Re: program enters dead loop with some certain move

[Simon Waters]

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Bing Bai wrote:
> Hi,
>  attached is an output of "xboard -debug". If I play the game
in exact
> this order, the program will
> enter a dead loop. I'll never get my turn again. I'm not sure
if the
> attached file is enough.

Hi Bing,

thanks for the report, this is a known issue fixed in 5.04.

The move e5d6 is an illegal move that Xboard does not recognise
as it doesn't completely track enpassant (or castling) status.

GNU Chess correctly recognises the move as illegal, and ignores
it, unfortunately GNU Chess 5.02 does not indicate the illegal
move to Xboard as required by the engine protocol, where as
recent versions of GNU Chess do send an illegal move message to
xboard.

Enpassant captures are only permitted on the move immediately
following a double pawn move, where the pawn maybe captured as
though it only moved one by an adjacent enemy pawn.

Here the black pawn moves to d5 on move 5 before the white pawn
got to e5 on move 8, so no enpassant capture was ever  possible
against the d pawn.

We recommend 5.05 as it has more features, and is generally more
robust against bad inputs of all forms. 5.06 is nearing release
which should offer further features, and stronger play.

Apologies for the bug.

 Simon
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