Author: Bas Hamstra
Date: 13:05:32 01/15/03
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On January 15, 2003 at 13:58:25, Russell Reagan wrote: >On January 15, 2003 at 07:49:44, Bas Hamstra wrote: > >>In think I understand now. You do it for the 2 rooks simulteneously. "Floodfill" >>(not the correct term, I know) does not necessarily have to start at bit 0, it >>can be anywhere. Wow. This really is an enhancement of the X ^ (X-2) trick. This >>opens interesting possibilities, like generating "UP" attacks for all rooks and >>queens at once, and masking only later (when it's needed) with a RookMask[Sq]. >> >>RookAttacks for one rook at a given square = RookMask[Sq] & UP & LEFT; >> >>(plus the same for the reversed bitboard) >> >>Bas. > >Hi Bas, > >How would you use x^(x-2) trick to generate "up" attacks and attacks in other >directions? First, forget about my previous post. Sorry if I am a bit slow. I can see how to do it for one piece though. Suppose you have a queen at c1 and want to generate UP attacks. - Shifted = Occupied << C3 // shift Occupied so that Queen is at A - shift Occupied so that queen is at A1 -
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