Computer Chess Club Archives




Subject: Re: A New Approach to Draw Detection by Move Repetition in Computer Ches

Author: Ed Schröder

Date: 07:14:51 07/30/04

Go up one level in this thread

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:
>>>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
>>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)

This page took 0 seconds to execute

Last modified: Thu, 15 Apr 21 08:11:13 -0700

Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.