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 PawnlessFlank = S( 20, 80);
175 constexpr Score RookOnPawn = S( 8, 24);
176 constexpr Score SliderOnQueen = S( 42, 21);
177 constexpr Score ThreatByPawnPush = S( 47, 26);
178 constexpr Score ThreatByRank = S( 16, 3);
179 constexpr Score ThreatBySafePawn = S(175,168);
180 constexpr Score TrappedRook = S( 92, 0);
181 constexpr Score WeakQueen = S( 50, 10);
182 constexpr Score WeakUnopposedPawn = S( 5, 25);
186 // Evaluation class computes and stores attacks tables and other working data
191 Evaluation() = delete;
192 explicit Evaluation(const Position& p) : pos(p) {}
193 Evaluation& operator=(const Evaluation&) = delete;
197 template<Color Us> void initialize();
198 template<Color Us, PieceType Pt> Score pieces();
199 template<Color Us> Score king() const;
200 template<Color Us> Score threats() const;
201 template<Color Us> Score passed() const;
202 template<Color Us> Score space() const;
203 ScaleFactor scale_factor(Value eg) const;
204 Score initiative(Value eg) const;
209 Bitboard mobilityArea[COLOR_NB];
210 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
212 // attackedBy[color][piece type] is a bitboard representing all squares
213 // attacked by a given color and piece type. Special "piece types" which
214 // is also calculated is ALL_PIECES.
215 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
217 // attackedBy2[color] are the squares attacked by 2 pieces of a given color,
218 // possibly via x-ray or by one pawn and one piece. Diagonal x-ray through
219 // pawn or squares attacked by 2 pawns are not explicitly added.
220 Bitboard attackedBy2[COLOR_NB];
222 // kingRing[color] are the squares adjacent to the king, plus (only for a
223 // king on its first rank) the squares two ranks in front. For instance,
224 // if black's king is on g8, kingRing[BLACK] is f8, h8, f7, g7, h7, f6, g6
225 // and h6. It is set to 0 when king safety evaluation is skipped.
226 Bitboard kingRing[COLOR_NB];
228 // kingAttackersCount[color] is the number of pieces of the given color
229 // which attack a square in the kingRing of the enemy king.
230 int kingAttackersCount[COLOR_NB];
232 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of
233 // the given color which attack a square in the kingRing of the enemy king.
234 // The weights of the individual piece types are given by the elements in
235 // the KingAttackWeights array.
236 int kingAttackersWeight[COLOR_NB];
238 // kingAttacksCount[color] is the number of attacks by the given color to
239 // squares directly adjacent to the enemy king. Pieces which attack more
240 // than one square are counted multiple times. For instance, if there is
241 // a white knight on g5 and black's king is on g8, this white knight adds 2
242 // to kingAttacksCount[WHITE].
243 int kingAttacksCount[COLOR_NB];
247 // Evaluation::initialize() computes king and pawn attacks, and the king ring
248 // bitboard for a given color. This is done at the beginning of the evaluation.
249 template<Tracing T> template<Color Us>
250 void Evaluation<T>::initialize() {
252 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
253 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
254 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
255 constexpr Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB: Rank7BB | Rank6BB);
257 // Find our pawns that are blocked or on the first two ranks
258 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
260 // Squares occupied by those pawns, by our king, or controlled by enemy pawns
261 // are excluded from the mobility area.
262 mobilityArea[Us] = ~(b | pos.square<KING>(Us) | pe->pawn_attacks(Them));
264 // Initialise attackedBy bitboards for kings and pawns
265 attackedBy[Us][KING] = pos.attacks_from<KING>(pos.square<KING>(Us));
266 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
267 attackedBy[Us][ALL_PIECES] = attackedBy[Us][KING] | attackedBy[Us][PAWN];
268 attackedBy2[Us] = attackedBy[Us][KING] & attackedBy[Us][PAWN];
270 // Init our king safety tables only if we are going to use them
271 if (pos.non_pawn_material(Them) >= RookValueMg + KnightValueMg)
273 kingRing[Us] = attackedBy[Us][KING];
274 if (relative_rank(Us, pos.square<KING>(Us)) == RANK_1)
275 kingRing[Us] |= shift<Up>(kingRing[Us]);
277 if (file_of(pos.square<KING>(Us)) == FILE_H)
278 kingRing[Us] |= shift<WEST>(kingRing[Us]);
280 else if (file_of(pos.square<KING>(Us)) == FILE_A)
281 kingRing[Us] |= shift<EAST>(kingRing[Us]);
283 kingAttackersCount[Them] = popcount(attackedBy[Us][KING] & pe->pawn_attacks(Them));
284 kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
287 kingRing[Us] = kingAttackersCount[Them] = 0;
291 // Evaluation::pieces() scores pieces of a given color and type
292 template<Tracing T> template<Color Us, PieceType Pt>
293 Score Evaluation<T>::pieces() {
295 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
296 constexpr Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
297 : Rank5BB | Rank4BB | Rank3BB);
298 const Square* pl = pos.squares<Pt>(Us);
302 Score score = SCORE_ZERO;
304 attackedBy[Us][Pt] = 0;
306 while ((s = *pl++) != SQ_NONE)
308 // Find attacked squares, including x-ray attacks for bishops and rooks
309 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
310 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
311 : pos.attacks_from<Pt>(s);
313 if (pos.blockers_for_king(Us) & s)
314 b &= LineBB[pos.square<KING>(Us)][s];
316 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
317 attackedBy[Us][Pt] |= b;
318 attackedBy[Us][ALL_PIECES] |= b;
320 if (b & kingRing[Them])
322 kingAttackersCount[Us]++;
323 kingAttackersWeight[Us] += KingAttackWeights[Pt];
324 kingAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
327 int mob = popcount(b & mobilityArea[Us]);
329 mobility[Us] += MobilityBonus[Pt - 2][mob];
331 // Penalty if the piece is far from the king
332 score -= KingProtector[Pt - 2] * distance(s, pos.square<KING>(Us));
334 if (Pt == BISHOP || Pt == KNIGHT)
336 // Bonus if piece is on an outpost square or can reach one
337 bb = OutpostRanks & ~pe->pawn_attacks_span(Them);
339 score += Outpost[Pt == BISHOP][bool(attackedBy[Us][PAWN] & s)] * 2;
341 else if (bb &= b & ~pos.pieces(Us))
342 score += Outpost[Pt == BISHOP][bool(attackedBy[Us][PAWN] & bb)];
344 // Bonus when behind a pawn
345 if ( relative_rank(Us, s) < RANK_5
346 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
347 score += MinorBehindPawn;
351 // Penalty according to number of pawns on the same color square as the bishop
352 score -= BishopPawns * pe->pawns_on_same_color_squares(Us, s);
354 // Bonus for bishop on a long diagonal which can "see" both center squares
355 if (more_than_one(Center & (attacks_bb<BISHOP>(s, pos.pieces(PAWN)) | s)))
356 score += LongDiagonalBishop;
359 // An important Chess960 pattern: A cornered bishop blocked by a friendly
360 // pawn diagonally in front of it is a very serious problem, especially
361 // when that pawn is also blocked.
364 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
366 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
367 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
368 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
369 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
376 // Bonus for aligning rook with enemy pawns on the same rank/file
377 if (relative_rank(Us, s) >= RANK_5)
378 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
380 // Bonus for rook on an open or semi-open file
381 if (pe->semiopen_file(Us, file_of(s)))
382 score += RookOnFile[bool(pe->semiopen_file(Them, file_of(s)))];
384 // Penalty when trapped by the king, even more if the king cannot castle
387 File kf = file_of(pos.square<KING>(Us));
388 if ((kf < FILE_E) == (file_of(s) < kf))
389 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
395 // Penalty if any relative pin or discovered attack against the queen
396 Bitboard queenPinners;
397 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
402 Trace::add(Pt, Us, score);
408 // Evaluation::king() assigns bonuses and penalties to a king of a given color
409 template<Tracing T> template<Color Us>
410 Score Evaluation<T>::king() const {
412 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
413 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
414 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
416 const Square ksq = pos.square<KING>(Us);
417 Bitboard weak, b, b1, b2, safe, unsafeChecks, pinned;
419 // King shelter and enemy pawns storm
420 Score score = pe->king_safety<Us>(pos, ksq);
422 // Main king safety evaluation
423 if (kingAttackersCount[Them] > 1 - pos.count<QUEEN>(Them))
428 // Attacked squares defended at most once by our queen or king
429 weak = attackedBy[Them][ALL_PIECES]
431 & (~attackedBy[Us][ALL_PIECES] | attackedBy[Us][KING] | attackedBy[Us][QUEEN]);
433 // Analyse the safe enemy's checks which are possible on next move
434 safe = ~pos.pieces(Them);
435 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
437 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
438 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
440 // Enemy queen safe checks
441 if ((b1 | b2) & attackedBy[Them][QUEEN] & safe & ~attackedBy[Us][QUEEN])
442 kingDanger += QueenSafeCheck;
444 b1 &= attackedBy[Them][ROOK];
445 b2 &= attackedBy[Them][BISHOP];
447 // Enemy rooks checks
449 kingDanger += RookSafeCheck;
453 // Enemy bishops checks
455 kingDanger += BishopSafeCheck;
459 // Enemy knights checks
460 b = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
462 kingDanger += KnightSafeCheck;
466 // Unsafe or occupied checking squares will also be considered, as long as
467 // the square is in the attacker's mobility area.
468 unsafeChecks &= mobilityArea[Them];
469 pinned = pos.blockers_for_king(Us) & pos.pieces(Us);
471 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
472 + 102 * kingAttacksCount[Them]
473 + 191 * popcount(kingRing[Us] & weak)
474 + 143 * popcount(pinned | unsafeChecks)
475 - 848 * !pos.count<QUEEN>(Them)
476 - 9 * mg_value(score) / 8
479 // Transform the kingDanger units into a Score, and subtract it from the evaluation
482 int mobilityDanger = mg_value(mobility[Them] - mobility[Us]);
483 kingDanger = std::max(0, kingDanger + mobilityDanger);
484 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
488 Bitboard kf = KingFlank[file_of(ksq)];
490 // Penalty when our king is on a pawnless flank
491 if (!(pos.pieces(PAWN) & kf))
492 score -= PawnlessFlank;
494 // Find the squares that opponent attacks in our king flank, and the squares
495 // which are attacked twice in that flank but not defended by our pawns.
496 b1 = attackedBy[Them][ALL_PIECES] & kf & Camp;
497 b2 = b1 & attackedBy2[Them] & ~attackedBy[Us][PAWN];
499 // King tropism, to anticipate slow motion attacks on our king
500 score -= CloseEnemies * (popcount(b1) + popcount(b2));
503 Trace::add(KING, Us, score);
509 // Evaluation::threats() assigns bonuses according to the types of the
510 // attacking and the attacked pieces.
511 template<Tracing T> template<Color Us>
512 Score Evaluation<T>::threats() const {
514 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
515 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
516 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
518 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safeThreats;
519 Score score = SCORE_ZERO;
521 // Non-pawn enemies attacked by a pawn
522 nonPawnEnemies = pos.pieces(Them) ^ pos.pieces(Them, PAWN);
524 // Our safe or protected pawns
525 b = pos.pieces(Us, PAWN)
526 & (~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES]);
528 safeThreats = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
529 score += ThreatBySafePawn * popcount(safeThreats);
531 // Squares strongly protected by the enemy, either because they defend the
532 // square with a pawn, or because they defend the square twice and we don't.
533 stronglyProtected = attackedBy[Them][PAWN]
534 | (attackedBy2[Them] & ~attackedBy2[Us]);
536 // Non-pawn enemies, strongly protected
537 defended = nonPawnEnemies & stronglyProtected;
539 // Enemies not strongly protected and under our attack
540 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
542 // Bonus according to the kind of attacking pieces
545 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
548 Square s = pop_lsb(&b);
549 score += ThreatByMinor[type_of(pos.piece_on(s))];
550 if (type_of(pos.piece_on(s)) != PAWN)
551 score += ThreatByRank * (int)relative_rank(Them, s);
554 b = (pos.pieces(Them, QUEEN) | weak) & attackedBy[Us][ROOK];
557 Square s = pop_lsb(&b);
558 score += ThreatByRook[type_of(pos.piece_on(s))];
559 if (type_of(pos.piece_on(s)) != PAWN)
560 score += ThreatByRank * (int)relative_rank(Them, s);
563 score += Hanging * popcount(weak & ~attackedBy[Them][ALL_PIECES]);
565 b = weak & attackedBy[Us][KING];
567 score += ThreatByKing[more_than_one(b)];
570 // Bonus for enemy unopposed weak pawns
571 if (pos.pieces(Us, ROOK, QUEEN))
572 score += WeakUnopposedPawn * pe->weak_unopposed(Them);
574 // Find squares where our pawns can push on the next move
575 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
576 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
578 // Keep only the squares which are not completely unsafe
579 b &= ~attackedBy[Them][PAWN]
580 & (attackedBy[Us][ALL_PIECES] | ~attackedBy[Them][ALL_PIECES]);
582 // Bonus for safe pawn threats on the next move
583 b = pawn_attacks_bb<Us>(b)
585 & ~attackedBy[Us][PAWN];
587 score += ThreatByPawnPush * popcount(b);
589 // Bonus for threats on the next moves against enemy queen
590 if (pos.count<QUEEN>(Them) == 1)
592 Square s = pos.square<QUEEN>(Them);
593 safeThreats = mobilityArea[Us] & ~stronglyProtected;
595 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
597 score += KnightOnQueen * popcount(b & safeThreats);
599 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
600 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
602 score += SliderOnQueen * popcount(b & safeThreats & attackedBy2[Us]);
605 // Connectivity: ensure that knights, bishops, rooks, and queens are protected
606 b = (pos.pieces(Us) ^ pos.pieces(Us, PAWN, KING)) & attackedBy[Us][ALL_PIECES];
607 score += Connectivity * popcount(b);
610 Trace::add(THREAT, Us, score);
615 // Evaluation::passed() evaluates the passed pawns and candidate passed
616 // pawns of the given color.
618 template<Tracing T> template<Color Us>
619 Score Evaluation<T>::passed() const {
621 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
622 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
624 auto king_proximity = [&](Color c, Square s) {
625 return std::min(distance(pos.square<KING>(c), s), 5);
628 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
629 Score score = SCORE_ZERO;
631 b = pe->passed_pawns(Us);
635 Square s = pop_lsb(&b);
637 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
639 bb = forward_file_bb(Us, s) & (attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
640 score -= HinderPassedPawn * popcount(bb);
642 int r = relative_rank(Us, s);
643 int w = PassedDanger[r];
645 Score bonus = PassedRank[r];
649 Square blockSq = s + Up;
651 // Adjust bonus based on the king's proximity
652 bonus += make_score(0, ( king_proximity(Them, blockSq) * 5
653 - king_proximity(Us, blockSq) * 2) * w);
655 // If blockSq is not the queening square then consider also a second push
657 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
659 // If the pawn is free to advance, then increase the bonus
660 if (pos.empty(blockSq))
662 // If there is a rook or queen attacking/defending the pawn from behind,
663 // consider all the squaresToQueen. Otherwise consider only the squares
664 // in the pawn's path attacked or occupied by the enemy.
665 defendedSquares = unsafeSquares = squaresToQueen = forward_file_bb(Us, s);
667 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
669 if (!(pos.pieces(Us) & bb))
670 defendedSquares &= attackedBy[Us][ALL_PIECES];
672 if (!(pos.pieces(Them) & bb))
673 unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
675 // If there aren't any enemy attacks, assign a big bonus. Otherwise
676 // assign a smaller bonus if the block square isn't attacked.
677 int k = !unsafeSquares ? 20 : !(unsafeSquares & blockSq) ? 9 : 0;
679 // If the path to the queen is fully defended, assign a big bonus.
680 // Otherwise assign a smaller bonus if the block square is defended.
681 if (defendedSquares == squaresToQueen)
684 else if (defendedSquares & blockSq)
687 bonus += make_score(k * w, k * w);
689 else if (pos.pieces(Us) & blockSq)
690 bonus += make_score(w + r * 2, w + r * 2);
693 // Scale down bonus for candidate passers which need more than one
694 // pawn push to become passed or have a pawn in front of them.
695 if ( !pos.pawn_passed(Us, s + Up)
696 || (pos.pieces(PAWN) & forward_file_bb(Us, s)))
699 score += bonus + PassedFile[file_of(s)];
703 Trace::add(PASSED, Us, score);
709 // Evaluation::space() computes the space evaluation for a given side. The
710 // space evaluation is a simple bonus based on the number of safe squares
711 // available for minor pieces on the central four files on ranks 2--4. Safe
712 // squares one, two or three squares behind a friendly pawn are counted
713 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
714 // improve play on game opening.
716 template<Tracing T> template<Color Us>
717 Score Evaluation<T>::space() const {
719 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
720 constexpr Bitboard SpaceMask =
721 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
722 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
724 if (pos.non_pawn_material() < SpaceThreshold)
727 // Find the safe squares for our pieces inside the area defined by
728 // SpaceMask. A square is unsafe if it is attacked by an enemy
729 // pawn, or if it is undefended and attacked by an enemy piece.
730 Bitboard safe = SpaceMask
731 & ~pos.pieces(Us, PAWN)
732 & ~attackedBy[Them][PAWN]
733 & (attackedBy[Us][ALL_PIECES] | ~attackedBy[Them][ALL_PIECES]);
735 // Find all squares which are at most three squares behind some friendly pawn
736 Bitboard behind = pos.pieces(Us, PAWN);
737 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
738 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
740 int bonus = popcount(safe) + popcount(behind & safe);
741 int weight = pos.count<ALL_PIECES>(Us) - 2 * pe->open_files();
743 Score score = make_score(bonus * weight * weight / 16, 0);
746 Trace::add(SPACE, Us, score);
752 // Evaluation::initiative() computes the initiative correction value
753 // for the position. It is a second order bonus/malus based on the
754 // known attacking/defending status of the players.
757 Score Evaluation<T>::initiative(Value eg) const {
759 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
760 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
762 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
763 && (pos.pieces(PAWN) & KingSide);
765 // Compute the initiative bonus for the attacking side
766 int complexity = 8 * outflanking
767 + 8 * pe->pawn_asymmetry()
768 + 12 * pos.count<PAWN>()
769 + 16 * pawnsOnBothFlanks
770 + 48 * !pos.non_pawn_material()
773 // Now apply the bonus: note that we find the attacking side by extracting
774 // the sign of the endgame value, and that we carefully cap the bonus so
775 // that the endgame score will never change sign after the bonus.
776 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
779 Trace::add(INITIATIVE, make_score(0, v));
781 return make_score(0, v);
785 // Evaluation::scale_factor() computes the scale factor for the winning side
788 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
790 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
791 int sf = me->scale_factor(pos, strongSide);
793 // If we don't already have an unusual scale factor, check for certain
794 // types of endgames, and use a lower scale for those.
795 if (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN)
797 if (pos.opposite_bishops())
799 // Endgame with opposite-colored bishops and no other pieces is almost a draw
800 if ( pos.non_pawn_material(WHITE) == BishopValueMg
801 && pos.non_pawn_material(BLACK) == BishopValueMg)
804 // Endgame with opposite-colored bishops, but also other pieces. Still
805 // a bit drawish, but not as drawish as with only the two bishops.
809 // Endings where weaker side can place his king in front of the enemy's
810 // pawns are drawish.
811 else if ( abs(eg) <= BishopValueEg
812 && pos.count<PAWN>(strongSide) <= 2
813 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
814 sf = 37 + 7 * pos.count<PAWN>(strongSide);
817 return ScaleFactor(sf);
821 // Evaluation::value() is the main function of the class. It computes the various
822 // parts of the evaluation and returns the value of the position from the point
823 // of view of the side to move.
826 Value Evaluation<T>::value() {
828 assert(!pos.checkers());
830 // Probe the material hash table
831 me = Material::probe(pos);
833 // If we have a specialized evaluation function for the current material
834 // configuration, call it and return.
835 if (me->specialized_eval_exists())
836 return me->evaluate(pos);
838 // Initialize score by reading the incrementally updated scores included in
839 // the position object (material + piece square tables) and the material
840 // imbalance. Score is computed internally from the white point of view.
841 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
843 // Probe the pawn hash table
844 pe = Pawns::probe(pos);
845 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
847 // Early exit if score is high
848 Value v = (mg_value(score) + eg_value(score)) / 2;
849 if (abs(v) > LazyThreshold)
850 return pos.side_to_move() == WHITE ? v : -v;
852 // Main evaluation begins here
857 // Pieces should be evaluated first (populate attack tables)
858 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
859 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
860 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
861 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
863 score += mobility[WHITE] - mobility[BLACK];
865 score += king< WHITE>() - king< BLACK>()
866 + threats<WHITE>() - threats<BLACK>()
867 + passed< WHITE>() - passed< BLACK>()
868 + space< WHITE>() - space< BLACK>();
870 score += initiative(eg_value(score));
872 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
873 ScaleFactor sf = scale_factor(eg_value(score));
874 v = mg_value(score) * int(me->game_phase())
875 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
877 v /= int(PHASE_MIDGAME);
879 // In case of tracing add all remaining individual evaluation terms
882 Trace::add(MATERIAL, pos.psq_score());
883 Trace::add(IMBALANCE, me->imbalance());
884 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
885 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
886 Trace::add(TOTAL, score);
889 return (pos.side_to_move() == WHITE ? v : -v) // Side to move point of view
896 /// evaluate() is the evaluator for the outer world. It returns a static
897 /// evaluation of the position from the point of view of the side to move.
899 Value Eval::evaluate(const Position& pos) {
900 return Evaluation<NO_TRACE>(pos).value();
904 /// trace() is like evaluate(), but instead of returning a value, it returns
905 /// a string (suitable for outputting to stdout) that contains the detailed
906 /// descriptions and values of each evaluation term. Useful for debugging.
908 std::string Eval::trace(const Position& pos) {
910 std::memset(scores, 0, sizeof(scores));
912 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
914 Value v = Evaluation<TRACE>(pos).value();
916 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
918 std::stringstream ss;
919 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
920 << " Term | White | Black | Total \n"
921 << " | MG EG | MG EG | MG EG \n"
922 << " ------------+-------------+-------------+------------\n"
923 << " Material | " << Term(MATERIAL)
924 << " Imbalance | " << Term(IMBALANCE)
925 << " Initiative | " << Term(INITIATIVE)
926 << " Pawns | " << Term(PAWN)
927 << " Knights | " << Term(KNIGHT)
928 << " Bishops | " << Term(BISHOP)
929 << " Rooks | " << Term(ROOK)
930 << " Queens | " << Term(QUEEN)
931 << " Mobility | " << Term(MOBILITY)
932 << " King safety | " << Term(KING)
933 << " Threats | " << Term(THREAT)
934 << " Passed | " << Term(PASSED)
935 << " Space | " << Term(SPACE)
936 << " ------------+-------------+-------------+------------\n"
937 << " Total | " << Term(TOTAL);
939 ss << "\nTotal evaluation: " << to_cp(v) << " (white side)\n";