Author: Robert Hyatt
Date: 14:59:15 01/30/99
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On January 30, 1999 at 15:15:33, Peter Fendrich wrote: >On January 30, 1999 at 14:34:15, Robert Hyatt wrote: > >>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 > >I just complement ~Hashkey when colors change. >I've done this for a long time now and it seems to work ok. >//Peter actually that is what I am testing... seems reasonable to me too...
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