Author: Walter Faxon
Date: 18:21:51 01/11/06
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On January 11, 2006 at 19:13:11, Stuart Cracraft wrote: >On January 11, 2006 at 09:44:57, Robert Hyatt wrote: > >>On January 10, 2006 at 18:10:15, Stuart Cracraft wrote: >> >>>Here's Butler Lampson, one of the inventors, of the Parc Alto >>>talking about Seymour Cray and population-count units: >>> >>>http://research.microsoft.com/users/gbell/craytalk/sld051.htm >> >>Seymour said the same thing about the "leading zero" instruction, which was >>about the same thing as "find first one bit (starting from left) since the >>instruction just counting the leading zeros up to the first one. The Crypto >>folks used both. >> >>And yes, the 7600/Cyber-176 was a fast box in its day. Chess 4.x used it to >>drub other chess programs for a few of years until a certain program moved to >>even faster hardware (the Cray-1). :) > >Great stuff. > >Wish I had a population count instruction and find first one bit instruction! > >I hear that these exist on some chips but are not advertised. BSF/BSR (Bit Scan Forward/Reverse) for Intel/AMD; see e.g., Crafty. They are not always faster than bit-twiddling code. If population count instructions existed on any mass-market chips, I'm sure hackers would have long since found and announced them. -W
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