Author: Gerd Isenberg
Date: 10:17:22 03/27/03
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On March 27, 2003 at 10:06:47, Dezhi Zhao wrote: >On March 27, 2003 at 05:35:10, Uri Blass wrote: > >>If I want to get rid of the least significant 1 of a BitBoard >>I do for a bitboard a >>a&=a-1 >> >>What is the fastest way to get rid of the most significant 1 of >>a bitboard? >> >>Is it slower than a&=a-1 and how much slower? >>(it cannot be faster otherwise popcount of crafty could use it). >> >>Uri > >To my best knowlege, there is no such well known trick for the most significant >bit. > >Maybe we can send a wish list to Intel and AMD for some new instructions. >To seed the list: > >1. bsfr : bit scan forward and reset >2. bsrr : bit scan backward and reset > >requirements: NOT in slow microcode or latency <= 2 cycle:) > >dzhao Agreed - at least bsf, bsr, btr reg64,reg64 <= 2 cycles each ;-) Gerd
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