zstd_decompress_block.h File Reference

#include <stddef.h>
#include "zstd.h"
#include "zstd_internal.h"
#include "zstd_decompress_internal.h"

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Functions
size_t	ZSTD_decompressBlock_internal (ZSTD_DCtx *dctx, void *dst, size_t dstCapacity, const void *src, size_t srcSize, const int frame)
void	ZSTD_buildFSETable (ZSTD_seqSymbol *dt, const short *normalizedCounter, unsigned maxSymbolValue, const U32 *baseValue, const U32 *nbAdditionalBits, unsigned tableLog)

Function Documentation

ZSTD_buildFSETable()

void ZSTD_buildFSETable	(	ZSTD_seqSymbol *	dt,
		const short *	normalizedCounter,
		unsigned	maxSymbolValue,
		const U32 *	baseValue,
		const U32 *	nbAdditionalBits,
		unsigned	tableLog
	)

Definition at line 368 of file zstd_decompress_block.c.

{
    ZSTD_seqSymbol* const tableDecode = dt+1;
    U16 symbolNext[MaxSeq+1];
 
    U32 const maxSV1 = maxSymbolValue + 1;
    U32 const tableSize = 1 << tableLog;
    U32 highThreshold = tableSize-1;
 
    /* Sanity Checks */
    assert(maxSymbolValue <= MaxSeq);
    assert(tableLog <= MaxFSELog);
 
    /* Init, lay down lowprob symbols */
    {   ZSTD_seqSymbol_header DTableH;
        DTableH.tableLog = tableLog;
        DTableH.fastMode = 1;
        {   S16 const largeLimit= (S16)(1 << (tableLog-1));
            U32 s;
            for (s=0; s<maxSV1; s++) {
                if (normalizedCounter[s]==-1) {
                    tableDecode[highThreshold--].baseValue = s;
                    symbolNext[s] = 1;
                } else {
                    if (normalizedCounter[s] >= largeLimit) DTableH.fastMode=0;
                    assert(normalizedCounter[s]>=0);
                    symbolNext[s] = (U16)normalizedCounter[s];
        }   }   }
        memcpy(dt, &DTableH, sizeof(DTableH));
    }
 
    /* Spread symbols */
    {   U32 const tableMask = tableSize-1;
        U32 const step = FSE_TABLESTEP(tableSize);
        U32 s, position = 0;
        for (s=0; s<maxSV1; s++) {
            int i;
            for (i=0; i<normalizedCounter[s]; i++) {
                tableDecode[position].baseValue = s;
                position = (position + step) & tableMask;
                while (position > highThreshold) position = (position + step) & tableMask;   /* lowprob area */
        }   }
        assert(position == 0); /* position must reach all cells once, otherwise normalizedCounter is incorrect */
    }
 
    /* Build Decoding table */
    {   U32 u;
        for (u=0; u<tableSize; u++) {
            U32 const symbol = tableDecode[u].baseValue;
            U32 const nextState = symbolNext[symbol]++;
            tableDecode[u].nbBits = (BYTE) (tableLog - BIT_highbit32(nextState) );
            tableDecode[u].nextState = (U16) ( (nextState << tableDecode[u].nbBits) - tableSize);
            assert(nbAdditionalBits[symbol] < 255);
            tableDecode[u].nbAdditionalBits = (BYTE)nbAdditionalBits[symbol];
            tableDecode[u].baseValue = baseValue[symbol];
    }   }
}

Referenced by ZSTD_loadDEntropy().

ZSTD_decompressBlock_internal()

size_t ZSTD_decompressBlock_internal	(	ZSTD_DCtx *	dctx,
		void *	dst,
		size_t	dstCapacity,
		const void *	src,
		size_t	srcSize,
		const int	frame
	)

Definition at line 1341 of file zstd_decompress_block.c.

{   /* blockType == blockCompressed */
    const BYTE* ip = (const BYTE*)src;
    /* isLongOffset must be true if there are long offsets.
     * Offsets are long if they are larger than 2^STREAM_ACCUMULATOR_MIN.
     * We don't expect that to be the case in 64-bit mode.
     * In block mode, window size is not known, so we have to be conservative.
     * (note: but it could be evaluated from current-lowLimit)
     */
    ZSTD_longOffset_e const isLongOffset = (ZSTD_longOffset_e)(MEM_32bits() && (!frame || (dctx->fParams.windowSize > (1ULL << STREAM_ACCUMULATOR_MIN))));
    DEBUGLOG(5, "ZSTD_decompressBlock_internal (size : %u)", (U32)srcSize);
 
    RETURN_ERROR_IF(srcSize >= ZSTD_BLOCKSIZE_MAX, srcSize_wrong, "");
 
    /* Decode literals section */
    {   size_t const litCSize = ZSTD_decodeLiteralsBlock(dctx, src, srcSize);
        DEBUGLOG(5, "ZSTD_decodeLiteralsBlock : %u", (U32)litCSize);
        if (ZSTD_isError(litCSize)) return litCSize;
        ip += litCSize;
        srcSize -= litCSize;
    }
 
    /* Build Decoding Tables */
    {
        /* These macros control at build-time which decompressor implementation
         * we use. If neither is defined, we do some inspection and dispatch at
         * runtime.
         */
#if !defined(ZSTD_FORCE_DECOMPRESS_SEQUENCES_SHORT) && \
    !defined(ZSTD_FORCE_DECOMPRESS_SEQUENCES_LONG)
        int usePrefetchDecoder = dctx->ddictIsCold;
#endif
        int nbSeq;
        size_t const seqHSize = ZSTD_decodeSeqHeaders(dctx, &nbSeq, ip, srcSize);
        if (ZSTD_isError(seqHSize)) return seqHSize;
        ip += seqHSize;
        srcSize -= seqHSize;
 
        RETURN_ERROR_IF(dst == NULL && nbSeq > 0, dstSize_tooSmall, "NULL not handled");
 
#if !defined(ZSTD_FORCE_DECOMPRESS_SEQUENCES_SHORT) && \
    !defined(ZSTD_FORCE_DECOMPRESS_SEQUENCES_LONG)
        if ( !usePrefetchDecoder
          && (!frame || (dctx->fParams.windowSize > (1<<24)))
          && (nbSeq>ADVANCED_SEQS) ) {  /* could probably use a larger nbSeq limit */
            U32 const shareLongOffsets = ZSTD_getLongOffsetsShare(dctx->OFTptr);
            U32 const minShare = MEM_64bits() ? 7 : 20; /* heuristic values, correspond to 2.73% and 7.81% */
            usePrefetchDecoder = (shareLongOffsets >= minShare);
        }
#endif
 
        dctx->ddictIsCold = 0;
 
#if !defined(ZSTD_FORCE_DECOMPRESS_SEQUENCES_SHORT) && \
    !defined(ZSTD_FORCE_DECOMPRESS_SEQUENCES_LONG)
        if (usePrefetchDecoder)
#endif
#ifndef ZSTD_FORCE_DECOMPRESS_SEQUENCES_SHORT
            return ZSTD_decompressSequencesLong(dctx, dst, dstCapacity, ip, srcSize, nbSeq, isLongOffset, frame);
#endif
 
#ifndef ZSTD_FORCE_DECOMPRESS_SEQUENCES_LONG
        /* else */
        return ZSTD_decompressSequences(dctx, dst, dstCapacity, ip, srcSize, nbSeq, isLongOffset, frame);
#endif
    }
}

Referenced by ZSTD_decompressContinue(), and ZSTD_decompressFrame().