Messages in this thread | | | Date | Mon, 1 Nov 2004 12:44:35 -0800 (PST) | From | dean gaudet <> | Subject | Re: [rc4-amd64] RC4 optimized for AMD64 |
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On Mon, 1 Nov 2004, Marc Bevand wrote:
> I have just published a small paper about optimizing RC4 for > AMD64 (x86-64). A working implementation is also provided: > > http://epita.fr/~bevand_m/papers/rc4-amd64.html > > Kernel people may be interested given the fact that Linux > already implements RC4.
you've made a non-portable flags assumption:
> dec %r11b > ror $8, %r8 # (ror does not change ZF) > jnz 1b
the contents of ZF are undefined after a rotation... most importantly they differ between p4 (ZF is set according to result) and k8 (ZF unchanged).
do you really measure a perf improvement from this assumption? note that p4 would prefer "sub $1, %r11b" here instead of dec... but the difference is likely minimal.
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