Author: Robert Hyatt
Date: 12:24:15 01/20/03
Go up one level in this thread
On January 20, 2003 at 13:58:19, John Merlino wrote: >On January 20, 2003 at 13:11:48, Eiko Bleicher wrote: > >>Hi, >> >>AFAIK the endgame tablebases like the Nalimov Tablebases use one byte per >>position. Thus, the max. length results in somewhere about 126 moves to win / >>loose. >> >>Now the question is this: How do these databases handle the positions that are >>mate in 130 or 140 or .... >> >>Any help would be greatly appreciated. >> >>Eiko > >First of all, it's an unsigned byte (8 bits), so it can handle mates up to 255 >(or 254, if the 255 value is used for something else, about which I am not >sure). I'm not exactly sure how Nalimov handles the 255 value. It can't go that far. Because it must have mate in N _and_ mated in N. For the 1-byte format, 126 is the max... > >But, in Chessmaster 9000, which also uses an unsigned byte to store this value, >all mates greater than or equal to 254 have the same value -- 254. Therefore, if >more than one move has a value of "Mate in 254", then any one of these moves may >be chosen as "best play". This may result in less than optimum play for two >reasons: > >1) One of these moves may be Mate in 254, and the other(s) may be Mate in much >more than 254. This isn't necessarily a bad thing, except for... >2) One of these moves may be a mate that will not be subject to the 50-move >rule, and the other(s) all will be draws with best play under the 50-move rule. > >jm If you do that, how do you possibly handle "mate in N" and "mated in N"???
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