Re: [gnugo-devel] bug in gnugo

[Gunnar Farneback]

I wrote:
> Caused by filllib. It wants to fill the liberty at E2 but notices that
> G7 becomes tactically critical then (was undefendable). To avoid that
> it suggests first playing the move attacking G7 after E2 was filled.
> Unfortunately that move happens to be C1, which can't be played before
> E2. This is not difficult to work around and I have a patch, but
> unless someone urgently wants to see it I'll wait until Savannah is
> back up to submit it.

Here it is.

- detect_tactical_blunder() revised

/Gunnar

Index: engine/utils.c
===================================================================
RCS file: /cvsroot/gnugo/gnugo/engine/utils.c,v
retrieving revision 1.83
diff -u -r1.83 utils.c
--- engine/utils.c      13 Nov 2003 22:48:42 -0000      1.83
+++ engine/utils.c      30 Dec 2003 22:23:04 -0000
@@ -1199,8 +1199,21 @@
       
       if (defense_effective && defense_point) {
        int dpos;
-       if (attack(pos, &dpos))
+       if (attack(pos, &dpos)) {
          *defense_point = dpos;
+         /* Check that this move is legal and effective also on the
+           * original board, otherwise find a tactical attack there
+           * instead.
+          */
+         popgo();
+         
+         if (!is_legal(dpos, color)
+             || play_attack_defend_n(color, 0, 1, dpos, pos))
+           attack(pos, defense_point);
+
+         /* Redo the move, we know that it won't fail. */
+         trymove(move, color, NULL, NO_MOVE, EMPTY, NO_MOVE);
+       }
        else {
          verbose = save_verbose;
          TRACE("No attack found (unexpectedly) on %1m after move at %1m.\n",