Author: Sune Fischer
Date: 14:36:52 07/14/03
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On July 14, 2003 at 17:15:50, Bas Hamstra wrote: >Hi Gerd, > >A while ago, in Leiden, Frans mentioned you had a trick to reduce the rotated bb >lookup tables by a factor 2, without further disadvantages. It had something to >do with the edges of the board, some "ray-states" you can ignore. I didn't >understand his short explanation back then. Could you explain? > >Best regards, >Bas. It's quite simple; the state of the attack rank (or file) doesn't depend on the outermost squares/bits. Those squares are attacked (or not) no matter if there is a piece standing there. So actually it is a factor 4 you save, because you need only 6 bit entries. There are other tricks you can do to compact them even more, but then more shifting is needed to unpack the information. I have written a sample move generator that uses this trick: http://www.geocities.com/ruleren/crbmg.zip -S.
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