Re: [gnugo-devel] owl.c cleaning

[Gunnar Farneback]

Paul wrote:
> fixing the bug above had brought a single pass:
> 
> owl1:304        PASS 0 [0]
> 
> the test must be fixable by improving owl_find_lunches() (that's one
> of the two new FIXMEs), but it doesn't mean we should leave the bug
> there.

Incidentally I already have a fix written for that.

/Gunnar

Index: engine/owl.c
===================================================================
RCS file: /cvsroot/gnugo/gnugo/engine/owl.c,v
retrieving revision 1.151
diff -u -r1.151 owl.c
--- engine/owl.c        22 Apr 2003 02:48:05 -0000      1.151
+++ engine/owl.c        27 Apr 2003 20:25:06 -0000
@@ -4316,6 +4316,21 @@
  *
  * 1b. The liberty is a topologically false eye with respect to the
  *     goal dragon.
+ *
+ * This is not quite good enough though, as shown in this position:
+ *
+ * ----------
+ * OX.X.OO...
+ * OXX.OOX.O.
+ * O.XXXXX.O.
+ * OOOOOOOOO.
+ *
+ * The four O stones are regarded as inessential after inclusion of
+ * rule 1b, which is clearly inappropriate. To solve this problem we
+ * modify the rule:
+ *
+ * 1b'. The liberty is a topologically false eye with respect to the
+ *      goal dragon and is adjacent to no empty vertex.
  */
 
 static void
@@ -4456,6 +4471,17 @@
                }
                if (diagonal_goal + (off_board >= 2) < 2)
                  essential = 1;
+               else {
+                 /* Check that the liberty is adjacent to no empty
+                  * vertex, as required by 1b'.
+                  */
+                 for (s = 0; s < 4; s++) {
+                   if (board[bpos + delta[s]] == EMPTY) {
+                     essential = 1;
+                     break;
+                   }
+                 }
+               }
              }
 
              if (essential)