Re: [gnugo-devel] abort on inconsistent genmove result

[Gunnar Farneback]

Arend wrote:
> This was here caused by fill_liberty(). I am not familiar with the code
> there, but I guess it should now be rather easy to track the problem
> down.

The appended patch fixes the problem in fill_liberty(). As an extra
bonus I have included a revision of filllib_confirm_safety(), solving
filllib:39.

- bugfix in fill_liberty()
- filllib_confirm_safety() revised

/Gunnar

Index: engine/filllib.c
===================================================================
RCS file: /cvsroot/gnugo/gnugo/engine/filllib.c,v
retrieving revision 1.24
diff -u -r1.24 filllib.c
--- engine/filllib.c    10 Sep 2002 20:17:27 -0000      1.24
+++ engine/filllib.c    16 Sep 2002 14:36:00 -0000
@@ -305,12 +305,16 @@
        if (board[pos + d] == other
            && worm[pos + d].attack_codes[0] != 0) {
          /* Just pick some other liberty. */
+         /* FIXME: Something is odd about this code. */
          int libs[2];
          if (findlib(pos + d, 2, libs) > 1) {
            if (is_legal(libs[0], color))
              *move = libs[0];
            else if (is_legal(libs[1], color))
              *move = libs[1];
+           else
+             continue;
+           
            DEBUG(DEBUG_FILLLIB, "Filllib: Found at %1m.\n", *move);
            return 1;
          }
@@ -517,7 +521,7 @@
          && !play_attack_defend_n(color, 0, 1, move, pos2)) {
        int adj;
        adj = chainlinks(pos2, adjs);
-       /* It seems unlikely that we would ever get adjacent strings
+       /* It seems unlikely that we would ever get no adjacent strings
          * here, but if it should happen we simply give up and say the
          * move is unsafe.
         */
@@ -529,6 +533,24 @@
       }
     }
 
+  /* Next attempt are diagonal neighbors. */
+  if (apos == NO_MOVE) {
+    for (k = 4; k < 8; k++)
+      if (board[move + delta[k]] == color) {
+       apos = move + delta[k];
+       break;
+      }
+  }
+
+  /* And two steps away. */
+  if (apos == NO_MOVE) {
+    for (k = 0; k < 4; k++)
+      if (board[move + 2 * delta[k]] == color) {
+       apos = move + 2 * delta[k];
+       break;
+      }
+  }
+  
   /* We should have found something by now. If not something's
    * probably broken elsewhere. Declare the move unsafe if it happens.
    */