2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2020 The Stockfish developers (see AUTHORS file)
5 Stockfish is free software: you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation, either version 3 of the License, or
8 (at your option) any later version.
10 Stockfish is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
15 You should have received a copy of the GNU General Public License
16 along with this program. If not, see <http://www.gnu.org/licenses/>.
20 #include <cstring> // For std::memset
29 // Polynomial material imbalance parameters
31 constexpr int QuadraticOurs[][PIECE_TYPE_NB] = {
33 // pair pawn knight bishop rook queen
34 {1438 }, // Bishop pair
36 { 32, 255, -62 }, // Knight OUR PIECES
37 { 0, 104, 4, 0 }, // Bishop
38 { -26, -2, 47, 105, -208 }, // Rook
39 {-189, 24, 117, 133, -134, -6 } // Queen
42 constexpr int QuadraticTheirs[][PIECE_TYPE_NB] = {
44 // pair pawn knight bishop rook queen
47 { 9, 63, }, // Knight OUR PIECES
48 { 59, 65, 42, }, // Bishop
49 { 46, 39, 24, -24, }, // Rook
50 { 97, 100, -42, 137, 268, } // Queen
53 // Endgame evaluation and scaling functions are accessed directly and not through
54 // the function maps because they correspond to more than one material hash key.
55 Endgame<KXK> EvaluateKXK[] = { Endgame<KXK>(WHITE), Endgame<KXK>(BLACK) };
57 Endgame<KBPsK> ScaleKBPsK[] = { Endgame<KBPsK>(WHITE), Endgame<KBPsK>(BLACK) };
58 Endgame<KQKRPs> ScaleKQKRPs[] = { Endgame<KQKRPs>(WHITE), Endgame<KQKRPs>(BLACK) };
59 Endgame<KPsK> ScaleKPsK[] = { Endgame<KPsK>(WHITE), Endgame<KPsK>(BLACK) };
60 Endgame<KPKP> ScaleKPKP[] = { Endgame<KPKP>(WHITE), Endgame<KPKP>(BLACK) };
62 // Helper used to detect a given material distribution
63 bool is_KXK(const Position& pos, Color us) {
64 return !more_than_one(pos.pieces(~us))
65 && pos.non_pawn_material(us) >= RookValueMg;
68 bool is_KBPsK(const Position& pos, Color us) {
69 return pos.non_pawn_material(us) == BishopValueMg
70 && pos.count<PAWN >(us) >= 1;
73 bool is_KQKRPs(const Position& pos, Color us) {
74 return !pos.count<PAWN>(us)
75 && pos.non_pawn_material(us) == QueenValueMg
76 && pos.count<ROOK>(~us) == 1
77 && pos.count<PAWN>(~us) >= 1;
81 /// imbalance() calculates the imbalance by comparing the piece count of each
82 /// piece type for both colors.
85 int imbalance(const int pieceCount[][PIECE_TYPE_NB]) {
87 constexpr Color Them = ~Us;
91 // Second-degree polynomial material imbalance, by Tord Romstad
92 for (int pt1 = NO_PIECE_TYPE; pt1 <= QUEEN; ++pt1)
94 if (!pieceCount[Us][pt1])
97 int v = QuadraticOurs[pt1][pt1] * pieceCount[Us][pt1];
99 for (int pt2 = NO_PIECE_TYPE; pt2 < pt1; ++pt2)
100 v += QuadraticOurs[pt1][pt2] * pieceCount[Us][pt2]
101 + QuadraticTheirs[pt1][pt2] * pieceCount[Them][pt2];
103 bonus += pieceCount[Us][pt1] * v;
114 /// Material::probe() looks up the current position's material configuration in
115 /// the material hash table. It returns a pointer to the Entry if the position
116 /// is found. Otherwise a new Entry is computed and stored there, so we don't
117 /// have to recompute all when the same material configuration occurs again.
119 Entry* probe(const Position& pos) {
121 Key key = pos.material_key();
122 Entry* e = pos.this_thread()->materialTable[key];
127 std::memset(e, 0, sizeof(Entry));
129 e->factor[WHITE] = e->factor[BLACK] = (uint8_t)SCALE_FACTOR_NORMAL;
131 Value npm_w = pos.non_pawn_material(WHITE);
132 Value npm_b = pos.non_pawn_material(BLACK);
133 Value npm = std::clamp(npm_w + npm_b, EndgameLimit, MidgameLimit);
135 // Map total non-pawn material into [PHASE_ENDGAME, PHASE_MIDGAME]
136 e->gamePhase = Phase(((npm - EndgameLimit) * PHASE_MIDGAME) / (MidgameLimit - EndgameLimit));
138 // Let's look if we have a specialized evaluation function for this particular
139 // material configuration. Firstly we look for a fixed configuration one, then
140 // for a generic one if the previous search failed.
141 if ((e->evaluationFunction = Endgames::probe<Value>(key)) != nullptr)
144 for (Color c : { WHITE, BLACK })
147 e->evaluationFunction = &EvaluateKXK[c];
151 // OK, we didn't find any special evaluation function for the current material
152 // configuration. Is there a suitable specialized scaling function?
153 const auto* sf = Endgames::probe<ScaleFactor>(key);
157 e->scalingFunction[sf->strongSide] = sf; // Only strong color assigned
161 // We didn't find any specialized scaling function, so fall back on generic
162 // ones that refer to more than one material distribution. Note that in this
163 // case we don't return after setting the function.
164 for (Color c : { WHITE, BLACK })
166 if (is_KBPsK(pos, c))
167 e->scalingFunction[c] = &ScaleKBPsK[c];
169 else if (is_KQKRPs(pos, c))
170 e->scalingFunction[c] = &ScaleKQKRPs[c];
173 if (npm_w + npm_b == VALUE_ZERO && pos.pieces(PAWN)) // Only pawns on the board
175 if (!pos.count<PAWN>(BLACK))
177 assert(pos.count<PAWN>(WHITE) >= 2);
179 e->scalingFunction[WHITE] = &ScaleKPsK[WHITE];
181 else if (!pos.count<PAWN>(WHITE))
183 assert(pos.count<PAWN>(BLACK) >= 2);
185 e->scalingFunction[BLACK] = &ScaleKPsK[BLACK];
187 else if (pos.count<PAWN>(WHITE) == 1 && pos.count<PAWN>(BLACK) == 1)
189 // This is a special case because we set scaling functions
190 // for both colors instead of only one.
191 e->scalingFunction[WHITE] = &ScaleKPKP[WHITE];
192 e->scalingFunction[BLACK] = &ScaleKPKP[BLACK];
196 // Zero or just one pawn makes it difficult to win, even with a small material
197 // advantage. This catches some trivial draws like KK, KBK and KNK and gives a
198 // drawish scale factor for cases such as KRKBP and KmmKm (except for KBBKN).
199 if (!pos.count<PAWN>(WHITE) && npm_w - npm_b <= BishopValueMg)
200 e->factor[WHITE] = uint8_t(npm_w < RookValueMg ? SCALE_FACTOR_DRAW :
201 npm_b <= BishopValueMg ? 4 : 14);
203 if (!pos.count<PAWN>(BLACK) && npm_b - npm_w <= BishopValueMg)
204 e->factor[BLACK] = uint8_t(npm_b < RookValueMg ? SCALE_FACTOR_DRAW :
205 npm_w <= BishopValueMg ? 4 : 14);
207 // Evaluate the material imbalance. We use PIECE_TYPE_NONE as a place holder
208 // for the bishop pair "extended piece", which allows us to be more flexible
209 // in defining bishop pair bonuses.
210 const int pieceCount[COLOR_NB][PIECE_TYPE_NB] = {
211 { pos.count<BISHOP>(WHITE) > 1, pos.count<PAWN>(WHITE), pos.count<KNIGHT>(WHITE),
212 pos.count<BISHOP>(WHITE) , pos.count<ROOK>(WHITE), pos.count<QUEEN >(WHITE) },
213 { pos.count<BISHOP>(BLACK) > 1, pos.count<PAWN>(BLACK), pos.count<KNIGHT>(BLACK),
214 pos.count<BISHOP>(BLACK) , pos.count<ROOK>(BLACK), pos.count<QUEEN >(BLACK) } };
216 e->value = int16_t((imbalance<WHITE>(pieceCount) - imbalance<BLACK>(pieceCount)) / 16);
220 } // namespace Material