Author: Andrew Shapira
Date: 09:35:50 09/22/05
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"There is no way to do that" is a pretty strong statement. Where's the proof? On September 22, 2005 at 03:47:58, Gerd Isenberg wrote: >On September 22, 2005 at 02:40:22, Andrew Shapira wrote: > >>Yeah, I know about http://graphics.stanford.edu/~seander/bithacks.html >> - I have used it and some other web sites extensively. I have racked my brains >>for 2 days, on the couch, in the shower, in bed, while walking around, and still >>haven't figured it out. My sense is that it seems doable, and that a solution >>could involve subtracting x from (2^n)-1. This might be a high-order analog of >>the x-1 term that occurs in the expression x^(x-1) that comes up in low-order >>bit computations. > >Nope, to answer your original question again, hopefully more clearly. >There is no cheap way with the operators you mentioned to mask MS1B. >The LS1B tricks works due to two's complement, or one's complement plus one. >It has something to do with carry propagation which unfortunately only works in >one direction as we don't have reverse arithmetic ;-) > >Gerd
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