78 lines
2.6 KiB
C
78 lines
2.6 KiB
C
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// Copyright (c) 2012 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef MEDIA_BASE_BIT_READER_H_
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#define MEDIA_BASE_BIT_READER_H_
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#include <sys/types.h>
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#include "base/basictypes.h"
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#include "base/logging.h"
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#include "media/base/media_export.h"
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namespace media {
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// A class to read bit streams.
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class MEDIA_EXPORT BitReader {
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public:
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// Initialize the reader to start reading at |data|, |size| being size
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// of |data| in bytes.
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BitReader(const uint8* data, off_t size);
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~BitReader();
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// Read |num_bits| next bits from stream and return in |*out|, first bit
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// from the stream starting at |num_bits| position in |*out|.
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// |num_bits| cannot be larger than the bits the type can hold.
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// Return false if the given number of bits cannot be read (not enough
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// bits in the stream), true otherwise. When return false, the stream will
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// enter a state where further ReadBits/SkipBits operations will always
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// return false unless |num_bits| is 0. The type |T| has to be a primitive
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// integer type.
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template<typename T> bool ReadBits(int num_bits, T *out) {
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DCHECK_LE(num_bits, static_cast<int>(sizeof(T) * 8));
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uint64 temp;
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bool ret = ReadBitsInternal(num_bits, &temp);
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*out = static_cast<T>(temp);
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return ret;
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}
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// Skip |num_bits| next bits from stream. Return false if the given number of
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// bits cannot be skipped (not enough bits in the stream), true otherwise.
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// When return false, the stream will enter a state where further ReadBits/
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// SkipBits operations will always return false unless |num_bits| is 0.
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bool SkipBits(int num_bits);
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// Returns the number of bits available for reading.
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int bits_available() const;
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private:
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// Help function used by ReadBits to avoid inlining the bit reading logic.
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bool ReadBitsInternal(int num_bits, uint64* out);
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// Advance to the next byte, loading it into curr_byte_.
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// If the num_remaining_bits_in_curr_byte_ is 0 after this function returns,
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// the stream has reached the end.
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void UpdateCurrByte();
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// Pointer to the next unread (not in curr_byte_) byte in the stream.
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const uint8* data_;
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// Bytes left in the stream (without the curr_byte_).
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off_t bytes_left_;
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// Contents of the current byte; first unread bit starting at position
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// 8 - num_remaining_bits_in_curr_byte_ from MSB.
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uint8 curr_byte_;
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// Number of bits remaining in curr_byte_
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int num_remaining_bits_in_curr_byte_;
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private:
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DISALLOW_COPY_AND_ASSIGN(BitReader);
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};
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} // namespace media
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#endif // MEDIA_BASE_BIT_READER_H_
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