Bug hunt

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Article #1876

#1876

From: Simon Waters
Date: Sun, 13 Jan 2002 16:55

33 lines
2004 bytes

Noted a bug in the GNU chess code.

White to move.
White Kd6, White Pc7
Black Kb7

If the program is set to search a specific depth it find Kd7 no
problem

If the search is interrupted or runs out of time it plays c8=N
and draws. Since Ctrl-C or SIGINT justs sets the TIMEOUT flag
the behaviour is as expected.

Dropping diagnostics in to the Search (Not SearchRoot) routine
part of search.c hints that the score being backed up the tree
becomes -MATE when it should be +MATE or something similar.....

      if (flags & TIMEOUT)
      {
 
         best = (ply & 1 ? rootscore : -rootscore);
         return (best);
      }

A couple of fiddles with the "best =" line resolve the problem,
but I can't figure out the right thing to do here, or whether
this is the bug or just a bit of the code sensitive to the real
bug.

Anyone with a better understanding of this piece of code care to
comment?

 Simon, needing to understand the PVS code better.

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From: Simon Waters <Simon@wretched.demon.co.uk>
Newsgroups: gnu.chess
Subject: Bug hunt
Date: Sun, 13 Jan 2002 16:55:47 +0000
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