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#ifndef __COMPRESSION_RANGECODER_H
#define __COMPRESSION_RANGECODER_H
#include "IInOutStreams.h"
#define kNumTopBits 24
#define kTopValue (1 << kNumTopBits)
typedef struct CRangeDecoder
{
UINT32 m_Range;
UINT32 m_Code;
} CRangeDecoder;
INLINE void RangeDecoderInit(
ISequentialInStream *in_stream,
CRangeDecoder *rangeDecoder)
{
int i;
rangeDecoder->m_Code = 0;
rangeDecoder->m_Range = (UINT32)(-1);
for(i = 0; i < 5; i++)
rangeDecoder->m_Code = (rangeDecoder->m_Code << 8) | InStreamReadByte(in_stream);
}
INLINE UINT32 RangeDecodeDirectBits(
ISequentialInStream *in_stream,
CRangeDecoder *rangeDecoder,
UINT32 aNumTotalBits)
{
UINT32 aRange = rangeDecoder->m_Range;
UINT32 aCode = rangeDecoder->m_Code;
UINT32 aResult = 0;
UINT32 i;
for (i = aNumTotalBits; i > 0; i--)
{
UINT32 t;
aRange >>= 1;
t = (aCode - aRange) >> 31;
aCode -= aRange & (t - 1);
aResult = (aResult << 1) | (1 - t);
if (aRange < kTopValue)
{
aCode = (aCode << 8) | InStreamReadByte(in_stream);
aRange <<= 8;
}
}
rangeDecoder->m_Range = aRange;
rangeDecoder->m_Code = aCode;
return aResult;
}
#endif
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