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 // Scale factors used when one side has no more pawns
35 const int NoPawnsSF[4] = { 6, 12, 32 };
37 // Polynomial material balance parameters
39 // pair pawn knight bishop rook queen
40 const int LinearCoefficients[6] = { 1852, -162, -1122, -183, 249, -52 };
42 const int QuadraticCoefficientsSameColor[][PIECE_TYPE_NB] = {
43 // pair pawn knight bishop rook queen
46 { 35, 271, -4 }, // Knight
47 { 0, 105, 4, 0 }, // Bishop
48 { -27, -2, 46, 100, -141 }, // Rook
49 { 58, 29, 83, 148, -163, 0 } // Queen
52 const int QuadraticCoefficientsOppositeColor[][PIECE_TYPE_NB] = {
54 // pair pawn knight bishop rook queen
57 { 10, 62, 0 }, // Knight OUR PIECES
58 { 57, 64, 39, 0 }, // Bishop
59 { 50, 40, 23, -22, 0 }, // Rook
60 { 106, 101, 3, 151, 171, 0 } // Queen
63 // Endgame evaluation and scaling functions are accessed directly and not through
64 // the function maps because they correspond to more then one material hash key.
65 Endgame<KmmKm> EvaluateKmmKm[] = { Endgame<KmmKm>(WHITE), Endgame<KmmKm>(BLACK) };
66 Endgame<KXK> EvaluateKXK[] = { Endgame<KXK>(WHITE), Endgame<KXK>(BLACK) };
68 Endgame<KBPsK> ScaleKBPsK[] = { Endgame<KBPsK>(WHITE), Endgame<KBPsK>(BLACK) };
69 Endgame<KQKRPs> ScaleKQKRPs[] = { Endgame<KQKRPs>(WHITE), Endgame<KQKRPs>(BLACK) };
70 Endgame<KPsK> ScaleKPsK[] = { Endgame<KPsK>(WHITE), Endgame<KPsK>(BLACK) };
71 Endgame<KPKP> ScaleKPKP[] = { Endgame<KPKP>(WHITE), Endgame<KPKP>(BLACK) };
73 // Helper templates used to detect a given material distribution
74 template<Color Us> bool is_KXK(const Position& pos) {
75 const Color Them = (Us == WHITE ? BLACK : WHITE);
76 return !pos.count<PAWN>(Them)
77 && pos.non_pawn_material(Them) == VALUE_ZERO
78 && pos.non_pawn_material(Us) >= RookValueMg;
81 template<Color Us> bool is_KBPsKs(const Position& pos) {
82 return pos.non_pawn_material(Us) == BishopValueMg
83 && pos.count<BISHOP>(Us) == 1
84 && pos.count<PAWN >(Us) >= 1;
87 template<Color Us> bool is_KQKRPs(const Position& pos) {
88 const Color Them = (Us == WHITE ? BLACK : WHITE);
89 return !pos.count<PAWN>(Us)
90 && pos.non_pawn_material(Us) == QueenValueMg
91 && pos.count<QUEEN>(Us) == 1
92 && pos.count<ROOK>(Them) == 1
93 && pos.count<PAWN>(Them) >= 1;
96 /// imbalance() calculates the imbalance by comparing the piece count of each
97 /// piece type for both colors.
100 int imbalance(const int pieceCount[][PIECE_TYPE_NB]) {
102 const Color Them = (Us == WHITE ? BLACK : WHITE);
107 // Second-degree polynomial material imbalance by Tord Romstad
108 for (pt1 = NO_PIECE_TYPE; pt1 <= QUEEN; ++pt1)
110 pc = pieceCount[Us][pt1];
114 v = LinearCoefficients[pt1];
116 for (pt2 = NO_PIECE_TYPE; pt2 <= pt1; ++pt2)
117 v += QuadraticCoefficientsSameColor[pt1][pt2] * pieceCount[Us][pt2]
118 + QuadraticCoefficientsOppositeColor[pt1][pt2] * pieceCount[Them][pt2];
129 /// Material::probe() takes a position object as input, looks up a MaterialEntry
130 /// object, and returns a pointer to it. If the material configuration is not
131 /// already present in the table, it is computed and stored there, so we don't
132 /// have to recompute everything when the same material configuration occurs again.
134 Entry* probe(const Position& pos, Table& entries, Endgames& endgames) {
136 Key key = pos.material_key();
137 Entry* e = entries[key];
139 // If e->key matches the position's material hash key, it means that we
140 // have analysed this material configuration before, and we can simply
141 // return the information we found the last time instead of recomputing it.
145 std::memset(e, 0, sizeof(Entry));
147 e->factor[WHITE] = e->factor[BLACK] = (uint8_t)SCALE_FACTOR_NORMAL;
148 e->gamePhase = game_phase(pos);
150 // Let's look if we have a specialized evaluation function for this particular
151 // material configuration. Firstly we look for a fixed configuration one, then
152 // for a generic one if the previous search failed.
153 if (endgames.probe(key, e->evaluationFunction))
156 if (is_KXK<WHITE>(pos))
158 e->evaluationFunction = &EvaluateKXK[WHITE];
162 if (is_KXK<BLACK>(pos))
164 e->evaluationFunction = &EvaluateKXK[BLACK];
168 if (!pos.pieces(PAWN) && !pos.pieces(ROOK) && !pos.pieces(QUEEN))
170 // Minor piece endgame with at least one minor piece per side and
171 // no pawns. Note that the case KmmK is already handled by KXK.
172 assert((pos.pieces(WHITE, KNIGHT) | pos.pieces(WHITE, BISHOP)));
173 assert((pos.pieces(BLACK, KNIGHT) | pos.pieces(BLACK, BISHOP)));
175 if ( pos.count<BISHOP>(WHITE) + pos.count<KNIGHT>(WHITE) <= 2
176 && pos.count<BISHOP>(BLACK) + pos.count<KNIGHT>(BLACK) <= 2)
178 e->evaluationFunction = &EvaluateKmmKm[pos.side_to_move()];
183 // OK, we didn't find any special evaluation function for the current
184 // material configuration. Is there a suitable scaling function?
186 // We face problems when there are several conflicting applicable
187 // scaling functions and we need to decide which one to use.
188 EndgameBase<ScaleFactor>* sf;
190 if (endgames.probe(key, sf))
192 e->scalingFunction[sf->color()] = sf;
196 // Generic scaling functions that refer to more then one material
197 // distribution. They should be probed after the specialized ones.
198 // Note that these ones don't return after setting the function.
199 if (is_KBPsKs<WHITE>(pos))
200 e->scalingFunction[WHITE] = &ScaleKBPsK[WHITE];
202 if (is_KBPsKs<BLACK>(pos))
203 e->scalingFunction[BLACK] = &ScaleKBPsK[BLACK];
205 if (is_KQKRPs<WHITE>(pos))
206 e->scalingFunction[WHITE] = &ScaleKQKRPs[WHITE];
208 else if (is_KQKRPs<BLACK>(pos))
209 e->scalingFunction[BLACK] = &ScaleKQKRPs[BLACK];
211 Value npm_w = pos.non_pawn_material(WHITE);
212 Value npm_b = pos.non_pawn_material(BLACK);
214 if (npm_w + npm_b == VALUE_ZERO)
216 if (!pos.count<PAWN>(BLACK))
218 assert(pos.count<PAWN>(WHITE) >= 2);
219 e->scalingFunction[WHITE] = &ScaleKPsK[WHITE];
221 else if (!pos.count<PAWN>(WHITE))
223 assert(pos.count<PAWN>(BLACK) >= 2);
224 e->scalingFunction[BLACK] = &ScaleKPsK[BLACK];
226 else if (pos.count<PAWN>(WHITE) == 1 && pos.count<PAWN>(BLACK) == 1)
228 // This is a special case because we set scaling functions
229 // for both colors instead of only one.
230 e->scalingFunction[WHITE] = &ScaleKPKP[WHITE];
231 e->scalingFunction[BLACK] = &ScaleKPKP[BLACK];
235 // No pawns makes it difficult to win, even with a material advantage. This
236 // catches some trivial draws like KK, KBK and KNK
237 if (!pos.count<PAWN>(WHITE) && npm_w - npm_b <= BishopValueMg)
239 e->factor[WHITE] = (uint8_t)
240 (npm_w == npm_b || npm_w < RookValueMg ? 0 : NoPawnsSF[std::min(pos.count<BISHOP>(WHITE), 2)]);
243 if (!pos.count<PAWN>(BLACK) && npm_b - npm_w <= BishopValueMg)
245 e->factor[BLACK] = (uint8_t)
246 (npm_w == npm_b || npm_b < RookValueMg ? 0 : NoPawnsSF[std::min(pos.count<BISHOP>(BLACK), 2)]);
249 if (pos.count<PAWN>(WHITE) == 1 && npm_w - npm_b <= BishopValueMg)
251 e->factor[WHITE] = (uint8_t) SCALE_FACTOR_ONEPAWN;
254 if (pos.count<PAWN>(BLACK) == 1 && npm_b - npm_w <= BishopValueMg)
256 e->factor[BLACK] = (uint8_t) SCALE_FACTOR_ONEPAWN;
259 // Compute the space weight
260 if (npm_w + npm_b >= 2 * QueenValueMg + 4 * RookValueMg + 2 * KnightValueMg)
262 int minorPieceCount = pos.count<KNIGHT>(WHITE) + pos.count<BISHOP>(WHITE)
263 + pos.count<KNIGHT>(BLACK) + pos.count<BISHOP>(BLACK);
265 e->spaceWeight = make_score(minorPieceCount * minorPieceCount, 0);
268 // Evaluate the material imbalance. We use PIECE_TYPE_NONE as a place holder
269 // for the bishop pair "extended piece", which allows us to be more flexible
270 // in defining bishop pair bonuses.
271 const int pieceCount[COLOR_NB][PIECE_TYPE_NB] = {
272 { pos.count<BISHOP>(WHITE) > 1, pos.count<PAWN>(WHITE), pos.count<KNIGHT>(WHITE),
273 pos.count<BISHOP>(WHITE) , pos.count<ROOK>(WHITE), pos.count<QUEEN >(WHITE) },
274 { pos.count<BISHOP>(BLACK) > 1, pos.count<PAWN>(BLACK), pos.count<KNIGHT>(BLACK),
275 pos.count<BISHOP>(BLACK) , pos.count<ROOK>(BLACK), pos.count<QUEEN >(BLACK) } };
277 e->value = (int16_t)((imbalance<WHITE>(pieceCount) - imbalance<BLACK>(pieceCount)) / 16);
282 /// Material::game_phase() calculates the phase given the current
283 /// position. Because the phase is strictly a function of the material, it
284 /// is stored in MaterialEntry.
286 Phase game_phase(const Position& pos) {
288 Value npm = pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK);
290 return npm >= MidgameLimit ? PHASE_MIDGAME
291 : npm <= EndgameLimit ? PHASE_ENDGAME
292 : Phase(((npm - EndgameLimit) * 128) / (MidgameLimit - EndgameLimit));
295 } // namespace Material