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, b3, 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, the squares
443 // which they attack twice in that flank, and the squares that we defend.
444 b1 = attackedBy[Them][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
445 b2 = b1 & attackedBy2[Them];
446 b3 = attackedBy[Us][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
448 int kingFlankAttack = popcount(b1) + popcount(b2);
449 int kingFlankDefense = popcount(b3);
451 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
452 + 185 * popcount(kingRing[Us] & weak)
453 + 148 * popcount(unsafeChecks)
454 + 98 * popcount(pos.blockers_for_king(Us))
455 + 69 * kingAttacksCount[Them]
456 + 4 * (kingFlankAttack - kingFlankDefense)
457 + 3 * kingFlankAttack * kingFlankAttack / 8
458 + mg_value(mobility[Them] - mobility[Us])
459 - 873 * !pos.count<QUEEN>(Them)
460 - 100 * bool(attackedBy[Us][KNIGHT] & attackedBy[Us][KING])
461 - 35 * bool(attackedBy[Us][BISHOP] & attackedBy[Us][KING])
462 - 6 * mg_value(score) / 8
465 // Transform the kingDanger units into a Score, and subtract it from the evaluation
466 if (kingDanger > 100)
467 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
469 // Penalty when our king is on a pawnless flank
470 if (!(pos.pieces(PAWN) & KingFlank[file_of(ksq)]))
471 score -= PawnlessFlank;
473 // Penalty if king flank is under attack, potentially moving toward the king
474 score -= FlankAttacks * kingFlankAttack;
477 Trace::add(KING, Us, score);
483 // Evaluation::threats() assigns bonuses according to the types of the
484 // attacking and the attacked pieces.
485 template<Tracing T> template<Color Us>
486 Score Evaluation<T>::threats() const {
488 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
489 constexpr Direction Up = pawn_push(Us);
490 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
492 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe;
493 Score score = SCORE_ZERO;
496 nonPawnEnemies = pos.pieces(Them) & ~pos.pieces(PAWN);
498 // Squares strongly protected by the enemy, either because they defend the
499 // square with a pawn, or because they defend the square twice and we don't.
500 stronglyProtected = attackedBy[Them][PAWN]
501 | (attackedBy2[Them] & ~attackedBy2[Us]);
503 // Non-pawn enemies, strongly protected
504 defended = nonPawnEnemies & stronglyProtected;
506 // Enemies not strongly protected and under our attack
507 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
509 // Bonus according to the kind of attacking pieces
512 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
514 score += ThreatByMinor[type_of(pos.piece_on(pop_lsb(&b)))];
516 b = weak & attackedBy[Us][ROOK];
518 score += ThreatByRook[type_of(pos.piece_on(pop_lsb(&b)))];
520 if (weak & attackedBy[Us][KING])
521 score += ThreatByKing;
523 b = ~attackedBy[Them][ALL_PIECES]
524 | (nonPawnEnemies & attackedBy2[Us]);
525 score += Hanging * popcount(weak & b);
528 // Bonus for restricting their piece moves
529 b = attackedBy[Them][ALL_PIECES]
531 & attackedBy[Us][ALL_PIECES];
533 score += RestrictedPiece * popcount(b);
535 // Protected or unattacked squares
536 safe = ~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES];
538 // Bonus for attacking enemy pieces with our relatively safe pawns
539 b = pos.pieces(Us, PAWN) & safe;
540 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
541 score += ThreatBySafePawn * popcount(b);
543 // Find squares where our pawns can push on the next move
544 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
545 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
547 // Keep only the squares which are relatively safe
548 b &= ~attackedBy[Them][PAWN] & safe;
550 // Bonus for safe pawn threats on the next move
551 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
552 score += ThreatByPawnPush * popcount(b);
554 // Bonus for threats on the next moves against enemy queen
555 if (pos.count<QUEEN>(Them) == 1)
557 Square s = pos.square<QUEEN>(Them);
558 safe = mobilityArea[Us] & ~stronglyProtected;
560 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
562 score += KnightOnQueen * popcount(b & safe);
564 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
565 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
567 score += SliderOnQueen * popcount(b & safe & attackedBy2[Us]);
571 Trace::add(THREAT, Us, score);
576 // Evaluation::passed() evaluates the passed pawns and candidate passed
577 // pawns of the given color.
579 template<Tracing T> template<Color Us>
580 Score Evaluation<T>::passed() const {
582 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
583 constexpr Direction Up = pawn_push(Us);
585 auto king_proximity = [&](Color c, Square s) {
586 return std::min(distance(pos.square<KING>(c), s), 5);
589 Bitboard b, bb, squaresToQueen, unsafeSquares;
590 Score score = SCORE_ZERO;
592 b = pe->passed_pawns(Us);
596 Square s = pop_lsb(&b);
598 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
600 int r = relative_rank(Us, s);
602 Score bonus = PassedRank[r];
607 Square blockSq = s + Up;
609 // Adjust bonus based on the king's proximity
610 bonus += make_score(0, ( king_proximity(Them, blockSq) * 5
611 - king_proximity(Us, blockSq) * 2) * w);
613 // If blockSq is not the queening square then consider also a second push
615 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
617 // If the pawn is free to advance, then increase the bonus
618 if (pos.empty(blockSq))
620 squaresToQueen = forward_file_bb(Us, s);
621 unsafeSquares = passed_pawn_span(Us, s);
623 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN);
625 if (!(pos.pieces(Them) & bb))
626 unsafeSquares &= attackedBy[Them][ALL_PIECES];
628 // If there are no enemy attacks on passed pawn span, assign a big bonus.
629 // Otherwise assign a smaller bonus if the path to queen is not attacked
630 // and even smaller bonus if it is attacked but block square is not.
631 int k = !unsafeSquares ? 35 :
632 !(unsafeSquares & squaresToQueen) ? 20 :
633 !(unsafeSquares & blockSq) ? 9 :
636 // Assign a larger bonus if the block square is defended
637 if ((pos.pieces(Us) & bb) || (attackedBy[Us][ALL_PIECES] & blockSq))
640 bonus += make_score(k * w, k * w);
644 // Scale down bonus for candidate passers which need more than one
645 // pawn push to become passed, or have a pawn in front of them.
646 if ( !pos.pawn_passed(Us, s + Up)
647 || (pos.pieces(PAWN) & (s + Up)))
650 score += bonus - PassedFile * map_to_queenside(file_of(s));
654 Trace::add(PASSED, Us, score);
660 // Evaluation::space() computes the space evaluation for a given side. The
661 // space evaluation is a simple bonus based on the number of safe squares
662 // available for minor pieces on the central four files on ranks 2--4. Safe
663 // squares one, two or three squares behind a friendly pawn are counted
664 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
665 // improve play on game opening.
667 template<Tracing T> template<Color Us>
668 Score Evaluation<T>::space() const {
670 if (pos.non_pawn_material() < SpaceThreshold)
673 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
674 constexpr Direction Down = -pawn_push(Us);
675 constexpr Bitboard SpaceMask =
676 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
677 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
679 // Find the available squares for our pieces inside the area defined by SpaceMask
680 Bitboard safe = SpaceMask
681 & ~pos.pieces(Us, PAWN)
682 & ~attackedBy[Them][PAWN];
684 // Find all squares which are at most three squares behind some friendly pawn
685 Bitboard behind = pos.pieces(Us, PAWN);
686 behind |= shift<Down>(behind);
687 behind |= shift<Down+Down>(behind);
689 int bonus = popcount(safe) + popcount(behind & safe & ~attackedBy[Them][ALL_PIECES]);
690 int weight = pos.count<ALL_PIECES>(Us) - 1;
691 Score score = make_score(bonus * weight * weight / 16, 0);
694 Trace::add(SPACE, Us, score);
700 // Evaluation::initiative() computes the initiative correction value
701 // for the position. It is a second order bonus/malus based on the
702 // known attacking/defending status of the players.
705 Score Evaluation<T>::initiative(Score score) const {
707 Value mg = mg_value(score);
708 Value eg = eg_value(score);
710 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
711 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
713 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
714 && (pos.pieces(PAWN) & KingSide);
716 bool almostUnwinnable = !pe->passed_count()
718 && !pawnsOnBothFlanks;
720 // Compute the initiative bonus for the attacking side
721 int complexity = 9 * pe->passed_count()
722 + 11 * pos.count<PAWN>()
724 + 21 * pawnsOnBothFlanks
725 + 51 * !pos.non_pawn_material()
726 - 43 * almostUnwinnable
729 // Now apply the bonus: note that we find the attacking side by extracting the
730 // sign of the midgame or endgame values, and that we carefully cap the bonus
731 // so that the midgame and endgame scores do not change sign after the bonus.
732 int u = ((mg > 0) - (mg < 0)) * std::max(std::min(complexity + 50, 0), -abs(mg));
733 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
736 Trace::add(INITIATIVE, make_score(u, v));
738 return make_score(u, v);
742 // Evaluation::scale_factor() computes the scale factor for the winning side
745 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
747 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
748 int sf = me->scale_factor(pos, strongSide);
750 // If scale is not already specific, scale down the endgame via general heuristics
751 if (sf == SCALE_FACTOR_NORMAL)
753 if ( pos.opposite_bishops()
754 && pos.non_pawn_material() == 2 * BishopValueMg)
755 sf = 16 + 4 * pe->passed_count();
757 sf = std::min(sf, 36 + (pos.opposite_bishops() ? 2 : 7) * pos.count<PAWN>(strongSide));
759 sf = std::max(0, sf - (pos.rule50_count() - 12) / 4);
762 return ScaleFactor(sf);
766 // Evaluation::value() is the main function of the class. It computes the various
767 // parts of the evaluation and returns the value of the position from the point
768 // of view of the side to move.
771 Value Evaluation<T>::value() {
773 assert(!pos.checkers());
775 // Probe the material hash table
776 me = Material::probe(pos);
778 // If we have a specialized evaluation function for the current material
779 // configuration, call it and return.
780 if (me->specialized_eval_exists())
781 return me->evaluate(pos);
783 // Initialize score by reading the incrementally updated scores included in
784 // the position object (material + piece square tables) and the material
785 // imbalance. Score is computed internally from the white point of view.
786 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
788 // Probe the pawn hash table
789 pe = Pawns::probe(pos);
790 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
792 // Early exit if score is high
793 Value v = (mg_value(score) + eg_value(score)) / 2;
794 if (abs(v) > LazyThreshold + pos.non_pawn_material() / 64)
795 return pos.side_to_move() == WHITE ? v : -v;
797 // Main evaluation begins here
802 // Pieces should be evaluated first (populate attack tables)
803 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
804 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
805 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
806 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
808 score += mobility[WHITE] - mobility[BLACK];
810 score += king< WHITE>() - king< BLACK>()
811 + threats<WHITE>() - threats<BLACK>()
812 + passed< WHITE>() - passed< BLACK>()
813 + space< WHITE>() - space< BLACK>();
815 score += initiative(score);
817 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
818 ScaleFactor sf = scale_factor(eg_value(score));
819 v = mg_value(score) * int(me->game_phase())
820 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
824 // In case of tracing add all remaining individual evaluation terms
827 Trace::add(MATERIAL, pos.psq_score());
828 Trace::add(IMBALANCE, me->imbalance());
829 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
830 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
831 Trace::add(TOTAL, score);
834 return (pos.side_to_move() == WHITE ? v : -v) // Side to move point of view
841 /// evaluate() is the evaluator for the outer world. It returns a static
842 /// evaluation of the position from the point of view of the side to move.
844 Value Eval::evaluate(const Position& pos) {
845 return Evaluation<NO_TRACE>(pos).value();
849 /// trace() is like evaluate(), but instead of returning a value, it returns
850 /// a string (suitable for outputting to stdout) that contains the detailed
851 /// descriptions and values of each evaluation term. Useful for debugging.
853 std::string Eval::trace(const Position& pos) {
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";