You are calculating array offsets over and over. The fast way to do this in C is more like: 

    int len;
    char* pBeg= SvPV(...,len);
    char* pSrc= pBeg + len;
    char* pDst= SvPV(....) + len;
    while(  pBeg <= pSrc  ) {
        if(  ! *pDst  ) {
            *pDst= *pSrc;
        }
        --pSrc;
        --pDst;
    }

[download]

- tye        

In reply to Re^3: Challenge: CPU-optimized byte-wise or-equals (for a meter of beer) (addr math) by tye
in thread Challenge: CPU-optimized byte-wise or-equals (for a meter of beer) by dragonchild

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