Author: Dan Homan
Date: 07:28:24 07/15/99
I've decided to make some free time for myself this summer to work on my chess program. I've decided to do a complete re-write of EXchess from the ground up, using 0x88. My plan in writting previous versions of EXchess has always been to make everything as easy to understand as possible. I want to keep that in the new version, but I would also like to go faster! I have some ideas on making/unmaking moves during the search. In previous versions of EXchess, I have just done position copies for each new ply and had no need for an unmake routine. Several people told me it was faster to make/unmake but my experiments didn't show much improvement. I want to do unmake in the new version of my program, and I would like to make it as efficient as possible. One idea I had was just doing a bit-shift to undo moves. The idea is that a square on my board would be an int (or perhaps int64), but only the first 4 bits would store piece/color information. Then I could store 8 (or 16) "states" for a given square - all in order of how they occurred in the tree. My unmake move would just be a bit-shift on the appropriate squares. I have one concern with this - How many times can the state of a given square change in the tree? My feeling is that there will be situations where the state of a square will change more than 8 (or even 16) times. (I score any repeated position as a draw, so that may make these situations relatively rare, but just one such situation could be a big problem in a game.) I could have a scheme for storing the "lost" information in these rare cases, but I wonder if the speed-up from this idea is significant enough to warrant the added complexity? I would welcome any other ideas people have for making a fast "unmake" routine. - Dan
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