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, 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( 36, 12);
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 & attackedBy[Us][PAWN] & ~pe->pawn_attacks_span(Them);
310 score += Outpost * (Pt == KNIGHT ? 2 : 1);
312 else if (bb & b & ~pos.pieces(Us))
313 score += Outpost / (Pt == KNIGHT ? 1 : 2);
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 * pos.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 (pos.is_on_semiopen_file(Us, s))
359 score += RookOnFile[bool(pos.is_on_semiopen_file(Them, 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 - 35 * bool(attackedBy[Us][BISHOP] & attackedBy[Us][KING])
468 + 150 * popcount(pos.blockers_for_king(Us) | unsafeChecks)
469 - 873 * !pos.count<QUEEN>(Them)
470 - 6 * mg_value(score) / 8
471 + mg_value(mobility[Them] - mobility[Us])
472 + 5 * kingFlankAttacks * kingFlankAttacks / 16
475 // Transform the kingDanger units into a Score, and subtract it from the evaluation
476 if (kingDanger > 100)
477 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
479 // Penalty when our king is on a pawnless flank
480 if (!(pos.pieces(PAWN) & KingFlank[file_of(ksq)]))
481 score -= PawnlessFlank;
483 // Penalty if king flank is under attack, potentially moving toward the king
484 score -= FlankAttacks * kingFlankAttacks;
487 Trace::add(KING, Us, score);
493 // Evaluation::threats() assigns bonuses according to the types of the
494 // attacking and the attacked pieces.
495 template<Tracing T> template<Color Us>
496 Score Evaluation<T>::threats() const {
498 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
499 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
500 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
502 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe;
503 Score score = SCORE_ZERO;
506 nonPawnEnemies = pos.pieces(Them) & ~pos.pieces(PAWN);
508 // Squares strongly protected by the enemy, either because they defend the
509 // square with a pawn, or because they defend the square twice and we don't.
510 stronglyProtected = attackedBy[Them][PAWN]
511 | (attackedBy2[Them] & ~attackedBy2[Us]);
513 // Non-pawn enemies, strongly protected
514 defended = nonPawnEnemies & stronglyProtected;
516 // Enemies not strongly protected and under our attack
517 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
519 // Safe or protected squares
520 safe = ~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES];
522 // Bonus according to the kind of attacking pieces
525 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
528 Square s = pop_lsb(&b);
529 score += ThreatByMinor[type_of(pos.piece_on(s))];
530 if (type_of(pos.piece_on(s)) != PAWN)
531 score += ThreatByRank * (int)relative_rank(Them, s);
534 b = weak & attackedBy[Us][ROOK];
537 Square s = pop_lsb(&b);
538 score += ThreatByRook[type_of(pos.piece_on(s))];
539 if (type_of(pos.piece_on(s)) != PAWN)
540 score += ThreatByRank * (int)relative_rank(Them, s);
543 if (weak & attackedBy[Us][KING])
544 score += ThreatByKing;
546 b = ~attackedBy[Them][ALL_PIECES]
547 | (nonPawnEnemies & attackedBy2[Us]);
548 score += Hanging * popcount(weak & b);
551 // Bonus for restricting their piece moves
552 b = attackedBy[Them][ALL_PIECES]
554 & attackedBy[Us][ALL_PIECES];
556 score += RestrictedPiece * popcount(b);
558 // Bonus for enemy unopposed weak pawns
559 if (pos.pieces(Us, ROOK, QUEEN))
560 score += WeakUnopposedPawn * pe->weak_unopposed(Them);
562 // Find squares where our pawns can push on the next move
563 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
564 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
566 // Keep only the squares which are relatively safe
567 b &= ~attackedBy[Them][PAWN] & safe;
569 // Bonus for safe pawn threats on the next move
570 b = pawn_attacks_bb<Us>(b) & pos.pieces(Them);
571 score += ThreatByPawnPush * popcount(b);
573 // Our safe or protected pawns
574 b = pos.pieces(Us, PAWN) & safe;
576 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
577 score += ThreatBySafePawn * popcount(b);
579 // Bonus for threats on the next moves against enemy queen
580 if (pos.count<QUEEN>(Them) == 1)
582 Square s = pos.square<QUEEN>(Them);
583 safe = mobilityArea[Us] & ~stronglyProtected;
585 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
587 score += KnightOnQueen * popcount(b & safe);
589 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
590 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
592 score += SliderOnQueen * popcount(b & safe & attackedBy2[Us]);
596 Trace::add(THREAT, Us, score);
601 // Evaluation::passed() evaluates the passed pawns and candidate passed
602 // pawns of the given color.
604 template<Tracing T> template<Color Us>
605 Score Evaluation<T>::passed() const {
607 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
608 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
610 auto king_proximity = [&](Color c, Square s) {
611 return std::min(distance(pos.square<KING>(c), s), 5);
614 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
615 Score score = SCORE_ZERO;
617 b = pe->passed_pawns(Us);
621 Square s = pop_lsb(&b);
623 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
625 int r = relative_rank(Us, s);
627 Score bonus = PassedRank[r];
631 int w = (r-2) * (r-2) + 2;
632 Square blockSq = s + Up;
634 // Adjust bonus based on the king's proximity
635 bonus += make_score(0, ( king_proximity(Them, blockSq) * 5
636 - king_proximity(Us, blockSq) * 2) * w);
638 // If blockSq is not the queening square then consider also a second push
640 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
642 // If the pawn is free to advance, then increase the bonus
643 if (pos.empty(blockSq))
645 // If there is a rook or queen attacking/defending the pawn from behind,
646 // consider all the squaresToQueen. Otherwise consider only the squares
647 // in the pawn's path attacked or occupied by the enemy.
648 defendedSquares = unsafeSquares = squaresToQueen = forward_file_bb(Us, s);
650 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN);
652 if (!(pos.pieces(Us) & bb))
653 defendedSquares &= attackedBy[Us][ALL_PIECES];
655 if (!(pos.pieces(Them) & bb))
656 unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
658 // If there aren't any enemy attacks, assign a big bonus. Otherwise
659 // assign a smaller bonus if the block square isn't attacked.
660 int k = !unsafeSquares ? 20 : !(unsafeSquares & blockSq) ? 9 : 0;
662 // Assign a larger bonus if the block square is defended.
663 if (defendedSquares & blockSq)
666 bonus += make_score(k * w, k * w);
670 // Scale down bonus for candidate passers which need more than one
671 // pawn push to become passed, or have a pawn in front of them.
672 if ( !pos.pawn_passed(Us, s + Up)
673 || (pos.pieces(PAWN) & forward_file_bb(Us, s)))
676 score += bonus + PassedFile[file_of(s)];
680 Trace::add(PASSED, Us, score);
686 // Evaluation::space() computes the space evaluation for a given side. The
687 // space evaluation is a simple bonus based on the number of safe squares
688 // available for minor pieces on the central four files on ranks 2--4. Safe
689 // squares one, two or three squares behind a friendly pawn are counted
690 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
691 // improve play on game opening.
693 template<Tracing T> template<Color Us>
694 Score Evaluation<T>::space() const {
696 if (pos.non_pawn_material() < SpaceThreshold)
699 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
700 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
701 constexpr Bitboard SpaceMask =
702 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
703 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
705 // Find the available squares for our pieces inside the area defined by SpaceMask
706 Bitboard safe = SpaceMask
707 & ~pos.pieces(Us, PAWN)
708 & ~attackedBy[Them][PAWN];
710 // Find all squares which are at most three squares behind some friendly pawn
711 Bitboard behind = pos.pieces(Us, PAWN);
712 behind |= shift<Down>(behind);
713 behind |= shift<Down+Down>(behind);
715 int bonus = popcount(safe) + popcount(behind & safe);
716 int weight = pos.count<ALL_PIECES>(Us) - 1;
717 Score score = make_score(bonus * weight * weight / 16, 0);
720 Trace::add(SPACE, Us, score);
726 // Evaluation::initiative() computes the initiative correction value
727 // for the position. It is a second order bonus/malus based on the
728 // known attacking/defending status of the players.
731 Score Evaluation<T>::initiative(Value eg) const {
733 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
734 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
736 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
737 && (pos.pieces(PAWN) & KingSide);
739 // Compute the initiative bonus for the attacking side
740 int complexity = 9 * pe->passed_count()
741 + 11 * pos.count<PAWN>()
743 + 18 * pawnsOnBothFlanks
744 + 49 * !pos.non_pawn_material()
747 // Now apply the bonus: note that we find the attacking side by extracting
748 // the sign of the endgame value, and that we carefully cap the bonus so
749 // that the endgame score will never change sign after the bonus.
750 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
753 Trace::add(INITIATIVE, make_score(0, v));
755 return make_score(0, v);
759 // Evaluation::scale_factor() computes the scale factor for the winning side
762 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
764 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
765 int sf = me->scale_factor(pos, strongSide);
767 // If scale is not already specific, scale down the endgame via general heuristics
768 if (sf == SCALE_FACTOR_NORMAL)
770 if ( pos.opposite_bishops()
771 && pos.non_pawn_material() == 2 * BishopValueMg)
772 sf = 16 + 4 * pe->passed_count();
774 sf = std::min(40 + (pos.opposite_bishops() ? 2 : 7) * pos.count<PAWN>(strongSide), sf);
778 return ScaleFactor(sf);
782 // Evaluation::value() is the main function of the class. It computes the various
783 // parts of the evaluation and returns the value of the position from the point
784 // of view of the side to move.
787 Value Evaluation<T>::value() {
789 assert(!pos.checkers());
791 // Probe the material hash table
792 me = Material::probe(pos);
794 // If we have a specialized evaluation function for the current material
795 // configuration, call it and return.
796 if (me->specialized_eval_exists())
797 return me->evaluate(pos);
799 // Initialize score by reading the incrementally updated scores included in
800 // the position object (material + piece square tables) and the material
801 // imbalance. Score is computed internally from the white point of view.
802 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
804 // Probe the pawn hash table
805 pe = Pawns::probe(pos);
806 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
808 // Early exit if score is high
809 Value v = (mg_value(score) + eg_value(score)) / 2;
810 if (abs(v) > (LazyThreshold + pos.non_pawn_material() / 64))
811 return pos.side_to_move() == WHITE ? v : -v;
813 // Main evaluation begins here
818 // Pieces should be evaluated first (populate attack tables)
819 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
820 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
821 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
822 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
824 score += mobility[WHITE] - mobility[BLACK];
826 score += king< WHITE>() - king< BLACK>()
827 + threats<WHITE>() - threats<BLACK>()
828 + passed< WHITE>() - passed< BLACK>()
829 + space< WHITE>() - space< BLACK>();
831 score += initiative(eg_value(score));
833 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
834 ScaleFactor sf = scale_factor(eg_value(score));
835 v = mg_value(score) * int(me->game_phase())
836 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
840 // In case of tracing add all remaining individual evaluation terms
843 Trace::add(MATERIAL, pos.psq_score());
844 Trace::add(IMBALANCE, me->imbalance());
845 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
846 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
847 Trace::add(TOTAL, score);
850 return (pos.side_to_move() == WHITE ? v : -v) // Side to move point of view
857 /// evaluate() is the evaluator for the outer world. It returns a static
858 /// evaluation of the position from the point of view of the side to move.
860 Value Eval::evaluate(const Position& pos) {
861 return Evaluation<NO_TRACE>(pos).value();
865 /// trace() is like evaluate(), but instead of returning a value, it returns
866 /// a string (suitable for outputting to stdout) that contains the detailed
867 /// descriptions and values of each evaluation term. Useful for debugging.
869 std::string Eval::trace(const Position& pos) {
871 std::memset(scores, 0, sizeof(scores));
873 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
875 Value v = Evaluation<TRACE>(pos).value();
877 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
879 std::stringstream ss;
880 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
881 << " Term | White | Black | Total \n"
882 << " | MG EG | MG EG | MG EG \n"
883 << " ------------+-------------+-------------+------------\n"
884 << " Material | " << Term(MATERIAL)
885 << " Imbalance | " << Term(IMBALANCE)
886 << " Pawns | " << Term(PAWN)
887 << " Knights | " << Term(KNIGHT)
888 << " Bishops | " << Term(BISHOP)
889 << " Rooks | " << Term(ROOK)
890 << " Queens | " << Term(QUEEN)
891 << " Mobility | " << Term(MOBILITY)
892 << " King safety | " << Term(KING)
893 << " Threats | " << Term(THREAT)
894 << " Passed | " << Term(PASSED)
895 << " Space | " << Term(SPACE)
896 << " Initiative | " << Term(INITIATIVE)
897 << " ------------+-------------+-------------+------------\n"
898 << " Total | " << Term(TOTAL);
900 ss << "\nTotal evaluation: " << to_cp(v) << " (white side)\n";