Author: Andrew Williams
Date: 13:24:28 08/23/03
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On August 23, 2003 at 15:23:45, Uri Blass wrote: >I am afraid that I did not understand it. >I remember claims that it is possible to do it fast. >How is it possible? > >Suppose that you find that the white rook stops attacking a square. > >If you remember only that a white rook attacked the square without remembering >more information then how do you know that there is not another rook that is >attacking the same square? > >If you check that there is not another white rook that is attacking the same >square before updating the attack array then it does not sound so cheap to do >it. > >Uri When *I* talk about attackboards, I mean that every square has a 32-bit unsigned integer associated with it. Each bit in one of these unsigned integers represents one piece. If the bit is 1, it means that the piece represented by that bit attacks the square. You are never going to be able to update this structure very quickly. The issue is, can you justify the time it takes to update this structure with the benefits you get from the information in it? When I make a move, I do this (note that promotions, enpassand and castling are a bit different): 1. Create a 32-bit uint which has a bit set for the moving piece, the captured piece (if any) plus any piece which attacks the from square or the to square. 2. Go over all 64 squares, masking out the attacks identified in (1) above. 3. Go through all the pieces that were affected (not the captured piece of course) and generate their attacks and mask them into the 64-uint array. I would re-iterate that since I do this on every make-move, this is not an efficient use of time, *unless* I use the information I get from it wisely. However, another reason for doing it might be that I put a *lot* of time and effort into getting it working properly; there's an element of pride that would prevent me from ditching it, even if I were convinced that it is a bad idea. Since I'm an amateur at this, I can afford this luxury. Andrew
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