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ext/zstd/contrib/linux-kernel/lib/zstd/fse.h  view on Meta::CPAN

typedef struct {
	unsigned short newState;
	unsigned char symbol;
	unsigned char nbBits;
} FSE_decode_t; /* size == U32 */

ZSTD_STATIC void FSE_initDState(FSE_DState_t *DStatePtr, BIT_DStream_t *bitD, const FSE_DTable *dt)
{
	const void *ptr = dt;
	const FSE_DTableHeader *const DTableH = (const FSE_DTableHeader *)ptr;
	DStatePtr->state = BIT_readBits(bitD, DTableH->tableLog);
	BIT_reloadDStream(bitD);
	DStatePtr->table = dt + 1;
}

ZSTD_STATIC BYTE FSE_peekSymbol(const FSE_DState_t *DStatePtr)
{
	FSE_decode_t const DInfo = ((const FSE_decode_t *)(DStatePtr->table))[DStatePtr->state];
	return DInfo.symbol;
}

ZSTD_STATIC void FSE_updateState(FSE_DState_t *DStatePtr, BIT_DStream_t *bitD)
{
	FSE_decode_t const DInfo = ((const FSE_decode_t *)(DStatePtr->table))[DStatePtr->state];
	U32 const nbBits = DInfo.nbBits;
	size_t const lowBits = BIT_readBits(bitD, nbBits);
	DStatePtr->state = DInfo.newState + lowBits;
}

ZSTD_STATIC BYTE FSE_decodeSymbol(FSE_DState_t *DStatePtr, BIT_DStream_t *bitD)
{
	FSE_decode_t const DInfo = ((const FSE_decode_t *)(DStatePtr->table))[DStatePtr->state];
	U32 const nbBits = DInfo.nbBits;
	BYTE const symbol = DInfo.symbol;
	size_t const lowBits = BIT_readBits(bitD, nbBits);

	DStatePtr->state = DInfo.newState + lowBits;
	return symbol;
}

/*! FSE_decodeSymbolFast() :
	unsafe, only works if no symbol has a probability > 50% */
ZSTD_STATIC BYTE FSE_decodeSymbolFast(FSE_DState_t *DStatePtr, BIT_DStream_t *bitD)
{
	FSE_decode_t const DInfo = ((const FSE_decode_t *)(DStatePtr->table))[DStatePtr->state];
	U32 const nbBits = DInfo.nbBits;
	BYTE const symbol = DInfo.symbol;
	size_t const lowBits = BIT_readBitsFast(bitD, nbBits);

	DStatePtr->state = DInfo.newState + lowBits;
	return symbol;
}

ZSTD_STATIC unsigned FSE_endOfDState(const FSE_DState_t *DStatePtr) { return DStatePtr->state == 0; }

/* **************************************************************
*  Tuning parameters
****************************************************************/
/*!MEMORY_USAGE :
*  Memory usage formula : N->2^N Bytes (examples : 10 -> 1KB; 12 -> 4KB ; 16 -> 64KB; 20 -> 1MB; etc.)
*  Increasing memory usage improves compression ratio
*  Reduced memory usage can improve speed, due to cache effect
*  Recommended max value is 14, for 16KB, which nicely fits into Intel x86 L1 cache */
#ifndef FSE_MAX_MEMORY_USAGE
#define FSE_MAX_MEMORY_USAGE 14
#endif
#ifndef FSE_DEFAULT_MEMORY_USAGE
#define FSE_DEFAULT_MEMORY_USAGE 13
#endif

/*!FSE_MAX_SYMBOL_VALUE :
*  Maximum symbol value authorized.
*  Required for proper stack allocation */
#ifndef FSE_MAX_SYMBOL_VALUE
#define FSE_MAX_SYMBOL_VALUE 255
#endif

/* **************************************************************
*  template functions type & suffix
****************************************************************/
#define FSE_FUNCTION_TYPE BYTE
#define FSE_FUNCTION_EXTENSION
#define FSE_DECODE_TYPE FSE_decode_t

/* ***************************************************************
*  Constants
*****************************************************************/
#define FSE_MAX_TABLELOG (FSE_MAX_MEMORY_USAGE - 2)
#define FSE_MAX_TABLESIZE (1U << FSE_MAX_TABLELOG)
#define FSE_MAXTABLESIZE_MASK (FSE_MAX_TABLESIZE - 1)
#define FSE_DEFAULT_TABLELOG (FSE_DEFAULT_MEMORY_USAGE - 2)
#define FSE_MIN_TABLELOG 5

#define FSE_TABLELOG_ABSOLUTE_MAX 15
#if FSE_MAX_TABLELOG > FSE_TABLELOG_ABSOLUTE_MAX
#error "FSE_MAX_TABLELOG > FSE_TABLELOG_ABSOLUTE_MAX is not supported"
#endif

#define FSE_TABLESTEP(tableSize) ((tableSize >> 1) + (tableSize >> 3) + 3)

#endif /* FSE_H */