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) 2015-2019 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
35 enum Tracing { NO_TRACE, TRACE };
37 enum Term { // The first 8 entries are reserved for PieceType
38 MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, INITIATIVE, TOTAL, TERM_NB
41 Score scores[TERM_NB][COLOR_NB];
43 double to_cp(Value v) { return double(v) / PawnValueEg; }
45 void add(int idx, Color c, Score s) {
49 void add(int idx, Score w, Score b = SCORE_ZERO) {
50 scores[idx][WHITE] = w;
51 scores[idx][BLACK] = b;
54 std::ostream& operator<<(std::ostream& os, Score s) {
55 os << std::setw(5) << to_cp(mg_value(s)) << " "
56 << std::setw(5) << to_cp(eg_value(s));
60 std::ostream& operator<<(std::ostream& os, Term t) {
62 if (t == MATERIAL || t == IMBALANCE || t == INITIATIVE || t == TOTAL)
63 os << " ---- ----" << " | " << " ---- ----";
65 os << scores[t][WHITE] << " | " << scores[t][BLACK];
67 os << " | " << scores[t][WHITE] - scores[t][BLACK] << "\n";
72 using namespace Trace;
76 // Threshold for lazy and space evaluation
77 constexpr Value LazyThreshold = Value(1400);
78 constexpr Value SpaceThreshold = Value(12222);
80 // KingAttackWeights[PieceType] contains king attack weights by piece type
81 constexpr int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 77, 55, 44, 10 };
83 // Penalties for enemy's safe checks
84 constexpr int QueenSafeCheck = 780;
85 constexpr int RookSafeCheck = 1080;
86 constexpr int BishopSafeCheck = 635;
87 constexpr int KnightSafeCheck = 790;
89 #define S(mg, eg) make_score(mg, eg)
91 // MobilityBonus[PieceType-2][attacked] contains bonuses for middle and end game,
92 // indexed by piece type and number of attacked squares in the mobility area.
93 constexpr Score MobilityBonus[][32] = {
94 { S(-62,-81), S(-53,-56), S(-12,-30), S( -4,-14), S( 3, 8), S( 13, 15), // Knights
95 S( 22, 23), S( 28, 27), S( 33, 33) },
96 { S(-48,-59), S(-20,-23), S( 16, -3), S( 26, 13), S( 38, 24), S( 51, 42), // Bishops
97 S( 55, 54), S( 63, 57), S( 63, 65), S( 68, 73), S( 81, 78), S( 81, 86),
98 S( 91, 88), S( 98, 97) },
99 { S(-58,-76), S(-27,-18), S(-15, 28), S(-10, 55), S( -5, 69), S( -2, 82), // Rooks
100 S( 9,112), S( 16,118), S( 30,132), S( 29,142), S( 32,155), S( 38,165),
101 S( 46,166), S( 48,169), S( 58,171) },
102 { S(-39,-36), S(-21,-15), S( 3, 8), S( 3, 18), S( 14, 34), S( 22, 54), // Queens
103 S( 28, 61), S( 41, 73), S( 43, 79), S( 48, 92), S( 56, 94), S( 60,104),
104 S( 60,113), S( 66,120), S( 67,123), S( 70,126), S( 71,133), S( 73,136),
105 S( 79,140), S( 88,143), S( 88,148), S( 99,166), S(102,170), S(102,175),
106 S(106,184), S(109,191), S(113,206), S(116,212) }
109 // RookOnFile[semiopen/open] contains bonuses for each rook when there is
110 // no (friendly) pawn on the rook file.
111 constexpr Score RookOnFile[] = { S(18, 7), S(44, 20) };
113 // ThreatByMinor/ByRook[attacked PieceType] contains bonuses according to
114 // which piece type attacks which one. Attacks on lesser pieces which are
115 // pawn-defended are not considered.
116 constexpr Score ThreatByMinor[PIECE_TYPE_NB] = {
117 S(0, 0), S(0, 31), S(39, 42), S(57, 44), S(68, 112), S(62, 120)
120 constexpr Score ThreatByRook[PIECE_TYPE_NB] = {
121 S(0, 0), S(0, 24), S(38, 71), S(38, 61), S(0, 38), S(51, 38)
124 // PassedRank[Rank] contains a bonus according to the rank of a passed pawn
125 constexpr Score PassedRank[RANK_NB] = {
126 S(0, 0), S(10, 28), S(17, 33), S(15, 41), S(62, 72), S(168, 177), S(276, 260)
129 // Assorted bonuses and penalties
130 constexpr Score BishopPawns = S( 3, 7);
131 constexpr Score CorneredBishop = S( 50, 50);
132 constexpr Score FlankAttacks = S( 8, 0);
133 constexpr Score Hanging = S( 69, 36);
134 constexpr Score KingProtector = S( 7, 8);
135 constexpr Score KnightOnQueen = S( 16, 12);
136 constexpr Score LongDiagonalBishop = S( 45, 0);
137 constexpr Score MinorBehindPawn = S( 18, 3);
138 constexpr Score Outpost = S( 18, 6);
139 constexpr Score PassedFile = S( 11, 8);
140 constexpr Score PawnlessFlank = S( 17, 95);
141 constexpr Score RestrictedPiece = S( 7, 7);
142 constexpr Score RookOnPawn = S( 10, 32);
143 constexpr Score SliderOnQueen = S( 59, 18);
144 constexpr Score ThreatByKing = S( 24, 89);
145 constexpr Score ThreatByPawnPush = S( 48, 39);
146 constexpr Score ThreatByRank = S( 13, 0);
147 constexpr Score ThreatBySafePawn = S(173, 94);
148 constexpr Score TrappedRook = S( 47, 4);
149 constexpr Score WeakQueen = S( 49, 15);
153 // Evaluation class computes and stores attacks tables and other working data
158 Evaluation() = delete;
159 explicit Evaluation(const Position& p) : pos(p) {}
160 Evaluation& operator=(const Evaluation&) = delete;
164 template<Color Us> void initialize();
165 template<Color Us, PieceType Pt> Score pieces();
166 template<Color Us> Score king() const;
167 template<Color Us> Score threats() const;
168 template<Color Us> Score passed() const;
169 template<Color Us> Score space() const;
170 ScaleFactor scale_factor(Value eg) const;
171 Score initiative(Value eg) const;
176 Bitboard mobilityArea[COLOR_NB];
177 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
179 // attackedBy[color][piece type] is a bitboard representing all squares
180 // attacked by a given color and piece type. Special "piece types" which
181 // is also calculated is ALL_PIECES.
182 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
184 // attackedBy2[color] are the squares attacked by at least 2 units of a given
185 // color, including x-rays. But diagonal x-rays through pawns are not computed.
186 Bitboard attackedBy2[COLOR_NB];
188 // kingRing[color] are the squares adjacent to the king plus some other
189 // very near squares, depending on king position.
190 Bitboard kingRing[COLOR_NB];
192 // kingAttackersCount[color] is the number of pieces of the given color
193 // which attack a square in the kingRing of the enemy king.
194 int kingAttackersCount[COLOR_NB];
196 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of
197 // the given color which attack a square in the kingRing of the enemy king.
198 // The weights of the individual piece types are given by the elements in
199 // the KingAttackWeights array.
200 int kingAttackersWeight[COLOR_NB];
202 // kingAttacksCount[color] is the number of attacks by the given color to
203 // squares directly adjacent to the enemy king. Pieces which attack more
204 // than one square are counted multiple times. For instance, if there is
205 // a white knight on g5 and black's king is on g8, this white knight adds 2
206 // to kingAttacksCount[WHITE].
207 int kingAttacksCount[COLOR_NB];
211 // Evaluation::initialize() computes king and pawn attacks, and the king ring
212 // bitboard for a given color. This is done at the beginning of the evaluation.
213 template<Tracing T> template<Color Us>
214 void Evaluation<T>::initialize() {
216 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
217 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
218 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
219 constexpr Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB : Rank7BB | Rank6BB);
221 const Square ksq = pos.square<KING>(Us);
223 Bitboard dblAttackByPawn = pawn_double_attacks_bb<Us>(pos.pieces(Us, PAWN));
225 // Find our pawns that are blocked or on the first two ranks
226 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
228 // Squares occupied by those pawns, by our king or queen or controlled by
229 // enemy pawns are excluded from the mobility area.
230 mobilityArea[Us] = ~(b | pos.pieces(Us, KING, QUEEN) | pe->pawn_attacks(Them));
232 // Initialize attackedBy[] for king and pawns
233 attackedBy[Us][KING] = pos.attacks_from<KING>(ksq);
234 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
235 attackedBy[Us][ALL_PIECES] = attackedBy[Us][KING] | attackedBy[Us][PAWN];
236 attackedBy2[Us] = dblAttackByPawn | (attackedBy[Us][KING] & attackedBy[Us][PAWN]);
238 // Init our king safety tables
239 kingRing[Us] = attackedBy[Us][KING];
240 if (relative_rank(Us, ksq) == RANK_1)
241 kingRing[Us] |= shift<Up>(kingRing[Us]);
243 if (file_of(ksq) == FILE_H)
244 kingRing[Us] |= shift<WEST>(kingRing[Us]);
246 else if (file_of(ksq) == FILE_A)
247 kingRing[Us] |= shift<EAST>(kingRing[Us]);
249 kingAttackersCount[Them] = popcount(kingRing[Us] & pe->pawn_attacks(Them));
250 kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
252 // Remove from kingRing[] the squares defended by two pawns
253 kingRing[Us] &= ~dblAttackByPawn;
257 // Evaluation::pieces() scores pieces of a given color and type
258 template<Tracing T> template<Color Us, PieceType Pt>
259 Score Evaluation<T>::pieces() {
261 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
262 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
263 constexpr Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
264 : Rank5BB | Rank4BB | Rank3BB);
265 const Square* pl = pos.squares<Pt>(Us);
268 Score score = SCORE_ZERO;
270 attackedBy[Us][Pt] = 0;
272 for (Square s = *pl; s != SQ_NONE; s = *++pl)
274 // Find attacked squares, including x-ray attacks for bishops and rooks
275 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
276 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
277 : pos.attacks_from<Pt>(s);
279 if (pos.blockers_for_king(Us) & s)
280 b &= LineBB[pos.square<KING>(Us)][s];
282 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
283 attackedBy[Us][Pt] |= b;
284 attackedBy[Us][ALL_PIECES] |= b;
286 if (b & kingRing[Them])
288 kingAttackersCount[Us]++;
289 kingAttackersWeight[Us] += KingAttackWeights[Pt];
290 kingAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
293 int mob = popcount(b & mobilityArea[Us]);
295 mobility[Us] += MobilityBonus[Pt - 2][mob];
297 if (Pt == BISHOP || Pt == KNIGHT)
299 // Bonus if piece is on an outpost square or can reach one
300 bb = OutpostRanks & attackedBy[Us][PAWN] & ~pe->pawn_attacks_span(Them);
302 score += Outpost * (Pt == KNIGHT ? 4 : 2);
304 else if (bb & b & ~pos.pieces(Us))
305 score += Outpost * (Pt == KNIGHT ? 2 : 1);
307 // Knight and Bishop bonus for being right behind a pawn
308 if (shift<Down>(pos.pieces(PAWN)) & s)
309 score += MinorBehindPawn;
311 // Penalty if the piece is far from the king
312 score -= KingProtector * distance(s, pos.square<KING>(Us));
316 // Penalty according to number of pawns on the same color square as the
317 // bishop, bigger when the center files are blocked with pawns.
318 Bitboard blocked = pos.pieces(Us, PAWN) & shift<Down>(pos.pieces());
320 score -= BishopPawns * pos.pawns_on_same_color_squares(Us, s)
321 * (1 + popcount(blocked & CenterFiles));
323 // Bonus for bishop on a long diagonal which can "see" both center squares
324 if (more_than_one(attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & Center))
325 score += LongDiagonalBishop;
328 // An important Chess960 pattern: A cornered bishop blocked by a friendly
329 // pawn diagonally in front of it is a very serious problem, especially
330 // when that pawn is also blocked.
333 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
335 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
336 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
337 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
338 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
345 // Bonus for aligning rook with enemy pawns on the same rank/file
346 if (relative_rank(Us, s) >= RANK_5)
347 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
349 // Bonus for rook on an open or semi-open file
350 if (pos.is_on_semiopen_file(Us, s))
351 score += RookOnFile[bool(pos.is_on_semiopen_file(Them, s))];
353 // Penalty when trapped by the king, even more if the king cannot castle
356 File kf = file_of(pos.square<KING>(Us));
357 if ((kf < FILE_E) == (file_of(s) < kf))
358 score -= TrappedRook * (1 + !pos.castling_rights(Us));
364 // Penalty if any relative pin or discovered attack against the queen
365 Bitboard queenPinners;
366 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
371 Trace::add(Pt, Us, score);
377 // Evaluation::king() assigns bonuses and penalties to a king of a given color
378 template<Tracing T> template<Color Us>
379 Score Evaluation<T>::king() const {
381 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
382 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
383 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
385 Bitboard weak, b1, b2, safe, unsafeChecks = 0;
386 Bitboard rookChecks, queenChecks, bishopChecks, knightChecks;
388 const Square ksq = pos.square<KING>(Us);
390 // Init the score with king shelter and enemy pawns storm
391 Score score = pe->king_safety<Us>(pos);
393 // Attacked squares defended at most once by our queen or king
394 weak = attackedBy[Them][ALL_PIECES]
396 & (~attackedBy[Us][ALL_PIECES] | attackedBy[Us][KING] | attackedBy[Us][QUEEN]);
398 // Analyse the safe enemy's checks which are possible on next move
399 safe = ~pos.pieces(Them);
400 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
402 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
403 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
405 // Enemy rooks checks
406 rookChecks = b1 & safe & attackedBy[Them][ROOK];
409 kingDanger += RookSafeCheck;
411 unsafeChecks |= b1 & attackedBy[Them][ROOK];
413 // Enemy queen safe checks: we count them only if they are from squares from
414 // which we can't give a rook check, because rook checks are more valuable.
415 queenChecks = (b1 | b2)
416 & attackedBy[Them][QUEEN]
418 & ~attackedBy[Us][QUEEN]
422 kingDanger += QueenSafeCheck;
424 // Enemy bishops checks: we count them only if they are from squares from
425 // which we can't give a queen check, because queen checks are more valuable.
427 & attackedBy[Them][BISHOP]
432 kingDanger += BishopSafeCheck;
434 unsafeChecks |= b2 & attackedBy[Them][BISHOP];
436 // Enemy knights checks
437 knightChecks = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
439 if (knightChecks & safe)
440 kingDanger += KnightSafeCheck;
442 unsafeChecks |= knightChecks;
444 // Unsafe or occupied checking squares will also be considered, as long as
445 // the square is in the attacker's mobility area.
446 unsafeChecks &= mobilityArea[Them];
448 // Find the squares that opponent attacks in our king flank, and the squares
449 // which are attacked twice in that flank.
450 b1 = attackedBy[Them][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
451 b2 = b1 & attackedBy2[Them];
453 int kingFlankAttacks = popcount(b1) + popcount(b2);
455 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
456 + 69 * kingAttacksCount[Them]
457 + 185 * popcount(kingRing[Us] & weak)
458 - 100 * bool(attackedBy[Us][KNIGHT] & attackedBy[Us][KING])
459 - 35 * bool(attackedBy[Us][BISHOP] & attackedBy[Us][KING])
460 + 150 * popcount(pos.blockers_for_king(Us) | unsafeChecks)
461 - 873 * !pos.count<QUEEN>(Them)
462 - 6 * mg_value(score) / 8
463 + mg_value(mobility[Them] - mobility[Us])
464 + 5 * kingFlankAttacks * kingFlankAttacks / 16
467 // Transform the kingDanger units into a Score, and subtract it from the evaluation
468 if (kingDanger > 100)
469 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
471 // Penalty when our king is on a pawnless flank
472 if (!(pos.pieces(PAWN) & KingFlank[file_of(ksq)]))
473 score -= PawnlessFlank;
475 // Penalty if king flank is under attack, potentially moving toward the king
476 score -= FlankAttacks * kingFlankAttacks;
479 Trace::add(KING, Us, score);
485 // Evaluation::threats() assigns bonuses according to the types of the
486 // attacking and the attacked pieces.
487 template<Tracing T> template<Color Us>
488 Score Evaluation<T>::threats() const {
490 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
491 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
492 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
494 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe;
495 Score score = SCORE_ZERO;
498 nonPawnEnemies = pos.pieces(Them) & ~pos.pieces(PAWN);
500 // Squares strongly protected by the enemy, either because they defend the
501 // square with a pawn, or because they defend the square twice and we don't.
502 stronglyProtected = attackedBy[Them][PAWN]
503 | (attackedBy2[Them] & ~attackedBy2[Us]);
505 // Non-pawn enemies, strongly protected
506 defended = nonPawnEnemies & stronglyProtected;
508 // Enemies not strongly protected and under our attack
509 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
511 // Safe or protected squares
512 safe = ~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES];
514 // Bonus according to the kind of attacking pieces
517 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
520 Square s = pop_lsb(&b);
521 score += ThreatByMinor[type_of(pos.piece_on(s))];
522 if (type_of(pos.piece_on(s)) != PAWN)
523 score += ThreatByRank * (int)relative_rank(Them, s);
526 b = weak & attackedBy[Us][ROOK];
529 Square s = pop_lsb(&b);
530 score += ThreatByRook[type_of(pos.piece_on(s))];
531 if (type_of(pos.piece_on(s)) != PAWN)
532 score += ThreatByRank * (int)relative_rank(Them, s);
535 if (weak & attackedBy[Us][KING])
536 score += ThreatByKing;
538 b = ~attackedBy[Them][ALL_PIECES]
539 | (nonPawnEnemies & attackedBy2[Us]);
540 score += Hanging * popcount(weak & b);
543 // Bonus for restricting their piece moves
544 b = attackedBy[Them][ALL_PIECES]
546 & attackedBy[Us][ALL_PIECES];
548 score += RestrictedPiece * popcount(b);
550 // Find squares where our pawns can push on the next move
551 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
552 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
554 // Keep only the squares which are relatively safe
555 b &= ~attackedBy[Them][PAWN] & safe;
557 // Bonus for safe pawn threats on the next move
558 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
559 score += ThreatByPawnPush * popcount(b);
561 // Our safe or protected pawns
562 b = pos.pieces(Us, PAWN) & safe;
564 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
565 score += ThreatBySafePawn * popcount(b);
567 // Bonus for threats on the next moves against enemy queen
568 if (pos.count<QUEEN>(Them) == 1)
570 Square s = pos.square<QUEEN>(Them);
571 safe = mobilityArea[Us] & ~stronglyProtected;
573 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
575 score += KnightOnQueen * popcount(b & safe);
577 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
578 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
580 score += SliderOnQueen * popcount(b & safe & attackedBy2[Us]);
584 Trace::add(THREAT, Us, score);
589 // Evaluation::passed() evaluates the passed pawns and candidate passed
590 // pawns of the given color.
592 template<Tracing T> template<Color Us>
593 Score Evaluation<T>::passed() const {
595 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
596 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
598 auto king_proximity = [&](Color c, Square s) {
599 return std::min(distance(pos.square<KING>(c), s), 5);
602 Bitboard b, bb, squaresToQueen, unsafeSquares;
603 Score score = SCORE_ZERO;
605 b = pe->passed_pawns(Us);
609 Square s = pop_lsb(&b);
611 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
613 int r = relative_rank(Us, s);
616 Score bonus = PassedRank[r];
621 Square blockSq = s + Up;
623 // Adjust bonus based on the king's proximity
624 bonus += make_score(0, ( king_proximity(Them, blockSq) * 5
625 - king_proximity(Us, blockSq) * 2) * w);
627 // If blockSq is not the queening square then consider also a second push
629 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
631 // If the pawn is free to advance, then increase the bonus
632 if (pos.empty(blockSq))
634 squaresToQueen = forward_file_bb(Us, s);
635 unsafeSquares = passed_pawn_span(Us, s);
637 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN);
639 if (!(pos.pieces(Them) & bb))
640 unsafeSquares &= attackedBy[Them][ALL_PIECES];
642 // If there are no enemy attacks on passed pawn span, assign a big bonus.
643 // Otherwise assign a smaller bonus if the path to queen is not attacked
644 // and even smaller bonus if it is attacked but block square is not.
645 int k = !unsafeSquares ? 35 :
646 !(unsafeSquares & squaresToQueen) ? 20 :
647 !(unsafeSquares & blockSq) ? 9 :
650 // Assign a larger bonus if the block square is defended
651 if ((pos.pieces(Us) & bb) || (attackedBy[Us][ALL_PIECES] & blockSq))
654 bonus += make_score(k * w, k * w);
658 // Scale down bonus for candidate passers which need more than one
659 // pawn push to become passed, or have a pawn in front of them.
660 if ( !pos.pawn_passed(Us, s + Up)
661 || (pos.pieces(PAWN) & (s + Up)))
664 score += bonus - PassedFile * std::min(f, ~f);
668 Trace::add(PASSED, Us, score);
674 // Evaluation::space() computes the space evaluation for a given side. The
675 // space evaluation is a simple bonus based on the number of safe squares
676 // available for minor pieces on the central four files on ranks 2--4. Safe
677 // squares one, two or three squares behind a friendly pawn are counted
678 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
679 // improve play on game opening.
681 template<Tracing T> template<Color Us>
682 Score Evaluation<T>::space() const {
684 if (pos.non_pawn_material() < SpaceThreshold)
687 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
688 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
689 constexpr Bitboard SpaceMask =
690 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
691 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
693 // Find the available squares for our pieces inside the area defined by SpaceMask
694 Bitboard safe = SpaceMask
695 & ~pos.pieces(Us, PAWN)
696 & ~attackedBy[Them][PAWN];
698 // Find all squares which are at most three squares behind some friendly pawn
699 Bitboard behind = pos.pieces(Us, PAWN);
700 behind |= shift<Down>(behind);
701 behind |= shift<Down+Down>(behind);
703 int bonus = popcount(safe) + popcount(behind & safe & ~attackedBy[Them][ALL_PIECES]);
704 int weight = pos.count<ALL_PIECES>(Us) - 1;
705 Score score = make_score(bonus * weight * weight / 16, 0);
708 Trace::add(SPACE, Us, score);
714 // Evaluation::initiative() computes the initiative correction value
715 // for the position. It is a second order bonus/malus based on the
716 // known attacking/defending status of the players.
719 Score Evaluation<T>::initiative(Value eg) const {
721 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
722 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
724 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
725 && (pos.pieces(PAWN) & KingSide);
727 // Compute the initiative bonus for the attacking side
728 int complexity = 9 * pe->passed_count()
729 + 11 * pos.count<PAWN>()
731 + 18 * pawnsOnBothFlanks
732 + 49 * !pos.non_pawn_material()
735 // Now apply the bonus: note that we find the attacking side by extracting
736 // the sign of the endgame value, and that we carefully cap the bonus so
737 // that the endgame score will never change sign after the bonus.
738 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
741 Trace::add(INITIATIVE, make_score(0, v));
743 return make_score(0, v);
747 // Evaluation::scale_factor() computes the scale factor for the winning side
750 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
752 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
753 int sf = me->scale_factor(pos, strongSide);
755 // If scale is not already specific, scale down the endgame via general heuristics
756 if (sf == SCALE_FACTOR_NORMAL)
758 if ( pos.opposite_bishops()
759 && pos.non_pawn_material() == 2 * BishopValueMg)
760 sf = 16 + 4 * pe->passed_count();
762 sf = std::min(40 + (pos.opposite_bishops() ? 2 : 7) * pos.count<PAWN>(strongSide), sf);
766 return ScaleFactor(sf);
770 // Evaluation::value() is the main function of the class. It computes the various
771 // parts of the evaluation and returns the value of the position from the point
772 // of view of the side to move.
775 Value Evaluation<T>::value() {
777 assert(!pos.checkers());
779 // Probe the material hash table
780 me = Material::probe(pos);
782 // If we have a specialized evaluation function for the current material
783 // configuration, call it and return.
784 if (me->specialized_eval_exists())
785 return me->evaluate(pos);
787 // Initialize score by reading the incrementally updated scores included in
788 // the position object (material + piece square tables) and the material
789 // imbalance. Score is computed internally from the white point of view.
790 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
792 // Probe the pawn hash table
793 pe = Pawns::probe(pos);
794 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
796 // Early exit if score is high
797 Value v = (mg_value(score) + eg_value(score)) / 2;
798 if (abs(v) > LazyThreshold + pos.non_pawn_material() / 64)
799 return pos.side_to_move() == WHITE ? v : -v;
801 // Main evaluation begins here
806 // Pieces should be evaluated first (populate attack tables)
807 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
808 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
809 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
810 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
812 score += mobility[WHITE] - mobility[BLACK];
814 score += king< WHITE>() - king< BLACK>()
815 + threats<WHITE>() - threats<BLACK>()
816 + passed< WHITE>() - passed< BLACK>()
817 + space< WHITE>() - space< BLACK>();
819 score += initiative(eg_value(score));
821 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
822 ScaleFactor sf = scale_factor(eg_value(score));
823 v = mg_value(score) * int(me->game_phase())
824 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
828 // In case of tracing add all remaining individual evaluation terms
831 Trace::add(MATERIAL, pos.psq_score());
832 Trace::add(IMBALANCE, me->imbalance());
833 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
834 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
835 Trace::add(TOTAL, score);
838 return (pos.side_to_move() == WHITE ? v : -v) // Side to move point of view
845 /// evaluate() is the evaluator for the outer world. It returns a static
846 /// evaluation of the position from the point of view of the side to move.
848 Value Eval::evaluate(const Position& pos) {
849 return Evaluation<NO_TRACE>(pos).value();
853 /// trace() is like evaluate(), but instead of returning a value, it returns
854 /// a string (suitable for outputting to stdout) that contains the detailed
855 /// descriptions and values of each evaluation term. Useful for debugging.
857 std::string Eval::trace(const Position& pos) {
859 std::memset(scores, 0, sizeof(scores));
861 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
863 Value v = Evaluation<TRACE>(pos).value();
865 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
867 std::stringstream ss;
868 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
869 << " Term | White | Black | Total \n"
870 << " | MG EG | MG EG | MG EG \n"
871 << " ------------+-------------+-------------+------------\n"
872 << " Material | " << Term(MATERIAL)
873 << " Imbalance | " << Term(IMBALANCE)
874 << " Pawns | " << Term(PAWN)
875 << " Knights | " << Term(KNIGHT)
876 << " Bishops | " << Term(BISHOP)
877 << " Rooks | " << Term(ROOK)
878 << " Queens | " << Term(QUEEN)
879 << " Mobility | " << Term(MOBILITY)
880 << " King safety | " << Term(KING)
881 << " Threats | " << Term(THREAT)
882 << " Passed | " << Term(PASSED)
883 << " Space | " << Term(SPACE)
884 << " Initiative | " << Term(INITIATIVE)
885 << " ------------+-------------+-------------+------------\n"
886 << " Total | " << Term(TOTAL);
888 ss << "\nTotal evaluation: " << to_cp(v) << " (white side)\n";