Re: [gnugo-devel] Floating point arithmetics

[nando]

Hi again,

Following patch and results are relative to nando_7_1.1

The basic idea is simple : reduce the branching factor by progressively
constraining the "delta-distances" between the candidate moves.

Performance impact :

Total nodes: 1624509689 (-1.7%) 2968938 (-eps) 13043774 (-4.3%)
Total time: 8348.65 (-2.1%) (8352.54)

Regressions delta :

break_in:100    pass [0] [0]   (fails in nando_7_1.1)
nicklas2:2103   FAIL C1 [PASS]
nngs:1260       PASS G18 [G18|F18]

I was about to analyze those, but I've just got an emergency with a
severe crash on our main server. I'll try to come back to it as soon
as I can.

-- nando

- new heuristic to reduce branching factor in connection reading.

Index: engine/readconnect.c
===================================================================
RCS file: /cvsroot/gnugo/gnugo/engine/readconnect.c,v
retrieving revision 1.83
diff -u -p -r1.83 readconnect.c
--- engine/readconnect.c        24 Aug 2004 14:39:53 -0000      1.83
+++ engine/readconnect.c        20 Sep 2004 08:02:06 -0000
@@ -2601,16 +2601,28 @@ find_connection_moves(int str1, int str2
 
   /* Filter out moves with distance at least 1.5 more than the best
    * move, or with distance higher than the cutoff specified.
+   *
+   * In order to further reduce the branching factor, a decreasing
+   * cutoff is applied between candidates. For instance, in this case
+   *   1. d    2. d+0.5   3. d+1.0   4. d+1.5
+   * the 4th candidate will be tested, while in following one
+   *   1. d    2. d+0.1   3. d+0.2   4. d+1.5
+   * it will be discarded.
    */
   if (num_moves <= 1 || !is_ko(moves[0], color_to_move, NULL))
     distance_limit = distances[0] + FP(1.5);
   else
     distance_limit = distances[1] + FP(1.5);
 
-  for (r = 0; r < num_moves; r++)
+  for (r = 0; r < num_moves; r++) {
+    if (r > 0
+       && distances[r] > distances[r-1]
+       && distances[r] - distances[r-1] > (8 - r) * FP(0.2))
+      break;
     if (distances[r] > distance_limit
        || distances[r] > cutoff)
       break;
+  }
   num_moves = r;
 
   return num_moves;