Author: Christophe Theron
Date: 16:43:51 07/30/04
Go up one level in this thread
On July 30, 2004 at 10:14:51, Ed Schröder wrote:
>On July 29, 2004 at 17:34:11, Christophe Theron wrote:
>
>>On July 29, 2004 at 14:07:10, Robert Hyatt wrote:
>>
>>>On July 29, 2004 at 06:26:52, Gian-Carlo Pascutto wrote:
>>>
>>>>http://arxiv.org/ftp/cs/papers/0406/0406038.pdf
>>>>
>>>>I stumbled onto this when doing a search for Axon.
>>>>Not seen it mentioned here yet.
>>>>
>>>>They also have a paper about hashing out which I can't
>>>>download.
>>>>
>>>>--
>>>>GCP
>>>
>>>
>>>Doesn't strike me as particularly interesting. IE it almost seems that they
>>>don't realize that most programs store positions in a repetition list as 64 bit
>>>Zobrist integers...
>>
>>
>>
>>Actually I think it might be interesting.
>>
>>Recently, when I was rewriting the core of the Chess Tiger engine, I realized
>>that I could get even more speed by not computing the hash keys during the
>>quiescence search for example.
>>
>>In my case, it would have meant some more changes in the engine and the way I do
>>QSearch. But for some programs, it could be interesting.
>>
>>The problem then is how do you check for repetitions?
>>
>>If you allow checks and escape from checks in your QSearch, and if you actually
>>extend them in some way, you have to detect repetitions.
>>
>>So a lightweight, hash key free, repetitions detector is a must in this case.
>
>Father Christophe,
>
>For QS in the case you are using checks consider to compare moves only as most
>repetitions go as follows:
>
> Qh6-g6+ (depth-3)
> Kg8-h8 (depth-2)
> Qg6-h6+ (depth-1)
> Kh8-g8 (depth+0) -> current position
>
> if (from[depth+0]==to[depth-2] && to[depth+0]==from[depth-2]
> && from[depth-1]==to[depth-3] && to[depth-1]==from[depth-3]) -> draw
>
>I have used this in my 6502 days in QS only and it worked like a charm.
>Regarding speed (IMO) nothing can beat this because in 90% of all cases the
>first compare will fail, so actually you are doing just one compare in 90% of
>all QS cases.
>
>Ed (grandfather)
Yes, I have been doing this in the 16 bits version of Chess Tiger for a while.
Unfortunately I have came across many cases that were not detected by this
simple (and efficient, that's right) approach.
So I really wanted an algorithm that could detect all the cases.
Christophe
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