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, stronglyProtected, 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 // Squares strongly protected by the opponent, either because they attack the
549 // square with a pawn, or because they attack the square twice and we don't.
550 stronglyProtected = ei.attackedBy[Them][PAWN]
551 | (ei.attackedBy2[Them] & ~ei.attackedBy2[Us]);
553 // Non-pawn enemies, strongly protected
554 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN))
557 // Enemies not strongly protected and under our attack
558 weak = pos.pieces(Them)
560 & ei.attackedBy[Us][ALL_PIECES];
562 // Add a bonus according to the kind of attacking pieces
565 b = (defended | weak) & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
568 Square s = pop_lsb(&b);
569 score += ThreatByMinor[type_of(pos.piece_on(s))];
570 if (type_of(pos.piece_on(s)) != PAWN)
571 score += ThreatByRank * (int)relative_rank(Them, s);
574 b = (pos.pieces(Them, QUEEN) | weak) & ei.attackedBy[Us][ROOK];
577 Square s = pop_lsb(&b);
578 score += ThreatByRook[type_of(pos.piece_on(s))];
579 if (type_of(pos.piece_on(s)) != PAWN)
580 score += ThreatByRank * (int)relative_rank(Them, s);
583 score += Hanging * popcount(weak & ~ei.attackedBy[Them][ALL_PIECES]);
585 b = weak & ei.attackedBy[Us][KING];
587 score += ThreatByKing[more_than_one(b)];
590 // Bonus if some pawns can safely push and attack an enemy piece
591 b = pos.pieces(Us, PAWN) & ~TRank7BB;
592 b = shift<Up>(b | (shift<Up>(b & TRank2BB) & ~pos.pieces()));
595 & ~ei.attackedBy[Them][PAWN]
596 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
598 b = (shift<Left>(b) | shift<Right>(b))
600 & ~ei.attackedBy[Us][PAWN];
602 score += ThreatByPawnPush * popcount(b);
605 Trace::add(THREAT, Us, score);
611 // evaluate_passer_pawns() evaluates the passed pawns and candidate passed
612 // pawns of the given color.
614 template<Color Us, bool DoTrace>
615 Score evaluate_passer_pawns(const Position& pos, const EvalInfo& ei) {
617 const Color Them = (Us == WHITE ? BLACK : WHITE);
619 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
620 Score score = SCORE_ZERO;
622 b = ei.pe->passed_pawns(Us);
626 Square s = pop_lsb(&b);
628 assert(!(pos.pieces(PAWN) & forward_bb(Us, s)));
630 bb = forward_bb(Us, s) & (ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
631 score -= HinderPassedPawn * popcount(bb);
633 int r = relative_rank(Us, s) - RANK_2;
634 int rr = r * (r - 1);
636 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
640 Square blockSq = s + pawn_push(Us);
642 // Adjust bonus based on the king's proximity
643 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
644 - distance(pos.square<KING>(Us ), blockSq) * 2 * rr;
646 // If blockSq is not the queening square then consider also a second push
647 if (relative_rank(Us, blockSq) != RANK_8)
648 ebonus -= distance(pos.square<KING>(Us), blockSq + pawn_push(Us)) * rr;
650 // If the pawn is free to advance, then increase the bonus
651 if (pos.empty(blockSq))
653 // If there is a rook or queen attacking/defending the pawn from behind,
654 // consider all the squaresToQueen. Otherwise consider only the squares
655 // in the pawn's path attacked or occupied by the enemy.
656 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
658 bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
660 if (!(pos.pieces(Us) & bb))
661 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
663 if (!(pos.pieces(Them) & bb))
664 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
666 // If there aren't any enemy attacks, assign a big bonus. Otherwise
667 // assign a smaller bonus if the block square isn't attacked.
668 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
670 // If the path to the queen is fully defended, assign a big bonus.
671 // Otherwise assign a smaller bonus if the block square is defended.
672 if (defendedSquares == squaresToQueen)
675 else if (defendedSquares & blockSq)
678 mbonus += k * rr, ebonus += k * rr;
680 else if (pos.pieces(Us) & blockSq)
681 mbonus += rr + r * 2, ebonus += rr + r * 2;
684 // Scale down bonus for candidate passers which need more than one
685 // pawn push to become passed.
686 if (!pos.pawn_passed(Us, s + pawn_push(Us)))
687 mbonus /= 2, ebonus /= 2;
689 score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
693 Trace::add(PASSED, Us, score);
699 // evaluate_space() computes the space evaluation for a given side. The
700 // space evaluation is a simple bonus based on the number of safe squares
701 // available for minor pieces on the central four files on ranks 2--4. Safe
702 // squares one, two or three squares behind a friendly pawn are counted
703 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
704 // improve play on game opening.
706 Score evaluate_space(const Position& pos, const EvalInfo& ei) {
708 const Color Them = (Us == WHITE ? BLACK : WHITE);
709 const Bitboard SpaceMask =
710 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
711 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
713 // Find the safe squares for our pieces inside the area defined by
714 // SpaceMask. A square is unsafe if it is attacked by an enemy
715 // pawn, or if it is undefended and attacked by an enemy piece.
716 Bitboard safe = SpaceMask
717 & ~pos.pieces(Us, PAWN)
718 & ~ei.attackedBy[Them][PAWN]
719 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
721 // Find all squares which are at most three squares behind some friendly pawn
722 Bitboard behind = pos.pieces(Us, PAWN);
723 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
724 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
726 // Since SpaceMask[Us] is fully on our half of the board...
727 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
729 // ...count safe + (behind & safe) with a single popcount.
730 int bonus = popcount((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
731 bonus = std::min(16, bonus);
732 int weight = pos.count<ALL_PIECES>(Us) - 2 * ei.pe->open_files();
734 return make_score(bonus * weight * weight / 18, 0);
738 // evaluate_initiative() computes the initiative correction value for the
739 // position, i.e., second order bonus/malus based on the known attacking/defending
740 // status of the players.
741 Score evaluate_initiative(const Position& pos, int asymmetry, Value eg) {
743 int kingDistance = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
744 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
745 int pawns = pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK);
746 bool bothFlanks = (pos.pieces(PAWN) & QueenSide) && (pos.pieces(PAWN) & KingSide);
748 // Compute the initiative bonus for the attacking side
749 int initiative = 8 * (asymmetry + kingDistance - 17) + 12 * pawns + 16 * bothFlanks;
751 // Now apply the bonus: note that we find the attacking side by extracting
752 // the sign of the endgame value, and that we carefully cap the bonus so
753 // that the endgame score will never change sign after the bonus.
754 int value = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg));
756 return make_score(0, value);
760 // evaluate_scale_factor() computes the scale factor for the winning side
761 ScaleFactor evaluate_scale_factor(const Position& pos, const EvalInfo& ei, Value eg) {
763 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
764 ScaleFactor sf = ei.me->scale_factor(pos, strongSide);
766 // If we don't already have an unusual scale factor, check for certain
767 // types of endgames, and use a lower scale for those.
768 if (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN)
770 if (pos.opposite_bishops())
772 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
773 // is almost a draw, in case of KBP vs KB, it is even more a draw.
774 if ( pos.non_pawn_material(WHITE) == BishopValueMg
775 && pos.non_pawn_material(BLACK) == BishopValueMg)
776 return more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
778 // Endgame with opposite-colored bishops, but also other pieces. Still
779 // a bit drawish, but not as drawish as with only the two bishops.
780 return ScaleFactor(46);
782 // Endings where weaker side can place his king in front of the opponent's
783 // pawns are drawish.
784 else if ( abs(eg) <= BishopValueEg
785 && pos.count<PAWN>(strongSide) <= 2
786 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
787 return ScaleFactor(37 + 7 * pos.count<PAWN>(strongSide));
796 /// evaluate() is the main evaluation function. It returns a static evaluation
797 /// of the position from the point of view of the side to move.
799 template<bool DoTrace>
800 Value Eval::evaluate(const Position& pos) {
802 assert(!pos.checkers());
804 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
808 // Probe the material hash table
809 ei.me = Material::probe(pos);
811 // If we have a specialized evaluation function for the current material
812 // configuration, call it and return.
813 if (ei.me->specialized_eval_exists())
814 return ei.me->evaluate(pos);
816 // Initialize score by reading the incrementally updated scores included in
817 // the position object (material + piece square tables) and the material
818 // imbalance. Score is computed internally from the white point of view.
819 Score score = pos.psq_score() + ei.me->imbalance();
821 // Probe the pawn hash table
822 ei.pe = Pawns::probe(pos);
823 score += ei.pe->pawns_score();
825 // Early exit if score is high
826 v = (mg_value(score) + eg_value(score)) / 2;
827 if (abs(v) > LazyThreshold)
828 return pos.side_to_move() == WHITE ? v : -v;
830 // Initialize attack and king safety bitboards
831 eval_init<WHITE>(pos, ei);
832 eval_init<BLACK>(pos, ei);
834 // Evaluate all pieces but king and pawns
835 score += evaluate_pieces<DoTrace>(pos, ei, mobility);
836 score += mobility[WHITE] - mobility[BLACK];
838 // Evaluate kings after all other pieces because we need full attack
839 // information when computing the king safety evaluation.
840 score += evaluate_king<WHITE, DoTrace>(pos, ei)
841 - evaluate_king<BLACK, DoTrace>(pos, ei);
843 // Evaluate tactical threats, we need full attack information including king
844 score += evaluate_threats<WHITE, DoTrace>(pos, ei)
845 - evaluate_threats<BLACK, DoTrace>(pos, ei);
847 // Evaluate passed pawns, we need full attack information including king
848 score += evaluate_passer_pawns<WHITE, DoTrace>(pos, ei)
849 - evaluate_passer_pawns<BLACK, DoTrace>(pos, ei);
851 // Evaluate space for both sides, only during opening
852 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
853 score += evaluate_space<WHITE>(pos, ei)
854 - evaluate_space<BLACK>(pos, ei);
856 // Evaluate position potential for the winning side
857 score += evaluate_initiative(pos, ei.pe->pawn_asymmetry(), eg_value(score));
859 // Evaluate scale factor for the winning side
860 ScaleFactor sf = evaluate_scale_factor(pos, ei, eg_value(score));
862 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
863 v = mg_value(score) * int(ei.me->game_phase())
864 + eg_value(score) * int(PHASE_MIDGAME - ei.me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
866 v /= int(PHASE_MIDGAME);
868 // In case of tracing add all remaining individual evaluation terms
871 Trace::add(MATERIAL, pos.psq_score());
872 Trace::add(IMBALANCE, ei.me->imbalance());
873 Trace::add(PAWN, ei.pe->pawns_score());
874 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
875 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
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";