2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2021 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
28 #define S(mg, eg) make_score(mg, eg)
30 // Polynomial material imbalance parameters
32 // One Score parameter for each pair (our piece, another of our pieces)
33 constexpr Score QuadraticOurs[][PIECE_TYPE_NB] = {
35 // bishop pair pawn knight bishop rook queen
36 {S(1419, 1455) }, // Bishop pair
37 {S( 101, 28), S( 37, 39) }, // Pawn
38 {S( 57, 64), S(249, 187), S(-49, -62) }, // Knight OUR PIECE 1
39 {S( 0, 0), S(118, 137), S( 10, 27), S( 0, 0) }, // Bishop
40 {S( -63, -68), S( -5, 3), S(100, 81), S(132, 118), S(-246, -244) }, // Rook
41 {S(-210, -211), S( 37, 14), S(147, 141), S(161, 105), S(-158, -174), S(-9,-31) } // Queen
44 // One Score parameter for each pair (our piece, their piece)
45 constexpr Score QuadraticTheirs[][PIECE_TYPE_NB] = {
47 // bishop pair pawn knight bishop rook queen
49 {S( 33, 30) }, // Pawn
50 {S( 46, 18), S(106, 84) }, // Knight OUR PIECE
51 {S( 75, 35), S( 59, 44), S( 60, 15) }, // Bishop
52 {S( 26, 35), S( 6, 22), S( 38, 39), S(-12, -2) }, // Rook
53 {S( 97, 93), S(100, 163), S(-58, -91), S(112, 192), S(276, 225) } // 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_KBPsK(const Position& pos, Color us) {
74 return pos.non_pawn_material(us) == BishopValueMg
75 && pos.count<PAWN >(us) >= 1;
78 bool is_KQKRPs(const Position& pos, Color us) {
79 return !pos.count<PAWN>(us)
80 && pos.non_pawn_material(us) == QueenValueMg
81 && pos.count<ROOK>(~us) == 1
82 && pos.count<PAWN>(~us) >= 1;
86 /// imbalance() calculates the imbalance by comparing the piece count of each
87 /// piece type for both colors.
90 Score imbalance(const int pieceCount[][PIECE_TYPE_NB]) {
92 constexpr Color Them = ~Us;
94 Score bonus = SCORE_ZERO;
96 // Second-degree polynomial material imbalance, by Tord Romstad
97 for (int pt1 = NO_PIECE_TYPE; pt1 <= QUEEN; ++pt1)
99 if (!pieceCount[Us][pt1])
102 int v = QuadraticOurs[pt1][pt1] * 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;
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;
136 Value npm_w = pos.non_pawn_material(WHITE);
137 Value npm_b = pos.non_pawn_material(BLACK);
138 Value npm = std::clamp(npm_w + npm_b, EndgameLimit, MidgameLimit);
140 // Map total non-pawn material into [PHASE_ENDGAME, PHASE_MIDGAME]
141 e->gamePhase = Phase(((npm - EndgameLimit) * PHASE_MIDGAME) / (MidgameLimit - EndgameLimit));
143 // Let's look if we have a specialized evaluation function for this particular
144 // material configuration. Firstly we look for a fixed configuration one, then
145 // for a generic one if the previous search failed.
146 if ((e->evaluationFunction = Endgames::probe<Value>(key)) != nullptr)
149 for (Color c : { WHITE, BLACK })
152 e->evaluationFunction = &EvaluateKXK[c];
156 // OK, we didn't find any special evaluation function for the current material
157 // configuration. Is there a suitable specialized scaling function?
158 const auto* sf = Endgames::probe<ScaleFactor>(key);
162 e->scalingFunction[sf->strongSide] = sf; // Only strong color assigned
166 // We didn't find any specialized scaling function, so fall back on generic
167 // ones that refer to more than one material distribution. Note that in this
168 // case we don't return after setting the function.
169 for (Color c : { WHITE, BLACK })
171 if (is_KBPsK(pos, c))
172 e->scalingFunction[c] = &ScaleKBPsK[c];
174 else if (is_KQKRPs(pos, c))
175 e->scalingFunction[c] = &ScaleKQKRPs[c];
178 if (npm_w + npm_b == VALUE_ZERO && pos.pieces(PAWN)) // Only pawns on the board
180 if (!pos.count<PAWN>(BLACK))
182 assert(pos.count<PAWN>(WHITE) >= 2);
184 e->scalingFunction[WHITE] = &ScaleKPsK[WHITE];
186 else if (!pos.count<PAWN>(WHITE))
188 assert(pos.count<PAWN>(BLACK) >= 2);
190 e->scalingFunction[BLACK] = &ScaleKPsK[BLACK];
192 else if (pos.count<PAWN>(WHITE) == 1 && pos.count<PAWN>(BLACK) == 1)
194 // This is a special case because we set scaling functions
195 // for both colors instead of only one.
196 e->scalingFunction[WHITE] = &ScaleKPKP[WHITE];
197 e->scalingFunction[BLACK] = &ScaleKPKP[BLACK];
201 // Zero or just one pawn makes it difficult to win, even with a small material
202 // advantage. This catches some trivial draws like KK, KBK and KNK and gives a
203 // drawish scale factor for cases such as KRKBP and KmmKm (except for KBBKN).
204 if (!pos.count<PAWN>(WHITE) && npm_w - npm_b <= BishopValueMg)
205 e->factor[WHITE] = uint8_t(npm_w < RookValueMg ? SCALE_FACTOR_DRAW :
206 npm_b <= BishopValueMg ? 4 : 14);
208 if (!pos.count<PAWN>(BLACK) && npm_b - npm_w <= BishopValueMg)
209 e->factor[BLACK] = uint8_t(npm_b < RookValueMg ? SCALE_FACTOR_DRAW :
210 npm_w <= BishopValueMg ? 4 : 14);
212 // Evaluate the material imbalance. We use PIECE_TYPE_NONE as a place holder
213 // for the bishop pair "extended piece", which allows us to be more flexible
214 // in defining bishop pair bonuses.
215 const int pieceCount[COLOR_NB][PIECE_TYPE_NB] = {
216 { pos.count<BISHOP>(WHITE) > 1, pos.count<PAWN>(WHITE), pos.count<KNIGHT>(WHITE),
217 pos.count<BISHOP>(WHITE) , pos.count<ROOK>(WHITE), pos.count<QUEEN >(WHITE) },
218 { pos.count<BISHOP>(BLACK) > 1, pos.count<PAWN>(BLACK), pos.count<KNIGHT>(BLACK),
219 pos.count<BISHOP>(BLACK) , pos.count<ROOK>(BLACK), pos.count<QUEEN >(BLACK) } };
221 e->score = (imbalance<WHITE>(pieceCount) - imbalance<BLACK>(pieceCount)) / 16;
225 } // namespace Material