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( 16, 5);
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 = (Us == WHITE ? NORTH : SOUTH);
217 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
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 kingRing[Us] = attackedBy[Us][KING];
239 if (relative_rank(Us, ksq) == RANK_1)
240 kingRing[Us] |= shift<Up>(kingRing[Us]);
242 if (file_of(ksq) == FILE_H)
243 kingRing[Us] |= shift<WEST>(kingRing[Us]);
245 else if (file_of(ksq) == FILE_A)
246 kingRing[Us] |= shift<EAST>(kingRing[Us]);
248 kingAttackersCount[Them] = popcount(kingRing[Us] & pe->pawn_attacks(Them));
249 kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
251 // Remove from kingRing[] the squares defended by two pawns
252 kingRing[Us] &= ~dblAttackByPawn;
256 // Evaluation::pieces() scores pieces of a given color and type
257 template<Tracing T> template<Color Us, PieceType Pt>
258 Score Evaluation<T>::pieces() {
260 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
261 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
262 constexpr Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
263 : Rank5BB | Rank4BB | Rank3BB);
264 const Square* pl = pos.squares<Pt>(Us);
267 Score score = SCORE_ZERO;
269 attackedBy[Us][Pt] = 0;
271 for (Square s = *pl; s != SQ_NONE; s = *++pl)
273 // Find attacked squares, including x-ray attacks for bishops and rooks
274 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
275 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
276 : pos.attacks_from<Pt>(s);
278 if (pos.blockers_for_king(Us) & s)
279 b &= LineBB[pos.square<KING>(Us)][s];
281 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
282 attackedBy[Us][Pt] |= b;
283 attackedBy[Us][ALL_PIECES] |= b;
285 if (b & kingRing[Them])
287 kingAttackersCount[Us]++;
288 kingAttackersWeight[Us] += KingAttackWeights[Pt];
289 kingAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
292 int mob = popcount(b & mobilityArea[Us]);
294 mobility[Us] += MobilityBonus[Pt - 2][mob];
296 if (Pt == BISHOP || Pt == KNIGHT)
298 // Bonus if piece is on an outpost square or can reach one
299 bb = OutpostRanks & attackedBy[Us][PAWN] & ~pe->pawn_attacks_span(Them);
301 score += Outpost * (Pt == KNIGHT ? 4 : 2);
303 else if (bb & b & ~pos.pieces(Us))
304 score += Outpost * (Pt == KNIGHT ? 2 : 1);
306 // Knight and Bishop bonus for being right behind a pawn
307 if (shift<Down>(pos.pieces(PAWN)) & s)
308 score += MinorBehindPawn;
310 // Penalty if the piece is far from the king
311 score -= KingProtector * distance(s, pos.square<KING>(Us));
315 // Penalty according to number of pawns on the same color square as the
316 // bishop, bigger when the center files are blocked with pawns.
317 Bitboard blocked = pos.pieces(Us, PAWN) & shift<Down>(pos.pieces());
319 score -= BishopPawns * pos.pawns_on_same_color_squares(Us, s)
320 * (1 + popcount(blocked & CenterFiles));
322 // Bonus for bishop on a long diagonal which can "see" both center squares
323 if (more_than_one(attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & Center))
324 score += LongDiagonalBishop;
327 // An important Chess960 pattern: A cornered bishop blocked by a friendly
328 // pawn diagonally in front of it is a very serious problem, especially
329 // when that pawn is also blocked.
332 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
334 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
335 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
336 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
337 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
344 // Bonus for rook on the same file as a queen
345 if (file_bb(s) & pos.pieces(QUEEN))
346 score += RookOnQueenFile;
348 // Bonus for rook on an open or semi-open file
349 if (pos.is_on_semiopen_file(Us, s))
350 score += RookOnFile[pos.is_on_semiopen_file(Them, s)];
352 // Penalty when trapped by the king, even more if the king cannot castle
355 File kf = file_of(pos.square<KING>(Us));
356 if ((kf < FILE_E) == (file_of(s) < kf))
357 score -= TrappedRook * (1 + !pos.castling_rights(Us));
363 // Penalty if any relative pin or discovered attack against the queen
364 Bitboard queenPinners;
365 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
370 Trace::add(Pt, Us, score);
376 // Evaluation::king() assigns bonuses and penalties to a king of a given color
377 template<Tracing T> template<Color Us>
378 Score Evaluation<T>::king() const {
380 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
381 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
382 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
384 Bitboard weak, b1, b2, safe, unsafeChecks = 0;
385 Bitboard rookChecks, queenChecks, bishopChecks, knightChecks;
387 const Square ksq = pos.square<KING>(Us);
389 // Init the score with king shelter and enemy pawns storm
390 Score score = pe->king_safety<Us>(pos);
392 // Attacked squares defended at most once by our queen or king
393 weak = attackedBy[Them][ALL_PIECES]
395 & (~attackedBy[Us][ALL_PIECES] | attackedBy[Us][KING] | attackedBy[Us][QUEEN]);
397 // Analyse the safe enemy's checks which are possible on next move
398 safe = ~pos.pieces(Them);
399 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
401 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
402 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
404 // Enemy rooks checks
405 rookChecks = b1 & safe & attackedBy[Them][ROOK];
408 kingDanger += RookSafeCheck;
410 unsafeChecks |= b1 & attackedBy[Them][ROOK];
412 // Enemy queen safe checks: we count them only if they are from squares from
413 // which we can't give a rook check, because rook checks are more valuable.
414 queenChecks = (b1 | b2)
415 & attackedBy[Them][QUEEN]
417 & ~attackedBy[Us][QUEEN]
421 kingDanger += QueenSafeCheck;
423 // Enemy bishops checks: we count them only if they are from squares from
424 // which we can't give a queen check, because queen checks are more valuable.
426 & attackedBy[Them][BISHOP]
431 kingDanger += BishopSafeCheck;
433 unsafeChecks |= b2 & attackedBy[Them][BISHOP];
435 // Enemy knights checks
436 knightChecks = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
438 if (knightChecks & safe)
439 kingDanger += KnightSafeCheck;
441 unsafeChecks |= knightChecks;
443 // Find the squares that opponent attacks in our king flank, and the squares
444 // which are attacked twice in that flank.
445 b1 = attackedBy[Them][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
446 b2 = b1 & attackedBy2[Them];
448 int kingFlankAttacks = popcount(b1) + popcount(b2);
450 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
451 + 69 * kingAttacksCount[Them]
452 + 185 * popcount(kingRing[Us] & weak)
453 - 100 * bool(attackedBy[Us][KNIGHT] & attackedBy[Us][KING])
454 - 35 * bool(attackedBy[Us][BISHOP] & attackedBy[Us][KING])
455 + 148 * popcount(unsafeChecks)
456 + 98 * popcount(pos.blockers_for_king(Us))
457 - 873 * !pos.count<QUEEN>(Them)
458 - 6 * mg_value(score) / 8
459 + mg_value(mobility[Them] - mobility[Us])
460 + 3 * kingFlankAttacks * kingFlankAttacks / 8
463 // Transform the kingDanger units into a Score, and subtract it from the evaluation
464 if (kingDanger > 100)
465 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
467 // Penalty when our king is on a pawnless flank
468 if (!(pos.pieces(PAWN) & KingFlank[file_of(ksq)]))
469 score -= PawnlessFlank;
471 // Penalty if king flank is under attack, potentially moving toward the king
472 score -= FlankAttacks * kingFlankAttacks;
475 Trace::add(KING, Us, score);
481 // Evaluation::threats() assigns bonuses according to the types of the
482 // attacking and the attacked pieces.
483 template<Tracing T> template<Color Us>
484 Score Evaluation<T>::threats() const {
486 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
487 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
488 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
490 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe;
491 Score score = SCORE_ZERO;
494 nonPawnEnemies = pos.pieces(Them) & ~pos.pieces(PAWN);
496 // Squares strongly protected by the enemy, either because they defend the
497 // square with a pawn, or because they defend the square twice and we don't.
498 stronglyProtected = attackedBy[Them][PAWN]
499 | (attackedBy2[Them] & ~attackedBy2[Us]);
501 // Non-pawn enemies, strongly protected
502 defended = nonPawnEnemies & stronglyProtected;
504 // Enemies not strongly protected and under our attack
505 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
507 // Bonus according to the kind of attacking pieces
510 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
512 score += ThreatByMinor[type_of(pos.piece_on(pop_lsb(&b)))];
514 b = weak & attackedBy[Us][ROOK];
516 score += ThreatByRook[type_of(pos.piece_on(pop_lsb(&b)))];
518 if (weak & attackedBy[Us][KING])
519 score += ThreatByKing;
521 b = ~attackedBy[Them][ALL_PIECES]
522 | (nonPawnEnemies & attackedBy2[Us]);
523 score += Hanging * popcount(weak & b);
526 // Bonus for restricting their piece moves
527 b = attackedBy[Them][ALL_PIECES]
529 & attackedBy[Us][ALL_PIECES];
531 score += RestrictedPiece * popcount(b);
533 // Protected or unattacked squares
534 safe = ~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES];
536 // Bonus for attacking enemy pieces with our relatively safe pawns
537 b = pos.pieces(Us, PAWN) & safe;
538 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
539 score += ThreatBySafePawn * popcount(b);
541 // Find squares where our pawns can push on the next move
542 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
543 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
545 // Keep only the squares which are relatively safe
546 b &= ~attackedBy[Them][PAWN] & safe;
548 // Bonus for safe pawn threats on the next move
549 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
550 score += ThreatByPawnPush * popcount(b);
552 // Bonus for threats on the next moves against enemy queen
553 if (pos.count<QUEEN>(Them) == 1)
555 Square s = pos.square<QUEEN>(Them);
556 safe = mobilityArea[Us] & ~stronglyProtected;
558 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
560 score += KnightOnQueen * popcount(b & safe);
562 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
563 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
565 score += SliderOnQueen * popcount(b & safe & attackedBy2[Us]);
569 Trace::add(THREAT, Us, score);
574 // Evaluation::passed() evaluates the passed pawns and candidate passed
575 // pawns of the given color.
577 template<Tracing T> template<Color Us>
578 Score Evaluation<T>::passed() const {
580 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
581 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
583 auto king_proximity = [&](Color c, Square s) {
584 return std::min(distance(pos.square<KING>(c), s), 5);
587 Bitboard b, bb, squaresToQueen, unsafeSquares;
588 Score score = SCORE_ZERO;
590 b = pe->passed_pawns(Us);
594 Square s = pop_lsb(&b);
596 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
598 int r = relative_rank(Us, s);
601 Score bonus = PassedRank[r];
606 Square blockSq = s + Up;
608 // Adjust bonus based on the king's proximity
609 bonus += make_score(0, ( king_proximity(Them, blockSq) * 5
610 - king_proximity(Us, blockSq) * 2) * w);
612 // If blockSq is not the queening square then consider also a second push
614 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
616 // If the pawn is free to advance, then increase the bonus
617 if (pos.empty(blockSq))
619 squaresToQueen = forward_file_bb(Us, s);
620 unsafeSquares = passed_pawn_span(Us, s);
622 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN);
624 if (!(pos.pieces(Them) & bb))
625 unsafeSquares &= attackedBy[Them][ALL_PIECES];
627 // If there are no enemy attacks on passed pawn span, assign a big bonus.
628 // Otherwise assign a smaller bonus if the path to queen is not attacked
629 // and even smaller bonus if it is attacked but block square is not.
630 int k = !unsafeSquares ? 35 :
631 !(unsafeSquares & squaresToQueen) ? 20 :
632 !(unsafeSquares & blockSq) ? 9 :
635 // Assign a larger bonus if the block square is defended
636 if ((pos.pieces(Us) & bb) || (attackedBy[Us][ALL_PIECES] & blockSq))
639 bonus += make_score(k * w, k * w);
643 // Scale down bonus for candidate passers which need more than one
644 // pawn push to become passed, or have a pawn in front of them.
645 if ( !pos.pawn_passed(Us, s + Up)
646 || (pos.pieces(PAWN) & (s + Up)))
649 score += bonus - PassedFile * map_to_queenside(f);
653 Trace::add(PASSED, Us, score);
659 // Evaluation::space() computes the space evaluation for a given side. The
660 // space evaluation is a simple bonus based on the number of safe squares
661 // available for minor pieces on the central four files on ranks 2--4. Safe
662 // squares one, two or three squares behind a friendly pawn are counted
663 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
664 // improve play on game opening.
666 template<Tracing T> template<Color Us>
667 Score Evaluation<T>::space() const {
669 if (pos.non_pawn_material() < SpaceThreshold)
672 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
673 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
674 constexpr Bitboard SpaceMask =
675 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
676 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
678 // Find the available squares for our pieces inside the area defined by SpaceMask
679 Bitboard safe = SpaceMask
680 & ~pos.pieces(Us, PAWN)
681 & ~attackedBy[Them][PAWN];
683 // Find all squares which are at most three squares behind some friendly pawn
684 Bitboard behind = pos.pieces(Us, PAWN);
685 behind |= shift<Down>(behind);
686 behind |= shift<Down+Down>(behind);
688 int bonus = popcount(safe) + popcount(behind & safe & ~attackedBy[Them][ALL_PIECES]);
689 int weight = pos.count<ALL_PIECES>(Us) - 1;
690 Score score = make_score(bonus * weight * weight / 16, 0);
693 Trace::add(SPACE, Us, score);
699 // Evaluation::initiative() computes the initiative correction value
700 // for the position. It is a second order bonus/malus based on the
701 // known attacking/defending status of the players.
704 Score Evaluation<T>::initiative(Score score) const {
706 Value mg = mg_value(score);
707 Value eg = eg_value(score);
709 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
710 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
712 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
713 && (pos.pieces(PAWN) & KingSide);
715 bool almostUnwinnable = !pe->passed_count()
717 && !pawnsOnBothFlanks;
719 // Compute the initiative bonus for the attacking side
720 int complexity = 9 * pe->passed_count()
721 + 11 * pos.count<PAWN>()
723 + 18 * pawnsOnBothFlanks
724 + 49 * !pos.non_pawn_material()
725 - 36 * almostUnwinnable
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)
754 sf = 16 + 4 * pe->passed_count();
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) {
854 std::memset(scores, 0, sizeof(scores));
856 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
858 Value v = Evaluation<TRACE>(pos).value();
860 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
862 std::stringstream ss;
863 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
864 << " Term | White | Black | Total \n"
865 << " | MG EG | MG EG | MG EG \n"
866 << " ------------+-------------+-------------+------------\n"
867 << " Material | " << Term(MATERIAL)
868 << " Imbalance | " << Term(IMBALANCE)
869 << " Pawns | " << Term(PAWN)
870 << " Knights | " << Term(KNIGHT)
871 << " Bishops | " << Term(BISHOP)
872 << " Rooks | " << Term(ROOK)
873 << " Queens | " << Term(QUEEN)
874 << " Mobility | " << Term(MOBILITY)
875 << " King safety | " << Term(KING)
876 << " Threats | " << Term(THREAT)
877 << " Passed | " << Term(PASSED)
878 << " Space | " << Term(SPACE)
879 << " Initiative | " << Term(INITIATIVE)
880 << " ------------+-------------+-------------+------------\n"
881 << " Total | " << Term(TOTAL);
883 ss << "\nTotal evaluation: " << to_cp(v) << " (white side)\n";