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
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
22 #include <cstring> // For std::memset
35 enum Term { // First 8 entries are for PieceType
36 MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, TOTAL, TERM_NB
39 double scores[TERM_NB][COLOR_NB][PHASE_NB];
41 double to_cp(Value v) { return double(v) / PawnValueEg; }
43 void add(int idx, Color c, Score s) {
44 scores[idx][c][MG] = to_cp(mg_value(s));
45 scores[idx][c][EG] = to_cp(eg_value(s));
48 void add(int idx, Score w, Score b = SCORE_ZERO) {
49 add(idx, WHITE, w); add(idx, BLACK, b);
52 std::ostream& operator<<(std::ostream& os, Term t) {
54 if (t == MATERIAL || t == IMBALANCE || t == Term(PAWN) || t == TOTAL)
55 os << " --- --- | --- --- | ";
57 os << std::setw(5) << scores[t][WHITE][MG] << " "
58 << std::setw(5) << scores[t][WHITE][EG] << " | "
59 << std::setw(5) << scores[t][BLACK][MG] << " "
60 << std::setw(5) << scores[t][BLACK][EG] << " | ";
62 os << std::setw(5) << scores[t][WHITE][MG] - scores[t][BLACK][MG] << " "
63 << std::setw(5) << scores[t][WHITE][EG] - scores[t][BLACK][EG] << " \n";
69 using namespace Trace;
71 // Struct EvalInfo contains various information computed and collected
72 // by the evaluation functions.
75 // attackedBy[color][piece type] is a bitboard representing all squares
76 // attacked by a given color and piece type (can be also ALL_PIECES).
77 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
79 // kingRing[color] is the zone around the king which is considered
80 // by the king safety evaluation. This consists of the squares directly
81 // adjacent to the king, and the three (or two, for a king on an edge file)
82 // squares two ranks in front of the king. For instance, if black's king
83 // is on g8, kingRing[BLACK] is a bitboard containing the squares f8, h8,
84 // f7, g7, h7, f6, g6 and h6.
85 Bitboard kingRing[COLOR_NB];
87 // kingAttackersCount[color] is the number of pieces of the given color
88 // which attack a square in the kingRing of the enemy king.
89 int kingAttackersCount[COLOR_NB];
91 // kingAttackersWeight[color] is the sum of the "weight" of the pieces of the
92 // given color which attack a square in the kingRing of the enemy king. The
93 // weights of the individual piece types are given by the elements in the
94 // KingAttackWeights array.
95 int kingAttackersWeight[COLOR_NB];
97 // kingAdjacentZoneAttacksCount[color] is the number of attacks by the given
98 // color to squares directly adjacent to the enemy king. Pieces which attack
99 // more than one square are counted multiple times. For instance, if there is
100 // a white knight on g5 and black's king is on g8, this white knight adds 2
101 // to kingAdjacentZoneAttacksCount[WHITE].
102 int kingAdjacentZoneAttacksCount[COLOR_NB];
104 Bitboard pinnedPieces[COLOR_NB];
109 // Evaluation weights, indexed by the corresponding evaluation term
110 enum { Mobility, PawnStructure, PassedPawns, Space, KingSafety };
112 const struct Weight { int mg, eg; } Weights[] = {
113 {289, 344}, {233, 201}, {221, 273}, {46, 0}, {322, 0}
116 Score operator*(Score s, const Weight& w) {
117 return make_score(mg_value(s) * w.mg / 256, eg_value(s) * w.eg / 256);
121 #define V(v) Value(v)
122 #define S(mg, eg) make_score(mg, eg)
124 // MobilityBonus[PieceType][attacked] contains bonuses for middle and end
125 // game, indexed by piece type and number of attacked squares not occupied by
127 const Score MobilityBonus[][32] = {
129 { S(-70,-52), S(-52,-37), S( -7,-17), S( 0, -6), S( 8, 5), S( 16, 9), // Knights
130 S( 23, 20), S( 31, 21), S( 36, 22) },
131 { S(-49,-44), S(-22,-13), S( 16, 0), S( 27, 11), S( 38, 19), S( 52, 34), // Bishops
132 S( 56, 44), S( 65, 47), S( 67, 51), S( 73, 56), S( 81, 59), S( 83, 69),
133 S( 95, 72), S(100, 75) },
134 { S(-49,-57), S(-22,-14), S(-10, 18), S( -5, 39), S( -4, 50), S( -2, 58), // Rooks
135 S( 6, 78), S( 11, 86), S( 17, 92), S( 19,103), S( 26,111), S( 27,115),
136 S( 36,119), S( 41,121), S( 50,122) },
137 { S(-41,-24), S(-26, -8), S( 0, 6), S( 2, 14), S( 12, 27), S( 21, 40), // Queens
138 S( 22, 45), S( 37, 55), S( 40, 57), S( 43, 63), S( 50, 68), S( 52, 74),
139 S( 56, 80), S( 66, 84), S( 68, 85), S( 69, 88), S( 71, 92), S( 72, 94),
140 S( 80, 96), S( 89, 98), S( 94,101), S(102,113), S(106,114), S(107,116),
141 S(112,125), S(113,127), S(117,137), S(122,143) }
144 // Mask of allowed outpost squares indexed by color
145 const Bitboard OutpostMask[COLOR_NB] = {
146 Rank4BB | Rank5BB | Rank6BB, Rank5BB | Rank4BB | Rank3BB
149 // Outpost[knight/bishop][supported by pawn] contains bonuses for knights and
150 // bishops outposts, bigger if outpost piece is supported by a pawn.
151 const Score Outpost[][2] = {
152 { S(42,11), S(63,17) }, // Knights
153 { S(18, 5), S(27, 8) } // Bishops
156 // ReachableOutpost[knight/bishop][supported by pawn] contains bonuses for knights and
157 // bishops which can reach a outpost square in one move, bigger if outpost square is supported by a pawn.
158 const Score ReachableOutpost[][2] = {
159 { S(21, 5), S(31, 8) }, // Knights
160 { S( 8, 2), S(13, 4) } // Bishops
163 // Threat[minor/rook][attacked PieceType] contains
164 // bonuses according to which piece type attacks which one.
165 // Attacks on lesser pieces which are pawn defended are not considered.
166 const Score Threat[2][PIECE_TYPE_NB] = {
167 { S(0, 0), S(0, 32), S(25, 39), S(28, 44), S(42, 98), S(35,105) }, // Minor attacks
168 { S(0, 0), S(0, 27), S(26, 57), S(26, 57), S( 0, 30), S(23, 51) } // Rook attacks
171 // ThreatenedByPawn[PieceType] contains a penalty according to which piece
172 // type is attacked by a pawn.
173 const Score ThreatenedByPawn[PIECE_TYPE_NB] = {
174 S(0, 0), S(0, 0), S(107, 138), S(84, 122), S(114, 203), S(121, 217)
177 // Passed[mg/eg][rank] contains midgame and endgame bonuses for passed pawns.
178 // We don't use a Score because we process the two components independently.
179 const Value Passed[][RANK_NB] = {
180 { V(0), V( 1), V(34), V(90), V(214), V(328) },
181 { V(7), V(14), V(37), V(63), V(134), V(189) }
184 // PassedFile[File] contains a bonus according to the file of a passed pawn.
185 const Score PassedFile[] = {
186 S( 12, 10), S( 3, 10), S( 1, -8), S(-27, -12),
187 S(-27, -12), S( 1, -8), S( 3, 10), S( 12, 10)
190 const Score ThreatenedByHangingPawn = S(40, 60);
192 // Assorted bonuses and penalties used by evaluation
193 const Score KingOnOne = S( 2, 58);
194 const Score KingOnMany = S( 6,125);
195 const Score RookOnPawn = S( 7, 27);
196 const Score RookOnOpenFile = S(43, 21);
197 const Score RookOnSemiOpenFile = S(19, 10);
198 const Score BishopPawns = S( 8, 12);
199 const Score MinorBehindPawn = S(16, 0);
200 const Score TrappedRook = S(92, 0);
201 const Score Unstoppable = S( 0, 20);
202 const Score Hanging = S(31, 26);
203 const Score PawnAttackThreat = S(20, 20);
204 const Score Checked = S(20, 20);
206 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
207 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
208 // happen in Chess960 games.
209 const Score TrappedBishopA1H1 = S(50, 50);
214 // SpaceMask[Color] contains the area of the board which is considered
215 // by the space evaluation. In the middlegame, each side is given a bonus
216 // based on how many squares inside this area are safe and available for
217 // friendly minor pieces.
218 const Bitboard SpaceMask[COLOR_NB] = {
219 (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank2BB | Rank3BB | Rank4BB),
220 (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank7BB | Rank6BB | Rank5BB)
223 // King danger constants and variables. The king danger scores are looked-up
224 // in KingDanger[]. Various little "meta-bonuses" measuring the strength
225 // of the enemy attack are added up into an integer, which is used as an
226 // index to KingDanger[].
227 Score KingDanger[512];
229 // KingAttackWeights[PieceType] contains king attack weights by piece type
230 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 7, 5, 4, 1 };
232 // Penalties for enemy's safe checks
233 const int QueenContactCheck = 89;
234 const int QueenCheck = 50;
235 const int RookCheck = 45;
236 const int BishopCheck = 6;
237 const int KnightCheck = 14;
240 // init_eval_info() initializes king bitboards for given color adding
241 // pawn attacks. To be done at the beginning of the evaluation.
244 void init_eval_info(const Position& pos, EvalInfo& ei) {
246 const Color Them = (Us == WHITE ? BLACK : WHITE);
247 const Square Down = (Us == WHITE ? DELTA_S : DELTA_N);
249 ei.pinnedPieces[Us] = pos.pinned_pieces(Us);
250 Bitboard b = ei.attackedBy[Them][KING] = pos.attacks_from<KING>(pos.square<KING>(Them));
251 ei.attackedBy[Them][ALL_PIECES] |= b;
252 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
254 // Init king safety tables only if we are going to use them
255 if (pos.non_pawn_material(Us) >= QueenValueMg)
257 ei.kingRing[Them] = b | shift_bb<Down>(b);
258 b &= ei.attackedBy[Us][PAWN];
259 ei.kingAttackersCount[Us] = b ? popcount<Max15>(b) : 0;
260 ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
263 ei.kingRing[Them] = ei.kingAttackersCount[Us] = 0;
267 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given color
269 template<PieceType Pt, Color Us, bool DoTrace>
270 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility, const Bitboard* mobilityArea) {
274 Score score = SCORE_ZERO;
276 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
277 const Color Them = (Us == WHITE ? BLACK : WHITE);
278 const Square* pl = pos.squares<Pt>(Us);
280 ei.attackedBy[Us][Pt] = 0;
282 while ((s = *pl++) != SQ_NONE)
284 // Find attacked squares, including x-ray attacks for bishops and rooks
285 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
286 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
287 : pos.attacks_from<Pt>(s);
289 if (ei.pinnedPieces[Us] & s)
290 b &= LineBB[pos.square<KING>(Us)][s];
292 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
294 if (b & ei.kingRing[Them])
296 ei.kingAttackersCount[Us]++;
297 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
298 bb = b & ei.attackedBy[Them][KING];
300 ei.kingAdjacentZoneAttacksCount[Us] += popcount<Max15>(bb);
304 b &= ~( ei.attackedBy[Them][KNIGHT]
305 | ei.attackedBy[Them][BISHOP]
306 | ei.attackedBy[Them][ROOK]);
308 int mob = popcount<Pt == QUEEN ? Full : Max15>(b & mobilityArea[Us]);
310 mobility[Us] += MobilityBonus[Pt][mob];
312 if (Pt == BISHOP || Pt == KNIGHT)
314 // Bonus for outpost squares
315 bb = OutpostMask[Us] & ~ei.pi->pawn_attacks_span(Them);
317 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & s)];
320 bb &= b & ~pos.pieces(Us);
322 score += ReachableOutpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & bb)];
325 // Bonus when behind a pawn
326 if ( relative_rank(Us, s) < RANK_5
327 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
328 score += MinorBehindPawn;
330 // Penalty for pawns on same color square of bishop
332 score -= BishopPawns * ei.pi->pawns_on_same_color_squares(Us, s);
334 // An important Chess960 pattern: A cornered bishop blocked by a friendly
335 // pawn diagonally in front of it is a very serious problem, especially
336 // when that pawn is also blocked.
339 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
341 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? DELTA_E : DELTA_W);
342 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
343 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
344 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
351 // Bonus for aligning with enemy pawns on the same rank/file
352 if (relative_rank(Us, s) >= RANK_5)
354 Bitboard alignedPawns = pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s];
356 score += popcount<Max15>(alignedPawns) * RookOnPawn;
359 // Bonus when on an open or semi-open file
360 if (ei.pi->semiopen_file(Us, file_of(s)))
361 score += ei.pi->semiopen_file(Them, file_of(s)) ? RookOnOpenFile : RookOnSemiOpenFile;
363 // Penalize when trapped by the king, even more if king cannot castle
364 if (mob <= 3 && !ei.pi->semiopen_file(Us, file_of(s)))
366 Square ksq = pos.square<KING>(Us);
368 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
369 && (rank_of(ksq) == rank_of(s) || relative_rank(Us, ksq) == RANK_1)
370 && !ei.pi->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
371 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
377 Trace::add(Pt, Us, score);
379 // Recursively call evaluate_pieces() of next piece type until KING excluded
380 return score - evaluate_pieces<NextPt, Them, DoTrace>(pos, ei, mobility, mobilityArea);
384 Score evaluate_pieces<KING, WHITE, false>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
386 Score evaluate_pieces<KING, WHITE, true>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
389 // evaluate_king() assigns bonuses and penalties to a king of a given color
391 template<Color Us, bool DoTrace>
392 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
394 const Color Them = (Us == WHITE ? BLACK : WHITE);
396 Bitboard undefended, b, b1, b2, safe;
398 const Square ksq = pos.square<KING>(Us);
400 // King shelter and enemy pawns storm
401 Score score = ei.pi->king_safety<Us>(pos, ksq);
403 // Main king safety evaluation
404 if (ei.kingAttackersCount[Them])
406 // Find the attacked squares around the king which have no defenders
407 // apart from the king itself
408 undefended = ei.attackedBy[Them][ALL_PIECES]
409 & ei.attackedBy[Us][KING]
410 & ~( ei.attackedBy[Us][PAWN] | ei.attackedBy[Us][KNIGHT]
411 | ei.attackedBy[Us][BISHOP] | ei.attackedBy[Us][ROOK]
412 | ei.attackedBy[Us][QUEEN]);
414 // Initialize the 'attackUnits' variable, which is used later on as an
415 // index into the KingDanger[] array. The initial value is based on the
416 // number and types of the enemy's attacking pieces, the number of
417 // attacked and undefended squares around our king and the quality of
418 // the pawn shelter (current 'score' value).
419 attackUnits = std::min(72, ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them])
420 + 9 * ei.kingAdjacentZoneAttacksCount[Them]
421 + 27 * popcount<Max15>(undefended)
422 + 11 * !!ei.pinnedPieces[Us]
423 - 64 * !pos.count<QUEEN>(Them)
424 - mg_value(score) / 8;
426 // Analyse the enemy's safe queen contact checks. Firstly, find the
427 // undefended squares around the king reachable by the enemy queen...
428 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);
431 // ...and then remove squares not supported by another enemy piece
432 b &= ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
433 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][ROOK]
434 | ei.attackedBy[Them][KING];
437 attackUnits += QueenContactCheck * popcount<Max15>(b);
440 // Analyse the enemy's safe distance checks for sliders and knights
441 safe = ~(ei.attackedBy[Us][ALL_PIECES] | pos.pieces(Them));
443 b1 = pos.attacks_from<ROOK >(ksq) & safe;
444 b2 = pos.attacks_from<BISHOP>(ksq) & safe;
446 // Enemy queen safe checks
447 b = (b1 | b2) & ei.attackedBy[Them][QUEEN];
450 attackUnits += QueenCheck * popcount<Max15>(b);
454 // Enemy rooks safe checks
455 b = b1 & ei.attackedBy[Them][ROOK];
458 attackUnits += RookCheck * popcount<Max15>(b);
462 // Enemy bishops safe checks
463 b = b2 & ei.attackedBy[Them][BISHOP];
466 attackUnits += BishopCheck * popcount<Max15>(b);
470 // Enemy knights safe checks
471 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT] & safe;
474 attackUnits += KnightCheck * popcount<Max15>(b);
478 // Finally, extract the king danger score from the KingDanger[]
479 // array and subtract the score from evaluation.
480 score -= KingDanger[std::max(std::min(attackUnits, 399), 0)];
484 Trace::add(KING, Us, score);
490 // evaluate_threats() assigns bonuses according to the type of attacking piece
491 // and the type of attacked one.
493 template<Color Us, bool DoTrace>
494 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
496 const Color Them = (Us == WHITE ? BLACK : WHITE);
497 const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
498 const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE);
499 const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
500 const Bitboard TRank2BB = (Us == WHITE ? Rank2BB : Rank7BB);
501 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
503 enum { Minor, Rook };
505 Bitboard b, weak, defended, safeThreats;
506 Score score = SCORE_ZERO;
508 // Non-pawn enemies attacked by a pawn
509 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Us][PAWN];
513 b = pos.pieces(Us, PAWN) & ( ~ei.attackedBy[Them][ALL_PIECES]
514 | ei.attackedBy[Us][ALL_PIECES]);
516 safeThreats = (shift_bb<Right>(b) | shift_bb<Left>(b)) & weak;
518 if (weak ^ safeThreats)
519 score += ThreatenedByHangingPawn;
522 score += ThreatenedByPawn[type_of(pos.piece_on(pop_lsb(&safeThreats)))];
525 // Non-pawn enemies defended by a pawn
526 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Them][PAWN];
528 // Enemies not defended by a pawn and under our attack
529 weak = pos.pieces(Them)
530 & ~ei.attackedBy[Them][PAWN]
531 & ei.attackedBy[Us][ALL_PIECES];
533 // Add a bonus according to the kind of attacking pieces
536 b = (defended | weak) & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
538 score += Threat[Minor][type_of(pos.piece_on(pop_lsb(&b)))];
540 b = (pos.pieces(Them, QUEEN) | weak) & ei.attackedBy[Us][ROOK];
542 score += Threat[Rook ][type_of(pos.piece_on(pop_lsb(&b)))];
544 b = weak & ~ei.attackedBy[Them][ALL_PIECES];
546 score += Hanging * popcount<Max15>(b);
548 b = weak & ei.attackedBy[Us][KING];
550 score += more_than_one(b) ? KingOnMany : KingOnOne;
553 // Bonus if some pawns can safely push and attack an enemy piece
554 b = pos.pieces(Us, PAWN) & ~TRank7BB;
555 b = shift_bb<Up>(b | (shift_bb<Up>(b & TRank2BB) & ~pos.pieces()));
558 & ~ei.attackedBy[Them][PAWN]
559 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
561 b = (shift_bb<Left>(b) | shift_bb<Right>(b))
563 & ~ei.attackedBy[Us][PAWN];
566 score += popcount<Max15>(b) * PawnAttackThreat;
569 Trace::add(THREAT, Us, score);
575 // evaluate_passed_pawns() evaluates the passed pawns of the given color
577 template<Color Us, bool DoTrace>
578 Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
580 const Color Them = (Us == WHITE ? BLACK : WHITE);
582 Bitboard b, squaresToQueen, defendedSquares, unsafeSquares;
583 Score score = SCORE_ZERO;
585 b = ei.pi->passed_pawns(Us);
589 Square s = pop_lsb(&b);
591 assert(pos.pawn_passed(Us, s));
593 int r = relative_rank(Us, s) - RANK_2;
594 int rr = r * (r - 1);
596 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
600 Square blockSq = s + pawn_push(Us);
602 // Adjust bonus based on the king's proximity
603 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
604 - distance(pos.square<KING>(Us ), blockSq) * 2 * rr;
606 // If blockSq is not the queening square then consider also a second push
607 if (relative_rank(Us, blockSq) != RANK_8)
608 ebonus -= distance(pos.square<KING>(Us), blockSq + pawn_push(Us)) * rr;
610 // If the pawn is free to advance, then increase the bonus
611 if (pos.empty(blockSq))
613 // If there is a rook or queen attacking/defending the pawn from behind,
614 // consider all the squaresToQueen. Otherwise consider only the squares
615 // in the pawn's path attacked or occupied by the enemy.
616 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
618 Bitboard bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
620 if (!(pos.pieces(Us) & bb))
621 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
623 if (!(pos.pieces(Them) & bb))
624 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
626 // If there aren't any enemy attacks, assign a big bonus. Otherwise
627 // assign a smaller bonus if the block square isn't attacked.
628 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
630 // If the path to queen is fully defended, assign a big bonus.
631 // Otherwise assign a smaller bonus if the block square is defended.
632 if (defendedSquares == squaresToQueen)
635 else if (defendedSquares & blockSq)
638 mbonus += k * rr, ebonus += k * rr;
640 else if (pos.pieces(Us) & blockSq)
641 mbonus += rr * 3 + r * 2 + 3, ebonus += rr + r * 2;
644 if (pos.count<PAWN>(Us) < pos.count<PAWN>(Them))
645 ebonus += ebonus / 4;
647 score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
651 Trace::add(PASSED, Us, score * Weights[PassedPawns]);
653 // Add the scores to the middlegame and endgame eval
654 return score * Weights[PassedPawns];
658 // evaluate_space() computes the space evaluation for a given side. The
659 // space evaluation is a simple bonus based on the number of safe squares
660 // available for minor pieces on the central four files on ranks 2--4. Safe
661 // squares one, two or three squares behind a friendly pawn are counted
662 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
663 // improve play on game opening.
665 Score evaluate_space(const Position& pos, const EvalInfo& ei) {
667 const Color Them = (Us == WHITE ? BLACK : WHITE);
669 // Find the safe squares for our pieces inside the area defined by
670 // SpaceMask[]. A square is unsafe if it is attacked by an enemy
671 // pawn, or if it is undefended and attacked by an enemy piece.
672 Bitboard safe = SpaceMask[Us]
673 & ~pos.pieces(Us, PAWN)
674 & ~ei.attackedBy[Them][PAWN]
675 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
677 // Find all squares which are at most three squares behind some friendly pawn
678 Bitboard behind = pos.pieces(Us, PAWN);
679 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
680 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
682 // Since SpaceMask[Us] is fully on our half of the board...
683 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
685 // ...count safe + (behind & safe) with a single popcount
686 int bonus = popcount<Full>((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
687 int weight = pos.count<KNIGHT>(Us) + pos.count<BISHOP>(Us)
688 + pos.count<KNIGHT>(Them) + pos.count<BISHOP>(Them);
690 return make_score(bonus * weight * weight, 0);
694 // evaluate_initiative() computes the initiative correction value for the
695 // position, i.e. second order bonus/malus based on the known attacking/defending
696 // status of the players.
697 Score evaluate_initiative(const Position& pos, int asymmetry, Value eg) {
699 int kingDistance = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
700 int pawns = pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK);
702 // Compute the initiative bonus for the attacking side
703 int initiative = 8 * (pawns + asymmetry + kingDistance - 15);
705 // Now apply the bonus: note that we find the attacking side by extracting
706 // the sign of the endgame value, and that we carefully cap the bonus so
707 // that the endgame score will never be divided by more than two.
708 int value = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg / 2));
710 return make_score(0, value);
716 /// evaluate() is the main evaluation function. It returns a static evaluation
717 /// of the position always from the point of view of the side to move.
719 template<bool DoTrace>
720 Value Eval::evaluate(const Position& pos) {
722 assert(!pos.checkers());
725 Score score, mobility[2] = { SCORE_ZERO, SCORE_ZERO };
727 // Initialize score by reading the incrementally updated scores included
728 // in the position object (material + piece square tables).
729 // Score is computed from the point of view of white.
730 score = pos.psq_score();
732 // Probe the material hash table
733 Material::Entry* me = Material::probe(pos);
734 score += me->imbalance();
736 // If we have a specialized evaluation function for the current material
737 // configuration, call it and return.
738 if (me->specialized_eval_exists())
739 return me->evaluate(pos);
741 // Probe the pawn hash table
742 ei.pi = Pawns::probe(pos);
743 score += ei.pi->pawns_score() * Weights[PawnStructure];
745 // Initialize attack and king safety bitboards
746 ei.attackedBy[WHITE][ALL_PIECES] = ei.attackedBy[BLACK][ALL_PIECES] = 0;
747 init_eval_info<WHITE>(pos, ei);
748 init_eval_info<BLACK>(pos, ei);
750 // Pawns blocked or on ranks 2 and 3. Will be excluded from the mobility area
751 Bitboard blockedPawns[] = {
752 pos.pieces(WHITE, PAWN) & (shift_bb<DELTA_S>(pos.pieces()) | Rank2BB | Rank3BB),
753 pos.pieces(BLACK, PAWN) & (shift_bb<DELTA_N>(pos.pieces()) | Rank7BB | Rank6BB)
756 // Do not include in mobility squares protected by enemy pawns, or occupied
757 // by our blocked pawns or king.
758 Bitboard mobilityArea[] = {
759 ~(ei.attackedBy[BLACK][PAWN] | blockedPawns[WHITE] | pos.square<KING>(WHITE)),
760 ~(ei.attackedBy[WHITE][PAWN] | blockedPawns[BLACK] | pos.square<KING>(BLACK))
763 // Evaluate pieces and mobility
764 score += evaluate_pieces<KNIGHT, WHITE, DoTrace>(pos, ei, mobility, mobilityArea);
765 score += (mobility[WHITE] - mobility[BLACK]) * Weights[Mobility];
767 // Evaluate kings after all other pieces because we need complete attack
768 // information when computing the king safety evaluation.
769 score += evaluate_king<WHITE, DoTrace>(pos, ei)
770 - evaluate_king<BLACK, DoTrace>(pos, ei);
772 // Evaluate tactical threats, we need full attack information including king
773 score += evaluate_threats<WHITE, DoTrace>(pos, ei)
774 - evaluate_threats<BLACK, DoTrace>(pos, ei);
776 // Evaluate passed pawns, we need full attack information including king
777 score += evaluate_passed_pawns<WHITE, DoTrace>(pos, ei)
778 - evaluate_passed_pawns<BLACK, DoTrace>(pos, ei);
780 // If both sides have only pawns, score for potential unstoppable pawns
781 if (!pos.non_pawn_material(WHITE) && !pos.non_pawn_material(BLACK))
784 if ((b = ei.pi->passed_pawns(WHITE)) != 0)
785 score += int(relative_rank(WHITE, frontmost_sq(WHITE, b))) * Unstoppable;
787 if ((b = ei.pi->passed_pawns(BLACK)) != 0)
788 score -= int(relative_rank(BLACK, frontmost_sq(BLACK, b))) * Unstoppable;
791 // Evaluate space for both sides, only during opening
792 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
793 score += (evaluate_space<WHITE>(pos, ei) - evaluate_space<BLACK>(pos, ei)) * Weights[Space];
795 // Evaluate position potential for the winning side
796 score += evaluate_initiative(pos, ei.pi->pawn_asymmetry(), eg_value(score));
798 // Scale winning side if position is more drawish than it appears
799 Color strongSide = eg_value(score) > VALUE_DRAW ? WHITE : BLACK;
800 ScaleFactor sf = me->scale_factor(pos, strongSide);
802 // If we don't already have an unusual scale factor, check for certain
803 // types of endgames, and use a lower scale for those.
804 if ( me->game_phase() < PHASE_MIDGAME
805 && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
807 if (pos.opposite_bishops())
809 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
810 // is almost a draw, in case of KBP vs KB is even more a draw.
811 if ( pos.non_pawn_material(WHITE) == BishopValueMg
812 && pos.non_pawn_material(BLACK) == BishopValueMg)
813 sf = more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
815 // Endgame with opposite-colored bishops, but also other pieces. Still
816 // a bit drawish, but not as drawish as with only the two bishops.
818 sf = ScaleFactor(46 * sf / SCALE_FACTOR_NORMAL);
820 // Endings where weaker side can place his king in front of the opponent's
821 // pawns are drawish.
822 else if ( abs(eg_value(score)) <= BishopValueEg
823 && ei.pi->pawn_span(strongSide) <= 1
824 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
825 sf = ei.pi->pawn_span(strongSide) ? ScaleFactor(51) : ScaleFactor(37);
828 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
829 Value v = mg_value(score) * int(me->game_phase())
830 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
832 v /= int(PHASE_MIDGAME);
834 // In case of tracing add all single evaluation terms
837 Trace::add(MATERIAL, pos.psq_score());
838 Trace::add(IMBALANCE, me->imbalance());
839 Trace::add(PAWN, ei.pi->pawns_score());
840 Trace::add(MOBILITY, mobility[WHITE] * Weights[Mobility]
841 , mobility[BLACK] * Weights[Mobility]);
842 Trace::add(SPACE, evaluate_space<WHITE>(pos, ei) * Weights[Space]
843 , evaluate_space<BLACK>(pos, ei) * Weights[Space]);
844 Trace::add(TOTAL, score);
847 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
850 // Explicit template instantiations
851 template Value Eval::evaluate<true >(const Position&);
852 template Value Eval::evaluate<false>(const Position&);
855 /// trace() is like evaluate(), but instead of returning a value, it returns
856 /// a string (suitable for outputting to stdout) that contains the detailed
857 /// descriptions and values of each evaluation term. Useful for debugging.
859 std::string Eval::trace(const Position& pos) {
861 std::memset(scores, 0, sizeof(scores));
863 Value v = evaluate<true>(pos);
864 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
866 std::stringstream ss;
867 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
868 << " Eval term | White | Black | Total \n"
869 << " | MG EG | MG EG | MG EG \n"
870 << "----------------+-------------+-------------+-------------\n"
871 << " Material | " << Term(MATERIAL)
872 << " Imbalance | " << Term(IMBALANCE)
873 << " Pawns | " << Term(PAWN)
874 << " Knights | " << Term(KNIGHT)
875 << " Bishop | " << Term(BISHOP)
876 << " Rooks | " << Term(ROOK)
877 << " Queens | " << Term(QUEEN)
878 << " Mobility | " << Term(MOBILITY)
879 << " King safety | " << Term(KING)
880 << " Threats | " << Term(THREAT)
881 << " Passed pawns | " << Term(PASSED)
882 << " Space | " << Term(SPACE)
883 << "----------------+-------------+-------------+-------------\n"
884 << " Total | " << Term(TOTAL);
886 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";
892 /// init() computes evaluation weights, usually at startup
896 const int MaxSlope = 8700;
897 const int Peak = 1280000;
900 for (int i = 0; i < 400; ++i)
902 t = std::min(Peak, std::min(i * i * 27, t + MaxSlope));
903 KingDanger[i] = make_score(t / 1000, 0) * Weights[KingSafety];