src/material.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 "material.h"
  27
  28
  29 ////
  30 //// Local definitions
  31 ////
  32
  33 namespace {
  34
  35   const Value BishopPairMidgameBonus = Value(100);
  36   const Value BishopPairEndgameBonus = Value(100);
  37
  38   Key KPKMaterialKey, KKPMaterialKey;
  39   Key KBNKMaterialKey, KKBNMaterialKey;
  40   Key KRKPMaterialKey, KPKRMaterialKey;
  41   Key KRKBMaterialKey, KBKRMaterialKey;
  42   Key KRKNMaterialKey, KNKRMaterialKey;
  43   Key KQKRMaterialKey, KRKQMaterialKey;
  44   Key KRPKRMaterialKey, KRKRPMaterialKey;
  45   Key KRPPKRPMaterialKey, KRPKRPPMaterialKey;
  46   Key KNNKMaterialKey, KKNNMaterialKey;
  47   Key KBPKBMaterialKey, KBKBPMaterialKey;
  48   Key KBPKNMaterialKey, KNKBPMaterialKey;
  49   Key KNPKMaterialKey, KKNPMaterialKey;
  50   Key KPKPMaterialKey;
  51
  52 };
  53
  54
  55 ////
  56 //// Functions
  57 ////
  58
  59 /// MaterialInfo::init() is called during program initialization.  It
  60 /// precomputes material hash keys for a few basic endgames, in order
  61 /// to make it easy to recognize such endgames when they occur.
  62
  63 void MaterialInfo::init() {
  64   KPKMaterialKey = Position::zobMaterial[WHITE][PAWN][1];
  65   KKPMaterialKey = Position::zobMaterial[BLACK][PAWN][1];
  66   KBNKMaterialKey =
  67     Position::zobMaterial[WHITE][BISHOP][1] ^
  68     Position::zobMaterial[WHITE][KNIGHT][1];
  69   KKBNMaterialKey =
  70     Position::zobMaterial[BLACK][BISHOP][1] ^
  71     Position::zobMaterial[BLACK][KNIGHT][1];
  72   KRKPMaterialKey =
  73     Position::zobMaterial[WHITE][ROOK][1] ^
  74     Position::zobMaterial[BLACK][PAWN][1];
  75   KPKRMaterialKey =
  76     Position::zobMaterial[WHITE][PAWN][1] ^
  77     Position::zobMaterial[BLACK][ROOK][1];
  78   KRKBMaterialKey =
  79     Position::zobMaterial[WHITE][ROOK][1] ^
  80     Position::zobMaterial[BLACK][BISHOP][1];
  81   KBKRMaterialKey =
  82     Position::zobMaterial[WHITE][BISHOP][1] ^
  83     Position::zobMaterial[BLACK][ROOK][1];
  84   KRKNMaterialKey =
  85     Position::zobMaterial[WHITE][ROOK][1] ^
  86     Position::zobMaterial[BLACK][KNIGHT][1];
  87   KNKRMaterialKey =
  88     Position::zobMaterial[WHITE][KNIGHT][1] ^
  89     Position::zobMaterial[BLACK][ROOK][1];
  90   KQKRMaterialKey =
  91     Position::zobMaterial[WHITE][QUEEN][1] ^
  92     Position::zobMaterial[BLACK][ROOK][1];
  93   KRKQMaterialKey =
  94     Position::zobMaterial[WHITE][ROOK][1] ^
  95     Position::zobMaterial[BLACK][QUEEN][1];
  96   KRPKRMaterialKey =
  97     Position::zobMaterial[WHITE][ROOK][1] ^
  98     Position::zobMaterial[WHITE][PAWN][1] ^
  99     Position::zobMaterial[BLACK][ROOK][1];
 100   KRKRPMaterialKey =
 101     Position::zobMaterial[WHITE][ROOK][1] ^
 102     Position::zobMaterial[BLACK][ROOK][1] ^
 103     Position::zobMaterial[BLACK][PAWN][1];
 104   KRPPKRPMaterialKey =
 105     Position::zobMaterial[WHITE][ROOK][1] ^
 106     Position::zobMaterial[WHITE][PAWN][1] ^
 107     Position::zobMaterial[WHITE][PAWN][2] ^
 108     Position::zobMaterial[BLACK][ROOK][1] ^
 109     Position::zobMaterial[BLACK][PAWN][1];
 110   KRPKRPPMaterialKey =
 111     Position::zobMaterial[WHITE][ROOK][1] ^
 112     Position::zobMaterial[WHITE][PAWN][1] ^
 113     Position::zobMaterial[BLACK][ROOK][1] ^
 114     Position::zobMaterial[BLACK][PAWN][1] ^
 115     Position::zobMaterial[BLACK][PAWN][2];
 116   KNNKMaterialKey =
 117     Position::zobMaterial[WHITE][KNIGHT][1] ^
 118     Position::zobMaterial[WHITE][KNIGHT][2];
 119   KKNNMaterialKey =
 120     Position::zobMaterial[BLACK][KNIGHT][1] ^
 121     Position::zobMaterial[BLACK][KNIGHT][2];
 122   KBPKBMaterialKey =
 123     Position::zobMaterial[WHITE][BISHOP][1] ^
 124     Position::zobMaterial[WHITE][PAWN][1] ^
 125     Position::zobMaterial[BLACK][BISHOP][1];
 126   KBKBPMaterialKey =
 127     Position::zobMaterial[WHITE][BISHOP][1] ^
 128     Position::zobMaterial[BLACK][BISHOP][1] ^
 129     Position::zobMaterial[BLACK][PAWN][1];
 130   KBPKNMaterialKey =
 131     Position::zobMaterial[WHITE][BISHOP][1] ^
 132     Position::zobMaterial[WHITE][PAWN][1] ^
 133     Position::zobMaterial[BLACK][KNIGHT][1];
 134   KNKBPMaterialKey =
 135     Position::zobMaterial[WHITE][KNIGHT][1] ^
 136     Position::zobMaterial[BLACK][BISHOP][1] ^
 137     Position::zobMaterial[BLACK][PAWN][1];
 138   KNPKMaterialKey =
 139     Position::zobMaterial[WHITE][KNIGHT][1] ^
 140     Position::zobMaterial[WHITE][PAWN][1];
 141   KKNPMaterialKey =
 142     Position::zobMaterial[BLACK][KNIGHT][1] ^
 143     Position::zobMaterial[BLACK][PAWN][1];
 144   KPKPMaterialKey =
 145     Position::zobMaterial[WHITE][PAWN][1] ^
 146     Position::zobMaterial[BLACK][PAWN][1];
 147 }
 148
 149
 150 /// Constructor for the MaterialInfoTable class.
 151
 152 MaterialInfoTable::MaterialInfoTable(unsigned numOfEntries) {
 153   size = numOfEntries;
 154   entries = new MaterialInfo[size];
 155   if(entries == NULL) {
 156     std::cerr << "Failed to allocate " << (numOfEntries * sizeof(MaterialInfo))
 157               << " bytes for material hash table." << std::endl;
 158     exit(EXIT_FAILURE);
 159   }
 160   this->clear();
 161 }
 162
 163
 164 /// Destructor for the MaterialInfoTable class.
 165
 166 MaterialInfoTable::~MaterialInfoTable() {
 167   delete [] entries;
 168 }
 169
 170
 171 /// MaterialInfoTable::clear() clears a material hash table by setting
 172 /// all entries to 0.
 173
 174 void MaterialInfoTable::clear() {
 175   memset(entries, 0, size * sizeof(MaterialInfo));
 176 }
 177
 178
 179 /// MaterialInfoTable::get_material_info() takes a position object as input,
 180 /// computes or looks up a MaterialInfo object, and returns a pointer to it.
 181 /// If the material configuration is not already present in the table, it
 182 /// is stored there, so we don't have to recompute everything when the
 183 /// same material configuration occurs again.
 184
 185 MaterialInfo *MaterialInfoTable::get_material_info(const Position &pos) {
 186   Key key = pos.get_material_key();
 187   int index = key & (size - 1);
 188   MaterialInfo *mi = entries + index;
 189
 190   // If mi->key matches the position's material hash key, it means that we
 191   // have analysed this material configuration before, and we can simply
 192   // return the information we found the last time instead of recomputing it:
 193   if(mi->key == key)
 194     return mi;
 195
 196   // Clear the MaterialInfo object, and set its key:
 197   mi->clear();
 198   mi->key = key;
 199
 200   // A special case before looking for a specialized evaluation function:
 201   // KNN vs K is a draw:
 202   if(key == KNNKMaterialKey || key == KKNNMaterialKey) {
 203     mi->factor[WHITE] = mi->factor[BLACK] = 0;
 204     return mi;
 205   }
 206
 207   // Let's look if we have a specialized evaluation function for this
 208   // particular material configuration:
 209   if(key == KPKMaterialKey) {
 210     mi->evaluationFunction = &EvaluateKPK;
 211     return mi;
 212   }
 213   else if(key == KKPMaterialKey) {
 214     mi->evaluationFunction = &EvaluateKKP;
 215     return mi;
 216   }
 217   else if(key == KBNKMaterialKey) {
 218     mi->evaluationFunction = &EvaluateKBNK;
 219     return mi;
 220   }
 221   else if(key == KKBNMaterialKey) {
 222     mi->evaluationFunction = &EvaluateKKBN;
 223     return mi;
 224   }
 225   else if(key == KRKPMaterialKey) {
 226     mi->evaluationFunction = &EvaluateKRKP;
 227     return mi;
 228   }
 229   else if(key == KPKRMaterialKey) {
 230     mi->evaluationFunction = &EvaluateKPKR;
 231     return mi;
 232   }
 233   else if(key == KRKBMaterialKey) {
 234     mi->evaluationFunction = &EvaluateKRKB;
 235     return mi;
 236   }
 237   else if(key == KBKRMaterialKey) {
 238     mi->evaluationFunction = &EvaluateKBKR;
 239     return mi;
 240   }
 241   else if(key == KRKNMaterialKey) {
 242     mi->evaluationFunction = &EvaluateKRKN;
 243     return mi;
 244   }
 245   else if(key == KNKRMaterialKey) {
 246     mi->evaluationFunction = &EvaluateKNKR;
 247     return mi;
 248   }
 249   else if(key == KQKRMaterialKey) {
 250     mi->evaluationFunction = &EvaluateKQKR;
 251     return mi;
 252   }
 253   else if(key == KRKQMaterialKey) {
 254     mi->evaluationFunction = &EvaluateKRKQ;
 255     return mi;
 256   }
 257   else if(pos.non_pawn_material(BLACK) == Value(0) &&
 258           pos.pawn_count(BLACK) == 0 &&
 259           pos.non_pawn_material(WHITE) >= RookValueEndgame) {
 260     mi->evaluationFunction = &EvaluateKXK;
 261     return mi;
 262   }
 263   else if(pos.non_pawn_material(WHITE) == Value(0) &&
 264           pos.pawn_count(WHITE) == 0 &&
 265           pos.non_pawn_material(BLACK) >= RookValueEndgame) {
 266     mi->evaluationFunction = &EvaluateKKX;
 267     return mi;
 268   }
 269
 270   // OK, we didn't find any special evaluation function for the current
 271   // material configuration.  Is there a suitable scaling function?
 272   //
 273   // The code below is rather messy, and it could easily get worse later,
 274   // if we decide to add more special cases.  We face problems when there
 275   // are several conflicting applicable scaling functions and we need to
 276   // decide which one to use.
 277
 278   if(key == KRPKRMaterialKey) {
 279     mi->scalingFunction[WHITE] = &ScaleKRPKR;
 280     return mi;
 281   }
 282   if(key == KRKRPMaterialKey) {
 283     mi->scalingFunction[BLACK] = &ScaleKRKRP;
 284     return mi;
 285   }
 286   if(key == KRPPKRPMaterialKey) {
 287     mi->scalingFunction[WHITE] = &ScaleKRPPKRP;
 288     return mi;
 289   }
 290   else if(key == KRPKRPPMaterialKey) {
 291     mi->scalingFunction[BLACK] = &ScaleKRPKRPP;
 292     return mi;
 293   }
 294   if(key == KBPKBMaterialKey) {
 295     mi->scalingFunction[WHITE] = &ScaleKBPKB;
 296     return mi;
 297   }
 298   if(key == KBKBPMaterialKey) {
 299     mi->scalingFunction[BLACK] = &ScaleKBKBP;
 300     return mi;
 301   }
 302   if(key == KBPKNMaterialKey) {
 303     mi->scalingFunction[WHITE] = &ScaleKBPKN;
 304     return mi;
 305   }
 306   if(key == KNKBPMaterialKey) {
 307     mi->scalingFunction[BLACK] = &ScaleKNKBP;
 308     return mi;
 309   }
 310   if(key == KNPKMaterialKey) {
 311     mi->scalingFunction[WHITE] = &ScaleKNPK;
 312     return mi;
 313   }
 314   if(key == KKNPMaterialKey) {
 315     mi->scalingFunction[BLACK] = &ScaleKKNP;
 316     return mi;
 317   }
 318
 319   if(pos.non_pawn_material(WHITE) == BishopValueMidgame &&
 320      pos.bishop_count(WHITE) == 1 && pos.pawn_count(WHITE) >= 1)
 321     mi->scalingFunction[WHITE] = &ScaleKBPK;
 322   if(pos.non_pawn_material(BLACK) == BishopValueMidgame &&
 323      pos.bishop_count(BLACK) == 1 && pos.pawn_count(BLACK) >= 1)
 324     mi->scalingFunction[BLACK] = &ScaleKKBP;
 325
 326   if(pos.pawn_count(WHITE) == 0 &&
 327      pos.non_pawn_material(WHITE) == QueenValueMidgame &&
 328      pos.queen_count(WHITE) == 1 &&
 329      pos.rook_count(BLACK) == 1 && pos.pawn_count(BLACK) >= 1)
 330     mi->scalingFunction[WHITE] = &ScaleKQKRP;
 331   else if(pos.pawn_count(BLACK) == 0 &&
 332           pos.non_pawn_material(BLACK) == QueenValueMidgame &&
 333           pos.queen_count(BLACK) == 1 &&
 334           pos.rook_count(WHITE) == 1 && pos.pawn_count(WHITE) >= 1)
 335     mi->scalingFunction[BLACK] = &ScaleKRPKQ;
 336
 337   if(pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) == Value(0)) {
 338     if(pos.pawn_count(BLACK) == 0) {
 339       assert(pos.pawn_count(WHITE) >= 2);
 340       mi->scalingFunction[WHITE] = &ScaleKPsK;
 341     }
 342     else if(pos.pawn_count(WHITE) == 0) {
 343       assert(pos.pawn_count(BLACK) >= 2);
 344       mi->scalingFunction[BLACK] = &ScaleKKPs;
 345     }
 346     else if(pos.pawn_count(WHITE) == 1 && pos.pawn_count(BLACK) == 1) {
 347       mi->scalingFunction[WHITE] = &ScaleKPKPw;
 348       mi->scalingFunction[BLACK] = &ScaleKPKPb;
 349     }
 350   }
 351
 352   // Evaluate the material balance.
 353
 354   Color c;
 355   int sign;
 356   Value egValue = Value(0), mgValue = Value(0);
 357
 358   for(c = WHITE, sign = 1; c <= BLACK; c++, sign = -sign) {
 359
 360     // No pawns makes it difficult to win, even with a material advantage:
 361     if(pos.pawn_count(c) == 0 &&
 362        pos.non_pawn_material(c) - pos.non_pawn_material(opposite_color(c))
 363        <= BishopValueMidgame) {
 364       if(pos.non_pawn_material(c) == pos.non_pawn_material(opposite_color(c)))
 365         mi->factor[c] = 0;
 366       else if(pos.non_pawn_material(c) < RookValueMidgame)
 367         mi->factor[c] = 0;
 368       else {
 369         switch(pos.bishop_count(c)) {
 370         case 2:
 371           mi->factor[c] = 32; break;
 372         case 1:
 373           mi->factor[c] = 12; break;
 374         case 0:
 375           mi->factor[c] = 6; break;
 376         }
 377       }
 378     }
 379
 380     // Bishop pair:
 381     if(pos.bishop_count(c) >= 2) {
 382       mgValue += sign * BishopPairMidgameBonus;
 383       egValue += sign * BishopPairEndgameBonus;
 384     }
 385
 386     // Knights are stronger when there are many pawns on the board.  The
 387     // formula is taken from Larry Kaufman's paper "The Evaluation of Material
 388     // Imbalances in Chess":
 389     // http://mywebpages.comcast.net/danheisman/Articles/evaluation_of_material_imbalance.htm
 390     mgValue += sign * Value(pos.knight_count(c)*(pos.pawn_count(c)-5)*16);
 391     egValue += sign * Value(pos.knight_count(c)*(pos.pawn_count(c)-5)*16);
 392
 393     // Redundancy of major pieces, again based on Kaufman's paper:
 394     if(pos.rook_count(c) >= 1) {
 395       Value v = Value((pos.rook_count(c) - 1) * 32 + pos.queen_count(c) * 16);
 396       mgValue -= sign * v;
 397       egValue -= sign * v;
 398     }
 399
 400   }
 401
 402   mi->mgValue = int16_t(mgValue);
 403   mi->egValue = int16_t(egValue);
 404
 405   return mi;
 406 }