[RC5] Re: CPU speeds
b.ford at qut.edu.au
Thu Jun 10 12:07:00 EDT 1999
> the AMD K6-2 with 350 Mhz produces only 550 KiloKeys / s. You say, that
> all the code of the d.net client is integer code. I thought AMD is in
> Integer code as fast or faster than Intel.
> Or it is just normal, when his AMD is so slow?
Normal. Clock count on the K6/K6-2 is ~610 clocks per key.
It is mainly due to the vector decode of the ROL instruction; ROL
being very important in the RC5 algorithm.
Presumably a ROL reg,cl becomes:
alu mov temp1,reg
alu mov temp2,ecx
alux shl reg,cl
alu neg temp2
alux shr temp1,temp2
alu or reg,temp1
ie. It takes 4 clocks though there are pairing opportunities in the
(<RANT> The above is all guess work. Wish AMD would just tell
us what the vector decodes are and whether they all end up in the
X pipe or just the shifts. </RANT>)
On Intel PPro/PII/PIII the ROL instruction is 1 clock pairable.
There is some hope that on the K6-2 the clock count can be
brought down to similar to a P5-MMX (464.5 clocks/key) using a
variant of the RC5-MMX code. However a recent contest between
two programmers was unable to do so.
Feel free to play with the cores available at
Bruce Ford b.ford at qut.edu.au
Teaching and Learning Support Services Ph: +61 7 3864 1178
Queensland University of Technology
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