Author: Robert Hyatt
Date: 07:33:20 02/02/01
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On February 02, 2001 at 00:57:30, David Rasmussen wrote: >On February 01, 2001 at 18:43:58, Robert Hyatt wrote: > >>On February 01, 2001 at 15:26:43, David Rasmussen wrote: >> >>>On February 01, 2001 at 10:37:04, Robert Hyatt wrote: >>> >>>> >>>>You can look at my code named "GenerateCheckEvasions()" but the idea is >>>>this (simplified and maybe wrong): >>>> >>>>1. If I am checked by a single piece, capture it. >>>> >>>>2. If I am checked by a single sliding piece, interpose. >>>> >>>>3. If I am checked by either 1 or two pieces, move the king out of the check. >>>> >>>>for 3, you might think that I have to check for legality after generating a >>>>king move, but it isn't needed. If the checking piece is a slider, I have to >>>>move in any direction but +/- the checking direction. Bitmaps handle all of >>>>this easily, so that I can produce moves that I _know_ are legal. >>> >>>OK, I am aware of the idea of a CheckEvasions() function. I just didn't see >>>anybody talking about checking moves only. I assumed you meant you were able to >>>generate _all_ moves legally, somehow. >> >> >>No, sorry. Although it is probably possible to do so by bitboard tricks >>dealing with diagonals/ranks/files passing through the king's square.. > >Yes, but can it be done without losing performance, or even with a performance >gain overall? I guess we don't know. I am not a fan of generating only legal moves for the general case. Since most moves are legal, unless you start off in check, doing the extra legality work is a headache, particularly since most of those moves likely won't be searched anyway, thanks to alpha/beta. I did the check evasion code because there almost all moves produced by a normal move generator will be illegal, and rejecting them takes longer to do after they are generated and tried than it takes to simply not generate them in the first place.
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