static size_t ZSTD_compressSubBlock_multi()

in lib/compress/zstd_compress_superblock.c [431:555]

• 113 lines of code
• 17 McCabe index (conditional complexity)

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;
    const BYTE* const lstart = seqStorePtr->litStart;
    const BYTE* const lend = seqStorePtr->lit;
    const BYTE* lp = 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 targetCBlockSize = cctxParams->targetCBlockSize;
    size_t litSize, seqCount;
    int writeLitEntropy = entropyMetadata->hufMetadata.hType == set_compressed;
    int writeSeqEntropy = 1;
    int lastSequence = 0;

    DEBUGLOG(5, "ZSTD_compressSubBlock_multi (litSize=%u, nbSeq=%u)",
                (unsigned)(lend-lp), (unsigned)(send-sstart));

    litSize = 0;
    seqCount = 0;
    do {
        size_t cBlockSizeEstimate = 0;
        if (sstart == send) {
            lastSequence = 1;
        } else {
            const seqDef* const sequence = sp + seqCount;
            lastSequence = sequence == send - 1;
            litSize += ZSTD_getSequenceLength(seqStorePtr, sequence).litLength;
            seqCount++;
        }
        if (lastSequence) {
            assert(lp <= lend);
            assert(litSize <= (size_t)(lend - lp));
            litSize = (size_t)(lend - lp);
        }
        /* I think there is an optimization opportunity here.
         * Calling ZSTD_estimateSubBlockSize for every sequence can be wasteful
         * since it recalculates estimate from scratch.
         * For example, it would recount literal distribution and symbol codes every time.
         */
        cBlockSizeEstimate = ZSTD_estimateSubBlockSize(lp, litSize, ofCodePtr, llCodePtr, mlCodePtr, seqCount,
                                                       &nextCBlock->entropy, entropyMetadata,
                                                       workspace, wkspSize, writeLitEntropy, writeSeqEntropy);
        if (cBlockSizeEstimate > targetCBlockSize || lastSequence) {
            int litEntropyWritten = 0;
            int seqEntropyWritten = 0;
            const size_t decompressedSize = ZSTD_seqDecompressedSize(seqStorePtr, sp, seqCount, litSize, lastSequence);
            const size_t cSize = ZSTD_compressSubBlock(&nextCBlock->entropy, entropyMetadata,
                                                       sp, seqCount,
                                                       lp, litSize,
                                                       llCodePtr, mlCodePtr, ofCodePtr,
                                                       cctxParams,
                                                       op, oend-op,
                                                       bmi2, writeLitEntropy, writeSeqEntropy,
                                                       &litEntropyWritten, &seqEntropyWritten,
                                                       lastBlock && lastSequence);
            FORWARD_IF_ERROR(cSize, "ZSTD_compressSubBlock failed");
            if (cSize > 0 && cSize < decompressedSize) {
                DEBUGLOG(5, "Committed the sub-block");
                assert(ip + decompressedSize <= iend);
                ip += decompressedSize;
                sp += seqCount;
                lp += litSize;
                op += cSize;
                llCodePtr += seqCount;
                mlCodePtr += seqCount;
                ofCodePtr += seqCount;
                litSize = 0;
                seqCount = 0;
                /* Entropy only needs to be written once */
                if (litEntropyWritten) {
                    writeLitEntropy = 0;
                }
                if (seqEntropyWritten) {
                    writeSeqEntropy = 0;
                }
            }
        }
    } while (!lastSequence);
    if (writeLitEntropy) {
        DEBUGLOG(5, "ZSTD_compressSubBlock_multi has literal entropy tables unwritten");
        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, "ZSTD_compressSubBlock_multi has sequence entropy tables unwritten");
        return 0;
    }
    if (ip < iend) {
        size_t const cSize = ZSTD_noCompressBlock(op, oend - op, ip, iend - ip, lastBlock);
        DEBUGLOG(5, "ZSTD_compressSubBlock_multi last sub-block uncompressed, %zu bytes", (size_t)(iend - ip));
        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) {
            seqDef const* 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");
    return op-ostart;
}