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 ThreatByHangingPawn = S(71, 61);
194 const Score ThreatByRank = S(16, 3);
195 const Score Hanging = S(48, 27);
196 const Score ThreatByPawnPush = S(38, 22);
197 const Score HinderPassedPawn = S( 7, 0);
199 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
200 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
201 // happen in Chess960 games.
202 const Score TrappedBishopA1H1 = S(50, 50);
207 // KingAttackWeights[PieceType] contains king attack weights by piece type
208 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 78, 56, 45, 11 };
210 // Penalties for enemy's safe checks
211 const int QueenCheck = 745;
212 const int RookCheck = 688;
213 const int BishopCheck = 588;
214 const int KnightCheck = 924;
216 // Threshold for lazy evaluation
217 const Value LazyThreshold = Value(1500);
219 // eval_init() initializes king and attack bitboards for a given color
220 // adding pawn attacks. To be done at the beginning of the evaluation.
223 void eval_init(const Position& pos, EvalInfo& ei) {
225 const Color Them = (Us == WHITE ? BLACK : WHITE);
226 const Square Up = (Us == WHITE ? NORTH : SOUTH);
227 const Square Down = (Us == WHITE ? SOUTH : NORTH);
228 const Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB: Rank7BB | Rank6BB);
230 // Find our pawns on the first two ranks, and those which are blocked
231 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
233 // Squares occupied by those pawns, by our king, or controlled by enemy pawns
234 // are excluded from the mobility area.
235 ei.mobilityArea[Us] = ~(b | pos.square<KING>(Us) | ei.pe->pawn_attacks(Them));
237 // Initialise the attack bitboards with the king and pawn information
238 b = ei.attackedBy[Us][KING] = pos.attacks_from<KING>(pos.square<KING>(Us));
239 ei.attackedBy[Us][PAWN] = ei.pe->pawn_attacks(Us);
241 ei.attackedBy2[Us] = b & ei.attackedBy[Us][PAWN];
242 ei.attackedBy[Us][ALL_PIECES] = b | ei.attackedBy[Us][PAWN];
244 // Init our king safety tables only if we are going to use them
245 if (pos.non_pawn_material(Them) >= QueenValueMg)
247 ei.kingRing[Us] = b | shift<Up>(b);
248 ei.kingAttackersCount[Them] = popcount(b & ei.pe->pawn_attacks(Them));
249 ei.kingAdjacentZoneAttacksCount[Them] = ei.kingAttackersWeight[Them] = 0;
252 ei.kingRing[Us] = ei.kingAttackersCount[Them] = 0;
256 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given
259 template<bool DoTrace, Color Us = WHITE, PieceType Pt = KNIGHT>
260 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility) {
262 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
263 const Color Them = (Us == WHITE ? BLACK : WHITE);
264 const Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
265 : Rank5BB | Rank4BB | Rank3BB);
266 const Square* pl = pos.squares<Pt>(Us);
270 Score score = SCORE_ZERO;
272 ei.attackedBy[Us][Pt] = 0;
274 while ((s = *pl++) != SQ_NONE)
276 // Find attacked squares, including x-ray attacks for bishops and rooks
277 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
278 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
279 : pos.attacks_from<Pt>(s);
281 if (pos.pinned_pieces(Us) & s)
282 b &= LineBB[pos.square<KING>(Us)][s];
284 ei.attackedBy2[Us] |= ei.attackedBy[Us][ALL_PIECES] & b;
285 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
287 if (b & ei.kingRing[Them])
289 ei.kingAttackersCount[Us]++;
290 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
291 ei.kingAdjacentZoneAttacksCount[Us] += popcount(b & ei.attackedBy[Them][KING]);
294 int mob = popcount(b & ei.mobilityArea[Us]);
296 mobility[Us] += MobilityBonus[Pt][mob];
298 if (Pt == BISHOP || Pt == KNIGHT)
300 // Bonus for outpost squares
301 bb = OutpostRanks & ~ei.pe->pawn_attacks_span(Them);
303 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & s)] * 2;
306 bb &= b & ~pos.pieces(Us);
308 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & bb)];
311 // Bonus when behind a pawn
312 if ( relative_rank(Us, s) < RANK_5
313 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
314 score += MinorBehindPawn;
316 // Penalty for pawns on the same color square as the bishop
318 score -= BishopPawns * ei.pe->pawns_on_same_color_squares(Us, s);
320 // An important Chess960 pattern: A cornered bishop blocked by a friendly
321 // pawn diagonally in front of it is a very serious problem, especially
322 // when that pawn is also blocked.
325 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
327 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
328 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
329 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
330 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
337 // Bonus for aligning with enemy pawns on the same rank/file
338 if (relative_rank(Us, s) >= RANK_5)
339 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
341 // Bonus when on an open or semi-open file
342 if (ei.pe->semiopen_file(Us, file_of(s)))
343 score += RookOnFile[!!ei.pe->semiopen_file(Them, file_of(s))];
345 // Penalty when trapped by the king, even more if the king cannot castle
348 Square ksq = pos.square<KING>(Us);
350 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
351 && !ei.pe->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
352 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
358 // Penalty if any relative pin or discovered attack against the queen
360 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, pinners))
366 Trace::add(Pt, Us, score);
368 // Recursively call evaluate_pieces() of next piece type until KING is excluded
369 return score - evaluate_pieces<DoTrace, Them, NextPt>(pos, ei, mobility);
373 Score evaluate_pieces<false, WHITE, KING>(const Position&, EvalInfo&, Score*) { return SCORE_ZERO; }
375 Score evaluate_pieces< true, WHITE, KING>(const Position&, EvalInfo&, Score*) { return SCORE_ZERO; }
378 // evaluate_king() assigns bonuses and penalties to a king of a given color
380 const Bitboard CenterFiles = FileCBB | FileDBB | FileEBB | FileFBB;
382 const Bitboard KingFlank[FILE_NB] = {
383 CenterFiles >> 2, CenterFiles >> 2, CenterFiles >> 2, CenterFiles, CenterFiles,
384 CenterFiles << 2, CenterFiles << 2, CenterFiles << 2
387 template<Color Us, bool DoTrace>
388 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
390 const Color Them = (Us == WHITE ? BLACK : WHITE);
391 const Square Up = (Us == WHITE ? NORTH : SOUTH);
392 const Bitboard Camp = (Us == WHITE ? ~Bitboard(0) ^ Rank6BB ^ Rank7BB ^ Rank8BB
393 : ~Bitboard(0) ^ Rank1BB ^ Rank2BB ^ Rank3BB);
395 const Square ksq = pos.square<KING>(Us);
396 Bitboard undefended, b, b1, b2, safe, other;
399 // King shelter and enemy pawns storm
400 Score score = ei.pe->king_safety<Us>(pos, ksq);
402 // Main king safety evaluation
403 if (ei.kingAttackersCount[Them])
405 // Find the attacked squares which are defended only by our king...
406 undefended = ei.attackedBy[Them][ALL_PIECES]
407 & ei.attackedBy[Us][KING]
408 & ~ei.attackedBy2[Us];
410 // ... and those which are not defended at all in the larger king ring
411 b = ei.attackedBy[Them][ALL_PIECES] & ~ei.attackedBy[Us][ALL_PIECES]
412 & ei.kingRing[Us] & ~pos.pieces(Them);
414 // Initialize the 'kingDanger' variable, which will be transformed
415 // later into a king danger score. The initial value is based on the
416 // number and types of the enemy's attacking pieces, the number of
417 // attacked and undefended squares around our king and the quality of
418 // the pawn shelter (current 'score' value).
419 kingDanger = std::min(807, ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them])
420 + 101 * ei.kingAdjacentZoneAttacksCount[Them]
421 + 235 * popcount(undefended)
422 + 134 * (popcount(b) + !!pos.pinned_pieces(Us))
423 - 717 * !pos.count<QUEEN>(Them)
424 - 7 * mg_value(score) / 5 - 5;
426 // Analyse the safe enemy's checks which are possible on next move
427 safe = ~pos.pieces(Them);
428 safe &= ~ei.attackedBy[Us][ALL_PIECES] | (undefended & ei.attackedBy2[Them]);
430 b1 = pos.attacks_from<ROOK >(ksq);
431 b2 = pos.attacks_from<BISHOP>(ksq);
433 // Enemy queen safe checks
434 if ((b1 | b2) & ei.attackedBy[Them][QUEEN] & safe)
435 kingDanger += QueenCheck;
437 // For minors and rooks, also consider the square safe if attacked twice,
438 // and only defended by our queen.
439 safe |= ei.attackedBy2[Them]
440 & ~(ei.attackedBy2[Us] | pos.pieces(Them))
441 & ei.attackedBy[Us][QUEEN];
443 // Some other potential checks are also analysed, even from squares
444 // currently occupied by the opponent own pieces, as long as the square
445 // is not attacked by our pawns, and is not occupied by a blocked pawn.
446 other = ~( ei.attackedBy[Us][PAWN]
447 | (pos.pieces(Them, PAWN) & shift<Up>(pos.pieces(PAWN))));
449 // Enemy rooks safe and other checks
450 if (b1 & ei.attackedBy[Them][ROOK] & safe)
451 kingDanger += RookCheck;
453 else if (b1 & ei.attackedBy[Them][ROOK] & other)
456 // Enemy bishops safe and other checks
457 if (b2 & ei.attackedBy[Them][BISHOP] & safe)
458 kingDanger += BishopCheck;
460 else if (b2 & ei.attackedBy[Them][BISHOP] & other)
463 // Enemy knights safe and other checks
464 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT];
466 kingDanger += KnightCheck;
471 // Transform the kingDanger units into a Score, and substract it from the evaluation
473 score -= make_score(std::min(kingDanger * kingDanger / 4096, 2 * int(BishopValueMg)), 0);
476 // King tropism: firstly, find squares that opponent attacks in our king flank
477 File kf = file_of(ksq);
478 b = ei.attackedBy[Them][ALL_PIECES] & KingFlank[kf] & Camp;
480 assert(((Us == WHITE ? b << 4 : b >> 4) & b) == 0);
481 assert(popcount(Us == WHITE ? b << 4 : b >> 4) == popcount(b));
483 // Secondly, add the squares which are attacked twice in that flank and
484 // which are not defended by our pawns.
485 b = (Us == WHITE ? b << 4 : b >> 4)
486 | (b & ei.attackedBy2[Them] & ~ei.attackedBy[Us][PAWN]);
488 score -= CloseEnemies * popcount(b);
490 // Penalty when our king is on a pawnless flank
491 if (!(pos.pieces(PAWN) & KingFlank[kf]))
492 score -= PawnlessFlank;
495 Trace::add(KING, Us, score);
501 // evaluate_threats() assigns bonuses according to the types of the attacking
502 // and the attacked pieces.
504 template<Color Us, bool DoTrace>
505 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
507 const Color Them = (Us == WHITE ? BLACK : WHITE);
508 const Square Up = (Us == WHITE ? NORTH : SOUTH);
509 const Square Left = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
510 const Square Right = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
511 const Bitboard TRank2BB = (Us == WHITE ? Rank2BB : Rank7BB);
512 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
514 Bitboard b, weak, defended, safeThreats;
515 Score score = SCORE_ZERO;
517 // Non-pawn enemies attacked by a pawn
518 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Us][PAWN];
522 b = pos.pieces(Us, PAWN) & ( ~ei.attackedBy[Them][ALL_PIECES]
523 | ei.attackedBy[Us][ALL_PIECES]);
525 safeThreats = (shift<Right>(b) | shift<Left>(b)) & weak;
527 if (weak ^ safeThreats)
528 score += ThreatByHangingPawn;
531 score += ThreatBySafePawn[type_of(pos.piece_on(pop_lsb(&safeThreats)))];
534 // Non-pawn enemies defended by a pawn
535 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Them][PAWN];
537 // Enemies not defended by a pawn and under our attack
538 weak = pos.pieces(Them)
539 & ~ei.attackedBy[Them][PAWN]
540 & ei.attackedBy[Us][ALL_PIECES];
542 // Add a bonus according to the kind of attacking pieces
545 b = (defended | weak) & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
548 Square s = pop_lsb(&b);
549 score += ThreatByMinor[type_of(pos.piece_on(s))];
550 if (type_of(pos.piece_on(s)) != PAWN)
551 score += ThreatByRank * (int)relative_rank(Them, s);
554 b = (pos.pieces(Them, QUEEN) | weak) & ei.attackedBy[Us][ROOK];
557 Square s = pop_lsb(&b);
558 score += ThreatByRook[type_of(pos.piece_on(s))];
559 if (type_of(pos.piece_on(s)) != PAWN)
560 score += ThreatByRank * (int)relative_rank(Them, s);
563 score += Hanging * popcount(weak & ~ei.attackedBy[Them][ALL_PIECES]);
565 b = weak & ei.attackedBy[Us][KING];
567 score += ThreatByKing[more_than_one(b)];
570 // Bonus if some pawns can safely push and attack an enemy piece
571 b = pos.pieces(Us, PAWN) & ~TRank7BB;
572 b = shift<Up>(b | (shift<Up>(b & TRank2BB) & ~pos.pieces()));
575 & ~ei.attackedBy[Them][PAWN]
576 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
578 b = (shift<Left>(b) | shift<Right>(b))
580 & ~ei.attackedBy[Us][PAWN];
582 score += ThreatByPawnPush * popcount(b);
585 Trace::add(THREAT, Us, score);
591 // evaluate_passer_pawns() evaluates the passed pawns and candidate passed
592 // pawns of the given color.
594 template<Color Us, bool DoTrace>
595 Score evaluate_passer_pawns(const Position& pos, const EvalInfo& ei) {
597 const Color Them = (Us == WHITE ? BLACK : WHITE);
599 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
600 Score score = SCORE_ZERO;
602 b = ei.pe->passed_pawns(Us);
606 Square s = pop_lsb(&b);
608 assert(!(pos.pieces(PAWN) & forward_bb(Us, s)));
610 bb = forward_bb(Us, s) & (ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
611 score -= HinderPassedPawn * popcount(bb);
613 int r = relative_rank(Us, s) - RANK_2;
614 int rr = r * (r - 1);
616 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
620 Square blockSq = s + pawn_push(Us);
622 // Adjust bonus based on the king's proximity
623 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
624 - distance(pos.square<KING>(Us ), blockSq) * 2 * rr;
626 // If blockSq is not the queening square then consider also a second push
627 if (relative_rank(Us, blockSq) != RANK_8)
628 ebonus -= distance(pos.square<KING>(Us), blockSq + pawn_push(Us)) * rr;
630 // If the pawn is free to advance, then increase the bonus
631 if (pos.empty(blockSq))
633 // If there is a rook or queen attacking/defending the pawn from behind,
634 // consider all the squaresToQueen. Otherwise consider only the squares
635 // in the pawn's path attacked or occupied by the enemy.
636 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
638 bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
640 if (!(pos.pieces(Us) & bb))
641 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
643 if (!(pos.pieces(Them) & bb))
644 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
646 // If there aren't any enemy attacks, assign a big bonus. Otherwise
647 // assign a smaller bonus if the block square isn't attacked.
648 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
650 // If the path to the queen is fully defended, assign a big bonus.
651 // Otherwise assign a smaller bonus if the block square is defended.
652 if (defendedSquares == squaresToQueen)
655 else if (defendedSquares & blockSq)
658 mbonus += k * rr, ebonus += k * rr;
660 else if (pos.pieces(Us) & blockSq)
661 mbonus += rr + r * 2, ebonus += rr + r * 2;
664 // Scale down bonus for candidate passers which need more than one pawn
665 // push to become passed.
666 if (!pos.pawn_passed(Us, s + pawn_push(Us)))
667 mbonus /= 2, ebonus /= 2;
669 score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
673 Trace::add(PASSED, Us, score);
675 // Add the scores to the middlegame and endgame eval
680 // evaluate_space() computes the space evaluation for a given side. The
681 // space evaluation is a simple bonus based on the number of safe squares
682 // available for minor pieces on the central four files on ranks 2--4. Safe
683 // squares one, two or three squares behind a friendly pawn are counted
684 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
685 // improve play on game opening.
687 Score evaluate_space(const Position& pos, const EvalInfo& ei) {
689 const Color Them = (Us == WHITE ? BLACK : WHITE);
690 const Bitboard SpaceMask =
691 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
692 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
694 // Find the safe squares for our pieces inside the area defined by
695 // SpaceMask. A square is unsafe if it is attacked by an enemy
696 // pawn, or if it is undefended and attacked by an enemy piece.
697 Bitboard safe = SpaceMask
698 & ~pos.pieces(Us, PAWN)
699 & ~ei.attackedBy[Them][PAWN]
700 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
702 // Find all squares which are at most three squares behind some friendly pawn
703 Bitboard behind = pos.pieces(Us, PAWN);
704 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
705 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
707 // Since SpaceMask[Us] is fully on our half of the board...
708 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
710 // ...count safe + (behind & safe) with a single popcount.
711 int bonus = popcount((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
712 bonus = std::min(16, bonus);
713 int weight = pos.count<ALL_PIECES>(Us) - 2 * ei.pe->open_files();
715 return make_score(bonus * weight * weight / 18, 0);
719 // evaluate_initiative() computes the initiative correction value for the
720 // position, i.e., second order bonus/malus based on the known attacking/defending
721 // status of the players.
722 Score evaluate_initiative(const Position& pos, int asymmetry, Value eg) {
724 int kingDistance = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
725 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
726 int pawns = pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK);
728 // Compute the initiative bonus for the attacking side
729 int initiative = 8 * (asymmetry + kingDistance - 15) + 12 * pawns;
731 // Now apply the bonus: note that we find the attacking side by extracting
732 // the sign of the endgame value, and that we carefully cap the bonus so
733 // that the endgame score will never be divided by more than two.
734 int value = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg / 2));
736 return make_score(0, value);
740 // evaluate_scale_factor() computes the scale factor for the winning side
741 ScaleFactor evaluate_scale_factor(const Position& pos, const EvalInfo& ei, Value eg) {
743 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
744 ScaleFactor sf = ei.me->scale_factor(pos, strongSide);
746 // If we don't already have an unusual scale factor, check for certain
747 // types of endgames, and use a lower scale for those.
748 if (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN)
750 if (pos.opposite_bishops())
752 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
753 // is almost a draw, in case of KBP vs KB, it is even more a draw.
754 if ( pos.non_pawn_material(WHITE) == BishopValueMg
755 && pos.non_pawn_material(BLACK) == BishopValueMg)
756 return more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
758 // Endgame with opposite-colored bishops, but also other pieces. Still
759 // a bit drawish, but not as drawish as with only the two bishops.
760 return ScaleFactor(46);
762 // Endings where weaker side can place his king in front of the opponent's
763 // pawns are drawish.
764 else if ( abs(eg) <= BishopValueEg
765 && pos.count<PAWN>(strongSide) <= 2
766 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
767 return ScaleFactor(37 + 7 * pos.count<PAWN>(strongSide));
776 /// evaluate() is the main evaluation function. It returns a static evaluation
777 /// of the position from the point of view of the side to move.
779 template<bool DoTrace>
780 Value Eval::evaluate(const Position& pos) {
782 assert(!pos.checkers());
784 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
788 // Probe the material hash table
789 ei.me = Material::probe(pos);
791 // If we have a specialized evaluation function for the current material
792 // configuration, call it and return.
793 if (ei.me->specialized_eval_exists())
794 return ei.me->evaluate(pos);
796 // Initialize score by reading the incrementally updated scores included in
797 // the position object (material + piece square tables) and the material
798 // imbalance. Score is computed internally from the white point of view.
799 Score score = pos.psq_score() + ei.me->imbalance();
801 // Probe the pawn hash table
802 ei.pe = Pawns::probe(pos);
803 score += ei.pe->pawns_score();
805 // Early exit if score is high
806 v = (mg_value(score) + eg_value(score)) / 2;
807 if (abs(v) > LazyThreshold)
808 return pos.side_to_move() == WHITE ? v : -v;
810 // Initialize attack and king safety bitboards
811 eval_init<WHITE>(pos, ei);
812 eval_init<BLACK>(pos, ei);
814 // Evaluate all pieces but king and pawns
815 score += evaluate_pieces<DoTrace>(pos, ei, mobility);
816 score += mobility[WHITE] - mobility[BLACK];
818 // Evaluate kings after all other pieces because we need full attack
819 // information when computing the king safety evaluation.
820 score += evaluate_king<WHITE, DoTrace>(pos, ei)
821 - evaluate_king<BLACK, DoTrace>(pos, ei);
823 // Evaluate tactical threats, we need full attack information including king
824 score += evaluate_threats<WHITE, DoTrace>(pos, ei)
825 - evaluate_threats<BLACK, DoTrace>(pos, ei);
827 // Evaluate passed pawns, we need full attack information including king
828 score += evaluate_passer_pawns<WHITE, DoTrace>(pos, ei)
829 - evaluate_passer_pawns<BLACK, DoTrace>(pos, ei);
831 // Evaluate space for both sides, only during opening
832 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
833 score += evaluate_space<WHITE>(pos, ei)
834 - evaluate_space<BLACK>(pos, ei);
836 // Evaluate position potential for the winning side
837 score += evaluate_initiative(pos, ei.pe->pawn_asymmetry(), eg_value(score));
839 // Evaluate scale factor for the winning side
840 ScaleFactor sf = evaluate_scale_factor(pos, ei, eg_value(score));
842 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
843 v = mg_value(score) * int(ei.me->game_phase())
844 + eg_value(score) * int(PHASE_MIDGAME - ei.me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
846 v /= int(PHASE_MIDGAME);
848 // In case of tracing add all remaining individual evaluation terms
851 Trace::add(MATERIAL, pos.psq_score());
852 Trace::add(IMBALANCE, ei.me->imbalance());
853 Trace::add(PAWN, ei.pe->pawns_score());
854 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
855 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
856 Trace::add(SPACE, evaluate_space<WHITE>(pos, ei)
857 , evaluate_space<BLACK>(pos, ei));
858 Trace::add(TOTAL, score);
861 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
864 // Explicit template instantiations
865 template Value Eval::evaluate<true >(const Position&);
866 template Value Eval::evaluate<false>(const Position&);
869 /// trace() is like evaluate(), but instead of returning a value, it returns
870 /// a string (suitable for outputting to stdout) that contains the detailed
871 /// descriptions and values of each evaluation term. Useful for debugging.
873 std::string Eval::trace(const Position& pos) {
875 std::memset(scores, 0, sizeof(scores));
877 Value v = evaluate<true>(pos);
878 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
880 std::stringstream ss;
881 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
882 << " Eval term | White | Black | Total \n"
883 << " | MG EG | MG EG | MG EG \n"
884 << "----------------+-------------+-------------+-------------\n"
885 << " Material | " << Term(MATERIAL)
886 << " Imbalance | " << Term(IMBALANCE)
887 << " Pawns | " << Term(PAWN)
888 << " Knights | " << Term(KNIGHT)
889 << " Bishop | " << Term(BISHOP)
890 << " Rooks | " << Term(ROOK)
891 << " Queens | " << Term(QUEEN)
892 << " Mobility | " << Term(MOBILITY)
893 << " King safety | " << Term(KING)
894 << " Threats | " << Term(THREAT)
895 << " Passed pawns | " << Term(PASSED)
896 << " Space | " << Term(SPACE)
897 << "----------------+-------------+-------------+-------------\n"
898 << " Total | " << Term(TOTAL);
900 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";