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Subject: Re: Bitscanning on the Opteron

Author: Jeremiah Penery

Date: 17:27:29 12/05/03

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On December 05, 2003 at 13:53:08, Russell Reagan wrote:

>On December 05, 2003 at 08:52:10, Anthony Cozzie wrote:
>
>>Three questions:
>>
>>1. What is the performance of the hardware bitscan, that is:
>>
>>__asm("bsf %0, %1")
>
>I didn't benchmark it this time, but IIRC, I wrote this test a while back when
>Gerd and others here were discussing bitscanning for the Athlon. The bsf
>instruction on a P3 is ridiculously fast, like 4 cycles or something, and like
>40 on the Athlon.

You exaggerated a bit. :)  I think it's more like 2-3 cycles for P3 and 12 for
Athlon.



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