[gnugo-devel] readconnect patch

[Gunnar Farneback]

This is a patch to readconnect.c.

- add_array() in readconnect.c simplified
- bugfix in moves_to_connect_in_two_moves()
- sgf traces turned off in quiescence_capture()

The bugfix in moves_to_connect_in_two_moves() causes 5 unexpected
passes in test suite connect.tst (cases 6, 24, 27, 48, 68). Turning
off sgf traces in quiescence_capture() eliminates distracting
variations generated by the naive_ladder() call.

I'm slowly starting to find my way around the readconnect code. I have
a fairly good idea how to add testing of additional connecting moves.
What's still a mystery to me is how to fix disconnect mistakes in e.g.
the basic position in test case 2 of connect.tst. I'm just getting
lost in the maze of calls

recursive_disconnect() ->
prevent_connection_two_moves() ->
connection_two_moves() ->
connected_one_move() ->
connection_one_move()

and similar. Returning to connect:2, the problem is to try to
disconnect the two space jump on the third line between G17 and K17.

   A B C D E F G H J K L M N O P Q R S T
19 . . . . . . . . . . . . . . . . . . . 19
18 . . . . . . . . . . . . . . . . . . . 18
17 . . . . O . X . . X . O . . . . . . . 17
16 . . . + . . . . . + . . . . . X . . . 16
15 . . . . O . . . . . . O . . . . . . . 15
14 . . . . . . . . . . . . . . . . . . . 14
13 . . . . O . O . O . O . . . . . . . . 13

What basically happens is that it first tries to determine whether X
can connect the two stones at all. This involves trying the moves
X H17 (generated by connection_two_moves())
O J17 (generated by connected_one_move())
to get to the position 

   A B C D E F G H J K L M N O P Q R S T
19 . . . . . . . . . . . . . . . . . . . 19
18 . . . . . . . . . . . . . . . . . . . 18
17 . . . . O . X X O X . O . . . . . . . 17
16 . . . + . . . . . + . . . . . X . . . 16
15 . . . . O . . . . . . O . . . . . . . 15
14 . . . . . . . . . . . . . . . . . . . 14
13 . . . . O . O . O . O . . . . . . . . 13

and then connection_one_move() says "no, no connection" and the
variation is disregarded. After trying the symmetric moves X J17 and O
H17 with the same result it gives up and says "G17 and K17 are
disconnected as it stands". Clearly something goes wrong here but I
don't know how to deal with it. One can notice that
recursive_connect() manages to find a connection, but this involves
other code than the functionns called from recursive_disconnect().

Tristan, could you try to explain the overall structure of the code?
Which function needs to be improved/bugfixed to solve the mistake
above?

/Gunnar

Index: engine/readconnect.c
===================================================================
RCS file: /cvsroot/gnugo/gnugo/engine/readconnect.c,v
retrieving revision 1.8
diff -u -r1.8 readconnect.c
--- engine/readconnect.c        2001/10/13 15:29:15     1.8
+++ engine/readconnect.c        2001/10/28 12:11:58
@@ -63,16 +63,15 @@
 int nodes_connect=0,max_nodes_connect=2000,max_connect_depth=64;
 
 static int add_array (int *array, int elt) {
-  int r, add = 1;
+  int r;
   
-  for (r = 1; ((r < array[0] + 1) && add); r++)
+  for (r = 1; r < array[0] + 1; r++)
     if (array[r] == elt)
-      add = 0;
-  if (add) {
-    array[0]++;
-    array[array[0]] = elt;
-  }
-  return add;
+      return 0;
+
+  array[0]++;
+  array[array[0]] = elt;
+  return 1;
 }
 
 static int element_array (int *array,int elt) {
@@ -259,19 +258,19 @@
        add_array(moves, WEST(libs[r]));
       }
     }
-    else if (board[EAST(libs[r])] == EMPTY) {
+    if (board[EAST(libs[r])] == EMPTY) {
       if (liberty_of_string(EAST(libs[r]), str2)) {
        add_array(moves, libs[r]);
        add_array(moves, EAST(libs[r]));
       }
     }
-    else if (board[SOUTH(libs[r])] == EMPTY) {
+    if (board[SOUTH(libs[r])] == EMPTY) {
       if (liberty_of_string(SOUTH(libs[r]), str2)) {
        add_array(moves, libs[r]);
        add_array(moves, SOUTH(libs[r]));
       }
     }
-    else if (board[NORTH(libs[r])] == EMPTY) {
+    if (board[NORTH(libs[r])] == EMPTY) {
       if (liberty_of_string(NORTH(libs[r]), str2)) {
        add_array(moves, libs[r]);
        add_array(moves, NORTH(libs[r]));
@@ -543,13 +542,28 @@
 }
  
 static int quiescence_capture (int str, int *move) {
+  SGFTree *save_sgf_dumptree = sgf_dumptree;
+  int save_count_variations = count_variations;
+  int result = 0;
+
+  /* We turn off the sgf traces here to avoid cluttering them up with
+   * naive_ladder moves.
+   */
+  sgf_dumptree = NULL;
+  count_variations = 0;
+
   if (countlib(str) == 1) {
     findlib(str, 1, move);
-    return WIN;
+    result = WIN;
   }
   else if (countlib(str) == 2)
-    return naive_ladder(str, move);
-  return 0;
+    result = naive_ladder(str, move);
+
+  /* Turn the sgf traces back on. */
+  sgf_dumptree = save_sgf_dumptree;
+  count_variations = save_count_variations;
+
+  return result;
 }
 
 /* static int capture_one_move (int str) { */