Author: Robert Hyatt
Date: 11:34:15 01/30/99
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On January 30, 1999 at 13:34:46, William Bryant wrote: >On January 30, 1999 at 11:23:31, Robert Hyatt wrote: > >>On January 30, 1999 at 09:59:38, Steve Maughan wrote: >> >>>I have a couple of question regarding hash tables - can anyone help? >>> >>>1 I see in the Crafty code that the flag for a hash entry can be "value is >>>worthless". What is the condition for storing this type of entry? >>> >> >>that's an entry that has been 'cleared'. IE the score/bound is totally >>no good because something changed at the root that caused the piece/square >>tables to be recomputed... which means scores will change. I set the type >>to 'worthless' because the 'move' stored in such a position is still good for >>move ordering, but the score/bound is not. >> >>if I just cleared the entire entry, I'd lose the move ordering stuff the table >>contains... this way I just lose the score. >> >> >>>2 Is it advisable to store the a) the side to move b)Enpassant square c) >>>castling right in the hash code? ie assign a random value that is XORed for >>>these conditions. >> >> >>you _must_. I do it by dynamically updating the hash signature when I make a >>move that makes an enpassant possible, and updating it again when I make a move >>that makes the EP capture impossible. Ditto for castling. If you don't do this >>you will get matches that are wrong, and results that are wrong. >> >>> >>>All help appreciated. >>> >>>Steve Maughan > >I may have the wrong impression, but I though you maintained different hash >tables depending on the side to move, ie a white-to-move table, and a >black-to-move table. > >Can this be done by simple using an XOR value for side to move > (ie include it if white to move, exclude it if white not to move). > >This would double the amount of available hash table space for me. up to you... I am testing this myself, in fact... and it seems to be just as good as the wtm/btm tables... you have to xor in a random number for positions where you have wtm, but that is all that is needed... > >Thanks. > >William Bryant
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