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 // Values modified by Joona Kiiski
41 const Value MidgameLimit = Value(15581);
42 const Value EndgameLimit = Value(3998);
44 // Polynomial material balance parameters
45 const Value RedundantQueenPenalty = Value(320);
46 const Value RedundantRookPenalty = Value(554);
47 const int LinearCoefficients[6] = { 1617, -162, -1172, -190, 105, 26 };
49 const int QuadraticCoefficientsSameColor[][6] = {
50 { 7, 7, 7, 7, 7, 7 }, { 39, 2, 7, 7, 7, 7 }, { 35, 271, -4, 7, 7, 7 },
51 { 7, 25, 4, 7, 7, 7 }, { -27, -2, 46, 100, 56, 7 }, { 58, 29, 83, 148, -3, -25 } };
53 const int QuadraticCoefficientsOppositeColor[][6] = {
54 { 41, 41, 41, 41, 41, 41 }, { 37, 41, 41, 41, 41, 41 }, { 10, 62, 41, 41, 41, 41 },
55 { 57, 64, 39, 41, 41, 41 }, { 50, 40, 23, -22, 41, 41 }, { 106, 101, 3, 151, 171, 41 } };
57 // Named endgame evaluation and scaling functions, these
58 // are accessed direcly and not through the function maps.
59 EvaluationFunction<KmmKm> EvaluateKmmKm(WHITE);
60 EvaluationFunction<KXK> EvaluateKXK(WHITE), EvaluateKKX(BLACK);
61 ScalingFunction<KBPsK> ScaleKBPsK(WHITE), ScaleKKBPs(BLACK);
62 ScalingFunction<KQKRPs> ScaleKQKRPs(WHITE), ScaleKRPsKQ(BLACK);
63 ScalingFunction<KPsK> ScaleKPsK(WHITE), ScaleKKPs(BLACK);
64 ScalingFunction<KPKP> ScaleKPKPw(WHITE), ScaleKPKPb(BLACK);
66 typedef EndgameEvaluationFunctionBase EF;
67 typedef EndgameScalingFunctionBase SF;
75 /// EndgameFunctions class stores endgame evaluation and scaling functions
76 /// in two std::map. Because STL library is not guaranteed to be thread
77 /// safe even for read access, the maps, although with identical content,
78 /// are replicated for each thread. This is faster then using locks.
80 class EndgameFunctions {
84 template<class T> T* get(Key key) const;
87 template<class T> void add(const string& keyCode);
89 static Key buildKey(const string& keyCode);
90 static const string swapColors(const string& keyCode);
92 // Here we store two maps, for evaluate and scaling functions
93 pair<map<Key, EF*>, map<Key, SF*> > maps;
95 // Maps accessing functions returning const and non-const references
96 template<typename T> const map<Key, T*>& get() const { return maps.first; }
97 template<typename T> map<Key, T*>& get() { return maps.first; }
100 // Explicit specializations of a member function shall be declared in
101 // the namespace of which the class template is a member.
102 template<> const map<Key, SF*>&
103 EndgameFunctions::get<SF>() const { return maps.second; }
105 template<> map<Key, SF*>&
106 EndgameFunctions::get<SF>() { return maps.second; }
113 /// MaterialInfoTable c'tor and d'tor, called once by each thread
115 MaterialInfoTable::MaterialInfoTable(unsigned int numOfEntries) {
118 entries = new MaterialInfo[size];
119 funcs = new EndgameFunctions();
121 if (!entries || !funcs)
123 cerr << "Failed to allocate " << numOfEntries * sizeof(MaterialInfo)
124 << " bytes for material hash table." << endl;
125 Application::exit_with_failure();
129 MaterialInfoTable::~MaterialInfoTable() {
136 /// MaterialInfoTable::game_phase() calculate the phase given the current
137 /// position. Because the phase is strictly a function of the material, it
138 /// is stored in MaterialInfo.
140 Phase MaterialInfoTable::game_phase(const Position& pos) {
142 Value npm = pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK);
144 if (npm >= MidgameLimit)
145 return PHASE_MIDGAME;
146 else if (npm <= EndgameLimit)
147 return PHASE_ENDGAME;
149 return Phase(((npm - EndgameLimit) * 128) / (MidgameLimit - EndgameLimit));
152 /// MaterialInfoTable::get_material_info() takes a position object as input,
153 /// computes or looks up a MaterialInfo object, and returns a pointer to it.
154 /// If the material configuration is not already present in the table, it
155 /// is stored there, so we don't have to recompute everything when the
156 /// same material configuration occurs again.
158 MaterialInfo* MaterialInfoTable::get_material_info(const Position& pos) {
160 Key key = pos.get_material_key();
161 int index = key & (size - 1);
162 MaterialInfo* mi = entries + index;
164 // If mi->key matches the position's material hash key, it means that we
165 // have analysed this material configuration before, and we can simply
166 // return the information we found the last time instead of recomputing it.
170 // Clear the MaterialInfo object, and set its key
174 // Calculate game phase
175 mi->gamePhase = MaterialInfoTable::game_phase(pos);
177 // Let's look if we have a specialized evaluation function for this
178 // particular material configuration. First we look for a fixed
179 // configuration one, then a generic one if previous search failed.
180 if ((mi->evaluationFunction = funcs->get<EF>(key)) != NULL)
183 else if ( pos.non_pawn_material(BLACK) == Value(0)
184 && pos.piece_count(BLACK, PAWN) == 0
185 && pos.non_pawn_material(WHITE) >= RookValueMidgame)
187 mi->evaluationFunction = &EvaluateKXK;
190 else if ( pos.non_pawn_material(WHITE) == Value(0)
191 && pos.piece_count(WHITE, PAWN) == 0
192 && pos.non_pawn_material(BLACK) >= RookValueMidgame)
194 mi->evaluationFunction = &EvaluateKKX;
197 else if ( pos.pieces(PAWN) == EmptyBoardBB
198 && pos.pieces(ROOK) == EmptyBoardBB
199 && pos.pieces(QUEEN) == EmptyBoardBB)
201 // Minor piece endgame with at least one minor piece per side and
202 // no pawns. Note that the case KmmK is already handled by KXK.
203 assert((pos.pieces(KNIGHT, WHITE) | pos.pieces(BISHOP, WHITE)));
204 assert((pos.pieces(KNIGHT, BLACK) | pos.pieces(BISHOP, BLACK)));
206 if ( pos.piece_count(WHITE, BISHOP) + pos.piece_count(WHITE, KNIGHT) <= 2
207 && pos.piece_count(BLACK, BISHOP) + pos.piece_count(BLACK, KNIGHT) <= 2)
209 mi->evaluationFunction = &EvaluateKmmKm;
214 // OK, we didn't find any special evaluation function for the current
215 // material configuration. Is there a suitable scaling function?
217 // The code below is rather messy, and it could easily get worse later,
218 // if we decide to add more special cases. We face problems when there
219 // are several conflicting applicable scaling functions and we need to
220 // decide which one to use.
223 if ((sf = funcs->get<SF>(key)) != NULL)
225 mi->scalingFunction[sf->color()] = sf;
229 // Generic scaling functions that refer to more then one material
230 // distribution. Should be probed after the specialized ones.
231 // Note that these ones don't return after setting the function.
232 if ( pos.non_pawn_material(WHITE) == BishopValueMidgame
233 && pos.piece_count(WHITE, BISHOP) == 1
234 && pos.piece_count(WHITE, PAWN) >= 1)
235 mi->scalingFunction[WHITE] = &ScaleKBPsK;
237 if ( pos.non_pawn_material(BLACK) == BishopValueMidgame
238 && pos.piece_count(BLACK, BISHOP) == 1
239 && pos.piece_count(BLACK, PAWN) >= 1)
240 mi->scalingFunction[BLACK] = &ScaleKKBPs;
242 if ( pos.piece_count(WHITE, PAWN) == 0
243 && pos.non_pawn_material(WHITE) == QueenValueMidgame
244 && pos.piece_count(WHITE, QUEEN) == 1
245 && pos.piece_count(BLACK, ROOK) == 1
246 && pos.piece_count(BLACK, PAWN) >= 1)
247 mi->scalingFunction[WHITE] = &ScaleKQKRPs;
249 else if ( pos.piece_count(BLACK, PAWN) == 0
250 && pos.non_pawn_material(BLACK) == QueenValueMidgame
251 && pos.piece_count(BLACK, QUEEN) == 1
252 && pos.piece_count(WHITE, ROOK) == 1
253 && pos.piece_count(WHITE, PAWN) >= 1)
254 mi->scalingFunction[BLACK] = &ScaleKRPsKQ;
256 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) == Value(0))
258 if (pos.piece_count(BLACK, PAWN) == 0)
260 assert(pos.piece_count(WHITE, PAWN) >= 2);
261 mi->scalingFunction[WHITE] = &ScaleKPsK;
263 else if (pos.piece_count(WHITE, PAWN) == 0)
265 assert(pos.piece_count(BLACK, PAWN) >= 2);
266 mi->scalingFunction[BLACK] = &ScaleKKPs;
268 else if (pos.piece_count(WHITE, PAWN) == 1 && pos.piece_count(BLACK, PAWN) == 1)
270 // This is a special case because we set scaling functions
271 // for both colors instead of only one.
272 mi->scalingFunction[WHITE] = &ScaleKPKPw;
273 mi->scalingFunction[BLACK] = &ScaleKPKPb;
277 // Compute the space weight
278 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >=
279 2*QueenValueMidgame + 4*RookValueMidgame + 2*KnightValueMidgame)
281 int minorPieceCount = pos.piece_count(WHITE, KNIGHT)
282 + pos.piece_count(BLACK, KNIGHT)
283 + pos.piece_count(WHITE, BISHOP)
284 + pos.piece_count(BLACK, BISHOP);
286 mi->spaceWeight = minorPieceCount * minorPieceCount;
289 // Evaluate the material balance
290 const int pieceCount[2][6] = { { pos.piece_count(WHITE, BISHOP) > 1, pos.piece_count(WHITE, PAWN), pos.piece_count(WHITE, KNIGHT),
291 pos.piece_count(WHITE, BISHOP), pos.piece_count(WHITE, ROOK), pos.piece_count(WHITE, QUEEN) },
292 { pos.piece_count(BLACK, BISHOP) > 1, pos.piece_count(BLACK, PAWN), pos.piece_count(BLACK, KNIGHT),
293 pos.piece_count(BLACK, BISHOP), pos.piece_count(BLACK, ROOK), pos.piece_count(BLACK, QUEEN) } };
298 for (c = WHITE, sign = 1; c <= BLACK; c++, sign = -sign)
300 // No pawns makes it difficult to win, even with a material advantage
301 if ( pos.piece_count(c, PAWN) == 0
302 && pos.non_pawn_material(c) - pos.non_pawn_material(opposite_color(c)) <= BishopValueMidgame)
304 if ( pos.non_pawn_material(c) == pos.non_pawn_material(opposite_color(c))
305 || pos.non_pawn_material(c) < RookValueMidgame)
309 switch (pos.piece_count(c, BISHOP)) {
323 // Redundancy of major pieces, formula based on Kaufman's paper
324 // "The Evaluation of Material Imbalances in Chess"
325 // http://mywebpages.comcast.net/danheisman/Articles/evaluation_of_material_imbalance.htm
326 if (pieceCount[c][ROOK] >= 1)
327 matValue -= sign * ((pieceCount[c][ROOK] - 1) * RedundantRookPenalty + pieceCount[c][QUEEN] * RedundantQueenPenalty);
329 them = opposite_color(c);
331 // Second-degree polynomial material imbalance by Tord Romstad
333 // We use NO_PIECE_TYPE as a place holder for the bishop pair "extended piece",
334 // this allow us to be more flexible in defining bishop pair bonuses.
335 for (int pt1 = NO_PIECE_TYPE; pt1 <= QUEEN; pt1++)
337 int c1 = sign * pieceCount[c][pt1];
341 matValue += c1 * LinearCoefficients[pt1];
343 for (int pt2 = NO_PIECE_TYPE; pt2 <= pt1; pt2++)
345 matValue += c1 * pieceCount[c][pt2] * QuadraticCoefficientsSameColor[pt1][pt2];
346 matValue += c1 * pieceCount[them][pt2] * QuadraticCoefficientsOppositeColor[pt1][pt2];
350 mi->value = int16_t(matValue / 16);
355 /// EndgameFunctions member definitions.
357 EndgameFunctions::EndgameFunctions() {
359 add<EvaluationFunction<KNNK> >("KNNK");
360 add<EvaluationFunction<KPK> >("KPK");
361 add<EvaluationFunction<KBNK> >("KBNK");
362 add<EvaluationFunction<KRKP> >("KRKP");
363 add<EvaluationFunction<KRKB> >("KRKB");
364 add<EvaluationFunction<KRKN> >("KRKN");
365 add<EvaluationFunction<KQKR> >("KQKR");
366 add<EvaluationFunction<KBBKN> >("KBBKN");
368 add<ScalingFunction<KNPK> >("KNPK");
369 add<ScalingFunction<KRPKR> >("KRPKR");
370 add<ScalingFunction<KBPKB> >("KBPKB");
371 add<ScalingFunction<KBPPKB> >("KBPPKB");
372 add<ScalingFunction<KBPKN> >("KBPKN");
373 add<ScalingFunction<KRPPKRP> >("KRPPKRP");
374 add<ScalingFunction<KRPPKRP> >("KRPPKRP");
377 EndgameFunctions::~EndgameFunctions() {
379 for (map<Key, EF*>::iterator it = maps.first.begin(); it != maps.first.end(); ++it)
382 for (map<Key, SF*>::iterator it = maps.second.begin(); it != maps.second.end(); ++it)
386 Key EndgameFunctions::buildKey(const string& keyCode) {
388 assert(keyCode.length() > 0 && keyCode[0] == 'K');
389 assert(keyCode.length() < 8);
394 // Build up a fen string with the given pieces, note that
395 // the fen string could be of an illegal position.
396 for (size_t i = 0; i < keyCode.length(); i++)
398 if (keyCode[i] == 'K')
401 s << char(upcase? toupper(keyCode[i]) : tolower(keyCode[i]));
403 s << 8 - keyCode.length() << "/8/8/8/8/8/8/8 w -";
404 return Position(s.str()).get_material_key();
407 const string EndgameFunctions::swapColors(const string& keyCode) {
409 // Build corresponding key for the opposite color: "KBPKN" -> "KNKBP"
410 size_t idx = keyCode.find("K", 1);
411 return keyCode.substr(idx) + keyCode.substr(0, idx);
415 void EndgameFunctions::add(const string& keyCode) {
417 typedef typename T::Base F;
419 get<F>().insert(pair<Key, F*>(buildKey(keyCode), new T(WHITE)));
420 get<F>().insert(pair<Key, F*>(buildKey(swapColors(keyCode)), new T(BLACK)));
424 T* EndgameFunctions::get(Key key) const {
426 typename map<Key, T*>::const_iterator it(get<T>().find(key));
427 return (it != get<T>().end() ? it->second : NULL);