Author: Gerd Isenberg
Date: 13:25:26 01/31/02
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On January 31, 2002 at 15:25:55, Severi Salminen wrote: >Hi! > >This is what I got from intel about bsf/bsr instructions. I asked this: "In what >situations bsf/bsr eax,VARIABLE changes the contents of eax, if VARIABLE is 0?" > >This is what they say: > >"Although the value appears unchanged in some cases, the definition of this >instruction applies to all IA-32 processors starting with the Intel 386. That >stated, the BSR and BSF instructions both work as defined on all processors >previously noted. So even though it might be deterministic in a specific >implementation, no information will be provided on special cases." > >So practically I got no info at all. Still it is just speculation to try to >guess if there are systems where eax might be changed. In Requiem I make a small >test (which of course can't cover all situations) to see if bsf/bsr changes eax >in above situation and exit if this is that case. > >Severi Thanks for information. It seems that all implementation behave deterministic and leave the target register unchanged if VARIABLE is Null. As soon as we have bsf for 64Bit register, it dosn't matter anyway. Gerd
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