src/tree.cpp

   1 /* Copyright (C) 2007-2011 Vincent Ollivier
   2  *
   3  * Purple Haze is free software: you can redistribute it and/or modify
   4  * it under the terms of the GNU General Public License as published by
   5  * the Free Software Foundation, either version 3 of the License, or
   6  * (at your option) any later version.
   7  *
   8  * Purple Haze is distributed in the hope that it will be useful,
   9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  11  * GNU General Public License for more details.
  12  *
  13  * You should have received a copy of the GNU General Public License
  14  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  15  */
  16
  17 #include "tree.h"
  18
  19 bool Tree::has_repetition_draw()
  20 {
  21     Position& current_position = tree[tree_top];
  22     if (current_position.halfmove() >= 99) {
  23         return 0; // Fifty-move rule
  24     }
  25     if (tree_top < 4) {
  26         return false;
  27     }
  28     Hash& pos = current_position.hash();
  29     int previous_halfmove = current_position.halfmove();
  30     for (int i = tree_top - 2; i >= 0; i -= 2) {
  31         if (tree[i].hash() == pos) {
  32             return true; // Second repetition
  33         }
  34         if (tree[i].halfmove() > previous_halfmove) { // Halfmove reseted
  35             return false; // No previous repetition possible
  36         }
  37         previous_halfmove = tree[i].halfmove();
  38     }
  39     return false;
  40 }