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Subject: Re: Resources about rotated bitboards

Author: Alessandro Damiani

Date: 11:26:32 01/16/04

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>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



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