Author: Bas Hamstra
Date: 01:50:55 06/21/00
Go up one level in this thread
On June 21, 2000 at 04:29:07, blass uri wrote: >On June 21, 2000 at 00:06:21, James Robertson wrote: > >>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 > >You use only 64*256 array for rank_attacks so I do not understand why do you >need 8*64*256 array. > >Uri I think he just means one array entry is 8 bytes. It is the normal 2-dimensial array, see above code: rank_attacks[0][65]. Bas.
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