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 QuadraticCoefficientsSameSide[][PIECE_TYPE_NB] = {
37 // pair pawn knight bishop rook queen
40 { 35, 271, -4 }, // knight OUR PIECES
41 { 0, 105, 4, 0 }, // Bishop
42 { -27, -2, 46, 100, -141 }, // Rook
43 {-177, 25, 129, 142, -137, 0 } // Queen
46 const int QuadraticCoefficientsOppositeSide[][PIECE_TYPE_NB] = {
48 // pair pawn knight bishop rook queen
51 { 10, 62, 0 }, // Knight OUR PIECES
52 { 57, 64, 39, 0 }, // Bishop
53 { 50, 40, 23, -22, 0 }, // Rook
54 { 98, 105, -39, 141, 274, 0 } // Queen
57 // Endgame evaluation and scaling functions are accessed directly and not through
58 // the function maps because they correspond to more than one material hash key.
59 Endgame<KXK> EvaluateKXK[] = { Endgame<KXK>(WHITE), Endgame<KXK>(BLACK) };
61 Endgame<KBPsK> ScaleKBPsK[] = { Endgame<KBPsK>(WHITE), Endgame<KBPsK>(BLACK) };
62 Endgame<KQKRPs> ScaleKQKRPs[] = { Endgame<KQKRPs>(WHITE), Endgame<KQKRPs>(BLACK) };
63 Endgame<KPsK> ScaleKPsK[] = { Endgame<KPsK>(WHITE), Endgame<KPsK>(BLACK) };
64 Endgame<KPKP> ScaleKPKP[] = { Endgame<KPKP>(WHITE), Endgame<KPKP>(BLACK) };
66 // Helper templates used to detect a given material distribution
67 template<Color Us> bool is_KXK(const Position& pos) {
68 const Color Them = (Us == WHITE ? BLACK : WHITE);
69 return !pos.count<PAWN>(Them)
70 && pos.non_pawn_material(Them) == VALUE_ZERO
71 && pos.non_pawn_material(Us) >= RookValueMg;
74 template<Color Us> bool is_KBPsKs(const Position& pos) {
75 return pos.non_pawn_material(Us) == BishopValueMg
76 && pos.count<BISHOP>(Us) == 1
77 && pos.count<PAWN >(Us) >= 1;
80 template<Color Us> bool is_KQKRPs(const Position& pos) {
81 const Color Them = (Us == WHITE ? BLACK : WHITE);
82 return !pos.count<PAWN>(Us)
83 && pos.non_pawn_material(Us) == QueenValueMg
84 && pos.count<QUEEN>(Us) == 1
85 && pos.count<ROOK>(Them) == 1
86 && pos.count<PAWN>(Them) >= 1;
89 /// imbalance() calculates the imbalance by comparing the piece count of each
90 /// piece type for both colors.
93 int imbalance(const int pieceCount[][PIECE_TYPE_NB]) {
95 const Color Them = (Us == WHITE ? BLACK : WHITE);
100 // Second-degree polynomial material imbalance by Tord Romstad
101 for (pt1 = NO_PIECE_TYPE; pt1 <= QUEEN; ++pt1)
103 pc = pieceCount[Us][pt1];
107 v = LinearCoefficients[pt1];
109 for (pt2 = NO_PIECE_TYPE; pt2 <= pt1; ++pt2)
110 v += QuadraticCoefficientsSameSide[pt1][pt2] * pieceCount[Us][pt2]
111 + QuadraticCoefficientsOppositeSide[pt1][pt2] * pieceCount[Them][pt2];
123 /// Material::probe() takes a position object as input, looks up a MaterialEntry
124 /// object, and returns a pointer to it. If the material configuration is not
125 /// already present in the table, it is computed and stored there, so we don't
126 /// have to recompute everything when the same material configuration occurs again.
128 Entry* probe(const Position& pos, Table& entries, Endgames& endgames) {
130 Key key = pos.material_key();
131 Entry* e = entries[key];
133 // If e->key matches the position's material hash key, it means that we
134 // have analysed this material configuration before, and we can simply
135 // return the information we found the last time instead of recomputing it.
139 std::memset(e, 0, sizeof(Entry));
141 e->factor[WHITE] = e->factor[BLACK] = (uint8_t)SCALE_FACTOR_NORMAL;
142 e->gamePhase = game_phase(pos);
144 // Let's look if we have a specialized evaluation function for this particular
145 // material configuration. Firstly we look for a fixed configuration one, then
146 // for a generic one if the previous search failed.
147 if (endgames.probe(key, e->evaluationFunction))
150 if (is_KXK<WHITE>(pos))
152 e->evaluationFunction = &EvaluateKXK[WHITE];
156 if (is_KXK<BLACK>(pos))
158 e->evaluationFunction = &EvaluateKXK[BLACK];
162 // OK, we didn't find any special evaluation function for the current
163 // material configuration. Is there a suitable scaling function?
165 // We face problems when there are several conflicting applicable
166 // scaling functions and we need to decide which one to use.
167 EndgameBase<ScaleFactor>* sf;
169 if (endgames.probe(key, sf))
171 e->scalingFunction[sf->color()] = sf;
175 // Generic scaling functions that refer to more than one material
176 // distribution. They should be probed after the specialized ones.
177 // Note that these ones don't return after setting the function.
178 if (is_KBPsKs<WHITE>(pos))
179 e->scalingFunction[WHITE] = &ScaleKBPsK[WHITE];
181 if (is_KBPsKs<BLACK>(pos))
182 e->scalingFunction[BLACK] = &ScaleKBPsK[BLACK];
184 if (is_KQKRPs<WHITE>(pos))
185 e->scalingFunction[WHITE] = &ScaleKQKRPs[WHITE];
187 else if (is_KQKRPs<BLACK>(pos))
188 e->scalingFunction[BLACK] = &ScaleKQKRPs[BLACK];
190 Value npm_w = pos.non_pawn_material(WHITE);
191 Value npm_b = pos.non_pawn_material(BLACK);
193 if (npm_w + npm_b == VALUE_ZERO && pos.pieces(PAWN))
195 if (!pos.count<PAWN>(BLACK))
197 assert(pos.count<PAWN>(WHITE) >= 2);
198 e->scalingFunction[WHITE] = &ScaleKPsK[WHITE];
200 else if (!pos.count<PAWN>(WHITE))
202 assert(pos.count<PAWN>(BLACK) >= 2);
203 e->scalingFunction[BLACK] = &ScaleKPsK[BLACK];
205 else if (pos.count<PAWN>(WHITE) == 1 && pos.count<PAWN>(BLACK) == 1)
207 // This is a special case because we set scaling functions
208 // for both colors instead of only one.
209 e->scalingFunction[WHITE] = &ScaleKPKP[WHITE];
210 e->scalingFunction[BLACK] = &ScaleKPKP[BLACK];
214 // No pawns makes it difficult to win, even with a material advantage. This
215 // catches some trivial draws like KK, KBK and KNK and gives a very drawish
216 // scale factor for cases such as KRKBP and KmmKm (except for KBBKN).
217 if (!pos.count<PAWN>(WHITE) && npm_w - npm_b <= BishopValueMg)
218 e->factor[WHITE] = uint8_t(npm_w < RookValueMg ? SCALE_FACTOR_DRAW : npm_b <= BishopValueMg ? 4 : 12);
220 if (!pos.count<PAWN>(BLACK) && npm_b - npm_w <= BishopValueMg)
221 e->factor[BLACK] = uint8_t(npm_b < RookValueMg ? SCALE_FACTOR_DRAW : npm_w <= BishopValueMg ? 4 : 12);
223 if (pos.count<PAWN>(WHITE) == 1 && npm_w - npm_b <= BishopValueMg)
224 e->factor[WHITE] = (uint8_t) SCALE_FACTOR_ONEPAWN;
226 if (pos.count<PAWN>(BLACK) == 1 && npm_b - npm_w <= BishopValueMg)
227 e->factor[BLACK] = (uint8_t) SCALE_FACTOR_ONEPAWN;
229 // Compute the space weight
230 if (npm_w + npm_b >= 2 * QueenValueMg + 4 * RookValueMg + 2 * KnightValueMg)
232 int minorPieceCount = pos.count<KNIGHT>(WHITE) + pos.count<BISHOP>(WHITE)
233 + pos.count<KNIGHT>(BLACK) + pos.count<BISHOP>(BLACK);
235 e->spaceWeight = make_score(minorPieceCount * minorPieceCount, 0);
238 // Evaluate the material imbalance. We use PIECE_TYPE_NONE as a place holder
239 // for the bishop pair "extended piece", which allows us to be more flexible
240 // in defining bishop pair bonuses.
241 const int pieceCount[COLOR_NB][PIECE_TYPE_NB] = {
242 { pos.count<BISHOP>(WHITE) > 1, pos.count<PAWN>(WHITE), pos.count<KNIGHT>(WHITE),
243 pos.count<BISHOP>(WHITE) , pos.count<ROOK>(WHITE), pos.count<QUEEN >(WHITE) },
244 { pos.count<BISHOP>(BLACK) > 1, pos.count<PAWN>(BLACK), pos.count<KNIGHT>(BLACK),
245 pos.count<BISHOP>(BLACK) , pos.count<ROOK>(BLACK), pos.count<QUEEN >(BLACK) } };
247 e->value = (int16_t)((imbalance<WHITE>(pieceCount) - imbalance<BLACK>(pieceCount)) / 16);
252 /// Material::game_phase() calculates the phase given the current
253 /// position. Because the phase is strictly a function of the material, it
254 /// is stored in MaterialEntry.
256 Phase game_phase(const Position& pos) {
258 Value npm = pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK);
260 return npm >= MidgameLimit ? PHASE_MIDGAME
261 : npm <= EndgameLimit ? PHASE_ENDGAME
262 : Phase(((npm - EndgameLimit) * 128) / (MidgameLimit - EndgameLimit));
265 } // namespace Material