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 OtherCheck = S(10, 10);
194 const Score ThreatByHangingPawn = S(71, 61);
195 const Score LooseEnemies = S( 0, 25);
196 const Score WeakQueen = S(50, 10);
197 const Score Hanging = S(48, 27);
198 const Score ThreatByPawnPush = S(38, 22);
199 const Score PawnlessFlank = S(20, 80);
200 const Score HinderPassedPawn = S( 7, 0);
201 const Score ThreatByRank = S(16, 3);
203 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
204 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
205 // happen in Chess960 games.
206 const Score TrappedBishopA1H1 = S(50, 50);
211 // KingAttackWeights[PieceType] contains king attack weights by piece type
212 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 78, 56, 45, 11 };
214 // Penalties for enemy's safe checks
215 const int QueenContactCheck = 997;
216 const int QueenCheck = 745;
217 const int RookCheck = 688;
218 const int BishopCheck = 588;
219 const int KnightCheck = 924;
222 // eval_init() initializes king and attack bitboards for a given color
223 // adding pawn attacks. To be done at the beginning of the evaluation.
226 void eval_init(const Position& pos, EvalInfo& ei) {
228 const Color Them = (Us == WHITE ? BLACK : WHITE);
229 const Square Down = (Us == WHITE ? SOUTH : NORTH);
231 ei.pinnedPieces[Us] = pos.pinned_pieces(Us);
232 Bitboard b = ei.attackedBy[Them][KING];
233 ei.attackedBy[Them][ALL_PIECES] |= b;
234 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
235 ei.attackedBy2[Us] = ei.attackedBy[Us][PAWN] & ei.attackedBy[Us][KING];
237 // Init king safety tables only if we are going to use them
238 if (pos.non_pawn_material(Us) >= QueenValueMg)
240 ei.kingRing[Them] = b | shift<Down>(b);
241 b &= ei.attackedBy[Us][PAWN];
242 ei.kingAttackersCount[Us] = popcount(b);
243 ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
246 ei.kingRing[Them] = ei.kingAttackersCount[Us] = 0;
250 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given
253 template<bool DoTrace, Color Us = WHITE, PieceType Pt = KNIGHT>
254 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility,
255 const Bitboard* mobilityArea) {
258 Score score = SCORE_ZERO;
260 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
261 const Color Them = (Us == WHITE ? BLACK : WHITE);
262 const Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
263 : Rank5BB | Rank4BB | Rank3BB);
264 const Square* pl = pos.squares<Pt>(Us);
266 ei.attackedBy[Us][Pt] = 0;
268 while ((s = *pl++) != SQ_NONE)
270 // Find attacked squares, including x-ray attacks for bishops and rooks
271 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
272 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
273 : pos.attacks_from<Pt>(s);
275 if (ei.pinnedPieces[Us] & s)
276 b &= LineBB[pos.square<KING>(Us)][s];
278 ei.attackedBy2[Us] |= ei.attackedBy[Us][ALL_PIECES] & b;
279 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
281 if (b & ei.kingRing[Them])
283 ei.kingAttackersCount[Us]++;
284 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
285 ei.kingAdjacentZoneAttacksCount[Us] += popcount(b & ei.attackedBy[Them][KING]);
289 b &= ~( ei.attackedBy[Them][KNIGHT]
290 | ei.attackedBy[Them][BISHOP]
291 | ei.attackedBy[Them][ROOK]);
293 int mob = popcount(b & mobilityArea[Us]);
295 mobility[Us] += MobilityBonus[Pt][mob];
297 if (Pt == BISHOP || Pt == KNIGHT)
299 // Bonus for outpost squares
300 bb = OutpostRanks & ~ei.pi->pawn_attacks_span(Them);
302 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & s)];
305 bb &= b & ~pos.pieces(Us);
307 score += ReachableOutpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & bb)];
310 // Bonus when behind a pawn
311 if ( relative_rank(Us, s) < RANK_5
312 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
313 score += MinorBehindPawn;
315 // Penalty for pawns on the same color square as the bishop
317 score -= BishopPawns * ei.pi->pawns_on_same_color_squares(Us, s);
319 // An important Chess960 pattern: A cornered bishop blocked by a friendly
320 // pawn diagonally in front of it is a very serious problem, especially
321 // when that pawn is also blocked.
324 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
326 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
327 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
328 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
329 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
336 // Bonus for aligning with enemy pawns on the same rank/file
337 if (relative_rank(Us, s) >= RANK_5)
338 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
340 // Bonus when on an open or semi-open file
341 if (ei.pi->semiopen_file(Us, file_of(s)))
342 score += RookOnFile[!!ei.pi->semiopen_file(Them, file_of(s))];
344 // Penalize when trapped by the king, even more if the king cannot castle
347 Square ksq = pos.square<KING>(Us);
349 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
350 && !ei.pi->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
351 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
357 // Penalty if any relative pin or discovered attack against the queen
359 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, pinners))
365 Trace::add(Pt, Us, score);
367 // Recursively call evaluate_pieces() of next piece type until KING is excluded
368 return score - evaluate_pieces<DoTrace, Them, NextPt>(pos, ei, mobility, mobilityArea);
372 Score evaluate_pieces<false, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
374 Score evaluate_pieces< true, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
377 // evaluate_king() assigns bonuses and penalties to a king of a given color
379 const Bitboard WhiteCamp = Rank1BB | Rank2BB | Rank3BB | Rank4BB | Rank5BB;
380 const Bitboard BlackCamp = Rank8BB | Rank7BB | Rank6BB | Rank5BB | Rank4BB;
381 const Bitboard QueenSide = FileABB | FileBBB | FileCBB | FileDBB;
382 const Bitboard CenterFiles = FileCBB | FileDBB | FileEBB | FileFBB;
383 const Bitboard KingSide = FileEBB | FileFBB | FileGBB | FileHBB;
385 const Bitboard KingFlank[COLOR_NB][FILE_NB] = {
386 { QueenSide & WhiteCamp, QueenSide & WhiteCamp, QueenSide & WhiteCamp, CenterFiles & WhiteCamp,
387 CenterFiles & WhiteCamp, KingSide & WhiteCamp, KingSide & WhiteCamp, KingSide & WhiteCamp },
388 { QueenSide & BlackCamp, QueenSide & BlackCamp, QueenSide & BlackCamp, CenterFiles & BlackCamp,
389 CenterFiles & BlackCamp, KingSide & BlackCamp, KingSide & BlackCamp, KingSide & BlackCamp },
392 template<Color Us, bool DoTrace>
393 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
395 const Color Them = (Us == WHITE ? BLACK : WHITE);
396 const Square Up = (Us == WHITE ? NORTH : SOUTH);
398 Bitboard undefended, b, b1, b2, safe, other;
400 const Square ksq = pos.square<KING>(Us);
402 // King shelter and enemy pawns storm
403 Score score = ei.pi->king_safety<Us>(pos, ksq);
405 // Main king safety evaluation
406 if (ei.kingAttackersCount[Them])
408 // Find the attacked squares which are defended only by the king...
409 undefended = ei.attackedBy[Them][ALL_PIECES]
410 & ei.attackedBy[Us][KING]
411 & ~ei.attackedBy2[Us];
413 // ... and those which are not defended at all in the larger king ring
414 b = ei.attackedBy[Them][ALL_PIECES] & ~ei.attackedBy[Us][ALL_PIECES]
415 & ei.kingRing[Us] & ~pos.pieces(Them);
417 // Initialize the 'kingDanger' variable, which will be transformed
418 // later into a king danger score. The initial value is based on the
419 // number and types of the enemy's attacking pieces, the number of
420 // attacked and undefended squares around our king and the quality of
421 // the pawn shelter (current 'score' value).
422 kingDanger = std::min(807, ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them])
423 + 101 * ei.kingAdjacentZoneAttacksCount[Them]
424 + 235 * popcount(undefended)
425 + 134 * (popcount(b) + !!ei.pinnedPieces[Us])
426 - 717 * !pos.count<QUEEN>(Them)
427 - 7 * mg_value(score) / 5 - 5;
429 // Analyse the enemy's safe queen contact checks. Firstly, find the
430 // undefended squares around the king reachable by the enemy queen...
431 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);
433 // ...and keep squares supported by another enemy piece
434 kingDanger += QueenContactCheck * popcount(b & ei.attackedBy2[Them]);
436 // Analyse the safe enemy's checks which are possible on next move...
437 safe = ~(ei.attackedBy[Us][ALL_PIECES] | pos.pieces(Them));
439 // ... and some other potential checks, only requiring the square to be
440 // safe from pawn-attacks, and not being occupied by a blocked pawn.
441 other = ~( ei.attackedBy[Us][PAWN]
442 | (pos.pieces(Them, PAWN) & shift<Up>(pos.pieces(PAWN))));
444 b1 = pos.attacks_from<ROOK >(ksq);
445 b2 = pos.attacks_from<BISHOP>(ksq);
447 // Enemy queen safe checks
448 if ((b1 | b2) & ei.attackedBy[Them][QUEEN] & safe)
449 kingDanger += QueenCheck;
451 // For other pieces, also consider the square safe if attacked twice,
452 // and only defended by a queen.
453 safe |= ei.attackedBy2[Them]
454 & ~(ei.attackedBy2[Us] | pos.pieces(Them))
455 & ei.attackedBy[Us][QUEEN];
457 // Enemy rooks safe and other checks
458 if (b1 & ei.attackedBy[Them][ROOK] & safe)
459 kingDanger += RookCheck;
461 else if (b1 & ei.attackedBy[Them][ROOK] & other)
464 // Enemy bishops safe and other checks
465 if (b2 & ei.attackedBy[Them][BISHOP] & safe)
466 kingDanger += BishopCheck;
468 else if (b2 & ei.attackedBy[Them][BISHOP] & other)
471 // Enemy knights safe and other checks
472 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT];
474 kingDanger += KnightCheck;
479 // Compute the king danger score and subtract it from the evaluation
481 score -= make_score(std::min(kingDanger * kingDanger / 4096, 2 * int(BishopValueMg)), 0);
484 // King tropism: firstly, find squares that opponent attacks in our king flank
485 File kf = file_of(ksq);
486 b = ei.attackedBy[Them][ALL_PIECES] & KingFlank[Us][kf];
488 assert(((Us == WHITE ? b << 4 : b >> 4) & b) == 0);
489 assert(popcount(Us == WHITE ? b << 4 : b >> 4) == popcount(b));
491 // Secondly, add the squares which are attacked twice in that flank and
492 // which are not defended by our pawns.
493 b = (Us == WHITE ? b << 4 : b >> 4)
494 | (b & ei.attackedBy2[Them] & ~ei.attackedBy[Us][PAWN]);
496 score -= CloseEnemies * popcount(b);
498 // Penalty when our king is on a pawnless flank
499 if (!(pos.pieces(PAWN) & (KingFlank[WHITE][kf] | KingFlank[BLACK][kf])))
500 score -= PawnlessFlank;
503 Trace::add(KING, Us, score);
509 // evaluate_threats() assigns bonuses according to the types of the attacking
510 // and the attacked pieces.
512 template<Color Us, bool DoTrace>
513 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
515 const Color Them = (Us == WHITE ? BLACK : WHITE);
516 const Square Up = (Us == WHITE ? NORTH : SOUTH);
517 const Square Left = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
518 const Square Right = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
519 const Bitboard TRank2BB = (Us == WHITE ? Rank2BB : Rank7BB);
520 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
522 enum { Minor, Rook };
524 Bitboard b, weak, defended, safeThreats;
525 Score score = SCORE_ZERO;
527 // Small bonus if the opponent has loose pawns or pieces
528 if ( (pos.pieces(Them) ^ pos.pieces(Them, QUEEN, KING))
529 & ~(ei.attackedBy[Us][ALL_PIECES] | ei.attackedBy[Them][ALL_PIECES]))
530 score += LooseEnemies;
532 // Non-pawn enemies attacked by a pawn
533 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Us][PAWN];
537 b = pos.pieces(Us, PAWN) & ( ~ei.attackedBy[Them][ALL_PIECES]
538 | ei.attackedBy[Us][ALL_PIECES]);
540 safeThreats = (shift<Right>(b) | shift<Left>(b)) & weak;
542 if (weak ^ safeThreats)
543 score += ThreatByHangingPawn;
546 score += ThreatBySafePawn[type_of(pos.piece_on(pop_lsb(&safeThreats)))];
549 // Non-pawn enemies defended by a pawn
550 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Them][PAWN];
552 // Enemies not defended by a pawn and under our attack
553 weak = pos.pieces(Them)
554 & ~ei.attackedBy[Them][PAWN]
555 & ei.attackedBy[Us][ALL_PIECES];
557 // Add a bonus according to the kind of attacking pieces
560 b = (defended | weak) & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
563 Square s = pop_lsb(&b);
564 score += Threat[Minor][type_of(pos.piece_on(s))];
565 if (type_of(pos.piece_on(s)) != PAWN)
566 score += ThreatByRank * (int)relative_rank(Them, s);
569 b = (pos.pieces(Them, QUEEN) | weak) & ei.attackedBy[Us][ROOK];
572 Square s = pop_lsb(&b);
573 score += Threat[Rook][type_of(pos.piece_on(s))];
574 if (type_of(pos.piece_on(s)) != PAWN)
575 score += ThreatByRank * (int)relative_rank(Them, s);
578 score += Hanging * popcount(weak & ~ei.attackedBy[Them][ALL_PIECES]);
580 b = weak & ei.attackedBy[Us][KING];
582 score += ThreatByKing[more_than_one(b)];
585 // Bonus if some pawns can safely push and attack an enemy piece
586 b = pos.pieces(Us, PAWN) & ~TRank7BB;
587 b = shift<Up>(b | (shift<Up>(b & TRank2BB) & ~pos.pieces()));
590 & ~ei.attackedBy[Them][PAWN]
591 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
593 b = (shift<Left>(b) | shift<Right>(b))
595 & ~ei.attackedBy[Us][PAWN];
597 score += ThreatByPawnPush * popcount(b);
600 Trace::add(THREAT, Us, score);
606 // evaluate_passed_pawns() evaluates the passed pawns of the given color
608 template<Color Us, bool DoTrace>
609 Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
611 const Color Them = (Us == WHITE ? BLACK : WHITE);
613 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
614 Score score = SCORE_ZERO;
616 b = ei.pi->passed_pawns(Us);
620 Square s = pop_lsb(&b);
622 assert(pos.pawn_passed(Us, s));
623 assert(!(pos.pieces(PAWN) & forward_bb(Us, s)));
625 bb = forward_bb(Us, s) & (ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
626 score -= HinderPassedPawn * popcount(bb);
628 int r = relative_rank(Us, s) - RANK_2;
629 int rr = r * (r - 1);
631 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
635 Square blockSq = s + pawn_push(Us);
637 // Adjust bonus based on the king's proximity
638 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
639 - distance(pos.square<KING>(Us ), blockSq) * 2 * rr;
641 // If blockSq is not the queening square then consider also a second push
642 if (relative_rank(Us, blockSq) != RANK_8)
643 ebonus -= distance(pos.square<KING>(Us), blockSq + pawn_push(Us)) * rr;
645 // If the pawn is free to advance, then increase the bonus
646 if (pos.empty(blockSq))
648 // If there is a rook or queen attacking/defending the pawn from behind,
649 // consider all the squaresToQueen. Otherwise consider only the squares
650 // in the pawn's path attacked or occupied by the enemy.
651 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
653 bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
655 if (!(pos.pieces(Us) & bb))
656 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
658 if (!(pos.pieces(Them) & bb))
659 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
661 // If there aren't any enemy attacks, assign a big bonus. Otherwise
662 // assign a smaller bonus if the block square isn't attacked.
663 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
665 // If the path to the queen is fully defended, assign a big bonus.
666 // Otherwise assign a smaller bonus if the block square is defended.
667 if (defendedSquares == squaresToQueen)
670 else if (defendedSquares & blockSq)
673 mbonus += k * rr, ebonus += k * rr;
675 else if (pos.pieces(Us) & blockSq)
676 mbonus += rr + r * 2, ebonus += rr + r * 2;
679 // Assign a small bonus when no pieces left (unstoppable)
680 if (!pos.non_pawn_material(Us) && !pos.non_pawn_material(Them))
683 score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
687 Trace::add(PASSED, Us, score);
689 // Add the scores to the middlegame and endgame eval
694 // evaluate_space() computes the space evaluation for a given side. The
695 // space evaluation is a simple bonus based on the number of safe squares
696 // available for minor pieces on the central four files on ranks 2--4. Safe
697 // squares one, two or three squares behind a friendly pawn are counted
698 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
699 // improve play on game opening.
701 Score evaluate_space(const Position& pos, const EvalInfo& ei) {
703 const Color Them = (Us == WHITE ? BLACK : WHITE);
704 const Bitboard SpaceMask =
705 Us == WHITE ? (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank2BB | Rank3BB | Rank4BB)
706 : (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank7BB | Rank6BB | Rank5BB);
708 // Find the safe squares for our pieces inside the area defined by
709 // SpaceMask. A square is unsafe if it is attacked by an enemy
710 // pawn, or if it is undefended and attacked by an enemy piece.
711 Bitboard safe = SpaceMask
712 & ~pos.pieces(Us, PAWN)
713 & ~ei.attackedBy[Them][PAWN]
714 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
716 // Find all squares which are at most three squares behind some friendly pawn
717 Bitboard behind = pos.pieces(Us, PAWN);
718 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
719 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
721 // Since SpaceMask[Us] is fully on our half of the board...
722 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
724 // ...count safe + (behind & safe) with a single popcount
725 int bonus = popcount((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
726 bonus = std::min(16, bonus);
727 int weight = pos.count<ALL_PIECES>(Us) - 2 * ei.pi->open_files();
729 return make_score(bonus * weight * weight / 18, 0);
733 // evaluate_initiative() computes the initiative correction value for the
734 // position, i.e., second order bonus/malus based on the known attacking/defending
735 // status of the players.
736 Score evaluate_initiative(const Position& pos, int asymmetry, Value eg) {
738 int kingDistance = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
739 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
740 int pawns = pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK);
742 // Compute the initiative bonus for the attacking side
743 int initiative = 8 * (asymmetry + kingDistance - 15) + 12 * pawns;
745 // Now apply the bonus: note that we find the attacking side by extracting
746 // the sign of the endgame value, and that we carefully cap the bonus so
747 // that the endgame score will never be divided by more than two.
748 int value = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg / 2));
750 return make_score(0, value);
754 // evaluate_scale_factor() computes the scale factor for the winning side
755 ScaleFactor evaluate_scale_factor(const Position& pos, const EvalInfo& ei, Value eg) {
757 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
758 ScaleFactor sf = ei.me->scale_factor(pos, strongSide);
760 // If we don't already have an unusual scale factor, check for certain
761 // types of endgames, and use a lower scale for those.
762 if ( ei.me->game_phase() < PHASE_MIDGAME
763 && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
765 if (pos.opposite_bishops())
767 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
768 // is almost a draw, in case of KBP vs KB, it is even more a draw.
769 if ( pos.non_pawn_material(WHITE) == BishopValueMg
770 && pos.non_pawn_material(BLACK) == BishopValueMg)
771 sf = more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
773 // Endgame with opposite-colored bishops, but also other pieces. Still
774 // a bit drawish, but not as drawish as with only the two bishops.
776 sf = ScaleFactor(46);
778 // Endings where weaker side can place his king in front of the opponent's
779 // pawns are drawish.
780 else if ( abs(eg) <= BishopValueEg
781 && pos.count<PAWN>(strongSide) <= 2
782 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
783 sf = ScaleFactor(37 + 7 * pos.count<PAWN>(strongSide));
792 /// evaluate() is the main evaluation function. It returns a static evaluation
793 /// of the position from the point of view of the side to move.
795 template<bool DoTrace>
796 Value Eval::evaluate(const Position& pos) {
798 assert(!pos.checkers());
800 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
803 // Probe the material hash table
804 ei.me = Material::probe(pos);
806 // If we have a specialized evaluation function for the current material
807 // configuration, call it and return.
808 if (ei.me->specialized_eval_exists())
809 return ei.me->evaluate(pos);
811 // Initialize score by reading the incrementally updated scores included in
812 // the position object (material + piece square tables) and the material
813 // imbalance. Score is computed internally from the white point of view.
814 Score score = pos.psq_score() + ei.me->imbalance();
816 // Probe the pawn hash table
817 ei.pi = Pawns::probe(pos);
818 score += ei.pi->pawns_score();
820 // Initialize attack and king safety bitboards
821 ei.attackedBy[WHITE][ALL_PIECES] = ei.attackedBy[BLACK][ALL_PIECES] = 0;
822 ei.attackedBy[WHITE][KING] = pos.attacks_from<KING>(pos.square<KING>(WHITE));
823 ei.attackedBy[BLACK][KING] = pos.attacks_from<KING>(pos.square<KING>(BLACK));
824 eval_init<WHITE>(pos, ei);
825 eval_init<BLACK>(pos, ei);
827 // Pawns blocked or on ranks 2 and 3 will be excluded from the mobility area
828 Bitboard blockedPawns[] = {
829 pos.pieces(WHITE, PAWN) & (shift<SOUTH>(pos.pieces()) | Rank2BB | Rank3BB),
830 pos.pieces(BLACK, PAWN) & (shift<NORTH>(pos.pieces()) | Rank7BB | Rank6BB)
833 // Do not include in mobility area squares protected by enemy pawns, or occupied
834 // by our blocked pawns or king.
835 Bitboard mobilityArea[] = {
836 ~(ei.attackedBy[BLACK][PAWN] | blockedPawns[WHITE] | pos.square<KING>(WHITE)),
837 ~(ei.attackedBy[WHITE][PAWN] | blockedPawns[BLACK] | pos.square<KING>(BLACK))
840 // Evaluate all pieces but king and pawns
841 score += evaluate_pieces<DoTrace>(pos, ei, mobility, mobilityArea);
842 score += mobility[WHITE] - mobility[BLACK];
844 // Evaluate kings after all other pieces because we need full attack
845 // information when computing the king safety evaluation.
846 score += evaluate_king<WHITE, DoTrace>(pos, ei)
847 - evaluate_king<BLACK, DoTrace>(pos, ei);
849 // Evaluate tactical threats, we need full attack information including king
850 score += evaluate_threats<WHITE, DoTrace>(pos, ei)
851 - evaluate_threats<BLACK, DoTrace>(pos, ei);
853 // Evaluate passed pawns, we need full attack information including king
854 score += evaluate_passed_pawns<WHITE, DoTrace>(pos, ei)
855 - evaluate_passed_pawns<BLACK, DoTrace>(pos, ei);
857 // Evaluate space for both sides, only during opening
858 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
859 score += evaluate_space<WHITE>(pos, ei)
860 - evaluate_space<BLACK>(pos, ei);
862 // Evaluate position potential for the winning side
863 score += evaluate_initiative(pos, ei.pi->pawn_asymmetry(), eg_value(score));
865 // Evaluate scale factor for the winning side
866 ScaleFactor sf = evaluate_scale_factor(pos, ei, eg_value(score));
868 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
869 Value v = mg_value(score) * int(ei.me->game_phase())
870 + eg_value(score) * int(PHASE_MIDGAME - ei.me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
872 v /= int(PHASE_MIDGAME);
874 // In case of tracing add all remaining individual evaluation terms
877 Trace::add(MATERIAL, pos.psq_score());
878 Trace::add(IMBALANCE, ei.me->imbalance());
879 Trace::add(PAWN, ei.pi->pawns_score());
880 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
881 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
882 Trace::add(SPACE, evaluate_space<WHITE>(pos, ei)
883 , evaluate_space<BLACK>(pos, ei));
884 Trace::add(TOTAL, score);
887 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
890 // Explicit template instantiations
891 template Value Eval::evaluate<true >(const Position&);
892 template Value Eval::evaluate<false>(const Position&);
895 /// trace() is like evaluate(), but instead of returning a value, it returns
896 /// a string (suitable for outputting to stdout) that contains the detailed
897 /// descriptions and values of each evaluation term. Useful for debugging.
899 std::string Eval::trace(const Position& pos) {
901 std::memset(scores, 0, sizeof(scores));
903 Value v = evaluate<true>(pos);
904 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
906 std::stringstream ss;
907 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
908 << " Eval term | White | Black | Total \n"
909 << " | MG EG | MG EG | MG EG \n"
910 << "----------------+-------------+-------------+-------------\n"
911 << " Material | " << Term(MATERIAL)
912 << " Imbalance | " << Term(IMBALANCE)
913 << " Pawns | " << Term(PAWN)
914 << " Knights | " << Term(KNIGHT)
915 << " Bishop | " << Term(BISHOP)
916 << " Rooks | " << Term(ROOK)
917 << " Queens | " << Term(QUEEN)
918 << " Mobility | " << Term(MOBILITY)
919 << " King safety | " << Term(KING)
920 << " Threats | " << Term(THREAT)
921 << " Passed pawns | " << Term(PASSED)
922 << " Space | " << Term(SPACE)
923 << "----------------+-------------+-------------+-------------\n"
924 << " Total | " << Term(TOTAL);
926 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";