Author: Robert Hyatt
Date: 14:01:45 02/24/99
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On February 24, 1999 at 15:09:52, Larry Griffiths wrote: >On February 23, 1999 at 16:40:50, Robert Hyatt wrote: > >>On February 23, 1999 at 14:33:03, Larry Griffiths wrote: >> >>>Dan, >>> >>>I read your post on hash collisions. I have tried some hamming distance >>>code and I see little difference when compared to generating random >>>numbers. I have been thinking of writing code that does what you said >>>where 64 bits must have 32 bits (or 50%) turned on in each number. I also see >>>where there are many references to the 12 pieces times 64 squares = 768 >>>hash codes. Since the a Bishop can only control 32 possible squares and >>>there are 4 bishops, then 128 of the 768 are unused. Also, Pawns only >>>use 48 squares for each side, so 32 squares are unused by pawns. >>>768-128-48 leaves 592 hashcodes for the piece square table. >>>Food for thought? Errors in my thinking? >>> >>>Larry. >> >> >>A couple. First there are 12 _types_ of pieces. And since each side has >>two bishops on opposite colors, all 64 random numbers are needed for the >>bishops. >> >>you can get away with leaving 16 out of the pawn random numbers since none >>exist on the 1st/8th rank. There are not 4 sets of 64 numbers for the 4 >>bishops. There are two sets of 64, one for black bishops, one for white >>bishops. Because the bishops are not 'unique' and are interchangable. In >>fact, after promoting to a B, that B is identical to the B that existed early >>in the game on the same color square. >> >>So you _could_ reduce this to 752 numbers... but then you need a few more >>for things like castling status, enpassant status, so you take those back >>again. > > >Bob, > >I can get away with leaving 16 out of the pawn random numbers and I have >two pawn tables so 16 * 2 = 32. So I could reduce this to 768-32 or 736? > >I also saw a post that your table is 1024 entries. What are the other >4 tables (256 entries) used for? > >Thanks for your reply. > >Larry :-) I think that was Don's post about 1024. I have exactly 12 * 64 entries in mine... and yes you can safely leave those table entries 0 since they will never be used anyway... but don't forget you need to handle enpassant and castling privileges as well for both sides...
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