Author: Steffen Jakob
Date: 07:04:48 12/19/03
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On December 19, 2003 at 09:31:33, Uri Blass wrote: >On December 19, 2003 at 09:03:15, Steffen Jakob wrote: > >>On December 19, 2003 at 08:29:00, Uri Blass wrote: >> >>>>>If you use pseudo-random numbers for zobrist hashing it is always possible to >>>>>get a collision. Yes, this is paranoid. :-) >>>> >>>>No need to use pseudo random numbers. >>>> >>>>It is possible to store all the board with 192 bits easily as was explained in >>>>another post. >>>> >>>>Uri >>> >>>Here is the relevant post. >> >>This encoding is not appropriate for being used as a hash key. You have these >>192 bits. To get the index into the hash table you filter some of those bits. >>With the encoding of the posting which you mentioned it is very likely that a >>lot of similar positions are mapped to the same index. Therefore you will not >>use the hash table in an efficient way. It will be efficient with zobrist >>hashing. > >When looking again at that post I agree that it does not give side to move and >castling in the 192 bits but I think that it is not hard to change it to do it. > >12 bits for the squares of the kings >62 bits to give the empty squares of other pieces. > >The rest of the squares are at most 15 white pieces and 15 black pieces and you >can give 30 bits for side of the rest of the squares and every 3 squares now >have 5^3<2^7 options so you can use 7 bits for every 3 non empty squares or 70 >more bits. > >Now you have:12+62+30+70=184 bits. > >side to move castling right and en passent can be easily stored in 8 bits. > >side to move is 1 bit >castling rights is 4 bits >enpassent right is 3 bits because 000 means no enpassent capture is possible >001 means that the first suspected pawn can be captured by enpassent rule and it >is impossible to have 8 pawns that we suspect them because if white has 8 pawns >in a4 b4,c4,...h4 it is obvious that enpassent capture is impossible. Is this a reply to my last posting? Did you read it? :-) Greetings, Steffen.
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