Author: Uri Blass
Date: 00:17:19 03/08/03
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On March 08, 2003 at 01:42:15, Robert Hyatt wrote: >On March 08, 2003 at 01:29:46, Joel wrote: > >>Hey All, >> >>Just wondering what everyone thinks is the best way to implement a pawn hash >>table? >> >>At the moment I am incrementally generating a seperate pair of pawn hash keys, >>and using them to index a table - very similar to how my transposition table >>works. >> >>Is it possible to do _significantly_ better than this? It seems to be somewhat >>expensive to do, although having said that my NPS still went up at least 20% in >>most situations. > >That is what everyone since chess 4.x has done. Two signatures, one for >all pieces and pawns, one just for pawns. > Not everyone. There are a lot of programs without pawn hash tables and there are even a lot of chess programs without hash tables. I remember that I found something like 10% speed reduction in nps from adding bitboards for passed pawns,isolated pawns and protected passed pawns by pawns and I earned more than it in speed from other changes. I still do not evaluate passed pawns when they are not protected by a pawn and I think that the question how to evaluate passed pawns relative to the kings and other things is more important than pawn hash tables(Maybe it is good to give some small static bonus for passed pawns but I did not like this idea because I know that there are cases when passed pawns are trapped and these cases are not rare). Another point is to evaluate king relative to pawns and not only passed pawns because one of the problems of movei in endgames is that it always assumes that the best place for the king is the centre and it may be a problem also in case when there are no passed pawns. > > > > >> >>I am not really worried about effeciency as much as some other people here, so I >>guess I am really asking whether I am missing something major. > >Doesn't sound like it. But you will end up storing more than just a score for >the position. IE passed pawn locations, weak pawn locations (or bitmaps that >feature them). Etc... How many bits do you need to do it? The simplest way that I think about asks for 192 bits for that information when usually most of them are 0's(maybe it is not very important because even with small number of hash entries you have not a lot of pawn structures). There can be in theory 8 passed pawns for white or 8 passed pawns for black If you want to store every square then you need 6 bits for every square so you need 6*8 bits only for white passed pawns and 6*8 bits for black passed pawns. If the same is for weak pawns you get 192 bits in your hash tables for pawns. Uri > >> >>Regards, >>Joel
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