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][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] = {
122 { S(-75,-76), S(-56,-54), S( -9,-26), S( -2,-10), S( 6, 5), S( 15, 11), // Knights
123 S( 22, 26), S( 30, 28), S( 36, 29) },
124 { S(-48,-58), S(-21,-19), S( 16, -2), S( 26, 12), S( 37, 22), S( 51, 42), // Bishops
125 S( 54, 54), S( 63, 58), S( 65, 63), S( 71, 70), S( 79, 74), S( 81, 86),
126 S( 92, 90), S( 97, 94) },
127 { S(-56,-78), S(-25,-18), S(-11, 26), S( -5, 55), S( -4, 70), S( -1, 81), // Rooks
128 S( 8,109), S( 14,120), S( 21,128), S( 23,143), S( 31,154), S( 32,160),
129 S( 43,165), S( 49,168), S( 59,169) },
130 { S(-40,-35), S(-25,-12), S( 2, 7), S( 4, 19), S( 14, 37), S( 24, 55), // Queens
131 S( 25, 62), S( 40, 76), S( 43, 79), S( 47, 87), S( 54, 94), S( 56,102),
132 S( 60,111), S( 70,116), S( 72,118), S( 73,122), S( 75,128), S( 77,130),
133 S( 85,133), S( 94,136), S( 99,140), S(108,157), S(112,158), S(113,161),
134 S(118,174), S(119,177), S(123,191), S(128,199) }
137 // Outpost[knight/bishop][supported by pawn] contains bonuses for minor
138 // pieces if they can reach an outpost square, bigger if that square is
139 // supported by a pawn. If the minor piece occupies an outpost square
140 // then score is doubled.
141 const Score Outpost[][2] = {
142 { S(22, 6), S(33, 9) }, // Knight
143 { S( 9, 2), S(14, 4) } // Bishop
146 // RookOnFile[semiopen/open] contains bonuses for each rook when there is no
147 // friendly pawn on the rook file.
148 const Score RookOnFile[2] = { S(20, 7), S(45, 20) };
150 // ThreatBySafePawn[PieceType] contains bonuses according to which piece
151 // type is attacked by a pawn which is protected or is not attacked.
152 const Score ThreatBySafePawn[PIECE_TYPE_NB] = {
153 S(0, 0), S(0, 0), S(176, 139), S(131, 127), S(217, 218), S(203, 215)
156 // ThreatByMinor/ByRook[attacked PieceType] contains bonuses according to
157 // which piece type attacks which one. Attacks on lesser pieces which are
158 // pawn-defended are not considered.
159 const Score ThreatByMinor[PIECE_TYPE_NB] = {
160 S(0, 0), S(0, 33), S(45, 43), S(46, 47), S(72, 107), S(48, 118)
163 const Score ThreatByRook[PIECE_TYPE_NB] = {
164 S(0, 0), S(0, 25), S(40, 62), S(40, 59), S( 0, 34), S(35, 48)
167 // ThreatByKing[on one/on many] contains bonuses for king attacks on
168 // pawns or pieces which are not pawn-defended.
169 const Score ThreatByKing[2] = { S(3, 62), S(9, 138) };
171 // Passed[mg/eg][Rank] contains midgame and endgame bonuses for passed pawns.
172 // We don't use a Score because we process the two components independently.
173 const Value Passed[][RANK_NB] = {
174 { V(5), V( 5), V(31), V(73), V(166), V(252) },
175 { V(7), V(14), V(38), V(73), V(166), V(252) }
178 // PassedFile[File] contains a bonus according to the file of a passed pawn
179 const Score PassedFile[FILE_NB] = {
180 S( 9, 10), S( 2, 10), S( 1, -8), S(-20,-12),
181 S(-20,-12), S( 1, -8), S( 2, 10), S( 9, 10)
184 // Assorted bonuses and penalties used by evaluation
185 const Score MinorBehindPawn = S(16, 0);
186 const Score BishopPawns = S( 8, 12);
187 const Score RookOnPawn = S( 8, 24);
188 const Score TrappedRook = S(92, 0);
189 const Score WeakQueen = S(50, 10);
190 const Score OtherCheck = S(10, 10);
191 const Score CloseEnemies = S( 7, 0);
192 const Score PawnlessFlank = S(20, 80);
193 const Score LooseEnemies = S( 0, 25);
194 const Score ThreatByHangingPawn = S(71, 61);
195 const Score ThreatByRank = S(16, 3);
196 const Score Hanging = S(48, 27);
197 const Score ThreatByPawnPush = S(38, 22);
198 const Score HinderPassedPawn = S( 7, 0);
200 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
201 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
202 // happen in Chess960 games.
203 const Score TrappedBishopA1H1 = S(50, 50);
208 // KingAttackWeights[PieceType] contains king attack weights by piece type
209 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 78, 56, 45, 11 };
211 // Penalties for enemy's safe checks
212 const int QueenContactCheck = 997;
213 const int QueenCheck = 745;
214 const int RookCheck = 688;
215 const int BishopCheck = 588;
216 const int KnightCheck = 924;
218 // Threshold for lazy evaluation
219 const Value LazyThreshold = Value(1500);
221 // eval_init() initializes king and attack bitboards for a given color
222 // adding pawn attacks. To be done at the beginning of the evaluation.
225 void eval_init(const Position& pos, EvalInfo& ei) {
227 const Color Them = (Us == WHITE ? BLACK : WHITE);
228 const Square Up = (Us == WHITE ? NORTH : SOUTH);
229 const Square Down = (Us == WHITE ? SOUTH : NORTH);
230 const Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB: Rank7BB | Rank6BB);
232 // Find our pawns on the first two ranks, and those which are blocked
233 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
235 // Squares occupied by those pawns, by our king, or controlled by enemy pawns
236 // are excluded from the mobility area.
237 ei.mobilityArea[Us] = ~(b | pos.square<KING>(Us) | ei.pe->pawn_attacks(Them));
239 // Initialise the attack bitboards with the king and pawn information
240 b = ei.attackedBy[Us][KING] = pos.attacks_from<KING>(pos.square<KING>(Us));
241 ei.attackedBy[Us][PAWN] = ei.pe->pawn_attacks(Us);
243 ei.attackedBy2[Us] = b & ei.attackedBy[Us][PAWN];
244 ei.attackedBy[Us][ALL_PIECES] = b | ei.attackedBy[Us][PAWN];
246 // Init our king safety tables only if we are going to use them
247 if (pos.non_pawn_material(Them) >= QueenValueMg)
249 ei.kingRing[Us] = b | shift<Up>(b);
250 ei.kingAttackersCount[Them] = popcount(b & ei.pe->pawn_attacks(Them));
251 ei.kingAdjacentZoneAttacksCount[Them] = ei.kingAttackersWeight[Them] = 0;
254 ei.kingRing[Us] = ei.kingAttackersCount[Them] = 0;
258 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given
261 template<bool DoTrace, Color Us = WHITE, PieceType Pt = KNIGHT>
262 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility) {
264 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
265 const Color Them = (Us == WHITE ? BLACK : WHITE);
266 const Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
267 : Rank5BB | Rank4BB | Rank3BB);
268 const Square* pl = pos.squares<Pt>(Us);
272 Score score = SCORE_ZERO;
274 ei.attackedBy[Us][Pt] = 0;
276 while ((s = *pl++) != SQ_NONE)
278 // Find attacked squares, including x-ray attacks for bishops and rooks
279 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
280 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
281 : pos.attacks_from<Pt>(s);
283 if (pos.pinned_pieces(Us) & s)
284 b &= LineBB[pos.square<KING>(Us)][s];
286 ei.attackedBy2[Us] |= ei.attackedBy[Us][ALL_PIECES] & b;
287 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
289 if (b & ei.kingRing[Them])
291 ei.kingAttackersCount[Us]++;
292 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
293 ei.kingAdjacentZoneAttacksCount[Us] += popcount(b & ei.attackedBy[Them][KING]);
297 b &= ~( ei.attackedBy[Them][KNIGHT]
298 | ei.attackedBy[Them][BISHOP]
299 | ei.attackedBy[Them][ROOK]);
301 int mob = popcount(b & ei.mobilityArea[Us]);
303 mobility[Us] += MobilityBonus[Pt][mob];
305 if (Pt == BISHOP || Pt == KNIGHT)
307 // Bonus for outpost squares
308 bb = OutpostRanks & ~ei.pe->pawn_attacks_span(Them);
310 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & s)] * 2;
313 bb &= b & ~pos.pieces(Us);
315 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & bb)];
318 // Bonus when behind a pawn
319 if ( relative_rank(Us, s) < RANK_5
320 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
321 score += MinorBehindPawn;
323 // Penalty for pawns on the same color square as the bishop
325 score -= BishopPawns * ei.pe->pawns_on_same_color_squares(Us, s);
327 // An important Chess960 pattern: A cornered bishop blocked by a friendly
328 // pawn diagonally in front of it is a very serious problem, especially
329 // when that pawn is also blocked.
332 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
334 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
335 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
336 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
337 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
344 // Bonus for aligning with enemy pawns on the same rank/file
345 if (relative_rank(Us, s) >= RANK_5)
346 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
348 // Bonus when on an open or semi-open file
349 if (ei.pe->semiopen_file(Us, file_of(s)))
350 score += RookOnFile[!!ei.pe->semiopen_file(Them, file_of(s))];
352 // Penalty when trapped by the king, even more if the king cannot castle
355 Square ksq = pos.square<KING>(Us);
357 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
358 && !ei.pe->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
359 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
365 // Penalty if any relative pin or discovered attack against the queen
367 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, pinners))
373 Trace::add(Pt, Us, score);
375 // Recursively call evaluate_pieces() of next piece type until KING is excluded
376 return score - evaluate_pieces<DoTrace, Them, NextPt>(pos, ei, mobility);
380 Score evaluate_pieces<false, WHITE, KING>(const Position&, EvalInfo&, Score*) { return SCORE_ZERO; }
382 Score evaluate_pieces< true, WHITE, KING>(const Position&, EvalInfo&, Score*) { return SCORE_ZERO; }
385 // evaluate_king() assigns bonuses and penalties to a king of a given color
387 const Bitboard CenterFiles = FileCBB | FileDBB | FileEBB | FileFBB;
389 const Bitboard KingFlank[FILE_NB] = {
390 CenterFiles >> 2, CenterFiles >> 2, CenterFiles >> 2, CenterFiles, CenterFiles,
391 CenterFiles << 2, CenterFiles << 2, CenterFiles << 2
394 template<Color Us, bool DoTrace>
395 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
397 const Color Them = (Us == WHITE ? BLACK : WHITE);
398 const Square Up = (Us == WHITE ? NORTH : SOUTH);
399 const Bitboard Camp = (Us == WHITE ? ~Bitboard(0) ^ Rank6BB ^ Rank7BB ^ Rank8BB
400 : ~Bitboard(0) ^ Rank1BB ^ Rank2BB ^ Rank3BB);
402 const Square ksq = pos.square<KING>(Us);
403 Bitboard undefended, b, b1, b2, safe, other;
406 // King shelter and enemy pawns storm
407 Score score = ei.pe->king_safety<Us>(pos, ksq);
409 // Main king safety evaluation
410 if (ei.kingAttackersCount[Them])
412 // Find the attacked squares which are defended only by our king...
413 undefended = ei.attackedBy[Them][ALL_PIECES]
414 & ei.attackedBy[Us][KING]
415 & ~ei.attackedBy2[Us];
417 // ... and those which are not defended at all in the larger king ring
418 b = ei.attackedBy[Them][ALL_PIECES] & ~ei.attackedBy[Us][ALL_PIECES]
419 & ei.kingRing[Us] & ~pos.pieces(Them);
421 // Initialize the 'kingDanger' variable, which will be transformed
422 // later into a king danger score. The initial value is based on the
423 // number and types of the enemy's attacking pieces, the number of
424 // attacked and undefended squares around our king and the quality of
425 // the pawn shelter (current 'score' value).
426 kingDanger = std::min(807, ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them])
427 + 101 * ei.kingAdjacentZoneAttacksCount[Them]
428 + 235 * popcount(undefended)
429 + 134 * (popcount(b) + !!pos.pinned_pieces(Us))
430 - 717 * !pos.count<QUEEN>(Them)
431 - 7 * mg_value(score) / 5 - 5;
433 // Analyse the enemy's safe queen contact checks. Firstly, find the
434 // undefended squares around our king reachable by the enemy queen...
435 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);
437 // ...and keep squares supported by another enemy piece.
438 kingDanger += QueenContactCheck * popcount(b & ei.attackedBy2[Them]);
440 // Analyse the safe enemy's checks which are possible on next move
441 safe = ~(ei.attackedBy[Us][ALL_PIECES] | pos.pieces(Them));
443 b1 = pos.attacks_from<ROOK >(ksq);
444 b2 = pos.attacks_from<BISHOP>(ksq);
446 // Enemy queen safe checks
447 if ((b1 | b2) & ei.attackedBy[Them][QUEEN] & safe)
448 kingDanger += QueenCheck;
450 // For minors and rooks, also consider the square safe if attacked twice,
451 // and only defended by our queen.
452 safe |= ei.attackedBy2[Them]
453 & ~(ei.attackedBy2[Us] | pos.pieces(Them))
454 & ei.attackedBy[Us][QUEEN];
456 // Some other potential checks are also analysed, even from squares
457 // currently occupied by the opponent own pieces, as long as the square
458 // is not attacked by our pawns, and is not occupied by a blocked pawn.
459 other = ~( ei.attackedBy[Us][PAWN]
460 | (pos.pieces(Them, PAWN) & shift<Up>(pos.pieces(PAWN))));
462 // Enemy rooks safe and other checks
463 if (b1 & ei.attackedBy[Them][ROOK] & safe)
464 kingDanger += RookCheck;
466 else if (b1 & ei.attackedBy[Them][ROOK] & other)
469 // Enemy bishops safe and other checks
470 if (b2 & ei.attackedBy[Them][BISHOP] & safe)
471 kingDanger += BishopCheck;
473 else if (b2 & ei.attackedBy[Them][BISHOP] & other)
476 // Enemy knights safe and other checks
477 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT];
479 kingDanger += KnightCheck;
484 // Transform the kingDanger units into a Score, and substract it from the evaluation
486 score -= make_score(std::min(kingDanger * kingDanger / 4096, 2 * int(BishopValueMg)), 0);
489 // King tropism: firstly, find squares that opponent attacks in our king flank
490 File kf = file_of(ksq);
491 b = ei.attackedBy[Them][ALL_PIECES] & KingFlank[kf] & Camp;
493 assert(((Us == WHITE ? b << 4 : b >> 4) & b) == 0);
494 assert(popcount(Us == WHITE ? b << 4 : b >> 4) == popcount(b));
496 // Secondly, add the squares which are attacked twice in that flank and
497 // which are not defended by our pawns.
498 b = (Us == WHITE ? b << 4 : b >> 4)
499 | (b & ei.attackedBy2[Them] & ~ei.attackedBy[Us][PAWN]);
501 score -= CloseEnemies * popcount(b);
503 // Penalty when our king is on a pawnless flank
504 if (!(pos.pieces(PAWN) & KingFlank[kf]))
505 score -= PawnlessFlank;
508 Trace::add(KING, Us, score);
514 // evaluate_threats() assigns bonuses according to the types of the attacking
515 // and the attacked pieces.
517 template<Color Us, bool DoTrace>
518 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
520 const Color Them = (Us == WHITE ? BLACK : WHITE);
521 const Square Up = (Us == WHITE ? NORTH : SOUTH);
522 const Square Left = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
523 const Square Right = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
524 const Bitboard TRank2BB = (Us == WHITE ? Rank2BB : Rank7BB);
525 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
527 Bitboard b, weak, defended, safeThreats;
528 Score score = SCORE_ZERO;
530 // Small bonus if the opponent has loose pawns or pieces
531 if ( (pos.pieces(Them) ^ pos.pieces(Them, QUEEN, KING))
532 & ~(ei.attackedBy[Us][ALL_PIECES] | ei.attackedBy[Them][ALL_PIECES]))
533 score += LooseEnemies;
535 // Non-pawn enemies attacked by a pawn
536 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Us][PAWN];
540 b = pos.pieces(Us, PAWN) & ( ~ei.attackedBy[Them][ALL_PIECES]
541 | ei.attackedBy[Us][ALL_PIECES]);
543 safeThreats = (shift<Right>(b) | shift<Left>(b)) & weak;
545 if (weak ^ safeThreats)
546 score += ThreatByHangingPawn;
549 score += ThreatBySafePawn[type_of(pos.piece_on(pop_lsb(&safeThreats)))];
552 // Non-pawn enemies defended by a pawn
553 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Them][PAWN];
555 // Enemies not defended by a pawn and under our attack
556 weak = pos.pieces(Them)
557 & ~ei.attackedBy[Them][PAWN]
558 & ei.attackedBy[Us][ALL_PIECES];
560 // Add a bonus according to the kind of attacking pieces
563 b = (defended | weak) & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
566 Square s = pop_lsb(&b);
567 score += ThreatByMinor[type_of(pos.piece_on(s))];
568 if (type_of(pos.piece_on(s)) != PAWN)
569 score += ThreatByRank * (int)relative_rank(Them, s);
572 b = (pos.pieces(Them, QUEEN) | weak) & ei.attackedBy[Us][ROOK];
575 Square s = pop_lsb(&b);
576 score += ThreatByRook[type_of(pos.piece_on(s))];
577 if (type_of(pos.piece_on(s)) != PAWN)
578 score += ThreatByRank * (int)relative_rank(Them, s);
581 score += Hanging * popcount(weak & ~ei.attackedBy[Them][ALL_PIECES]);
583 b = weak & ei.attackedBy[Us][KING];
585 score += ThreatByKing[more_than_one(b)];
588 // Bonus if some pawns can safely push and attack an enemy piece
589 b = pos.pieces(Us, PAWN) & ~TRank7BB;
590 b = shift<Up>(b | (shift<Up>(b & TRank2BB) & ~pos.pieces()));
593 & ~ei.attackedBy[Them][PAWN]
594 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
596 b = (shift<Left>(b) | shift<Right>(b))
598 & ~ei.attackedBy[Us][PAWN];
600 score += ThreatByPawnPush * popcount(b);
603 Trace::add(THREAT, Us, score);
609 // evaluate_passer_pawns() evaluates the passed pawns and candidate passed
610 // pawns of the given color.
612 template<Color Us, bool DoTrace>
613 Score evaluate_passer_pawns(const Position& pos, const EvalInfo& ei) {
615 const Color Them = (Us == WHITE ? BLACK : WHITE);
617 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
618 Score score = SCORE_ZERO;
620 b = ei.pe->passed_pawns(Us);
624 Square s = pop_lsb(&b);
626 assert(!(pos.pieces(PAWN) & forward_bb(Us, s)));
628 bb = forward_bb(Us, s) & (ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
629 score -= HinderPassedPawn * popcount(bb);
631 int r = relative_rank(Us, s) - RANK_2;
632 int rr = r * (r - 1);
634 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
638 Square blockSq = s + pawn_push(Us);
640 // Adjust bonus based on the king's proximity
641 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
642 - distance(pos.square<KING>(Us ), blockSq) * 2 * rr;
644 // If blockSq is not the queening square then consider also a second push
645 if (relative_rank(Us, blockSq) != RANK_8)
646 ebonus -= distance(pos.square<KING>(Us), blockSq + pawn_push(Us)) * rr;
648 // If the pawn is free to advance, then increase the bonus
649 if (pos.empty(blockSq))
651 // If there is a rook or queen attacking/defending the pawn from behind,
652 // consider all the squaresToQueen. Otherwise consider only the squares
653 // in the pawn's path attacked or occupied by the enemy.
654 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
656 bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
658 if (!(pos.pieces(Us) & bb))
659 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
661 if (!(pos.pieces(Them) & bb))
662 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
664 // If there aren't any enemy attacks, assign a big bonus. Otherwise
665 // assign a smaller bonus if the block square isn't attacked.
666 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
668 // If the path to the queen is fully defended, assign a big bonus.
669 // Otherwise assign a smaller bonus if the block square is defended.
670 if (defendedSquares == squaresToQueen)
673 else if (defendedSquares & blockSq)
676 mbonus += k * rr, ebonus += k * rr;
678 else if (pos.pieces(Us) & blockSq)
679 mbonus += rr + r * 2, ebonus += rr + r * 2;
682 // Assign a small bonus when the opponent has no pieces left
683 if (!pos.non_pawn_material(Them))
686 // Scale down bonus for candidate passers which need more than one pawn
687 // push to become passed.
688 if (!pos.pawn_passed(Us, s + pawn_push(Us)))
689 mbonus /= 2, ebonus /= 2;
691 score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
695 Trace::add(PASSED, Us, score);
697 // Add the scores to the middlegame and endgame eval
702 // evaluate_space() computes the space evaluation for a given side. The
703 // space evaluation is a simple bonus based on the number of safe squares
704 // available for minor pieces on the central four files on ranks 2--4. Safe
705 // squares one, two or three squares behind a friendly pawn are counted
706 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
707 // improve play on game opening.
709 Score evaluate_space(const Position& pos, const EvalInfo& ei) {
711 const Color Them = (Us == WHITE ? BLACK : WHITE);
712 const Bitboard SpaceMask =
713 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
714 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
716 // Find the safe squares for our pieces inside the area defined by
717 // SpaceMask. A square is unsafe if it is attacked by an enemy
718 // pawn, or if it is undefended and attacked by an enemy piece.
719 Bitboard safe = SpaceMask
720 & ~pos.pieces(Us, PAWN)
721 & ~ei.attackedBy[Them][PAWN]
722 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
724 // Find all squares which are at most three squares behind some friendly pawn
725 Bitboard behind = pos.pieces(Us, PAWN);
726 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
727 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
729 // Since SpaceMask[Us] is fully on our half of the board...
730 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
732 // ...count safe + (behind & safe) with a single popcount.
733 int bonus = popcount((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
734 bonus = std::min(16, bonus);
735 int weight = pos.count<ALL_PIECES>(Us) - 2 * ei.pe->open_files();
737 return make_score(bonus * weight * weight / 18, 0);
741 // evaluate_initiative() computes the initiative correction value for the
742 // position, i.e., second order bonus/malus based on the known attacking/defending
743 // status of the players.
744 Score evaluate_initiative(const Position& pos, int asymmetry, Value eg) {
746 int kingDistance = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
747 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
748 int pawns = pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK);
750 // Compute the initiative bonus for the attacking side
751 int initiative = 8 * (asymmetry + kingDistance - 15) + 12 * pawns;
753 // Now apply the bonus: note that we find the attacking side by extracting
754 // the sign of the endgame value, and that we carefully cap the bonus so
755 // that the endgame score will never be divided by more than two.
756 int value = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg / 2));
758 return make_score(0, value);
762 // evaluate_scale_factor() computes the scale factor for the winning side
763 ScaleFactor evaluate_scale_factor(const Position& pos, const EvalInfo& ei, Value eg) {
765 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
766 ScaleFactor sf = ei.me->scale_factor(pos, strongSide);
768 // If we don't already have an unusual scale factor, check for certain
769 // types of endgames, and use a lower scale for those.
770 if ( ei.me->game_phase() < PHASE_MIDGAME
771 && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
773 if (pos.opposite_bishops())
775 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
776 // is almost a draw, in case of KBP vs KB, it is even more a draw.
777 if ( pos.non_pawn_material(WHITE) == BishopValueMg
778 && pos.non_pawn_material(BLACK) == BishopValueMg)
779 sf = more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
781 // Endgame with opposite-colored bishops, but also other pieces. Still
782 // a bit drawish, but not as drawish as with only the two bishops.
784 sf = ScaleFactor(46);
786 // Endings where weaker side can place his king in front of the opponent's
787 // pawns are drawish.
788 else if ( abs(eg) <= BishopValueEg
789 && pos.count<PAWN>(strongSide) <= 2
790 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
791 sf = ScaleFactor(37 + 7 * pos.count<PAWN>(strongSide));
800 /// evaluate() is the main evaluation function. It returns a static evaluation
801 /// of the position from the point of view of the side to move.
803 template<bool DoTrace>
804 Value Eval::evaluate(const Position& pos) {
806 assert(!pos.checkers());
808 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
812 // Probe the material hash table
813 ei.me = Material::probe(pos);
815 // If we have a specialized evaluation function for the current material
816 // configuration, call it and return.
817 if (ei.me->specialized_eval_exists())
818 return ei.me->evaluate(pos);
820 // Initialize score by reading the incrementally updated scores included in
821 // the position object (material + piece square tables) and the material
822 // imbalance. Score is computed internally from the white point of view.
823 Score score = pos.psq_score() + ei.me->imbalance();
825 // Probe the pawn hash table
826 ei.pe = Pawns::probe(pos);
827 score += ei.pe->pawns_score();
829 // Early exit if score is high
830 v = (mg_value(score) + eg_value(score)) / 2;
831 if (abs(v) > LazyThreshold)
832 return pos.side_to_move() == WHITE ? v : -v;
834 // Initialize attack and king safety bitboards
835 eval_init<WHITE>(pos, ei);
836 eval_init<BLACK>(pos, ei);
838 // Evaluate all pieces but king and pawns
839 score += evaluate_pieces<DoTrace>(pos, ei, mobility);
840 score += mobility[WHITE] - mobility[BLACK];
842 // Evaluate kings after all other pieces because we need full attack
843 // information when computing the king safety evaluation.
844 score += evaluate_king<WHITE, DoTrace>(pos, ei)
845 - evaluate_king<BLACK, DoTrace>(pos, ei);
847 // Evaluate tactical threats, we need full attack information including king
848 score += evaluate_threats<WHITE, DoTrace>(pos, ei)
849 - evaluate_threats<BLACK, DoTrace>(pos, ei);
851 // Evaluate passed pawns, we need full attack information including king
852 score += evaluate_passer_pawns<WHITE, DoTrace>(pos, ei)
853 - evaluate_passer_pawns<BLACK, DoTrace>(pos, ei);
855 // Evaluate space for both sides, only during opening
856 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
857 score += evaluate_space<WHITE>(pos, ei)
858 - evaluate_space<BLACK>(pos, ei);
860 // Evaluate position potential for the winning side
861 score += evaluate_initiative(pos, ei.pe->pawn_asymmetry(), eg_value(score));
863 // Evaluate scale factor for the winning side
864 ScaleFactor sf = evaluate_scale_factor(pos, ei, eg_value(score));
866 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
867 v = mg_value(score) * int(ei.me->game_phase())
868 + eg_value(score) * int(PHASE_MIDGAME - ei.me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
870 v /= int(PHASE_MIDGAME);
872 // In case of tracing add all remaining individual evaluation terms
875 Trace::add(MATERIAL, pos.psq_score());
876 Trace::add(IMBALANCE, ei.me->imbalance());
877 Trace::add(PAWN, ei.pe->pawns_score());
878 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
879 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
880 Trace::add(SPACE, evaluate_space<WHITE>(pos, ei)
881 , evaluate_space<BLACK>(pos, ei));
882 Trace::add(TOTAL, score);
885 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
888 // Explicit template instantiations
889 template Value Eval::evaluate<true >(const Position&);
890 template Value Eval::evaluate<false>(const Position&);
893 /// trace() is like evaluate(), but instead of returning a value, it returns
894 /// a string (suitable for outputting to stdout) that contains the detailed
895 /// descriptions and values of each evaluation term. Useful for debugging.
897 std::string Eval::trace(const Position& pos) {
899 std::memset(scores, 0, sizeof(scores));
901 Value v = evaluate<true>(pos);
902 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
904 std::stringstream ss;
905 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
906 << " Eval term | White | Black | Total \n"
907 << " | MG EG | MG EG | MG EG \n"
908 << "----------------+-------------+-------------+-------------\n"
909 << " Material | " << Term(MATERIAL)
910 << " Imbalance | " << Term(IMBALANCE)
911 << " Pawns | " << Term(PAWN)
912 << " Knights | " << Term(KNIGHT)
913 << " Bishop | " << Term(BISHOP)
914 << " Rooks | " << Term(ROOK)
915 << " Queens | " << Term(QUEEN)
916 << " Mobility | " << Term(MOBILITY)
917 << " King safety | " << Term(KING)
918 << " Threats | " << Term(THREAT)
919 << " Passed pawns | " << Term(PASSED)
920 << " Space | " << Term(SPACE)
921 << "----------------+-------------+-------------+-------------\n"
922 << " Total | " << Term(TOTAL);
924 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";