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) 2015-2018 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 constexpr Bitboard QueenSide = FileABB | FileBBB | FileCBB | FileDBB;
77 constexpr Bitboard CenterFiles = FileCBB | FileDBB | FileEBB | FileFBB;
78 constexpr Bitboard KingSide = FileEBB | FileFBB | FileGBB | FileHBB;
79 constexpr Bitboard Center = (FileDBB | FileEBB) & (Rank4BB | Rank5BB);
81 constexpr Bitboard KingFlank[FILE_NB] = {
82 QueenSide, QueenSide, QueenSide,
83 CenterFiles, CenterFiles,
84 KingSide, KingSide, KingSide
87 // Threshold for lazy and space evaluation
88 constexpr Value LazyThreshold = Value(1500);
89 constexpr Value SpaceThreshold = Value(12222);
91 // KingAttackWeights[PieceType] contains king attack weights by piece type
92 constexpr int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 78, 56, 45, 11 };
94 // Penalties for enemy's safe checks
95 constexpr int QueenSafeCheck = 780;
96 constexpr int RookSafeCheck = 880;
97 constexpr int BishopSafeCheck = 435;
98 constexpr int KnightSafeCheck = 790;
100 #define S(mg, eg) make_score(mg, eg)
102 // MobilityBonus[PieceType-2][attacked] contains bonuses for middle and end game,
103 // indexed by piece type and number of attacked squares in the mobility area.
104 constexpr Score MobilityBonus[][32] = {
105 { S(-75,-76), S(-57,-54), S( -9,-28), S( -2,-10), S( 6, 5), S( 14, 12), // Knights
106 S( 22, 26), S( 29, 29), S( 36, 29) },
107 { S(-48,-59), S(-20,-23), S( 16, -3), S( 26, 13), S( 38, 24), S( 51, 42), // Bishops
108 S( 55, 54), S( 63, 57), S( 63, 65), S( 68, 73), S( 81, 78), S( 81, 86),
109 S( 91, 88), S( 98, 97) },
110 { S(-58,-76), S(-27,-18), S(-15, 28), S(-10, 55), S( -5, 69), S( -2, 82), // Rooks
111 S( 9,112), S( 16,118), S( 30,132), S( 29,142), S( 32,155), S( 38,165),
112 S( 46,166), S( 48,169), S( 58,171) },
113 { S(-39,-36), S(-21,-15), S( 3, 8), S( 3, 18), S( 14, 34), S( 22, 54), // Queens
114 S( 28, 61), S( 41, 73), S( 43, 79), S( 48, 92), S( 56, 94), S( 60,104),
115 S( 60,113), S( 66,120), S( 67,123), S( 70,126), S( 71,133), S( 73,136),
116 S( 79,140), S( 88,143), S( 88,148), S( 99,166), S(102,170), S(102,175),
117 S(106,184), S(109,191), S(113,206), S(116,212) }
120 // Outpost[knight/bishop][supported by pawn] contains bonuses for minor
121 // pieces if they occupy or can reach an outpost square, bigger if that
122 // square is supported by a pawn.
123 constexpr Score Outpost[][2] = {
124 { S(22, 6), S(36,12) }, // Knight
125 { S( 9, 2), S(15, 5) } // Bishop
128 // RookOnFile[semiopen/open] contains bonuses for each rook when there is
129 // no (friendly) pawn on the rook file.
130 constexpr Score RookOnFile[] = { S(20, 7), S(45, 20) };
132 // ThreatByMinor/ByRook[attacked PieceType] contains bonuses according to
133 // which piece type attacks which one. Attacks on lesser pieces which are
134 // pawn-defended are not considered.
135 constexpr Score ThreatByMinor[PIECE_TYPE_NB] = {
136 S(0, 0), S(0, 31), S(39, 42), S(57, 44), S(68, 112), S(47, 120)
139 constexpr Score ThreatByRook[PIECE_TYPE_NB] = {
140 S(0, 0), S(0, 24), S(38, 71), S(38, 61), S(0, 38), S(36, 38)
143 // ThreatByKing[on one/on many] contains bonuses for king attacks on
144 // pawns or pieces which are not pawn-defended.
145 constexpr Score ThreatByKing[] = { S(3, 65), S(9, 145) };
147 // PassedRank[Rank] contains a bonus according to the rank of a passed pawn
148 constexpr Score PassedRank[RANK_NB] = {
149 S(0, 0), S(5, 7), S(5, 13), S(32, 42), S(70, 70), S(172, 170), S(217, 269)
152 // PassedFile[File] contains a bonus according to the file of a passed pawn
153 constexpr Score PassedFile[FILE_NB] = {
154 S( 9, 10), S(2, 10), S(1, -8), S(-20,-12),
155 S(-20,-12), S(1, -8), S(2, 10), S( 9, 10)
158 // PassedDanger[Rank] contains a term to weight the passed score
159 constexpr int PassedDanger[RANK_NB] = { 0, 0, 0, 2, 7, 12, 19 };
161 // KingProtector[PieceType-2] contains a penalty according to distance from king
162 constexpr Score KingProtector[] = { S(3, 5), S(4, 3), S(3, 0), S(1, -1) };
164 // Assorted bonuses and penalties
165 constexpr Score BishopPawns = S( 8, 12);
166 constexpr Score CloseEnemies = S( 7, 0);
167 constexpr Score Connectivity = S( 3, 1);
168 constexpr Score CorneredBishop = S( 50, 50);
169 constexpr Score Hanging = S( 52, 30);
170 constexpr Score HinderPassedPawn = S( 8, 1);
171 constexpr Score KnightOnQueen = S( 21, 11);
172 constexpr Score LongDiagonalBishop = S( 22, 0);
173 constexpr Score MinorBehindPawn = S( 16, 0);
174 constexpr Score Overload = S( 10, 5);
175 constexpr Score PawnlessFlank = S( 20, 80);
176 constexpr Score RookOnPawn = S( 8, 24);
177 constexpr Score SliderOnQueen = S( 42, 21);
178 constexpr Score ThreatByPawnPush = S( 47, 26);
179 constexpr Score ThreatByRank = S( 16, 3);
180 constexpr Score ThreatBySafePawn = S(175,168);
181 constexpr Score TrappedRook = S( 92, 0);
182 constexpr Score WeakQueen = S( 50, 10);
183 constexpr Score WeakUnopposedPawn = S( 5, 25);
187 // Evaluation class computes and stores attacks tables and other working data
192 Evaluation() = delete;
193 explicit Evaluation(const Position& p) : pos(p) {}
194 Evaluation& operator=(const Evaluation&) = delete;
198 template<Color Us> void initialize();
199 template<Color Us, PieceType Pt> Score pieces();
200 template<Color Us> Score king() const;
201 template<Color Us> Score threats() const;
202 template<Color Us> Score passed() const;
203 template<Color Us> Score space() const;
204 ScaleFactor scale_factor(Value eg) const;
205 Score initiative(Value eg) const;
210 Bitboard mobilityArea[COLOR_NB];
211 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
213 // attackedBy[color][piece type] is a bitboard representing all squares
214 // attacked by a given color and piece type. Special "piece types" which
215 // is also calculated is ALL_PIECES.
216 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
218 // attackedBy2[color] are the squares attacked by 2 pieces of a given color,
219 // possibly via x-ray or by one pawn and one piece. Diagonal x-ray through
220 // pawn or squares attacked by 2 pawns are not explicitly added.
221 Bitboard attackedBy2[COLOR_NB];
223 // kingRing[color] are the squares adjacent to the king, plus (only for a
224 // king on its first rank) the squares two ranks in front. For instance,
225 // if black's king is on g8, kingRing[BLACK] is f8, h8, f7, g7, h7, f6, g6
226 // and h6. It is set to 0 when king safety evaluation is skipped.
227 Bitboard kingRing[COLOR_NB];
229 // kingAttackersCount[color] is the number of pieces of the given color
230 // which attack a square in the kingRing of the enemy king.
231 int kingAttackersCount[COLOR_NB];
233 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of
234 // the given color which attack a square in the kingRing of the enemy king.
235 // The weights of the individual piece types are given by the elements in
236 // the KingAttackWeights array.
237 int kingAttackersWeight[COLOR_NB];
239 // kingAttacksCount[color] is the number of attacks by the given color to
240 // squares directly adjacent to the enemy king. Pieces which attack more
241 // than one square are counted multiple times. For instance, if there is
242 // a white knight on g5 and black's king is on g8, this white knight adds 2
243 // to kingAttacksCount[WHITE].
244 int kingAttacksCount[COLOR_NB];
248 // Evaluation::initialize() computes king and pawn attacks, and the king ring
249 // bitboard for a given color. This is done at the beginning of the evaluation.
250 template<Tracing T> template<Color Us>
251 void Evaluation<T>::initialize() {
253 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
254 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
255 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
256 constexpr Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB: Rank7BB | Rank6BB);
258 // Find our pawns that are blocked or on the first two ranks
259 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
261 // Squares occupied by those pawns, by our king, or controlled by enemy pawns
262 // are excluded from the mobility area.
263 mobilityArea[Us] = ~(b | pos.square<KING>(Us) | pe->pawn_attacks(Them));
265 // Initialise attackedBy bitboards for kings and pawns
266 attackedBy[Us][KING] = pos.attacks_from<KING>(pos.square<KING>(Us));
267 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
268 attackedBy[Us][ALL_PIECES] = attackedBy[Us][KING] | attackedBy[Us][PAWN];
269 attackedBy2[Us] = attackedBy[Us][KING] & attackedBy[Us][PAWN];
271 // Init our king safety tables only if we are going to use them
272 if (pos.non_pawn_material(Them) >= RookValueMg + KnightValueMg)
274 kingRing[Us] = attackedBy[Us][KING];
275 if (relative_rank(Us, pos.square<KING>(Us)) == RANK_1)
276 kingRing[Us] |= shift<Up>(kingRing[Us]);
278 if (file_of(pos.square<KING>(Us)) == FILE_H)
279 kingRing[Us] |= shift<WEST>(kingRing[Us]);
281 else if (file_of(pos.square<KING>(Us)) == FILE_A)
282 kingRing[Us] |= shift<EAST>(kingRing[Us]);
284 kingAttackersCount[Them] = popcount(attackedBy[Us][KING] & pe->pawn_attacks(Them));
285 kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
288 kingRing[Us] = kingAttackersCount[Them] = 0;
292 // Evaluation::pieces() scores pieces of a given color and type
293 template<Tracing T> template<Color Us, PieceType Pt>
294 Score Evaluation<T>::pieces() {
296 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
297 constexpr Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
298 : Rank5BB | Rank4BB | Rank3BB);
299 const Square* pl = pos.squares<Pt>(Us);
303 Score score = SCORE_ZERO;
306 attackedBy[Us][Pt] = 0;
308 while ((s = *pl++) != SQ_NONE)
310 // Find attacked squares, including x-ray attacks for bishops and rooks
311 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
312 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
313 : pos.attacks_from<Pt>(s);
315 if (pos.blockers_for_king(Us) & s)
316 b &= LineBB[pos.square<KING>(Us)][s];
318 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
319 attackedBy[Us][Pt] |= b;
320 attackedBy[Us][ALL_PIECES] |= b;
322 if (b & kingRing[Them])
324 kingAttackersCount[Us]++;
325 kingAttackersWeight[Us] += KingAttackWeights[Pt];
326 kingAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
329 mob = (Pt == KNIGHT || Pt == BISHOP) ? popcount(b & mobilityArea[Us] & ~pos.pieces(Us, QUEEN))
330 : popcount(b & mobilityArea[Us]);
332 mobility[Us] += MobilityBonus[Pt - 2][mob];
334 // Penalty if the piece is far from the king
335 score -= KingProtector[Pt - 2] * distance(s, pos.square<KING>(Us));
337 if (Pt == BISHOP || Pt == KNIGHT)
339 // Bonus if piece is on an outpost square or can reach one
340 bb = OutpostRanks & ~pe->pawn_attacks_span(Them);
342 score += Outpost[Pt == BISHOP][bool(attackedBy[Us][PAWN] & s)] * 2;
344 else if (bb &= b & ~pos.pieces(Us))
345 score += Outpost[Pt == BISHOP][bool(attackedBy[Us][PAWN] & bb)];
347 // Bonus when behind a pawn
348 if ( relative_rank(Us, s) < RANK_5
349 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
350 score += MinorBehindPawn;
354 // Penalty according to number of pawns on the same color square as the bishop
355 score -= BishopPawns * pe->pawns_on_same_color_squares(Us, s);
357 // Bonus for bishop on a long diagonal which can "see" both center squares
358 if (more_than_one(Center & (attacks_bb<BISHOP>(s, pos.pieces(PAWN)) | s)))
359 score += LongDiagonalBishop;
362 // An important Chess960 pattern: A cornered bishop blocked by a friendly
363 // pawn diagonally in front of it is a very serious problem, especially
364 // when that pawn is also blocked.
367 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
369 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
370 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
371 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
372 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
379 // Bonus for aligning rook with enemy pawns on the same rank/file
380 if (relative_rank(Us, s) >= RANK_5)
381 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
383 // Bonus for rook on an open or semi-open file
384 if (pe->semiopen_file(Us, file_of(s)))
385 score += RookOnFile[bool(pe->semiopen_file(Them, file_of(s)))];
387 // Penalty when trapped by the king, even more if the king cannot castle
390 File kf = file_of(pos.square<KING>(Us));
391 if ((kf < FILE_E) == (file_of(s) < kf))
392 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
398 // Penalty if any relative pin or discovered attack against the queen
399 Bitboard queenPinners;
400 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
405 Trace::add(Pt, Us, score);
411 // Evaluation::king() assigns bonuses and penalties to a king of a given color
412 template<Tracing T> template<Color Us>
413 Score Evaluation<T>::king() const {
415 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
416 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
417 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
419 const Square ksq = pos.square<KING>(Us);
420 Bitboard weak, b, b1, b2, safe, unsafeChecks, pinned;
422 // King shelter and enemy pawns storm
423 Score score = pe->king_safety<Us>(pos, ksq);
425 // Main king safety evaluation
426 if (kingAttackersCount[Them] > 1 - pos.count<QUEEN>(Them))
431 // Attacked squares defended at most once by our queen or king
432 weak = attackedBy[Them][ALL_PIECES]
434 & (~attackedBy[Us][ALL_PIECES] | attackedBy[Us][KING] | attackedBy[Us][QUEEN]);
436 // Analyse the safe enemy's checks which are possible on next move
437 safe = ~pos.pieces(Them);
438 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
440 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
441 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
443 // Enemy queen safe checks
444 if ((b1 | b2) & attackedBy[Them][QUEEN] & safe & ~attackedBy[Us][QUEEN])
445 kingDanger += QueenSafeCheck;
447 b1 &= attackedBy[Them][ROOK];
448 b2 &= attackedBy[Them][BISHOP];
450 // Enemy rooks checks
452 kingDanger += RookSafeCheck;
456 // Enemy bishops checks
458 kingDanger += BishopSafeCheck;
462 // Enemy knights checks
463 b = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
465 kingDanger += KnightSafeCheck;
469 // Unsafe or occupied checking squares will also be considered, as long as
470 // the square is in the attacker's mobility area.
471 unsafeChecks &= mobilityArea[Them];
472 pinned = pos.blockers_for_king(Us) & pos.pieces(Us);
474 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
475 + 102 * kingAttacksCount[Them]
476 + 191 * popcount(kingRing[Us] & weak)
477 + 143 * popcount(pinned | unsafeChecks)
478 - 848 * !pos.count<QUEEN>(Them)
479 - 9 * mg_value(score) / 8
482 // Transform the kingDanger units into a Score, and subtract it from the evaluation
485 int mobilityDanger = mg_value(mobility[Them] - mobility[Us]);
486 kingDanger = std::max(0, kingDanger + mobilityDanger);
487 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
491 Bitboard kf = KingFlank[file_of(ksq)];
493 // Penalty when our king is on a pawnless flank
494 if (!(pos.pieces(PAWN) & kf))
495 score -= PawnlessFlank;
497 // Find the squares that opponent attacks in our king flank, and the squares
498 // which are attacked twice in that flank but not defended by our pawns.
499 b1 = attackedBy[Them][ALL_PIECES] & kf & Camp;
500 b2 = b1 & attackedBy2[Them] & ~attackedBy[Us][PAWN];
502 // King tropism, to anticipate slow motion attacks on our king
503 score -= CloseEnemies * (popcount(b1) + popcount(b2));
506 Trace::add(KING, Us, score);
512 // Evaluation::threats() assigns bonuses according to the types of the
513 // attacking and the attacked pieces.
514 template<Tracing T> template<Color Us>
515 Score Evaluation<T>::threats() const {
517 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
518 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
519 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
521 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safeThreats;
522 Score score = SCORE_ZERO;
525 nonPawnEnemies = pos.pieces(Them) ^ pos.pieces(Them, PAWN);
527 // Our safe or protected pawns
528 b = pos.pieces(Us, PAWN)
529 & (~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES]);
531 safeThreats = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
532 score += ThreatBySafePawn * popcount(safeThreats);
534 // Squares strongly protected by the enemy, either because they defend the
535 // square with a pawn, or because they defend the square twice and we don't.
536 stronglyProtected = attackedBy[Them][PAWN]
537 | (attackedBy2[Them] & ~attackedBy2[Us]);
539 // Non-pawn enemies, strongly protected
540 defended = nonPawnEnemies & stronglyProtected;
542 // Enemies not strongly protected and under our attack
543 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
545 // Bonus according to the kind of attacking pieces
548 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
551 Square s = pop_lsb(&b);
552 score += ThreatByMinor[type_of(pos.piece_on(s))];
553 if (type_of(pos.piece_on(s)) != PAWN)
554 score += ThreatByRank * (int)relative_rank(Them, s);
557 b = (pos.pieces(Them, QUEEN) | weak) & attackedBy[Us][ROOK];
560 Square s = pop_lsb(&b);
561 score += ThreatByRook[type_of(pos.piece_on(s))];
562 if (type_of(pos.piece_on(s)) != PAWN)
563 score += ThreatByRank * (int)relative_rank(Them, s);
566 score += Hanging * popcount(weak & ~attackedBy[Them][ALL_PIECES]);
568 b = weak & attackedBy[Us][KING];
570 score += ThreatByKing[more_than_one(b)];
573 // Bonus for enemy unopposed weak pawns
574 if (pos.pieces(Us, ROOK, QUEEN))
575 score += WeakUnopposedPawn * pe->weak_unopposed(Them);
577 // Find squares where our pawns can push on the next move
578 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
579 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
581 // Keep only the squares which are not completely unsafe
582 b &= ~attackedBy[Them][PAWN]
583 & (attackedBy[Us][ALL_PIECES] | ~attackedBy[Them][ALL_PIECES]);
585 // Bonus for safe pawn threats on the next move
586 b = pawn_attacks_bb<Us>(b)
588 & ~attackedBy[Us][PAWN];
590 score += ThreatByPawnPush * popcount(b);
592 // Bonus for threats on the next moves against enemy queen
593 if (pos.count<QUEEN>(Them) == 1)
595 Square s = pos.square<QUEEN>(Them);
596 safeThreats = mobilityArea[Us] & ~stronglyProtected;
598 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
600 score += KnightOnQueen * popcount(b & safeThreats);
602 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
603 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
605 score += SliderOnQueen * popcount(b & safeThreats & attackedBy2[Us]);
608 // Connectivity: ensure that knights, bishops, rooks, and queens are protected
609 b = (pos.pieces(Us) ^ pos.pieces(Us, PAWN, KING)) & attackedBy[Us][ALL_PIECES];
610 score += Connectivity * popcount(b);
612 // Bonus for overload (non-pawn enemies attacked and defended exactly once)
614 & attackedBy[Us][ALL_PIECES] & ~attackedBy2[Us]
615 & attackedBy[Them][ALL_PIECES] & ~attackedBy2[Them];
616 score += Overload * popcount(b);
619 Trace::add(THREAT, Us, score);
624 // Evaluation::passed() evaluates the passed pawns and candidate passed
625 // pawns of the given color.
627 template<Tracing T> template<Color Us>
628 Score Evaluation<T>::passed() const {
630 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
631 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
633 auto king_proximity = [&](Color c, Square s) {
634 return std::min(distance(pos.square<KING>(c), s), 5);
637 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
638 Score score = SCORE_ZERO;
640 b = pe->passed_pawns(Us);
644 Square s = pop_lsb(&b);
646 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
648 bb = forward_file_bb(Us, s) & (attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
649 score -= HinderPassedPawn * popcount(bb);
651 int r = relative_rank(Us, s);
652 int w = PassedDanger[r];
654 Score bonus = PassedRank[r];
658 Square blockSq = s + Up;
660 // Adjust bonus based on the king's proximity
661 bonus += make_score(0, ( king_proximity(Them, blockSq) * 5
662 - king_proximity(Us, blockSq) * 2) * w);
664 // If blockSq is not the queening square then consider also a second push
666 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
668 // If the pawn is free to advance, then increase the bonus
669 if (pos.empty(blockSq))
671 // If there is a rook or queen attacking/defending the pawn from behind,
672 // consider all the squaresToQueen. Otherwise consider only the squares
673 // in the pawn's path attacked or occupied by the enemy.
674 defendedSquares = unsafeSquares = squaresToQueen = forward_file_bb(Us, s);
676 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
678 if (!(pos.pieces(Us) & bb))
679 defendedSquares &= attackedBy[Us][ALL_PIECES];
681 if (!(pos.pieces(Them) & bb))
682 unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
684 // If there aren't any enemy attacks, assign a big bonus. Otherwise
685 // assign a smaller bonus if the block square isn't attacked.
686 int k = !unsafeSquares ? 20 : !(unsafeSquares & blockSq) ? 9 : 0;
688 // If the path to the queen is fully defended, assign a big bonus.
689 // Otherwise assign a smaller bonus if the block square is defended.
690 if (defendedSquares == squaresToQueen)
693 else if (defendedSquares & blockSq)
696 bonus += make_score(k * w, k * w);
698 else if (pos.pieces(Us) & blockSq)
699 bonus += make_score(w + r * 2, w + r * 2);
702 // Scale down bonus for candidate passers which need more than one
703 // pawn push to become passed or have a pawn in front of them.
704 if ( !pos.pawn_passed(Us, s + Up)
705 || (pos.pieces(PAWN) & forward_file_bb(Us, s)))
708 score += bonus + PassedFile[file_of(s)];
712 Trace::add(PASSED, Us, score);
718 // Evaluation::space() computes the space evaluation for a given side. The
719 // space evaluation is a simple bonus based on the number of safe squares
720 // available for minor pieces on the central four files on ranks 2--4. Safe
721 // squares one, two or three squares behind a friendly pawn are counted
722 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
723 // improve play on game opening.
725 template<Tracing T> template<Color Us>
726 Score Evaluation<T>::space() const {
728 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
729 constexpr Bitboard SpaceMask =
730 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
731 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
733 if (pos.non_pawn_material() < SpaceThreshold)
736 // Find the safe squares for our pieces inside the area defined by
737 // SpaceMask. A square is unsafe if it is attacked by an enemy
738 // pawn, or if it is undefended and attacked by an enemy piece.
739 Bitboard safe = SpaceMask
740 & ~pos.pieces(Us, PAWN)
741 & ~attackedBy[Them][PAWN];
743 // Find all squares which are at most three squares behind some friendly pawn
744 Bitboard behind = pos.pieces(Us, PAWN);
745 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
746 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
748 int bonus = popcount(safe) + popcount(behind & safe);
749 int weight = pos.count<ALL_PIECES>(Us) - 2 * pe->open_files();
751 Score score = make_score(bonus * weight * weight / 16, 0);
754 Trace::add(SPACE, Us, score);
760 // Evaluation::initiative() computes the initiative correction value
761 // for the position. It is a second order bonus/malus based on the
762 // known attacking/defending status of the players.
765 Score Evaluation<T>::initiative(Value eg) const {
767 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
768 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
770 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
771 && (pos.pieces(PAWN) & KingSide);
773 // Compute the initiative bonus for the attacking side
774 int complexity = 8 * outflanking
775 + 8 * pe->pawn_asymmetry()
776 + 12 * pos.count<PAWN>()
777 + 16 * pawnsOnBothFlanks
778 + 48 * !pos.non_pawn_material()
781 // Now apply the bonus: note that we find the attacking side by extracting
782 // the sign of the endgame value, and that we carefully cap the bonus so
783 // that the endgame score will never change sign after the bonus.
784 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
787 Trace::add(INITIATIVE, make_score(0, v));
789 return make_score(0, v);
793 // Evaluation::scale_factor() computes the scale factor for the winning side
796 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
798 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
799 int sf = me->scale_factor(pos, strongSide);
801 // If we don't already have an unusual scale factor, check for certain
802 // types of endgames, and use a lower scale for those.
803 if (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN)
805 if (pos.opposite_bishops())
807 // Endgame with opposite-colored bishops and no other pieces is almost a draw
808 if ( pos.non_pawn_material(WHITE) == BishopValueMg
809 && pos.non_pawn_material(BLACK) == BishopValueMg)
812 // Endgame with opposite-colored bishops, but also other pieces. Still
813 // a bit drawish, but not as drawish as with only the two bishops.
817 // Endings where weaker side can place his king in front of the enemy's
818 // pawns are drawish.
819 else if ( abs(eg) <= BishopValueEg
820 && pos.count<PAWN>(strongSide) <= 2
821 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
822 sf = 37 + 7 * pos.count<PAWN>(strongSide);
825 return ScaleFactor(sf);
829 // Evaluation::value() is the main function of the class. It computes the various
830 // parts of the evaluation and returns the value of the position from the point
831 // of view of the side to move.
834 Value Evaluation<T>::value() {
836 assert(!pos.checkers());
838 // Probe the material hash table
839 me = Material::probe(pos);
841 // If we have a specialized evaluation function for the current material
842 // configuration, call it and return.
843 if (me->specialized_eval_exists())
844 return me->evaluate(pos);
846 // Initialize score by reading the incrementally updated scores included in
847 // the position object (material + piece square tables) and the material
848 // imbalance. Score is computed internally from the white point of view.
849 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
851 // Probe the pawn hash table
852 pe = Pawns::probe(pos);
853 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
855 // Early exit if score is high
856 Value v = (mg_value(score) + eg_value(score)) / 2;
857 if (abs(v) > LazyThreshold)
858 return pos.side_to_move() == WHITE ? v : -v;
860 // Main evaluation begins here
865 // Pieces should be evaluated first (populate attack tables)
866 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
867 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
868 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
869 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
871 score += mobility[WHITE] - mobility[BLACK];
873 score += king< WHITE>() - king< BLACK>()
874 + threats<WHITE>() - threats<BLACK>()
875 + passed< WHITE>() - passed< BLACK>()
876 + space< WHITE>() - space< BLACK>();
878 score += initiative(eg_value(score));
880 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
881 ScaleFactor sf = scale_factor(eg_value(score));
882 v = mg_value(score) * int(me->game_phase())
883 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
885 v /= int(PHASE_MIDGAME);
887 // In case of tracing add all remaining individual evaluation terms
890 Trace::add(MATERIAL, pos.psq_score());
891 Trace::add(IMBALANCE, me->imbalance());
892 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
893 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
894 Trace::add(TOTAL, score);
897 return (pos.side_to_move() == WHITE ? v : -v) // Side to move point of view
904 /// evaluate() is the evaluator for the outer world. It returns a static
905 /// evaluation of the position from the point of view of the side to move.
907 Value Eval::evaluate(const Position& pos) {
908 return Evaluation<NO_TRACE>(pos).value();
912 /// trace() is like evaluate(), but instead of returning a value, it returns
913 /// a string (suitable for outputting to stdout) that contains the detailed
914 /// descriptions and values of each evaluation term. Useful for debugging.
916 std::string Eval::trace(const Position& pos) {
918 std::memset(scores, 0, sizeof(scores));
920 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
922 Value v = Evaluation<TRACE>(pos).value();
924 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
926 std::stringstream ss;
927 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
928 << " Term | White | Black | Total \n"
929 << " | MG EG | MG EG | MG EG \n"
930 << " ------------+-------------+-------------+------------\n"
931 << " Material | " << Term(MATERIAL)
932 << " Imbalance | " << Term(IMBALANCE)
933 << " Initiative | " << Term(INITIATIVE)
934 << " Pawns | " << Term(PAWN)
935 << " Knights | " << Term(KNIGHT)
936 << " Bishops | " << Term(BISHOP)
937 << " Rooks | " << Term(ROOK)
938 << " Queens | " << Term(QUEEN)
939 << " Mobility | " << Term(MOBILITY)
940 << " King safety | " << Term(KING)
941 << " Threats | " << Term(THREAT)
942 << " Passed | " << Term(PASSED)
943 << " Space | " << Term(SPACE)
944 << " ------------+-------------+-------------+------------\n"
945 << " Total | " << Term(TOTAL);
947 ss << "\nTotal evaluation: " << to_cp(v) << " (white side)\n";