2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
5 Copyright (C) 2015-2016 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
7 Stockfish is free software: you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation, either version 3 of the License, or
10 (at your option) any later version.
12 Stockfish is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <http://www.gnu.org/licenses/>.
23 #include <cstring> // For std::memset
36 enum Term { // The first 8 entries are for PieceType
37 MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, TOTAL, TERM_NB
40 double scores[TERM_NB][COLOR_NB][PHASE_NB];
42 double to_cp(Value v) { return double(v) / PawnValueEg; }
44 void add(int idx, Color c, Score s) {
45 scores[idx][c][MG] = to_cp(mg_value(s));
46 scores[idx][c][EG] = to_cp(eg_value(s));
49 void add(int idx, Score w, Score b = SCORE_ZERO) {
50 add(idx, WHITE, w); add(idx, BLACK, b);
53 std::ostream& operator<<(std::ostream& os, Term t) {
55 if (t == MATERIAL || t == IMBALANCE || t == Term(PAWN) || t == TOTAL)
56 os << " --- --- | --- --- | ";
58 os << std::setw(5) << scores[t][WHITE][MG] << " "
59 << std::setw(5) << scores[t][WHITE][EG] << " | "
60 << std::setw(5) << scores[t][BLACK][MG] << " "
61 << std::setw(5) << scores[t][BLACK][EG] << " | ";
63 os << std::setw(5) << scores[t][WHITE][MG] - scores[t][BLACK][MG] << " "
64 << std::setw(5) << scores[t][WHITE][EG] - scores[t][BLACK][EG] << " \n";
70 using namespace Trace;
72 // Struct EvalInfo contains various information computed and collected
73 // by the evaluation functions.
76 // attackedBy[color][piece type] is a bitboard representing all squares
77 // attacked by a given color and piece type (can be also ALL_PIECES).
78 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
80 // attackedBy2[color] are the squares attacked by 2 pieces of a given color,
81 // possibly via x-ray or by one pawn and one piece. Diagonal x-ray through
82 // pawn or squares attacked by 2 pawns are not explicitly added.
83 Bitboard attackedBy2[COLOR_NB];
85 // kingRing[color] is the zone around the king which is considered
86 // by the king safety evaluation. This consists of the squares directly
87 // adjacent to the king, and the three (or two, for a king on an edge file)
88 // squares two ranks in front of the king. For instance, if black's king
89 // is on g8, kingRing[BLACK] is a bitboard containing the squares f8, h8,
90 // f7, g7, h7, f6, g6 and h6.
91 Bitboard kingRing[COLOR_NB];
93 // kingAttackersCount[color] is the number of pieces of the given color
94 // which attack a square in the kingRing of the enemy king.
95 int kingAttackersCount[COLOR_NB];
97 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of the
98 // given color which attack a square in the kingRing of the enemy king. The
99 // weights of the individual piece types are given by the elements in the
100 // KingAttackWeights array.
101 int kingAttackersWeight[COLOR_NB];
103 // kingAdjacentZoneAttacksCount[color] is the number of attacks by the given
104 // color to squares directly adjacent to the enemy king. Pieces which attack
105 // more than one square are counted multiple times. For instance, if there is
106 // a white knight on g5 and black's king is on g8, this white knight adds 2
107 // to kingAdjacentZoneAttacksCount[WHITE].
108 int kingAdjacentZoneAttacksCount[COLOR_NB];
110 Bitboard pinnedPieces[COLOR_NB];
115 #define V(v) Value(v)
116 #define S(mg, eg) make_score(mg, eg)
118 // MobilityBonus[PieceType][attacked] contains bonuses for middle and end
119 // game, indexed by piece type and number of attacked squares in the MobilityArea.
120 const Score MobilityBonus[][32] = {
122 { S(-75,-76), S(-56,-54), S( -9,-26), S( -2,-10), S( 6, 5), S( 15, 11), // Knights
123 S( 22, 26), S( 30, 28), S( 36, 29) },
124 { S(-48,-58), S(-21,-19), S( 16, -2), S( 26, 12), S( 37, 22), S( 51, 42), // Bishops
125 S( 54, 54), S( 63, 58), S( 65, 63), S( 71, 70), S( 79, 74), S( 81, 86),
126 S( 92, 90), S( 97, 94) },
127 { S(-56,-78), S(-25,-18), S(-11, 26), S( -5, 55), S( -4, 70), S( -1, 81), // Rooks
128 S( 8,109), S( 14,120), S( 21,128), S( 23,143), S( 31,154), S( 32,160),
129 S( 43,165), S( 49,168), S( 59,169) },
130 { S(-40,-35), S(-25,-12), S( 2, 7), S( 4, 19), S( 14, 37), S( 24, 55), // Queens
131 S( 25, 62), S( 40, 76), S( 43, 79), S( 47, 87), S( 54, 94), S( 56,102),
132 S( 60,111), S( 70,116), S( 72,118), S( 73,122), S( 75,128), S( 77,130),
133 S( 85,133), S( 94,136), S( 99,140), S(108,157), S(112,158), S(113,161),
134 S(118,174), S(119,177), S(123,191), S(128,199) }
137 // Outpost[knight/bishop][supported by pawn] contains bonuses for knights and
138 // bishops outposts, bigger if outpost piece is supported by a pawn.
139 const Score Outpost[][2] = {
140 { S(43,11), S(65,20) }, // Knights
141 { S(20, 3), S(29, 8) } // Bishops
144 // ReachableOutpost[knight/bishop][supported by pawn] contains bonuses for
145 // knights and bishops which can reach an outpost square in one move, bigger
146 // if outpost square is supported by a pawn.
147 const Score ReachableOutpost[][2] = {
148 { S(21, 5), S(35, 8) }, // Knights
149 { S( 8, 0), S(14, 4) } // Bishops
152 // RookOnFile[semiopen/open] contains bonuses for each rook when there is no
153 // friendly pawn on the rook file.
154 const Score RookOnFile[2] = { S(20, 7), S(45, 20) };
156 // ThreatBySafePawn[PieceType] contains bonuses according to which piece
157 // type is attacked by a pawn which is protected or is not attacked.
158 const Score ThreatBySafePawn[PIECE_TYPE_NB] = {
159 S(0, 0), S(0, 0), S(176, 139), S(131, 127), S(217, 218), S(203, 215) };
161 // Threat[by minor/by rook][attacked PieceType] contains
162 // bonuses according to which piece type attacks which one.
163 // Attacks on lesser pieces which are pawn-defended are not considered.
164 const Score Threat[][PIECE_TYPE_NB] = {
165 { S(0, 0), S(0, 33), S(45, 43), S(46, 47), S(72,107), S(48,118) }, // by Minor
166 { S(0, 0), S(0, 25), S(40, 62), S(40, 59), S( 0, 34), S(35, 48) } // by Rook
169 // ThreatByKing[on one/on many] contains bonuses for King attacks on
170 // pawns or pieces which are not pawn-defended.
171 const Score ThreatByKing[2] = { S(3, 62), S(9, 138) };
173 // Passed[mg/eg][Rank] contains midgame and endgame bonuses for passed pawns.
174 // We don't use a Score because we process the two components independently.
175 const Value Passed[][RANK_NB] = {
176 { V(5), V( 5), V(31), V(73), V(166), V(252) },
177 { V(7), V(14), V(38), V(73), V(166), V(252) }
180 // PassedFile[File] contains a bonus according to the file of a passed pawn
181 const Score PassedFile[FILE_NB] = {
182 S( 9, 10), S( 2, 10), S( 1, -8), S(-20,-12),
183 S(-20,-12), S( 1, -8), S( 2, 10), S( 9, 10)
186 // Assorted bonuses and penalties used by evaluation
187 const Score MinorBehindPawn = S(16, 0);
188 const Score BishopPawns = S( 8, 12);
189 const Score RookOnPawn = S( 8, 24);
190 const Score TrappedRook = S(92, 0);
191 const Score CloseEnemies = S( 7, 0);
192 const Score SafeCheck = S(20, 20);
193 const Score OtherCheck = S(10, 10);
194 const Score ThreatByHangingPawn = S(71, 61);
195 const Score LooseEnemies = S( 0, 25);
196 const Score WeakQueen = S(35, 0);
197 const Score Hanging = S(48, 27);
198 const Score ThreatByPawnPush = S(38, 22);
199 const Score Unstoppable = S( 0, 20);
201 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
202 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
203 // happen in Chess960 games.
204 const Score TrappedBishopA1H1 = S(50, 50);
209 // King danger constants and variables. The king danger scores are looked-up
210 // in KingDanger[]. Various little "meta-bonuses" measuring the strength
211 // of the enemy attack are added up into an integer, which is used as an
212 // index to KingDanger[].
213 Score KingDanger[400];
215 // KingAttackWeights[PieceType] contains king attack weights by piece type
216 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 7, 5, 4, 1 };
218 // Penalties for enemy's safe checks
219 const int QueenContactCheck = 89;
220 const int QueenCheck = 62;
221 const int RookCheck = 57;
222 const int BishopCheck = 48;
223 const int KnightCheck = 78;
226 // eval_init() initializes king and attack bitboards for a given color
227 // adding pawn attacks. To be done at the beginning of the evaluation.
230 void eval_init(const Position& pos, EvalInfo& ei) {
232 const Color Them = (Us == WHITE ? BLACK : WHITE);
233 const Square Down = (Us == WHITE ? DELTA_S : DELTA_N);
235 ei.pinnedPieces[Us] = pos.pinned_pieces(Us);
236 Bitboard b = ei.attackedBy[Them][KING];
237 ei.attackedBy[Them][ALL_PIECES] |= b;
238 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
239 ei.attackedBy2[Us] = ei.attackedBy[Us][PAWN] & ei.attackedBy[Us][KING];
241 // Init king safety tables only if we are going to use them
242 if (pos.non_pawn_material(Us) >= QueenValueMg)
244 ei.kingRing[Them] = b | shift_bb<Down>(b);
245 b &= ei.attackedBy[Us][PAWN];
246 ei.kingAttackersCount[Us] = popcount(b);
247 ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
250 ei.kingRing[Them] = ei.kingAttackersCount[Us] = 0;
254 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given
257 template<bool DoTrace, Color Us = WHITE, PieceType Pt = KNIGHT>
258 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility,
259 const Bitboard* mobilityArea) {
262 Score score = SCORE_ZERO;
264 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
265 const Color Them = (Us == WHITE ? BLACK : WHITE);
266 const Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
267 : Rank5BB | Rank4BB | Rank3BB);
268 const Square* pl = pos.squares<Pt>(Us);
270 ei.attackedBy[Us][Pt] = 0;
272 while ((s = *pl++) != SQ_NONE)
274 // Find attacked squares, including x-ray attacks for bishops and rooks
275 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
276 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
277 : pos.attacks_from<Pt>(s);
279 if (ei.pinnedPieces[Us] & s)
280 b &= LineBB[pos.square<KING>(Us)][s];
282 ei.attackedBy2[Us] |= ei.attackedBy[Us][ALL_PIECES] & b;
283 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
285 if (b & ei.kingRing[Them])
287 ei.kingAttackersCount[Us]++;
288 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
289 ei.kingAdjacentZoneAttacksCount[Us] += popcount(b & ei.attackedBy[Them][KING]);
293 b &= ~( ei.attackedBy[Them][KNIGHT]
294 | ei.attackedBy[Them][BISHOP]
295 | ei.attackedBy[Them][ROOK]);
297 int mob = popcount(b & mobilityArea[Us]);
299 mobility[Us] += MobilityBonus[Pt][mob];
301 if (Pt == BISHOP || Pt == KNIGHT)
303 // Bonus for outpost squares
304 bb = OutpostRanks & ~ei.pi->pawn_attacks_span(Them);
306 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & s)];
309 bb &= b & ~pos.pieces(Us);
311 score += ReachableOutpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & bb)];
314 // Bonus when behind a pawn
315 if ( relative_rank(Us, s) < RANK_5
316 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
317 score += MinorBehindPawn;
319 // Penalty for pawns on the same color square as the bishop
321 score -= BishopPawns * ei.pi->pawns_on_same_color_squares(Us, s);
323 // An important Chess960 pattern: A cornered bishop blocked by a friendly
324 // pawn diagonally in front of it is a very serious problem, especially
325 // when that pawn is also blocked.
328 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
330 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? DELTA_E : DELTA_W);
331 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
332 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
333 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
340 // Bonus for aligning with enemy pawns on the same rank/file
341 if (relative_rank(Us, s) >= RANK_5)
342 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
344 // Bonus when on an open or semi-open file
345 if (ei.pi->semiopen_file(Us, file_of(s)))
346 score += RookOnFile[!!ei.pi->semiopen_file(Them, file_of(s))];
348 // Penalize when trapped by the king, even more if the king cannot castle
351 Square ksq = pos.square<KING>(Us);
353 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
354 && (rank_of(ksq) == rank_of(s) || relative_rank(Us, ksq) == RANK_1)
355 && !ei.pi->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
356 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
362 // Penalty if any relative pin or discovered attack against the queen
364 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, pinners))
370 Trace::add(Pt, Us, score);
372 // Recursively call evaluate_pieces() of next piece type until KING is excluded
373 return score - evaluate_pieces<DoTrace, Them, NextPt>(pos, ei, mobility, mobilityArea);
377 Score evaluate_pieces<false, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
379 Score evaluate_pieces< true, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
382 // evaluate_king() assigns bonuses and penalties to a king of a given color
384 const Bitboard WhiteCamp = Rank1BB | Rank2BB | Rank3BB | Rank4BB | Rank5BB;
385 const Bitboard BlackCamp = Rank8BB | Rank7BB | Rank6BB | Rank5BB | Rank4BB;
386 const Bitboard QueenSide = FileABB | FileBBB | FileCBB | FileDBB;
387 const Bitboard CenterFiles = FileCBB | FileDBB | FileEBB | FileFBB;
388 const Bitboard KingSide = FileEBB | FileFBB | FileGBB | FileHBB;
390 const Bitboard KingFlank[COLOR_NB][FILE_NB] = {
391 { QueenSide & WhiteCamp, QueenSide & WhiteCamp, QueenSide & WhiteCamp, CenterFiles & WhiteCamp,
392 CenterFiles & WhiteCamp, KingSide & WhiteCamp, KingSide & WhiteCamp, KingSide & WhiteCamp },
393 { QueenSide & BlackCamp, QueenSide & BlackCamp, QueenSide & BlackCamp, CenterFiles & BlackCamp,
394 CenterFiles & BlackCamp, KingSide & BlackCamp, KingSide & BlackCamp, KingSide & BlackCamp },
397 template<Color Us, bool DoTrace>
398 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
400 const Color Them = (Us == WHITE ? BLACK : WHITE);
401 const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
403 Bitboard undefended, b, b1, b2, safe, other;
405 const Square ksq = pos.square<KING>(Us);
407 // King shelter and enemy pawns storm
408 Score score = ei.pi->king_safety<Us>(pos, ksq);
410 // Main king safety evaluation
411 if (ei.kingAttackersCount[Them])
413 // Find the attacked squares which are defended only by the king...
414 undefended = ei.attackedBy[Them][ALL_PIECES]
415 & ei.attackedBy[Us][KING]
416 & ~ei.attackedBy2[Us];
418 // ... and those which are not defended at all in the larger king ring
419 b = ei.attackedBy[Them][ALL_PIECES] & ~ei.attackedBy[Us][ALL_PIECES]
420 & ei.kingRing[Us] & ~pos.pieces(Them);
422 // Initialize the 'attackUnits' variable, which is used later on as an
423 // index into the KingDanger[] array. The initial value is based on the
424 // number and types of the enemy's attacking pieces, the number of
425 // attacked and undefended squares around our king and the quality of
426 // the pawn shelter (current 'score' value).
427 attackUnits = std::min(72, ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them])
428 + 9 * ei.kingAdjacentZoneAttacksCount[Them]
429 + 21 * popcount(undefended)
430 + 12 * (popcount(b) + !!ei.pinnedPieces[Us])
431 - 64 * !pos.count<QUEEN>(Them)
432 - mg_value(score) / 8;
434 // Analyse the enemy's safe queen contact checks. Firstly, find the
435 // undefended squares around the king reachable by the enemy queen...
436 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);
438 // ...and keep squares supported by another enemy piece
439 attackUnits += QueenContactCheck * popcount(b & ei.attackedBy2[Them]);
441 // Analyse the safe enemy's checks which are possible on next move...
442 safe = ~(ei.attackedBy[Us][ALL_PIECES] | pos.pieces(Them));
444 // ... and some other potential checks, only requiring the square to be
445 // safe from pawn-attacks, and not being occupied by a blocked pawn.
446 other = ~( ei.attackedBy[Us][PAWN]
447 | (pos.pieces(Them, PAWN) & shift_bb<Up>(pos.pieces(PAWN))));
449 b1 = pos.attacks_from<ROOK >(ksq);
450 b2 = pos.attacks_from<BISHOP>(ksq);
452 // Enemy queen safe checks
453 if ((b1 | b2) & ei.attackedBy[Them][QUEEN] & safe)
454 attackUnits += QueenCheck, score -= SafeCheck;
456 // For other pieces, also consider the square safe if attacked twice,
457 // and only defended by a queen.
458 safe |= ei.attackedBy2[Them]
459 & ~(ei.attackedBy2[Us] | pos.pieces(Them))
460 & ei.attackedBy[Us][QUEEN];
462 // Enemy rooks safe and other checks
463 if (b1 & ei.attackedBy[Them][ROOK] & safe)
464 attackUnits += RookCheck, score -= SafeCheck;
466 else if (b1 & ei.attackedBy[Them][ROOK] & other)
469 // Enemy bishops safe and other checks
470 if (b2 & ei.attackedBy[Them][BISHOP] & safe)
471 attackUnits += BishopCheck, score -= SafeCheck;
473 else if (b2 & ei.attackedBy[Them][BISHOP] & other)
476 // Enemy knights safe and other checks
477 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT];
479 attackUnits += KnightCheck, score -= SafeCheck;
484 // Finally, extract the king danger score from the KingDanger[]
485 // array and subtract the score from the evaluation.
486 score -= KingDanger[std::max(std::min(attackUnits, 399), 0)];
489 // King tropism: firstly, find squares that opponent attacks in our king flank
490 b = ei.attackedBy[Them][ALL_PIECES] & KingFlank[Us][file_of(ksq)];
492 assert(((Us == WHITE ? b << 4 : b >> 4) & b) == 0);
493 assert(popcount(Us == WHITE ? b << 4 : b >> 4) == popcount(b));
495 // Secondly, add the squares which are attacked twice in that flank and
496 // which are not defended by our pawns.
497 b = (Us == WHITE ? b << 4 : b >> 4)
498 | (b & ei.attackedBy2[Them] & ~ei.attackedBy[Us][PAWN]);
500 score -= CloseEnemies * popcount(b);
503 Trace::add(KING, Us, score);
509 // evaluate_threats() assigns bonuses according to the types of the attacking
510 // and the attacked pieces.
512 template<Color Us, bool DoTrace>
513 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
515 const Color Them = (Us == WHITE ? BLACK : WHITE);
516 const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
517 const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE);
518 const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
519 const Bitboard TRank2BB = (Us == WHITE ? Rank2BB : Rank7BB);
520 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
522 enum { Minor, Rook };
524 Bitboard b, weak, defended, safeThreats;
525 Score score = SCORE_ZERO;
527 // Small bonus if the opponent has loose pawns or pieces
528 if ( (pos.pieces(Them) ^ pos.pieces(Them, QUEEN, KING))
529 & ~(ei.attackedBy[Us][ALL_PIECES] | ei.attackedBy[Them][ALL_PIECES]))
530 score += LooseEnemies;
532 // Non-pawn enemies attacked by a pawn
533 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Us][PAWN];
537 b = pos.pieces(Us, PAWN) & ( ~ei.attackedBy[Them][ALL_PIECES]
538 | ei.attackedBy[Us][ALL_PIECES]);
540 safeThreats = (shift_bb<Right>(b) | shift_bb<Left>(b)) & weak;
542 if (weak ^ safeThreats)
543 score += ThreatByHangingPawn;
546 score += ThreatBySafePawn[type_of(pos.piece_on(pop_lsb(&safeThreats)))];
549 // Non-pawn enemies defended by a pawn
550 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Them][PAWN];
552 // Enemies not defended by a pawn and under our attack
553 weak = pos.pieces(Them)
554 & ~ei.attackedBy[Them][PAWN]
555 & ei.attackedBy[Us][ALL_PIECES];
557 // Add a bonus according to the kind of attacking pieces
560 b = (defended | weak) & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
562 score += Threat[Minor][type_of(pos.piece_on(pop_lsb(&b)))];
564 b = (pos.pieces(Them, QUEEN) | weak) & ei.attackedBy[Us][ROOK];
566 score += Threat[Rook ][type_of(pos.piece_on(pop_lsb(&b)))];
568 score += Hanging * popcount(weak & ~ei.attackedBy[Them][ALL_PIECES]);
570 b = weak & ei.attackedBy[Us][KING];
572 score += ThreatByKing[more_than_one(b)];
575 // Bonus if some pawns can safely push and attack an enemy piece
576 b = pos.pieces(Us, PAWN) & ~TRank7BB;
577 b = shift_bb<Up>(b | (shift_bb<Up>(b & TRank2BB) & ~pos.pieces()));
580 & ~ei.attackedBy[Them][PAWN]
581 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
583 b = (shift_bb<Left>(b) | shift_bb<Right>(b))
585 & ~ei.attackedBy[Us][PAWN];
587 score += ThreatByPawnPush * popcount(b);
590 Trace::add(THREAT, Us, score);
596 // evaluate_passed_pawns() evaluates the passed pawns of the given color
598 template<Color Us, bool DoTrace>
599 Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
601 const Color Them = (Us == WHITE ? BLACK : WHITE);
603 Bitboard b, squaresToQueen, defendedSquares, unsafeSquares;
604 Score score = SCORE_ZERO;
606 b = ei.pi->passed_pawns(Us);
610 Square s = pop_lsb(&b);
612 assert(pos.pawn_passed(Us, s));
613 assert(!(pos.pieces(PAWN) & forward_bb(Us, s)));
615 int r = relative_rank(Us, s) - RANK_2;
616 int rr = r * (r - 1);
618 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
622 Square blockSq = s + pawn_push(Us);
624 // Adjust bonus based on the king's proximity
625 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
626 - distance(pos.square<KING>(Us ), blockSq) * 2 * rr;
628 // If blockSq is not the queening square then consider also a second push
629 if (relative_rank(Us, blockSq) != RANK_8)
630 ebonus -= distance(pos.square<KING>(Us), blockSq + pawn_push(Us)) * rr;
632 // If the pawn is free to advance, then increase the bonus
633 if (pos.empty(blockSq))
635 // If there is a rook or queen attacking/defending the pawn from behind,
636 // consider all the squaresToQueen. Otherwise consider only the squares
637 // in the pawn's path attacked or occupied by the enemy.
638 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
640 Bitboard bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
642 if (!(pos.pieces(Us) & bb))
643 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
645 if (!(pos.pieces(Them) & bb))
646 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
648 // If there aren't any enemy attacks, assign a big bonus. Otherwise
649 // assign a smaller bonus if the block square isn't attacked.
650 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
652 // If the path to the queen is fully defended, assign a big bonus.
653 // Otherwise assign a smaller bonus if the block square is defended.
654 if (defendedSquares == squaresToQueen)
657 else if (defendedSquares & blockSq)
660 mbonus += k * rr, ebonus += k * rr;
662 else if (pos.pieces(Us) & blockSq)
663 mbonus += rr + r * 2, ebonus += rr + r * 2;
666 score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
670 Trace::add(PASSED, Us, score);
672 // Add the scores to the middlegame and endgame eval
677 // evaluate_space() computes the space evaluation for a given side. The
678 // space evaluation is a simple bonus based on the number of safe squares
679 // available for minor pieces on the central four files on ranks 2--4. Safe
680 // squares one, two or three squares behind a friendly pawn are counted
681 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
682 // improve play on game opening.
684 Score evaluate_space(const Position& pos, const EvalInfo& ei) {
686 const Color Them = (Us == WHITE ? BLACK : WHITE);
687 const Bitboard SpaceMask =
688 Us == WHITE ? (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank2BB | Rank3BB | Rank4BB)
689 : (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank7BB | Rank6BB | Rank5BB);
691 // Find the safe squares for our pieces inside the area defined by
692 // SpaceMask. A square is unsafe if it is attacked by an enemy
693 // pawn, or if it is undefended and attacked by an enemy piece.
694 Bitboard safe = SpaceMask
695 & ~pos.pieces(Us, PAWN)
696 & ~ei.attackedBy[Them][PAWN]
697 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
699 // Find all squares which are at most three squares behind some friendly pawn
700 Bitboard behind = pos.pieces(Us, PAWN);
701 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
702 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
704 // Since SpaceMask[Us] is fully on our half of the board...
705 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
707 // ...count safe + (behind & safe) with a single popcount
708 int bonus = popcount((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
709 bonus = std::min(16, bonus);
710 int weight = pos.count<ALL_PIECES>(Us) - 2 * ei.pi->open_files();
712 return make_score(bonus * weight * weight / 18, 0);
716 // evaluate_initiative() computes the initiative correction value for the
717 // position, i.e., second order bonus/malus based on the known attacking/defending
718 // status of the players.
719 Score evaluate_initiative(const Position& pos, int asymmetry, Value eg) {
721 int kingDistance = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
722 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
723 int pawns = pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK);
725 // Compute the initiative bonus for the attacking side
726 int initiative = 8 * (asymmetry + kingDistance - 15) + 12 * pawns;
728 // Now apply the bonus: note that we find the attacking side by extracting
729 // the sign of the endgame value, and that we carefully cap the bonus so
730 // that the endgame score will never be divided by more than two.
731 int value = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg / 2));
733 return make_score(0, value);
737 // evaluate_scale_factor() computes the scale factor for the winning side
738 ScaleFactor evaluate_scale_factor(const Position& pos, const EvalInfo& ei, Value eg) {
740 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
741 ScaleFactor sf = ei.me->scale_factor(pos, strongSide);
743 // If we don't already have an unusual scale factor, check for certain
744 // types of endgames, and use a lower scale for those.
745 if ( ei.me->game_phase() < PHASE_MIDGAME
746 && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
748 if (pos.opposite_bishops())
750 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
751 // is almost a draw, in case of KBP vs KB, it is even more a draw.
752 if ( pos.non_pawn_material(WHITE) == BishopValueMg
753 && pos.non_pawn_material(BLACK) == BishopValueMg)
754 sf = more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
756 // Endgame with opposite-colored bishops, but also other pieces. Still
757 // a bit drawish, but not as drawish as with only the two bishops.
759 sf = ScaleFactor(46);
761 // Endings where weaker side can place his king in front of the opponent's
762 // pawns are drawish.
763 else if ( abs(eg) <= BishopValueEg
764 && pos.count<PAWN>(strongSide) <= 2
765 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
766 sf = ScaleFactor(37 + 7 * pos.count<PAWN>(strongSide));
775 /// evaluate() is the main evaluation function. It returns a static evaluation
776 /// of the position from the point of view of the side to move.
778 template<bool DoTrace>
779 Value Eval::evaluate(const Position& pos) {
781 assert(!pos.checkers());
783 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
786 // Probe the material hash table
787 ei.me = Material::probe(pos);
789 // If we have a specialized evaluation function for the current material
790 // configuration, call it and return.
791 if (ei.me->specialized_eval_exists())
792 return ei.me->evaluate(pos);
794 // Initialize score by reading the incrementally updated scores included in
795 // the position object (material + piece square tables) and the material
796 // imbalance. Score is computed internally from the white point of view.
797 Score score = pos.psq_score() + ei.me->imbalance();
799 // Probe the pawn hash table
800 ei.pi = Pawns::probe(pos);
801 score += ei.pi->pawns_score();
803 // Initialize attack and king safety bitboards
804 ei.attackedBy[WHITE][ALL_PIECES] = ei.attackedBy[BLACK][ALL_PIECES] = 0;
805 ei.attackedBy[WHITE][KING] = pos.attacks_from<KING>(pos.square<KING>(WHITE));
806 ei.attackedBy[BLACK][KING] = pos.attacks_from<KING>(pos.square<KING>(BLACK));
807 eval_init<WHITE>(pos, ei);
808 eval_init<BLACK>(pos, ei);
810 // Pawns blocked or on ranks 2 and 3 will be excluded from the mobility area
811 Bitboard blockedPawns[] = {
812 pos.pieces(WHITE, PAWN) & (shift_bb<DELTA_S>(pos.pieces()) | Rank2BB | Rank3BB),
813 pos.pieces(BLACK, PAWN) & (shift_bb<DELTA_N>(pos.pieces()) | Rank7BB | Rank6BB)
816 // Do not include in mobility area squares protected by enemy pawns, or occupied
817 // by our blocked pawns or king.
818 Bitboard mobilityArea[] = {
819 ~(ei.attackedBy[BLACK][PAWN] | blockedPawns[WHITE] | pos.square<KING>(WHITE)),
820 ~(ei.attackedBy[WHITE][PAWN] | blockedPawns[BLACK] | pos.square<KING>(BLACK))
823 // Evaluate all pieces but king and pawns
824 score += evaluate_pieces<DoTrace>(pos, ei, mobility, mobilityArea);
825 score += mobility[WHITE] - mobility[BLACK];
827 // Evaluate kings after all other pieces because we need full attack
828 // information when computing the king safety evaluation.
829 score += evaluate_king<WHITE, DoTrace>(pos, ei)
830 - evaluate_king<BLACK, DoTrace>(pos, ei);
832 // Evaluate tactical threats, we need full attack information including king
833 score += evaluate_threats<WHITE, DoTrace>(pos, ei)
834 - evaluate_threats<BLACK, DoTrace>(pos, ei);
836 // Evaluate passed pawns, we need full attack information including king
837 score += evaluate_passed_pawns<WHITE, DoTrace>(pos, ei)
838 - evaluate_passed_pawns<BLACK, DoTrace>(pos, ei);
840 // If both sides have only pawns, score for potential unstoppable pawns
841 if (!pos.non_pawn_material(WHITE) && !pos.non_pawn_material(BLACK))
844 if ((b = ei.pi->passed_pawns(WHITE)) != 0)
845 score += Unstoppable * int(relative_rank(WHITE, frontmost_sq(WHITE, b)));
847 if ((b = ei.pi->passed_pawns(BLACK)) != 0)
848 score -= Unstoppable * int(relative_rank(BLACK, frontmost_sq(BLACK, b)));
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.pi->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 Value 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.pi->pawns_score());
874 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
875 Trace::add(SPACE, evaluate_space<WHITE>(pos, ei)
876 , evaluate_space<BLACK>(pos, ei));
877 Trace::add(TOTAL, score);
880 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
883 // Explicit template instantiations
884 template Value Eval::evaluate<true >(const Position&);
885 template Value Eval::evaluate<false>(const Position&);
888 /// trace() is like evaluate(), but instead of returning a value, it returns
889 /// a string (suitable for outputting to stdout) that contains the detailed
890 /// descriptions and values of each evaluation term. Useful for debugging.
892 std::string Eval::trace(const Position& pos) {
894 std::memset(scores, 0, sizeof(scores));
896 Value v = evaluate<true>(pos);
897 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
899 std::stringstream ss;
900 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
901 << " Eval term | White | Black | Total \n"
902 << " | MG EG | MG EG | MG EG \n"
903 << "----------------+-------------+-------------+-------------\n"
904 << " Material | " << Term(MATERIAL)
905 << " Imbalance | " << Term(IMBALANCE)
906 << " Pawns | " << Term(PAWN)
907 << " Knights | " << Term(KNIGHT)
908 << " Bishop | " << Term(BISHOP)
909 << " Rooks | " << Term(ROOK)
910 << " Queens | " << Term(QUEEN)
911 << " Mobility | " << Term(MOBILITY)
912 << " King safety | " << Term(KING)
913 << " Threats | " << Term(THREAT)
914 << " Passed pawns | " << Term(PASSED)
915 << " Space | " << Term(SPACE)
916 << "----------------+-------------+-------------+-------------\n"
917 << " Total | " << Term(TOTAL);
919 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";
925 /// init() computes evaluation weights, usually at startup
929 const int MaxSlope = 322;
930 const int Peak = 47410;
933 for (int i = 0; i < 400; ++i)
935 t = std::min(Peak, std::min(i * i - 16, t + MaxSlope));
936 KingDanger[i] = make_score(t * 268 / 7700, 0);