zstd/lib/decompress/zstd_decompress.c

/*
    zstd - standard compression library
    Copyright (C) 2014-2016, Yann Collet.

    BSD 2-Clause License (http://www.opensource.org/licenses/bsd-license.php)

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions are
    met:
    * Redistributions of source code must retain the above copyright
    notice, this list of conditions and the following disclaimer.
    * Redistributions in binary form must reproduce the above
    copyright notice, this list of conditions and the following disclaimer
    in the documentation and/or other materials provided with the
    distribution.
    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
    A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
    OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
    SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
    LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
    DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
    THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
    (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
    OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

    You can contact the author at :
    - zstd homepage : http://www.zstd.net
*/

/* ***************************************************************
*  Tuning parameters
*****************************************************************/
/*!
 * HEAPMODE :
 * Select how default decompression function ZSTD_decompress() will allocate memory,
 * in memory stack (0), or in memory heap (1, requires malloc())
 */
#ifndef ZSTD_HEAPMODE
#  define ZSTD_HEAPMODE 1
#endif

/*!
*  LEGACY_SUPPORT :
*  if set to 1, ZSTD_decompress() can decode older formats (v0.1+)
*/
#ifndef ZSTD_LEGACY_SUPPORT
#  define ZSTD_LEGACY_SUPPORT 0
#endif


/*-*******************************************************
*  Dependencies
*********************************************************/
#include <string.h>      /* memcpy, memmove, memset */
#include <stdio.h>       /* debug only : printf */
#include "mem.h"         /* low level memory routines */
#define XXH_STATIC_LINKING_ONLY   /* XXH64_state_t */
#include "xxhash.h"      /* XXH64_* */
#define FSE_STATIC_LINKING_ONLY
#include "fse.h"
#define HUF_STATIC_LINKING_ONLY
#include "huf.h"
#include "zstd_internal.h"

#if defined(ZSTD_LEGACY_SUPPORT) && (ZSTD_LEGACY_SUPPORT>=1)
#  include "zstd_legacy.h"
#endif


/*-*******************************************************
*  Compiler specifics
*********************************************************/
#ifdef _MSC_VER    /* Visual Studio */
#  define FORCE_INLINE static __forceinline
#  include <intrin.h>                    /* For Visual 2005 */
#  pragma warning(disable : 4127)        /* disable: C4127: conditional expression is constant */
#  pragma warning(disable : 4324)        /* disable: C4324: padded structure */
#else
#  ifdef __GNUC__
#    define FORCE_INLINE static inline __attribute__((always_inline))
#  else
#    define FORCE_INLINE static inline
#  endif
#endif


/*-*************************************
*  Macros
***************************************/
#define ZSTD_isError ERR_isError   /* for inlining */
#define FSE_isError  ERR_isError
#define HUF_isError  ERR_isError


/*_*******************************************************
*  Memory operations
**********************************************************/
static void ZSTD_copy4(void* dst, const void* src) { memcpy(dst, src, 4); }


/*-*************************************************************
*   Context management
***************************************************************/
typedef enum { ZSTDds_getFrameHeaderSize, ZSTDds_decodeFrameHeader,
               ZSTDds_decodeBlockHeader, ZSTDds_decompressBlock,
               ZSTDds_decompressLastBlock, ZSTDds_checkChecksum,
               ZSTDds_decodeSkippableHeader, ZSTDds_skipFrame } ZSTD_dStage;

struct ZSTD_DCtx_s
{
    FSE_DTable LLTable[FSE_DTABLE_SIZE_U32(LLFSELog)];
    FSE_DTable OffTable[FSE_DTABLE_SIZE_U32(OffFSELog)];
    FSE_DTable MLTable[FSE_DTABLE_SIZE_U32(MLFSELog)];
    HUF_DTable hufTable[HUF_DTABLE_SIZE(HufLog)];  /* can accommodate HUF_decompress4X */
    const void* previousDstEnd;
    const void* base;
    const void* vBase;
    const void* dictEnd;
    size_t expected;
    U32 rep[ZSTD_REP_NUM];
    ZSTD_frameParams fParams;
    blockType_e bType;   /* used in ZSTD_decompressContinue(), to transfer blockType between header decoding and block decoding stages */
    ZSTD_dStage stage;
    U32 litEntropy;
    U32 fseEntropy;
    XXH64_state_t xxhState;
    size_t headerSize;
    U32 dictID;
    const BYTE* litPtr;
    ZSTD_customMem customMem;
    size_t litBufSize;
    size_t litSize;
    size_t rleSize;
    BYTE litBuffer[ZSTD_BLOCKSIZE_ABSOLUTEMAX + WILDCOPY_OVERLENGTH];
    BYTE headerBuffer[ZSTD_FRAMEHEADERSIZE_MAX];
};  /* typedef'd to ZSTD_DCtx within "zstd_static.h" */

size_t ZSTD_sizeofDCtx (const ZSTD_DCtx* dctx) { return sizeof(*dctx); }

size_t ZSTD_estimateDCtxSize(void) { return sizeof(ZSTD_DCtx); }

size_t ZSTD_decompressBegin(ZSTD_DCtx* dctx)
{
    dctx->expected = ZSTD_frameHeaderSize_min;
    dctx->stage = ZSTDds_getFrameHeaderSize;
    dctx->previousDstEnd = NULL;
    dctx->base = NULL;
    dctx->vBase = NULL;
    dctx->dictEnd = NULL;
    dctx->hufTable[0] = (HUF_DTable)((HufLog)*0x1000001);
    dctx->litEntropy = dctx->fseEntropy = 0;
    dctx->dictID = 0;
    { int i; for (i=0; i<ZSTD_REP_NUM; i++) dctx->rep[i] = repStartValue[i]; }
    return 0;
}

ZSTD_DCtx* ZSTD_createDCtx_advanced(ZSTD_customMem customMem)
{
    ZSTD_DCtx* dctx;

    if (!customMem.customAlloc && !customMem.customFree)
        customMem = defaultCustomMem;

    if (!customMem.customAlloc || !customMem.customFree)
        return NULL;

    dctx = (ZSTD_DCtx*) customMem.customAlloc(customMem.opaque, sizeof(ZSTD_DCtx));
    if (!dctx) return NULL;
    memcpy(&dctx->customMem, &customMem, sizeof(ZSTD_customMem));
    ZSTD_decompressBegin(dctx);
    return dctx;
}

ZSTD_DCtx* ZSTD_createDCtx(void)
{
    return ZSTD_createDCtx_advanced(defaultCustomMem);
}

size_t ZSTD_freeDCtx(ZSTD_DCtx* dctx)
{
    if (dctx==NULL) return 0;   /* support free on NULL */
    dctx->customMem.customFree(dctx->customMem.opaque, dctx);
    return 0;   /* reserved as a potential error code in the future */
}

void ZSTD_copyDCtx(ZSTD_DCtx* dstDCtx, const ZSTD_DCtx* srcDCtx)
{
    memcpy(dstDCtx, srcDCtx,
           sizeof(ZSTD_DCtx) - (ZSTD_BLOCKSIZE_ABSOLUTEMAX+WILDCOPY_OVERLENGTH + ZSTD_frameHeaderSize_max));  /* no need to copy workspace */
}


/*-*************************************************************
*   Decompression section
***************************************************************/

/* See compression format details in : zstd_compression_format.md */

/** ZSTD_frameHeaderSize() :
*   srcSize must be >= ZSTD_frameHeaderSize_min.
*   @return : size of the Frame Header */
static size_t ZSTD_frameHeaderSize(const void* src, size_t srcSize)
{
    if (srcSize < ZSTD_frameHeaderSize_min) return ERROR(srcSize_wrong);
    {   BYTE const fhd = ((const BYTE*)src)[4];
        U32 const dictID= fhd & 3;
        U32 const singleSegment = (fhd >> 5) & 1;
        U32 const fcsId = fhd >> 6;
        return ZSTD_frameHeaderSize_min + !singleSegment + ZSTD_did_fieldSize[dictID] + ZSTD_fcs_fieldSize[fcsId]
                + (singleSegment && !ZSTD_fcs_fieldSize[fcsId]);
    }
}


/** ZSTD_getFrameParams() :
*   decode Frame Header, or require larger `srcSize`.
*   @return : 0, `fparamsPtr` is correctly filled,
*            >0, `srcSize` is too small, result is expected `srcSize`,
*             or an error code, which can be tested using ZSTD_isError() */
size_t ZSTD_getFrameParams(ZSTD_frameParams* fparamsPtr, const void* src, size_t srcSize)
{
    const BYTE* ip = (const BYTE*)src;

    if (srcSize < ZSTD_frameHeaderSize_min) return ZSTD_frameHeaderSize_min;
    if (MEM_readLE32(src) != ZSTD_MAGICNUMBER) {
        if ((MEM_readLE32(src) & 0xFFFFFFF0U) == ZSTD_MAGIC_SKIPPABLE_START) {
            if (srcSize < ZSTD_skippableHeaderSize) return ZSTD_skippableHeaderSize; /* magic number + skippable frame length */
            memset(fparamsPtr, 0, sizeof(*fparamsPtr));
            fparamsPtr->frameContentSize = MEM_readLE32((const char *)src + 4);
            fparamsPtr->windowSize = 0; /* windowSize==0 means a frame is skippable */
            return 0;
        }
        return ERROR(prefix_unknown);
    }

    /* ensure there is enough `srcSize` to fully read/decode frame header */
    { size_t const fhsize = ZSTD_frameHeaderSize(src, srcSize);
      if (srcSize < fhsize) return fhsize; }

    {   BYTE const fhdByte = ip[4];
        size_t pos = 5;
        U32 const dictIDSizeCode = fhdByte&3;
        U32 const checksumFlag = (fhdByte>>2)&1;
        U32 const singleSegment = (fhdByte>>5)&1;
        U32 const fcsID = fhdByte>>6;
        U32 const windowSizeMax = 1U << ZSTD_WINDOWLOG_MAX;
        U32 windowSize = 0;
        U32 dictID = 0;
        U64 frameContentSize = 0;
        if ((fhdByte & 0x08) != 0) return ERROR(frameParameter_unsupported);   /* reserved bits, which must be zero */
        if (!singleSegment) {
            BYTE const wlByte = ip[pos++];
            U32 const windowLog = (wlByte >> 3) + ZSTD_WINDOWLOG_ABSOLUTEMIN;
            if (windowLog > ZSTD_WINDOWLOG_MAX) return ERROR(frameParameter_unsupported);
            windowSize = (1U << windowLog);
            windowSize += (windowSize >> 3) * (wlByte&7);
        }

        switch(dictIDSizeCode)
        {
            default:   /* impossible */
            case 0 : break;
            case 1 : dictID = ip[pos]; pos++; break;
            case 2 : dictID = MEM_readLE16(ip+pos); pos+=2; break;
            case 3 : dictID = MEM_readLE32(ip+pos); pos+=4; break;
        }
        switch(fcsID)
        {
            default:   /* impossible */
            case 0 : if (singleSegment) frameContentSize = ip[pos]; break;
            case 1 : frameContentSize = MEM_readLE16(ip+pos)+256; break;
            case 2 : frameContentSize = MEM_readLE32(ip+pos); break;
            case 3 : frameContentSize = MEM_readLE64(ip+pos); break;
        }
        if (!windowSize) windowSize = (U32)frameContentSize;
        if (windowSize > windowSizeMax) return ERROR(frameParameter_unsupported);
        fparamsPtr->frameContentSize = frameContentSize;
        fparamsPtr->windowSize = windowSize;
        fparamsPtr->dictID = dictID;
        fparamsPtr->checksumFlag = checksumFlag;
    }
    return 0;
}


/** ZSTD_getDecompressedSize() :
*   compatible with legacy mode
*   @return : decompressed size if known, 0 otherwise
              note : 0 can mean any of the following :
                   - decompressed size is not present within frame header
                   - frame header unknown / not supported
                   - frame header not complete (`srcSize` too small) */
unsigned long long ZSTD_getDecompressedSize(const void* src, size_t srcSize)
{
#if defined(ZSTD_LEGACY_SUPPORT) && (ZSTD_LEGACY_SUPPORT==1)
    if (ZSTD_isLegacy(src, srcSize)) return ZSTD_getDecompressedSize_legacy(src, srcSize);
#endif
    {   ZSTD_frameParams fparams;
        size_t const frResult = ZSTD_getFrameParams(&fparams, src, srcSize);
        if (frResult!=0) return 0;
        return fparams.frameContentSize;
    }
}


/** ZSTD_decodeFrameHeader() :
*   `srcSize` must be the size provided by ZSTD_frameHeaderSize().
*   @return : 0 if success, or an error code, which can be tested using ZSTD_isError() */
static size_t ZSTD_decodeFrameHeader(ZSTD_DCtx* dctx, const void* src, size_t srcSize)
{
    size_t const result = ZSTD_getFrameParams(&(dctx->fParams), src, srcSize);
    if (dctx->fParams.dictID && (dctx->dictID != dctx->fParams.dictID)) return ERROR(dictionary_wrong);
    if (dctx->fParams.checksumFlag) XXH64_reset(&dctx->xxhState, 0);
    return result;
}


typedef struct
{
    blockType_e blockType;
    U32 lastBlock;
    U32 origSize;
} blockProperties_t;

/*! ZSTD_getcBlockSize() :
*   Provides the size of compressed block from block header `src` */
size_t ZSTD_getcBlockSize(const void* src, size_t srcSize, blockProperties_t* bpPtr)
{
    if (srcSize < ZSTD_blockHeaderSize) return ERROR(srcSize_wrong);
    {   U32 const cBlockHeader = MEM_readLE24(src);
        U32 const cSize = cBlockHeader >> 3;
        bpPtr->lastBlock = cBlockHeader & 1;
        bpPtr->blockType = (blockType_e)((cBlockHeader >> 1) & 3);
        bpPtr->origSize = cSize;   /* only useful for RLE */
        if (bpPtr->blockType == bt_rle) return 1;
        if (bpPtr->blockType == bt_reserved) return ERROR(corruption_detected);
        return cSize;
    }
}


static size_t ZSTD_copyRawBlock(void* dst, size_t dstCapacity, const void* src, size_t srcSize)
{
    if (srcSize > dstCapacity) return ERROR(dstSize_tooSmall);
    memcpy(dst, src, srcSize);
    return srcSize;
}


static size_t ZSTD_setRleBlock(void* dst, size_t dstCapacity, const void* src, size_t srcSize, size_t regenSize)
{
    if (srcSize != 1) return ERROR(srcSize_wrong);
    if (regenSize > dstCapacity) return ERROR(dstSize_tooSmall);
    memset(dst, *(const BYTE*)src, regenSize);
    return regenSize;
}

/*! ZSTD_decodeLiteralsBlock() :
    @return : nb of bytes read from src (< srcSize ) */
size_t ZSTD_decodeLiteralsBlock(ZSTD_DCtx* dctx,
                          const void* src, size_t srcSize)   /* note : srcSize < BLOCKSIZE */
{
    if (srcSize < MIN_CBLOCK_SIZE) return ERROR(corruption_detected);

    {   const BYTE* const istart = (const BYTE*) src;
        symbolEncodingType_e const litEncType = (symbolEncodingType_e)(istart[0] & 3);

        switch(litEncType)
        {
        case set_repeat:
            if (dctx->litEntropy==0) return ERROR(dictionary_corrupted);
            /* fall-through */
        case set_compressed:
            if (srcSize < 5) return ERROR(corruption_detected);   /* srcSize >= MIN_CBLOCK_SIZE == 3; here we need up to 5 for case 3 */
            {   size_t lhSize, litSize, litCSize;
                U32 singleStream=0;
                U32 const lhlCode = (istart[0] >> 2) & 3;
                U32 const lhc = MEM_readLE32(istart);
                switch(lhlCode)
                {
                case 0: case 1: default:   /* note : default is impossible, since lhlCode into [0..3] */
                    /* 2 - 2 - 10 - 10 */
                    {   singleStream = !lhlCode;
                        lhSize = 3;
                        litSize  = (lhc >> 4) & 0x3FF;
                        litCSize = (lhc >> 14) & 0x3FF;
                        break;
                    }
                case 2:
                    /* 2 - 2 - 14 - 14 */
                    {   lhSize = 4;
                        litSize  = (lhc >> 4) & 0x3FFF;
                        litCSize = lhc >> 18;
                        break;
                    }
                case 3:
                    /* 2 - 2 - 18 - 18 */
                    {   lhSize = 5;
                        litSize  = (lhc >> 4) & 0x3FFFF;
                        litCSize = (lhc >> 22) + (istart[4] << 10);
                        break;
                    }
                }
                if (litSize > ZSTD_BLOCKSIZE_ABSOLUTEMAX) return ERROR(corruption_detected);
                if (litCSize + lhSize > srcSize) return ERROR(corruption_detected);

                if (HUF_isError((litEncType==set_repeat) ?
                                    ( singleStream ?
                                        HUF_decompress1X_usingDTable(dctx->litBuffer, litSize, istart+lhSize, litCSize, dctx->hufTable) :
                                        HUF_decompress4X_usingDTable(dctx->litBuffer, litSize, istart+lhSize, litCSize, dctx->hufTable) ) :
                                    ( singleStream ?
                                        HUF_decompress1X2_DCtx(dctx->hufTable, dctx->litBuffer, litSize, istart+lhSize, litCSize) :
                                        HUF_decompress4X_hufOnly (dctx->hufTable, dctx->litBuffer, litSize, istart+lhSize, litCSize)) ))
                    return ERROR(corruption_detected);

                dctx->litPtr = dctx->litBuffer;
                dctx->litBufSize = ZSTD_BLOCKSIZE_ABSOLUTEMAX+WILDCOPY_OVERLENGTH;
                dctx->litSize = litSize;
                dctx->litEntropy = 1;
                return litCSize + lhSize;
            }

        case set_basic:
            {   size_t litSize, lhSize;
                U32 const lhlCode = ((istart[0]) >> 2) & 3;
                switch(lhlCode)
                {
                case 0: case 2: default:   /* note : default is impossible, since lhlCode into [0..3] */
                    lhSize = 1;
                    litSize = istart[0] >> 3;
                    break;
                case 1:
                    lhSize = 2;
                    litSize = MEM_readLE16(istart) >> 4;
                    break;
                case 3:
                    lhSize = 3;
                    litSize = MEM_readLE24(istart) >> 4;
                    break;
                }

                if (lhSize+litSize+WILDCOPY_OVERLENGTH > srcSize) {  /* risk reading beyond src buffer with wildcopy */
                    if (litSize+lhSize > srcSize) return ERROR(corruption_detected);
                    memcpy(dctx->litBuffer, istart+lhSize, litSize);
                    dctx->litPtr = dctx->litBuffer;
                    dctx->litBufSize = ZSTD_BLOCKSIZE_ABSOLUTEMAX+8;
                    dctx->litSize = litSize;
                    return lhSize+litSize;
                }
                /* direct reference into compressed stream */
                dctx->litPtr = istart+lhSize;
                dctx->litBufSize = srcSize-lhSize;
                dctx->litSize = litSize;
                return lhSize+litSize;
            }

        case set_rle:
            {   U32 const lhlCode = ((istart[0]) >> 2) & 3;
                size_t litSize, lhSize;
                switch(lhlCode)
                {
                case 0: case 2: default:   /* note : default is impossible, since lhlCode into [0..3] */
                    lhSize = 1;
                    litSize = istart[0] >> 3;
                    break;
                case 1:
                    lhSize = 2;
                    litSize = MEM_readLE16(istart) >> 4;
                    break;
                case 3:
                    lhSize = 3;
                    litSize = MEM_readLE24(istart) >> 4;
                    if (srcSize<4) return ERROR(corruption_detected);   /* srcSize >= MIN_CBLOCK_SIZE == 3; here we need lhSize+1 = 4 */
                    break;
                }
                if (litSize > ZSTD_BLOCKSIZE_ABSOLUTEMAX) return ERROR(corruption_detected);
                memset(dctx->litBuffer, istart[lhSize], litSize);
                dctx->litPtr = dctx->litBuffer;
                dctx->litBufSize = ZSTD_BLOCKSIZE_ABSOLUTEMAX+WILDCOPY_OVERLENGTH;
                dctx->litSize = litSize;
                return lhSize+1;
            }
        default:
            return ERROR(corruption_detected);   /* impossible */
        }

    }
}


/*! ZSTD_buildSeqTable() :
    @return : nb bytes read from src,
              or an error code if it fails, testable with ZSTD_isError()
*/
FORCE_INLINE size_t ZSTD_buildSeqTable(FSE_DTable* DTable, symbolEncodingType_e type, U32 max, U32 maxLog,
                                 const void* src, size_t srcSize,
                                 const S16* defaultNorm, U32 defaultLog, U32 flagRepeatTable)
{
    switch(type)
    {
    case set_rle :
        if (!srcSize) return ERROR(srcSize_wrong);
        if ( (*(const BYTE*)src) > max) return ERROR(corruption_detected);
        FSE_buildDTable_rle(DTable, *(const BYTE*)src);   /* if *src > max, data is corrupted */
        return 1;
    case set_basic :
        FSE_buildDTable(DTable, defaultNorm, max, defaultLog);
        return 0;
    case set_repeat:
        if (!flagRepeatTable) return ERROR(corruption_detected);
        return 0;
    default :   /* impossible */
    case set_compressed :
        {   U32 tableLog;
            S16 norm[MaxSeq+1];
            size_t const headerSize = FSE_readNCount(norm, &max, &tableLog, src, srcSize);
            if (FSE_isError(headerSize)) return ERROR(corruption_detected);
            if (tableLog > maxLog) return ERROR(corruption_detected);
            FSE_buildDTable(DTable, norm, max, tableLog);
            return headerSize;
    }   }
}


size_t ZSTD_decodeSeqHeaders(int* nbSeqPtr,
                             FSE_DTable* DTableLL, FSE_DTable* DTableML, FSE_DTable* DTableOffb, U32 flagRepeatTable,
                             const void* src, size_t srcSize)
{
    const BYTE* const istart = (const BYTE* const)src;
    const BYTE* const iend = istart + srcSize;
    const BYTE* ip = istart;

    /* check */
    if (srcSize < MIN_SEQUENCES_SIZE) return ERROR(srcSize_wrong);

    /* SeqHead */
    {   int nbSeq = *ip++;
        if (!nbSeq) { *nbSeqPtr=0; return 1; }
        if (nbSeq > 0x7F) {
            if (nbSeq == 0xFF)
                nbSeq = MEM_readLE16(ip) + LONGNBSEQ, ip+=2;
            else
                nbSeq = ((nbSeq-0x80)<<8) + *ip++;
        }
        *nbSeqPtr = nbSeq;
    }

    /* FSE table descriptors */
    if (ip+4 > iend) return ERROR(srcSize_wrong); /* minimum possible size */
    {   symbolEncodingType_e const LLtype = (symbolEncodingType_e)(*ip >> 6);
        symbolEncodingType_e const OFtype = (symbolEncodingType_e)((*ip >> 4) & 3);
        symbolEncodingType_e const MLtype = (symbolEncodingType_e)((*ip >> 2) & 3);
        ip++;

        /* Build DTables */
        {   size_t const llhSize = ZSTD_buildSeqTable(DTableLL, LLtype, MaxLL, LLFSELog, ip, iend-ip, LL_defaultNorm, LL_defaultNormLog, flagRepeatTable);
            if (ZSTD_isError(llhSize)) return ERROR(corruption_detected);
            ip += llhSize;
        }
        {   size_t const ofhSize = ZSTD_buildSeqTable(DTableOffb, OFtype, MaxOff, OffFSELog, ip, iend-ip, OF_defaultNorm, OF_defaultNormLog, flagRepeatTable);
            if (ZSTD_isError(ofhSize)) return ERROR(corruption_detected);
            ip += ofhSize;
        }
        {   size_t const mlhSize = ZSTD_buildSeqTable(DTableML, MLtype, MaxML, MLFSELog, ip, iend-ip, ML_defaultNorm, ML_defaultNormLog, flagRepeatTable);
            if (ZSTD_isError(mlhSize)) return ERROR(corruption_detected);
            ip += mlhSize;
    }   }

    return ip-istart;
}


typedef struct {
    size_t litLength;
    size_t matchLength;
    size_t offset;
} seq_t;

typedef struct {
    BIT_DStream_t DStream;
    FSE_DState_t stateLL;
    FSE_DState_t stateOffb;
    FSE_DState_t stateML;
    U32 prevOffset[ZSTD_REP_NUM];
} seqState_t;


static seq_t ZSTD_decodeSequence(seqState_t* seqState)
{
    seq_t seq;

    U32 const llCode = FSE_peekSymbol(&(seqState->stateLL));
    U32 const mlCode = FSE_peekSymbol(&(seqState->stateML));
    U32 const ofCode = FSE_peekSymbol(&(seqState->stateOffb));   /* <= maxOff, by table construction */

    U32 const llBits = LL_bits[llCode];
    U32 const mlBits = ML_bits[mlCode];
    U32 const ofBits = ofCode;
    U32 const totalBits = llBits+mlBits+ofBits;

    static const U32 LL_base[MaxLL+1] = {
                             0,  1,  2,  3,  4,  5,  6,  7,  8,  9,   10,    11,    12,    13,    14,     15,
                            16, 18, 20, 22, 24, 28, 32, 40, 48, 64, 0x80, 0x100, 0x200, 0x400, 0x800, 0x1000,
                            0x2000, 0x4000, 0x8000, 0x10000 };

    static const U32 ML_base[MaxML+1] = {
                             3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13,   14,    15,    16,    17,    18,
                            19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29,   30,    31,    32,    33,    34,
                            35, 37, 39, 41, 43, 47, 51, 59, 67, 83, 99, 0x83, 0x103, 0x203, 0x403, 0x803,
                            0x1003, 0x2003, 0x4003, 0x8003, 0x10003 };

    static const U32 OF_base[MaxOff+1] = {
                 0,        1,       1,       5,     0xD,     0x1D,     0x3D,     0x7D,
                 0xFD,   0x1FD,   0x3FD,   0x7FD,   0xFFD,   0x1FFD,   0x3FFD,   0x7FFD,
                 0xFFFD, 0x1FFFD, 0x3FFFD, 0x7FFFD, 0xFFFFD, 0x1FFFFD, 0x3FFFFD, 0x7FFFFD,
                 0xFFFFFD, 0x1FFFFFD, 0x3FFFFFD, 0x7FFFFFD, 0xFFFFFFD };

    /* sequence */
    {   size_t offset;
        if (!ofCode)
            offset = 0;
        else {
            offset = OF_base[ofCode] + BIT_readBits(&(seqState->DStream), ofBits);   /* <=  (ZSTD_WINDOWLOG_MAX-1) bits */
            if (MEM_32bits()) BIT_reloadDStream(&(seqState->DStream));
        }

        if (ofCode <= 1) {
            if ((llCode == 0) & (offset <= 1)) offset = 1-offset;
            if (offset) {
                U32 const temp = seqState->prevOffset[offset];
                if (offset != 1) seqState->prevOffset[2] = seqState->prevOffset[1];
                seqState->prevOffset[1] = seqState->prevOffset[0];
                seqState->prevOffset[0] = offset = temp;
            } else {
                offset = seqState->prevOffset[0];
            }
        } else {
            seqState->prevOffset[2] = seqState->prevOffset[1];
            seqState->prevOffset[1] = seqState->prevOffset[0];
            seqState->prevOffset[0] = (U32)offset;
        }
        seq.offset = offset;
    }

    seq.matchLength = ML_base[mlCode] + ((mlCode>31) ? BIT_readBits(&(seqState->DStream), mlBits) : 0);   /* <=  16 bits */
    if (MEM_32bits() && (mlBits+llBits>24)) BIT_reloadDStream(&(seqState->DStream));

    seq.litLength = LL_base[llCode] + ((llCode>15) ? BIT_readBits(&(seqState->DStream), llBits) : 0);   /* <=  16 bits */
    if (MEM_32bits() ||
       (totalBits > 64 - 7 - (LLFSELog+MLFSELog+OffFSELog)) ) BIT_reloadDStream(&(seqState->DStream));

    /* ANS state update */
    FSE_updateState(&(seqState->stateLL), &(seqState->DStream));   /* <=  9 bits */
    FSE_updateState(&(seqState->stateML), &(seqState->DStream));   /* <=  9 bits */
    if (MEM_32bits()) BIT_reloadDStream(&(seqState->DStream));     /* <= 18 bits */
    FSE_updateState(&(seqState->stateOffb), &(seqState->DStream)); /* <=  8 bits */

    return seq;
}


FORCE_INLINE
size_t ZSTD_execSequence(BYTE* op,
                                BYTE* const oend, seq_t sequence,
                                const BYTE** litPtr, const BYTE* const litLimit_w,
                                const BYTE* const base, const BYTE* const vBase, const BYTE* const dictEnd)
{
    BYTE* const oLitEnd = op + sequence.litLength;
    size_t const sequenceLength = sequence.litLength + sequence.matchLength;
    BYTE* const oMatchEnd = op + sequenceLength;   /* risk : address space overflow (32-bits) */
    BYTE* const oend_w = oend - WILDCOPY_OVERLENGTH;
    const BYTE* const iLitEnd = *litPtr + sequence.litLength;
    const BYTE* match = oLitEnd - sequence.offset;

    /* check */
    if ((oLitEnd>oend_w) | (oMatchEnd>oend)) return ERROR(dstSize_tooSmall); /* last match must start at a minimum distance of WILDCOPY_OVERLENGTH from oend */
    if (iLitEnd > litLimit_w) return ERROR(corruption_detected);   /* over-read beyond lit buffer */

    /* copy Literals */
    ZSTD_wildcopy(op, *litPtr, sequence.litLength);   /* note : since oLitEnd <= oend-WILDCOPY_OVERLENGTH, no risk of overwrite beyond oend */
    op = oLitEnd;
    *litPtr = iLitEnd;   /* update for next sequence */

    /* copy Match */
    if (sequence.offset > (size_t)(oLitEnd - base)) {
        /* offset beyond prefix */
        if (sequence.offset > (size_t)(oLitEnd - vBase)) return ERROR(corruption_detected);
        match = dictEnd - (base-match);
        if (match + sequence.matchLength <= dictEnd) {
            memmove(oLitEnd, match, sequence.matchLength);
            return sequenceLength;
        }
        /* span extDict & currentPrefixSegment */
        {   size_t const length1 = dictEnd - match;
            memmove(oLitEnd, match, length1);
            op = oLitEnd + length1;
            sequence.matchLength -= length1;
            match = base;
    }   }

    /* match within prefix */
    if (sequence.offset < 8) {
        /* close range match, overlap */
        static const U32 dec32table[] = { 0, 1, 2, 1, 4, 4, 4, 4 };   /* added */
        static const int dec64table[] = { 8, 8, 8, 7, 8, 9,10,11 };   /* substracted */
        int const sub2 = dec64table[sequence.offset];
        op[0] = match[0];
        op[1] = match[1];
        op[2] = match[2];
        op[3] = match[3];
        match += dec32table[sequence.offset];
        ZSTD_copy4(op+4, match);
        match -= sub2;
    } else {
        ZSTD_copy8(op, match);
    }
    op += 8; match += 8;

    if (oMatchEnd > oend-(16-MINMATCH)) {
        if (op < oend_w) {
            ZSTD_wildcopy(op, match, oend_w - op);
            match += oend_w - op;
            op = oend_w;
        }
        while (op < oMatchEnd) *op++ = *match++;
    } else {
        ZSTD_wildcopy(op, match, sequence.matchLength-8);   /* works even if matchLength < 8 */
    }
    return sequenceLength;
}


static size_t ZSTD_decompressSequences(
                               ZSTD_DCtx* dctx,
                               void* dst, size_t maxDstSize,
                         const void* seqStart, size_t seqSize)
{
    const BYTE* ip = (const BYTE*)seqStart;
    const BYTE* const iend = ip + seqSize;
    BYTE* const ostart = (BYTE* const)dst;
    BYTE* const oend = ostart + maxDstSize;
    BYTE* op = ostart;
    const BYTE* litPtr = dctx->litPtr;
    const BYTE* const litLimit_w = litPtr + dctx->litBufSize - WILDCOPY_OVERLENGTH;
    const BYTE* const litEnd = litPtr + dctx->litSize;
    FSE_DTable* DTableLL = dctx->LLTable;
    FSE_DTable* DTableML = dctx->MLTable;
    FSE_DTable* DTableOffb = dctx->OffTable;
    const BYTE* const base = (const BYTE*) (dctx->base);
    const BYTE* const vBase = (const BYTE*) (dctx->vBase);
    const BYTE* const dictEnd = (const BYTE*) (dctx->dictEnd);
    int nbSeq;

    /* Build Decoding Tables */
    {   size_t const seqHSize = ZSTD_decodeSeqHeaders(&nbSeq, DTableLL, DTableML, DTableOffb, dctx->fseEntropy, ip, seqSize);
        if (ZSTD_isError(seqHSize)) return seqHSize;
        ip += seqHSize;
    }

    /* Regen sequences */
    if (nbSeq) {
        seqState_t seqState;
        dctx->fseEntropy = 1;
        { U32 i; for (i=0; i<ZSTD_REP_NUM; i++) seqState.prevOffset[i] = dctx->rep[i]; }
        { size_t const errorCode = BIT_initDStream(&(seqState.DStream), ip, iend-ip);
          if (ERR_isError(errorCode)) return ERROR(corruption_detected); }
        FSE_initDState(&(seqState.stateLL), &(seqState.DStream), DTableLL);
        FSE_initDState(&(seqState.stateOffb), &(seqState.DStream), DTableOffb);
        FSE_initDState(&(seqState.stateML), &(seqState.DStream), DTableML);

        for ( ; (BIT_reloadDStream(&(seqState.DStream)) <= BIT_DStream_completed) && nbSeq ; ) {
            nbSeq--;
            {   seq_t const sequence = ZSTD_decodeSequence(&seqState);
                size_t const oneSeqSize = ZSTD_execSequence(op, oend, sequence, &litPtr, litLimit_w, base, vBase, dictEnd);
                if (ZSTD_isError(oneSeqSize)) return oneSeqSize;
                op += oneSeqSize;
        }   }

        /* check if reached exact end */
        if (nbSeq) return ERROR(corruption_detected);
        /* save reps for next block */
        { U32 i; for (i=0; i<ZSTD_REP_NUM; i++) dctx->rep[i] = (U32)(seqState.prevOffset[i]); }
    }

    /* last literal segment */
    {   size_t const lastLLSize = litEnd - litPtr;
        if (lastLLSize > (size_t)(oend-op)) return ERROR(dstSize_tooSmall);
        memcpy(op, litPtr, lastLLSize);
        op += lastLLSize;
    }

    return op-ostart;
}


static void ZSTD_checkContinuity(ZSTD_DCtx* dctx, const void* dst)
{
    if (dst != dctx->previousDstEnd) {   /* not contiguous */
        dctx->dictEnd = dctx->previousDstEnd;
        dctx->vBase = (const char*)dst - ((const char*)(dctx->previousDstEnd) - (const char*)(dctx->base));
        dctx->base = dst;
        dctx->previousDstEnd = dst;
    }
}


static size_t ZSTD_decompressBlock_internal(ZSTD_DCtx* dctx,
                            void* dst, size_t dstCapacity,
                      const void* src, size_t srcSize)
{   /* blockType == blockCompressed */
    const BYTE* ip = (const BYTE*)src;

    if (srcSize >= ZSTD_BLOCKSIZE_ABSOLUTEMAX) return ERROR(srcSize_wrong);

    /* Decode literals sub-block */
    {   size_t const litCSize = ZSTD_decodeLiteralsBlock(dctx, src, srcSize);
        if (ZSTD_isError(litCSize)) return litCSize;
        ip += litCSize;
        srcSize -= litCSize;
    }
    return ZSTD_decompressSequences(dctx, dst, dstCapacity, ip, srcSize);
}


size_t ZSTD_decompressBlock(ZSTD_DCtx* dctx,
                            void* dst, size_t dstCapacity,
                      const void* src, size_t srcSize)
{
    size_t dSize;
    ZSTD_checkContinuity(dctx, dst);
    dSize = ZSTD_decompressBlock_internal(dctx, dst, dstCapacity, src, srcSize);
    dctx->previousDstEnd = (char*)dst + dSize;
    return dSize;
}


/** ZSTD_insertBlock() :
    insert `src` block into `dctx` history. Useful to track uncompressed blocks. */
ZSTDLIB_API size_t ZSTD_insertBlock(ZSTD_DCtx* dctx, const void* blockStart, size_t blockSize)
{
    ZSTD_checkContinuity(dctx, blockStart);
    dctx->previousDstEnd = (const char*)blockStart + blockSize;
    return blockSize;
}


size_t ZSTD_generateNxBytes(void* dst, size_t dstCapacity, BYTE byte, size_t length)
{
    if (length > dstCapacity) return ERROR(dstSize_tooSmall);
    memset(dst, byte, length);
    return length;
}


/*! ZSTD_decompressFrame() :
*   `dctx` must be properly initialized */
static size_t ZSTD_decompressFrame(ZSTD_DCtx* dctx,
                                 void* dst, size_t dstCapacity,
                                 const void* src, size_t srcSize)
{
    const BYTE* ip = (const BYTE*)src;
    BYTE* const ostart = (BYTE* const)dst;
    BYTE* const oend = ostart + dstCapacity;
    BYTE* op = ostart;
    size_t remainingSize = srcSize;

    /* check */
    if (srcSize < ZSTD_frameHeaderSize_min+ZSTD_blockHeaderSize) return ERROR(srcSize_wrong);

    /* Frame Header */
    {   size_t const frameHeaderSize = ZSTD_frameHeaderSize(src, ZSTD_frameHeaderSize_min);
        size_t result;
        if (ZSTD_isError(frameHeaderSize)) return frameHeaderSize;
        if (srcSize < frameHeaderSize+ZSTD_blockHeaderSize) return ERROR(srcSize_wrong);
        result = ZSTD_decodeFrameHeader(dctx, src, frameHeaderSize);
        if (ZSTD_isError(result)) return result;
        ip += frameHeaderSize; remainingSize -= frameHeaderSize;
    }

    /* Loop on each block */
    while (1) {
        size_t decodedSize;
        blockProperties_t blockProperties;
        size_t const cBlockSize = ZSTD_getcBlockSize(ip, remainingSize, &blockProperties);
        if (ZSTD_isError(cBlockSize)) return cBlockSize;

        ip += ZSTD_blockHeaderSize;
        remainingSize -= ZSTD_blockHeaderSize;
        if (cBlockSize > remainingSize) return ERROR(srcSize_wrong);

        switch(blockProperties.blockType)
        {
        case bt_compressed:
            decodedSize = ZSTD_decompressBlock_internal(dctx, op, oend-op, ip, cBlockSize);
            break;
        case bt_raw :
            decodedSize = ZSTD_copyRawBlock(op, oend-op, ip, cBlockSize);
            break;
        case bt_rle :
            decodedSize = ZSTD_generateNxBytes(op, oend-op, *ip, blockProperties.origSize);
            break;
        case bt_reserved :
        default:
            return ERROR(corruption_detected);
        }

        if (ZSTD_isError(decodedSize)) return decodedSize;
        if (dctx->fParams.checksumFlag) XXH64_update(&dctx->xxhState, op, decodedSize);
        op += decodedSize;
        ip += cBlockSize;
        remainingSize -= cBlockSize;
        if (blockProperties.lastBlock) break;
    }

    if (dctx->fParams.checksumFlag) {   /* Frame content checksum verification */
        U32 const checkCalc = (U32)XXH64_digest(&dctx->xxhState);
        U32 checkRead;
        if (remainingSize<4) return ERROR(checksum_wrong);
        checkRead = MEM_readLE32(ip);
        if (checkRead != checkCalc) return ERROR(checksum_wrong);
        remainingSize -= 4;
    }

    if (remainingSize) return ERROR(srcSize_wrong);
    return op-ostart;
}


/*! ZSTD_decompress_usingPreparedDCtx() :
*   Same as ZSTD_decompress_usingDict, but using a reference context `preparedDCtx`, where dictionary has been loaded.
*   It avoids reloading the dictionary each time.
*   `preparedDCtx` must have been properly initialized using ZSTD_decompressBegin_usingDict().
*   Requires 2 contexts : 1 for reference (preparedDCtx), which will not be modified, and 1 to run the decompression operation (dctx) */
size_t ZSTD_decompress_usingPreparedDCtx(ZSTD_DCtx* dctx, const ZSTD_DCtx* refDCtx,
                                         void* dst, size_t dstCapacity,
                                   const void* src, size_t srcSize)
{
    ZSTD_copyDCtx(dctx, refDCtx);
    ZSTD_checkContinuity(dctx, dst);
    return ZSTD_decompressFrame(dctx, dst, dstCapacity, src, srcSize);
}


size_t ZSTD_decompress_usingDict(ZSTD_DCtx* dctx,
                                 void* dst, size_t dstCapacity,
                                 const void* src, size_t srcSize,
                                 const void* dict, size_t dictSize)
{
#if defined(ZSTD_LEGACY_SUPPORT) && (ZSTD_LEGACY_SUPPORT==1)
    if (ZSTD_isLegacy(src, srcSize)) return ZSTD_decompressLegacy(dst, dstCapacity, src, srcSize, dict, dictSize);
#endif
    ZSTD_decompressBegin_usingDict(dctx, dict, dictSize);
    ZSTD_checkContinuity(dctx, dst);
    return ZSTD_decompressFrame(dctx, dst, dstCapacity, src, srcSize);
}


size_t ZSTD_decompressDCtx(ZSTD_DCtx* dctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize)
{
    return ZSTD_decompress_usingDict(dctx, dst, dstCapacity, src, srcSize, NULL, 0);
}


size_t ZSTD_decompress(void* dst, size_t dstCapacity, const void* src, size_t srcSize)
{
#if defined(ZSTD_HEAPMODE) && (ZSTD_HEAPMODE==1)
    size_t regenSize;
    ZSTD_DCtx* const dctx = ZSTD_createDCtx();
    if (dctx==NULL) return ERROR(memory_allocation);
    regenSize = ZSTD_decompressDCtx(dctx, dst, dstCapacity, src, srcSize);
    ZSTD_freeDCtx(dctx);
    return regenSize;
#else   /* stack mode */
    ZSTD_DCtx dctx;
    return ZSTD_decompressDCtx(&dctx, dst, dstCapacity, src, srcSize);
#endif
}


/*-**********************************
*   Streaming Decompression API
************************************/
size_t ZSTD_nextSrcSizeToDecompress(ZSTD_DCtx* dctx) { return dctx->expected; }

ZSTD_nextInputType_e ZSTD_nextInputType(ZSTD_DCtx* dctx) {
    switch(dctx->stage)
    {
    default:   /* should not happen */
    case ZSTDds_getFrameHeaderSize:
    case ZSTDds_decodeFrameHeader:
        return ZSTDnit_frameHeader;
    case ZSTDds_decodeBlockHeader:
        return ZSTDnit_blockHeader;
    case ZSTDds_decompressBlock:
        return ZSTDnit_block;
    case ZSTDds_decompressLastBlock:
        return ZSTDnit_lastBlock;
    case ZSTDds_checkChecksum:
        return ZSTDnit_checksum;
    case ZSTDds_decodeSkippableHeader:
    case ZSTDds_skipFrame:
        return ZSTDnit_skippableFrame;
    }
}

int ZSTD_isSkipFrame(ZSTD_DCtx* dctx) { return dctx->stage == ZSTDds_skipFrame; }   /* for zbuff */

/** ZSTD_decompressContinue() :
*   @return : nb of bytes generated into `dst` (necessarily <= `dstCapacity)
*             or an error code, which can be tested using ZSTD_isError() */
size_t ZSTD_decompressContinue(ZSTD_DCtx* dctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize)
{
    /* Sanity check */
    if (srcSize != dctx->expected) return ERROR(srcSize_wrong);
    if (dstCapacity) ZSTD_checkContinuity(dctx, dst);

    switch (dctx->stage)
    {
    case ZSTDds_getFrameHeaderSize :
        if (srcSize != ZSTD_frameHeaderSize_min) return ERROR(srcSize_wrong);   /* impossible */
        if ((MEM_readLE32(src) & 0xFFFFFFF0U) == ZSTD_MAGIC_SKIPPABLE_START) {
            memcpy(dctx->headerBuffer, src, ZSTD_frameHeaderSize_min);
            dctx->expected = ZSTD_skippableHeaderSize - ZSTD_frameHeaderSize_min; /* magic number + skippable frame length */
            dctx->stage = ZSTDds_decodeSkippableHeader;
            return 0;
        }
        dctx->headerSize = ZSTD_frameHeaderSize(src, ZSTD_frameHeaderSize_min);
        if (ZSTD_isError(dctx->headerSize)) return dctx->headerSize;
        memcpy(dctx->headerBuffer, src, ZSTD_frameHeaderSize_min);
        if (dctx->headerSize > ZSTD_frameHeaderSize_min) {
            dctx->expected = dctx->headerSize - ZSTD_frameHeaderSize_min;
            dctx->stage = ZSTDds_decodeFrameHeader;
            return 0;
        }
        dctx->expected = 0;   /* not necessary to copy more */

    case ZSTDds_decodeFrameHeader:
        {   size_t result;
            memcpy(dctx->headerBuffer + ZSTD_frameHeaderSize_min, src, dctx->expected);
            result = ZSTD_decodeFrameHeader(dctx, dctx->headerBuffer, dctx->headerSize);
            if (ZSTD_isError(result)) return result;
            dctx->expected = ZSTD_blockHeaderSize;
            dctx->stage = ZSTDds_decodeBlockHeader;
            return 0;
        }
    case ZSTDds_decodeBlockHeader:
        {   blockProperties_t bp;
            size_t const cBlockSize = ZSTD_getcBlockSize(src, ZSTD_blockHeaderSize, &bp);
            if (ZSTD_isError(cBlockSize)) return cBlockSize;
            dctx->expected = cBlockSize;
            dctx->bType = bp.blockType;
            dctx->rleSize = bp.origSize;
            if (cBlockSize) {
                dctx->stage = bp.lastBlock ? ZSTDds_decompressLastBlock : ZSTDds_decompressBlock;
                return 0;
            }
            /* empty block */
            if (bp.lastBlock) {
                if (dctx->fParams.checksumFlag) {
                    dctx->expected = 4;
                    dctx->stage = ZSTDds_checkChecksum;
                } else {
                    dctx->expected = 0; /* end of frame */
                    dctx->stage = ZSTDds_getFrameHeaderSize;
                }
            } else {
                dctx->expected = 3;  /* go directly to next header */
                dctx->stage = ZSTDds_decodeBlockHeader;
            }
            return 0;
        }
    case ZSTDds_decompressLastBlock:
    case ZSTDds_decompressBlock:
        {   size_t rSize;
            switch(dctx->bType)
            {
            case bt_compressed:
                rSize = ZSTD_decompressBlock_internal(dctx, dst, dstCapacity, src, srcSize);
                break;
            case bt_raw :
                rSize = ZSTD_copyRawBlock(dst, dstCapacity, src, srcSize);
                break;
            case bt_rle :
                rSize = ZSTD_setRleBlock(dst, dstCapacity, src, srcSize, dctx->rleSize);
                break;
            case bt_reserved :   /* should never happen */
            default:
                return ERROR(corruption_detected);
            }
            if (ZSTD_isError(rSize)) return rSize;
            if (dctx->fParams.checksumFlag) XXH64_update(&dctx->xxhState, dst, rSize);

            if (dctx->stage == ZSTDds_decompressLastBlock) {   /* end of frame */
                if (dctx->fParams.checksumFlag) {  /* another round for frame checksum */
                    dctx->expected = 4;
                    dctx->stage = ZSTDds_checkChecksum;
                } else {
                    dctx->expected = 0;   /* ends here */
                    dctx->stage = ZSTDds_getFrameHeaderSize;
                }
            } else {
                dctx->stage = ZSTDds_decodeBlockHeader;
                dctx->expected = ZSTD_blockHeaderSize;
                dctx->previousDstEnd = (char*)dst + rSize;
            }
            return rSize;
        }
    case ZSTDds_checkChecksum:
        {   U32 const h32 = (U32)XXH64_digest(&dctx->xxhState);
            U32 const check32 = MEM_readLE32(src);   /* srcSize == 4, guaranteed by dctx->expected */
            if (check32 != h32) return ERROR(checksum_wrong);
            dctx->expected = 0;
            dctx->stage = ZSTDds_getFrameHeaderSize;
            return 0;
        }
    case ZSTDds_decodeSkippableHeader:
        {   memcpy(dctx->headerBuffer + ZSTD_frameHeaderSize_min, src, dctx->expected);
            dctx->expected = MEM_readLE32(dctx->headerBuffer + 4);
            dctx->stage = ZSTDds_skipFrame;
            return 0;
        }
    case ZSTDds_skipFrame:
        {   dctx->expected = 0;
            dctx->stage = ZSTDds_getFrameHeaderSize;
            return 0;
        }
    default:
        return ERROR(GENERIC);   /* impossible */
    }
}


static size_t ZSTD_refDictContent(ZSTD_DCtx* dctx, const void* dict, size_t dictSize)
{
    dctx->dictEnd = dctx->previousDstEnd;
    dctx->vBase = (const char*)dict - ((const char*)(dctx->previousDstEnd) - (const char*)(dctx->base));
    dctx->base = dict;
    dctx->previousDstEnd = (const char*)dict + dictSize;
    return 0;
}

static size_t ZSTD_loadEntropy(ZSTD_DCtx* dctx, const void* const dict, size_t const dictSize)
{
    const BYTE* dictPtr = (const BYTE*)dict;
    const BYTE* const dictEnd = dictPtr + dictSize;

    {   size_t const hSize = HUF_readDTableX4(dctx->hufTable, dict, dictSize);
        if (HUF_isError(hSize)) return ERROR(dictionary_corrupted);
        dictPtr += hSize;
    }

    {   short offcodeNCount[MaxOff+1];
        U32 offcodeMaxValue=MaxOff, offcodeLog=OffFSELog;
        size_t const offcodeHeaderSize = FSE_readNCount(offcodeNCount, &offcodeMaxValue, &offcodeLog, dictPtr, dictEnd-dictPtr);
        if (FSE_isError(offcodeHeaderSize)) return ERROR(dictionary_corrupted);
        { size_t const errorCode = FSE_buildDTable(dctx->OffTable, offcodeNCount, offcodeMaxValue, offcodeLog);
          if (FSE_isError(errorCode)) return ERROR(dictionary_corrupted); }
        dictPtr += offcodeHeaderSize;
    }

    {   short matchlengthNCount[MaxML+1];
        unsigned matchlengthMaxValue = MaxML, matchlengthLog = MLFSELog;
        size_t const matchlengthHeaderSize = FSE_readNCount(matchlengthNCount, &matchlengthMaxValue, &matchlengthLog, dictPtr, dictEnd-dictPtr);
        if (FSE_isError(matchlengthHeaderSize)) return ERROR(dictionary_corrupted);
        { size_t const errorCode = FSE_buildDTable(dctx->MLTable, matchlengthNCount, matchlengthMaxValue, matchlengthLog);
          if (FSE_isError(errorCode)) return ERROR(dictionary_corrupted); }
        dictPtr += matchlengthHeaderSize;
    }

    {   short litlengthNCount[MaxLL+1];
        unsigned litlengthMaxValue = MaxLL, litlengthLog = LLFSELog;
        size_t const litlengthHeaderSize = FSE_readNCount(litlengthNCount, &litlengthMaxValue, &litlengthLog, dictPtr, dictEnd-dictPtr);
        if (FSE_isError(litlengthHeaderSize)) return ERROR(dictionary_corrupted);
        { size_t const errorCode = FSE_buildDTable(dctx->LLTable, litlengthNCount, litlengthMaxValue, litlengthLog);
          if (FSE_isError(errorCode)) return ERROR(dictionary_corrupted); }
        dictPtr += litlengthHeaderSize;
    }

    if (dictPtr+12 > dictEnd) return ERROR(dictionary_corrupted);
    dctx->rep[0] = MEM_readLE32(dictPtr+0); if (dctx->rep[0] >= dictSize) return ERROR(dictionary_corrupted);
    dctx->rep[1] = MEM_readLE32(dictPtr+4); if (dctx->rep[1] >= dictSize) return ERROR(dictionary_corrupted);
    dctx->rep[2] = MEM_readLE32(dictPtr+8); if (dctx->rep[2] >= dictSize) return ERROR(dictionary_corrupted);
    dictPtr += 12;

    dctx->litEntropy = dctx->fseEntropy = 1;
    return dictPtr - (const BYTE*)dict;
}

static size_t ZSTD_decompress_insertDictionary(ZSTD_DCtx* dctx, const void* dict, size_t dictSize)
{
    if (dictSize < 8) return ZSTD_refDictContent(dctx, dict, dictSize);
    {   U32 const magic = MEM_readLE32(dict);
        if (magic != ZSTD_DICT_MAGIC) {
            return ZSTD_refDictContent(dctx, dict, dictSize);   /* pure content mode */
    }   }
    dctx->dictID = MEM_readLE32((const char*)dict + 4);

    /* load entropy tables */
    dict = (const char*)dict + 8;
    dictSize -= 8;
    {   size_t const eSize = ZSTD_loadEntropy(dctx, dict, dictSize);
        if (ZSTD_isError(eSize)) return ERROR(dictionary_corrupted);
        dict = (const char*)dict + eSize;
        dictSize -= eSize;
    }

    /* reference dictionary content */
    return ZSTD_refDictContent(dctx, dict, dictSize);
}


size_t ZSTD_decompressBegin_usingDict(ZSTD_DCtx* dctx, const void* dict, size_t dictSize)
{
    { size_t const errorCode = ZSTD_decompressBegin(dctx);
      if (ZSTD_isError(errorCode)) return errorCode; }

    if (dict && dictSize) {
        size_t const errorCode = ZSTD_decompress_insertDictionary(dctx, dict, dictSize);
        if (ZSTD_isError(errorCode)) return ERROR(dictionary_corrupted);
    }

    return 0;
}


struct ZSTD_DDict_s {
    void* dict;
    size_t dictSize;
    ZSTD_DCtx* refContext;
};  /* typedef'd tp ZSTD_CDict within zstd.h */

ZSTD_DDict* ZSTD_createDDict_advanced(const void* dict, size_t dictSize, ZSTD_customMem customMem)
{
    if (!customMem.customAlloc && !customMem.customFree)
        customMem = defaultCustomMem;

    if (!customMem.customAlloc || !customMem.customFree)
        return NULL;

    {   ZSTD_DDict* const ddict = (ZSTD_DDict*) customMem.customAlloc(customMem.opaque, sizeof(*ddict));
        void* const dictContent = customMem.customAlloc(customMem.opaque, dictSize);
        ZSTD_DCtx* const dctx = ZSTD_createDCtx_advanced(customMem);

        if (!dictContent || !ddict || !dctx) {
            customMem.customFree(customMem.opaque, dictContent);
            customMem.customFree(customMem.opaque, ddict);
            customMem.customFree(customMem.opaque, dctx);
            return NULL;
        }

        memcpy(dictContent, dict, dictSize);
        {   size_t const errorCode = ZSTD_decompressBegin_usingDict(dctx, dictContent, dictSize);
            if (ZSTD_isError(errorCode)) {
                customMem.customFree(customMem.opaque, dictContent);
                customMem.customFree(customMem.opaque, ddict);
                customMem.customFree(customMem.opaque, dctx);
                return NULL;
        }   }

        ddict->dict = dictContent;
        ddict->dictSize = dictSize;
        ddict->refContext = dctx;
        return ddict;
    }
}

/*! ZSTD_createDDict() :
*   Create a digested dictionary, ready to start decompression without startup delay.
*   `dict` can be released after `ZSTD_DDict` creation */
ZSTD_DDict* ZSTD_createDDict(const void* dict, size_t dictSize)
{
    ZSTD_customMem const allocator = { NULL, NULL, NULL };
    return ZSTD_createDDict_advanced(dict, dictSize, allocator);
}

size_t ZSTD_freeDDict(ZSTD_DDict* ddict)
{
    ZSTD_freeFunction const cFree = ddict->refContext->customMem.customFree;
    void* const opaque = ddict->refContext->customMem.opaque;
    ZSTD_freeDCtx(ddict->refContext);
    cFree(opaque, ddict->dict);
    cFree(opaque, ddict);
    return 0;
}

/*! ZSTD_decompress_usingDDict() :
*   Decompression using a pre-digested Dictionary
*   Use dictionary without significant overhead. */
ZSTDLIB_API size_t ZSTD_decompress_usingDDict(ZSTD_DCtx* dctx,
                                           void* dst, size_t dstCapacity,
                                     const void* src, size_t srcSize,
                                     const ZSTD_DDict* ddict)
{
#if defined(ZSTD_LEGACY_SUPPORT) && (ZSTD_LEGACY_SUPPORT==1)
    if (ZSTD_isLegacy(src, srcSize)) return ZSTD_decompressLegacy(dst, dstCapacity, src, srcSize, ddict->dict, ddict->dictSize);
#endif
    return ZSTD_decompress_usingPreparedDCtx(dctx, ddict->refContext,
                                           dst, dstCapacity,
                                           src, srcSize);
}