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(5, 18), S(12, 23), S(10, 31), S(57, 62), S(163, 167), S(271, 250)
129 // PassedFile[File] contains a bonus according to the file of a passed pawn
130 constexpr Score PassedFile[FILE_NB] = {
131 S( -1, 7), S( 0, 9), S(-9, -8), S(-30,-14),
132 S(-30,-14), S(-9, -8), S( 0, 9), S( -1, 7)
135 // Assorted bonuses and penalties
136 constexpr Score BishopPawns = S( 3, 7);
137 constexpr Score CorneredBishop = S( 50, 50);
138 constexpr Score FlankAttacks = S( 8, 0);
139 constexpr Score Hanging = S( 69, 36);
140 constexpr Score KingProtector = S( 7, 8);
141 constexpr Score KnightOnQueen = S( 16, 12);
142 constexpr Score LongDiagonalBishop = S( 45, 0);
143 constexpr Score MinorBehindPawn = S( 18, 3);
144 constexpr Score Outpost = S( 36, 12);
145 constexpr Score PawnlessFlank = S( 17, 95);
146 constexpr Score RestrictedPiece = S( 7, 7);
147 constexpr Score RookOnPawn = S( 10, 32);
148 constexpr Score SliderOnQueen = S( 59, 18);
149 constexpr Score ThreatByKing = S( 24, 89);
150 constexpr Score ThreatByPawnPush = S( 48, 39);
151 constexpr Score ThreatByRank = S( 13, 0);
152 constexpr Score ThreatBySafePawn = S(173, 94);
153 constexpr Score TrappedRook = S( 47, 4);
154 constexpr Score WeakQueen = S( 49, 15);
158 // Evaluation class computes and stores attacks tables and other working data
163 Evaluation() = delete;
164 explicit Evaluation(const Position& p) : pos(p) {}
165 Evaluation& operator=(const Evaluation&) = delete;
169 template<Color Us> void initialize();
170 template<Color Us, PieceType Pt> Score pieces();
171 template<Color Us> Score king() const;
172 template<Color Us> Score threats() const;
173 template<Color Us> Score passed() const;
174 template<Color Us> Score space() const;
175 ScaleFactor scale_factor(Value eg) const;
176 Score initiative(Value eg) const;
181 Bitboard mobilityArea[COLOR_NB];
182 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
184 // attackedBy[color][piece type] is a bitboard representing all squares
185 // attacked by a given color and piece type. Special "piece types" which
186 // is also calculated is ALL_PIECES.
187 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
189 // attackedBy2[color] are the squares attacked by at least 2 units of a given
190 // color, including x-rays. But diagonal x-rays through pawns are not computed.
191 Bitboard attackedBy2[COLOR_NB];
193 // kingRing[color] are the squares adjacent to the king, plus (only for a
194 // king on its first rank) the squares two ranks in front. For instance,
195 // if black's king is on g8, kingRing[BLACK] is f8, h8, f7, g7, h7, f6, g6
197 Bitboard kingRing[COLOR_NB];
199 // kingAttackersCount[color] is the number of pieces of the given color
200 // which attack a square in the kingRing of the enemy king.
201 int kingAttackersCount[COLOR_NB];
203 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of
204 // the given color which attack a square in the kingRing of the enemy king.
205 // The weights of the individual piece types are given by the elements in
206 // the KingAttackWeights array.
207 int kingAttackersWeight[COLOR_NB];
209 // kingAttacksCount[color] is the number of attacks by the given color to
210 // squares directly adjacent to the enemy king. Pieces which attack more
211 // than one square are counted multiple times. For instance, if there is
212 // a white knight on g5 and black's king is on g8, this white knight adds 2
213 // to kingAttacksCount[WHITE].
214 int kingAttacksCount[COLOR_NB];
218 // Evaluation::initialize() computes king and pawn attacks, and the king ring
219 // bitboard for a given color. This is done at the beginning of the evaluation.
220 template<Tracing T> template<Color Us>
221 void Evaluation<T>::initialize() {
223 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
224 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
225 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
226 constexpr Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB: Rank7BB | Rank6BB);
228 const Square ksq = pos.square<KING>(Us);
230 Bitboard dblAttackByPawn = pawn_double_attacks_bb<Us>(pos.pieces(Us, PAWN));
232 // Find our pawns that are blocked or on the first two ranks
233 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
235 // Squares occupied by those pawns, by our king or queen or controlled by
236 // enemy pawns are excluded from the mobility area.
237 mobilityArea[Us] = ~(b | pos.pieces(Us, KING, QUEEN) | pe->pawn_attacks(Them));
239 // Initialize attackedBy[] for king and pawns
240 attackedBy[Us][KING] = pos.attacks_from<KING>(ksq);
241 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
242 attackedBy[Us][ALL_PIECES] = attackedBy[Us][KING] | attackedBy[Us][PAWN];
243 attackedBy2[Us] = dblAttackByPawn | (attackedBy[Us][KING] & attackedBy[Us][PAWN]);
245 // Init our king safety tables
246 kingRing[Us] = attackedBy[Us][KING];
247 if (relative_rank(Us, ksq) == RANK_1)
248 kingRing[Us] |= shift<Up>(kingRing[Us]);
250 if (file_of(ksq) == FILE_H)
251 kingRing[Us] |= shift<WEST>(kingRing[Us]);
253 else if (file_of(ksq) == FILE_A)
254 kingRing[Us] |= shift<EAST>(kingRing[Us]);
256 kingAttackersCount[Them] = popcount(kingRing[Us] & pe->pawn_attacks(Them));
257 kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
259 // Remove from kingRing[] the squares defended by two pawns
260 kingRing[Us] &= ~dblAttackByPawn;
264 // Evaluation::pieces() scores pieces of a given color and type
265 template<Tracing T> template<Color Us, PieceType Pt>
266 Score Evaluation<T>::pieces() {
268 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
269 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
270 constexpr Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
271 : Rank5BB | Rank4BB | Rank3BB);
272 const Square* pl = pos.squares<Pt>(Us);
275 Score score = SCORE_ZERO;
277 attackedBy[Us][Pt] = 0;
279 for (Square s = *pl; s != SQ_NONE; s = *++pl)
281 // Find attacked squares, including x-ray attacks for bishops and rooks
282 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
283 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
284 : pos.attacks_from<Pt>(s);
286 if (pos.blockers_for_king(Us) & s)
287 b &= LineBB[pos.square<KING>(Us)][s];
289 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
290 attackedBy[Us][Pt] |= b;
291 attackedBy[Us][ALL_PIECES] |= b;
293 if (b & kingRing[Them])
295 kingAttackersCount[Us]++;
296 kingAttackersWeight[Us] += KingAttackWeights[Pt];
297 kingAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
300 int mob = popcount(b & mobilityArea[Us]);
302 mobility[Us] += MobilityBonus[Pt - 2][mob];
304 if (Pt == BISHOP || Pt == KNIGHT)
306 // Bonus if piece is on an outpost square or can reach one
307 bb = OutpostRanks & attackedBy[Us][PAWN] & ~pe->pawn_attacks_span(Them);
309 score += Outpost * (Pt == KNIGHT ? 2 : 1);
311 else if (bb & b & ~pos.pieces(Us))
312 score += Outpost / (Pt == KNIGHT ? 1 : 2);
314 // Knight and Bishop bonus for being right behind a pawn
315 if (shift<Down>(pos.pieces(PAWN)) & s)
316 score += MinorBehindPawn;
318 // Penalty if the piece is far from the king
319 score -= KingProtector * distance(s, pos.square<KING>(Us));
323 // Penalty according to number of pawns on the same color square as the
324 // bishop, bigger when the center files are blocked with pawns.
325 Bitboard blocked = pos.pieces(Us, PAWN) & shift<Down>(pos.pieces());
327 score -= BishopPawns * pos.pawns_on_same_color_squares(Us, s)
328 * (1 + popcount(blocked & CenterFiles));
330 // Bonus for bishop on a long diagonal which can "see" both center squares
331 if (more_than_one(attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & Center))
332 score += LongDiagonalBishop;
335 // An important Chess960 pattern: A cornered bishop blocked by a friendly
336 // pawn diagonally in front of it is a very serious problem, especially
337 // when that pawn is also blocked.
340 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
342 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
343 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
344 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
345 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
352 // Bonus for aligning rook with enemy pawns on the same rank/file
353 if (relative_rank(Us, s) >= RANK_5)
354 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
356 // Bonus for rook on an open or semi-open file
357 if (pos.is_on_semiopen_file(Us, s))
358 score += RookOnFile[bool(pos.is_on_semiopen_file(Them, s))];
360 // Penalty when trapped by the king, even more if the king cannot castle
363 File kf = file_of(pos.square<KING>(Us));
364 if ((kf < FILE_E) == (file_of(s) < kf))
365 score -= TrappedRook * (1 + !pos.castling_rights(Us));
371 // Penalty if any relative pin or discovered attack against the queen
372 Bitboard queenPinners;
373 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
378 Trace::add(Pt, Us, score);
384 // Evaluation::king() assigns bonuses and penalties to a king of a given color
385 template<Tracing T> template<Color Us>
386 Score Evaluation<T>::king() const {
388 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
389 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
390 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
392 Bitboard weak, b1, b2, safe, unsafeChecks = 0;
393 Bitboard rookChecks, queenChecks, bishopChecks, knightChecks;
395 const Square ksq = pos.square<KING>(Us);
397 // Init the score with king shelter and enemy pawns storm
398 Score score = pe->king_safety<Us>(pos);
400 // Attacked squares defended at most once by our queen or king
401 weak = attackedBy[Them][ALL_PIECES]
403 & (~attackedBy[Us][ALL_PIECES] | attackedBy[Us][KING] | attackedBy[Us][QUEEN]);
405 // Analyse the safe enemy's checks which are possible on next move
406 safe = ~pos.pieces(Them);
407 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
409 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
410 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
412 // Enemy rooks checks
413 rookChecks = b1 & safe & attackedBy[Them][ROOK];
416 kingDanger += RookSafeCheck;
418 unsafeChecks |= b1 & attackedBy[Them][ROOK];
420 // Enemy queen safe checks: we count them only if they are from squares from
421 // which we can't give a rook check, because rook checks are more valuable.
422 queenChecks = (b1 | b2)
423 & attackedBy[Them][QUEEN]
425 & ~attackedBy[Us][QUEEN]
429 kingDanger += QueenSafeCheck;
431 // Enemy bishops checks: we count them only if they are from squares from
432 // which we can't give a queen check, because queen checks are more valuable.
434 & attackedBy[Them][BISHOP]
439 kingDanger += BishopSafeCheck;
441 unsafeChecks |= b2 & attackedBy[Them][BISHOP];
443 // Enemy knights checks
444 knightChecks = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
446 if (knightChecks & safe)
447 kingDanger += KnightSafeCheck;
449 unsafeChecks |= knightChecks;
451 // Unsafe or occupied checking squares will also be considered, as long as
452 // the square is in the attacker's mobility area.
453 unsafeChecks &= mobilityArea[Them];
455 // Find the squares that opponent attacks in our king flank, and the squares
456 // which are attacked twice in that flank.
457 b1 = attackedBy[Them][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
458 b2 = b1 & attackedBy2[Them];
460 int kingFlankAttacks = popcount(b1) + popcount(b2);
462 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
463 + 69 * kingAttacksCount[Them]
464 + 185 * popcount(kingRing[Us] & weak)
465 - 100 * bool(attackedBy[Us][KNIGHT] & attackedBy[Us][KING])
466 - 35 * bool(attackedBy[Us][BISHOP] & attackedBy[Us][KING])
467 + 150 * popcount(pos.blockers_for_king(Us) | unsafeChecks)
468 - 873 * !pos.count<QUEEN>(Them)
469 - 6 * mg_value(score) / 8
470 + mg_value(mobility[Them] - mobility[Us])
471 + 5 * kingFlankAttacks * kingFlankAttacks / 16
474 // Transform the kingDanger units into a Score, and subtract it from the evaluation
475 if (kingDanger > 100)
476 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
478 // Penalty when our king is on a pawnless flank
479 if (!(pos.pieces(PAWN) & KingFlank[file_of(ksq)]))
480 score -= PawnlessFlank;
482 // Penalty if king flank is under attack, potentially moving toward the king
483 score -= FlankAttacks * kingFlankAttacks;
486 Trace::add(KING, Us, score);
492 // Evaluation::threats() assigns bonuses according to the types of the
493 // attacking and the attacked pieces.
494 template<Tracing T> template<Color Us>
495 Score Evaluation<T>::threats() const {
497 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
498 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
499 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
501 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe;
502 Score score = SCORE_ZERO;
505 nonPawnEnemies = pos.pieces(Them) & ~pos.pieces(PAWN);
507 // Squares strongly protected by the enemy, either because they defend the
508 // square with a pawn, or because they defend the square twice and we don't.
509 stronglyProtected = attackedBy[Them][PAWN]
510 | (attackedBy2[Them] & ~attackedBy2[Us]);
512 // Non-pawn enemies, strongly protected
513 defended = nonPawnEnemies & stronglyProtected;
515 // Enemies not strongly protected and under our attack
516 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
518 // Safe or protected squares
519 safe = ~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES];
521 // Bonus according to the kind of attacking pieces
524 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
527 Square s = pop_lsb(&b);
528 score += ThreatByMinor[type_of(pos.piece_on(s))];
529 if (type_of(pos.piece_on(s)) != PAWN)
530 score += ThreatByRank * (int)relative_rank(Them, s);
533 b = weak & attackedBy[Us][ROOK];
536 Square s = pop_lsb(&b);
537 score += ThreatByRook[type_of(pos.piece_on(s))];
538 if (type_of(pos.piece_on(s)) != PAWN)
539 score += ThreatByRank * (int)relative_rank(Them, s);
542 if (weak & attackedBy[Us][KING])
543 score += ThreatByKing;
545 b = ~attackedBy[Them][ALL_PIECES]
546 | (nonPawnEnemies & attackedBy2[Us]);
547 score += Hanging * popcount(weak & b);
550 // Bonus for restricting their piece moves
551 b = attackedBy[Them][ALL_PIECES]
553 & attackedBy[Us][ALL_PIECES];
555 score += RestrictedPiece * popcount(b);
557 // Find squares where our pawns can push on the next move
558 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
559 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
561 // Keep only the squares which are relatively safe
562 b &= ~attackedBy[Them][PAWN] & safe;
564 // Bonus for safe pawn threats on the next move
565 b = pawn_attacks_bb<Us>(b) & pos.pieces(Them);
566 score += ThreatByPawnPush * popcount(b);
568 // Our safe or protected pawns
569 b = pos.pieces(Us, PAWN) & safe;
571 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
572 score += ThreatBySafePawn * popcount(b);
574 // Bonus for threats on the next moves against enemy queen
575 if (pos.count<QUEEN>(Them) == 1)
577 Square s = pos.square<QUEEN>(Them);
578 safe = mobilityArea[Us] & ~stronglyProtected;
580 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
582 score += KnightOnQueen * popcount(b & safe);
584 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
585 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
587 score += SliderOnQueen * popcount(b & safe & attackedBy2[Us]);
591 Trace::add(THREAT, Us, score);
596 // Evaluation::passed() evaluates the passed pawns and candidate passed
597 // pawns of the given color.
599 template<Tracing T> template<Color Us>
600 Score Evaluation<T>::passed() const {
602 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
603 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
605 auto king_proximity = [&](Color c, Square s) {
606 return std::min(distance(pos.square<KING>(c), s), 5);
609 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
610 Score score = SCORE_ZERO;
612 b = pe->passed_pawns(Us);
616 Square s = pop_lsb(&b);
618 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
620 int r = relative_rank(Us, s);
622 Score bonus = PassedRank[r];
626 int w = (r-2) * (r-2) + 2;
627 Square blockSq = s + Up;
629 // Adjust bonus based on the king's proximity
630 bonus += make_score(0, ( king_proximity(Them, blockSq) * 5
631 - king_proximity(Us, blockSq) * 2) * w);
633 // If blockSq is not the queening square then consider also a second push
635 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
637 // If the pawn is free to advance, then increase the bonus
638 if (pos.empty(blockSq))
640 // If there is a rook or queen attacking/defending the pawn from behind,
641 // consider all the squaresToQueen. Otherwise consider only the squares
642 // in the pawn's path attacked or occupied by the enemy.
643 defendedSquares = unsafeSquares = squaresToQueen = forward_file_bb(Us, s);
645 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN);
647 if (!(pos.pieces(Us) & bb))
648 defendedSquares &= attackedBy[Us][ALL_PIECES];
650 if (!(pos.pieces(Them) & bb))
651 unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
653 // If there aren't any enemy attacks, assign a big bonus. Otherwise
654 // assign a smaller bonus if the block square isn't attacked.
655 int k = !unsafeSquares ? 20 : !(unsafeSquares & blockSq) ? 9 : 0;
657 // Assign a larger bonus if the block square is defended.
658 if (defendedSquares & blockSq)
661 bonus += make_score(k * w, k * w);
665 // Scale down bonus for candidate passers which need more than one
666 // pawn push to become passed, or have a pawn in front of them.
667 if ( !pos.pawn_passed(Us, s + Up)
668 || (pos.pieces(PAWN) & forward_file_bb(Us, s)))
671 score += bonus + PassedFile[file_of(s)];
675 Trace::add(PASSED, Us, score);
681 // Evaluation::space() computes the space evaluation for a given side. The
682 // space evaluation is a simple bonus based on the number of safe squares
683 // available for minor pieces on the central four files on ranks 2--4. Safe
684 // squares one, two or three squares behind a friendly pawn are counted
685 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
686 // improve play on game opening.
688 template<Tracing T> template<Color Us>
689 Score Evaluation<T>::space() const {
691 if (pos.non_pawn_material() < SpaceThreshold)
694 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
695 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
696 constexpr Bitboard SpaceMask =
697 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
698 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
700 // Find the available squares for our pieces inside the area defined by SpaceMask
701 Bitboard safe = SpaceMask
702 & ~pos.pieces(Us, PAWN)
703 & ~attackedBy[Them][PAWN];
705 // Find all squares which are at most three squares behind some friendly pawn
706 Bitboard behind = pos.pieces(Us, PAWN);
707 behind |= shift<Down>(behind);
708 behind |= shift<Down+Down>(behind);
710 int bonus = popcount(safe) + popcount(behind & safe);
711 int weight = pos.count<ALL_PIECES>(Us) - 1;
712 Score score = make_score(bonus * weight * weight / 16, 0);
715 Trace::add(SPACE, Us, score);
721 // Evaluation::initiative() computes the initiative correction value
722 // for the position. It is a second order bonus/malus based on the
723 // known attacking/defending status of the players.
726 Score Evaluation<T>::initiative(Value eg) const {
728 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
729 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
731 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
732 && (pos.pieces(PAWN) & KingSide);
734 // Compute the initiative bonus for the attacking side
735 int complexity = 9 * pe->passed_count()
736 + 11 * pos.count<PAWN>()
738 + 18 * pawnsOnBothFlanks
739 + 49 * !pos.non_pawn_material()
742 // Now apply the bonus: note that we find the attacking side by extracting
743 // the sign of the endgame value, and that we carefully cap the bonus so
744 // that the endgame score will never change sign after the bonus.
745 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
748 Trace::add(INITIATIVE, make_score(0, v));
750 return make_score(0, v);
754 // Evaluation::scale_factor() computes the scale factor for the winning side
757 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
759 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
760 int sf = me->scale_factor(pos, strongSide);
762 // If scale is not already specific, scale down the endgame via general heuristics
763 if (sf == SCALE_FACTOR_NORMAL)
765 if ( pos.opposite_bishops()
766 && pos.non_pawn_material() == 2 * BishopValueMg)
767 sf = 16 + 4 * pe->passed_count();
769 sf = std::min(40 + (pos.opposite_bishops() ? 2 : 7) * pos.count<PAWN>(strongSide), sf);
773 return ScaleFactor(sf);
777 // Evaluation::value() is the main function of the class. It computes the various
778 // parts of the evaluation and returns the value of the position from the point
779 // of view of the side to move.
782 Value Evaluation<T>::value() {
784 assert(!pos.checkers());
786 // Probe the material hash table
787 me = Material::probe(pos);
789 // If we have a specialized evaluation function for the current material
790 // configuration, call it and return.
791 if (me->specialized_eval_exists())
792 return me->evaluate(pos);
794 // Initialize score by reading the incrementally updated scores included in
795 // the position object (material + piece square tables) and the material
796 // imbalance. Score is computed internally from the white point of view.
797 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
799 // Probe the pawn hash table
800 pe = Pawns::probe(pos);
801 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
803 // Early exit if score is high
804 Value v = (mg_value(score) + eg_value(score)) / 2;
805 if (abs(v) > (LazyThreshold + pos.non_pawn_material() / 64))
806 return pos.side_to_move() == WHITE ? v : -v;
808 // Main evaluation begins here
813 // Pieces should be evaluated first (populate attack tables)
814 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
815 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
816 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
817 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
819 score += mobility[WHITE] - mobility[BLACK];
821 score += king< WHITE>() - king< BLACK>()
822 + threats<WHITE>() - threats<BLACK>()
823 + passed< WHITE>() - passed< BLACK>()
824 + space< WHITE>() - space< BLACK>();
826 score += initiative(eg_value(score));
828 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
829 ScaleFactor sf = scale_factor(eg_value(score));
830 v = mg_value(score) * int(me->game_phase())
831 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
835 // In case of tracing add all remaining individual evaluation terms
838 Trace::add(MATERIAL, pos.psq_score());
839 Trace::add(IMBALANCE, me->imbalance());
840 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
841 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
842 Trace::add(TOTAL, score);
845 return (pos.side_to_move() == WHITE ? v : -v) // Side to move point of view
852 /// evaluate() is the evaluator for the outer world. It returns a static
853 /// evaluation of the position from the point of view of the side to move.
855 Value Eval::evaluate(const Position& pos) {
856 return Evaluation<NO_TRACE>(pos).value();
860 /// trace() is like evaluate(), but instead of returning a value, it returns
861 /// a string (suitable for outputting to stdout) that contains the detailed
862 /// descriptions and values of each evaluation term. Useful for debugging.
864 std::string Eval::trace(const Position& pos) {
866 std::memset(scores, 0, sizeof(scores));
868 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
870 Value v = Evaluation<TRACE>(pos).value();
872 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
874 std::stringstream ss;
875 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
876 << " Term | White | Black | Total \n"
877 << " | MG EG | MG EG | MG EG \n"
878 << " ------------+-------------+-------------+------------\n"
879 << " Material | " << Term(MATERIAL)
880 << " Imbalance | " << Term(IMBALANCE)
881 << " Pawns | " << Term(PAWN)
882 << " Knights | " << Term(KNIGHT)
883 << " Bishops | " << Term(BISHOP)
884 << " Rooks | " << Term(ROOK)
885 << " Queens | " << Term(QUEEN)
886 << " Mobility | " << Term(MOBILITY)
887 << " King safety | " << Term(KING)
888 << " Threats | " << Term(THREAT)
889 << " Passed | " << Term(PASSED)
890 << " Space | " << Term(SPACE)
891 << " Initiative | " << Term(INITIATIVE)
892 << " ------------+-------------+-------------+------------\n"
893 << " Total | " << Term(TOTAL);
895 ss << "\nTotal evaluation: " << to_cp(v) << " (white side)\n";