2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2009 Marco Costalba
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
35 //// Local definitions
40 const Value BishopPairMidgameBonus = Value(109);
41 const Value BishopPairEndgameBonus = Value(97);
43 Key KNNKMaterialKey, KKNNMaterialKey;
52 /// See header for a class description. It is declared here to avoid
53 /// to include <map> in the header file.
55 class EndgameFunctions {
59 EndgameEvaluationFunctionBase* getEEF(Key key) const;
60 EndgameScalingFunctionBase* getESF(Key key, Color* c) const;
63 void add(const string& keyCode, EndgameEvaluationFunctionBase* f);
64 void add(const string& keyCode, Color c, EndgameScalingFunctionBase* f);
65 Key buildKey(const string& keyCode);
70 EndgameScalingFunctionBase* fun;
73 std::map<Key, EndgameEvaluationFunctionBase*> EEFmap;
74 std::map<Key, ScalingInfo> ESFmap;
83 /// Constructor for the MaterialInfoTable class
85 MaterialInfoTable::MaterialInfoTable(unsigned int numOfEntries) {
88 entries = new MaterialInfo[size];
89 funcs = new EndgameFunctions();
90 if (!entries || !funcs)
92 std::cerr << "Failed to allocate " << (numOfEntries * sizeof(MaterialInfo))
93 << " bytes for material hash table." << std::endl;
94 Application::exit_with_failure();
100 /// Destructor for the MaterialInfoTable class
102 MaterialInfoTable::~MaterialInfoTable() {
109 /// MaterialInfoTable::clear() clears a material hash table by setting
110 /// all entries to 0.
112 void MaterialInfoTable::clear() {
114 memset(entries, 0, size * sizeof(MaterialInfo));
118 /// MaterialInfoTable::get_material_info() takes a position object as input,
119 /// computes or looks up a MaterialInfo object, and returns a pointer to it.
120 /// If the material configuration is not already present in the table, it
121 /// is stored there, so we don't have to recompute everything when the
122 /// same material configuration occurs again.
124 MaterialInfo* MaterialInfoTable::get_material_info(const Position& pos) {
126 Key key = pos.get_material_key();
127 int index = key & (size - 1);
128 MaterialInfo* mi = entries + index;
130 // If mi->key matches the position's material hash key, it means that we
131 // have analysed this material configuration before, and we can simply
132 // return the information we found the last time instead of recomputing it.
136 // Clear the MaterialInfo object, and set its key
140 // A special case before looking for a specialized evaluation function
141 // KNN vs K is a draw.
142 if (key == KNNKMaterialKey || key == KKNNMaterialKey)
144 mi->factor[WHITE] = mi->factor[BLACK] = 0;
148 // Let's look if we have a specialized evaluation function for this
149 // particular material configuration. First we look for a fixed
150 // configuration one, then a generic one if previous search failed.
151 if ((mi->evaluationFunction = funcs->getEEF(key)) != NULL)
154 else if ( pos.non_pawn_material(BLACK) == Value(0)
155 && pos.piece_count(BLACK, PAWN) == 0
156 && pos.non_pawn_material(WHITE) >= RookValueEndgame)
158 mi->evaluationFunction = &EvaluateKXK;
161 else if ( pos.non_pawn_material(WHITE) == Value(0)
162 && pos.piece_count(WHITE, PAWN) == 0
163 && pos.non_pawn_material(BLACK) >= RookValueEndgame)
165 mi->evaluationFunction = &EvaluateKKX;
168 else if ( pos.pawns() == EmptyBoardBB
169 && pos.rooks() == EmptyBoardBB
170 && pos.queens() == EmptyBoardBB)
172 // Minor piece endgame with at least one minor piece per side,
174 assert(pos.knights(WHITE) | pos.bishops(WHITE));
175 assert(pos.knights(BLACK) | pos.bishops(BLACK));
177 if ( pos.piece_count(WHITE, BISHOP) + pos.piece_count(WHITE, KNIGHT) <= 2
178 && pos.piece_count(BLACK, BISHOP) + pos.piece_count(BLACK, KNIGHT) <= 2)
180 mi->evaluationFunction = &EvaluateKmmKm;
185 // OK, we didn't find any special evaluation function for the current
186 // material configuration. Is there a suitable scaling function?
188 // The code below is rather messy, and it could easily get worse later,
189 // if we decide to add more special cases. We face problems when there
190 // are several conflicting applicable scaling functions and we need to
191 // decide which one to use.
193 EndgameScalingFunctionBase* sf;
195 if ((sf = funcs->getESF(key, &c)) != NULL)
197 mi->scalingFunction[c] = sf;
201 if ( pos.non_pawn_material(WHITE) == BishopValueMidgame
202 && pos.piece_count(WHITE, BISHOP) == 1
203 && pos.piece_count(WHITE, PAWN) >= 1)
204 mi->scalingFunction[WHITE] = &ScaleKBPK;
206 if ( pos.non_pawn_material(BLACK) == BishopValueMidgame
207 && pos.piece_count(BLACK, BISHOP) == 1
208 && pos.piece_count(BLACK, PAWN) >= 1)
209 mi->scalingFunction[BLACK] = &ScaleKKBP;
211 if ( pos.piece_count(WHITE, PAWN) == 0
212 && pos.non_pawn_material(WHITE) == QueenValueMidgame
213 && pos.piece_count(WHITE, QUEEN) == 1
214 && pos.piece_count(BLACK, ROOK) == 1
215 && pos.piece_count(BLACK, PAWN) >= 1)
216 mi->scalingFunction[WHITE] = &ScaleKQKRP;
218 else if ( pos.piece_count(BLACK, PAWN) == 0
219 && pos.non_pawn_material(BLACK) == QueenValueMidgame
220 && pos.piece_count(BLACK, QUEEN) == 1
221 && pos.piece_count(WHITE, ROOK) == 1
222 && pos.piece_count(WHITE, PAWN) >= 1)
223 mi->scalingFunction[BLACK] = &ScaleKRPKQ;
225 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) == Value(0))
227 if (pos.piece_count(BLACK, PAWN) == 0)
229 assert(pos.piece_count(WHITE, PAWN) >= 2);
230 mi->scalingFunction[WHITE] = &ScaleKPsK;
232 else if (pos.piece_count(WHITE, PAWN) == 0)
234 assert(pos.piece_count(BLACK, PAWN) >= 2);
235 mi->scalingFunction[BLACK] = &ScaleKKPs;
237 else if (pos.piece_count(WHITE, PAWN) == 1 && pos.piece_count(BLACK, PAWN) == 1)
239 mi->scalingFunction[WHITE] = &ScaleKPKPw;
240 mi->scalingFunction[BLACK] = &ScaleKPKPb;
244 // Compute the space weight
245 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >=
246 2*QueenValueMidgame + 4*RookValueMidgame + 2*KnightValueMidgame)
248 int minorPieceCount = pos.piece_count(WHITE, KNIGHT)
249 + pos.piece_count(BLACK, KNIGHT)
250 + pos.piece_count(WHITE, BISHOP)
251 + pos.piece_count(BLACK, BISHOP);
253 mi->spaceWeight = minorPieceCount * minorPieceCount;
256 // Evaluate the material balance
259 Value egValue = Value(0);
260 Value mgValue = Value(0);
262 for (c = WHITE, sign = 1; c <= BLACK; c++, sign = -sign)
264 // No pawns makes it difficult to win, even with a material advantage
265 if ( pos.piece_count(c, PAWN) == 0
266 && pos.non_pawn_material(c) - pos.non_pawn_material(opposite_color(c)) <= BishopValueMidgame)
268 if ( pos.non_pawn_material(c) == pos.non_pawn_material(opposite_color(c))
269 || pos.non_pawn_material(c) < RookValueMidgame)
273 switch (pos.piece_count(c, BISHOP)) {
288 if (pos.piece_count(c, BISHOP) >= 2)
290 mgValue += sign * BishopPairMidgameBonus;
291 egValue += sign * BishopPairEndgameBonus;
294 // Knights are stronger when there are many pawns on the board. The
295 // formula is taken from Larry Kaufman's paper "The Evaluation of Material
296 // Imbalances in Chess":
297 // http://mywebpages.comcast.net/danheisman/Articles/evaluation_of_material_imbalance.htm
298 mgValue += sign * Value(pos.piece_count(c, KNIGHT)*(pos.piece_count(c, PAWN)-5)*16);
299 egValue += sign * Value(pos.piece_count(c, KNIGHT)*(pos.piece_count(c, PAWN)-5)*16);
301 // Redundancy of major pieces, again based on Kaufman's paper:
302 if (pos.piece_count(c, ROOK) >= 1)
304 Value v = Value((pos.piece_count(c, ROOK) - 1) * 32 + pos.piece_count(c, QUEEN) * 16);
309 mi->mgValue = int16_t(mgValue);
310 mi->egValue = int16_t(egValue);
315 /// EndgameFunctions member definitions. This class is used to store the maps
316 /// of end game and scaling functions that MaterialInfoTable will query for
317 /// each key. The maps are constant and are populated only at construction,
318 /// but are per-thread instead of globals to avoid expensive locks.
320 EndgameFunctions::EndgameFunctions() {
322 KNNKMaterialKey = buildKey("KNNK");
323 KKNNMaterialKey = buildKey("KKNN");
325 add("KPK", &EvaluateKPK);
326 add("KKP", &EvaluateKKP);
327 add("KBNK", &EvaluateKBNK);
328 add("KKBN", &EvaluateKKBN);
329 add("KRKP", &EvaluateKRKP);
330 add("KPKR", &EvaluateKPKR);
331 add("KRKB", &EvaluateKRKB);
332 add("KBKR", &EvaluateKBKR);
333 add("KRKN", &EvaluateKRKN);
334 add("KNKR", &EvaluateKNKR);
335 add("KQKR", &EvaluateKQKR);
336 add("KRKQ", &EvaluateKRKQ);
337 add("KBBKN", &EvaluateKBBKN);
338 add("KNKBB", &EvaluateKNKBB);
340 add("KNPK", WHITE, &ScaleKNPK);
341 add("KKNP", BLACK, &ScaleKKNP);
342 add("KRPKR", WHITE, &ScaleKRPKR);
343 add("KRKRP", BLACK, &ScaleKRKRP);
344 add("KBPKB", WHITE, &ScaleKBPKB);
345 add("KBKBP", BLACK, &ScaleKBKBP);
346 add("KBPPKB", WHITE, &ScaleKBPPKB);
347 add("KBKBPP", BLACK, &ScaleKBKBPP);
348 add("KBPKN", WHITE, &ScaleKBPKN);
349 add("KNKBP", BLACK, &ScaleKNKBP);
350 add("KRPPKRP", WHITE, &ScaleKRPPKRP);
351 add("KRPKRPP", BLACK, &ScaleKRPKRPP);
352 add("KRPPKRP", WHITE, &ScaleKRPPKRP);
353 add("KRPKRPP", BLACK, &ScaleKRPKRPP);
356 Key EndgameFunctions::buildKey(const string& keyCode) {
358 assert(keyCode.length() > 0 && keyCode[0] == 'K');
359 assert(keyCode.length() < 8);
364 // Build up a fen substring with the given pieces, note
365 // that the fen string could be of an illegal position.
366 for (size_t i = 0; i < keyCode.length(); i++)
368 if (keyCode[i] == 'K')
371 s << char(upcase? toupper(keyCode[i]) : tolower(keyCode[i]));
373 s << 8 - keyCode.length() << "/8/8/8/8/8/8/8 w -";
374 return Position(s.str()).get_material_key();
377 void EndgameFunctions::add(const string& keyCode, EndgameEvaluationFunctionBase* f) {
379 EEFmap.insert(std::pair<Key, EndgameEvaluationFunctionBase*>(buildKey(keyCode), f));
382 void EndgameFunctions::add(const string& keyCode, Color c, EndgameScalingFunctionBase* f) {
384 ScalingInfo s = {c, f};
385 ESFmap.insert(std::pair<Key, ScalingInfo>(buildKey(keyCode), s));
388 EndgameEvaluationFunctionBase* EndgameFunctions::getEEF(Key key) const {
390 std::map<Key, EndgameEvaluationFunctionBase*>::const_iterator it(EEFmap.find(key));
391 return (it != EEFmap.end() ? it->second : NULL);
394 EndgameScalingFunctionBase* EndgameFunctions::getESF(Key key, Color* c) const {
396 std::map<Key, ScalingInfo>::const_iterator it(ESFmap.find(key));
397 if (it == ESFmap.end())
401 return it->second.fun;