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 { // 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 // kingRing[color] is the zone around the king which is considered
81 // by the king safety evaluation. This consists of the squares directly
82 // adjacent to the king, and the three (or two, for a king on an edge file)
83 // squares two ranks in front of the king. For instance, if black's king
84 // is on g8, kingRing[BLACK] is a bitboard containing the squares f8, h8,
85 // f7, g7, h7, f6, g6 and h6.
86 Bitboard kingRing[COLOR_NB];
88 // kingAttackersCount[color] is the number of pieces of the given color
89 // which attack a square in the kingRing of the enemy king.
90 int kingAttackersCount[COLOR_NB];
92 // kingAttackersWeight[color] is the sum of the "weight" of the pieces of the
93 // given color which attack a square in the kingRing of the enemy king. The
94 // weights of the individual piece types are given by the elements in the
95 // KingAttackWeights array.
96 int kingAttackersWeight[COLOR_NB];
98 // kingAdjacentZoneAttacksCount[color] is the number of attacks by the given
99 // color to squares directly adjacent to the enemy king. Pieces which attack
100 // more than one square are counted multiple times. For instance, if there is
101 // a white knight on g5 and black's king is on g8, this white knight adds 2
102 // to kingAdjacentZoneAttacksCount[WHITE].
103 int kingAdjacentZoneAttacksCount[COLOR_NB];
105 Bitboard pinnedPieces[COLOR_NB];
111 // Evaluation weights, indexed by the corresponding evaluation term
112 enum { PawnStructure, PassedPawns, Space, KingSafety };
114 const struct Weight { int mg, eg; } Weights[] = {
115 {214, 203}, {193, 262}, {47, 0}, {330, 0} };
117 Score operator*(Score s, const Weight& w) {
118 return make_score(mg_value(s) * w.mg / 256, eg_value(s) * w.eg / 256);
122 #define V(v) Value(v)
123 #define S(mg, eg) make_score(mg, eg)
125 // MobilityBonus[PieceType][attacked] contains bonuses for middle and end
126 // game, indexed by piece type and number of attacked squares in the MobilityArea.
127 const Score MobilityBonus[][32] = {
129 { S(-75,-76), S(-56,-54), S(- 9,-26), S( -2,-10), S( 6, 5), S( 15, 11), // Knights
130 S( 22, 26), S( 30, 28), S( 36, 29) },
131 { S(-48,-58), S(-21,-19), S( 16, -2), S( 26, 12), S( 37, 22), S( 51, 42), // Bishops
132 S( 54, 54), S( 63, 58), S( 65, 63), S( 71, 70), S( 79, 74), S( 81, 86),
133 S( 92, 90), S( 97, 94) },
134 { S(-56,-78), S(-25,-18), S(-11, 26), S( -5, 55), S( -4, 70), S( -1, 81), // Rooks
135 S( 8,109), S( 14,120), S( 21,128), S( 23,143), S( 31,154), S( 32,160),
136 S( 43,165), S( 49,168), S( 59,169) },
137 { S(-40,-35), S(-25,-12), S( 2, 7), S( 4, 19), S( 14, 37), S( 24, 55), // Queens
138 S( 25, 62), S( 40, 76), S( 43, 79), S( 47, 87), S( 54, 94), S( 56,102),
139 S( 60,111), S( 70,116), S( 72,118), S( 73,122), S( 75,128), S( 77,130),
140 S( 85,133), S( 94,136), S( 99,140), S(108,157), S(112,158), S(113,161),
141 S(118,174), S(119,177), S(123,191), S(128,199) }
144 // Outpost[knight/bishop][supported by pawn] contains bonuses for knights and
145 // bishops outposts, bigger if outpost piece is supported by a pawn.
146 const Score Outpost[][2] = {
147 { S(42,11), S(63,17) }, // Knights
148 { S(18, 5), S(27, 8) } // Bishops
151 // ReachableOutpost[knight/bishop][supported by pawn] contains bonuses for
152 // knights and bishops which can reach an outpost square in one move, bigger
153 // if outpost square is supported by a pawn.
154 const Score ReachableOutpost[][2] = {
155 { S(21, 5), S(31, 8) }, // Knights
156 { S( 8, 2), S(13, 4) } // Bishops
159 // RookOnFile[semiopen/open] contains bonuses for each rook when there is no
160 // friendly pawn on the rook file.
161 const Score RookOnFile[2] = { S(19, 10), S(43, 21) };
163 // ThreatBySafePawn[PieceType] contains bonuses according to which piece
164 // type is attacked by a pawn which is protected or not attacked.
165 const Score ThreatBySafePawn[PIECE_TYPE_NB] = {
166 S(0, 0), S(0, 0), S(176, 139), S(131, 127), S(217, 218), S(203, 215) };
168 // Threat[by minor/by rook][attacked PieceType] contains
169 // bonuses according to which piece type attacks which one.
170 // Attacks on lesser pieces which are pawn defended are not considered.
171 const Score Threat[][PIECE_TYPE_NB] = {
172 { S(0, 0), S(0, 33), S(45, 43), S(46, 47), S(72,107), S(48,118) }, // by Minor
173 { S(0, 0), S(0, 25), S(40, 62), S(40, 59), S( 0, 34), S(35, 48) } // by Rook
176 // ThreatByKing[on one/on many] contains bonuses for King attacks on
177 // pawns or pieces which are not pawn defended.
178 const Score ThreatByKing[2] = { S(3, 62), S(9, 138) };
180 // Passed[mg/eg][Rank] contains midgame and endgame bonuses for passed pawns.
181 // We don't use a Score because we process the two components independently.
182 const Value Passed[][RANK_NB] = {
183 { V(0), V( 1), V(34), V(90), V(214), V(328) },
184 { V(7), V(14), V(37), V(63), V(134), V(189) }
187 // PassedFile[File] contains a bonus according to the file of a passed pawn
188 const Score PassedFile[FILE_NB] = {
189 S( 12, 10), S( 3, 10), S( 1, -8), S(-27,-12),
190 S(-27,-12), S( 1, -8), S( 3, 10), S( 12, 10)
193 // Assorted bonuses and penalties used by evaluation
194 const Score MinorBehindPawn = S(16, 0);
195 const Score BishopPawns = S( 8, 12);
196 const Score RookOnPawn = S( 7, 27);
197 const Score TrappedRook = S(92, 0);
198 const Score Checked = S(20, 20);
199 const Score ThreatByHangingPawn = S(70, 63);
200 const Score Hanging = S(48, 28);
201 const Score ThreatByPawnPush = S(31, 19);
202 const Score Unstoppable = S( 0, 20);
204 // Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
205 // a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
206 // happen in Chess960 games.
207 const Score TrappedBishopA1H1 = S(50, 50);
212 // King danger constants and variables. The king danger scores are looked-up
213 // in KingDanger[]. Various little "meta-bonuses" measuring the strength
214 // of the enemy attack are added up into an integer, which is used as an
215 // index to KingDanger[].
216 Score KingDanger[512];
218 // KingAttackWeights[PieceType] contains king attack weights by piece type
219 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 7, 5, 4, 1 };
221 // Penalties for enemy's safe checks
222 const int QueenContactCheck = 89;
223 const int QueenCheck = 50;
224 const int RookCheck = 45;
225 const int BishopCheck = 6;
226 const int KnightCheck = 14;
229 // eval_init() initializes king and attack bitboards for given color
230 // adding pawn attacks. To be done at the beginning of the evaluation.
233 void eval_init(const Position& pos, EvalInfo& ei) {
235 const Color Them = (Us == WHITE ? BLACK : WHITE);
236 const Square Down = (Us == WHITE ? DELTA_S : DELTA_N);
238 ei.pinnedPieces[Us] = pos.pinned_pieces(Us);
239 Bitboard b = ei.attackedBy[Them][KING] = pos.attacks_from<KING>(pos.square<KING>(Them));
240 ei.attackedBy[Them][ALL_PIECES] |= b;
241 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][PAWN] = ei.pi->pawn_attacks(Us);
243 // Init king safety tables only if we are going to use them
244 if (pos.non_pawn_material(Us) >= QueenValueMg)
246 ei.kingRing[Them] = b | shift_bb<Down>(b);
247 b &= ei.attackedBy[Us][PAWN];
248 ei.kingAttackersCount[Us] = b ? popcount<Max15>(b) : 0;
249 ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
252 ei.kingRing[Them] = ei.kingAttackersCount[Us] = 0;
256 // evaluate_pieces() assigns bonuses and penalties to the pieces of a given
259 template<bool DoTrace, Color Us = WHITE, PieceType Pt = KNIGHT>
260 Score evaluate_pieces(const Position& pos, EvalInfo& ei, Score* mobility,
261 const Bitboard* mobilityArea) {
264 Score score = SCORE_ZERO;
266 const PieceType NextPt = (Us == WHITE ? Pt : PieceType(Pt + 1));
267 const Color Them = (Us == WHITE ? BLACK : WHITE);
268 const Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
269 : Rank5BB | Rank4BB | Rank3BB);
270 const Square* pl = pos.squares<Pt>(Us);
272 ei.attackedBy[Us][Pt] = 0;
274 while ((s = *pl++) != SQ_NONE)
276 // Find attacked squares, including x-ray attacks for bishops and rooks
277 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(Us, QUEEN))
278 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(Us, ROOK, QUEEN))
279 : pos.attacks_from<Pt>(s);
281 if (ei.pinnedPieces[Us] & s)
282 b &= LineBB[pos.square<KING>(Us)][s];
284 ei.attackedBy[Us][ALL_PIECES] |= ei.attackedBy[Us][Pt] |= b;
286 if (b & ei.kingRing[Them])
288 ei.kingAttackersCount[Us]++;
289 ei.kingAttackersWeight[Us] += KingAttackWeights[Pt];
290 bb = b & ei.attackedBy[Them][KING];
292 ei.kingAdjacentZoneAttacksCount[Us] += popcount<Max15>(bb);
296 b &= ~( ei.attackedBy[Them][KNIGHT]
297 | ei.attackedBy[Them][BISHOP]
298 | ei.attackedBy[Them][ROOK]);
300 int mob = popcount<Pt == QUEEN ? Full : Max15>(b & mobilityArea[Us]);
302 mobility[Us] += MobilityBonus[Pt][mob];
304 if (Pt == BISHOP || Pt == KNIGHT)
306 // Bonus for outpost squares
307 bb = OutpostRanks & ~ei.pi->pawn_attacks_span(Them);
309 score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & s)];
312 bb &= b & ~pos.pieces(Us);
314 score += ReachableOutpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & bb)];
317 // Bonus when behind a pawn
318 if ( relative_rank(Us, s) < RANK_5
319 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
320 score += MinorBehindPawn;
322 // Penalty for pawns on same color square of bishop
324 score -= BishopPawns * ei.pi->pawns_on_same_color_squares(Us, s);
326 // An important Chess960 pattern: A cornered bishop blocked by a friendly
327 // pawn diagonally in front of it is a very serious problem, especially
328 // when that pawn is also blocked.
331 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
333 Square d = pawn_push(Us) + (file_of(s) == FILE_A ? DELTA_E : DELTA_W);
334 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
335 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
336 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
343 // Bonus for aligning with enemy pawns on the same rank/file
344 if (relative_rank(Us, s) >= RANK_5)
346 Bitboard alignedPawns = pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s];
348 score += RookOnPawn * popcount<Max15>(alignedPawns);
351 // Bonus when on an open or semi-open file
352 if (ei.pi->semiopen_file(Us, file_of(s)))
353 score += RookOnFile[!!ei.pi->semiopen_file(Them, file_of(s))];
355 // Penalize when trapped by the king, even more if king cannot castle
358 Square ksq = pos.square<KING>(Us);
360 if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
361 && (rank_of(ksq) == rank_of(s) || relative_rank(Us, ksq) == RANK_1)
362 && !ei.pi->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))
363 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
369 Trace::add(Pt, Us, score);
371 // Recursively call evaluate_pieces() of next piece type until KING excluded
372 return score - evaluate_pieces<DoTrace, Them, NextPt>(pos, ei, mobility, mobilityArea);
376 Score evaluate_pieces<false, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
378 Score evaluate_pieces< true, WHITE, KING>(const Position&, EvalInfo&, Score*, const Bitboard*) { return SCORE_ZERO; }
381 // evaluate_king() assigns bonuses and penalties to a king of a given color
383 template<Color Us, bool DoTrace>
384 Score evaluate_king(const Position& pos, const EvalInfo& ei) {
386 const Color Them = (Us == WHITE ? BLACK : WHITE);
388 Bitboard undefended, b, b1, b2, safe;
390 const Square ksq = pos.square<KING>(Us);
392 // King shelter and enemy pawns storm
393 Score score = ei.pi->king_safety<Us>(pos, ksq);
395 // Main king safety evaluation
396 if (ei.kingAttackersCount[Them])
398 // Find the attacked squares around the king which have no defenders
399 // apart from the king itself.
400 undefended = ei.attackedBy[Them][ALL_PIECES]
401 & ei.attackedBy[Us][KING]
402 & ~( ei.attackedBy[Us][PAWN] | ei.attackedBy[Us][KNIGHT]
403 | ei.attackedBy[Us][BISHOP] | ei.attackedBy[Us][ROOK]
404 | ei.attackedBy[Us][QUEEN]);
406 // Initialize the 'attackUnits' variable, which is used later on as an
407 // index into the KingDanger[] array. The initial value is based on the
408 // number and types of the enemy's attacking pieces, the number of
409 // attacked and undefended squares around our king and the quality of
410 // the pawn shelter (current 'score' value).
411 attackUnits = std::min(72, ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them])
412 + 9 * ei.kingAdjacentZoneAttacksCount[Them]
413 + 27 * popcount<Max15>(undefended)
414 + 11 * !!ei.pinnedPieces[Us]
415 - 64 * !pos.count<QUEEN>(Them)
416 - mg_value(score) / 8;
418 // Analyse the enemy's safe queen contact checks. Firstly, find the
419 // undefended squares around the king reachable by the enemy queen...
420 b = undefended & ei.attackedBy[Them][QUEEN] & ~pos.pieces(Them);
423 // ...and then remove squares not supported by another enemy piece
424 b &= ei.attackedBy[Them][PAWN] | ei.attackedBy[Them][KNIGHT]
425 | ei.attackedBy[Them][BISHOP] | ei.attackedBy[Them][ROOK]
426 | ei.attackedBy[Them][KING];
429 attackUnits += QueenContactCheck * popcount<Max15>(b);
432 // Analyse the enemy's safe distance checks for sliders and knights
433 safe = ~(ei.attackedBy[Us][ALL_PIECES] | pos.pieces(Them));
435 b1 = pos.attacks_from<ROOK >(ksq) & safe;
436 b2 = pos.attacks_from<BISHOP>(ksq) & safe;
438 // Enemy queen safe checks
439 b = (b1 | b2) & ei.attackedBy[Them][QUEEN];
442 attackUnits += QueenCheck * popcount<Max15>(b);
446 // Enemy rooks safe checks
447 b = b1 & ei.attackedBy[Them][ROOK];
450 attackUnits += RookCheck * popcount<Max15>(b);
454 // Enemy bishops safe checks
455 b = b2 & ei.attackedBy[Them][BISHOP];
458 attackUnits += BishopCheck * popcount<Max15>(b);
462 // Enemy knights safe checks
463 b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT] & safe;
466 attackUnits += KnightCheck * popcount<Max15>(b);
470 // Finally, extract the king danger score from the KingDanger[]
471 // array and subtract the score from evaluation.
472 score -= KingDanger[std::max(std::min(attackUnits, 399), 0)];
476 Trace::add(KING, Us, score);
482 // evaluate_threats() assigns bonuses according to the type of attacking piece
483 // and the type of attacked one.
485 template<Color Us, bool DoTrace>
486 Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
488 const Color Them = (Us == WHITE ? BLACK : WHITE);
489 const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
490 const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE);
491 const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
492 const Bitboard TRank2BB = (Us == WHITE ? Rank2BB : Rank7BB);
493 const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
495 enum { Minor, Rook };
497 Bitboard b, weak, defended, safeThreats;
498 Score score = SCORE_ZERO;
500 // Non-pawn enemies attacked by a pawn
501 weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Us][PAWN];
505 b = pos.pieces(Us, PAWN) & ( ~ei.attackedBy[Them][ALL_PIECES]
506 | ei.attackedBy[Us][ALL_PIECES]);
508 safeThreats = (shift_bb<Right>(b) | shift_bb<Left>(b)) & weak;
510 if (weak ^ safeThreats)
511 score += ThreatByHangingPawn;
514 score += ThreatBySafePawn[type_of(pos.piece_on(pop_lsb(&safeThreats)))];
517 // Non-pawn enemies defended by a pawn
518 defended = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & ei.attackedBy[Them][PAWN];
520 // Enemies not defended by a pawn and under our attack
521 weak = pos.pieces(Them)
522 & ~ei.attackedBy[Them][PAWN]
523 & ei.attackedBy[Us][ALL_PIECES];
525 // Add a bonus according to the kind of attacking pieces
528 b = (defended | weak) & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
530 score += Threat[Minor][type_of(pos.piece_on(pop_lsb(&b)))];
532 b = (pos.pieces(Them, QUEEN) | weak) & ei.attackedBy[Us][ROOK];
534 score += Threat[Rook ][type_of(pos.piece_on(pop_lsb(&b)))];
536 b = weak & ~ei.attackedBy[Them][ALL_PIECES];
538 score += Hanging * popcount<Max15>(b);
540 b = weak & ei.attackedBy[Us][KING];
542 score += ThreatByKing[more_than_one(b)];
545 // Bonus if some pawns can safely push and attack an enemy piece
546 b = pos.pieces(Us, PAWN) & ~TRank7BB;
547 b = shift_bb<Up>(b | (shift_bb<Up>(b & TRank2BB) & ~pos.pieces()));
550 & ~ei.attackedBy[Them][PAWN]
551 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
553 b = (shift_bb<Left>(b) | shift_bb<Right>(b))
555 & ~ei.attackedBy[Us][PAWN];
558 score += ThreatByPawnPush * popcount<Max15>(b);
561 Trace::add(THREAT, Us, score);
567 // evaluate_passed_pawns() evaluates the passed pawns of the given color
569 template<Color Us, bool DoTrace>
570 Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
572 const Color Them = (Us == WHITE ? BLACK : WHITE);
574 Bitboard b, squaresToQueen, defendedSquares, unsafeSquares;
575 Score score = SCORE_ZERO;
577 b = ei.pi->passed_pawns(Us);
581 Square s = pop_lsb(&b);
583 assert(pos.pawn_passed(Us, s));
585 int r = relative_rank(Us, s) - RANK_2;
586 int rr = r * (r - 1);
588 Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];
592 Square blockSq = s + pawn_push(Us);
594 // Adjust bonus based on the king's proximity
595 ebonus += distance(pos.square<KING>(Them), blockSq) * 5 * rr
596 - distance(pos.square<KING>(Us ), blockSq) * 2 * rr;
598 // If blockSq is not the queening square then consider also a second push
599 if (relative_rank(Us, blockSq) != RANK_8)
600 ebonus -= distance(pos.square<KING>(Us), blockSq + pawn_push(Us)) * rr;
602 // If the pawn is free to advance, then increase the bonus
603 if (pos.empty(blockSq))
605 // If there is a rook or queen attacking/defending the pawn from behind,
606 // consider all the squaresToQueen. Otherwise consider only the squares
607 // in the pawn's path attacked or occupied by the enemy.
608 defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
610 Bitboard bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
612 if (!(pos.pieces(Us) & bb))
613 defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
615 if (!(pos.pieces(Them) & bb))
616 unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
618 // If there aren't any enemy attacks, assign a big bonus. Otherwise
619 // assign a smaller bonus if the block square isn't attacked.
620 int k = !unsafeSquares ? 18 : !(unsafeSquares & blockSq) ? 8 : 0;
622 // If the path to queen is fully defended, assign a big bonus.
623 // Otherwise assign a smaller bonus if the block square is defended.
624 if (defendedSquares == squaresToQueen)
627 else if (defendedSquares & blockSq)
630 mbonus += k * rr, ebonus += k * rr;
632 else if (pos.pieces(Us) & blockSq)
633 mbonus += rr * 3 + r * 2 + 3, ebonus += rr + r * 2;
636 if (pos.count<PAWN>(Us) < pos.count<PAWN>(Them))
637 ebonus += ebonus / 4;
639 score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
643 Trace::add(PASSED, Us, score * Weights[PassedPawns]);
645 // Add the scores to the middlegame and endgame eval
646 return score * Weights[PassedPawns];
650 // evaluate_space() computes the space evaluation for a given side. The
651 // space evaluation is a simple bonus based on the number of safe squares
652 // available for minor pieces on the central four files on ranks 2--4. Safe
653 // squares one, two or three squares behind a friendly pawn are counted
654 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
655 // improve play on game opening.
657 Score evaluate_space(const Position& pos, const EvalInfo& ei) {
659 const Color Them = (Us == WHITE ? BLACK : WHITE);
660 const Bitboard SpaceMask =
661 Us == WHITE ? (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank2BB | Rank3BB | Rank4BB)
662 : (FileCBB | FileDBB | FileEBB | FileFBB) & (Rank7BB | Rank6BB | Rank5BB);
664 // Find the safe squares for our pieces inside the area defined by
665 // SpaceMask. A square is unsafe if it is attacked by an enemy
666 // pawn, or if it is undefended and attacked by an enemy piece.
667 Bitboard safe = SpaceMask
668 & ~pos.pieces(Us, PAWN)
669 & ~ei.attackedBy[Them][PAWN]
670 & (ei.attackedBy[Us][ALL_PIECES] | ~ei.attackedBy[Them][ALL_PIECES]);
672 // Find all squares which are at most three squares behind some friendly pawn
673 Bitboard behind = pos.pieces(Us, PAWN);
674 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
675 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
677 // Since SpaceMask[Us] is fully on our half of the board...
678 assert(unsigned(safe >> (Us == WHITE ? 32 : 0)) == 0);
680 // ...count safe + (behind & safe) with a single popcount
681 int bonus = popcount<Full>((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
682 int weight = pos.count<KNIGHT>(Us) + pos.count<BISHOP>(Us)
683 + pos.count<KNIGHT>(Them) + pos.count<BISHOP>(Them);
685 return make_score(bonus * weight * weight, 0);
689 // evaluate_initiative() computes the initiative correction value for the
690 // position, i.e. second order bonus/malus based on the known attacking/defending
691 // status of the players.
692 Score evaluate_initiative(const Position& pos, int asymmetry, Value eg) {
694 int kingDistance = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
695 int pawns = pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK);
697 // Compute the initiative bonus for the attacking side
698 int initiative = 8 * (pawns + asymmetry + kingDistance - 15);
700 // Now apply the bonus: note that we find the attacking side by extracting
701 // the sign of the endgame value, and that we carefully cap the bonus so
702 // that the endgame score will never be divided by more than two.
703 int value = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg / 2));
705 return make_score(0, value);
709 // evaluate_scale_factor() computes the scale factor for the winning side
710 ScaleFactor evaluate_scale_factor(const Position& pos, const EvalInfo& ei, Score score) {
712 Color strongSide = eg_value(score) > VALUE_DRAW ? WHITE : BLACK;
713 ScaleFactor sf = ei.me->scale_factor(pos, strongSide);
715 // If we don't already have an unusual scale factor, check for certain
716 // types of endgames, and use a lower scale for those.
717 if ( ei.me->game_phase() < PHASE_MIDGAME
718 && (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
720 if (pos.opposite_bishops())
722 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
723 // is almost a draw, in case of KBP vs KB is even more a draw.
724 if ( pos.non_pawn_material(WHITE) == BishopValueMg
725 && pos.non_pawn_material(BLACK) == BishopValueMg)
726 sf = more_than_one(pos.pieces(PAWN)) ? ScaleFactor(31) : ScaleFactor(9);
728 // Endgame with opposite-colored bishops, but also other pieces. Still
729 // a bit drawish, but not as drawish as with only the two bishops.
731 sf = ScaleFactor(46 * sf / SCALE_FACTOR_NORMAL);
733 // Endings where weaker side can place his king in front of the opponent's
734 // pawns are drawish.
735 else if ( abs(eg_value(score)) <= BishopValueEg
736 && ei.pi->pawn_span(strongSide) <= 1
737 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
738 sf = ei.pi->pawn_span(strongSide) ? ScaleFactor(51) : ScaleFactor(37);
747 /// evaluate() is the main evaluation function. It returns a static evaluation
748 /// of the position from the point of view of the side to move.
750 template<bool DoTrace>
751 Value Eval::evaluate(const Position& pos) {
753 assert(!pos.checkers());
756 Score score, mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
758 // Initialize score by reading the incrementally updated scores included in
759 // the position object (material + piece square tables). Score is computed
760 // internally from the white point of view.
761 score = pos.psq_score();
763 // Probe the material hash table
764 ei.me = Material::probe(pos);
765 score += ei.me->imbalance();
767 // If we have a specialized evaluation function for the current material
768 // configuration, call it and return.
769 if (ei.me->specialized_eval_exists())
770 return ei.me->evaluate(pos);
772 // Probe the pawn hash table
773 ei.pi = Pawns::probe(pos);
774 score += ei.pi->pawns_score() * Weights[PawnStructure];
776 // Initialize attack and king safety bitboards
777 ei.attackedBy[WHITE][ALL_PIECES] = ei.attackedBy[BLACK][ALL_PIECES] = 0;
778 eval_init<WHITE>(pos, ei);
779 eval_init<BLACK>(pos, ei);
781 // Pawns blocked or on ranks 2 and 3 will be excluded from the mobility area
782 Bitboard blockedPawns[] = {
783 pos.pieces(WHITE, PAWN) & (shift_bb<DELTA_S>(pos.pieces()) | Rank2BB | Rank3BB),
784 pos.pieces(BLACK, PAWN) & (shift_bb<DELTA_N>(pos.pieces()) | Rank7BB | Rank6BB)
787 // Do not include in mobility area squares protected by enemy pawns, or occupied
788 // by our blocked pawns or king.
789 Bitboard mobilityArea[] = {
790 ~(ei.attackedBy[BLACK][PAWN] | blockedPawns[WHITE] | pos.square<KING>(WHITE)),
791 ~(ei.attackedBy[WHITE][PAWN] | blockedPawns[BLACK] | pos.square<KING>(BLACK))
794 // Evaluate all pieces but king and pawns
795 score += evaluate_pieces<DoTrace>(pos, ei, mobility, mobilityArea);
796 score += mobility[WHITE] - mobility[BLACK];
798 // Evaluate kings after all other pieces because we need full attack
799 // information when computing the king safety evaluation.
800 score += evaluate_king<WHITE, DoTrace>(pos, ei)
801 - evaluate_king<BLACK, DoTrace>(pos, ei);
803 // Evaluate tactical threats, we need full attack information including king
804 score += evaluate_threats<WHITE, DoTrace>(pos, ei)
805 - evaluate_threats<BLACK, DoTrace>(pos, ei);
807 // Evaluate passed pawns, we need full attack information including king
808 score += evaluate_passed_pawns<WHITE, DoTrace>(pos, ei)
809 - evaluate_passed_pawns<BLACK, DoTrace>(pos, ei);
811 // If both sides have only pawns, score for potential unstoppable pawns
812 if (!pos.non_pawn_material(WHITE) && !pos.non_pawn_material(BLACK))
815 if ((b = ei.pi->passed_pawns(WHITE)) != 0)
816 score += Unstoppable * int(relative_rank(WHITE, frontmost_sq(WHITE, b)));
818 if ((b = ei.pi->passed_pawns(BLACK)) != 0)
819 score -= Unstoppable * int(relative_rank(BLACK, frontmost_sq(BLACK, b)));
822 // Evaluate space for both sides, only during opening
823 if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
824 score += ( evaluate_space<WHITE>(pos, ei)
825 - evaluate_space<BLACK>(pos, ei)) * Weights[Space];
827 // Evaluate position potential for the winning side
828 score += evaluate_initiative(pos, ei.pi->pawn_asymmetry(), eg_value(score));
830 // Evaluate scale factor for the winning side
831 ScaleFactor sf = evaluate_scale_factor(pos, ei, score);
833 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
834 Value v = mg_value(score) * int(ei.me->game_phase())
835 + eg_value(score) * int(PHASE_MIDGAME - ei.me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
837 v /= int(PHASE_MIDGAME);
839 // In case of tracing add all remaining individual evaluation terms
842 Trace::add(MATERIAL, pos.psq_score());
843 Trace::add(IMBALANCE, ei.me->imbalance());
844 Trace::add(PAWN, ei.pi->pawns_score() * Weights[PawnStructure]);
845 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
846 Trace::add(SPACE, evaluate_space<WHITE>(pos, ei) * Weights[Space]
847 , evaluate_space<BLACK>(pos, ei) * Weights[Space]);
848 Trace::add(TOTAL, score);
851 return (pos.side_to_move() == WHITE ? v : -v) + Eval::Tempo; // Side to move point of view
854 // Explicit template instantiations
855 template Value Eval::evaluate<true >(const Position&);
856 template Value Eval::evaluate<false>(const Position&);
859 /// trace() is like evaluate(), but instead of returning a value, it returns
860 /// a string (suitable for outputting to stdout) that contains the detailed
861 /// descriptions and values of each evaluation term. Useful for debugging.
863 std::string Eval::trace(const Position& pos) {
865 std::memset(scores, 0, sizeof(scores));
867 Value v = evaluate<true>(pos);
868 v = pos.side_to_move() == WHITE ? v : -v; // White's point of view
870 std::stringstream ss;
871 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
872 << " Eval term | White | Black | Total \n"
873 << " | MG EG | MG EG | MG EG \n"
874 << "----------------+-------------+-------------+-------------\n"
875 << " Material | " << Term(MATERIAL)
876 << " Imbalance | " << Term(IMBALANCE)
877 << " Pawns | " << Term(PAWN)
878 << " Knights | " << Term(KNIGHT)
879 << " Bishop | " << Term(BISHOP)
880 << " Rooks | " << Term(ROOK)
881 << " Queens | " << Term(QUEEN)
882 << " Mobility | " << Term(MOBILITY)
883 << " King safety | " << Term(KING)
884 << " Threats | " << Term(THREAT)
885 << " Passed pawns | " << Term(PASSED)
886 << " Space | " << Term(SPACE)
887 << "----------------+-------------+-------------+-------------\n"
888 << " Total | " << Term(TOTAL);
890 ss << "\nTotal Evaluation: " << to_cp(v) << " (white side)\n";
896 /// init() computes evaluation weights, usually at startup
900 const int MaxSlope = 8700;
901 const int Peak = 1280000;
904 for (int i = 0; i < 400; ++i)
906 t = std::min(Peak, std::min(i * i * 27, t + MaxSlope));
907 KingDanger[i] = make_score(t / 1000, 0) * Weights[KingSafety];