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Subject: Re: Nalimov TB question

Author: Gian-Carlo Pascutto

Date: 05:14:32 11/12/01

Go up one level in this thread

On November 12, 2001 at 06:59:51, Bas Hamstra wrote:

>On November 12, 2001 at 04:46:19, Gian-Carlo Pascutto wrote:
>>On November 11, 2001 at 19:42:29, Bas Hamstra wrote:
>>>Is there any documentation about linking Nalimov?
>>probe.txt, which comes with the generator
>>>I am not sure what score a probe() should return. I set up a FINE that is a mate
>>>in 23 (verified on nalimov's online TB site). However, when my probing function
>>>returns 32756. Some debugging in TBIndex.cpp learns that initially it found 113
>>>that is then converted to 32756 by macro S_to_L. Doesn't seem right. Shouldn't
>>>it just return the number of moves to mate eventually? Peeking in Crafty seems
>>>to indicate so.
>>I figured out the conversion formula by setting up some positions
>>and looking at the values I got back until I figured it out.
>>In Sjeng, it looks like this:
>>if (tbScore == bev_broken) return KINGCAP;
>>  EGTBHits++;
>>  if (tbScore > 0)
>>  {
>>        return ((tbScore-bev_mi1)*2+INF-ply-1);
>>  }
>>  else if (tbScore < 0)
>>  {
>>        return ((tbScore+bev_mi1)*2-INF+ply);
>>  }
>>  return 0;
>Hi GianCarlo,
>I saw this in Crafty too. But that doesn't give me a realistic value at all.
>However if I use L_bev_mi1 (like in ExChess) in stead it comes more in the right
>direction. But that gives me a M13 in stead of the M23.
>(I checked in TBIndex.cpp the right squares are found)

M23 = ((M13-1)*2)-1

If you compare this to the formula above you will see it is similar.

I'm sorry I cannot be of more help, but I think the best thing
to do is not to try to figure out how other formulas work (depends
too much on how you represent mate scores in your program), but
to set up a few positions where you know what the score should be,
and look at what the probing function gives you back.

By comparing the two, it should not be hard to arrive at the correct
formula for your program. At least, thats how I did it :)


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