Author: Alessandro Damiani
Date: 13:06:22 01/16/04
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On January 16, 2004 at 15:51:42, Gerd Isenberg wrote: >On January 16, 2004 at 14:26:32, Alessandro Damiani wrote: > >> >>>i was asking because i'm generating all attacks in all positions (also the leaf >>>nodes), which takes a significant amount of time. i thought my >>>looping-over-bitboards was terribly slow, then i replaced it by the kogge-stone >>>stuff that was posted here a while ago, and it got even slower ;-) >>>so the next thing to try would be rotated bitboards, but it's rather a lot of >>>work to implement, i'm afraid. >> >>When I started working on my engine years back I first implemented the Chess 4.0 >>style attack tables. Then I read about Bob's Rotated Bitboards. I liked the >>idea, but found keeping updated rotated representations of the board too >>complicated. I therefore developed my own way of determining the attacked >>squares. I call it Rotated Indices. As its name suggests it keeps updated the >>indices used to access the attack tables. In contrast to Rotated Bitboards you >>don't have to extract the index out of the rotated bitboards, it is already >>there. The code is very simple. >> >>If you really want to implement Rotated Bitboards then you have to do it, >>waiting doesn't help. ;-) But, if you don't want to spend more than two hours >>for the implementation then you may have a look at Rotated Indices. You can find >>the source code on my homepage under "Chess programming: Bitboards in Fortress": >>http://freeweb.econophone.ch/fortress >> >>Alessandro >> ....eine Einbuchtung im Raum > >After looking a while to your source, i think your code is very similar to mine, >except the data density of your Indices and the identifiers ;-) > >// slide indices: >unsigned int SlideIndexH[8], // horizontal > SlideIndexV[8], // vertical > SlideIndexRU[16], // right up (RU) > SlideIndexRD[16]; // right down (RD) > >I use(d) something like this: > >// slide indices == rotated bitboards: >unsigned char SlideIndexH[8], // horizontal > SlideIndexV[8], // vertical > SlideIndexRU[8], // right up (RU) > SlideIndexRD[8]; // right down (RD) > >But with bitboard declaration instead of BYTE[8] (what about a union?). >The only trick is to pack the 15 diagonals byte aligned into eight bytes and >address them in this manner. > >rightupIdx = (sq-Rank(sq)) & 7; >rightDownIdx = (~sq-Rank(sq)) & 7; > >My drawback was the byte access with zero extending to 32-bit. >Your drawback is to update four SlideIndices additionally to the none rotated >one and i had only three additional ones. > Which additional non rotated one do you mean? Alessandro
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