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
5 Copyright (C) 2015-2018 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
7 Stockfish is free software: you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation, either version 3 of the License, or
10 (at your option) any later version.
12 Stockfish is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <http://www.gnu.org/licenses/>.
23 #include <cstring> // For std::memset
34 const Bitboard Center = (FileDBB | FileEBB) & (Rank4BB | Rank5BB);
35 const Bitboard QueenSide = FileABB | FileBBB | FileCBB | FileDBB;
36 const Bitboard CenterFiles = FileCBB | FileDBB | FileEBB | FileFBB;
37 const Bitboard KingSide = FileEBB | FileFBB | FileGBB | FileHBB;
39 const Bitboard KingFlank[FILE_NB] = {
40 QueenSide, QueenSide, QueenSide, CenterFiles, CenterFiles, KingSide, KingSide, KingSide
45 enum Tracing {NO_TRACE, TRACE};
47 enum Term { // The first 8 entries are for PieceType
48 MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, INITIATIVE, TOTAL, TERM_NB
51 double scores[TERM_NB][COLOR_NB][PHASE_NB];
53 double to_cp(Value v) { return double(v) / PawnValueEg; }
55 void add(int idx, Color c, Score s) {
56 scores[idx][c][MG] = to_cp(mg_value(s));
57 scores[idx][c][EG] = to_cp(eg_value(s));
60 void add(int idx, Score w, Score b = SCORE_ZERO) {
61 add(idx, WHITE, w); add(idx, BLACK, b);
64 std::ostream& operator<<(std::ostream& os, Term t) {
66 if (t == MATERIAL || t == IMBALANCE || t == Term(PAWN) || t == INITIATIVE || t == TOTAL)
67 os << " --- --- | --- --- | ";
69 os << std::setw(5) << scores[t][WHITE][MG] << " "
70 << std::setw(5) << scores[t][WHITE][EG] << " | "
71 << std::setw(5) << scores[t][BLACK][MG] << " "
72 << std::setw(5) << scores[t][BLACK][EG] << " | ";
74 os << std::setw(5) << scores[t][WHITE][MG] - scores[t][BLACK][MG] << " "
75 << std::setw(5) << scores[t][WHITE][EG] - scores[t][BLACK][EG] << " \n";
81 using namespace Trace;
83 // Evaluation class contains various information computed and collected
84 // by the evaluation functions.
85 template<Tracing T = NO_TRACE>
89 Evaluation() = delete;
90 Evaluation(const Position& p) : pos(p) {}
91 Evaluation& operator=(const Evaluation&) = delete;
96 // Evaluation helpers (used when calling value())
97 template<Color Us> void initialize();
98 template<Color Us> Score evaluate_king();
99 template<Color Us> Score evaluate_threats();
100 template<Color Us> Score evaluate_passed_pawns();
101 template<Color Us> Score evaluate_space();
102 template<Color Us, PieceType Pt> Score evaluate_pieces();
103 ScaleFactor evaluate_scale_factor(Value eg);
104 Score evaluate_initiative(Value eg);
110 Bitboard mobilityArea[COLOR_NB];
111 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
113 // attackedBy[color][piece type] is a bitboard representing all squares
114 // attacked by a given color and piece type. Special "piece types" which are
115 // also calculated are QUEEN_DIAGONAL and ALL_PIECES.
116 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
118 // attackedBy2[color] are the squares attacked by 2 pieces of a given color,
119 // possibly via x-ray or by one pawn and one piece. Diagonal x-ray through
120 // pawn or squares attacked by 2 pawns are not explicitly added.
121 Bitboard attackedBy2[COLOR_NB];
123 // kingRing[color] is the zone around the king which is considered
124 // by the king safety evaluation. This consists of the squares directly
125 // adjacent to the king, and (only for a king on its first rank) the
126 // squares two ranks in front of the king. For instance, if black's king
127 // is on g8, kingRing[BLACK] is a bitboard containing the squares f8, h8,
128 // f7, g7, h7, f6, g6 and h6.
129 Bitboard kingRing[COLOR_NB];
131 // kingAttackersCount[color] is the number of pieces of the given color
132 // which attack a square in the kingRing of the enemy king.
133 int kingAttackersCount[COLOR_NB];
135 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of the
136 // given color which attack a square in the kingRing of the enemy king. The
137 // weights of the individual piece types are given by the elements in the
138 // KingAttackWeights array.
139 int kingAttackersWeight[COLOR_NB];
141 // kingAdjacentZoneAttacksCount[color] is the number of attacks by the given
142 // color to squares directly adjacent to the enemy king. Pieces which attack
143 // more than one square are counted multiple times. For instance, if there is
144 // a white knight on g5 and black's king is on g8, this white knight adds 2
145 // to kingAdjacentZoneAttacksCount[WHITE].
146 int kingAdjacentZoneAttacksCount[COLOR_NB];
149 #define V(v) Value(v)
150 #define S(mg, eg) make_score(mg, eg)
152 // MobilityBonus[PieceType-2][attacked] contains bonuses for middle and end game,
153 // indexed by piece type and number of attacked squares in the mobility area.
154 const Score MobilityBonus[][32] = {
155 { S(-75,-76), S(-57,-54), S( -9,-28), S( -2,-10), S( 6, 5), S( 14, 12), // Knights
156 S( 22, 26), S( 29, 29), S( 36, 29) },
157 { S(-48,-59), S(-20,-23), S( 16, -3), S( 26, 13), S( 38, 24), S( 51, 42), // Bishops
158 S( 55, 54), S( 63, 57), S( 63, 65), S( 68, 73), S( 81, 78), S( 81, 86),
159 S( 91, 88), S( 98, 97) },
160 { S(-58,-76), S(-27,-18), S(-15, 28), S(-10, 55), S( -5, 69), S( -2, 82), // Rooks
161 S( 9,112), S( 16,118), S( 30,132), S( 29,142), S( 32,155), S( 38,165),
162 S( 46,166), S( 48,169), S( 58,171) },
163 { S(-39,-36), S(-21,-15), S( 3, 8), S( 3, 18), S( 14, 34), S( 22, 54), // Queens
164 S( 28, 61), S( 41, 73), S( 43, 79), S( 48, 92), S( 56, 94), S( 60,104),
165 S( 60,113), S( 66,120), S( 67,123), S( 70,126), S( 71,133), S( 73,136),
166 S( 79,140), S( 88,143), S( 88,148), S( 99,166), S(102,170), S(102,175),
167 S(106,184), S(109,191), S(113,206), S(116,212) }
170 // Outpost[knight/bishop][supported by pawn] contains bonuses for minor
171 // pieces if they can reach an outpost square, bigger if that square is
172 // supported by a pawn. If the minor piece occupies an outpost square
173 // then score is doubled.
174 const Score Outpost[][2] = {
175 { S(22, 6), S(36,12) }, // Knight
176 { S( 9, 2), S(15, 5) } // Bishop
179 // RookOnFile[semiopen/open] contains bonuses for each rook when there is no
180 // friendly pawn on the rook file.
181 const Score RookOnFile[] = { S(20, 7), S(45, 20) };
183 // ThreatByMinor/ByRook[attacked PieceType] contains bonuses according to
184 // which piece type attacks which one. Attacks on lesser pieces which are
185 // pawn-defended are not considered.
186 const Score ThreatByMinor[PIECE_TYPE_NB] = {
187 S(0, 0), S(0, 33), S(45, 43), S(46, 47), S(72, 107), S(48, 118)
190 const Score ThreatByRook[PIECE_TYPE_NB] = {
191 S(0, 0), S(0, 25), S(40, 62), S(40, 59), S(0, 34), S(35, 48)
194 // ThreatByKing[on one/on many] contains bonuses for king attacks on
195 // pawns or pieces which are not pawn-defended.
196 const Score ThreatByKing[] = { S(3, 62), S(9, 138) };
198 // Passed[mg/eg][Rank] contains midgame and endgame bonuses for passed pawns.
199 // We don't use a Score because we process the two components independently.
200 const Value Passed[][RANK_NB] = {
201 { V(5), V( 5), V(31), V(73), V(166), V(252) },
202 { V(7), V(14), V(38), V(73), V(166), V(252) }
205 // PassedFile[File] contains a bonus according to the file of a passed pawn
206 const Score PassedFile[FILE_NB] = {
207 S( 9, 10), S( 2, 10), S( 1, -8), S(-20,-12),
208 S(-20,-12), S( 1, -8), S( 2, 10), S( 9, 10)
211 // KingProtector[PieceType-2] contains a bonus according to distance from king
212 const Score KingProtector[] = { S(-3, -5), S(-4, -3), S(-3, 0), S(-1, 1) };
214 // Assorted bonuses and penalties used by evaluation
215 const Score MinorBehindPawn = S( 16, 0);
216 const Score BishopPawns = S( 8, 12);
217 const Score LongRangedBishop = S( 22, 0);
218 const Score RookOnPawn = S( 8, 24);
219 const Score TrappedRook = S( 92, 0);
220 const Score WeakQueen = S( 50, 10);
221 const Score CloseEnemies = S( 7, 0);
222 const Score PawnlessFlank = S( 20, 80);
223 const Score ThreatBySafePawn = S(192,175);
224 const Score ThreatByRank = S( 16, 3);
225 const Score Hanging = S( 48, 27);
226 const Score WeakUnopposedPawn = S( 5, 25);
227 const Score ThreatByPawnPush = S( 38, 22);
228 const Score ThreatByAttackOnQueen = S( 38, 22);
229 const Score HinderPassedPawn = S( 7, 0);
230 const Score TrappedBishopA1H1 = S( 50, 50);
235 // KingAttackWeights[PieceType] contains king attack weights by piece type
236 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 78, 56, 45, 11 };
238 // Penalties for enemy's safe checks
239 const int QueenSafeCheck = 780;
240 const int RookSafeCheck = 880;
241 const int BishopSafeCheck = 435;
242 const int KnightSafeCheck = 790;
244 // Threshold for lazy and space evaluation
245 const Value LazyThreshold = Value(1500);
246 const Value SpaceThreshold = Value(12222);
249 // initialize() computes king and pawn attacks, and the king ring bitboard
250 // for a given color. This is done at the beginning of the evaluation.
252 template<Tracing T> template<Color Us>
253 void Evaluation<T>::initialize() {
255 const Color Them = (Us == WHITE ? BLACK : WHITE);
256 const Direction Up = (Us == WHITE ? NORTH : SOUTH);
257 const Direction Down = (Us == WHITE ? SOUTH : NORTH);
258 const Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB: Rank7BB | Rank6BB);
260 // Find our pawns on the first two ranks, and those which are blocked
261 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
263 // Squares occupied by those pawns, by our king, or controlled by enemy pawns
264 // are excluded from the mobility area.
265 mobilityArea[Us] = ~(b | pos.square<KING>(Us) | pe->pawn_attacks(Them));
267 // Initialise the attack bitboards with the king and pawn information
268 b = attackedBy[Us][KING] = pos.attacks_from<KING>(pos.square<KING>(Us));
269 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
271 attackedBy2[Us] = b & attackedBy[Us][PAWN];
272 attackedBy[Us][ALL_PIECES] = b | attackedBy[Us][PAWN];
274 // Init our king safety tables only if we are going to use them
275 if (pos.non_pawn_material(Them) >= RookValueMg + KnightValueMg)
278 if (relative_rank(Us, pos.square<KING>(Us)) == RANK_1)
279 kingRing[Us] |= shift<Up>(b);
281 kingAttackersCount[Them] = popcount(b & pe->pawn_attacks(Them));
282 kingAdjacentZoneAttacksCount[Them] = kingAttackersWeight[Them] = 0;
285 kingRing[Us] = kingAttackersCount[Them] = 0;
289 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given
292 template<Tracing T> template<Color Us, PieceType Pt>
293 Score Evaluation<T>::evaluate_pieces() {
295 const Color Them = (Us == WHITE ? BLACK : WHITE);
296 const Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
297 : Rank5BB | Rank4BB | Rank3BB);
298 const Square* pl = pos.squares<Pt>(Us);
302 Score score = SCORE_ZERO;
304 attackedBy[Us][Pt] = 0;
307 attackedBy[Us][QUEEN_DIAGONAL] = 0;
309 while ((s = *pl++) != SQ_NONE)
311 // Find attacked squares, including x-ray attacks for bishops and rooks
312 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
313 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
314 : pos.attacks_from<Pt>(s);
316 if (pos.pinned_pieces(Us) & s)
317 b &= LineBB[pos.square<KING>(Us)][s];
319 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
320 attackedBy[Us][ALL_PIECES] |= attackedBy[Us][Pt] |= b;
323 attackedBy[Us][QUEEN_DIAGONAL] |= b & PseudoAttacks[BISHOP][s];
325 if (b & kingRing[Them])
327 kingAttackersCount[Us]++;
328 kingAttackersWeight[Us] += KingAttackWeights[Pt];
329 kingAdjacentZoneAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
332 int mob = popcount(b & mobilityArea[Us]);
334 mobility[Us] += MobilityBonus[Pt - 2][mob];
336 // Bonus for this piece as a king protector
337 score += KingProtector[Pt - 2] * distance(s, pos.square<KING>(Us));
339 if (Pt == BISHOP || Pt == KNIGHT)
341 // Bonus for outpost squares
342 bb = OutpostRanks & ~pe->pawn_attacks_span(Them);
344 score += Outpost[Pt == BISHOP][bool(attackedBy[Us][PAWN] & s)] * 2;
347 bb &= b & ~pos.pieces(Us);
349 score += Outpost[Pt == BISHOP][bool(attackedBy[Us][PAWN] & bb)];
352 // Bonus when behind a pawn
353 if ( relative_rank(Us, s) < RANK_5
354 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
355 score += MinorBehindPawn;
359 // Penalty for pawns on the same color square as the bishop
360 score -= BishopPawns * pe->pawns_on_same_color_squares(Us, s);
362 // Bonus for bishop on a long diagonal which can "see" both center squares
363 if (more_than_one(Center & (attacks_bb<BISHOP>(s, pos.pieces(PAWN)) | s)))
364 score += LongRangedBishop;
367 // An important Chess960 pattern: A cornered bishop blocked by a friendly
368 // pawn diagonally in front of it is a very serious problem, especially
369 // when that pawn is also blocked.
372 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
374 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
375 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
376 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
377 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
384 // Bonus for aligning with enemy pawns on the same rank/file
385 if (relative_rank(Us, s) >= RANK_5)
386 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
388 // Bonus when on an open or semi-open file
389 if (pe->semiopen_file(Us, file_of(s)))
390 score += RookOnFile[bool(pe->semiopen_file(Them, file_of(s)))];
392 // Penalty when trapped by the king, even more if the king cannot castle
395 Square ksq = pos.square<KING>(Us);
397 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
398 && !pe->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
399 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
405 // Penalty if any relative pin or discovered attack against the queen
407 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, pinners))
413 Trace::add(Pt, Us, score);
419 // evaluate_king() assigns bonuses and penalties to a king of a given color
421 template<Tracing T> template<Color Us>
422 Score Evaluation<T>::evaluate_king() {
424 const Color Them = (Us == WHITE ? BLACK : WHITE);
425 const Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
426 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
428 const Square ksq = pos.square<KING>(Us);
429 Bitboard weak, b, b1, b2, safe, unsafeChecks;
431 // King shelter and enemy pawns storm
432 Score score = pe->king_safety<Us>(pos, ksq);
434 // Main king safety evaluation
435 if (kingAttackersCount[Them] > (1 - pos.count<QUEEN>(Them)))
437 // Attacked squares defended at most once by our queen or king
438 weak = attackedBy[Them][ALL_PIECES]
440 & (attackedBy[Us][KING] | attackedBy[Us][QUEEN] | ~attackedBy[Us][ALL_PIECES]);
442 int kingDanger = unsafeChecks = 0;
444 // Analyse the safe enemy's checks which are possible on next move
445 safe = ~pos.pieces(Them);
446 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
448 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
449 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
451 // Enemy queen safe checks
452 if ((b1 | b2) & attackedBy[Them][QUEEN] & safe & ~attackedBy[Us][QUEEN])
453 kingDanger += QueenSafeCheck;
455 b1 &= attackedBy[Them][ROOK];
456 b2 &= attackedBy[Them][BISHOP];
458 // Enemy rooks checks
460 kingDanger += RookSafeCheck;
464 // Enemy bishops checks
466 kingDanger += BishopSafeCheck;
470 // Enemy knights checks
471 b = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
473 kingDanger += KnightSafeCheck;
477 // Unsafe or occupied checking squares will also be considered, as long as
478 // the square is in the attacker's mobility area.
479 unsafeChecks &= mobilityArea[Them];
481 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
482 + 102 * kingAdjacentZoneAttacksCount[Them]
483 + 191 * popcount(kingRing[Us] & weak)
484 + 143 * popcount(pos.pinned_pieces(Us) | unsafeChecks)
485 - 848 * !pos.count<QUEEN>(Them)
486 - 9 * mg_value(score) / 8
489 // Transform the kingDanger units into a Score, and substract it from the evaluation
491 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
494 // King tropism: firstly, find squares that opponent attacks in our king flank
495 File kf = file_of(ksq);
496 b = attackedBy[Them][ALL_PIECES] & KingFlank[kf] & Camp;
498 assert(((Us == WHITE ? b << 4 : b >> 4) & b) == 0);
499 assert(popcount(Us == WHITE ? b << 4 : b >> 4) == popcount(b));
501 // Secondly, add the squares which are attacked twice in that flank and
502 // which are not defended by our pawns.
503 b = (Us == WHITE ? b << 4 : b >> 4)
504 | (b & attackedBy2[Them] & ~attackedBy[Us][PAWN]);
506 score -= CloseEnemies * popcount(b);
508 // Penalty when our king is on a pawnless flank
509 if (!(pos.pieces(PAWN) & KingFlank[kf]))
510 score -= PawnlessFlank;
513 Trace::add(KING, Us, score);
519 // evaluate_threats() assigns bonuses according to the types of the attacking
520 // and the attacked pieces.
522 template<Tracing T> template<Color Us>
523 Score Evaluation<T>::evaluate_threats() {
525 const Color Them = (Us == WHITE ? BLACK : WHITE);
526 const Direction Up = (Us == WHITE ? NORTH : SOUTH);
527 const Direction Left = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
528 const Direction Right = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
529 const Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
531 Bitboard b, weak, defended, stronglyProtected, safeThreats;
532 Score score = SCORE_ZERO;
534 // Non-pawn enemies attacked by a pawn
535 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & attackedBy[Us][PAWN];
539 b = pos.pieces(Us, PAWN) & ( ~attackedBy[Them][ALL_PIECES]
540 | attackedBy[Us][ALL_PIECES]);
542 safeThreats = (shift<Right>(b) | shift<Left>(b)) & weak;
544 score += ThreatBySafePawn * popcount(safeThreats);
547 // Squares strongly protected by the opponent, either because they attack the
548 // square with a pawn, or because they attack the square twice and we don't.
549 stronglyProtected = attackedBy[Them][PAWN]
550 | (attackedBy2[Them] & ~attackedBy2[Us]);
552 // Non-pawn enemies, strongly protected
553 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN))
556 // Enemies not strongly protected and under our attack
557 weak = pos.pieces(Them)
559 & attackedBy[Us][ALL_PIECES];
561 // Add a bonus according to the kind of attacking pieces
564 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
567 Square s = pop_lsb(&b);
568 score += ThreatByMinor[type_of(pos.piece_on(s))];
569 if (type_of(pos.piece_on(s)) != PAWN)
570 score += ThreatByRank * (int)relative_rank(Them, s);
573 b = (pos.pieces(Them, QUEEN) | weak) & attackedBy[Us][ROOK];
576 Square s = pop_lsb(&b);
577 score += ThreatByRook[type_of(pos.piece_on(s))];
578 if (type_of(pos.piece_on(s)) != PAWN)
579 score += ThreatByRank * (int)relative_rank(Them, s);
582 score += Hanging * popcount(weak & ~attackedBy[Them][ALL_PIECES]);
584 b = weak & attackedBy[Us][KING];
586 score += ThreatByKing[more_than_one(b)];
589 // Bonus for opponent unopposed weak pawns
590 if (pos.pieces(Us, ROOK, QUEEN))
591 score += WeakUnopposedPawn * pe->weak_unopposed(Them);
593 // Find squares where our pawns can push on the next move
594 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
595 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
597 // Keep only the squares which are not completely unsafe
598 b &= ~attackedBy[Them][PAWN]
599 & (attackedBy[Us][ALL_PIECES] | ~attackedBy[Them][ALL_PIECES]);
601 // Add a bonus for each new pawn threats from those squares
602 b = (shift<Left>(b) | shift<Right>(b))
604 & ~attackedBy[Us][PAWN];
606 score += ThreatByPawnPush * popcount(b);
608 // Add a bonus for safe slider attack threats on opponent queen
609 safeThreats = ~pos.pieces(Us) & ~attackedBy2[Them] & attackedBy2[Us];
610 b = (attackedBy[Us][BISHOP] & attackedBy[Them][QUEEN_DIAGONAL])
611 | (attackedBy[Us][ROOK ] & attackedBy[Them][QUEEN] & ~attackedBy[Them][QUEEN_DIAGONAL]);
613 score += ThreatByAttackOnQueen * popcount(b & safeThreats);
616 Trace::add(THREAT, Us, score);
622 // evaluate_passed_pawns() evaluates the passed pawns and candidate passed
623 // pawns of the given color.
625 template<Tracing T> template<Color Us>
626 Score Evaluation<T>::evaluate_passed_pawns() {
628 const Color Them = (Us == WHITE ? BLACK : WHITE);
629 const Direction Up = (Us == WHITE ? NORTH : SOUTH);
631 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
632 Score score = SCORE_ZERO;
634 b = pe->passed_pawns(Us);
638 Square s = pop_lsb(&b);
640 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
642 bb = forward_file_bb(Us, s) & (attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
643 score -= HinderPassedPawn * popcount(bb);
645 int r = relative_rank(Us, s) - RANK_2;
646 int rr = r * (r - 1);
648 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
652 Square blockSq = s + Up;
654 // Adjust bonus based on the king's proximity
655 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
656 - distance(pos.square<KING>( Us), blockSq) * 2 * rr;
658 // If blockSq is not the queening square then consider also a second push
659 if (relative_rank(Us, blockSq) != RANK_8)
660 ebonus -= distance(pos.square<KING>(Us), blockSq + Up) * rr;
662 // If the pawn is free to advance, then increase the bonus
663 if (pos.empty(blockSq))
665 // If there is a rook or queen attacking/defending the pawn from behind,
666 // consider all the squaresToQueen. Otherwise consider only the squares
667 // in the pawn's path attacked or occupied by the enemy.
668 defendedSquares = unsafeSquares = squaresToQueen = forward_file_bb(Us, s);
670 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
672 if (!(pos.pieces(Us) & bb))
673 defendedSquares &= attackedBy[Us][ALL_PIECES];
675 if (!(pos.pieces(Them) & bb))
676 unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
678 // If there aren't any enemy attacks, assign a big bonus. Otherwise
679 // assign a smaller bonus if the block square isn't attacked.
680 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
682 // If the path to the queen is fully defended, assign a big bonus.
683 // Otherwise assign a smaller bonus if the block square is defended.
684 if (defendedSquares == squaresToQueen)
687 else if (defendedSquares & blockSq)
690 mbonus += k * rr, ebonus += k * rr;
692 else if (pos.pieces(Us) & blockSq)
693 mbonus += rr + r * 2, ebonus += rr + r * 2;
696 // Scale down bonus for candidate passers which need more than one
697 // pawn push to become passed or have a pawn in front of them.
698 if (!pos.pawn_passed(Us, s + Up) || (pos.pieces(PAWN) & forward_file_bb(Us, s)))
699 mbonus /= 2, ebonus /= 2;
701 score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
705 Trace::add(PASSED, Us, score);
711 // evaluate_space() computes the space evaluation for a given side. The
712 // space evaluation is a simple bonus based on the number of safe squares
713 // available for minor pieces on the central four files on ranks 2--4. Safe
714 // squares one, two or three squares behind a friendly pawn are counted
715 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
716 // improve play on game opening.
718 template<Tracing T> template<Color Us>
719 Score Evaluation<T>::evaluate_space() {
721 const Color Them = (Us == WHITE ? BLACK : WHITE);
722 const Bitboard SpaceMask =
723 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
724 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
726 // Find the safe squares for our pieces inside the area defined by
727 // SpaceMask. A square is unsafe if it is attacked by an enemy
728 // pawn, or if it is undefended and attacked by an enemy piece.
729 Bitboard safe = SpaceMask
730 & ~pos.pieces(Us, PAWN)
731 & ~attackedBy[Them][PAWN]
732 & (attackedBy[Us][ALL_PIECES] | ~attackedBy[Them][ALL_PIECES]);
734 // Find all squares which are at most three squares behind some friendly pawn
735 Bitboard behind = pos.pieces(Us, PAWN);
736 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
737 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
739 // Since SpaceMask[Us] is fully on our half of the board...
740 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
742 // ...count safe + (behind & safe) with a single popcount.
743 int bonus = popcount((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
744 int weight = pos.count<ALL_PIECES>(Us) - 2 * pe->open_files();
746 return make_score(bonus * weight * weight / 16, 0);
750 // evaluate_initiative() computes the initiative correction value for the
751 // position, i.e., second order bonus/malus based on the known attacking/defending
752 // status of the players.
755 Score Evaluation<T>::evaluate_initiative(Value eg) {
757 int kingDistance = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
758 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
759 bool bothFlanks = (pos.pieces(PAWN) & QueenSide) && (pos.pieces(PAWN) & KingSide);
761 // Compute the initiative bonus for the attacking side
762 int initiative = 8 * (pe->pawn_asymmetry() + kingDistance - 17) + 12 * pos.count<PAWN>() + 16 * bothFlanks;
764 // Now apply the bonus: note that we find the attacking side by extracting
765 // the sign of the endgame value, and that we carefully cap the bonus so
766 // that the endgame score will never change sign after the bonus.
767 int v = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg));
770 Trace::add(INITIATIVE, make_score(0, v));
772 return make_score(0, v);
776 // evaluate_scale_factor() computes the scale factor for the winning side
779 ScaleFactor Evaluation<T>::evaluate_scale_factor(Value eg) {
781 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
782 ScaleFactor sf = me->scale_factor(pos, strongSide);
784 // If we don't already have an unusual scale factor, check for certain
785 // types of endgames, and use a lower scale for those.
786 if (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN)
788 if (pos.opposite_bishops())
790 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
791 // is almost a draw, in case of KBP vs KB, it is even more a draw.
792 if ( pos.non_pawn_material(WHITE) == BishopValueMg
793 && pos.non_pawn_material(BLACK) == BishopValueMg)
794 return more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
796 // Endgame with opposite-colored bishops, but also other pieces. Still
797 // a bit drawish, but not as drawish as with only the two bishops.
798 return ScaleFactor(46);
800 // Endings where weaker side can place his king in front of the opponent's
801 // pawns are drawish.
802 else if ( abs(eg) <= BishopValueEg
803 && pos.count<PAWN>(strongSide) <= 2
804 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
805 return ScaleFactor(37 + 7 * pos.count<PAWN>(strongSide));
812 // value() is the main function of the class. It computes the various parts of
813 // the evaluation and returns the value of the position from the point of view
814 // of the side to move.
817 Value Evaluation<T>::value() {
819 assert(!pos.checkers());
821 // Probe the material hash table
822 me = Material::probe(pos);
824 // If we have a specialized evaluation function for the current material
825 // configuration, call it and return.
826 if (me->specialized_eval_exists())
827 return me->evaluate(pos);
829 // Initialize score by reading the incrementally updated scores included in
830 // the position object (material + piece square tables) and the material
831 // imbalance. Score is computed internally from the white point of view.
832 Score score = pos.psq_score() + me->imbalance() + Eval::Contempt;
834 // Probe the pawn hash table
835 pe = Pawns::probe(pos);
836 score += pe->pawns_score();
838 // Early exit if score is high
839 Value v = (mg_value(score) + eg_value(score)) / 2;
840 if (abs(v) > LazyThreshold)
841 return pos.side_to_move() == WHITE ? v : -v;
843 // Main evaluation begins here
848 score += evaluate_pieces<WHITE, KNIGHT>() - evaluate_pieces<BLACK, KNIGHT>();
849 score += evaluate_pieces<WHITE, BISHOP>() - evaluate_pieces<BLACK, BISHOP>();
850 score += evaluate_pieces<WHITE, ROOK >() - evaluate_pieces<BLACK, ROOK >();
851 score += evaluate_pieces<WHITE, QUEEN >() - evaluate_pieces<BLACK, QUEEN >();
853 score += mobility[WHITE] - mobility[BLACK];
855 score += evaluate_king<WHITE>()
856 - evaluate_king<BLACK>();
858 score += evaluate_threats<WHITE>()
859 - evaluate_threats<BLACK>();
861 score += evaluate_passed_pawns<WHITE>()
862 - evaluate_passed_pawns<BLACK>();
864 if (pos.non_pawn_material() >= SpaceThreshold)
865 score += evaluate_space<WHITE>()
866 - evaluate_space<BLACK>();
868 score += evaluate_initiative(eg_value(score));
870 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
871 ScaleFactor sf = evaluate_scale_factor(eg_value(score));
872 v = mg_value(score) * int(me->game_phase())
873 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
875 v /= int(PHASE_MIDGAME);
877 // In case of tracing add all remaining individual evaluation terms
880 Trace::add(MATERIAL, pos.psq_score());
881 Trace::add(IMBALANCE, me->imbalance());
882 Trace::add(PAWN, pe->pawns_score());
883 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
884 if (pos.non_pawn_material() >= SpaceThreshold)
885 Trace::add(SPACE, evaluate_space<WHITE>()
886 , evaluate_space<BLACK>());
887 Trace::add(TOTAL, score);
890 return pos.side_to_move() == WHITE ? v : -v; // Side to move point of view
895 Score Eval::Contempt = SCORE_ZERO;
897 /// evaluate() is the evaluator for the outer world. It returns a static evaluation
898 /// of the position from the point of view of the side to move.
900 Value Eval::evaluate(const Position& pos)
902 return Evaluation<>(pos).value() + Eval::Tempo;
905 /// trace() is like evaluate(), but instead of returning a value, it returns
906 /// a string (suitable for outputting to stdout) that contains the detailed
907 /// descriptions and values of each evaluation term. Useful for debugging.
909 std::string Eval::trace(const Position& pos) {
911 std::memset(scores, 0, sizeof(scores));
913 Value v = Evaluation<TRACE>(pos).value() + Eval::Tempo;
914 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
916 std::stringstream ss;
917 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
918 << " Eval term | White | Black | Total \n"
919 << " | MG EG | MG EG | MG EG \n"
920 << "----------------+-------------+-------------+-------------\n"
921 << " Material | " << Term(MATERIAL)
922 << " Imbalance | " << Term(IMBALANCE)
923 << " Pawns | " << Term(PAWN)
924 << " Knights | " << Term(KNIGHT)
925 << " Bishops | " << Term(BISHOP)
926 << " Rooks | " << Term(ROOK)
927 << " Queens | " << Term(QUEEN)
928 << " Mobility | " << Term(MOBILITY)
929 << " King safety | " << Term(KING)
930 << " Threats | " << Term(THREAT)
931 << " Passed pawns | " << Term(PASSED)
932 << " Space | " << Term(SPACE)
933 << " Initiative | " << Term(INITIATIVE)
934 << "----------------+-------------+-------------+-------------\n"
935 << " Total | " << Term(TOTAL);
937 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";