Author: Robert Hyatt
Date: 17:59:28 08/19/99
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On August 19, 1999 at 18:12:35, Johannes Buchner wrote: >Hi there ! > >I just wanted to know if anybody out there knows a different way how to do this >than using table-lookups like crafty. Is really no other mathematical >possibility ? By the way, do you know any Internet resources that deal with >problems like this (I think there is a method to do popcount without >table-lookups, e.g.) ? In the 'Dark Thought' description they're talking about >'Hacker's memory', a 'well-known collection of programming tricks'. Ever heard >of it ? I haven't ! >So if you know anything intersting about that topic, please let me know (and all >the otherz of course !) > > Thanks Johannes Crafty doesn't use a table look-up, unless it is on a non-intel machine. On the Intel platform, it uses BSF/BSR hardware instructions. Other processors have such instructions (Cray has leading-zero which is the same thing). There's no mathematical method to compute this that anyone knows of, although that doesn't mean no such method exists. But there are a lot of bit-twiddling tricks... you can find many of them in the Crafty source scattered around.
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