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) 2015-2016 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.
76 // attackedBy[color][piece type] is a bitboard representing all squares
77 // attacked by a given color and piece type (can be also ALL_PIECES).
78 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
80 // attackedBy2[color] are the squares attacked by 2 pieces of a given color,
81 // possibly via x-ray or by one pawn and one piece. Diagonal x-ray through
82 // pawn or squares attacked by 2 pawns are not explicitly added.
83 Bitboard attackedBy2[COLOR_NB];
85 // kingRing[color] is the zone around the king which is considered
86 // by the king safety evaluation. This consists of the squares directly
87 // adjacent to the king, and the three (or two, for a king on an edge file)
88 // squares two ranks in front of the king. For instance, if black's king
89 // is on g8, kingRing[BLACK] is a bitboard containing the squares f8, h8,
90 // f7, g7, h7, f6, g6 and h6.
91 Bitboard kingRing[COLOR_NB];
93 // kingAttackersCount[color] is the number of pieces of the given color
94 // which attack a square in the kingRing of the enemy king.
95 int kingAttackersCount[COLOR_NB];
97 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of the
98 // given color which attack a square in the kingRing of the enemy king. The
99 // weights of the individual piece types are given by the elements in the
100 // KingAttackWeights array.
101 int kingAttackersWeight[COLOR_NB];
103 // kingAdjacentZoneAttacksCount[color] is the number of attacks by the given
104 // color to squares directly adjacent to the enemy king. Pieces which attack
105 // more than one square are counted multiple times. For instance, if there is
106 // a white knight on g5 and black's king is on g8, this white knight adds 2
107 // to kingAdjacentZoneAttacksCount[WHITE].
108 int kingAdjacentZoneAttacksCount[COLOR_NB];
110 Bitboard pinnedPieces[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
119 // game, indexed by piece type and number of attacked squares in the MobilityArea.
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 knights and
138 // bishops outposts, bigger if outpost piece is supported by a pawn.
139 const Score Outpost[][2] = {
140 { S(43,11), S(65,20) }, // Knights
141 { S(20, 3), S(29, 8) } // Bishops
144 // ReachableOutpost[knight/bishop][supported by pawn] contains bonuses for
145 // knights and bishops which can reach an outpost square in one move, bigger
146 // if outpost square is supported by a pawn.
147 const Score ReachableOutpost[][2] = {
148 { S(21, 5), S(35, 8) }, // Knights
149 { S( 8, 0), S(14, 4) } // Bishops
152 // RookOnFile[semiopen/open] contains bonuses for each rook when there is no
153 // friendly pawn on the rook file.
154 const Score RookOnFile[2] = { S(20, 7), S(45, 20) };
156 // ThreatBySafePawn[PieceType] contains bonuses according to which piece
157 // type is attacked by a pawn which is protected or is not attacked.
158 const Score ThreatBySafePawn[PIECE_TYPE_NB] = {
159 S(0, 0), S(0, 0), S(176, 139), S(131, 127), S(217, 218), S(203, 215)
162 // Threat[by minor/by rook][attacked PieceType] contains
163 // bonuses according to which piece type attacks which one.
164 // Attacks on lesser pieces which are pawn-defended are not considered.
165 const Score Threat[][PIECE_TYPE_NB] = {
166 { S(0, 0), S(0, 33), S(45, 43), S(46, 47), S(72,107), S(48,118) }, // by Minor
167 { S(0, 0), S(0, 25), S(40, 62), S(40, 59), S( 0, 34), S(35, 48) } // by Rook
170 // ThreatByKing[on one/on many] contains bonuses for King attacks on
171 // pawns or pieces which are not pawn-defended.
172 const Score ThreatByKing[2] = { S(3, 62), S(9, 138) };
174 // Passed[mg/eg][Rank] contains midgame and endgame bonuses for passed pawns.
175 // We don't use a Score because we process the two components independently.
176 const Value Passed[][RANK_NB] = {
177 { V(5), V( 5), V(31), V(73), V(166), V(252) },
178 { V(7), V(14), V(38), V(73), V(166), V(252) }
181 // PassedFile[File] contains a bonus according to the file of a passed pawn
182 const Score PassedFile[FILE_NB] = {
183 S( 9, 10), S( 2, 10), S( 1, -8), S(-20,-12),
184 S(-20,-12), S( 1, -8), S( 2, 10), S( 9, 10)
187 // Assorted bonuses and penalties used by evaluation
188 const Score MinorBehindPawn = S(16, 0);
189 const Score BishopPawns = S( 8, 12);
190 const Score RookOnPawn = S( 8, 24);
191 const Score TrappedRook = S(92, 0);
192 const Score CloseEnemies = S( 7, 0);
193 const Score SafeCheck = S(20, 20);
194 const Score OtherCheck = S(10, 10);
195 const Score ThreatByHangingPawn = S(71, 61);
196 const Score LooseEnemies = S( 0, 25);
197 const Score WeakQueen = S(50, 10);
198 const Score Hanging = S(48, 27);
199 const Score ThreatByPawnPush = S(38, 22);
200 const Score PawnlessFlank = S(20, 80);
201 const Score HinderPassedPawn = S( 7, 0);
202 const Score ThreatByRank = S(16, 3);
204 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
205 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
206 // happen in Chess960 games.
207 const Score TrappedBishopA1H1 = S(50, 50);
212 // KingAttackWeights[PieceType] contains king attack weights by piece type
213 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 78, 56, 45, 11 };
215 // Penalties for enemy's safe checks
216 const int QueenContactCheck = 997;
217 const int QueenCheck = 695;
218 const int RookCheck = 638;
219 const int BishopCheck = 538;
220 const int KnightCheck = 874;
223 // eval_init() initializes king and attack bitboards for a given color
224 // adding pawn attacks. To be done at the beginning of the evaluation.
227 void eval_init(const Position& pos, EvalInfo& ei) {
229 const Color Them = (Us == WHITE ? BLACK : WHITE);
230 const Square Down = (Us == WHITE ? SOUTH : NORTH);
232 ei.pinnedPieces[Us] = pos.pinned_pieces(Us);
233 Bitboard b = ei.attackedBy[Them][KING];
234 ei.attackedBy[Them][ALL_PIECES] |= b;
235 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
236 ei.attackedBy2[Us] = ei.attackedBy[Us][PAWN] & ei.attackedBy[Us][KING];
238 // Init king safety tables only if we are going to use them
239 if (pos.non_pawn_material(Us) >= QueenValueMg)
241 ei.kingRing[Them] = b | shift<Down>(b);
242 b &= ei.attackedBy[Us][PAWN];
243 ei.kingAttackersCount[Us] = popcount(b);
244 ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
247 ei.kingRing[Them] = ei.kingAttackersCount[Us] = 0;
251 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given
254 template<bool DoTrace, Color Us = WHITE, PieceType Pt = KNIGHT>
255 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility,
256 const Bitboard* mobilityArea) {
259 Score score = SCORE_ZERO;
261 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
262 const Color Them = (Us == WHITE ? BLACK : WHITE);
263 const Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
264 : Rank5BB | Rank4BB | Rank3BB);
265 const Square* pl = pos.squares<Pt>(Us);
267 ei.attackedBy[Us][Pt] = 0;
269 while ((s = *pl++) != SQ_NONE)
271 // Find attacked squares, including x-ray attacks for bishops and rooks
272 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
273 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
274 : pos.attacks_from<Pt>(s);
276 if (ei.pinnedPieces[Us] & s)
277 b &= LineBB[pos.square<KING>(Us)][s];
279 ei.attackedBy2[Us] |= ei.attackedBy[Us][ALL_PIECES] & b;
280 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
282 if (b & ei.kingRing[Them])
284 ei.kingAttackersCount[Us]++;
285 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
286 ei.kingAdjacentZoneAttacksCount[Us] += popcount(b & ei.attackedBy[Them][KING]);
290 b &= ~( ei.attackedBy[Them][KNIGHT]
291 | ei.attackedBy[Them][BISHOP]
292 | ei.attackedBy[Them][ROOK]);
294 int mob = popcount(b & mobilityArea[Us]);
296 mobility[Us] += MobilityBonus[Pt][mob];
298 if (Pt == BISHOP || Pt == KNIGHT)
300 // Bonus for outpost squares
301 bb = OutpostRanks & ~ei.pi->pawn_attacks_span(Them);
303 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & s)];
306 bb &= b & ~pos.pieces(Us);
308 score += ReachableOutpost[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.pi->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.pi->semiopen_file(Us, file_of(s)))
343 score += RookOnFile[!!ei.pi->semiopen_file(Them, file_of(s))];
345 // Penalize 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.pi->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, mobilityArea);
373 Score evaluate_pieces<false, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
375 Score evaluate_pieces< true, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
378 // evaluate_king() assigns bonuses and penalties to a king of a given color
380 const Bitboard WhiteCamp = Rank1BB | Rank2BB | Rank3BB | Rank4BB | Rank5BB;
381 const Bitboard BlackCamp = Rank8BB | Rank7BB | Rank6BB | Rank5BB | Rank4BB;
382 const Bitboard QueenSide = FileABB | FileBBB | FileCBB | FileDBB;
383 const Bitboard CenterFiles = FileCBB | FileDBB | FileEBB | FileFBB;
384 const Bitboard KingSide = FileEBB | FileFBB | FileGBB | FileHBB;
386 const Bitboard KingFlank[COLOR_NB][FILE_NB] = {
387 { QueenSide & WhiteCamp, QueenSide & WhiteCamp, QueenSide & WhiteCamp, CenterFiles & WhiteCamp,
388 CenterFiles & WhiteCamp, KingSide & WhiteCamp, KingSide & WhiteCamp, KingSide & WhiteCamp },
389 { QueenSide & BlackCamp, QueenSide & BlackCamp, QueenSide & BlackCamp, CenterFiles & BlackCamp,
390 CenterFiles & BlackCamp, KingSide & BlackCamp, KingSide & BlackCamp, KingSide & BlackCamp },
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);
399 Bitboard undefended, b, b1, b2, safe, other;
401 const Square ksq = pos.square<KING>(Us);
403 // King shelter and enemy pawns storm
404 Score score = ei.pi->king_safety<Us>(pos, ksq);
406 // Main king safety evaluation
407 if (ei.kingAttackersCount[Them])
409 // Find the attacked squares which are defended only by the king...
410 undefended = ei.attackedBy[Them][ALL_PIECES]
411 & ei.attackedBy[Us][KING]
412 & ~ei.attackedBy2[Us];
414 // ... and those which are not defended at all in the larger king ring
415 b = ei.attackedBy[Them][ALL_PIECES] & ~ei.attackedBy[Us][ALL_PIECES]
416 & ei.kingRing[Us] & ~pos.pieces(Them);
418 // Initialize the 'kingDanger' variable, which will be transformed
419 // later into a king danger score. The initial value is based on the
420 // number and types of the enemy's attacking pieces, the number of
421 // attacked and undefended squares around our king and the quality of
422 // the pawn shelter (current 'score' value).
423 kingDanger = std::min(807, ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them])
424 + 101 * ei.kingAdjacentZoneAttacksCount[Them]
425 + 235 * popcount(undefended)
426 + 134 * (popcount(b) + !!ei.pinnedPieces[Us])
427 - 717 * !pos.count<QUEEN>(Them)
428 - 7 * mg_value(score) / 5 - 5;
430 // Analyse the enemy's safe queen contact checks. Firstly, find the
431 // undefended squares around the king reachable by the enemy queen...
432 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);
434 // ...and keep squares supported by another enemy piece
435 kingDanger += QueenContactCheck * popcount(b & ei.attackedBy2[Them]);
437 // Analyse the safe enemy's checks which are possible on next move...
438 safe = ~(ei.attackedBy[Us][ALL_PIECES] | pos.pieces(Them));
440 // ... and some other potential checks, only requiring the square to be
441 // safe from pawn-attacks, and not being occupied by a blocked pawn.
442 other = ~( ei.attackedBy[Us][PAWN]
443 | (pos.pieces(Them, PAWN) & shift<Up>(pos.pieces(PAWN))));
445 b1 = pos.attacks_from<ROOK >(ksq);
446 b2 = pos.attacks_from<BISHOP>(ksq);
448 // Enemy queen safe checks
449 if ((b1 | b2) & ei.attackedBy[Them][QUEEN] & safe)
450 kingDanger += QueenCheck, score -= SafeCheck;
452 // For other pieces, also consider the square safe if attacked twice,
453 // and only defended by a queen.
454 safe |= ei.attackedBy2[Them]
455 & ~(ei.attackedBy2[Us] | pos.pieces(Them))
456 & ei.attackedBy[Us][QUEEN];
458 // Enemy rooks safe and other checks
459 if (b1 & ei.attackedBy[Them][ROOK] & safe)
460 kingDanger += RookCheck, score -= SafeCheck;
462 else if (b1 & ei.attackedBy[Them][ROOK] & other)
465 // Enemy bishops safe and other checks
466 if (b2 & ei.attackedBy[Them][BISHOP] & safe)
467 kingDanger += BishopCheck, score -= SafeCheck;
469 else if (b2 & ei.attackedBy[Them][BISHOP] & other)
472 // Enemy knights safe and other checks
473 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT];
475 kingDanger += KnightCheck, score -= SafeCheck;
480 // Compute the king danger score and subtract it from the evaluation
482 score -= make_score(std::min(kingDanger * kingDanger / 4096, 2 * int(BishopValueMg)), 0);
485 // King tropism: firstly, find squares that opponent attacks in our king flank
486 File kf = file_of(ksq);
487 b = ei.attackedBy[Them][ALL_PIECES] & KingFlank[Us][kf];
489 assert(((Us == WHITE ? b << 4 : b >> 4) & b) == 0);
490 assert(popcount(Us == WHITE ? b << 4 : b >> 4) == popcount(b));
492 // Secondly, add the squares which are attacked twice in that flank and
493 // which are not defended by our pawns.
494 b = (Us == WHITE ? b << 4 : b >> 4)
495 | (b & ei.attackedBy2[Them] & ~ei.attackedBy[Us][PAWN]);
497 score -= CloseEnemies * popcount(b);
499 // Penalty when our king is on a pawnless flank
500 if (!(pos.pieces(PAWN) & (KingFlank[WHITE][kf] | KingFlank[BLACK][kf])))
501 score -= PawnlessFlank;
504 Trace::add(KING, Us, score);
510 // evaluate_threats() assigns bonuses according to the types of the attacking
511 // and the attacked pieces.
513 template<Color Us, bool DoTrace>
514 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
516 const Color Them = (Us == WHITE ? BLACK : WHITE);
517 const Square Up = (Us == WHITE ? NORTH : SOUTH);
518 const Square Left = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
519 const Square Right = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
520 const Bitboard TRank2BB = (Us == WHITE ? Rank2BB : Rank7BB);
521 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
523 enum { Minor, Rook };
525 Bitboard b, weak, defended, safeThreats;
526 Score score = SCORE_ZERO;
528 // Small bonus if the opponent has loose pawns or pieces
529 if ( (pos.pieces(Them) ^ pos.pieces(Them, QUEEN, KING))
530 & ~(ei.attackedBy[Us][ALL_PIECES] | ei.attackedBy[Them][ALL_PIECES]))
531 score += LooseEnemies;
533 // Non-pawn enemies attacked by a pawn
534 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Us][PAWN];
538 b = pos.pieces(Us, PAWN) & ( ~ei.attackedBy[Them][ALL_PIECES]
539 | ei.attackedBy[Us][ALL_PIECES]);
541 safeThreats = (shift<Right>(b) | shift<Left>(b)) & weak;
543 if (weak ^ safeThreats)
544 score += ThreatByHangingPawn;
547 score += ThreatBySafePawn[type_of(pos.piece_on(pop_lsb(&safeThreats)))];
550 // Non-pawn enemies defended by a pawn
551 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Them][PAWN];
553 // Enemies not defended by a pawn and under our attack
554 weak = pos.pieces(Them)
555 & ~ei.attackedBy[Them][PAWN]
556 & ei.attackedBy[Us][ALL_PIECES];
558 // Add a bonus according to the kind of attacking pieces
561 b = (defended | weak) & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
564 Square s = pop_lsb(&b);
565 score += Threat[Minor][type_of(pos.piece_on(s))];
566 if (type_of(pos.piece_on(s)) != PAWN)
567 score += ThreatByRank * (int)relative_rank(Them, s);
570 b = (pos.pieces(Them, QUEEN) | weak) & ei.attackedBy[Us][ROOK];
573 Square s = pop_lsb(&b);
574 score += Threat[Rook][type_of(pos.piece_on(s))];
575 if (type_of(pos.piece_on(s)) != PAWN)
576 score += ThreatByRank * (int)relative_rank(Them, s);
579 score += Hanging * popcount(weak & ~ei.attackedBy[Them][ALL_PIECES]);
581 b = weak & ei.attackedBy[Us][KING];
583 score += ThreatByKing[more_than_one(b)];
586 // Bonus if some pawns can safely push and attack an enemy piece
587 b = pos.pieces(Us, PAWN) & ~TRank7BB;
588 b = shift<Up>(b | (shift<Up>(b & TRank2BB) & ~pos.pieces()));
591 & ~ei.attackedBy[Them][PAWN]
592 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
594 b = (shift<Left>(b) | shift<Right>(b))
596 & ~ei.attackedBy[Us][PAWN];
598 score += ThreatByPawnPush * popcount(b);
601 Trace::add(THREAT, Us, score);
607 // evaluate_passed_pawns() evaluates the passed pawns of the given color
609 template<Color Us, bool DoTrace>
610 Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
612 const Color Them = (Us == WHITE ? BLACK : WHITE);
614 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
615 Score score = SCORE_ZERO;
617 b = ei.pi->passed_pawns(Us);
621 Square s = pop_lsb(&b);
623 assert(pos.pawn_passed(Us, s));
624 assert(!(pos.pieces(PAWN) & forward_bb(Us, s)));
626 bb = forward_bb(Us, s) & (ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
627 score -= HinderPassedPawn * popcount(bb);
629 int r = relative_rank(Us, s) - RANK_2;
630 int rr = r * (r - 1);
632 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
636 Square blockSq = s + pawn_push(Us);
638 // Adjust bonus based on the king's proximity
639 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
640 - distance(pos.square<KING>(Us ), blockSq) * 2 * rr;
642 // If blockSq is not the queening square then consider also a second push
643 if (relative_rank(Us, blockSq) != RANK_8)
644 ebonus -= distance(pos.square<KING>(Us), blockSq + pawn_push(Us)) * rr;
646 // If the pawn is free to advance, then increase the bonus
647 if (pos.empty(blockSq))
649 // If there is a rook or queen attacking/defending the pawn from behind,
650 // consider all the squaresToQueen. Otherwise consider only the squares
651 // in the pawn's path attacked or occupied by the enemy.
652 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
654 bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
656 if (!(pos.pieces(Us) & bb))
657 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
659 if (!(pos.pieces(Them) & bb))
660 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
662 // If there aren't any enemy attacks, assign a big bonus. Otherwise
663 // assign a smaller bonus if the block square isn't attacked.
664 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
666 // If the path to the queen is fully defended, assign a big bonus.
667 // Otherwise assign a smaller bonus if the block square is defended.
668 if (defendedSquares == squaresToQueen)
671 else if (defendedSquares & blockSq)
674 mbonus += k * rr, ebonus += k * rr;
676 else if (pos.pieces(Us) & blockSq)
677 mbonus += rr + r * 2, ebonus += rr + r * 2;
680 // Assign a small bonus when no pieces left (unstoppable)
681 if (!pos.non_pawn_material(Us) && !pos.non_pawn_material(Them))
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 ? (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank2BB | Rank3BB | Rank4BB)
707 : (FileCBB | FileDBB | FileEBB | FileFBB) & (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.pi->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 };
804 // Probe the material hash table
805 ei.me = Material::probe(pos);
807 // If we have a specialized evaluation function for the current material
808 // configuration, call it and return.
809 if (ei.me->specialized_eval_exists())
810 return ei.me->evaluate(pos);
812 // Initialize score by reading the incrementally updated scores included in
813 // the position object (material + piece square tables) and the material
814 // imbalance. Score is computed internally from the white point of view.
815 Score score = pos.psq_score() + ei.me->imbalance();
817 // Probe the pawn hash table
818 ei.pi = Pawns::probe(pos);
819 score += ei.pi->pawns_score();
821 // Initialize attack and king safety bitboards
822 ei.attackedBy[WHITE][ALL_PIECES] = ei.attackedBy[BLACK][ALL_PIECES] = 0;
823 ei.attackedBy[WHITE][KING] = pos.attacks_from<KING>(pos.square<KING>(WHITE));
824 ei.attackedBy[BLACK][KING] = pos.attacks_from<KING>(pos.square<KING>(BLACK));
825 eval_init<WHITE>(pos, ei);
826 eval_init<BLACK>(pos, ei);
828 // Pawns blocked or on ranks 2 and 3 will be excluded from the mobility area
829 Bitboard blockedPawns[] = {
830 pos.pieces(WHITE, PAWN) & (shift<SOUTH>(pos.pieces()) | Rank2BB | Rank3BB),
831 pos.pieces(BLACK, PAWN) & (shift<NORTH>(pos.pieces()) | Rank7BB | Rank6BB)
834 // Do not include in mobility area squares protected by enemy pawns, or occupied
835 // by our blocked pawns or king.
836 Bitboard mobilityArea[] = {
837 ~(ei.attackedBy[BLACK][PAWN] | blockedPawns[WHITE] | pos.square<KING>(WHITE)),
838 ~(ei.attackedBy[WHITE][PAWN] | blockedPawns[BLACK] | pos.square<KING>(BLACK))
841 // Evaluate all pieces but king and pawns
842 score += evaluate_pieces<DoTrace>(pos, ei, mobility, mobilityArea);
843 score += mobility[WHITE] - mobility[BLACK];
845 // Evaluate kings after all other pieces because we need full attack
846 // information when computing the king safety evaluation.
847 score += evaluate_king<WHITE, DoTrace>(pos, ei)
848 - evaluate_king<BLACK, DoTrace>(pos, ei);
850 // Evaluate tactical threats, we need full attack information including king
851 score += evaluate_threats<WHITE, DoTrace>(pos, ei)
852 - evaluate_threats<BLACK, DoTrace>(pos, ei);
854 // Evaluate passed pawns, we need full attack information including king
855 score += evaluate_passed_pawns<WHITE, DoTrace>(pos, ei)
856 - evaluate_passed_pawns<BLACK, DoTrace>(pos, ei);
858 // Evaluate space for both sides, only during opening
859 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
860 score += evaluate_space<WHITE>(pos, ei)
861 - evaluate_space<BLACK>(pos, ei);
863 // Evaluate position potential for the winning side
864 score += evaluate_initiative(pos, ei.pi->pawn_asymmetry(), eg_value(score));
866 // Evaluate scale factor for the winning side
867 ScaleFactor sf = evaluate_scale_factor(pos, ei, eg_value(score));
869 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
870 Value v = mg_value(score) * int(ei.me->game_phase())
871 + eg_value(score) * int(PHASE_MIDGAME - ei.me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
873 v /= int(PHASE_MIDGAME);
875 // In case of tracing add all remaining individual evaluation terms
878 Trace::add(MATERIAL, pos.psq_score());
879 Trace::add(IMBALANCE, ei.me->imbalance());
880 Trace::add(PAWN, ei.pi->pawns_score());
881 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
882 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
883 Trace::add(SPACE, evaluate_space<WHITE>(pos, ei)
884 , evaluate_space<BLACK>(pos, ei));
885 Trace::add(TOTAL, score);
888 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
891 // Explicit template instantiations
892 template Value Eval::evaluate<true >(const Position&);
893 template Value Eval::evaluate<false>(const Position&);
896 /// trace() is like evaluate(), but instead of returning a value, it returns
897 /// a string (suitable for outputting to stdout) that contains the detailed
898 /// descriptions and values of each evaluation term. Useful for debugging.
900 std::string Eval::trace(const Position& pos) {
902 std::memset(scores, 0, sizeof(scores));
904 Value v = evaluate<true>(pos);
905 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
907 std::stringstream ss;
908 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
909 << " Eval term | White | Black | Total \n"
910 << " | MG EG | MG EG | MG EG \n"
911 << "----------------+-------------+-------------+-------------\n"
912 << " Material | " << Term(MATERIAL)
913 << " Imbalance | " << Term(IMBALANCE)
914 << " Pawns | " << Term(PAWN)
915 << " Knights | " << Term(KNIGHT)
916 << " Bishop | " << Term(BISHOP)
917 << " Rooks | " << Term(ROOK)
918 << " Queens | " << Term(QUEEN)
919 << " Mobility | " << Term(MOBILITY)
920 << " King safety | " << Term(KING)
921 << " Threats | " << Term(THREAT)
922 << " Passed pawns | " << Term(PASSED)
923 << " Space | " << Term(SPACE)
924 << "----------------+-------------+-------------+-------------\n"
925 << " Total | " << Term(TOTAL);
927 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";