static size_t FSE_readNCount()

in lib/legacy/zstd_v02.c [1178:1288]
105 lines of code
18 McCabe index (conditional complexity)

static size_t FSE_readNCount (short* normalizedCounter, unsigned* maxSVPtr, unsigned* tableLogPtr,
                 const void* headerBuffer, size_t hbSize)
{
    const BYTE* const istart = (const BYTE*) headerBuffer;
    const BYTE* const iend = istart + hbSize;
    const BYTE* ip = istart;
    int nbBits;
    int remaining;
    int threshold;
    U32 bitStream;
    int bitCount;
    unsigned charnum = 0;
    int previous0 = 0;

    if (hbSize < 4) return ERROR(srcSize_wrong);
    bitStream = MEM_readLE32(ip);
    nbBits = (bitStream & 0xF) + FSE_MIN_TABLELOG;   /* extract tableLog */
    if (nbBits > FSE_TABLELOG_ABSOLUTE_MAX) return ERROR(tableLog_tooLarge);
    bitStream >>= 4;
    bitCount = 4;
    *tableLogPtr = nbBits;
    remaining = (1<<nbBits)+1;
    threshold = 1<<nbBits;
    nbBits++;

    while ((remaining>1) && (charnum<=*maxSVPtr))
    {
        if (previous0)
        {
            unsigned n0 = charnum;
            while ((bitStream & 0xFFFF) == 0xFFFF)
            {
                n0+=24;
                if (ip < iend-5)
                {
                    ip+=2;
                    bitStream = MEM_readLE32(ip) >> bitCount;
                }
                else
                {
                    bitStream >>= 16;
                    bitCount+=16;
                }
            }
            while ((bitStream & 3) == 3)
            {
                n0+=3;
                bitStream>>=2;
                bitCount+=2;
            }
            n0 += bitStream & 3;
            bitCount += 2;
            if (n0 > *maxSVPtr) return ERROR(maxSymbolValue_tooSmall);
            while (charnum < n0) normalizedCounter[charnum++] = 0;
            if ((ip <= iend-7) || (ip + (bitCount>>3) <= iend-4))
            {
                ip += bitCount>>3;
                bitCount &= 7;
                bitStream = MEM_readLE32(ip) >> bitCount;
            }
            else
                bitStream >>= 2;
        }
        {
            const short max = (short)((2*threshold-1)-remaining);
            short count;

            if ((bitStream & (threshold-1)) < (U32)max)
            {
                count = (short)(bitStream & (threshold-1));
                bitCount   += nbBits-1;
            }
            else
            {
                count = (short)(bitStream & (2*threshold-1));
                if (count >= threshold) count -= max;
                bitCount   += nbBits;
            }

            count--;   /* extra accuracy */
            remaining -= FSE_abs(count);
            normalizedCounter[charnum++] = 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);
            }
        }
    }
    if (remaining != 1) return ERROR(GENERIC);
    *maxSVPtr = charnum-1;

    ip += (bitCount+7)>>3;
    if ((size_t)(ip-istart) > hbSize) return ERROR(srcSize_wrong);
    return ip-istart;
}