Author: Robert Hyatt
Date: 06:59:58 09/19/01
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On September 19, 2001 at 06:30:56, Dominic C. Marcello wrote: > As far as the penalty for using 64 bit bitboards on a 32 bit machine, with >intel's mmx registers on the Pent pro and later, the penalty can almost >disappear with a little inline assembly. Some instructions are not avallable for >use with the mmx registers though. For instand, bsr and bsf ( bit scan reverse >and forward) have no mmx instruction equivalent, but there is an mmx equivalent >for and, nand, or, xor (but not not), as well as left and right shifts. It's a >lot faster than treating the bitboard as two seperate double words, and if intel >would just add a bit scanning function to it, bitboards could be operated on >exclusively in the mmx registers. >There's also some newer instructions on the pent IV, one of which would allow >you to extract an 8 bit rank from a 64 byte board. The problem with MMX is that compilers are not supporting it to work on long long (or __int64) data types. This means we have to resort to assembly. And that lengthens the development cycle significantly.
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