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 Marco Costalba
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/>.
33 #include "ucioption.h"
37 //// Local definitions
42 const int Sign[2] = {1, -1};
44 // Evaluation grain size, must be a power of 2.
45 const int GrainSize = 4;
48 int WeightMobilityMidgame = 0x100;
49 int WeightMobilityEndgame = 0x100;
50 int WeightPawnStructureMidgame = 0x100;
51 int WeightPawnStructureEndgame = 0x100;
52 int WeightPassedPawnsMidgame = 0x100;
53 int WeightPassedPawnsEndgame = 0x100;
54 int WeightKingSafety[2] = { 0x100, 0x100 };
57 // Internal evaluation weights. These are applied on top of the evaluation
58 // weights read from UCI parameters. The purpose is to be able to change
59 // the evaluation weights while keeping the default values of the UCI
60 // parameters at 100, which looks prettier.
61 const int WeightMobilityMidgameInternal = 0x100;
62 const int WeightMobilityEndgameInternal = 0x100;
63 const int WeightPawnStructureMidgameInternal = 0x100;
64 const int WeightPawnStructureEndgameInternal = 0x100;
65 const int WeightPassedPawnsMidgameInternal = 0x100;
66 const int WeightPassedPawnsEndgameInternal = 0x100;
67 const int WeightKingSafetyInternal = 0x110;
68 const int WeightKingOppSafetyInternal = 0x110;
69 const int WeightSpaceInternal = 0x30;
71 // Visually better to define tables constants
74 // Knight mobility bonus in middle game and endgame, indexed by the number
75 // of attacked squares not occupied by friendly piecess.
76 const Value MidgameKnightMobilityBonus[] = {
78 V(-30), V(-20),V(-10), V(0), V(10), V(20), V(25), V(30), V(30)
81 const Value EndgameKnightMobilityBonus[] = {
83 V(-30), V(-20),V(-10), V(0), V(10), V(20), V(25), V(30), V(30)
86 // Bishop mobility bonus in middle game and endgame, indexed by the number
87 // of attacked squares not occupied by friendly pieces. X-ray attacks through
88 // queens are also included.
89 const Value MidgameBishopMobilityBonus[] = {
91 V(-30), V(-15), V(0), V(15), V(30), V(45), V(58), V(66),
92 // 8 9 10 11 12 13 14 15
93 V( 72), V( 76), V(78), V(80), V(81), V(82), V(83), V(83)
96 const Value EndgameBishopMobilityBonus[] = {
98 V(-30), V(-15), V(0), V(15), V(30), V(45), V(58), V(66),
99 // 8 9 10 11 12 13 14 15
100 V( 72), V( 76), V(78), V(80), V(81), V(82), V(83), V(83)
103 // Rook mobility bonus in middle game and endgame, indexed by the number
104 // of attacked squares not occupied by friendly pieces. X-ray attacks through
105 // queens and rooks are also included.
106 const Value MidgameRookMobilityBonus[] = {
108 V(-18), V(-12), V(-6), V(0), V(6), V(12), V(16), V(21),
109 // 8 9 10 11 12 13 14 15
110 V( 24), V( 27), V(28), V(29), V(30), V(31), V(32), V(33)
113 const Value EndgameRookMobilityBonus[] = {
115 V(-30), V(-18), V(-6), V(6), V(18), V(30), V(42), V(54),
116 // 8 9 10 11 12 13 14 15
117 V( 66), V( 74), V(78), V(80), V(81), V(82), V(83), V(83)
120 // Queen mobility bonus in middle game and endgame, indexed by the number
121 // of attacked squares not occupied by friendly pieces.
122 const Value MidgameQueenMobilityBonus[] = {
124 V(-10), V(-8), V(-6), V(-4), V(-2), V( 0), V( 2), V( 4),
125 // 8 9 10 11 12 13 14 15
126 V( 6), V( 8), V(10), V(12), V(13), V(14), V(15), V(16),
127 // 16 17 18 19 20 21 22 23
128 V( 16), V(16), V(16), V(16), V(16), V(16), V(16), V(16),
129 // 24 25 26 27 28 29 30 31
130 V( 16), V(16), V(16), V(16), V(16), V(16), V(16), V(16)
133 const Value EndgameQueenMobilityBonus[] = {
135 V(-20),V(-15),V(-10), V(-5), V( 0), V( 5), V(10), V(15),
136 // 8 9 10 11 12 13 14 15
137 V( 19), V(23), V(27), V(29), V(30), V(30), V(30), V(30),
138 // 16 17 18 19 20 21 22 23
139 V( 30), V(30), V(30), V(30), V(30), V(30), V(30), V(30),
140 // 24 25 26 27 28 29 30 31
141 V( 30), V(30), V(30), V(30), V(30), V(30), V(30), V(30)
144 // Outpost bonuses for knights and bishops, indexed by square (from white's
146 const Value KnightOutpostBonus[64] = {
148 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0), // 1
149 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0), // 2
150 V(0), V(0), V(5),V(10),V(10), V(5), V(0), V(0), // 3
151 V(0), V(5),V(20),V(30),V(30),V(20), V(5), V(0), // 4
152 V(0),V(10),V(30),V(40),V(40),V(30),V(10), V(0), // 5
153 V(0), V(5),V(20),V(20),V(20),V(20), V(5), V(0), // 6
154 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0), // 7
155 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0) // 8
158 const Value BishopOutpostBonus[64] = {
160 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0), // 1
161 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0), // 2
162 V(0), V(0), V(5), V(5), V(5), V(5), V(0), V(0), // 3
163 V(0), V(5),V(10),V(10),V(10),V(10), V(5), V(0), // 4
164 V(0),V(10),V(20),V(20),V(20),V(20),V(10), V(0), // 5
165 V(0), V(5), V(8), V(8), V(8), V(8), V(5), V(0), // 6
166 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0), // 7
167 V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0) // 8
170 // Bonus for unstoppable passed pawns:
171 const Value UnstoppablePawnValue = Value(0x500);
173 // Rooks and queens on the 7th rank:
174 const Value MidgameRookOn7thBonus = Value(50);
175 const Value EndgameRookOn7thBonus = Value(100);
176 const Value MidgameQueenOn7thBonus = Value(25);
177 const Value EndgameQueenOn7thBonus = Value(50);
179 // Rooks on open files:
180 const Value RookOpenFileBonus = Value(40);
181 const Value RookHalfOpenFileBonus = Value(20);
183 // Penalty for rooks trapped inside a friendly king which has lost the
185 const Value TrappedRookPenalty = Value(180);
187 // Penalty for a bishop on a7/h7 (a2/h2 for black) which is trapped by
189 const Value TrappedBishopA7H7Penalty = Value(300);
191 // Bitboard masks for detecting trapped bishops on a7/h7 (a2/h2 for black):
192 const Bitboard MaskA7H7[2] = {
193 ((1ULL << SQ_A7) | (1ULL << SQ_H7)),
194 ((1ULL << SQ_A2) | (1ULL << SQ_H2))
197 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
198 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
199 // happen in Chess960 games.
200 const Value TrappedBishopA1H1Penalty = Value(100);
202 // Bitboard masks for detecting trapped bishops on a1/h1 (a8/h8 for black):
203 const Bitboard MaskA1H1[2] = {
204 ((1ULL << SQ_A1) | (1ULL << SQ_H1)),
205 ((1ULL << SQ_A8) | (1ULL << SQ_H8))
208 // The SpaceMask[color] contains area of the board which is consdered by
209 // the space evaluation. In the middle game, each side is given a bonus
210 // based on how many squares inside this area are safe and available for
211 // friendly minor pieces.
212 const Bitboard SpaceMask[2] = {
213 (1ULL<<SQ_C2) | (1ULL<<SQ_D2) | (1ULL<<SQ_E2) | (1ULL<<SQ_F2) |
214 (1ULL<<SQ_C3) | (1ULL<<SQ_D3) | (1ULL<<SQ_E3) | (1ULL<<SQ_F3) |
215 (1ULL<<SQ_C4) | (1ULL<<SQ_D4) | (1ULL<<SQ_E4) | (1ULL<<SQ_F4),
216 (1ULL<<SQ_C7) | (1ULL<<SQ_D7) | (1ULL<<SQ_E7) | (1ULL<<SQ_F7) |
217 (1ULL<<SQ_C6) | (1ULL<<SQ_D6) | (1ULL<<SQ_E6) | (1ULL<<SQ_F6) |
218 (1ULL<<SQ_C5) | (1ULL<<SQ_D5) | (1ULL<<SQ_E5) | (1ULL<<SQ_F5)
221 /// King safety constants and variables. The king safety scores are taken
222 /// from the array SafetyTable[]. Various little "meta-bonuses" measuring
223 /// the strength of the attack are added up into an integer, which is used
224 /// as an index to SafetyTable[].
226 // Attack weights for each piece type.
227 const int QueenAttackWeight = 5;
228 const int RookAttackWeight = 3;
229 const int BishopAttackWeight = 2;
230 const int KnightAttackWeight = 2;
232 // Bonuses for safe checks for each piece type.
233 int QueenContactCheckBonus = 3;
234 int QueenCheckBonus = 2;
235 int RookCheckBonus = 1;
236 int BishopCheckBonus = 1;
237 int KnightCheckBonus = 1;
238 int DiscoveredCheckBonus = 3;
240 // Scan for queen contact mates?
241 const bool QueenContactMates = true;
243 // Bonus for having a mate threat.
244 int MateThreatBonus = 3;
246 // InitKingDanger[] contains bonuses based on the position of the defending
248 const int InitKingDanger[64] = {
249 2, 0, 2, 5, 5, 2, 0, 2,
250 2, 2, 4, 8, 8, 4, 2, 2,
251 7, 10, 12, 12, 12, 12, 10, 7,
252 15, 15, 15, 15, 15, 15, 15, 15,
253 15, 15, 15, 15, 15, 15, 15, 15,
254 15, 15, 15, 15, 15, 15, 15, 15,
255 15, 15, 15, 15, 15, 15, 15, 15,
256 15, 15, 15, 15, 15, 15, 15, 15
259 // SafetyTable[] contains the actual king safety scores. It is initialized
261 Value SafetyTable[100];
263 // Pawn and material hash tables, indexed by the current thread id
264 PawnInfoTable *PawnTable[8] = {0, 0, 0, 0, 0, 0, 0, 0};
265 MaterialInfoTable *MaterialTable[8] = {0, 0, 0, 0, 0, 0, 0, 0};
267 // Sizes of pawn and material hash tables
268 const int PawnTableSize = 16384;
269 const int MaterialTableSize = 1024;
271 // Array which gives the number of nonzero bits in an 8-bit integer:
272 uint8_t BitCount8Bit[256];
274 // Function prototypes
275 void evaluate_knight(const Position &p, Square s, Color us, EvalInfo &ei);
276 void evaluate_bishop(const Position &p, Square s, Color us, EvalInfo &ei);
277 void evaluate_rook(const Position &p, Square s, Color us, EvalInfo &ei);
278 void evaluate_queen(const Position &p, Square s, Color us, EvalInfo &ei);
279 void evaluate_king(const Position &p, Square s, Color us, EvalInfo &ei);
281 void evaluate_passed_pawns(const Position &pos, EvalInfo &ei);
282 void evaluate_trapped_bishop_a7h7(const Position &pos, Square s, Color us,
284 void evaluate_trapped_bishop_a1h1(const Position &pos, Square s, Color us,
287 void evaluate_space(const Position &p, Color us, EvalInfo &ei);
288 inline Value apply_weight(Value v, int w);
289 Value scale_by_game_phase(Value mv, Value ev, Phase ph, const ScaleFactor sf[]);
291 int count_1s_8bit(Bitboard b);
293 int compute_weight(int uciWeight, int internalWeight);
294 int weight_option(const std::string& opt, int weight);
304 /// evaluate() is the main evaluation function. It always computes two
305 /// values, an endgame score and a middle game score, and interpolates
306 /// between them based on the remaining material.
308 Value evaluate(const Position &pos, EvalInfo &ei, int threadID) {
311 assert(threadID >= 0 && threadID < THREAD_MAX);
313 memset(&ei, 0, sizeof(EvalInfo));
315 // Initialize by reading the incrementally updated scores included in the
316 // position object (material + piece square tables)
317 ei.mgValue = pos.mg_value();
318 ei.egValue = pos.eg_value();
320 // Probe the material hash table
321 ei.mi = MaterialTable[threadID]->get_material_info(pos);
322 ei.mgValue += ei.mi->mg_value();
323 ei.egValue += ei.mi->eg_value();
325 // If we have a specialized evaluation function for the current material
326 // configuration, call it and return
327 if (ei.mi->specialized_eval_exists())
328 return ei.mi->evaluate(pos);
330 // After get_material_info() call that modifies them
331 ScaleFactor factor[2];
332 factor[WHITE] = ei.mi->scale_factor(pos, WHITE);
333 factor[BLACK] = ei.mi->scale_factor(pos, BLACK);
335 // Probe the pawn hash table
336 ei.pi = PawnTable[threadID]->get_pawn_info(pos);
337 ei.mgValue += apply_weight(ei.pi->mg_value(), WeightPawnStructureMidgame);
338 ei.egValue += apply_weight(ei.pi->eg_value(), WeightPawnStructureEndgame);
340 // Initialize king attack bitboards and king attack zones for both sides
341 ei.attackedBy[WHITE][KING] = pos.piece_attacks<KING>(pos.king_square(WHITE));
342 ei.attackedBy[BLACK][KING] = pos.piece_attacks<KING>(pos.king_square(BLACK));
343 ei.kingZone[WHITE] = ei.attackedBy[BLACK][KING] | (ei.attackedBy[BLACK][KING] >> 8);
344 ei.kingZone[BLACK] = ei.attackedBy[WHITE][KING] | (ei.attackedBy[WHITE][KING] << 8);
346 // Initialize pawn attack bitboards for both sides
347 ei.attackedBy[WHITE][PAWN] = ((pos.pawns(WHITE) << 9) & ~FileABB) | ((pos.pawns(WHITE) << 7) & ~FileHBB);
348 ei.attackedBy[BLACK][PAWN] = ((pos.pawns(BLACK) >> 7) & ~FileABB) | ((pos.pawns(BLACK) >> 9) & ~FileHBB);
349 ei.kingAttackersCount[WHITE] = count_1s_max_15(ei.attackedBy[WHITE][PAWN] & ei.attackedBy[BLACK][KING])/2;
350 ei.kingAttackersCount[BLACK] = count_1s_max_15(ei.attackedBy[BLACK][PAWN] & ei.attackedBy[WHITE][KING])/2;
353 for (Color c = WHITE; c <= BLACK; c++)
356 for (int i = 0; i < pos.piece_count(c, KNIGHT); i++)
357 evaluate_knight(pos, pos.piece_list(c, KNIGHT, i), c, ei);
360 for (int i = 0; i < pos.piece_count(c, BISHOP); i++)
361 evaluate_bishop(pos, pos.piece_list(c, BISHOP, i), c, ei);
364 for (int i = 0; i < pos.piece_count(c, ROOK); i++)
365 evaluate_rook(pos, pos.piece_list(c, ROOK, i), c, ei);
368 for(int i = 0; i < pos.piece_count(c, QUEEN); i++)
369 evaluate_queen(pos, pos.piece_list(c, QUEEN, i), c, ei);
371 // Special pattern: trapped bishops on a7/h7/a2/h2
372 Bitboard b = pos.bishops(c) & MaskA7H7[c];
375 Square s = pop_1st_bit(&b);
376 evaluate_trapped_bishop_a7h7(pos, s, c, ei);
379 // Special pattern: trapped bishops on a1/h1/a8/h8 in Chess960:
382 b = pos.bishops(c) & MaskA1H1[c];
385 Square s = pop_1st_bit(&b);
386 evaluate_trapped_bishop_a1h1(pos, s, c, ei);
390 // Sum up all attacked squares
391 ei.attackedBy[c][0] = ei.attackedBy[c][PAWN] | ei.attackedBy[c][KNIGHT]
392 | ei.attackedBy[c][BISHOP] | ei.attackedBy[c][ROOK]
393 | ei.attackedBy[c][QUEEN] | ei.attackedBy[c][KING];
396 // Kings. Kings are evaluated after all other pieces for both sides,
397 // because we need complete attack information for all pieces when computing
398 // the king safety evaluation.
399 for (Color c = WHITE; c <= BLACK; c++)
400 evaluate_king(pos, pos.king_square(c), c, ei);
402 // Evaluate passed pawns. We evaluate passed pawns for both sides at once,
403 // because we need to know which side promotes first in positions where
404 // both sides have an unstoppable passed pawn.
405 if (ei.pi->passed_pawns())
406 evaluate_passed_pawns(pos, ei);
408 Phase phase = pos.game_phase();
410 // Middle-game specific evaluation terms
411 if (phase > PHASE_ENDGAME)
413 // Pawn storms in positions with opposite castling.
414 if ( square_file(pos.king_square(WHITE)) >= FILE_E
415 && square_file(pos.king_square(BLACK)) <= FILE_D)
417 ei.mgValue += ei.pi->queenside_storm_value(WHITE)
418 - ei.pi->kingside_storm_value(BLACK);
420 else if ( square_file(pos.king_square(WHITE)) <= FILE_D
421 && square_file(pos.king_square(BLACK)) >= FILE_E)
423 ei.mgValue += ei.pi->kingside_storm_value(WHITE)
424 - ei.pi->queenside_storm_value(BLACK);
426 // Evaluate space for both sides
427 if (ei.mi->space_weight() > 0)
429 evaluate_space(pos, WHITE, ei);
430 evaluate_space(pos, BLACK, ei);
435 ei.mgValue += apply_weight(ei.mgMobility, WeightMobilityMidgame);
436 ei.egValue += apply_weight(ei.egMobility, WeightMobilityEndgame);
438 // If we don't already have an unusual scale factor, check for opposite
439 // colored bishop endgames, and use a lower scale for those
440 if ( phase < PHASE_MIDGAME
441 && pos.opposite_colored_bishops()
442 && ( (factor[WHITE] == SCALE_FACTOR_NORMAL && ei.egValue > Value(0))
443 || (factor[BLACK] == SCALE_FACTOR_NORMAL && ei.egValue < Value(0))))
447 // Only the two bishops ?
448 if ( pos.non_pawn_material(WHITE) == BishopValueMidgame
449 && pos.non_pawn_material(BLACK) == BishopValueMidgame)
451 // Check for KBP vs KB with only a single pawn that is almost
452 // certainly a draw or at least two pawns.
453 bool one_pawn = (pos.piece_count(WHITE, PAWN) + pos.piece_count(BLACK, PAWN) == 1);
454 sf = one_pawn ? ScaleFactor(8) : ScaleFactor(32);
457 // Endgame with opposite-colored bishops, but also other pieces. Still
458 // a bit drawish, but not as drawish as with only the two bishops.
459 sf = ScaleFactor(50);
461 if (factor[WHITE] == SCALE_FACTOR_NORMAL)
463 if (factor[BLACK] == SCALE_FACTOR_NORMAL)
467 // Interpolate between the middle game and the endgame score, and
469 Color stm = pos.side_to_move();
471 Value v = Sign[stm] * scale_by_game_phase(ei.mgValue, ei.egValue, phase, factor);
473 return (ei.mateThreat[stm] == MOVE_NONE ? v : 8 * QueenValueMidgame - v);
477 /// quick_evaluate() does a very approximate evaluation of the current position.
478 /// It currently considers only material and piece square table scores. Perhaps
479 /// we should add scores from the pawn and material hash tables?
481 Value quick_evaluate(const Position &pos) {
486 ScaleFactor sf[2] = {SCALE_FACTOR_NORMAL, SCALE_FACTOR_NORMAL};
488 Value mgv = pos.mg_value();
489 Value egv = pos.eg_value();
490 Phase ph = pos.game_phase();
491 Color stm = pos.side_to_move();
493 return Sign[stm] * scale_by_game_phase(mgv, egv, ph, sf);
497 /// init_eval() initializes various tables used by the evaluation function.
499 void init_eval(int threads) {
501 assert(threads <= THREAD_MAX);
503 for (int i = 0; i < THREAD_MAX; i++)
508 delete MaterialTable[i];
510 MaterialTable[i] = NULL;
514 PawnTable[i] = new PawnInfoTable(PawnTableSize);
515 if (!MaterialTable[i])
516 MaterialTable[i] = new MaterialInfoTable(MaterialTableSize);
519 for (Bitboard b = 0ULL; b < 256ULL; b++)
520 BitCount8Bit[b] = count_1s(b);
524 /// quit_eval() releases heap-allocated memory at program termination.
528 for (int i = 0; i < THREAD_MAX; i++)
531 delete MaterialTable[i];
536 /// read_weights() reads evaluation weights from the corresponding UCI
539 void read_weights(Color us) {
541 WeightMobilityMidgame = weight_option("Mobility (Middle Game)", WeightMobilityMidgameInternal);
542 WeightMobilityEndgame = weight_option("Mobility (Endgame)", WeightMobilityEndgameInternal);
543 WeightPawnStructureMidgame = weight_option("Pawn Structure (Middle Game)", WeightPawnStructureMidgameInternal);
544 WeightPawnStructureEndgame = weight_option("Pawn Structure (Endgame)", WeightPawnStructureEndgameInternal);
545 WeightPassedPawnsMidgame = weight_option("Passed Pawns (Middle Game)", WeightPassedPawnsMidgameInternal);
546 WeightPassedPawnsEndgame = weight_option("Passed Pawns (Endgame)", WeightPassedPawnsEndgameInternal);
548 Color them = opposite_color(us);
550 WeightKingSafety[us] = weight_option("Cowardice", WeightKingSafetyInternal);
551 WeightKingSafety[them] = weight_option("Aggressiveness", WeightKingOppSafetyInternal);
552 WeightSpace = weight_option("Space", WeightSpaceInternal);
560 // evaluate_common() computes terms common to all pieces attack
562 int evaluate_common(const Position&p, const Bitboard& b, Color us, EvalInfo& ei,
563 int AttackWeight, const Value* mgBonus, const Value* egBonus,
564 Square s = SQ_NONE, const Value* OutpostBonus = NULL) {
566 Color them = opposite_color(us);
569 if (b & ei.kingZone[us])
571 ei.kingAttackersCount[us]++;
572 ei.kingAttackersWeight[us] += AttackWeight;
573 Bitboard bb = (b & ei.attackedBy[them][KING]);
575 ei.kingAdjacentZoneAttacksCount[us] += count_1s_max_15(bb);
578 // Remove squares protected by enemy pawns
579 Bitboard bb = (b & ~ei.attackedBy[them][PAWN]);
582 int mob = count_1s_max_15(bb & ~p.pieces_of_color(us));
583 ei.mgMobility += Sign[us] * mgBonus[mob];
584 ei.egMobility += Sign[us] * egBonus[mob];
586 // Bishop and Knight outposts
587 if (!OutpostBonus || !p.square_is_weak(s, them))
590 // Initial bonus based on square
592 v = bonus = OutpostBonus[relative_square(us, s)];
594 // Increase bonus if supported by pawn, especially if the opponent has
595 // no minor piece which can exchange the outpost piece
596 if (v && (p.pawn_attacks(them, s) & p.pawns(us)))
599 if ( p.piece_count(them, KNIGHT) == 0
600 && (SquaresByColorBB[square_color(s)] & p.bishops(them)) == EmptyBoardBB)
603 ei.mgValue += Sign[us] * bonus;
604 ei.egValue += Sign[us] * bonus;
609 // evaluate_knight() assigns bonuses and penalties to a knight of a given
610 // color on a given square.
612 void evaluate_knight(const Position &p, Square s, Color us, EvalInfo &ei) {
614 Bitboard b = p.piece_attacks<KNIGHT>(s);
615 ei.attackedBy[us][KNIGHT] |= b;
617 // King attack, mobility and outposts
618 evaluate_common(p, b, us, ei, KnightAttackWeight, MidgameKnightMobilityBonus,
619 EndgameKnightMobilityBonus, s, KnightOutpostBonus);
623 // evaluate_bishop() assigns bonuses and penalties to a bishop of a given
624 // color on a given square.
626 void evaluate_bishop(const Position &p, Square s, Color us, EvalInfo &ei) {
628 Bitboard b = bishop_attacks_bb(s, p.occupied_squares() & ~p.queens(us));
629 ei.attackedBy[us][BISHOP] |= b;
631 // King attack, mobility and outposts
632 evaluate_common(p, b, us, ei, BishopAttackWeight, MidgameBishopMobilityBonus,
633 EndgameBishopMobilityBonus, s, BishopOutpostBonus);
637 // evaluate_rook() assigns bonuses and penalties to a rook of a given
638 // color on a given square.
640 void evaluate_rook(const Position &p, Square s, Color us, EvalInfo &ei) {
642 Bitboard b = rook_attacks_bb(s, p.occupied_squares() & ~p.rooks_and_queens(us));
643 ei.attackedBy[us][ROOK] |= b;
645 // King attack and mobility
646 int mob = evaluate_common(p, b, us, ei, RookAttackWeight, MidgameRookMobilityBonus,
647 EndgameRookMobilityBonus);
650 Color them = opposite_color(us);
652 if ( relative_rank(us, s) == RANK_7
653 && relative_rank(us, p.king_square(them)) == RANK_8)
655 ei.mgValue += Sign[us] * MidgameRookOn7thBonus;
656 ei.egValue += Sign[us] * EndgameRookOn7thBonus;
659 // Open and half-open files
660 File f = square_file(s);
661 if (ei.pi->file_is_half_open(us, f))
663 if (ei.pi->file_is_half_open(them, f))
665 ei.mgValue += Sign[us] * RookOpenFileBonus;
666 ei.egValue += Sign[us] * RookOpenFileBonus;
670 ei.mgValue += Sign[us] * RookHalfOpenFileBonus;
671 ei.egValue += Sign[us] * RookHalfOpenFileBonus;
675 // Penalize rooks which are trapped inside a king. Penalize more if
676 // king has lost right to castle
677 if (mob > 6 || ei.pi->file_is_half_open(us, f))
680 Square ksq = p.king_square(us);
682 if ( square_file(ksq) >= FILE_E
683 && square_file(s) > square_file(ksq)
684 && (relative_rank(us, ksq) == RANK_1 || square_rank(ksq) == square_rank(s)))
686 // Is there a half-open file between the king and the edge of the board?
687 if (!ei.pi->has_open_file_to_right(us, square_file(ksq)))
688 ei.mgValue -= p.can_castle(us)? Sign[us] * ((TrappedRookPenalty - mob * 16) / 2)
689 : Sign[us] * (TrappedRookPenalty - mob * 16);
691 else if ( square_file(ksq) <= FILE_D
692 && square_file(s) < square_file(ksq)
693 && (relative_rank(us, ksq) == RANK_1 || square_rank(ksq) == square_rank(s)))
695 // Is there a half-open file between the king and the edge of the board?
696 if (!ei.pi->has_open_file_to_left(us, square_file(ksq)))
697 ei.mgValue -= p.can_castle(us)? Sign[us] * ((TrappedRookPenalty - mob * 16) / 2)
698 : Sign[us] * (TrappedRookPenalty - mob * 16);
703 // evaluate_queen() assigns bonuses and penalties to a queen of a given
704 // color on a given square.
706 void evaluate_queen(const Position &p, Square s, Color us, EvalInfo &ei) {
708 Bitboard b = p.piece_attacks<QUEEN>(s);
709 ei.attackedBy[us][QUEEN] |= b;
711 // King attack and mobility
712 evaluate_common(p, b, us, ei, QueenAttackWeight, MidgameQueenMobilityBonus,
713 EndgameQueenMobilityBonus);
716 Color them = opposite_color(us);
718 if ( relative_rank(us, s) == RANK_7
719 && relative_rank(us, p.king_square(them)) == RANK_8)
721 ei.mgValue += Sign[us] * MidgameQueenOn7thBonus;
722 ei.egValue += Sign[us] * EndgameQueenOn7thBonus;
726 inline Bitboard shiftRowsDown(const Bitboard& b, int num) {
728 return b >> (num << 3);
731 // evaluate_king() assigns bonuses and penalties to a king of a given
732 // color on a given square.
734 void evaluate_king(const Position &p, Square s, Color us, EvalInfo &ei) {
736 int shelter = 0, sign = Sign[us];
739 if (relative_rank(us, s) <= RANK_4)
741 Bitboard pawns = p.pawns(us) & this_and_neighboring_files_bb(s);
742 Rank r = square_rank(s);
743 for (int i = 1; i < 4; i++)
744 shelter += count_1s_8bit(shiftRowsDown(pawns, r+i*sign)) * (128>>i);
746 ei.mgValue += sign * Value(shelter);
749 // King safety. This is quite complicated, and is almost certainly far
750 // from optimally tuned.
751 Color them = opposite_color(us);
753 if ( p.piece_count(them, QUEEN) >= 1
754 && ei.kingAttackersCount[them] >= 2
755 && p.non_pawn_material(them) >= QueenValueMidgame + RookValueMidgame
756 && ei.kingAdjacentZoneAttacksCount[them])
758 // Is it the attackers turn to move?
759 bool sente = (them == p.side_to_move());
761 // Find the attacked squares around the king which has no defenders
762 // apart from the king itself
763 Bitboard undefended =
764 ei.attacked_by(them) & ~ei.attacked_by(us, PAWN)
765 & ~ei.attacked_by(us, KNIGHT) & ~ei.attacked_by(us, BISHOP)
766 & ~ei.attacked_by(us, ROOK) & ~ei.attacked_by(us, QUEEN)
767 & ei.attacked_by(us, KING);
769 Bitboard occ = p.occupied_squares(), b, b2;
771 // Initialize the 'attackUnits' variable, which is used later on as an
772 // index to the SafetyTable[] array. The initial value is based on the
773 // number and types of the attacking pieces, the number of attacked and
774 // undefended squares around the king, the square of the king, and the
775 // quality of the pawn shelter.
777 Min((ei.kingAttackersCount[them] * ei.kingAttackersWeight[them]) / 2, 25)
778 + (ei.kingAdjacentZoneAttacksCount[them] + count_1s_max_15(undefended)) * 3
779 + InitKingDanger[relative_square(us, s)] - (shelter >> 5);
781 // Analyse safe queen contact checks
782 b = undefended & ei.attacked_by(them, QUEEN) & ~p.pieces_of_color(them);
785 Bitboard attackedByOthers =
786 ei.attacked_by(them, PAWN) | ei.attacked_by(them, KNIGHT)
787 | ei.attacked_by(them, BISHOP) | ei.attacked_by(them, ROOK);
789 b &= attackedByOthers;
792 // The bitboard b now contains the squares available for safe queen
794 int count = count_1s_max_15(b);
795 attackUnits += QueenContactCheckBonus * count * (sente ? 2 : 1);
797 // Is there a mate threat?
798 if (QueenContactMates && !p.is_check())
800 Bitboard escapeSquares =
801 p.piece_attacks<KING>(s) & ~p.pieces_of_color(us) & ~attackedByOthers;
805 Square from, to = pop_1st_bit(&b);
806 if (!(escapeSquares & ~queen_attacks_bb(to, occ & ClearMaskBB[s])))
808 // We have a mate, unless the queen is pinned or there
809 // is an X-ray attack through the queen.
810 for (int i = 0; i < p.piece_count(them, QUEEN); i++)
812 from = p.piece_list(them, QUEEN, i);
813 if ( bit_is_set(p.piece_attacks<QUEEN>(from), to)
814 && !bit_is_set(p.pinned_pieces(them), from)
815 && !(rook_attacks_bb(to, occ & ClearMaskBB[from]) & p.rooks_and_queens(us))
816 && !(rook_attacks_bb(to, occ & ClearMaskBB[from]) & p.rooks_and_queens(us)))
818 ei.mateThreat[them] = make_move(from, to);
826 // Analyse safe distance checks
827 if (QueenCheckBonus > 0 || RookCheckBonus > 0)
829 b = p.piece_attacks<ROOK>(s) & ~p.pieces_of_color(them) & ~ei.attacked_by(us);
832 b2 = b & ei.attacked_by(them, QUEEN);
834 attackUnits += QueenCheckBonus * count_1s_max_15(b2);
837 b2 = b & ei.attacked_by(them, ROOK);
839 attackUnits += RookCheckBonus * count_1s_max_15(b2);
841 if (QueenCheckBonus > 0 || BishopCheckBonus > 0)
843 b = p.piece_attacks<BISHOP>(s) & ~p.pieces_of_color(them) & ~ei.attacked_by(us);
846 b2 = b & ei.attacked_by(them, QUEEN);
848 attackUnits += QueenCheckBonus * count_1s_max_15(b2);
851 b2 = b & ei.attacked_by(them, BISHOP);
853 attackUnits += BishopCheckBonus * count_1s_max_15(b2);
855 if (KnightCheckBonus > 0)
857 b = p.piece_attacks<KNIGHT>(s) & ~p.pieces_of_color(them) & ~ei.attacked_by(us);
860 b2 = b & ei.attacked_by(them, KNIGHT);
862 attackUnits += KnightCheckBonus * count_1s_max_15(b2);
865 // Analyse discovered checks (only for non-pawns right now, consider
866 // adding pawns later).
867 if (DiscoveredCheckBonus)
869 b = p.discovered_check_candidates(them) & ~p.pawns();
871 attackUnits += DiscoveredCheckBonus * count_1s_max_15(b) * (sente? 2 : 1);
874 // Has a mate threat been found? We don't do anything here if the
875 // side with the mating move is the side to move, because in that
876 // case the mating side will get a huge bonus at the end of the main
877 // evaluation function instead.
878 if (ei.mateThreat[them] != MOVE_NONE)
879 attackUnits += MateThreatBonus;
881 // Ensure that attackUnits is between 0 and 99, in order to avoid array
882 // out of bounds errors:
886 if (attackUnits >= 100)
889 // Finally, extract the king safety score from the SafetyTable[] array.
890 // Add the score to the evaluation, and also to ei.futilityMargin. The
891 // reason for adding the king safety score to the futility margin is
892 // that the king safety scores can sometimes be very big, and that
893 // capturing a single attacking piece can therefore result in a score
894 // change far bigger than the value of the captured piece.
895 Value v = apply_weight(SafetyTable[attackUnits], WeightKingSafety[us]);
897 ei.mgValue -= sign * v;
899 if (us == p.side_to_move())
900 ei.futilityMargin += v;
905 // evaluate_passed_pawns() evaluates the passed pawns for both sides.
907 void evaluate_passed_pawns(const Position &pos, EvalInfo &ei) {
909 bool hasUnstoppable[2] = {false, false};
910 int movesToGo[2] = {100, 100};
912 for (Color us = WHITE; us <= BLACK; us++)
914 Color them = opposite_color(us);
915 Square ourKingSq = pos.king_square(us);
916 Square theirKingSq = pos.king_square(them);
917 Bitboard b = ei.pi->passed_pawns() & pos.pawns(us), b2, b3, b4;
921 Square s = pop_1st_bit(&b);
923 assert(pos.piece_on(s) == pawn_of_color(us));
924 assert(pos.pawn_is_passed(us, s));
926 int r = int(relative_rank(us, s) - RANK_2);
927 int tr = Max(0, r * (r - 1));
928 Square blockSq = s + pawn_push(us);
930 // Base bonus based on rank
931 Value mbonus = Value(20 * tr);
932 Value ebonus = Value(10 + r * r * 10);
934 // Adjust bonus based on king proximity
935 ebonus -= Value(square_distance(ourKingSq, blockSq) * 3 * tr);
936 ebonus -= Value(square_distance(ourKingSq, blockSq + pawn_push(us)) * 1 * tr);
937 ebonus += Value(square_distance(theirKingSq, blockSq) * 6 * tr);
939 // If the pawn is free to advance, increase bonus
940 if (tr != 0 && pos.square_is_empty(blockSq))
942 b2 = squares_in_front_of(us, s);
943 b3 = b2 & ei.attacked_by(them);
944 b4 = b2 & ei.attacked_by(us);
946 // If there is an enemy rook or queen attacking the pawn from behind,
947 // add all X-ray attacks by the rook or queen.
948 if ( bit_is_set(ei.attacked_by(them,ROOK) | ei.attacked_by(them,QUEEN),s)
949 && (squares_behind(us, s) & pos.rooks_and_queens(them)))
952 if ((b2 & pos.pieces_of_color(them)) == EmptyBoardBB)
954 // There are no enemy pieces in the pawn's path! Are any of the
955 // squares in the pawn's path attacked by the enemy?
956 if (b3 == EmptyBoardBB)
957 // No enemy attacks, huge bonus!
958 ebonus += Value(tr * (b2 == b4 ? 17 : 15));
960 // OK, there are enemy attacks. Are those squares which are
961 // attacked by the enemy also attacked by us? If yes, big bonus
962 // (but smaller than when there are no enemy attacks), if no,
963 // somewhat smaller bonus.
964 ebonus += Value(tr * ((b3 & b4) == b3 ? 13 : 8));
968 // There are some enemy pieces in the pawn's path. While this is
969 // sad, we still assign a moderate bonus if all squares in the path
970 // which are either occupied by or attacked by enemy pieces are
971 // also attacked by us.
972 if (((b3 | (b2 & pos.pieces_of_color(them))) & ~b4) == EmptyBoardBB)
973 ebonus += Value(tr * 6);
975 // At last, add a small bonus when there are no *friendly* pieces
976 // in the pawn's path.
977 if ((b2 & pos.pieces_of_color(us)) == EmptyBoardBB)
981 // If the pawn is supported by a friendly pawn, increase bonus
982 b2 = pos.pawns(us) & neighboring_files_bb(s);
984 ebonus += Value(r * 20);
985 else if (pos.pawn_attacks(them, s) & b2)
986 ebonus += Value(r * 12);
988 // If the other side has only a king, check whether the pawn is
990 if (pos.non_pawn_material(them) == Value(0))
995 qsq = relative_square(us, make_square(square_file(s), RANK_8));
996 d = square_distance(s, qsq)
997 - square_distance(theirKingSq, qsq)
998 + (us != pos.side_to_move());
1002 int mtg = RANK_8 - relative_rank(us, s);
1003 int blockerCount = count_1s_max_15(squares_in_front_of(us,s) & pos.occupied_squares());
1004 mtg += blockerCount;
1008 hasUnstoppable[us] = true;
1009 movesToGo[us] = Min(movesToGo[us], mtg);
1013 // Rook pawns are a special case: They are sometimes worse, and
1014 // sometimes better than other passed pawns. It is difficult to find
1015 // good rules for determining whether they are good or bad. For now,
1016 // we try the following: Increase the value for rook pawns if the
1017 // other side has no pieces apart from a knight, and decrease the
1018 // value if the other side has a rook or queen.
1019 if (square_file(s) == FILE_A || square_file(s) == FILE_H)
1021 if( pos.non_pawn_material(them) <= KnightValueMidgame
1022 && pos.piece_count(them, KNIGHT) <= 1)
1023 ebonus += ebonus / 4;
1024 else if(pos.rooks_and_queens(them))
1025 ebonus -= ebonus / 4;
1028 // Add the scores for this pawn to the middle game and endgame eval.
1029 ei.mgValue += apply_weight(Sign[us] * mbonus, WeightPassedPawnsMidgame);
1030 ei.egValue += apply_weight(Sign[us] * ebonus, WeightPassedPawnsEndgame);
1034 // Does either side have an unstoppable passed pawn?
1035 if (hasUnstoppable[WHITE] && !hasUnstoppable[BLACK])
1036 ei.egValue += UnstoppablePawnValue - Value(0x40 * movesToGo[WHITE]);
1037 else if (hasUnstoppable[BLACK] && !hasUnstoppable[WHITE])
1038 ei.egValue -= UnstoppablePawnValue - Value(0x40 * movesToGo[BLACK]);
1039 else if (hasUnstoppable[BLACK] && hasUnstoppable[WHITE])
1041 // Both sides have unstoppable pawns! Try to find out who queens
1042 // first. We begin by transforming 'movesToGo' to the number of
1043 // plies until the pawn queens for both sides.
1044 movesToGo[WHITE] *= 2;
1045 movesToGo[BLACK] *= 2;
1046 movesToGo[pos.side_to_move()]--;
1048 // If one side queens at least three plies before the other, that
1050 if (movesToGo[WHITE] <= movesToGo[BLACK] - 3)
1051 ei.egValue += UnstoppablePawnValue - Value(0x40 * (movesToGo[WHITE]/2));
1052 else if(movesToGo[BLACK] <= movesToGo[WHITE] - 3)
1053 ei.egValue -= UnstoppablePawnValue - Value(0x40 * (movesToGo[BLACK]/2));
1055 // We could also add some rules about the situation when one side
1056 // queens exactly one ply before the other: Does the first queen
1057 // check the opponent's king, or attack the opponent's queening square?
1058 // This is slightly tricky to get right, because it is possible that
1059 // the opponent's king has moved somewhere before the first pawn queens.
1064 // evaluate_trapped_bishop_a7h7() determines whether a bishop on a7/h7
1065 // (a2/h2 for black) is trapped by enemy pawns, and assigns a penalty
1068 void evaluate_trapped_bishop_a7h7(const Position &pos, Square s, Color us,
1070 assert(square_is_ok(s));
1071 assert(pos.piece_on(s) == bishop_of_color(us));
1073 Square b6 = relative_square(us, (square_file(s) == FILE_A) ? SQ_B6 : SQ_G6);
1074 Square b8 = relative_square(us, (square_file(s) == FILE_A) ? SQ_B8 : SQ_G8);
1076 if ( pos.piece_on(b6) == pawn_of_color(opposite_color(us))
1077 && pos.see(s, b6) < 0
1078 && pos.see(s, b8) < 0)
1080 ei.mgValue -= Sign[us] * TrappedBishopA7H7Penalty;
1081 ei.egValue -= Sign[us] * TrappedBishopA7H7Penalty;
1086 // evaluate_trapped_bishop_a1h1() determines whether a bishop on a1/h1
1087 // (a8/h8 for black) is trapped by a friendly pawn on b2/g2 (b7/g7 for
1088 // black), and assigns a penalty if it is. This pattern can obviously
1089 // only occur in Chess960 games.
1091 void evaluate_trapped_bishop_a1h1(const Position &pos, Square s, Color us,
1093 Piece pawn = pawn_of_color(us);
1097 assert(square_is_ok(s));
1098 assert(pos.piece_on(s) == bishop_of_color(us));
1100 if (square_file(s) == FILE_A)
1102 b2 = relative_square(us, SQ_B2);
1103 b3 = relative_square(us, SQ_B3);
1104 c3 = relative_square(us, SQ_C3);
1108 b2 = relative_square(us, SQ_G2);
1109 b3 = relative_square(us, SQ_G3);
1110 c3 = relative_square(us, SQ_F3);
1113 if (pos.piece_on(b2) == pawn)
1117 if (!pos.square_is_empty(b3))
1118 penalty = 2*TrappedBishopA1H1Penalty;
1119 else if (pos.piece_on(c3) == pawn)
1120 penalty = TrappedBishopA1H1Penalty;
1122 penalty = TrappedBishopA1H1Penalty / 2;
1124 ei.mgValue -= Sign[us] * penalty;
1125 ei.egValue -= Sign[us] * penalty;
1130 // evaluate_space() computes the space evaluation for a given side. The
1131 // space evaluation is a simple bonus based on the number of safe squares
1132 // available for minor pieces on the central four files on ranks 2--4. Safe
1133 // squares one, two or three squares behind a friendly pawn are counted
1134 // twice. Finally, the space bonus is scaled by a weight taken from the
1135 // material hash table.
1137 void evaluate_space(const Position &pos, Color us, EvalInfo &ei) {
1139 Color them = opposite_color(us);
1141 // Find the safe squares for our pieces inside the area defined by
1142 // SpaceMask[us]. A square is unsafe it is attacked by an enemy
1143 // pawn, or if it is undefended and attacked by an enemy piece.
1145 Bitboard safeSquares = SpaceMask[us]
1147 & ~ei.attacked_by(them, PAWN)
1148 & ~(~ei.attacked_by(us) & ei.attacked_by(them));
1150 // Find all squares which are at most three squares behind some friendly
1152 Bitboard behindFriendlyPawns = pos.pawns(us);
1155 behindFriendlyPawns |= (behindFriendlyPawns >> 8);
1156 behindFriendlyPawns |= (behindFriendlyPawns >> 16);
1160 behindFriendlyPawns |= (behindFriendlyPawns << 8);
1161 behindFriendlyPawns |= (behindFriendlyPawns << 16);
1164 int space = count_1s_max_15(safeSquares)
1165 + count_1s_max_15(behindFriendlyPawns & safeSquares);
1167 ei.mgValue += Sign[us] * apply_weight(Value(space * ei.mi->space_weight()), WeightSpace);
1171 // apply_weight() applies an evaluation weight to a value
1173 inline Value apply_weight(Value v, int w) {
1174 return (v*w) / 0x100;
1178 // scale_by_game_phase() interpolates between a middle game and an endgame
1179 // score, based on game phase. It also scales the return value by a
1180 // ScaleFactor array.
1182 Value scale_by_game_phase(Value mv, Value ev, Phase ph, const ScaleFactor sf[]) {
1184 assert(mv > -VALUE_INFINITE && mv < VALUE_INFINITE);
1185 assert(ev > -VALUE_INFINITE && ev < VALUE_INFINITE);
1186 assert(ph >= PHASE_ENDGAME && ph <= PHASE_MIDGAME);
1188 ev = apply_scale_factor(ev, sf[(ev > Value(0) ? WHITE : BLACK)]);
1190 Value result = Value(int((mv * ph + ev * (128 - ph)) / 128));
1191 return Value(int(result) & ~(GrainSize - 1));
1195 // count_1s_8bit() counts the number of nonzero bits in the 8 least
1196 // significant bits of a Bitboard. This function is used by the king
1197 // shield evaluation.
1199 int count_1s_8bit(Bitboard b) {
1200 return int(BitCount8Bit[b & 0xFF]);
1204 // compute_weight() computes the value of an evaluation weight, by combining
1205 // an UCI-configurable weight with an internal weight.
1207 int compute_weight(int uciWeight, int internalWeight) {
1209 uciWeight = (uciWeight * 0x100) / 100;
1210 return (uciWeight * internalWeight) / 0x100;
1214 // helper used in read_weights()
1215 int weight_option(const std::string& opt, int weight) {
1217 return compute_weight(get_option_value_int(opt), weight);
1221 // init_safety() initizes the king safety evaluation, based on UCI
1222 // parameters. It is called from read_weights().
1224 void init_safety() {
1226 QueenContactCheckBonus = get_option_value_int("Queen Contact Check Bonus");
1227 QueenCheckBonus = get_option_value_int("Queen Check Bonus");
1228 RookCheckBonus = get_option_value_int("Rook Check Bonus");
1229 BishopCheckBonus = get_option_value_int("Bishop Check Bonus");
1230 KnightCheckBonus = get_option_value_int("Knight Check Bonus");
1231 DiscoveredCheckBonus = get_option_value_int("Discovered Check Bonus");
1232 MateThreatBonus = get_option_value_int("Mate Threat Bonus");
1234 int maxSlope = get_option_value_int("King Safety Max Slope");
1235 int peak = get_option_value_int("King Safety Max Value") * 256 / 100;
1236 double a = get_option_value_int("King Safety Coefficient") / 100.0;
1237 double b = get_option_value_int("King Safety X Intercept");
1238 bool quad = (get_option_value_string("King Safety Curve") == "Quadratic");
1239 bool linear = (get_option_value_string("King Safety Curve") == "Linear");
1241 for (int i = 0; i < 100; i++)
1244 SafetyTable[i] = Value(0);
1246 SafetyTable[i] = Value((int)(a * (i - b) * (i - b)));
1248 SafetyTable[i] = Value((int)(100 * a * (i - b)));
1251 for (int i = 0; i < 100; i++)
1253 if (SafetyTable[i+1] - SafetyTable[i] > maxSlope)
1254 for (int j = i + 1; j < 100; j++)
1255 SafetyTable[j] = SafetyTable[j-1] + Value(maxSlope);
1257 if (SafetyTable[i] > Value(peak))
1258 SafetyTable[i] = Value(peak);