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
22 #include <cstring> // For std::memset
31 // Polynomial material imbalance parameters
33 // pair pawn knight bishop rook queen
34 const int Linear[6] = { 1852, -162, -1122, -183, 249, -154 };
36 const int QuadraticOurs[][PIECE_TYPE_NB] = {
38 // pair pawn knight bishop rook queen
41 { 35, 271, -4 }, // Knight OUR PIECES
42 { 0, 105, 4, 0 }, // Bishop
43 { -27, -2, 46, 100, -141 }, // Rook
44 {-177, 25, 129, 142, -137, 0 } // Queen
47 const int QuadraticTheirs[][PIECE_TYPE_NB] = {
49 // pair pawn knight bishop rook queen
52 { 10, 62, 0 }, // Knight OUR PIECES
53 { 57, 64, 39, 0 }, // Bishop
54 { 50, 40, 23, -22, 0 }, // Rook
55 { 98, 105, -39, 141, 274, 0 } // Queen
58 // Endgame evaluation and scaling functions are accessed directly and not through
59 // the function maps because they correspond to more than one material hash key.
60 Endgame<KXK> EvaluateKXK[] = { Endgame<KXK>(WHITE), Endgame<KXK>(BLACK) };
62 Endgame<KBPsK> ScaleKBPsK[] = { Endgame<KBPsK>(WHITE), Endgame<KBPsK>(BLACK) };
63 Endgame<KQKRPs> ScaleKQKRPs[] = { Endgame<KQKRPs>(WHITE), Endgame<KQKRPs>(BLACK) };
64 Endgame<KPsK> ScaleKPsK[] = { Endgame<KPsK>(WHITE), Endgame<KPsK>(BLACK) };
65 Endgame<KPKP> ScaleKPKP[] = { Endgame<KPKP>(WHITE), Endgame<KPKP>(BLACK) };
67 // Helper templates used to detect a given material distribution
68 template<Color Us> bool is_KXK(const Position& pos) {
69 const Color Them = (Us == WHITE ? BLACK : WHITE);
70 return !more_than_one(pos.pieces(Them))
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);
99 // Second-degree polynomial material imbalance by Tord Romstad
100 for (int pt1 = NO_PIECE_TYPE; pt1 <= QUEEN; ++pt1)
102 if (!pieceCount[Us][pt1])
107 for (int pt2 = NO_PIECE_TYPE; pt2 <= pt1; ++pt2)
108 v += QuadraticOurs[pt1][pt2] * pieceCount[Us][pt2]
109 + QuadraticTheirs[pt1][pt2] * pieceCount[Them][pt2];
111 bonus += pieceCount[Us][pt1] * v;
121 /// Material::probe() looks up the current position's material configuration in
122 /// the material hash table. It returns a pointer to the Entry if the position
123 /// is found. Otherwise a new Entry is computed and stored there, so we don't
124 /// have to recompute all when the same material configuration occurs again.
126 Entry* probe(const Position& pos) {
128 Key key = pos.material_key();
129 Entry* e = pos.this_thread()->materialTable[key];
134 std::memset(e, 0, sizeof(Entry));
136 e->factor[WHITE] = e->factor[BLACK] = (uint8_t)SCALE_FACTOR_NORMAL;
137 e->gamePhase = pos.game_phase();
139 // Let's look if we have a specialized evaluation function for this particular
140 // material configuration. Firstly we look for a fixed configuration one, then
141 // for a generic one if the previous search failed.
142 if (pos.this_thread()->endgames.probe(key, e->evaluationFunction))
145 if (is_KXK<WHITE>(pos))
147 e->evaluationFunction = &EvaluateKXK[WHITE];
151 if (is_KXK<BLACK>(pos))
153 e->evaluationFunction = &EvaluateKXK[BLACK];
157 // OK, we didn't find any special evaluation function for the current material
158 // configuration. Is there a suitable specialized scaling function?
159 EndgameBase<ScaleFactor>* sf;
161 if (pos.this_thread()->endgames.probe(key, sf))
163 e->scalingFunction[sf->strong_side()] = sf; // Only strong color assigned
167 // We didn't find any specialized scaling function, so fall back on generic
168 // ones that refer to more than one material distribution. Note that in this
169 // case we don't return after setting the function.
170 if (is_KBPsKs<WHITE>(pos))
171 e->scalingFunction[WHITE] = &ScaleKBPsK[WHITE];
173 if (is_KBPsKs<BLACK>(pos))
174 e->scalingFunction[BLACK] = &ScaleKBPsK[BLACK];
176 if (is_KQKRPs<WHITE>(pos))
177 e->scalingFunction[WHITE] = &ScaleKQKRPs[WHITE];
179 else if (is_KQKRPs<BLACK>(pos))
180 e->scalingFunction[BLACK] = &ScaleKQKRPs[BLACK];
182 Value npm_w = pos.non_pawn_material(WHITE);
183 Value npm_b = pos.non_pawn_material(BLACK);
185 if (npm_w + npm_b == VALUE_ZERO && pos.pieces(PAWN)) // Only pawns on the board
187 if (!pos.count<PAWN>(BLACK))
189 assert(pos.count<PAWN>(WHITE) >= 2);
191 e->scalingFunction[WHITE] = &ScaleKPsK[WHITE];
193 else if (!pos.count<PAWN>(WHITE))
195 assert(pos.count<PAWN>(BLACK) >= 2);
197 e->scalingFunction[BLACK] = &ScaleKPsK[BLACK];
199 else if (pos.count<PAWN>(WHITE) == 1 && pos.count<PAWN>(BLACK) == 1)
201 // This is a special case because we set scaling functions
202 // for both colors instead of only one.
203 e->scalingFunction[WHITE] = &ScaleKPKP[WHITE];
204 e->scalingFunction[BLACK] = &ScaleKPKP[BLACK];
208 // Zero or just one pawn makes it difficult to win, even with a small material
209 // advantage. This catches some trivial draws like KK, KBK and KNK and gives a
210 // drawish scale factor for cases such as KRKBP and KmmKm (except for KBBKN).
211 if (!pos.count<PAWN>(WHITE) && npm_w - npm_b <= BishopValueMg)
212 e->factor[WHITE] = uint8_t(npm_w < RookValueMg ? SCALE_FACTOR_DRAW :
213 npm_b <= BishopValueMg ? 4 : 12);
215 if (!pos.count<PAWN>(BLACK) && npm_b - npm_w <= BishopValueMg)
216 e->factor[BLACK] = uint8_t(npm_b < RookValueMg ? SCALE_FACTOR_DRAW :
217 npm_w <= BishopValueMg ? 4 : 12);
219 if (pos.count<PAWN>(WHITE) == 1 && npm_w - npm_b <= BishopValueMg)
220 e->factor[WHITE] = (uint8_t) SCALE_FACTOR_ONEPAWN;
222 if (pos.count<PAWN>(BLACK) == 1 && npm_b - npm_w <= BishopValueMg)
223 e->factor[BLACK] = (uint8_t) SCALE_FACTOR_ONEPAWN;
225 // Evaluate the material imbalance. We use PIECE_TYPE_NONE as a place holder
226 // for the bishop pair "extended piece", which allows us to be more flexible
227 // in defining bishop pair bonuses.
228 const int PieceCount[COLOR_NB][PIECE_TYPE_NB] = {
229 { pos.count<BISHOP>(WHITE) > 1, pos.count<PAWN>(WHITE), pos.count<KNIGHT>(WHITE),
230 pos.count<BISHOP>(WHITE) , pos.count<ROOK>(WHITE), pos.count<QUEEN >(WHITE) },
231 { pos.count<BISHOP>(BLACK) > 1, pos.count<PAWN>(BLACK), pos.count<KNIGHT>(BLACK),
232 pos.count<BISHOP>(BLACK) , pos.count<ROOK>(BLACK), pos.count<QUEEN >(BLACK) } };
234 e->value = int16_t((imbalance<WHITE>(PieceCount) - imbalance<BLACK>(PieceCount)) / 16);
238 } // namespace Material