I am sure that dd is faster than XS, but here is an XS snippet (although I am not sure about the signed/unsigned or if I need to actually detect unicode bytes, assuming normal 8 bit bytes): 

char *
swapstring(str)
        SV *str
      INIT:
        STRLEN len;
        char* buf = SvPVbyte(str, len);
    CODE:

        while(len--){
        asm("ror $4,%1" : "+r" (buf[len]));
        }
        RETVAL = buf;
    OUTPUT:
        RETVAL

[download]
the ror idea comes from stackoverflow.
edit: Doh! Nevermind, this produces 56781234 -> 12345678, which is not what was asked.

In reply to Re: Fastest byteswap (little endian to big endian (eg. 34127856 -> 12345678) by FreeBeerReekingMonk
in thread Fastest byteswap (little endian to big endian (eg. 34127856 -> 12345678) by james28909

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