Function HUF_readCTable

freebsd/contrib/openzfs/module/zstd/lib/zstd.c:8514–8562

size_t HUF_readCTable (HUF_CElt* CTable, unsigned* maxSymbolValuePtr, const void* src, size_t srcSize, unsigned* hasZeroWeights)
{
    BYTE huffWeight[HUF_SYMBOLVALUE_MAX + 1];   /* init not required, even though some static analyzer may complain */
    U32 rankVal[HUF_TABLELOG_ABSOLUTEMAX + 1];   /* large enough for values from 0 to 16 */
    U32 tableLog = 0;
    U32 nbSymbols = 0;

    /* get symbol weights */
    CHECK_V_F(readSize, HUF_readStats(huffWeight, HUF_SYMBOLVALUE_MAX+1, rankVal, &nbSymbols, &tableLog, src, srcSize));

    /* check result */
    if (tableLog > HUF_TABLELOG_MAX) return ERROR(tableLog_tooLarge);
    if (nbSymbols > *maxSymbolValuePtr+1) return ERROR(maxSymbolValue_tooSmall);

    /* Prepare base value per rank */
    {   U32 n, nextRankStart = 0;
        for (n=1; n<=tableLog; n++) {
            U32 current = nextRankStart;
            nextRankStart += (rankVal[n] << (n-1));
            rankVal[n] = current;
    }   }

    /* fill nbBits */
    *hasZeroWeights = 0;
    {   U32 n; for (n=0; n<nbSymbols; n++) {
            const U32 w = huffWeight[n];
            *hasZeroWeights |= (w == 0);
            CTable[n].nbBits = (BYTE)(tableLog + 1 - w) & -(w != 0);
    }   }

    /* fill val */
    {   U16 nbPerRank[HUF_TABLELOG_MAX+2]  = {0};  /* support w=0=>n=tableLog+1 */
        U16 valPerRank[HUF_TABLELOG_MAX+2] = {0};
        { U32 n; for (n=0; n<nbSymbols; n++) nbPerRank[CTable[n].nbBits]++; }
        /* determine stating value per rank */
        valPerRank[tableLog+1] = 0;   /* for w==0 */
        {   U16 min = 0;
            U32 n; for (n=tableLog; n>0; n--) {  /* start at n=tablelog <-> w=1 */
                valPerRank[n] = min;     /* get starting value within each rank */
                min += nbPerRank[n];
                min >>= 1;
        }   }
        /* assign value within rank, symbol order */
        { U32 n; for (n=0; n<nbSymbols; n++) CTable[n].val = valPerRank[CTable[n].nbBits]++; }
    }

    *maxSymbolValuePtr = nbSymbols - 1;
    return readSize;
}

U32 HUF_getNbBits(const void* symbolTable, U32 symbolValue)
{