[gnugo-devel] optics patch

[Paul Pogonyshev]

this patch fixes ninestones:290 (one of the tests i've submitted
recently). it has no other impact on regressions.

- evaluate_diagonal_intersection() tries additional moves to
  defend a diagonal
- does_secure() made global and moved to reading.c

Paul


Index: optics.c
===================================================================
RCS file: /cvsroot/gnugo/gnugo/engine/optics.c,v
retrieving revision 1.62
diff -u -p -r1.62 optics.c
--- optics.c    30 Dec 2002 20:11:09 -0000      1.62
+++ optics.c    1 Jan 2003 20:28:57 -0000
@@ -1681,6 +1681,11 @@ evaluate_diagonal_intersection(int m, in
     return 0.0;
 
   if (board[pos] == EMPTY) {
+    int your_safety = safe_move(pos, other);
+
+    apos = pos;
+    dpos = pos;
+
     /* We should normally have a safe move, but occasionally it may
      * happen that it's not safe. There are complications, however,
      * with a position like this:
@@ -1694,9 +1699,6 @@ evaluate_diagonal_intersection(int m, in
      * Therefore we ignore our own safety if opponent's safety depends
      * on ko.
      */
-
-    int your_safety = safe_move(pos, other);
-    
     if (your_safety == 0)
       value = 0.0;
     else if (your_safety != WIN)
@@ -1704,16 +1706,43 @@ evaluate_diagonal_intersection(int m, in
     else {                           /* So your_safety == WIN. */
       int our_safety = safe_move(pos, color);
       
-      if (our_safety == 0)
-        value = 2.0;
+      if (our_safety == 0) {
+       int k;
+
+       value = 2.0;
+
+       /* This check is intended to fix a certain special case, but might
+        * be helpful in other situations as well. Consider this position,
+        * happened in owl reading deep enough:
+        *
+        * |XXXXX
+        * |XOOXX
+        * |O.OOX
+        * |.OXX.
+        * +-----
+        *
+        * Without this check, the corner eye is considered false, not half-
+        * eye. Thus, owl thinks that the capture gains at most one eye and
+        * gives up.
+        */
+       for (k = 4; k < 8; k++) {
+         int diagonal = pos + delta[k];
+         int lib;
+
+         if (board[diagonal] == other && findlib(diagonal, 1, &lib) == 1) {
+           if (does_secure(color, lib, pos)) {
+             value = 1.0;
+             apos = lib;
+             break;
+           }
+         }
+       }
+      }
       else if (our_safety == WIN)
         value = 1.0;
       else                           /* our_safety depends on ko. */
         value = b;
     }
-
-    apos = pos;
-    dpos = pos;
   }
   else if (board[pos] == color) {
     /* This stone had better be safe, otherwise we wouldn't have an

Index: reading.c
===================================================================
RCS file: /cvsroot/gnugo/gnugo/engine/reading.c,v
retrieving revision 1.94
diff -u -p -r1.94 reading.c
--- reading.c   22 Dec 2002 20:17:43 -0000      1.94
+++ reading.c   1 Jan 2003 20:33:53 -0000
@@ -5483,6 +5483,22 @@ safe_move(int move, int color)
 }
 
 
+/* Checks if a move by color makes an opponent move at pos a self atari.
+ */
+int
+does_secure(int color, int move, int pos)
+{
+  int result = 0;
+  if (trymove(move, color, NULL, NO_MOVE, EMPTY, NO_MOVE)) {
+    if (is_self_atari(pos, OTHER_COLOR(color)))
+      result = 1;
+    popgo();
+  }
+  
+  return result;
+}
+
+
 /* ===================== Statistics  ============================= */
 
 

Index: readconnect.c
===================================================================
RCS file: /cvsroot/gnugo/gnugo/engine/readconnect.c,v
retrieving revision 1.40
diff -u -p -r1.40 readconnect.c
--- readconnect.c       14 Nov 2002 07:40:53 -0000      1.40
+++ readconnect.c       1 Jan 2003 20:47:19 -0000
@@ -1782,7 +1782,6 @@ static void compute_connection_distances
                                         struct connection_data *conn);
 static void print_connection_distances(struct connection_data *conn);
 static int trivial_connection(int str1, int str2, int *move);
-static int does_secure(int color, int move, int pos);
 static int does_secure_through_ladder(int color, int move, int pos);
 static int ladder_capture(int str, int *move);
 static int ladder_capturable(int pos, int color);
@@ -3073,22 +3072,6 @@ trivial_connection(int str1, int str2, i
   /* Turn the sgf traces back on. */
   sgf_dumptree = save_sgf_dumptree;
   count_variations = save_count_variations;
-  
-  return result;
-}
-
-
-/* True if a move by color makes an opponent move at pos a self atari.
- */
-static int
-does_secure(int color, int move, int pos)
-{
-  int result = 0;
-  if (trymove(move, color, NULL, NO_MOVE, EMPTY, NO_MOVE)) {
-    if (is_self_atari(pos, OTHER_COLOR(color)))
-      result = 1;
-    popgo();
-  }
   
   return result;
 }

Index: liberty.h
===================================================================
RCS file: /cvsroot/gnugo/gnugo/engine/liberty.h,v
retrieving revision 1.145
diff -u -p -r1.145 liberty.h
--- liberty.h   25 Dec 2002 20:26:44 -0000      1.145
+++ liberty.h   1 Jan 2003 22:09:44 -0000
@@ -173,7 +173,7 @@ int is_edge_vertex(int pos);
 /* Count and/or find liberties at (pos). */
 int countlib(int str);
 int findlib(int str, int maxlib, int *libs);
-int fastlib(int pos, int color, int ignore_capture);
+int fastlib(int pos, int color, int ignore_captures);
 int approxlib(int pos, int color, int maxlib, int *libs);
 int accuratelib(int pos, int color, int maxlib, int *libs);
 int count_common_libs(int str1, int str2);
@@ -374,6 +374,7 @@ void set_temporary_depth_values(int d, i
 void restore_depth_values(void);
 
 int safe_move(int move, int color);
+int does_secure(int color, int move, int pos);
 
 void join_dragons(int d1, int d2);
 int dragon_escape(char goal[BOARDMAX], int color, char escape_value[BOARDMAX]);