[gnugo-devel] reading patch

[Gunnar Farnebäck]

This patch allows self atari in special_rescue_moves() when it may set
up a snapback. Regression results:

owl1:351        PASS 1 E11 [1 (PASS|E11|F19|G18)]
reading:218     pass
2 PASS (1 PASS, 1 pass)
Total nodes: 1675790408 3161119 13118597 (+0.16% -0.0056% -0.015%)

- special_rescue_moves() revised to allow self atari moves which may
  set up a snapback

/Gunnar

Index: engine/reading.c
===================================================================
RCS file: /cvsroot/gnugo/gnugo/engine/reading.c,v
retrieving revision 1.156
diff -u -r1.156 reading.c
--- engine/reading.c    7 Dec 2004 04:50:02 -0000       1.156
+++ engine/reading.c    7 Mar 2005 14:04:51 -0000
@@ -1840,10 +1840,12 @@
 {
   int color = board[str];
   int other = OTHER_COLOR(color);
+  int otherlib;
   int k;
 
   /* Use approxlib() to test for trivial capture. */
-  if (approxlib(lib, other, 3, NULL) > 2)
+  otherlib = approxlib(lib, other, 3, NULL);
+  if (otherlib > 2)
     return;
 
   /* Loop over the four neighbours of the liberty, (lib + d). */
@@ -1851,8 +1853,8 @@
     int d = delta[k];
     if (board[lib + d] == EMPTY) {
 
-      /* Don't play into a self atari. */
-      if (is_self_atari(lib + d, color))
+      /* Don't play into a self atari unless we have a potential snapback. */
+      if (is_self_atari(lib + d, color) && otherlib > 1)
        continue;
 
       /* Be more demanding when the string has four liberties. (Mostly