draw.cpp

   1 /***************************************************************************
   2                       draw.cpp  -  Draw recognition
   3                              -------------------
   4     begin                : Sun Sep 28 2007
   5     copyright            : (C) 2007 by Maurizio Monge
   6     email                : monge@linuz.sns.it
   7  ***************************************************************************/
   8
   9 /***************************************************************************
  10  *                                                                         *
  11  *   This program is free software; you can redistribute it and/or modify  *
  12  *   it under the terms of the GNU General Public License as published by  *
  13  *   the Free Software Foundation; either version 2 of the License, or     *
  14  *   (at your option) any later version.                                   *
  15  *                                                                         *
  16  ***************************************************************************/
  17
  18 #include "engine.h"
  19 #include "search.h"
  20
  21 /* check if the position can be considered draw for 50mvs rule or repetition */
  22 bool Engine::check_draw()
  23 {
  24     if(board.fifty >= 100) /* 50mvs rule */
  25         return true;
  26
  27     return board.insufficient_material() || check_repetition(2);
  28 }
  29
  30 bool Engine::check_repetition(int nfold)
  31 {
  32     /* for the latest reversible moves check if the hash value
  33         (for this player) is the same         */
  34     int first_candidate = MAX(save_buf_num - board.fifty, 0);
  35
  36     /* -4 because it is impossible that the previous position is
  37        equal to the  current one :) */
  38     for(int i=save_buf_num-4;i>=first_candidate;i-=2)
  39     {
  40         if(board.hash == save_buf[i].hash_key)
  41         {
  42             nfold--;
  43             if(nfold <= 1)
  44                 return true;
  45         }
  46     }
  47
  48     return false;
  49 }
  50
  51 /* check if the position can be considered draw for 50mvs rule or repetition */
  52 bool SearchRoot::check_draw(int curr_ply)
  53 {
  54     if(board.fifty >= 100) /* 50mvs rule */
  55         return true;
  56
  57     return board.insufficient_material() || check_repetition(curr_ply, 2);
  58 }
  59
  60 bool SearchRoot::check_repetition(int curr_ply, int nfold)
  61 {
  62     int first_candidate1 = MAX(curr_ply - board.fifty, 0);
  63
  64     /* -4 because it is impossible that the previous position is
  65        equal to the  current one :) */
  66     for(int i=curr_ply-4;i>=first_candidate1;i-=2)
  67     {
  68         if(board.hash == stack[i].save_buf.hash_key)
  69         {
  70             nfold--;
  71             if(nfold <= 1)
  72                 return true;
  73         }
  74     }
  75
  76     int first_candidate2 = MAX(engine->save_buf_num + curr_ply - (board.fifty & ~1), 0);
  77
  78     /* -4 because it is impossible that the previous position is
  79        equal to the  current one :) */
  80     for(int i=first_candidate2; i<engine->save_buf_num; i+=2)
  81     {
  82         if(board.hash == engine->save_buf[i].hash_key)
  83         {
  84             nfold--;
  85             if(nfold <= 1)
  86                 return true;
  87         }
  88     }
  89
  90     return false;
  91 }
  92
  93 bool Board::insufficient_material()
  94 {
  95     for(int i=0;i<2;i++)
  96     {
  97         int mt = (i ? 5 : -1);
  98
  99         if(mat_tracking[PAWN+mt].count > 0
 100           || mat_tracking[QUEEN+mt].count > 0
 101           || mat_tracking[ROOK+mt].count > 0)
 102           return false;
 103
 104         /* ok, unless the 2 bishop are on squares of the same color :) */
 105         if(mat_tracking[BISHOP+mt].count >= 2)
 106           return false;
 107
 108         if(mat_tracking[KNIGHT+mt].count >= 1 &&
 109             mat_tracking[BISHOP+mt].count >= 1)
 110           return false;
 111
 112         /* 3 knights can checkmate :) */
 113         if(mat_tracking[KNIGHT+mt].count >= 3)
 114           return false;
 115     }
 116     return true;
 117 }