2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2013 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 // Scale factors used when one side has no more pawns
35 const int NoPawnsSF[4] = { 6, 12, 32 };
37 // Polynomial material balance parameters
38 const Value RedundantQueen = Value(320);
39 const Value RedundantRook = Value(554);
41 // pair pawn knight bishop rook queen
42 const int LinearCoefficients[6] = { 1617, -162, -1172, -190, 105, 26 };
44 const int QuadraticCoefficientsSameColor[][PIECE_TYPE_NB] = {
45 // pair pawn knight bishop rook queen
48 { 35, 271, -4 }, // Knight
49 { 7, 105, 4, 7 }, // Bishop
50 { -27, -2, 46, 100, 56 }, // Rook
51 { 58, 29, 83, 148, -3, -25 } // Queen
54 const int QuadraticCoefficientsOppositeColor[][PIECE_TYPE_NB] = {
56 // pair pawn knight bishop rook queen
57 { 41 }, // Bishop pair
59 { 10, 62, 41 }, // Knight OUR PIECES
60 { 57, 64, 39, 41 }, // Bishop
61 { 50, 40, 23, -22, 41 }, // Rook
62 { 106, 101, 3, 151, 171, 41 } // Queen
65 // Endgame evaluation and scaling functions accessed direcly and not through
66 // the function maps because correspond to more then one material hash key.
67 Endgame<KmmKm> EvaluateKmmKm[] = { Endgame<KmmKm>(WHITE), Endgame<KmmKm>(BLACK) };
68 Endgame<KXK> EvaluateKXK[] = { Endgame<KXK>(WHITE), Endgame<KXK>(BLACK) };
70 Endgame<KBPsK> ScaleKBPsK[] = { Endgame<KBPsK>(WHITE), Endgame<KBPsK>(BLACK) };
71 Endgame<KQKRPs> ScaleKQKRPs[] = { Endgame<KQKRPs>(WHITE), Endgame<KQKRPs>(BLACK) };
72 Endgame<KPsK> ScaleKPsK[] = { Endgame<KPsK>(WHITE), Endgame<KPsK>(BLACK) };
73 Endgame<KPKP> ScaleKPKP[] = { Endgame<KPKP>(WHITE), Endgame<KPKP>(BLACK) };
75 // Helper templates used to detect a given material distribution
76 template<Color Us> bool is_KXK(const Position& pos) {
77 const Color Them = (Us == WHITE ? BLACK : WHITE);
78 return !pos.count<PAWN>(Them)
79 && pos.non_pawn_material(Them) == VALUE_ZERO
80 && pos.non_pawn_material(Us) >= RookValueMg;
83 template<Color Us> bool is_KBPsKs(const Position& pos) {
84 return pos.non_pawn_material(Us) == BishopValueMg
85 && pos.count<BISHOP>(Us) == 1
86 && pos.count<PAWN >(Us) >= 1;
89 template<Color Us> bool is_KQKRPs(const Position& pos) {
90 const Color Them = (Us == WHITE ? BLACK : WHITE);
91 return !pos.count<PAWN>(Us)
92 && pos.non_pawn_material(Us) == QueenValueMg
93 && pos.count<QUEEN>(Us) == 1
94 && pos.count<ROOK>(Them) == 1
95 && pos.count<PAWN>(Them) >= 1;
98 /// imbalance() calculates imbalance comparing piece count of each
99 /// piece type for both colors.
102 int imbalance(const int pieceCount[][PIECE_TYPE_NB]) {
104 const Color Them = (Us == WHITE ? BLACK : WHITE);
109 // Redundancy of major pieces, formula based on Kaufman's paper
110 // "The Evaluation of Material Imbalances in Chess"
111 if (pieceCount[Us][ROOK] > 0)
112 value -= RedundantRook * (pieceCount[Us][ROOK] - 1)
113 + RedundantQueen * pieceCount[Us][QUEEN];
115 // Second-degree polynomial material imbalance by Tord Romstad
116 for (pt1 = NO_PIECE_TYPE; pt1 <= QUEEN; pt1++)
118 pc = pieceCount[Us][pt1];
122 v = LinearCoefficients[pt1];
124 for (pt2 = NO_PIECE_TYPE; pt2 <= pt1; pt2++)
125 v += QuadraticCoefficientsSameColor[pt1][pt2] * pieceCount[Us][pt2]
126 + QuadraticCoefficientsOppositeColor[pt1][pt2] * pieceCount[Them][pt2];
137 /// Material::probe() takes a position object as input, looks up a MaterialEntry
138 /// object, and returns a pointer to it. If the material configuration is not
139 /// already present in the table, it is computed and stored there, so we don't
140 /// have to recompute everything when the same material configuration occurs again.
142 Entry* probe(const Position& pos, Table& entries, Endgames& endgames) {
144 Key key = pos.material_key();
145 Entry* e = entries[key];
147 // If e->key matches the position's material hash key, it means that we
148 // have analysed this material configuration before, and we can simply
149 // return the information we found the last time instead of recomputing it.
153 std::memset(e, 0, sizeof(Entry));
155 e->factor[WHITE] = e->factor[BLACK] = (uint8_t)SCALE_FACTOR_NORMAL;
156 e->gamePhase = game_phase(pos);
158 // Let's look if we have a specialized evaluation function for this
159 // particular material configuration. First we look for a fixed
160 // configuration one, then a generic one if previous search failed.
161 if (endgames.probe(key, e->evaluationFunction))
164 if (is_KXK<WHITE>(pos))
166 e->evaluationFunction = &EvaluateKXK[WHITE];
170 if (is_KXK<BLACK>(pos))
172 e->evaluationFunction = &EvaluateKXK[BLACK];
176 if (!pos.pieces(PAWN) && !pos.pieces(ROOK) && !pos.pieces(QUEEN))
178 // Minor piece endgame with at least one minor piece per side and
179 // no pawns. Note that the case KmmK is already handled by KXK.
180 assert((pos.pieces(WHITE, KNIGHT) | pos.pieces(WHITE, BISHOP)));
181 assert((pos.pieces(BLACK, KNIGHT) | pos.pieces(BLACK, BISHOP)));
183 if ( pos.count<BISHOP>(WHITE) + pos.count<KNIGHT>(WHITE) <= 2
184 && pos.count<BISHOP>(BLACK) + pos.count<KNIGHT>(BLACK) <= 2)
186 e->evaluationFunction = &EvaluateKmmKm[pos.side_to_move()];
191 // OK, we didn't find any special evaluation function for the current
192 // material configuration. Is there a suitable scaling function?
194 // We face problems when there are several conflicting applicable
195 // scaling functions and we need to decide which one to use.
196 EndgameBase<ScaleFactor>* sf;
198 if (endgames.probe(key, sf))
200 e->scalingFunction[sf->color()] = sf;
204 // Generic scaling functions that refer to more then one material
205 // distribution. Should be probed after the specialized ones.
206 // Note that these ones don't return after setting the function.
207 if (is_KBPsKs<WHITE>(pos))
208 e->scalingFunction[WHITE] = &ScaleKBPsK[WHITE];
210 if (is_KBPsKs<BLACK>(pos))
211 e->scalingFunction[BLACK] = &ScaleKBPsK[BLACK];
213 if (is_KQKRPs<WHITE>(pos))
214 e->scalingFunction[WHITE] = &ScaleKQKRPs[WHITE];
216 else if (is_KQKRPs<BLACK>(pos))
217 e->scalingFunction[BLACK] = &ScaleKQKRPs[BLACK];
219 Value npm_w = pos.non_pawn_material(WHITE);
220 Value npm_b = pos.non_pawn_material(BLACK);
222 if (npm_w + npm_b == VALUE_ZERO)
224 if (!pos.count<PAWN>(BLACK))
226 assert(pos.count<PAWN>(WHITE) >= 2);
227 e->scalingFunction[WHITE] = &ScaleKPsK[WHITE];
229 else if (!pos.count<PAWN>(WHITE))
231 assert(pos.count<PAWN>(BLACK) >= 2);
232 e->scalingFunction[BLACK] = &ScaleKPsK[BLACK];
234 else if (pos.count<PAWN>(WHITE) == 1 && pos.count<PAWN>(BLACK) == 1)
236 // This is a special case because we set scaling functions
237 // for both colors instead of only one.
238 e->scalingFunction[WHITE] = &ScaleKPKP[WHITE];
239 e->scalingFunction[BLACK] = &ScaleKPKP[BLACK];
243 // No pawns makes it difficult to win, even with a material advantage. This
244 // catches some trivial draws like KK, KBK and KNK
245 if (!pos.count<PAWN>(WHITE) && npm_w - npm_b <= BishopValueMg)
247 e->factor[WHITE] = (uint8_t)
248 (npm_w == npm_b || npm_w < RookValueMg ? 0 : NoPawnsSF[std::min(pos.count<BISHOP>(WHITE), 2)]);
251 if (!pos.count<PAWN>(BLACK) && npm_b - npm_w <= BishopValueMg)
253 e->factor[BLACK] = (uint8_t)
254 (npm_w == npm_b || npm_b < RookValueMg ? 0 : NoPawnsSF[std::min(pos.count<BISHOP>(BLACK), 2)]);
257 // Compute the space weight
258 if (npm_w + npm_b >= 2 * QueenValueMg + 4 * RookValueMg + 2 * KnightValueMg)
260 int minorPieceCount = pos.count<KNIGHT>(WHITE) + pos.count<BISHOP>(WHITE)
261 + pos.count<KNIGHT>(BLACK) + pos.count<BISHOP>(BLACK);
263 e->spaceWeight = make_score(minorPieceCount * minorPieceCount, 0);
266 // Evaluate the material imbalance. We use PIECE_TYPE_NONE as a place holder
267 // for the bishop pair "extended piece", this allow us to be more flexible
268 // in defining bishop pair bonuses.
269 const int pieceCount[COLOR_NB][PIECE_TYPE_NB] = {
270 { pos.count<BISHOP>(WHITE) > 1, pos.count<PAWN>(WHITE), pos.count<KNIGHT>(WHITE),
271 pos.count<BISHOP>(WHITE) , pos.count<ROOK>(WHITE), pos.count<QUEEN >(WHITE) },
272 { pos.count<BISHOP>(BLACK) > 1, pos.count<PAWN>(BLACK), pos.count<KNIGHT>(BLACK),
273 pos.count<BISHOP>(BLACK) , pos.count<ROOK>(BLACK), pos.count<QUEEN >(BLACK) } };
275 e->value = (int16_t)((imbalance<WHITE>(pieceCount) - imbalance<BLACK>(pieceCount)) / 16);
280 /// Material::game_phase() calculates the phase given the current
281 /// position. Because the phase is strictly a function of the material, it
282 /// is stored in MaterialEntry.
284 Phase game_phase(const Position& pos) {
286 Value npm = pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK);
288 return npm >= MidgameLimit ? PHASE_MIDGAME
289 : npm <= EndgameLimit ? PHASE_ENDGAME
290 : Phase(((npm - EndgameLimit) * 128) / (MidgameLimit - EndgameLimit));
293 } // namespace Material