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, 81, 52, 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(21, 4), S(47, 25) };
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(6, 32), S(59, 41), S(79, 56), S(90, 119), S(79, 161)
120 constexpr Score ThreatByRook[PIECE_TYPE_NB] = {
121 S(0, 0), S(3, 44), 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( 32, 10);
139 constexpr Score PassedFile = S( 11, 8);
140 constexpr Score PawnlessFlank = S( 17, 95);
141 constexpr Score RestrictedPiece = S( 7, 7);
142 constexpr Score RookOnQueenFile = S( 7, 6);
143 constexpr Score SliderOnQueen = S( 59, 18);
144 constexpr Score ThreatByKing = S( 24, 89);
145 constexpr Score ThreatByPawnPush = S( 48, 39);
146 constexpr Score ThreatBySafePawn = S(173, 94);
147 constexpr Score TrappedRook = S( 47, 4);
148 constexpr Score WeakQueen = S( 49, 15);
152 // Evaluation class computes and stores attacks tables and other working data
157 Evaluation() = delete;
158 explicit Evaluation(const Position& p) : pos(p) {}
159 Evaluation& operator=(const Evaluation&) = delete;
163 template<Color Us> void initialize();
164 template<Color Us, PieceType Pt> Score pieces();
165 template<Color Us> Score king() const;
166 template<Color Us> Score threats() const;
167 template<Color Us> Score passed() const;
168 template<Color Us> Score space() const;
169 ScaleFactor scale_factor(Value eg) const;
170 Score initiative(Score score) const;
175 Bitboard mobilityArea[COLOR_NB];
176 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
178 // attackedBy[color][piece type] is a bitboard representing all squares
179 // attacked by a given color and piece type. Special "piece types" which
180 // is also calculated is ALL_PIECES.
181 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
183 // attackedBy2[color] are the squares attacked by at least 2 units of a given
184 // color, including x-rays. But diagonal x-rays through pawns are not computed.
185 Bitboard attackedBy2[COLOR_NB];
187 // kingRing[color] are the squares adjacent to the king plus some other
188 // very near squares, depending on king position.
189 Bitboard kingRing[COLOR_NB];
191 // kingAttackersCount[color] is the number of pieces of the given color
192 // which attack a square in the kingRing of the enemy king.
193 int kingAttackersCount[COLOR_NB];
195 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of
196 // the given color which attack a square in the kingRing of the enemy king.
197 // The weights of the individual piece types are given by the elements in
198 // the KingAttackWeights array.
199 int kingAttackersWeight[COLOR_NB];
201 // kingAttacksCount[color] is the number of attacks by the given color to
202 // squares directly adjacent to the enemy king. Pieces which attack more
203 // than one square are counted multiple times. For instance, if there is
204 // a white knight on g5 and black's king is on g8, this white knight adds 2
205 // to kingAttacksCount[WHITE].
206 int kingAttacksCount[COLOR_NB];
210 // Evaluation::initialize() computes king and pawn attacks, and the king ring
211 // bitboard for a given color. This is done at the beginning of the evaluation.
212 template<Tracing T> template<Color Us>
213 void Evaluation<T>::initialize() {
215 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
216 constexpr Direction Up = pawn_push(Us);
217 constexpr Direction Down = -Up;
218 constexpr Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB : Rank7BB | Rank6BB);
220 const Square ksq = pos.square<KING>(Us);
222 Bitboard dblAttackByPawn = pawn_double_attacks_bb<Us>(pos.pieces(Us, PAWN));
224 // Find our pawns that are blocked or on the first two ranks
225 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
227 // Squares occupied by those pawns, by our king or queen or controlled by
228 // enemy pawns are excluded from the mobility area.
229 mobilityArea[Us] = ~(b | pos.pieces(Us, KING, QUEEN) | pe->pawn_attacks(Them));
231 // Initialize attackedBy[] for king and pawns
232 attackedBy[Us][KING] = pos.attacks_from<KING>(ksq);
233 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
234 attackedBy[Us][ALL_PIECES] = attackedBy[Us][KING] | attackedBy[Us][PAWN];
235 attackedBy2[Us] = dblAttackByPawn | (attackedBy[Us][KING] & attackedBy[Us][PAWN]);
237 // Init our king safety tables
238 Square s = make_square(clamp(file_of(ksq), FILE_B, FILE_G),
239 clamp(rank_of(ksq), RANK_2, RANK_7));
240 kingRing[Us] = s | PseudoAttacks[KING][s];
242 kingAttackersCount[Them] = popcount(kingRing[Us] & pe->pawn_attacks(Them));
243 kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
245 // Remove from kingRing[] the squares defended by two pawns
246 kingRing[Us] &= ~dblAttackByPawn;
250 // Evaluation::pieces() scores pieces of a given color and type
251 template<Tracing T> template<Color Us, PieceType Pt>
252 Score Evaluation<T>::pieces() {
254 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
255 constexpr Direction Down = -pawn_push(Us);
256 constexpr Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
257 : Rank5BB | Rank4BB | Rank3BB);
258 const Square* pl = pos.squares<Pt>(Us);
261 Score score = SCORE_ZERO;
263 attackedBy[Us][Pt] = 0;
265 for (Square s = *pl; s != SQ_NONE; s = *++pl)
267 // Find attacked squares, including x-ray attacks for bishops and rooks
268 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
269 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
270 : pos.attacks_from<Pt>(s);
272 if (pos.blockers_for_king(Us) & s)
273 b &= LineBB[pos.square<KING>(Us)][s];
275 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
276 attackedBy[Us][Pt] |= b;
277 attackedBy[Us][ALL_PIECES] |= b;
279 if (b & kingRing[Them])
281 kingAttackersCount[Us]++;
282 kingAttackersWeight[Us] += KingAttackWeights[Pt];
283 kingAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
286 int mob = popcount(b & mobilityArea[Us]);
288 mobility[Us] += MobilityBonus[Pt - 2][mob];
290 if (Pt == BISHOP || Pt == KNIGHT)
292 // Bonus if piece is on an outpost square or can reach one
293 bb = OutpostRanks & attackedBy[Us][PAWN] & ~pe->pawn_attacks_span(Them);
295 score += Outpost * (Pt == KNIGHT ? 2 : 1);
297 else if (Pt == KNIGHT && bb & b & ~pos.pieces(Us))
300 // Knight and Bishop bonus for being right behind a pawn
301 if (shift<Down>(pos.pieces(PAWN)) & s)
302 score += MinorBehindPawn;
304 // Penalty if the piece is far from the king
305 score -= KingProtector * distance(s, pos.square<KING>(Us));
309 // Penalty according to number of pawns on the same color square as the
310 // bishop, bigger when the center files are blocked with pawns.
311 Bitboard blocked = pos.pieces(Us, PAWN) & shift<Down>(pos.pieces());
313 score -= BishopPawns * pos.pawns_on_same_color_squares(Us, s)
314 * (1 + popcount(blocked & CenterFiles));
316 // Bonus for bishop on a long diagonal which can "see" both center squares
317 if (more_than_one(attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & Center))
318 score += LongDiagonalBishop;
321 // An important Chess960 pattern: A cornered bishop blocked by a friendly
322 // pawn diagonally in front of it is a very serious problem, especially
323 // when that pawn is also blocked.
326 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
328 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
329 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
330 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
331 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
338 // Bonus for rook on the same file as a queen
339 if (file_bb(s) & pos.pieces(QUEEN))
340 score += RookOnQueenFile;
342 // Bonus for rook on an open or semi-open file
343 if (pos.is_on_semiopen_file(Us, s))
344 score += RookOnFile[pos.is_on_semiopen_file(Them, s)];
346 // Penalty when trapped by the king, even more if the king cannot castle
349 File kf = file_of(pos.square<KING>(Us));
350 if ((kf < FILE_E) == (file_of(s) < kf))
351 score -= TrappedRook * (1 + !pos.castling_rights(Us));
357 // Penalty if any relative pin or discovered attack against the queen
358 Bitboard queenPinners;
359 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
364 Trace::add(Pt, Us, score);
370 // Evaluation::king() assigns bonuses and penalties to a king of a given color
371 template<Tracing T> template<Color Us>
372 Score Evaluation<T>::king() const {
374 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
375 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
376 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
378 Bitboard weak, b1, b2, safe, unsafeChecks = 0;
379 Bitboard rookChecks, queenChecks, bishopChecks, knightChecks;
381 const Square ksq = pos.square<KING>(Us);
383 // Init the score with king shelter and enemy pawns storm
384 Score score = pe->king_safety<Us>(pos);
386 // Attacked squares defended at most once by our queen or king
387 weak = attackedBy[Them][ALL_PIECES]
389 & (~attackedBy[Us][ALL_PIECES] | attackedBy[Us][KING] | attackedBy[Us][QUEEN]);
391 // Analyse the safe enemy's checks which are possible on next move
392 safe = ~pos.pieces(Them);
393 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
395 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
396 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
398 // Enemy rooks checks
399 rookChecks = b1 & safe & attackedBy[Them][ROOK];
402 kingDanger += RookSafeCheck;
404 unsafeChecks |= b1 & attackedBy[Them][ROOK];
406 // Enemy queen safe checks: we count them only if they are from squares from
407 // which we can't give a rook check, because rook checks are more valuable.
408 queenChecks = (b1 | b2)
409 & attackedBy[Them][QUEEN]
411 & ~attackedBy[Us][QUEEN]
415 kingDanger += QueenSafeCheck;
417 // Enemy bishops checks: we count them only if they are from squares from
418 // which we can't give a queen check, because queen checks are more valuable.
420 & attackedBy[Them][BISHOP]
425 kingDanger += BishopSafeCheck;
427 unsafeChecks |= b2 & attackedBy[Them][BISHOP];
429 // Enemy knights checks
430 knightChecks = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
432 if (knightChecks & safe)
433 kingDanger += KnightSafeCheck;
435 unsafeChecks |= knightChecks;
437 // Find the squares that opponent attacks in our king flank, and the squares
438 // which are attacked twice in that flank.
439 b1 = attackedBy[Them][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
440 b2 = b1 & attackedBy2[Them];
442 int kingFlankAttacks = popcount(b1) + popcount(b2);
444 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
445 + 185 * popcount(kingRing[Us] & weak)
446 + 148 * popcount(unsafeChecks)
447 + 98 * popcount(pos.blockers_for_king(Us))
448 + 69 * kingAttacksCount[Them]
449 + 3 * kingFlankAttacks * kingFlankAttacks / 8
450 + mg_value(mobility[Them] - mobility[Us])
451 - 873 * !pos.count<QUEEN>(Them)
452 - 100 * bool(attackedBy[Us][KNIGHT] & attackedBy[Us][KING])
453 - 35 * bool(attackedBy[Us][BISHOP] & attackedBy[Us][KING])
454 - 6 * mg_value(score) / 8
457 // Transform the kingDanger units into a Score, and subtract it from the evaluation
458 if (kingDanger > 100)
459 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
461 // Penalty when our king is on a pawnless flank
462 if (!(pos.pieces(PAWN) & KingFlank[file_of(ksq)]))
463 score -= PawnlessFlank;
465 // Penalty if king flank is under attack, potentially moving toward the king
466 score -= FlankAttacks * kingFlankAttacks;
469 Trace::add(KING, Us, score);
475 // Evaluation::threats() assigns bonuses according to the types of the
476 // attacking and the attacked pieces.
477 template<Tracing T> template<Color Us>
478 Score Evaluation<T>::threats() const {
480 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
481 constexpr Direction Up = pawn_push(Us);
482 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
484 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe;
485 Score score = SCORE_ZERO;
488 nonPawnEnemies = pos.pieces(Them) & ~pos.pieces(PAWN);
490 // Squares strongly protected by the enemy, either because they defend the
491 // square with a pawn, or because they defend the square twice and we don't.
492 stronglyProtected = attackedBy[Them][PAWN]
493 | (attackedBy2[Them] & ~attackedBy2[Us]);
495 // Non-pawn enemies, strongly protected
496 defended = nonPawnEnemies & stronglyProtected;
498 // Enemies not strongly protected and under our attack
499 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
501 // Bonus according to the kind of attacking pieces
504 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
506 score += ThreatByMinor[type_of(pos.piece_on(pop_lsb(&b)))];
508 b = weak & attackedBy[Us][ROOK];
510 score += ThreatByRook[type_of(pos.piece_on(pop_lsb(&b)))];
512 if (weak & attackedBy[Us][KING])
513 score += ThreatByKing;
515 b = ~attackedBy[Them][ALL_PIECES]
516 | (nonPawnEnemies & attackedBy2[Us]);
517 score += Hanging * popcount(weak & b);
520 // Bonus for restricting their piece moves
521 b = attackedBy[Them][ALL_PIECES]
523 & attackedBy[Us][ALL_PIECES];
525 score += RestrictedPiece * popcount(b);
527 // Protected or unattacked squares
528 safe = ~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES];
530 // Bonus for attacking enemy pieces with our relatively safe pawns
531 b = pos.pieces(Us, PAWN) & safe;
532 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
533 score += ThreatBySafePawn * popcount(b);
535 // Find squares where our pawns can push on the next move
536 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
537 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
539 // Keep only the squares which are relatively safe
540 b &= ~attackedBy[Them][PAWN] & safe;
542 // Bonus for safe pawn threats on the next move
543 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
544 score += ThreatByPawnPush * popcount(b);
546 // Bonus for threats on the next moves against enemy queen
547 if (pos.count<QUEEN>(Them) == 1)
549 Square s = pos.square<QUEEN>(Them);
550 safe = mobilityArea[Us] & ~stronglyProtected;
552 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
554 score += KnightOnQueen * popcount(b & safe);
556 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
557 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
559 score += SliderOnQueen * popcount(b & safe & attackedBy2[Us]);
563 Trace::add(THREAT, Us, score);
568 // Evaluation::passed() evaluates the passed pawns and candidate passed
569 // pawns of the given color.
571 template<Tracing T> template<Color Us>
572 Score Evaluation<T>::passed() const {
574 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
575 constexpr Direction Up = pawn_push(Us);
577 auto king_proximity = [&](Color c, Square s) {
578 return std::min(distance(pos.square<KING>(c), s), 5);
581 Bitboard b, bb, squaresToQueen, unsafeSquares;
582 Score score = SCORE_ZERO;
584 b = pe->passed_pawns(Us);
588 Square s = pop_lsb(&b);
590 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
592 int r = relative_rank(Us, s);
594 Score bonus = PassedRank[r];
599 Square blockSq = s + Up;
601 // Adjust bonus based on the king's proximity
602 bonus += make_score(0, ( king_proximity(Them, blockSq) * 5
603 - king_proximity(Us, blockSq) * 2) * w);
605 // If blockSq is not the queening square then consider also a second push
607 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
609 // If the pawn is free to advance, then increase the bonus
610 if (pos.empty(blockSq))
612 squaresToQueen = forward_file_bb(Us, s);
613 unsafeSquares = passed_pawn_span(Us, s);
615 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN);
617 if (!(pos.pieces(Them) & bb))
618 unsafeSquares &= attackedBy[Them][ALL_PIECES];
620 // If there are no enemy attacks on passed pawn span, assign a big bonus.
621 // Otherwise assign a smaller bonus if the path to queen is not attacked
622 // and even smaller bonus if it is attacked but block square is not.
623 int k = !unsafeSquares ? 35 :
624 !(unsafeSquares & squaresToQueen) ? 20 :
625 !(unsafeSquares & blockSq) ? 9 :
628 // Assign a larger bonus if the block square is defended
629 if ((pos.pieces(Us) & bb) || (attackedBy[Us][ALL_PIECES] & blockSq))
632 bonus += make_score(k * w, k * w);
636 // Scale down bonus for candidate passers which need more than one
637 // pawn push to become passed, or have a pawn in front of them.
638 if ( !pos.pawn_passed(Us, s + Up)
639 || (pos.pieces(PAWN) & (s + Up)))
642 score += bonus - PassedFile * map_to_queenside(file_of(s));
646 Trace::add(PASSED, Us, score);
652 // Evaluation::space() computes the space evaluation for a given side. The
653 // space evaluation is a simple bonus based on the number of safe squares
654 // available for minor pieces on the central four files on ranks 2--4. Safe
655 // squares one, two or three squares behind a friendly pawn are counted
656 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
657 // improve play on game opening.
659 template<Tracing T> template<Color Us>
660 Score Evaluation<T>::space() const {
662 if (pos.non_pawn_material() < SpaceThreshold)
665 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
666 constexpr Direction Down = -pawn_push(Us);
667 constexpr Bitboard SpaceMask =
668 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
669 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
671 // Find the available squares for our pieces inside the area defined by SpaceMask
672 Bitboard safe = SpaceMask
673 & ~pos.pieces(Us, PAWN)
674 & ~attackedBy[Them][PAWN];
676 // Find all squares which are at most three squares behind some friendly pawn
677 Bitboard behind = pos.pieces(Us, PAWN);
678 behind |= shift<Down>(behind);
679 behind |= shift<Down+Down>(behind);
681 int bonus = popcount(safe) + popcount(behind & safe & ~attackedBy[Them][ALL_PIECES]);
682 int weight = pos.count<ALL_PIECES>(Us) - 1;
683 Score score = make_score(bonus * weight * weight / 16, 0);
686 Trace::add(SPACE, Us, score);
692 // Evaluation::initiative() computes the initiative correction value
693 // for the position. It is a second order bonus/malus based on the
694 // known attacking/defending status of the players.
697 Score Evaluation<T>::initiative(Score score) const {
699 Value mg = mg_value(score);
700 Value eg = eg_value(score);
702 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
703 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
705 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
706 && (pos.pieces(PAWN) & KingSide);
708 bool almostUnwinnable = !pe->passed_count()
710 && !pawnsOnBothFlanks;
712 // Compute the initiative bonus for the attacking side
713 int complexity = 9 * pe->passed_count()
714 + 11 * pos.count<PAWN>()
716 + 21 * pawnsOnBothFlanks
717 + 51 * !pos.non_pawn_material()
718 - 43 * almostUnwinnable
721 // Now apply the bonus: note that we find the attacking side by extracting the
722 // sign of the midgame or endgame values, and that we carefully cap the bonus
723 // so that the midgame and endgame scores do not change sign after the bonus.
724 int u = ((mg > 0) - (mg < 0)) * std::max(std::min(complexity + 50, 0), -abs(mg));
725 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
728 Trace::add(INITIATIVE, make_score(u, v));
730 return make_score(u, v);
734 // Evaluation::scale_factor() computes the scale factor for the winning side
737 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
739 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
740 int sf = me->scale_factor(pos, strongSide);
742 // If scale is not already specific, scale down the endgame via general heuristics
743 if (sf == SCALE_FACTOR_NORMAL)
745 if ( pos.opposite_bishops()
746 && pos.non_pawn_material() == 2 * BishopValueMg)
747 sf = 16 + 4 * pe->passed_count();
749 sf = std::min(sf, 36 + (pos.opposite_bishops() ? 2 : 7) * pos.count<PAWN>(strongSide));
751 sf = std::max(0, sf - (pos.rule50_count() - 12) / 4);
754 return ScaleFactor(sf);
758 // Evaluation::value() is the main function of the class. It computes the various
759 // parts of the evaluation and returns the value of the position from the point
760 // of view of the side to move.
763 Value Evaluation<T>::value() {
765 assert(!pos.checkers());
767 // Probe the material hash table
768 me = Material::probe(pos);
770 // If we have a specialized evaluation function for the current material
771 // configuration, call it and return.
772 if (me->specialized_eval_exists())
773 return me->evaluate(pos);
775 // Initialize score by reading the incrementally updated scores included in
776 // the position object (material + piece square tables) and the material
777 // imbalance. Score is computed internally from the white point of view.
778 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
780 // Probe the pawn hash table
781 pe = Pawns::probe(pos);
782 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
784 // Early exit if score is high
785 Value v = (mg_value(score) + eg_value(score)) / 2;
786 if (abs(v) > LazyThreshold + pos.non_pawn_material() / 64)
787 return pos.side_to_move() == WHITE ? v : -v;
789 // Main evaluation begins here
794 // Pieces should be evaluated first (populate attack tables)
795 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
796 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
797 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
798 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
800 score += mobility[WHITE] - mobility[BLACK];
802 score += king< WHITE>() - king< BLACK>()
803 + threats<WHITE>() - threats<BLACK>()
804 + passed< WHITE>() - passed< BLACK>()
805 + space< WHITE>() - space< BLACK>();
807 score += initiative(score);
809 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
810 ScaleFactor sf = scale_factor(eg_value(score));
811 v = mg_value(score) * int(me->game_phase())
812 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
816 // In case of tracing add all remaining individual evaluation terms
819 Trace::add(MATERIAL, pos.psq_score());
820 Trace::add(IMBALANCE, me->imbalance());
821 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
822 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
823 Trace::add(TOTAL, score);
826 return (pos.side_to_move() == WHITE ? v : -v) // Side to move point of view
833 /// evaluate() is the evaluator for the outer world. It returns a static
834 /// evaluation of the position from the point of view of the side to move.
836 Value Eval::evaluate(const Position& pos) {
837 return Evaluation<NO_TRACE>(pos).value();
841 /// trace() is like evaluate(), but instead of returning a value, it returns
842 /// a string (suitable for outputting to stdout) that contains the detailed
843 /// descriptions and values of each evaluation term. Useful for debugging.
845 std::string Eval::trace(const Position& pos) {
847 std::memset(scores, 0, sizeof(scores));
849 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
851 Value v = Evaluation<TRACE>(pos).value();
853 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
855 std::stringstream ss;
856 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
857 << " Term | White | Black | Total \n"
858 << " | MG EG | MG EG | MG EG \n"
859 << " ------------+-------------+-------------+------------\n"
860 << " Material | " << Term(MATERIAL)
861 << " Imbalance | " << Term(IMBALANCE)
862 << " Pawns | " << Term(PAWN)
863 << " Knights | " << Term(KNIGHT)
864 << " Bishops | " << Term(BISHOP)
865 << " Rooks | " << Term(ROOK)
866 << " Queens | " << Term(QUEEN)
867 << " Mobility | " << Term(MOBILITY)
868 << " King safety | " << Term(KING)
869 << " Threats | " << Term(THREAT)
870 << " Passed | " << Term(PASSED)
871 << " Space | " << Term(SPACE)
872 << " Initiative | " << Term(INITIATIVE)
873 << " ------------+-------------+-------------+------------\n"
874 << " Total | " << Term(TOTAL);
876 ss << "\nTotal evaluation: " << to_cp(v) << " (white side)\n";