Ticket #163: fix2.patch

engine/board.c

@@ -1577 +1577 @@
          * conditional ko capture.
          */
         if (pos != board_ko_pos && !DIAGONAL_NEIGHBORS(kpos, kom_pos))
-              return 0;
+          return 0;
         break;
 
       default:

engine/owl.c

@@ -1359 +1359 @@
   *this_resultb = 0;
 
   if (!komaster_trymove(move, color, move_name, apos, &ko_move, ko_allowed)) {
-    /* Move was not allowed because of komaster. We want to check, if this
-     * situation is double ko and when it is, we won semeai.
-     */
-    int libs[MAX_LIBERTIES];
-    int n;
-    int nlib;
-    int sworm;
-    int worm_color;
-
-    for (sworm = 0; sworm < s_worms; sworm++) {
-      worm_color = board[semeai_worms[sworm]];
-      if (worm_color == color && *this_resulta == 0) {
-        /* We only check up to MAX_LIBERTIES, due to performance reasons. When we
-         * have more liberties we have some outside liberties to fill and these
-         * moves will be tried later (and double ko situation will be found).
-         */
-        nlib = findlib(semeai_worms[sworm], MAX_LIBERTIES, libs);
-        if (nlib > MAX_LIBERTIES)
-          return 0;
-
-        for (n = 0; n < nlib; n++)
-          if (is_ko(libs[n], OTHER_COLOR(color), NULL)) {
-            /* Our dragon has double ko, but we have to check if opponent dragon
-             * doesn't have outside liberties or double ko.
-             */
-            *this_resulta = WIN;
-            *this_resultb = WIN;
-          }
-      }
-      else if (worm_color == OTHER_COLOR(color)) {
-        nlib = findlib(semeai_worms[sworm], 2, libs);
-        if (nlib > 2)
-          /* In double ko situation the opponent can have only
-           * a single eye and a ko outside liberty to be sure that we
-           * will always win double ko. */
-          return 0;
+    int kpos;
+    if (is_ko(move, color, &kpos)) {
+      /* Move was not allowed because of komaster. We want to check, if this
+       * situation is double ko and when it is, we won semeai.
+       */
+      int libs[MAX_LIBERTIES];
+      int n;
+      int nlib;
+      int sworm;
+      int worm_color;
+      int other = OTHER_COLOR(color);
+
+      for (sworm = 0; sworm < s_worms; sworm++) {
+        worm_color = board[semeai_worms[sworm]];
+        if (worm_color == color) {
+          /* We only check up to MAX_LIBERTIES, due to performance reasons. When we
+           * have more liberties we have some outside liberties to fill and these
+           * moves will be tried later (and double ko situation will be found).
+           */
+          nlib = findlib(semeai_worms[sworm], MAX_LIBERTIES, libs);
+          if (nlib > MAX_LIBERTIES)
+            return 0;
+
+          for (n = 0; n < nlib; n++)
+            if (is_ko(libs[n], other, NULL)) {
+              /* Check if situation is not a nested ko capture. */
+              if (DIAGONAL_NEIGHBORS(libs[n], kpos))
+                return 0;
+
+              /* Our dragon has double ko, but we have to check if opponent dragon
+               * doesn't have outside liberties or double ko.
+               */
+              *this_resulta = WIN;
+              *this_resultb = WIN;
+            }
+        }
+        else if (worm_color == other) {
+          if (countlib(semeai_worms[sworm]) > 2)
+            /* In double ko situation the opponent can have only
+             * a single eye and a ko outside liberty to be sure that we
+             * will always win double ko. */
+            return 0;
+        }
       }
+      if (*this_resulta == WIN)
+        return 1;
     }
 
-    if (*this_resulta == WIN)
-      return 1;
-
     return 0;
   }