Author: James Robertson
Date: 21:06:21 06/20/00
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On June 20, 2000 at 22:49:30, Dave Gomboc wrote: >On June 20, 2000 at 14:58:54, James Robertson wrote: > >>On June 20, 2000 at 12:18:06, Ralf Elvsén wrote: >> >>>I'm asking about things I don't have much personal experience from >>>so forgive me if this is a stupid question. With BB, as I understand >>>it, one usually have a lot of precomputed BB-arrays, like bishopsMoves[square], >>>maybe blocks[from][to] or the rotated BB-stuff. Is this causing problems >>>for the cache? How much precomputed stuff is needed in 0x88 compared to this? >>> >>>Ralf >> >>I'll answer your second question first. A tiny amount (guesstimate, maybe 1k) is >>needed for 0x88. Bitboards require much more... almost 600k for core arrays on >>my program. Crafty uses some funky thing called compact attacks which I guess >>compacts the attacks. I don't know how it works. (Dr. Hyatt, could you please >>explain how it works and what it's advantages are?) >> >>The precomputed arrays are usually in the form of attacks for ranks and files. >>To try to stuff all bishop or rook moves into one array is a bad idea. For >>instance, in my program, rook moves would require an array of dimensions >>8*64*256*256 bytes = 33MB! >> >>Taking two arrays, one for ranks and one files (each 8*64*256 = 131072 bytes) is >>a lot better. >> >>James > >Can you elaborate on what you are doing, how you are doing it, and why you are >doing it? 256 Kb sounds like quite a lot of storage. Why? Because I know how, and it is a lot of fun. What? Basically, I use the square the piece is standing on and the rank/file/diagonal I am trying to find moves for as indices into my tables. For instance, say I want to find rank moves for a rook on a1 (the first rank), and my bitboard of occupied pieces looks like: 10000010 // a1 through h1 00000000 // a2 through h2, etc. 00000000 00100000 00000000 00000100 00000000 00000000 I then extract the first 8 bits (10000010 = 65 in decimal) and the piece's square ( = a1 = 0) and rank_attacks[0][65]; returns a bitboard that looks like: 01111110 00000000 00000000 00000000 00000000 00000000 00000000 00000000 Voila, you have all the rank moves for that rook. James > >Dave
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