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::update_checkers() updates checkers info, used in do_move()
321 template<PieceType Piece>
322 inline void Position::update_checkers(Bitboard* pCheckersBB, Square ksq, Square from,
323 Square to, Bitboard dcCandidates) {
325 if (Piece != KING && bit_is_set(piece_attacks<Piece>(ksq), to))
326 set_bit(pCheckersBB, to);
328 if (Piece != QUEEN && bit_is_set(dcCandidates, from))
331 (*pCheckersBB) |= (piece_attacks<ROOK>(ksq) & rooks_and_queens(side_to_move()));
334 (*pCheckersBB) |= (piece_attacks<BISHOP>(ksq) & bishops_and_queens(side_to_move()));
339 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
340 /// king) pieces for the given color.
341 Bitboard Position::pinned_pieces(Color c) const {
343 Square ksq = king_square(c);
344 return hidden_checks<ROOK, true>(c, ksq) | hidden_checks<BISHOP, true>(c, ksq);
348 /// Position:discovered_check_candidates() returns a bitboard containing all
349 /// pieces for the given side which are candidates for giving a discovered
350 /// check. The code is almost the same as the function for finding pinned
353 Bitboard Position::discovered_check_candidates(Color c) const {
355 Square ksq = king_square(opposite_color(c));
356 return hidden_checks<ROOK, false>(c, ksq) | hidden_checks<BISHOP, false>(c, ksq);
360 /// Position:hidden_checks<>() returns a bitboard of all pinned (against the
361 /// king) pieces for the given color and for the given pinner type. Or, when
362 /// template parameter FindPinned is false, the pinned pieces of opposite color
363 /// that are, indeed, the pieces candidate for a discovery check.
364 template<PieceType Piece, bool FindPinned>
365 Bitboard Position::hidden_checks(Color c, Square ksq) const {
368 Bitboard sliders, result = EmptyBoardBB;
370 if (Piece == ROOK) // Resolved at compile time
371 sliders = rooks_and_queens(FindPinned ? opposite_color(c) : c) & RookPseudoAttacks[ksq];
373 sliders = bishops_and_queens(FindPinned ? opposite_color(c) : c) & BishopPseudoAttacks[ksq];
375 if (sliders && (!FindPinned || (sliders & ~checkersBB)))
377 // King blockers are candidate pinned pieces
378 Bitboard candidate_pinned = piece_attacks<Piece>(ksq) & pieces_of_color(c);
380 // Pinners are sliders, not checkers, that give check when
381 // candidate pinned are removed.
382 Bitboard pinners = (FindPinned ? sliders & ~checkersBB : sliders);
385 pinners &= rook_attacks_bb(ksq, occupied_squares() ^ candidate_pinned);
387 pinners &= bishop_attacks_bb(ksq, occupied_squares() ^ candidate_pinned);
389 // Finally for each pinner find the corresponding pinned piece (if same color of king)
390 // or discovery checker (if opposite color) among the candidates.
393 s = pop_1st_bit(&pinners);
394 result |= (squares_between(s, ksq) & candidate_pinned);
401 /// Position::attacks_to() computes a bitboard containing all pieces which
402 /// attacks a given square. There are two versions of this function: One
403 /// which finds attackers of both colors, and one which only finds the
404 /// attackers for one side.
406 Bitboard Position::attacks_to(Square s) const {
408 return (pawn_attacks(BLACK, s) & pawns(WHITE))
409 | (pawn_attacks(WHITE, s) & pawns(BLACK))
410 | (piece_attacks<KNIGHT>(s) & pieces_of_type(KNIGHT))
411 | (piece_attacks<ROOK>(s) & rooks_and_queens())
412 | (piece_attacks<BISHOP>(s) & bishops_and_queens())
413 | (piece_attacks<KING>(s) & pieces_of_type(KING));
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. Move must not be MOVE_NONE.
680 bool Position::move_is_capture(Move m) const {
682 assert(m != MOVE_NONE);
684 return ( !square_is_empty(move_to(m))
685 && (color_of_piece_on(move_to(m)) == opposite_color(side_to_move()))
691 /// Position::backup() is called when making a move. All information
692 /// necessary to restore the position when the move is later unmade
693 /// is saved to an UndoInfo object. The function Position::restore
694 /// does the reverse operation: When one does a backup followed by
695 /// a restore with the same UndoInfo object, the position is restored
696 /// to the state before backup was called.
698 void Position::backup(UndoInfo& u) const {
700 u.castleRights = castleRights;
701 u.epSquare = epSquare;
702 u.checkersBB = checkersBB;
705 u.materialKey = materialKey;
707 u.lastMove = lastMove;
710 u.capture = NO_PIECE_TYPE;
714 /// Position::restore() is called when unmaking a move. It copies back
715 /// the information backed up during a previous call to Position::backup.
717 void Position::restore(const UndoInfo& u) {
719 castleRights = u.castleRights;
720 epSquare = u.epSquare;
721 checkersBB = u.checkersBB;
724 materialKey = u.materialKey;
726 lastMove = u.lastMove;
729 // u.capture is restored in undo_move()
732 /// Position::do_move() makes a move, and backs up all information necessary
733 /// to undo the move to an UndoInfo object. The move is assumed to be legal.
734 /// Pseudo-legal moves should be filtered out before this function is called.
735 /// There are two versions of this function, one which takes only the move and
736 /// the UndoInfo as input, and one which takes a third parameter, a bitboard of
737 /// discovered check candidates. The second version is faster, because knowing
738 /// the discovered check candidates makes it easier to update the checkersBB
739 /// member variable in the position object.
741 void Position::do_move(Move m, UndoInfo& u) {
743 do_move(m, u, discovered_check_candidates(side_to_move()));
746 void Position::do_move(Move m, UndoInfo& u, Bitboard dcCandidates) {
749 assert(move_is_ok(m));
751 // Back up the necessary information to our UndoInfo object (except the
752 // captured piece, which is taken care of later.
755 // Save the current key to the history[] array, in order to be able to
756 // detect repetition draws.
757 history[gamePly] = key;
759 // Increment the 50 moves rule draw counter. Resetting it to zero in the
760 // case of non-reversible moves is taken care of later.
763 if (move_is_castle(m))
765 else if (move_promotion(m))
766 do_promotion_move(m, u);
767 else if (move_is_ep(m))
771 Color us = side_to_move();
772 Color them = opposite_color(us);
773 Square from = move_from(m);
774 Square to = move_to(m);
776 assert(color_of_piece_on(from) == us);
777 assert(color_of_piece_on(to) == them || piece_on(to) == EMPTY);
779 PieceType piece = type_of_piece_on(from);
780 PieceType capture = type_of_piece_on(to);
785 do_capture_move(m, capture, them, to);
789 clear_bit(&(byColorBB[us]), from);
790 clear_bit(&(byTypeBB[piece]), from);
791 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
792 set_bit(&(byColorBB[us]), to);
793 set_bit(&(byTypeBB[piece]), to);
794 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
795 board[to] = board[from];
799 key ^= zobrist[us][piece][from] ^ zobrist[us][piece][to];
801 // Update incremental scores
802 mgValue -= mg_pst(us, piece, from);
803 mgValue += mg_pst(us, piece, to);
804 egValue -= eg_pst(us, piece, from);
805 egValue += eg_pst(us, piece, to);
807 // If the moving piece was a king, update the king square
811 // Reset en passant square
812 if (epSquare != SQ_NONE)
814 key ^= zobEp[epSquare];
818 // If the moving piece was a pawn do some special extra work
821 // Reset rule 50 draw counter
824 // Update pawn hash key
825 pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
827 // Set en passant square, only if moved pawn can be captured
828 if (abs(int(to) - int(from)) == 16)
830 if ( (us == WHITE && (pawn_attacks(WHITE, from + DELTA_N) & pawns(BLACK)))
831 || (us == BLACK && (pawn_attacks(BLACK, from + DELTA_S) & pawns(WHITE))))
833 epSquare = Square((int(from) + int(to)) / 2);
834 key ^= zobEp[epSquare];
839 // Update piece lists
840 pieceList[us][piece][index[from]] = to;
841 index[to] = index[from];
843 // Update castle rights
844 key ^= zobCastle[castleRights];
845 castleRights &= castleRightsMask[from];
846 castleRights &= castleRightsMask[to];
847 key ^= zobCastle[castleRights];
849 // Update checkers bitboard, piece must be already moved
850 checkersBB = EmptyBoardBB;
851 Square ksq = king_square(them);
855 update_checkers<PAWN>(&checkersBB, ksq, from, to, dcCandidates);
859 update_checkers<KNIGHT>(&checkersBB, ksq, from, to, dcCandidates);
863 update_checkers<BISHOP>(&checkersBB, ksq, from, to, dcCandidates);
867 update_checkers<ROOK>(&checkersBB, ksq, from, to, dcCandidates);
871 update_checkers<QUEEN>(&checkersBB, ksq, from, to, dcCandidates);
875 update_checkers<KING>(&checkersBB, ksq, from, to, dcCandidates);
885 key ^= zobSideToMove;
886 sideToMove = opposite_color(sideToMove);
889 mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
890 egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
895 /// Position::do_capture_move() is a private method used to update captured
896 /// piece info. It is called from the main Position::do_move function.
898 void Position::do_capture_move(Move m, PieceType capture, Color them, Square to) {
900 assert(capture != KING);
902 // Remove captured piece
903 clear_bit(&(byColorBB[them]), to);
904 clear_bit(&(byTypeBB[capture]), to);
907 key ^= zobrist[them][capture][to];
909 // If the captured piece was a pawn, update pawn hash key
911 pawnKey ^= zobrist[them][PAWN][to];
913 // Update incremental scores
914 mgValue -= mg_pst(them, capture, to);
915 egValue -= eg_pst(them, capture, to);
917 assert(!move_promotion(m) || capture != PAWN);
921 npMaterial[them] -= piece_value_midgame(capture);
923 // Update material hash key
924 materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];
926 // Update piece count
927 pieceCount[them][capture]--;
930 pieceList[them][capture][index[to]] = pieceList[them][capture][pieceCount[them][capture]];
931 index[pieceList[them][capture][index[to]]] = index[to];
933 // Reset rule 50 counter
938 /// Position::do_castle_move() is a private method used to make a castling
939 /// move. It is called from the main Position::do_move function. Note that
940 /// castling moves are encoded as "king captures friendly rook" moves, for
941 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
943 void Position::do_castle_move(Move m) {
946 assert(move_is_ok(m));
947 assert(move_is_castle(m));
949 Color us = side_to_move();
950 Color them = opposite_color(us);
952 // Find source squares for king and rook
953 Square kfrom = move_from(m);
954 Square rfrom = move_to(m); // HACK: See comment at beginning of function
957 assert(piece_on(kfrom) == king_of_color(us));
958 assert(piece_on(rfrom) == rook_of_color(us));
960 // Find destination squares for king and rook
961 if (rfrom > kfrom) // O-O
963 kto = relative_square(us, SQ_G1);
964 rto = relative_square(us, SQ_F1);
966 kto = relative_square(us, SQ_C1);
967 rto = relative_square(us, SQ_D1);
970 // Remove pieces from source squares
971 clear_bit(&(byColorBB[us]), kfrom);
972 clear_bit(&(byTypeBB[KING]), kfrom);
973 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
974 clear_bit(&(byColorBB[us]), rfrom);
975 clear_bit(&(byTypeBB[ROOK]), rfrom);
976 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
978 // Put pieces on destination squares
979 set_bit(&(byColorBB[us]), kto);
980 set_bit(&(byTypeBB[KING]), kto);
981 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
982 set_bit(&(byColorBB[us]), rto);
983 set_bit(&(byTypeBB[ROOK]), rto);
984 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
986 // Update board array
987 board[kfrom] = board[rfrom] = EMPTY;
988 board[kto] = king_of_color(us);
989 board[rto] = rook_of_color(us);
991 // Update king square
992 kingSquare[us] = kto;
994 // Update piece lists
995 pieceList[us][KING][index[kfrom]] = kto;
996 pieceList[us][ROOK][index[rfrom]] = rto;
997 int tmp = index[rfrom];
998 index[kto] = index[kfrom];
1001 // Update incremental scores
1002 mgValue -= mg_pst(us, KING, kfrom);
1003 mgValue += mg_pst(us, KING, kto);
1004 egValue -= eg_pst(us, KING, kfrom);
1005 egValue += eg_pst(us, KING, kto);
1006 mgValue -= mg_pst(us, ROOK, rfrom);
1007 mgValue += mg_pst(us, ROOK, rto);
1008 egValue -= eg_pst(us, ROOK, rfrom);
1009 egValue += eg_pst(us, ROOK, rto);
1012 key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1013 key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1015 // Clear en passant square
1016 if(epSquare != SQ_NONE)
1018 key ^= zobEp[epSquare];
1022 // Update castling rights
1023 key ^= zobCastle[castleRights];
1024 castleRights &= castleRightsMask[kfrom];
1025 key ^= zobCastle[castleRights];
1027 // Reset rule 50 counter
1030 // Update checkers BB
1031 checkersBB = attacks_to(king_square(them), us);
1035 /// Position::do_promotion_move() is a private method used to make a promotion
1036 /// move. It is called from the main Position::do_move function. The
1037 /// UndoInfo object, which has been initialized in Position::do_move, is
1038 /// used to store the captured piece (if any).
1040 void Position::do_promotion_move(Move m, UndoInfo &u) {
1044 PieceType capture, promotion;
1047 assert(move_is_ok(m));
1048 assert(move_promotion(m));
1050 us = side_to_move();
1051 them = opposite_color(us);
1052 from = move_from(m);
1055 assert(relative_rank(us, to) == RANK_8);
1056 assert(piece_on(from) == pawn_of_color(us));
1057 assert(color_of_piece_on(to) == them || square_is_empty(to));
1059 capture = type_of_piece_on(to);
1063 u.capture = capture;
1064 do_capture_move(m, capture, them, to);
1068 clear_bit(&(byColorBB[us]), from);
1069 clear_bit(&(byTypeBB[PAWN]), from);
1070 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1071 board[from] = EMPTY;
1073 // Insert promoted piece
1074 promotion = move_promotion(m);
1075 assert(promotion >= KNIGHT && promotion <= QUEEN);
1076 set_bit(&(byColorBB[us]), to);
1077 set_bit(&(byTypeBB[promotion]), to);
1078 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1079 board[to] = piece_of_color_and_type(us, promotion);
1082 key ^= zobrist[us][PAWN][from] ^ zobrist[us][promotion][to];
1084 // Update pawn hash key
1085 pawnKey ^= zobrist[us][PAWN][from];
1087 // Update material key
1088 materialKey ^= zobMaterial[us][PAWN][pieceCount[us][PAWN]];
1089 materialKey ^= zobMaterial[us][promotion][pieceCount[us][promotion]+1];
1091 // Update piece counts
1092 pieceCount[us][PAWN]--;
1093 pieceCount[us][promotion]++;
1095 // Update piece lists
1096 pieceList[us][PAWN][index[from]] = pieceList[us][PAWN][pieceCount[us][PAWN]];
1097 index[pieceList[us][PAWN][index[from]]] = index[from];
1098 pieceList[us][promotion][pieceCount[us][promotion] - 1] = to;
1099 index[to] = pieceCount[us][promotion] - 1;
1101 // Update incremental scores
1102 mgValue -= mg_pst(us, PAWN, from);
1103 mgValue += mg_pst(us, promotion, to);
1104 egValue -= eg_pst(us, PAWN, from);
1105 egValue += eg_pst(us, promotion, to);
1108 npMaterial[us] += piece_value_midgame(promotion);
1110 // Clear the en passant square
1111 if (epSquare != SQ_NONE)
1113 key ^= zobEp[epSquare];
1117 // Update castle rights
1118 key ^= zobCastle[castleRights];
1119 castleRights &= castleRightsMask[to];
1120 key ^= zobCastle[castleRights];
1122 // Reset rule 50 counter
1125 // Update checkers BB
1126 checkersBB = attacks_to(king_square(them), us);
1130 /// Position::do_ep_move() is a private method used to make an en passant
1131 /// capture. It is called from the main Position::do_move function. Because
1132 /// the captured piece is always a pawn, we don't need to pass an UndoInfo
1133 /// object in which to store the captured piece.
1135 void Position::do_ep_move(Move m) {
1138 Square from, to, capsq;
1141 assert(move_is_ok(m));
1142 assert(move_is_ep(m));
1144 us = side_to_move();
1145 them = opposite_color(us);
1146 from = move_from(m);
1148 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1150 assert(to == epSquare);
1151 assert(relative_rank(us, to) == RANK_6);
1152 assert(piece_on(to) == EMPTY);
1153 assert(piece_on(from) == pawn_of_color(us));
1154 assert(piece_on(capsq) == pawn_of_color(them));
1156 // Remove captured piece
1157 clear_bit(&(byColorBB[them]), capsq);
1158 clear_bit(&(byTypeBB[PAWN]), capsq);
1159 clear_bit(&(byTypeBB[0]), capsq); // HACK: byTypeBB[0] == occupied squares
1160 board[capsq] = EMPTY;
1162 // Remove moving piece from source square
1163 clear_bit(&(byColorBB[us]), from);
1164 clear_bit(&(byTypeBB[PAWN]), from);
1165 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1167 // Put moving piece on destination square
1168 set_bit(&(byColorBB[us]), to);
1169 set_bit(&(byTypeBB[PAWN]), to);
1170 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1171 board[to] = board[from];
1172 board[from] = EMPTY;
1174 // Update material hash key
1175 materialKey ^= zobMaterial[them][PAWN][pieceCount[them][PAWN]];
1177 // Update piece count
1178 pieceCount[them][PAWN]--;
1180 // Update piece list
1181 pieceList[us][PAWN][index[from]] = to;
1182 index[to] = index[from];
1183 pieceList[them][PAWN][index[capsq]] = pieceList[them][PAWN][pieceCount[them][PAWN]];
1184 index[pieceList[them][PAWN][index[capsq]]] = index[capsq];
1187 key ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1188 key ^= zobrist[them][PAWN][capsq];
1189 key ^= zobEp[epSquare];
1191 // Update pawn hash key
1192 pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1193 pawnKey ^= zobrist[them][PAWN][capsq];
1195 // Update incremental scores
1196 mgValue -= mg_pst(them, PAWN, capsq);
1197 mgValue -= mg_pst(us, PAWN, from);
1198 mgValue += mg_pst(us, PAWN, to);
1199 egValue -= eg_pst(them, PAWN, capsq);
1200 egValue -= eg_pst(us, PAWN, from);
1201 egValue += eg_pst(us, PAWN, to);
1203 // Reset en passant square
1206 // Reset rule 50 counter
1209 // Update checkers BB
1210 checkersBB = attacks_to(king_square(them), us);
1214 /// Position::undo_move() unmakes a move. When it returns, the position should
1215 /// be restored to exactly the same state as before the move was made. It is
1216 /// important that Position::undo_move is called with the same move and UndoInfo
1217 /// object as the earlier call to Position::do_move.
1219 void Position::undo_move(Move m, const UndoInfo &u) {
1222 assert(move_is_ok(m));
1225 sideToMove = opposite_color(sideToMove);
1227 // Restore information from our UndoInfo object (except the captured piece,
1228 // which is taken care of later)
1231 if (move_is_castle(m))
1232 undo_castle_move(m);
1233 else if (move_promotion(m))
1234 undo_promotion_move(m, u);
1235 else if (move_is_ep(m))
1241 PieceType piece, capture;
1243 us = side_to_move();
1244 them = opposite_color(us);
1245 from = move_from(m);
1248 assert(piece_on(from) == EMPTY);
1249 assert(color_of_piece_on(to) == us);
1251 // Put the piece back at the source square
1252 piece = type_of_piece_on(to);
1253 set_bit(&(byColorBB[us]), from);
1254 set_bit(&(byTypeBB[piece]), from);
1255 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1256 board[from] = piece_of_color_and_type(us, piece);
1258 // Clear the destination square
1259 clear_bit(&(byColorBB[us]), to);
1260 clear_bit(&(byTypeBB[piece]), to);
1261 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1263 // If the moving piece was a king, update the king square
1265 kingSquare[us] = from;
1267 // Update piece list
1268 pieceList[us][piece][index[to]] = from;
1269 index[from] = index[to];
1271 capture = u.capture;
1275 assert(capture != KING);
1277 // Replace the captured piece
1278 set_bit(&(byColorBB[them]), to);
1279 set_bit(&(byTypeBB[capture]), to);
1280 set_bit(&(byTypeBB[0]), to);
1281 board[to] = piece_of_color_and_type(them, capture);
1284 if (capture != PAWN)
1285 npMaterial[them] += piece_value_midgame(capture);
1287 // Update piece list
1288 pieceList[them][capture][pieceCount[them][capture]] = to;
1289 index[to] = pieceCount[them][capture];
1291 // Update piece count
1292 pieceCount[them][capture]++;
1301 /// Position::undo_castle_move() is a private method used to unmake a castling
1302 /// move. It is called from the main Position::undo_move function. Note that
1303 /// castling moves are encoded as "king captures friendly rook" moves, for
1304 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1306 void Position::undo_castle_move(Move m) {
1308 assert(move_is_ok(m));
1309 assert(move_is_castle(m));
1311 // When we have arrived here, some work has already been done by
1312 // Position::undo_move. In particular, the side to move has been switched,
1313 // so the code below is correct.
1314 Color us = side_to_move();
1316 // Find source squares for king and rook
1317 Square kfrom = move_from(m);
1318 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1321 // Find destination squares for king and rook
1322 if (rfrom > kfrom) // O-O
1324 kto = relative_square(us, SQ_G1);
1325 rto = relative_square(us, SQ_F1);
1327 kto = relative_square(us, SQ_C1);
1328 rto = relative_square(us, SQ_D1);
1331 assert(piece_on(kto) == king_of_color(us));
1332 assert(piece_on(rto) == rook_of_color(us));
1334 // Remove pieces from destination squares
1335 clear_bit(&(byColorBB[us]), kto);
1336 clear_bit(&(byTypeBB[KING]), kto);
1337 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1338 clear_bit(&(byColorBB[us]), rto);
1339 clear_bit(&(byTypeBB[ROOK]), rto);
1340 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1342 // Put pieces on source squares
1343 set_bit(&(byColorBB[us]), kfrom);
1344 set_bit(&(byTypeBB[KING]), kfrom);
1345 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1346 set_bit(&(byColorBB[us]), rfrom);
1347 set_bit(&(byTypeBB[ROOK]), rfrom);
1348 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1351 board[rto] = board[kto] = EMPTY;
1352 board[rfrom] = rook_of_color(us);
1353 board[kfrom] = king_of_color(us);
1355 // Update king square
1356 kingSquare[us] = kfrom;
1358 // Update piece lists
1359 pieceList[us][KING][index[kto]] = kfrom;
1360 pieceList[us][ROOK][index[rto]] = rfrom;
1361 int tmp = index[rto]; // Necessary because we may have rto == kfrom in FRC.
1362 index[kfrom] = index[kto];
1367 /// Position::undo_promotion_move() is a private method used to unmake a
1368 /// promotion move. It is called from the main Position::do_move
1369 /// function. The UndoInfo object, which has been initialized in
1370 /// Position::do_move, is used to put back the captured piece (if any).
1372 void Position::undo_promotion_move(Move m, const UndoInfo &u) {
1376 PieceType capture, promotion;
1378 assert(move_is_ok(m));
1379 assert(move_promotion(m));
1381 // When we have arrived here, some work has already been done by
1382 // Position::undo_move. In particular, the side to move has been switched,
1383 // so the code below is correct.
1384 us = side_to_move();
1385 them = opposite_color(us);
1386 from = move_from(m);
1389 assert(relative_rank(us, to) == RANK_8);
1390 assert(piece_on(from) == EMPTY);
1392 // Remove promoted piece
1393 promotion = move_promotion(m);
1394 assert(piece_on(to)==piece_of_color_and_type(us, promotion));
1395 assert(promotion >= KNIGHT && promotion <= QUEEN);
1396 clear_bit(&(byColorBB[us]), to);
1397 clear_bit(&(byTypeBB[promotion]), to);
1398 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1400 // Insert pawn at source square
1401 set_bit(&(byColorBB[us]), from);
1402 set_bit(&(byTypeBB[PAWN]), from);
1403 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1404 board[from] = pawn_of_color(us);
1407 npMaterial[us] -= piece_value_midgame(promotion);
1409 // Update piece list
1410 pieceList[us][PAWN][pieceCount[us][PAWN]] = from;
1411 index[from] = pieceCount[us][PAWN];
1412 pieceList[us][promotion][index[to]] =
1413 pieceList[us][promotion][pieceCount[us][promotion] - 1];
1414 index[pieceList[us][promotion][index[to]]] = index[to];
1416 // Update piece counts
1417 pieceCount[us][promotion]--;
1418 pieceCount[us][PAWN]++;
1420 capture = u.capture;
1424 assert(capture != KING);
1426 // Insert captured piece:
1427 set_bit(&(byColorBB[them]), to);
1428 set_bit(&(byTypeBB[capture]), to);
1429 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1430 board[to] = piece_of_color_and_type(them, capture);
1432 // Update material. Because the move is a promotion move, we know
1433 // that the captured piece cannot be a pawn.
1434 assert(capture != PAWN);
1435 npMaterial[them] += piece_value_midgame(capture);
1437 // Update piece list
1438 pieceList[them][capture][pieceCount[them][capture]] = to;
1439 index[to] = pieceCount[them][capture];
1441 // Update piece count
1442 pieceCount[them][capture]++;
1448 /// Position::undo_ep_move() is a private method used to unmake an en passant
1449 /// capture. It is called from the main Position::undo_move function. Because
1450 /// the captured piece is always a pawn, we don't need to pass an UndoInfo
1451 /// object from which to retrieve the captured piece.
1453 void Position::undo_ep_move(Move m) {
1455 assert(move_is_ok(m));
1456 assert(move_is_ep(m));
1458 // When we have arrived here, some work has already been done by
1459 // Position::undo_move. In particular, the side to move has been switched,
1460 // so the code below is correct.
1461 Color us = side_to_move();
1462 Color them = opposite_color(us);
1463 Square from = move_from(m);
1464 Square to = move_to(m);
1465 Square capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1467 assert(to == ep_square());
1468 assert(relative_rank(us, to) == RANK_6);
1469 assert(piece_on(to) == pawn_of_color(us));
1470 assert(piece_on(from) == EMPTY);
1471 assert(piece_on(capsq) == EMPTY);
1473 // Replace captured piece
1474 set_bit(&(byColorBB[them]), capsq);
1475 set_bit(&(byTypeBB[PAWN]), capsq);
1476 set_bit(&(byTypeBB[0]), capsq);
1477 board[capsq] = pawn_of_color(them);
1479 // Remove moving piece from destination square
1480 clear_bit(&(byColorBB[us]), to);
1481 clear_bit(&(byTypeBB[PAWN]), to);
1482 clear_bit(&(byTypeBB[0]), to);
1485 // Replace moving piece at source square
1486 set_bit(&(byColorBB[us]), from);
1487 set_bit(&(byTypeBB[PAWN]), from);
1488 set_bit(&(byTypeBB[0]), from);
1489 board[from] = pawn_of_color(us);
1491 // Update piece list:
1492 pieceList[us][PAWN][index[to]] = from;
1493 index[from] = index[to];
1494 pieceList[them][PAWN][pieceCount[them][PAWN]] = capsq;
1495 index[capsq] = pieceCount[them][PAWN];
1497 // Update piece count:
1498 pieceCount[them][PAWN]++;
1502 /// Position::do_null_move makes() a "null move": It switches the side to move
1503 /// and updates the hash key without executing any move on the board.
1505 void Position::do_null_move(UndoInfo &u) {
1508 assert(!is_check());
1510 // Back up the information necessary to undo the null move to the supplied
1511 // UndoInfo object. In the case of a null move, the only thing we need to
1512 // remember is the last move made and the en passant square.
1513 u.lastMove = lastMove;
1514 u.epSquare = epSquare;
1516 // Save the current key to the history[] array, in order to be able to
1517 // detect repetition draws.
1518 history[gamePly] = key;
1520 // Update the necessary information
1521 sideToMove = opposite_color(sideToMove);
1522 if (epSquare != SQ_NONE)
1523 key ^= zobEp[epSquare];
1528 key ^= zobSideToMove;
1530 mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1531 egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1537 /// Position::undo_null_move() unmakes a "null move".
1539 void Position::undo_null_move(const UndoInfo &u) {
1542 assert(!is_check());
1544 // Restore information from the supplied UndoInfo object:
1545 lastMove = u.lastMove;
1546 epSquare = u.epSquare;
1547 if (epSquare != SQ_NONE)
1548 key ^= zobEp[epSquare];
1550 // Update the necessary information.
1551 sideToMove = opposite_color(sideToMove);
1554 key ^= zobSideToMove;
1556 mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1557 egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1563 /// Position::see() is a static exchange evaluator: It tries to estimate the
1564 /// material gain or loss resulting from a move. There are three versions of
1565 /// this function: One which takes a destination square as input, one takes a
1566 /// move, and one which takes a 'from' and a 'to' square. The function does
1567 /// not yet understand promotions or en passant captures.
1569 int Position::see(Square to) const {
1571 assert(square_is_ok(to));
1572 return see(SQ_NONE, to);
1575 int Position::see(Move m) const {
1577 assert(move_is_ok(m));
1578 return see(move_from(m), move_to(m));
1581 int Position::see(Square from, Square to) const {
1584 static const int seeValues[18] = {
1585 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1586 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1587 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1588 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1592 Bitboard attackers, occ, b;
1594 assert(square_is_ok(from) || from == SQ_NONE);
1595 assert(square_is_ok(to));
1597 // Initialize colors
1598 Color us = (from != SQ_NONE ? color_of_piece_on(from) : opposite_color(color_of_piece_on(to)));
1599 Color them = opposite_color(us);
1601 // Initialize pieces
1602 Piece piece = piece_on(from);
1603 Piece capture = piece_on(to);
1605 // Find all attackers to the destination square, with the moving piece
1606 // removed, but possibly an X-ray attacker added behind it.
1607 occ = occupied_squares();
1609 // Handle enpassant moves
1610 if (ep_square() == to && type_of_piece_on(from) == PAWN)
1612 assert(capture == EMPTY);
1614 Square capQq = (side_to_move() == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1615 capture = piece_on(capQq);
1617 assert(type_of_piece_on(capQq) == PAWN);
1619 // Remove the captured pawn
1620 clear_bit(&occ, capQq);
1625 clear_bit(&occ, from);
1626 attackers = (rook_attacks_bb(to, occ) & rooks_and_queens())
1627 | (bishop_attacks_bb(to, occ) & bishops_and_queens())
1628 | (piece_attacks<KNIGHT>(to) & knights())
1629 | (piece_attacks<KING>(to) & kings())
1630 | (pawn_attacks(WHITE, to) & pawns(BLACK))
1631 | (pawn_attacks(BLACK, to) & pawns(WHITE));
1633 if (from != SQ_NONE)
1636 // If we don't have any attacker we are finished
1637 if ((attackers & pieces_of_color(us)) == EmptyBoardBB)
1640 // Locate the least valuable attacker to the destination square
1641 // and use it to initialize from square.
1643 for (pt = PAWN; !(attackers & pieces_of_color_and_type(us, pt)); pt++)
1646 from = first_1(attackers & pieces_of_color_and_type(us, pt));
1647 piece = piece_on(from);
1650 // If the opponent has no attackers we are finished
1651 if ((attackers & pieces_of_color(them)) == EmptyBoardBB)
1652 return seeValues[capture];
1654 attackers &= occ; // Remove the moving piece
1656 // The destination square is defended, which makes things rather more
1657 // difficult to compute. We proceed by building up a "swap list" containing
1658 // the material gain or loss at each stop in a sequence of captures to the
1659 // destination square, where the sides alternately capture, and always
1660 // capture with the least valuable piece. After each capture, we look for
1661 // new X-ray attacks from behind the capturing piece.
1662 int lastCapturingPieceValue = seeValues[piece];
1663 int swapList[32], n = 1;
1667 swapList[0] = seeValues[capture];
1670 // Locate the least valuable attacker for the side to move. The loop
1671 // below looks like it is potentially infinite, but it isn't. We know
1672 // that the side to move still has at least one attacker left.
1673 for (pt = PAWN; !(attackers & pieces_of_color_and_type(c, pt)); pt++)
1676 // Remove the attacker we just found from the 'attackers' bitboard,
1677 // and scan for new X-ray attacks behind the attacker.
1678 b = attackers & pieces_of_color_and_type(c, pt);
1680 attackers |= (rook_attacks_bb(to, occ) & rooks_and_queens())
1681 | (bishop_attacks_bb(to, occ) & bishops_and_queens());
1685 // Add the new entry to the swap list
1687 swapList[n] = -swapList[n - 1] + lastCapturingPieceValue;
1690 // Remember the value of the capturing piece, and change the side to move
1691 // before beginning the next iteration
1692 lastCapturingPieceValue = seeValues[pt];
1693 c = opposite_color(c);
1695 // Stop after a king capture
1696 if (pt == KING && (attackers & pieces_of_color(c)))
1699 swapList[n++] = 100;
1702 } while (attackers & pieces_of_color(c));
1704 // Having built the swap list, we negamax through it to find the best
1705 // achievable score from the point of view of the side to move
1707 swapList[n-1] = Min(-swapList[n], swapList[n-1]);
1713 /// Position::clear() erases the position object to a pristine state, with an
1714 /// empty board, white to move, and no castling rights.
1716 void Position::clear() {
1718 for (int i = 0; i < 64; i++)
1724 for (int i = 0; i < 2; i++)
1725 byColorBB[i] = EmptyBoardBB;
1727 for (int i = 0; i < 7; i++)
1729 byTypeBB[i] = EmptyBoardBB;
1730 pieceCount[0][i] = pieceCount[1][i] = 0;
1731 for (int j = 0; j < 8; j++)
1732 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1735 checkersBB = EmptyBoardBB;
1737 lastMove = MOVE_NONE;
1740 castleRights = NO_CASTLES;
1741 initialKFile = FILE_E;
1742 initialKRFile = FILE_H;
1743 initialQRFile = FILE_A;
1750 /// Position::reset_game_ply() simply sets gamePly to 0. It is used from the
1751 /// UCI interface code, whenever a non-reversible move is made in a
1752 /// 'position fen <fen> moves m1 m2 ...' command. This makes it possible
1753 /// for the program to handle games of arbitrary length, as long as the GUI
1754 /// handles draws by the 50 move rule correctly.
1756 void Position::reset_game_ply() {
1762 /// Position::put_piece() puts a piece on the given square of the board,
1763 /// updating the board array, bitboards, and piece counts.
1765 void Position::put_piece(Piece p, Square s) {
1767 Color c = color_of_piece(p);
1768 PieceType pt = type_of_piece(p);
1771 index[s] = pieceCount[c][pt];
1772 pieceList[c][pt][index[s]] = s;
1774 set_bit(&(byTypeBB[pt]), s);
1775 set_bit(&(byColorBB[c]), s);
1776 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1778 pieceCount[c][pt]++;
1785 /// Position::allow_oo() gives the given side the right to castle kingside.
1786 /// Used when setting castling rights during parsing of FEN strings.
1788 void Position::allow_oo(Color c) {
1790 castleRights |= (1 + int(c));
1794 /// Position::allow_ooo() gives the given side the right to castle queenside.
1795 /// Used when setting castling rights during parsing of FEN strings.
1797 void Position::allow_ooo(Color c) {
1799 castleRights |= (4 + 4*int(c));
1803 /// Position::compute_key() computes the hash key of the position. The hash
1804 /// key is usually updated incrementally as moves are made and unmade, the
1805 /// compute_key() function is only used when a new position is set up, and
1806 /// to verify the correctness of the hash key when running in debug mode.
1808 Key Position::compute_key() const {
1810 Key result = Key(0ULL);
1812 for (Square s = SQ_A1; s <= SQ_H8; s++)
1813 if (square_is_occupied(s))
1814 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1816 if (ep_square() != SQ_NONE)
1817 result ^= zobEp[ep_square()];
1819 result ^= zobCastle[castleRights];
1820 if (side_to_move() == BLACK)
1821 result ^= zobSideToMove;
1827 /// Position::compute_pawn_key() computes the hash key of the position. The
1828 /// hash key is usually updated incrementally as moves are made and unmade,
1829 /// the compute_pawn_key() function is only used when a new position is set
1830 /// up, and to verify the correctness of the pawn hash key when running in
1833 Key Position::compute_pawn_key() const {
1835 Key result = Key(0ULL);
1839 for (Color c = WHITE; c <= BLACK; c++)
1844 s = pop_1st_bit(&b);
1845 result ^= zobrist[c][PAWN][s];
1852 /// Position::compute_material_key() computes the hash key of the position.
1853 /// The hash key is usually updated incrementally as moves are made and unmade,
1854 /// the compute_material_key() function is only used when a new position is set
1855 /// up, and to verify the correctness of the material hash key when running in
1858 Key Position::compute_material_key() const {
1860 Key result = Key(0ULL);
1861 for (Color c = WHITE; c <= BLACK; c++)
1862 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1864 int count = piece_count(c, pt);
1865 for (int i = 0; i <= count; i++)
1866 result ^= zobMaterial[c][pt][i];
1872 /// Position::compute_mg_value() and Position::compute_eg_value() compute the
1873 /// incremental scores for the middle game and the endgame. These functions
1874 /// are used to initialize the incremental scores when a new position is set
1875 /// up, and to verify that the scores are correctly updated by do_move
1876 /// and undo_move when the program is running in debug mode.
1878 Value Position::compute_mg_value() const {
1880 Value result = Value(0);
1884 for (Color c = WHITE; c <= BLACK; c++)
1885 for (PieceType pt = PAWN; pt <= KING; pt++)
1887 b = pieces_of_color_and_type(c, pt);
1890 s = pop_1st_bit(&b);
1891 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1892 result += mg_pst(c, pt, s);
1895 result += (side_to_move() == WHITE)? TempoValueMidgame / 2 : -TempoValueMidgame / 2;
1899 Value Position::compute_eg_value() const {
1901 Value result = Value(0);
1905 for (Color c = WHITE; c <= BLACK; c++)
1906 for (PieceType pt = PAWN; pt <= KING; pt++)
1908 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 += eg_pst(c, pt, s);
1916 result += (side_to_move() == WHITE)? TempoValueEndgame / 2 : -TempoValueEndgame / 2;
1921 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1922 /// game material score for the given side. Material scores are updated
1923 /// incrementally during the search, this function is only used while
1924 /// initializing a new Position object.
1926 Value Position::compute_non_pawn_material(Color c) const {
1928 Value result = Value(0);
1931 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1933 Bitboard b = pieces_of_color_and_type(c, pt);
1936 s = pop_1st_bit(&b);
1937 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1938 result += piece_value_midgame(pt);
1945 /// Position::is_mate() returns true or false depending on whether the
1946 /// side to move is checkmated. Note that this function is currently very
1947 /// slow, and shouldn't be used frequently inside the search.
1949 bool Position::is_mate() const {
1953 MovePicker mp = MovePicker(*this, false, MOVE_NONE, EmptySearchStack, Depth(0));
1954 return mp.get_next_move() == MOVE_NONE;
1960 /// Position::is_draw() tests whether the position is drawn by material,
1961 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1962 /// must be done by the search.
1964 bool Position::is_draw() const {
1966 // Draw by material?
1968 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1971 // Draw by the 50 moves rule?
1972 if (rule50 > 100 || (rule50 == 100 && !is_check()))
1975 // Draw by repetition?
1976 for (int i = 2; i < Min(gamePly, rule50); i += 2)
1977 if (history[gamePly - i] == key)
1984 /// Position::has_mate_threat() tests whether a given color has a mate in one
1985 /// from the current position. This function is quite slow, but it doesn't
1986 /// matter, because it is currently only called from PV nodes, which are rare.
1988 bool Position::has_mate_threat(Color c) {
1991 Color stm = side_to_move();
1993 // The following lines are useless and silly, but prevents gcc from
1994 // emitting a stupid warning stating that u1.lastMove and u1.epSquare might
1995 // be used uninitialized.
1996 u1.lastMove = lastMove;
1997 u1.epSquare = epSquare;
2002 // If the input color is not equal to the side to move, do a null move
2006 MoveStack mlist[120];
2008 bool result = false;
2010 // Generate legal moves
2011 count = generate_legal_moves(*this, mlist);
2013 // Loop through the moves, and see if one of them is mate
2014 for (int i = 0; i < count; i++)
2016 do_move(mlist[i].move, u2);
2020 undo_move(mlist[i].move, u2);
2023 // Undo null move, if necessary
2031 /// Position::init_zobrist() is a static member function which initializes the
2032 /// various arrays used to compute hash keys.
2034 void Position::init_zobrist() {
2036 for (int i = 0; i < 2; i++)
2037 for (int j = 0; j < 8; j++)
2038 for (int k = 0; k < 64; k++)
2039 zobrist[i][j][k] = Key(genrand_int64());
2041 for (int i = 0; i < 64; i++)
2042 zobEp[i] = Key(genrand_int64());
2044 for (int i = 0; i < 16; i++)
2045 zobCastle[i] = genrand_int64();
2047 zobSideToMove = genrand_int64();
2049 for (int i = 0; i < 2; i++)
2050 for (int j = 0; j < 8; j++)
2051 for (int k = 0; k < 16; k++)
2052 zobMaterial[i][j][k] = (k > 0)? Key(genrand_int64()) : Key(0LL);
2054 for (int i = 0; i < 16; i++)
2055 zobMaterial[0][KING][i] = zobMaterial[1][KING][i] = Key(0ULL);
2059 /// Position::init_piece_square_tables() initializes the piece square tables.
2060 /// This is a two-step operation: First, the white halves of the tables are
2061 /// copied from the MgPST[][] and EgPST[][] arrays, with a small random number
2062 /// added to each entry if the "Randomness" UCI parameter is non-zero.
2063 /// Second, the black halves of the tables are initialized by mirroring
2064 /// and changing the sign of the corresponding white scores.
2066 void Position::init_piece_square_tables() {
2068 int r = get_option_value_int("Randomness"), i;
2069 for (Square s = SQ_A1; s <= SQ_H8; s++)
2070 for (Piece p = WP; p <= WK; p++)
2072 i = (r == 0)? 0 : (genrand_int32() % (r*2) - r);
2073 MgPieceSquareTable[p][s] = Value(MgPST[p][s] + i);
2074 EgPieceSquareTable[p][s] = Value(EgPST[p][s] + i);
2077 for (Square s = SQ_A1; s <= SQ_H8; s++)
2078 for (Piece p = BP; p <= BK; p++)
2080 MgPieceSquareTable[p][s] = -MgPieceSquareTable[p-8][flip_square(s)];
2081 EgPieceSquareTable[p][s] = -EgPieceSquareTable[p-8][flip_square(s)];
2086 /// Position::flipped_copy() makes a copy of the input position, but with
2087 /// the white and black sides reversed. This is only useful for debugging,
2088 /// especially for finding evaluation symmetry bugs.
2090 void Position::flipped_copy(const Position &pos) {
2092 assert(pos.is_ok());
2097 for (Square s = SQ_A1; s <= SQ_H8; s++)
2098 if (!pos.square_is_empty(s))
2099 put_piece(Piece(int(pos.piece_on(s)) ^ 8), flip_square(s));
2102 sideToMove = opposite_color(pos.side_to_move());
2105 if (pos.can_castle_kingside(WHITE)) allow_oo(BLACK);
2106 if (pos.can_castle_queenside(WHITE)) allow_ooo(BLACK);
2107 if (pos.can_castle_kingside(BLACK)) allow_oo(WHITE);
2108 if (pos.can_castle_queenside(BLACK)) allow_ooo(WHITE);
2110 initialKFile = pos.initialKFile;
2111 initialKRFile = pos.initialKRFile;
2112 initialQRFile = pos.initialQRFile;
2114 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
2115 castleRightsMask[sq] = ALL_CASTLES;
2117 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
2118 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
2119 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
2120 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
2121 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
2122 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
2124 // En passant square
2125 if (pos.epSquare != SQ_NONE)
2126 epSquare = flip_square(pos.epSquare);
2132 key = compute_key();
2133 pawnKey = compute_pawn_key();
2134 materialKey = compute_material_key();
2136 // Incremental scores
2137 mgValue = compute_mg_value();
2138 egValue = compute_eg_value();
2141 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
2142 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
2148 /// Position::is_ok() performs some consitency checks for the position object.
2149 /// This is meant to be helpful when debugging.
2151 bool Position::is_ok(int* failedStep) const {
2153 // What features of the position should be verified?
2154 static const bool debugBitboards = false;
2155 static const bool debugKingCount = false;
2156 static const bool debugKingCapture = false;
2157 static const bool debugCheckerCount = false;
2158 static const bool debugKey = false;
2159 static const bool debugMaterialKey = false;
2160 static const bool debugPawnKey = false;
2161 static const bool debugIncrementalEval = false;
2162 static const bool debugNonPawnMaterial = false;
2163 static const bool debugPieceCounts = false;
2164 static const bool debugPieceList = false;
2166 if (failedStep) *failedStep = 1;
2169 if (!color_is_ok(side_to_move()))
2172 // Are the king squares in the position correct?
2173 if (failedStep) (*failedStep)++;
2174 if (piece_on(king_square(WHITE)) != WK)
2177 if (failedStep) (*failedStep)++;
2178 if (piece_on(king_square(BLACK)) != BK)
2182 if (failedStep) (*failedStep)++;
2183 if (!file_is_ok(initialKRFile))
2186 if (!file_is_ok(initialQRFile))
2189 // Do both sides have exactly one king?
2190 if (failedStep) (*failedStep)++;
2193 int kingCount[2] = {0, 0};
2194 for (Square s = SQ_A1; s <= SQ_H8; s++)
2195 if (type_of_piece_on(s) == KING)
2196 kingCount[color_of_piece_on(s)]++;
2198 if(kingCount[0] != 1 || kingCount[1] != 1)
2202 // Can the side to move capture the opponent's king?
2203 if (failedStep) (*failedStep)++;
2204 if (debugKingCapture)
2206 Color us = side_to_move();
2207 Color them = opposite_color(us);
2208 Square ksq = king_square(them);
2209 if (square_is_attacked(ksq, us))
2213 // Is there more than 2 checkers?
2214 if (failedStep) (*failedStep)++;
2215 if (debugCheckerCount && count_1s(checkersBB) > 2)
2219 if (failedStep) (*failedStep)++;
2222 // The intersection of the white and black pieces must be empty
2223 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
2226 // The union of the white and black pieces must be equal to all
2228 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
2231 // Separate piece type bitboards must have empty intersections
2232 for (PieceType p1 = PAWN; p1 <= KING; p1++)
2233 for (PieceType p2 = PAWN; p2 <= KING; p2++)
2234 if (p1 != p2 && (pieces_of_type(p1) & pieces_of_type(p2)))
2238 // En passant square OK?
2239 if (failedStep) (*failedStep)++;
2240 if (ep_square() != SQ_NONE)
2242 // The en passant square must be on rank 6, from the point of view of the
2244 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
2249 if (failedStep) (*failedStep)++;
2250 if (debugKey && key != compute_key())
2253 // Pawn hash key OK?
2254 if (failedStep) (*failedStep)++;
2255 if (debugPawnKey && pawnKey != compute_pawn_key())
2258 // Material hash key OK?
2259 if (failedStep) (*failedStep)++;
2260 if (debugMaterialKey && materialKey != compute_material_key())
2263 // Incremental eval OK?
2264 if (failedStep) (*failedStep)++;
2265 if (debugIncrementalEval)
2267 if (mgValue != compute_mg_value())
2270 if (egValue != compute_eg_value())
2274 // Non-pawn material OK?
2275 if (failedStep) (*failedStep)++;
2276 if (debugNonPawnMaterial)
2278 if(npMaterial[WHITE] != compute_non_pawn_material(WHITE))
2281 if(npMaterial[BLACK] != compute_non_pawn_material(BLACK))
2286 if (failedStep) (*failedStep)++;
2287 if (debugPieceCounts)
2288 for (Color c = WHITE; c <= BLACK; c++)
2289 for (PieceType pt = PAWN; pt <= KING; pt++)
2290 if (pieceCount[c][pt] != count_1s(pieces_of_color_and_type(c, pt)))
2293 if (failedStep) (*failedStep)++;
2296 for(Color c = WHITE; c <= BLACK; c++)
2297 for(PieceType pt = PAWN; pt <= KING; pt++)
2298 for(int i = 0; i < pieceCount[c][pt]; i++)
2300 if (piece_on(piece_list(c, pt, i)) != piece_of_color_and_type(c, pt))
2303 if (index[piece_list(c, pt, i)] != i)
2307 if (failedStep) *failedStep = 0;