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 Marco Costalba
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/>.
35 #include "ucioption.h"
42 extern SearchStack EmptySearchStack;
44 int Position::castleRightsMask[64];
46 Key Position::zobrist[2][8][64];
47 Key Position::zobEp[64];
48 Key Position::zobCastle[16];
49 Key Position::zobMaterial[2][8][16];
50 Key Position::zobSideToMove;
52 Value Position::MgPieceSquareTable[16][64];
53 Value Position::EgPieceSquareTable[16][64];
55 static bool RequestPending = false;
63 Position::Position(const Position &pos) {
67 Position::Position(const std::string &fen) {
72 /// Position::from_fen() initializes the position object with the given FEN
73 /// string. This function is not very robust - make sure that input FENs are
74 /// correct (this is assumed to be the responsibility of the GUI).
76 void Position::from_fen(const std::string &fen) {
78 static const std::string pieceLetters = "KQRBNPkqrbnp";
79 static const Piece pieces[] = { WK, WQ, WR, WB, WN, WP, BK, BQ, BR, BB, BN, BP };
87 for ( ; fen[i] != ' '; i++)
91 // Skip the given number of files
92 file += (fen[i] - '1' + 1);
95 else if (fen[i] == '/')
101 size_t idx = pieceLetters.find(fen[i]);
102 if (idx == std::string::npos)
104 std::cout << "Error in FEN at character " << i << std::endl;
107 Square square = make_square(file, rank);
108 put_piece(pieces[idx], square);
114 if (fen[i] != 'w' && fen[i] != 'b')
116 std::cout << "Error in FEN at character " << i << std::endl;
119 sideToMove = (fen[i] == 'w' ? WHITE : BLACK);
125 std::cout << "Error in FEN at character " << i << std::endl;
130 while(strchr("KQkqabcdefghABCDEFGH-", fen[i])) {
134 else if(fen[i] == 'K') allow_oo(WHITE);
135 else if(fen[i] == 'Q') allow_ooo(WHITE);
136 else if(fen[i] == 'k') allow_oo(BLACK);
137 else if(fen[i] == 'q') allow_ooo(BLACK);
138 else if(fen[i] >= 'A' && fen[i] <= 'H') {
139 File rookFile, kingFile = FILE_NONE;
140 for(Square square = SQ_B1; square <= SQ_G1; square++)
141 if(piece_on(square) == WK)
142 kingFile = square_file(square);
143 if(kingFile == FILE_NONE) {
144 std::cout << "Error in FEN at character " << i << std::endl;
147 initialKFile = kingFile;
148 rookFile = File(fen[i] - 'A') + FILE_A;
149 if(rookFile < initialKFile) {
151 initialQRFile = rookFile;
155 initialKRFile = rookFile;
158 else if(fen[i] >= 'a' && fen[i] <= 'h') {
159 File rookFile, kingFile = FILE_NONE;
160 for(Square square = SQ_B8; square <= SQ_G8; square++)
161 if(piece_on(square) == BK)
162 kingFile = square_file(square);
163 if(kingFile == FILE_NONE) {
164 std::cout << "Error in FEN at character " << i << std::endl;
167 initialKFile = kingFile;
168 rookFile = File(fen[i] - 'a') + FILE_A;
169 if(rookFile < initialKFile) {
171 initialQRFile = rookFile;
175 initialKRFile = rookFile;
179 std::cout << "Error in FEN at character " << i << std::endl;
186 while (fen[i] == ' ')
190 if ( i < fen.length() - 2
191 && (fen[i] >= 'a' && fen[i] <= 'h')
192 && (fen[i+1] == '3' || fen[i+1] == '6'))
193 epSquare = square_from_string(fen.substr(i, 2));
195 // Various initialisation
196 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
197 castleRightsMask[sq] = ALL_CASTLES;
199 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO|WHITE_OOO);
200 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO|BLACK_OOO);
201 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
202 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
203 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
204 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
209 pawnKey = compute_pawn_key();
210 materialKey = compute_material_key();
211 mgValue = compute_mg_value();
212 egValue = compute_eg_value();
213 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
214 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
218 /// Position::to_fen() converts the position object to a FEN string. This is
219 /// probably only useful for debugging.
221 const std::string Position::to_fen() const {
223 static const std::string pieceLetters = " PNBRQK pnbrqk";
227 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
230 for (File file = FILE_A; file <= FILE_H; file++)
232 Square sq = make_square(file, rank);
233 if (!square_is_occupied(sq))
239 fen += (char)skip + '0';
242 fen += pieceLetters[piece_on(sq)];
245 fen += (char)skip + '0';
247 fen += (rank > RANK_1 ? '/' : ' ');
249 fen += (sideToMove == WHITE ? "w " : "b ");
250 if (castleRights != NO_CASTLES)
252 if (can_castle_kingside(WHITE)) fen += 'K';
253 if (can_castle_queenside(WHITE)) fen += 'Q';
254 if (can_castle_kingside(BLACK)) fen += 'k';
255 if (can_castle_queenside(BLACK)) fen += 'q';
260 if (ep_square() != SQ_NONE)
261 fen += square_to_string(ep_square());
269 /// Position::print() prints an ASCII representation of the position to
270 /// the standard output. If a move is given then also the san is print.
272 void Position::print(Move m) const {
274 static const std::string pieceLetters = " PNBRQK PNBRQK .";
276 // Check for reentrancy, as example when called from inside
277 // MovePicker that is used also here in move_to_san()
281 RequestPending = true;
283 std::cout << std::endl;
286 std::string col = (color_of_piece_on(move_from(m)) == BLACK ? ".." : "");
287 std::cout << "Move is: " << col << move_to_san(*this, m) << std::endl;
289 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
291 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl;
292 for (File file = FILE_A; file <= FILE_H; file++)
294 Square sq = make_square(file, rank);
295 Piece piece = piece_on(sq);
296 if (piece == EMPTY && square_color(sq) == WHITE)
299 char col = (color_of_piece_on(sq) == BLACK ? '=' : ' ');
300 std::cout << '|' << col << pieceLetters[piece] << col;
302 std::cout << '|' << std::endl;
304 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl
305 << "Fen is: " << to_fen() << std::endl
306 << "Key is: " << key << std::endl;
308 RequestPending = false;
312 /// Position::copy() creates a copy of the input position.
314 void Position::copy(const Position &pos) {
316 memcpy(this, &pos, sizeof(Position));
320 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
321 /// king) pieces for the given color.
322 Bitboard Position::pinned_pieces(Color c) const {
324 Square ksq = king_square(c);
325 return hidden_checks<ROOK, true>(c, ksq) | hidden_checks<BISHOP, true>(c, ksq);
329 /// Position:discovered_check_candidates() returns a bitboard containing all
330 /// pieces for the given side which are candidates for giving a discovered
331 /// check. The code is almost the same as the function for finding pinned
334 Bitboard Position::discovered_check_candidates(Color c) const {
336 Square ksq = king_square(opposite_color(c));
337 return hidden_checks<ROOK, false>(c, ksq) | hidden_checks<BISHOP, false>(c, ksq);
341 /// Position:hidden_checks<>() returns a bitboard of all pinned (against the
342 /// king) pieces for the given color and for the given pinner type. Or, when
343 /// template parameter FindPinned is false, the pinned pieces of opposite color
344 /// that are, indeed, the pieces candidate for a discovery check.
345 template<PieceType Piece, bool FindPinned>
346 Bitboard Position::hidden_checks(Color c, Square ksq) const {
349 Bitboard sliders, result = EmptyBoardBB;
351 if (Piece == ROOK) // Resolved at compile time
352 sliders = rooks_and_queens(FindPinned ? opposite_color(c) : c) & RookPseudoAttacks[ksq];
354 sliders = bishops_and_queens(FindPinned ? opposite_color(c) : c) & BishopPseudoAttacks[ksq];
356 if (sliders && (!FindPinned || (sliders & ~checkersBB)))
358 // King blockers are candidate pinned pieces
359 Bitboard candidate_pinned = piece_attacks<Piece>(ksq) & pieces_of_color(c);
361 // Pinners are sliders, not checkers, that give check when
362 // candidate pinned are removed.
363 Bitboard pinners = (FindPinned ? sliders & ~checkersBB : sliders);
366 pinners &= rook_attacks_bb(ksq, occupied_squares() ^ candidate_pinned);
368 pinners &= bishop_attacks_bb(ksq, occupied_squares() ^ candidate_pinned);
370 // Finally for each pinner find the corresponding pinned piece (if same color of king)
371 // or discovery checker (if opposite color) among the candidates.
374 s = pop_1st_bit(&pinners);
375 result |= (squares_between(s, ksq) & candidate_pinned);
382 /// Position::square_is_attacked() checks whether the given side attacks the
385 bool Position::square_is_attacked(Square s, Color c) const {
387 return (pawn_attacks(opposite_color(c), s) & pawns(c))
388 || (piece_attacks<KNIGHT>(s) & knights(c))
389 || (piece_attacks<KING>(s) & kings(c))
390 || (piece_attacks<ROOK>(s) & rooks_and_queens(c))
391 || (piece_attacks<BISHOP>(s) & bishops_and_queens(c));
395 /// Position::attacks_to() computes a bitboard containing all pieces which
396 /// attacks a given square. There are two versions of this function: One
397 /// which finds attackers of both colors, and one which only finds the
398 /// attackers for one side.
400 Bitboard Position::attacks_to(Square s) const {
402 return (pawn_attacks(BLACK, s) & pawns(WHITE))
403 | (pawn_attacks(WHITE, s) & pawns(BLACK))
404 | (piece_attacks<KNIGHT>(s) & pieces_of_type(KNIGHT))
405 | (piece_attacks<ROOK>(s) & rooks_and_queens())
406 | (piece_attacks<BISHOP>(s) & bishops_and_queens())
407 | (piece_attacks<KING>(s) & pieces_of_type(KING));
410 Bitboard Position::attacks_to(Square s, Color c) const {
412 return attacks_to(s) & pieces_of_color(c);
416 /// Position::piece_attacks_square() tests whether the piece on square f
417 /// attacks square t.
419 bool Position::piece_attacks_square(Square f, Square t) const {
421 assert(square_is_ok(f));
422 assert(square_is_ok(t));
426 case WP: return pawn_attacks_square(WHITE, f, t);
427 case BP: return pawn_attacks_square(BLACK, f, t);
428 case WN: case BN: return piece_attacks_square<KNIGHT>(f, t);
429 case WB: case BB: return piece_attacks_square<BISHOP>(f, t);
430 case WR: case BR: return piece_attacks_square<ROOK>(f, t);
431 case WQ: case BQ: return piece_attacks_square<QUEEN>(f, t);
432 case WK: case BK: return piece_attacks_square<KING>(f, t);
439 /// Position::move_attacks_square() tests whether a move from the current
440 /// position attacks a given square. Only attacks by the moving piece are
441 /// considered; the function does not handle X-ray attacks.
443 bool Position::move_attacks_square(Move m, Square s) const {
445 assert(move_is_ok(m));
446 assert(square_is_ok(s));
448 Square f = move_from(m), t = move_to(m);
450 assert(square_is_occupied(f));
454 case WP: return pawn_attacks_square(WHITE, t, s);
455 case BP: return pawn_attacks_square(BLACK, t, s);
456 case WN: case BN: return piece_attacks_square<KNIGHT>(t, s);
457 case WB: case BB: return piece_attacks_square<BISHOP>(t, s);
458 case WR: case BR: return piece_attacks_square<ROOK>(t, s);
459 case WQ: case BQ: return piece_attacks_square<QUEEN>(t, s);
460 case WK: case BK: return piece_attacks_square<KING>(t, s);
467 /// Position::find_checkers() computes the checkersBB bitboard, which
468 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
469 /// currently works by calling Position::attacks_to, which is probably
470 /// inefficient. Consider rewriting this function to use the last move
471 /// played, like in non-bitboard versions of Glaurung.
473 void Position::find_checkers() {
475 Color us = side_to_move();
476 checkersBB = attacks_to(king_square(us), opposite_color(us));
480 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal.
481 /// There are two versions of this function: One which takes only a
482 /// move as input, and one which takes a move and a bitboard of pinned
483 /// pieces. The latter function is faster, and should always be preferred
484 /// when a pinned piece bitboard has already been computed.
486 bool Position::pl_move_is_legal(Move m) const {
488 return pl_move_is_legal(m, pinned_pieces(side_to_move()));
491 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
494 assert(move_is_ok(m));
495 assert(pinned == pinned_pieces(side_to_move()));
497 // If we're in check, all pseudo-legal moves are legal, because our
498 // check evasion generator only generates true legal moves.
502 // Castling moves are checked for legality during move generation.
503 if (move_is_castle(m))
506 Color us = side_to_move();
507 Color them = opposite_color(us);
508 Square from = move_from(m);
509 Square ksq = king_square(us);
511 assert(color_of_piece_on(from) == us);
512 assert(piece_on(ksq) == king_of_color(us));
514 // En passant captures are a tricky special case. Because they are
515 // rather uncommon, we do it simply by testing whether the king is attacked
516 // after the move is made
519 Square to = move_to(m);
520 Square capsq = make_square(square_file(to), square_rank(from));
521 Bitboard b = occupied_squares();
523 assert(to == ep_square());
524 assert(piece_on(from) == pawn_of_color(us));
525 assert(piece_on(capsq) == pawn_of_color(them));
526 assert(piece_on(to) == EMPTY);
529 clear_bit(&b, capsq);
532 return !(rook_attacks_bb(ksq, b) & rooks_and_queens(them))
533 && !(bishop_attacks_bb(ksq, b) & bishops_and_queens(them));
536 // If the moving piece is a king, check whether the destination
537 // square is attacked by the opponent.
539 return !(square_is_attacked(move_to(m), them));
541 // A non-king move is legal if and only if it is not pinned or it
542 // is moving along the ray towards or away from the king.
543 return ( !bit_is_set(pinned, from)
544 || (direction_between_squares(from, ksq) == direction_between_squares(move_to(m), ksq)));
548 /// Position::move_is_check() tests whether a pseudo-legal move is a check.
549 /// There are two versions of this function: One which takes only a move as
550 /// input, and one which takes a move and a bitboard of discovered check
551 /// candidates. The latter function is faster, and should always be preferred
552 /// when a discovered check candidates bitboard has already been computed.
554 bool Position::move_is_check(Move m) const {
556 Bitboard dc = discovered_check_candidates(side_to_move());
557 return move_is_check(m, dc);
560 bool Position::move_is_check(Move m, Bitboard dcCandidates) const {
563 assert(move_is_ok(m));
564 assert(dcCandidates == discovered_check_candidates(side_to_move()));
566 Color us = side_to_move();
567 Color them = opposite_color(us);
568 Square from = move_from(m);
569 Square to = move_to(m);
570 Square ksq = king_square(them);
572 assert(color_of_piece_on(from) == us);
573 assert(piece_on(ksq) == king_of_color(them));
575 // Proceed according to the type of the moving piece
576 switch (type_of_piece_on(from))
580 if (bit_is_set(pawn_attacks(them, ksq), to)) // Normal check?
583 if ( bit_is_set(dcCandidates, from) // Discovered check?
584 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
587 if (move_promotion(m)) // Promotion with check?
589 Bitboard b = occupied_squares();
592 switch (move_promotion(m))
595 return bit_is_set(piece_attacks<KNIGHT>(to), ksq);
597 return bit_is_set(bishop_attacks_bb(to, b), ksq);
599 return bit_is_set(rook_attacks_bb(to, b), ksq);
601 return bit_is_set(queen_attacks_bb(to, b), ksq);
606 // En passant capture with check? We have already handled the case
607 // of direct checks and ordinary discovered check, the only case we
608 // need to handle is the unusual case of a discovered check through the
610 else if (move_is_ep(m))
612 Square capsq = make_square(square_file(to), square_rank(from));
613 Bitboard b = occupied_squares();
615 clear_bit(&b, capsq);
617 return (rook_attacks_bb(ksq, b) & rooks_and_queens(us))
618 ||(bishop_attacks_bb(ksq, b) & bishops_and_queens(us));
623 return bit_is_set(dcCandidates, from) // Discovered check?
624 || bit_is_set(piece_attacks<KNIGHT>(ksq), to); // Normal check?
627 return bit_is_set(dcCandidates, from) // Discovered check?
628 || bit_is_set(piece_attacks<BISHOP>(ksq), to); // Normal check?
631 return bit_is_set(dcCandidates, from) // Discovered check?
632 || bit_is_set(piece_attacks<ROOK>(ksq), to); // Normal check?
635 // Discovered checks are impossible!
636 assert(!bit_is_set(dcCandidates, from));
637 return bit_is_set(piece_attacks<QUEEN>(ksq), to); // Normal check?
641 if ( bit_is_set(dcCandidates, from)
642 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
645 // Castling with check?
646 if (move_is_castle(m))
648 Square kfrom, kto, rfrom, rto;
649 Bitboard b = occupied_squares();
655 kto = relative_square(us, SQ_G1);
656 rto = relative_square(us, SQ_F1);
658 kto = relative_square(us, SQ_C1);
659 rto = relative_square(us, SQ_D1);
661 clear_bit(&b, kfrom);
662 clear_bit(&b, rfrom);
665 return bit_is_set(rook_attacks_bb(rto, b), ksq);
669 default: // NO_PIECE_TYPE
677 /// Position::move_is_capture() tests whether a move from the current
678 /// position is a capture.
680 bool Position::move_is_capture(Move m) const {
682 return ( !square_is_empty(move_to(m))
683 && (color_of_piece_on(move_to(m)) == opposite_color(side_to_move()))
689 /// Position::backup() is called when making a move. All information
690 /// necessary to restore the position when the move is later unmade
691 /// is saved to an UndoInfo object. The function Position::restore
692 /// does the reverse operation: When one does a backup followed by
693 /// a restore with the same UndoInfo object, the position is restored
694 /// to the state before backup was called.
696 void Position::backup(UndoInfo& u) const {
698 u.castleRights = castleRights;
699 u.epSquare = epSquare;
700 u.checkersBB = checkersBB;
703 u.materialKey = materialKey;
705 u.lastMove = lastMove;
708 u.capture = NO_PIECE_TYPE;
712 /// Position::restore() is called when unmaking a move. It copies back
713 /// the information backed up during a previous call to Position::backup.
715 void Position::restore(const UndoInfo& u) {
717 castleRights = u.castleRights;
718 epSquare = u.epSquare;
719 checkersBB = u.checkersBB;
722 materialKey = u.materialKey;
724 lastMove = u.lastMove;
727 // u.capture is restored in undo_move()
730 /// Position::do_move() makes a move, and backs up all information necessary
731 /// to undo the move to an UndoInfo object. The move is assumed to be legal.
732 /// Pseudo-legal moves should be filtered out before this function is called.
733 /// There are two versions of this function, one which takes only the move and
734 /// the UndoInfo as input, and one which takes a third parameter, a bitboard of
735 /// discovered check candidates. The second version is faster, because knowing
736 /// the discovered check candidates makes it easier to update the checkersBB
737 /// member variable in the position object.
739 void Position::do_move(Move m, UndoInfo& u) {
741 do_move(m, u, discovered_check_candidates(side_to_move()));
744 void Position::do_move(Move m, UndoInfo& u, Bitboard dcCandidates) {
747 assert(move_is_ok(m));
749 // Back up the necessary information to our UndoInfo object (except the
750 // captured piece, which is taken care of later.
753 // Save the current key to the history[] array, in order to be able to
754 // detect repetition draws.
755 history[gamePly] = key;
757 // Increment the 50 moves rule draw counter. Resetting it to zero in the
758 // case of non-reversible moves is taken care of later.
761 if (move_is_castle(m))
763 else if (move_promotion(m))
764 do_promotion_move(m, u);
765 else if (move_is_ep(m))
769 Color us = side_to_move();
770 Color them = opposite_color(us);
771 Square from = move_from(m);
772 Square to = move_to(m);
774 assert(color_of_piece_on(from) == us);
775 assert(color_of_piece_on(to) == them || piece_on(to) == EMPTY);
777 PieceType piece = type_of_piece_on(from);
778 PieceType capture = type_of_piece_on(to);
783 do_capture_move(m, capture, them, to);
787 clear_bit(&(byColorBB[us]), from);
788 clear_bit(&(byTypeBB[piece]), from);
789 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
790 set_bit(&(byColorBB[us]), to);
791 set_bit(&(byTypeBB[piece]), to);
792 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
793 board[to] = board[from];
797 key ^= zobrist[us][piece][from] ^ zobrist[us][piece][to];
799 // Update incremental scores
800 mgValue -= mg_pst(us, piece, from);
801 mgValue += mg_pst(us, piece, to);
802 egValue -= eg_pst(us, piece, from);
803 egValue += eg_pst(us, piece, to);
805 // If the moving piece was a king, update the king square
809 // If the move was a double pawn push, set the en passant square.
810 // This code is a bit ugly right now, and should be cleaned up later.
812 if (epSquare != SQ_NONE)
814 key ^= zobEp[epSquare];
819 if (abs(int(to) - int(from)) == 16)
822 && (pawn_attacks(WHITE, from + DELTA_N) & pawns(BLACK)))
824 && (pawn_attacks(BLACK, from + DELTA_S) & pawns(WHITE))))
826 epSquare = Square((int(from) + int(to)) / 2);
827 key ^= zobEp[epSquare];
830 // Reset rule 50 draw counter
833 // Update pawn hash key
834 pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
836 // Update piece lists
837 pieceList[us][piece][index[from]] = to;
838 index[to] = index[from];
840 // Update castle rights
841 key ^= zobCastle[castleRights];
842 castleRights &= castleRightsMask[from];
843 castleRights &= castleRightsMask[to];
844 key ^= zobCastle[castleRights];
846 // Update checkers bitboard
847 checkersBB = EmptyBoardBB;
848 Square ksq = king_square(them);
852 if (bit_is_set(pawn_attacks(them, ksq), to))
853 set_bit(&checkersBB, to);
855 if (bit_is_set(dcCandidates, from))
856 checkersBB |= ( (piece_attacks<ROOK>(ksq) & rooks_and_queens(us))
857 |(piece_attacks<BISHOP>(ksq) & bishops_and_queens(us)));
861 if (bit_is_set(piece_attacks<KNIGHT>(ksq), to))
862 set_bit(&checkersBB, to);
864 if (bit_is_set(dcCandidates, from))
865 checkersBB |= ( (piece_attacks<ROOK>(ksq) & rooks_and_queens(us))
866 |(piece_attacks<BISHOP>(ksq) & bishops_and_queens(us)));
870 if (bit_is_set(piece_attacks<BISHOP>(ksq), to))
871 set_bit(&checkersBB, to);
873 if (bit_is_set(dcCandidates, from))
874 checkersBB |= (piece_attacks<ROOK>(ksq) & rooks_and_queens(us));
878 if (bit_is_set(piece_attacks<ROOK>(ksq), to))
879 set_bit(&checkersBB, to);
881 if (bit_is_set(dcCandidates, from))
882 checkersBB |= (piece_attacks<BISHOP>(ksq) & bishops_and_queens(us));
886 if (bit_is_set(piece_attacks<QUEEN>(ksq), to))
887 set_bit(&checkersBB, to);
891 if (bit_is_set(dcCandidates, from))
892 checkersBB |= ( (piece_attacks<ROOK>(ksq) & rooks_and_queens(us))
893 |(piece_attacks<BISHOP>(ksq) & bishops_and_queens(us)));
903 key ^= zobSideToMove;
904 sideToMove = opposite_color(sideToMove);
907 mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
908 egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
914 /// Position::do_capture_move() is a private method used to update captured
915 /// piece info. It is called from the main Position::do_move function.
917 void Position::do_capture_move(Move m, PieceType capture, Color them, Square to) {
919 assert(capture != KING);
921 // Remove captured piece
922 clear_bit(&(byColorBB[them]), to);
923 clear_bit(&(byTypeBB[capture]), to);
926 key ^= zobrist[them][capture][to];
928 // If the captured piece was a pawn, update pawn hash key
930 pawnKey ^= zobrist[them][PAWN][to];
932 // Update incremental scores
933 mgValue -= mg_pst(them, capture, to);
934 egValue -= eg_pst(them, capture, to);
936 assert(!move_promotion(m) || capture != PAWN);
940 npMaterial[them] -= piece_value_midgame(capture);
942 // Update material hash key
943 materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];
945 // Update piece count
946 pieceCount[them][capture]--;
949 pieceList[them][capture][index[to]] = pieceList[them][capture][pieceCount[them][capture]];
950 index[pieceList[them][capture][index[to]]] = index[to];
952 // Reset rule 50 counter
957 /// Position::do_castle_move() is a private method used to make a castling
958 /// move. It is called from the main Position::do_move function. Note that
959 /// castling moves are encoded as "king captures friendly rook" moves, for
960 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
962 void Position::do_castle_move(Move m) {
965 assert(move_is_ok(m));
966 assert(move_is_castle(m));
968 Color us = side_to_move();
969 Color them = opposite_color(us);
971 // Find source squares for king and rook
972 Square kfrom = move_from(m);
973 Square rfrom = move_to(m); // HACK: See comment at beginning of function
976 assert(piece_on(kfrom) == king_of_color(us));
977 assert(piece_on(rfrom) == rook_of_color(us));
979 // Find destination squares for king and rook
980 if (rfrom > kfrom) // O-O
982 kto = relative_square(us, SQ_G1);
983 rto = relative_square(us, SQ_F1);
985 kto = relative_square(us, SQ_C1);
986 rto = relative_square(us, SQ_D1);
989 // Remove pieces from source squares
990 clear_bit(&(byColorBB[us]), kfrom);
991 clear_bit(&(byTypeBB[KING]), kfrom);
992 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
993 clear_bit(&(byColorBB[us]), rfrom);
994 clear_bit(&(byTypeBB[ROOK]), rfrom);
995 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
997 // Put pieces on destination squares
998 set_bit(&(byColorBB[us]), kto);
999 set_bit(&(byTypeBB[KING]), kto);
1000 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1001 set_bit(&(byColorBB[us]), rto);
1002 set_bit(&(byTypeBB[ROOK]), rto);
1003 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1005 // Update board array
1006 board[kfrom] = board[rfrom] = EMPTY;
1007 board[kto] = king_of_color(us);
1008 board[rto] = rook_of_color(us);
1010 // Update king square
1011 kingSquare[us] = kto;
1013 // Update piece lists
1014 pieceList[us][KING][index[kfrom]] = kto;
1015 pieceList[us][ROOK][index[rfrom]] = rto;
1016 int tmp = index[rfrom];
1017 index[kto] = index[kfrom];
1020 // Update incremental scores
1021 mgValue -= mg_pst(us, KING, kfrom);
1022 mgValue += mg_pst(us, KING, kto);
1023 egValue -= eg_pst(us, KING, kfrom);
1024 egValue += eg_pst(us, KING, kto);
1025 mgValue -= mg_pst(us, ROOK, rfrom);
1026 mgValue += mg_pst(us, ROOK, rto);
1027 egValue -= eg_pst(us, ROOK, rfrom);
1028 egValue += eg_pst(us, ROOK, rto);
1031 key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1032 key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1034 // Clear en passant square
1035 if(epSquare != SQ_NONE)
1037 key ^= zobEp[epSquare];
1041 // Update castling rights
1042 key ^= zobCastle[castleRights];
1043 castleRights &= castleRightsMask[kfrom];
1044 key ^= zobCastle[castleRights];
1046 // Reset rule 50 counter
1049 // Update checkers BB
1050 checkersBB = attacks_to(king_square(them), us);
1054 /// Position::do_promotion_move() is a private method used to make a promotion
1055 /// move. It is called from the main Position::do_move function. The
1056 /// UndoInfo object, which has been initialized in Position::do_move, is
1057 /// used to store the captured piece (if any).
1059 void Position::do_promotion_move(Move m, UndoInfo &u) {
1063 PieceType capture, promotion;
1066 assert(move_is_ok(m));
1067 assert(move_promotion(m));
1069 us = side_to_move();
1070 them = opposite_color(us);
1071 from = move_from(m);
1074 assert(relative_rank(us, to) == RANK_8);
1075 assert(piece_on(from) == pawn_of_color(us));
1076 assert(color_of_piece_on(to) == them || square_is_empty(to));
1078 capture = type_of_piece_on(to);
1082 u.capture = capture;
1083 do_capture_move(m, capture, them, to);
1087 clear_bit(&(byColorBB[us]), from);
1088 clear_bit(&(byTypeBB[PAWN]), from);
1089 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1090 board[from] = EMPTY;
1092 // Insert promoted piece
1093 promotion = move_promotion(m);
1094 assert(promotion >= KNIGHT && promotion <= QUEEN);
1095 set_bit(&(byColorBB[us]), to);
1096 set_bit(&(byTypeBB[promotion]), to);
1097 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1098 board[to] = piece_of_color_and_type(us, promotion);
1101 key ^= zobrist[us][PAWN][from] ^ zobrist[us][promotion][to];
1103 // Update pawn hash key
1104 pawnKey ^= zobrist[us][PAWN][from];
1106 // Update material key
1107 materialKey ^= zobMaterial[us][PAWN][pieceCount[us][PAWN]];
1108 materialKey ^= zobMaterial[us][promotion][pieceCount[us][promotion]+1];
1110 // Update piece counts
1111 pieceCount[us][PAWN]--;
1112 pieceCount[us][promotion]++;
1114 // Update piece lists
1115 pieceList[us][PAWN][index[from]] = pieceList[us][PAWN][pieceCount[us][PAWN]];
1116 index[pieceList[us][PAWN][index[from]]] = index[from];
1117 pieceList[us][promotion][pieceCount[us][promotion] - 1] = to;
1118 index[to] = pieceCount[us][promotion] - 1;
1120 // Update incremental scores
1121 mgValue -= mg_pst(us, PAWN, from);
1122 mgValue += mg_pst(us, promotion, to);
1123 egValue -= eg_pst(us, PAWN, from);
1124 egValue += eg_pst(us, promotion, to);
1127 npMaterial[us] += piece_value_midgame(promotion);
1129 // Clear the en passant square
1130 if (epSquare != SQ_NONE)
1132 key ^= zobEp[epSquare];
1136 // Update castle rights
1137 key ^= zobCastle[castleRights];
1138 castleRights &= castleRightsMask[to];
1139 key ^= zobCastle[castleRights];
1141 // Reset rule 50 counter
1144 // Update checkers BB
1145 checkersBB = attacks_to(king_square(them), us);
1149 /// Position::do_ep_move() is a private method used to make an en passant
1150 /// capture. It is called from the main Position::do_move function. Because
1151 /// the captured piece is always a pawn, we don't need to pass an UndoInfo
1152 /// object in which to store the captured piece.
1154 void Position::do_ep_move(Move m) {
1157 Square from, to, capsq;
1160 assert(move_is_ok(m));
1161 assert(move_is_ep(m));
1163 us = side_to_move();
1164 them = opposite_color(us);
1165 from = move_from(m);
1167 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1169 assert(to == epSquare);
1170 assert(relative_rank(us, to) == RANK_6);
1171 assert(piece_on(to) == EMPTY);
1172 assert(piece_on(from) == pawn_of_color(us));
1173 assert(piece_on(capsq) == pawn_of_color(them));
1175 // Remove captured piece
1176 clear_bit(&(byColorBB[them]), capsq);
1177 clear_bit(&(byTypeBB[PAWN]), capsq);
1178 clear_bit(&(byTypeBB[0]), capsq); // HACK: byTypeBB[0] == occupied squares
1179 board[capsq] = EMPTY;
1181 // Remove moving piece from source square
1182 clear_bit(&(byColorBB[us]), from);
1183 clear_bit(&(byTypeBB[PAWN]), from);
1184 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1186 // Put moving piece on destination square
1187 set_bit(&(byColorBB[us]), to);
1188 set_bit(&(byTypeBB[PAWN]), to);
1189 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1190 board[to] = board[from];
1191 board[from] = EMPTY;
1193 // Update material hash key
1194 materialKey ^= zobMaterial[them][PAWN][pieceCount[them][PAWN]];
1196 // Update piece count
1197 pieceCount[them][PAWN]--;
1199 // Update piece list
1200 pieceList[us][PAWN][index[from]] = to;
1201 index[to] = index[from];
1202 pieceList[them][PAWN][index[capsq]] = pieceList[them][PAWN][pieceCount[them][PAWN]];
1203 index[pieceList[them][PAWN][index[capsq]]] = index[capsq];
1206 key ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1207 key ^= zobrist[them][PAWN][capsq];
1208 key ^= zobEp[epSquare];
1210 // Update pawn hash key
1211 pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1212 pawnKey ^= zobrist[them][PAWN][capsq];
1214 // Update incremental scores
1215 mgValue -= mg_pst(them, PAWN, capsq);
1216 mgValue -= mg_pst(us, PAWN, from);
1217 mgValue += mg_pst(us, PAWN, to);
1218 egValue -= eg_pst(them, PAWN, capsq);
1219 egValue -= eg_pst(us, PAWN, from);
1220 egValue += eg_pst(us, PAWN, to);
1222 // Reset en passant square
1225 // Reset rule 50 counter
1228 // Update checkers BB
1229 checkersBB = attacks_to(king_square(them), us);
1233 /// Position::undo_move() unmakes a move. When it returns, the position should
1234 /// be restored to exactly the same state as before the move was made. It is
1235 /// important that Position::undo_move is called with the same move and UndoInfo
1236 /// object as the earlier call to Position::do_move.
1238 void Position::undo_move(Move m, const UndoInfo &u) {
1241 assert(move_is_ok(m));
1244 sideToMove = opposite_color(sideToMove);
1246 // Restore information from our UndoInfo object (except the captured piece,
1247 // which is taken care of later)
1250 if (move_is_castle(m))
1251 undo_castle_move(m);
1252 else if (move_promotion(m))
1253 undo_promotion_move(m, u);
1254 else if (move_is_ep(m))
1260 PieceType piece, capture;
1262 us = side_to_move();
1263 them = opposite_color(us);
1264 from = move_from(m);
1267 assert(piece_on(from) == EMPTY);
1268 assert(color_of_piece_on(to) == us);
1270 // Put the piece back at the source square
1271 piece = type_of_piece_on(to);
1272 set_bit(&(byColorBB[us]), from);
1273 set_bit(&(byTypeBB[piece]), from);
1274 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1275 board[from] = piece_of_color_and_type(us, piece);
1277 // Clear the destination square
1278 clear_bit(&(byColorBB[us]), to);
1279 clear_bit(&(byTypeBB[piece]), to);
1280 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1282 // If the moving piece was a king, update the king square
1284 kingSquare[us] = from;
1286 // Update piece list
1287 pieceList[us][piece][index[to]] = from;
1288 index[from] = index[to];
1290 capture = u.capture;
1294 assert(capture != KING);
1296 // Replace the captured piece
1297 set_bit(&(byColorBB[them]), to);
1298 set_bit(&(byTypeBB[capture]), to);
1299 set_bit(&(byTypeBB[0]), to);
1300 board[to] = piece_of_color_and_type(them, capture);
1303 if (capture != PAWN)
1304 npMaterial[them] += piece_value_midgame(capture);
1306 // Update piece list
1307 pieceList[them][capture][pieceCount[them][capture]] = to;
1308 index[to] = pieceCount[them][capture];
1310 // Update piece count
1311 pieceCount[them][capture]++;
1320 /// Position::undo_castle_move() is a private method used to unmake a castling
1321 /// move. It is called from the main Position::undo_move function. Note that
1322 /// castling moves are encoded as "king captures friendly rook" moves, for
1323 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1325 void Position::undo_castle_move(Move m) {
1327 assert(move_is_ok(m));
1328 assert(move_is_castle(m));
1330 // When we have arrived here, some work has already been done by
1331 // Position::undo_move. In particular, the side to move has been switched,
1332 // so the code below is correct.
1333 Color us = side_to_move();
1335 // Find source squares for king and rook
1336 Square kfrom = move_from(m);
1337 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1340 // Find destination squares for king and rook
1341 if (rfrom > kfrom) // O-O
1343 kto = relative_square(us, SQ_G1);
1344 rto = relative_square(us, SQ_F1);
1346 kto = relative_square(us, SQ_C1);
1347 rto = relative_square(us, SQ_D1);
1350 assert(piece_on(kto) == king_of_color(us));
1351 assert(piece_on(rto) == rook_of_color(us));
1353 // Remove pieces from destination squares
1354 clear_bit(&(byColorBB[us]), kto);
1355 clear_bit(&(byTypeBB[KING]), kto);
1356 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1357 clear_bit(&(byColorBB[us]), rto);
1358 clear_bit(&(byTypeBB[ROOK]), rto);
1359 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1361 // Put pieces on source squares
1362 set_bit(&(byColorBB[us]), kfrom);
1363 set_bit(&(byTypeBB[KING]), kfrom);
1364 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1365 set_bit(&(byColorBB[us]), rfrom);
1366 set_bit(&(byTypeBB[ROOK]), rfrom);
1367 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1370 board[rto] = board[kto] = EMPTY;
1371 board[rfrom] = rook_of_color(us);
1372 board[kfrom] = king_of_color(us);
1374 // Update king square
1375 kingSquare[us] = kfrom;
1377 // Update piece lists
1378 pieceList[us][KING][index[kto]] = kfrom;
1379 pieceList[us][ROOK][index[rto]] = rfrom;
1380 int tmp = index[rto]; // Necessary because we may have rto == kfrom in FRC.
1381 index[kfrom] = index[kto];
1386 /// Position::undo_promotion_move() is a private method used to unmake a
1387 /// promotion move. It is called from the main Position::do_move
1388 /// function. The UndoInfo object, which has been initialized in
1389 /// Position::do_move, is used to put back the captured piece (if any).
1391 void Position::undo_promotion_move(Move m, const UndoInfo &u) {
1395 PieceType capture, promotion;
1397 assert(move_is_ok(m));
1398 assert(move_promotion(m));
1400 // When we have arrived here, some work has already been done by
1401 // Position::undo_move. In particular, the side to move has been switched,
1402 // so the code below is correct.
1403 us = side_to_move();
1404 them = opposite_color(us);
1405 from = move_from(m);
1408 assert(relative_rank(us, to) == RANK_8);
1409 assert(piece_on(from) == EMPTY);
1411 // Remove promoted piece
1412 promotion = move_promotion(m);
1413 assert(piece_on(to)==piece_of_color_and_type(us, promotion));
1414 assert(promotion >= KNIGHT && promotion <= QUEEN);
1415 clear_bit(&(byColorBB[us]), to);
1416 clear_bit(&(byTypeBB[promotion]), to);
1417 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1419 // Insert pawn at source square
1420 set_bit(&(byColorBB[us]), from);
1421 set_bit(&(byTypeBB[PAWN]), from);
1422 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1423 board[from] = pawn_of_color(us);
1426 npMaterial[us] -= piece_value_midgame(promotion);
1428 // Update piece list
1429 pieceList[us][PAWN][pieceCount[us][PAWN]] = from;
1430 index[from] = pieceCount[us][PAWN];
1431 pieceList[us][promotion][index[to]] =
1432 pieceList[us][promotion][pieceCount[us][promotion] - 1];
1433 index[pieceList[us][promotion][index[to]]] = index[to];
1435 // Update piece counts
1436 pieceCount[us][promotion]--;
1437 pieceCount[us][PAWN]++;
1439 capture = u.capture;
1443 assert(capture != KING);
1445 // Insert captured piece:
1446 set_bit(&(byColorBB[them]), to);
1447 set_bit(&(byTypeBB[capture]), to);
1448 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1449 board[to] = piece_of_color_and_type(them, capture);
1451 // Update material. Because the move is a promotion move, we know
1452 // that the captured piece cannot be a pawn.
1453 assert(capture != PAWN);
1454 npMaterial[them] += piece_value_midgame(capture);
1456 // Update piece list
1457 pieceList[them][capture][pieceCount[them][capture]] = to;
1458 index[to] = pieceCount[them][capture];
1460 // Update piece count
1461 pieceCount[them][capture]++;
1467 /// Position::undo_ep_move() is a private method used to unmake an en passant
1468 /// capture. It is called from the main Position::undo_move function. Because
1469 /// the captured piece is always a pawn, we don't need to pass an UndoInfo
1470 /// object from which to retrieve the captured piece.
1472 void Position::undo_ep_move(Move m) {
1474 assert(move_is_ok(m));
1475 assert(move_is_ep(m));
1477 // When we have arrived here, some work has already been done by
1478 // Position::undo_move. In particular, the side to move has been switched,
1479 // so the code below is correct.
1480 Color us = side_to_move();
1481 Color them = opposite_color(us);
1482 Square from = move_from(m);
1483 Square to = move_to(m);
1484 Square capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1486 assert(to == ep_square());
1487 assert(relative_rank(us, to) == RANK_6);
1488 assert(piece_on(to) == pawn_of_color(us));
1489 assert(piece_on(from) == EMPTY);
1490 assert(piece_on(capsq) == EMPTY);
1492 // Replace captured piece
1493 set_bit(&(byColorBB[them]), capsq);
1494 set_bit(&(byTypeBB[PAWN]), capsq);
1495 set_bit(&(byTypeBB[0]), capsq);
1496 board[capsq] = pawn_of_color(them);
1498 // Remove moving piece from destination square
1499 clear_bit(&(byColorBB[us]), to);
1500 clear_bit(&(byTypeBB[PAWN]), to);
1501 clear_bit(&(byTypeBB[0]), to);
1504 // Replace moving piece at source square
1505 set_bit(&(byColorBB[us]), from);
1506 set_bit(&(byTypeBB[PAWN]), from);
1507 set_bit(&(byTypeBB[0]), from);
1508 board[from] = pawn_of_color(us);
1510 // Update piece list:
1511 pieceList[us][PAWN][index[to]] = from;
1512 index[from] = index[to];
1513 pieceList[them][PAWN][pieceCount[them][PAWN]] = capsq;
1514 index[capsq] = pieceCount[them][PAWN];
1516 // Update piece count:
1517 pieceCount[them][PAWN]++;
1521 /// Position::do_null_move makes() a "null move": It switches the side to move
1522 /// and updates the hash key without executing any move on the board.
1524 void Position::do_null_move(UndoInfo &u) {
1527 assert(!is_check());
1529 // Back up the information necessary to undo the null move to the supplied
1530 // UndoInfo object. In the case of a null move, the only thing we need to
1531 // remember is the last move made and the en passant square.
1532 u.lastMove = lastMove;
1533 u.epSquare = epSquare;
1535 // Save the current key to the history[] array, in order to be able to
1536 // detect repetition draws.
1537 history[gamePly] = key;
1539 // Update the necessary information
1540 sideToMove = opposite_color(sideToMove);
1541 if (epSquare != SQ_NONE)
1542 key ^= zobEp[epSquare];
1547 key ^= zobSideToMove;
1549 mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1550 egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1556 /// Position::undo_null_move() unmakes a "null move".
1558 void Position::undo_null_move(const UndoInfo &u) {
1561 assert(!is_check());
1563 // Restore information from the supplied UndoInfo object:
1564 lastMove = u.lastMove;
1565 epSquare = u.epSquare;
1566 if (epSquare != SQ_NONE)
1567 key ^= zobEp[epSquare];
1569 // Update the necessary information.
1570 sideToMove = opposite_color(sideToMove);
1573 key ^= zobSideToMove;
1575 mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1576 egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1582 /// Position::see() is a static exchange evaluator: It tries to estimate the
1583 /// material gain or loss resulting from a move. There are two versions of
1584 /// this function: One which takes a move as input, and one which takes a
1585 /// 'from' and a 'to' square. The function does not yet understand promotions
1586 /// or en passant captures.
1588 int Position::see(Move m) const {
1590 assert(move_is_ok(m));
1591 return see(move_from(m), move_to(m));
1594 int Position::see(Square from, Square to) const {
1596 // Approximate material values, with pawn = 1
1597 static const int seeValues[18] = {
1598 0, 1, 3, 3, 5, 10, 100, 0, 0, 1, 3, 3, 5, 10, 100, 0, 0, 0
1601 Bitboard attackers, occ, b;
1603 assert(square_is_ok(from));
1604 assert(square_is_ok(to));
1606 // Initialize colors
1607 Color us = color_of_piece_on(from);
1608 Color them = opposite_color(us);
1610 // Initialize pieces
1611 Piece piece = piece_on(from);
1612 Piece capture = piece_on(to);
1614 // Find all attackers to the destination square, with the moving piece
1615 // removed, but possibly an X-ray attacker added behind it.
1616 occ = occupied_squares();
1617 clear_bit(&occ, from);
1618 attackers = (rook_attacks_bb(to, occ) & rooks_and_queens())
1619 | (bishop_attacks_bb(to, occ) & bishops_and_queens())
1620 | (piece_attacks<KNIGHT>(to) & knights())
1621 | (piece_attacks<KING>(to) & kings())
1622 | (pawn_attacks(WHITE, to) & pawns(BLACK))
1623 | (pawn_attacks(BLACK, to) & pawns(WHITE));
1625 // If the opponent has no attackers, we are finished
1626 if ((attackers & pieces_of_color(them)) == EmptyBoardBB)
1627 return seeValues[capture];
1629 attackers &= occ; // Remove the moving piece
1631 // The destination square is defended, which makes things rather more
1632 // difficult to compute. We proceed by building up a "swap list" containing
1633 // the material gain or loss at each stop in a sequence of captures to the
1634 // destination square, where the sides alternately capture, and always
1635 // capture with the least valuable piece. After each capture, we look for
1636 // new X-ray attacks from behind the capturing piece.
1637 int lastCapturingPieceValue = seeValues[piece];
1638 int swapList[32], n = 1;
1642 swapList[0] = seeValues[capture];
1645 // Locate the least valuable attacker for the side to move. The loop
1646 // below looks like it is potentially infinite, but it isn't. We know
1647 // that the side to move still has at least one attacker left.
1648 for (pt = PAWN; !(attackers & pieces_of_color_and_type(c, pt)); pt++)
1651 // Remove the attacker we just found from the 'attackers' bitboard,
1652 // and scan for new X-ray attacks behind the attacker.
1653 b = attackers & pieces_of_color_and_type(c, pt);
1655 attackers |= (rook_attacks_bb(to, occ) & rooks_and_queens())
1656 | (bishop_attacks_bb(to, occ) & bishops_and_queens());
1660 // Add the new entry to the swap list
1662 swapList[n] = -swapList[n - 1] + lastCapturingPieceValue;
1665 // Remember the value of the capturing piece, and change the side to move
1666 // before beginning the next iteration
1667 lastCapturingPieceValue = seeValues[pt];
1668 c = opposite_color(c);
1670 // Stop after a king capture
1671 if (pt == KING && (attackers & pieces_of_color(c)))
1674 swapList[n++] = 100;
1677 } while (attackers & pieces_of_color(c));
1679 // Having built the swap list, we negamax through it to find the best
1680 // achievable score from the point of view of the side to move
1682 swapList[n-1] = Min(-swapList[n], swapList[n-1]);
1688 /// Position::clear() erases the position object to a pristine state, with an
1689 /// empty board, white to move, and no castling rights.
1691 void Position::clear() {
1693 for (int i = 0; i < 64; i++)
1699 for (int i = 0; i < 2; i++)
1700 byColorBB[i] = EmptyBoardBB;
1702 for (int i = 0; i < 7; i++)
1704 byTypeBB[i] = EmptyBoardBB;
1705 pieceCount[0][i] = pieceCount[1][i] = 0;
1706 for (int j = 0; j < 8; j++)
1707 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1710 checkersBB = EmptyBoardBB;
1712 lastMove = MOVE_NONE;
1715 castleRights = NO_CASTLES;
1716 initialKFile = FILE_E;
1717 initialKRFile = FILE_H;
1718 initialQRFile = FILE_A;
1725 /// Position::reset_game_ply() simply sets gamePly to 0. It is used from the
1726 /// UCI interface code, whenever a non-reversible move is made in a
1727 /// 'position fen <fen> moves m1 m2 ...' command. This makes it possible
1728 /// for the program to handle games of arbitrary length, as long as the GUI
1729 /// handles draws by the 50 move rule correctly.
1731 void Position::reset_game_ply() {
1737 /// Position::put_piece() puts a piece on the given square of the board,
1738 /// updating the board array, bitboards, and piece counts.
1740 void Position::put_piece(Piece p, Square s) {
1742 Color c = color_of_piece(p);
1743 PieceType pt = type_of_piece(p);
1746 index[s] = pieceCount[c][pt];
1747 pieceList[c][pt][index[s]] = s;
1749 set_bit(&(byTypeBB[pt]), s);
1750 set_bit(&(byColorBB[c]), s);
1751 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1753 pieceCount[c][pt]++;
1760 /// Position::allow_oo() gives the given side the right to castle kingside.
1761 /// Used when setting castling rights during parsing of FEN strings.
1763 void Position::allow_oo(Color c) {
1765 castleRights |= (1 + int(c));
1769 /// Position::allow_ooo() gives the given side the right to castle queenside.
1770 /// Used when setting castling rights during parsing of FEN strings.
1772 void Position::allow_ooo(Color c) {
1774 castleRights |= (4 + 4*int(c));
1778 /// Position::compute_key() computes the hash key of the position. The hash
1779 /// key is usually updated incrementally as moves are made and unmade, the
1780 /// compute_key() function is only used when a new position is set up, and
1781 /// to verify the correctness of the hash key when running in debug mode.
1783 Key Position::compute_key() const {
1785 Key result = Key(0ULL);
1787 for (Square s = SQ_A1; s <= SQ_H8; s++)
1788 if (square_is_occupied(s))
1789 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1791 if (ep_square() != SQ_NONE)
1792 result ^= zobEp[ep_square()];
1794 result ^= zobCastle[castleRights];
1795 if (side_to_move() == BLACK)
1796 result ^= zobSideToMove;
1802 /// Position::compute_pawn_key() computes the hash key of the position. The
1803 /// hash key is usually updated incrementally as moves are made and unmade,
1804 /// the compute_pawn_key() function is only used when a new position is set
1805 /// up, and to verify the correctness of the pawn hash key when running in
1808 Key Position::compute_pawn_key() const {
1810 Key result = Key(0ULL);
1814 for (Color c = WHITE; c <= BLACK; c++)
1819 s = pop_1st_bit(&b);
1820 result ^= zobrist[c][PAWN][s];
1827 /// Position::compute_material_key() computes the hash key of the position.
1828 /// The hash key is usually updated incrementally as moves are made and unmade,
1829 /// the compute_material_key() function is only used when a new position is set
1830 /// up, and to verify the correctness of the material hash key when running in
1833 Key Position::compute_material_key() const {
1835 Key result = Key(0ULL);
1836 for (Color c = WHITE; c <= BLACK; c++)
1837 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1839 int count = piece_count(c, pt);
1840 for (int i = 0; i <= count; i++)
1841 result ^= zobMaterial[c][pt][i];
1847 /// Position::compute_mg_value() and Position::compute_eg_value() compute the
1848 /// incremental scores for the middle game and the endgame. These functions
1849 /// are used to initialize the incremental scores when a new position is set
1850 /// up, and to verify that the scores are correctly updated by do_move
1851 /// and undo_move when the program is running in debug mode.
1853 Value Position::compute_mg_value() const {
1855 Value result = Value(0);
1859 for (Color c = WHITE; c <= BLACK; c++)
1860 for (PieceType pt = PAWN; pt <= KING; pt++)
1862 b = pieces_of_color_and_type(c, pt);
1865 s = pop_1st_bit(&b);
1866 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1867 result += mg_pst(c, pt, s);
1870 result += (side_to_move() == WHITE)? TempoValueMidgame / 2 : -TempoValueMidgame / 2;
1874 Value Position::compute_eg_value() const {
1876 Value result = Value(0);
1880 for (Color c = WHITE; c <= BLACK; c++)
1881 for (PieceType pt = PAWN; pt <= KING; pt++)
1883 b = pieces_of_color_and_type(c, pt);
1886 s = pop_1st_bit(&b);
1887 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1888 result += eg_pst(c, pt, s);
1891 result += (side_to_move() == WHITE)? TempoValueEndgame / 2 : -TempoValueEndgame / 2;
1896 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1897 /// game material score for the given side. Material scores are updated
1898 /// incrementally during the search, this function is only used while
1899 /// initializing a new Position object.
1901 Value Position::compute_non_pawn_material(Color c) const {
1903 Value result = Value(0);
1906 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1908 Bitboard b = pieces_of_color_and_type(c, pt);
1911 s = pop_1st_bit(&b);
1912 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1913 result += piece_value_midgame(pt);
1920 /// Position::is_mate() returns true or false depending on whether the
1921 /// side to move is checkmated. Note that this function is currently very
1922 /// slow, and shouldn't be used frequently inside the search.
1924 bool Position::is_mate() {
1928 MovePicker mp = MovePicker(*this, false, MOVE_NONE, EmptySearchStack, Depth(0));
1929 return mp.get_next_move() == MOVE_NONE;
1935 /// Position::is_draw() tests whether the position is drawn by material,
1936 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1937 /// must be done by the search.
1939 bool Position::is_draw() const {
1941 // Draw by material?
1943 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1946 // Draw by the 50 moves rule?
1947 if (rule50 > 100 || (rule50 == 100 && !is_check()))
1950 // Draw by repetition?
1951 for (int i = 2; i < Min(gamePly, rule50); i += 2)
1952 if (history[gamePly - i] == key)
1959 /// Position::has_mate_threat() tests whether a given color has a mate in one
1960 /// from the current position. This function is quite slow, but it doesn't
1961 /// matter, because it is currently only called from PV nodes, which are rare.
1963 bool Position::has_mate_threat(Color c) {
1966 Color stm = side_to_move();
1968 // The following lines are useless and silly, but prevents gcc from
1969 // emitting a stupid warning stating that u1.lastMove and u1.epSquare might
1970 // be used uninitialized.
1971 u1.lastMove = lastMove;
1972 u1.epSquare = epSquare;
1977 // If the input color is not equal to the side to move, do a null move
1981 MoveStack mlist[120];
1983 bool result = false;
1985 // Generate legal moves
1986 count = generate_legal_moves(*this, mlist);
1988 // Loop through the moves, and see if one of them is mate
1989 for (int i = 0; i < count; i++)
1991 do_move(mlist[i].move, u2);
1995 undo_move(mlist[i].move, u2);
1998 // Undo null move, if necessary
2006 /// Position::init_zobrist() is a static member function which initializes the
2007 /// various arrays used to compute hash keys.
2009 void Position::init_zobrist() {
2011 for (int i = 0; i < 2; i++)
2012 for (int j = 0; j < 8; j++)
2013 for (int k = 0; k < 64; k++)
2014 zobrist[i][j][k] = Key(genrand_int64());
2016 for (int i = 0; i < 64; i++)
2017 zobEp[i] = Key(genrand_int64());
2019 for (int i = 0; i < 16; i++)
2020 zobCastle[i] = genrand_int64();
2022 zobSideToMove = genrand_int64();
2024 for (int i = 0; i < 2; i++)
2025 for (int j = 0; j < 8; j++)
2026 for (int k = 0; k < 16; k++)
2027 zobMaterial[i][j][k] = (k > 0)? Key(genrand_int64()) : Key(0LL);
2029 for (int i = 0; i < 16; i++)
2030 zobMaterial[0][KING][i] = zobMaterial[1][KING][i] = Key(0ULL);
2034 /// Position::init_piece_square_tables() initializes the piece square tables.
2035 /// This is a two-step operation: First, the white halves of the tables are
2036 /// copied from the MgPST[][] and EgPST[][] arrays, with a small random number
2037 /// added to each entry if the "Randomness" UCI parameter is non-zero.
2038 /// Second, the black halves of the tables are initialized by mirroring
2039 /// and changing the sign of the corresponding white scores.
2041 void Position::init_piece_square_tables() {
2043 int r = get_option_value_int("Randomness"), i;
2044 for (Square s = SQ_A1; s <= SQ_H8; s++)
2045 for (Piece p = WP; p <= WK; p++)
2047 i = (r == 0)? 0 : (genrand_int32() % (r*2) - r);
2048 MgPieceSquareTable[p][s] = Value(MgPST[p][s] + i);
2049 EgPieceSquareTable[p][s] = Value(EgPST[p][s] + i);
2052 for (Square s = SQ_A1; s <= SQ_H8; s++)
2053 for (Piece p = BP; p <= BK; p++)
2055 MgPieceSquareTable[p][s] = -MgPieceSquareTable[p-8][flip_square(s)];
2056 EgPieceSquareTable[p][s] = -EgPieceSquareTable[p-8][flip_square(s)];
2061 /// Position::flipped_copy() makes a copy of the input position, but with
2062 /// the white and black sides reversed. This is only useful for debugging,
2063 /// especially for finding evaluation symmetry bugs.
2065 void Position::flipped_copy(const Position &pos) {
2067 assert(pos.is_ok());
2072 for (Square s = SQ_A1; s <= SQ_H8; s++)
2073 if (!pos.square_is_empty(s))
2074 put_piece(Piece(int(pos.piece_on(s)) ^ 8), flip_square(s));
2077 sideToMove = opposite_color(pos.side_to_move());
2080 if (pos.can_castle_kingside(WHITE)) allow_oo(BLACK);
2081 if (pos.can_castle_queenside(WHITE)) allow_ooo(BLACK);
2082 if (pos.can_castle_kingside(BLACK)) allow_oo(WHITE);
2083 if (pos.can_castle_queenside(BLACK)) allow_ooo(WHITE);
2085 initialKFile = pos.initialKFile;
2086 initialKRFile = pos.initialKRFile;
2087 initialQRFile = pos.initialQRFile;
2089 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
2090 castleRightsMask[sq] = ALL_CASTLES;
2092 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
2093 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
2094 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
2095 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
2096 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
2097 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
2099 // En passant square
2100 if (pos.epSquare != SQ_NONE)
2101 epSquare = flip_square(pos.epSquare);
2107 key = compute_key();
2108 pawnKey = compute_pawn_key();
2109 materialKey = compute_material_key();
2111 // Incremental scores
2112 mgValue = compute_mg_value();
2113 egValue = compute_eg_value();
2116 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
2117 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
2123 /// Position::is_ok() performs some consitency checks for the position object.
2124 /// This is meant to be helpful when debugging.
2126 bool Position::is_ok(int* failedStep) const {
2128 // What features of the position should be verified?
2129 static const bool debugBitboards = false;
2130 static const bool debugKingCount = false;
2131 static const bool debugKingCapture = false;
2132 static const bool debugCheckerCount = false;
2133 static const bool debugKey = false;
2134 static const bool debugMaterialKey = false;
2135 static const bool debugPawnKey = false;
2136 static const bool debugIncrementalEval = false;
2137 static const bool debugNonPawnMaterial = false;
2138 static const bool debugPieceCounts = false;
2139 static const bool debugPieceList = false;
2141 if (failedStep) *failedStep = 1;
2144 if (!color_is_ok(side_to_move()))
2147 // Are the king squares in the position correct?
2148 if (failedStep) (*failedStep)++;
2149 if (piece_on(king_square(WHITE)) != WK)
2152 if (failedStep) (*failedStep)++;
2153 if (piece_on(king_square(BLACK)) != BK)
2157 if (failedStep) (*failedStep)++;
2158 if (!file_is_ok(initialKRFile))
2161 if (!file_is_ok(initialQRFile))
2164 // Do both sides have exactly one king?
2165 if (failedStep) (*failedStep)++;
2168 int kingCount[2] = {0, 0};
2169 for (Square s = SQ_A1; s <= SQ_H8; s++)
2170 if (type_of_piece_on(s) == KING)
2171 kingCount[color_of_piece_on(s)]++;
2173 if(kingCount[0] != 1 || kingCount[1] != 1)
2177 // Can the side to move capture the opponent's king?
2178 if (failedStep) (*failedStep)++;
2179 if (debugKingCapture)
2181 Color us = side_to_move();
2182 Color them = opposite_color(us);
2183 Square ksq = king_square(them);
2184 if (square_is_attacked(ksq, us))
2188 // Is there more than 2 checkers?
2189 if (failedStep) (*failedStep)++;
2190 if (debugCheckerCount && count_1s(checkersBB) > 2)
2194 if (failedStep) (*failedStep)++;
2197 // The intersection of the white and black pieces must be empty
2198 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
2201 // The union of the white and black pieces must be equal to all
2203 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
2206 // Separate piece type bitboards must have empty intersections
2207 for (PieceType p1 = PAWN; p1 <= KING; p1++)
2208 for (PieceType p2 = PAWN; p2 <= KING; p2++)
2209 if (p1 != p2 && (pieces_of_type(p1) & pieces_of_type(p2)))
2213 // En passant square OK?
2214 if (failedStep) (*failedStep)++;
2215 if (ep_square() != SQ_NONE)
2217 // The en passant square must be on rank 6, from the point of view of the
2219 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
2224 if (failedStep) (*failedStep)++;
2225 if (debugKey && key != compute_key())
2228 // Pawn hash key OK?
2229 if (failedStep) (*failedStep)++;
2230 if (debugPawnKey && pawnKey != compute_pawn_key())
2233 // Material hash key OK?
2234 if (failedStep) (*failedStep)++;
2235 if (debugMaterialKey && materialKey != compute_material_key())
2238 // Incremental eval OK?
2239 if (failedStep) (*failedStep)++;
2240 if (debugIncrementalEval)
2242 if (mgValue != compute_mg_value())
2245 if (egValue != compute_eg_value())
2249 // Non-pawn material OK?
2250 if (failedStep) (*failedStep)++;
2251 if (debugNonPawnMaterial)
2253 if(npMaterial[WHITE] != compute_non_pawn_material(WHITE))
2256 if(npMaterial[BLACK] != compute_non_pawn_material(BLACK))
2261 if (failedStep) (*failedStep)++;
2262 if (debugPieceCounts)
2263 for (Color c = WHITE; c <= BLACK; c++)
2264 for (PieceType pt = PAWN; pt <= KING; pt++)
2265 if (pieceCount[c][pt] != count_1s(pieces_of_color_and_type(c, pt)))
2268 if (failedStep) (*failedStep)++;
2271 for(Color c = WHITE; c <= BLACK; c++)
2272 for(PieceType pt = PAWN; pt <= KING; pt++)
2273 for(int i = 0; i < pieceCount[c][pt]; i++)
2275 if (piece_on(piece_list(c, pt, i)) != piece_of_color_and_type(c, pt))
2278 if (index[piece_list(c, pt, i)] != i)
2282 if (failedStep) *failedStep = 0;