2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 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/>.
29 // Values modified by Joona Kiiski
30 const Value MidgameLimit = Value(15581);
31 const Value EndgameLimit = Value(3998);
33 // Scale factors used when one side has no more pawns
34 const int NoPawnsSF[4] = { 6, 12, 32 };
36 // Polynomial material balance parameters
37 const Value RedundantQueenPenalty = Value(320);
38 const Value RedundantRookPenalty = Value(554);
40 const int LinearCoefficients[6] = { 1617, -162, -1172, -190, 105, 26 };
42 const int QuadraticCoefficientsSameColor[][8] = {
43 { 7, 7, 7, 7, 7, 7 }, { 39, 2, 7, 7, 7, 7 }, { 35, 271, -4, 7, 7, 7 },
44 { 7, 25, 4, 7, 7, 7 }, { -27, -2, 46, 100, 56, 7 }, { 58, 29, 83, 148, -3, -25 } };
46 const int QuadraticCoefficientsOppositeColor[][8] = {
47 { 41, 41, 41, 41, 41, 41 }, { 37, 41, 41, 41, 41, 41 }, { 10, 62, 41, 41, 41, 41 },
48 { 57, 64, 39, 41, 41, 41 }, { 50, 40, 23, -22, 41, 41 }, { 106, 101, 3, 151, 171, 41 } };
50 // Endgame evaluation and scaling functions accessed direcly and not through
51 // the function maps because correspond to more then one material hash key.
52 Endgame<Value, KmmKm> EvaluateKmmKm[] = { Endgame<Value, KmmKm>(WHITE), Endgame<Value, KmmKm>(BLACK) };
53 Endgame<Value, KXK> EvaluateKXK[] = { Endgame<Value, KXK>(WHITE), Endgame<Value, KXK>(BLACK) };
55 Endgame<ScaleFactor, KBPsK> ScaleKBPsK[] = { Endgame<ScaleFactor, KBPsK>(WHITE), Endgame<ScaleFactor, KBPsK>(BLACK) };
56 Endgame<ScaleFactor, KQKRPs> ScaleKQKRPs[] = { Endgame<ScaleFactor, KQKRPs>(WHITE), Endgame<ScaleFactor, KQKRPs>(BLACK) };
57 Endgame<ScaleFactor, KPsK> ScaleKPsK[] = { Endgame<ScaleFactor, KPsK>(WHITE), Endgame<ScaleFactor, KPsK>(BLACK) };
58 Endgame<ScaleFactor, KPKP> ScaleKPKP[] = { Endgame<ScaleFactor, KPKP>(WHITE), Endgame<ScaleFactor, KPKP>(BLACK) };
60 // Helper templates used to detect a given material distribution
61 template<Color Us> bool is_KXK(const Position& pos) {
62 const Color Them = (Us == WHITE ? BLACK : WHITE);
63 return pos.non_pawn_material(Them) == VALUE_ZERO
64 && pos.piece_count(Them, PAWN) == 0
65 && pos.non_pawn_material(Us) >= RookValueMidgame;
68 template<Color Us> bool is_KBPsKs(const Position& pos) {
69 return pos.non_pawn_material(Us) == BishopValueMidgame
70 && pos.piece_count(Us, BISHOP) == 1
71 && pos.piece_count(Us, PAWN) >= 1;
74 template<Color Us> bool is_KQKRPs(const Position& pos) {
75 const Color Them = (Us == WHITE ? BLACK : WHITE);
76 return pos.piece_count(Us, PAWN) == 0
77 && pos.non_pawn_material(Us) == QueenValueMidgame
78 && pos.piece_count(Us, QUEEN) == 1
79 && pos.piece_count(Them, ROOK) == 1
80 && pos.piece_count(Them, PAWN) >= 1;
86 /// MaterialInfoTable c'tor and d'tor allocate and free the space for Endgames
88 void MaterialInfoTable::init() { Base::init(); if (!funcs) funcs = new Endgames(); }
89 MaterialInfoTable::~MaterialInfoTable() { delete funcs; }
92 /// MaterialInfoTable::get_material_info() takes a position object as input,
93 /// computes or looks up a MaterialInfo object, and returns a pointer to it.
94 /// If the material configuration is not already present in the table, it
95 /// is stored there, so we don't have to recompute everything when the
96 /// same material configuration occurs again.
98 MaterialInfo* MaterialInfoTable::get_material_info(const Position& pos) const {
100 Key key = pos.get_material_key();
101 MaterialInfo* mi = probe(key);
103 // If mi->key matches the position's material hash key, it means that we
104 // have analysed this material configuration before, and we can simply
105 // return the information we found the last time instead of recomputing it.
109 // Initialize MaterialInfo entry
110 memset(mi, 0, sizeof(MaterialInfo));
112 mi->factor[WHITE] = mi->factor[BLACK] = (uint8_t)SCALE_FACTOR_NORMAL;
115 mi->gamePhase = MaterialInfoTable::game_phase(pos);
117 // Let's look if we have a specialized evaluation function for this
118 // particular material configuration. First we look for a fixed
119 // configuration one, then a generic one if previous search failed.
120 if ((mi->evaluationFunction = funcs->get<EndgameBase<Value> >(key)) != NULL)
123 if (is_KXK<WHITE>(pos))
125 mi->evaluationFunction = &EvaluateKXK[WHITE];
129 if (is_KXK<BLACK>(pos))
131 mi->evaluationFunction = &EvaluateKXK[BLACK];
135 if (!pos.pieces(PAWN) && !pos.pieces(ROOK) && !pos.pieces(QUEEN))
137 // Minor piece endgame with at least one minor piece per side and
138 // no pawns. Note that the case KmmK is already handled by KXK.
139 assert((pos.pieces(KNIGHT, WHITE) | pos.pieces(BISHOP, WHITE)));
140 assert((pos.pieces(KNIGHT, BLACK) | pos.pieces(BISHOP, BLACK)));
142 if ( pos.piece_count(WHITE, BISHOP) + pos.piece_count(WHITE, KNIGHT) <= 2
143 && pos.piece_count(BLACK, BISHOP) + pos.piece_count(BLACK, KNIGHT) <= 2)
145 mi->evaluationFunction = &EvaluateKmmKm[WHITE];
150 // OK, we didn't find any special evaluation function for the current
151 // material configuration. Is there a suitable scaling function?
153 // We face problems when there are several conflicting applicable
154 // scaling functions and we need to decide which one to use.
155 EndgameBase<ScaleFactor>* sf;
157 if ((sf = funcs->get<EndgameBase<ScaleFactor> >(key)) != NULL)
159 mi->scalingFunction[sf->color()] = sf;
163 // Generic scaling functions that refer to more then one material
164 // distribution. Should be probed after the specialized ones.
165 // Note that these ones don't return after setting the function.
166 if (is_KBPsKs<WHITE>(pos))
167 mi->scalingFunction[WHITE] = &ScaleKBPsK[WHITE];
169 if (is_KBPsKs<BLACK>(pos))
170 mi->scalingFunction[BLACK] = &ScaleKBPsK[BLACK];
172 if (is_KQKRPs<WHITE>(pos))
173 mi->scalingFunction[WHITE] = &ScaleKQKRPs[WHITE];
175 else if (is_KQKRPs<BLACK>(pos))
176 mi->scalingFunction[BLACK] = &ScaleKQKRPs[BLACK];
178 Value npm_w = pos.non_pawn_material(WHITE);
179 Value npm_b = pos.non_pawn_material(BLACK);
181 if (npm_w + npm_b == VALUE_ZERO)
183 if (pos.piece_count(BLACK, PAWN) == 0)
185 assert(pos.piece_count(WHITE, PAWN) >= 2);
186 mi->scalingFunction[WHITE] = &ScaleKPsK[WHITE];
188 else if (pos.piece_count(WHITE, PAWN) == 0)
190 assert(pos.piece_count(BLACK, PAWN) >= 2);
191 mi->scalingFunction[BLACK] = &ScaleKPsK[BLACK];
193 else if (pos.piece_count(WHITE, PAWN) == 1 && pos.piece_count(BLACK, PAWN) == 1)
195 // This is a special case because we set scaling functions
196 // for both colors instead of only one.
197 mi->scalingFunction[WHITE] = &ScaleKPKP[WHITE];
198 mi->scalingFunction[BLACK] = &ScaleKPKP[BLACK];
202 // No pawns makes it difficult to win, even with a material advantage
203 if (pos.piece_count(WHITE, PAWN) == 0 && npm_w - npm_b <= BishopValueMidgame)
205 mi->factor[WHITE] = uint8_t
206 (npm_w == npm_b || npm_w < RookValueMidgame ? 0 : NoPawnsSF[Min(pos.piece_count(WHITE, BISHOP), 2)]);
209 if (pos.piece_count(BLACK, PAWN) == 0 && npm_b - npm_w <= BishopValueMidgame)
211 mi->factor[BLACK] = uint8_t
212 (npm_w == npm_b || npm_b < RookValueMidgame ? 0 : NoPawnsSF[Min(pos.piece_count(BLACK, BISHOP), 2)]);
215 // Compute the space weight
216 if (npm_w + npm_b >= 2 * QueenValueMidgame + 4 * RookValueMidgame + 2 * KnightValueMidgame)
218 int minorPieceCount = pos.piece_count(WHITE, KNIGHT) + pos.piece_count(WHITE, BISHOP)
219 + pos.piece_count(BLACK, KNIGHT) + pos.piece_count(BLACK, BISHOP);
221 mi->spaceWeight = minorPieceCount * minorPieceCount;
224 // Evaluate the material imbalance. We use PIECE_TYPE_NONE as a place holder
225 // for the bishop pair "extended piece", this allow us to be more flexible
226 // in defining bishop pair bonuses.
227 const int pieceCount[2][8] = {
228 { pos.piece_count(WHITE, BISHOP) > 1, pos.piece_count(WHITE, PAWN), pos.piece_count(WHITE, KNIGHT),
229 pos.piece_count(WHITE, BISHOP) , pos.piece_count(WHITE, ROOK), pos.piece_count(WHITE, QUEEN) },
230 { pos.piece_count(BLACK, BISHOP) > 1, pos.piece_count(BLACK, PAWN), pos.piece_count(BLACK, KNIGHT),
231 pos.piece_count(BLACK, BISHOP) , pos.piece_count(BLACK, ROOK), pos.piece_count(BLACK, QUEEN) } };
233 mi->value = int16_t((imbalance<WHITE>(pieceCount) - imbalance<BLACK>(pieceCount)) / 16);
238 /// MaterialInfoTable::imbalance() calculates imbalance comparing piece count of each
239 /// piece type for both colors.
242 int MaterialInfoTable::imbalance(const int pieceCount[][8]) {
244 const Color Them = (Us == WHITE ? BLACK : WHITE);
249 // Redundancy of major pieces, formula based on Kaufman's paper
250 // "The Evaluation of Material Imbalances in Chess"
251 if (pieceCount[Us][ROOK] > 0)
252 value -= RedundantRookPenalty * (pieceCount[Us][ROOK] - 1)
253 + RedundantQueenPenalty * pieceCount[Us][QUEEN];
255 // Second-degree polynomial material imbalance by Tord Romstad
256 for (pt1 = PIECE_TYPE_NONE; pt1 <= QUEEN; pt1++)
258 pc = pieceCount[Us][pt1];
262 v = LinearCoefficients[pt1];
264 for (pt2 = PIECE_TYPE_NONE; pt2 <= pt1; pt2++)
265 v += QuadraticCoefficientsSameColor[pt1][pt2] * pieceCount[Us][pt2]
266 + QuadraticCoefficientsOppositeColor[pt1][pt2] * pieceCount[Them][pt2];
274 /// MaterialInfoTable::game_phase() calculates the phase given the current
275 /// position. Because the phase is strictly a function of the material, it
276 /// is stored in MaterialInfo.
278 Phase MaterialInfoTable::game_phase(const Position& pos) {
280 Value npm = pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK);
282 return npm >= MidgameLimit ? PHASE_MIDGAME
283 : npm <= EndgameLimit ? PHASE_ENDGAME
284 : Phase(((npm - EndgameLimit) * 128) / (MidgameLimit - EndgameLimit));