147 lines
4.0 KiB
C++
147 lines
4.0 KiB
C++
/*
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Copyright (c) 2014, Conor Stokes
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All rights reserved.
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Redistribution and use in source and binary forms, with or without
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modification, are permitted provided that the following conditions are met:
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1. Redistributions of source code must retain the above copyright notice, this
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list of conditions and the following disclaimer.
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2. Redistributions in binary form must reproduce the above copyright notice,
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this list of conditions and the following disclaimer in the documentation
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and/or other materials provided with the distribution.
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
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ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
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ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#ifndef READ_BIT_STREAM_H__
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#define READ_BIT_STREAM_H__
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#pragma once
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#include <stdint.h>
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#include <stdlib.h>
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#ifdef _MSC_VER
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#define RBS_INLINE __forceinline
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#else
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#define RBS_INLINE inline
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#endif
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// Very simple reader bitstream, note it does not do any overflow checking, etc.
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class ReadBitstream
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{
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public:
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// Construct the bitstream with a fixed byte buffer (which should be padded out to multiples of 8 bytes, as we read in 8 byte chunks).
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ReadBitstream( const uint8_t* buffer, size_t bufferSize );
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~ReadBitstream() {}
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// Read a number of bits
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uint32_t Read( uint32_t bitcount );
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// Get the buffer size of this in bytes
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size_t Size() const { return m_bufferSize; }
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uint32_t ReadVInt();
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private:
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uint64_t m_bitBuffer;
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const uint8_t* m_buffer;
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const uint8_t* m_cursor;
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size_t m_bufferSize;
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uint32_t m_bitsLeft;
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};
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inline ReadBitstream::ReadBitstream( const uint8_t* buffer, size_t bufferSize )
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{
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m_cursor =
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m_buffer = buffer;
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m_bufferSize = bufferSize;
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if ( bufferSize >= 8 )
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{
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m_bitBuffer = m_cursor[ 0 ];
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m_bitBuffer |= static_cast< uint64_t >( m_cursor[ 1 ] ) << 8;
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m_bitBuffer |= static_cast< uint64_t >( m_cursor[ 2 ] ) << 16;
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m_bitBuffer |= static_cast< uint64_t >( m_cursor[ 3 ] ) << 24;
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m_bitBuffer |= static_cast< uint64_t >( m_cursor[ 4 ] ) << 32;
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m_bitBuffer |= static_cast< uint64_t >( m_cursor[ 5 ] ) << 40;
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m_bitBuffer |= static_cast< uint64_t >( m_cursor[ 6 ] ) << 48;
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m_bitBuffer |= static_cast< uint64_t >( m_cursor[ 7 ] ) << 56;
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m_cursor += 8;
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m_bitsLeft = 64;
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}
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else
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{
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m_bitsLeft = 0;
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}
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}
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RBS_INLINE uint32_t ReadBitstream::Read( uint32_t bitCount )
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{
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uint64_t mask = ( 1 << bitCount ) - 1;
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uint32_t result = static_cast< uint32_t >( ( m_bitBuffer >> ( 64 - m_bitsLeft ) ) & mask );
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if ( m_bitsLeft < bitCount )
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{
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m_bitBuffer = m_cursor[ 0 ];
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m_bitBuffer |= static_cast< uint64_t >( m_cursor[ 1 ] ) << 8;
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m_bitBuffer |= static_cast< uint64_t >( m_cursor[ 2 ] ) << 16;
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m_bitBuffer |= static_cast< uint64_t >( m_cursor[ 3 ] ) << 24;
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m_bitBuffer |= static_cast< uint64_t >( m_cursor[ 4 ] ) << 32;
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m_bitBuffer |= static_cast< uint64_t >( m_cursor[ 5 ] ) << 40;
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m_bitBuffer |= static_cast< uint64_t >( m_cursor[ 6 ] ) << 48;
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m_bitBuffer |= static_cast< uint64_t >( m_cursor[ 7 ] ) << 56;
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m_cursor += 8;
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result |= static_cast< uint32_t >( m_bitBuffer << m_bitsLeft ) & mask;
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m_bitsLeft = 64 - ( bitCount - m_bitsLeft );
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}
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else
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{
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m_bitsLeft -= bitCount;
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}
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return result;
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}
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RBS_INLINE uint32_t ReadBitstream::ReadVInt()
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{
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uint32_t bitsToShift = 0;
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uint32_t result = 0;
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uint32_t readByte;
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do
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{
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readByte = Read( 8 );
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result |= ( readByte & 0x7F ) << bitsToShift;
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bitsToShift += 7;
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} while ( readByte & 0x80 );
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return result;
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}
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#endif // -- READ_BIT_STREAM_H__
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