Author: Eiko Bleicher
Date: 12:22:54 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. > >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 You need one code for draw and one for "broken" (illegal) positions. I don't know the Chessmaster Tables in detail, but the Nalimov Tablebases store also the "losing" numbers, thus dividing the maximal length by two. Anyway, this isn't the main point of discussion, as there _is_ a certain limit, that in some endgames is too low. The method of always using the maximum length code for this is the way _I_ would implment that, as it still delivers the information about win/loss. I just thought that someone had any better idea (except going towards 16 bit :o). But indeed the information that a certain position is won in > MAX moves isn't very useful if the oponent is playing optimal, as you can just guess the right moves; you can even get farer away from a mate. Eiko
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.