[gnugo-devel] endgame8 problems

[Paul Pogonyshev]

- endgame_analyze_worm_liberties() revised

this patch makes gnu go pass the recently added tests endgame:803,804.
unfortunately, it makes trevorc:1060 fail again. i think it is
acceptable, since gnu go used to find K11 move while analyzing K12
worm, but now it sees that it can be "defended" by playing on K13 - a
false eye. since this false eye has to be filled no matter what, it
now thinks that there is no reason to prevent black from playing K13.
it currently has no means to see that it will have to add J13 later.

this can be fixed by some kind of backfilling. e.g., black could
backfill at N11, making N13 an inessential liberty. then, if white
backfills at K13, gnu go will see that K11 is worth a point. however,
it's quite complicated and unclear (when to backfill, when not...) so
i think we can live with this failure for now.

regression delta is 2 passes (endgame:803,804), 1 fail (trevorc:1060).

Paul


Index: engine/endgame.c
===================================================================
RCS file: /cvsroot/gnugo/gnugo/engine/endgame.c,v
retrieving revision 1.3
diff -u -p -r1.3 endgame.c
--- engine/endgame.c    22 Feb 2003 05:19:14 -0000      1.3
+++ engine/endgame.c    22 Feb 2003 23:42:33 -0000
@@ -74,10 +74,10 @@ endgame(int color)
  * position, although black sacrifice one point by playing in white's 
territory,
  * he forces white to eventually capture the black string, losing three points.
  * However, white has to play at `*' sooner or later if black doesn't take
- * that point, so the move is worth 3 - 1 - 1 = 1 point only, not two.
+ * that vertex, so the move is worth 3 - 1 - 1 = 1 point only, not two.
  *
  * This function is able to find such moves. Algorithm is based on finding
- * such called "inessential liberties". This are defined as liberties, which
+ * such called "inessential liberties". These are defined as liberties, which
  * satisfy five conditions:
  *
  *     1) they are not within an eye (not in someone's territory),
@@ -88,7 +88,7 @@ endgame(int color)
  *     5) they are safe to fill with stones of other than the worm's color.
  *
  * Such liberties are supposed to never become territory (they can't become
- * and additional eye for the worm under consideration), the worm cannot
+ * an additional eye for the worm under consideration), the worm cannot
  * connect to something via such a liberty and they will (or at least can)
  * be eventually filled by either of the players.
  *
@@ -106,6 +106,8 @@ endgame_analyze_worm_liberties(int pos, 
   int essential_libs[MAXLIBS];
   int inessential_liberties = 0;
   int inessential_libs[MAXLIBS];
+  int false_eye_liberties = 0;
+  int false_eye_libs[MAXLIBS];
   int num_attacks;
   int num_attacks2;
   int attacks[MAXLIBS];
@@ -156,6 +158,8 @@ endgame_analyze_worm_liberties(int pos, 
        else
          inessential_libs[inessential_liberties++] = lib;
       }
+      else if (is_false_eye(half_eye, lib) && !false_eye_territory[lib])
+       false_eye_libs[false_eye_liberties++] = lib;
     }
   }
 
@@ -193,7 +197,8 @@ endgame_analyze_worm_liberties(int pos, 
              int i;
 
              /* If the attack cannot be defended against by playing on
-              * another essential liberty or by capturing an opponent
+              * another essential liberty, filling a pure false eye (an
+              * eye which can't become territory) or capturing an opponent
               * string in atari, keep it for now.
               */
              for (i = 0; i < essential_liberties; i++) {
@@ -203,22 +208,29 @@ endgame_analyze_worm_liberties(int pos, 
              }
 
              if (i == essential_liberties) {
-               int adj[MAXCHAIN];
-               int adjs;
-
-               adjs = chainlinks2(pos, adj, 1);
-               for (i = 0; i < adjs; i++) {
-                 int lib2;
-                 findlib(adj[i], 1, &lib2);
-                 if (lib2 != dpos && !is_proper_eye_space(lib2)
-                     && does_defend(lib2, pos))
+               for (i = 0; i < false_eye_liberties; i++) {
+                 if (does_defend(false_eye_libs[i], pos))
                    break;
                }
 
-               if (i == adjs) {
-                 attacks[num_attacks] = lib;
-                 defenses[num_attacks] = dpos;
-                 num_attacks++;
+               if (i == false_eye_liberties) {
+                 int adj[MAXCHAIN];
+                 int adjs;
+
+                 adjs = chainlinks2(pos, adj, 1);
+                 for (i = 0; i < adjs; i++) {
+                   int lib2;
+                   findlib(adj[i], 1, &lib2);
+                   if (lib2 != dpos && !is_proper_eye_space(lib2)
+                       && does_defend(lib2, pos))
+                     break;
+                 }
+
+                 if (i == adjs) {
+                   attacks[num_attacks] = lib;
+                   defenses[num_attacks] = dpos;
+                   num_attacks++;
+                 }
                }
              }
            }
@@ -316,7 +328,7 @@ endgame_analyze_worm_liberties(int pos, 
       }
       else {
        /* This must be the only attack (filling all inessential liberties
-        * an atari.
+        * gives an atari).
         */
        ASSERT1(num_attacks == 1, pos);
        attacks[num_attacks2++] = attacks[k];