Author: Russell Reagan
Date: 11:02:09 04/05/03
Regarding hashing of the en passant square and castling rights, I have a few questions. I think I understand this now. I'd just like some verification. You should only hash the en passant square if it is possible for an enemy pawn to execute the en passant capture. This means, ideally, that if there is a pawn present to make the capture, but it is pinned and cannot legally make the capture, that you should not hash the en passant square. Is this correct? Regarding when to include castling rights in the hash signature, consider the following position, with and without castling rights set. [D]4k3/8/8/8/2b5/8/2PP4/4K2R w Notice that the white king cannot castle since the black bishop attacks f1. If this position arose 3 times, but with differing castling rights, then that is NOT a draw by repetition. Correct? The rule that I'm reading is from the FIDE Laws of Chess: "Positions are not the same...if the right to castle has been changed temporarily or permanently." In short, the rules are... 1. Always hash the board data. 2. Always hash the side to move. 3. Always hash the castling rights. 4. Only hash the en passant square if an enemy pawn can legally execute the en passant capture on the next move. 5. Never hash the fifty move counter. Let me know if I'm misunderstanding anything. Thanks.
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