Author: Russell Reagan
Date: 08:48:37 06/08/03
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On June 08, 2003 at 04:53:02, Geoff wrote: >1) What format is each position stored in ? >Does it just store position for say white and infer info for black ? Positions are not stored. For simplicity's sake, you can think of the EGTB file as a big array that is saved to a file. You compute the index into that array by taking the squares of the pieces and concatenating their binary representations together. Then you just do an array lookup into the big file, and it will report back a score, for example: draw, mate in 5, etc. >2) Does it store the whole position or use some symmetry tricks ? They use symmetry tricks, rotation tricks, and other tricks for kings and pawns since their positions on the board can be limited (Example: if the king can be captured, that position is illegal, a pawn cannot be on the first or last rank, etc.). >3) How were the tables created in the first place, quite a tricky algoritm I >would imagine !! Let's say that you wanted to generate the endgame tablebases for all 3-piece endings. Here is a simplified way that it might work. - Generate all of the possible positions that contain 3-pieces, storing each position in an array. This would be all positions containing a white king, black king, and some other piece. - Loop over the array and find all positions where the king can be captured by the side to move and mark them as illegal, otherwise mark the position as a draw. - Find all positions that are "mate in 0", and mark them as such. - Find all positions that are "mate in 0", find the positions that can be reached from those positions, and mark them as "mate in 1". -Find all positions that are "mate in 1", find the positions that can be reached from those positions, and mark them as "mate in 2". -Continue this process until you loop through the entire array and don't make any changes. Now you write this data to a file and you're done. Of course, you would have a very, very basic EGTB. It wouldn't be small in size (compared to the Nalimov EGTBs), but it would work. Hope this helps.
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