2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 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/>.
34 #include "ucioption.h"
40 Key Position::zobrist[2][8][64];
41 Key Position::zobEp[64];
42 Key Position::zobCastle[16];
43 Key Position::zobSideToMove;
44 Key Position::zobExclusion;
46 Score Position::PieceSquareTable[16][64];
48 // Material values arrays, indexed by Piece
49 const Value Position::PieceValueMidgame[17] = {
51 PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
52 RookValueMidgame, QueenValueMidgame, VALUE_ZERO,
53 VALUE_ZERO, VALUE_ZERO,
54 PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
55 RookValueMidgame, QueenValueMidgame
58 const Value Position::PieceValueEndgame[17] = {
60 PawnValueEndgame, KnightValueEndgame, BishopValueEndgame,
61 RookValueEndgame, QueenValueEndgame, VALUE_ZERO,
62 VALUE_ZERO, VALUE_ZERO,
63 PawnValueEndgame, KnightValueEndgame, BishopValueEndgame,
64 RookValueEndgame, QueenValueEndgame
67 // Material values array used by SEE, indexed by PieceType
68 const Value Position::seeValues[] = {
70 PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
71 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10
77 // Bonus for having the side to move (modified by Joona Kiiski)
78 const Score TempoValue = make_score(48, 22);
80 struct PieceLetters : public std::map<char, Piece> {
84 operator[]('K') = WK; operator[]('k') = BK;
85 operator[]('Q') = WQ; operator[]('q') = BQ;
86 operator[]('R') = WR; operator[]('r') = BR;
87 operator[]('B') = WB; operator[]('b') = BB;
88 operator[]('N') = WN; operator[]('n') = BN;
89 operator[]('P') = WP; operator[]('p') = BP;
90 operator[](' ') = PIECE_NONE;
91 operator[]('.') = PIECE_NONE_DARK_SQ;
94 char from_piece(Piece p) const {
96 std::map<char, Piece>::const_iterator it;
97 for (it = begin(); it != end(); ++it)
106 PieceLetters pieceLetters;
112 CheckInfo::CheckInfo(const Position& pos) {
114 Color us = pos.side_to_move();
115 Color them = opposite_color(us);
117 ksq = pos.king_square(them);
118 dcCandidates = pos.discovered_check_candidates(us);
120 checkSq[PAWN] = pos.attacks_from<PAWN>(ksq, them);
121 checkSq[KNIGHT] = pos.attacks_from<KNIGHT>(ksq);
122 checkSq[BISHOP] = pos.attacks_from<BISHOP>(ksq);
123 checkSq[ROOK] = pos.attacks_from<ROOK>(ksq);
124 checkSq[QUEEN] = checkSq[BISHOP] | checkSq[ROOK];
125 checkSq[KING] = EmptyBoardBB;
129 /// Position c'tors. Here we always create a copy of the original position
130 /// or the FEN string, we want the new born Position object do not depend
131 /// on any external data so we detach state pointer from the source one.
133 Position::Position(const Position& pos, int th) {
135 memcpy(this, &pos, sizeof(Position));
136 detach(); // Always detach() in copy c'tor to avoid surprises
141 Position::Position(const string& fen, bool isChess960, int th) {
143 from_fen(fen, isChess960);
148 /// Position::detach() copies the content of the current state and castling
149 /// masks inside the position itself. This is needed when the st pointee could
150 /// become stale, as example because the caller is about to going out of scope.
152 void Position::detach() {
156 st->previous = NULL; // as a safe guard
160 /// Position::from_fen() initializes the position object with the given FEN
161 /// string. This function is not very robust - make sure that input FENs are
162 /// correct (this is assumed to be the responsibility of the GUI).
164 void Position::from_fen(const string& fen, bool isChess960) {
166 A FEN string defines a particular position using only the ASCII character set.
168 A FEN string contains six fields. The separator between fields is a space. The fields are:
170 1) Piece placement (from white's perspective). Each rank is described, starting with rank 8 and ending
171 with rank 1; within each rank, the contents of each square are described from file A through file H.
172 Following the Standard Algebraic Notation (SAN), each piece is identified by a single letter taken
173 from the standard English names. White pieces are designated using upper-case letters ("PNBRQK")
174 while Black take lowercase ("pnbrqk"). Blank squares are noted using digits 1 through 8 (the number
175 of blank squares), and "/" separate ranks.
177 2) Active color. "w" means white moves next, "b" means black.
179 3) Castling availability. If neither side can castle, this is "-". Otherwise, this has one or more
180 letters: "K" (White can castle kingside), "Q" (White can castle queenside), "k" (Black can castle
181 kingside), and/or "q" (Black can castle queenside).
183 4) En passant target square in algebraic notation. If there's no en passant target square, this is "-".
184 If a pawn has just made a 2-square move, this is the position "behind" the pawn. This is recorded
185 regardless of whether there is a pawn in position to make an en passant capture.
187 5) Halfmove clock: This is the number of halfmoves since the last pawn advance or capture. This is used
188 to determine if a draw can be claimed under the fifty-move rule.
190 6) Fullmove number: The number of the full move. It starts at 1, and is incremented after Black's move.
195 std::istringstream ss(fen);
200 // 1. Piece placement field
201 while (ss.get(token) && token != ' ')
203 if (pieceLetters.find(token) != pieceLetters.end())
205 put_piece(pieceLetters[token], sq);
208 else if (isdigit(token))
209 sq += Square(token - '0'); // Skip the given number of files
210 else if (token == '/')
211 sq -= SQ_A3; // Jump back of 2 rows
217 if (!ss.get(token) || (token != 'w' && token != 'b'))
220 sideToMove = (token == 'w' ? WHITE : BLACK);
222 if (!ss.get(token) || token != ' ')
225 // 3. Castling availability
226 while (ss.get(token) && token != ' ')
227 if (!set_castling_rights(token))
230 // 4. En passant square
232 if ( (ss.get(col) && (col >= 'a' && col <= 'h'))
233 && (ss.get(row) && (row == '3' || row == '6')))
235 st->epSquare = make_square(file_from_char(col), rank_from_char(row));
237 // Ignore if no capture is possible
238 Color them = opposite_color(sideToMove);
239 if (!(attacks_from<PAWN>(st->epSquare, them) & pieces(PAWN, sideToMove)))
240 st->epSquare = SQ_NONE;
247 // 6. Fullmove number
249 startPosPlyCounter = (fmn - 1) * 2 + int(sideToMove == BLACK);
251 // Various initialisations
252 castleRightsMask[make_square(initialKFile, RANK_1)] ^= WHITE_OO | WHITE_OOO;
253 castleRightsMask[make_square(initialKFile, RANK_8)] ^= BLACK_OO | BLACK_OOO;
254 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
255 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
256 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
257 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
259 chess960 = isChess960;
262 st->key = compute_key();
263 st->pawnKey = compute_pawn_key();
264 st->materialKey = compute_material_key();
265 st->value = compute_value();
266 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
267 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
271 cout << "Error in FEN string: " << fen << endl;
275 /// Position::set_castling_rights() sets castling parameters castling avaiability.
276 /// This function is compatible with 3 standards: Normal FEN standard, Shredder-FEN
277 /// that uses the letters of the columns on which the rooks began the game instead
278 /// of KQkq and also X-FEN standard that, in case of Chess960, if an inner Rook is
279 /// associated with the castling right, the traditional castling tag will be replaced
280 /// by the file letter of the involved rook as for the Shredder-FEN.
282 bool Position::set_castling_rights(char token) {
284 Color c = token >= 'a' ? BLACK : WHITE;
285 Square sqA = (c == WHITE ? SQ_A1 : SQ_A8);
286 Square sqH = (c == WHITE ? SQ_H1 : SQ_H8);
287 Piece rook = (c == WHITE ? WR : BR);
289 initialKFile = square_file(king_square(c));
290 token = char(toupper(token));
294 for (Square sq = sqH; sq >= sqA; sq--)
295 if (piece_on(sq) == rook)
298 initialKRFile = square_file(sq);
302 else if (token == 'Q')
304 for (Square sq = sqA; sq <= sqH; sq++)
305 if (piece_on(sq) == rook)
308 initialQRFile = square_file(sq);
312 else if (token >= 'A' && token <= 'H')
314 File rookFile = File(token - 'A') + FILE_A;
315 if (rookFile < initialKFile)
318 initialQRFile = rookFile;
323 initialKRFile = rookFile;
333 /// Position::to_fen() returns a FEN representation of the position. In case
334 /// of Chess960 the Shredder-FEN notation is used. Mainly a debugging function.
336 const string Position::to_fen() const {
342 for (Rank rank = RANK_8; rank >= RANK_1; rank--, fen += '/')
344 for (File file = FILE_A; file <= FILE_H; file++)
346 sq = make_square(file, rank);
348 if (square_is_occupied(sq))
355 fen += pieceLetters.from_piece(piece_on(sq));
367 fen += (sideToMove == WHITE ? " w " : " b ");
369 if (st->castleRights != CASTLES_NONE)
371 if (can_castle_kingside(WHITE))
372 fen += chess960 ? char(toupper(file_to_char(initialKRFile))) : 'K';
374 if (can_castle_queenside(WHITE))
375 fen += chess960 ? char(toupper(file_to_char(initialQRFile))) : 'Q';
377 if (can_castle_kingside(BLACK))
378 fen += chess960 ? file_to_char(initialKRFile) : 'k';
380 if (can_castle_queenside(BLACK))
381 fen += chess960 ? file_to_char(initialQRFile) : 'q';
385 fen += (ep_square() == SQ_NONE ? " -" : " " + square_to_string(ep_square()));
390 /// Position::print() prints an ASCII representation of the position to
391 /// the standard output. If a move is given then also the san is printed.
393 void Position::print(Move move) const {
395 const char* dottedLine = "\n+---+---+---+---+---+---+---+---+\n";
399 Position p(*this, thread());
400 string dd = (color_of_piece_on(move_from(move)) == BLACK ? ".." : "");
401 cout << "\nMove is: " << dd << move_to_san(p, move);
404 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
406 cout << dottedLine << '|';
407 for (File file = FILE_A; file <= FILE_H; file++)
409 Square sq = make_square(file, rank);
410 Piece piece = piece_on(sq);
412 if (piece == PIECE_NONE && square_color(sq) == DARK)
413 piece = PIECE_NONE_DARK_SQ;
415 char c = (color_of_piece_on(sq) == BLACK ? '=' : ' ');
416 cout << c << pieceLetters.from_piece(piece) << c << '|';
419 cout << dottedLine << "Fen is: " << to_fen() << "\nKey is: " << st->key << endl;
423 /// Position:hidden_checkers<>() returns a bitboard of all pinned (against the
424 /// king) pieces for the given color and for the given pinner type. Or, when
425 /// template parameter FindPinned is false, the pieces of the given color
426 /// candidate for a discovery check against the enemy king.
427 /// Bitboard checkersBB must be already updated when looking for pinners.
429 template<bool FindPinned>
430 Bitboard Position::hidden_checkers(Color c) const {
432 Bitboard result = EmptyBoardBB;
433 Bitboard pinners = pieces_of_color(FindPinned ? opposite_color(c) : c);
435 // Pinned pieces protect our king, dicovery checks attack
437 Square ksq = king_square(FindPinned ? c : opposite_color(c));
439 // Pinners are sliders, not checkers, that give check when candidate pinned is removed
440 pinners &= (pieces(ROOK, QUEEN) & RookPseudoAttacks[ksq]) | (pieces(BISHOP, QUEEN) & BishopPseudoAttacks[ksq]);
442 if (FindPinned && pinners)
443 pinners &= ~st->checkersBB;
447 Square s = pop_1st_bit(&pinners);
448 Bitboard b = squares_between(s, ksq) & occupied_squares();
452 if ( !(b & (b - 1)) // Only one bit set?
453 && (b & pieces_of_color(c))) // Is an our piece?
460 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
461 /// king) pieces for the given color. Note that checkersBB bitboard must
462 /// be already updated.
464 Bitboard Position::pinned_pieces(Color c) const {
466 return hidden_checkers<true>(c);
470 /// Position:discovered_check_candidates() returns a bitboard containing all
471 /// pieces for the given side which are candidates for giving a discovered
472 /// check. Contrary to pinned_pieces() here there is no need of checkersBB
473 /// to be already updated.
475 Bitboard Position::discovered_check_candidates(Color c) const {
477 return hidden_checkers<false>(c);
480 /// Position::attackers_to() computes a bitboard containing all pieces which
481 /// attacks a given square.
483 Bitboard Position::attackers_to(Square s) const {
485 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
486 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
487 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
488 | (attacks_from<ROOK>(s) & pieces(ROOK, QUEEN))
489 | (attacks_from<BISHOP>(s) & pieces(BISHOP, QUEEN))
490 | (attacks_from<KING>(s) & pieces(KING));
493 Bitboard Position::attackers_to(Square s, Bitboard occ) const {
495 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
496 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
497 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
498 | (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
499 | (bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN))
500 | (attacks_from<KING>(s) & pieces(KING));
503 /// Position::attacks_from() computes a bitboard of all attacks
504 /// of a given piece put in a given square.
506 Bitboard Position::attacks_from(Piece p, Square s) const {
508 assert(square_is_ok(s));
512 case WB: case BB: return attacks_from<BISHOP>(s);
513 case WR: case BR: return attacks_from<ROOK>(s);
514 case WQ: case BQ: return attacks_from<QUEEN>(s);
515 default: return StepAttacksBB[p][s];
519 Bitboard Position::attacks_from(Piece p, Square s, Bitboard occ) {
521 assert(square_is_ok(s));
525 case WB: case BB: return bishop_attacks_bb(s, occ);
526 case WR: case BR: return rook_attacks_bb(s, occ);
527 case WQ: case BQ: return bishop_attacks_bb(s, occ) | rook_attacks_bb(s, occ);
528 default: return StepAttacksBB[p][s];
533 /// Position::move_attacks_square() tests whether a move from the current
534 /// position attacks a given square.
536 bool Position::move_attacks_square(Move m, Square s) const {
538 assert(move_is_ok(m));
539 assert(square_is_ok(s));
542 Square f = move_from(m), t = move_to(m);
544 assert(square_is_occupied(f));
546 if (bit_is_set(attacks_from(piece_on(f), t), s))
549 // Move the piece and scan for X-ray attacks behind it
550 occ = occupied_squares();
551 do_move_bb(&occ, make_move_bb(f, t));
552 xray = ( (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
553 |(bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN)))
554 & pieces_of_color(color_of_piece_on(f));
556 // If we have attacks we need to verify that are caused by our move
557 // and are not already existent ones.
558 return xray && (xray ^ (xray & attacks_from<QUEEN>(s)));
562 /// Position::find_checkers() computes the checkersBB bitboard, which
563 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
564 /// currently works by calling Position::attackers_to, which is probably
565 /// inefficient. Consider rewriting this function to use the last move
566 /// played, like in non-bitboard versions of Glaurung.
568 void Position::find_checkers() {
570 Color us = side_to_move();
571 st->checkersBB = attackers_to(king_square(us)) & pieces_of_color(opposite_color(us));
575 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
577 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
580 assert(move_is_ok(m));
581 assert(pinned == pinned_pieces(side_to_move()));
583 Color us = side_to_move();
584 Square from = move_from(m);
586 assert(color_of_piece_on(from) == us);
587 assert(piece_on(king_square(us)) == make_piece(us, KING));
589 // En passant captures are a tricky special case. Because they are
590 // rather uncommon, we do it simply by testing whether the king is attacked
591 // after the move is made
594 Color them = opposite_color(us);
595 Square to = move_to(m);
596 Square capsq = make_square(square_file(to), square_rank(from));
597 Square ksq = king_square(us);
598 Bitboard b = occupied_squares();
600 assert(to == ep_square());
601 assert(piece_on(from) == make_piece(us, PAWN));
602 assert(piece_on(capsq) == make_piece(them, PAWN));
603 assert(piece_on(to) == PIECE_NONE);
606 clear_bit(&b, capsq);
609 return !(rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, them))
610 && !(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, them));
613 // If the moving piece is a king, check whether the destination
614 // square is attacked by the opponent. Castling moves are checked
615 // for legality during move generation.
616 if (type_of_piece_on(from) == KING)
617 return move_is_castle(m) || !(attackers_to(move_to(m)) & pieces_of_color(opposite_color(us)));
619 // A non-king move is legal if and only if it is not pinned or it
620 // is moving along the ray towards or away from the king.
622 || !bit_is_set(pinned, from)
623 || squares_aligned(from, move_to(m), king_square(us));
627 /// Position::move_is_legal() takes a position and a (not necessarily pseudo-legal)
628 /// move and tests whether the move is legal. This version is not very fast and
629 /// should be used only in non time-critical paths.
631 bool Position::move_is_legal(const Move m) const {
633 MoveStack mlist[MAX_MOVES];
634 MoveStack *cur, *last = generate<MV_PSEUDO_LEGAL>(*this, mlist);
636 for (cur = mlist; cur != last; cur++)
638 return pl_move_is_legal(m, pinned_pieces(sideToMove));
644 /// Fast version of Position::move_is_legal() that takes a position a move and
645 /// a bitboard of pinned pieces as input, and tests whether the move is legal.
647 bool Position::move_is_legal(const Move m, Bitboard pinned) const {
650 assert(pinned == pinned_pieces(sideToMove));
652 Color us = sideToMove;
653 Color them = opposite_color(sideToMove);
654 Square from = move_from(m);
655 Square to = move_to(m);
656 Piece pc = piece_on(from);
658 // Use a slower but simpler function for uncommon cases
659 if (move_is_special(m))
660 return move_is_legal(m);
662 // Is not a promotion, so promotion piece must be empty
663 if (move_promotion_piece(m) - 2 != PIECE_TYPE_NONE)
666 // If the from square is not occupied by a piece belonging to the side to
667 // move, the move is obviously not legal.
668 if (pc == PIECE_NONE || color_of_piece(pc) != us)
671 // The destination square cannot be occupied by a friendly piece
672 if (color_of_piece_on(to) == us)
675 // Handle the special case of a pawn move
676 if (type_of_piece(pc) == PAWN)
678 // Move direction must be compatible with pawn color
679 int direction = to - from;
680 if ((us == WHITE) != (direction > 0))
683 // We have already handled promotion moves, so destination
684 // cannot be on the 8/1th rank.
685 if (square_rank(to) == RANK_8 || square_rank(to) == RANK_1)
688 // Proceed according to the square delta between the origin and
689 // destination squares.
696 // Capture. The destination square must be occupied by an enemy
697 // piece (en passant captures was handled earlier).
698 if (color_of_piece_on(to) != them)
701 // From and to files must be one file apart, avoids a7h5
702 if (abs(square_file(from) - square_file(to)) != 1)
708 // Pawn push. The destination square must be empty.
709 if (!square_is_empty(to))
714 // Double white pawn push. The destination square must be on the fourth
715 // rank, and both the destination square and the square between the
716 // source and destination squares must be empty.
717 if ( square_rank(to) != RANK_4
718 || !square_is_empty(to)
719 || !square_is_empty(from + DELTA_N))
724 // Double black pawn push. The destination square must be on the fifth
725 // rank, and both the destination square and the square between the
726 // source and destination squares must be empty.
727 if ( square_rank(to) != RANK_5
728 || !square_is_empty(to)
729 || !square_is_empty(from + DELTA_S))
737 else if (!bit_is_set(attacks_from(pc, from), to))
742 // In case of king moves under check we have to remove king so to catch
743 // as invalid moves like b1a1 when opposite queen is on c1.
744 if (type_of_piece_on(from) == KING)
746 Bitboard b = occupied_squares();
748 if (attackers_to(move_to(m), b) & pieces_of_color(opposite_color(us)))
753 Bitboard target = checkers();
754 Square checksq = pop_1st_bit(&target);
756 if (target) // double check ? In this case a king move is required
759 // Our move must be a blocking evasion or a capture of the checking piece
760 target = squares_between(checksq, king_square(us)) | checkers();
761 if (!bit_is_set(target, move_to(m)))
766 // The move is pseudo-legal, check if it is also legal
767 return pl_move_is_legal(m, pinned);
771 /// Position::move_gives_check() tests whether a pseudo-legal move is a check
773 bool Position::move_gives_check(Move m) const {
775 return move_gives_check(m, CheckInfo(*this));
778 bool Position::move_gives_check(Move m, const CheckInfo& ci) const {
781 assert(move_is_ok(m));
782 assert(ci.dcCandidates == discovered_check_candidates(side_to_move()));
783 assert(color_of_piece_on(move_from(m)) == side_to_move());
784 assert(piece_on(ci.ksq) == make_piece(opposite_color(side_to_move()), KING));
786 Square from = move_from(m);
787 Square to = move_to(m);
788 PieceType pt = type_of_piece_on(from);
791 if (bit_is_set(ci.checkSq[pt], to))
795 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
797 // For pawn and king moves we need to verify also direction
798 if ( (pt != PAWN && pt != KING)
799 || !squares_aligned(from, to, ci.ksq))
803 // Can we skip the ugly special cases ?
804 if (!move_is_special(m))
807 Color us = side_to_move();
808 Bitboard b = occupied_squares();
810 // Promotion with check ?
811 if (move_is_promotion(m))
815 switch (move_promotion_piece(m))
818 return bit_is_set(attacks_from<KNIGHT>(to), ci.ksq);
820 return bit_is_set(bishop_attacks_bb(to, b), ci.ksq);
822 return bit_is_set(rook_attacks_bb(to, b), ci.ksq);
824 return bit_is_set(queen_attacks_bb(to, b), ci.ksq);
830 // En passant capture with check ? We have already handled the case
831 // of direct checks and ordinary discovered check, the only case we
832 // need to handle is the unusual case of a discovered check through
833 // the captured pawn.
836 Square capsq = make_square(square_file(to), square_rank(from));
838 clear_bit(&b, capsq);
840 return (rook_attacks_bb(ci.ksq, b) & pieces(ROOK, QUEEN, us))
841 ||(bishop_attacks_bb(ci.ksq, b) & pieces(BISHOP, QUEEN, us));
844 // Castling with check ?
845 if (move_is_castle(m))
847 Square kfrom, kto, rfrom, rto;
853 kto = relative_square(us, SQ_G1);
854 rto = relative_square(us, SQ_F1);
856 kto = relative_square(us, SQ_C1);
857 rto = relative_square(us, SQ_D1);
859 clear_bit(&b, kfrom);
860 clear_bit(&b, rfrom);
863 return bit_is_set(rook_attacks_bb(rto, b), ci.ksq);
870 /// Position::do_setup_move() makes a permanent move on the board. It should
871 /// be used when setting up a position on board. You can't undo the move.
873 void Position::do_setup_move(Move m) {
879 // Reset "game ply" in case we made a non-reversible move.
880 // "game ply" is used for repetition detection.
884 // Update the number of plies played from the starting position
885 startPosPlyCounter++;
887 // Our StateInfo newSt is about going out of scope so copy
888 // its content before it disappears.
893 /// Position::do_move() makes a move, and saves all information necessary
894 /// to a StateInfo object. The move is assumed to be legal. Pseudo-legal
895 /// moves should be filtered out before this function is called.
897 void Position::do_move(Move m, StateInfo& newSt) {
900 do_move(m, newSt, ci, move_gives_check(m, ci));
903 void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveIsCheck) {
906 assert(move_is_ok(m));
907 assert(&newSt != st);
912 // Copy some fields of old state to our new StateInfo object except the
913 // ones which are recalculated from scratch anyway, then switch our state
914 // pointer to point to the new, ready to be updated, state.
915 struct ReducedStateInfo {
916 Key pawnKey, materialKey;
917 int castleRights, rule50, gamePly, pliesFromNull;
923 memcpy(&newSt, st, sizeof(ReducedStateInfo));
928 // Save the current key to the history[] array, in order to be able to
929 // detect repetition draws.
930 history[st->gamePly++] = key;
932 // Update side to move
933 key ^= zobSideToMove;
935 // Increment the 50 moves rule draw counter. Resetting it to zero in the
936 // case of non-reversible moves is taken care of later.
940 if (move_is_castle(m))
947 Color us = side_to_move();
948 Color them = opposite_color(us);
949 Square from = move_from(m);
950 Square to = move_to(m);
951 bool ep = move_is_ep(m);
952 bool pm = move_is_promotion(m);
954 Piece piece = piece_on(from);
955 PieceType pt = type_of_piece(piece);
956 PieceType capture = ep ? PAWN : type_of_piece_on(to);
958 assert(color_of_piece_on(from) == us);
959 assert(color_of_piece_on(to) == them || square_is_empty(to));
960 assert(!(ep || pm) || piece == make_piece(us, PAWN));
961 assert(!pm || relative_rank(us, to) == RANK_8);
964 do_capture_move(key, capture, them, to, ep);
967 key ^= zobrist[us][pt][from] ^ zobrist[us][pt][to];
969 // Reset en passant square
970 if (st->epSquare != SQ_NONE)
972 key ^= zobEp[st->epSquare];
973 st->epSquare = SQ_NONE;
976 // Update castle rights, try to shortcut a common case
977 int cm = castleRightsMask[from] & castleRightsMask[to];
978 if (cm != ALL_CASTLES && ((cm & st->castleRights) != st->castleRights))
980 key ^= zobCastle[st->castleRights];
981 st->castleRights &= castleRightsMask[from];
982 st->castleRights &= castleRightsMask[to];
983 key ^= zobCastle[st->castleRights];
986 // Prefetch TT access as soon as we know key is updated
987 prefetch((char*)TT.first_entry(key));
990 Bitboard move_bb = make_move_bb(from, to);
991 do_move_bb(&(byColorBB[us]), move_bb);
992 do_move_bb(&(byTypeBB[pt]), move_bb);
993 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
995 board[to] = board[from];
996 board[from] = PIECE_NONE;
998 // Update piece lists, note that index[from] is not updated and
999 // becomes stale. This works as long as index[] is accessed just
1000 // by known occupied squares.
1001 index[to] = index[from];
1002 pieceList[us][pt][index[to]] = to;
1004 // If the moving piece was a pawn do some special extra work
1007 // Reset rule 50 draw counter
1010 // Update pawn hash key and prefetch in L1/L2 cache
1011 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1013 // Set en passant square, only if moved pawn can be captured
1014 if ((to ^ from) == 16)
1016 if (attacks_from<PAWN>(from + (us == WHITE ? DELTA_N : DELTA_S), us) & pieces(PAWN, them))
1018 st->epSquare = Square((int(from) + int(to)) / 2);
1019 key ^= zobEp[st->epSquare];
1023 if (pm) // promotion ?
1025 PieceType promotion = move_promotion_piece(m);
1027 assert(promotion >= KNIGHT && promotion <= QUEEN);
1029 // Insert promoted piece instead of pawn
1030 clear_bit(&(byTypeBB[PAWN]), to);
1031 set_bit(&(byTypeBB[promotion]), to);
1032 board[to] = make_piece(us, promotion);
1034 // Update piece counts
1035 pieceCount[us][promotion]++;
1036 pieceCount[us][PAWN]--;
1038 // Update material key
1039 st->materialKey ^= zobrist[us][PAWN][pieceCount[us][PAWN]];
1040 st->materialKey ^= zobrist[us][promotion][pieceCount[us][promotion]-1];
1042 // Update piece lists, move the last pawn at index[to] position
1043 // and shrink the list. Add a new promotion piece to the list.
1044 Square lastPawnSquare = pieceList[us][PAWN][pieceCount[us][PAWN]];
1045 index[lastPawnSquare] = index[to];
1046 pieceList[us][PAWN][index[lastPawnSquare]] = lastPawnSquare;
1047 pieceList[us][PAWN][pieceCount[us][PAWN]] = SQ_NONE;
1048 index[to] = pieceCount[us][promotion] - 1;
1049 pieceList[us][promotion][index[to]] = to;
1051 // Partially revert hash keys update
1052 key ^= zobrist[us][PAWN][to] ^ zobrist[us][promotion][to];
1053 st->pawnKey ^= zobrist[us][PAWN][to];
1055 // Partially revert and update incremental scores
1056 st->value -= pst(us, PAWN, to);
1057 st->value += pst(us, promotion, to);
1060 st->npMaterial[us] += PieceValueMidgame[promotion];
1064 // Prefetch pawn and material hash tables
1065 Threads[threadID].pawnTable.prefetch(st->pawnKey);
1066 Threads[threadID].materialTable.prefetch(st->materialKey);
1068 // Update incremental scores
1069 st->value += pst_delta(piece, from, to);
1071 // Set capture piece
1072 st->capturedType = capture;
1074 // Update the key with the final value
1077 // Update checkers bitboard, piece must be already moved
1078 st->checkersBB = EmptyBoardBB;
1083 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
1087 if (bit_is_set(ci.checkSq[pt], to))
1088 st->checkersBB = SetMaskBB[to];
1091 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
1094 st->checkersBB |= (attacks_from<ROOK>(ci.ksq) & pieces(ROOK, QUEEN, us));
1097 st->checkersBB |= (attacks_from<BISHOP>(ci.ksq) & pieces(BISHOP, QUEEN, us));
1103 sideToMove = opposite_color(sideToMove);
1104 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1110 /// Position::do_capture_move() is a private method used to update captured
1111 /// piece info. It is called from the main Position::do_move function.
1113 void Position::do_capture_move(Key& key, PieceType capture, Color them, Square to, bool ep) {
1115 assert(capture != KING);
1119 // If the captured piece was a pawn, update pawn hash key,
1120 // otherwise update non-pawn material.
1121 if (capture == PAWN)
1123 if (ep) // en passant ?
1125 capsq = (them == BLACK)? (to - DELTA_N) : (to - DELTA_S);
1127 assert(to == st->epSquare);
1128 assert(relative_rank(opposite_color(them), to) == RANK_6);
1129 assert(piece_on(to) == PIECE_NONE);
1130 assert(piece_on(capsq) == make_piece(them, PAWN));
1132 board[capsq] = PIECE_NONE;
1134 st->pawnKey ^= zobrist[them][PAWN][capsq];
1137 st->npMaterial[them] -= PieceValueMidgame[capture];
1139 // Remove captured piece
1140 clear_bit(&(byColorBB[them]), capsq);
1141 clear_bit(&(byTypeBB[capture]), capsq);
1142 clear_bit(&(byTypeBB[0]), capsq);
1145 key ^= zobrist[them][capture][capsq];
1147 // Update incremental scores
1148 st->value -= pst(them, capture, capsq);
1150 // Update piece count
1151 pieceCount[them][capture]--;
1153 // Update material hash key
1154 st->materialKey ^= zobrist[them][capture][pieceCount[them][capture]];
1156 // Update piece list, move the last piece at index[capsq] position
1158 // WARNING: This is a not perfectly revresible operation. When we
1159 // will reinsert the captured piece in undo_move() we will put it
1160 // at the end of the list and not in its original place, it means
1161 // index[] and pieceList[] are not guaranteed to be invariant to a
1162 // do_move() + undo_move() sequence.
1163 Square lastPieceSquare = pieceList[them][capture][pieceCount[them][capture]];
1164 index[lastPieceSquare] = index[capsq];
1165 pieceList[them][capture][index[lastPieceSquare]] = lastPieceSquare;
1166 pieceList[them][capture][pieceCount[them][capture]] = SQ_NONE;
1168 // Reset rule 50 counter
1173 /// Position::do_castle_move() is a private method used to make a castling
1174 /// move. It is called from the main Position::do_move function. Note that
1175 /// castling moves are encoded as "king captures friendly rook" moves, for
1176 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1178 void Position::do_castle_move(Move m) {
1180 assert(move_is_ok(m));
1181 assert(move_is_castle(m));
1183 Color us = side_to_move();
1184 Color them = opposite_color(us);
1186 // Reset capture field
1187 st->capturedType = PIECE_TYPE_NONE;
1189 // Find source squares for king and rook
1190 Square kfrom = move_from(m);
1191 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1194 assert(piece_on(kfrom) == make_piece(us, KING));
1195 assert(piece_on(rfrom) == make_piece(us, ROOK));
1197 // Find destination squares for king and rook
1198 if (rfrom > kfrom) // O-O
1200 kto = relative_square(us, SQ_G1);
1201 rto = relative_square(us, SQ_F1);
1203 kto = relative_square(us, SQ_C1);
1204 rto = relative_square(us, SQ_D1);
1207 // Remove pieces from source squares:
1208 clear_bit(&(byColorBB[us]), kfrom);
1209 clear_bit(&(byTypeBB[KING]), kfrom);
1210 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1211 clear_bit(&(byColorBB[us]), rfrom);
1212 clear_bit(&(byTypeBB[ROOK]), rfrom);
1213 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1215 // Put pieces on destination squares:
1216 set_bit(&(byColorBB[us]), kto);
1217 set_bit(&(byTypeBB[KING]), kto);
1218 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1219 set_bit(&(byColorBB[us]), rto);
1220 set_bit(&(byTypeBB[ROOK]), rto);
1221 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1223 // Update board array
1224 Piece king = make_piece(us, KING);
1225 Piece rook = make_piece(us, ROOK);
1226 board[kfrom] = board[rfrom] = PIECE_NONE;
1230 // Update piece lists
1231 pieceList[us][KING][index[kfrom]] = kto;
1232 pieceList[us][ROOK][index[rfrom]] = rto;
1233 int tmp = index[rfrom]; // In Chess960 could be rto == kfrom
1234 index[kto] = index[kfrom];
1237 // Update incremental scores
1238 st->value += pst_delta(king, kfrom, kto);
1239 st->value += pst_delta(rook, rfrom, rto);
1242 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1243 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1245 // Clear en passant square
1246 if (st->epSquare != SQ_NONE)
1248 st->key ^= zobEp[st->epSquare];
1249 st->epSquare = SQ_NONE;
1252 // Update castling rights
1253 st->key ^= zobCastle[st->castleRights];
1254 st->castleRights &= castleRightsMask[kfrom];
1255 st->key ^= zobCastle[st->castleRights];
1257 // Reset rule 50 counter
1260 // Update checkers BB
1261 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
1264 sideToMove = opposite_color(sideToMove);
1265 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1271 /// Position::undo_move() unmakes a move. When it returns, the position should
1272 /// be restored to exactly the same state as before the move was made.
1274 void Position::undo_move(Move m) {
1277 assert(move_is_ok(m));
1279 sideToMove = opposite_color(sideToMove);
1281 if (move_is_castle(m))
1283 undo_castle_move(m);
1287 Color us = side_to_move();
1288 Color them = opposite_color(us);
1289 Square from = move_from(m);
1290 Square to = move_to(m);
1291 bool ep = move_is_ep(m);
1292 bool pm = move_is_promotion(m);
1294 PieceType pt = type_of_piece_on(to);
1296 assert(square_is_empty(from));
1297 assert(color_of_piece_on(to) == us);
1298 assert(!pm || relative_rank(us, to) == RANK_8);
1299 assert(!ep || to == st->previous->epSquare);
1300 assert(!ep || relative_rank(us, to) == RANK_6);
1301 assert(!ep || piece_on(to) == make_piece(us, PAWN));
1303 if (pm) // promotion ?
1305 PieceType promotion = move_promotion_piece(m);
1308 assert(promotion >= KNIGHT && promotion <= QUEEN);
1309 assert(piece_on(to) == make_piece(us, promotion));
1311 // Replace promoted piece with a pawn
1312 clear_bit(&(byTypeBB[promotion]), to);
1313 set_bit(&(byTypeBB[PAWN]), to);
1315 // Update piece counts
1316 pieceCount[us][promotion]--;
1317 pieceCount[us][PAWN]++;
1319 // Update piece list replacing promotion piece with a pawn
1320 Square lastPromotionSquare = pieceList[us][promotion][pieceCount[us][promotion]];
1321 index[lastPromotionSquare] = index[to];
1322 pieceList[us][promotion][index[lastPromotionSquare]] = lastPromotionSquare;
1323 pieceList[us][promotion][pieceCount[us][promotion]] = SQ_NONE;
1324 index[to] = pieceCount[us][PAWN] - 1;
1325 pieceList[us][PAWN][index[to]] = to;
1328 // Put the piece back at the source square
1329 Bitboard move_bb = make_move_bb(to, from);
1330 do_move_bb(&(byColorBB[us]), move_bb);
1331 do_move_bb(&(byTypeBB[pt]), move_bb);
1332 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
1334 board[from] = make_piece(us, pt);
1335 board[to] = PIECE_NONE;
1337 // Update piece list
1338 index[from] = index[to];
1339 pieceList[us][pt][index[from]] = from;
1341 if (st->capturedType)
1346 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1348 assert(st->capturedType != KING);
1349 assert(!ep || square_is_empty(capsq));
1351 // Restore the captured piece
1352 set_bit(&(byColorBB[them]), capsq);
1353 set_bit(&(byTypeBB[st->capturedType]), capsq);
1354 set_bit(&(byTypeBB[0]), capsq);
1356 board[capsq] = make_piece(them, st->capturedType);
1358 // Update piece count
1359 pieceCount[them][st->capturedType]++;
1361 // Update piece list, add a new captured piece in capsq square
1362 index[capsq] = pieceCount[them][st->capturedType] - 1;
1363 pieceList[them][st->capturedType][index[capsq]] = capsq;
1366 // Finally point our state pointer back to the previous state
1373 /// Position::undo_castle_move() is a private method used to unmake a castling
1374 /// move. It is called from the main Position::undo_move function. Note that
1375 /// castling moves are encoded as "king captures friendly rook" moves, for
1376 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1378 void Position::undo_castle_move(Move m) {
1380 assert(move_is_ok(m));
1381 assert(move_is_castle(m));
1383 // When we have arrived here, some work has already been done by
1384 // Position::undo_move. In particular, the side to move has been switched,
1385 // so the code below is correct.
1386 Color us = side_to_move();
1388 // Find source squares for king and rook
1389 Square kfrom = move_from(m);
1390 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1393 // Find destination squares for king and rook
1394 if (rfrom > kfrom) // O-O
1396 kto = relative_square(us, SQ_G1);
1397 rto = relative_square(us, SQ_F1);
1399 kto = relative_square(us, SQ_C1);
1400 rto = relative_square(us, SQ_D1);
1403 assert(piece_on(kto) == make_piece(us, KING));
1404 assert(piece_on(rto) == make_piece(us, ROOK));
1406 // Remove pieces from destination squares:
1407 clear_bit(&(byColorBB[us]), kto);
1408 clear_bit(&(byTypeBB[KING]), kto);
1409 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1410 clear_bit(&(byColorBB[us]), rto);
1411 clear_bit(&(byTypeBB[ROOK]), rto);
1412 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1414 // Put pieces on source squares:
1415 set_bit(&(byColorBB[us]), kfrom);
1416 set_bit(&(byTypeBB[KING]), kfrom);
1417 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1418 set_bit(&(byColorBB[us]), rfrom);
1419 set_bit(&(byTypeBB[ROOK]), rfrom);
1420 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1423 board[rto] = board[kto] = PIECE_NONE;
1424 board[rfrom] = make_piece(us, ROOK);
1425 board[kfrom] = make_piece(us, KING);
1427 // Update piece lists
1428 pieceList[us][KING][index[kto]] = kfrom;
1429 pieceList[us][ROOK][index[rto]] = rfrom;
1430 int tmp = index[rto]; // In Chess960 could be rto == kfrom
1431 index[kfrom] = index[kto];
1434 // Finally point our state pointer back to the previous state
1441 /// Position::do_null_move makes() a "null move": It switches the side to move
1442 /// and updates the hash key without executing any move on the board.
1444 void Position::do_null_move(StateInfo& backupSt) {
1447 assert(!in_check());
1449 // Back up the information necessary to undo the null move to the supplied
1450 // StateInfo object.
1451 // Note that differently from normal case here backupSt is actually used as
1452 // a backup storage not as a new state to be used.
1453 backupSt.key = st->key;
1454 backupSt.epSquare = st->epSquare;
1455 backupSt.value = st->value;
1456 backupSt.previous = st->previous;
1457 backupSt.pliesFromNull = st->pliesFromNull;
1458 st->previous = &backupSt;
1460 // Save the current key to the history[] array, in order to be able to
1461 // detect repetition draws.
1462 history[st->gamePly++] = st->key;
1464 // Update the necessary information
1465 if (st->epSquare != SQ_NONE)
1466 st->key ^= zobEp[st->epSquare];
1468 st->key ^= zobSideToMove;
1469 prefetch((char*)TT.first_entry(st->key));
1471 sideToMove = opposite_color(sideToMove);
1472 st->epSquare = SQ_NONE;
1474 st->pliesFromNull = 0;
1475 st->value += (sideToMove == WHITE) ? TempoValue : -TempoValue;
1479 /// Position::undo_null_move() unmakes a "null move".
1481 void Position::undo_null_move() {
1484 assert(!in_check());
1486 // Restore information from the our backup StateInfo object
1487 StateInfo* backupSt = st->previous;
1488 st->key = backupSt->key;
1489 st->epSquare = backupSt->epSquare;
1490 st->value = backupSt->value;
1491 st->previous = backupSt->previous;
1492 st->pliesFromNull = backupSt->pliesFromNull;
1494 // Update the necessary information
1495 sideToMove = opposite_color(sideToMove);
1501 /// Position::see() is a static exchange evaluator: It tries to estimate the
1502 /// material gain or loss resulting from a move. There are three versions of
1503 /// this function: One which takes a destination square as input, one takes a
1504 /// move, and one which takes a 'from' and a 'to' square. The function does
1505 /// not yet understand promotions captures.
1507 int Position::see_sign(Move m) const {
1509 assert(move_is_ok(m));
1511 Square from = move_from(m);
1512 Square to = move_to(m);
1514 // Early return if SEE cannot be negative because captured piece value
1515 // is not less then capturing one. Note that king moves always return
1516 // here because king midgame value is set to 0.
1517 if (midgame_value_of_piece_on(to) >= midgame_value_of_piece_on(from))
1523 int Position::see(Move m) const {
1526 Bitboard occupied, attackers, stmAttackers, b;
1527 int swapList[32], slIndex = 1;
1528 PieceType capturedType, pt;
1531 assert(move_is_ok(m));
1533 // As castle moves are implemented as capturing the rook, they have
1534 // SEE == RookValueMidgame most of the times (unless the rook is under
1536 if (move_is_castle(m))
1539 from = move_from(m);
1541 capturedType = type_of_piece_on(to);
1542 occupied = occupied_squares();
1544 // Handle en passant moves
1545 if (st->epSquare == to && type_of_piece_on(from) == PAWN)
1547 Square capQq = (side_to_move() == WHITE ? to - DELTA_N : to - DELTA_S);
1549 assert(capturedType == PIECE_TYPE_NONE);
1550 assert(type_of_piece_on(capQq) == PAWN);
1552 // Remove the captured pawn
1553 clear_bit(&occupied, capQq);
1554 capturedType = PAWN;
1557 // Find all attackers to the destination square, with the moving piece
1558 // removed, but possibly an X-ray attacker added behind it.
1559 clear_bit(&occupied, from);
1560 attackers = attackers_to(to, occupied);
1562 // If the opponent has no attackers we are finished
1563 stm = opposite_color(color_of_piece_on(from));
1564 stmAttackers = attackers & pieces_of_color(stm);
1566 return seeValues[capturedType];
1568 // The destination square is defended, which makes things rather more
1569 // difficult to compute. We proceed by building up a "swap list" containing
1570 // the material gain or loss at each stop in a sequence of captures to the
1571 // destination square, where the sides alternately capture, and always
1572 // capture with the least valuable piece. After each capture, we look for
1573 // new X-ray attacks from behind the capturing piece.
1574 swapList[0] = seeValues[capturedType];
1575 capturedType = type_of_piece_on(from);
1578 // Locate the least valuable attacker for the side to move. The loop
1579 // below looks like it is potentially infinite, but it isn't. We know
1580 // that the side to move still has at least one attacker left.
1581 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1584 // Remove the attacker we just found from the 'occupied' bitboard,
1585 // and scan for new X-ray attacks behind the attacker.
1586 b = stmAttackers & pieces(pt);
1587 occupied ^= (b & (~b + 1));
1588 attackers |= (rook_attacks_bb(to, occupied) & pieces(ROOK, QUEEN))
1589 | (bishop_attacks_bb(to, occupied) & pieces(BISHOP, QUEEN));
1591 attackers &= occupied; // Cut out pieces we've already done
1593 // Add the new entry to the swap list
1594 assert(slIndex < 32);
1595 swapList[slIndex] = -swapList[slIndex - 1] + seeValues[capturedType];
1598 // Remember the value of the capturing piece, and change the side to
1599 // move before beginning the next iteration.
1601 stm = opposite_color(stm);
1602 stmAttackers = attackers & pieces_of_color(stm);
1604 // Stop before processing a king capture
1605 if (capturedType == KING && stmAttackers)
1607 assert(slIndex < 32);
1608 swapList[slIndex++] = QueenValueMidgame*10;
1611 } while (stmAttackers);
1613 // Having built the swap list, we negamax through it to find the best
1614 // achievable score from the point of view of the side to move.
1616 swapList[slIndex-1] = Min(-swapList[slIndex], swapList[slIndex-1]);
1622 /// Position::clear() erases the position object to a pristine state, with an
1623 /// empty board, white to move, and no castling rights.
1625 void Position::clear() {
1628 memset(st, 0, sizeof(StateInfo));
1629 st->epSquare = SQ_NONE;
1630 startPosPlyCounter = 0;
1633 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1634 memset(byTypeBB, 0, sizeof(Bitboard) * 8);
1635 memset(pieceCount, 0, sizeof(int) * 2 * 8);
1636 memset(index, 0, sizeof(int) * 64);
1638 for (int i = 0; i < 64; i++)
1639 board[i] = PIECE_NONE;
1641 for (int i = 0; i < 8; i++)
1642 for (int j = 0; j < 16; j++)
1643 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1645 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
1646 castleRightsMask[sq] = ALL_CASTLES;
1649 initialKFile = FILE_E;
1650 initialKRFile = FILE_H;
1651 initialQRFile = FILE_A;
1655 /// Position::put_piece() puts a piece on the given square of the board,
1656 /// updating the board array, pieces list, bitboards, and piece counts.
1658 void Position::put_piece(Piece p, Square s) {
1660 Color c = color_of_piece(p);
1661 PieceType pt = type_of_piece(p);
1664 index[s] = pieceCount[c][pt]++;
1665 pieceList[c][pt][index[s]] = s;
1667 set_bit(&(byTypeBB[pt]), s);
1668 set_bit(&(byColorBB[c]), s);
1669 set_bit(&(byTypeBB[0]), s); // HACK: byTypeBB[0] contains all occupied squares.
1673 /// Position::compute_key() computes the hash key of the position. The hash
1674 /// key is usually updated incrementally as moves are made and unmade, the
1675 /// compute_key() function is only used when a new position is set up, and
1676 /// to verify the correctness of the hash key when running in debug mode.
1678 Key Position::compute_key() const {
1680 Key result = zobCastle[st->castleRights];
1682 for (Square s = SQ_A1; s <= SQ_H8; s++)
1683 if (square_is_occupied(s))
1684 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1686 if (ep_square() != SQ_NONE)
1687 result ^= zobEp[ep_square()];
1689 if (side_to_move() == BLACK)
1690 result ^= zobSideToMove;
1696 /// Position::compute_pawn_key() computes the hash key of the position. The
1697 /// hash key is usually updated incrementally as moves are made and unmade,
1698 /// the compute_pawn_key() function is only used when a new position is set
1699 /// up, and to verify the correctness of the pawn hash key when running in
1702 Key Position::compute_pawn_key() const {
1707 for (Color c = WHITE; c <= BLACK; c++)
1709 b = pieces(PAWN, c);
1711 result ^= zobrist[c][PAWN][pop_1st_bit(&b)];
1717 /// Position::compute_material_key() computes the hash key of the position.
1718 /// The hash key is usually updated incrementally as moves are made and unmade,
1719 /// the compute_material_key() function is only used when a new position is set
1720 /// up, and to verify the correctness of the material hash key when running in
1723 Key Position::compute_material_key() const {
1728 for (Color c = WHITE; c <= BLACK; c++)
1729 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1731 count = piece_count(c, pt);
1732 for (int i = 0; i < count; i++)
1733 result ^= zobrist[c][pt][i];
1739 /// Position::compute_value() compute the incremental scores for the middle
1740 /// game and the endgame. These functions are used to initialize the incremental
1741 /// scores when a new position is set up, and to verify that the scores are correctly
1742 /// updated by do_move and undo_move when the program is running in debug mode.
1743 Score Position::compute_value() const {
1746 Score result = SCORE_ZERO;
1748 for (Color c = WHITE; c <= BLACK; c++)
1749 for (PieceType pt = PAWN; pt <= KING; pt++)
1753 result += pst(c, pt, pop_1st_bit(&b));
1756 result += (side_to_move() == WHITE ? TempoValue / 2 : -TempoValue / 2);
1761 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1762 /// game material value for the given side. Material values are updated
1763 /// incrementally during the search, this function is only used while
1764 /// initializing a new Position object.
1766 Value Position::compute_non_pawn_material(Color c) const {
1768 Value result = VALUE_ZERO;
1770 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1771 result += piece_count(c, pt) * PieceValueMidgame[pt];
1777 /// Position::is_draw() tests whether the position is drawn by material,
1778 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1779 /// must be done by the search.
1781 bool Position::is_draw() const {
1783 // Draw by material?
1785 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1788 // Draw by the 50 moves rule?
1789 if (st->rule50 > 99 && !is_mate())
1792 // Draw by repetition?
1793 for (int i = 4, e = Min(Min(st->gamePly, st->rule50), st->pliesFromNull); i <= e; i += 2)
1794 if (history[st->gamePly - i] == st->key)
1801 /// Position::is_mate() returns true or false depending on whether the
1802 /// side to move is checkmated.
1804 bool Position::is_mate() const {
1806 MoveStack moves[MAX_MOVES];
1807 return in_check() && generate<MV_LEGAL>(*this, moves) == moves;
1811 /// Position::init_zobrist() is a static member function which initializes at
1812 /// startup the various arrays used to compute hash keys.
1814 void Position::init_zobrist() {
1819 for (i = 0; i < 2; i++) for (j = 0; j < 8; j++) for (k = 0; k < 64; k++)
1820 zobrist[i][j][k] = rk.rand<Key>();
1822 for (i = 0; i < 64; i++)
1823 zobEp[i] = rk.rand<Key>();
1825 for (i = 0; i < 16; i++)
1826 zobCastle[i] = rk.rand<Key>();
1828 zobSideToMove = rk.rand<Key>();
1829 zobExclusion = rk.rand<Key>();
1833 /// Position::init_piece_square_tables() initializes the piece square tables.
1834 /// This is a two-step operation: First, the white halves of the tables are
1835 /// copied from the MgPST[][] and EgPST[][] arrays. Second, the black halves
1836 /// of the tables are initialized by mirroring and changing the sign of the
1837 /// corresponding white scores.
1839 void Position::init_piece_square_tables() {
1841 for (Square s = SQ_A1; s <= SQ_H8; s++)
1842 for (Piece p = WP; p <= WK; p++)
1843 PieceSquareTable[p][s] = make_score(MgPST[p][s], EgPST[p][s]);
1845 for (Square s = SQ_A1; s <= SQ_H8; s++)
1846 for (Piece p = BP; p <= BK; p++)
1847 PieceSquareTable[p][s] = -PieceSquareTable[p-8][flip_square(s)];
1851 /// Position::flip() flips position with the white and black sides reversed. This
1852 /// is only useful for debugging especially for finding evaluation symmetry bugs.
1854 void Position::flip() {
1858 // Make a copy of current position before to start changing
1859 const Position pos(*this, threadID);
1862 threadID = pos.thread();
1865 for (Square s = SQ_A1; s <= SQ_H8; s++)
1866 if (!pos.square_is_empty(s))
1867 put_piece(Piece(pos.piece_on(s) ^ 8), flip_square(s));
1870 sideToMove = opposite_color(pos.side_to_move());
1873 if (pos.can_castle_kingside(WHITE)) do_allow_oo(BLACK);
1874 if (pos.can_castle_queenside(WHITE)) do_allow_ooo(BLACK);
1875 if (pos.can_castle_kingside(BLACK)) do_allow_oo(WHITE);
1876 if (pos.can_castle_queenside(BLACK)) do_allow_ooo(WHITE);
1878 initialKFile = pos.initialKFile;
1879 initialKRFile = pos.initialKRFile;
1880 initialQRFile = pos.initialQRFile;
1882 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
1883 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
1884 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
1885 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
1886 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
1887 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
1889 // En passant square
1890 if (pos.st->epSquare != SQ_NONE)
1891 st->epSquare = flip_square(pos.st->epSquare);
1897 st->key = compute_key();
1898 st->pawnKey = compute_pawn_key();
1899 st->materialKey = compute_material_key();
1901 // Incremental scores
1902 st->value = compute_value();
1905 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
1906 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
1912 /// Position::is_ok() performs some consitency checks for the position object.
1913 /// This is meant to be helpful when debugging.
1915 bool Position::is_ok(int* failedStep) const {
1917 // What features of the position should be verified?
1918 const bool debugAll = false;
1920 const bool debugBitboards = debugAll || false;
1921 const bool debugKingCount = debugAll || false;
1922 const bool debugKingCapture = debugAll || false;
1923 const bool debugCheckerCount = debugAll || false;
1924 const bool debugKey = debugAll || false;
1925 const bool debugMaterialKey = debugAll || false;
1926 const bool debugPawnKey = debugAll || false;
1927 const bool debugIncrementalEval = debugAll || false;
1928 const bool debugNonPawnMaterial = debugAll || false;
1929 const bool debugPieceCounts = debugAll || false;
1930 const bool debugPieceList = debugAll || false;
1931 const bool debugCastleSquares = debugAll || false;
1933 if (failedStep) *failedStep = 1;
1936 if (!color_is_ok(side_to_move()))
1939 // Are the king squares in the position correct?
1940 if (failedStep) (*failedStep)++;
1941 if (piece_on(king_square(WHITE)) != WK)
1944 if (failedStep) (*failedStep)++;
1945 if (piece_on(king_square(BLACK)) != BK)
1949 if (failedStep) (*failedStep)++;
1950 if (!file_is_ok(initialKRFile))
1953 if (!file_is_ok(initialQRFile))
1956 // Do both sides have exactly one king?
1957 if (failedStep) (*failedStep)++;
1960 int kingCount[2] = {0, 0};
1961 for (Square s = SQ_A1; s <= SQ_H8; s++)
1962 if (type_of_piece_on(s) == KING)
1963 kingCount[color_of_piece_on(s)]++;
1965 if (kingCount[0] != 1 || kingCount[1] != 1)
1969 // Can the side to move capture the opponent's king?
1970 if (failedStep) (*failedStep)++;
1971 if (debugKingCapture)
1973 Color us = side_to_move();
1974 Color them = opposite_color(us);
1975 Square ksq = king_square(them);
1976 if (attackers_to(ksq) & pieces_of_color(us))
1980 // Is there more than 2 checkers?
1981 if (failedStep) (*failedStep)++;
1982 if (debugCheckerCount && count_1s<CNT32>(st->checkersBB) > 2)
1986 if (failedStep) (*failedStep)++;
1989 // The intersection of the white and black pieces must be empty
1990 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
1993 // The union of the white and black pieces must be equal to all
1995 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
1998 // Separate piece type bitboards must have empty intersections
1999 for (PieceType p1 = PAWN; p1 <= KING; p1++)
2000 for (PieceType p2 = PAWN; p2 <= KING; p2++)
2001 if (p1 != p2 && (pieces(p1) & pieces(p2)))
2005 // En passant square OK?
2006 if (failedStep) (*failedStep)++;
2007 if (ep_square() != SQ_NONE)
2009 // The en passant square must be on rank 6, from the point of view of the
2011 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
2016 if (failedStep) (*failedStep)++;
2017 if (debugKey && st->key != compute_key())
2020 // Pawn hash key OK?
2021 if (failedStep) (*failedStep)++;
2022 if (debugPawnKey && st->pawnKey != compute_pawn_key())
2025 // Material hash key OK?
2026 if (failedStep) (*failedStep)++;
2027 if (debugMaterialKey && st->materialKey != compute_material_key())
2030 // Incremental eval OK?
2031 if (failedStep) (*failedStep)++;
2032 if (debugIncrementalEval && st->value != compute_value())
2035 // Non-pawn material OK?
2036 if (failedStep) (*failedStep)++;
2037 if (debugNonPawnMaterial)
2039 if (st->npMaterial[WHITE] != compute_non_pawn_material(WHITE))
2042 if (st->npMaterial[BLACK] != compute_non_pawn_material(BLACK))
2047 if (failedStep) (*failedStep)++;
2048 if (debugPieceCounts)
2049 for (Color c = WHITE; c <= BLACK; c++)
2050 for (PieceType pt = PAWN; pt <= KING; pt++)
2051 if (pieceCount[c][pt] != count_1s<CNT32>(pieces(pt, c)))
2054 if (failedStep) (*failedStep)++;
2056 for (Color c = WHITE; c <= BLACK; c++)
2057 for (PieceType pt = PAWN; pt <= KING; pt++)
2058 for (int i = 0; i < pieceCount[c][pt]; i++)
2060 if (piece_on(piece_list(c, pt, i)) != make_piece(c, pt))
2063 if (index[piece_list(c, pt, i)] != i)
2067 if (failedStep) (*failedStep)++;
2068 if (debugCastleSquares)
2070 for (Color c = WHITE; c <= BLACK; c++)
2072 if (can_castle_kingside(c) && piece_on(initial_kr_square(c)) != make_piece(c, ROOK))
2075 if (can_castle_queenside(c) && piece_on(initial_qr_square(c)) != make_piece(c, ROOK))
2078 if (castleRightsMask[initial_kr_square(WHITE)] != (ALL_CASTLES ^ WHITE_OO))
2080 if (castleRightsMask[initial_qr_square(WHITE)] != (ALL_CASTLES ^ WHITE_OOO))
2082 if (castleRightsMask[initial_kr_square(BLACK)] != (ALL_CASTLES ^ BLACK_OO))
2084 if (castleRightsMask[initial_qr_square(BLACK)] != (ALL_CASTLES ^ BLACK_OOO))
2088 if (failedStep) *failedStep = 0;