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
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] = { 1667, -168, -1027, -166, 238, -138 };
36 const int QuadraticOurs[][PIECE_TYPE_NB] = {
38 // pair pawn knight bishop rook queen
41 { 32, 255, -3 }, // Knight OUR PIECES
42 { 0, 104, 4, 0 }, // Bishop
43 { -26, -2, 47, 105, -149 }, // Rook
44 {-185, 24, 122, 137, -134, 0 } // Queen
47 const int QuadraticTheirs[][PIECE_TYPE_NB] = {
49 // pair pawn knight bishop rook queen
52 { 9, 63, 0 }, // Knight OUR PIECES
53 { 59, 65, 42, 0 }, // Bishop
54 { 46, 39, 24, -24, 0 }, // Rook
55 { 101, 100, -37, 141, 268, 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 used to detect a given material distribution
68 bool is_KXK(const Position& pos, Color us) {
69 return !more_than_one(pos.pieces(~us))
70 && pos.non_pawn_material(us) >= RookValueMg;
73 bool is_KBPsKs(const Position& pos, Color us) {
74 return pos.non_pawn_material(us) == BishopValueMg
75 && pos.count<BISHOP>(us) == 1
76 && pos.count<PAWN >(us) >= 1;
79 bool is_KQKRPs(const Position& pos, Color us) {
80 return !pos.count<PAWN>(us)
81 && pos.non_pawn_material(us) == QueenValueMg
82 && pos.count<QUEEN>(us) == 1
83 && pos.count<ROOK>(~us) == 1
84 && pos.count<PAWN>(~us) >= 1;
87 /// imbalance() calculates the imbalance by comparing the piece count of each
88 /// piece type for both colors.
90 int imbalance(const int pieceCount[][PIECE_TYPE_NB]) {
92 const Color Them = (Us == WHITE ? BLACK : WHITE);
96 // Second-degree polynomial material imbalance by Tord Romstad
97 for (int pt1 = NO_PIECE_TYPE; pt1 <= QUEEN; ++pt1)
99 if (!pieceCount[Us][pt1])
104 for (int pt2 = NO_PIECE_TYPE; pt2 <= pt1; ++pt2)
105 v += QuadraticOurs[pt1][pt2] * pieceCount[Us][pt2]
106 + QuadraticTheirs[pt1][pt2] * pieceCount[Them][pt2];
108 bonus += pieceCount[Us][pt1] * v;
118 /// Material::probe() looks up the current position's material configuration in
119 /// the material hash table. It returns a pointer to the Entry if the position
120 /// is found. Otherwise a new Entry is computed and stored there, so we don't
121 /// have to recompute all when the same material configuration occurs again.
123 Entry* probe(const Position& pos) {
125 Key key = pos.material_key();
126 Entry* e = pos.this_thread()->materialTable[key];
131 std::memset(e, 0, sizeof(Entry));
133 e->factor[WHITE] = e->factor[BLACK] = (uint8_t)SCALE_FACTOR_NORMAL;
134 e->gamePhase = pos.game_phase();
136 // Let's look if we have a specialized evaluation function for this particular
137 // material configuration. Firstly we look for a fixed configuration one, then
138 // for a generic one if the previous search failed.
139 if ((e->evaluationFunction = pos.this_thread()->endgames.probe<Value>(key)) != nullptr)
142 for (Color c = WHITE; c <= BLACK; ++c)
145 e->evaluationFunction = &EvaluateKXK[c];
149 // OK, we didn't find any special evaluation function for the current material
150 // configuration. Is there a suitable specialized scaling function?
151 EndgameBase<ScaleFactor>* sf;
153 if ((sf = pos.this_thread()->endgames.probe<ScaleFactor>(key)) != nullptr)
155 e->scalingFunction[sf->strong_side()] = sf; // Only strong color assigned
159 // We didn't find any specialized scaling function, so fall back on generic
160 // ones that refer to more than one material distribution. Note that in this
161 // case we don't return after setting the function.
162 for (Color c = WHITE; c <= BLACK; ++c)
164 if (is_KBPsKs(pos, c))
165 e->scalingFunction[c] = &ScaleKBPsK[c];
167 else if (is_KQKRPs(pos, c))
168 e->scalingFunction[c] = &ScaleKQKRPs[c];
171 Value npm_w = pos.non_pawn_material(WHITE);
172 Value npm_b = pos.non_pawn_material(BLACK);
174 if (npm_w + npm_b == VALUE_ZERO && pos.pieces(PAWN)) // Only pawns on the board
176 if (!pos.count<PAWN>(BLACK))
178 assert(pos.count<PAWN>(WHITE) >= 2);
180 e->scalingFunction[WHITE] = &ScaleKPsK[WHITE];
182 else if (!pos.count<PAWN>(WHITE))
184 assert(pos.count<PAWN>(BLACK) >= 2);
186 e->scalingFunction[BLACK] = &ScaleKPsK[BLACK];
188 else if (pos.count<PAWN>(WHITE) == 1 && pos.count<PAWN>(BLACK) == 1)
190 // This is a special case because we set scaling functions
191 // for both colors instead of only one.
192 e->scalingFunction[WHITE] = &ScaleKPKP[WHITE];
193 e->scalingFunction[BLACK] = &ScaleKPKP[BLACK];
197 // Zero or just one pawn makes it difficult to win, even with a small material
198 // advantage. This catches some trivial draws like KK, KBK and KNK and gives a
199 // drawish scale factor for cases such as KRKBP and KmmKm (except for KBBKN).
200 if (!pos.count<PAWN>(WHITE) && npm_w - npm_b <= BishopValueMg)
201 e->factor[WHITE] = uint8_t(npm_w < RookValueMg ? SCALE_FACTOR_DRAW :
202 npm_b <= BishopValueMg ? 4 : 14);
204 if (!pos.count<PAWN>(BLACK) && npm_b - npm_w <= BishopValueMg)
205 e->factor[BLACK] = uint8_t(npm_b < RookValueMg ? SCALE_FACTOR_DRAW :
206 npm_w <= BishopValueMg ? 4 : 14);
208 if (pos.count<PAWN>(WHITE) == 1 && npm_w - npm_b <= BishopValueMg)
209 e->factor[WHITE] = (uint8_t) SCALE_FACTOR_ONEPAWN;
211 if (pos.count<PAWN>(BLACK) == 1 && npm_b - npm_w <= BishopValueMg)
212 e->factor[BLACK] = (uint8_t) SCALE_FACTOR_ONEPAWN;
214 // Evaluate the material imbalance. We use PIECE_TYPE_NONE as a place holder
215 // for the bishop pair "extended piece", which allows us to be more flexible
216 // in defining bishop pair bonuses.
217 const int PieceCount[COLOR_NB][PIECE_TYPE_NB] = {
218 { pos.count<BISHOP>(WHITE) > 1, pos.count<PAWN>(WHITE), pos.count<KNIGHT>(WHITE),
219 pos.count<BISHOP>(WHITE) , pos.count<ROOK>(WHITE), pos.count<QUEEN >(WHITE) },
220 { pos.count<BISHOP>(BLACK) > 1, pos.count<PAWN>(BLACK), pos.count<KNIGHT>(BLACK),
221 pos.count<BISHOP>(BLACK) , pos.count<ROOK>(BLACK), pos.count<QUEEN >(BLACK) } };
223 e->value = int16_t((imbalance<WHITE>(PieceCount) - imbalance<BLACK>(PieceCount)) / 16);
227 } // namespace Material