Author: Eugene Nalimov
Date: 13:28:39 08/29/05
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On August 29, 2005 at 15:57:51, Joshua Shriver wrote: >Good Afternoon, > > What is the WDL format? I've unsuccessfully been able to find information >on it. Is it a chess specific compression of general data? > >-Josh Store only Win/Draw/Lost value for every position, not the full value (Win in N/Draw/Lost in N). The simplest way to encode them would be to fit 5 values in a byte. 3**5 == 243, that is less than 256 different values, so you can store them into a byte. When probing you can easily get a value by using 243-element decode table (much faster than divisions). Other possibility would be to store 4 values into a byte -- 2 bits per position. Such table would be larger by itself, but it may compresses better -- when I experimented resulting compressed tables were smaller. Or you can store 2 tables -- one with Win/No Win, and other with Lost/No Lost. Presumable they will compress even better, and in lot of cases during the search you will probe only one of them, because that is all you need to know. Of course all those tables have drawback: you should assume that chess program that uses only them will be able to win a won position. E.g. it knows that OTB position is won. It know that out of all moves 3 moves also lead to won positions. Unfortunately it may not be able to figure out that current position is (say) mate in 30, move A leads to mate in 29, while moves B and C -- to mate in 35, and it may decide to make the wrong move. Hopefully such situation is rare enough, but I suspect it is more often when position is complex enough -- i.e. exactly when you need TBs. Thanks, Eugene >> >>It's just computational problem, all you need is 1 array of 2 TB to >>generate it, and after that supercompress it to WDL format. DTZ is >>perhaps interesting to generate if your goal is to publish near to >>maximin positions, but from computerchess viewpoint what matters is the >>result in the game. That can be either one of the next 3: win, draw or loss. >> >>Supercompressed this EGTB in wdl is like 3GB. >> >>Additional i'm interested in knowing what from their database what the longest >>win is for the KRB side in the KRBNKRB egtb. >> >>Vincent
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