Author: Dave Gomboc
Date: 19:03:43 04/04/03
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On April 04, 2003 at 16:11:48, Dieter Buerssner wrote: >On April 04, 2003 at 15:06:37, Russell Reagan wrote: > >>As far as an example, try this: >> >> rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq e3 0 1 >> >>The en passant square is e3. > >Only for the FEN Standard, the ep square must be e3 here. A very doubious rule >(I think it is wrong) in that Standard. For the search of an engine (for example >for hashing), there is no need to set/hash the ep square, when the pawn cannot >be captured. And then your problem is gone ... One might still argue, that in >the few real ep-cases, hash could even help when you ignore ep. Perhaps - I >don't think, it don't think you could gain much. > >BTW. Setting the ep target and hashing it always yields in bugs in one typical >method of repetition detection (comparing with previous hash signatures): When >the position is on the board the second time, you won't see it ... Not hashing >ep target could yield in similar bugs. Setting ep target only when a ep capture >is possible will solve those problems. However, one subtle problem could remain: >it seems that the pawn can be captured ep, but it really cant't be captured >because the capturing pawn is pinned to the king. This might be rather expensive >to detect in the inner loops of the search. > >Regards, >Dieter It's also possible that the pawn is not pinned, but capturing en-passant is illegal: White Kh5, Pf5; Black Ra5, Pg7. 1...g5, now White's f-pawn is not pinned, but 2. fxg6 is illegal. Junior at least used to not hash e.p. status. I saw a big (like -3 or -4) fail-low once because of that. Dave
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