2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
5 Copyright (C) 2015-2017 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
7 Stockfish is free software: you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation, either version 3 of the License, or
10 (at your option) any later version.
12 Stockfish is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <http://www.gnu.org/licenses/>.
23 #include <cstring> // For std::memset
36 enum Term { // The first 8 entries are for PieceType
37 MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, TOTAL, TERM_NB
40 double scores[TERM_NB][COLOR_NB][PHASE_NB];
42 double to_cp(Value v) { return double(v) / PawnValueEg; }
44 void add(int idx, Color c, Score s) {
45 scores[idx][c][MG] = to_cp(mg_value(s));
46 scores[idx][c][EG] = to_cp(eg_value(s));
49 void add(int idx, Score w, Score b = SCORE_ZERO) {
50 add(idx, WHITE, w); add(idx, BLACK, b);
53 std::ostream& operator<<(std::ostream& os, Term t) {
55 if (t == MATERIAL || t == IMBALANCE || t == Term(PAWN) || t == TOTAL)
56 os << " --- --- | --- --- | ";
58 os << std::setw(5) << scores[t][WHITE][MG] << " "
59 << std::setw(5) << scores[t][WHITE][EG] << " | "
60 << std::setw(5) << scores[t][BLACK][MG] << " "
61 << std::setw(5) << scores[t][BLACK][EG] << " | ";
63 os << std::setw(5) << scores[t][WHITE][MG] - scores[t][BLACK][MG] << " "
64 << std::setw(5) << scores[t][WHITE][EG] - scores[t][BLACK][EG] << " \n";
70 using namespace Trace;
72 // Struct EvalInfo contains various information computed and collected
73 // by the evaluation functions.
78 Bitboard mobilityArea[COLOR_NB];
80 // attackedBy[color][piece type] is a bitboard representing all squares
81 // attacked by a given color and piece type (can be also ALL_PIECES).
82 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
84 // attackedBy2[color] are the squares attacked by 2 pieces of a given color,
85 // possibly via x-ray or by one pawn and one piece. Diagonal x-ray through
86 // pawn or squares attacked by 2 pawns are not explicitly added.
87 Bitboard attackedBy2[COLOR_NB];
89 // kingRing[color] is the zone around the king which is considered
90 // by the king safety evaluation. This consists of the squares directly
91 // adjacent to the king, and the three (or two, for a king on an edge file)
92 // squares two ranks in front of the king. For instance, if black's king
93 // is on g8, kingRing[BLACK] is a bitboard containing the squares f8, h8,
94 // f7, g7, h7, f6, g6 and h6.
95 Bitboard kingRing[COLOR_NB];
97 // kingAttackersCount[color] is the number of pieces of the given color
98 // which attack a square in the kingRing of the enemy king.
99 int kingAttackersCount[COLOR_NB];
101 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of the
102 // given color which attack a square in the kingRing of the enemy king. The
103 // weights of the individual piece types are given by the elements in the
104 // KingAttackWeights array.
105 int kingAttackersWeight[COLOR_NB];
107 // kingAdjacentZoneAttacksCount[color] is the number of attacks by the given
108 // color to squares directly adjacent to the enemy king. Pieces which attack
109 // more than one square are counted multiple times. For instance, if there is
110 // a white knight on g5 and black's king is on g8, this white knight adds 2
111 // to kingAdjacentZoneAttacksCount[WHITE].
112 int kingAdjacentZoneAttacksCount[COLOR_NB];
115 #define V(v) Value(v)
116 #define S(mg, eg) make_score(mg, eg)
118 // MobilityBonus[PieceType][attacked] contains bonuses for middle and end game,
119 // indexed by piece type and number of attacked squares in the mobility area.
120 const Score MobilityBonus[][32] = {
122 { S(-75,-76), S(-57,-54), S( -9,-28), S( -2,-10), S( 6, 5), S( 14, 12), // Knights
123 S( 22, 26), S( 29, 29), S( 36, 29) },
124 { S(-48,-59), S(-20,-23), S( 16, -3), S( 26, 13), S( 38, 24), S( 51, 42), // Bishops
125 S( 55, 54), S( 63, 57), S( 63, 65), S( 68, 73), S( 81, 78), S( 81, 86),
126 S( 91, 88), S( 98, 97) },
127 { S(-60,-77), S(-26,-20), S(-11, 27), S( -6, 57), S( -3, 69), S( -1, 82), // Rooks
128 S( 10,109), S( 16,121), S( 24,131), S( 25,143), S( 32,155), S( 32,163),
129 S( 43,167), S( 48,171), S( 56,173) },
130 { S(-39,-36), S(-21,-15), S( 3, 8), S( 3, 18), S( 14, 34), S( 22, 54), // Queens
131 S( 28, 61), S( 41, 73), S( 43, 79), S( 48, 92), S( 56, 94), S( 60,104),
132 S( 60,113), S( 66,120), S( 67,123), S( 70,126), S( 71,133), S( 73,136),
133 S( 79,140), S( 88,143), S( 88,148), S( 99,166), S(102,170), S(102,175),
134 S(106,184), S(109,191), S(113,206), S(116,212) }
137 // Outpost[knight/bishop][supported by pawn] contains bonuses for minor
138 // pieces if they can reach an outpost square, bigger if that square is
139 // supported by a pawn. If the minor piece occupies an outpost square
140 // then score is doubled.
141 const Score Outpost[][2] = {
142 { S(22, 6), S(33, 9) }, // Knight
143 { S( 9, 2), S(14, 4) } // Bishop
146 // RookOnFile[semiopen/open] contains bonuses for each rook when there is no
147 // friendly pawn on the rook file.
148 const Score RookOnFile[2] = { S(20, 7), S(45, 20) };
150 // ThreatBySafePawn[PieceType] contains bonuses according to which piece
151 // type is attacked by a pawn which is protected or is not attacked.
152 const Score ThreatBySafePawn[PIECE_TYPE_NB] = {
153 S(0, 0), S(0, 0), S(176, 139), S(131, 127), S(217, 218), S(203, 215)
156 // ThreatByMinor/ByRook[attacked PieceType] contains bonuses according to
157 // which piece type attacks which one. Attacks on lesser pieces which are
158 // pawn-defended are not considered.
159 const Score ThreatByMinor[PIECE_TYPE_NB] = {
160 S(0, 0), S(0, 33), S(45, 43), S(46, 47), S(72, 107), S(48, 118)
163 const Score ThreatByRook[PIECE_TYPE_NB] = {
164 S(0, 0), S(0, 25), S(40, 62), S(40, 59), S( 0, 34), S(35, 48)
167 // ThreatByKing[on one/on many] contains bonuses for king attacks on
168 // pawns or pieces which are not pawn-defended.
169 const Score ThreatByKing[2] = { S(3, 62), S(9, 138) };
171 // Passed[mg/eg][Rank] contains midgame and endgame bonuses for passed pawns.
172 // We don't use a Score because we process the two components independently.
173 const Value Passed[][RANK_NB] = {
174 { V(5), V( 5), V(31), V(73), V(166), V(252) },
175 { V(7), V(14), V(38), V(73), V(166), V(252) }
178 // PassedFile[File] contains a bonus according to the file of a passed pawn
179 const Score PassedFile[FILE_NB] = {
180 S( 9, 10), S( 2, 10), S( 1, -8), S(-20,-12),
181 S(-20,-12), S( 1, -8), S( 2, 10), S( 9, 10)
184 // Protector[PieceType][distance] contains a protecting bonus for our king,
185 // indexed by piece type and distance between the piece and the king.
186 const Score Protector[PIECE_TYPE_NB][8] = {
188 { S(0, 0), S( 7, 9), S( 7, 1), S( 1, 5), S(-10,-4), S( -1,-4), S( -7,-3), S(-16,-10) }, // Knight
189 { S(0, 0), S(11, 8), S(-7,-1), S(-1,-2), S( -1,-7), S(-11,-3), S( -9,-1), S(-16, -1) }, // Bishop
190 { S(0, 0), S(10, 0), S(-2, 2), S(-5, 4), S( -6, 2), S(-14,-3), S( -2,-9), S(-12, -7) }, // Rook
191 { S(0, 0), S( 3,-5), S( 2,-5), S(-4, 0), S( -9,-6), S(-4, 7), S(-13,-7), S(-10, -7) } // Queen
194 // Assorted bonuses and penalties used by evaluation
195 const Score MinorBehindPawn = S(16, 0);
196 const Score BishopPawns = S( 8, 12);
197 const Score RookOnPawn = S( 8, 24);
198 const Score TrappedRook = S(92, 0);
199 const Score WeakQueen = S(50, 10);
200 const Score OtherCheck = S(10, 10);
201 const Score CloseEnemies = S( 7, 0);
202 const Score PawnlessFlank = S(20, 80);
203 const Score ThreatByHangingPawn = S(71, 61);
204 const Score ThreatByRank = S(16, 3);
205 const Score Hanging = S(48, 27);
206 const Score ThreatByPawnPush = S(38, 22);
207 const Score HinderPassedPawn = S( 7, 0);
209 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
210 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
211 // happen in Chess960 games.
212 const Score TrappedBishopA1H1 = S(50, 50);
217 // KingAttackWeights[PieceType] contains king attack weights by piece type
218 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 78, 56, 45, 11 };
220 // Penalties for enemy's safe checks
221 const int QueenCheck = 745;
222 const int RookCheck = 688;
223 const int BishopCheck = 588;
224 const int KnightCheck = 924;
226 // Threshold for lazy evaluation
227 const Value LazyThreshold = Value(1500);
229 // eval_init() initializes king and attack bitboards for a given color
230 // adding pawn attacks. To be done at the beginning of the evaluation.
233 void eval_init(const Position& pos, EvalInfo& ei) {
235 const Color Them = (Us == WHITE ? BLACK : WHITE);
236 const Square Up = (Us == WHITE ? NORTH : SOUTH);
237 const Square Down = (Us == WHITE ? SOUTH : NORTH);
238 const Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB: Rank7BB | Rank6BB);
240 // Find our pawns on the first two ranks, and those which are blocked
241 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
243 // Squares occupied by those pawns, by our king, or controlled by enemy pawns
244 // are excluded from the mobility area.
245 ei.mobilityArea[Us] = ~(b | pos.square<KING>(Us) | ei.pe->pawn_attacks(Them));
247 // Initialise the attack bitboards with the king and pawn information
248 b = ei.attackedBy[Us][KING] = pos.attacks_from<KING>(pos.square<KING>(Us));
249 ei.attackedBy[Us][PAWN] = ei.pe->pawn_attacks(Us);
251 ei.attackedBy2[Us] = b & ei.attackedBy[Us][PAWN];
252 ei.attackedBy[Us][ALL_PIECES] = b | ei.attackedBy[Us][PAWN];
254 // Init our king safety tables only if we are going to use them
255 if (pos.non_pawn_material(Them) >= QueenValueMg)
257 ei.kingRing[Us] = b | shift<Up>(b);
258 ei.kingAttackersCount[Them] = popcount(b & ei.pe->pawn_attacks(Them));
259 ei.kingAdjacentZoneAttacksCount[Them] = ei.kingAttackersWeight[Them] = 0;
262 ei.kingRing[Us] = ei.kingAttackersCount[Them] = 0;
266 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given
269 template<bool DoTrace, Color Us = WHITE, PieceType Pt = KNIGHT>
270 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility) {
272 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
273 const Color Them = (Us == WHITE ? BLACK : WHITE);
274 const Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
275 : Rank5BB | Rank4BB | Rank3BB);
276 const Square* pl = pos.squares<Pt>(Us);
280 Score score = SCORE_ZERO;
282 ei.attackedBy[Us][Pt] = 0;
284 while ((s = *pl++) != SQ_NONE)
286 // Find attacked squares, including x-ray attacks for bishops and rooks
287 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
288 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
289 : pos.attacks_from<Pt>(s);
291 if (pos.pinned_pieces(Us) & s)
292 b &= LineBB[pos.square<KING>(Us)][s];
294 ei.attackedBy2[Us] |= ei.attackedBy[Us][ALL_PIECES] & b;
295 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
297 if (b & ei.kingRing[Them])
299 ei.kingAttackersCount[Us]++;
300 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
301 ei.kingAdjacentZoneAttacksCount[Us] += popcount(b & ei.attackedBy[Them][KING]);
304 int mob = popcount(b & ei.mobilityArea[Us]);
306 mobility[Us] += MobilityBonus[Pt][mob];
308 // Bonus for this piece as a king protector
309 score += Protector[Pt][distance(s, pos.square<KING>(Us))];
311 if (Pt == BISHOP || Pt == KNIGHT)
313 // Bonus for outpost squares
314 bb = OutpostRanks & ~ei.pe->pawn_attacks_span(Them);
316 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & s)] * 2;
319 bb &= b & ~pos.pieces(Us);
321 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & bb)];
324 // Bonus when behind a pawn
325 if ( relative_rank(Us, s) < RANK_5
326 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
327 score += MinorBehindPawn;
329 // Penalty for pawns on the same color square as the bishop
331 score -= BishopPawns * ei.pe->pawns_on_same_color_squares(Us, s);
333 // An important Chess960 pattern: A cornered bishop blocked by a friendly
334 // pawn diagonally in front of it is a very serious problem, especially
335 // when that pawn is also blocked.
338 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
340 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
341 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
342 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
343 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
350 // Bonus for aligning with enemy pawns on the same rank/file
351 if (relative_rank(Us, s) >= RANK_5)
352 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
354 // Bonus when on an open or semi-open file
355 if (ei.pe->semiopen_file(Us, file_of(s)))
356 score += RookOnFile[!!ei.pe->semiopen_file(Them, file_of(s))];
358 // Penalty when trapped by the king, even more if the king cannot castle
361 Square ksq = pos.square<KING>(Us);
363 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
364 && !ei.pe->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
365 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
371 // Penalty if any relative pin or discovered attack against the queen
373 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, pinners))
379 Trace::add(Pt, Us, score);
381 // Recursively call evaluate_pieces() of next piece type until KING is excluded
382 return score - evaluate_pieces<DoTrace, Them, NextPt>(pos, ei, mobility);
386 Score evaluate_pieces<false, WHITE, KING>(const Position&, EvalInfo&, Score*) { return SCORE_ZERO; }
388 Score evaluate_pieces< true, WHITE, KING>(const Position&, EvalInfo&, Score*) { return SCORE_ZERO; }
391 // evaluate_king() assigns bonuses and penalties to a king of a given color
393 const Bitboard QueenSide = FileABB | FileBBB | FileCBB | FileDBB;
394 const Bitboard CenterFiles = FileCBB | FileDBB | FileEBB | FileFBB;
395 const Bitboard KingSide = FileEBB | FileFBB | FileGBB | FileHBB;
397 const Bitboard KingFlank[FILE_NB] = {
398 QueenSide, QueenSide, QueenSide, CenterFiles, CenterFiles, KingSide, KingSide, KingSide
401 template<Color Us, bool DoTrace>
402 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
404 const Color Them = (Us == WHITE ? BLACK : WHITE);
405 const Square Up = (Us == WHITE ? NORTH : SOUTH);
406 const Bitboard Camp = (Us == WHITE ? ~Bitboard(0) ^ Rank6BB ^ Rank7BB ^ Rank8BB
407 : ~Bitboard(0) ^ Rank1BB ^ Rank2BB ^ Rank3BB);
409 const Square ksq = pos.square<KING>(Us);
410 Bitboard undefended, b, b1, b2, safe, other;
413 // King shelter and enemy pawns storm
414 Score score = ei.pe->king_safety<Us>(pos, ksq);
416 // Main king safety evaluation
417 if (ei.kingAttackersCount[Them])
419 // Find the attacked squares which are defended only by our king...
420 undefended = ei.attackedBy[Them][ALL_PIECES]
421 & ei.attackedBy[Us][KING]
422 & ~ei.attackedBy2[Us];
424 // ... and those which are not defended at all in the larger king ring
425 b = ei.attackedBy[Them][ALL_PIECES] & ~ei.attackedBy[Us][ALL_PIECES]
426 & ei.kingRing[Us] & ~pos.pieces(Them);
428 // Initialize the 'kingDanger' variable, which will be transformed
429 // later into a king danger score. The initial value is based on the
430 // number and types of the enemy's attacking pieces, the number of
431 // attacked and undefended squares around our king and the quality of
432 // the pawn shelter (current 'score' value).
433 kingDanger = std::min(807, ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them])
434 + 101 * ei.kingAdjacentZoneAttacksCount[Them]
435 + 235 * popcount(undefended)
436 + 134 * (popcount(b) + !!pos.pinned_pieces(Us))
437 - 717 * !pos.count<QUEEN>(Them)
438 - 7 * mg_value(score) / 5 - 5;
440 // Analyse the safe enemy's checks which are possible on next move
441 safe = ~pos.pieces(Them);
442 safe &= ~ei.attackedBy[Us][ALL_PIECES] | (undefended & ei.attackedBy2[Them]);
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 minors and rooks, also consider the square safe if attacked twice,
452 // and only defended by our queen.
453 safe |= ei.attackedBy2[Them]
454 & ~(ei.attackedBy2[Us] | pos.pieces(Them))
455 & ei.attackedBy[Us][QUEEN];
457 // Some other potential checks are also analysed, even from squares
458 // currently occupied by the opponent own pieces, as long as the square
459 // is not attacked by our pawns, and is not occupied by a blocked pawn.
460 other = ~( ei.attackedBy[Us][PAWN]
461 | (pos.pieces(Them, PAWN) & shift<Up>(pos.pieces(PAWN))));
463 // Enemy rooks safe and other checks
464 if (b1 & ei.attackedBy[Them][ROOK] & safe)
465 kingDanger += RookCheck;
467 else if (b1 & ei.attackedBy[Them][ROOK] & other)
470 // Enemy bishops safe and other checks
471 if (b2 & ei.attackedBy[Them][BISHOP] & safe)
472 kingDanger += BishopCheck;
474 else if (b2 & ei.attackedBy[Them][BISHOP] & other)
477 // Enemy knights safe and other checks
478 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT];
480 kingDanger += KnightCheck;
485 // Transform the kingDanger units into a Score, and substract it from the evaluation
487 score -= make_score(std::min(kingDanger * kingDanger / 4096, 2 * int(BishopValueMg)), 0);
490 // King tropism: firstly, find squares that opponent attacks in our king flank
491 File kf = file_of(ksq);
492 b = ei.attackedBy[Them][ALL_PIECES] & KingFlank[kf] & Camp;
494 assert(((Us == WHITE ? b << 4 : b >> 4) & b) == 0);
495 assert(popcount(Us == WHITE ? b << 4 : b >> 4) == popcount(b));
497 // Secondly, add the squares which are attacked twice in that flank and
498 // which are not defended by our pawns.
499 b = (Us == WHITE ? b << 4 : b >> 4)
500 | (b & ei.attackedBy2[Them] & ~ei.attackedBy[Us][PAWN]);
502 score -= CloseEnemies * popcount(b);
504 // Penalty when our king is on a pawnless flank
505 if (!(pos.pieces(PAWN) & KingFlank[kf]))
506 score -= PawnlessFlank;
509 Trace::add(KING, Us, score);
515 // evaluate_threats() assigns bonuses according to the types of the attacking
516 // and the attacked pieces.
518 template<Color Us, bool DoTrace>
519 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
521 const Color Them = (Us == WHITE ? BLACK : WHITE);
522 const Square Up = (Us == WHITE ? NORTH : SOUTH);
523 const Square Left = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
524 const Square Right = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
525 const Bitboard TRank2BB = (Us == WHITE ? Rank2BB : Rank7BB);
526 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
528 Bitboard b, weak, defended, safeThreats;
529 Score score = SCORE_ZERO;
531 // Non-pawn enemies attacked by a pawn
532 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Us][PAWN];
536 b = pos.pieces(Us, PAWN) & ( ~ei.attackedBy[Them][ALL_PIECES]
537 | ei.attackedBy[Us][ALL_PIECES]);
539 safeThreats = (shift<Right>(b) | shift<Left>(b)) & weak;
541 if (weak ^ safeThreats)
542 score += ThreatByHangingPawn;
545 score += ThreatBySafePawn[type_of(pos.piece_on(pop_lsb(&safeThreats)))];
548 // Non-pawn enemies defended by a pawn
549 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Them][PAWN];
551 // Enemies not defended by a pawn and under our attack
552 weak = pos.pieces(Them)
553 & ~ei.attackedBy[Them][PAWN]
554 & ei.attackedBy[Us][ALL_PIECES];
556 // Add a bonus according to the kind of attacking pieces
559 b = (defended | weak) & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
562 Square s = pop_lsb(&b);
563 score += ThreatByMinor[type_of(pos.piece_on(s))];
564 if (type_of(pos.piece_on(s)) != PAWN)
565 score += ThreatByRank * (int)relative_rank(Them, s);
568 b = (pos.pieces(Them, QUEEN) | weak) & ei.attackedBy[Us][ROOK];
571 Square s = pop_lsb(&b);
572 score += ThreatByRook[type_of(pos.piece_on(s))];
573 if (type_of(pos.piece_on(s)) != PAWN)
574 score += ThreatByRank * (int)relative_rank(Them, s);
577 score += Hanging * popcount(weak & ~ei.attackedBy[Them][ALL_PIECES]);
579 b = weak & ei.attackedBy[Us][KING];
581 score += ThreatByKing[more_than_one(b)];
584 // Bonus if some pawns can safely push and attack an enemy piece
585 b = pos.pieces(Us, PAWN) & ~TRank7BB;
586 b = shift<Up>(b | (shift<Up>(b & TRank2BB) & ~pos.pieces()));
589 & ~ei.attackedBy[Them][PAWN]
590 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
592 b = (shift<Left>(b) | shift<Right>(b))
594 & ~ei.attackedBy[Us][PAWN];
596 score += ThreatByPawnPush * popcount(b);
599 Trace::add(THREAT, Us, score);
605 // evaluate_passer_pawns() evaluates the passed pawns and candidate passed
606 // pawns of the given color.
608 template<Color Us, bool DoTrace>
609 Score evaluate_passer_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.pe->passed_pawns(Us);
620 Square s = pop_lsb(&b);
622 assert(!(pos.pieces(PAWN) & forward_bb(Us, s)));
624 bb = forward_bb(Us, s) & (ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
625 score -= HinderPassedPawn * popcount(bb);
627 int r = relative_rank(Us, s) - RANK_2;
628 int rr = r * (r - 1);
630 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
634 Square blockSq = s + pawn_push(Us);
636 // Adjust bonus based on the king's proximity
637 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
638 - distance(pos.square<KING>(Us ), blockSq) * 2 * rr;
640 // If blockSq is not the queening square then consider also a second push
641 if (relative_rank(Us, blockSq) != RANK_8)
642 ebonus -= distance(pos.square<KING>(Us), blockSq + pawn_push(Us)) * rr;
644 // If the pawn is free to advance, then increase the bonus
645 if (pos.empty(blockSq))
647 // If there is a rook or queen attacking/defending the pawn from behind,
648 // consider all the squaresToQueen. Otherwise consider only the squares
649 // in the pawn's path attacked or occupied by the enemy.
650 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
652 bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
654 if (!(pos.pieces(Us) & bb))
655 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
657 if (!(pos.pieces(Them) & bb))
658 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
660 // If there aren't any enemy attacks, assign a big bonus. Otherwise
661 // assign a smaller bonus if the block square isn't attacked.
662 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
664 // If the path to the queen is fully defended, assign a big bonus.
665 // Otherwise assign a smaller bonus if the block square is defended.
666 if (defendedSquares == squaresToQueen)
669 else if (defendedSquares & blockSq)
672 mbonus += k * rr, ebonus += k * rr;
674 else if (pos.pieces(Us) & blockSq)
675 mbonus += rr + r * 2, ebonus += rr + r * 2;
678 // Scale down bonus for candidate passers which need more than one pawn
679 // push to become passed.
680 if (!pos.pawn_passed(Us, s + pawn_push(Us)))
681 mbonus /= 2, ebonus /= 2;
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 ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
706 : CenterFiles & (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.pe->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);
741 bool bothFlanks = (pos.pieces(PAWN) & QueenSide) && (pos.pieces(PAWN) & KingSide);
743 // Compute the initiative bonus for the attacking side
744 int initiative = 8 * (asymmetry + kingDistance - 17) + 12 * pawns + 16 * bothFlanks;
746 // Now apply the bonus: note that we find the attacking side by extracting
747 // the sign of the endgame value, and that we carefully cap the bonus so
748 // that the endgame score will never change sign after the bonus.
749 int value = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg));
751 return make_score(0, value);
755 // evaluate_scale_factor() computes the scale factor for the winning side
756 ScaleFactor evaluate_scale_factor(const Position& pos, const EvalInfo& ei, Value eg) {
758 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
759 ScaleFactor sf = ei.me->scale_factor(pos, strongSide);
761 // If we don't already have an unusual scale factor, check for certain
762 // types of endgames, and use a lower scale for those.
763 if (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 return 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.
775 return ScaleFactor(46);
777 // Endings where weaker side can place his king in front of the opponent's
778 // pawns are drawish.
779 else if ( abs(eg) <= BishopValueEg
780 && pos.count<PAWN>(strongSide) <= 2
781 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
782 return ScaleFactor(37 + 7 * pos.count<PAWN>(strongSide));
791 /// evaluate() is the main evaluation function. It returns a static evaluation
792 /// of the position from the point of view of the side to move.
794 template<bool DoTrace>
795 Value Eval::evaluate(const Position& pos) {
797 assert(!pos.checkers());
799 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.pe = Pawns::probe(pos);
818 score += ei.pe->pawns_score();
820 // Early exit if score is high
821 v = (mg_value(score) + eg_value(score)) / 2;
822 if (abs(v) > LazyThreshold)
823 return pos.side_to_move() == WHITE ? v : -v;
825 // Initialize attack and king safety bitboards
826 eval_init<WHITE>(pos, ei);
827 eval_init<BLACK>(pos, ei);
829 // Evaluate all pieces but king and pawns
830 score += evaluate_pieces<DoTrace>(pos, ei, mobility);
831 score += mobility[WHITE] - mobility[BLACK];
833 // Evaluate kings after all other pieces because we need full attack
834 // information when computing the king safety evaluation.
835 score += evaluate_king<WHITE, DoTrace>(pos, ei)
836 - evaluate_king<BLACK, DoTrace>(pos, ei);
838 // Evaluate tactical threats, we need full attack information including king
839 score += evaluate_threats<WHITE, DoTrace>(pos, ei)
840 - evaluate_threats<BLACK, DoTrace>(pos, ei);
842 // Evaluate passed pawns, we need full attack information including king
843 score += evaluate_passer_pawns<WHITE, DoTrace>(pos, ei)
844 - evaluate_passer_pawns<BLACK, DoTrace>(pos, ei);
846 // Evaluate space for both sides, only during opening
847 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
848 score += evaluate_space<WHITE>(pos, ei)
849 - evaluate_space<BLACK>(pos, ei);
851 // Evaluate position potential for the winning side
852 score += evaluate_initiative(pos, ei.pe->pawn_asymmetry(), eg_value(score));
854 // Evaluate scale factor for the winning side
855 ScaleFactor sf = evaluate_scale_factor(pos, ei, eg_value(score));
857 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
858 v = mg_value(score) * int(ei.me->game_phase())
859 + eg_value(score) * int(PHASE_MIDGAME - ei.me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
861 v /= int(PHASE_MIDGAME);
863 // In case of tracing add all remaining individual evaluation terms
866 Trace::add(MATERIAL, pos.psq_score());
867 Trace::add(IMBALANCE, ei.me->imbalance());
868 Trace::add(PAWN, ei.pe->pawns_score());
869 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
870 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
871 Trace::add(SPACE, evaluate_space<WHITE>(pos, ei)
872 , evaluate_space<BLACK>(pos, ei));
873 Trace::add(TOTAL, score);
876 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
879 // Explicit template instantiations
880 template Value Eval::evaluate<true >(const Position&);
881 template Value Eval::evaluate<false>(const Position&);
884 /// trace() is like evaluate(), but instead of returning a value, it returns
885 /// a string (suitable for outputting to stdout) that contains the detailed
886 /// descriptions and values of each evaluation term. Useful for debugging.
888 std::string Eval::trace(const Position& pos) {
890 std::memset(scores, 0, sizeof(scores));
892 Value v = evaluate<true>(pos);
893 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
895 std::stringstream ss;
896 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
897 << " Eval term | White | Black | Total \n"
898 << " | MG EG | MG EG | MG EG \n"
899 << "----------------+-------------+-------------+-------------\n"
900 << " Material | " << Term(MATERIAL)
901 << " Imbalance | " << Term(IMBALANCE)
902 << " Pawns | " << Term(PAWN)
903 << " Knights | " << Term(KNIGHT)
904 << " Bishop | " << Term(BISHOP)
905 << " Rooks | " << Term(ROOK)
906 << " Queens | " << Term(QUEEN)
907 << " Mobility | " << Term(MOBILITY)
908 << " King safety | " << Term(KING)
909 << " Threats | " << Term(THREAT)
910 << " Passed pawns | " << Term(PASSED)
911 << " Space | " << Term(SPACE)
912 << "----------------+-------------+-------------+-------------\n"
913 << " Total | " << Term(TOTAL);
915 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";