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Seriuos bug in gnuchess 5.0


From: Roger . Edgren
Subject: Seriuos bug in gnuchess 5.0
Date: Thu, 9 Aug 2001 17:15:14 +0300

Hi,

I think I may have found a rather serious bug in Gnuchess 5.0. It seems that
in some cases you can move pieces in a way that does not take you out of a
checked state and which results in the king actually being taken by the
opponent. Here is a sample game that does just that:

     white   black
  1.  d4      e6
  2.  e4      Nc6
  3.  Nc3     Nf6
  4.  d5      exd5
  5.  exd5    Ne5
  6.  Nf3     Nxf3+
  7.  gxf3    Bc5
  8.  Bg5     O-O
  9.  f4      a5
 10.  Qd3     d6
 11.  O-O-O   Bxf2
 12.  Qb5     Bg4
 13.  Rd4     Bxd4
 14.  Qxb7    Bxc3
 15.  bxc3    Bd7
 16.  Qxa8    Qxa8
 17.  c4      Qd8
 18.  Bxf6    Qxf6
 19.  Bh3     Bxh3
 20.  Re1     Qxf4+

At this point the board looks like this:

. . . . . r k .
. . p . . p p p
. . . p . . . .
p . . P . . . .
. . P . . q . .
. . . . . . . b
P . P . . . . P
. . K . R . . .

white's king is in check by black's queen, but, ignoring this, white moves
Rook to f1, after which Black's queen actually take white's king, thus:

 21.  Rf1     Qxc1     

which result in the board looking like this:

. . . . . r k .
. . p . . p p p
. . . p . . . .
p . . P . . . .
. . P . . . . .
. . . . . . . b
P . P . . . . P
. . q . . R . . 

and white no longer has any king :). Actually, I've discovered that gnuchess
continue to believe that the king is in the same position and continues
playing.

To repeat the bug, use the included pgn-file and load it (it contains the
game state up to and including turn 20). Set gnuchess to manual and enter
"Qxf4+", "Rf1" and then "Qxc1".


A question: We rely rather heavily on gnuchess for a 3D multiplayer chess
game (for linux) and would like to know if you actively develop gnuchess and
have any plans to fix this bug in the near future? 


Best Regards,


Roger Edgren.
__________________________________________
Roger Edgren
Software Engineer
Nokia Home Communications
Diskettgatan 11, 583 35 Linköping, SWEDEN
Phone: +46 13 461 14 41 
Fax: +46 13 461 19 98
__________________________________________

"Democracy is four wolves and a sheep voting on dinner." -- Robert A.
Heinlein 

Attachment: bug.pgn
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