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(35, 0);
198 const Score Hanging = S(48, 27);
199 const Score ThreatByPawnPush = S(38, 22);
200 const Score Unstoppable = S( 0, 20);
201 const Score PawnlessFlank = S(20, 80);
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 = 695;
217 const int RookCheck = 638;
218 const int BishopCheck = 538;
219 const int KnightCheck = 874;
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 && (rank_of(ksq) == rank_of(s) || relative_rank(Us, ksq) == RANK_1)
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]);
563 score += Threat[Minor][type_of(pos.piece_on(pop_lsb(&b)))];
565 b = (pos.pieces(Them, QUEEN) | weak) & ei.attackedBy[Us][ROOK];
567 score += Threat[Rook ][type_of(pos.piece_on(pop_lsb(&b)))];
569 score += Hanging * popcount(weak & ~ei.attackedBy[Them][ALL_PIECES]);
571 b = weak & ei.attackedBy[Us][KING];
573 score += ThreatByKing[more_than_one(b)];
576 // Bonus if some pawns can safely push and attack an enemy piece
577 b = pos.pieces(Us, PAWN) & ~TRank7BB;
578 b = shift<Up>(b | (shift<Up>(b & TRank2BB) & ~pos.pieces()));
581 & ~ei.attackedBy[Them][PAWN]
582 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
584 b = (shift<Left>(b) | shift<Right>(b))
586 & ~ei.attackedBy[Us][PAWN];
588 score += ThreatByPawnPush * popcount(b);
591 Trace::add(THREAT, Us, score);
597 // evaluate_passed_pawns() evaluates the passed pawns of the given color
599 template<Color Us, bool DoTrace>
600 Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
602 const Color Them = (Us == WHITE ? BLACK : WHITE);
604 Bitboard b, squaresToQueen, defendedSquares, unsafeSquares;
605 Score score = SCORE_ZERO;
607 b = ei.pi->passed_pawns(Us);
611 Square s = pop_lsb(&b);
613 assert(pos.pawn_passed(Us, s));
614 assert(!(pos.pieces(PAWN) & forward_bb(Us, s)));
616 int r = relative_rank(Us, s) - RANK_2;
617 int rr = r * (r - 1);
619 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
623 Square blockSq = s + pawn_push(Us);
625 // Adjust bonus based on the king's proximity
626 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
627 - distance(pos.square<KING>(Us ), blockSq) * 2 * rr;
629 // If blockSq is not the queening square then consider also a second push
630 if (relative_rank(Us, blockSq) != RANK_8)
631 ebonus -= distance(pos.square<KING>(Us), blockSq + pawn_push(Us)) * rr;
633 // If the pawn is free to advance, then increase the bonus
634 if (pos.empty(blockSq))
636 // If there is a rook or queen attacking/defending the pawn from behind,
637 // consider all the squaresToQueen. Otherwise consider only the squares
638 // in the pawn's path attacked or occupied by the enemy.
639 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
641 Bitboard bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
643 if (!(pos.pieces(Us) & bb))
644 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
646 if (!(pos.pieces(Them) & bb))
647 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
649 // If there aren't any enemy attacks, assign a big bonus. Otherwise
650 // assign a smaller bonus if the block square isn't attacked.
651 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
653 // If the path to the queen is fully defended, assign a big bonus.
654 // Otherwise assign a smaller bonus if the block square is defended.
655 if (defendedSquares == squaresToQueen)
658 else if (defendedSquares & blockSq)
661 mbonus += k * rr, ebonus += k * rr;
663 else if (pos.pieces(Us) & blockSq)
664 mbonus += rr + r * 2, ebonus += rr + r * 2;
667 score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
671 Trace::add(PASSED, Us, score);
673 // Add the scores to the middlegame and endgame eval
678 // evaluate_space() computes the space evaluation for a given side. The
679 // space evaluation is a simple bonus based on the number of safe squares
680 // available for minor pieces on the central four files on ranks 2--4. Safe
681 // squares one, two or three squares behind a friendly pawn are counted
682 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
683 // improve play on game opening.
685 Score evaluate_space(const Position& pos, const EvalInfo& ei) {
687 const Color Them = (Us == WHITE ? BLACK : WHITE);
688 const Bitboard SpaceMask =
689 Us == WHITE ? (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank2BB | Rank3BB | Rank4BB)
690 : (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank7BB | Rank6BB | Rank5BB);
692 // Find the safe squares for our pieces inside the area defined by
693 // SpaceMask. A square is unsafe if it is attacked by an enemy
694 // pawn, or if it is undefended and attacked by an enemy piece.
695 Bitboard safe = SpaceMask
696 & ~pos.pieces(Us, PAWN)
697 & ~ei.attackedBy[Them][PAWN]
698 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
700 // Find all squares which are at most three squares behind some friendly pawn
701 Bitboard behind = pos.pieces(Us, PAWN);
702 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
703 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
705 // Since SpaceMask[Us] is fully on our half of the board...
706 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
708 // ...count safe + (behind & safe) with a single popcount
709 int bonus = popcount((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
710 bonus = std::min(16, bonus);
711 int weight = pos.count<ALL_PIECES>(Us) - 2 * ei.pi->open_files();
713 return make_score(bonus * weight * weight / 18, 0);
717 // evaluate_initiative() computes the initiative correction value for the
718 // position, i.e., second order bonus/malus based on the known attacking/defending
719 // status of the players.
720 Score evaluate_initiative(const Position& pos, int asymmetry, Value eg) {
722 int kingDistance = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
723 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
724 int pawns = pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK);
726 // Compute the initiative bonus for the attacking side
727 int initiative = 8 * (asymmetry + kingDistance - 15) + 12 * pawns;
729 // Now apply the bonus: note that we find the attacking side by extracting
730 // the sign of the endgame value, and that we carefully cap the bonus so
731 // that the endgame score will never be divided by more than two.
732 int value = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg / 2));
734 return make_score(0, value);
738 // evaluate_scale_factor() computes the scale factor for the winning side
739 ScaleFactor evaluate_scale_factor(const Position& pos, const EvalInfo& ei, Value eg) {
741 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
742 ScaleFactor sf = ei.me->scale_factor(pos, strongSide);
744 // If we don't already have an unusual scale factor, check for certain
745 // types of endgames, and use a lower scale for those.
746 if ( ei.me->game_phase() < PHASE_MIDGAME
747 && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
749 if (pos.opposite_bishops())
751 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
752 // is almost a draw, in case of KBP vs KB, it is even more a draw.
753 if ( pos.non_pawn_material(WHITE) == BishopValueMg
754 && pos.non_pawn_material(BLACK) == BishopValueMg)
755 sf = more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
757 // Endgame with opposite-colored bishops, but also other pieces. Still
758 // a bit drawish, but not as drawish as with only the two bishops.
760 sf = 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 sf = 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 };
787 // Probe the material hash table
788 ei.me = Material::probe(pos);
790 // If we have a specialized evaluation function for the current material
791 // configuration, call it and return.
792 if (ei.me->specialized_eval_exists())
793 return ei.me->evaluate(pos);
795 // Initialize score by reading the incrementally updated scores included in
796 // the position object (material + piece square tables) and the material
797 // imbalance. Score is computed internally from the white point of view.
798 Score score = pos.psq_score() + ei.me->imbalance();
800 // Probe the pawn hash table
801 ei.pi = Pawns::probe(pos);
802 score += ei.pi->pawns_score();
804 // Initialize attack and king safety bitboards
805 ei.attackedBy[WHITE][ALL_PIECES] = ei.attackedBy[BLACK][ALL_PIECES] = 0;
806 ei.attackedBy[WHITE][KING] = pos.attacks_from<KING>(pos.square<KING>(WHITE));
807 ei.attackedBy[BLACK][KING] = pos.attacks_from<KING>(pos.square<KING>(BLACK));
808 eval_init<WHITE>(pos, ei);
809 eval_init<BLACK>(pos, ei);
811 // Pawns blocked or on ranks 2 and 3 will be excluded from the mobility area
812 Bitboard blockedPawns[] = {
813 pos.pieces(WHITE, PAWN) & (shift<SOUTH>(pos.pieces()) | Rank2BB | Rank3BB),
814 pos.pieces(BLACK, PAWN) & (shift<NORTH>(pos.pieces()) | Rank7BB | Rank6BB)
817 // Do not include in mobility area squares protected by enemy pawns, or occupied
818 // by our blocked pawns or king.
819 Bitboard mobilityArea[] = {
820 ~(ei.attackedBy[BLACK][PAWN] | blockedPawns[WHITE] | pos.square<KING>(WHITE)),
821 ~(ei.attackedBy[WHITE][PAWN] | blockedPawns[BLACK] | pos.square<KING>(BLACK))
824 // Evaluate all pieces but king and pawns
825 score += evaluate_pieces<DoTrace>(pos, ei, mobility, mobilityArea);
826 score += mobility[WHITE] - mobility[BLACK];
828 // Evaluate kings after all other pieces because we need full attack
829 // information when computing the king safety evaluation.
830 score += evaluate_king<WHITE, DoTrace>(pos, ei)
831 - evaluate_king<BLACK, DoTrace>(pos, ei);
833 // Evaluate tactical threats, we need full attack information including king
834 score += evaluate_threats<WHITE, DoTrace>(pos, ei)
835 - evaluate_threats<BLACK, DoTrace>(pos, ei);
837 // Evaluate passed pawns, we need full attack information including king
838 score += evaluate_passed_pawns<WHITE, DoTrace>(pos, ei)
839 - evaluate_passed_pawns<BLACK, DoTrace>(pos, ei);
841 // If both sides have only pawns, score for potential unstoppable pawns
842 if (!pos.non_pawn_material(WHITE) && !pos.non_pawn_material(BLACK))
845 if ((b = ei.pi->passed_pawns(WHITE)) != 0)
846 score += Unstoppable * int(relative_rank(WHITE, frontmost_sq(WHITE, b)));
848 if ((b = ei.pi->passed_pawns(BLACK)) != 0)
849 score -= Unstoppable * int(relative_rank(BLACK, frontmost_sq(BLACK, b)));
852 // Evaluate space for both sides, only during opening
853 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
854 score += evaluate_space<WHITE>(pos, ei)
855 - evaluate_space<BLACK>(pos, ei);
857 // Evaluate position potential for the winning side
858 score += evaluate_initiative(pos, ei.pi->pawn_asymmetry(), eg_value(score));
860 // Evaluate scale factor for the winning side
861 ScaleFactor sf = evaluate_scale_factor(pos, ei, eg_value(score));
863 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
864 Value v = mg_value(score) * int(ei.me->game_phase())
865 + eg_value(score) * int(PHASE_MIDGAME - ei.me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
867 v /= int(PHASE_MIDGAME);
869 // In case of tracing add all remaining individual evaluation terms
872 Trace::add(MATERIAL, pos.psq_score());
873 Trace::add(IMBALANCE, ei.me->imbalance());
874 Trace::add(PAWN, ei.pi->pawns_score());
875 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
876 Trace::add(SPACE, evaluate_space<WHITE>(pos, ei)
877 , evaluate_space<BLACK>(pos, ei));
878 Trace::add(TOTAL, score);
881 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
884 // Explicit template instantiations
885 template Value Eval::evaluate<true >(const Position&);
886 template Value Eval::evaluate<false>(const Position&);
889 /// trace() is like evaluate(), but instead of returning a value, it returns
890 /// a string (suitable for outputting to stdout) that contains the detailed
891 /// descriptions and values of each evaluation term. Useful for debugging.
893 std::string Eval::trace(const Position& pos) {
895 std::memset(scores, 0, sizeof(scores));
897 Value v = evaluate<true>(pos);
898 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
900 std::stringstream ss;
901 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
902 << " Eval term | White | Black | Total \n"
903 << " | MG EG | MG EG | MG EG \n"
904 << "----------------+-------------+-------------+-------------\n"
905 << " Material | " << Term(MATERIAL)
906 << " Imbalance | " << Term(IMBALANCE)
907 << " Pawns | " << Term(PAWN)
908 << " Knights | " << Term(KNIGHT)
909 << " Bishop | " << Term(BISHOP)
910 << " Rooks | " << Term(ROOK)
911 << " Queens | " << Term(QUEEN)
912 << " Mobility | " << Term(MOBILITY)
913 << " King safety | " << Term(KING)
914 << " Threats | " << Term(THREAT)
915 << " Passed pawns | " << Term(PASSED)
916 << " Space | " << Term(SPACE)
917 << "----------------+-------------+-------------+-------------\n"
918 << " Total | " << Term(TOTAL);
920 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";