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Subject: Re: definition of clones: Danchess an Crafty (another note)

Author: Dan Honeycutt

Date: 07:34:01 02/18/04

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On February 17, 2004 at 20:58:28, Robert Hyatt wrote:

>On February 17, 2004 at 17:38:13, Dan Honeycutt wrote:
>
>>I realize I'm adding where you are subtracting due to different numbering.  What
>>I'm saying is that 3/4 of the time I still have to make "an adjustment" to the
>>value bsf/bsr gives.  Do you not have to make an adjustment 4/4 of the time, or
>>do you have to make 2 adjustments?
>>
>>Dan H.
>
>
>I do it at the end, one time.  IE for the Opteron, it looks like this:
>
>movq    %rax,63
>bsfq    %rbx, %rcx
>subq    %rcx, %rax    ; done, result in rax (64 bit reg).
>
>for X86, I do it in three steps:
>
>first check one half, then add 32,
>second check other half
>subtract from 63
>
>I can post the x86 if you want...

I'm with you.  on x86 I'm

check one half, if there is a bit I'm done
check other half
add 32

I get a slight advantage on 32 bit but more on 64 bit where I do nothing but you
still have to subtract.

Thanks for the help.
Dan H.



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