76 lines
2.7 KiB
C
76 lines
2.7 KiB
C
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/*
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* Copyright 2015 The WebRTC Project Authors. All rights reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#ifndef WEBRTC_BASE_BITBUFFER_H_
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#define WEBRTC_BASE_BITBUFFER_H_
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#include "webrtc/base/common.h"
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namespace rtc {
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// A class, similar to ByteBuffer, that can parse bit-sized data out of a set of
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// bytes. Has a similar API to the read-only parts of ByteBuffer, plus methods
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// for reading bit-sized data and processing exponential golomb encoded data.
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// Sizes/counts specify bits/bytes, for clarity.
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// Byte order is assumed big-endian/network.
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class BitBuffer {
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public:
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BitBuffer(const uint8* bytes, size_t byte_count);
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// The remaining bits in the byte buffer.
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uint64 RemainingBitCount() const;
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// Reads byte-sized values from the buffer. Returns false if there isn't
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// enough data left for the specified type.
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bool ReadUInt8(uint8* val);
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bool ReadUInt16(uint16* val);
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bool ReadUInt32(uint32* val);
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// Reads bit-sized values from the buffer. Returns false if there isn't enough
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// data left for the specified type.
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bool ReadBits(uint32* val, size_t bit_count);
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// Peeks bit-sized values from the buffer. Returns false if there isn't enough
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// data left for the specified type. Doesn't move the current read offset.
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bool PeekBits(uint32* val, size_t bit_count);
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// Reads the exponential golomb encoded value at the current bit offset.
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// Exponential golomb values are encoded as:
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// 1) x = source val + 1
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// 2) In binary, write [countbits(x) - 1] 0s, then x
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// To decode, we count the number of leading 0 bits, read that many + 1 bits,
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// and increment the result by 1.
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// Returns false if there isn't enough data left for the specified type, or if
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// the value wouldn't fit in a uint32.
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bool ReadExponentialGolomb(uint32* val);
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// Moves current position |byte_count| bytes forward. Returns false if
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// there aren't enough bytes left in the buffer.
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bool ConsumeBytes(size_t byte_count);
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// Moves current position |bit_count| bits forward. Returns false if
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// there aren't enough bits left in the buffer.
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bool ConsumeBits(size_t bit_count);
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private:
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const uint8* const bytes_;
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// The total size of |bytes_|.
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size_t byte_count_;
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// The current offset, in bytes, from the start of |bytes_|.
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size_t byte_offset_;
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// The current offset, in bits, into the current byte.
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size_t bit_offset_;
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DISALLOW_COPY_AND_ASSIGN(BitBuffer);
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};
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} // namespace rtc
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#endif // WEBRTC_BASE_BITBUFFER_H_
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