[RC5] AMD 3DNow enhancement?

Bruce Ford b.ford at qut.edu.au
Wed Sep 16 12:48:51 EDT 1998


>     The use of FPU code to crack RC5 has been suggested a couple of times
>     on this list.  I only know of one attempt, by Bruce Ford to implement
>     a core using this hardware.  I criticized it for using non-pairable
>     FPU instructions (i.e., the normal integer core couldn't pair
>     instructions with a low-throughput FPU extension).

A criticism which was unfounded by the way.

The Pentium, which was the processor being discussed, uses the U pipe for 
all FPU instructions except for FXCH which is V pipe.  When the manuals talk 
of "pairability" of an FPU instruction it is soley wrt the FXCH instruction.

As far as decoding is concerned, no integer instructions pair with FPU 
instructions.  They should execute in parallel but to see what happens in 
practice please refer to the earlier discussion.

The FPU code to do one "cycle" of round 1 of the RC5 algorithm may be 
found at http://altern.org/rguyom/fputest.asm.  Feel free to modify this in any 
way which would make it useful.

Bruce Ford

--
To unsubscribe, send 'unsubscribe rc5' to majordomo at lists.distributed.net
rc5-digest subscribers replace rc5 with rc5-digest

--
To unsubscribe, send 'unsubscribe rc5' to majordomo at lists.distributed.net
rc5-digest subscribers replace rc5 with rc5-digest



More information about the rc5 mailing list