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 // OutpostRank[Rank] contains a bonus according to the rank of the outpost
130 constexpr Score OutpostRank[RANK_NB] = {
131 S(0, 0), S(0, 0), S(0, 0), S(28, 18), S(30, 24), S(32, 19)
134 // Assorted bonuses and penalties
135 constexpr Score BishopPawns = S( 3, 7);
136 constexpr Score CorneredBishop = S( 50, 50);
137 constexpr Score FlankAttacks = S( 8, 0);
138 constexpr Score Hanging = S( 69, 36);
139 constexpr Score KingProtector = S( 7, 8);
140 constexpr Score KnightOnQueen = S( 16, 12);
141 constexpr Score LongDiagonalBishop = S( 45, 0);
142 constexpr Score MinorBehindPawn = S( 18, 3);
143 constexpr Score Outpost = S( 32, 10);
144 constexpr Score PassedFile = S( 11, 8);
145 constexpr Score PawnlessFlank = S( 17, 95);
146 constexpr Score RestrictedPiece = S( 7, 7);
147 constexpr Score RookOnQueenFile = S( 7, 6);
148 constexpr Score SliderOnQueen = S( 59, 18);
149 constexpr Score ThreatByKing = S( 24, 89);
150 constexpr Score ThreatByPawnPush = S( 48, 39);
151 constexpr Score ThreatBySafePawn = S(173, 94);
152 constexpr Score TrappedRook = S( 47, 4);
153 constexpr Score WeakQueen = S( 49, 15);
157 // Evaluation class computes and stores attacks tables and other working data
162 Evaluation() = delete;
163 explicit Evaluation(const Position& p) : pos(p) {}
164 Evaluation& operator=(const Evaluation&) = delete;
168 template<Color Us> void initialize();
169 template<Color Us, PieceType Pt> Score pieces();
170 template<Color Us> Score king() const;
171 template<Color Us> Score threats() const;
172 template<Color Us> Score passed() const;
173 template<Color Us> Score space() const;
174 ScaleFactor scale_factor(Value eg) const;
175 Score initiative(Score score) const;
180 Bitboard mobilityArea[COLOR_NB];
181 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
183 // attackedBy[color][piece type] is a bitboard representing all squares
184 // attacked by a given color and piece type. Special "piece types" which
185 // is also calculated is ALL_PIECES.
186 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
188 // attackedBy2[color] are the squares attacked by at least 2 units of a given
189 // color, including x-rays. But diagonal x-rays through pawns are not computed.
190 Bitboard attackedBy2[COLOR_NB];
192 // kingRing[color] are the squares adjacent to the king plus some other
193 // very near squares, depending on king position.
194 Bitboard kingRing[COLOR_NB];
196 // kingAttackersCount[color] is the number of pieces of the given color
197 // which attack a square in the kingRing of the enemy king.
198 int kingAttackersCount[COLOR_NB];
200 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of
201 // the given color which attack a square in the kingRing of the enemy king.
202 // The weights of the individual piece types are given by the elements in
203 // the KingAttackWeights array.
204 int kingAttackersWeight[COLOR_NB];
206 // kingAttacksCount[color] is the number of attacks by the given color to
207 // squares directly adjacent to the enemy king. Pieces which attack more
208 // than one square are counted multiple times. For instance, if there is
209 // a white knight on g5 and black's king is on g8, this white knight adds 2
210 // to kingAttacksCount[WHITE].
211 int kingAttacksCount[COLOR_NB];
215 // Evaluation::initialize() computes king and pawn attacks, and the king ring
216 // bitboard for a given color. This is done at the beginning of the evaluation.
217 template<Tracing T> template<Color Us>
218 void Evaluation<T>::initialize() {
220 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
221 constexpr Direction Up = pawn_push(Us);
222 constexpr Direction Down = -Up;
223 constexpr Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB : Rank7BB | Rank6BB);
225 const Square ksq = pos.square<KING>(Us);
227 Bitboard dblAttackByPawn = pawn_double_attacks_bb<Us>(pos.pieces(Us, PAWN));
229 // Find our pawns that are blocked or on the first two ranks
230 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
232 // Squares occupied by those pawns, by our king or queen or controlled by
233 // enemy pawns are excluded from the mobility area.
234 mobilityArea[Us] = ~(b | pos.pieces(Us, KING, QUEEN) | pe->pawn_attacks(Them));
236 // Initialize attackedBy[] for king and pawns
237 attackedBy[Us][KING] = pos.attacks_from<KING>(ksq);
238 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
239 attackedBy[Us][ALL_PIECES] = attackedBy[Us][KING] | attackedBy[Us][PAWN];
240 attackedBy2[Us] = dblAttackByPawn | (attackedBy[Us][KING] & attackedBy[Us][PAWN]);
242 // Init our king safety tables
243 Square s = make_square(clamp(file_of(ksq), FILE_B, FILE_G),
244 clamp(rank_of(ksq), RANK_2, RANK_7));
245 kingRing[Us] = s | PseudoAttacks[KING][s];
247 kingAttackersCount[Them] = popcount(kingRing[Us] & pe->pawn_attacks(Them));
248 kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
250 // Remove from kingRing[] the squares defended by two pawns
251 kingRing[Us] &= ~dblAttackByPawn;
255 // Evaluation::pieces() scores pieces of a given color and type
256 template<Tracing T> template<Color Us, PieceType Pt>
257 Score Evaluation<T>::pieces() {
259 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
260 constexpr Direction Down = -pawn_push(Us);
261 constexpr Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
262 : Rank5BB | Rank4BB | Rank3BB);
263 const Square* pl = pos.squares<Pt>(Us);
266 Score score = SCORE_ZERO;
268 attackedBy[Us][Pt] = 0;
270 for (Square s = *pl; s != SQ_NONE; s = *++pl)
272 // Find attacked squares, including x-ray attacks for bishops and rooks
273 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
274 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
275 : pos.attacks_from<Pt>(s);
277 if (pos.blockers_for_king(Us) & s)
278 b &= LineBB[pos.square<KING>(Us)][s];
280 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
281 attackedBy[Us][Pt] |= b;
282 attackedBy[Us][ALL_PIECES] |= b;
284 if (b & kingRing[Them])
286 kingAttackersCount[Us]++;
287 kingAttackersWeight[Us] += KingAttackWeights[Pt];
288 kingAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
291 int mob = popcount(b & mobilityArea[Us]);
293 mobility[Us] += MobilityBonus[Pt - 2][mob];
295 if (Pt == BISHOP || Pt == KNIGHT)
297 // Bonus if piece is on an outpost square or can reach one
298 bb = OutpostRanks & attackedBy[Us][PAWN] & ~pe->pawn_attacks_span(Them);
300 score += OutpostRank[relative_rank(Us, s)] * (Pt == KNIGHT ? 2 : 1);
302 else if (Pt == KNIGHT && bb & b & ~pos.pieces(Us))
305 // Knight and Bishop bonus for being right behind a pawn
306 if (shift<Down>(pos.pieces(PAWN)) & s)
307 score += MinorBehindPawn;
309 // Penalty if the piece is far from the king
310 score -= KingProtector * distance(s, pos.square<KING>(Us));
314 // Penalty according to number of pawns on the same color square as the
315 // bishop, bigger when the center files are blocked with pawns.
316 Bitboard blocked = pos.pieces(Us, PAWN) & shift<Down>(pos.pieces());
318 score -= BishopPawns * pos.pawns_on_same_color_squares(Us, s)
319 * (1 + popcount(blocked & CenterFiles));
321 // Bonus for bishop on a long diagonal which can "see" both center squares
322 if (more_than_one(attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & Center))
323 score += LongDiagonalBishop;
326 // An important Chess960 pattern: A cornered bishop blocked by a friendly
327 // pawn diagonally in front of it is a very serious problem, especially
328 // when that pawn is also blocked.
331 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
333 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
334 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
335 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
336 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
343 // Bonus for rook on the same file as a queen
344 if (file_bb(s) & pos.pieces(QUEEN))
345 score += RookOnQueenFile;
347 // Bonus for rook on an open or semi-open file
348 if (pos.is_on_semiopen_file(Us, s))
349 score += RookOnFile[pos.is_on_semiopen_file(Them, s)];
351 // Penalty when trapped by the king, even more if the king cannot castle
354 File kf = file_of(pos.square<KING>(Us));
355 if ((kf < FILE_E) == (file_of(s) < kf))
356 score -= TrappedRook * (1 + !pos.castling_rights(Us));
362 // Penalty if any relative pin or discovered attack against the queen
363 Bitboard queenPinners;
364 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
369 Trace::add(Pt, Us, score);
375 // Evaluation::king() assigns bonuses and penalties to a king of a given color
376 template<Tracing T> template<Color Us>
377 Score Evaluation<T>::king() const {
379 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
380 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
381 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
383 Bitboard weak, b1, b2, safe, unsafeChecks = 0;
384 Bitboard rookChecks, queenChecks, bishopChecks, knightChecks;
386 const Square ksq = pos.square<KING>(Us);
388 // Init the score with king shelter and enemy pawns storm
389 Score score = pe->king_safety<Us>(pos);
391 // Attacked squares defended at most once by our queen or king
392 weak = attackedBy[Them][ALL_PIECES]
394 & (~attackedBy[Us][ALL_PIECES] | attackedBy[Us][KING] | attackedBy[Us][QUEEN]);
396 // Analyse the safe enemy's checks which are possible on next move
397 safe = ~pos.pieces(Them);
398 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
400 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
401 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
403 // Enemy rooks checks
404 rookChecks = b1 & safe & attackedBy[Them][ROOK];
407 kingDanger += RookSafeCheck;
409 unsafeChecks |= b1 & attackedBy[Them][ROOK];
411 // Enemy queen safe checks: we count them only if they are from squares from
412 // which we can't give a rook check, because rook checks are more valuable.
413 queenChecks = (b1 | b2)
414 & attackedBy[Them][QUEEN]
416 & ~attackedBy[Us][QUEEN]
420 kingDanger += QueenSafeCheck;
422 // Enemy bishops checks: we count them only if they are from squares from
423 // which we can't give a queen check, because queen checks are more valuable.
425 & attackedBy[Them][BISHOP]
430 kingDanger += BishopSafeCheck;
432 unsafeChecks |= b2 & attackedBy[Them][BISHOP];
434 // Enemy knights checks
435 knightChecks = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
437 if (knightChecks & safe)
438 kingDanger += KnightSafeCheck;
440 unsafeChecks |= knightChecks;
442 // Find the squares that opponent attacks in our king flank, and the squares
443 // which are attacked twice in that flank.
444 b1 = attackedBy[Them][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
445 b2 = b1 & attackedBy2[Them];
447 int kingFlankAttacks = popcount(b1) + popcount(b2);
449 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
450 + 185 * popcount(kingRing[Us] & weak)
451 + 148 * popcount(unsafeChecks)
452 + 98 * popcount(pos.blockers_for_king(Us))
453 + 69 * kingAttacksCount[Them]
454 + 3 * kingFlankAttacks * kingFlankAttacks / 8
455 + mg_value(mobility[Them] - mobility[Us])
456 - 873 * !pos.count<QUEEN>(Them)
457 - 100 * bool(attackedBy[Us][KNIGHT] & attackedBy[Us][KING])
458 - 35 * bool(attackedBy[Us][BISHOP] & attackedBy[Us][KING])
459 - 6 * mg_value(score) / 8
462 // Transform the kingDanger units into a Score, and subtract it from the evaluation
463 if (kingDanger > 100)
464 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
466 // Penalty when our king is on a pawnless flank
467 if (!(pos.pieces(PAWN) & KingFlank[file_of(ksq)]))
468 score -= PawnlessFlank;
470 // Penalty if king flank is under attack, potentially moving toward the king
471 score -= FlankAttacks * kingFlankAttacks;
474 Trace::add(KING, Us, score);
480 // Evaluation::threats() assigns bonuses according to the types of the
481 // attacking and the attacked pieces.
482 template<Tracing T> template<Color Us>
483 Score Evaluation<T>::threats() const {
485 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
486 constexpr Direction Up = pawn_push(Us);
487 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
489 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe;
490 Score score = SCORE_ZERO;
493 nonPawnEnemies = pos.pieces(Them) & ~pos.pieces(PAWN);
495 // Squares strongly protected by the enemy, either because they defend the
496 // square with a pawn, or because they defend the square twice and we don't.
497 stronglyProtected = attackedBy[Them][PAWN]
498 | (attackedBy2[Them] & ~attackedBy2[Us]);
500 // Non-pawn enemies, strongly protected
501 defended = nonPawnEnemies & stronglyProtected;
503 // Enemies not strongly protected and under our attack
504 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
506 // Bonus according to the kind of attacking pieces
509 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
511 score += ThreatByMinor[type_of(pos.piece_on(pop_lsb(&b)))];
513 b = weak & attackedBy[Us][ROOK];
515 score += ThreatByRook[type_of(pos.piece_on(pop_lsb(&b)))];
517 if (weak & attackedBy[Us][KING])
518 score += ThreatByKing;
520 b = ~attackedBy[Them][ALL_PIECES]
521 | (nonPawnEnemies & attackedBy2[Us]);
522 score += Hanging * popcount(weak & b);
525 // Bonus for restricting their piece moves
526 b = attackedBy[Them][ALL_PIECES]
528 & attackedBy[Us][ALL_PIECES];
530 score += RestrictedPiece * popcount(b);
532 // Protected or unattacked squares
533 safe = ~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES];
535 // Bonus for attacking enemy pieces with our relatively safe pawns
536 b = pos.pieces(Us, PAWN) & safe;
537 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
538 score += ThreatBySafePawn * popcount(b);
540 // Find squares where our pawns can push on the next move
541 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
542 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
544 // Keep only the squares which are relatively safe
545 b &= ~attackedBy[Them][PAWN] & safe;
547 // Bonus for safe pawn threats on the next move
548 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
549 score += ThreatByPawnPush * popcount(b);
551 // Bonus for threats on the next moves against enemy queen
552 if (pos.count<QUEEN>(Them) == 1)
554 Square s = pos.square<QUEEN>(Them);
555 safe = mobilityArea[Us] & ~stronglyProtected;
557 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
559 score += KnightOnQueen * popcount(b & safe);
561 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
562 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
564 score += SliderOnQueen * popcount(b & safe & attackedBy2[Us]);
568 Trace::add(THREAT, Us, score);
573 // Evaluation::passed() evaluates the passed pawns and candidate passed
574 // pawns of the given color.
576 template<Tracing T> template<Color Us>
577 Score Evaluation<T>::passed() const {
579 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
580 constexpr Direction Up = pawn_push(Us);
582 auto king_proximity = [&](Color c, Square s) {
583 return std::min(distance(pos.square<KING>(c), s), 5);
586 Bitboard b, bb, squaresToQueen, unsafeSquares;
587 Score score = SCORE_ZERO;
589 b = pe->passed_pawns(Us);
593 Square s = pop_lsb(&b);
595 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
597 int r = relative_rank(Us, s);
599 Score bonus = PassedRank[r];
604 Square blockSq = s + Up;
606 // Adjust bonus based on the king's proximity
607 bonus += make_score(0, ( king_proximity(Them, blockSq) * 5
608 - king_proximity(Us, blockSq) * 2) * w);
610 // If blockSq is not the queening square then consider also a second push
612 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
614 // If the pawn is free to advance, then increase the bonus
615 if (pos.empty(blockSq))
617 squaresToQueen = forward_file_bb(Us, s);
618 unsafeSquares = passed_pawn_span(Us, s);
620 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN);
622 if (!(pos.pieces(Them) & bb))
623 unsafeSquares &= attackedBy[Them][ALL_PIECES];
625 // If there are no enemy attacks on passed pawn span, assign a big bonus.
626 // Otherwise assign a smaller bonus if the path to queen is not attacked
627 // and even smaller bonus if it is attacked but block square is not.
628 int k = !unsafeSquares ? 35 :
629 !(unsafeSquares & squaresToQueen) ? 20 :
630 !(unsafeSquares & blockSq) ? 9 :
633 // Assign a larger bonus if the block square is defended
634 if ((pos.pieces(Us) & bb) || (attackedBy[Us][ALL_PIECES] & blockSq))
637 bonus += make_score(k * w, k * w);
641 // Scale down bonus for candidate passers which need more than one
642 // pawn push to become passed, or have a pawn in front of them.
643 if ( !pos.pawn_passed(Us, s + Up)
644 || (pos.pieces(PAWN) & (s + Up)))
647 score += bonus - PassedFile * map_to_queenside(file_of(s));
651 Trace::add(PASSED, Us, score);
657 // Evaluation::space() computes the space evaluation for a given side. The
658 // space evaluation is a simple bonus based on the number of safe squares
659 // available for minor pieces on the central four files on ranks 2--4. Safe
660 // squares one, two or three squares behind a friendly pawn are counted
661 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
662 // improve play on game opening.
664 template<Tracing T> template<Color Us>
665 Score Evaluation<T>::space() const {
667 if (pos.non_pawn_material() < SpaceThreshold)
670 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
671 constexpr Direction Down = -pawn_push(Us);
672 constexpr Bitboard SpaceMask =
673 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
674 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
676 // Find the available squares for our pieces inside the area defined by SpaceMask
677 Bitboard safe = SpaceMask
678 & ~pos.pieces(Us, PAWN)
679 & ~attackedBy[Them][PAWN];
681 // Find all squares which are at most three squares behind some friendly pawn
682 Bitboard behind = pos.pieces(Us, PAWN);
683 behind |= shift<Down>(behind);
684 behind |= shift<Down+Down>(behind);
686 int bonus = popcount(safe) + popcount(behind & safe & ~attackedBy[Them][ALL_PIECES]);
687 int weight = pos.count<ALL_PIECES>(Us) - 1;
688 Score score = make_score(bonus * weight * weight / 16, 0);
691 Trace::add(SPACE, Us, score);
697 // Evaluation::initiative() computes the initiative correction value
698 // for the position. It is a second order bonus/malus based on the
699 // known attacking/defending status of the players.
702 Score Evaluation<T>::initiative(Score score) const {
704 Value mg = mg_value(score);
705 Value eg = eg_value(score);
707 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
708 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
710 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
711 && (pos.pieces(PAWN) & KingSide);
713 bool almostUnwinnable = !pe->passed_count()
715 && !pawnsOnBothFlanks;
717 // Compute the initiative bonus for the attacking side
718 int complexity = 9 * pe->passed_count()
719 + 11 * pos.count<PAWN>()
721 + 21 * pawnsOnBothFlanks
722 + 51 * !pos.non_pawn_material()
723 - 43 * almostUnwinnable
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)
752 sf = 16 + 4 * pe->passed_count();
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) {
852 std::memset(scores, 0, sizeof(scores));
854 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
856 Value v = Evaluation<TRACE>(pos).value();
858 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
860 std::stringstream ss;
861 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
862 << " Term | White | Black | Total \n"
863 << " | MG EG | MG EG | MG EG \n"
864 << " ------------+-------------+-------------+------------\n"
865 << " Material | " << Term(MATERIAL)
866 << " Imbalance | " << Term(IMBALANCE)
867 << " Pawns | " << Term(PAWN)
868 << " Knights | " << Term(KNIGHT)
869 << " Bishops | " << Term(BISHOP)
870 << " Rooks | " << Term(ROOK)
871 << " Queens | " << Term(QUEEN)
872 << " Mobility | " << Term(MOBILITY)
873 << " King safety | " << Term(KING)
874 << " Threats | " << Term(THREAT)
875 << " Passed | " << Term(PASSED)
876 << " Space | " << Term(SPACE)
877 << " Initiative | " << Term(INITIATIVE)
878 << " ------------+-------------+-------------+------------\n"
879 << " Total | " << Term(TOTAL);
881 ss << "\nTotal evaluation: " << to_cp(v) << " (white side)\n";