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/>.
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 RedundantQueenPenalty = Value(320);
39 const Value RedundantRookPenalty = Value(554);
41 const int LinearCoefficients[6] = { 1617, -162, -1172, -190, 105, 26 };
43 const int QuadraticCoefficientsSameColor[][PIECE_TYPE_NB] = {
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[][PIECE_TYPE_NB] = {
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) >= RookValueMg;
69 template<Color Us> bool is_KBPsKs(const Position& pos) {
70 return pos.non_pawn_material(Us) == BishopValueMg
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) == QueenValueMg
79 && pos.piece_count(Us, QUEEN) == 1
80 && pos.piece_count(Them, ROOK) == 1
81 && pos.piece_count(Them, PAWN) >= 1;
84 /// imbalance() calculates imbalance comparing piece count of each
85 /// piece type for both colors.
88 int imbalance(const int pieceCount[][PIECE_TYPE_NB]) {
90 const Color Them = (Us == WHITE ? BLACK : WHITE);
95 // Redundancy of major pieces, formula based on Kaufman's paper
96 // "The Evaluation of Material Imbalances in Chess"
97 if (pieceCount[Us][ROOK] > 0)
98 value -= RedundantRookPenalty * (pieceCount[Us][ROOK] - 1)
99 + RedundantQueenPenalty * pieceCount[Us][QUEEN];
101 // Second-degree polynomial material imbalance by Tord Romstad
102 for (pt1 = NO_PIECE_TYPE; pt1 <= QUEEN; pt1++)
104 pc = pieceCount[Us][pt1];
108 v = LinearCoefficients[pt1];
110 for (pt2 = NO_PIECE_TYPE; pt2 <= pt1; pt2++)
111 v += QuadraticCoefficientsSameColor[pt1][pt2] * pieceCount[Us][pt2]
112 + QuadraticCoefficientsOppositeColor[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 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
145 // particular material configuration. First we look for a fixed
146 // configuration one, then a generic one if 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 if (!pos.pieces(PAWN) && !pos.pieces(ROOK) && !pos.pieces(QUEEN))
164 // Minor piece endgame with at least one minor piece per side and
165 // no pawns. Note that the case KmmK is already handled by KXK.
166 assert((pos.pieces(WHITE, KNIGHT) | pos.pieces(WHITE, BISHOP)));
167 assert((pos.pieces(BLACK, KNIGHT) | pos.pieces(BLACK, BISHOP)));
169 if ( pos.piece_count(WHITE, BISHOP) + pos.piece_count(WHITE, KNIGHT) <= 2
170 && pos.piece_count(BLACK, BISHOP) + pos.piece_count(BLACK, KNIGHT) <= 2)
172 e->evaluationFunction = &EvaluateKmmKm[pos.side_to_move()];
177 // OK, we didn't find any special evaluation function for the current
178 // material configuration. Is there a suitable scaling function?
180 // We face problems when there are several conflicting applicable
181 // scaling functions and we need to decide which one to use.
182 EndgameBase<ScaleFactor>* sf;
184 if (endgames.probe(key, sf))
186 e->scalingFunction[sf->color()] = sf;
190 // Generic scaling functions that refer to more then one material
191 // distribution. Should be probed after the specialized ones.
192 // Note that these ones don't return after setting the function.
193 if (is_KBPsKs<WHITE>(pos))
194 e->scalingFunction[WHITE] = &ScaleKBPsK[WHITE];
196 if (is_KBPsKs<BLACK>(pos))
197 e->scalingFunction[BLACK] = &ScaleKBPsK[BLACK];
199 if (is_KQKRPs<WHITE>(pos))
200 e->scalingFunction[WHITE] = &ScaleKQKRPs[WHITE];
202 else if (is_KQKRPs<BLACK>(pos))
203 e->scalingFunction[BLACK] = &ScaleKQKRPs[BLACK];
205 Value npm_w = pos.non_pawn_material(WHITE);
206 Value npm_b = pos.non_pawn_material(BLACK);
208 if (npm_w + npm_b == VALUE_ZERO)
210 if (pos.piece_count(BLACK, PAWN) == 0)
212 assert(pos.piece_count(WHITE, PAWN) >= 2);
213 e->scalingFunction[WHITE] = &ScaleKPsK[WHITE];
215 else if (pos.piece_count(WHITE, PAWN) == 0)
217 assert(pos.piece_count(BLACK, PAWN) >= 2);
218 e->scalingFunction[BLACK] = &ScaleKPsK[BLACK];
220 else if (pos.piece_count(WHITE, PAWN) == 1 && pos.piece_count(BLACK, PAWN) == 1)
222 // This is a special case because we set scaling functions
223 // for both colors instead of only one.
224 e->scalingFunction[WHITE] = &ScaleKPKP[WHITE];
225 e->scalingFunction[BLACK] = &ScaleKPKP[BLACK];
229 // No pawns makes it difficult to win, even with a material advantage
230 if (pos.piece_count(WHITE, PAWN) == 0 && npm_w - npm_b <= BishopValueMg)
232 e->factor[WHITE] = (uint8_t)
233 (npm_w == npm_b || npm_w < RookValueMg ? 0 : NoPawnsSF[std::min(pos.piece_count(WHITE, BISHOP), 2)]);
236 if (pos.piece_count(BLACK, PAWN) == 0 && npm_b - npm_w <= BishopValueMg)
238 e->factor[BLACK] = (uint8_t)
239 (npm_w == npm_b || npm_b < RookValueMg ? 0 : NoPawnsSF[std::min(pos.piece_count(BLACK, BISHOP), 2)]);
242 // Compute the space weight
243 if (npm_w + npm_b >= 2 * QueenValueMg + 4 * RookValueMg + 2 * KnightValueMg)
245 int minorPieceCount = pos.piece_count(WHITE, KNIGHT) + pos.piece_count(WHITE, BISHOP)
246 + pos.piece_count(BLACK, KNIGHT) + pos.piece_count(BLACK, BISHOP);
248 e->spaceWeight = minorPieceCount * minorPieceCount;
251 // Evaluate the material imbalance. We use PIECE_TYPE_NONE as a place holder
252 // for the bishop pair "extended piece", this allow us to be more flexible
253 // in defining bishop pair bonuses.
254 const int pieceCount[COLOR_NB][PIECE_TYPE_NB] = {
255 { pos.piece_count(WHITE, BISHOP) > 1, pos.piece_count(WHITE, PAWN), pos.piece_count(WHITE, KNIGHT),
256 pos.piece_count(WHITE, BISHOP) , pos.piece_count(WHITE, ROOK), pos.piece_count(WHITE, QUEEN) },
257 { pos.piece_count(BLACK, BISHOP) > 1, pos.piece_count(BLACK, PAWN), pos.piece_count(BLACK, KNIGHT),
258 pos.piece_count(BLACK, BISHOP) , pos.piece_count(BLACK, ROOK), pos.piece_count(BLACK, QUEEN) } };
260 e->value = (int16_t)((imbalance<WHITE>(pieceCount) - imbalance<BLACK>(pieceCount)) / 16);
265 /// Material::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 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));
278 } // namespace Material