2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
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/>.
30 // Values modified by Joona Kiiski
31 const Value MidgameLimit = Value(15581);
32 const Value EndgameLimit = Value(3998);
34 // Polynomial material balance parameters
35 const Value RedundantQueenPenalty = Value(320);
36 const Value RedundantRookPenalty = Value(554);
38 const int LinearCoefficients[6] = { 1617, -162, -1172, -190, 105, 26 };
40 const int QuadraticCoefficientsSameColor[][8] = {
41 { 7, 7, 7, 7, 7, 7 }, { 39, 2, 7, 7, 7, 7 }, { 35, 271, -4, 7, 7, 7 },
42 { 7, 25, 4, 7, 7, 7 }, { -27, -2, 46, 100, 56, 7 }, { 58, 29, 83, 148, -3, -25 } };
44 const int QuadraticCoefficientsOppositeColor[][8] = {
45 { 41, 41, 41, 41, 41, 41 }, { 37, 41, 41, 41, 41, 41 }, { 10, 62, 41, 41, 41, 41 },
46 { 57, 64, 39, 41, 41, 41 }, { 50, 40, 23, -22, 41, 41 }, { 106, 101, 3, 151, 171, 41 } };
48 typedef EndgameEvaluationFunctionBase EF;
49 typedef EndgameScalingFunctionBase SF;
50 typedef map<Key, EF*> EFMap;
51 typedef map<Key, SF*> SFMap;
53 // Endgame evaluation and scaling functions accessed direcly and not through
54 // the function maps because correspond to more then one material hash key.
55 EvaluationFunction<KmmKm> EvaluateKmmKm[] = { EvaluationFunction<KmmKm>(WHITE), EvaluationFunction<KmmKm>(BLACK) };
56 EvaluationFunction<KXK> EvaluateKXK[] = { EvaluationFunction<KXK>(WHITE), EvaluationFunction<KXK>(BLACK) };
57 ScalingFunction<KBPsK> ScaleKBPsK[] = { ScalingFunction<KBPsK>(WHITE), ScalingFunction<KBPsK>(BLACK) };
58 ScalingFunction<KQKRPs> ScaleKQKRPs[] = { ScalingFunction<KQKRPs>(WHITE), ScalingFunction<KQKRPs>(BLACK) };
59 ScalingFunction<KPsK> ScaleKPsK[] = { ScalingFunction<KPsK>(WHITE), ScalingFunction<KPsK>(BLACK) };
60 ScalingFunction<KPKP> ScaleKPKP[] = { ScalingFunction<KPKP>(WHITE), ScalingFunction<KPKP>(BLACK) };
62 // Helper templates used to detect a given material distribution
63 template<Color Us> bool is_KXK(const Position& pos) {
64 const Color Them = (Us == WHITE ? BLACK : WHITE);
65 return pos.non_pawn_material(Them) == VALUE_ZERO
66 && pos.piece_count(Them, PAWN) == 0
67 && pos.non_pawn_material(Us) >= RookValueMidgame;
70 template<Color Us> bool is_KBPsKs(const Position& pos) {
71 return pos.non_pawn_material(Us) == BishopValueMidgame
72 && pos.piece_count(Us, BISHOP) == 1
73 && pos.piece_count(Us, PAWN) >= 1;
76 template<Color Us> bool is_KQKRPs(const Position& pos) {
77 const Color Them = (Us == WHITE ? BLACK : WHITE);
78 return pos.piece_count(Us, PAWN) == 0
79 && pos.non_pawn_material(Us) == QueenValueMidgame
80 && pos.piece_count(Us, QUEEN) == 1
81 && pos.piece_count(Them, ROOK) == 1
82 && pos.piece_count(Them, PAWN) >= 1;
87 /// EndgameFunctions class stores endgame evaluation and scaling functions
88 /// in two std::map. Because STL library is not guaranteed to be thread
89 /// safe even for read access, the maps, although with identical content,
90 /// are replicated for each thread. This is faster then using locks.
92 class EndgameFunctions {
96 template<class T> T* get(Key key) const;
99 template<class T> void add(const string& keyCode);
101 static Key buildKey(const string& keyCode);
102 static const string swapColors(const string& keyCode);
104 // Here we store two maps, for evaluate and scaling functions...
105 pair<EFMap, SFMap> maps;
107 // ...and here is the accessing template function
108 template<typename T> const map<Key, T*>& get() const;
111 // Explicit specializations of a member function shall be declared in
112 // the namespace of which the class template is a member.
113 template<> const EFMap& EndgameFunctions::get<EF>() const { return maps.first; }
114 template<> const SFMap& EndgameFunctions::get<SF>() const { return maps.second; }
117 /// MaterialInfoTable c'tor and d'tor allocate and free the space for EndgameFunctions
119 MaterialInfoTable::MaterialInfoTable() { funcs = new EndgameFunctions(); }
120 MaterialInfoTable::~MaterialInfoTable() { delete funcs; }
123 /// MaterialInfoTable::get_material_info() takes a position object as input,
124 /// computes or looks up a MaterialInfo object, and returns a pointer to it.
125 /// If the material configuration is not already present in the table, it
126 /// is stored there, so we don't have to recompute everything when the
127 /// same material configuration occurs again.
129 MaterialInfo* MaterialInfoTable::get_material_info(const Position& pos) const {
131 Key key = pos.get_material_key();
132 MaterialInfo* mi = find(key);
134 // If mi->key matches the position's material hash key, it means that we
135 // have analysed this material configuration before, and we can simply
136 // return the information we found the last time instead of recomputing it.
140 // Initialize MaterialInfo entry
141 memset(mi, 0, sizeof(MaterialInfo));
143 mi->factor[WHITE] = mi->factor[BLACK] = (uint8_t)SCALE_FACTOR_NORMAL;
146 mi->gamePhase = MaterialInfoTable::game_phase(pos);
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->get<EF>(key)) != NULL)
154 if (is_KXK<WHITE>(pos))
156 mi->evaluationFunction = &EvaluateKXK[WHITE];
160 if (is_KXK<BLACK>(pos))
162 mi->evaluationFunction = &EvaluateKXK[BLACK];
166 if (!pos.pieces(PAWN) && !pos.pieces(ROOK) && !pos.pieces(QUEEN))
168 // Minor piece endgame with at least one minor piece per side and
169 // no pawns. Note that the case KmmK is already handled by KXK.
170 assert((pos.pieces(KNIGHT, WHITE) | pos.pieces(BISHOP, WHITE)));
171 assert((pos.pieces(KNIGHT, BLACK) | pos.pieces(BISHOP, BLACK)));
173 if ( pos.piece_count(WHITE, BISHOP) + pos.piece_count(WHITE, KNIGHT) <= 2
174 && pos.piece_count(BLACK, BISHOP) + pos.piece_count(BLACK, KNIGHT) <= 2)
176 mi->evaluationFunction = &EvaluateKmmKm[WHITE];
181 // OK, we didn't find any special evaluation function for the current
182 // material configuration. Is there a suitable scaling function?
184 // We face problems when there are several conflicting applicable
185 // scaling functions and we need to decide which one to use.
188 if ((sf = funcs->get<SF>(key)) != NULL)
190 mi->scalingFunction[sf->color()] = sf;
194 // Generic scaling functions that refer to more then one material
195 // distribution. Should be probed after the specialized ones.
196 // Note that these ones don't return after setting the function.
197 if (is_KBPsKs<WHITE>(pos))
198 mi->scalingFunction[WHITE] = &ScaleKBPsK[WHITE];
200 if (is_KBPsKs<BLACK>(pos))
201 mi->scalingFunction[BLACK] = &ScaleKBPsK[BLACK];
203 if (is_KQKRPs<WHITE>(pos))
204 mi->scalingFunction[WHITE] = &ScaleKQKRPs[WHITE];
206 else if (is_KQKRPs<BLACK>(pos))
207 mi->scalingFunction[BLACK] = &ScaleKQKRPs[BLACK];
209 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) == VALUE_ZERO)
211 if (pos.piece_count(BLACK, PAWN) == 0)
213 assert(pos.piece_count(WHITE, PAWN) >= 2);
214 mi->scalingFunction[WHITE] = &ScaleKPsK[WHITE];
216 else if (pos.piece_count(WHITE, PAWN) == 0)
218 assert(pos.piece_count(BLACK, PAWN) >= 2);
219 mi->scalingFunction[BLACK] = &ScaleKPsK[BLACK];
221 else if (pos.piece_count(WHITE, PAWN) == 1 && pos.piece_count(BLACK, PAWN) == 1)
223 // This is a special case because we set scaling functions
224 // for both colors instead of only one.
225 mi->scalingFunction[WHITE] = &ScaleKPKP[WHITE];
226 mi->scalingFunction[BLACK] = &ScaleKPKP[BLACK];
230 // No pawns makes it difficult to win, even with a material advantage
231 for (Color c = WHITE; c <= BLACK; c++)
232 if ( pos.piece_count(c, PAWN) == 0
233 && pos.non_pawn_material(c) - pos.non_pawn_material(opposite_color(c)) <= BishopValueMidgame)
235 if ( pos.non_pawn_material(c) == pos.non_pawn_material(opposite_color(c))
236 || pos.non_pawn_material(c) < RookValueMidgame)
240 switch (pos.piece_count(c, BISHOP)) {
254 // Compute the space weight
255 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >=
256 2*QueenValueMidgame + 4*RookValueMidgame + 2*KnightValueMidgame)
258 int minorPieceCount = pos.piece_count(WHITE, KNIGHT)
259 + pos.piece_count(WHITE, BISHOP)
260 + pos.piece_count(BLACK, KNIGHT)
261 + pos.piece_count(BLACK, BISHOP);
263 mi->spaceWeight = minorPieceCount * minorPieceCount;
266 // Evaluate the material imbalance. We use PIECE_TYPE_NONE as a place holder
267 // for the bishop pair "extended piece", this allow us to be more flexible
268 // in defining bishop pair bonuses.
269 const int pieceCount[2][8] = {
270 { pos.piece_count(WHITE, BISHOP) > 1, pos.piece_count(WHITE, PAWN), pos.piece_count(WHITE, KNIGHT),
271 pos.piece_count(WHITE, BISHOP), pos.piece_count(WHITE, ROOK), pos.piece_count(WHITE, QUEEN) },
272 { pos.piece_count(BLACK, BISHOP) > 1, pos.piece_count(BLACK, PAWN), pos.piece_count(BLACK, KNIGHT),
273 pos.piece_count(BLACK, BISHOP), pos.piece_count(BLACK, ROOK), pos.piece_count(BLACK, QUEEN) } };
275 mi->value = (int16_t)(imbalance<WHITE>(pieceCount) - imbalance<BLACK>(pieceCount)) / 16;
280 /// MaterialInfoTable::imbalance() calculates imbalance comparing piece count of each
281 /// piece type for both colors.
284 int MaterialInfoTable::imbalance(const int pieceCount[][8]) {
286 const Color Them = (Us == WHITE ? BLACK : WHITE);
288 int pt1, pt2, pc, vv;
291 // Redundancy of major pieces, formula based on Kaufman's paper
292 // "The Evaluation of Material Imbalances in Chess"
293 if (pieceCount[Us][ROOK] > 0)
294 value -= RedundantRookPenalty * (pieceCount[Us][ROOK] - 1)
295 + RedundantQueenPenalty * pieceCount[Us][QUEEN];
297 // Second-degree polynomial material imbalance by Tord Romstad
298 for (pt1 = PIECE_TYPE_NONE; pt1 <= QUEEN; pt1++)
300 pc = pieceCount[Us][pt1];
304 vv = LinearCoefficients[pt1];
306 for (pt2 = PIECE_TYPE_NONE; pt2 <= pt1; pt2++)
307 vv += QuadraticCoefficientsSameColor[pt1][pt2] * pieceCount[Us][pt2]
308 + QuadraticCoefficientsOppositeColor[pt1][pt2] * pieceCount[Them][pt2];
316 /// MaterialInfoTable::game_phase() calculates the phase given the current
317 /// position. Because the phase is strictly a function of the material, it
318 /// is stored in MaterialInfo.
320 Phase MaterialInfoTable::game_phase(const Position& pos) {
322 Value npm = pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK);
324 if (npm >= MidgameLimit)
325 return PHASE_MIDGAME;
327 if (npm <= EndgameLimit)
328 return PHASE_ENDGAME;
330 return Phase(((npm - EndgameLimit) * 128) / (MidgameLimit - EndgameLimit));
334 /// EndgameFunctions member definitions
336 EndgameFunctions::EndgameFunctions() {
338 add<EvaluationFunction<KNNK> >("KNNK");
339 add<EvaluationFunction<KPK> >("KPK");
340 add<EvaluationFunction<KBNK> >("KBNK");
341 add<EvaluationFunction<KRKP> >("KRKP");
342 add<EvaluationFunction<KRKB> >("KRKB");
343 add<EvaluationFunction<KRKN> >("KRKN");
344 add<EvaluationFunction<KQKR> >("KQKR");
345 add<EvaluationFunction<KBBKN> >("KBBKN");
347 add<ScalingFunction<KNPK> >("KNPK");
348 add<ScalingFunction<KRPKR> >("KRPKR");
349 add<ScalingFunction<KBPKB> >("KBPKB");
350 add<ScalingFunction<KBPPKB> >("KBPPKB");
351 add<ScalingFunction<KBPKN> >("KBPKN");
352 add<ScalingFunction<KRPPKRP> >("KRPPKRP");
355 EndgameFunctions::~EndgameFunctions() {
357 for (EFMap::const_iterator it = maps.first.begin(); it != maps.first.end(); ++it)
360 for (SFMap::const_iterator it = maps.second.begin(); it != maps.second.end(); ++it)
364 Key EndgameFunctions::buildKey(const string& keyCode) {
366 assert(keyCode.length() > 0 && keyCode.length() < 8);
367 assert(keyCode[0] == 'K');
372 // Build up a fen string with the given pieces, note that
373 // the fen string could be of an illegal position.
374 for (size_t i = 0; i < keyCode.length(); i++)
376 if (keyCode[i] == 'K')
379 fen += char(upcase ? toupper(keyCode[i]) : tolower(keyCode[i]));
381 fen += char(8 - keyCode.length() + '0');
382 fen += "/8/8/8/8/8/8/8 w - -";
383 return Position(fen, false, 0).get_material_key();
386 const string EndgameFunctions::swapColors(const string& keyCode) {
388 // Build corresponding key for the opposite color: "KBPKN" -> "KNKBP"
389 size_t idx = keyCode.find('K', 1);
390 return keyCode.substr(idx) + keyCode.substr(0, idx);
394 void EndgameFunctions::add(const string& keyCode) {
396 typedef typename T::Base F;
397 typedef map<Key, F*> M;
399 const_cast<M&>(get<F>()).insert(pair<Key, F*>(buildKey(keyCode), new T(WHITE)));
400 const_cast<M&>(get<F>()).insert(pair<Key, F*>(buildKey(swapColors(keyCode)), new T(BLACK)));
404 T* EndgameFunctions::get(Key key) const {
406 typename map<Key, T*>::const_iterator it = get<T>().find(key);
407 return it != get<T>().end() ? it->second : NULL;