Author: Sune Fischer
Date: 11:34:28 02/01/02
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On February 01, 2002 at 11:42:05, Alvaro Jose Povoa Cardoso wrote: Hi :) >In my checkers (portuguese/spanish version with long jumps) program I use the >four bitboard ray technique for the four directions for each of the 32 square >for the king jumps (with 32bit bitboards). Could tell a bit more about this ray technique? Preferably every single detail :) >And then I use the BSF/BSR assembler instructions for finding the moves. >Since the PC processor speed is evolving much faster than the memory/FSB speed I >would like ask if there is a significant performance diference between this >technique and the rotated bitboards with 'large' tables for chess. >I did not started yet my chess engine, but I want to start with bitboards so I >would like your opinions if this technique is fast enough for the sliding >pieces. >It seams to me that there is less data needed for these operations and >consequentely all this will be on L1 cache most of the time. >I also understand this technique better than rotated bitboards. I tried a few days ago a different technique with reversed bitboards. It used very small tables and it could do about 17 million bishop attack boards per second. I counted the number of 64 bit operations needed in the rutine, and found that one 64-bit operation took an average of 3.3 clock cycles (I ignored all '=' which may is also count as 64-bit operations?). I think 3.3 clock cycles is pretty good, I think it must be running entirely in L1 cache like yours. I have not tested rotated, so I can't compare. Unfortunately reversed boards has one major drawback, they split every attack board into two boards, which spells trouble later on. I devised a scheme to quickly reverse the board back, but I need to do two bitscans and two more 64-bit operations. The slowdown will probably be too much to be worth while. >Best regards, >Alvaro Cardoso Cheers, Sune.
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