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) 2015-2020 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, 81, 52, 44, 10 };
83 // Penalties for enemy's safe checks
84 constexpr int QueenSafeCheck = 772;
85 constexpr int RookSafeCheck = 1084;
86 constexpr int BishopSafeCheck = 645;
87 constexpr int KnightSafeCheck = 792;
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), // Knight
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), // Bishop
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(-60,-78), S(-20,-17), S( 2, 23), S( 3, 39), S( 3, 70), S( 11, 99), // Rook
100 S( 22,103), S( 31,121), S( 40,134), S( 40,139), S( 41,158), S( 48,164),
101 S( 57,168), S( 57,169), S( 62,172) },
102 { S(-34,-36), S(-15,-21), S(-10, -1), S(-10, 22), S( 20, 41), S( 23, 56), // Queen
103 S( 23, 59), S( 35, 75), S( 38, 78), S( 53, 96), S( 64, 96), S( 65,100),
104 S( 65,121), S( 66,127), S( 67,131), S( 67,133), S( 72,136), S( 72,141),
105 S( 77,147), S( 79,150), S( 93,151), S(108,168), S(108,168), S(108,171),
106 S(110,182), S(114,182), S(114,192), S(116,219) }
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(19, 7), S(48, 29) };
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(5, 32), S(57, 41), S(77, 56), S(88, 119), S(79, 161)
120 constexpr Score ThreatByRook[PIECE_TYPE_NB] = {
121 S(0, 0), S(3, 46), S(37, 68), S(42, 60), S(0, 38), S(58, 41)
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 BishopKingProtector = S( 6, 9);
135 constexpr Score KnightKingProtector = S( 8, 9);
136 constexpr Score KnightOnQueen = S( 16, 11);
137 constexpr Score LongDiagonalBishop = S( 45, 0);
138 constexpr Score MinorBehindPawn = S( 18, 3);
139 constexpr Score KnightOutpost = S( 56, 36);
140 constexpr Score BishopOutpost = S( 30, 23);
141 constexpr Score ReachableOutpost = S( 31, 22);
142 constexpr Score PassedFile = S( 11, 8);
143 constexpr Score PawnlessFlank = S( 17, 95);
144 constexpr Score RestrictedPiece = S( 7, 7);
145 constexpr Score RookOnQueenFile = S( 5, 9);
146 constexpr Score SliderOnQueen = S( 59, 18);
147 constexpr Score ThreatByKing = S( 24, 89);
148 constexpr Score ThreatByPawnPush = S( 48, 39);
149 constexpr Score ThreatBySafePawn = S(173, 94);
150 constexpr Score TrappedRook = S( 55, 13);
151 constexpr Score WeakQueen = S( 51, 14);
152 constexpr Score WeakQueenProtection = S( 15, 0);
156 // Evaluation class computes and stores attacks tables and other working data
161 Evaluation() = delete;
162 explicit Evaluation(const Position& p) : pos(p) {}
163 Evaluation& operator=(const Evaluation&) = delete;
167 template<Color Us> void initialize();
168 template<Color Us, PieceType Pt> Score pieces();
169 template<Color Us> Score king() const;
170 template<Color Us> Score threats() const;
171 template<Color Us> Score passed() const;
172 template<Color Us> Score space() const;
173 ScaleFactor scale_factor(Value eg) const;
174 Score initiative(Score score) const;
179 Bitboard mobilityArea[COLOR_NB];
180 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
182 // attackedBy[color][piece type] is a bitboard representing all squares
183 // attacked by a given color and piece type. Special "piece types" which
184 // is also calculated is ALL_PIECES.
185 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
187 // attackedBy2[color] are the squares attacked by at least 2 units of a given
188 // color, including x-rays. But diagonal x-rays through pawns are not computed.
189 Bitboard attackedBy2[COLOR_NB];
191 // kingRing[color] are the squares adjacent to the king plus some other
192 // very near squares, depending on king position.
193 Bitboard kingRing[COLOR_NB];
195 // kingAttackersCount[color] is the number of pieces of the given color
196 // which attack a square in the kingRing of the enemy king.
197 int kingAttackersCount[COLOR_NB];
199 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of
200 // the given color which attack a square in the kingRing of the enemy king.
201 // The weights of the individual piece types are given by the elements in
202 // the KingAttackWeights array.
203 int kingAttackersWeight[COLOR_NB];
205 // kingAttacksCount[color] is the number of attacks by the given color to
206 // squares directly adjacent to the enemy king. Pieces which attack more
207 // than one square are counted multiple times. For instance, if there is
208 // a white knight on g5 and black's king is on g8, this white knight adds 2
209 // to kingAttacksCount[WHITE].
210 int kingAttacksCount[COLOR_NB];
214 // Evaluation::initialize() computes king and pawn attacks, and the king ring
215 // bitboard for a given color. This is done at the beginning of the evaluation.
216 template<Tracing T> template<Color Us>
217 void Evaluation<T>::initialize() {
219 constexpr Color Them = ~Us;
220 constexpr Direction Up = pawn_push(Us);
221 constexpr Direction Down = -Up;
222 constexpr Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB : Rank7BB | Rank6BB);
224 const Square ksq = pos.square<KING>(Us);
226 Bitboard dblAttackByPawn = pawn_double_attacks_bb<Us>(pos.pieces(Us, PAWN));
228 // Find our pawns that are blocked or on the first two ranks
229 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
231 // Squares occupied by those pawns, by our king or queen, by blockers to attacks on our king
232 // or controlled by enemy pawns are excluded from the mobility area.
233 mobilityArea[Us] = ~(b | pos.pieces(Us, KING, QUEEN) | pos.blockers_for_king(Us) | pe->pawn_attacks(Them));
235 // Initialize attackedBy[] for king and pawns
236 attackedBy[Us][KING] = pos.attacks_from<KING>(ksq);
237 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
238 attackedBy[Us][ALL_PIECES] = attackedBy[Us][KING] | attackedBy[Us][PAWN];
239 attackedBy2[Us] = dblAttackByPawn | (attackedBy[Us][KING] & attackedBy[Us][PAWN]);
241 // Init our king safety tables
242 Square s = make_square(Utility::clamp(file_of(ksq), FILE_B, FILE_G),
243 Utility::clamp(rank_of(ksq), RANK_2, RANK_7));
244 kingRing[Us] = PseudoAttacks[KING][s] | s;
246 kingAttackersCount[Them] = popcount(kingRing[Us] & pe->pawn_attacks(Them));
247 kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
249 // Remove from kingRing[] the squares defended by two pawns
250 kingRing[Us] &= ~dblAttackByPawn;
254 // Evaluation::pieces() scores pieces of a given color and type
255 template<Tracing T> template<Color Us, PieceType Pt>
256 Score Evaluation<T>::pieces() {
258 constexpr Color Them = ~Us;
259 constexpr Direction Down = -pawn_push(Us);
260 constexpr Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
261 : Rank5BB | Rank4BB | Rank3BB);
262 const Square* pl = pos.squares<Pt>(Us);
265 Score score = SCORE_ZERO;
267 attackedBy[Us][Pt] = 0;
269 for (Square s = *pl; s != SQ_NONE; s = *++pl)
271 // Find attacked squares, including x-ray attacks for bishops and rooks
272 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
273 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
274 : pos.attacks_from<Pt>(s);
276 if (pos.blockers_for_king(Us) & s)
277 b &= LineBB[pos.square<KING>(Us)][s];
279 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
280 attackedBy[Us][Pt] |= b;
281 attackedBy[Us][ALL_PIECES] |= b;
283 if (b & kingRing[Them])
285 kingAttackersCount[Us]++;
286 kingAttackersWeight[Us] += KingAttackWeights[Pt];
287 kingAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
290 int mob = popcount(b & mobilityArea[Us]);
292 mobility[Us] += MobilityBonus[Pt - 2][mob];
294 if (Pt == BISHOP || Pt == KNIGHT)
296 // Bonus if piece is on an outpost square or can reach one
297 bb = OutpostRanks & attackedBy[Us][PAWN] & ~pe->pawn_attacks_span(Them);
299 score += (Pt == KNIGHT) ? KnightOutpost : BishopOutpost;
300 else if (Pt == KNIGHT && bb & b & ~pos.pieces(Us))
301 score += ReachableOutpost;
303 // Bonus for a knight or bishop shielded by pawn
304 if (shift<Down>(pos.pieces(PAWN)) & s)
305 score += MinorBehindPawn;
307 // Penalty if the piece is far from the king
308 score -= (Pt == KNIGHT ? KnightKingProtector
309 : BishopKingProtector) * distance(pos.square<KING>(Us), s);
313 // Penalty according to number of pawns on the same color square as the
314 // bishop, bigger when the center files are blocked with pawns and smaller
315 // when the bishop is outside the pawn chain.
316 Bitboard blocked = pos.pieces(Us, PAWN) & shift<Down>(pos.pieces());
318 score -= BishopPawns * pos.pawns_on_same_color_squares(Us, s)
319 * (!(attackedBy[Us][PAWN] & s) + popcount(blocked & CenterFiles));
321 // Bonus for bishop on a long diagonal which can "see" both center squares
322 if (more_than_one(attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & Center))
323 score += LongDiagonalBishop;
325 // An important Chess960 pattern: a cornered bishop blocked by a friendly
326 // pawn diagonally in front of it is a very serious problem, especially
327 // when that pawn is also blocked.
328 if ( pos.is_chess960()
329 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
331 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
332 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
333 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
334 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
342 // Bonus for rook on the same file as a queen
343 if (file_bb(s) & pos.pieces(QUEEN))
344 score += RookOnQueenFile;
346 // Bonus for rook on an open or semi-open file
347 if (pos.is_on_semiopen_file(Us, s))
348 score += RookOnFile[pos.is_on_semiopen_file(Them, s)];
350 // Penalty when trapped by the king, even more if the king cannot castle
353 File kf = file_of(pos.square<KING>(Us));
354 if ((kf < FILE_E) == (file_of(s) < kf))
355 score -= TrappedRook * (1 + !pos.castling_rights(Us));
361 // Penalty if any relative pin or discovered attack against the queen
362 Bitboard queenPinners;
363 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
368 Trace::add(Pt, Us, score);
374 // Evaluation::king() assigns bonuses and penalties to a king of a given color
375 template<Tracing T> template<Color Us>
376 Score Evaluation<T>::king() const {
378 constexpr Color Them = ~Us;
379 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
380 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
382 Bitboard weak, b1, b2, b3, safe, unsafeChecks = 0;
383 Bitboard rookChecks, queenChecks, bishopChecks, knightChecks;
385 const Square ksq = pos.square<KING>(Us);
387 // Init the score with king shelter and enemy pawns storm
388 Score score = pe->king_safety<Us>(pos);
390 // Attacked squares defended at most once by our queen or king
391 weak = attackedBy[Them][ALL_PIECES]
393 & (~attackedBy[Us][ALL_PIECES] | attackedBy[Us][KING] | attackedBy[Us][QUEEN]);
395 // Analyse the safe enemy's checks which are possible on next move
396 safe = ~pos.pieces(Them);
397 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
399 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
400 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
402 // Enemy rooks checks
403 rookChecks = b1 & safe & attackedBy[Them][ROOK];
405 kingDanger += more_than_one(rookChecks) ? RookSafeCheck * 175/100
408 unsafeChecks |= b1 & attackedBy[Them][ROOK];
410 // Enemy queen safe checks: we count them only if they are from squares from
411 // which we can't give a rook check, because rook checks are more valuable.
412 queenChecks = (b1 | b2)
413 & attackedBy[Them][QUEEN]
415 & ~attackedBy[Us][QUEEN]
418 kingDanger += more_than_one(queenChecks) ? QueenSafeCheck * 145/100
421 // Enemy bishops checks: we count them only if they are from squares from
422 // which we can't give a queen check, because queen checks are more valuable.
424 & attackedBy[Them][BISHOP]
428 kingDanger += more_than_one(bishopChecks) ? BishopSafeCheck * 3/2
431 unsafeChecks |= b2 & attackedBy[Them][BISHOP];
433 // Enemy knights checks
434 knightChecks = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
435 if (knightChecks & safe)
436 kingDanger += more_than_one(knightChecks & safe) ? KnightSafeCheck * 162/100
439 unsafeChecks |= knightChecks;
441 // Find the squares that opponent attacks in our king flank, the squares
442 // which they attack twice in that flank, and the squares that we defend.
443 b1 = attackedBy[Them][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
444 b2 = b1 & attackedBy2[Them];
445 b3 = attackedBy[Us][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
447 int kingFlankAttack = popcount(b1) + popcount(b2);
448 int kingFlankDefense = popcount(b3);
450 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
451 + 185 * popcount(kingRing[Us] & weak)
452 + 148 * popcount(unsafeChecks)
453 + 98 * popcount(pos.blockers_for_king(Us))
454 + 69 * kingAttacksCount[Them]
455 + 3 * kingFlankAttack * kingFlankAttack / 8
456 + mg_value(mobility[Them] - mobility[Us])
457 - 873 * !pos.count<QUEEN>(Them)
458 - 100 * bool(attackedBy[Us][KNIGHT] & attackedBy[Us][KING])
459 - 6 * mg_value(score) / 8
460 - 4 * kingFlankDefense
463 // Transform the kingDanger units into a Score, and subtract it from the evaluation
464 if (kingDanger > 100)
465 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
467 // Penalty when our king is on a pawnless flank
468 if (!(pos.pieces(PAWN) & KingFlank[file_of(ksq)]))
469 score -= PawnlessFlank;
471 // Penalty if king flank is under attack, potentially moving toward the king
472 score -= FlankAttacks * kingFlankAttack;
475 Trace::add(KING, Us, score);
481 // Evaluation::threats() assigns bonuses according to the types of the
482 // attacking and the attacked pieces.
483 template<Tracing T> template<Color Us>
484 Score Evaluation<T>::threats() const {
486 constexpr Color Them = ~Us;
487 constexpr Direction Up = pawn_push(Us);
488 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
490 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe;
491 Score score = SCORE_ZERO;
494 nonPawnEnemies = pos.pieces(Them) & ~pos.pieces(PAWN);
496 // Squares strongly protected by the enemy, either because they defend the
497 // square with a pawn, or because they defend the square twice and we don't.
498 stronglyProtected = attackedBy[Them][PAWN]
499 | (attackedBy2[Them] & ~attackedBy2[Us]);
501 // Non-pawn enemies, strongly protected
502 defended = nonPawnEnemies & stronglyProtected;
504 // Enemies not strongly protected and under our attack
505 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
507 // Bonus according to the kind of attacking pieces
510 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
512 score += ThreatByMinor[type_of(pos.piece_on(pop_lsb(&b)))];
514 b = weak & attackedBy[Us][ROOK];
516 score += ThreatByRook[type_of(pos.piece_on(pop_lsb(&b)))];
518 if (weak & attackedBy[Us][KING])
519 score += ThreatByKing;
521 b = ~attackedBy[Them][ALL_PIECES]
522 | (nonPawnEnemies & attackedBy2[Us]);
523 score += Hanging * popcount(weak & b);
525 // Additional bonus if weak piece is only protected by a queen
526 score += WeakQueenProtection * popcount(weak & attackedBy[Them][QUEEN]);
529 // Bonus for restricting their piece moves
530 b = attackedBy[Them][ALL_PIECES]
532 & attackedBy[Us][ALL_PIECES];
533 score += RestrictedPiece * popcount(b);
535 // Protected or unattacked squares
536 safe = ~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES];
538 // Bonus for attacking enemy pieces with our relatively safe pawns
539 b = pos.pieces(Us, PAWN) & safe;
540 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
541 score += ThreatBySafePawn * popcount(b);
543 // Find squares where our pawns can push on the next move
544 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
545 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
547 // Keep only the squares which are relatively safe
548 b &= ~attackedBy[Them][PAWN] & safe;
550 // Bonus for safe pawn threats on the next move
551 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
552 score += ThreatByPawnPush * popcount(b);
554 // Bonus for threats on the next moves against enemy queen
555 if (pos.count<QUEEN>(Them) == 1)
557 Square s = pos.square<QUEEN>(Them);
558 safe = mobilityArea[Us] & ~stronglyProtected;
560 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
562 score += KnightOnQueen * popcount(b & safe);
564 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
565 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
567 score += SliderOnQueen * popcount(b & safe & attackedBy2[Us]);
571 Trace::add(THREAT, Us, score);
576 // Evaluation::passed() evaluates the passed pawns and candidate passed
577 // pawns of the given color.
579 template<Tracing T> template<Color Us>
580 Score Evaluation<T>::passed() const {
582 constexpr Color Them = ~Us;
583 constexpr Direction Up = pawn_push(Us);
584 constexpr Direction Down = -Up;
586 auto king_proximity = [&](Color c, Square s) {
587 return std::min(distance(pos.square<KING>(c), s), 5);
590 Bitboard b, bb, squaresToQueen, unsafeSquares, candidatePassers, leverable;
591 Score score = SCORE_ZERO;
593 b = pe->passed_pawns(Us);
595 candidatePassers = b & shift<Down>(pos.pieces(Them, PAWN));
596 if (candidatePassers)
598 // Can we lever the blocker of a candidate passer?
599 leverable = shift<Up>(pos.pieces(Us, PAWN))
601 & (~attackedBy2[Them] | attackedBy[Us][ALL_PIECES])
602 & (~(attackedBy[Them][KNIGHT] | attackedBy[Them][BISHOP])
603 | (attackedBy[Us ][KNIGHT] | attackedBy[Us ][BISHOP]));
605 // Remove candidate otherwise
606 b &= ~candidatePassers
607 | shift<WEST>(leverable)
608 | shift<EAST>(leverable);
613 Square s = pop_lsb(&b);
615 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
617 int r = relative_rank(Us, s);
619 Score bonus = PassedRank[r];
624 Square blockSq = s + Up;
626 // Adjust bonus based on the king's proximity
627 bonus += make_score(0, ( (king_proximity(Them, blockSq) * 19) / 4
628 - king_proximity(Us, blockSq) * 2) * w);
630 // If blockSq is not the queening square then consider also a second push
632 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
634 // If the pawn is free to advance, then increase the bonus
635 if (pos.empty(blockSq))
637 squaresToQueen = forward_file_bb(Us, s);
638 unsafeSquares = passed_pawn_span(Us, s);
640 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN);
642 if (!(pos.pieces(Them) & bb))
643 unsafeSquares &= attackedBy[Them][ALL_PIECES];
645 // If there are no enemy attacks on passed pawn span, assign a big bonus.
646 // Otherwise assign a smaller bonus if the path to queen is not attacked
647 // and even smaller bonus if it is attacked but block square is not.
648 int k = !unsafeSquares ? 35 :
649 !(unsafeSquares & squaresToQueen) ? 20 :
650 !(unsafeSquares & blockSq) ? 9 :
653 // Assign a larger bonus if the block square is defended
654 if ((pos.pieces(Us) & bb) || (attackedBy[Us][ALL_PIECES] & blockSq))
657 bonus += make_score(k * w, k * w);
661 score += bonus - PassedFile * edge_distance(file_of(s));
665 Trace::add(PASSED, Us, score);
671 // Evaluation::space() computes the space evaluation for a given side. The
672 // space evaluation is a simple bonus based on the number of safe squares
673 // available for minor pieces on the central four files on ranks 2--4. Safe
674 // squares one, two or three squares behind a friendly pawn are counted
675 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
676 // improve play on game opening.
678 template<Tracing T> template<Color Us>
679 Score Evaluation<T>::space() const {
681 if (pos.non_pawn_material() < SpaceThreshold)
684 constexpr Color Them = ~Us;
685 constexpr Direction Down = -pawn_push(Us);
686 constexpr Bitboard SpaceMask =
687 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
688 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
690 // Find the available squares for our pieces inside the area defined by SpaceMask
691 Bitboard safe = SpaceMask
692 & ~pos.pieces(Us, PAWN)
693 & ~attackedBy[Them][PAWN];
695 // Find all squares which are at most three squares behind some friendly pawn
696 Bitboard behind = pos.pieces(Us, PAWN);
697 behind |= shift<Down>(behind);
698 behind |= shift<Down+Down>(behind);
700 int bonus = popcount(safe) + popcount(behind & safe & ~attackedBy[Them][ALL_PIECES]);
701 int weight = pos.count<ALL_PIECES>(Us) - 3 + std::min(pe->blocked_count(), 9);
702 Score score = make_score(bonus * weight * weight / 16, 0);
705 Trace::add(SPACE, Us, score);
711 // Evaluation::initiative() computes the initiative correction value
712 // for the position. It is a second order bonus/malus based on the
713 // known attacking/defending status of the players.
716 Score Evaluation<T>::initiative(Score score) const {
718 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
719 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
721 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
722 && (pos.pieces(PAWN) & KingSide);
724 bool almostUnwinnable = outflanking < 0
725 && !pawnsOnBothFlanks;
727 bool infiltration = rank_of(pos.square<KING>(WHITE)) > RANK_4
728 || rank_of(pos.square<KING>(BLACK)) < RANK_5;
730 // Compute the initiative bonus for the attacking side
731 int complexity = 9 * pe->passed_count()
732 + 11 * pos.count<PAWN>()
734 + 21 * pawnsOnBothFlanks
736 + 51 * !pos.non_pawn_material()
737 - 43 * almostUnwinnable
740 Value mg = mg_value(score);
741 Value eg = eg_value(score);
743 // Now apply the bonus: note that we find the attacking side by extracting the
744 // sign of the midgame or endgame values, and that we carefully cap the bonus
745 // so that the midgame and endgame scores do not change sign after the bonus.
746 int u = ((mg > 0) - (mg < 0)) * Utility::clamp(complexity + 50, -abs(mg), 0);
747 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
750 Trace::add(INITIATIVE, make_score(u, v));
752 return make_score(u, v);
756 // Evaluation::scale_factor() computes the scale factor for the winning side
759 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
761 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
762 int sf = me->scale_factor(pos, strongSide);
764 // If scale is not already specific, scale down the endgame via general heuristics
765 if (sf == SCALE_FACTOR_NORMAL)
767 if (pos.opposite_bishops())
769 if ( pos.non_pawn_material(WHITE) == BishopValueMg
770 && pos.non_pawn_material(BLACK) == BishopValueMg)
773 sf = 22 + 3 * pos.count<ALL_PIECES>(strongSide);
776 sf = std::min(sf, 36 + 7 * pos.count<PAWN>(strongSide));
778 sf = std::max(0, sf - (pos.rule50_count() - 12) / 4);
781 return ScaleFactor(sf);
785 // Evaluation::value() is the main function of the class. It computes the various
786 // parts of the evaluation and returns the value of the position from the point
787 // of view of the side to move.
790 Value Evaluation<T>::value() {
792 assert(!pos.checkers());
794 // Probe the material hash table
795 me = Material::probe(pos);
797 // If we have a specialized evaluation function for the current material
798 // configuration, call it and return.
799 if (me->specialized_eval_exists())
800 return me->evaluate(pos);
802 // Initialize score by reading the incrementally updated scores included in
803 // the position object (material + piece square tables) and the material
804 // imbalance. Score is computed internally from the white point of view.
805 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
807 // Probe the pawn hash table
808 pe = Pawns::probe(pos);
809 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
811 // Early exit if score is high
812 Value v = (mg_value(score) + eg_value(score)) / 2;
813 if (abs(v) > LazyThreshold + pos.non_pawn_material() / 64)
814 return pos.side_to_move() == WHITE ? v : -v;
816 // Main evaluation begins here
821 // Pieces evaluated first (also populates attackedBy, attackedBy2).
822 // Note that the order of evaluation of the terms is left unspecified
823 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
824 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
825 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
826 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
828 score += mobility[WHITE] - mobility[BLACK];
830 // More complex interactions that require fully populated attack bitboards
831 score += king< WHITE>() - king< BLACK>()
832 + threats<WHITE>() - threats<BLACK>()
833 + passed< WHITE>() - passed< BLACK>()
834 + space< WHITE>() - space< BLACK>();
836 score += initiative(score);
838 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
839 ScaleFactor sf = scale_factor(eg_value(score));
840 v = mg_value(score) * int(me->game_phase())
841 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
845 // In case of tracing add all remaining individual evaluation terms
848 Trace::add(MATERIAL, pos.psq_score());
849 Trace::add(IMBALANCE, me->imbalance());
850 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
851 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
852 Trace::add(TOTAL, score);
855 return (pos.side_to_move() == WHITE ? v : -v) + Tempo; // Side to move point of view
861 /// evaluate() is the evaluator for the outer world. It returns a static
862 /// evaluation of the position from the point of view of the side to move.
864 Value Eval::evaluate(const Position& pos) {
865 return Evaluation<NO_TRACE>(pos).value();
869 /// trace() is like evaluate(), but instead of returning a value, it returns
870 /// a string (suitable for outputting to stdout) that contains the detailed
871 /// descriptions and values of each evaluation term. Useful for debugging.
873 std::string Eval::trace(const Position& pos) {
876 return "Total evaluation: none (in check)";
878 std::memset(scores, 0, sizeof(scores));
880 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
882 Value v = Evaluation<TRACE>(pos).value();
884 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
886 std::stringstream ss;
887 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
888 << " Term | White | Black | Total \n"
889 << " | MG EG | MG EG | MG EG \n"
890 << " ------------+-------------+-------------+------------\n"
891 << " Material | " << Term(MATERIAL)
892 << " Imbalance | " << Term(IMBALANCE)
893 << " Pawns | " << Term(PAWN)
894 << " Knights | " << Term(KNIGHT)
895 << " Bishops | " << Term(BISHOP)
896 << " Rooks | " << Term(ROOK)
897 << " Queens | " << Term(QUEEN)
898 << " Mobility | " << Term(MOBILITY)
899 << " King safety | " << Term(KING)
900 << " Threats | " << Term(THREAT)
901 << " Passed | " << Term(PASSED)
902 << " Space | " << Term(SPACE)
903 << " Initiative | " << Term(INITIATIVE)
904 << " ------------+-------------+-------------+------------\n"
905 << " Total | " << Term(TOTAL);
907 ss << "\nTotal evaluation: " << to_cp(v) << " (white side)\n";