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 // Scale factors used when one side has no more pawns
35 const uint8_t NoPawnsSF[4] = { 6, 12, 32 };
37 // Polynomial material balance parameters
38 const Value RedundantQueenPenalty = Value(320);
39 const Value RedundantRookPenalty = Value(554);
41 const int LinearCoefficients[6] = { 1617, -162, -1172, -190, 105, 26 };
43 const int QuadraticCoefficientsSameColor[][8] = {
44 { 7, 7, 7, 7, 7, 7 }, { 39, 2, 7, 7, 7, 7 }, { 35, 271, -4, 7, 7, 7 },
45 { 7, 25, 4, 7, 7, 7 }, { -27, -2, 46, 100, 56, 7 }, { 58, 29, 83, 148, -3, -25 } };
47 const int QuadraticCoefficientsOppositeColor[][8] = {
48 { 41, 41, 41, 41, 41, 41 }, { 37, 41, 41, 41, 41, 41 }, { 10, 62, 41, 41, 41, 41 },
49 { 57, 64, 39, 41, 41, 41 }, { 50, 40, 23, -22, 41, 41 }, { 106, 101, 3, 151, 171, 41 } };
51 typedef EndgameEvaluationFunctionBase EF;
52 typedef EndgameScalingFunctionBase SF;
53 typedef map<Key, EF*> EFMap;
54 typedef map<Key, SF*> SFMap;
56 // Endgame evaluation and scaling functions accessed direcly and not through
57 // the function maps because correspond to more then one material hash key.
58 EvaluationFunction<KmmKm> EvaluateKmmKm[] = { EvaluationFunction<KmmKm>(WHITE), EvaluationFunction<KmmKm>(BLACK) };
59 EvaluationFunction<KXK> EvaluateKXK[] = { EvaluationFunction<KXK>(WHITE), EvaluationFunction<KXK>(BLACK) };
60 ScalingFunction<KBPsK> ScaleKBPsK[] = { ScalingFunction<KBPsK>(WHITE), ScalingFunction<KBPsK>(BLACK) };
61 ScalingFunction<KQKRPs> ScaleKQKRPs[] = { ScalingFunction<KQKRPs>(WHITE), ScalingFunction<KQKRPs>(BLACK) };
62 ScalingFunction<KPsK> ScaleKPsK[] = { ScalingFunction<KPsK>(WHITE), ScalingFunction<KPsK>(BLACK) };
63 ScalingFunction<KPKP> ScaleKPKP[] = { ScalingFunction<KPKP>(WHITE), ScalingFunction<KPKP>(BLACK) };
65 // Helper templates used to detect a given material distribution
66 template<Color Us> bool is_KXK(const Position& pos) {
67 const Color Them = (Us == WHITE ? BLACK : WHITE);
68 return pos.non_pawn_material(Them) == VALUE_ZERO
69 && pos.piece_count(Them, PAWN) == 0
70 && pos.non_pawn_material(Us) >= RookValueMidgame;
73 template<Color Us> bool is_KBPsKs(const Position& pos) {
74 return pos.non_pawn_material(Us) == BishopValueMidgame
75 && pos.piece_count(Us, BISHOP) == 1
76 && pos.piece_count(Us, PAWN) >= 1;
79 template<Color Us> bool is_KQKRPs(const Position& pos) {
80 const Color Them = (Us == WHITE ? BLACK : WHITE);
81 return pos.piece_count(Us, PAWN) == 0
82 && pos.non_pawn_material(Us) == QueenValueMidgame
83 && pos.piece_count(Us, QUEEN) == 1
84 && pos.piece_count(Them, ROOK) == 1
85 && pos.piece_count(Them, PAWN) >= 1;
90 /// EndgameFunctions class stores endgame evaluation and scaling functions
91 /// in two std::map. Because STL library is not guaranteed to be thread
92 /// safe even for read access, the maps, although with identical content,
93 /// are replicated for each thread. This is faster then using locks.
95 class EndgameFunctions {
99 template<class T> T* get(Key key) const;
102 template<class T> void add(const string& keyCode);
104 static Key buildKey(const string& keyCode);
105 static const string swapColors(const string& keyCode);
107 // Here we store two maps, for evaluate and scaling functions...
108 pair<EFMap, SFMap> maps;
110 // ...and here is the accessing template function
111 template<typename T> const map<Key, T*>& get() const;
114 // Explicit specializations of a member function shall be declared in
115 // the namespace of which the class template is a member.
116 template<> const EFMap& EndgameFunctions::get<EF>() const { return maps.first; }
117 template<> const SFMap& EndgameFunctions::get<SF>() const { return maps.second; }
120 /// MaterialInfoTable c'tor and d'tor allocate and free the space for EndgameFunctions
122 MaterialInfoTable::MaterialInfoTable() { funcs = new EndgameFunctions(); }
123 MaterialInfoTable::~MaterialInfoTable() { delete funcs; }
126 /// MaterialInfoTable::get_material_info() takes a position object as input,
127 /// computes or looks up a MaterialInfo object, and returns a pointer to it.
128 /// If the material configuration is not already present in the table, it
129 /// is stored there, so we don't have to recompute everything when the
130 /// same material configuration occurs again.
132 MaterialInfo* MaterialInfoTable::get_material_info(const Position& pos) const {
134 Key key = pos.get_material_key();
135 MaterialInfo* mi = find(key);
137 // If mi->key matches the position's material hash key, it means that we
138 // have analysed this material configuration before, and we can simply
139 // return the information we found the last time instead of recomputing it.
143 // Initialize MaterialInfo entry
144 memset(mi, 0, sizeof(MaterialInfo));
146 mi->factor[WHITE] = mi->factor[BLACK] = (uint8_t)SCALE_FACTOR_NORMAL;
149 mi->gamePhase = MaterialInfoTable::game_phase(pos);
151 // Let's look if we have a specialized evaluation function for this
152 // particular material configuration. First we look for a fixed
153 // configuration one, then a generic one if previous search failed.
154 if ((mi->evaluationFunction = funcs->get<EF>(key)) != NULL)
157 if (is_KXK<WHITE>(pos))
159 mi->evaluationFunction = &EvaluateKXK[WHITE];
163 if (is_KXK<BLACK>(pos))
165 mi->evaluationFunction = &EvaluateKXK[BLACK];
169 if (!pos.pieces(PAWN) && !pos.pieces(ROOK) && !pos.pieces(QUEEN))
171 // Minor piece endgame with at least one minor piece per side and
172 // no pawns. Note that the case KmmK is already handled by KXK.
173 assert((pos.pieces(KNIGHT, WHITE) | pos.pieces(BISHOP, WHITE)));
174 assert((pos.pieces(KNIGHT, BLACK) | pos.pieces(BISHOP, BLACK)));
176 if ( pos.piece_count(WHITE, BISHOP) + pos.piece_count(WHITE, KNIGHT) <= 2
177 && pos.piece_count(BLACK, BISHOP) + pos.piece_count(BLACK, KNIGHT) <= 2)
179 mi->evaluationFunction = &EvaluateKmmKm[WHITE];
184 // OK, we didn't find any special evaluation function for the current
185 // material configuration. Is there a suitable scaling function?
187 // We face problems when there are several conflicting applicable
188 // scaling functions and we need to decide which one to use.
191 if ((sf = funcs->get<SF>(key)) != NULL)
193 mi->scalingFunction[sf->color()] = sf;
197 // Generic scaling functions that refer to more then one material
198 // distribution. Should be probed after the specialized ones.
199 // Note that these ones don't return after setting the function.
200 if (is_KBPsKs<WHITE>(pos))
201 mi->scalingFunction[WHITE] = &ScaleKBPsK[WHITE];
203 if (is_KBPsKs<BLACK>(pos))
204 mi->scalingFunction[BLACK] = &ScaleKBPsK[BLACK];
206 if (is_KQKRPs<WHITE>(pos))
207 mi->scalingFunction[WHITE] = &ScaleKQKRPs[WHITE];
209 else if (is_KQKRPs<BLACK>(pos))
210 mi->scalingFunction[BLACK] = &ScaleKQKRPs[BLACK];
212 Value npm_w = pos.non_pawn_material(WHITE);
213 Value npm_b = pos.non_pawn_material(BLACK);
215 if (npm_w + npm_b == VALUE_ZERO)
217 if (pos.piece_count(BLACK, PAWN) == 0)
219 assert(pos.piece_count(WHITE, PAWN) >= 2);
220 mi->scalingFunction[WHITE] = &ScaleKPsK[WHITE];
222 else if (pos.piece_count(WHITE, PAWN) == 0)
224 assert(pos.piece_count(BLACK, PAWN) >= 2);
225 mi->scalingFunction[BLACK] = &ScaleKPsK[BLACK];
227 else if (pos.piece_count(WHITE, PAWN) == 1 && pos.piece_count(BLACK, PAWN) == 1)
229 // This is a special case because we set scaling functions
230 // for both colors instead of only one.
231 mi->scalingFunction[WHITE] = &ScaleKPKP[WHITE];
232 mi->scalingFunction[BLACK] = &ScaleKPKP[BLACK];
236 // No pawns makes it difficult to win, even with a material advantage
237 if (pos.piece_count(WHITE, PAWN) == 0 && npm_w - npm_b <= BishopValueMidgame)
240 (npm_w == npm_b || npm_w < RookValueMidgame ? 0 : NoPawnsSF[Min(pos.piece_count(WHITE, BISHOP), 2)]);
243 if (pos.piece_count(BLACK, PAWN) == 0 && npm_b - npm_w <= BishopValueMidgame)
246 (npm_w == npm_b || npm_b < RookValueMidgame ? 0 : NoPawnsSF[Min(pos.piece_count(BLACK, BISHOP), 2)]);
249 // Compute the space weight
250 if (npm_w + npm_b >= 2 * QueenValueMidgame + 4 * RookValueMidgame + 2 * KnightValueMidgame)
252 int minorPieceCount = pos.piece_count(WHITE, KNIGHT) + pos.piece_count(WHITE, BISHOP)
253 + pos.piece_count(BLACK, KNIGHT) + pos.piece_count(BLACK, BISHOP);
255 mi->spaceWeight = minorPieceCount * minorPieceCount;
258 // Evaluate the material imbalance. We use PIECE_TYPE_NONE as a place holder
259 // for the bishop pair "extended piece", this allow us to be more flexible
260 // in defining bishop pair bonuses.
261 const int pieceCount[2][8] = {
262 { pos.piece_count(WHITE, BISHOP) > 1, pos.piece_count(WHITE, PAWN), pos.piece_count(WHITE, KNIGHT),
263 pos.piece_count(WHITE, BISHOP) , pos.piece_count(WHITE, ROOK), pos.piece_count(WHITE, QUEEN) },
264 { pos.piece_count(BLACK, BISHOP) > 1, pos.piece_count(BLACK, PAWN), pos.piece_count(BLACK, KNIGHT),
265 pos.piece_count(BLACK, BISHOP) , pos.piece_count(BLACK, ROOK), pos.piece_count(BLACK, QUEEN) } };
267 mi->value = (int16_t)(imbalance<WHITE>(pieceCount) - imbalance<BLACK>(pieceCount)) / 16;
272 /// MaterialInfoTable::imbalance() calculates imbalance comparing piece count of each
273 /// piece type for both colors.
276 int MaterialInfoTable::imbalance(const int pieceCount[][8]) {
278 const Color Them = (Us == WHITE ? BLACK : WHITE);
280 int pt1, pt2, pc, vv;
283 // Redundancy of major pieces, formula based on Kaufman's paper
284 // "The Evaluation of Material Imbalances in Chess"
285 if (pieceCount[Us][ROOK] > 0)
286 value -= RedundantRookPenalty * (pieceCount[Us][ROOK] - 1)
287 + RedundantQueenPenalty * pieceCount[Us][QUEEN];
289 // Second-degree polynomial material imbalance by Tord Romstad
290 for (pt1 = PIECE_TYPE_NONE; pt1 <= QUEEN; pt1++)
292 pc = pieceCount[Us][pt1];
296 vv = LinearCoefficients[pt1];
298 for (pt2 = PIECE_TYPE_NONE; pt2 <= pt1; pt2++)
299 vv += QuadraticCoefficientsSameColor[pt1][pt2] * pieceCount[Us][pt2]
300 + QuadraticCoefficientsOppositeColor[pt1][pt2] * pieceCount[Them][pt2];
308 /// MaterialInfoTable::game_phase() calculates the phase given the current
309 /// position. Because the phase is strictly a function of the material, it
310 /// is stored in MaterialInfo.
312 Phase MaterialInfoTable::game_phase(const Position& pos) {
314 Value npm = pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK);
316 if (npm >= MidgameLimit)
317 return PHASE_MIDGAME;
319 if (npm <= EndgameLimit)
320 return PHASE_ENDGAME;
322 return Phase(((npm - EndgameLimit) * 128) / (MidgameLimit - EndgameLimit));
326 /// EndgameFunctions member definitions
328 EndgameFunctions::EndgameFunctions() {
330 add<EvaluationFunction<KNNK> >("KNNK");
331 add<EvaluationFunction<KPK> >("KPK");
332 add<EvaluationFunction<KBNK> >("KBNK");
333 add<EvaluationFunction<KRKP> >("KRKP");
334 add<EvaluationFunction<KRKB> >("KRKB");
335 add<EvaluationFunction<KRKN> >("KRKN");
336 add<EvaluationFunction<KQKR> >("KQKR");
337 add<EvaluationFunction<KBBKN> >("KBBKN");
339 add<ScalingFunction<KNPK> >("KNPK");
340 add<ScalingFunction<KRPKR> >("KRPKR");
341 add<ScalingFunction<KBPKB> >("KBPKB");
342 add<ScalingFunction<KBPPKB> >("KBPPKB");
343 add<ScalingFunction<KBPKN> >("KBPKN");
344 add<ScalingFunction<KRPPKRP> >("KRPPKRP");
347 EndgameFunctions::~EndgameFunctions() {
349 for (EFMap::const_iterator it = maps.first.begin(); it != maps.first.end(); ++it)
352 for (SFMap::const_iterator it = maps.second.begin(); it != maps.second.end(); ++it)
356 Key EndgameFunctions::buildKey(const string& keyCode) {
358 assert(keyCode.length() > 0 && keyCode.length() < 8);
359 assert(keyCode[0] == 'K');
364 // Build up a fen string with the given pieces, note that
365 // 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 fen += char(upcase ? toupper(keyCode[i]) : tolower(keyCode[i]));
373 fen += char(8 - keyCode.length() + '0');
374 fen += "/8/8/8/8/8/8/8 w - -";
375 return Position(fen, false, 0).get_material_key();
378 const string EndgameFunctions::swapColors(const string& keyCode) {
380 // Build corresponding key for the opposite color: "KBPKN" -> "KNKBP"
381 size_t idx = keyCode.find('K', 1);
382 return keyCode.substr(idx) + keyCode.substr(0, idx);
386 void EndgameFunctions::add(const string& keyCode) {
388 typedef typename T::Base F;
389 typedef map<Key, F*> M;
391 const_cast<M&>(get<F>()).insert(pair<Key, F*>(buildKey(keyCode), new T(WHITE)));
392 const_cast<M&>(get<F>()).insert(pair<Key, F*>(buildKey(swapColors(keyCode)), new T(BLACK)));
396 T* EndgameFunctions::get(Key key) const {
398 typename map<Key, T*>::const_iterator it = get<T>().find(key);
399 return it != get<T>().end() ? it->second : NULL;