Author: Robert Hyatt
Date: 11:03:24 01/29/02
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On January 29, 2002 at 10:47:40, Les Fernandez wrote: >On January 29, 2002 at 09:57:30, Robert Hyatt wrote: > >>On January 28, 2002 at 17:48:48, Les Fernandez wrote: >> >>>Just curious to know what is the best being done now for storing a chess >>>position. In the worse case scenario (castling right exists) it takes me 162 >>>bits to store 32 pieces, color, location, side to move, castling, enpassant, >>>promotion, ce and pv. Now if castling rights do not exist then the worse case >>>scenario for the above is 81 bits. Much further reduction in bits/position is >>>possible but at the moment I am interested in the above. >>> >>>Thanks in advance, >>> >>>Les >> >> >>How can you store a complete chess position without castling rights in 81 >>bits? castling rights are certainly not 81 bits of information to get you >>up to 162. >> >>Something is wrong. > >Hi Bob, > >The point is that in cases where castling is not available there exists a >minimum of 4 rotations that can be applied to a board, top-bot and left-right. >The method I discuss to store a position requires 9 bits to store piece, color >and x and y location. 32x9=288 and then 36 bits are needed to store the other >pertinent things about the position. (288+36)/4=81 bits/position on avg. just >as Uri explained here (thx Uri sorry Bob if I was not clear). I thought the >scheme I used to store a piece using only 9 bits was different and would >appreciate feedback here. > >Thanks, > >Les I think your math is wrong. If you need 288+36 bits to store one position, you need 288+36-2 bits to store 1/4 of that number of positions. This is log math and you _subtract_ exponents, not divide. ie 2^32 / 4 == 2^30, _not_ 2^8 That is where I am getting lost in your description...
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