Ticket #199: gunnar_7_12.7c.diff

patterns/conn.db

@@ -629 +629 @@
 Bc
 dA
 
-;((attack(A) && lib(A) < 4) || (attack(B) && lib(B) < 4))
+;((attack(A) && !distrust_tactics_helper(A))
+; || (attack(B) && !distrust_tactics_helper(B)))
 ;&& !disconnect_helper(c,d)
 
 

patterns/helpers.c

@@ -808 +808 @@
 }
 
 
+/* This helper is intended to detect semeai kind of positions where
+ * the tactical reading can't be trusted enough to allow amalgamation
+ * over presumably tactically dead strings.
+ *
+ * It has turned out to be best not to trust tactical reading of three
+ * and four liberty strings at all. Not trusting two liberty strings
+ * leads to an underamalgamation and unnecessarily many dragons on the
+ * board. Therefore we try to detect two liberty strings with an
+ * enclosed nakade, which after capturing leads to an unreliable
+ * reading at three or four liberties.
+ *
+ * More specifically we check whether the string has a neighbor with
+ * the following properties:
+ * 1. At least three stones in size.
+ * 2. All its liberties are common liberties with the string.
+ * 3. It has no second order liberties.
+ * 4. Its liberties are adjacent to no other strings than itself and
+ *    the primary string.
+ *
+ * If we find such a neighbor 1 is returned, otherwise 0.
+ */
+int distrust_tactics_helper(int str)
+{
+  int color = board[str];
+  int adj;
+  int adjs[MAXCHAIN];
+  int k;
+  int r;
+  int s;
+  int lib = countlib(str);
+
+  ASSERT1(IS_STONE(board[str]), str);
+  
+  if (lib > 2)
+    return 1;
+  else if (lib == 1)
+    return 0;
+  
+  adj = chainlinks3(str, adjs, lib);
+  for (r = 0; r < adj; r++) {
+    int nakade = 1;
+    int adjlib;
+    int adjlibs[3];
+    if (countstones(adjs[r]) < 3)
+      continue;
+    adjlib = findlib(adjs[r], 3, adjlibs);
+    for (s = 0; s < adjlib; s++) {
+      int str_found = 0;
+      for (k = 0; k < 4; k++) {
+        int pos = adjlibs[s] + delta[k];
+        if (board[pos] == EMPTY
+            && !liberty_of_string(pos, adjs[r]))
+          nakade = 0;
+        else if (board[pos] == color) {
+          if (same_string(pos, str))
+            str_found = 1;
+          else
+            nakade = 0;
+        }
+        else if (board[pos] == OTHER_COLOR(color)
+                 && !same_string(pos, adjs[r]))
+          nakade = 0;
+      }
+      if (!str_found)
+        nakade = 0;
+    }
+    if (nakade)
+      return 1;
+  }
+  
+  return 0;
+}
+
 /*
  * LOCAL Variables:
  * tab-width: 8

patterns/patterns.h

@@ -326 +326 @@
 int adjacent_to_defendable_stone_in_atari(int str);
 void backfill_replace(int move, int str);
 int break_mirror_helper(int str, int color);
+int distrust_tactics_helper(int str);
 int disconnect_helper(int apos, int bpos);