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(1500);
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( 9, 3);
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);
155 constexpr Score WeakUnopposedPawn = S( 12, 23);
159 // Evaluation class computes and stores attacks tables and other working data
164 Evaluation() = delete;
165 explicit Evaluation(const Position& p) : pos(p) {}
166 Evaluation& operator=(const Evaluation&) = delete;
170 template<Color Us> void initialize();
171 template<Color Us, PieceType Pt> Score pieces();
172 template<Color Us> Score king() const;
173 template<Color Us> Score threats() const;
174 template<Color Us> Score passed() const;
175 template<Color Us> Score space() const;
176 ScaleFactor scale_factor(Value eg) const;
177 Score initiative(Value eg) const;
182 Bitboard mobilityArea[COLOR_NB];
183 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
185 // attackedBy[color][piece type] is a bitboard representing all squares
186 // attacked by a given color and piece type. Special "piece types" which
187 // is also calculated is ALL_PIECES.
188 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
190 // attackedBy2[color] are the squares attacked by 2 pieces of a given color,
191 // possibly via x-ray or by one pawn and one piece. Diagonal x-ray through
192 // pawn or squares attacked by 2 pawns are not explicitly added.
193 Bitboard attackedBy2[COLOR_NB];
195 // kingRing[color] are the squares adjacent to the king, plus (only for a
196 // king on its first rank) the squares two ranks in front. For instance,
197 // if black's king is on g8, kingRing[BLACK] is f8, h8, f7, g7, h7, f6, g6
199 Bitboard kingRing[COLOR_NB];
201 // kingAttackersCount[color] is the number of pieces of the given color
202 // which attack a square in the kingRing of the enemy king.
203 int kingAttackersCount[COLOR_NB];
205 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of
206 // the given color which attack a square in the kingRing of the enemy king.
207 // The weights of the individual piece types are given by the elements in
208 // the KingAttackWeights array.
209 int kingAttackersWeight[COLOR_NB];
211 // kingAttacksCount[color] is the number of attacks by the given color to
212 // squares directly adjacent to the enemy king. Pieces which attack more
213 // than one square are counted multiple times. For instance, if there is
214 // a white knight on g5 and black's king is on g8, this white knight adds 2
215 // to kingAttacksCount[WHITE].
216 int kingAttacksCount[COLOR_NB];
220 // Evaluation::initialize() computes king and pawn attacks, and the king ring
221 // bitboard for a given color. This is done at the beginning of the evaluation.
222 template<Tracing T> template<Color Us>
223 void Evaluation<T>::initialize() {
225 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
226 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
227 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
228 constexpr Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB: Rank7BB | Rank6BB);
230 const Square ksq = pos.square<KING>(Us);
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] = 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] &= ~pawn_double_attacks_bb<Us>(pos.pieces(Us, PAWN));
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 & ~pe->pawn_attacks_span(Them);
309 score += Outpost * (Pt == KNIGHT ? 4 : 2)
310 * (1 + bool(attackedBy[Us][PAWN] & s));
312 else if (bb &= b & ~pos.pieces(Us))
313 score += Outpost * (Pt == KNIGHT ? 2 : 1)
314 * (1 + bool(attackedBy[Us][PAWN] & bb));
316 // Knight and Bishop bonus for being right behind a pawn
317 if (shift<Down>(pos.pieces(PAWN)) & s)
318 score += MinorBehindPawn;
320 // Penalty if the piece is far from the king
321 score -= KingProtector * distance(s, pos.square<KING>(Us));
325 // Penalty according to number of pawns on the same color square as the
326 // bishop, bigger when the center files are blocked with pawns.
327 Bitboard blocked = pos.pieces(Us, PAWN) & shift<Down>(pos.pieces());
329 score -= BishopPawns * pe->pawns_on_same_color_squares(Us, s)
330 * (1 + popcount(blocked & CenterFiles));
332 // Bonus for bishop on a long diagonal which can "see" both center squares
333 if (more_than_one(attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & Center))
334 score += LongDiagonalBishop;
337 // An important Chess960 pattern: A cornered bishop blocked by a friendly
338 // pawn diagonally in front of it is a very serious problem, especially
339 // when that pawn is also blocked.
342 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
344 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
345 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
346 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
347 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
354 // Bonus for aligning rook with enemy pawns on the same rank/file
355 if (relative_rank(Us, s) >= RANK_5)
356 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
358 // Bonus for rook on an open or semi-open file
359 if (pe->semiopen_file(Us, file_of(s)))
360 score += RookOnFile[bool(pe->semiopen_file(Them, file_of(s)))];
362 // Penalty when trapped by the king, even more if the king cannot castle
365 File kf = file_of(pos.square<KING>(Us));
366 if ((kf < FILE_E) == (file_of(s) < kf))
367 score -= TrappedRook * (1 + !pos.castling_rights(Us));
373 // Penalty if any relative pin or discovered attack against the queen
374 Bitboard queenPinners;
375 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
380 Trace::add(Pt, Us, score);
386 // Evaluation::king() assigns bonuses and penalties to a king of a given color
387 template<Tracing T> template<Color Us>
388 Score Evaluation<T>::king() const {
390 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
391 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
392 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
394 Bitboard weak, b1, b2, safe, unsafeChecks = 0;
395 Bitboard rookChecks, queenChecks, bishopChecks, knightChecks;
397 const Square ksq = pos.square<KING>(Us);
399 // Init the score with king shelter and enemy pawns storm
400 Score score = pe->king_safety<Us>(pos);
402 // Attacked squares defended at most once by our queen or king
403 weak = attackedBy[Them][ALL_PIECES]
405 & (~attackedBy[Us][ALL_PIECES] | attackedBy[Us][KING] | attackedBy[Us][QUEEN]);
407 // Analyse the safe enemy's checks which are possible on next move
408 safe = ~pos.pieces(Them);
409 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
411 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
412 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
414 // Enemy rooks checks
415 rookChecks = b1 & safe & attackedBy[Them][ROOK];
418 kingDanger += RookSafeCheck;
420 unsafeChecks |= b1 & attackedBy[Them][ROOK];
422 // Enemy queen safe checks: we count them only if they are from squares from
423 // which we can't give a rook check, because rook checks are more valuable.
424 queenChecks = (b1 | b2)
425 & attackedBy[Them][QUEEN]
427 & ~attackedBy[Us][QUEEN]
431 kingDanger += QueenSafeCheck;
433 // Enemy bishops checks: we count them only if they are from squares from
434 // which we can't give a queen check, because queen checks are more valuable.
436 & attackedBy[Them][BISHOP]
441 kingDanger += BishopSafeCheck;
443 unsafeChecks |= b2 & attackedBy[Them][BISHOP];
445 // Enemy knights checks
446 knightChecks = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
448 if (knightChecks & safe)
449 kingDanger += KnightSafeCheck;
451 unsafeChecks |= knightChecks;
453 // Unsafe or occupied checking squares will also be considered, as long as
454 // the square is in the attacker's mobility area.
455 unsafeChecks &= mobilityArea[Them];
457 // Find the squares that opponent attacks in our king flank, and the squares
458 // which are attacked twice in that flank.
459 b1 = attackedBy[Them][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
460 b2 = b1 & attackedBy2[Them];
462 int kingFlankAttacks = popcount(b1) + popcount(b2);
464 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
465 + 69 * kingAttacksCount[Them]
466 + 185 * popcount(kingRing[Us] & weak)
467 - 100 * bool(attackedBy[Us][KNIGHT] & attackedBy[Us][KING])
468 + 150 * popcount(pos.blockers_for_king(Us) | unsafeChecks)
469 - 873 * !pos.count<QUEEN>(Them)
470 - 6 * mg_value(score) / 8
471 + mg_value(mobility[Them] - mobility[Us])
472 + 5 * kingFlankAttacks * kingFlankAttacks / 16
475 // Transform the kingDanger units into a Score, and subtract it from the evaluation
477 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
479 // Penalty when our king is on a pawnless flank
480 if (!(pos.pieces(PAWN) & KingFlank[file_of(ksq)]))
481 score -= PawnlessFlank;
483 // Penalty if king flank is under attack, potentially moving toward the king
484 score -= FlankAttacks * kingFlankAttacks;
487 Trace::add(KING, Us, score);
493 // Evaluation::threats() assigns bonuses according to the types of the
494 // attacking and the attacked pieces.
495 template<Tracing T> template<Color Us>
496 Score Evaluation<T>::threats() const {
498 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
499 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
500 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
502 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe;
503 Score score = SCORE_ZERO;
506 nonPawnEnemies = pos.pieces(Them) & ~pos.pieces(PAWN);
508 // Squares strongly protected by the enemy, either because they defend the
509 // square with a pawn, or because they defend the square twice and we don't.
510 stronglyProtected = attackedBy[Them][PAWN]
511 | (attackedBy2[Them] & ~attackedBy2[Us]);
513 // Non-pawn enemies, strongly protected
514 defended = nonPawnEnemies & stronglyProtected;
516 // Enemies not strongly protected and under our attack
517 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
519 // Safe or protected squares
520 safe = ~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES];
522 // Bonus according to the kind of attacking pieces
525 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
528 Square s = pop_lsb(&b);
529 score += ThreatByMinor[type_of(pos.piece_on(s))];
530 if (type_of(pos.piece_on(s)) != PAWN)
531 score += ThreatByRank * (int)relative_rank(Them, s);
534 b = weak & attackedBy[Us][ROOK];
537 Square s = pop_lsb(&b);
538 score += ThreatByRook[type_of(pos.piece_on(s))];
539 if (type_of(pos.piece_on(s)) != PAWN)
540 score += ThreatByRank * (int)relative_rank(Them, s);
543 if (weak & attackedBy[Us][KING])
544 score += ThreatByKing;
546 b = ~attackedBy[Them][ALL_PIECES]
547 | (nonPawnEnemies & attackedBy2[Us]);
548 score += Hanging * popcount(weak & b);
551 // Bonus for restricting their piece moves
552 b = attackedBy[Them][ALL_PIECES]
554 & attackedBy[Us][ALL_PIECES];
556 score += RestrictedPiece * popcount(b);
558 // Bonus for enemy unopposed weak pawns
559 if (pos.pieces(Us, ROOK, QUEEN))
560 score += WeakUnopposedPawn * pe->weak_unopposed(Them);
562 // Find squares where our pawns can push on the next move
563 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
564 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
566 // Keep only the squares which are relatively safe
567 b &= ~attackedBy[Them][PAWN] & safe;
569 // Bonus for safe pawn threats on the next move
570 b = pawn_attacks_bb<Us>(b) & pos.pieces(Them);
571 score += ThreatByPawnPush * popcount(b);
573 // Our safe or protected pawns
574 b = pos.pieces(Us, PAWN) & safe;
576 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
577 score += ThreatBySafePawn * popcount(b);
579 // Bonus for threats on the next moves against enemy queen
580 if (pos.count<QUEEN>(Them) == 1)
582 Square s = pos.square<QUEEN>(Them);
583 safe = mobilityArea[Us] & ~stronglyProtected;
585 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
587 score += KnightOnQueen * popcount(b & safe);
589 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
590 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
592 score += SliderOnQueen * popcount(b & safe & attackedBy2[Us]);
596 Trace::add(THREAT, Us, score);
601 // Evaluation::passed() evaluates the passed pawns and candidate passed
602 // pawns of the given color.
604 template<Tracing T> template<Color Us>
605 Score Evaluation<T>::passed() const {
607 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
608 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
610 auto king_proximity = [&](Color c, Square s) {
611 return std::min(distance(pos.square<KING>(c), s), 5);
614 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
615 Score score = SCORE_ZERO;
617 b = pe->passed_pawns(Us);
621 Square s = pop_lsb(&b);
623 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
625 int r = relative_rank(Us, s);
627 Score bonus = PassedRank[r];
631 int w = (r-2) * (r-2) + 2;
632 Square blockSq = s + Up;
634 // Adjust bonus based on the king's proximity
635 bonus += make_score(0, ( king_proximity(Them, blockSq) * 5
636 - king_proximity(Us, blockSq) * 2) * w);
638 // If blockSq is not the queening square then consider also a second push
640 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
642 // If the pawn is free to advance, then increase the bonus
643 if (pos.empty(blockSq))
645 // If there is a rook or queen attacking/defending the pawn from behind,
646 // consider all the squaresToQueen. Otherwise consider only the squares
647 // in the pawn's path attacked or occupied by the enemy.
648 defendedSquares = unsafeSquares = squaresToQueen = forward_file_bb(Us, s);
650 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
652 if (!(pos.pieces(Us) & bb))
653 defendedSquares &= attackedBy[Us][ALL_PIECES];
655 if (!(pos.pieces(Them) & bb))
656 unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
658 // If there aren't any enemy attacks, assign a big bonus. Otherwise
659 // assign a smaller bonus if the block square isn't attacked.
660 int k = !unsafeSquares ? 20 : !(unsafeSquares & blockSq) ? 9 : 0;
662 // If the path to the queen is fully defended, assign a big bonus.
663 // Otherwise assign a smaller bonus if the block square is defended.
664 if (defendedSquares == squaresToQueen)
667 else if (defendedSquares & blockSq)
670 bonus += make_score(k * w, k * w);
674 // Scale down bonus for candidate passers which need more than one
675 // pawn push to become passed, or have a pawn in front of them.
676 if ( !pos.pawn_passed(Us, s + Up)
677 || (pos.pieces(PAWN) & forward_file_bb(Us, s)))
680 score += bonus + PassedFile[file_of(s)];
684 Trace::add(PASSED, Us, score);
690 // Evaluation::space() computes the space evaluation for a given side. The
691 // space evaluation is a simple bonus based on the number of safe squares
692 // available for minor pieces on the central four files on ranks 2--4. Safe
693 // squares one, two or three squares behind a friendly pawn are counted
694 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
695 // improve play on game opening.
697 template<Tracing T> template<Color Us>
698 Score Evaluation<T>::space() const {
700 if (pos.non_pawn_material() < SpaceThreshold)
703 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
704 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
705 constexpr Bitboard SpaceMask =
706 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
707 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
709 // Find the available squares for our pieces inside the area defined by SpaceMask
710 Bitboard safe = SpaceMask
711 & ~pos.pieces(Us, PAWN)
712 & ~attackedBy[Them][PAWN];
714 // Find all squares which are at most three squares behind some friendly pawn
715 Bitboard behind = pos.pieces(Us, PAWN);
716 behind |= shift<Down>(behind);
717 behind |= shift<Down>(shift<Down>(behind));
719 int bonus = popcount(safe) + popcount(behind & safe);
720 int weight = pos.count<ALL_PIECES>(Us)
721 - 2 * popcount(pe->semiopenFiles[WHITE] & pe->semiopenFiles[BLACK]);
723 Score score = make_score(bonus * weight * weight / 16, 0);
726 Trace::add(SPACE, Us, score);
732 // Evaluation::initiative() computes the initiative correction value
733 // for the position. It is a second order bonus/malus based on the
734 // known attacking/defending status of the players.
737 Score Evaluation<T>::initiative(Value eg) const {
739 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
740 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
742 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
743 && (pos.pieces(PAWN) & KingSide);
745 // Compute the initiative bonus for the attacking side
746 int complexity = 9 * pe->pawn_asymmetry()
747 + 11 * pos.count<PAWN>()
749 + 18 * pawnsOnBothFlanks
750 + 49 * !pos.non_pawn_material()
753 // Now apply the bonus: note that we find the attacking side by extracting
754 // the sign of the endgame value, and that we carefully cap the bonus so
755 // that the endgame score will never change sign after the bonus.
756 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
759 Trace::add(INITIATIVE, make_score(0, v));
761 return make_score(0, v);
765 // Evaluation::scale_factor() computes the scale factor for the winning side
768 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
770 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
771 int sf = me->scale_factor(pos, strongSide);
773 // If scale is not already specific, scale down the endgame via general heuristics
774 if (sf == SCALE_FACTOR_NORMAL)
776 if ( pos.opposite_bishops()
777 && pos.non_pawn_material(WHITE) == BishopValueMg
778 && pos.non_pawn_material(BLACK) == BishopValueMg)
779 sf = 8 + 4 * pe->pawn_asymmetry();
781 sf = std::min(40 + (pos.opposite_bishops() ? 2 : 7) * pos.count<PAWN>(strongSide), sf);
785 return ScaleFactor(sf);
789 // Evaluation::value() is the main function of the class. It computes the various
790 // parts of the evaluation and returns the value of the position from the point
791 // of view of the side to move.
794 Value Evaluation<T>::value() {
796 assert(!pos.checkers());
798 // Probe the material hash table
799 me = Material::probe(pos);
801 // If we have a specialized evaluation function for the current material
802 // configuration, call it and return.
803 if (me->specialized_eval_exists())
804 return me->evaluate(pos);
806 // Initialize score by reading the incrementally updated scores included in
807 // the position object (material + piece square tables) and the material
808 // imbalance. Score is computed internally from the white point of view.
809 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
811 // Probe the pawn hash table
812 pe = Pawns::probe(pos);
813 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
815 // Early exit if score is high
816 Value v = (mg_value(score) + eg_value(score)) / 2;
817 if (abs(v) > LazyThreshold)
818 return pos.side_to_move() == WHITE ? v : -v;
820 // Main evaluation begins here
825 // Pieces should be evaluated first (populate attack tables)
826 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
827 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
828 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
829 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
831 score += mobility[WHITE] - mobility[BLACK];
833 score += king< WHITE>() - king< BLACK>()
834 + threats<WHITE>() - threats<BLACK>()
835 + passed< WHITE>() - passed< BLACK>()
836 + space< WHITE>() - space< BLACK>();
838 score += initiative(eg_value(score));
840 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
841 ScaleFactor sf = scale_factor(eg_value(score));
842 v = mg_value(score) * int(me->game_phase())
843 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
847 // In case of tracing add all remaining individual evaluation terms
850 Trace::add(MATERIAL, pos.psq_score());
851 Trace::add(IMBALANCE, me->imbalance());
852 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
853 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
854 Trace::add(TOTAL, score);
857 return (pos.side_to_move() == WHITE ? v : -v) // Side to move point of view
864 /// evaluate() is the evaluator for the outer world. It returns a static
865 /// evaluation of the position from the point of view of the side to move.
867 Value Eval::evaluate(const Position& pos) {
868 return Evaluation<NO_TRACE>(pos).value();
872 /// trace() is like evaluate(), but instead of returning a value, it returns
873 /// a string (suitable for outputting to stdout) that contains the detailed
874 /// descriptions and values of each evaluation term. Useful for debugging.
876 std::string Eval::trace(const Position& pos) {
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";