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(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( 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 ReachableOutpost = S( 32, 10);
143 constexpr Score RookOnQueenFile = S( 7, 6);
144 constexpr Score SliderOnQueen = S( 59, 18);
145 constexpr Score ThreatByKing = S( 24, 89);
146 constexpr Score ThreatByPawnPush = S( 48, 39);
147 constexpr Score ThreatBySafePawn = S(173, 94);
148 constexpr Score TrappedRook = S( 52, 10);
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(Score score) 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 = pawn_push(Us);
218 constexpr Direction Down = -Up;
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, by blockers to attacks on our king
229 // or controlled by enemy pawns are excluded from the mobility area.
230 mobilityArea[Us] = ~(b | pos.pieces(Us, KING, QUEEN) | pos.blockers_for_king(Us) | 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 Square s = make_square(clamp(file_of(ksq), FILE_B, FILE_G),
240 clamp(rank_of(ksq), RANK_2, RANK_7));
241 kingRing[Us] = PseudoAttacks[KING][s] | s;
243 kingAttackersCount[Them] = popcount(kingRing[Us] & pe->pawn_attacks(Them));
244 kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
246 // Remove from kingRing[] the squares defended by two pawns
247 kingRing[Us] &= ~dblAttackByPawn;
251 // Evaluation::pieces() scores pieces of a given color and type
252 template<Tracing T> template<Color Us, PieceType Pt>
253 Score Evaluation<T>::pieces() {
255 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
256 constexpr Direction Down = -pawn_push(Us);
257 constexpr Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
258 : Rank5BB | Rank4BB | Rank3BB);
259 const Square* pl = pos.squares<Pt>(Us);
262 Score score = SCORE_ZERO;
264 attackedBy[Us][Pt] = 0;
266 for (Square s = *pl; s != SQ_NONE; s = *++pl)
268 // Find attacked squares, including x-ray attacks for bishops and rooks
269 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
270 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
271 : pos.attacks_from<Pt>(s);
273 if (pos.blockers_for_king(Us) & s)
274 b &= LineBB[pos.square<KING>(Us)][s];
276 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
277 attackedBy[Us][Pt] |= b;
278 attackedBy[Us][ALL_PIECES] |= b;
280 if (b & kingRing[Them])
282 kingAttackersCount[Us]++;
283 kingAttackersWeight[Us] += KingAttackWeights[Pt];
284 kingAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
287 int mob = popcount(b & mobilityArea[Us]);
289 mobility[Us] += MobilityBonus[Pt - 2][mob];
291 if (Pt == BISHOP || Pt == KNIGHT)
293 // Bonus if piece is on an outpost square or can reach one
294 bb = OutpostRanks & attackedBy[Us][PAWN] & ~pe->pawn_attacks_span(Them);
296 score += Outpost * (Pt == KNIGHT ? 2 : 1);
298 else if (Pt == KNIGHT && bb & b & ~pos.pieces(Us))
299 score += ReachableOutpost;
301 // Knight and Bishop bonus for being right behind a pawn
302 if (shift<Down>(pos.pieces(PAWN)) & s)
303 score += MinorBehindPawn;
305 // Penalty if the piece is far from the king
306 score -= KingProtector * distance(s, pos.square<KING>(Us));
310 // Penalty according to number of pawns on the same color square as the
311 // bishop, bigger when the center files are blocked with pawns.
312 Bitboard blocked = pos.pieces(Us, PAWN) & shift<Down>(pos.pieces());
314 score -= BishopPawns * pos.pawns_on_same_color_squares(Us, s)
315 * (1 + popcount(blocked & CenterFiles));
317 // Bonus for bishop on a long diagonal which can "see" both center squares
318 if (more_than_one(attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & Center))
319 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.
324 if ( pos.is_chess960()
325 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
327 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
328 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
329 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
330 : 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, b3, 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, the squares
438 // which they attack twice in that flank, and the squares that we defend.
439 b1 = attackedBy[Them][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
440 b2 = b1 & attackedBy2[Them];
441 b3 = attackedBy[Us][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
443 int kingFlankAttack = popcount(b1) + popcount(b2);
444 int kingFlankDefense = popcount(b3);
446 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
447 + 185 * popcount(kingRing[Us] & weak)
448 + 148 * popcount(unsafeChecks)
449 + 98 * popcount(pos.blockers_for_king(Us))
450 + 69 * kingAttacksCount[Them]
451 + 3 * kingFlankAttack * kingFlankAttack / 8
452 + mg_value(mobility[Them] - mobility[Us])
453 - 873 * !pos.count<QUEEN>(Them)
454 - 100 * bool(attackedBy[Us][KNIGHT] & attackedBy[Us][KING])
455 - 6 * mg_value(score) / 8
456 - 4 * kingFlankDefense
459 // Transform the kingDanger units into a Score, and subtract it from the evaluation
460 if (kingDanger > 100)
461 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
463 // Penalty when our king is on a pawnless flank
464 if (!(pos.pieces(PAWN) & KingFlank[file_of(ksq)]))
465 score -= PawnlessFlank;
467 // Penalty if king flank is under attack, potentially moving toward the king
468 score -= FlankAttacks * kingFlankAttack;
471 Trace::add(KING, Us, score);
477 // Evaluation::threats() assigns bonuses according to the types of the
478 // attacking and the attacked pieces.
479 template<Tracing T> template<Color Us>
480 Score Evaluation<T>::threats() const {
482 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
483 constexpr Direction Up = pawn_push(Us);
484 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
486 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe;
487 Score score = SCORE_ZERO;
490 nonPawnEnemies = pos.pieces(Them) & ~pos.pieces(PAWN);
492 // Squares strongly protected by the enemy, either because they defend the
493 // square with a pawn, or because they defend the square twice and we don't.
494 stronglyProtected = attackedBy[Them][PAWN]
495 | (attackedBy2[Them] & ~attackedBy2[Us]);
497 // Non-pawn enemies, strongly protected
498 defended = nonPawnEnemies & stronglyProtected;
500 // Enemies not strongly protected and under our attack
501 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
503 // Bonus according to the kind of attacking pieces
506 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
508 score += ThreatByMinor[type_of(pos.piece_on(pop_lsb(&b)))];
510 b = weak & attackedBy[Us][ROOK];
512 score += ThreatByRook[type_of(pos.piece_on(pop_lsb(&b)))];
514 if (weak & attackedBy[Us][KING])
515 score += ThreatByKing;
517 b = ~attackedBy[Them][ALL_PIECES]
518 | (nonPawnEnemies & attackedBy2[Us]);
519 score += Hanging * popcount(weak & b);
522 // Bonus for restricting their piece moves
523 b = attackedBy[Them][ALL_PIECES]
525 & attackedBy[Us][ALL_PIECES];
526 score += RestrictedPiece * popcount(b);
528 // Protected or unattacked squares
529 safe = ~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES];
531 // Bonus for attacking enemy pieces with our relatively safe pawns
532 b = pos.pieces(Us, PAWN) & safe;
533 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
534 score += ThreatBySafePawn * popcount(b);
536 // Find squares where our pawns can push on the next move
537 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
538 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
540 // Keep only the squares which are relatively safe
541 b &= ~attackedBy[Them][PAWN] & safe;
543 // Bonus for safe pawn threats on the next move
544 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
545 score += ThreatByPawnPush * popcount(b);
547 // Bonus for threats on the next moves against enemy queen
548 if (pos.count<QUEEN>(Them) == 1)
550 Square s = pos.square<QUEEN>(Them);
551 safe = mobilityArea[Us] & ~stronglyProtected;
553 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
555 score += KnightOnQueen * popcount(b & safe);
557 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
558 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
560 score += SliderOnQueen * popcount(b & safe & attackedBy2[Us]);
564 Trace::add(THREAT, Us, score);
569 // Evaluation::passed() evaluates the passed pawns and candidate passed
570 // pawns of the given color.
572 template<Tracing T> template<Color Us>
573 Score Evaluation<T>::passed() const {
575 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
576 constexpr Direction Up = pawn_push(Us);
578 auto king_proximity = [&](Color c, Square s) {
579 return std::min(distance(pos.square<KING>(c), s), 5);
582 Bitboard b, bb, squaresToQueen, unsafeSquares;
583 Score score = SCORE_ZERO;
585 b = pe->passed_pawns(Us);
589 Square s = pop_lsb(&b);
591 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
593 int r = relative_rank(Us, s);
595 Score bonus = PassedRank[r];
600 Square blockSq = s + Up;
602 // Adjust bonus based on the king's proximity
603 bonus += make_score(0, ( (king_proximity(Them, blockSq) * 19) / 4
604 - king_proximity(Us, blockSq) * 2) * w);
606 // If blockSq is not the queening square then consider also a second push
608 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
610 // If the pawn is free to advance, then increase the bonus
611 if (pos.empty(blockSq))
613 squaresToQueen = forward_file_bb(Us, s);
614 unsafeSquares = passed_pawn_span(Us, s);
616 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN);
618 if (!(pos.pieces(Them) & bb))
619 unsafeSquares &= attackedBy[Them][ALL_PIECES];
621 // If there are no enemy attacks on passed pawn span, assign a big bonus.
622 // Otherwise assign a smaller bonus if the path to queen is not attacked
623 // and even smaller bonus if it is attacked but block square is not.
624 int k = !unsafeSquares ? 35 :
625 !(unsafeSquares & squaresToQueen) ? 20 :
626 !(unsafeSquares & blockSq) ? 9 :
629 // Assign a larger bonus if the block square is defended
630 if ((pos.pieces(Us) & bb) || (attackedBy[Us][ALL_PIECES] & blockSq))
633 bonus += make_score(k * w, k * w);
637 // Scale down bonus for candidate passers which need more than one
638 // pawn push to become passed, or have a pawn in front of them.
639 if ( !pos.pawn_passed(Us, s + Up)
640 || (pos.pieces(PAWN) & (s + Up)))
643 score += bonus - PassedFile * map_to_queenside(file_of(s));
647 Trace::add(PASSED, Us, score);
653 // Evaluation::space() computes the space evaluation for a given side. The
654 // space evaluation is a simple bonus based on the number of safe squares
655 // available for minor pieces on the central four files on ranks 2--4. Safe
656 // squares one, two or three squares behind a friendly pawn are counted
657 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
658 // improve play on game opening.
660 template<Tracing T> template<Color Us>
661 Score Evaluation<T>::space() const {
663 if (pos.non_pawn_material() < SpaceThreshold)
666 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
667 constexpr Direction Down = -pawn_push(Us);
668 constexpr Bitboard SpaceMask =
669 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
670 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
672 // Find the available squares for our pieces inside the area defined by SpaceMask
673 Bitboard safe = SpaceMask
674 & ~pos.pieces(Us, PAWN)
675 & ~attackedBy[Them][PAWN];
677 // Find all squares which are at most three squares behind some friendly pawn
678 Bitboard behind = pos.pieces(Us, PAWN);
679 behind |= shift<Down>(behind);
680 behind |= shift<Down+Down>(behind);
682 int bonus = popcount(safe) + popcount(behind & safe & ~attackedBy[Them][ALL_PIECES]);
683 int weight = pos.count<ALL_PIECES>(Us) - 1;
684 Score score = make_score(bonus * weight * weight / 16, 0);
687 Trace::add(SPACE, Us, score);
693 // Evaluation::initiative() computes the initiative correction value
694 // for the position. It is a second order bonus/malus based on the
695 // known attacking/defending status of the players.
698 Score Evaluation<T>::initiative(Score score) const {
700 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
701 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
703 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
704 && (pos.pieces(PAWN) & KingSide);
706 bool almostUnwinnable = !pe->passed_count()
708 && !pawnsOnBothFlanks;
710 bool infiltration = rank_of(pos.square<KING>(WHITE)) > RANK_4
711 || rank_of(pos.square<KING>(BLACK)) < RANK_5;
713 // Compute the initiative bonus for the attacking side
714 int complexity = 9 * pe->passed_count()
715 + 11 * pos.count<PAWN>()
717 + 21 * pawnsOnBothFlanks
719 + 51 * !pos.non_pawn_material()
720 - 43 * almostUnwinnable
723 Value mg = mg_value(score);
724 Value eg = eg_value(score);
726 // Now apply the bonus: note that we find the attacking side by extracting the
727 // sign of the midgame or endgame values, and that we carefully cap the bonus
728 // so that the midgame and endgame scores do not change sign after the bonus.
729 int u = ((mg > 0) - (mg < 0)) * std::max(std::min(complexity + 50, 0), -abs(mg));
730 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
733 Trace::add(INITIATIVE, make_score(u, v));
735 return make_score(u, v);
739 // Evaluation::scale_factor() computes the scale factor for the winning side
742 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
744 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
745 int sf = me->scale_factor(pos, strongSide);
747 // If scale is not already specific, scale down the endgame via general heuristics
748 if (sf == SCALE_FACTOR_NORMAL)
750 if ( pos.opposite_bishops()
751 && pos.non_pawn_material() == 2 * BishopValueMg)
754 sf = std::min(sf, 36 + (pos.opposite_bishops() ? 2 : 7) * pos.count<PAWN>(strongSide));
756 sf = std::max(0, sf - (pos.rule50_count() - 12) / 4);
759 return ScaleFactor(sf);
763 // Evaluation::value() is the main function of the class. It computes the various
764 // parts of the evaluation and returns the value of the position from the point
765 // of view of the side to move.
768 Value Evaluation<T>::value() {
770 assert(!pos.checkers());
772 // Probe the material hash table
773 me = Material::probe(pos);
775 // If we have a specialized evaluation function for the current material
776 // configuration, call it and return.
777 if (me->specialized_eval_exists())
778 return me->evaluate(pos);
780 // Initialize score by reading the incrementally updated scores included in
781 // the position object (material + piece square tables) and the material
782 // imbalance. Score is computed internally from the white point of view.
783 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
785 // Probe the pawn hash table
786 pe = Pawns::probe(pos);
787 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
789 // Early exit if score is high
790 Value v = (mg_value(score) + eg_value(score)) / 2;
791 if (abs(v) > LazyThreshold + pos.non_pawn_material() / 64)
792 return pos.side_to_move() == WHITE ? v : -v;
794 // Main evaluation begins here
799 // Pieces should be evaluated first (populate attack tables)
800 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
801 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
802 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
803 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
805 score += mobility[WHITE] - mobility[BLACK];
807 score += king< WHITE>() - king< BLACK>()
808 + threats<WHITE>() - threats<BLACK>()
809 + passed< WHITE>() - passed< BLACK>()
810 + space< WHITE>() - space< BLACK>();
812 score += initiative(score);
814 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
815 ScaleFactor sf = scale_factor(eg_value(score));
816 v = mg_value(score) * int(me->game_phase())
817 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
821 // In case of tracing add all remaining individual evaluation terms
824 Trace::add(MATERIAL, pos.psq_score());
825 Trace::add(IMBALANCE, me->imbalance());
826 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
827 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
828 Trace::add(TOTAL, score);
831 return (pos.side_to_move() == WHITE ? v : -v) // Side to move point of view
838 /// evaluate() is the evaluator for the outer world. It returns a static
839 /// evaluation of the position from the point of view of the side to move.
841 Value Eval::evaluate(const Position& pos) {
842 return Evaluation<NO_TRACE>(pos).value();
846 /// trace() is like evaluate(), but instead of returning a value, it returns
847 /// a string (suitable for outputting to stdout) that contains the detailed
848 /// descriptions and values of each evaluation term. Useful for debugging.
850 std::string Eval::trace(const Position& pos) {
853 return "Total evaluation: none (in check)";
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";