Author: Robert Hyatt
Date: 17:58:28 02/17/04
Go up one level in this thread
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...
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