Author: Vincent Diepeveen
Date: 06:26:15 01/28/02
Go up one level in this thread
On January 28, 2002 at 08:36:15, Sune Fischer wrote:
>Hi,
>I'm in the process of rewriting my entire movegen, now I'm going to need
>bitboards I've decided, but it seems there are different approaches.
i would not have taken that decision but if you must chose what to use,
my tip is to start with normal bitboards, changing them to rotated
later can always be done, but try to keep the RAM used for it low!
modifying normal bitboards to rotated bitboards is something you can
do later.
Reversed bitboards, we have seen a posting or 2 about it, but till there
is an implementation for that actually works, it is going to be interesting
to take a look at it without any serious plans.
Only the diagonals you need to take a look at at the design what is faster
for them. if that problem isn't solved in reversed bitboards, then obviously
rotated are going to be easier for you to take a look at.
It seems there are however many methods at the K7 + intel processors to
use with rotated bitboards. In isichess it seems smaller tables are
getting used than in crafty for this.
Others report they do it even different, but their speedresults are
not impressive.
>I found this link (it was actually dead, but google had it cached so I put it up
>for a short while)
>http://www.fys.ku.dk/~fischer/Temp/New%20Technology.htm
>
>It is about reversed bitboards, the author claims it is faster than rotated:
>
>"When taking account of memory latencies, calculating the piece attacks using
>the forward and reverse bitboards can be done significantly faster due to total
>independence on lookup tables and complex calculations. There are a few slight
>snags with the diagonal calculations, but they are minor."
>
>
>His description ("significantly faster") entrigues me (hehe) but I can't find
>anything else on reversed bitboards and I've never heard of them before.
>
>What's the catch, is there something he is not telling?
>
>-S.
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