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[gnugo-devel] Backspace crashes


From: Daniel Bump
Subject: [gnugo-devel] Backspace crashes
Date: Fri, 4 Jan 2002 11:11:54 -0800

Periodically we get reports of crashes from games played with
CGoban and moves taken back. To take a move back using CGoban
use the back arrow key. You can recognize these games by the
presence of variations in the sgf file.

We've never been able to find this bug.

I just looked at two examples of this:

http://mail.gnu.org/pipermail/gnugo-devel/2001-November/000422.html
http://mail.gnu.org/pipermail/gnugo-devel/2001-October/000364.html

I note that both these games involve passes by GNU Go.
In both games the human tried different variations and sometimes
GNU Go passed after a move didn't threaten anything.  Perhaps
when there are passes GNU Go gets confused about the number
of moves from start, since the gmp implements taking a move
back by regenerating the whole position based on the
number of moves that have been made.

The November bug looks easier to analyze.

The crucial problem is to reproduce the bug. If you run
GNU Go 3.0.0 with random seed 2, it will play the same
moves as in the game. But I can't get the crash to happen,
or even figure out exactly what he did. Note that the
diagram that GNU Go printed is at an earlier move than the
last moves in the sgf file. 

My first thought was that Bill backed up to around this
time then replayed A6, the last move before GNU Go started
passing, and got this crash. But that doesn't cause a crash.

Can anyone reproduce this crash?

Dan



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