/*

 * Copyright (c) Meta Platforms, Inc. and affiliates.

 * All rights reserved.

 *

 * This source code is licensed under both the BSD-style license (found in the

 * LICENSE file in the root directory of this source tree) and the GPLv2 (found

 * in the COPYING file in the root directory of this source tree).

 * You may select, at your option, one of the above-listed licenses.

 */

 /*-*************************************

 *  Dependencies

 ***************************************/

#include "zstd_compress_superblock.h"

#include "../common/zstd_internal.h"  /* ZSTD_getSequenceLength */

#include "hist.h"                     /* HIST_countFast_wksp */

#include "zstd_compress_internal.h"   /* ZSTD_[huf|fse|entropy]CTablesMetadata_t */

#include "zstd_compress_sequences.h"

#include "zstd_compress_literals.h"

/** ZSTD_compressSubBlock_literal() :

 *  Compresses literals section for a sub-block.

 *  When we have to write the Huffman table we will sometimes choose a header

 *  size larger than necessary. This is because we have to pick the header size

 *  before we know the table size + compressed size, so we have a bound on the

 *  table size. If we guessed incorrectly, we fall back to uncompressed literals.

 *

 *  We write the header when writeEntropy=1 and set entropyWritten=1 when we succeeded

 *  in writing the header, otherwise it is set to 0.

 *

 *  hufMetadata->hType has literals block type info.

 *      If it is set_basic, all sub-blocks literals section will be Raw_Literals_Block.

 *      If it is set_rle, all sub-blocks literals section will be RLE_Literals_Block.

 *      If it is set_compressed, first sub-block's literals section will be Compressed_Literals_Block

 *      If it is set_compressed, first sub-block's literals section will be Treeless_Literals_Block

 *      and the following sub-blocks' literals sections will be Treeless_Literals_Block.

 *  @return : compressed size of literals section of a sub-block

 *            Or 0 if unable to compress.

 *            Or error code */

static size_t

ZSTD_compressSubBlock_literal(const HUF_CElt* hufTable,

                              const ZSTD_hufCTablesMetadata_t* hufMetadata,

                              const BYTE* literals, size_t litSize,

                              void* dst, size_t dstSize,

                              const int bmi2, int writeEntropy, int* entropyWritten)

{

    size_t const header = writeEntropy ? 200 : 0;

    size_t const lhSize = 3 + (litSize >= (1 KB - header)) + (litSize >= (16 KB - header));

    BYTE* const ostart = (BYTE*)dst;

    BYTE* const oend = ostart + dstSize;

    BYTE* op = ostart + lhSize;

    U32 const singleStream = lhSize == 3;

    SymbolEncodingType_e hType = writeEntropy ? hufMetadata->hType : set_repeat;

    size_t cLitSize = 0;

    DEBUGLOG(5, "ZSTD_compressSubBlock_literal (litSize=%zu, lhSize=%zu, writeEntropy=%d)", litSize, lhSize, writeEntropy);

    *entropyWritten = 0;

    if (litSize == 0 || hufMetadata->hType == set_basic) {

      DEBUGLOG(5, "ZSTD_compressSubBlock_literal using raw literal");

      return ZSTD_noCompressLiterals(dst, dstSize, literals, litSize);

    } else if (hufMetadata->hType == set_rle) {

      DEBUGLOG(5, "ZSTD_compressSubBlock_literal using rle literal");

      return ZSTD_compressRleLiteralsBlock(dst, dstSize, literals, litSize);

    }

    assert(litSize > 0);

    assert(hufMetadata->hType == set_compressed || hufMetadata->hType == set_repeat);

    if (writeEntropy && hufMetadata->hType == set_compressed) {

        ZSTD_memcpy(op, hufMetadata->hufDesBuffer, hufMetadata->hufDesSize);

        op += hufMetadata->hufDesSize;

        cLitSize += hufMetadata->hufDesSize;

        DEBUGLOG(5, "ZSTD_compressSubBlock_literal (hSize=%zu)", hufMetadata->hufDesSize);

    }

    {   int const flags = bmi2 ? HUF_flags_bmi2 : 0;

        const size_t cSize = singleStream ? HUF_compress1X_usingCTable(op, (size_t)(oend-op), literals, litSize, hufTable, flags)

                                          : HUF_compress4X_usingCTable(op, (size_t)(oend-op), literals, litSize, hufTable, flags);

        op += cSize;

        cLitSize += cSize;

        if (cSize == 0 || ERR_isError(cSize)) {

            DEBUGLOG(5, "Failed to write entropy tables %s", ZSTD_getErrorName(cSize));

            return 0;

        }

        /* If we expand and we aren't writing a header then emit uncompressed */

        if (!writeEntropy && cLitSize >= litSize) {

            DEBUGLOG(5, "ZSTD_compressSubBlock_literal using raw literal because uncompressible");

            return ZSTD_noCompressLiterals(dst, dstSize, literals, litSize);

        }

        /* If we are writing headers then allow expansion that doesn't change our header size. */

        if (lhSize < (size_t)(3 + (cLitSize >= 1 KB) + (cLitSize >= 16 KB))) {

            assert(cLitSize > litSize);

            DEBUGLOG(5, "Literals expanded beyond allowed header size");

            return ZSTD_noCompressLiterals(dst, dstSize, literals, litSize);

        }

        DEBUGLOG(5, "ZSTD_compressSubBlock_literal (cSize=%zu)", cSize);

    }

    /* Build header */

    switch(lhSize)

    {

    case 3: /* 2 - 2 - 10 - 10 */

        {   U32 const lhc = hType + ((U32)(!singleStream) << 2) + ((U32)litSize<<4) + ((U32)cLitSize<<14);

            MEM_writeLE24(ostart, lhc);

            break;

        }

    case 4: /* 2 - 2 - 14 - 14 */

        {   U32 const lhc = hType + (2 << 2) + ((U32)litSize<<4) + ((U32)cLitSize<<18);

            MEM_writeLE32(ostart, lhc);

            break;

        }

    case 5: /* 2 - 2 - 18 - 18 */

        {   U32 const lhc = hType + (3 << 2) + ((U32)litSize<<4) + ((U32)cLitSize<<22);

            MEM_writeLE32(ostart, lhc);

            ostart[4] = (BYTE)(cLitSize >> 10);

            break;

        }

    default:  /* not possible : lhSize is {3,4,5} */

        assert(0);

    }

    *entropyWritten = 1;

    DEBUGLOG(5, "Compressed literals: %u -> %u", (U32)litSize, (U32)(op-ostart));

    return (size_t)(op-ostart);

}

static size_t

ZSTD_seqDecompressedSize(SeqStore_t const* seqStore,

                   const SeqDef* sequences, size_t nbSeqs,

                         size_t litSize, int lastSubBlock)

{

    size_t matchLengthSum = 0;

    size_t litLengthSum = 0;

    size_t n;

    for (n=0; n<nbSeqs; n++) {

        const ZSTD_SequenceLength seqLen = ZSTD_getSequenceLength(seqStore, sequences+n);

        litLengthSum += seqLen.litLength;

        matchLengthSum += seqLen.matchLength;

    }

    DEBUGLOG(5, "ZSTD_seqDecompressedSize: %u sequences from %p: %u literals + %u matchlength",

                (unsigned)nbSeqs, (const void*)sequences,

                (unsigned)litLengthSum, (unsigned)matchLengthSum);

    if (!lastSubBlock)

        assert(litLengthSum == litSize);

    else

        assert(litLengthSum <= litSize);

    (void)litLengthSum;

    return matchLengthSum + litSize;

}

/** ZSTD_compressSubBlock_sequences() :

 *  Compresses sequences section for a sub-block.

 *  fseMetadata->llType, fseMetadata->ofType, and fseMetadata->mlType have

 *  symbol compression modes for the super-block.

 *  The first successfully compressed block will have these in its header.

 *  We set entropyWritten=1 when we succeed in compressing the sequences.

 *  The following sub-blocks will always have repeat mode.

 *  @return : compressed size of sequences section of a sub-block

 *            Or 0 if it is unable to compress

 *            Or error code. */

static size_t

ZSTD_compressSubBlock_sequences(const ZSTD_fseCTables_t* fseTables,

                                const ZSTD_fseCTablesMetadata_t* fseMetadata,

                                const SeqDef* sequences, size_t nbSeq,

                                const BYTE* llCode, const BYTE* mlCode, const BYTE* ofCode,

                                const ZSTD_CCtx_params* cctxParams,

                                void* dst, size_t dstCapacity,

                                const int bmi2, int writeEntropy, int* entropyWritten)

{

    const int longOffsets = cctxParams->cParams.windowLog > STREAM_ACCUMULATOR_MIN;

    BYTE* const ostart = (BYTE*)dst;

    BYTE* const oend = ostart + dstCapacity;

    BYTE* op = ostart;

    BYTE* seqHead;

    DEBUGLOG(5, "ZSTD_compressSubBlock_sequences (nbSeq=%zu, writeEntropy=%d, longOffsets=%d)", nbSeq, writeEntropy, longOffsets);

    *entropyWritten = 0;

    /* Sequences Header */

    RETURN_ERROR_IF((oend-op) < 3 /*max nbSeq Size*/ + 1 /*seqHead*/,

                    dstSize_tooSmall, "");

    if (nbSeq < 128)

        *op++ = (BYTE)nbSeq;

    else if (nbSeq < LONGNBSEQ)

        op[0] = (BYTE)((nbSeq>>8) + 0x80), op[1] = (BYTE)nbSeq, op+=2;

    else

        op[0]=0xFF, MEM_writeLE16(op+1, (U16)(nbSeq - LONGNBSEQ)), op+=3;

    if (nbSeq==0) {

        return (size_t)(op - ostart);

    }

    /* seqHead : flags for FSE encoding type */

    seqHead = op++;

    DEBUGLOG(5, "ZSTD_compressSubBlock_sequences (seqHeadSize=%u)", (unsigned)(op-ostart));

    if (writeEntropy) {

        const U32 LLtype = fseMetadata->llType;

        const U32 Offtype = fseMetadata->ofType;

        const U32 MLtype = fseMetadata->mlType;

        DEBUGLOG(5, "ZSTD_compressSubBlock_sequences (fseTablesSize=%zu)", fseMetadata->fseTablesSize);

        *seqHead = (BYTE)((LLtype<<6) + (Offtype<<4) + (MLtype<<2));

        ZSTD_memcpy(op, fseMetadata->fseTablesBuffer, fseMetadata->fseTablesSize);

        op += fseMetadata->fseTablesSize;

    } else {

        const U32 repeat = set_repeat;

        *seqHead = (BYTE)((repeat<<6) + (repeat<<4) + (repeat<<2));

    }

    {   size_t const bitstreamSize = ZSTD_encodeSequences(

                                        op, (size_t)(oend - op),

                                        fseTables->matchlengthCTable, mlCode,

                                        fseTables->offcodeCTable, ofCode,

                                        fseTables->litlengthCTable, llCode,

                                        sequences, nbSeq,

                                        longOffsets, bmi2);

        FORWARD_IF_ERROR(bitstreamSize, "ZSTD_encodeSequences failed");

        op += bitstreamSize;

        /* zstd versions <= 1.3.4 mistakenly report corruption when

         * FSE_readNCount() receives a buffer < 4 bytes.

         * Fixed by https://github.com/facebook/zstd/pull/1146.

         * This can happen when the last set_compressed table present is 2

         * bytes and the bitstream is only one byte.

         * In this exceedingly rare case, we will simply emit an uncompressed

         * block, since it isn't worth optimizing.

         */

#ifndef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION

        if (writeEntropy && fseMetadata->lastCountSize && fseMetadata->lastCountSize + bitstreamSize < 4) {

            /* NCountSize >= 2 && bitstreamSize > 0 ==> lastCountSize == 3 */

            assert(fseMetadata->lastCountSize + bitstreamSize == 3);

            DEBUGLOG(5, "Avoiding bug in zstd decoder in versions <= 1.3.4 by "

                        "emitting an uncompressed block.");

            return 0;

        }

#endif

        DEBUGLOG(5, "ZSTD_compressSubBlock_sequences (bitstreamSize=%zu)", bitstreamSize);

    }

    /* zstd versions <= 1.4.0 mistakenly report error when

     * sequences section body size is less than 3 bytes.

     * Fixed by https://github.com/facebook/zstd/pull/1664.

     * This can happen when the previous sequences section block is compressed

     * with rle mode and the current block's sequences section is compressed

     * with repeat mode where sequences section body size can be 1 byte.

     */

#ifndef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION

    if (op-seqHead < 4) {

        DEBUGLOG(5, "Avoiding bug in zstd decoder in versions <= 1.4.0 by emitting "

                    "an uncompressed block when sequences are < 4 bytes");

        return 0;

    }

#endif

    *entropyWritten = 1;

    return (size_t)(op - ostart);

}

/** ZSTD_compressSubBlock() :

 *  Compresses a single sub-block.

 *  @return : compressed size of the sub-block

 *            Or 0 if it failed to compress. */

static size_t ZSTD_compressSubBlock(const ZSTD_entropyCTables_t* entropy,

                                    const ZSTD_entropyCTablesMetadata_t* entropyMetadata,

                                    const SeqDef* sequences, size_t nbSeq,

                                    const BYTE* literals, size_t litSize,

                                    const BYTE* llCode, const BYTE* mlCode, const BYTE* ofCode,

                                    const ZSTD_CCtx_params* cctxParams,

                                    void* dst, size_t dstCapacity,

                                    const int bmi2,

                                    int writeLitEntropy, int writeSeqEntropy,

                                    int* litEntropyWritten, int* seqEntropyWritten,

                                    U32 lastBlock)

{

    BYTE* const ostart = (BYTE*)dst;

    BYTE* const oend = ostart + dstCapacity;

    BYTE* op = ostart + ZSTD_blockHeaderSize;

    DEBUGLOG(5, "ZSTD_compressSubBlock (litSize=%zu, nbSeq=%zu, writeLitEntropy=%d, writeSeqEntropy=%d, lastBlock=%d)",

                litSize, nbSeq, writeLitEntropy, writeSeqEntropy, lastBlock);

    {   size_t cLitSize = ZSTD_compressSubBlock_literal((const HUF_CElt*)entropy->huf.CTable,

                                                        &entropyMetadata->hufMetadata, literals, litSize,

                                                        op, (size_t)(oend-op),

                                                        bmi2, writeLitEntropy, litEntropyWritten);

        FORWARD_IF_ERROR(cLitSize, "ZSTD_compressSubBlock_literal failed");

        if (cLitSize == 0) return 0;

        op += cLitSize;

    }

    {   size_t cSeqSize = ZSTD_compressSubBlock_sequences(&entropy->fse,

                                                  &entropyMetadata->fseMetadata,

                                                  sequences, nbSeq,

                                                  llCode, mlCode, ofCode,

                                                  cctxParams,

                                                  op, (size_t)(oend-op),

                                                  bmi2, writeSeqEntropy, seqEntropyWritten);

        FORWARD_IF_ERROR(cSeqSize, "ZSTD_compressSubBlock_sequences failed");

        if (cSeqSize == 0) return 0;

        op += cSeqSize;

    }

    /* Write block header */

    {   size_t cSize = (size_t)(op-ostart) - ZSTD_blockHeaderSize;

        U32 const cBlockHeader24 = lastBlock + (((U32)bt_compressed)<<1) + (U32)(cSize << 3);

        MEM_writeLE24(ostart, cBlockHeader24);

    }

    return (size_t)(op-ostart);

}

static size_t ZSTD_estimateSubBlockSize_literal(const BYTE* literals, size_t litSize,

                                                const ZSTD_hufCTables_t* huf,

                                                const ZSTD_hufCTablesMetadata_t* hufMetadata,

                                                void* workspace, size_t wkspSize,

                                                int writeEntropy)

{

    unsigned* const countWksp = (unsigned*)workspace;

    unsigned maxSymbolValue = 255;

    size_t literalSectionHeaderSize = 3; /* Use hard coded size of 3 bytes */

    if (hufMetadata->hType == set_basic) return litSize;

    else if (hufMetadata->hType == set_rle) return 1;

    else if (hufMetadata->hType == set_compressed || hufMetadata->hType == set_repeat) {

        size_t const largest = HIST_count_wksp (countWksp, &maxSymbolValue, (const BYTE*)literals, litSize, workspace, wkspSize);

        if (ZSTD_isError(largest)) return litSize;

        {   size_t cLitSizeEstimate = HUF_estimateCompressedSize((const HUF_CElt*)huf->CTable, countWksp, maxSymbolValue);

            if (writeEntropy) cLitSizeEstimate += hufMetadata->hufDesSize;

            return cLitSizeEstimate + literalSectionHeaderSize;

    }   }

    assert(0); /* impossible */

    return 0;

}

static size_t ZSTD_estimateSubBlockSize_symbolType(SymbolEncodingType_e type,

                        const BYTE* codeTable, unsigned maxCode,

                        size_t nbSeq, const FSE_CTable* fseCTable,

                        const U8* additionalBits,

                        short const* defaultNorm, U32 defaultNormLog, U32 defaultMax,

                        void* workspace, size_t wkspSize)

{

    unsigned* const countWksp = (unsigned*)workspace;

    const BYTE* ctp = codeTable;

    const BYTE* const ctStart = ctp;

    const BYTE* const ctEnd = ctStart + nbSeq;

    size_t cSymbolTypeSizeEstimateInBits = 0;

    unsigned max = maxCode;

    HIST_countFast_wksp(countWksp, &max, codeTable, nbSeq, workspace, wkspSize);  /* can't fail */

    if (type == set_basic) {

        /* We selected this encoding type, so it must be valid. */

        assert(max <= defaultMax);

        cSymbolTypeSizeEstimateInBits = max <= defaultMax

                ? ZSTD_crossEntropyCost(defaultNorm, defaultNormLog, countWksp, max)

                : ERROR(GENERIC);

    } else if (type == set_rle) {

        cSymbolTypeSizeEstimateInBits = 0;

    } else if (type == set_compressed || type == set_repeat) {

        cSymbolTypeSizeEstimateInBits = ZSTD_fseBitCost(fseCTable, countWksp, max);

    }

    if (ZSTD_isError(cSymbolTypeSizeEstimateInBits)) return nbSeq * 10;

    while (ctp < ctEnd) {

        if (additionalBits) cSymbolTypeSizeEstimateInBits += additionalBits[*ctp];

        else cSymbolTypeSizeEstimateInBits += *ctp; /* for offset, offset code is also the number of additional bits */

        ctp++;

    }

    return cSymbolTypeSizeEstimateInBits / 8;

}

static size_t ZSTD_estimateSubBlockSize_sequences(const BYTE* ofCodeTable,

                                                  const BYTE* llCodeTable,

                                                  const BYTE* mlCodeTable,

                                                  size_t nbSeq,

                                                  const ZSTD_fseCTables_t* fseTables,

                                                  const ZSTD_fseCTablesMetadata_t* fseMetadata,

                                                  void* workspace, size_t wkspSize,

                                                  int writeEntropy)

{

    size_t const sequencesSectionHeaderSize = 3; /* Use hard coded size of 3 bytes */

    size_t cSeqSizeEstimate = 0;

    if (nbSeq == 0) return sequencesSectionHeaderSize;

    cSeqSizeEstimate += ZSTD_estimateSubBlockSize_symbolType(fseMetadata->ofType, ofCodeTable, MaxOff,

                                         nbSeq, fseTables->offcodeCTable, NULL,

                                         OF_defaultNorm, OF_defaultNormLog, DefaultMaxOff,

                                         workspace, wkspSize);

    cSeqSizeEstimate += ZSTD_estimateSubBlockSize_symbolType(fseMetadata->llType, llCodeTable, MaxLL,

                                         nbSeq, fseTables->litlengthCTable, LL_bits,

                                         LL_defaultNorm, LL_defaultNormLog, MaxLL,

                                         workspace, wkspSize);

    cSeqSizeEstimate += ZSTD_estimateSubBlockSize_symbolType(fseMetadata->mlType, mlCodeTable, MaxML,

                                         nbSeq, fseTables->matchlengthCTable, ML_bits,

                                         ML_defaultNorm, ML_defaultNormLog, MaxML,

                                         workspace, wkspSize);

    if (writeEntropy) cSeqSizeEstimate += fseMetadata->fseTablesSize;

    return cSeqSizeEstimate + sequencesSectionHeaderSize;

}

typedef struct {

    size_t estLitSize;

    size_t estBlockSize;

} EstimatedBlockSize;

static EstimatedBlockSize ZSTD_estimateSubBlockSize(const BYTE* literals, size_t litSize,

                                        const BYTE* ofCodeTable,

                                        const BYTE* llCodeTable,

                                        const BYTE* mlCodeTable,

                                        size_t nbSeq,

                                        const ZSTD_entropyCTables_t* entropy,

                                        const ZSTD_entropyCTablesMetadata_t* entropyMetadata,

                                        void* workspace, size_t wkspSize,

                                        int writeLitEntropy, int writeSeqEntropy)

{

    EstimatedBlockSize ebs;

    ebs.estLitSize = ZSTD_estimateSubBlockSize_literal(literals, litSize,

                                                        &entropy->huf, &entropyMetadata->hufMetadata,

                                                        workspace, wkspSize, writeLitEntropy);

    ebs.estBlockSize = ZSTD_estimateSubBlockSize_sequences(ofCodeTable, llCodeTable, mlCodeTable,

                                                         nbSeq, &entropy->fse, &entropyMetadata->fseMetadata,

                                                         workspace, wkspSize, writeSeqEntropy);

    ebs.estBlockSize += ebs.estLitSize + ZSTD_blockHeaderSize;

    return ebs;

}

static int ZSTD_needSequenceEntropyTables(ZSTD_fseCTablesMetadata_t const* fseMetadata)

{

    if (fseMetadata->llType == set_compressed || fseMetadata->llType == set_rle)

        return 1;

    if (fseMetadata->mlType == set_compressed || fseMetadata->mlType == set_rle)

        return 1;

    if (fseMetadata->ofType == set_compressed || fseMetadata->ofType == set_rle)

        return 1;

    return 0;

}

static size_t countLiterals(SeqStore_t const* seqStore, const SeqDef* sp, size_t seqCount)

{

    size_t n, total = 0;

    assert(sp != NULL);

    for (n=0; n<seqCount; n++) {

        total += ZSTD_getSequenceLength(seqStore, sp+n).litLength;

    }

    DEBUGLOG(6, "countLiterals for %zu sequences from %p => %zu bytes", seqCount, (const void*)sp, total);

    return total;

}

#define BYTESCALE 256

static size_t sizeBlockSequences(const SeqDef* sp, size_t nbSeqs,

                size_t targetBudget, size_t avgLitCost, size_t avgSeqCost,

                int firstSubBlock)

{

    size_t n, budget = 0, inSize=0;

    /* entropy headers */

    size_t const headerSize = (size_t)firstSubBlock * 120 * BYTESCALE; /* generous estimate */

    assert(firstSubBlock==0 || firstSubBlock==1);

    budget += headerSize;

    /* first sequence => at least one sequence*/

    budget += sp[0].litLength * avgLitCost + avgSeqCost;

    if (budget > targetBudget) return 1;

    inSize = sp[0].litLength + (sp[0].mlBase+MINMATCH);

    /* loop over sequences */

    for (n=1; n<nbSeqs; n++) {

        size_t currentCost = sp[n].litLength * avgLitCost + avgSeqCost;

        budget += currentCost;

        inSize += sp[n].litLength + (sp[n].mlBase+MINMATCH);

        /* stop when sub-block budget is reached */

        if ( (budget > targetBudget)

            /* though continue to expand until the sub-block is deemed compressible */

          && (budget < inSize * BYTESCALE) )

            break;

    }

    return n;

}

/** ZSTD_compressSubBlock_multi() :

 *  Breaks super-block into multiple sub-blocks and compresses them.

 *  Entropy will be written into the first block.

 *  The following blocks use repeat_mode to compress.

 *  Sub-blocks are all compressed, except the last one when beneficial.

 *  @return : compressed size of the super block (which features multiple ZSTD blocks)

 *            or 0 if it failed to compress. */

static size_t ZSTD_compressSubBlock_multi(const SeqStore_t* seqStorePtr,

                            const ZSTD_compressedBlockState_t* prevCBlock,

                            ZSTD_compressedBlockState_t* nextCBlock,

                            const ZSTD_entropyCTablesMetadata_t* entropyMetadata,

                            const ZSTD_CCtx_params* cctxParams,

                                  void* dst, size_t dstCapacity,

                            const void* src, size_t srcSize,

                            const int bmi2, U32 lastBlock,

                            void* workspace, size_t wkspSize)

{

    const SeqDef* const sstart = seqStorePtr->sequencesStart;

    const SeqDef* const send = seqStorePtr->sequences;

    const SeqDef* sp = sstart; /* tracks progresses within seqStorePtr->sequences */

    size_t const nbSeqs = (size_t)(send - sstart);

    const BYTE* const lstart = seqStorePtr->litStart;

    const BYTE* const lend = seqStorePtr->lit;

    const BYTE* lp = lstart;

    size_t const nbLiterals = (size_t)(lend - lstart);

    BYTE const* ip = (BYTE const*)src;

    BYTE const* const iend = ip + srcSize;

    BYTE* const ostart = (BYTE*)dst;

    BYTE* const oend = ostart + dstCapacity;

    BYTE* op = ostart;

    const BYTE* llCodePtr = seqStorePtr->llCode;

    const BYTE* mlCodePtr = seqStorePtr->mlCode;

    const BYTE* ofCodePtr = seqStorePtr->ofCode;

    size_t const minTarget = ZSTD_TARGETCBLOCKSIZE_MIN; /* enforce minimum size, to reduce undesirable side effects */

    size_t const targetCBlockSize = MAX(minTarget, cctxParams->targetCBlockSize);

    int writeLitEntropy = (entropyMetadata->hufMetadata.hType == set_compressed);

    int writeSeqEntropy = 1;

    DEBUGLOG(5, "ZSTD_compressSubBlock_multi (srcSize=%u, litSize=%u, nbSeq=%u)",

               (unsigned)srcSize, (unsigned)(lend-lstart), (unsigned)(send-sstart));

        /* let's start by a general estimation for the full block */

    if (nbSeqs > 0) {

        EstimatedBlockSize const ebs =

                ZSTD_estimateSubBlockSize(lp, nbLiterals,

                                        ofCodePtr, llCodePtr, mlCodePtr, nbSeqs,

                                        &nextCBlock->entropy, entropyMetadata,

                                        workspace, wkspSize,

                                        writeLitEntropy, writeSeqEntropy);

        /* quick estimation */

        size_t const avgLitCost = nbLiterals ? (ebs.estLitSize * BYTESCALE) / nbLiterals : BYTESCALE;

        size_t const avgSeqCost = ((ebs.estBlockSize - ebs.estLitSize) * BYTESCALE) / nbSeqs;

        const size_t nbSubBlocks = MAX((ebs.estBlockSize + (targetCBlockSize/2)) / targetCBlockSize, 1);

        size_t n, avgBlockBudget, blockBudgetSupp=0;

        avgBlockBudget = (ebs.estBlockSize * BYTESCALE) / nbSubBlocks;

        DEBUGLOG(5, "estimated fullblock size=%u bytes ; avgLitCost=%.2f ; avgSeqCost=%.2f ; targetCBlockSize=%u, nbSubBlocks=%u ; avgBlockBudget=%.0f bytes",

                    (unsigned)ebs.estBlockSize, (double)avgLitCost/BYTESCALE, (double)avgSeqCost/BYTESCALE,

                    (unsigned)targetCBlockSize, (unsigned)nbSubBlocks, (double)avgBlockBudget/BYTESCALE);

        /* simplification: if estimates states that the full superblock doesn't compress, just bail out immediately

         * this will result in the production of a single uncompressed block covering @srcSize.*/

        if (ebs.estBlockSize > srcSize) return 0;

        /* compress and write sub-blocks */

        assert(nbSubBlocks>0);

        for (n=0; n < nbSubBlocks-1; n++) {

            /* determine nb of sequences for current sub-block + nbLiterals from next sequence */

            size_t const seqCount = sizeBlockSequences(sp, (size_t)(send-sp),

                                        avgBlockBudget + blockBudgetSupp, avgLitCost, avgSeqCost, n==0);

            /* if reached last sequence : break to last sub-block (simplification) */

            assert(seqCount <= (size_t)(send-sp));

            if (sp + seqCount == send) break;

            assert(seqCount > 0);

            /* compress sub-block */

            {   int litEntropyWritten = 0;

                int seqEntropyWritten = 0;

                size_t litSize = countLiterals(seqStorePtr, sp, seqCount);

                const size_t decompressedSize =

                        ZSTD_seqDecompressedSize(seqStorePtr, sp, seqCount, litSize, 0);

                size_t const cSize = ZSTD_compressSubBlock(&nextCBlock->entropy, entropyMetadata,

                                                sp, seqCount,

                                                lp, litSize,

                                                llCodePtr, mlCodePtr, ofCodePtr,

                                                cctxParams,

                                                op, (size_t)(oend-op),

                                                bmi2, writeLitEntropy, writeSeqEntropy,

                                                &litEntropyWritten, &seqEntropyWritten,

                                                0);

                FORWARD_IF_ERROR(cSize, "ZSTD_compressSubBlock failed");

                /* check compressibility, update state components */

                if (cSize > 0 && cSize < decompressedSize) {

                    DEBUGLOG(5, "Committed sub-block compressing %u bytes => %u bytes",

                                (unsigned)decompressedSize, (unsigned)cSize);

                    assert(ip + decompressedSize <= iend);

                    ip += decompressedSize;

                    lp += litSize;

                    op += cSize;

                    llCodePtr += seqCount;

                    mlCodePtr += seqCount;

                    ofCodePtr += seqCount;

                    /* Entropy only needs to be written once */

                    if (litEntropyWritten) {

                        writeLitEntropy = 0;

                    }

                    if (seqEntropyWritten) {

                        writeSeqEntropy = 0;

                    }

                    sp += seqCount;

                    blockBudgetSupp = 0;

            }   }

            /* otherwise : do not compress yet, coalesce current sub-block with following one */

        }

    } /* if (nbSeqs > 0) */

    /* write last block */

    DEBUGLOG(5, "Generate last sub-block: %u sequences remaining", (unsigned)(send - sp));

    {   int litEntropyWritten = 0;

        int seqEntropyWritten = 0;

        size_t litSize = (size_t)(lend - lp);

        size_t seqCount = (size_t)(send - sp);

        const size_t decompressedSize =

                ZSTD_seqDecompressedSize(seqStorePtr, sp, seqCount, litSize, 1);

        size_t const cSize = ZSTD_compressSubBlock(&nextCBlock->entropy, entropyMetadata,

                                            sp, seqCount,

                                            lp, litSize,

                                            llCodePtr, mlCodePtr, ofCodePtr,

                                            cctxParams,

                                            op, (size_t)(oend-op),

                                            bmi2, writeLitEntropy, writeSeqEntropy,

                                            &litEntropyWritten, &seqEntropyWritten,

                                            lastBlock);

        FORWARD_IF_ERROR(cSize, "ZSTD_compressSubBlock failed");

        /* update pointers, the nb of literals borrowed from next sequence must be preserved */

        if (cSize > 0 && cSize < decompressedSize) {

            DEBUGLOG(5, "Last sub-block compressed %u bytes => %u bytes",

                        (unsigned)decompressedSize, (unsigned)cSize);

            assert(ip + decompressedSize <= iend);

            ip += decompressedSize;

            lp += litSize;

            op += cSize;

            llCodePtr += seqCount;

            mlCodePtr += seqCount;

            ofCodePtr += seqCount;

            /* Entropy only needs to be written once */

            if (litEntropyWritten) {

                writeLitEntropy = 0;

            }

            if (seqEntropyWritten) {

                writeSeqEntropy = 0;

            }

            sp += seqCount;

        }

    }

    if (writeLitEntropy) {

        DEBUGLOG(5, "Literal entropy tables were never written");

        ZSTD_memcpy(&nextCBlock->entropy.huf, &prevCBlock->entropy.huf, sizeof(prevCBlock->entropy.huf));

    }

    if (writeSeqEntropy && ZSTD_needSequenceEntropyTables(&entropyMetadata->fseMetadata)) {

        /* If we haven't written our entropy tables, then we've violated our contract and

         * must emit an uncompressed block.

         */

        DEBUGLOG(5, "Sequence entropy tables were never written => cancel, emit an uncompressed block");

        return 0;

    }

    if (ip < iend) {

        /* some data left : last part of the block sent uncompressed */

        size_t const rSize = (size_t)((iend - ip));

        size_t const cSize = ZSTD_noCompressBlock(op, (size_t)(oend - op), ip, rSize, lastBlock);

        DEBUGLOG(5, "Generate last uncompressed sub-block of %u bytes", (unsigned)(rSize));

        FORWARD_IF_ERROR(cSize, "ZSTD_noCompressBlock failed");

        assert(cSize != 0);

        op += cSize;

        /* We have to regenerate the repcodes because we've skipped some sequences */

        if (sp < send) {

            const SeqDef* seq;

            Repcodes_t rep;

            ZSTD_memcpy(&rep, prevCBlock->rep, sizeof(rep));

            for (seq = sstart; seq < sp; ++seq) {

                ZSTD_updateRep(rep.rep, seq->offBase, ZSTD_getSequenceLength(seqStorePtr, seq).litLength == 0);

            }

            ZSTD_memcpy(nextCBlock->rep, &rep, sizeof(rep));

        }

    }

    DEBUGLOG(5, "ZSTD_compressSubBlock_multi compressed all subBlocks: total compressed size = %u",

                (unsigned)(op-ostart));

    return (size_t)(op-ostart);

}

size_t ZSTD_compressSuperBlock(ZSTD_CCtx* zc,

                               void* dst, size_t dstCapacity,

                               const void* src, size_t srcSize,

                               unsigned lastBlock)

{

    ZSTD_entropyCTablesMetadata_t entropyMetadata;

    FORWARD_IF_ERROR(ZSTD_buildBlockEntropyStats(&zc->seqStore,

          &zc->blockState.prevCBlock->entropy,

          &zc->blockState.nextCBlock->entropy,

          &zc->appliedParams,

          &entropyMetadata,

          zc->tmpWorkspace, zc->tmpWkspSize /* statically allocated in resetCCtx */), "");

    return ZSTD_compressSubBlock_multi(&zc->seqStore,

            zc->blockState.prevCBlock,

            zc->blockState.nextCBlock,

            &entropyMetadata,

            &zc->appliedParams,

            dst, dstCapacity,

            src, srcSize,

            zc->bmi2, lastBlock,

            zc->tmpWorkspace, zc->tmpWkspSize /* statically allocated in resetCCtx */);

}