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 QueenCheck = 745;
213 const int RookCheck = 688;
214 const int BishopCheck = 588;
215 const int KnightCheck = 924;
217 // Threshold for lazy evaluation
218 const Value LazyThreshold = Value(1500);
220 // eval_init() initializes king and attack bitboards for a given color
221 // adding pawn attacks. To be done at the beginning of the evaluation.
224 void eval_init(const Position& pos, EvalInfo& ei) {
226 const Color Them = (Us == WHITE ? BLACK : WHITE);
227 const Square Up = (Us == WHITE ? NORTH : SOUTH);
228 const Square Down = (Us == WHITE ? SOUTH : NORTH);
229 const Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB: Rank7BB | Rank6BB);
231 // Find our pawns on the first two ranks, and those which are blocked
232 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
234 // Squares occupied by those pawns, by our king, or controlled by enemy pawns
235 // are excluded from the mobility area.
236 ei.mobilityArea[Us] = ~(b | pos.square<KING>(Us) | ei.pe->pawn_attacks(Them));
238 // Initialise the attack bitboards with the king and pawn information
239 b = ei.attackedBy[Us][KING] = pos.attacks_from<KING>(pos.square<KING>(Us));
240 ei.attackedBy[Us][PAWN] = ei.pe->pawn_attacks(Us);
242 ei.attackedBy2[Us] = b & ei.attackedBy[Us][PAWN];
243 ei.attackedBy[Us][ALL_PIECES] = b | ei.attackedBy[Us][PAWN];
245 // Init our king safety tables only if we are going to use them
246 if (pos.non_pawn_material(Them) >= QueenValueMg)
248 ei.kingRing[Us] = b | shift<Up>(b);
249 ei.kingAttackersCount[Them] = popcount(b & ei.pe->pawn_attacks(Them));
250 ei.kingAdjacentZoneAttacksCount[Them] = ei.kingAttackersWeight[Them] = 0;
253 ei.kingRing[Us] = ei.kingAttackersCount[Them] = 0;
257 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given
260 template<bool DoTrace, Color Us = WHITE, PieceType Pt = KNIGHT>
261 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility) {
263 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
264 const Color Them = (Us == WHITE ? BLACK : WHITE);
265 const Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
266 : Rank5BB | Rank4BB | Rank3BB);
267 const Square* pl = pos.squares<Pt>(Us);
271 Score score = SCORE_ZERO;
273 ei.attackedBy[Us][Pt] = 0;
275 while ((s = *pl++) != SQ_NONE)
277 // Find attacked squares, including x-ray attacks for bishops and rooks
278 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
279 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
280 : pos.attacks_from<Pt>(s);
282 if (pos.pinned_pieces(Us) & s)
283 b &= LineBB[pos.square<KING>(Us)][s];
285 ei.attackedBy2[Us] |= ei.attackedBy[Us][ALL_PIECES] & b;
286 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
288 if (b & ei.kingRing[Them])
290 ei.kingAttackersCount[Us]++;
291 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
292 ei.kingAdjacentZoneAttacksCount[Us] += popcount(b & ei.attackedBy[Them][KING]);
296 b &= ~( ei.attackedBy[Them][KNIGHT]
297 | ei.attackedBy[Them][BISHOP]
298 | ei.attackedBy[Them][ROOK]);
300 int mob = popcount(b & ei.mobilityArea[Us]);
302 mobility[Us] += MobilityBonus[Pt][mob];
304 if (Pt == BISHOP || Pt == KNIGHT)
306 // Bonus for outpost squares
307 bb = OutpostRanks & ~ei.pe->pawn_attacks_span(Them);
309 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & s)] * 2;
312 bb &= b & ~pos.pieces(Us);
314 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & bb)];
317 // Bonus when behind a pawn
318 if ( relative_rank(Us, s) < RANK_5
319 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
320 score += MinorBehindPawn;
322 // Penalty for pawns on the same color square as the bishop
324 score -= BishopPawns * ei.pe->pawns_on_same_color_squares(Us, s);
326 // An important Chess960 pattern: A cornered bishop blocked by a friendly
327 // pawn diagonally in front of it is a very serious problem, especially
328 // when that pawn is also blocked.
331 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
333 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
334 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
335 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
336 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
343 // Bonus for aligning with enemy pawns on the same rank/file
344 if (relative_rank(Us, s) >= RANK_5)
345 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
347 // Bonus when on an open or semi-open file
348 if (ei.pe->semiopen_file(Us, file_of(s)))
349 score += RookOnFile[!!ei.pe->semiopen_file(Them, file_of(s))];
351 // Penalty when trapped by the king, even more if the king cannot castle
354 Square ksq = pos.square<KING>(Us);
356 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
357 && !ei.pe->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
358 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
364 // Penalty if any relative pin or discovered attack against the queen
366 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, pinners))
372 Trace::add(Pt, Us, score);
374 // Recursively call evaluate_pieces() of next piece type until KING is excluded
375 return score - evaluate_pieces<DoTrace, Them, NextPt>(pos, ei, mobility);
379 Score evaluate_pieces<false, WHITE, KING>(const Position&, EvalInfo&, Score*) { return SCORE_ZERO; }
381 Score evaluate_pieces< true, WHITE, KING>(const Position&, EvalInfo&, Score*) { return SCORE_ZERO; }
384 // evaluate_king() assigns bonuses and penalties to a king of a given color
386 const Bitboard CenterFiles = FileCBB | FileDBB | FileEBB | FileFBB;
388 const Bitboard KingFlank[FILE_NB] = {
389 CenterFiles >> 2, CenterFiles >> 2, CenterFiles >> 2, CenterFiles, CenterFiles,
390 CenterFiles << 2, CenterFiles << 2, CenterFiles << 2
393 template<Color Us, bool DoTrace>
394 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
396 const Color Them = (Us == WHITE ? BLACK : WHITE);
397 const Square Up = (Us == WHITE ? NORTH : SOUTH);
398 const Bitboard Camp = (Us == WHITE ? ~Bitboard(0) ^ Rank6BB ^ Rank7BB ^ Rank8BB
399 : ~Bitboard(0) ^ Rank1BB ^ Rank2BB ^ Rank3BB);
401 const Square ksq = pos.square<KING>(Us);
402 Bitboard undefended, b, b1, b2, safe, other;
405 // King shelter and enemy pawns storm
406 Score score = ei.pe->king_safety<Us>(pos, ksq);
408 // Main king safety evaluation
409 if (ei.kingAttackersCount[Them])
411 // Find the attacked squares which are defended only by our king...
412 undefended = ei.attackedBy[Them][ALL_PIECES]
413 & ei.attackedBy[Us][KING]
414 & ~ei.attackedBy2[Us];
416 // ... and those which are not defended at all in the larger king ring
417 b = ei.attackedBy[Them][ALL_PIECES] & ~ei.attackedBy[Us][ALL_PIECES]
418 & ei.kingRing[Us] & ~pos.pieces(Them);
420 // Initialize the 'kingDanger' variable, which will be transformed
421 // later into a king danger score. The initial value is based on the
422 // number and types of the enemy's attacking pieces, the number of
423 // attacked and undefended squares around our king and the quality of
424 // the pawn shelter (current 'score' value).
425 kingDanger = std::min(807, ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them])
426 + 101 * ei.kingAdjacentZoneAttacksCount[Them]
427 + 235 * popcount(undefended)
428 + 134 * (popcount(b) + !!pos.pinned_pieces(Us))
429 - 717 * !pos.count<QUEEN>(Them)
430 - 7 * mg_value(score) / 5 - 5;
432 // Analyse the safe enemy's checks which are possible on next move
433 safe = ~pos.pieces(Them);
434 safe &= ~ei.attackedBy[Us][ALL_PIECES] | (undefended & ei.attackedBy2[Them]);
436 b1 = pos.attacks_from<ROOK >(ksq);
437 b2 = pos.attacks_from<BISHOP>(ksq);
439 // Enemy queen safe checks
440 if ((b1 | b2) & ei.attackedBy[Them][QUEEN] & safe)
441 kingDanger += QueenCheck;
443 // For minors and rooks, also consider the square safe if attacked twice,
444 // and only defended by our queen.
445 safe |= ei.attackedBy2[Them]
446 & ~(ei.attackedBy2[Us] | pos.pieces(Them))
447 & ei.attackedBy[Us][QUEEN];
449 // Some other potential checks are also analysed, even from squares
450 // currently occupied by the opponent own pieces, as long as the square
451 // is not attacked by our pawns, and is not occupied by a blocked pawn.
452 other = ~( ei.attackedBy[Us][PAWN]
453 | (pos.pieces(Them, PAWN) & shift<Up>(pos.pieces(PAWN))));
455 // Enemy rooks safe and other checks
456 if (b1 & ei.attackedBy[Them][ROOK] & safe)
457 kingDanger += RookCheck;
459 else if (b1 & ei.attackedBy[Them][ROOK] & other)
462 // Enemy bishops safe and other checks
463 if (b2 & ei.attackedBy[Them][BISHOP] & safe)
464 kingDanger += BishopCheck;
466 else if (b2 & ei.attackedBy[Them][BISHOP] & other)
469 // Enemy knights safe and other checks
470 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT];
472 kingDanger += KnightCheck;
477 // Transform the kingDanger units into a Score, and substract it from the evaluation
479 score -= make_score(std::min(kingDanger * kingDanger / 4096, 2 * int(BishopValueMg)), 0);
482 // King tropism: firstly, find squares that opponent attacks in our king flank
483 File kf = file_of(ksq);
484 b = ei.attackedBy[Them][ALL_PIECES] & KingFlank[kf] & Camp;
486 assert(((Us == WHITE ? b << 4 : b >> 4) & b) == 0);
487 assert(popcount(Us == WHITE ? b << 4 : b >> 4) == popcount(b));
489 // Secondly, add the squares which are attacked twice in that flank and
490 // which are not defended by our pawns.
491 b = (Us == WHITE ? b << 4 : b >> 4)
492 | (b & ei.attackedBy2[Them] & ~ei.attackedBy[Us][PAWN]);
494 score -= CloseEnemies * popcount(b);
496 // Penalty when our king is on a pawnless flank
497 if (!(pos.pieces(PAWN) & KingFlank[kf]))
498 score -= PawnlessFlank;
501 Trace::add(KING, Us, score);
507 // evaluate_threats() assigns bonuses according to the types of the attacking
508 // and the attacked pieces.
510 template<Color Us, bool DoTrace>
511 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
513 const Color Them = (Us == WHITE ? BLACK : WHITE);
514 const Square Up = (Us == WHITE ? NORTH : SOUTH);
515 const Square Left = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
516 const Square Right = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
517 const Bitboard TRank2BB = (Us == WHITE ? Rank2BB : Rank7BB);
518 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
520 Bitboard b, weak, defended, safeThreats;
521 Score score = SCORE_ZERO;
523 // Small bonus if the opponent has loose pawns or pieces
524 if ( (pos.pieces(Them) ^ pos.pieces(Them, QUEEN, KING))
525 & ~(ei.attackedBy[Us][ALL_PIECES] | ei.attackedBy[Them][ALL_PIECES]))
526 score += LooseEnemies;
528 // Non-pawn enemies attacked by a pawn
529 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Us][PAWN];
533 b = pos.pieces(Us, PAWN) & ( ~ei.attackedBy[Them][ALL_PIECES]
534 | ei.attackedBy[Us][ALL_PIECES]);
536 safeThreats = (shift<Right>(b) | shift<Left>(b)) & weak;
538 if (weak ^ safeThreats)
539 score += ThreatByHangingPawn;
542 score += ThreatBySafePawn[type_of(pos.piece_on(pop_lsb(&safeThreats)))];
545 // Non-pawn enemies defended by a pawn
546 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Them][PAWN];
548 // Enemies not defended by a pawn and under our attack
549 weak = pos.pieces(Them)
550 & ~ei.attackedBy[Them][PAWN]
551 & ei.attackedBy[Us][ALL_PIECES];
553 // Add a bonus according to the kind of attacking pieces
556 b = (defended | weak) & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
559 Square s = pop_lsb(&b);
560 score += ThreatByMinor[type_of(pos.piece_on(s))];
561 if (type_of(pos.piece_on(s)) != PAWN)
562 score += ThreatByRank * (int)relative_rank(Them, s);
565 b = (pos.pieces(Them, QUEEN) | weak) & ei.attackedBy[Us][ROOK];
568 Square s = pop_lsb(&b);
569 score += ThreatByRook[type_of(pos.piece_on(s))];
570 if (type_of(pos.piece_on(s)) != PAWN)
571 score += ThreatByRank * (int)relative_rank(Them, s);
574 score += Hanging * popcount(weak & ~ei.attackedBy[Them][ALL_PIECES]);
576 b = weak & ei.attackedBy[Us][KING];
578 score += ThreatByKing[more_than_one(b)];
581 // Bonus if some pawns can safely push and attack an enemy piece
582 b = pos.pieces(Us, PAWN) & ~TRank7BB;
583 b = shift<Up>(b | (shift<Up>(b & TRank2BB) & ~pos.pieces()));
586 & ~ei.attackedBy[Them][PAWN]
587 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
589 b = (shift<Left>(b) | shift<Right>(b))
591 & ~ei.attackedBy[Us][PAWN];
593 score += ThreatByPawnPush * popcount(b);
596 Trace::add(THREAT, Us, score);
602 // evaluate_passer_pawns() evaluates the passed pawns and candidate passed
603 // pawns of the given color.
605 template<Color Us, bool DoTrace>
606 Score evaluate_passer_pawns(const Position& pos, const EvalInfo& ei) {
608 const Color Them = (Us == WHITE ? BLACK : WHITE);
610 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
611 Score score = SCORE_ZERO;
613 b = ei.pe->passed_pawns(Us);
617 Square s = pop_lsb(&b);
619 assert(!(pos.pieces(PAWN) & forward_bb(Us, s)));
621 bb = forward_bb(Us, s) & (ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
622 score -= HinderPassedPawn * popcount(bb);
624 int r = relative_rank(Us, s) - RANK_2;
625 int rr = r * (r - 1);
627 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
631 Square blockSq = s + pawn_push(Us);
633 // Adjust bonus based on the king's proximity
634 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
635 - distance(pos.square<KING>(Us ), blockSq) * 2 * rr;
637 // If blockSq is not the queening square then consider also a second push
638 if (relative_rank(Us, blockSq) != RANK_8)
639 ebonus -= distance(pos.square<KING>(Us), blockSq + pawn_push(Us)) * rr;
641 // If the pawn is free to advance, then increase the bonus
642 if (pos.empty(blockSq))
644 // If there is a rook or queen attacking/defending the pawn from behind,
645 // consider all the squaresToQueen. Otherwise consider only the squares
646 // in the pawn's path attacked or occupied by the enemy.
647 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
649 bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
651 if (!(pos.pieces(Us) & bb))
652 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
654 if (!(pos.pieces(Them) & bb))
655 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
657 // If there aren't any enemy attacks, assign a big bonus. Otherwise
658 // assign a smaller bonus if the block square isn't attacked.
659 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
661 // If the path to the queen is fully defended, assign a big bonus.
662 // Otherwise assign a smaller bonus if the block square is defended.
663 if (defendedSquares == squaresToQueen)
666 else if (defendedSquares & blockSq)
669 mbonus += k * rr, ebonus += k * rr;
671 else if (pos.pieces(Us) & blockSq)
672 mbonus += rr + r * 2, ebonus += rr + r * 2;
675 // Assign a small bonus when the opponent has no pieces left
676 if (!pos.non_pawn_material(Them))
679 // Scale down bonus for candidate passers which need more than one pawn
680 // push to become passed.
681 if (!pos.pawn_passed(Us, s + pawn_push(Us)))
682 mbonus /= 2, ebonus /= 2;
684 score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
688 Trace::add(PASSED, Us, score);
690 // Add the scores to the middlegame and endgame eval
695 // evaluate_space() computes the space evaluation for a given side. The
696 // space evaluation is a simple bonus based on the number of safe squares
697 // available for minor pieces on the central four files on ranks 2--4. Safe
698 // squares one, two or three squares behind a friendly pawn are counted
699 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
700 // improve play on game opening.
702 Score evaluate_space(const Position& pos, const EvalInfo& ei) {
704 const Color Them = (Us == WHITE ? BLACK : WHITE);
705 const Bitboard SpaceMask =
706 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
707 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
709 // Find the safe squares for our pieces inside the area defined by
710 // SpaceMask. A square is unsafe if it is attacked by an enemy
711 // pawn, or if it is undefended and attacked by an enemy piece.
712 Bitboard safe = SpaceMask
713 & ~pos.pieces(Us, PAWN)
714 & ~ei.attackedBy[Them][PAWN]
715 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
717 // Find all squares which are at most three squares behind some friendly pawn
718 Bitboard behind = pos.pieces(Us, PAWN);
719 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
720 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
722 // Since SpaceMask[Us] is fully on our half of the board...
723 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
725 // ...count safe + (behind & safe) with a single popcount.
726 int bonus = popcount((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
727 bonus = std::min(16, bonus);
728 int weight = pos.count<ALL_PIECES>(Us) - 2 * ei.pe->open_files();
730 return make_score(bonus * weight * weight / 18, 0);
734 // evaluate_initiative() computes the initiative correction value for the
735 // position, i.e., second order bonus/malus based on the known attacking/defending
736 // status of the players.
737 Score evaluate_initiative(const Position& pos, int asymmetry, Value eg) {
739 int kingDistance = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
740 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
741 int pawns = pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK);
743 // Compute the initiative bonus for the attacking side
744 int initiative = 8 * (asymmetry + kingDistance - 15) + 12 * pawns;
746 // Now apply the bonus: note that we find the attacking side by extracting
747 // the sign of the endgame value, and that we carefully cap the bonus so
748 // that the endgame score will never be divided by more than two.
749 int value = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg / 2));
751 return make_score(0, value);
755 // evaluate_scale_factor() computes the scale factor for the winning side
756 ScaleFactor evaluate_scale_factor(const Position& pos, const EvalInfo& ei, Value eg) {
758 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
759 ScaleFactor sf = ei.me->scale_factor(pos, strongSide);
761 // If we don't already have an unusual scale factor, check for certain
762 // types of endgames, and use a lower scale for those.
763 if ( ei.me->game_phase() < PHASE_MIDGAME
764 && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
766 if (pos.opposite_bishops())
768 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
769 // is almost a draw, in case of KBP vs KB, it is even more a draw.
770 if ( pos.non_pawn_material(WHITE) == BishopValueMg
771 && pos.non_pawn_material(BLACK) == BishopValueMg)
772 sf = more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
774 // Endgame with opposite-colored bishops, but also other pieces. Still
775 // a bit drawish, but not as drawish as with only the two bishops.
777 sf = ScaleFactor(46);
779 // Endings where weaker side can place his king in front of the opponent's
780 // pawns are drawish.
781 else if ( abs(eg) <= BishopValueEg
782 && pos.count<PAWN>(strongSide) <= 2
783 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
784 sf = ScaleFactor(37 + 7 * pos.count<PAWN>(strongSide));
793 /// evaluate() is the main evaluation function. It returns a static evaluation
794 /// of the position from the point of view of the side to move.
796 template<bool DoTrace>
797 Value Eval::evaluate(const Position& pos) {
799 assert(!pos.checkers());
801 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
805 // Probe the material hash table
806 ei.me = Material::probe(pos);
808 // If we have a specialized evaluation function for the current material
809 // configuration, call it and return.
810 if (ei.me->specialized_eval_exists())
811 return ei.me->evaluate(pos);
813 // Initialize score by reading the incrementally updated scores included in
814 // the position object (material + piece square tables) and the material
815 // imbalance. Score is computed internally from the white point of view.
816 Score score = pos.psq_score() + ei.me->imbalance();
818 // Probe the pawn hash table
819 ei.pe = Pawns::probe(pos);
820 score += ei.pe->pawns_score();
822 // Early exit if score is high
823 v = (mg_value(score) + eg_value(score)) / 2;
824 if (abs(v) > LazyThreshold)
825 return pos.side_to_move() == WHITE ? v : -v;
827 // Initialize attack and king safety bitboards
828 eval_init<WHITE>(pos, ei);
829 eval_init<BLACK>(pos, ei);
831 // Evaluate all pieces but king and pawns
832 score += evaluate_pieces<DoTrace>(pos, ei, mobility);
833 score += mobility[WHITE] - mobility[BLACK];
835 // Evaluate kings after all other pieces because we need full attack
836 // information when computing the king safety evaluation.
837 score += evaluate_king<WHITE, DoTrace>(pos, ei)
838 - evaluate_king<BLACK, DoTrace>(pos, ei);
840 // Evaluate tactical threats, we need full attack information including king
841 score += evaluate_threats<WHITE, DoTrace>(pos, ei)
842 - evaluate_threats<BLACK, DoTrace>(pos, ei);
844 // Evaluate passed pawns, we need full attack information including king
845 score += evaluate_passer_pawns<WHITE, DoTrace>(pos, ei)
846 - evaluate_passer_pawns<BLACK, DoTrace>(pos, ei);
848 // Evaluate space for both sides, only during opening
849 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
850 score += evaluate_space<WHITE>(pos, ei)
851 - evaluate_space<BLACK>(pos, ei);
853 // Evaluate position potential for the winning side
854 score += evaluate_initiative(pos, ei.pe->pawn_asymmetry(), eg_value(score));
856 // Evaluate scale factor for the winning side
857 ScaleFactor sf = evaluate_scale_factor(pos, ei, eg_value(score));
859 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
860 v = mg_value(score) * int(ei.me->game_phase())
861 + eg_value(score) * int(PHASE_MIDGAME - ei.me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
863 v /= int(PHASE_MIDGAME);
865 // In case of tracing add all remaining individual evaluation terms
868 Trace::add(MATERIAL, pos.psq_score());
869 Trace::add(IMBALANCE, ei.me->imbalance());
870 Trace::add(PAWN, ei.pe->pawns_score());
871 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
872 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
873 Trace::add(SPACE, evaluate_space<WHITE>(pos, ei)
874 , evaluate_space<BLACK>(pos, ei));
875 Trace::add(TOTAL, score);
878 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
881 // Explicit template instantiations
882 template Value Eval::evaluate<true >(const Position&);
883 template Value Eval::evaluate<false>(const Position&);
886 /// trace() is like evaluate(), but instead of returning a value, it returns
887 /// a string (suitable for outputting to stdout) that contains the detailed
888 /// descriptions and values of each evaluation term. Useful for debugging.
890 std::string Eval::trace(const Position& pos) {
892 std::memset(scores, 0, sizeof(scores));
894 Value v = evaluate<true>(pos);
895 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
897 std::stringstream ss;
898 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
899 << " Eval term | White | Black | Total \n"
900 << " | MG EG | MG EG | MG EG \n"
901 << "----------------+-------------+-------------+-------------\n"
902 << " Material | " << Term(MATERIAL)
903 << " Imbalance | " << Term(IMBALANCE)
904 << " Pawns | " << Term(PAWN)
905 << " Knights | " << Term(KNIGHT)
906 << " Bishop | " << Term(BISHOP)
907 << " Rooks | " << Term(ROOK)
908 << " Queens | " << Term(QUEEN)
909 << " Mobility | " << Term(MOBILITY)
910 << " King safety | " << Term(KING)
911 << " Threats | " << Term(THREAT)
912 << " Passed pawns | " << Term(PASSED)
913 << " Space | " << Term(SPACE)
914 << "----------------+-------------+-------------+-------------\n"
915 << " Total | " << Term(TOTAL);
917 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";