Computer Chess Club Archives




Subject: Re: Question for the MTD(f) experts

Author: Tord Romstad

Date: 04:36:57 04/14/04

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On April 14, 2004 at 06:40:00, Fabien Letouzey wrote:

>>It's really simple.  I store more information in the moves than most people.
>>Most of you, I guess, store only the from and to squares, and the promotion
>>piece in the case of pawn promotions.  I also store the moving piece, the
>>captured piece, and whether the move was an en passant capture.  This gives
>>me everything I need to update the hash key, without looking at the board
>>at all.  The price is that I need a bigger number of bits to store moves
>>in the transposition table.
>What about the castling rights?
>E.g. white plays Ra1a7, or black captures a white rook at h1.

As far as I can see, this shouldn't cause any problems.  When I store the
moving and captured pieces in the moves, it is easy to update the castling
rights in hash_make_move(), without checking the board position or moving
any pieces on the internal board.

At the moment, however, I simply don't hash castling rights or en passant
information.  For this reason (as you know), my PVs will occasionally
contain illegal moves.  Perhaps I should fix this problem, but that would
have the unfortunate consequence of making my old opening book file
unreadable.  I don't want to force my users to download the big opening
book again, or to have a separate hash key used only for opening book


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