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) 2015-2017 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
36 enum Term { // The first 8 entries are for PieceType
37 MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, TOTAL, TERM_NB
40 double scores[TERM_NB][COLOR_NB][PHASE_NB];
42 double to_cp(Value v) { return double(v) / PawnValueEg; }
44 void add(int idx, Color c, Score s) {
45 scores[idx][c][MG] = to_cp(mg_value(s));
46 scores[idx][c][EG] = to_cp(eg_value(s));
49 void add(int idx, Score w, Score b = SCORE_ZERO) {
50 add(idx, WHITE, w); add(idx, BLACK, b);
53 std::ostream& operator<<(std::ostream& os, Term t) {
55 if (t == MATERIAL || t == IMBALANCE || t == Term(PAWN) || t == TOTAL)
56 os << " --- --- | --- --- | ";
58 os << std::setw(5) << scores[t][WHITE][MG] << " "
59 << std::setw(5) << scores[t][WHITE][EG] << " | "
60 << std::setw(5) << scores[t][BLACK][MG] << " "
61 << std::setw(5) << scores[t][BLACK][EG] << " | ";
63 os << std::setw(5) << scores[t][WHITE][MG] - scores[t][BLACK][MG] << " "
64 << std::setw(5) << scores[t][WHITE][EG] - scores[t][BLACK][EG] << " \n";
70 using namespace Trace;
72 // Struct EvalInfo contains various information computed and collected
73 // by the evaluation functions.
78 Bitboard mobilityArea[COLOR_NB];
80 // attackedBy[color][piece type] is a bitboard representing all squares
81 // attacked by a given color and piece type (can be also ALL_PIECES).
82 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
84 // attackedBy2[color] are the squares attacked by 2 pieces of a given color,
85 // possibly via x-ray or by one pawn and one piece. Diagonal x-ray through
86 // pawn or squares attacked by 2 pawns are not explicitly added.
87 Bitboard attackedBy2[COLOR_NB];
89 // kingRing[color] is the zone around the king which is considered
90 // by the king safety evaluation. This consists of the squares directly
91 // adjacent to the king, and the three (or two, for a king on an edge file)
92 // squares two ranks in front of the king. For instance, if black's king
93 // is on g8, kingRing[BLACK] is a bitboard containing the squares f8, h8,
94 // f7, g7, h7, f6, g6 and h6.
95 Bitboard kingRing[COLOR_NB];
97 // kingAttackersCount[color] is the number of pieces of the given color
98 // which attack a square in the kingRing of the enemy king.
99 int kingAttackersCount[COLOR_NB];
101 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of the
102 // given color which attack a square in the kingRing of the enemy king. The
103 // weights of the individual piece types are given by the elements in the
104 // KingAttackWeights array.
105 int kingAttackersWeight[COLOR_NB];
107 // kingAdjacentZoneAttacksCount[color] is the number of attacks by the given
108 // color to squares directly adjacent to the enemy king. Pieces which attack
109 // more than one square are counted multiple times. For instance, if there is
110 // a white knight on g5 and black's king is on g8, this white knight adds 2
111 // to kingAdjacentZoneAttacksCount[WHITE].
112 int kingAdjacentZoneAttacksCount[COLOR_NB];
115 #define V(v) Value(v)
116 #define S(mg, eg) make_score(mg, eg)
118 // MobilityBonus[PieceType-2][attacked] contains bonuses for middle and end game,
119 // indexed by piece type and number of attacked squares in the mobility area.
120 const Score MobilityBonus[][32] = {
121 { S(-75,-76), S(-57,-54), S( -9,-28), S( -2,-10), S( 6, 5), S( 14, 12), // Knights
122 S( 22, 26), S( 29, 29), S( 36, 29) },
123 { S(-48,-59), S(-20,-23), S( 16, -3), S( 26, 13), S( 38, 24), S( 51, 42), // Bishops
124 S( 55, 54), S( 63, 57), S( 63, 65), S( 68, 73), S( 81, 78), S( 81, 86),
125 S( 91, 88), S( 98, 97) },
126 { S(-58,-76), S(-27,-18), S(-15, 28), S(-10, 55), S( -5, 69), S( -2, 82), // Rooks
127 S( 9,112), S( 16,118), S( 30,132), S( 29,142), S( 32,155), S( 38,165),
128 S( 46,166), S( 48,169), S( 58,171) },
129 { S(-39,-36), S(-21,-15), S( 3, 8), S( 3, 18), S( 14, 34), S( 22, 54), // Queens
130 S( 28, 61), S( 41, 73), S( 43, 79), S( 48, 92), S( 56, 94), S( 60,104),
131 S( 60,113), S( 66,120), S( 67,123), S( 70,126), S( 71,133), S( 73,136),
132 S( 79,140), S( 88,143), S( 88,148), S( 99,166), S(102,170), S(102,175),
133 S(106,184), S(109,191), S(113,206), S(116,212) }
136 // Outpost[knight/bishop][supported by pawn] contains bonuses for minor
137 // pieces if they can reach an outpost square, bigger if that square is
138 // supported by a pawn. If the minor piece occupies an outpost square
139 // then score is doubled.
140 const Score Outpost[][2] = {
141 { S(22, 6), S(33, 9) }, // Knight
142 { S( 9, 2), S(14, 4) } // Bishop
145 // RookOnFile[semiopen/open] contains bonuses for each rook when there is no
146 // friendly pawn on the rook file.
147 const Score RookOnFile[] = { S(20, 7), S(45, 20) };
149 // ThreatByMinor/ByRook[attacked PieceType] contains bonuses according to
150 // which piece type attacks which one. Attacks on lesser pieces which are
151 // pawn-defended are not considered.
152 const Score ThreatByMinor[PIECE_TYPE_NB] = {
153 S(0, 0), S(0, 33), S(45, 43), S(46, 47), S(72, 107), S(48, 118)
156 const Score ThreatByRook[PIECE_TYPE_NB] = {
157 S(0, 0), S(0, 25), S(40, 62), S(40, 59), S( 0, 34), S(35, 48)
160 // ThreatByKing[on one/on many] contains bonuses for king attacks on
161 // pawns or pieces which are not pawn-defended.
162 const Score ThreatByKing[] = { S(3, 62), S(9, 138) };
164 // Passed[mg/eg][Rank] contains midgame and endgame bonuses for passed pawns.
165 // We don't use a Score because we process the two components independently.
166 const Value Passed[][RANK_NB] = {
167 { V(5), V( 5), V(31), V(73), V(166), V(252) },
168 { V(7), V(14), V(38), V(73), V(166), V(252) }
171 // PassedFile[File] contains a bonus according to the file of a passed pawn
172 const Score PassedFile[FILE_NB] = {
173 S( 9, 10), S( 2, 10), S( 1, -8), S(-20,-12),
174 S(-20,-12), S( 1, -8), S( 2, 10), S( 9, 10)
177 // KingProtector[PieceType-2] contains a bonus according to distance from king
178 const Score KingProtector[] = { S(-3, -5), S(-4, -3), S(-3, 0), S(-1, 1) };
180 // Assorted bonuses and penalties used by evaluation
181 const Score MinorBehindPawn = S( 16, 0);
182 const Score BishopPawns = S( 8, 12);
183 const Score RookOnPawn = S( 8, 24);
184 const Score TrappedRook = S( 92, 0);
185 const Score WeakQueen = S( 50, 10);
186 const Score OtherCheck = S( 10, 10);
187 const Score CloseEnemies = S( 7, 0);
188 const Score PawnlessFlank = S( 20, 80);
189 const Score ThreatByHangingPawn = S( 71, 61);
190 const Score ThreatBySafePawn = S(182,175);
191 const Score ThreatByRank = S( 16, 3);
192 const Score Hanging = S( 48, 27);
193 const Score ThreatByPawnPush = S( 38, 22);
194 const Score HinderPassedPawn = S( 7, 0);
196 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
197 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
198 // happen in Chess960 games.
199 const Score TrappedBishopA1H1 = S(50, 50);
204 // KingAttackWeights[PieceType] contains king attack weights by piece type
205 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 78, 56, 45, 11 };
207 // Penalties for enemy's safe checks
208 const int QueenCheck = 780;
209 const int RookCheck = 880;
210 const int BishopCheck = 435;
211 const int KnightCheck = 790;
213 // Threshold for lazy and space evaluation
214 const Value LazyThreshold = Value(1500);
215 const Value SpaceThreshold = Value(12222);
217 // eval_init() initializes king and attack bitboards for a given color
218 // adding pawn attacks. To be done at the beginning of the evaluation.
221 void eval_init(const Position& pos, EvalInfo& ei) {
223 const Color Them = (Us == WHITE ? BLACK : WHITE);
224 const Square Up = (Us == WHITE ? NORTH : SOUTH);
225 const Square Down = (Us == WHITE ? SOUTH : NORTH);
226 const Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB: Rank7BB | Rank6BB);
228 // Find our pawns on the first two ranks, and those which are blocked
229 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
231 // Squares occupied by those pawns, by our king, or controlled by enemy pawns
232 // are excluded from the mobility area.
233 ei.mobilityArea[Us] = ~(b | pos.square<KING>(Us) | ei.pe->pawn_attacks(Them));
235 // Initialise the attack bitboards with the king and pawn information
236 b = ei.attackedBy[Us][KING] = pos.attacks_from<KING>(pos.square<KING>(Us));
237 ei.attackedBy[Us][PAWN] = ei.pe->pawn_attacks(Us);
239 ei.attackedBy2[Us] = b & ei.attackedBy[Us][PAWN];
240 ei.attackedBy[Us][ALL_PIECES] = b | ei.attackedBy[Us][PAWN];
242 // Init our king safety tables only if we are going to use them
243 if (pos.non_pawn_material(Them) >= QueenValueMg)
245 ei.kingRing[Us] = b | shift<Up>(b);
246 ei.kingAttackersCount[Them] = popcount(b & ei.pe->pawn_attacks(Them));
247 ei.kingAdjacentZoneAttacksCount[Them] = ei.kingAttackersWeight[Them] = 0;
250 ei.kingRing[Us] = ei.kingAttackersCount[Them] = 0;
254 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given
257 template<bool DoTrace, Color Us = WHITE, PieceType Pt = KNIGHT>
258 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility) {
260 const Color Them = (Us == WHITE ? BLACK : WHITE);
261 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
262 const Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
263 : Rank5BB | Rank4BB | Rank3BB);
264 const Square* pl = pos.squares<Pt>(Us);
268 Score score = SCORE_ZERO;
270 ei.attackedBy[Us][Pt] = 0;
272 while ((s = *pl++) != SQ_NONE)
274 // Find attacked squares, including x-ray attacks for bishops and rooks
275 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
276 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
277 : pos.attacks_from<Pt>(s);
279 if (pos.pinned_pieces(Us) & s)
280 b &= LineBB[pos.square<KING>(Us)][s];
282 ei.attackedBy2[Us] |= ei.attackedBy[Us][ALL_PIECES] & b;
283 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
285 if (b & ei.kingRing[Them])
287 ei.kingAttackersCount[Us]++;
288 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
289 ei.kingAdjacentZoneAttacksCount[Us] += popcount(b & ei.attackedBy[Them][KING]);
292 int mob = popcount(b & ei.mobilityArea[Us]);
294 mobility[Us] += MobilityBonus[Pt - 2][mob];
296 // Bonus for this piece as a king protector
297 score += KingProtector[Pt - 2] * distance(s, pos.square<KING>(Us));
299 if (Pt == BISHOP || Pt == KNIGHT)
301 // Bonus for outpost squares
302 bb = OutpostRanks & ~ei.pe->pawn_attacks_span(Them);
304 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & s)] * 2;
307 bb &= b & ~pos.pieces(Us);
309 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & bb)];
312 // Bonus when behind a pawn
313 if ( relative_rank(Us, s) < RANK_5
314 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
315 score += MinorBehindPawn;
317 // Penalty for pawns on the same color square as the bishop
319 score -= BishopPawns * ei.pe->pawns_on_same_color_squares(Us, s);
321 // An important Chess960 pattern: A cornered bishop blocked by a friendly
322 // pawn diagonally in front of it is a very serious problem, especially
323 // when that pawn is also blocked.
326 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
328 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
329 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
330 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
331 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
338 // Bonus for aligning with enemy pawns on the same rank/file
339 if (relative_rank(Us, s) >= RANK_5)
340 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
342 // Bonus when on an open or semi-open file
343 if (ei.pe->semiopen_file(Us, file_of(s)))
344 score += RookOnFile[!!ei.pe->semiopen_file(Them, file_of(s))];
346 // Penalty when trapped by the king, even more if the king cannot castle
349 Square ksq = pos.square<KING>(Us);
351 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
352 && !ei.pe->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
353 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
359 // Penalty if any relative pin or discovered attack against the queen
361 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, pinners))
367 Trace::add(Pt, Us, score);
369 // Recursively call evaluate_pieces() of next piece type until KING is excluded
370 return score - evaluate_pieces<DoTrace, Them, NextPt>(pos, ei, mobility);
374 Score evaluate_pieces<false, WHITE, KING>(const Position&, EvalInfo&, Score*) { return SCORE_ZERO; }
376 Score evaluate_pieces< true, WHITE, KING>(const Position&, EvalInfo&, Score*) { return SCORE_ZERO; }
379 // evaluate_king() assigns bonuses and penalties to a king of a given color
381 const Bitboard QueenSide = FileABB | FileBBB | FileCBB | FileDBB;
382 const Bitboard CenterFiles = FileCBB | FileDBB | FileEBB | FileFBB;
383 const Bitboard KingSide = FileEBB | FileFBB | FileGBB | FileHBB;
385 const Bitboard KingFlank[FILE_NB] = {
386 QueenSide, QueenSide, QueenSide, CenterFiles, CenterFiles, KingSide, KingSide, KingSide
389 template<Color Us, bool DoTrace>
390 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
392 const Color Them = (Us == WHITE ? BLACK : WHITE);
393 const Square Up = (Us == WHITE ? NORTH : SOUTH);
394 const Bitboard Camp = (Us == WHITE ? ~Bitboard(0) ^ Rank6BB ^ Rank7BB ^ Rank8BB
395 : ~Bitboard(0) ^ Rank1BB ^ Rank2BB ^ Rank3BB);
397 const Square ksq = pos.square<KING>(Us);
398 Bitboard undefended, b, b1, b2, safe, other;
401 // King shelter and enemy pawns storm
402 Score score = ei.pe->king_safety<Us>(pos, ksq);
404 // Main king safety evaluation
405 if (ei.kingAttackersCount[Them])
407 // Find the attacked squares which are defended only by our king...
408 undefended = ei.attackedBy[Them][ALL_PIECES]
409 & ei.attackedBy[Us][KING]
410 & ~ei.attackedBy2[Us];
412 // ... and those which are not defended at all in the larger king ring
413 b = ei.attackedBy[Them][ALL_PIECES] & ~ei.attackedBy[Us][ALL_PIECES]
414 & ei.kingRing[Us] & ~pos.pieces(Them);
416 // Initialize the 'kingDanger' variable, which will be transformed
417 // later into a king danger score. The initial value is based on the
418 // number and types of the enemy's attacking pieces, the number of
419 // attacked and undefended squares around our king and the quality of
420 // the pawn shelter (current 'score' value).
421 kingDanger = ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them]
422 + 102 * ei.kingAdjacentZoneAttacksCount[Them]
423 + 201 * popcount(undefended)
424 + 143 * (popcount(b) + !!pos.pinned_pieces(Us))
425 - 848 * !pos.count<QUEEN>(Them)
426 - 28 * mg_value(score) / 25 - 5;
428 // Analyse the safe enemy's checks which are possible on next move
429 safe = ~pos.pieces(Them);
430 safe &= ~ei.attackedBy[Us][ALL_PIECES] | (undefended & ei.attackedBy2[Them]);
432 b1 = pos.attacks_from<ROOK >(ksq);
433 b2 = pos.attacks_from<BISHOP>(ksq);
435 // Enemy queen safe checks
436 if ((b1 | b2) & ei.attackedBy[Them][QUEEN] & safe)
437 kingDanger += QueenCheck;
439 // For minors and rooks, also consider the square safe if attacked twice,
440 // and only defended by our queen.
441 safe |= ei.attackedBy2[Them]
442 & ~(ei.attackedBy2[Us] | pos.pieces(Them))
443 & ei.attackedBy[Us][QUEEN];
445 // Some other potential checks are also analysed, even from squares
446 // currently occupied by the opponent own pieces, as long as the square
447 // is not attacked by our pawns, and is not occupied by a blocked pawn.
448 other = ~( ei.attackedBy[Us][PAWN]
449 | (pos.pieces(Them, PAWN) & shift<Up>(pos.pieces(PAWN))));
451 // Enemy rooks safe and other checks
452 if (b1 & ei.attackedBy[Them][ROOK] & safe)
453 kingDanger += RookCheck;
455 else if (b1 & ei.attackedBy[Them][ROOK] & other)
458 // Enemy bishops safe and other checks
459 if (b2 & ei.attackedBy[Them][BISHOP] & safe)
460 kingDanger += BishopCheck;
462 else if (b2 & ei.attackedBy[Them][BISHOP] & other)
465 // Enemy knights safe and other checks
466 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT];
468 kingDanger += KnightCheck;
473 // Transform the kingDanger units into a Score, and substract it from the evaluation
475 score -= make_score(kingDanger * kingDanger / 4096, 0);
478 // King tropism: firstly, find squares that opponent attacks in our king flank
479 File kf = file_of(ksq);
480 b = ei.attackedBy[Them][ALL_PIECES] & KingFlank[kf] & Camp;
482 assert(((Us == WHITE ? b << 4 : b >> 4) & b) == 0);
483 assert(popcount(Us == WHITE ? b << 4 : b >> 4) == popcount(b));
485 // Secondly, add the squares which are attacked twice in that flank and
486 // which are not defended by our pawns.
487 b = (Us == WHITE ? b << 4 : b >> 4)
488 | (b & ei.attackedBy2[Them] & ~ei.attackedBy[Us][PAWN]);
490 score -= CloseEnemies * popcount(b);
492 // Penalty when our king is on a pawnless flank
493 if (!(pos.pieces(PAWN) & KingFlank[kf]))
494 score -= PawnlessFlank;
497 Trace::add(KING, Us, score);
503 // evaluate_threats() assigns bonuses according to the types of the attacking
504 // and the attacked pieces.
506 template<Color Us, bool DoTrace>
507 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
509 const Color Them = (Us == WHITE ? BLACK : WHITE);
510 const Square Up = (Us == WHITE ? NORTH : SOUTH);
511 const Square Left = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
512 const Square Right = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
513 const Bitboard TRank2BB = (Us == WHITE ? Rank2BB : Rank7BB);
514 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
516 Bitboard b, weak, defended, stronglyProtected, safeThreats;
517 Score score = SCORE_ZERO;
519 // Non-pawn enemies attacked by a pawn
520 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Us][PAWN];
524 b = pos.pieces(Us, PAWN) & ( ~ei.attackedBy[Them][ALL_PIECES]
525 | ei.attackedBy[Us][ALL_PIECES]);
527 safeThreats = (shift<Right>(b) | shift<Left>(b)) & weak;
529 score += ThreatBySafePawn * popcount(safeThreats);
531 if (weak ^ safeThreats)
532 score += ThreatByHangingPawn;
535 // Squares strongly protected by the opponent, either because they attack the
536 // square with a pawn, or because they attack the square twice and we don't.
537 stronglyProtected = ei.attackedBy[Them][PAWN]
538 | (ei.attackedBy2[Them] & ~ei.attackedBy2[Us]);
540 // Non-pawn enemies, strongly protected
541 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN))
544 // Enemies not strongly protected and under our attack
545 weak = pos.pieces(Them)
547 & ei.attackedBy[Us][ALL_PIECES];
549 // Add a bonus according to the kind of attacking pieces
552 b = (defended | weak) & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
555 Square s = pop_lsb(&b);
556 score += ThreatByMinor[type_of(pos.piece_on(s))];
557 if (type_of(pos.piece_on(s)) != PAWN)
558 score += ThreatByRank * (int)relative_rank(Them, s);
561 b = (pos.pieces(Them, QUEEN) | weak) & ei.attackedBy[Us][ROOK];
564 Square s = pop_lsb(&b);
565 score += ThreatByRook[type_of(pos.piece_on(s))];
566 if (type_of(pos.piece_on(s)) != PAWN)
567 score += ThreatByRank * (int)relative_rank(Them, s);
570 score += Hanging * popcount(weak & ~ei.attackedBy[Them][ALL_PIECES]);
572 b = weak & ei.attackedBy[Us][KING];
574 score += ThreatByKing[more_than_one(b)];
577 // Bonus if some pawns can safely push and attack an enemy piece
578 b = pos.pieces(Us, PAWN) & ~TRank7BB;
579 b = shift<Up>(b | (shift<Up>(b & TRank2BB) & ~pos.pieces()));
582 & ~ei.attackedBy[Them][PAWN]
583 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
585 b = (shift<Left>(b) | shift<Right>(b))
587 & ~ei.attackedBy[Us][PAWN];
589 score += ThreatByPawnPush * popcount(b);
592 Trace::add(THREAT, Us, score);
598 // evaluate_passer_pawns() evaluates the passed pawns and candidate passed
599 // pawns of the given color.
601 template<Color Us, bool DoTrace>
602 Score evaluate_passer_pawns(const Position& pos, const EvalInfo& ei) {
604 const Color Them = (Us == WHITE ? BLACK : WHITE);
606 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
607 Score score = SCORE_ZERO;
609 b = ei.pe->passed_pawns(Us);
613 Square s = pop_lsb(&b);
615 assert(!(pos.pieces(Them, PAWN) & forward_bb(Us, s + pawn_push(Us))));
617 bb = forward_bb(Us, s) & (ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
618 score -= HinderPassedPawn * popcount(bb);
620 int r = relative_rank(Us, s) - RANK_2;
621 int rr = r * (r - 1);
623 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
627 Square blockSq = s + pawn_push(Us);
629 // Adjust bonus based on the king's proximity
630 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
631 - distance(pos.square<KING>(Us ), blockSq) * 2 * rr;
633 // If blockSq is not the queening square then consider also a second push
634 if (relative_rank(Us, blockSq) != RANK_8)
635 ebonus -= distance(pos.square<KING>(Us), blockSq + pawn_push(Us)) * rr;
637 // If the pawn is free to advance, then increase the bonus
638 if (pos.empty(blockSq))
640 // If there is a rook or queen attacking/defending the pawn from behind,
641 // consider all the squaresToQueen. Otherwise consider only the squares
642 // in the pawn's path attacked or occupied by the enemy.
643 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
645 bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
647 if (!(pos.pieces(Us) & bb))
648 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
650 if (!(pos.pieces(Them) & bb))
651 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
653 // If there aren't any enemy attacks, assign a big bonus. Otherwise
654 // assign a smaller bonus if the block square isn't attacked.
655 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
657 // If the path to the queen is fully defended, assign a big bonus.
658 // Otherwise assign a smaller bonus if the block square is defended.
659 if (defendedSquares == squaresToQueen)
662 else if (defendedSquares & blockSq)
665 mbonus += k * rr, ebonus += k * rr;
667 else if (pos.pieces(Us) & blockSq)
668 mbonus += rr + r * 2, ebonus += rr + r * 2;
671 // Scale down bonus for candidate passers which need more than one
672 // pawn push to become passed or have a pawn in front of them.
673 if (!pos.pawn_passed(Us, s + pawn_push(Us)) || (pos.pieces(PAWN) & forward_bb(Us, s)))
674 mbonus /= 2, ebonus /= 2;
676 score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
680 Trace::add(PASSED, Us, score);
686 // evaluate_space() computes the space evaluation for a given side. The
687 // space evaluation is a simple bonus based on the number of safe squares
688 // available for minor pieces on the central four files on ranks 2--4. Safe
689 // squares one, two or three squares behind a friendly pawn are counted
690 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
691 // improve play on game opening.
693 Score evaluate_space(const Position& pos, const EvalInfo& ei) {
695 const Color Them = (Us == WHITE ? BLACK : WHITE);
696 const Bitboard SpaceMask =
697 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
698 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
700 // Find the safe squares for our pieces inside the area defined by
701 // SpaceMask. A square is unsafe if it is attacked by an enemy
702 // pawn, or if it is undefended and attacked by an enemy piece.
703 Bitboard safe = SpaceMask
704 & ~pos.pieces(Us, PAWN)
705 & ~ei.attackedBy[Them][PAWN]
706 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
708 // Find all squares which are at most three squares behind some friendly pawn
709 Bitboard behind = pos.pieces(Us, PAWN);
710 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
711 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
713 // Since SpaceMask[Us] is fully on our half of the board...
714 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
716 // ...count safe + (behind & safe) with a single popcount.
717 int bonus = popcount((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
718 int weight = pos.count<ALL_PIECES>(Us) - 2 * ei.pe->open_files();
720 return make_score(bonus * weight * weight / 16, 0);
724 // evaluate_initiative() computes the initiative correction value for the
725 // position, i.e., second order bonus/malus based on the known attacking/defending
726 // status of the players.
727 Score evaluate_initiative(const Position& pos, int asymmetry, Value eg) {
729 int kingDistance = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
730 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
731 bool bothFlanks = (pos.pieces(PAWN) & QueenSide) && (pos.pieces(PAWN) & KingSide);
733 // Compute the initiative bonus for the attacking side
734 int initiative = 8 * (asymmetry + kingDistance - 17) + 12 * pos.count<PAWN>() + 16 * bothFlanks;
736 // Now apply the bonus: note that we find the attacking side by extracting
737 // the sign of the endgame value, and that we carefully cap the bonus so
738 // that the endgame score will never change sign after the bonus.
739 int value = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg));
741 return make_score(0, value);
745 // evaluate_scale_factor() computes the scale factor for the winning side
746 ScaleFactor evaluate_scale_factor(const Position& pos, const EvalInfo& ei, Value eg) {
748 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
749 ScaleFactor sf = ei.me->scale_factor(pos, strongSide);
751 // If we don't already have an unusual scale factor, check for certain
752 // types of endgames, and use a lower scale for those.
753 if (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN)
755 if (pos.opposite_bishops())
757 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
758 // is almost a draw, in case of KBP vs KB, it is even more a draw.
759 if ( pos.non_pawn_material(WHITE) == BishopValueMg
760 && pos.non_pawn_material(BLACK) == BishopValueMg)
761 return more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
763 // Endgame with opposite-colored bishops, but also other pieces. Still
764 // a bit drawish, but not as drawish as with only the two bishops.
765 return ScaleFactor(46);
767 // Endings where weaker side can place his king in front of the opponent's
768 // pawns are drawish.
769 else if ( abs(eg) <= BishopValueEg
770 && pos.count<PAWN>(strongSide) <= 2
771 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
772 return ScaleFactor(37 + 7 * pos.count<PAWN>(strongSide));
781 /// evaluate() is the main evaluation function. It returns a static evaluation
782 /// of the position from the point of view of the side to move.
784 template<bool DoTrace>
785 Value Eval::evaluate(const Position& pos) {
787 assert(!pos.checkers());
789 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
793 // Probe the material hash table
794 ei.me = Material::probe(pos);
796 // If we have a specialized evaluation function for the current material
797 // configuration, call it and return.
798 if (ei.me->specialized_eval_exists())
799 return ei.me->evaluate(pos);
801 // Initialize score by reading the incrementally updated scores included in
802 // the position object (material + piece square tables) and the material
803 // imbalance. Score is computed internally from the white point of view.
804 Score score = pos.psq_score() + ei.me->imbalance();
806 // Probe the pawn hash table
807 ei.pe = Pawns::probe(pos);
808 score += ei.pe->pawns_score();
810 // Early exit if score is high
811 v = (mg_value(score) + eg_value(score)) / 2;
812 if (abs(v) > LazyThreshold)
813 return pos.side_to_move() == WHITE ? v : -v;
815 // Initialize attack and king safety bitboards
816 eval_init<WHITE>(pos, ei);
817 eval_init<BLACK>(pos, ei);
819 // Evaluate all pieces but king and pawns
820 score += evaluate_pieces<DoTrace>(pos, ei, mobility);
821 score += mobility[WHITE] - mobility[BLACK];
823 // Evaluate kings after all other pieces because we need full attack
824 // information when computing the king safety evaluation.
825 score += evaluate_king<WHITE, DoTrace>(pos, ei)
826 - evaluate_king<BLACK, DoTrace>(pos, ei);
828 // Evaluate tactical threats, we need full attack information including king
829 score += evaluate_threats<WHITE, DoTrace>(pos, ei)
830 - evaluate_threats<BLACK, DoTrace>(pos, ei);
832 // Evaluate passed pawns, we need full attack information including king
833 score += evaluate_passer_pawns<WHITE, DoTrace>(pos, ei)
834 - evaluate_passer_pawns<BLACK, DoTrace>(pos, ei);
836 // Evaluate space for both sides, only during opening
837 if (pos.non_pawn_material() >= SpaceThreshold)
838 score += evaluate_space<WHITE>(pos, ei)
839 - evaluate_space<BLACK>(pos, ei);
841 // Evaluate position potential for the winning side
842 score += evaluate_initiative(pos, ei.pe->pawn_asymmetry(), eg_value(score));
844 // Evaluate scale factor for the winning side
845 ScaleFactor sf = evaluate_scale_factor(pos, ei, eg_value(score));
847 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
848 v = mg_value(score) * int(ei.me->game_phase())
849 + eg_value(score) * int(PHASE_MIDGAME - ei.me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
851 v /= int(PHASE_MIDGAME);
853 // In case of tracing add all remaining individual evaluation terms
856 Trace::add(MATERIAL, pos.psq_score());
857 Trace::add(IMBALANCE, ei.me->imbalance());
858 Trace::add(PAWN, ei.pe->pawns_score());
859 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
860 if (pos.non_pawn_material() >= SpaceThreshold)
861 Trace::add(SPACE, evaluate_space<WHITE>(pos, ei)
862 , evaluate_space<BLACK>(pos, ei));
863 Trace::add(TOTAL, score);
866 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
869 // Explicit template instantiations
870 template Value Eval::evaluate<true >(const Position&);
871 template Value Eval::evaluate<false>(const Position&);
874 /// trace() is like evaluate(), but instead of returning a value, it returns
875 /// a string (suitable for outputting to stdout) that contains the detailed
876 /// descriptions and values of each evaluation term. Useful for debugging.
878 std::string Eval::trace(const Position& pos) {
880 std::memset(scores, 0, sizeof(scores));
882 Value v = evaluate<true>(pos);
883 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
885 std::stringstream ss;
886 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
887 << " Eval term | White | Black | Total \n"
888 << " | MG EG | MG EG | MG EG \n"
889 << "----------------+-------------+-------------+-------------\n"
890 << " Material | " << Term(MATERIAL)
891 << " Imbalance | " << Term(IMBALANCE)
892 << " Pawns | " << Term(PAWN)
893 << " Knights | " << Term(KNIGHT)
894 << " Bishop | " << Term(BISHOP)
895 << " Rooks | " << Term(ROOK)
896 << " Queens | " << Term(QUEEN)
897 << " Mobility | " << Term(MOBILITY)
898 << " King safety | " << Term(KING)
899 << " Threats | " << Term(THREAT)
900 << " Passed pawns | " << Term(PASSED)
901 << " Space | " << Term(SPACE)
902 << "----------------+-------------+-------------+-------------\n"
903 << " Total | " << Term(TOTAL);
905 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";