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(1500);
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, 77, 55, 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(18, 7), S(44, 20) };
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(0, 31), S(39, 42), S(57, 44), S(68, 112), S(62, 120)
120 constexpr Score ThreatByRook[PIECE_TYPE_NB] = {
121 S(0, 0), S(0, 24), 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(5, 18), S(12, 23), S(10, 31), S(57, 62), S(163, 167), S(271, 250)
129 // PassedFile[File] contains a bonus according to the file of a passed pawn
130 constexpr Score PassedFile[FILE_NB] = {
131 S( -1, 7), S( 0, 9), S(-9, -8), S(-30,-14),
132 S(-30,-14), S(-9, -8), S( 0, 9), S( -1, 7)
135 // Assorted bonuses and penalties
136 constexpr Score BishopPawns = S( 3, 7);
137 constexpr Score CorneredBishop = S( 50, 50);
138 constexpr Score FlankAttacks = S( 8, 0);
139 constexpr Score Hanging = S( 69, 36);
140 constexpr Score KingProtector = S( 7, 8);
141 constexpr Score KnightOnQueen = S( 16, 12);
142 constexpr Score LongDiagonalBishop = S( 45, 0);
143 constexpr Score MinorBehindPawn = S( 18, 3);
144 constexpr Score Outpost = S( 9, 3);
145 constexpr Score PawnlessFlank = S( 17, 95);
146 constexpr Score RestrictedPiece = S( 7, 7);
147 constexpr Score RookOnPawn = S( 10, 32);
148 constexpr Score SliderOnQueen = S( 59, 18);
149 constexpr Score ThreatByKing = S( 24, 89);
150 constexpr Score ThreatByPawnPush = S( 48, 39);
151 constexpr Score ThreatByRank = S( 13, 0);
152 constexpr Score ThreatBySafePawn = S(173, 94);
153 constexpr Score TrappedRook = S( 47, 4);
154 constexpr Score WeakQueen = S( 49, 15);
155 constexpr Score WeakUnopposedPawn = S( 12, 23);
159 // Evaluation class computes and stores attacks tables and other working data
164 Evaluation() = delete;
165 explicit Evaluation(const Position& p) : pos(p) {}
166 Evaluation& operator=(const Evaluation&) = delete;
170 template<Color Us> void initialize();
171 template<Color Us, PieceType Pt> Score pieces();
172 template<Color Us> Score king() const;
173 template<Color Us> Score threats() const;
174 template<Color Us> Score passed() const;
175 template<Color Us> Score space() const;
176 ScaleFactor scale_factor(Value eg) const;
177 Score initiative(Value eg) const;
182 Bitboard mobilityArea[COLOR_NB];
183 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
185 // attackedBy[color][piece type] is a bitboard representing all squares
186 // attacked by a given color and piece type. Special "piece types" which
187 // is also calculated is ALL_PIECES.
188 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
190 // attackedBy2[color] are the squares attacked by at least 2 units of a given
191 // color, including x-rays. But diagonal x-rays through pawns are not computed.
192 Bitboard attackedBy2[COLOR_NB];
194 // kingRing[color] are the squares adjacent to the king, plus (only for a
195 // king on its first rank) the squares two ranks in front. For instance,
196 // if black's king is on g8, kingRing[BLACK] is f8, h8, f7, g7, h7, f6, g6
198 Bitboard kingRing[COLOR_NB];
200 // kingAttackersCount[color] is the number of pieces of the given color
201 // which attack a square in the kingRing of the enemy king.
202 int kingAttackersCount[COLOR_NB];
204 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of
205 // the given color which attack a square in the kingRing of the enemy king.
206 // The weights of the individual piece types are given by the elements in
207 // the KingAttackWeights array.
208 int kingAttackersWeight[COLOR_NB];
210 // kingAttacksCount[color] is the number of attacks by the given color to
211 // squares directly adjacent to the enemy king. Pieces which attack more
212 // than one square are counted multiple times. For instance, if there is
213 // a white knight on g5 and black's king is on g8, this white knight adds 2
214 // to kingAttacksCount[WHITE].
215 int kingAttacksCount[COLOR_NB];
219 // Evaluation::initialize() computes king and pawn attacks, and the king ring
220 // bitboard for a given color. This is done at the beginning of the evaluation.
221 template<Tracing T> template<Color Us>
222 void Evaluation<T>::initialize() {
224 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
225 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
226 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
227 constexpr Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB: Rank7BB | Rank6BB);
229 const Square ksq = pos.square<KING>(Us);
231 Bitboard dblAttackByPawn = pawn_double_attacks_bb<Us>(pos.pieces(Us, PAWN));
233 // Find our pawns that are blocked or on the first two ranks
234 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
236 // Squares occupied by those pawns, by our king or queen or controlled by
237 // enemy pawns are excluded from the mobility area.
238 mobilityArea[Us] = ~(b | pos.pieces(Us, KING, QUEEN) | pe->pawn_attacks(Them));
240 // Initialize attackedBy[] for king and pawns
241 attackedBy[Us][KING] = pos.attacks_from<KING>(ksq);
242 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
243 attackedBy[Us][ALL_PIECES] = attackedBy[Us][KING] | attackedBy[Us][PAWN];
244 attackedBy2[Us] = dblAttackByPawn | (attackedBy[Us][KING] & attackedBy[Us][PAWN]);
246 // Init our king safety tables
247 kingRing[Us] = attackedBy[Us][KING];
248 if (relative_rank(Us, ksq) == RANK_1)
249 kingRing[Us] |= shift<Up>(kingRing[Us]);
251 if (file_of(ksq) == FILE_H)
252 kingRing[Us] |= shift<WEST>(kingRing[Us]);
254 else if (file_of(ksq) == FILE_A)
255 kingRing[Us] |= shift<EAST>(kingRing[Us]);
257 kingAttackersCount[Them] = popcount(kingRing[Us] & pe->pawn_attacks(Them));
258 kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
260 // Remove from kingRing[] the squares defended by two pawns
261 kingRing[Us] &= ~dblAttackByPawn;
265 // Evaluation::pieces() scores pieces of a given color and type
266 template<Tracing T> template<Color Us, PieceType Pt>
267 Score Evaluation<T>::pieces() {
269 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
270 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
271 constexpr Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
272 : Rank5BB | Rank4BB | Rank3BB);
273 const Square* pl = pos.squares<Pt>(Us);
276 Score score = SCORE_ZERO;
278 attackedBy[Us][Pt] = 0;
280 for (Square s = *pl; s != SQ_NONE; s = *++pl)
282 // Find attacked squares, including x-ray attacks for bishops and rooks
283 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
284 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
285 : pos.attacks_from<Pt>(s);
287 if (pos.blockers_for_king(Us) & s)
288 b &= LineBB[pos.square<KING>(Us)][s];
290 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
291 attackedBy[Us][Pt] |= b;
292 attackedBy[Us][ALL_PIECES] |= b;
294 if (b & kingRing[Them])
296 kingAttackersCount[Us]++;
297 kingAttackersWeight[Us] += KingAttackWeights[Pt];
298 kingAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
301 int mob = popcount(b & mobilityArea[Us]);
303 mobility[Us] += MobilityBonus[Pt - 2][mob];
305 if (Pt == BISHOP || Pt == KNIGHT)
307 // Bonus if piece is on an outpost square or can reach one
308 bb = OutpostRanks & ~pe->pawn_attacks_span(Them);
310 score += Outpost * (Pt == KNIGHT ? 4 : 2)
311 * ((attackedBy[Us][PAWN] & s) ? 2 : 1);
313 else if (bb &= b & ~pos.pieces(Us))
314 score += Outpost * (Pt == KNIGHT ? 2 : 1)
315 * ((attackedBy[Us][PAWN] & bb) ? 2 : 1);
317 // Knight and Bishop bonus for being right behind a pawn
318 if (shift<Down>(pos.pieces(PAWN)) & s)
319 score += MinorBehindPawn;
321 // Penalty if the piece is far from the king
322 score -= KingProtector * distance(s, pos.square<KING>(Us));
326 // Penalty according to number of pawns on the same color square as the
327 // bishop, bigger when the center files are blocked with pawns.
328 Bitboard blocked = pos.pieces(Us, PAWN) & shift<Down>(pos.pieces());
330 score -= BishopPawns * pos.pawns_on_same_color_squares(Us, s)
331 * (1 + popcount(blocked & CenterFiles));
333 // Bonus for bishop on a long diagonal which can "see" both center squares
334 if (more_than_one(attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & Center))
335 score += LongDiagonalBishop;
338 // An important Chess960 pattern: A cornered bishop blocked by a friendly
339 // pawn diagonally in front of it is a very serious problem, especially
340 // when that pawn is also blocked.
343 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
345 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
346 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
347 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
348 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
355 // Bonus for aligning rook with enemy pawns on the same rank/file
356 if (relative_rank(Us, s) >= RANK_5)
357 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
359 // Bonus for rook on an open or semi-open file
360 if (pos.is_semiopen_file(Us, file_of(s)))
361 score += RookOnFile[bool(pos.is_semiopen_file(Them, file_of(s)))];
363 // Penalty when trapped by the king, even more if the king cannot castle
366 File kf = file_of(pos.square<KING>(Us));
367 if ((kf < FILE_E) == (file_of(s) < kf))
368 score -= TrappedRook * (1 + !pos.castling_rights(Us));
374 // Penalty if any relative pin or discovered attack against the queen
375 Bitboard queenPinners;
376 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
381 Trace::add(Pt, Us, score);
387 // Evaluation::king() assigns bonuses and penalties to a king of a given color
388 template<Tracing T> template<Color Us>
389 Score Evaluation<T>::king() const {
391 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
392 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
393 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
395 Bitboard weak, b1, b2, safe, unsafeChecks = 0;
396 Bitboard rookChecks, queenChecks, bishopChecks, knightChecks;
398 const Square ksq = pos.square<KING>(Us);
400 // Init the score with king shelter and enemy pawns storm
401 Score score = pe->king_safety<Us>(pos);
403 // Attacked squares defended at most once by our queen or king
404 weak = attackedBy[Them][ALL_PIECES]
406 & (~attackedBy[Us][ALL_PIECES] | attackedBy[Us][KING] | attackedBy[Us][QUEEN]);
408 // Analyse the safe enemy's checks which are possible on next move
409 safe = ~pos.pieces(Them);
410 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
412 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
413 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
415 // Enemy rooks checks
416 rookChecks = b1 & safe & attackedBy[Them][ROOK];
419 kingDanger += RookSafeCheck;
421 unsafeChecks |= b1 & attackedBy[Them][ROOK];
423 // Enemy queen safe checks: we count them only if they are from squares from
424 // which we can't give a rook check, because rook checks are more valuable.
425 queenChecks = (b1 | b2)
426 & attackedBy[Them][QUEEN]
428 & ~attackedBy[Us][QUEEN]
432 kingDanger += QueenSafeCheck;
434 // Enemy bishops checks: we count them only if they are from squares from
435 // which we can't give a queen check, because queen checks are more valuable.
437 & attackedBy[Them][BISHOP]
442 kingDanger += BishopSafeCheck;
444 unsafeChecks |= b2 & attackedBy[Them][BISHOP];
446 // Enemy knights checks
447 knightChecks = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
449 if (knightChecks & safe)
450 kingDanger += KnightSafeCheck;
452 unsafeChecks |= knightChecks;
454 // Unsafe or occupied checking squares will also be considered, as long as
455 // the square is in the attacker's mobility area.
456 unsafeChecks &= mobilityArea[Them];
458 // Find the squares that opponent attacks in our king flank, and the squares
459 // which are attacked twice in that flank.
460 b1 = attackedBy[Them][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
461 b2 = b1 & attackedBy2[Them];
463 int kingFlankAttacks = popcount(b1) + popcount(b2);
465 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
466 + 69 * kingAttacksCount[Them]
467 + 185 * popcount(kingRing[Us] & weak)
468 - 100 * bool(attackedBy[Us][KNIGHT] & attackedBy[Us][KING])
469 - 35 * bool(attackedBy[Us][BISHOP] & attackedBy[Us][KING])
470 + 150 * popcount(pos.blockers_for_king(Us) | unsafeChecks)
471 - 873 * !pos.count<QUEEN>(Them)
472 - 6 * mg_value(score) / 8
473 + mg_value(mobility[Them] - mobility[Us])
474 + 5 * kingFlankAttacks * kingFlankAttacks / 16
477 // Transform the kingDanger units into a Score, and subtract it from the evaluation
478 if (kingDanger > 100)
479 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
481 // Penalty when our king is on a pawnless flank
482 if (!(pos.pieces(PAWN) & KingFlank[file_of(ksq)]))
483 score -= PawnlessFlank;
485 // Penalty if king flank is under attack, potentially moving toward the king
486 score -= FlankAttacks * kingFlankAttacks;
489 Trace::add(KING, Us, score);
495 // Evaluation::threats() assigns bonuses according to the types of the
496 // attacking and the attacked pieces.
497 template<Tracing T> template<Color Us>
498 Score Evaluation<T>::threats() const {
500 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
501 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
502 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
504 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe;
505 Score score = SCORE_ZERO;
508 nonPawnEnemies = pos.pieces(Them) & ~pos.pieces(PAWN);
510 // Squares strongly protected by the enemy, either because they defend the
511 // square with a pawn, or because they defend the square twice and we don't.
512 stronglyProtected = attackedBy[Them][PAWN]
513 | (attackedBy2[Them] & ~attackedBy2[Us]);
515 // Non-pawn enemies, strongly protected
516 defended = nonPawnEnemies & stronglyProtected;
518 // Enemies not strongly protected and under our attack
519 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
521 // Safe or protected squares
522 safe = ~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES];
524 // Bonus according to the kind of attacking pieces
527 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
530 Square s = pop_lsb(&b);
531 score += ThreatByMinor[type_of(pos.piece_on(s))];
532 if (type_of(pos.piece_on(s)) != PAWN)
533 score += ThreatByRank * (int)relative_rank(Them, s);
536 b = weak & attackedBy[Us][ROOK];
539 Square s = pop_lsb(&b);
540 score += ThreatByRook[type_of(pos.piece_on(s))];
541 if (type_of(pos.piece_on(s)) != PAWN)
542 score += ThreatByRank * (int)relative_rank(Them, s);
545 if (weak & attackedBy[Us][KING])
546 score += ThreatByKing;
548 b = ~attackedBy[Them][ALL_PIECES]
549 | (nonPawnEnemies & attackedBy2[Us]);
550 score += Hanging * popcount(weak & b);
553 // Bonus for restricting their piece moves
554 b = attackedBy[Them][ALL_PIECES]
556 & attackedBy[Us][ALL_PIECES];
558 score += RestrictedPiece * popcount(b);
560 // Bonus for enemy unopposed weak pawns
561 if (pos.pieces(Us, ROOK, QUEEN))
562 score += WeakUnopposedPawn * pe->weak_unopposed(Them);
564 // Find squares where our pawns can push on the next move
565 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
566 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
568 // Keep only the squares which are relatively safe
569 b &= ~attackedBy[Them][PAWN] & safe;
571 // Bonus for safe pawn threats on the next move
572 b = pawn_attacks_bb<Us>(b) & pos.pieces(Them);
573 score += ThreatByPawnPush * popcount(b);
575 // Our safe or protected pawns
576 b = pos.pieces(Us, PAWN) & safe;
578 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
579 score += ThreatBySafePawn * popcount(b);
581 // Bonus for threats on the next moves against enemy queen
582 if (pos.count<QUEEN>(Them) == 1)
584 Square s = pos.square<QUEEN>(Them);
585 safe = mobilityArea[Us] & ~stronglyProtected;
587 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
589 score += KnightOnQueen * popcount(b & safe);
591 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
592 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
594 score += SliderOnQueen * popcount(b & safe & attackedBy2[Us]);
598 Trace::add(THREAT, Us, score);
603 // Evaluation::passed() evaluates the passed pawns and candidate passed
604 // pawns of the given color.
606 template<Tracing T> template<Color Us>
607 Score Evaluation<T>::passed() const {
609 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
610 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
612 auto king_proximity = [&](Color c, Square s) {
613 return std::min(distance(pos.square<KING>(c), s), 5);
616 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
617 Score score = SCORE_ZERO;
619 b = pe->passed_pawns(Us);
623 Square s = pop_lsb(&b);
625 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
627 int r = relative_rank(Us, s);
629 Score bonus = PassedRank[r];
633 int w = (r-2) * (r-2) + 2;
634 Square blockSq = s + Up;
636 // Adjust bonus based on the king's proximity
637 bonus += make_score(0, ( king_proximity(Them, blockSq) * 5
638 - king_proximity(Us, blockSq) * 2) * w);
640 // If blockSq is not the queening square then consider also a second push
642 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
644 // If the pawn is free to advance, then increase the bonus
645 if (pos.empty(blockSq))
647 // If there is a rook or queen attacking/defending the pawn from behind,
648 // consider all the squaresToQueen. Otherwise consider only the squares
649 // in the pawn's path attacked or occupied by the enemy.
650 defendedSquares = unsafeSquares = squaresToQueen = forward_file_bb(Us, s);
652 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
654 if (!(pos.pieces(Us) & bb))
655 defendedSquares &= attackedBy[Us][ALL_PIECES];
657 if (!(pos.pieces(Them) & bb))
658 unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
660 // If there aren't any enemy attacks, assign a big bonus. Otherwise
661 // assign a smaller bonus if the block square isn't attacked.
662 int k = !unsafeSquares ? 20 : !(unsafeSquares & blockSq) ? 9 : 0;
664 // If the path to the queen is fully defended, assign a big bonus.
665 // Otherwise assign a smaller bonus if the block square is defended.
666 if (defendedSquares == squaresToQueen)
669 else if (defendedSquares & blockSq)
672 bonus += make_score(k * w, k * w);
676 // Scale down bonus for candidate passers which need more than one
677 // pawn push to become passed, or have a pawn in front of them.
678 if ( !pos.pawn_passed(Us, s + Up)
679 || (pos.pieces(PAWN) & forward_file_bb(Us, s)))
682 score += bonus + PassedFile[file_of(s)];
686 Trace::add(PASSED, Us, score);
692 // Evaluation::space() computes the space evaluation for a given side. The
693 // space evaluation is a simple bonus based on the number of safe squares
694 // available for minor pieces on the central four files on ranks 2--4. Safe
695 // squares one, two or three squares behind a friendly pawn are counted
696 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
697 // improve play on game opening.
699 template<Tracing T> template<Color Us>
700 Score Evaluation<T>::space() const {
702 if (pos.non_pawn_material() < SpaceThreshold)
705 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
706 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
707 constexpr Bitboard SpaceMask =
708 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
709 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
711 // Find the available squares for our pieces inside the area defined by SpaceMask
712 Bitboard safe = SpaceMask
713 & ~pos.pieces(Us, PAWN)
714 & ~attackedBy[Them][PAWN];
716 // Find all squares which are at most three squares behind some friendly pawn
717 Bitboard behind = pos.pieces(Us, PAWN);
718 behind |= shift<Down>(behind);
719 behind |= shift<Down+Down>(behind);
721 int bonus = popcount(safe) + popcount(behind & safe);
722 int weight = pos.count<ALL_PIECES>(Us) - 1;
723 Score score = make_score(bonus * weight * weight / 16, 0);
726 Trace::add(SPACE, Us, score);
732 // Evaluation::initiative() computes the initiative correction value
733 // for the position. It is a second order bonus/malus based on the
734 // known attacking/defending status of the players.
737 Score Evaluation<T>::initiative(Value eg) const {
739 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
740 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
742 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
743 && (pos.pieces(PAWN) & KingSide);
745 // Compute the initiative bonus for the attacking side
746 int complexity = 9 * pe->passed_count()
747 + 11 * pos.count<PAWN>()
749 + 18 * pawnsOnBothFlanks
750 + 49 * !pos.non_pawn_material()
753 // Now apply the bonus: note that we find the attacking side by extracting
754 // the sign of the endgame value, and that we carefully cap the bonus so
755 // that the endgame score will never change sign after the bonus.
756 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
759 Trace::add(INITIATIVE, make_score(0, v));
761 return make_score(0, v);
765 // Evaluation::scale_factor() computes the scale factor for the winning side
768 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
770 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
771 int sf = me->scale_factor(pos, strongSide);
773 // If scale is not already specific, scale down the endgame via general heuristics
774 if (sf == SCALE_FACTOR_NORMAL)
776 if ( pos.opposite_bishops()
777 && pos.non_pawn_material() == 2 * BishopValueMg)
778 sf = 16 + 4 * pe->passed_count();
780 sf = std::min(40 + (pos.opposite_bishops() ? 2 : 7) * pos.count<PAWN>(strongSide), sf);
784 return ScaleFactor(sf);
788 // Evaluation::value() is the main function of the class. It computes the various
789 // parts of the evaluation and returns the value of the position from the point
790 // of view of the side to move.
793 Value Evaluation<T>::value() {
795 assert(!pos.checkers());
797 // Probe the material hash table
798 me = Material::probe(pos);
800 // If we have a specialized evaluation function for the current material
801 // configuration, call it and return.
802 if (me->specialized_eval_exists())
803 return me->evaluate(pos);
805 // Initialize score by reading the incrementally updated scores included in
806 // the position object (material + piece square tables) and the material
807 // imbalance. Score is computed internally from the white point of view.
808 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
810 // Probe the pawn hash table
811 pe = Pawns::probe(pos);
812 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
814 // Early exit if score is high
815 Value v = (mg_value(score) + eg_value(score)) / 2;
816 if (abs(v) > LazyThreshold)
817 return pos.side_to_move() == WHITE ? v : -v;
819 // Main evaluation begins here
824 // Pieces should be evaluated first (populate attack tables)
825 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
826 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
827 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
828 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
830 score += mobility[WHITE] - mobility[BLACK];
832 score += king< WHITE>() - king< BLACK>()
833 + threats<WHITE>() - threats<BLACK>()
834 + passed< WHITE>() - passed< BLACK>()
835 + space< WHITE>() - space< BLACK>();
837 score += initiative(eg_value(score));
839 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
840 ScaleFactor sf = scale_factor(eg_value(score));
841 v = mg_value(score) * int(me->game_phase())
842 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
846 // In case of tracing add all remaining individual evaluation terms
849 Trace::add(MATERIAL, pos.psq_score());
850 Trace::add(IMBALANCE, me->imbalance());
851 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
852 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
853 Trace::add(TOTAL, score);
856 return (pos.side_to_move() == WHITE ? v : -v) // Side to move point of view
863 /// evaluate() is the evaluator for the outer world. It returns a static
864 /// evaluation of the position from the point of view of the side to move.
866 Value Eval::evaluate(const Position& pos) {
867 return Evaluation<NO_TRACE>(pos).value();
871 /// trace() is like evaluate(), but instead of returning a value, it returns
872 /// a string (suitable for outputting to stdout) that contains the detailed
873 /// descriptions and values of each evaluation term. Useful for debugging.
875 std::string Eval::trace(const Position& pos) {
877 std::memset(scores, 0, sizeof(scores));
879 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
881 Value v = Evaluation<TRACE>(pos).value();
883 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
885 std::stringstream ss;
886 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
887 << " Term | White | Black | Total \n"
888 << " | MG EG | MG EG | MG EG \n"
889 << " ------------+-------------+-------------+------------\n"
890 << " Material | " << Term(MATERIAL)
891 << " Imbalance | " << Term(IMBALANCE)
892 << " Pawns | " << Term(PAWN)
893 << " Knights | " << Term(KNIGHT)
894 << " Bishops | " << Term(BISHOP)
895 << " Rooks | " << Term(ROOK)
896 << " Queens | " << Term(QUEEN)
897 << " Mobility | " << Term(MOBILITY)
898 << " King safety | " << Term(KING)
899 << " Threats | " << Term(THREAT)
900 << " Passed | " << Term(PASSED)
901 << " Space | " << Term(SPACE)
902 << " Initiative | " << Term(INITIATIVE)
903 << " ------------+-------------+-------------+------------\n"
904 << " Total | " << Term(TOTAL);
906 ss << "\nTotal evaluation: " << to_cp(v) << " (white side)\n";