2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2012 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/>.
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 RedundantQueenPenalty = Value(320);
39 const Value RedundantRookPenalty = Value(554);
41 const int LinearCoefficients[6] = { 1617, -162, -1172, -190, 105, 26 };
43 const int QuadraticCoefficientsSameColor[][8] = {
44 { 7, 7, 7, 7, 7, 7 }, { 39, 2, 7, 7, 7, 7 }, { 35, 271, -4, 7, 7, 7 },
45 { 7, 25, 4, 7, 7, 7 }, { -27, -2, 46, 100, 56, 7 }, { 58, 29, 83, 148, -3, -25 } };
47 const int QuadraticCoefficientsOppositeColor[][8] = {
48 { 41, 41, 41, 41, 41, 41 }, { 37, 41, 41, 41, 41, 41 }, { 10, 62, 41, 41, 41, 41 },
49 { 57, 64, 39, 41, 41, 41 }, { 50, 40, 23, -22, 41, 41 }, { 106, 101, 3, 151, 171, 41 } };
51 // Endgame evaluation and scaling functions accessed direcly and not through
52 // the function maps because correspond to more then one material hash key.
53 Endgame<KmmKm> EvaluateKmmKm[] = { Endgame<KmmKm>(WHITE), Endgame<KmmKm>(BLACK) };
54 Endgame<KXK> EvaluateKXK[] = { Endgame<KXK>(WHITE), Endgame<KXK>(BLACK) };
56 Endgame<KBPsK> ScaleKBPsK[] = { Endgame<KBPsK>(WHITE), Endgame<KBPsK>(BLACK) };
57 Endgame<KQKRPs> ScaleKQKRPs[] = { Endgame<KQKRPs>(WHITE), Endgame<KQKRPs>(BLACK) };
58 Endgame<KPsK> ScaleKPsK[] = { Endgame<KPsK>(WHITE), Endgame<KPsK>(BLACK) };
59 Endgame<KPKP> ScaleKPKP[] = { Endgame<KPKP>(WHITE), Endgame<KPKP>(BLACK) };
61 // Helper templates used to detect a given material distribution
62 template<Color Us> bool is_KXK(const Position& pos) {
63 const Color Them = (Us == WHITE ? BLACK : WHITE);
64 return pos.non_pawn_material(Them) == VALUE_ZERO
65 && pos.piece_count(Them, PAWN) == 0
66 && pos.non_pawn_material(Us) >= RookValueMidgame;
69 template<Color Us> bool is_KBPsKs(const Position& pos) {
70 return pos.non_pawn_material(Us) == BishopValueMidgame
71 && pos.piece_count(Us, BISHOP) == 1
72 && pos.piece_count(Us, PAWN) >= 1;
75 template<Color Us> bool is_KQKRPs(const Position& pos) {
76 const Color Them = (Us == WHITE ? BLACK : WHITE);
77 return pos.piece_count(Us, PAWN) == 0
78 && pos.non_pawn_material(Us) == QueenValueMidgame
79 && pos.piece_count(Us, QUEEN) == 1
80 && pos.piece_count(Them, ROOK) == 1
81 && pos.piece_count(Them, PAWN) >= 1;
87 /// MaterialTable::probe() takes a position object as input, looks up a MaterialEntry
88 /// object, and returns a pointer to it. If the material configuration is not
89 /// already present in the table, it is computed and stored there, so we don't
90 /// have to recompute everything when the same material configuration occurs again.
92 MaterialEntry* MaterialTable::probe(const Position& pos) {
94 Key key = pos.material_key();
95 MaterialEntry* e = entries[key];
97 // If e->key matches the position's material hash key, it means that we
98 // have analysed this material configuration before, and we can simply
99 // return the information we found the last time instead of recomputing it.
103 memset(e, 0, sizeof(MaterialEntry));
105 e->factor[WHITE] = e->factor[BLACK] = (uint8_t)SCALE_FACTOR_NORMAL;
106 e->gamePhase = MaterialTable::game_phase(pos);
108 // Let's look if we have a specialized evaluation function for this
109 // particular material configuration. First we look for a fixed
110 // configuration one, then a generic one if previous search failed.
111 if (endgames.probe(key, e->evaluationFunction))
114 if (is_KXK<WHITE>(pos))
116 e->evaluationFunction = &EvaluateKXK[WHITE];
120 if (is_KXK<BLACK>(pos))
122 e->evaluationFunction = &EvaluateKXK[BLACK];
126 if (!pos.pieces(PAWN) && !pos.pieces(ROOK) && !pos.pieces(QUEEN))
128 // Minor piece endgame with at least one minor piece per side and
129 // no pawns. Note that the case KmmK is already handled by KXK.
130 assert((pos.pieces(WHITE, KNIGHT) | pos.pieces(WHITE, BISHOP)));
131 assert((pos.pieces(BLACK, KNIGHT) | pos.pieces(BLACK, BISHOP)));
133 if ( pos.piece_count(WHITE, BISHOP) + pos.piece_count(WHITE, KNIGHT) <= 2
134 && pos.piece_count(BLACK, BISHOP) + pos.piece_count(BLACK, KNIGHT) <= 2)
136 e->evaluationFunction = &EvaluateKmmKm[pos.side_to_move()];
141 // OK, we didn't find any special evaluation function for the current
142 // material configuration. Is there a suitable scaling function?
144 // We face problems when there are several conflicting applicable
145 // scaling functions and we need to decide which one to use.
146 EndgameBase<ScaleFactor>* sf;
148 if (endgames.probe(key, sf))
150 e->scalingFunction[sf->color()] = sf;
154 // Generic scaling functions that refer to more then one material
155 // distribution. Should be probed after the specialized ones.
156 // Note that these ones don't return after setting the function.
157 if (is_KBPsKs<WHITE>(pos))
158 e->scalingFunction[WHITE] = &ScaleKBPsK[WHITE];
160 if (is_KBPsKs<BLACK>(pos))
161 e->scalingFunction[BLACK] = &ScaleKBPsK[BLACK];
163 if (is_KQKRPs<WHITE>(pos))
164 e->scalingFunction[WHITE] = &ScaleKQKRPs[WHITE];
166 else if (is_KQKRPs<BLACK>(pos))
167 e->scalingFunction[BLACK] = &ScaleKQKRPs[BLACK];
169 Value npm_w = pos.non_pawn_material(WHITE);
170 Value npm_b = pos.non_pawn_material(BLACK);
172 if (npm_w + npm_b == VALUE_ZERO)
174 if (pos.piece_count(BLACK, PAWN) == 0)
176 assert(pos.piece_count(WHITE, PAWN) >= 2);
177 e->scalingFunction[WHITE] = &ScaleKPsK[WHITE];
179 else if (pos.piece_count(WHITE, PAWN) == 0)
181 assert(pos.piece_count(BLACK, PAWN) >= 2);
182 e->scalingFunction[BLACK] = &ScaleKPsK[BLACK];
184 else if (pos.piece_count(WHITE, PAWN) == 1 && pos.piece_count(BLACK, PAWN) == 1)
186 // This is a special case because we set scaling functions
187 // for both colors instead of only one.
188 e->scalingFunction[WHITE] = &ScaleKPKP[WHITE];
189 e->scalingFunction[BLACK] = &ScaleKPKP[BLACK];
193 // No pawns makes it difficult to win, even with a material advantage
194 if (pos.piece_count(WHITE, PAWN) == 0 && npm_w - npm_b <= BishopValueMidgame)
196 e->factor[WHITE] = (uint8_t)
197 (npm_w == npm_b || npm_w < RookValueMidgame ? 0 : NoPawnsSF[std::min(pos.piece_count(WHITE, BISHOP), 2)]);
200 if (pos.piece_count(BLACK, PAWN) == 0 && npm_b - npm_w <= BishopValueMidgame)
202 e->factor[BLACK] = (uint8_t)
203 (npm_w == npm_b || npm_b < RookValueMidgame ? 0 : NoPawnsSF[std::min(pos.piece_count(BLACK, BISHOP), 2)]);
206 // Compute the space weight
207 if (npm_w + npm_b >= 2 * QueenValueMidgame + 4 * RookValueMidgame + 2 * KnightValueMidgame)
209 int minorPieceCount = pos.piece_count(WHITE, KNIGHT) + pos.piece_count(WHITE, BISHOP)
210 + pos.piece_count(BLACK, KNIGHT) + pos.piece_count(BLACK, BISHOP);
212 e->spaceWeight = minorPieceCount * minorPieceCount;
215 // Evaluate the material imbalance. We use PIECE_TYPE_NONE as a place holder
216 // for the bishop pair "extended piece", this allow us to be more flexible
217 // in defining bishop pair bonuses.
218 const int pieceCount[2][8] = {
219 { pos.piece_count(WHITE, BISHOP) > 1, pos.piece_count(WHITE, PAWN), pos.piece_count(WHITE, KNIGHT),
220 pos.piece_count(WHITE, BISHOP) , pos.piece_count(WHITE, ROOK), pos.piece_count(WHITE, QUEEN) },
221 { pos.piece_count(BLACK, BISHOP) > 1, pos.piece_count(BLACK, PAWN), pos.piece_count(BLACK, KNIGHT),
222 pos.piece_count(BLACK, BISHOP) , pos.piece_count(BLACK, ROOK), pos.piece_count(BLACK, QUEEN) } };
224 e->value = (int16_t)((imbalance<WHITE>(pieceCount) - imbalance<BLACK>(pieceCount)) / 16);
229 /// MaterialTable::imbalance() calculates imbalance comparing piece count of each
230 /// piece type for both colors.
233 int MaterialTable::imbalance(const int pieceCount[][8]) {
235 const Color Them = (Us == WHITE ? BLACK : WHITE);
240 // Redundancy of major pieces, formula based on Kaufman's paper
241 // "The Evaluation of Material Imbalances in Chess"
242 if (pieceCount[Us][ROOK] > 0)
243 value -= RedundantRookPenalty * (pieceCount[Us][ROOK] - 1)
244 + RedundantQueenPenalty * pieceCount[Us][QUEEN];
246 // Second-degree polynomial material imbalance by Tord Romstad
247 for (pt1 = NO_PIECE_TYPE; pt1 <= QUEEN; pt1++)
249 pc = pieceCount[Us][pt1];
253 v = LinearCoefficients[pt1];
255 for (pt2 = NO_PIECE_TYPE; pt2 <= pt1; pt2++)
256 v += QuadraticCoefficientsSameColor[pt1][pt2] * pieceCount[Us][pt2]
257 + QuadraticCoefficientsOppositeColor[pt1][pt2] * pieceCount[Them][pt2];
265 /// MaterialTable::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 MaterialTable::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));