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);
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 at least 2 units of a given
190 // color, including x-rays. But diagonal x-rays through pawns are not computed.
191 Bitboard attackedBy2[COLOR_NB];
193 // kingRing[color] are the squares adjacent to the king plus some other
194 // very near squares, depending on king position.
195 Bitboard kingRing[COLOR_NB];
197 // kingAttackersCount[color] is the number of pieces of the given color
198 // which attack a square in the kingRing of the enemy king.
199 int kingAttackersCount[COLOR_NB];
201 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of
202 // the given color which attack a square in the kingRing of the enemy king.
203 // The weights of the individual piece types are given by the elements in
204 // the KingAttackWeights array.
205 int kingAttackersWeight[COLOR_NB];
207 // kingAttacksCount[color] is the number of attacks by the given color to
208 // squares directly adjacent to the enemy king. Pieces which attack more
209 // than one square are counted multiple times. For instance, if there is
210 // a white knight on g5 and black's king is on g8, this white knight adds 2
211 // to kingAttacksCount[WHITE].
212 int kingAttacksCount[COLOR_NB];
216 // Evaluation::initialize() computes king and pawn attacks, and the king ring
217 // bitboard for a given color. This is done at the beginning of the evaluation.
218 template<Tracing T> template<Color Us>
219 void Evaluation<T>::initialize() {
221 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
222 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
223 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
224 constexpr Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB: Rank7BB | Rank6BB);
226 const Square ksq = pos.square<KING>(Us);
228 Bitboard dblAttackByPawn = pawn_double_attacks_bb<Us>(pos.pieces(Us, PAWN));
230 // Find our pawns that are blocked or on the first two ranks
231 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
233 // Squares occupied by those pawns, by our king or queen or controlled by
234 // enemy pawns are excluded from the mobility area.
235 mobilityArea[Us] = ~(b | pos.pieces(Us, KING, QUEEN) | pe->pawn_attacks(Them));
237 // Initialize attackedBy[] for king and pawns
238 attackedBy[Us][KING] = pos.attacks_from<KING>(ksq);
239 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
240 attackedBy[Us][ALL_PIECES] = attackedBy[Us][KING] | attackedBy[Us][PAWN];
241 attackedBy2[Us] = dblAttackByPawn | (attackedBy[Us][KING] & attackedBy[Us][PAWN]);
243 // Init our king safety tables
244 kingRing[Us] = attackedBy[Us][KING];
245 if (relative_rank(Us, ksq) == RANK_1)
246 kingRing[Us] |= shift<Up>(kingRing[Us]);
248 if (file_of(ksq) == FILE_H)
249 kingRing[Us] |= shift<WEST>(kingRing[Us]);
251 else if (file_of(ksq) == FILE_A)
252 kingRing[Us] |= shift<EAST>(kingRing[Us]);
254 kingAttackersCount[Them] = popcount(kingRing[Us] & pe->pawn_attacks(Them));
255 kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
257 // Remove from kingRing[] the squares defended by two pawns
258 kingRing[Us] &= ~dblAttackByPawn;
262 // Evaluation::pieces() scores pieces of a given color and type
263 template<Tracing T> template<Color Us, PieceType Pt>
264 Score Evaluation<T>::pieces() {
266 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
267 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
268 constexpr Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
269 : Rank5BB | Rank4BB | Rank3BB);
270 const Square* pl = pos.squares<Pt>(Us);
273 Score score = SCORE_ZERO;
275 attackedBy[Us][Pt] = 0;
277 for (Square s = *pl; s != SQ_NONE; s = *++pl)
279 // Find attacked squares, including x-ray attacks for bishops and rooks
280 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
281 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
282 : pos.attacks_from<Pt>(s);
284 if (pos.blockers_for_king(Us) & s)
285 b &= LineBB[pos.square<KING>(Us)][s];
287 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
288 attackedBy[Us][Pt] |= b;
289 attackedBy[Us][ALL_PIECES] |= b;
291 if (b & kingRing[Them])
293 kingAttackersCount[Us]++;
294 kingAttackersWeight[Us] += KingAttackWeights[Pt];
295 kingAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
298 int mob = popcount(b & mobilityArea[Us]);
300 mobility[Us] += MobilityBonus[Pt - 2][mob];
302 if (Pt == BISHOP || Pt == KNIGHT)
304 // Bonus if piece is on an outpost square or can reach one
305 bb = OutpostRanks & attackedBy[Us][PAWN] & ~pe->pawn_attacks_span(Them);
307 score += Outpost * (Pt == KNIGHT ? 2 : 1);
309 else if (bb & b & ~pos.pieces(Us))
310 score += Outpost / (Pt == KNIGHT ? 1 : 2);
312 // Knight and Bishop bonus for being right behind a pawn
313 if (shift<Down>(pos.pieces(PAWN)) & s)
314 score += MinorBehindPawn;
316 // Penalty if the piece is far from the king
317 score -= KingProtector * distance(s, pos.square<KING>(Us));
321 // Penalty according to number of pawns on the same color square as the
322 // bishop, bigger when the center files are blocked with pawns.
323 Bitboard blocked = pos.pieces(Us, PAWN) & shift<Down>(pos.pieces());
325 score -= BishopPawns * pos.pawns_on_same_color_squares(Us, s)
326 * (1 + popcount(blocked & CenterFiles));
328 // Bonus for bishop on a long diagonal which can "see" both center squares
329 if (more_than_one(attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & Center))
330 score += LongDiagonalBishop;
333 // An important Chess960 pattern: A cornered bishop blocked by a friendly
334 // pawn diagonally in front of it is a very serious problem, especially
335 // when that pawn is also blocked.
338 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
340 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
341 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
342 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
343 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
350 // Bonus for aligning rook with enemy pawns on the same rank/file
351 if (relative_rank(Us, s) >= RANK_5)
352 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
354 // Bonus for rook on an open or semi-open file
355 if (pos.is_on_semiopen_file(Us, s))
356 score += RookOnFile[bool(pos.is_on_semiopen_file(Them, s))];
358 // Penalty when trapped by the king, even more if the king cannot castle
361 File kf = file_of(pos.square<KING>(Us));
362 if ((kf < FILE_E) == (file_of(s) < kf))
363 score -= TrappedRook * (1 + !pos.castling_rights(Us));
369 // Penalty if any relative pin or discovered attack against the queen
370 Bitboard queenPinners;
371 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
376 Trace::add(Pt, Us, score);
382 // Evaluation::king() assigns bonuses and penalties to a king of a given color
383 template<Tracing T> template<Color Us>
384 Score Evaluation<T>::king() const {
386 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
387 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
388 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
390 Bitboard weak, b1, b2, safe, unsafeChecks = 0;
391 Bitboard rookChecks, queenChecks, bishopChecks, knightChecks;
393 const Square ksq = pos.square<KING>(Us);
395 // Init the score with king shelter and enemy pawns storm
396 Score score = pe->king_safety<Us>(pos);
398 // Attacked squares defended at most once by our queen or king
399 weak = attackedBy[Them][ALL_PIECES]
401 & (~attackedBy[Us][ALL_PIECES] | attackedBy[Us][KING] | attackedBy[Us][QUEEN]);
403 // Analyse the safe enemy's checks which are possible on next move
404 safe = ~pos.pieces(Them);
405 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
407 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
408 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
410 // Enemy rooks checks
411 rookChecks = b1 & safe & attackedBy[Them][ROOK];
414 kingDanger += RookSafeCheck;
416 unsafeChecks |= b1 & attackedBy[Them][ROOK];
418 // Enemy queen safe checks: we count them only if they are from squares from
419 // which we can't give a rook check, because rook checks are more valuable.
420 queenChecks = (b1 | b2)
421 & attackedBy[Them][QUEEN]
423 & ~attackedBy[Us][QUEEN]
427 kingDanger += QueenSafeCheck;
429 // Enemy bishops checks: we count them only if they are from squares from
430 // which we can't give a queen check, because queen checks are more valuable.
432 & attackedBy[Them][BISHOP]
437 kingDanger += BishopSafeCheck;
439 unsafeChecks |= b2 & attackedBy[Them][BISHOP];
441 // Enemy knights checks
442 knightChecks = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
444 if (knightChecks & safe)
445 kingDanger += KnightSafeCheck;
447 unsafeChecks |= knightChecks;
449 // Unsafe or occupied checking squares will also be considered, as long as
450 // the square is in the attacker's mobility area.
451 unsafeChecks &= mobilityArea[Them];
453 // Find the squares that opponent attacks in our king flank, and the squares
454 // which are attacked twice in that flank.
455 b1 = attackedBy[Them][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
456 b2 = b1 & attackedBy2[Them];
458 int kingFlankAttacks = popcount(b1) + popcount(b2);
460 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
461 + 69 * kingAttacksCount[Them]
462 + 185 * popcount(kingRing[Us] & weak)
463 - 100 * bool(attackedBy[Us][KNIGHT] & attackedBy[Us][KING])
464 - 35 * bool(attackedBy[Us][BISHOP] & attackedBy[Us][KING])
465 + 150 * popcount(pos.blockers_for_king(Us) | unsafeChecks)
466 - 873 * !pos.count<QUEEN>(Them)
467 - 6 * mg_value(score) / 8
468 + mg_value(mobility[Them] - mobility[Us])
469 + 5 * kingFlankAttacks * kingFlankAttacks / 16
472 // Transform the kingDanger units into a Score, and subtract it from the evaluation
473 if (kingDanger > 100)
474 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
476 // Penalty when our king is on a pawnless flank
477 if (!(pos.pieces(PAWN) & KingFlank[file_of(ksq)]))
478 score -= PawnlessFlank;
480 // Penalty if king flank is under attack, potentially moving toward the king
481 score -= FlankAttacks * kingFlankAttacks;
484 Trace::add(KING, Us, score);
490 // Evaluation::threats() assigns bonuses according to the types of the
491 // attacking and the attacked pieces.
492 template<Tracing T> template<Color Us>
493 Score Evaluation<T>::threats() const {
495 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
496 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
497 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
499 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe;
500 Score score = SCORE_ZERO;
503 nonPawnEnemies = pos.pieces(Them) & ~pos.pieces(PAWN);
505 // Squares strongly protected by the enemy, either because they defend the
506 // square with a pawn, or because they defend the square twice and we don't.
507 stronglyProtected = attackedBy[Them][PAWN]
508 | (attackedBy2[Them] & ~attackedBy2[Us]);
510 // Non-pawn enemies, strongly protected
511 defended = nonPawnEnemies & stronglyProtected;
513 // Enemies not strongly protected and under our attack
514 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
516 // Safe or protected squares
517 safe = ~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES];
519 // Bonus according to the kind of attacking pieces
522 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
525 Square s = pop_lsb(&b);
526 score += ThreatByMinor[type_of(pos.piece_on(s))];
527 if (type_of(pos.piece_on(s)) != PAWN)
528 score += ThreatByRank * (int)relative_rank(Them, s);
531 b = weak & attackedBy[Us][ROOK];
534 Square s = pop_lsb(&b);
535 score += ThreatByRook[type_of(pos.piece_on(s))];
536 if (type_of(pos.piece_on(s)) != PAWN)
537 score += ThreatByRank * (int)relative_rank(Them, s);
540 if (weak & attackedBy[Us][KING])
541 score += ThreatByKing;
543 b = ~attackedBy[Them][ALL_PIECES]
544 | (nonPawnEnemies & attackedBy2[Us]);
545 score += Hanging * popcount(weak & b);
548 // Bonus for restricting their piece moves
549 b = attackedBy[Them][ALL_PIECES]
551 & attackedBy[Us][ALL_PIECES];
553 score += RestrictedPiece * popcount(b);
555 // Find squares where our pawns can push on the next move
556 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
557 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
559 // Keep only the squares which are relatively safe
560 b &= ~attackedBy[Them][PAWN] & safe;
562 // Bonus for safe pawn threats on the next move
563 b = pawn_attacks_bb<Us>(b) & pos.pieces(Them);
564 score += ThreatByPawnPush * popcount(b);
566 // Our safe or protected pawns
567 b = pos.pieces(Us, PAWN) & safe;
569 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
570 score += ThreatBySafePawn * popcount(b);
572 // Bonus for threats on the next moves against enemy queen
573 if (pos.count<QUEEN>(Them) == 1)
575 Square s = pos.square<QUEEN>(Them);
576 safe = mobilityArea[Us] & ~stronglyProtected;
578 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
580 score += KnightOnQueen * popcount(b & safe);
582 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
583 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
585 score += SliderOnQueen * popcount(b & safe & attackedBy2[Us]);
589 Trace::add(THREAT, Us, score);
594 // Evaluation::passed() evaluates the passed pawns and candidate passed
595 // pawns of the given color.
597 template<Tracing T> template<Color Us>
598 Score Evaluation<T>::passed() const {
600 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
601 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
603 auto king_proximity = [&](Color c, Square s) {
604 return std::min(distance(pos.square<KING>(c), s), 5);
607 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
608 Score score = SCORE_ZERO;
610 b = pe->passed_pawns(Us);
614 Square s = pop_lsb(&b);
616 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
618 int r = relative_rank(Us, s);
620 Score bonus = PassedRank[r];
624 int w = (r-2) * (r-2) + 2;
625 Square blockSq = s + Up;
627 // Adjust bonus based on the king's proximity
628 bonus += make_score(0, ( king_proximity(Them, blockSq) * 5
629 - king_proximity(Us, blockSq) * 2) * w);
631 // If blockSq is not the queening square then consider also a second push
633 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
635 // If the pawn is free to advance, then increase the bonus
636 if (pos.empty(blockSq))
638 // If there is a rook or queen attacking/defending the pawn from behind,
639 // consider all the squaresToQueen. Otherwise consider only the squares
640 // in the pawn's path attacked or occupied by the enemy.
641 defendedSquares = unsafeSquares = squaresToQueen = forward_file_bb(Us, s);
643 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN);
645 if (!(pos.pieces(Us) & bb))
646 defendedSquares &= attackedBy[Us][ALL_PIECES];
648 if (!(pos.pieces(Them) & bb))
649 unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
651 // If there aren't any enemy attacks, assign a big bonus. Otherwise
652 // assign a smaller bonus if the block square isn't attacked.
653 int k = !unsafeSquares ? 20 : !(unsafeSquares & blockSq) ? 9 : 0;
655 // Assign a larger bonus if the block square is defended.
656 if (defendedSquares & blockSq)
659 bonus += make_score(k * w, k * w);
663 // Scale down bonus for candidate passers which need more than one
664 // pawn push to become passed, or have a pawn in front of them.
665 if ( !pos.pawn_passed(Us, s + Up)
666 || (pos.pieces(PAWN) & forward_file_bb(Us, s)))
669 score += bonus + PassedFile[file_of(s)];
673 Trace::add(PASSED, Us, score);
679 // Evaluation::space() computes the space evaluation for a given side. The
680 // space evaluation is a simple bonus based on the number of safe squares
681 // available for minor pieces on the central four files on ranks 2--4. Safe
682 // squares one, two or three squares behind a friendly pawn are counted
683 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
684 // improve play on game opening.
686 template<Tracing T> template<Color Us>
687 Score Evaluation<T>::space() const {
689 if (pos.non_pawn_material() < SpaceThreshold)
692 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
693 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
694 constexpr Bitboard SpaceMask =
695 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
696 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
698 // Find the available squares for our pieces inside the area defined by SpaceMask
699 Bitboard safe = SpaceMask
700 & ~pos.pieces(Us, PAWN)
701 & ~attackedBy[Them][PAWN];
703 // Find all squares which are at most three squares behind some friendly pawn
704 Bitboard behind = pos.pieces(Us, PAWN);
705 behind |= shift<Down>(behind);
706 behind |= shift<Down+Down>(behind);
708 int bonus = popcount(safe) + popcount(behind & safe);
709 int weight = pos.count<ALL_PIECES>(Us) - 1;
710 Score score = make_score(bonus * weight * weight / 16, 0);
713 Trace::add(SPACE, Us, score);
719 // Evaluation::initiative() computes the initiative correction value
720 // for the position. It is a second order bonus/malus based on the
721 // known attacking/defending status of the players.
724 Score Evaluation<T>::initiative(Value eg) const {
726 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
727 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
729 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
730 && (pos.pieces(PAWN) & KingSide);
732 // Compute the initiative bonus for the attacking side
733 int complexity = 9 * pe->passed_count()
734 + 11 * pos.count<PAWN>()
736 + 18 * pawnsOnBothFlanks
737 + 49 * !pos.non_pawn_material()
740 // Now apply the bonus: note that we find the attacking side by extracting
741 // the sign of the endgame value, and that we carefully cap the bonus so
742 // that the endgame score will never change sign after the bonus.
743 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
746 Trace::add(INITIATIVE, make_score(0, v));
748 return make_score(0, v);
752 // Evaluation::scale_factor() computes the scale factor for the winning side
755 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
757 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
758 int sf = me->scale_factor(pos, strongSide);
760 // If scale is not already specific, scale down the endgame via general heuristics
761 if (sf == SCALE_FACTOR_NORMAL)
763 if ( pos.opposite_bishops()
764 && pos.non_pawn_material() == 2 * BishopValueMg)
765 sf = 16 + 4 * pe->passed_count();
767 sf = std::min(40 + (pos.opposite_bishops() ? 2 : 7) * pos.count<PAWN>(strongSide), sf);
771 return ScaleFactor(sf);
775 // Evaluation::value() is the main function of the class. It computes the various
776 // parts of the evaluation and returns the value of the position from the point
777 // of view of the side to move.
780 Value Evaluation<T>::value() {
782 assert(!pos.checkers());
784 // Probe the material hash table
785 me = Material::probe(pos);
787 // If we have a specialized evaluation function for the current material
788 // configuration, call it and return.
789 if (me->specialized_eval_exists())
790 return me->evaluate(pos);
792 // Initialize score by reading the incrementally updated scores included in
793 // the position object (material + piece square tables) and the material
794 // imbalance. Score is computed internally from the white point of view.
795 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
797 // Probe the pawn hash table
798 pe = Pawns::probe(pos);
799 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
801 // Early exit if score is high
802 Value v = (mg_value(score) + eg_value(score)) / 2;
803 if (abs(v) > LazyThreshold + pos.non_pawn_material() / 64)
804 return pos.side_to_move() == WHITE ? v : -v;
806 // Main evaluation begins here
811 // Pieces should be evaluated first (populate attack tables)
812 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
813 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
814 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
815 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
817 score += mobility[WHITE] - mobility[BLACK];
819 score += king< WHITE>() - king< BLACK>()
820 + threats<WHITE>() - threats<BLACK>()
821 + passed< WHITE>() - passed< BLACK>()
822 + space< WHITE>() - space< BLACK>();
824 score += initiative(eg_value(score));
826 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
827 ScaleFactor sf = scale_factor(eg_value(score));
828 v = mg_value(score) * int(me->game_phase())
829 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
833 // In case of tracing add all remaining individual evaluation terms
836 Trace::add(MATERIAL, pos.psq_score());
837 Trace::add(IMBALANCE, me->imbalance());
838 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
839 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
840 Trace::add(TOTAL, score);
843 return (pos.side_to_move() == WHITE ? v : -v) // Side to move point of view
850 /// evaluate() is the evaluator for the outer world. It returns a static
851 /// evaluation of the position from the point of view of the side to move.
853 Value Eval::evaluate(const Position& pos) {
854 return Evaluation<NO_TRACE>(pos).value();
858 /// trace() is like evaluate(), but instead of returning a value, it returns
859 /// a string (suitable for outputting to stdout) that contains the detailed
860 /// descriptions and values of each evaluation term. Useful for debugging.
862 std::string Eval::trace(const Position& pos) {
864 std::memset(scores, 0, sizeof(scores));
866 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
868 Value v = Evaluation<TRACE>(pos).value();
870 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
872 std::stringstream ss;
873 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
874 << " Term | White | Black | Total \n"
875 << " | MG EG | MG EG | MG EG \n"
876 << " ------------+-------------+-------------+------------\n"
877 << " Material | " << Term(MATERIAL)
878 << " Imbalance | " << Term(IMBALANCE)
879 << " Pawns | " << Term(PAWN)
880 << " Knights | " << Term(KNIGHT)
881 << " Bishops | " << Term(BISHOP)
882 << " Rooks | " << Term(ROOK)
883 << " Queens | " << Term(QUEEN)
884 << " Mobility | " << Term(MOBILITY)
885 << " King safety | " << Term(KING)
886 << " Threats | " << Term(THREAT)
887 << " Passed | " << Term(PASSED)
888 << " Space | " << Term(SPACE)
889 << " Initiative | " << Term(INITIATIVE)
890 << " ------------+-------------+-------------+------------\n"
891 << " Total | " << Term(TOTAL);
893 ss << "\nTotal evaluation: " << to_cp(v) << " (white side)\n";