Ticket #199: gunnar_7_13.9.diff

engine/optics.c

@@ -782 +782 @@
   int effective_eyesize;
   int bulk_score = 0;
   signed char chainlinks[BOARDMAX];
+  int contains_inset = 0;
 
   /* Stones inside eyespace which do not coincide with a false eye or
    * a halfeye.
@@ -815 +816 @@
         if (!chainlinks[neighbor]) {
           bulk_score += 4;
           mark_string(neighbor, chainlinks, 1);
+          /* In a position like this
+           *
+           * |OOO
+           * |X.O
+           * |OXO
+           * |.OO
+           * |.O
+           * |OO
+           *
+           * it would make sense to treat this as a single eyespace
+           * but the stone in atari on the edge splits it up in two
+           * separate eyespaces which are evaluated as 2222 and 1111
+           * respectively. Since they together in fact are 1122 this
+           * is way off. The best solution would be to to merge the
+           * eyespaces but since support for evaluating such eyespaces
+           * is missing we try to workaround it by setting pessimistic
+           * min to zero for both detected eyespaces.
+           *
+           * The code below does the detection of such stones called
+           * inset. Modification of pessimistic min is done later in
+           * the function.
+           */
+          if (countlib(neighbor) == 1
+              && attack(neighbor, NULL) != 0) {
+            int is_inset = 1;
+            int splits_eyespace = 0;
+            int m;
+
+            for (m = 0; m < 4; m++) {
+              if (ON_BOARD(neighbor + delta[m])) {
+                if (eye[neighbor + delta[m]].color == eye[pos].color) {
+                  if (eye[neighbor + delta[m]].origin != pos)
+                    splits_eyespace = 1;
+                }
+                else
+                  is_inset = 0;
+              }
+            }
+            contains_inset |= (is_inset & splits_eyespace);
+          }
         }
       }
       else if (!ON_BOARD(neighbor))
@@ -878 +919 @@
     DEBUG(DEBUG_EYES, "  pessimistic min revised to 1 (interior stones)\n");
   }
 
+  if (contains_inset) {
+    *pessimistic_min = 0;
+    DEBUG(DEBUG_EYES, "  pessimistic min revised to 0 (contains inset)\n");
+  }
+
   if (attack_point
       && *attack_point == NO_MOVE
       && max_eyes(value) != *pessimistic_min) {