reading at |data|, |size| being size
1.21 + // of |data| in bytes.
1.22 + BitReader(const uint8_t* data, off_t size);
1.23 + ~BitReader();
1.24 +
1.25 + // Read |num_bits| next bits from stream and return in |*out|, first bit
1.26 + // from the stream starting at |num_bits| position in |*out|.
1.27 + // |num_bits| cannot be larger than the bits the type can hold.
1.28 + // Return false if the given number of bits cannot be read (not enough
1.29 + // bits in the stream), true otherwise. When return false, the stream will
1.30 + // enter a state where further ReadBits/SkipBits operations will always
1.31 + // return false unless |num_bits| is 0. The type |T| has to be a primitive
1.32 + // integer type.
1.33 + template<typename T> bool ReadBits(int num_bits, T *out) {
1.34 + DCHECK_LE(num_bits, static_cast<int>(sizeof(T) * 8));
1.35 + uint64_t temp;
1.36 + bool ret = ReadBitsInternal(num_bits, &temp);
1.37 + *out = static_cast<T>(temp);
1.38 + return ret;
1.39 + }
1.40 +
1.41 + // Returns the number of bits available for reading.
1.42 + int bits_available() const;
1.43 +
1.44 + private:
1.45 + // Help function used by ReadBits to avoid inlining the bit reading logic.
1.46 + bool ReadBitsInternal(int num_bits, uint64_t* out);
1.47 +
1.48 + // Advance to the next byte, loading it into curr_byte_.
1.49 + // If the num_remaining_bits_in_curr_byte_ is 0 after this function returns,
1.50 + // the stream has reached the end.
1.51 + void UpdateCurrByte();
1.52 +
1.53 + // Pointer to the next unread (not in curr_byte_) byte in the stream.
1.54 + const uint8_t* data_;
1.55 +
1.56 + // Bytes left in the stream (without the curr_byte_).
1.57 + off_t bytes_left_;
1.58 +
1.59 + // Contents of the current byte; first unread bit starting at position
1.60 + // 8 - num_remaining_bits_in_curr_byte_ from MSB.
1.61 + uint8_t curr_byte_;
1.62 +
1.63 + // Number of bits remaining in curr_byte_
1.64 + int num_remaining_bits_in_curr_byte_;
1.65 +
1.66 + private:
1.67 + DISALLOW_COPY_AND_ASSIGN(BitReader);
1.68 +};
1.69 +
1.70 +} // namespace mp4_demuxer
1.71 +
1.72 +#endif // MEDIA_BASE_BIT_READER_H_
