Author: Robert Hyatt
Date: 09:41:13 01/13/05
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On January 13, 2005 at 12:15:52, Eugene Nalimov wrote: >On January 13, 2005 at 11:08:48, Robert Hyatt wrote: > >>On January 13, 2005 at 05:36:41, Tony Werten wrote: >> >>>Hi all, >>> >>> >>>when checking my own tables, I found out that the following (illegal ) position, >>>causes the Nalimov code( rather, the decompresssion code ) disabled further egtb >>>probes. >>> >>>No problem for normal use, just when you're doing something without checking if >>>the position is legal, it goes wrong. >>> >>>The position looks like it might have been optimized away, causing a probe >>>beyond the uncompressed size of the filechunck just read in, causing an >>>"invalid" flag on the tablebase, resulting in a disabling of the KNNkp >>>tablebase. >>> >>>[D]4K3/8/8/k7/8/1N6/p7/N7 w - - 0 0 >>> >>>Tony >> >> >>I believe this has always been a restriction. Since one way to compress the >>database (before the raw compression algorithm) is to weed out positions that >>are not possible, such as two kings on adjancent squares, both kings in check, >>pawns on illegal squares, etc. I suppose the probe code could be modified to do >>all the legality checks, but then it would have to be able to generate moves to >>see if a king is in check and the other side is on move, etc. It makes more >>sense for the chess engine to do that stuff since it knows about legality issues >>anyway... >> >>Perhaps Eugene will comment further... > >If you pass illegal position you'll get back either "unknown value" (if you are >lucky), or value for some other position. > >I definitely would not turn off further probing, but chess engine can. > >Thanks, >Eugene Aha... So this is something that was done by Tony's program, rather than the EGTB probe/decompression code? If I get "invalid" back, I just ignore it and keep going, I don't use that to say "this table is not present". In fact, I don't keep up with that, I just probe when I reach the right number of pieces and let your code return a value or a failure condition...
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