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/>.
22 #include <cstring> // For std::memset
34 enum Tracing { NO_TRACE, TRACE };
36 enum Term { // The first 8 entries are reserved for PieceType
37 MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, INITIATIVE, TOTAL, TERM_NB
40 Score scores[TERM_NB][COLOR_NB];
42 double to_cp(Value v) { return double(v) / PawnValueEg; }
44 void add(int idx, Color c, Score s) {
48 void add(int idx, Score w, Score b = SCORE_ZERO) {
49 scores[idx][WHITE] = w;
50 scores[idx][BLACK] = b;
53 std::ostream& operator<<(std::ostream& os, Score s) {
54 os << std::setw(5) << to_cp(mg_value(s)) << " "
55 << std::setw(5) << to_cp(eg_value(s));
59 std::ostream& operator<<(std::ostream& os, Term t) {
61 if (t == MATERIAL || t == IMBALANCE || t == INITIATIVE || t == TOTAL)
62 os << " ---- ----" << " | " << " ---- ----";
64 os << scores[t][WHITE] << " | " << scores[t][BLACK];
66 os << " | " << scores[t][WHITE] - scores[t][BLACK] << "\n";
71 using namespace Trace;
75 // Threshold for lazy and space evaluation
76 constexpr Value LazyThreshold = Value(1500);
77 constexpr Value SpaceThreshold = Value(12222);
79 // KingAttackWeights[PieceType] contains king attack weights by piece type
80 constexpr int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 77, 55, 44, 10 };
82 // Penalties for enemy's safe checks
83 constexpr int QueenSafeCheck = 780;
84 constexpr int RookSafeCheck = 1080;
85 constexpr int BishopSafeCheck = 635;
86 constexpr int KnightSafeCheck = 790;
88 #define S(mg, eg) make_score(mg, eg)
90 // MobilityBonus[PieceType-2][attacked] contains bonuses for middle and end game,
91 // indexed by piece type and number of attacked squares in the mobility area.
92 constexpr Score MobilityBonus[][32] = {
93 { S(-62,-81), S(-53,-56), S(-12,-30), S( -4,-14), S( 3, 8), S( 13, 15), // Knights
94 S( 22, 23), S( 28, 27), S( 33, 33) },
95 { S(-48,-59), S(-20,-23), S( 16, -3), S( 26, 13), S( 38, 24), S( 51, 42), // Bishops
96 S( 55, 54), S( 63, 57), S( 63, 65), S( 68, 73), S( 81, 78), S( 81, 86),
97 S( 91, 88), S( 98, 97) },
98 { S(-58,-76), S(-27,-18), S(-15, 28), S(-10, 55), S( -5, 69), S( -2, 82), // Rooks
99 S( 9,112), S( 16,118), S( 30,132), S( 29,142), S( 32,155), S( 38,165),
100 S( 46,166), S( 48,169), S( 58,171) },
101 { S(-39,-36), S(-21,-15), S( 3, 8), S( 3, 18), S( 14, 34), S( 22, 54), // Queens
102 S( 28, 61), S( 41, 73), S( 43, 79), S( 48, 92), S( 56, 94), S( 60,104),
103 S( 60,113), S( 66,120), S( 67,123), S( 70,126), S( 71,133), S( 73,136),
104 S( 79,140), S( 88,143), S( 88,148), S( 99,166), S(102,170), S(102,175),
105 S(106,184), S(109,191), S(113,206), S(116,212) }
108 // RookOnFile[semiopen/open] contains bonuses for each rook when there is
109 // no (friendly) pawn on the rook file.
110 constexpr Score RookOnFile[] = { S(18, 7), S(44, 20) };
112 // ThreatByMinor/ByRook[attacked PieceType] contains bonuses according to
113 // which piece type attacks which one. Attacks on lesser pieces which are
114 // pawn-defended are not considered.
115 constexpr Score ThreatByMinor[PIECE_TYPE_NB] = {
116 S(0, 0), S(0, 31), S(39, 42), S(57, 44), S(68, 112), S(62, 120)
119 constexpr Score ThreatByRook[PIECE_TYPE_NB] = {
120 S(0, 0), S(0, 24), S(38, 71), S(38, 61), S(0, 38), S(51, 38)
123 // PassedRank[Rank] contains a bonus according to the rank of a passed pawn
124 constexpr Score PassedRank[RANK_NB] = {
125 S(0, 0), S(5, 18), S(12, 23), S(10, 31), S(57, 62), S(163, 167), S(271, 250)
128 // PassedFile[File] contains a bonus according to the file of a passed pawn
129 constexpr Score PassedFile[FILE_NB] = {
130 S( -1, 7), S( 0, 9), S(-9, -8), S(-30,-14),
131 S(-30,-14), S(-9, -8), S( 0, 9), S( -1, 7)
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( 9, 3);
144 constexpr Score PawnlessFlank = S( 17, 95);
145 constexpr Score RestrictedPiece = S( 7, 7);
146 constexpr Score RookOnPawn = S( 10, 32);
147 constexpr Score SliderOnQueen = S( 59, 18);
148 constexpr Score ThreatByKing = S( 24, 89);
149 constexpr Score ThreatByPawnPush = S( 48, 39);
150 constexpr Score ThreatByRank = S( 13, 0);
151 constexpr Score ThreatBySafePawn = S(173, 94);
152 constexpr Score TrappedRook = S( 47, 4);
153 constexpr Score WeakQueen = S( 49, 15);
154 constexpr Score WeakUnopposedPawn = S( 12, 23);
158 // Evaluation class computes and stores attacks tables and other working data
163 Evaluation() = delete;
164 explicit Evaluation(const Position& p) : pos(p) {}
165 Evaluation& operator=(const Evaluation&) = delete;
169 template<Color Us> void initialize();
170 template<Color Us, PieceType Pt> Score pieces();
171 template<Color Us> Score king() const;
172 template<Color Us> Score threats() const;
173 template<Color Us> Score passed() const;
174 template<Color Us> Score space() const;
175 ScaleFactor scale_factor(Value eg) const;
176 Score initiative(Value eg) const;
181 Bitboard mobilityArea[COLOR_NB];
182 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
184 // attackedBy[color][piece type] is a bitboard representing all squares
185 // attacked by a given color and piece type. Special "piece types" which
186 // is also calculated is ALL_PIECES.
187 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
189 // attackedBy2[color] are the squares attacked by 2 pieces of a given color,
190 // possibly via x-ray or by one pawn and one piece. Diagonal x-ray through
191 // pawn or squares attacked by 2 pawns are not explicitly added.
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 // Find our pawns that are blocked or on the first two ranks
232 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
234 // Squares occupied by those pawns, by our king or queen or controlled by
235 // enemy pawns are excluded from the mobility area.
236 mobilityArea[Us] = ~(b | pos.pieces(Us, KING, QUEEN) | pe->pawn_attacks(Them));
238 // Initialize attackedBy[] for king and pawns
239 attackedBy[Us][KING] = pos.attacks_from<KING>(ksq);
240 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
241 attackedBy[Us][ALL_PIECES] = attackedBy[Us][KING] | attackedBy[Us][PAWN];
242 attackedBy2[Us] = attackedBy[Us][KING] & attackedBy[Us][PAWN];
244 // Init our king safety tables
245 kingRing[Us] = attackedBy[Us][KING];
246 if (relative_rank(Us, ksq) == RANK_1)
247 kingRing[Us] |= shift<Up>(kingRing[Us]);
249 if (file_of(ksq) == FILE_H)
250 kingRing[Us] |= shift<WEST>(kingRing[Us]);
252 else if (file_of(ksq) == FILE_A)
253 kingRing[Us] |= shift<EAST>(kingRing[Us]);
255 kingAttackersCount[Them] = popcount(kingRing[Us] & pe->pawn_attacks(Them));
256 kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
258 // Remove from kingRing[] the squares defended by two pawns
259 kingRing[Us] &= ~pawn_double_attacks_bb<Us>(pos.pieces(Us, PAWN));
263 // Evaluation::pieces() scores pieces of a given color and type
264 template<Tracing T> template<Color Us, PieceType Pt>
265 Score Evaluation<T>::pieces() {
267 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
268 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
269 constexpr Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
270 : Rank5BB | Rank4BB | Rank3BB);
271 const Square* pl = pos.squares<Pt>(Us);
274 Score score = SCORE_ZERO;
276 attackedBy[Us][Pt] = 0;
278 for (Square s = *pl; s != SQ_NONE; s = *++pl)
280 // Find attacked squares, including x-ray attacks for bishops and rooks
281 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
282 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
283 : pos.attacks_from<Pt>(s);
285 if (pos.blockers_for_king(Us) & s)
286 b &= LineBB[pos.square<KING>(Us)][s];
288 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
289 attackedBy[Us][Pt] |= b;
290 attackedBy[Us][ALL_PIECES] |= b;
292 if (b & kingRing[Them])
294 kingAttackersCount[Us]++;
295 kingAttackersWeight[Us] += KingAttackWeights[Pt];
296 kingAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
299 int mob = popcount(b & mobilityArea[Us]);
301 mobility[Us] += MobilityBonus[Pt - 2][mob];
303 if (Pt == BISHOP || Pt == KNIGHT)
305 // Bonus if piece is on an outpost square or can reach one
306 bb = OutpostRanks & ~pe->pawn_attacks_span(Them);
308 score += Outpost * (Pt == KNIGHT ? 4 : 2)
309 * (1 + bool(attackedBy[Us][PAWN] & s));
311 else if (bb &= b & ~pos.pieces(Us))
312 score += Outpost * (Pt == KNIGHT ? 2 : 1)
313 * (1 + bool(attackedBy[Us][PAWN] & bb));
315 // Knight and Bishop bonus for being right behind a pawn
316 if (shift<Down>(pos.pieces(PAWN)) & s)
317 score += MinorBehindPawn;
319 // Penalty if the piece is far from the king
320 score -= KingProtector * distance(s, pos.square<KING>(Us));
324 // Penalty according to number of pawns on the same color square as the
325 // bishop, bigger when the center files are blocked with pawns.
326 Bitboard blocked = pos.pieces(Us, PAWN) & shift<Down>(pos.pieces());
328 score -= BishopPawns * pe->pawns_on_same_color_squares(Us, s)
329 * (1 + popcount(blocked & CenterFiles));
331 // Bonus for bishop on a long diagonal which can "see" both center squares
332 if (more_than_one(attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & Center))
333 score += LongDiagonalBishop;
336 // An important Chess960 pattern: A cornered bishop blocked by a friendly
337 // pawn diagonally in front of it is a very serious problem, especially
338 // when that pawn is also blocked.
341 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
343 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
344 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
345 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
346 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
353 // Bonus for aligning rook with enemy pawns on the same rank/file
354 if (relative_rank(Us, s) >= RANK_5)
355 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
357 // Bonus for rook on an open or semi-open file
358 if (pe->semiopen_file(Us, file_of(s)))
359 score += RookOnFile[bool(pe->semiopen_file(Them, file_of(s)))];
361 // Penalty when trapped by the king, even more if the king cannot castle
364 File kf = file_of(pos.square<KING>(Us));
365 if ((kf < FILE_E) == (file_of(s) < kf))
366 score -= TrappedRook * (1 + !pos.castling_rights(Us));
372 // Penalty if any relative pin or discovered attack against the queen
373 Bitboard queenPinners;
374 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
379 Trace::add(Pt, Us, score);
385 // Evaluation::king() assigns bonuses and penalties to a king of a given color
386 template<Tracing T> template<Color Us>
387 Score Evaluation<T>::king() const {
389 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
390 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
391 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
393 Bitboard weak, b1, b2, safe, unsafeChecks = 0;
394 Bitboard rookChecks, queenChecks, bishopChecks, knightChecks;
396 const Square ksq = pos.square<KING>(Us);
398 // Init the score with king shelter and enemy pawns storm
399 Score score = pe->king_safety<Us>(pos);
401 // Attacked squares defended at most once by our queen or king
402 weak = attackedBy[Them][ALL_PIECES]
404 & (~attackedBy[Us][ALL_PIECES] | attackedBy[Us][KING] | attackedBy[Us][QUEEN]);
406 // Analyse the safe enemy's checks which are possible on next move
407 safe = ~pos.pieces(Them);
408 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
410 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
411 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
413 // Enemy rooks checks
414 rookChecks = b1 & safe & attackedBy[Them][ROOK];
417 kingDanger += RookSafeCheck;
419 unsafeChecks |= b1 & attackedBy[Them][ROOK];
421 // Enemy queen safe checks: we count them only if they are from squares from
422 // which we can't give a rook check, because rook checks are more valuable.
423 queenChecks = (b1 | b2)
424 & attackedBy[Them][QUEEN]
426 & ~attackedBy[Us][QUEEN]
430 kingDanger += QueenSafeCheck;
432 // Enemy bishops checks: we count them only if they are from squares from
433 // which we can't give a queen check, because queen checks are more valuable.
435 & attackedBy[Them][BISHOP]
440 kingDanger += BishopSafeCheck;
442 unsafeChecks |= b2 & attackedBy[Them][BISHOP];
444 // Enemy knights checks
445 knightChecks = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
447 if (knightChecks & safe)
448 kingDanger += KnightSafeCheck;
450 unsafeChecks |= knightChecks;
452 // Unsafe or occupied checking squares will also be considered, as long as
453 // the square is in the attacker's mobility area.
454 unsafeChecks &= mobilityArea[Them];
456 // Find the squares that opponent attacks in our king flank, and the squares
457 // which are attacked twice in that flank.
458 b1 = attackedBy[Them][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
459 b2 = b1 & attackedBy2[Them];
461 int kingFlankAttacks = popcount(b1) + popcount(b2);
463 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
464 + 69 * kingAttacksCount[Them]
465 + 185 * popcount(kingRing[Us] & weak)
466 - 100 * bool(attackedBy[Us][KNIGHT] & attackedBy[Us][KING])
467 + 150 * popcount(pos.blockers_for_king(Us) | unsafeChecks)
468 - 873 * !pos.count<QUEEN>(Them)
469 - 6 * mg_value(score) / 8
470 + mg_value(mobility[Them] - mobility[Us])
471 + 5 * kingFlankAttacks * kingFlankAttacks / 16
474 // Transform the kingDanger units into a Score, and subtract it from the evaluation
476 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
478 // Penalty when our king is on a pawnless flank
479 if (!(pos.pieces(PAWN) & KingFlank[file_of(ksq)]))
480 score -= PawnlessFlank;
482 // Penalty if king flank is under attack, potentially moving toward the king
483 score -= FlankAttacks * kingFlankAttacks;
486 Trace::add(KING, Us, score);
492 // Evaluation::threats() assigns bonuses according to the types of the
493 // attacking and the attacked pieces.
494 template<Tracing T> template<Color Us>
495 Score Evaluation<T>::threats() const {
497 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
498 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
499 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
501 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe;
502 Score score = SCORE_ZERO;
505 nonPawnEnemies = pos.pieces(Them) & ~pos.pieces(PAWN);
507 // Squares strongly protected by the enemy, either because they defend the
508 // square with a pawn, or because they defend the square twice and we don't.
509 stronglyProtected = attackedBy[Them][PAWN]
510 | (attackedBy2[Them] & ~attackedBy2[Us]);
512 // Non-pawn enemies, strongly protected
513 defended = nonPawnEnemies & stronglyProtected;
515 // Enemies not strongly protected and under our attack
516 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
518 // Safe or protected squares
519 safe = ~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES];
521 // Bonus according to the kind of attacking pieces
524 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
527 Square s = pop_lsb(&b);
528 score += ThreatByMinor[type_of(pos.piece_on(s))];
529 if (type_of(pos.piece_on(s)) != PAWN)
530 score += ThreatByRank * (int)relative_rank(Them, s);
533 b = weak & attackedBy[Us][ROOK];
536 Square s = pop_lsb(&b);
537 score += ThreatByRook[type_of(pos.piece_on(s))];
538 if (type_of(pos.piece_on(s)) != PAWN)
539 score += ThreatByRank * (int)relative_rank(Them, s);
542 if (weak & attackedBy[Us][KING])
543 score += ThreatByKing;
545 b = ~attackedBy[Them][ALL_PIECES]
546 | (nonPawnEnemies & attackedBy2[Us]);
547 score += Hanging * popcount(weak & b);
550 // Bonus for restricting their piece moves
551 b = attackedBy[Them][ALL_PIECES]
553 & attackedBy[Us][ALL_PIECES];
555 score += RestrictedPiece * popcount(b);
557 // Bonus for enemy unopposed weak pawns
558 if (pos.pieces(Us, ROOK, QUEEN))
559 score += WeakUnopposedPawn * pe->weak_unopposed(Them);
561 // Find squares where our pawns can push on the next move
562 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
563 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
565 // Keep only the squares which are relatively safe
566 b &= ~attackedBy[Them][PAWN] & safe;
568 // Bonus for safe pawn threats on the next move
569 b = pawn_attacks_bb<Us>(b) & pos.pieces(Them);
570 score += ThreatByPawnPush * popcount(b);
572 // Our safe or protected pawns
573 b = pos.pieces(Us, PAWN) & safe;
575 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
576 score += ThreatBySafePawn * popcount(b);
578 // Bonus for threats on the next moves against enemy queen
579 if (pos.count<QUEEN>(Them) == 1)
581 Square s = pos.square<QUEEN>(Them);
582 safe = mobilityArea[Us] & ~stronglyProtected;
584 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
586 score += KnightOnQueen * popcount(b & safe);
588 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
589 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
591 score += SliderOnQueen * popcount(b & safe & attackedBy2[Us]);
595 Trace::add(THREAT, Us, score);
600 // Evaluation::passed() evaluates the passed pawns and candidate passed
601 // pawns of the given color.
603 template<Tracing T> template<Color Us>
604 Score Evaluation<T>::passed() const {
606 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
607 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
609 auto king_proximity = [&](Color c, Square s) {
610 return std::min(distance(pos.square<KING>(c), s), 5);
613 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
614 Score score = SCORE_ZERO;
616 b = pe->passed_pawns(Us);
620 Square s = pop_lsb(&b);
622 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
624 int r = relative_rank(Us, s);
626 Score bonus = PassedRank[r];
630 int w = (r-2) * (r-2) + 2;
631 Square blockSq = s + Up;
633 // Adjust bonus based on the king's proximity
634 bonus += make_score(0, ( king_proximity(Them, blockSq) * 5
635 - king_proximity(Us, blockSq) * 2) * w);
637 // If blockSq is not the queening square then consider also a second push
639 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
641 // If the pawn is free to advance, then increase the bonus
642 if (pos.empty(blockSq))
644 // If there is a rook or queen attacking/defending the pawn from behind,
645 // consider all the squaresToQueen. Otherwise consider only the squares
646 // in the pawn's path attacked or occupied by the enemy.
647 defendedSquares = unsafeSquares = squaresToQueen = forward_file_bb(Us, s);
649 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
651 if (!(pos.pieces(Us) & bb))
652 defendedSquares &= attackedBy[Us][ALL_PIECES];
654 if (!(pos.pieces(Them) & bb))
655 unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
657 // If there aren't any enemy attacks, assign a big bonus. Otherwise
658 // assign a smaller bonus if the block square isn't attacked.
659 int k = !unsafeSquares ? 20 : !(unsafeSquares & blockSq) ? 9 : 0;
661 // If the path to the queen is fully defended, assign a big bonus.
662 // Otherwise assign a smaller bonus if the block square is defended.
663 if (defendedSquares == squaresToQueen)
666 else if (defendedSquares & blockSq)
669 bonus += make_score(k * w, k * w);
673 // Scale down bonus for candidate passers which need more than one
674 // pawn push to become passed, or have a pawn in front of them.
675 if ( !pos.pawn_passed(Us, s + Up)
676 || (pos.pieces(PAWN) & forward_file_bb(Us, s)))
679 score += bonus + PassedFile[file_of(s)];
683 Trace::add(PASSED, Us, score);
689 // Evaluation::space() computes the space evaluation for a given side. The
690 // space evaluation is a simple bonus based on the number of safe squares
691 // available for minor pieces on the central four files on ranks 2--4. Safe
692 // squares one, two or three squares behind a friendly pawn are counted
693 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
694 // improve play on game opening.
696 template<Tracing T> template<Color Us>
697 Score Evaluation<T>::space() const {
699 if (pos.non_pawn_material() < SpaceThreshold)
702 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
703 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
704 constexpr Bitboard SpaceMask =
705 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
706 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
708 // Find the available squares for our pieces inside the area defined by SpaceMask
709 Bitboard safe = SpaceMask
710 & ~pos.pieces(Us, PAWN)
711 & ~attackedBy[Them][PAWN];
713 // Find all squares which are at most three squares behind some friendly pawn
714 Bitboard behind = pos.pieces(Us, PAWN);
715 behind |= shift<Down>(behind);
716 behind |= shift<Down>(shift<Down>(behind));
718 int bonus = popcount(safe) + popcount(behind & safe);
719 int weight = pos.count<ALL_PIECES>(Us)
720 - 2 * popcount(pe->semiopenFiles[WHITE] & pe->semiopenFiles[BLACK]);
722 Score score = make_score(bonus * weight * weight / 16, 0);
725 Trace::add(SPACE, Us, score);
731 // Evaluation::initiative() computes the initiative correction value
732 // for the position. It is a second order bonus/malus based on the
733 // known attacking/defending status of the players.
736 Score Evaluation<T>::initiative(Value eg) const {
738 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
739 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
741 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
742 && (pos.pieces(PAWN) & KingSide);
744 // Compute the initiative bonus for the attacking side
745 int complexity = 9 * pe->passed_count()
746 + 11 * pos.count<PAWN>()
748 + 18 * pawnsOnBothFlanks
749 + 49 * !pos.non_pawn_material()
752 // Now apply the bonus: note that we find the attacking side by extracting
753 // the sign of the endgame value, and that we carefully cap the bonus so
754 // that the endgame score will never change sign after the bonus.
755 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
758 Trace::add(INITIATIVE, make_score(0, v));
760 return make_score(0, v);
764 // Evaluation::scale_factor() computes the scale factor for the winning side
767 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
769 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
770 int sf = me->scale_factor(pos, strongSide);
772 // If scale is not already specific, scale down the endgame via general heuristics
773 if (sf == SCALE_FACTOR_NORMAL)
775 if ( pos.opposite_bishops()
776 && pos.non_pawn_material(WHITE) == BishopValueMg
777 && pos.non_pawn_material(BLACK) == 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";