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ext/zstd/lib/common/entropy_common.c  view on Meta::CPAN

            remaining -= count < 0 ? -count : count;   /* -1 means +1 */
            normalizedCounter[charnum++] = (short)count;
            previous0 = !count;
            while (remaining < threshold) {
                nbBits--;
                threshold >>= 1;
            }

            if ((ip <= iend-7) || (ip + (bitCount>>3) <= iend-4)) {
                ip += bitCount>>3;
                bitCount &= 7;
            } else {
                bitCount -= (int)(8 * (iend - 4 - ip));
                ip = iend - 4;
            }
            bitStream = MEM_readLE32(ip) >> (bitCount & 31);
    }   }   /* while ((remaining>1) & (charnum<=*maxSVPtr)) */
    if (remaining != 1) return ERROR(corruption_detected);
    if (bitCount > 32) return ERROR(corruption_detected);
    *maxSVPtr = charnum-1;

    ip += (bitCount+7)>>3;
    return ip-istart;
}


/*! HUF_readStats() :
    Read compact Huffman tree, saved by HUF_writeCTable().
    `huffWeight` is destination buffer.
    `rankStats` is assumed to be a table of at least HUF_TABLELOG_MAX U32.
    @return : size read from `src` , or an error Code .
    Note : Needed by HUF_readCTable() and HUF_readDTableX?() .
*/
size_t HUF_readStats(BYTE* huffWeight, size_t hwSize, U32* rankStats,
                     U32* nbSymbolsPtr, U32* tableLogPtr,
                     const void* src, size_t srcSize)
{
    U32 weightTotal;
    const BYTE* ip = (const BYTE*) src;
    size_t iSize;
    size_t oSize;

    if (!srcSize) return ERROR(srcSize_wrong);
    iSize = ip[0];
    /* memset(huffWeight, 0, hwSize);   *//* is not necessary, even though some analyzer complain ... */

    if (iSize >= 128) {  /* special header */
        oSize = iSize - 127;
        iSize = ((oSize+1)/2);
        if (iSize+1 > srcSize) return ERROR(srcSize_wrong);
        if (oSize >= hwSize) return ERROR(corruption_detected);
        ip += 1;
        {   U32 n;
            for (n=0; n<oSize; n+=2) {
                huffWeight[n]   = ip[n/2] >> 4;
                huffWeight[n+1] = ip[n/2] & 15;
    }   }   }
    else  {   /* header compressed with FSE (normal case) */
        FSE_DTable fseWorkspace[FSE_DTABLE_SIZE_U32(6)];  /* 6 is max possible tableLog for HUF header (maybe even 5, to be tested) */
        if (iSize+1 > srcSize) return ERROR(srcSize_wrong);
        oSize = FSE_decompress_wksp(huffWeight, hwSize-1, ip+1, iSize, fseWorkspace, 6);   /* max (hwSize-1) values decoded, as last one is implied */
        if (FSE_isError(oSize)) return oSize;
    }

    /* collect weight stats */
    memset(rankStats, 0, (HUF_TABLELOG_MAX + 1) * sizeof(U32));
    weightTotal = 0;
    {   U32 n; for (n=0; n<oSize; n++) {
            if (huffWeight[n] >= HUF_TABLELOG_MAX) return ERROR(corruption_detected);
            rankStats[huffWeight[n]]++;
            weightTotal += (1 << huffWeight[n]) >> 1;
    }   }
    if (weightTotal == 0) return ERROR(corruption_detected);

    /* get last non-null symbol weight (implied, total must be 2^n) */
    {   U32 const tableLog = BIT_highbit32(weightTotal) + 1;
        if (tableLog > HUF_TABLELOG_MAX) return ERROR(corruption_detected);
        *tableLogPtr = tableLog;
        /* determine last weight */
        {   U32 const total = 1 << tableLog;
            U32 const rest = total - weightTotal;
            U32 const verif = 1 << BIT_highbit32(rest);
            U32 const lastWeight = BIT_highbit32(rest) + 1;
            if (verif != rest) return ERROR(corruption_detected);    /* last value must be a clean power of 2 */
            huffWeight[oSize] = (BYTE)lastWeight;
            rankStats[lastWeight]++;
    }   }

    /* check tree construction validity */
    if ((rankStats[1] < 2) || (rankStats[1] & 1)) return ERROR(corruption_detected);   /* by construction : at least 2 elts of rank 1, must be even */

    /* results */
    *nbSymbolsPtr = (U32)(oSize+1);
    return iSize+1;
}