lib/zstd_decompress.c

/*
    zstd - standard compression library
    Copyright (C) 2014-2015, 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 source repository : https://github.com/Cyan4973/zstd
    - ztsd public forum : https://groups.google.com/forum/#!forum/lz4c
*/

/* ***************************************************************
*  Tuning parameters
*****************************************************************/
/*!
 * HEAPMODE :
 * Select how default functions will allocate memory for their context,
 * in memory stack (0, fastest), or in memory heap (1, requires malloc())
 */
#ifndef ZSTD_HEAPMODE
#  define ZSTD_HEAPMODE 1
#endif /* ZSTD_HEAPMODE */

/*!
*  LEGACY_SUPPORT :
*  ZSTD_decompress() can decode older formats (starting from zstd 0.1+)
*/
#ifndef ZSTD_LEGACY_SUPPORT
#  define ZSTD_LEGACY_SUPPORT 1
#endif


/* *******************************************************
*  Includes
*********************************************************/
#include <stdlib.h>      /* calloc */
#include <string.h>      /* memcpy, memmove */
#include <stdio.h>       /* debug : printf */
#include "mem.h"         /* low level memory routines */
#include "zstd_static.h"
#include "zstd_internal.h"
#include "fse_static.h"
#include "huff0.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
#  define GCC_VERSION (__GNUC__ * 100 + __GNUC_MINOR__)
#  ifdef __GNUC__
#    define FORCE_INLINE static inline __attribute__((always_inline))
#  else
#    define FORCE_INLINE static inline
#  endif
#endif


/* *************************************
*  Local types
***************************************/
typedef struct
{
    blockType_t blockType;
    U32 origSize;
} blockProperties_t;


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


/* *************************************
*  Error Management
***************************************/
unsigned ZSTD_versionNumber (void) { return ZSTD_VERSION_NUMBER; }

/*! ZSTD_isError
*   tells if a return value is an error code */
unsigned ZSTD_isError(size_t code) { return ERR_isError(code); }

/*! ZSTD_getErrorName
*   provides error code string (useful for debugging) */
const char* ZSTD_getErrorName(size_t code) { return ERR_getErrorName(code); }


/* *************************************************************
*   Context management
***************************************************************/
struct ZSTD_DCtx_s
{
    U32 LLTable[FSE_DTABLE_SIZE_U32(LLFSELog)];
    U32 OffTable[FSE_DTABLE_SIZE_U32(OffFSELog)];
    U32 MLTable[FSE_DTABLE_SIZE_U32(MLFSELog)];
    void* previousDstEnd;
    void* base;
    void* vBase;
    void* dictEnd;
    size_t expected;
    blockType_t bType;
    U32 phase;
    const BYTE* litPtr;
    size_t litBufSize;
    size_t litSize;
    BYTE litBuffer[BLOCKSIZE + 8 /* margin for wildcopy */];
};   /* typedef'd to ZSTD_Dctx within "zstd_static.h" */

size_t ZSTD_resetDCtx(ZSTD_DCtx* dctx)
{
    dctx->expected = ZSTD_frameHeaderSize;
    dctx->phase = 0;
    dctx->previousDstEnd = NULL;
    dctx->base = NULL;
    dctx->vBase = NULL;
    dctx->dictEnd = NULL;
    return 0;
}

ZSTD_DCtx* ZSTD_createDCtx(void)
{
    ZSTD_DCtx* dctx = (ZSTD_DCtx*)malloc(sizeof(ZSTD_DCtx));
    if (dctx==NULL) return NULL;
    ZSTD_resetDCtx(dctx);
    return dctx;
}

size_t ZSTD_freeDCtx(ZSTD_DCtx* dctx)
{
    free(dctx);
    return 0;
}


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

size_t ZSTD_getcBlockSize(const void* src, size_t srcSize, blockProperties_t* bpPtr)
{
    const BYTE* const in = (const BYTE* const)src;
    BYTE headerFlags;
    U32 cSize;

    if (srcSize < 3) return ERROR(srcSize_wrong);

    headerFlags = *in;
    cSize = in[2] + (in[1]<<8) + ((in[0] & 7)<<16);

    bpPtr->blockType = (blockType_t)(headerFlags >> 6);
    bpPtr->origSize = (bpPtr->blockType == bt_rle) ? cSize : 0;

    if (bpPtr->blockType == bt_end) return 0;
    if (bpPtr->blockType == bt_rle) return 1;
    return cSize;
}

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


/** ZSTD_decompressLiterals
    @return : nb of bytes read from src, or an error code*/
static size_t ZSTD_decompressLiterals(void* dst, size_t* maxDstSizePtr,
                                const void* src, size_t srcSize)
{
    const BYTE* ip = (const BYTE*)src;

    const size_t litSize = (MEM_readLE32(src) & 0x1FFFFF) >> 2;   /* no buffer issue : srcSize >= MIN_CBLOCK_SIZE */
    const size_t litCSize = (MEM_readLE32(ip+2) & 0xFFFFFF) >> 5;   /* no buffer issue : srcSize >= MIN_CBLOCK_SIZE */

    if (litSize > *maxDstSizePtr) return ERROR(corruption_detected);
    if (litCSize + 5 > srcSize) return ERROR(corruption_detected);

    if (HUF_isError(HUF_decompress(dst, litSize, ip+5, litCSize))) return ERROR(corruption_detected);

    *maxDstSizePtr = litSize;
    return litCSize + 5;
}


/** 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 */
{
    const BYTE* const istart = (const BYTE*) src;

    /* any compressed block with literals segment must be at least this size */
    if (srcSize < MIN_CBLOCK_SIZE) return ERROR(corruption_detected);

    switch(*istart & 3)
    {
    /* compressed */
    case 0:
        {
            size_t litSize = BLOCKSIZE;
            const size_t readSize = ZSTD_decompressLiterals(dctx->litBuffer, &litSize, src, srcSize);
            dctx->litPtr = dctx->litBuffer;
            dctx->litBufSize = BLOCKSIZE+8;
            dctx->litSize = litSize;
            return readSize;   /* works if it's an error too */
        }
    case IS_RAW:
        {
            const size_t litSize = (MEM_readLE32(istart) & 0xFFFFFF) >> 2;   /* no buffer issue : srcSize >= MIN_CBLOCK_SIZE */
            if (litSize > srcSize-11)   /* risk of reading too far with wildcopy */
            {
                if (litSize > srcSize-3) return ERROR(corruption_detected);
                memcpy(dctx->litBuffer, istart, litSize);
                dctx->litPtr = dctx->litBuffer;
                dctx->litBufSize = BLOCKSIZE+8;
                dctx->litSize = litSize;
                return litSize+3;
            }
            /* direct reference into compressed stream */
            dctx->litPtr = istart+3;
            dctx->litBufSize = srcSize-3;
            dctx->litSize = litSize;
            return litSize+3;        }
    case IS_RLE:
        {
            const size_t litSize = (MEM_readLE32(istart) & 0xFFFFFF) >> 2;   /* no buffer issue : srcSize >= MIN_CBLOCK_SIZE */
            if (litSize > BLOCKSIZE) return ERROR(corruption_detected);
            memset(dctx->litBuffer, istart[3], litSize);
            dctx->litPtr = dctx->litBuffer;
            dctx->litBufSize = BLOCKSIZE+8;
            dctx->litSize = litSize;
            return 4;
        }
    default:
        return ERROR(corruption_detected);   /* forbidden nominal case */
    }
}


size_t ZSTD_decodeSeqHeaders(int* nbSeq, const BYTE** dumpsPtr, size_t* dumpsLengthPtr,
                         FSE_DTable* DTableLL, FSE_DTable* DTableML, FSE_DTable* DTableOffb,
                         const void* src, size_t srcSize)
{
    const BYTE* const istart = (const BYTE* const)src;
    const BYTE* ip = istart;
    const BYTE* const iend = istart + srcSize;
    U32 LLtype, Offtype, MLtype;
    U32 LLlog, Offlog, MLlog;
    size_t dumpsLength;

    /* check */
    if (srcSize < 5) return ERROR(srcSize_wrong);

    /* SeqHead */
    *nbSeq = MEM_readLE16(ip); ip+=2;
    LLtype  = *ip >> 6;
    Offtype = (*ip >> 4) & 3;
    MLtype  = (*ip >> 2) & 3;
    if (*ip & 2)
    {
        dumpsLength  = ip[2];
        dumpsLength += ip[1] << 8;
        ip += 3;
    }
    else
    {
        dumpsLength  = ip[1];
        dumpsLength += (ip[0] & 1) << 8;
        ip += 2;
    }
    *dumpsPtr = ip;
    ip += dumpsLength;
    *dumpsLengthPtr = dumpsLength;

    /* check */
    if (ip > iend-3) return ERROR(srcSize_wrong); /* min : all 3 are "raw", hence no header, but at least xxLog bits per type */

    /* sequences */
    {
        S16 norm[MaxML+1];    /* assumption : MaxML >= MaxLL >= MaxOff */
        size_t headerSize;

        /* Build DTables */
        switch(LLtype)
        {
        U32 max;
        case bt_rle :
            LLlog = 0;
            FSE_buildDTable_rle(DTableLL, *ip++); break;
        case bt_raw :
            LLlog = LLbits;
            FSE_buildDTable_raw(DTableLL, LLbits); break;
        default :
            max = MaxLL;
            headerSize = FSE_readNCount(norm, &max, &LLlog, ip, iend-ip);
            if (FSE_isError(headerSize)) return ERROR(GENERIC);
            if (LLlog > LLFSELog) return ERROR(corruption_detected);
            ip += headerSize;
            FSE_buildDTable(DTableLL, norm, max, LLlog);
        }

        switch(Offtype)
        {
        U32 max;
        case bt_rle :
            Offlog = 0;
            if (ip > iend-2) return ERROR(srcSize_wrong);   /* min : "raw", hence no header, but at least xxLog bits */
            FSE_buildDTable_rle(DTableOffb, *ip++ & MaxOff); /* if *ip > MaxOff, data is corrupted */
            break;
        case bt_raw :
            Offlog = Offbits;
            FSE_buildDTable_raw(DTableOffb, Offbits); break;
        default :
            max = MaxOff;
            headerSize = FSE_readNCount(norm, &max, &Offlog, ip, iend-ip);
            if (FSE_isError(headerSize)) return ERROR(GENERIC);
            if (Offlog > OffFSELog) return ERROR(corruption_detected);
            ip += headerSize;
            FSE_buildDTable(DTableOffb, norm, max, Offlog);
        }

        switch(MLtype)
        {
        U32 max;
        case bt_rle :
            MLlog = 0;
            if (ip > iend-2) return ERROR(srcSize_wrong); /* min : "raw", hence no header, but at least xxLog bits */
            FSE_buildDTable_rle(DTableML, *ip++); break;
        case bt_raw :
            MLlog = MLbits;
            FSE_buildDTable_raw(DTableML, MLbits); break;
        default :
            max = MaxML;
            headerSize = FSE_readNCount(norm, &max, &MLlog, ip, iend-ip);
            if (FSE_isError(headerSize)) return ERROR(GENERIC);
            if (MLlog > MLFSELog) return ERROR(corruption_detected);
            ip += headerSize;
            FSE_buildDTable(DTableML, norm, max, MLlog);
        }
    }

    return ip-istart;
}


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

typedef struct {
    BIT_DStream_t DStream;
    FSE_DState_t stateLL;
    FSE_DState_t stateOffb;
    FSE_DState_t stateML;
    size_t prevOffset;
    const BYTE* dumps;
    const BYTE* dumpsEnd;
} seqState_t;


/** ZSTD_decodeSequence
*   Decode the next sequence, defined as nbLiterals, PtrToLiterals, nbMatches, Offset
*   @seq : store sequence into this seq_t
*/
static void ZSTD_decodeSequence(seq_t* seq, seqState_t* seqState)
{
    size_t litLength;
    size_t prevOffset;
    size_t offset;
    size_t matchLength;
    const BYTE* dumps = seqState->dumps;
    const BYTE* const de = seqState->dumpsEnd;

    /* Literal length */
    litLength = FSE_decodeSymbol(&(seqState->stateLL), &(seqState->DStream));
    prevOffset = litLength ? seq->offset : seqState->prevOffset;
    seqState->prevOffset = seq->offset;
    if (litLength == MaxLL)
    {
        U32 add = *dumps++;
        if (add < 255) litLength += add;
        else
        {
            litLength = MEM_readLE32(dumps) & 0xFFFFFF;  /* no pb : dumps is always followed by seq tables > 1 byte */
            dumps += 3;
        }
        if (dumps >= de) dumps = de-1;   /* late correction, to avoid read overflow (data is now corrupted anyway) */
    }

    /* Offset */
    {
        static const U32 offsetPrefix[MaxOff+1] = {
                1 /*fake*/, 1, 2, 4, 8, 16, 32, 64, 128, 256,
                512, 1024, 2048, 4096, 8192, 16384, 32768, 65536, 131072, 262144,
                524288, 1048576, 2097152, 4194304, 8388608, 16777216, 33554432, /*fake*/ 1, 1, 1, 1, 1 };
        U32 offsetCode, nbBits;
        offsetCode = FSE_decodeSymbol(&(seqState->stateOffb), &(seqState->DStream));   /* <= maxOff, by table construction */
        if (MEM_32bits()) BIT_reloadDStream(&(seqState->DStream));
        nbBits = offsetCode - 1;
        if (offsetCode==0) nbBits = 0;   /* cmove */
        offset = offsetPrefix[offsetCode] + BIT_readBits(&(seqState->DStream), nbBits);
        if (MEM_32bits()) BIT_reloadDStream(&(seqState->DStream));
        if (offsetCode==0) offset = prevOffset;   /* cmove */
    }

    /* MatchLength */
    matchLength = FSE_decodeSymbol(&(seqState->stateML), &(seqState->DStream));
    if (matchLength == MaxML)
    {
        U32 add = *dumps++;
        if (add < 255) matchLength += add;
        else
        {
            matchLength = MEM_readLE32(dumps) & 0xFFFFFF;  /* no pb : dumps is always followed by seq tables > 1 byte */
            dumps += 3;
        }
        if (dumps >= de) dumps = de-1;   /* late correction, to avoid read overflow (data is now corrupted anyway) */
    }
    matchLength += MINMATCH;

    /* save result */
    seq->litLength = litLength;
    seq->offset = offset;
    seq->matchLength = matchLength;
    seqState->dumps = dumps;
}


FORCE_INLINE size_t ZSTD_execSequence(BYTE* op,
                                seq_t sequence,
                                const BYTE** litPtr, const BYTE* const litLimit_8,
                                BYTE* const base, BYTE* const vBase, BYTE* const dictEnd,
                                BYTE* const oend)
{
    static const int dec32table[] = {0, 1, 2, 1, 4, 4, 4, 4};   /* added */
    static const int dec64table[] = {8, 8, 8, 7, 8, 9,10,11};   /* substracted */
    const BYTE* const ostart = op;
    BYTE* const oLitEnd = op + sequence.litLength;
    BYTE* const oMatchEnd = op + sequence.litLength + sequence.matchLength;   /* risk : address space overflow (32-bits) */
    BYTE* const oend_8 = oend-8;
    const BYTE* const litEnd = *litPtr + sequence.litLength;

    /* check */
    if (oLitEnd > oend_8) return ERROR(dstSize_tooSmall);   /* last match must start at a minimum distance of 8 from oend */
    if (oMatchEnd > oend) return ERROR(dstSize_tooSmall);   /* overwrite beyond dst buffer */
    if (litEnd > litLimit_8) return ERROR(corruption_detected);   /* risk read beyond lit buffer */

    /* copy Literals */
    ZSTD_wildcopy(op, *litPtr, sequence.litLength);   /* note : oLitEnd <= oend-8 : no risk of overwrite beyond oend */
    op = oLitEnd;
    *litPtr = litEnd;   /* update for next sequence */

    /* copy Match */
    {
        const BYTE* match = op - sequence.offset;

        /* check */
        //if (match > op) return ERROR(corruption_detected);   /* address space overflow test (is clang optimizer wrongly removing this test ?) */
        if (sequence.offset > (size_t)op) return ERROR(corruption_detected);   /* address space overflow test (this test seems kept by clang optimizer) */

        if (match < base)
        {
            /* offset beyond prefix */
            if (match < vBase) return ERROR(corruption_detected);
            match = dictEnd - (base-match);
            if (match + sequence.matchLength <= dictEnd)
            {
                memcpy(op, match, sequence.matchLength);
                return oMatchEnd - ostart;
            }
            /* span extDict & currentPrefixSegment */
            {
                size_t length1 = dictEnd - match;
                memcpy(op, match, length1);
                op += length1;
                sequence.matchLength -= length1;
                match = base;
            }
        }

        {
            /* match within prefix */
            if (sequence.offset < 8)
            {
                /* close range match, overlap */
                const int dec64 = 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 -= dec64;
            }
            else
            {
                ZSTD_copy8(op, match);
            }
            op += 8; match += 8;

            if (oMatchEnd > oend-12)
            {
                if (op < oend_8)
                {
                    ZSTD_wildcopy(op, match, oend_8 - op);
                    match += oend_8 - op;
                    op = oend_8;
                }
                while (op < oMatchEnd) *op++ = *match++;
            }
            else
            {
                ZSTD_wildcopy(op, match, sequence.matchLength-8);   /* works even if matchLength < 8 */
            }
            return oMatchEnd - ostart;
        }

    }

}

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* op = ostart;
    BYTE* const oend = ostart + maxDstSize;
    size_t errorCode, dumpsLength;
    const BYTE* litPtr = dctx->litPtr;
    const BYTE* const litLimit_8 = litPtr + dctx->litBufSize - 8;
    const BYTE* const litEnd = litPtr + dctx->litSize;
    int nbSeq;
    const BYTE* dumps;
    U32* DTableLL = dctx->LLTable;
    U32* DTableML = dctx->MLTable;
    U32* DTableOffb = dctx->OffTable;
    BYTE* const base = (BYTE*) (dctx->base);
    BYTE* const vBase = (BYTE*) (dctx->vBase);
    BYTE* const dictEnd = (BYTE*) (dctx->dictEnd);

    /* Build Decoding Tables */
    errorCode = ZSTD_decodeSeqHeaders(&nbSeq, &dumps, &dumpsLength,
                                      DTableLL, DTableML, DTableOffb,
                                      ip, iend-ip);
    if (ZSTD_isError(errorCode)) return errorCode;
    ip += errorCode;

    /* Regen sequences */
    {
        seq_t sequence;
        seqState_t seqState;

        memset(&sequence, 0, sizeof(sequence));
        sequence.offset = 4;
        seqState.dumps = dumps;
        seqState.dumpsEnd = dumps + dumpsLength;
        seqState.prevOffset = 4;
        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>0) ; )
        {
            size_t oneSeqSize;
            nbSeq--;
            ZSTD_decodeSequence(&sequence, &seqState);
            oneSeqSize = ZSTD_execSequence(op, sequence, &litPtr, litLimit_8, base, vBase, dictEnd, oend);
            if (ZSTD_isError(oneSeqSize)) return oneSeqSize;
            op += oneSeqSize;
        }

        /* check if reached exact end */
        if ( !BIT_endOfDStream(&(seqState.DStream)) ) return ERROR(corruption_detected);   /* requested too much : data is corrupted */
        if (nbSeq<0) return ERROR(corruption_detected);   /* requested too many sequences : data is corrupted */

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

    return op-ostart;
}


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

    /* Decode literals sub-block */
    size_t litCSize = ZSTD_decodeLiteralsBlock(dctx, src, srcSize);
    if (ZSTD_isError(litCSize)) return litCSize;
    ip += litCSize;
    srcSize -= litCSize;

    return ZSTD_decompressSequences(dctx, dst, maxDstSize, ip, srcSize);
}


size_t ZSTD_decompressDCtx(ZSTD_DCtx* ctx, void* dst, size_t maxDstSize, const void* src, size_t srcSize)
{
    const BYTE* ip = (const BYTE*)src;
    const BYTE* iend = ip + srcSize;
    BYTE* const ostart = (BYTE* const)dst;
    BYTE* op = ostart;
    BYTE* const oend = ostart + maxDstSize;
    size_t remainingSize = srcSize;
    U32 magicNumber;
    blockProperties_t blockProperties;


    /* init */
    ctx->base = ctx->vBase = ctx->dictEnd = dst;

    /* Frame Header */
    if (srcSize < ZSTD_frameHeaderSize+ZSTD_blockHeaderSize) return ERROR(srcSize_wrong);
    magicNumber = MEM_readLE32(src);
#if defined(ZSTD_LEGACY_SUPPORT) && (ZSTD_LEGACY_SUPPORT==1)
    if (ZSTD_isLegacy(magicNumber))
        return ZSTD_decompressLegacy(dst, maxDstSize, src, srcSize, magicNumber);
#endif
    if (magicNumber != ZSTD_magicNumber) return ERROR(prefix_unknown);
    ip += ZSTD_frameHeaderSize; remainingSize -= ZSTD_frameHeaderSize;

    /* Loop on each block */
    while (1)
    {
        size_t decodedSize=0;
        size_t cBlockSize = ZSTD_getcBlockSize(ip, iend-ip, &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(ctx, op, oend-op, ip, cBlockSize);
            break;
        case bt_raw :
            decodedSize = ZSTD_copyRawBlock(op, oend-op, ip, cBlockSize);
            break;
        case bt_rle :
            return ERROR(GENERIC);   /* not yet supported */
            break;
        case bt_end :
            /* end of frame */
            if (remainingSize) return ERROR(srcSize_wrong);
            break;
        default:
            return ERROR(GENERIC);   /* impossible */
        }
        if (cBlockSize == 0) break;   /* bt_end */

        if (ZSTD_isError(decodedSize)) return decodedSize;
        op += decodedSize;
        ip += cBlockSize;
        remainingSize -= cBlockSize;
    }

    return op-ostart;
}

size_t ZSTD_decompress(void* dst, size_t maxDstSize, const void* src, size_t srcSize)
{
    ZSTD_DCtx ctx;
    return ZSTD_decompressDCtx(&ctx, dst, maxDstSize, src, srcSize);
}


/* ******************************
*  Streaming Decompression API
********************************/

size_t ZSTD_nextSrcSizeToDecompress(ZSTD_DCtx* dctx)
{
    return dctx->expected;
}

size_t ZSTD_decompressContinue(ZSTD_DCtx* ctx, void* dst, size_t maxDstSize, const void* src, size_t srcSize)
{
    /* Sanity check */
    if (srcSize != ctx->expected) return ERROR(srcSize_wrong);
    if (dst != ctx->previousDstEnd)  /* not contiguous */
    {
        ctx->dictEnd = ctx->previousDstEnd;
        if ((dst > ctx->base) && (dst < ctx->previousDstEnd))   /* rolling buffer : new segment right into tracked memory */
            ctx->base = (char*)dst + maxDstSize;   /* temporary affectation, for vBase calculation */
        ctx->vBase = (char*)dst - ((char*)(ctx->dictEnd) - (char*)(ctx->base));
        ctx->base = dst;
    }

    /* Decompress : frame header */
    if (ctx->phase == 0)
    {
        /* Check frame magic header */
        U32 magicNumber = MEM_readLE32(src);
        if (magicNumber != ZSTD_magicNumber) return ERROR(prefix_unknown);
        ctx->phase = 1;
        ctx->expected = ZSTD_blockHeaderSize;
        return 0;
    }

    /* Decompress : block header */
    if (ctx->phase == 1)
    {
        blockProperties_t bp;
        size_t blockSize = ZSTD_getcBlockSize(src, ZSTD_blockHeaderSize, &bp);
        if (ZSTD_isError(blockSize)) return blockSize;
        if (bp.blockType == bt_end)
        {
            ctx->expected = 0;
            ctx->phase = 0;
        }
        else
        {
            ctx->expected = blockSize;
            ctx->bType = bp.blockType;
            ctx->phase = 2;
        }

        ctx->previousDstEnd = dst;
        return 0;
    }

    /* Decompress : block content */
    {
        size_t rSize;
        switch(ctx->bType)
        {
        case bt_compressed:
            rSize = ZSTD_decompressBlock(ctx, dst, maxDstSize, src, srcSize);
            break;
        case bt_raw :
            rSize = ZSTD_copyRawBlock(dst, maxDstSize, src, srcSize);
            break;
        case bt_rle :
            return ERROR(GENERIC);   /* not yet handled */
            break;
        case bt_end :   /* should never happen (filtered at phase 1) */
            rSize = 0;
            break;
        default:
            return ERROR(GENERIC);
        }
        ctx->phase = 1;
        ctx->expected = ZSTD_blockHeaderSize;
        ctx->previousDstEnd = (char*)dst + rSize;
        return rSize;
    }

}