static int LZ4_compress_destSize_generic()

in Sources/aliyun-log-c-sdk/log_lz4.c [722:891]

• 125 lines of code
• 27 McCabe index (conditional complexity)

static int LZ4_compress_destSize_generic(
        void* const ctx,
        const char* const src,
        char* const dst,
        int*  const srcSizePtr,
        const int targetDstSize,
        const tableType_t tableType)
{
    const BYTE* ip = (const BYTE*) src;
    const BYTE* base = (const BYTE*) src;
    const BYTE* lowLimit = (const BYTE*) src;
    const BYTE* anchor = ip;
    const BYTE* const iend = ip + *srcSizePtr;
    const BYTE* const mflimit = iend - LOG_MFLIMIT;
    const BYTE* const matchlimit = iend - LOG_LASTLITERALS;

    BYTE* op = (BYTE*) dst;
    BYTE* const oend = op + targetDstSize;
    BYTE* const oMaxLit = op + targetDstSize - 2 /* offset */ - 8 /* because 8+LOG_MINMATCH==LOG_MFLIMIT */ - 1 /* token */;
    BYTE* const oMaxMatch = op + targetDstSize - (LOG_LASTLITERALS + 1 /* token */);
    BYTE* const oMaxSeq = oMaxLit - 1 /* token */;

    U32 forwardH;


    /* Init conditions */
    if (targetDstSize < 1) return 0;                                     /* Impossible to store anything */
    if ((U32)*srcSizePtr > (U32)LOG_LZ4_MAX_INPUT_SIZE) return 0;            /* Unsupported input size, too large (or negative) */
    if ((tableType == byU16) && (*srcSizePtr>=LZ4_64Klimit)) return 0;   /* Size too large (not within 64K limit) */
    if (*srcSizePtr<LOG_LZ4_minLength) goto _last_literals;                  /* Input too small, no compression (all literals) */

    /* First Byte */
    *srcSizePtr = 0;
    LZ4_putPosition(ip, ctx, tableType, base);
    ip++; forwardH = LZ4_hashPosition(ip, tableType);

    /* Main Loop */
    for ( ; ; )
    {
        const BYTE* match;
        BYTE* token;
        {
            const BYTE* forwardIp = ip;
            unsigned step = 1;
            unsigned searchMatchNb = 1 << LZ4_skipTrigger;

            /* Find a match */
            do {
                U32 h = forwardH;
                ip = forwardIp;
                forwardIp += step;
                step = (searchMatchNb++ >> LZ4_skipTrigger);

                if (unlikely(forwardIp > mflimit))
                    goto _last_literals;

                match = LZ4_getPositionOnHash(h, ctx, tableType, base);
                forwardH = LZ4_hashPosition(forwardIp, tableType);
                LZ4_putPositionOnHash(ip, h, ctx, tableType, base);

            } while ( ((tableType==byU16) ? 0 : (match + LOG_MAX_DISTANCE < ip))
                      || (LZ4_read32(match) != LZ4_read32(ip)) );
        }

        /* Catch up */
        while ((ip>anchor) && (match > lowLimit) && (unlikely(ip[-1]==match[-1]))) { ip--; match--; }

        {
            /* Encode Literal length */
            unsigned litLength = (unsigned)(ip - anchor);
            token = op++;
            if (op + ((litLength+240)/255) + litLength > oMaxLit)
            {
                /* Not enough space for a last match */
                op--;
                goto _last_literals;
            }
            if (litLength>=LOG_RUN_MASK)
            {
                unsigned len = litLength - LOG_RUN_MASK;
                *token=(LOG_RUN_MASK<<LOG_ML_BITS);
                for(; len >= 255 ; len-=255) *op++ = 255;
                *op++ = (BYTE)len;
            }
            else *token = (BYTE)(litLength<<LOG_ML_BITS);

            /* Copy Literals */
            LZ4_wildCopy(op, anchor, op+litLength);
            op += litLength;
        }

        _next_match:
        /* Encode Offset */
        LZ4_writeLE16(op, (U16)(ip-match)); op+=2;

        /* Encode MatchLength */
        {
            size_t matchLength;

            matchLength = LZ4_count(ip+LOG_MINMATCH, match+LOG_MINMATCH, matchlimit);

            if (op + ((matchLength+240)/255) > oMaxMatch)
            {
                /* Match description too long : reduce it */
                matchLength = (15-1) + (oMaxMatch-op) * 255;
            }
            //printf("offset %5i, matchLength%5i \n", (int)(ip-match), matchLength + LOG_MINMATCH);
            ip += LOG_MINMATCH + matchLength;

            if (matchLength>=LOG_ML_MASK)
            {
                *token += LOG_ML_MASK;
                matchLength -= LOG_ML_MASK;
                while (matchLength >= 255) { matchLength-=255; *op++ = 255; }
                *op++ = (BYTE)matchLength;
            }
            else *token += (BYTE)(matchLength);
        }

        anchor = ip;

        /* Test end of block */
        if (ip > mflimit) break;
        if (op > oMaxSeq) break;

        /* Fill table */
        LZ4_putPosition(ip-2, ctx, tableType, base);

        /* Test next position */
        match = LZ4_getPosition(ip, ctx, tableType, base);
        LZ4_putPosition(ip, ctx, tableType, base);
        if ( (match+LOG_MAX_DISTANCE>=ip)
             && (LZ4_read32(match)==LZ4_read32(ip)) )
        { token=op++; *token=0; goto _next_match; }

        /* Prepare next loop */
        forwardH = LZ4_hashPosition(++ip, tableType);
    }

    _last_literals:
    /* Encode Last Literals */
    {
        size_t lastRunSize = (size_t)(iend - anchor);
        if (op + 1 /* token */ + ((lastRunSize+240)/255) /* litLength */ + lastRunSize /* literals */ > oend)
        {
            /* adapt lastRunSize to fill 'dst' */
            lastRunSize  = (oend-op) - 1;
            lastRunSize -= (lastRunSize+240)/255;
        }
        ip = anchor + lastRunSize;

        if (lastRunSize >= LOG_RUN_MASK)
        {
            size_t accumulator = lastRunSize - LOG_RUN_MASK;
            *op++ = LOG_RUN_MASK << LOG_ML_BITS;
            for(; accumulator >= 255 ; accumulator-=255) *op++ = 255;
            *op++ = (BYTE) accumulator;
        }
        else
        {
            *op++ = (BYTE)(lastRunSize<<LOG_ML_BITS);
        }
        memcpy(op, anchor, lastRunSize);
        op += lastRunSize;
    }

    /* End */
    *srcSizePtr = (int) (((const char*)ip)-src);
    return (int) (((char*)op)-dst);
}