Author: Larry Griffiths
Date: 06:45:35 10/20/00
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On October 20, 2000 at 05:10:33, Severi Salminen wrote: > >>>How do I find n in a binary number 2^n? So f(1000b)=3? Now I just shift right: > >>Easiest answer is look at the crafty source. Intel has instructions >>BSF/BSR to do this. Or you can do a table lookup. Code for both >>approaches is included in Crafty. > >How fast are BSF and BSR? I know that pure shifting is very fast, but how many >shifts do I have to do to be slower than BSR or BSF? > >Severi I estimate that BSF or BSR executes in 1 clock cycle on my Pentium III machine. I have code that produces square numbers from my 64-bit bitboards. I could do about 90-120 million extracts a second with this code which consisted of scanning for the bit, storing the square number, reseting the bit, and looping looking for the next bit. Larry.
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