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 // Polynomial material balance parameters
32 // pair pawn knight bishop rook queen
33 const int LinearCoefficients[6] = { 1852, -162, -1122, -183, 249, -154 };
35 const int QuadraticCoefficientsSameColor[][PIECE_TYPE_NB] = {
36 // pair pawn knight bishop rook queen
39 { 35, 271, -4 }, // Knight
40 { 0, 105, 4, 0 }, // Bishop
41 { -27, -2, 46, 100, -141 }, // Rook
42 {-177, 25, 129, 142, -137, 0 } // Queen
45 const int QuadraticCoefficientsOppositeColor[][PIECE_TYPE_NB] = {
47 // pair pawn knight bishop rook queen
50 { 10, 62, 0 }, // Knight OUR PIECES
51 { 57, 64, 39, 0 }, // Bishop
52 { 50, 40, 23, -22, 0 }, // Rook
53 { 98, 105, -39, 141, 274, 0 } // Queen
56 // Endgame evaluation and scaling functions are accessed directly and not through
57 // the function maps because they correspond to more than one material hash key.
58 Endgame<KXK> EvaluateKXK[] = { Endgame<KXK>(WHITE), Endgame<KXK>(BLACK) };
60 Endgame<KBPsK> ScaleKBPsK[] = { Endgame<KBPsK>(WHITE), Endgame<KBPsK>(BLACK) };
61 Endgame<KQKRPs> ScaleKQKRPs[] = { Endgame<KQKRPs>(WHITE), Endgame<KQKRPs>(BLACK) };
62 Endgame<KPsK> ScaleKPsK[] = { Endgame<KPsK>(WHITE), Endgame<KPsK>(BLACK) };
63 Endgame<KPKP> ScaleKPKP[] = { Endgame<KPKP>(WHITE), Endgame<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.count<PAWN>(Them)
69 && pos.non_pawn_material(Them) == VALUE_ZERO
70 && pos.non_pawn_material(Us) >= RookValueMg;
73 template<Color Us> bool is_KBPsKs(const Position& pos) {
74 return pos.non_pawn_material(Us) == BishopValueMg
75 && pos.count<BISHOP>(Us) == 1
76 && pos.count<PAWN >(Us) >= 1;
79 template<Color Us> bool is_KQKRPs(const Position& pos) {
80 const Color Them = (Us == WHITE ? BLACK : WHITE);
81 return !pos.count<PAWN>(Us)
82 && pos.non_pawn_material(Us) == QueenValueMg
83 && pos.count<QUEEN>(Us) == 1
84 && pos.count<ROOK>(Them) == 1
85 && pos.count<PAWN>(Them) >= 1;
88 /// imbalance() calculates the imbalance by comparing the piece count of each
89 /// piece type for both colors.
92 int imbalance(const int pieceCount[][PIECE_TYPE_NB]) {
94 const Color Them = (Us == WHITE ? BLACK : WHITE);
99 // Second-degree polynomial material imbalance by Tord Romstad
100 for (pt1 = NO_PIECE_TYPE; pt1 <= QUEEN; ++pt1)
102 pc = pieceCount[Us][pt1];
106 v = LinearCoefficients[pt1];
108 for (pt2 = NO_PIECE_TYPE; pt2 <= pt1; ++pt2)
109 v += QuadraticCoefficientsSameColor[pt1][pt2] * pieceCount[Us][pt2]
110 + QuadraticCoefficientsOppositeColor[pt1][pt2] * pieceCount[Them][pt2];
122 /// Material::probe() takes a position object as input, looks up a MaterialEntry
123 /// object, and returns a pointer to it. If the material configuration is not
124 /// already present in the table, it is computed and stored there, so we don't
125 /// have to recompute everything when the same material configuration occurs again.
127 Entry* probe(const Position& pos, Table& entries, Endgames& endgames) {
129 Key key = pos.material_key();
130 Entry* e = entries[key];
132 // If e->key matches the position's material hash key, it means that we
133 // have analysed this material configuration before, and we can simply
134 // return the information we found the last time instead of recomputing it.
138 std::memset(e, 0, sizeof(Entry));
140 e->factor[WHITE] = e->factor[BLACK] = (uint8_t)SCALE_FACTOR_NORMAL;
141 e->gamePhase = game_phase(pos);
143 // Let's look if we have a specialized evaluation function for this particular
144 // material configuration. Firstly we look for a fixed configuration one, then
145 // for a generic one if the previous search failed.
146 if (endgames.probe(key, e->evaluationFunction))
149 if (is_KXK<WHITE>(pos))
151 e->evaluationFunction = &EvaluateKXK[WHITE];
155 if (is_KXK<BLACK>(pos))
157 e->evaluationFunction = &EvaluateKXK[BLACK];
161 // OK, we didn't find any special evaluation function for the current
162 // material configuration. Is there a suitable scaling function?
164 // We face problems when there are several conflicting applicable
165 // scaling functions and we need to decide which one to use.
166 EndgameBase<ScaleFactor>* sf;
168 if (endgames.probe(key, sf))
170 e->scalingFunction[sf->color()] = sf;
174 // Generic scaling functions that refer to more than one material
175 // distribution. They should be probed after the specialized ones.
176 // Note that these ones don't return after setting the function.
177 if (is_KBPsKs<WHITE>(pos))
178 e->scalingFunction[WHITE] = &ScaleKBPsK[WHITE];
180 if (is_KBPsKs<BLACK>(pos))
181 e->scalingFunction[BLACK] = &ScaleKBPsK[BLACK];
183 if (is_KQKRPs<WHITE>(pos))
184 e->scalingFunction[WHITE] = &ScaleKQKRPs[WHITE];
186 else if (is_KQKRPs<BLACK>(pos))
187 e->scalingFunction[BLACK] = &ScaleKQKRPs[BLACK];
189 Value npm_w = pos.non_pawn_material(WHITE);
190 Value npm_b = pos.non_pawn_material(BLACK);
192 if (npm_w + npm_b == VALUE_ZERO && pos.pieces(PAWN))
194 if (!pos.count<PAWN>(BLACK))
196 assert(pos.count<PAWN>(WHITE) >= 2);
197 e->scalingFunction[WHITE] = &ScaleKPsK[WHITE];
199 else if (!pos.count<PAWN>(WHITE))
201 assert(pos.count<PAWN>(BLACK) >= 2);
202 e->scalingFunction[BLACK] = &ScaleKPsK[BLACK];
204 else if (pos.count<PAWN>(WHITE) == 1 && pos.count<PAWN>(BLACK) == 1)
206 // This is a special case because we set scaling functions
207 // for both colors instead of only one.
208 e->scalingFunction[WHITE] = &ScaleKPKP[WHITE];
209 e->scalingFunction[BLACK] = &ScaleKPKP[BLACK];
213 // No pawns makes it difficult to win, even with a material advantage. This
214 // catches some trivial draws like KK, KBK and KNK and gives a very drawish
215 // scale factor for cases such as KRKBP and KmmKm (except for KBBKN).
216 if (!pos.count<PAWN>(WHITE) && npm_w - npm_b <= BishopValueMg)
217 e->factor[WHITE] = uint8_t(npm_w < RookValueMg ? SCALE_FACTOR_DRAW : npm_b <= BishopValueMg ? 4 : 12);
219 if (!pos.count<PAWN>(BLACK) && npm_b - npm_w <= BishopValueMg)
220 e->factor[BLACK] = uint8_t(npm_b < RookValueMg ? SCALE_FACTOR_DRAW : npm_w <= BishopValueMg ? 4 : 12);
222 if (pos.count<PAWN>(WHITE) == 1 && npm_w - npm_b <= BishopValueMg)
223 e->factor[WHITE] = (uint8_t) SCALE_FACTOR_ONEPAWN;
225 if (pos.count<PAWN>(BLACK) == 1 && npm_b - npm_w <= BishopValueMg)
226 e->factor[BLACK] = (uint8_t) SCALE_FACTOR_ONEPAWN;
228 // Compute the space weight
229 if (npm_w + npm_b >= 2 * QueenValueMg + 4 * RookValueMg + 2 * KnightValueMg)
231 int minorPieceCount = pos.count<KNIGHT>(WHITE) + pos.count<BISHOP>(WHITE)
232 + pos.count<KNIGHT>(BLACK) + pos.count<BISHOP>(BLACK);
234 e->spaceWeight = make_score(minorPieceCount * minorPieceCount, 0);
237 // Evaluate the material imbalance. We use PIECE_TYPE_NONE as a place holder
238 // for the bishop pair "extended piece", which allows us to be more flexible
239 // in defining bishop pair bonuses.
240 const int pieceCount[COLOR_NB][PIECE_TYPE_NB] = {
241 { pos.count<BISHOP>(WHITE) > 1, pos.count<PAWN>(WHITE), pos.count<KNIGHT>(WHITE),
242 pos.count<BISHOP>(WHITE) , pos.count<ROOK>(WHITE), pos.count<QUEEN >(WHITE) },
243 { pos.count<BISHOP>(BLACK) > 1, pos.count<PAWN>(BLACK), pos.count<KNIGHT>(BLACK),
244 pos.count<BISHOP>(BLACK) , pos.count<ROOK>(BLACK), pos.count<QUEEN >(BLACK) } };
246 e->value = (int16_t)((imbalance<WHITE>(pieceCount) - imbalance<BLACK>(pieceCount)) / 16);
251 /// Material::game_phase() calculates the phase given the current
252 /// position. Because the phase is strictly a function of the material, it
253 /// is stored in MaterialEntry.
255 Phase game_phase(const Position& pos) {
257 Value npm = pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK);
259 return npm >= MidgameLimit ? PHASE_MIDGAME
260 : npm <= EndgameLimit ? PHASE_ENDGAME
261 : Phase(((npm - EndgameLimit) * 128) / (MidgameLimit - EndgameLimit));
264 } // namespace Material