Re: No difference on my machine


Nathan and Frank in discussion about:

[Comparing 'xor eax, eax' with 'mov eax, 0' from the CLAX thread:]

Good one, Nathan! No difference on my P4, that I can notice. Replacing
"dec" with "sub" gives a big speedup, though...

Just tried with "sub" and it took a second longer in all but one run.

There shouldn't be a difference on any x86 except that xor eax,eax
is shorter and this will affect the code alignment after it.
So a replacment may sometimes (like the example in CLAX) slow down.

I cannot confirm that add/sub-1 is any faster than inc/dec on AMDs.
It again is of different size and may therefore affect timing like above.

__
wolfgang



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