Author: Uri Blass
Date: 11:15:37 09/10/02
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On September 10, 2002 at 14:04:28, Sune Fischer wrote: >On September 10, 2002 at 13:22:59, Uri Blass wrote: > >>On September 09, 2002 at 19:01:17, Gerd Isenberg wrote: >> >>>On September 09, 2002 at 18:39:51, Vincent Diepeveen wrote: >>> >>>>On September 09, 2002 at 16:13:00, Gerd Isenberg wrote: >>>> >>>>Hello, >>>> >>>>Just to be clear is the next path a legal one: >>>> isconnected(d4,d8) ==> >>>> d4 e3 d1 c1 b2 a3 a4 a5 b6 c6 d6 e6 f7 e8 d8 >>> >>>Yes, Vincent, exactly. >>> >>>With the following bitboard >>> >>>0x18201e010911221c >>> >>>0 0 0 1 1 0 0 0 18 >>>0 0 0 0 0 1 0 0 20 >>>0 1 1 1 1 0 0 0 1e >>>1 0 0 0 0 0 0 0 01 >>>1 0 0 1 0 0 0 0 09 >>>1 0 0 0 1 0 0 0 11 >>>0 1 0 0 0 1 0 0 22 >>>0 0 1 1 1 0 0 0 1c >> >>How do you get that bitboard? >> >> >>I do not understand why do you choose 1 for d4 and e3. >> >>d4 and e3 are controlled by black pawns so they cannot be squares that white >>piece is going to go. > >The examples are just meant to be hard to solve for the algorithm, to see if it >works even in the extreme conditions. >The position is not likely to occur of course, but if it can solve that, it can >solve anything. > >>I can think of a similiar path as a path for the white king. >> >>Another question is how do you plan to know the squares that are safe for the >>white king in the diagram. >> >>Evaluating this seems to me the main expensive problem and not calculating if >>2 squares are connected. > >If you use bitboards there is a chance you have something that can produce these >things quite fast. > >Imagine for instance a blocked pawn position, we want to know if the king can >get through. The bitboard might look like this: > >11111111 >11111111 >11111111 >00001000 >00010000 >11111111 >11111111 >11111111 > >can he walk from e2 to g6? >Turns out he can, but a rook or bishop of wrong color might not be able to help >him, this is what the floodfill algorithm can tell you (with a few >modifications). I do not understand your example where are the blocked pawns? I see that d4,e5 and every square in the first 3 ranks or the last 3 ranks is open for the king. I do not understand the reason for it. Uri
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