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) };
161 // Threat[by minor/by rook][attacked PieceType] contains
162 // bonuses according to which piece type attacks which one.
163 // Attacks on lesser pieces which are pawn-defended are not considered.
164 const Score Threat[][PIECE_TYPE_NB] = {
165 { S(0, 0), S(0, 33), S(45, 43), S(46, 47), S(72,107), S(48,118) }, // by Minor
166 { S(0, 0), S(0, 25), S(40, 62), S(40, 59), S( 0, 34), S(35, 48) } // by Rook
169 // ThreatByKing[on one/on many] contains bonuses for King attacks on
170 // pawns or pieces which are not pawn-defended.
171 const Score ThreatByKing[2] = { S(3, 62), S(9, 138) };
173 // Passed[mg/eg][Rank] contains midgame and endgame bonuses for passed pawns.
174 // We don't use a Score because we process the two components independently.
175 const Value Passed[][RANK_NB] = {
176 { V(5), V( 5), V(31), V(73), V(166), V(252) },
177 { V(7), V(14), V(38), V(73), V(166), V(252) }
180 // PassedFile[File] contains a bonus according to the file of a passed pawn
181 const Score PassedFile[FILE_NB] = {
182 S( 9, 10), S( 2, 10), S( 1, -8), S(-20,-12),
183 S(-20,-12), S( 1, -8), S( 2, 10), S( 9, 10)
186 // Assorted bonuses and penalties used by evaluation
187 const Score MinorBehindPawn = S(16, 0);
188 const Score BishopPawns = S( 8, 12);
189 const Score RookOnPawn = S( 8, 24);
190 const Score TrappedRook = S(92, 0);
191 const Score CloseEnemies = S( 7, 0);
192 const Score SafeCheck = S(20, 20);
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(35, 0);
197 const Score Hanging = S(48, 27);
198 const Score ThreatByPawnPush = S(38, 22);
199 const Score Unstoppable = S( 0, 20);
201 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
202 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
203 // happen in Chess960 games.
204 const Score TrappedBishopA1H1 = S(50, 50);
209 // KingAttackWeights[PieceType] contains king attack weights by piece type
210 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 78, 56, 45, 11 };
212 // Penalties for enemy's safe checks
213 const int QueenContactCheck = 997;
214 const int QueenCheck = 695;
215 const int RookCheck = 638;
216 const int BishopCheck = 538;
217 const int KnightCheck = 874;
220 // eval_init() initializes king and attack bitboards for a given color
221 // adding pawn attacks. To be done at the beginning of the evaluation.
224 void eval_init(const Position& pos, EvalInfo& ei) {
226 const Color Them = (Us == WHITE ? BLACK : WHITE);
227 const Square Down = (Us == WHITE ? DELTA_S : DELTA_N);
229 ei.pinnedPieces[Us] = pos.pinned_pieces(Us);
230 Bitboard b = ei.attackedBy[Them][KING];
231 ei.attackedBy[Them][ALL_PIECES] |= b;
232 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
233 ei.attackedBy2[Us] = ei.attackedBy[Us][PAWN] & ei.attackedBy[Us][KING];
235 // Init king safety tables only if we are going to use them
236 if (pos.non_pawn_material(Us) >= QueenValueMg)
238 ei.kingRing[Them] = b | shift_bb<Down>(b);
239 b &= ei.attackedBy[Us][PAWN];
240 ei.kingAttackersCount[Us] = popcount(b);
241 ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
244 ei.kingRing[Them] = ei.kingAttackersCount[Us] = 0;
248 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given
251 template<bool DoTrace, Color Us = WHITE, PieceType Pt = KNIGHT>
252 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility,
253 const Bitboard* mobilityArea) {
256 Score score = SCORE_ZERO;
258 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
259 const Color Them = (Us == WHITE ? BLACK : WHITE);
260 const Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
261 : Rank5BB | Rank4BB | Rank3BB);
262 const Square* pl = pos.squares<Pt>(Us);
264 ei.attackedBy[Us][Pt] = 0;
266 while ((s = *pl++) != SQ_NONE)
268 // Find attacked squares, including x-ray attacks for bishops and rooks
269 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
270 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
271 : pos.attacks_from<Pt>(s);
273 if (ei.pinnedPieces[Us] & s)
274 b &= LineBB[pos.square<KING>(Us)][s];
276 ei.attackedBy2[Us] |= ei.attackedBy[Us][ALL_PIECES] & b;
277 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
279 if (b & ei.kingRing[Them])
281 ei.kingAttackersCount[Us]++;
282 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
283 ei.kingAdjacentZoneAttacksCount[Us] += popcount(b & ei.attackedBy[Them][KING]);
287 b &= ~( ei.attackedBy[Them][KNIGHT]
288 | ei.attackedBy[Them][BISHOP]
289 | ei.attackedBy[Them][ROOK]);
291 int mob = popcount(b & mobilityArea[Us]);
293 mobility[Us] += MobilityBonus[Pt][mob];
295 if (Pt == BISHOP || Pt == KNIGHT)
297 // Bonus for outpost squares
298 bb = OutpostRanks & ~ei.pi->pawn_attacks_span(Them);
300 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & s)];
303 bb &= b & ~pos.pieces(Us);
305 score += ReachableOutpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & bb)];
308 // Bonus when behind a pawn
309 if ( relative_rank(Us, s) < RANK_5
310 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
311 score += MinorBehindPawn;
313 // Penalty for pawns on the same color square as the bishop
315 score -= BishopPawns * ei.pi->pawns_on_same_color_squares(Us, s);
317 // An important Chess960 pattern: A cornered bishop blocked by a friendly
318 // pawn diagonally in front of it is a very serious problem, especially
319 // when that pawn is also blocked.
322 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
324 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? DELTA_E : DELTA_W);
325 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
326 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
327 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
334 // Bonus for aligning with enemy pawns on the same rank/file
335 if (relative_rank(Us, s) >= RANK_5)
336 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
338 // Bonus when on an open or semi-open file
339 if (ei.pi->semiopen_file(Us, file_of(s)))
340 score += RookOnFile[!!ei.pi->semiopen_file(Them, file_of(s))];
342 // Penalize when trapped by the king, even more if the king cannot castle
345 Square ksq = pos.square<KING>(Us);
347 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
348 && (rank_of(ksq) == rank_of(s) || relative_rank(Us, ksq) == RANK_1)
349 && !ei.pi->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
350 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
356 // Penalty if any relative pin or discovered attack against the queen
358 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, pinners))
364 Trace::add(Pt, Us, score);
366 // Recursively call evaluate_pieces() of next piece type until KING is excluded
367 return score - evaluate_pieces<DoTrace, Them, NextPt>(pos, ei, mobility, mobilityArea);
371 Score evaluate_pieces<false, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
373 Score evaluate_pieces< true, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
376 // evaluate_king() assigns bonuses and penalties to a king of a given color
378 const Bitboard WhiteCamp = Rank1BB | Rank2BB | Rank3BB | Rank4BB | Rank5BB;
379 const Bitboard BlackCamp = Rank8BB | Rank7BB | Rank6BB | Rank5BB | Rank4BB;
380 const Bitboard QueenSide = FileABB | FileBBB | FileCBB | FileDBB;
381 const Bitboard CenterFiles = FileCBB | FileDBB | FileEBB | FileFBB;
382 const Bitboard KingSide = FileEBB | FileFBB | FileGBB | FileHBB;
384 const Bitboard KingFlank[COLOR_NB][FILE_NB] = {
385 { QueenSide & WhiteCamp, QueenSide & WhiteCamp, QueenSide & WhiteCamp, CenterFiles & WhiteCamp,
386 CenterFiles & WhiteCamp, KingSide & WhiteCamp, KingSide & WhiteCamp, KingSide & WhiteCamp },
387 { QueenSide & BlackCamp, QueenSide & BlackCamp, QueenSide & BlackCamp, CenterFiles & BlackCamp,
388 CenterFiles & BlackCamp, KingSide & BlackCamp, KingSide & BlackCamp, KingSide & BlackCamp },
391 template<Color Us, bool DoTrace>
392 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
394 const Color Them = (Us == WHITE ? BLACK : WHITE);
395 const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
397 Bitboard undefended, b, b1, b2, safe, other;
399 const Square ksq = pos.square<KING>(Us);
401 // King shelter and enemy pawns storm
402 Score score = ei.pi->king_safety<Us>(pos, ksq);
404 // Main king safety evaluation
405 if (ei.kingAttackersCount[Them])
407 // Find the attacked squares which are defended only by the king...
408 undefended = ei.attackedBy[Them][ALL_PIECES]
409 & ei.attackedBy[Us][KING]
410 & ~ei.attackedBy2[Us];
412 // ... and those which are not defended at all in the larger king ring
413 b = ei.attackedBy[Them][ALL_PIECES] & ~ei.attackedBy[Us][ALL_PIECES]
414 & ei.kingRing[Us] & ~pos.pieces(Them);
416 // Initialize the 'kingDanger' variable, which will be transformed
417 // later into a king danger score. The initial value is based on the
418 // number and types of the enemy's attacking pieces, the number of
419 // attacked and undefended squares around our king and the quality of
420 // the pawn shelter (current 'score' value).
421 kingDanger = std::min(807, ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them])
422 + 101 * ei.kingAdjacentZoneAttacksCount[Them]
423 + 235 * popcount(undefended)
424 + 134 * (popcount(b) + !!ei.pinnedPieces[Us])
425 - 717 * !pos.count<QUEEN>(Them)
426 - 7 * mg_value(score) / 5 - 5;
428 // Analyse the enemy's safe queen contact checks. Firstly, find the
429 // undefended squares around the king reachable by the enemy queen...
430 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);
432 // ...and keep squares supported by another enemy piece
433 kingDanger += QueenContactCheck * popcount(b & ei.attackedBy2[Them]);
435 // Analyse the safe enemy's checks which are possible on next move...
436 safe = ~(ei.attackedBy[Us][ALL_PIECES] | pos.pieces(Them));
438 // ... and some other potential checks, only requiring the square to be
439 // safe from pawn-attacks, and not being occupied by a blocked pawn.
440 other = ~( ei.attackedBy[Us][PAWN]
441 | (pos.pieces(Them, PAWN) & shift_bb<Up>(pos.pieces(PAWN))));
443 b1 = pos.attacks_from<ROOK >(ksq);
444 b2 = pos.attacks_from<BISHOP>(ksq);
446 // Enemy queen safe checks
447 if ((b1 | b2) & ei.attackedBy[Them][QUEEN] & safe)
448 kingDanger += QueenCheck, score -= SafeCheck;
450 // For other pieces, also consider the square safe if attacked twice,
451 // and only defended by a queen.
452 safe |= ei.attackedBy2[Them]
453 & ~(ei.attackedBy2[Us] | pos.pieces(Them))
454 & ei.attackedBy[Us][QUEEN];
456 // Enemy rooks safe and other checks
457 if (b1 & ei.attackedBy[Them][ROOK] & safe)
458 kingDanger += RookCheck, score -= SafeCheck;
460 else if (b1 & ei.attackedBy[Them][ROOK] & other)
463 // Enemy bishops safe and other checks
464 if (b2 & ei.attackedBy[Them][BISHOP] & safe)
465 kingDanger += BishopCheck, score -= SafeCheck;
467 else if (b2 & ei.attackedBy[Them][BISHOP] & other)
470 // Enemy knights safe and other checks
471 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT];
473 kingDanger += KnightCheck, score -= SafeCheck;
478 // Compute the king danger score and subtract it from the evaluation
480 score -= make_score(std::min(kingDanger * kingDanger / 4096, 2 * int(BishopValueMg)), 0);
483 // King tropism: firstly, find squares that opponent attacks in our king flank
484 b = ei.attackedBy[Them][ALL_PIECES] & KingFlank[Us][file_of(ksq)];
486 assert(((Us == WHITE ? b << 4 : b >> 4) & b) == 0);
487 assert(popcount(Us == WHITE ? b << 4 : b >> 4) == popcount(b));
489 // Secondly, add the squares which are attacked twice in that flank and
490 // which are not defended by our pawns.
491 b = (Us == WHITE ? b << 4 : b >> 4)
492 | (b & ei.attackedBy2[Them] & ~ei.attackedBy[Us][PAWN]);
494 score -= CloseEnemies * popcount(b);
497 Trace::add(KING, Us, score);
503 // evaluate_threats() assigns bonuses according to the types of the attacking
504 // and the attacked pieces.
506 template<Color Us, bool DoTrace>
507 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
509 const Color Them = (Us == WHITE ? BLACK : WHITE);
510 const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
511 const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE);
512 const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
513 const Bitboard TRank2BB = (Us == WHITE ? Rank2BB : Rank7BB);
514 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
516 enum { Minor, Rook };
518 Bitboard b, weak, defended, safeThreats;
519 Score score = SCORE_ZERO;
521 // Small bonus if the opponent has loose pawns or pieces
522 if ( (pos.pieces(Them) ^ pos.pieces(Them, QUEEN, KING))
523 & ~(ei.attackedBy[Us][ALL_PIECES] | ei.attackedBy[Them][ALL_PIECES]))
524 score += LooseEnemies;
526 // Non-pawn enemies attacked by a pawn
527 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Us][PAWN];
531 b = pos.pieces(Us, PAWN) & ( ~ei.attackedBy[Them][ALL_PIECES]
532 | ei.attackedBy[Us][ALL_PIECES]);
534 safeThreats = (shift_bb<Right>(b) | shift_bb<Left>(b)) & weak;
536 if (weak ^ safeThreats)
537 score += ThreatByHangingPawn;
540 score += ThreatBySafePawn[type_of(pos.piece_on(pop_lsb(&safeThreats)))];
543 // Non-pawn enemies defended by a pawn
544 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Them][PAWN];
546 // Enemies not defended by a pawn and under our attack
547 weak = pos.pieces(Them)
548 & ~ei.attackedBy[Them][PAWN]
549 & ei.attackedBy[Us][ALL_PIECES];
551 // Add a bonus according to the kind of attacking pieces
554 b = (defended | weak) & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
556 score += Threat[Minor][type_of(pos.piece_on(pop_lsb(&b)))];
558 b = (pos.pieces(Them, QUEEN) | weak) & ei.attackedBy[Us][ROOK];
560 score += Threat[Rook ][type_of(pos.piece_on(pop_lsb(&b)))];
562 score += Hanging * popcount(weak & ~ei.attackedBy[Them][ALL_PIECES]);
564 b = weak & ei.attackedBy[Us][KING];
566 score += ThreatByKing[more_than_one(b)];
569 // Bonus if some pawns can safely push and attack an enemy piece
570 b = pos.pieces(Us, PAWN) & ~TRank7BB;
571 b = shift_bb<Up>(b | (shift_bb<Up>(b & TRank2BB) & ~pos.pieces()));
574 & ~ei.attackedBy[Them][PAWN]
575 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
577 b = (shift_bb<Left>(b) | shift_bb<Right>(b))
579 & ~ei.attackedBy[Us][PAWN];
581 score += ThreatByPawnPush * popcount(b);
584 Trace::add(THREAT, Us, score);
590 // evaluate_passed_pawns() evaluates the passed pawns of the given color
592 template<Color Us, bool DoTrace>
593 Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
595 const Color Them = (Us == WHITE ? BLACK : WHITE);
597 Bitboard b, squaresToQueen, defendedSquares, unsafeSquares;
598 Score score = SCORE_ZERO;
600 b = ei.pi->passed_pawns(Us);
604 Square s = pop_lsb(&b);
606 assert(pos.pawn_passed(Us, s));
607 assert(!(pos.pieces(PAWN) & forward_bb(Us, s)));
609 int r = relative_rank(Us, s) - RANK_2;
610 int rr = r * (r - 1);
612 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
616 Square blockSq = s + pawn_push(Us);
618 // Adjust bonus based on the king's proximity
619 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
620 - distance(pos.square<KING>(Us ), blockSq) * 2 * rr;
622 // If blockSq is not the queening square then consider also a second push
623 if (relative_rank(Us, blockSq) != RANK_8)
624 ebonus -= distance(pos.square<KING>(Us), blockSq + pawn_push(Us)) * rr;
626 // If the pawn is free to advance, then increase the bonus
627 if (pos.empty(blockSq))
629 // If there is a rook or queen attacking/defending the pawn from behind,
630 // consider all the squaresToQueen. Otherwise consider only the squares
631 // in the pawn's path attacked or occupied by the enemy.
632 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
634 Bitboard bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
636 if (!(pos.pieces(Us) & bb))
637 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
639 if (!(pos.pieces(Them) & bb))
640 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
642 // If there aren't any enemy attacks, assign a big bonus. Otherwise
643 // assign a smaller bonus if the block square isn't attacked.
644 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
646 // If the path to the queen is fully defended, assign a big bonus.
647 // Otherwise assign a smaller bonus if the block square is defended.
648 if (defendedSquares == squaresToQueen)
651 else if (defendedSquares & blockSq)
654 mbonus += k * rr, ebonus += k * rr;
656 else if (pos.pieces(Us) & blockSq)
657 mbonus += rr + r * 2, ebonus += rr + r * 2;
660 score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
664 Trace::add(PASSED, Us, score);
666 // Add the scores to the middlegame and endgame eval
671 // evaluate_space() computes the space evaluation for a given side. The
672 // space evaluation is a simple bonus based on the number of safe squares
673 // available for minor pieces on the central four files on ranks 2--4. Safe
674 // squares one, two or three squares behind a friendly pawn are counted
675 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
676 // improve play on game opening.
678 Score evaluate_space(const Position& pos, const EvalInfo& ei) {
680 const Color Them = (Us == WHITE ? BLACK : WHITE);
681 const Bitboard SpaceMask =
682 Us == WHITE ? (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank2BB | Rank3BB | Rank4BB)
683 : (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank7BB | Rank6BB | Rank5BB);
685 // Find the safe squares for our pieces inside the area defined by
686 // SpaceMask. A square is unsafe if it is attacked by an enemy
687 // pawn, or if it is undefended and attacked by an enemy piece.
688 Bitboard safe = SpaceMask
689 & ~pos.pieces(Us, PAWN)
690 & ~ei.attackedBy[Them][PAWN]
691 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
693 // Find all squares which are at most three squares behind some friendly pawn
694 Bitboard behind = pos.pieces(Us, PAWN);
695 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
696 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
698 // Since SpaceMask[Us] is fully on our half of the board...
699 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
701 // ...count safe + (behind & safe) with a single popcount
702 int bonus = popcount((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
703 bonus = std::min(16, bonus);
704 int weight = pos.count<ALL_PIECES>(Us) - 2 * ei.pi->open_files();
706 return make_score(bonus * weight * weight / 18, 0);
710 // evaluate_initiative() computes the initiative correction value for the
711 // position, i.e., second order bonus/malus based on the known attacking/defending
712 // status of the players.
713 Score evaluate_initiative(const Position& pos, int asymmetry, Value eg) {
715 int kingDistance = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
716 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
717 int pawns = pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK);
719 // Compute the initiative bonus for the attacking side
720 int initiative = 8 * (asymmetry + kingDistance - 15) + 12 * pawns;
722 // Now apply the bonus: note that we find the attacking side by extracting
723 // the sign of the endgame value, and that we carefully cap the bonus so
724 // that the endgame score will never be divided by more than two.
725 int value = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg / 2));
727 return make_score(0, value);
731 // evaluate_scale_factor() computes the scale factor for the winning side
732 ScaleFactor evaluate_scale_factor(const Position& pos, const EvalInfo& ei, Value eg) {
734 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
735 ScaleFactor sf = ei.me->scale_factor(pos, strongSide);
737 // If we don't already have an unusual scale factor, check for certain
738 // types of endgames, and use a lower scale for those.
739 if ( ei.me->game_phase() < PHASE_MIDGAME
740 && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
742 if (pos.opposite_bishops())
744 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
745 // is almost a draw, in case of KBP vs KB, it is even more a draw.
746 if ( pos.non_pawn_material(WHITE) == BishopValueMg
747 && pos.non_pawn_material(BLACK) == BishopValueMg)
748 sf = more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
750 // Endgame with opposite-colored bishops, but also other pieces. Still
751 // a bit drawish, but not as drawish as with only the two bishops.
753 sf = ScaleFactor(46);
755 // Endings where weaker side can place his king in front of the opponent's
756 // pawns are drawish.
757 else if ( abs(eg) <= BishopValueEg
758 && pos.count<PAWN>(strongSide) <= 2
759 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
760 sf = ScaleFactor(37 + 7 * pos.count<PAWN>(strongSide));
769 /// evaluate() is the main evaluation function. It returns a static evaluation
770 /// of the position from the point of view of the side to move.
772 template<bool DoTrace>
773 Value Eval::evaluate(const Position& pos) {
775 assert(!pos.checkers());
777 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
780 // Probe the material hash table
781 ei.me = Material::probe(pos);
783 // If we have a specialized evaluation function for the current material
784 // configuration, call it and return.
785 if (ei.me->specialized_eval_exists())
786 return ei.me->evaluate(pos);
788 // Initialize score by reading the incrementally updated scores included in
789 // the position object (material + piece square tables) and the material
790 // imbalance. Score is computed internally from the white point of view.
791 Score score = pos.psq_score() + ei.me->imbalance();
793 // Probe the pawn hash table
794 ei.pi = Pawns::probe(pos);
795 score += ei.pi->pawns_score();
797 // Initialize attack and king safety bitboards
798 ei.attackedBy[WHITE][ALL_PIECES] = ei.attackedBy[BLACK][ALL_PIECES] = 0;
799 ei.attackedBy[WHITE][KING] = pos.attacks_from<KING>(pos.square<KING>(WHITE));
800 ei.attackedBy[BLACK][KING] = pos.attacks_from<KING>(pos.square<KING>(BLACK));
801 eval_init<WHITE>(pos, ei);
802 eval_init<BLACK>(pos, ei);
804 // Pawns blocked or on ranks 2 and 3 will be excluded from the mobility area
805 Bitboard blockedPawns[] = {
806 pos.pieces(WHITE, PAWN) & (shift_bb<DELTA_S>(pos.pieces()) | Rank2BB | Rank3BB),
807 pos.pieces(BLACK, PAWN) & (shift_bb<DELTA_N>(pos.pieces()) | Rank7BB | Rank6BB)
810 // Do not include in mobility area squares protected by enemy pawns, or occupied
811 // by our blocked pawns or king.
812 Bitboard mobilityArea[] = {
813 ~(ei.attackedBy[BLACK][PAWN] | blockedPawns[WHITE] | pos.square<KING>(WHITE)),
814 ~(ei.attackedBy[WHITE][PAWN] | blockedPawns[BLACK] | pos.square<KING>(BLACK))
817 // Evaluate all pieces but king and pawns
818 score += evaluate_pieces<DoTrace>(pos, ei, mobility, mobilityArea);
819 score += mobility[WHITE] - mobility[BLACK];
821 // Evaluate kings after all other pieces because we need full attack
822 // information when computing the king safety evaluation.
823 score += evaluate_king<WHITE, DoTrace>(pos, ei)
824 - evaluate_king<BLACK, DoTrace>(pos, ei);
826 // Evaluate tactical threats, we need full attack information including king
827 score += evaluate_threats<WHITE, DoTrace>(pos, ei)
828 - evaluate_threats<BLACK, DoTrace>(pos, ei);
830 // Evaluate passed pawns, we need full attack information including king
831 score += evaluate_passed_pawns<WHITE, DoTrace>(pos, ei)
832 - evaluate_passed_pawns<BLACK, DoTrace>(pos, ei);
834 // If both sides have only pawns, score for potential unstoppable pawns
835 if (!pos.non_pawn_material(WHITE) && !pos.non_pawn_material(BLACK))
838 if ((b = ei.pi->passed_pawns(WHITE)) != 0)
839 score += Unstoppable * int(relative_rank(WHITE, frontmost_sq(WHITE, b)));
841 if ((b = ei.pi->passed_pawns(BLACK)) != 0)
842 score -= Unstoppable * int(relative_rank(BLACK, frontmost_sq(BLACK, b)));
845 // Evaluate space for both sides, only during opening
846 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
847 score += evaluate_space<WHITE>(pos, ei)
848 - evaluate_space<BLACK>(pos, ei);
850 // Evaluate position potential for the winning side
851 score += evaluate_initiative(pos, ei.pi->pawn_asymmetry(), eg_value(score));
853 // Evaluate scale factor for the winning side
854 ScaleFactor sf = evaluate_scale_factor(pos, ei, eg_value(score));
856 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
857 Value v = mg_value(score) * int(ei.me->game_phase())
858 + eg_value(score) * int(PHASE_MIDGAME - ei.me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
860 v /= int(PHASE_MIDGAME);
862 // In case of tracing add all remaining individual evaluation terms
865 Trace::add(MATERIAL, pos.psq_score());
866 Trace::add(IMBALANCE, ei.me->imbalance());
867 Trace::add(PAWN, ei.pi->pawns_score());
868 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
869 Trace::add(SPACE, evaluate_space<WHITE>(pos, ei)
870 , evaluate_space<BLACK>(pos, ei));
871 Trace::add(TOTAL, score);
874 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
877 // Explicit template instantiations
878 template Value Eval::evaluate<true >(const Position&);
879 template Value Eval::evaluate<false>(const Position&);
882 /// trace() is like evaluate(), but instead of returning a value, it returns
883 /// a string (suitable for outputting to stdout) that contains the detailed
884 /// descriptions and values of each evaluation term. Useful for debugging.
886 std::string Eval::trace(const Position& pos) {
888 std::memset(scores, 0, sizeof(scores));
890 Value v = evaluate<true>(pos);
891 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
893 std::stringstream ss;
894 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
895 << " Eval term | White | Black | Total \n"
896 << " | MG EG | MG EG | MG EG \n"
897 << "----------------+-------------+-------------+-------------\n"
898 << " Material | " << Term(MATERIAL)
899 << " Imbalance | " << Term(IMBALANCE)
900 << " Pawns | " << Term(PAWN)
901 << " Knights | " << Term(KNIGHT)
902 << " Bishop | " << Term(BISHOP)
903 << " Rooks | " << Term(ROOK)
904 << " Queens | " << Term(QUEEN)
905 << " Mobility | " << Term(MOBILITY)
906 << " King safety | " << Term(KING)
907 << " Threats | " << Term(THREAT)
908 << " Passed pawns | " << Term(PASSED)
909 << " Space | " << Term(SPACE)
910 << "----------------+-------------+-------------+-------------\n"
911 << " Total | " << Term(TOTAL);
913 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";