2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2014 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/>.
20 #include <algorithm> // For std::min
30 // Values modified by Joona Kiiski
31 const Value MidgameLimit = Value(15581);
32 const Value EndgameLimit = Value(3998);
34 // Polynomial material balance parameters
36 // pair pawn knight bishop rook queen
37 const int LinearCoefficients[6] = { 1852, -162, -1122, -183, 249, -52 };
39 const int QuadraticCoefficientsSameColor[][PIECE_TYPE_NB] = {
40 // pair pawn knight bishop rook queen
43 { 35, 271, -4 }, // Knight
44 { 0, 105, 4, 0 }, // Bishop
45 { -27, -2, 46, 100, -141 }, // Rook
46 { 58, 29, 83, 148, -163, 0 } // Queen
49 const int QuadraticCoefficientsOppositeColor[][PIECE_TYPE_NB] = {
51 // pair pawn knight bishop rook queen
54 { 10, 62, 0 }, // Knight OUR PIECES
55 { 57, 64, 39, 0 }, // Bishop
56 { 50, 40, 23, -22, 0 }, // Rook
57 { 106, 101, 3, 151, 171, 0 } // Queen
60 // Endgame evaluation and scaling functions are accessed directly and not through
61 // the function maps because they correspond to more than one material hash key.
62 Endgame<KXK> EvaluateKXK[] = { Endgame<KXK>(WHITE), Endgame<KXK>(BLACK) };
64 Endgame<KBPsK> ScaleKBPsK[] = { Endgame<KBPsK>(WHITE), Endgame<KBPsK>(BLACK) };
65 Endgame<KQKRPs> ScaleKQKRPs[] = { Endgame<KQKRPs>(WHITE), Endgame<KQKRPs>(BLACK) };
66 Endgame<KPsK> ScaleKPsK[] = { Endgame<KPsK>(WHITE), Endgame<KPsK>(BLACK) };
67 Endgame<KPKP> ScaleKPKP[] = { Endgame<KPKP>(WHITE), Endgame<KPKP>(BLACK) };
69 // Helper templates used to detect a given material distribution
70 template<Color Us> bool is_KXK(const Position& pos) {
71 const Color Them = (Us == WHITE ? BLACK : WHITE);
72 return !pos.count<PAWN>(Them)
73 && pos.non_pawn_material(Them) == VALUE_ZERO
74 && pos.non_pawn_material(Us) >= RookValueMg;
77 template<Color Us> bool is_KBPsKs(const Position& pos) {
78 return pos.non_pawn_material(Us) == BishopValueMg
79 && pos.count<BISHOP>(Us) == 1
80 && pos.count<PAWN >(Us) >= 1;
83 template<Color Us> bool is_KQKRPs(const Position& pos) {
84 const Color Them = (Us == WHITE ? BLACK : WHITE);
85 return !pos.count<PAWN>(Us)
86 && pos.non_pawn_material(Us) == QueenValueMg
87 && pos.count<QUEEN>(Us) == 1
88 && pos.count<ROOK>(Them) == 1
89 && pos.count<PAWN>(Them) >= 1;
92 /// imbalance() calculates the imbalance by comparing the piece count of each
93 /// piece type for both colors.
96 int imbalance(const int pieceCount[][PIECE_TYPE_NB]) {
98 const Color Them = (Us == WHITE ? BLACK : WHITE);
103 // Second-degree polynomial material imbalance by Tord Romstad
104 for (pt1 = NO_PIECE_TYPE; pt1 <= QUEEN; ++pt1)
106 pc = pieceCount[Us][pt1];
110 v = LinearCoefficients[pt1];
112 for (pt2 = NO_PIECE_TYPE; pt2 <= pt1; ++pt2)
113 v += QuadraticCoefficientsSameColor[pt1][pt2] * pieceCount[Us][pt2]
114 + QuadraticCoefficientsOppositeColor[pt1][pt2] * pieceCount[Them][pt2];
119 // Queen vs. 3 minors slightly favours the minors
120 if (pieceCount[Us][QUEEN] == 1 && pieceCount[Them][QUEEN] == 0)
122 int n = pieceCount[Them][KNIGHT] - pieceCount[Us][KNIGHT];
123 int b = pieceCount[Them][BISHOP] - pieceCount[Us][BISHOP];
125 if ((n == 2 && b == 1) || (n == 1 && b == 2))
136 /// Material::probe() takes a position object as input, looks up a MaterialEntry
137 /// object, and returns a pointer to it. If the material configuration is not
138 /// already present in the table, it is computed and stored there, so we don't
139 /// have to recompute everything when the same material configuration occurs again.
141 Entry* probe(const Position& pos, Table& entries, Endgames& endgames) {
143 Key key = pos.material_key();
144 Entry* e = entries[key];
146 // If e->key matches the position's material hash key, it means that we
147 // have analysed this material configuration before, and we can simply
148 // return the information we found the last time instead of recomputing it.
152 std::memset(e, 0, sizeof(Entry));
154 e->factor[WHITE] = e->factor[BLACK] = (uint8_t)SCALE_FACTOR_NORMAL;
155 e->gamePhase = game_phase(pos);
157 // Let's look if we have a specialized evaluation function for this particular
158 // material configuration. Firstly we look for a fixed configuration one, then
159 // for a generic one if the previous search failed.
160 if (endgames.probe(key, e->evaluationFunction))
163 if (is_KXK<WHITE>(pos))
165 e->evaluationFunction = &EvaluateKXK[WHITE];
169 if (is_KXK<BLACK>(pos))
171 e->evaluationFunction = &EvaluateKXK[BLACK];
175 // OK, we didn't find any special evaluation function for the current
176 // material configuration. Is there a suitable scaling function?
178 // We face problems when there are several conflicting applicable
179 // scaling functions and we need to decide which one to use.
180 EndgameBase<ScaleFactor>* sf;
182 if (endgames.probe(key, sf))
184 e->scalingFunction[sf->color()] = sf;
188 // Generic scaling functions that refer to more than one material
189 // distribution. They should be probed after the specialized ones.
190 // Note that these ones don't return after setting the function.
191 if (is_KBPsKs<WHITE>(pos))
192 e->scalingFunction[WHITE] = &ScaleKBPsK[WHITE];
194 if (is_KBPsKs<BLACK>(pos))
195 e->scalingFunction[BLACK] = &ScaleKBPsK[BLACK];
197 if (is_KQKRPs<WHITE>(pos))
198 e->scalingFunction[WHITE] = &ScaleKQKRPs[WHITE];
200 else if (is_KQKRPs<BLACK>(pos))
201 e->scalingFunction[BLACK] = &ScaleKQKRPs[BLACK];
203 Value npm_w = pos.non_pawn_material(WHITE);
204 Value npm_b = pos.non_pawn_material(BLACK);
206 if (npm_w + npm_b == VALUE_ZERO && pos.pieces(PAWN))
208 if (!pos.count<PAWN>(BLACK))
210 assert(pos.count<PAWN>(WHITE) >= 2);
211 e->scalingFunction[WHITE] = &ScaleKPsK[WHITE];
213 else if (!pos.count<PAWN>(WHITE))
215 assert(pos.count<PAWN>(BLACK) >= 2);
216 e->scalingFunction[BLACK] = &ScaleKPsK[BLACK];
218 else if (pos.count<PAWN>(WHITE) == 1 && pos.count<PAWN>(BLACK) == 1)
220 // This is a special case because we set scaling functions
221 // for both colors instead of only one.
222 e->scalingFunction[WHITE] = &ScaleKPKP[WHITE];
223 e->scalingFunction[BLACK] = &ScaleKPKP[BLACK];
227 // No pawns makes it difficult to win, even with a material advantage. This
228 // catches some trivial draws like KK, KBK and KNK and gives a very drawish
229 // scale factor for cases such as KRKBP and KmmKm (except for KBBKN).
230 if (!pos.count<PAWN>(WHITE) && npm_w - npm_b <= BishopValueMg)
231 e->factor[WHITE] = uint8_t(npm_w < RookValueMg ? SCALE_FACTOR_DRAW : npm_b <= BishopValueMg ? 4 : 12);
233 if (!pos.count<PAWN>(BLACK) && npm_b - npm_w <= BishopValueMg)
234 e->factor[BLACK] = uint8_t(npm_b < RookValueMg ? SCALE_FACTOR_DRAW : npm_w <= BishopValueMg ? 4 : 12);
236 if (pos.count<PAWN>(WHITE) == 1 && npm_w - npm_b <= BishopValueMg)
237 e->factor[WHITE] = (uint8_t) SCALE_FACTOR_ONEPAWN;
239 if (pos.count<PAWN>(BLACK) == 1 && npm_b - npm_w <= BishopValueMg)
240 e->factor[BLACK] = (uint8_t) SCALE_FACTOR_ONEPAWN;
242 // Compute the space weight
243 if (npm_w + npm_b >= 2 * QueenValueMg + 4 * RookValueMg + 2 * KnightValueMg)
245 int minorPieceCount = pos.count<KNIGHT>(WHITE) + pos.count<BISHOP>(WHITE)
246 + pos.count<KNIGHT>(BLACK) + pos.count<BISHOP>(BLACK);
248 e->spaceWeight = make_score(minorPieceCount * minorPieceCount, 0);
251 // Evaluate the material imbalance. We use PIECE_TYPE_NONE as a place holder
252 // for the bishop pair "extended piece", which allows us to be more flexible
253 // in defining bishop pair bonuses.
254 const int pieceCount[COLOR_NB][PIECE_TYPE_NB] = {
255 { pos.count<BISHOP>(WHITE) > 1, pos.count<PAWN>(WHITE), pos.count<KNIGHT>(WHITE),
256 pos.count<BISHOP>(WHITE) , pos.count<ROOK>(WHITE), pos.count<QUEEN >(WHITE) },
257 { pos.count<BISHOP>(BLACK) > 1, pos.count<PAWN>(BLACK), pos.count<KNIGHT>(BLACK),
258 pos.count<BISHOP>(BLACK) , pos.count<ROOK>(BLACK), pos.count<QUEEN >(BLACK) } };
260 e->value = (int16_t)((imbalance<WHITE>(pieceCount) - imbalance<BLACK>(pieceCount)) / 16);
265 /// Material::game_phase() calculates the phase given the current
266 /// position. Because the phase is strictly a function of the material, it
267 /// is stored in MaterialEntry.
269 Phase game_phase(const Position& pos) {
271 Value npm = pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK);
273 return npm >= MidgameLimit ? PHASE_MIDGAME
274 : npm <= EndgameLimit ? PHASE_ENDGAME
275 : Phase(((npm - EndgameLimit) * 128) / (MidgameLimit - EndgameLimit));
278 } // namespace Material