2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
5 Copyright (C) 2015-2020 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
7 Stockfish is free software: you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation, either version 3 of the License, or
10 (at your option) any later version.
12 Stockfish is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <http://www.gnu.org/licenses/>.
23 #include <cstring> // For std::memset
35 enum Tracing { NO_TRACE, TRACE };
37 enum Term { // The first 8 entries are reserved for PieceType
38 MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, INITIATIVE, TOTAL, TERM_NB
41 Score scores[TERM_NB][COLOR_NB];
43 double to_cp(Value v) { return double(v) / PawnValueEg; }
45 void add(int idx, Color c, Score s) {
49 void add(int idx, Score w, Score b = SCORE_ZERO) {
50 scores[idx][WHITE] = w;
51 scores[idx][BLACK] = b;
54 std::ostream& operator<<(std::ostream& os, Score s) {
55 os << std::setw(5) << to_cp(mg_value(s)) << " "
56 << std::setw(5) << to_cp(eg_value(s));
60 std::ostream& operator<<(std::ostream& os, Term t) {
62 if (t == MATERIAL || t == IMBALANCE || t == INITIATIVE || t == TOTAL)
63 os << " ---- ----" << " | " << " ---- ----";
65 os << scores[t][WHITE] << " | " << scores[t][BLACK];
67 os << " | " << scores[t][WHITE] - scores[t][BLACK] << "\n";
72 using namespace Trace;
76 // Threshold for lazy and space evaluation
77 constexpr Value LazyThreshold = Value(1400);
78 constexpr Value SpaceThreshold = Value(12222);
80 // KingAttackWeights[PieceType] contains king attack weights by piece type
81 constexpr int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 81, 52, 44, 10 };
83 // Penalties for enemy's safe checks
84 constexpr int QueenSafeCheck = 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(5, 32), S(57, 41), S(77, 56), S(88, 119), S(79, 161)
120 constexpr Score ThreatByRook[PIECE_TYPE_NB] = {
121 S(0, 0), S(2, 44), S(36, 71), S(36, 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( 30, 21);
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( 52, 10);
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, by blockers to attacks on our king
228 // or controlled by enemy pawns are excluded from the mobility area.
229 mobilityArea[Us] = ~(b | pos.pieces(Us, KING, QUEEN) | pos.blockers_for_king(Us) | 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] = PseudoAttacks[KING][s] | 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;
320 // An important Chess960 pattern: a cornered bishop blocked by a friendly
321 // pawn diagonally in front of it is a very serious problem, especially
322 // when that pawn is also blocked.
323 if ( pos.is_chess960()
324 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
326 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
327 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
328 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
329 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
337 // Bonus for rook on the same file as a queen
338 if (file_bb(s) & pos.pieces(QUEEN))
339 score += RookOnQueenFile;
341 // Bonus for rook on an open or semi-open file
342 if (pos.is_on_semiopen_file(Us, s))
343 score += RookOnFile[pos.is_on_semiopen_file(Them, s)];
345 // Penalty when trapped by the king, even more if the king cannot castle
348 File kf = file_of(pos.square<KING>(Us));
349 if ((kf < FILE_E) == (file_of(s) < kf))
350 score -= TrappedRook * (1 + !pos.castling_rights(Us));
356 // Penalty if any relative pin or discovered attack against the queen
357 Bitboard queenPinners;
358 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
363 Trace::add(Pt, Us, score);
369 // Evaluation::king() assigns bonuses and penalties to a king of a given color
370 template<Tracing T> template<Color Us>
371 Score Evaluation<T>::king() const {
373 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
374 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
375 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
377 Bitboard weak, b1, b2, b3, safe, unsafeChecks = 0;
378 Bitboard rookChecks, queenChecks, bishopChecks, knightChecks;
380 const Square ksq = pos.square<KING>(Us);
382 // Init the score with king shelter and enemy pawns storm
383 Score score = pe->king_safety<Us>(pos);
385 // Attacked squares defended at most once by our queen or king
386 weak = attackedBy[Them][ALL_PIECES]
388 & (~attackedBy[Us][ALL_PIECES] | attackedBy[Us][KING] | attackedBy[Us][QUEEN]);
390 // Analyse the safe enemy's checks which are possible on next move
391 safe = ~pos.pieces(Them);
392 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
394 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
395 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
397 // Enemy rooks checks
398 rookChecks = b1 & safe & attackedBy[Them][ROOK];
401 kingDanger += RookSafeCheck;
403 unsafeChecks |= b1 & attackedBy[Them][ROOK];
405 // Enemy queen safe checks: we count them only if they are from squares from
406 // which we can't give a rook check, because rook checks are more valuable.
407 queenChecks = (b1 | b2)
408 & attackedBy[Them][QUEEN]
410 & ~attackedBy[Us][QUEEN]
414 kingDanger += QueenSafeCheck;
416 // Enemy bishops checks: we count them only if they are from squares from
417 // which we can't give a queen check, because queen checks are more valuable.
419 & attackedBy[Them][BISHOP]
424 kingDanger += BishopSafeCheck;
426 unsafeChecks |= b2 & attackedBy[Them][BISHOP];
428 // Enemy knights checks
429 knightChecks = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
431 if (knightChecks & safe)
432 kingDanger += KnightSafeCheck;
434 unsafeChecks |= knightChecks;
436 // Find the squares that opponent attacks in our king flank, the squares
437 // which they attack twice in that flank, and the squares that we defend.
438 b1 = attackedBy[Them][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
439 b2 = b1 & attackedBy2[Them];
440 b3 = attackedBy[Us][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
442 int kingFlankAttack = popcount(b1) + popcount(b2);
443 int kingFlankDefense = popcount(b3);
445 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
446 + 185 * popcount(kingRing[Us] & weak)
447 + 148 * popcount(unsafeChecks)
448 + 98 * popcount(pos.blockers_for_king(Us))
449 + 69 * kingAttacksCount[Them]
450 + 3 * kingFlankAttack * kingFlankAttack / 8
451 + mg_value(mobility[Them] - mobility[Us])
452 - 873 * !pos.count<QUEEN>(Them)
453 - 100 * bool(attackedBy[Us][KNIGHT] & attackedBy[Us][KING])
454 - 6 * mg_value(score) / 8
455 - 4 * kingFlankDefense
458 // Transform the kingDanger units into a Score, and subtract it from the evaluation
459 if (kingDanger > 100)
460 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
462 // Penalty when our king is on a pawnless flank
463 if (!(pos.pieces(PAWN) & KingFlank[file_of(ksq)]))
464 score -= PawnlessFlank;
466 // Penalty if king flank is under attack, potentially moving toward the king
467 score -= FlankAttacks * kingFlankAttack;
470 Trace::add(KING, Us, score);
476 // Evaluation::threats() assigns bonuses according to the types of the
477 // attacking and the attacked pieces.
478 template<Tracing T> template<Color Us>
479 Score Evaluation<T>::threats() const {
481 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
482 constexpr Direction Up = pawn_push(Us);
483 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
485 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe;
486 Score score = SCORE_ZERO;
489 nonPawnEnemies = pos.pieces(Them) & ~pos.pieces(PAWN);
491 // Squares strongly protected by the enemy, either because they defend the
492 // square with a pawn, or because they defend the square twice and we don't.
493 stronglyProtected = attackedBy[Them][PAWN]
494 | (attackedBy2[Them] & ~attackedBy2[Us]);
496 // Non-pawn enemies, strongly protected
497 defended = nonPawnEnemies & stronglyProtected;
499 // Enemies not strongly protected and under our attack
500 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
502 // Bonus according to the kind of attacking pieces
505 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
507 score += ThreatByMinor[type_of(pos.piece_on(pop_lsb(&b)))];
509 b = weak & attackedBy[Us][ROOK];
511 score += ThreatByRook[type_of(pos.piece_on(pop_lsb(&b)))];
513 if (weak & attackedBy[Us][KING])
514 score += ThreatByKing;
516 b = ~attackedBy[Them][ALL_PIECES]
517 | (nonPawnEnemies & attackedBy2[Us]);
518 score += Hanging * popcount(weak & b);
520 // Additional bonus if weak piece is only protected by a queen
521 score += make_score(14, 0) * popcount(weak & attackedBy[Them][QUEEN]);
524 // Bonus for restricting their piece moves
525 b = attackedBy[Them][ALL_PIECES]
527 & attackedBy[Us][ALL_PIECES];
528 score += RestrictedPiece * popcount(b);
530 // Protected or unattacked squares
531 safe = ~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES];
533 // Bonus for attacking enemy pieces with our relatively safe pawns
534 b = pos.pieces(Us, PAWN) & safe;
535 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
536 score += ThreatBySafePawn * popcount(b);
538 // Find squares where our pawns can push on the next move
539 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
540 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
542 // Keep only the squares which are relatively safe
543 b &= ~attackedBy[Them][PAWN] & safe;
545 // Bonus for safe pawn threats on the next move
546 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
547 score += ThreatByPawnPush * popcount(b);
549 // Bonus for threats on the next moves against enemy queen
550 if (pos.count<QUEEN>(Them) == 1)
552 Square s = pos.square<QUEEN>(Them);
553 safe = mobilityArea[Us] & ~stronglyProtected;
555 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
557 score += KnightOnQueen * popcount(b & safe);
559 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
560 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
562 score += SliderOnQueen * popcount(b & safe & attackedBy2[Us]);
566 Trace::add(THREAT, Us, score);
571 // Evaluation::passed() evaluates the passed pawns and candidate passed
572 // pawns of the given color.
574 template<Tracing T> template<Color Us>
575 Score Evaluation<T>::passed() const {
577 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
578 constexpr Direction Up = pawn_push(Us);
580 auto king_proximity = [&](Color c, Square s) {
581 return std::min(distance(pos.square<KING>(c), s), 5);
584 Bitboard b, bb, squaresToQueen, unsafeSquares;
585 Score score = SCORE_ZERO;
587 b = pe->passed_pawns(Us);
591 Square s = pop_lsb(&b);
593 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
595 int r = relative_rank(Us, s);
597 Score bonus = PassedRank[r];
602 Square blockSq = s + Up;
604 // Adjust bonus based on the king's proximity
605 bonus += make_score(0, ( (king_proximity(Them, blockSq) * 19) / 4
606 - king_proximity(Us, blockSq) * 2) * w);
608 // If blockSq is not the queening square then consider also a second push
610 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
612 // If the pawn is free to advance, then increase the bonus
613 if (pos.empty(blockSq))
615 squaresToQueen = forward_file_bb(Us, s);
616 unsafeSquares = passed_pawn_span(Us, s);
618 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN);
620 if (!(pos.pieces(Them) & bb))
621 unsafeSquares &= attackedBy[Them][ALL_PIECES];
623 // If there are no enemy attacks on passed pawn span, assign a big bonus.
624 // Otherwise assign a smaller bonus if the path to queen is not attacked
625 // and even smaller bonus if it is attacked but block square is not.
626 int k = !unsafeSquares ? 35 :
627 !(unsafeSquares & squaresToQueen) ? 20 :
628 !(unsafeSquares & blockSq) ? 9 :
631 // Assign a larger bonus if the block square is defended
632 if ((pos.pieces(Us) & bb) || (attackedBy[Us][ALL_PIECES] & blockSq))
635 bonus += make_score(k * w, k * w);
639 // Scale down bonus for candidate passers which need more than one
640 // pawn push to become passed, or have a pawn in front of them.
641 if ( !pos.pawn_passed(Us, s + Up)
642 || (pos.pieces(PAWN) & (s + Up)))
645 score += bonus - PassedFile * map_to_queenside(file_of(s));
649 Trace::add(PASSED, Us, score);
655 // Evaluation::space() computes the space evaluation for a given side. The
656 // space evaluation is a simple bonus based on the number of safe squares
657 // available for minor pieces on the central four files on ranks 2--4. Safe
658 // squares one, two or three squares behind a friendly pawn are counted
659 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
660 // improve play on game opening.
662 template<Tracing T> template<Color Us>
663 Score Evaluation<T>::space() const {
665 if (pos.non_pawn_material() < SpaceThreshold)
668 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
669 constexpr Direction Down = -pawn_push(Us);
670 constexpr Bitboard SpaceMask =
671 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
672 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
674 // Find the available squares for our pieces inside the area defined by SpaceMask
675 Bitboard safe = SpaceMask
676 & ~pos.pieces(Us, PAWN)
677 & ~attackedBy[Them][PAWN];
679 // Find all squares which are at most three squares behind some friendly pawn
680 Bitboard behind = pos.pieces(Us, PAWN);
681 behind |= shift<Down>(behind);
682 behind |= shift<Down+Down>(behind);
684 int bonus = popcount(safe) + popcount(behind & safe & ~attackedBy[Them][ALL_PIECES]);
685 int weight = pos.count<ALL_PIECES>(Us) - 1;
686 Score score = make_score(bonus * weight * weight / 16, 0);
689 Trace::add(SPACE, Us, score);
695 // Evaluation::initiative() computes the initiative correction value
696 // for the position. It is a second order bonus/malus based on the
697 // known attacking/defending status of the players.
700 Score Evaluation<T>::initiative(Score score) const {
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 bool infiltration = rank_of(pos.square<KING>(WHITE)) > RANK_4
713 || rank_of(pos.square<KING>(BLACK)) < RANK_5;
715 // Compute the initiative bonus for the attacking side
716 int complexity = 9 * pe->passed_count()
717 + 11 * pos.count<PAWN>()
719 + 21 * pawnsOnBothFlanks
721 + 51 * !pos.non_pawn_material()
722 - 43 * almostUnwinnable
725 Value mg = mg_value(score);
726 Value eg = eg_value(score);
728 // Now apply the bonus: note that we find the attacking side by extracting the
729 // sign of the midgame or endgame values, and that we carefully cap the bonus
730 // so that the midgame and endgame scores do not change sign after the bonus.
731 int u = ((mg > 0) - (mg < 0)) * std::max(std::min(complexity + 50, 0), -abs(mg));
732 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
735 Trace::add(INITIATIVE, make_score(u, v));
737 return make_score(u, v);
741 // Evaluation::scale_factor() computes the scale factor for the winning side
744 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
746 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
747 int sf = me->scale_factor(pos, strongSide);
749 // If scale is not already specific, scale down the endgame via general heuristics
750 if (sf == SCALE_FACTOR_NORMAL)
752 if ( pos.opposite_bishops()
753 && pos.non_pawn_material() == 2 * BishopValueMg)
756 sf = std::min(sf, 36 + (pos.opposite_bishops() ? 2 : 7) * pos.count<PAWN>(strongSide));
758 sf = std::max(0, sf - (pos.rule50_count() - 12) / 4);
761 return ScaleFactor(sf);
765 // Evaluation::value() is the main function of the class. It computes the various
766 // parts of the evaluation and returns the value of the position from the point
767 // of view of the side to move.
770 Value Evaluation<T>::value() {
772 assert(!pos.checkers());
774 // Probe the material hash table
775 me = Material::probe(pos);
777 // If we have a specialized evaluation function for the current material
778 // configuration, call it and return.
779 if (me->specialized_eval_exists())
780 return me->evaluate(pos);
782 // Initialize score by reading the incrementally updated scores included in
783 // the position object (material + piece square tables) and the material
784 // imbalance. Score is computed internally from the white point of view.
785 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
787 // Probe the pawn hash table
788 pe = Pawns::probe(pos);
789 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
791 // Early exit if score is high
792 Value v = (mg_value(score) + eg_value(score)) / 2;
793 if (abs(v) > LazyThreshold + pos.non_pawn_material() / 64)
794 return pos.side_to_move() == WHITE ? v : -v;
796 // Main evaluation begins here
801 // Pieces should be evaluated first (populate attack tables)
802 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
803 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
804 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
805 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
807 score += mobility[WHITE] - mobility[BLACK];
809 score += king< WHITE>() - king< BLACK>()
810 + threats<WHITE>() - threats<BLACK>()
811 + passed< WHITE>() - passed< BLACK>()
812 + space< WHITE>() - space< BLACK>();
814 score += initiative(score);
816 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
817 ScaleFactor sf = scale_factor(eg_value(score));
818 v = mg_value(score) * int(me->game_phase())
819 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
823 // In case of tracing add all remaining individual evaluation terms
826 Trace::add(MATERIAL, pos.psq_score());
827 Trace::add(IMBALANCE, me->imbalance());
828 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
829 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
830 Trace::add(TOTAL, score);
833 return (pos.side_to_move() == WHITE ? v : -v) // Side to move point of view
840 /// evaluate() is the evaluator for the outer world. It returns a static
841 /// evaluation of the position from the point of view of the side to move.
843 Value Eval::evaluate(const Position& pos) {
844 return Evaluation<NO_TRACE>(pos).value();
848 /// trace() is like evaluate(), but instead of returning a value, it returns
849 /// a string (suitable for outputting to stdout) that contains the detailed
850 /// descriptions and values of each evaluation term. Useful for debugging.
852 std::string Eval::trace(const Position& pos) {
855 return "Total evaluation: none (in check)";
857 std::memset(scores, 0, sizeof(scores));
859 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
861 Value v = Evaluation<TRACE>(pos).value();
863 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
865 std::stringstream ss;
866 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
867 << " Term | White | Black | Total \n"
868 << " | MG EG | MG EG | MG EG \n"
869 << " ------------+-------------+-------------+------------\n"
870 << " Material | " << Term(MATERIAL)
871 << " Imbalance | " << Term(IMBALANCE)
872 << " Pawns | " << Term(PAWN)
873 << " Knights | " << Term(KNIGHT)
874 << " Bishops | " << Term(BISHOP)
875 << " Rooks | " << Term(ROOK)
876 << " Queens | " << Term(QUEEN)
877 << " Mobility | " << Term(MOBILITY)
878 << " King safety | " << Term(KING)
879 << " Threats | " << Term(THREAT)
880 << " Passed | " << Term(PASSED)
881 << " Space | " << Term(SPACE)
882 << " Initiative | " << Term(INITIATIVE)
883 << " ------------+-------------+-------------+------------\n"
884 << " Total | " << Term(TOTAL);
886 ss << "\nTotal evaluation: " << to_cp(v) << " (white side)\n";