Author: Gerd Isenberg
Date: 09:28:35 09/19/04
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On September 19, 2004 at 10:38:03, Robert Hyatt wrote: >On September 18, 2004 at 17:12:23, E. Nielsen wrote: > >>On September 16, 2004 at 21:20:50, Uri Blass wrote: >> >>>...doing a loop on the 1's of a bitboard... >> >>Well, I suppose it depends on which representation you choose for your >>bitboard... >> >>If it is in two's-complement form (i.e. signed) you can find the rightmost 1-bit >>with following formula: >> >> x & (-x) >> > > >Finding the bit is not quite the same as finding the identity or number of the >bit. IE findihg bit for square e4 is easy. But if you want to know if it is >the e4 square, id bit # X, then that is harder. Fortunately modern processors >can do this easily... 9 cycles vector path isn't that easy for bsf/bsr on AMD64 ;-) For moves i like the idea of a 64-bit de Bruijn multiplication with the difference of two single from/to bits. Using the upper 11/12 bits as a unique result index per piece. A source piece specific lookup, to get either from/to squares of the move, and/or a unique move index over all kinds of pieces, even considering possible captured pieces. > > > > >> >>Regards, >>Eyðun Nielsen >> >>P.s.: And I would also recommend the book "Hacker's Delight" by Henry S. Warren, >>Jr. which is full of stuff like this. :)
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