2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
5 Copyright (C) 2015-2016 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
7 Stockfish is free software: you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation, either version 3 of the License, or
10 (at your option) any later version.
12 Stockfish is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <http://www.gnu.org/licenses/>.
23 #include <cstring> // For std::memset
36 enum Term { // The first 8 entries are for PieceType
37 MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, TOTAL, TERM_NB
40 double scores[TERM_NB][COLOR_NB][PHASE_NB];
42 double to_cp(Value v) { return double(v) / PawnValueEg; }
44 void add(int idx, Color c, Score s) {
45 scores[idx][c][MG] = to_cp(mg_value(s));
46 scores[idx][c][EG] = to_cp(eg_value(s));
49 void add(int idx, Score w, Score b = SCORE_ZERO) {
50 add(idx, WHITE, w); add(idx, BLACK, b);
53 std::ostream& operator<<(std::ostream& os, Term t) {
55 if (t == MATERIAL || t == IMBALANCE || t == Term(PAWN) || t == TOTAL)
56 os << " --- --- | --- --- | ";
58 os << std::setw(5) << scores[t][WHITE][MG] << " "
59 << std::setw(5) << scores[t][WHITE][EG] << " | "
60 << std::setw(5) << scores[t][BLACK][MG] << " "
61 << std::setw(5) << scores[t][BLACK][EG] << " | ";
63 os << std::setw(5) << scores[t][WHITE][MG] - scores[t][BLACK][MG] << " "
64 << std::setw(5) << scores[t][WHITE][EG] - scores[t][BLACK][EG] << " \n";
70 using namespace Trace;
72 // Struct EvalInfo contains various information computed and collected
73 // by the evaluation functions.
76 // attackedBy[color][piece type] is a bitboard representing all squares
77 // attacked by a given color and piece type (can be also ALL_PIECES).
78 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
80 // attackedBy2[color] are the squares attacked by 2 pieces of a given color,
81 // possibly via x-ray or by one pawn and one piece. Diagonal x-ray through
82 // pawn or squares attacked by 2 pawns are not explicitly added.
83 Bitboard attackedBy2[COLOR_NB];
85 // kingRing[color] is the zone around the king which is considered
86 // by the king safety evaluation. This consists of the squares directly
87 // adjacent to the king, and the three (or two, for a king on an edge file)
88 // squares two ranks in front of the king. For instance, if black's king
89 // is on g8, kingRing[BLACK] is a bitboard containing the squares f8, h8,
90 // f7, g7, h7, f6, g6 and h6.
91 Bitboard kingRing[COLOR_NB];
93 // kingAttackersCount[color] is the number of pieces of the given color
94 // which attack a square in the kingRing of the enemy king.
95 int kingAttackersCount[COLOR_NB];
97 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of the
98 // given color which attack a square in the kingRing of the enemy king. The
99 // weights of the individual piece types are given by the elements in the
100 // KingAttackWeights array.
101 int kingAttackersWeight[COLOR_NB];
103 // kingAdjacentZoneAttacksCount[color] is the number of attacks by the given
104 // color to squares directly adjacent to the enemy king. Pieces which attack
105 // more than one square are counted multiple times. For instance, if there is
106 // a white knight on g5 and black's king is on g8, this white knight adds 2
107 // to kingAdjacentZoneAttacksCount[WHITE].
108 int kingAdjacentZoneAttacksCount[COLOR_NB];
110 Bitboard pinnedPieces[COLOR_NB];
115 #define V(v) Value(v)
116 #define S(mg, eg) make_score(mg, eg)
118 // MobilityBonus[PieceType][attacked] contains bonuses for middle and end
119 // game, indexed by piece type and number of attacked squares in the MobilityArea.
120 const Score MobilityBonus[][32] = {
122 { S(-75,-76), S(-56,-54), S( -9,-26), S( -2,-10), S( 6, 5), S( 15, 11), // Knights
123 S( 22, 26), S( 30, 28), S( 36, 29) },
124 { S(-48,-58), S(-21,-19), S( 16, -2), S( 26, 12), S( 37, 22), S( 51, 42), // Bishops
125 S( 54, 54), S( 63, 58), S( 65, 63), S( 71, 70), S( 79, 74), S( 81, 86),
126 S( 92, 90), S( 97, 94) },
127 { S(-56,-78), S(-25,-18), S(-11, 26), S( -5, 55), S( -4, 70), S( -1, 81), // Rooks
128 S( 8,109), S( 14,120), S( 21,128), S( 23,143), S( 31,154), S( 32,160),
129 S( 43,165), S( 49,168), S( 59,169) },
130 { S(-40,-35), S(-25,-12), S( 2, 7), S( 4, 19), S( 14, 37), S( 24, 55), // Queens
131 S( 25, 62), S( 40, 76), S( 43, 79), S( 47, 87), S( 54, 94), S( 56,102),
132 S( 60,111), S( 70,116), S( 72,118), S( 73,122), S( 75,128), S( 77,130),
133 S( 85,133), S( 94,136), S( 99,140), S(108,157), S(112,158), S(113,161),
134 S(118,174), S(119,177), S(123,191), S(128,199) }
137 // Outpost[knight/bishop][supported by pawn] contains bonuses for knights and
138 // bishops outposts, bigger if outpost piece is supported by a pawn.
139 const Score Outpost[][2] = {
140 { S(43,11), S(65,20) }, // Knights
141 { S(20, 3), S(29, 8) } // Bishops
144 // ReachableOutpost[knight/bishop][supported by pawn] contains bonuses for
145 // knights and bishops which can reach an outpost square in one move, bigger
146 // if outpost square is supported by a pawn.
147 const Score ReachableOutpost[][2] = {
148 { S(21, 5), S(35, 8) }, // Knights
149 { S( 8, 0), S(14, 4) } // Bishops
152 // RookOnFile[semiopen/open] contains bonuses for each rook when there is no
153 // friendly pawn on the rook file.
154 const Score RookOnFile[2] = { S(20, 7), S(45, 20) };
156 // ThreatBySafePawn[PieceType] contains bonuses according to which piece
157 // type is attacked by a pawn which is protected or is not attacked.
158 const Score ThreatBySafePawn[PIECE_TYPE_NB] = {
159 S(0, 0), S(0, 0), S(176, 139), S(131, 127), S(217, 218), S(203, 215)
162 // Threat[by minor/by rook][attacked PieceType] contains
163 // bonuses according to which piece type attacks which one.
164 // Attacks on lesser pieces which are pawn-defended are not considered.
165 const Score Threat[][PIECE_TYPE_NB] = {
166 { S(0, 0), S(0, 33), S(45, 43), S(46, 47), S(72,107), S(48,118) }, // by Minor
167 { S(0, 0), S(0, 25), S(40, 62), S(40, 59), S( 0, 34), S(35, 48) } // by Rook
170 // ThreatByKing[on one/on many] contains bonuses for King attacks on
171 // pawns or pieces which are not pawn-defended.
172 const Score ThreatByKing[2] = { S(3, 62), S(9, 138) };
174 // Passed[mg/eg][Rank] contains midgame and endgame bonuses for passed pawns.
175 // We don't use a Score because we process the two components independently.
176 const Value Passed[][RANK_NB] = {
177 { V(5), V( 5), V(31), V(73), V(166), V(252) },
178 { V(7), V(14), V(38), V(73), V(166), V(252) }
181 // PassedFile[File] contains a bonus according to the file of a passed pawn
182 const Score PassedFile[FILE_NB] = {
183 S( 9, 10), S( 2, 10), S( 1, -8), S(-20,-12),
184 S(-20,-12), S( 1, -8), S( 2, 10), S( 9, 10)
187 // Assorted bonuses and penalties used by evaluation
188 const Score MinorBehindPawn = S(16, 0);
189 const Score BishopPawns = S( 8, 12);
190 const Score RookOnPawn = S( 8, 24);
191 const Score TrappedRook = S(92, 0);
192 const Score CloseEnemies = S( 7, 0);
193 const Score SafeCheck = S(20, 20);
194 const Score OtherCheck = S(10, 10);
195 const Score ThreatByHangingPawn = S(71, 61);
196 const Score LooseEnemies = S( 0, 25);
197 const Score WeakQueen = S(50, 10);
198 const Score Hanging = S(48, 27);
199 const Score ThreatByPawnPush = S(38, 22);
200 const Score Unstoppable = S( 0, 45);
201 const Score PawnlessFlank = S(20, 80);
202 const Score HinderPassedPawn = S( 7, 0);
203 const Score ThreatByRank = S(16, 3);
205 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
206 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
207 // happen in Chess960 games.
208 const Score TrappedBishopA1H1 = S(50, 50);
213 // KingAttackWeights[PieceType] contains king attack weights by piece type
214 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 78, 56, 45, 11 };
216 // Penalties for enemy's safe checks
217 const int QueenContactCheck = 997;
218 const int QueenCheck = 695;
219 const int RookCheck = 638;
220 const int BishopCheck = 538;
221 const int KnightCheck = 874;
224 // eval_init() initializes king and attack bitboards for a given color
225 // adding pawn attacks. To be done at the beginning of the evaluation.
228 void eval_init(const Position& pos, EvalInfo& ei) {
230 const Color Them = (Us == WHITE ? BLACK : WHITE);
231 const Square Down = (Us == WHITE ? SOUTH : NORTH);
233 ei.pinnedPieces[Us] = pos.pinned_pieces(Us);
234 Bitboard b = ei.attackedBy[Them][KING];
235 ei.attackedBy[Them][ALL_PIECES] |= b;
236 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
237 ei.attackedBy2[Us] = ei.attackedBy[Us][PAWN] & ei.attackedBy[Us][KING];
239 // Init king safety tables only if we are going to use them
240 if (pos.non_pawn_material(Us) >= QueenValueMg)
242 ei.kingRing[Them] = b | shift<Down>(b);
243 b &= ei.attackedBy[Us][PAWN];
244 ei.kingAttackersCount[Us] = popcount(b);
245 ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
248 ei.kingRing[Them] = ei.kingAttackersCount[Us] = 0;
252 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given
255 template<bool DoTrace, Color Us = WHITE, PieceType Pt = KNIGHT>
256 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility,
257 const Bitboard* mobilityArea) {
260 Score score = SCORE_ZERO;
262 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
263 const Color Them = (Us == WHITE ? BLACK : WHITE);
264 const Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
265 : Rank5BB | Rank4BB | Rank3BB);
266 const Square* pl = pos.squares<Pt>(Us);
268 ei.attackedBy[Us][Pt] = 0;
270 while ((s = *pl++) != SQ_NONE)
272 // Find attacked squares, including x-ray attacks for bishops and rooks
273 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
274 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
275 : pos.attacks_from<Pt>(s);
277 if (ei.pinnedPieces[Us] & s)
278 b &= LineBB[pos.square<KING>(Us)][s];
280 ei.attackedBy2[Us] |= ei.attackedBy[Us][ALL_PIECES] & b;
281 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
283 if (b & ei.kingRing[Them])
285 ei.kingAttackersCount[Us]++;
286 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
287 ei.kingAdjacentZoneAttacksCount[Us] += popcount(b & ei.attackedBy[Them][KING]);
291 b &= ~( ei.attackedBy[Them][KNIGHT]
292 | ei.attackedBy[Them][BISHOP]
293 | ei.attackedBy[Them][ROOK]);
295 int mob = popcount(b & mobilityArea[Us]);
297 mobility[Us] += MobilityBonus[Pt][mob];
299 if (Pt == BISHOP || Pt == KNIGHT)
301 // Bonus for outpost squares
302 bb = OutpostRanks & ~ei.pi->pawn_attacks_span(Them);
304 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & s)];
307 bb &= b & ~pos.pieces(Us);
309 score += ReachableOutpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & bb)];
312 // Bonus when behind a pawn
313 if ( relative_rank(Us, s) < RANK_5
314 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
315 score += MinorBehindPawn;
317 // Penalty for pawns on the same color square as the bishop
319 score -= BishopPawns * ei.pi->pawns_on_same_color_squares(Us, s);
321 // An important Chess960 pattern: A cornered bishop blocked by a friendly
322 // pawn diagonally in front of it is a very serious problem, especially
323 // when that pawn is also blocked.
326 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
328 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
329 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
330 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
331 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
338 // Bonus for aligning with enemy pawns on the same rank/file
339 if (relative_rank(Us, s) >= RANK_5)
340 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
342 // Bonus when on an open or semi-open file
343 if (ei.pi->semiopen_file(Us, file_of(s)))
344 score += RookOnFile[!!ei.pi->semiopen_file(Them, file_of(s))];
346 // Penalize when trapped by the king, even more if the king cannot castle
349 Square ksq = pos.square<KING>(Us);
351 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
352 && !ei.pi->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
353 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
359 // Penalty if any relative pin or discovered attack against the queen
361 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, pinners))
367 Trace::add(Pt, Us, score);
369 // Recursively call evaluate_pieces() of next piece type until KING is excluded
370 return score - evaluate_pieces<DoTrace, Them, NextPt>(pos, ei, mobility, mobilityArea);
374 Score evaluate_pieces<false, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
376 Score evaluate_pieces< true, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
379 // evaluate_king() assigns bonuses and penalties to a king of a given color
381 const Bitboard WhiteCamp = Rank1BB | Rank2BB | Rank3BB | Rank4BB | Rank5BB;
382 const Bitboard BlackCamp = Rank8BB | Rank7BB | Rank6BB | Rank5BB | Rank4BB;
383 const Bitboard QueenSide = FileABB | FileBBB | FileCBB | FileDBB;
384 const Bitboard CenterFiles = FileCBB | FileDBB | FileEBB | FileFBB;
385 const Bitboard KingSide = FileEBB | FileFBB | FileGBB | FileHBB;
387 const Bitboard KingFlank[COLOR_NB][FILE_NB] = {
388 { QueenSide & WhiteCamp, QueenSide & WhiteCamp, QueenSide & WhiteCamp, CenterFiles & WhiteCamp,
389 CenterFiles & WhiteCamp, KingSide & WhiteCamp, KingSide & WhiteCamp, KingSide & WhiteCamp },
390 { QueenSide & BlackCamp, QueenSide & BlackCamp, QueenSide & BlackCamp, CenterFiles & BlackCamp,
391 CenterFiles & BlackCamp, KingSide & BlackCamp, KingSide & BlackCamp, KingSide & BlackCamp },
394 template<Color Us, bool DoTrace>
395 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
397 const Color Them = (Us == WHITE ? BLACK : WHITE);
398 const Square Up = (Us == WHITE ? NORTH : SOUTH);
400 Bitboard undefended, b, b1, b2, safe, other;
402 const Square ksq = pos.square<KING>(Us);
404 // King shelter and enemy pawns storm
405 Score score = ei.pi->king_safety<Us>(pos, ksq);
407 // Main king safety evaluation
408 if (ei.kingAttackersCount[Them])
410 // Find the attacked squares which are defended only by the king...
411 undefended = ei.attackedBy[Them][ALL_PIECES]
412 & ei.attackedBy[Us][KING]
413 & ~ei.attackedBy2[Us];
415 // ... and those which are not defended at all in the larger king ring
416 b = ei.attackedBy[Them][ALL_PIECES] & ~ei.attackedBy[Us][ALL_PIECES]
417 & ei.kingRing[Us] & ~pos.pieces(Them);
419 // Initialize the 'kingDanger' variable, which will be transformed
420 // later into a king danger score. The initial value is based on the
421 // number and types of the enemy's attacking pieces, the number of
422 // attacked and undefended squares around our king and the quality of
423 // the pawn shelter (current 'score' value).
424 kingDanger = std::min(807, ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them])
425 + 101 * ei.kingAdjacentZoneAttacksCount[Them]
426 + 235 * popcount(undefended)
427 + 134 * (popcount(b) + !!ei.pinnedPieces[Us])
428 - 717 * !pos.count<QUEEN>(Them)
429 - 7 * mg_value(score) / 5 - 5;
431 // Analyse the enemy's safe queen contact checks. Firstly, find the
432 // undefended squares around the king reachable by the enemy queen...
433 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);
435 // ...and keep squares supported by another enemy piece
436 kingDanger += QueenContactCheck * popcount(b & ei.attackedBy2[Them]);
438 // Analyse the safe enemy's checks which are possible on next move...
439 safe = ~(ei.attackedBy[Us][ALL_PIECES] | pos.pieces(Them));
441 // ... and some other potential checks, only requiring the square to be
442 // safe from pawn-attacks, and not being occupied by a blocked pawn.
443 other = ~( ei.attackedBy[Us][PAWN]
444 | (pos.pieces(Them, PAWN) & shift<Up>(pos.pieces(PAWN))));
446 b1 = pos.attacks_from<ROOK >(ksq);
447 b2 = pos.attacks_from<BISHOP>(ksq);
449 // Enemy queen safe checks
450 if ((b1 | b2) & ei.attackedBy[Them][QUEEN] & safe)
451 kingDanger += QueenCheck, score -= SafeCheck;
453 // For other pieces, also consider the square safe if attacked twice,
454 // and only defended by a queen.
455 safe |= ei.attackedBy2[Them]
456 & ~(ei.attackedBy2[Us] | pos.pieces(Them))
457 & ei.attackedBy[Us][QUEEN];
459 // Enemy rooks safe and other checks
460 if (b1 & ei.attackedBy[Them][ROOK] & safe)
461 kingDanger += RookCheck, score -= SafeCheck;
463 else if (b1 & ei.attackedBy[Them][ROOK] & other)
466 // Enemy bishops safe and other checks
467 if (b2 & ei.attackedBy[Them][BISHOP] & safe)
468 kingDanger += BishopCheck, score -= SafeCheck;
470 else if (b2 & ei.attackedBy[Them][BISHOP] & other)
473 // Enemy knights safe and other checks
474 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT];
476 kingDanger += KnightCheck, score -= SafeCheck;
481 // Compute the king danger score and subtract it from the evaluation
483 score -= make_score(std::min(kingDanger * kingDanger / 4096, 2 * int(BishopValueMg)), 0);
486 // King tropism: firstly, find squares that opponent attacks in our king flank
487 File kf = file_of(ksq);
488 b = ei.attackedBy[Them][ALL_PIECES] & KingFlank[Us][kf];
490 assert(((Us == WHITE ? b << 4 : b >> 4) & b) == 0);
491 assert(popcount(Us == WHITE ? b << 4 : b >> 4) == popcount(b));
493 // Secondly, add the squares which are attacked twice in that flank and
494 // which are not defended by our pawns.
495 b = (Us == WHITE ? b << 4 : b >> 4)
496 | (b & ei.attackedBy2[Them] & ~ei.attackedBy[Us][PAWN]);
498 score -= CloseEnemies * popcount(b);
500 // Penalty when our king is on a pawnless flank
501 if (!(pos.pieces(PAWN) & (KingFlank[WHITE][kf] | KingFlank[BLACK][kf])))
502 score -= PawnlessFlank;
505 Trace::add(KING, Us, score);
511 // evaluate_threats() assigns bonuses according to the types of the attacking
512 // and the attacked pieces.
514 template<Color Us, bool DoTrace>
515 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
517 const Color Them = (Us == WHITE ? BLACK : WHITE);
518 const Square Up = (Us == WHITE ? NORTH : SOUTH);
519 const Square Left = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
520 const Square Right = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
521 const Bitboard TRank2BB = (Us == WHITE ? Rank2BB : Rank7BB);
522 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
524 enum { Minor, Rook };
526 Bitboard b, weak, defended, safeThreats;
527 Score score = SCORE_ZERO;
529 // Small bonus if the opponent has loose pawns or pieces
530 if ( (pos.pieces(Them) ^ pos.pieces(Them, QUEEN, KING))
531 & ~(ei.attackedBy[Us][ALL_PIECES] | ei.attackedBy[Them][ALL_PIECES]))
532 score += LooseEnemies;
534 // Non-pawn enemies attacked by a pawn
535 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Us][PAWN];
539 b = pos.pieces(Us, PAWN) & ( ~ei.attackedBy[Them][ALL_PIECES]
540 | ei.attackedBy[Us][ALL_PIECES]);
542 safeThreats = (shift<Right>(b) | shift<Left>(b)) & weak;
544 if (weak ^ safeThreats)
545 score += ThreatByHangingPawn;
548 score += ThreatBySafePawn[type_of(pos.piece_on(pop_lsb(&safeThreats)))];
551 // Non-pawn enemies defended by a pawn
552 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Them][PAWN];
554 // Enemies not defended by a pawn and under our attack
555 weak = pos.pieces(Them)
556 & ~ei.attackedBy[Them][PAWN]
557 & ei.attackedBy[Us][ALL_PIECES];
559 // Add a bonus according to the kind of attacking pieces
562 b = (defended | weak) & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
565 Square s = pop_lsb(&b);
566 score += Threat[Minor][type_of(pos.piece_on(s))];
567 if (type_of(pos.piece_on(s)) != PAWN)
568 score += ThreatByRank * (int)relative_rank(Them, s);
571 b = (pos.pieces(Them, QUEEN) | weak) & ei.attackedBy[Us][ROOK];
574 Square s = pop_lsb(&b);
575 score += Threat[Rook][type_of(pos.piece_on(s))];
576 if (type_of(pos.piece_on(s)) != PAWN)
577 score += ThreatByRank * (int)relative_rank(Them, s);
580 score += Hanging * popcount(weak & ~ei.attackedBy[Them][ALL_PIECES]);
582 b = weak & ei.attackedBy[Us][KING];
584 score += ThreatByKing[more_than_one(b)];
587 // Bonus if some pawns can safely push and attack an enemy piece
588 b = pos.pieces(Us, PAWN) & ~TRank7BB;
589 b = shift<Up>(b | (shift<Up>(b & TRank2BB) & ~pos.pieces()));
592 & ~ei.attackedBy[Them][PAWN]
593 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
595 b = (shift<Left>(b) | shift<Right>(b))
597 & ~ei.attackedBy[Us][PAWN];
599 score += ThreatByPawnPush * popcount(b);
602 Trace::add(THREAT, Us, score);
608 // evaluate_passed_pawns() evaluates the passed pawns of the given color
610 template<Color Us, bool DoTrace>
611 Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
613 const Color Them = (Us == WHITE ? BLACK : WHITE);
615 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
616 Score score = SCORE_ZERO;
618 b = ei.pi->passed_pawns(Us);
622 Square s = pop_lsb(&b);
624 assert(pos.pawn_passed(Us, s));
625 assert(!(pos.pieces(PAWN) & forward_bb(Us, s)));
627 bb = forward_bb(Us, s) & (ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
628 score -= HinderPassedPawn * popcount(bb);
630 int r = relative_rank(Us, s) - RANK_2;
631 int rr = r * (r - 1);
633 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
637 Square blockSq = s + pawn_push(Us);
639 // Adjust bonus based on the king's proximity
640 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
641 - distance(pos.square<KING>(Us ), blockSq) * 2 * rr;
643 // If blockSq is not the queening square then consider also a second push
644 if (relative_rank(Us, blockSq) != RANK_8)
645 ebonus -= distance(pos.square<KING>(Us), blockSq + pawn_push(Us)) * rr;
647 // If the pawn is free to advance, then increase the bonus
648 if (pos.empty(blockSq))
650 // If there is a rook or queen attacking/defending the pawn from behind,
651 // consider all the squaresToQueen. Otherwise consider only the squares
652 // in the pawn's path attacked or occupied by the enemy.
653 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
655 bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
657 if (!(pos.pieces(Us) & bb))
658 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
660 if (!(pos.pieces(Them) & bb))
661 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
663 // If there aren't any enemy attacks, assign a big bonus. Otherwise
664 // assign a smaller bonus if the block square isn't attacked.
665 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
667 // If the path to the queen is fully defended, assign a big bonus.
668 // Otherwise assign a smaller bonus if the block square is defended.
669 if (defendedSquares == squaresToQueen)
672 else if (defendedSquares & blockSq)
675 mbonus += k * rr, ebonus += k * rr;
677 else if (pos.pieces(Us) & blockSq)
678 mbonus += rr + r * 2, ebonus += rr + r * 2;
681 score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
685 Trace::add(PASSED, Us, score);
687 // Add the scores to the middlegame and endgame eval
692 // evaluate_space() computes the space evaluation for a given side. The
693 // space evaluation is a simple bonus based on the number of safe squares
694 // available for minor pieces on the central four files on ranks 2--4. Safe
695 // squares one, two or three squares behind a friendly pawn are counted
696 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
697 // improve play on game opening.
699 Score evaluate_space(const Position& pos, const EvalInfo& ei) {
701 const Color Them = (Us == WHITE ? BLACK : WHITE);
702 const Bitboard SpaceMask =
703 Us == WHITE ? (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank2BB | Rank3BB | Rank4BB)
704 : (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank7BB | Rank6BB | Rank5BB);
706 // Find the safe squares for our pieces inside the area defined by
707 // SpaceMask. A square is unsafe if it is attacked by an enemy
708 // pawn, or if it is undefended and attacked by an enemy piece.
709 Bitboard safe = SpaceMask
710 & ~pos.pieces(Us, PAWN)
711 & ~ei.attackedBy[Them][PAWN]
712 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
714 // Find all squares which are at most three squares behind some friendly pawn
715 Bitboard behind = pos.pieces(Us, PAWN);
716 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
717 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
719 // Since SpaceMask[Us] is fully on our half of the board...
720 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
722 // ...count safe + (behind & safe) with a single popcount
723 int bonus = popcount((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
724 bonus = std::min(16, bonus);
725 int weight = pos.count<ALL_PIECES>(Us) - 2 * ei.pi->open_files();
727 return make_score(bonus * weight * weight / 18, 0);
731 // evaluate_initiative() computes the initiative correction value for the
732 // position, i.e., second order bonus/malus based on the known attacking/defending
733 // status of the players.
734 Score evaluate_initiative(const Position& pos, int asymmetry, Value eg) {
736 int kingDistance = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
737 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
738 int pawns = pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK);
740 // Compute the initiative bonus for the attacking side
741 int initiative = 8 * (asymmetry + kingDistance - 15) + 12 * pawns;
743 // Now apply the bonus: note that we find the attacking side by extracting
744 // the sign of the endgame value, and that we carefully cap the bonus so
745 // that the endgame score will never be divided by more than two.
746 int value = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg / 2));
748 return make_score(0, value);
752 // evaluate_scale_factor() computes the scale factor for the winning side
753 ScaleFactor evaluate_scale_factor(const Position& pos, const EvalInfo& ei, Value eg) {
755 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
756 ScaleFactor sf = ei.me->scale_factor(pos, strongSide);
758 // If we don't already have an unusual scale factor, check for certain
759 // types of endgames, and use a lower scale for those.
760 if ( ei.me->game_phase() < PHASE_MIDGAME
761 && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
763 if (pos.opposite_bishops())
765 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
766 // is almost a draw, in case of KBP vs KB, it is even more a draw.
767 if ( pos.non_pawn_material(WHITE) == BishopValueMg
768 && pos.non_pawn_material(BLACK) == BishopValueMg)
769 sf = more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
771 // Endgame with opposite-colored bishops, but also other pieces. Still
772 // a bit drawish, but not as drawish as with only the two bishops.
774 sf = ScaleFactor(46);
776 // Endings where weaker side can place his king in front of the opponent's
777 // pawns are drawish.
778 else if ( abs(eg) <= BishopValueEg
779 && pos.count<PAWN>(strongSide) <= 2
780 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
781 sf = ScaleFactor(37 + 7 * pos.count<PAWN>(strongSide));
790 /// evaluate() is the main evaluation function. It returns a static evaluation
791 /// of the position from the point of view of the side to move.
793 template<bool DoTrace>
794 Value Eval::evaluate(const Position& pos) {
796 assert(!pos.checkers());
798 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
801 // Probe the material hash table
802 ei.me = Material::probe(pos);
804 // If we have a specialized evaluation function for the current material
805 // configuration, call it and return.
806 if (ei.me->specialized_eval_exists())
807 return ei.me->evaluate(pos);
809 // Initialize score by reading the incrementally updated scores included in
810 // the position object (material + piece square tables) and the material
811 // imbalance. Score is computed internally from the white point of view.
812 Score score = pos.psq_score() + ei.me->imbalance();
814 // Probe the pawn hash table
815 ei.pi = Pawns::probe(pos);
816 score += ei.pi->pawns_score();
818 // Initialize attack and king safety bitboards
819 ei.attackedBy[WHITE][ALL_PIECES] = ei.attackedBy[BLACK][ALL_PIECES] = 0;
820 ei.attackedBy[WHITE][KING] = pos.attacks_from<KING>(pos.square<KING>(WHITE));
821 ei.attackedBy[BLACK][KING] = pos.attacks_from<KING>(pos.square<KING>(BLACK));
822 eval_init<WHITE>(pos, ei);
823 eval_init<BLACK>(pos, ei);
825 // Pawns blocked or on ranks 2 and 3 will be excluded from the mobility area
826 Bitboard blockedPawns[] = {
827 pos.pieces(WHITE, PAWN) & (shift<SOUTH>(pos.pieces()) | Rank2BB | Rank3BB),
828 pos.pieces(BLACK, PAWN) & (shift<NORTH>(pos.pieces()) | Rank7BB | Rank6BB)
831 // Do not include in mobility area squares protected by enemy pawns, or occupied
832 // by our blocked pawns or king.
833 Bitboard mobilityArea[] = {
834 ~(ei.attackedBy[BLACK][PAWN] | blockedPawns[WHITE] | pos.square<KING>(WHITE)),
835 ~(ei.attackedBy[WHITE][PAWN] | blockedPawns[BLACK] | pos.square<KING>(BLACK))
838 // Evaluate all pieces but king and pawns
839 score += evaluate_pieces<DoTrace>(pos, ei, mobility, mobilityArea);
840 score += mobility[WHITE] - mobility[BLACK];
842 // Evaluate kings after all other pieces because we need full attack
843 // information when computing the king safety evaluation.
844 score += evaluate_king<WHITE, DoTrace>(pos, ei)
845 - evaluate_king<BLACK, DoTrace>(pos, ei);
847 // Evaluate tactical threats, we need full attack information including king
848 score += evaluate_threats<WHITE, DoTrace>(pos, ei)
849 - evaluate_threats<BLACK, DoTrace>(pos, ei);
851 // Evaluate passed pawns, we need full attack information including king
852 score += evaluate_passed_pawns<WHITE, DoTrace>(pos, ei)
853 - evaluate_passed_pawns<BLACK, DoTrace>(pos, ei);
855 // If both sides have only pawns, score for potential unstoppable pawns
856 if (!pos.non_pawn_material(WHITE) && !pos.non_pawn_material(BLACK))
858 if (ei.pi->passed_pawns(WHITE))
859 score += Unstoppable;
861 if (ei.pi->passed_pawns(BLACK))
862 score -= Unstoppable;
865 // Evaluate space for both sides, only during opening
866 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
867 score += evaluate_space<WHITE>(pos, ei)
868 - evaluate_space<BLACK>(pos, ei);
870 // Evaluate position potential for the winning side
871 score += evaluate_initiative(pos, ei.pi->pawn_asymmetry(), eg_value(score));
873 // Evaluate scale factor for the winning side
874 ScaleFactor sf = evaluate_scale_factor(pos, ei, eg_value(score));
876 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
877 Value v = mg_value(score) * int(ei.me->game_phase())
878 + eg_value(score) * int(PHASE_MIDGAME - ei.me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
880 v /= int(PHASE_MIDGAME);
882 // In case of tracing add all remaining individual evaluation terms
885 Trace::add(MATERIAL, pos.psq_score());
886 Trace::add(IMBALANCE, ei.me->imbalance());
887 Trace::add(PAWN, ei.pi->pawns_score());
888 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
889 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
890 Trace::add(SPACE, evaluate_space<WHITE>(pos, ei)
891 , evaluate_space<BLACK>(pos, ei));
892 Trace::add(TOTAL, score);
895 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
898 // Explicit template instantiations
899 template Value Eval::evaluate<true >(const Position&);
900 template Value Eval::evaluate<false>(const Position&);
903 /// trace() is like evaluate(), but instead of returning a value, it returns
904 /// a string (suitable for outputting to stdout) that contains the detailed
905 /// descriptions and values of each evaluation term. Useful for debugging.
907 std::string Eval::trace(const Position& pos) {
909 std::memset(scores, 0, sizeof(scores));
911 Value v = evaluate<true>(pos);
912 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
914 std::stringstream ss;
915 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
916 << " Eval term | White | Black | Total \n"
917 << " | MG EG | MG EG | MG EG \n"
918 << "----------------+-------------+-------------+-------------\n"
919 << " Material | " << Term(MATERIAL)
920 << " Imbalance | " << Term(IMBALANCE)
921 << " Pawns | " << Term(PAWN)
922 << " Knights | " << Term(KNIGHT)
923 << " Bishop | " << Term(BISHOP)
924 << " Rooks | " << Term(ROOK)
925 << " Queens | " << Term(QUEEN)
926 << " Mobility | " << Term(MOBILITY)
927 << " King safety | " << Term(KING)
928 << " Threats | " << Term(THREAT)
929 << " Passed pawns | " << Term(PASSED)
930 << " Space | " << Term(SPACE)
931 << "----------------+-------------+-------------+-------------\n"
932 << " Total | " << Term(TOTAL);
934 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";