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 // Find the squares that opponent attacks in our king flank, and the squares
445 // which are attacked twice in that flank.
446 b1 = attackedBy[Them][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
447 b2 = b1 & attackedBy2[Them];
449 int kingFlankAttacks = popcount(b1) + popcount(b2);
451 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
452 + 69 * kingAttacksCount[Them]
453 + 185 * popcount(kingRing[Us] & weak)
454 - 100 * bool(attackedBy[Us][KNIGHT] & attackedBy[Us][KING])
455 - 35 * bool(attackedBy[Us][BISHOP] & attackedBy[Us][KING])
456 + 148 * popcount(unsafeChecks)
457 + 98 * popcount(pos.blockers_for_king(Us))
458 - 873 * !pos.count<QUEEN>(Them)
459 - 6 * mg_value(score) / 8
460 + mg_value(mobility[Them] - mobility[Us])
461 + 5 * kingFlankAttacks * kingFlankAttacks / 16
464 // Transform the kingDanger units into a Score, and subtract it from the evaluation
465 if (kingDanger > 100)
466 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
468 // Penalty when our king is on a pawnless flank
469 if (!(pos.pieces(PAWN) & KingFlank[file_of(ksq)]))
470 score -= PawnlessFlank;
472 // Penalty if king flank is under attack, potentially moving toward the king
473 score -= FlankAttacks * kingFlankAttacks;
476 Trace::add(KING, Us, score);
482 // Evaluation::threats() assigns bonuses according to the types of the
483 // attacking and the attacked pieces.
484 template<Tracing T> template<Color Us>
485 Score Evaluation<T>::threats() const {
487 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
488 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
489 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
491 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe;
492 Score score = SCORE_ZERO;
495 nonPawnEnemies = pos.pieces(Them) & ~pos.pieces(PAWN);
497 // Squares strongly protected by the enemy, either because they defend the
498 // square with a pawn, or because they defend the square twice and we don't.
499 stronglyProtected = attackedBy[Them][PAWN]
500 | (attackedBy2[Them] & ~attackedBy2[Us]);
502 // Non-pawn enemies, strongly protected
503 defended = nonPawnEnemies & stronglyProtected;
505 // Enemies not strongly protected and under our attack
506 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
508 // Bonus according to the kind of attacking pieces
511 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
514 Square s = pop_lsb(&b);
515 score += ThreatByMinor[type_of(pos.piece_on(s))];
516 if (type_of(pos.piece_on(s)) != PAWN)
517 score += ThreatByRank * (int)relative_rank(Them, s);
520 b = weak & attackedBy[Us][ROOK];
523 Square s = pop_lsb(&b);
524 score += ThreatByRook[type_of(pos.piece_on(s))];
525 if (type_of(pos.piece_on(s)) != PAWN)
526 score += ThreatByRank * (int)relative_rank(Them, s);
529 if (weak & attackedBy[Us][KING])
530 score += ThreatByKing;
532 b = ~attackedBy[Them][ALL_PIECES]
533 | (nonPawnEnemies & attackedBy2[Us]);
534 score += Hanging * popcount(weak & b);
537 // Bonus for restricting their piece moves
538 b = attackedBy[Them][ALL_PIECES]
540 & attackedBy[Us][ALL_PIECES];
542 score += RestrictedPiece * popcount(b);
544 // Protected or unattacked squares
545 safe = ~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES];
547 // Bonus for attacking enemy pieces with our relatively safe pawns
548 b = pos.pieces(Us, PAWN) & safe;
549 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
550 score += ThreatBySafePawn * popcount(b);
552 // Find squares where our pawns can push on the next move
553 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
554 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
556 // Keep only the squares which are relatively safe
557 b &= ~attackedBy[Them][PAWN] & safe;
559 // Bonus for safe pawn threats on the next move
560 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
561 score += ThreatByPawnPush * popcount(b);
563 // Bonus for threats on the next moves against enemy queen
564 if (pos.count<QUEEN>(Them) == 1)
566 Square s = pos.square<QUEEN>(Them);
567 safe = mobilityArea[Us] & ~stronglyProtected;
569 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
571 score += KnightOnQueen * popcount(b & safe);
573 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
574 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
576 score += SliderOnQueen * popcount(b & safe & attackedBy2[Us]);
580 Trace::add(THREAT, Us, score);
585 // Evaluation::passed() evaluates the passed pawns and candidate passed
586 // pawns of the given color.
588 template<Tracing T> template<Color Us>
589 Score Evaluation<T>::passed() const {
591 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
592 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
594 auto king_proximity = [&](Color c, Square s) {
595 return std::min(distance(pos.square<KING>(c), s), 5);
598 Bitboard b, bb, squaresToQueen, unsafeSquares;
599 Score score = SCORE_ZERO;
601 b = pe->passed_pawns(Us);
605 Square s = pop_lsb(&b);
607 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
609 int r = relative_rank(Us, s);
612 Score bonus = PassedRank[r];
617 Square blockSq = s + Up;
619 // Adjust bonus based on the king's proximity
620 bonus += make_score(0, ( king_proximity(Them, blockSq) * 5
621 - king_proximity(Us, blockSq) * 2) * w);
623 // If blockSq is not the queening square then consider also a second push
625 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
627 // If the pawn is free to advance, then increase the bonus
628 if (pos.empty(blockSq))
630 squaresToQueen = forward_file_bb(Us, s);
631 unsafeSquares = passed_pawn_span(Us, s);
633 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN);
635 if (!(pos.pieces(Them) & bb))
636 unsafeSquares &= attackedBy[Them][ALL_PIECES];
638 // If there are no enemy attacks on passed pawn span, assign a big bonus.
639 // Otherwise assign a smaller bonus if the path to queen is not attacked
640 // and even smaller bonus if it is attacked but block square is not.
641 int k = !unsafeSquares ? 35 :
642 !(unsafeSquares & squaresToQueen) ? 20 :
643 !(unsafeSquares & blockSq) ? 9 :
646 // Assign a larger bonus if the block square is defended
647 if ((pos.pieces(Us) & bb) || (attackedBy[Us][ALL_PIECES] & blockSq))
650 bonus += make_score(k * w, k * w);
654 // Scale down bonus for candidate passers which need more than one
655 // pawn push to become passed, or have a pawn in front of them.
656 if ( !pos.pawn_passed(Us, s + Up)
657 || (pos.pieces(PAWN) & (s + Up)))
660 score += bonus - PassedFile * std::min(f, ~f);
664 Trace::add(PASSED, Us, score);
670 // Evaluation::space() computes the space evaluation for a given side. The
671 // space evaluation is a simple bonus based on the number of safe squares
672 // available for minor pieces on the central four files on ranks 2--4. Safe
673 // squares one, two or three squares behind a friendly pawn are counted
674 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
675 // improve play on game opening.
677 template<Tracing T> template<Color Us>
678 Score Evaluation<T>::space() const {
680 if (pos.non_pawn_material() < SpaceThreshold)
683 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
684 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
685 constexpr Bitboard SpaceMask =
686 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
687 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
689 // Find the available squares for our pieces inside the area defined by SpaceMask
690 Bitboard safe = SpaceMask
691 & ~pos.pieces(Us, PAWN)
692 & ~attackedBy[Them][PAWN];
694 // Find all squares which are at most three squares behind some friendly pawn
695 Bitboard behind = pos.pieces(Us, PAWN);
696 behind |= shift<Down>(behind);
697 behind |= shift<Down+Down>(behind);
699 int bonus = popcount(safe) + popcount(behind & safe & ~attackedBy[Them][ALL_PIECES]);
700 int weight = pos.count<ALL_PIECES>(Us) - 1;
701 Score score = make_score(bonus * weight * weight / 16, 0);
704 Trace::add(SPACE, Us, score);
710 // Evaluation::initiative() computes the initiative correction value
711 // for the position. It is a second order bonus/malus based on the
712 // known attacking/defending status of the players.
715 Score Evaluation<T>::initiative(Value eg) const {
717 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
718 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
720 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
721 && (pos.pieces(PAWN) & KingSide);
723 // Compute the initiative bonus for the attacking side
724 int complexity = 9 * pe->passed_count()
725 + 11 * pos.count<PAWN>()
727 + 18 * pawnsOnBothFlanks
728 + 49 * !pos.non_pawn_material()
731 // Now apply the bonus: note that we find the attacking side by extracting
732 // the sign of the endgame value, and that we carefully cap the bonus so
733 // that the endgame score will never change sign after the bonus.
734 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
737 Trace::add(INITIATIVE, make_score(0, v));
739 return make_score(0, v);
743 // Evaluation::scale_factor() computes the scale factor for the winning side
746 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
748 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
749 int sf = me->scale_factor(pos, strongSide);
751 // If scale is not already specific, scale down the endgame via general heuristics
752 if (sf == SCALE_FACTOR_NORMAL)
754 if ( pos.opposite_bishops()
755 && pos.non_pawn_material() == 2 * BishopValueMg)
756 sf = 16 + 4 * pe->passed_count();
758 sf = std::min(40 + (pos.opposite_bishops() ? 2 : 7) * pos.count<PAWN>(strongSide), sf);
762 return ScaleFactor(sf);
766 // Evaluation::value() is the main function of the class. It computes the various
767 // parts of the evaluation and returns the value of the position from the point
768 // of view of the side to move.
771 Value Evaluation<T>::value() {
773 assert(!pos.checkers());
775 // Probe the material hash table
776 me = Material::probe(pos);
778 // If we have a specialized evaluation function for the current material
779 // configuration, call it and return.
780 if (me->specialized_eval_exists())
781 return me->evaluate(pos);
783 // Initialize score by reading the incrementally updated scores included in
784 // the position object (material + piece square tables) and the material
785 // imbalance. Score is computed internally from the white point of view.
786 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
788 // Probe the pawn hash table
789 pe = Pawns::probe(pos);
790 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
792 // Early exit if score is high
793 Value v = (mg_value(score) + eg_value(score)) / 2;
794 if (abs(v) > LazyThreshold + pos.non_pawn_material() / 64)
795 return pos.side_to_move() == WHITE ? v : -v;
797 // Main evaluation begins here
802 // Pieces should be evaluated first (populate attack tables)
803 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
804 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
805 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
806 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
808 score += mobility[WHITE] - mobility[BLACK];
810 score += king< WHITE>() - king< BLACK>()
811 + threats<WHITE>() - threats<BLACK>()
812 + passed< WHITE>() - passed< BLACK>()
813 + space< WHITE>() - space< BLACK>();
815 score += initiative(eg_value(score));
817 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
818 ScaleFactor sf = scale_factor(eg_value(score));
819 v = mg_value(score) * int(me->game_phase())
820 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
824 // In case of tracing add all remaining individual evaluation terms
827 Trace::add(MATERIAL, pos.psq_score());
828 Trace::add(IMBALANCE, me->imbalance());
829 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
830 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
831 Trace::add(TOTAL, score);
834 return (pos.side_to_move() == WHITE ? v : -v) // Side to move point of view
841 /// evaluate() is the evaluator for the outer world. It returns a static
842 /// evaluation of the position from the point of view of the side to move.
844 Value Eval::evaluate(const Position& pos) {
845 return Evaluation<NO_TRACE>(pos).value();
849 /// trace() is like evaluate(), but instead of returning a value, it returns
850 /// a string (suitable for outputting to stdout) that contains the detailed
851 /// descriptions and values of each evaluation term. Useful for debugging.
853 std::string Eval::trace(const Position& pos) {
855 std::memset(scores, 0, sizeof(scores));
857 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
859 Value v = Evaluation<TRACE>(pos).value();
861 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
863 std::stringstream ss;
864 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
865 << " Term | White | Black | Total \n"
866 << " | MG EG | MG EG | MG EG \n"
867 << " ------------+-------------+-------------+------------\n"
868 << " Material | " << Term(MATERIAL)
869 << " Imbalance | " << Term(IMBALANCE)
870 << " Pawns | " << Term(PAWN)
871 << " Knights | " << Term(KNIGHT)
872 << " Bishops | " << Term(BISHOP)
873 << " Rooks | " << Term(ROOK)
874 << " Queens | " << Term(QUEEN)
875 << " Mobility | " << Term(MOBILITY)
876 << " King safety | " << Term(KING)
877 << " Threats | " << Term(THREAT)
878 << " Passed | " << Term(PASSED)
879 << " Space | " << Term(SPACE)
880 << " Initiative | " << Term(INITIATIVE)
881 << " ------------+-------------+-------------+------------\n"
882 << " Total | " << Term(TOTAL);
884 ss << "\nTotal evaluation: " << to_cp(v) << " (white side)\n";