quote:Original post by samgzman Even if you could run SSE2 and 3DNOW code together, you can''t run them in parallel straight up. So the point is defeated just go with SSE2.
damn amd''S they need HT so one thread can use 3dnow and the other sse :D, erhm do pentiums with HT have 2 SSE2 paths? or do they have to share one SSE2?
IFooBar: Intel has apparently adopted AMD''s extended CPUID convention, just to avoid conflict. No Intel CPU I know of has 3DNow! - pity.
Narcist: > SSE is superior to 3dnow anyway, 3dnow works on 2 floats at a time, SSE works on 4 floats I prefer 3DNow - nicer instructions, and 4 floats/op is usually ''too big'' (4.4 dot product, the first multiply is great, then you''re just shuffling stuff around).
SSE/3DNow processor support is correct, except SSE - that''s only available on the Intel side starting with PIII. The problem with runtime conditional code is that it carries some overhead with it. Best to rewrite the whole algorithm in 3DNow, vs. splitting at the sqrt / dotproduct level.
> if i detect 3dnow and sse (and maybe sse2) can i use them at the same time? Yes! I did this in my CLOD refine code (crazy-optimized), because of course 8 registers wasn''t enough. You still have the limit of one fadd and 1 fmul op / clock though.
HT CPUs share execution resources (hoping that one ''processor'' is not using all of them) - this hurts optimized code, obviously.
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