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, -157 };
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 {-161, 30, 126, 144, -127, 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 { 103, 90, -40, 142, 268, 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];
126 /// Material::probe() takes a position object as input, looks up a MaterialEntry
127 /// object, and returns a pointer to it. If the material configuration is not
128 /// already present in the table, it is computed and stored there, so we don't
129 /// have to recompute everything when the same material configuration occurs again.
131 Entry* probe(const Position& pos, Table& entries, Endgames& endgames) {
133 Key key = pos.material_key();
134 Entry* e = entries[key];
136 // If e->key matches the position's material hash key, it means that we
137 // have analysed this material configuration before, and we can simply
138 // return the information we found the last time instead of recomputing it.
142 std::memset(e, 0, sizeof(Entry));
144 e->factor[WHITE] = e->factor[BLACK] = (uint8_t)SCALE_FACTOR_NORMAL;
145 e->gamePhase = game_phase(pos);
147 // Let's look if we have a specialized evaluation function for this particular
148 // material configuration. Firstly we look for a fixed configuration one, then
149 // for a generic one if the previous search failed.
150 if (endgames.probe(key, e->evaluationFunction))
153 if (is_KXK<WHITE>(pos))
155 e->evaluationFunction = &EvaluateKXK[WHITE];
159 if (is_KXK<BLACK>(pos))
161 e->evaluationFunction = &EvaluateKXK[BLACK];
165 // OK, we didn't find any special evaluation function for the current
166 // material configuration. Is there a suitable scaling function?
168 // We face problems when there are several conflicting applicable
169 // scaling functions and we need to decide which one to use.
170 EndgameBase<ScaleFactor>* sf;
172 if (endgames.probe(key, sf))
174 e->scalingFunction[sf->color()] = sf;
178 // Generic scaling functions that refer to more than one material
179 // distribution. They should be probed after the specialized ones.
180 // Note that these ones don't return after setting the function.
181 if (is_KBPsKs<WHITE>(pos))
182 e->scalingFunction[WHITE] = &ScaleKBPsK[WHITE];
184 if (is_KBPsKs<BLACK>(pos))
185 e->scalingFunction[BLACK] = &ScaleKBPsK[BLACK];
187 if (is_KQKRPs<WHITE>(pos))
188 e->scalingFunction[WHITE] = &ScaleKQKRPs[WHITE];
190 else if (is_KQKRPs<BLACK>(pos))
191 e->scalingFunction[BLACK] = &ScaleKQKRPs[BLACK];
193 Value npm_w = pos.non_pawn_material(WHITE);
194 Value npm_b = pos.non_pawn_material(BLACK);
196 if (npm_w + npm_b == VALUE_ZERO && pos.pieces(PAWN))
198 if (!pos.count<PAWN>(BLACK))
200 assert(pos.count<PAWN>(WHITE) >= 2);
201 e->scalingFunction[WHITE] = &ScaleKPsK[WHITE];
203 else if (!pos.count<PAWN>(WHITE))
205 assert(pos.count<PAWN>(BLACK) >= 2);
206 e->scalingFunction[BLACK] = &ScaleKPsK[BLACK];
208 else if (pos.count<PAWN>(WHITE) == 1 && pos.count<PAWN>(BLACK) == 1)
210 // This is a special case because we set scaling functions
211 // for both colors instead of only one.
212 e->scalingFunction[WHITE] = &ScaleKPKP[WHITE];
213 e->scalingFunction[BLACK] = &ScaleKPKP[BLACK];
217 // No pawns makes it difficult to win, even with a material advantage. This
218 // catches some trivial draws like KK, KBK and KNK and gives a very drawish
219 // scale factor for cases such as KRKBP and KmmKm (except for KBBKN).
220 if (!pos.count<PAWN>(WHITE) && npm_w - npm_b <= BishopValueMg)
221 e->factor[WHITE] = uint8_t(npm_w < RookValueMg ? SCALE_FACTOR_DRAW : npm_b <= BishopValueMg ? 4 : 12);
223 if (!pos.count<PAWN>(BLACK) && npm_b - npm_w <= BishopValueMg)
224 e->factor[BLACK] = uint8_t(npm_b < RookValueMg ? SCALE_FACTOR_DRAW : npm_w <= BishopValueMg ? 4 : 12);
226 if (pos.count<PAWN>(WHITE) == 1 && npm_w - npm_b <= BishopValueMg)
227 e->factor[WHITE] = (uint8_t) SCALE_FACTOR_ONEPAWN;
229 if (pos.count<PAWN>(BLACK) == 1 && npm_b - npm_w <= BishopValueMg)
230 e->factor[BLACK] = (uint8_t) SCALE_FACTOR_ONEPAWN;
232 // Compute the space weight
233 if (npm_w + npm_b >= 2 * QueenValueMg + 4 * RookValueMg + 2 * KnightValueMg)
235 int minorPieceCount = pos.count<KNIGHT>(WHITE) + pos.count<BISHOP>(WHITE)
236 + pos.count<KNIGHT>(BLACK) + pos.count<BISHOP>(BLACK);
238 e->spaceWeight = make_score(minorPieceCount * minorPieceCount, 0);
241 // Evaluate the material imbalance. We use PIECE_TYPE_NONE as a place holder
242 // for the bishop pair "extended piece", which allows us to be more flexible
243 // in defining bishop pair bonuses.
244 const int pieceCount[COLOR_NB][PIECE_TYPE_NB] = {
245 { pos.count<BISHOP>(WHITE) > 1, pos.count<PAWN>(WHITE), pos.count<KNIGHT>(WHITE),
246 pos.count<BISHOP>(WHITE) , pos.count<ROOK>(WHITE), pos.count<QUEEN >(WHITE) },
247 { pos.count<BISHOP>(BLACK) > 1, pos.count<PAWN>(BLACK), pos.count<KNIGHT>(BLACK),
248 pos.count<BISHOP>(BLACK) , pos.count<ROOK>(BLACK), pos.count<QUEEN >(BLACK) } };
250 e->value = (int16_t)((imbalance<WHITE>(pieceCount) - imbalance<BLACK>(pieceCount)) / 16);
255 /// Material::game_phase() calculates the phase given the current
256 /// position. Because the phase is strictly a function of the material, it
257 /// is stored in MaterialEntry.
259 Phase game_phase(const Position& pos) {
261 Value npm = pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK);
263 return npm >= MidgameLimit ? PHASE_MIDGAME
264 : npm <= EndgameLimit ? PHASE_ENDGAME
265 : Phase(((npm - EndgameLimit) * 128) / (MidgameLimit - EndgameLimit));
268 } // namespace Material