[RC5] Athlon core contribution

Jonas Maebe jonas.maebe at rug.ac.be
Fri Dec 6 17:12:18 EST 2002

On vrijdag, dec 6, 2002, at 16:59 Europe/Brussels, Stephen Garrison 

> I would disagree because I believe that the change from a 64-bit key 
> to a
> 72-bit key may result in significant difficulties when trying to
> effectively use the AltiVec unit since each 128-bit Altivec register 
> will
> now only be able to hold one key.

Doesn't the rc5 altivec core use bitslicing, ie. it processes n bits of 
(128/n) keys at once? (I don't know how big n is) Going to a larger 
keysize still means that you need more iterations of course, but not 
that you need massive changes (except maybe in scheduling those 
iterations optimally). After all, altivec cannot handle vectors with 64 
bit elements either (only 32, 16 and 8 bit ones are supported), so if 
the whole key had to be handled at once, it wouldn't have worked for 
rc5-64 either.


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