2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
5 Copyright (C) 2015-2016 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
7 Stockfish is free software: you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation, either version 3 of the License, or
10 (at your option) any later version.
12 Stockfish is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <http://www.gnu.org/licenses/>.
21 #include <algorithm> // For std::min
23 #include <cstring> // For std::memset
32 // Polynomial material imbalance parameters
34 // pair pawn knight bishop rook queen
35 const int Linear[6] = { 1667, -168, -1027, -166, 238, -138 };
37 const int QuadraticOurs[][PIECE_TYPE_NB] = {
39 // pair pawn knight bishop rook queen
42 { 32, 255, -3 }, // Knight OUR PIECES
43 { 0, 104, 4, 0 }, // Bishop
44 { -26, -2, 47, 105, -149 }, // Rook
45 {-185, 24, 122, 137, -134, 0 } // Queen
48 const int QuadraticTheirs[][PIECE_TYPE_NB] = {
50 // pair pawn knight bishop rook queen
53 { 9, 63, 0 }, // Knight OUR PIECES
54 { 59, 65, 42, 0 }, // Bishop
55 { 46, 39, 24, -24, 0 }, // Rook
56 { 101, 100, -37, 141, 268, 0 } // Queen
59 // Endgame evaluation and scaling functions are accessed directly and not through
60 // the function maps because they correspond to more than one material hash key.
61 Endgame<KXK> EvaluateKXK[] = { Endgame<KXK>(WHITE), Endgame<KXK>(BLACK) };
63 Endgame<KBPsK> ScaleKBPsK[] = { Endgame<KBPsK>(WHITE), Endgame<KBPsK>(BLACK) };
64 Endgame<KQKRPs> ScaleKQKRPs[] = { Endgame<KQKRPs>(WHITE), Endgame<KQKRPs>(BLACK) };
65 Endgame<KPsK> ScaleKPsK[] = { Endgame<KPsK>(WHITE), Endgame<KPsK>(BLACK) };
66 Endgame<KPKP> ScaleKPKP[] = { Endgame<KPKP>(WHITE), Endgame<KPKP>(BLACK) };
68 // Helper used to detect a given material distribution
69 bool is_KXK(const Position& pos, Color us) {
70 return !more_than_one(pos.pieces(~us))
71 && pos.non_pawn_material(us) >= RookValueMg;
74 bool is_KBPsKs(const Position& pos, Color us) {
75 return pos.non_pawn_material(us) == BishopValueMg
76 && pos.count<BISHOP>(us) == 1
77 && pos.count<PAWN >(us) >= 1;
80 bool is_KQKRPs(const Position& pos, Color us) {
81 return !pos.count<PAWN>(us)
82 && pos.non_pawn_material(us) == QueenValueMg
83 && pos.count<QUEEN>(us) == 1
84 && pos.count<ROOK>(~us) == 1
85 && pos.count<PAWN>(~us) >= 1;
88 /// imbalance() calculates the imbalance by comparing the piece count of each
89 /// piece type for both colors.
91 int imbalance(const int pieceCount[][PIECE_TYPE_NB]) {
93 const Color Them = (Us == WHITE ? BLACK : WHITE);
97 // Second-degree polynomial material imbalance by Tord Romstad
98 for (int pt1 = NO_PIECE_TYPE; pt1 <= QUEEN; ++pt1)
100 if (!pieceCount[Us][pt1])
105 for (int pt2 = NO_PIECE_TYPE; pt2 <= pt1; ++pt2)
106 v += QuadraticOurs[pt1][pt2] * pieceCount[Us][pt2]
107 + QuadraticTheirs[pt1][pt2] * pieceCount[Them][pt2];
109 bonus += pieceCount[Us][pt1] * v;
119 /// Material::probe() looks up the current position's material configuration in
120 /// the material hash table. It returns a pointer to the Entry if the position
121 /// is found. Otherwise a new Entry is computed and stored there, so we don't
122 /// have to recompute all when the same material configuration occurs again.
124 Entry* probe(const Position& pos) {
126 Key key = pos.material_key();
127 Entry* e = pos.this_thread()->materialTable[key];
132 std::memset(e, 0, sizeof(Entry));
134 e->factor[WHITE] = e->factor[BLACK] = (uint8_t)SCALE_FACTOR_NORMAL;
135 e->gamePhase = pos.game_phase();
137 // Let's look if we have a specialized evaluation function for this particular
138 // material configuration. Firstly we look for a fixed configuration one, then
139 // for a generic one if the previous search failed.
140 if ((e->evaluationFunction = pos.this_thread()->endgames.probe<Value>(key)) != nullptr)
143 for (Color c = WHITE; c <= BLACK; ++c)
146 e->evaluationFunction = &EvaluateKXK[c];
150 // OK, we didn't find any special evaluation function for the current material
151 // configuration. Is there a suitable specialized scaling function?
152 EndgameBase<ScaleFactor>* sf;
154 if ((sf = pos.this_thread()->endgames.probe<ScaleFactor>(key)) != nullptr)
156 e->scalingFunction[sf->strong_side()] = sf; // Only strong color assigned
160 // We didn't find any specialized scaling function, so fall back on generic
161 // ones that refer to more than one material distribution. Note that in this
162 // case we don't return after setting the function.
163 for (Color c = WHITE; c <= BLACK; ++c)
165 if (is_KBPsKs(pos, c))
166 e->scalingFunction[c] = &ScaleKBPsK[c];
168 else if (is_KQKRPs(pos, c))
169 e->scalingFunction[c] = &ScaleKQKRPs[c];
172 Value npm_w = pos.non_pawn_material(WHITE);
173 Value npm_b = pos.non_pawn_material(BLACK);
175 if (npm_w + npm_b == VALUE_ZERO && pos.pieces(PAWN)) // Only pawns on the board
177 if (!pos.count<PAWN>(BLACK))
179 assert(pos.count<PAWN>(WHITE) >= 2);
181 e->scalingFunction[WHITE] = &ScaleKPsK[WHITE];
183 else if (!pos.count<PAWN>(WHITE))
185 assert(pos.count<PAWN>(BLACK) >= 2);
187 e->scalingFunction[BLACK] = &ScaleKPsK[BLACK];
189 else if (pos.count<PAWN>(WHITE) == 1 && pos.count<PAWN>(BLACK) == 1)
191 // This is a special case because we set scaling functions
192 // for both colors instead of only one.
193 e->scalingFunction[WHITE] = &ScaleKPKP[WHITE];
194 e->scalingFunction[BLACK] = &ScaleKPKP[BLACK];
198 // Zero or just one pawn makes it difficult to win, even with a small material
199 // advantage. This catches some trivial draws like KK, KBK and KNK and gives a
200 // drawish scale factor for cases such as KRKBP and KmmKm (except for KBBKN).
201 if (!pos.count<PAWN>(WHITE) && npm_w - npm_b <= BishopValueMg)
202 e->factor[WHITE] = uint8_t(npm_w < RookValueMg ? SCALE_FACTOR_DRAW :
203 npm_b <= BishopValueMg ? 4 : 14);
205 if (!pos.count<PAWN>(BLACK) && npm_b - npm_w <= BishopValueMg)
206 e->factor[BLACK] = uint8_t(npm_b < RookValueMg ? SCALE_FACTOR_DRAW :
207 npm_w <= BishopValueMg ? 4 : 14);
209 if (pos.count<PAWN>(WHITE) == 1 && npm_w - npm_b <= BishopValueMg)
210 e->factor[WHITE] = (uint8_t) SCALE_FACTOR_ONEPAWN;
212 if (pos.count<PAWN>(BLACK) == 1 && npm_b - npm_w <= BishopValueMg)
213 e->factor[BLACK] = (uint8_t) SCALE_FACTOR_ONEPAWN;
215 // Evaluate the material imbalance. We use PIECE_TYPE_NONE as a place holder
216 // for the bishop pair "extended piece", which allows us to be more flexible
217 // in defining bishop pair bonuses.
218 const int PieceCount[COLOR_NB][PIECE_TYPE_NB] = {
219 { pos.count<BISHOP>(WHITE) > 1, pos.count<PAWN>(WHITE), pos.count<KNIGHT>(WHITE),
220 pos.count<BISHOP>(WHITE) , pos.count<ROOK>(WHITE), pos.count<QUEEN >(WHITE) },
221 { pos.count<BISHOP>(BLACK) > 1, pos.count<PAWN>(BLACK), pos.count<KNIGHT>(BLACK),
222 pos.count<BISHOP>(BLACK) , pos.count<ROOK>(BLACK), pos.count<QUEEN >(BLACK) } };
224 e->value = int16_t((imbalance<WHITE>(PieceCount) - imbalance<BLACK>(PieceCount)) / 16);
228 } // namespace Material