src/history.cpp

   1 /*
   2   Glaurung, a UCI chess playing engine.
   3   Copyright (C) 2004-2008 Tord Romstad
   4
   5   Glaurung is free software: you can redistribute it and/or modify
   6   it under the terms of the GNU General Public License as published by
   7   the Free Software Foundation, either version 3 of the License, or
   8   (at your option) any later version.
   9
  10   Glaurung is distributed in the hope that it will be useful,
  11   but WITHOUT ANY WARRANTY; without even the implied warranty of
  12   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13   GNU General Public License for more details.
  14
  15   You should have received a copy of the GNU General Public License
  16   along with this program.  If not, see <http://www.gnu.org/licenses/>.
  17 */
  18
  19
  20 ////
  21 //// Includes
  22 ////
  23
  24 #include <cassert>
  25
  26 #include "history.h"
  27
  28
  29 ////
  30 //// Functions
  31 ////
  32
  33 /// Constructor
  34
  35 History::History() {
  36   this->clear();
  37 }
  38
  39
  40 /// History::clear() clears the history tables.
  41
  42 void History::clear() {
  43   memset(history, 0, 2 * 8 * 64 * sizeof(int));
  44   memset(successCount, 0, 2 * 8 * 64 * sizeof(int));
  45   memset(failureCount, 0, 2 * 8 * 64 * sizeof(int));
  46 }
  47
  48
  49 /// History::success() registers a move as being successful.  This is done
  50 /// whenever a non-capturing move causes a beta cutoff in the main search.
  51 /// The three parameters are the moving piece, the move itself, and the
  52 /// search depth.
  53
  54 void History::success(Piece p, Move m, Depth d) {
  55   assert(piece_is_ok(p));
  56   assert(move_is_ok(m));
  57
  58   history[p][move_to(m)] += int(d) * int(d);
  59   successCount[p][move_to(m)]++;
  60
  61   // Prevent history overflow:
  62   if(history[p][move_to(m)] >= HistoryMax)
  63     for(int i = 0; i < 16; i++)
  64       for(int j = 0; j < 64; j++)
  65         history[i][j] /= 2;
  66 }
  67
  68
  69 /// History::failure() registers a move as being unsuccessful.  The function is
  70 /// called for each non-capturing move which failed to produce a beta cutoff
  71 /// at a node where a beta cutoff was finally found.
  72
  73 void History::failure(Piece p, Move m) {
  74   assert(piece_is_ok(p));
  75   assert(move_is_ok(m));
  76
  77   failureCount[p][move_to(m)]++;
  78 }
  79
  80
  81 /// History::move_ordering_score() returns an integer value used to order the
  82 /// non-capturing moves in the MovePicker class.
  83
  84 int History::move_ordering_score(Piece p, Move m) const {
  85   assert(piece_is_ok(p));
  86   assert(move_is_ok(m));
  87
  88   return history[p][move_to(m)];
  89 }
  90
  91
  92 /// History::ok_to_prune() decides whether a move has been sufficiently
  93 /// unsuccessful that it makes sense to prune it entirely.
  94
  95 bool History::ok_to_prune(Piece p, Move m, Depth d) const {
  96   assert(piece_is_ok(p));
  97   assert(move_is_ok(m));
  98
  99   return (int(d) * successCount[p][move_to(m)] < failureCount[p][move_to(m)]);
 100 }