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])) {
136 else if(fen[i] == 'K') allow_oo(WHITE);
137 else if(fen[i] == 'Q') allow_ooo(WHITE);
138 else if(fen[i] == 'k') allow_oo(BLACK);
139 else if(fen[i] == 'q') allow_ooo(BLACK);
140 else if(fen[i] >= 'A' && fen[i] <= 'H') {
141 File rookFile, kingFile = FILE_NONE;
142 for(Square square = SQ_B1; square <= SQ_G1; square++)
143 if(piece_on(square) == WK)
144 kingFile = square_file(square);
145 if(kingFile == FILE_NONE) {
146 std::cout << "Error in FEN at character " << i << std::endl;
149 initialKFile = kingFile;
150 rookFile = File(fen[i] - 'A') + FILE_A;
151 if(rookFile < initialKFile) {
153 initialQRFile = rookFile;
157 initialKRFile = rookFile;
160 else if(fen[i] >= 'a' && fen[i] <= 'h') {
161 File rookFile, kingFile = FILE_NONE;
162 for(Square square = SQ_B8; square <= SQ_G8; square++)
163 if(piece_on(square) == BK)
164 kingFile = square_file(square);
165 if(kingFile == FILE_NONE) {
166 std::cout << "Error in FEN at character " << i << std::endl;
169 initialKFile = kingFile;
170 rookFile = File(fen[i] - 'a') + FILE_A;
171 if(rookFile < initialKFile) {
173 initialQRFile = rookFile;
177 initialKRFile = rookFile;
181 std::cout << "Error in FEN at character " << i << std::endl;
188 while (fen[i] == ' ')
192 if ( i < fen.length() - 2
193 && (fen[i] >= 'a' && fen[i] <= 'h')
194 && (fen[i+1] == '3' || fen[i+1] == '6'))
195 epSquare = square_from_string(fen.substr(i, 2));
197 // Various initialisation
198 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
199 castleRightsMask[sq] = ALL_CASTLES;
201 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO|WHITE_OOO);
202 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO|BLACK_OOO);
203 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
204 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
205 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
206 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
211 pawnKey = compute_pawn_key();
212 materialKey = compute_material_key();
213 mgValue = compute_mg_value();
214 egValue = compute_eg_value();
215 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
216 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
220 /// Position::to_fen() converts the position object to a FEN string. This is
221 /// probably only useful for debugging.
223 const std::string Position::to_fen() const {
225 static const std::string pieceLetters = " PNBRQK pnbrqk";
229 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
232 for (File file = FILE_A; file <= FILE_H; file++)
234 Square sq = make_square(file, rank);
235 if (!square_is_occupied(sq))
241 fen += (char)skip + '0';
244 fen += pieceLetters[piece_on(sq)];
247 fen += (char)skip + '0';
249 fen += (rank > RANK_1 ? '/' : ' ');
251 fen += (sideToMove == WHITE ? "w " : "b ");
252 if (castleRights != NO_CASTLES)
254 if (can_castle_kingside(WHITE)) fen += 'K';
255 if (can_castle_queenside(WHITE)) fen += 'Q';
256 if (can_castle_kingside(BLACK)) fen += 'k';
257 if (can_castle_queenside(BLACK)) fen += 'q';
262 if (ep_square() != SQ_NONE)
263 fen += square_to_string(ep_square());
271 /// Position::print() prints an ASCII representation of the position to
272 /// the standard output. If a move is given then also the san is print.
274 void Position::print(Move m) const {
276 static const std::string pieceLetters = " PNBRQK PNBRQK .";
278 // Check for reentrancy, as example when called from inside
279 // MovePicker that is used also here in move_to_san()
283 RequestPending = true;
285 std::cout << std::endl;
288 std::string col = (color_of_piece_on(move_from(m)) == BLACK ? ".." : "");
289 std::cout << "Move is: " << col << move_to_san(*this, m) << std::endl;
291 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
293 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl;
294 for (File file = FILE_A; file <= FILE_H; file++)
296 Square sq = make_square(file, rank);
297 Piece piece = piece_on(sq);
298 if (piece == EMPTY && square_color(sq) == WHITE)
301 char col = (color_of_piece_on(sq) == BLACK ? '=' : ' ');
302 std::cout << '|' << col << pieceLetters[piece] << col;
304 std::cout << '|' << std::endl;
306 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl
307 << "Fen is: " << to_fen() << std::endl
308 << "Key is: " << key << std::endl;
310 RequestPending = false;
314 /// Position::copy() creates a copy of the input position.
316 void Position::copy(const Position &pos) {
318 memcpy(this, &pos, sizeof(Position));
322 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
323 /// king) pieces for the given color.
324 Bitboard Position::pinned_pieces(Color c) const {
326 if (pinned[c] != ~EmptyBoardBB)
330 Square ksq = king_square(c);
331 pinned[c] = hidden_checks<ROOK, true>(c, ksq, p1) | hidden_checks<BISHOP, true>(c, ksq, p2);
332 pinners[c] = p1 | p2;
336 Bitboard Position::pinned_pieces(Color c, Bitboard& p) const {
338 if (pinned[c] == ~EmptyBoardBB)
345 Bitboard Position::discovered_check_candidates(Color c) const {
347 if (dcCandidates[c] != ~EmptyBoardBB)
348 return dcCandidates[c];
351 Square ksq = king_square(opposite_color(c));
352 dcCandidates[c] = hidden_checks<ROOK, false>(c, ksq, dummy) | hidden_checks<BISHOP, false>(c, ksq, dummy);
353 return dcCandidates[c];
356 /// Position:hidden_checks<>() returns a bitboard of all pinned (against the
357 /// king) pieces for the given color and for the given pinner type. Or, when
358 /// template parameter FindPinned is false, the pinned pieces of opposite color
359 /// that are, indeed, the pieces candidate for a discovery check.
360 template<PieceType Piece, bool FindPinned>
361 Bitboard Position::hidden_checks(Color c, Square ksq, Bitboard& pinners) const {
364 Bitboard sliders, result = EmptyBoardBB;
366 if (Piece == ROOK) // Resolved at compile time
367 sliders = rooks_and_queens(FindPinned ? opposite_color(c) : c) & RookPseudoAttacks[ksq];
369 sliders = bishops_and_queens(FindPinned ? opposite_color(c) : c) & BishopPseudoAttacks[ksq];
371 if (sliders && (!FindPinned || (sliders & ~checkersBB)))
373 // King blockers are candidate pinned pieces
374 Bitboard candidate_pinned = piece_attacks<Piece>(ksq) & pieces_of_color(c);
376 // Pinners are sliders, not checkers, that give check when
377 // candidate pinned are removed.
378 pinners = (FindPinned ? sliders & ~checkersBB : sliders);
381 pinners &= rook_attacks_bb(ksq, occupied_squares() ^ candidate_pinned);
383 pinners &= bishop_attacks_bb(ksq, occupied_squares() ^ candidate_pinned);
385 // Finally for each pinner find the corresponding pinned piece (if same color of king)
386 // or discovery checker (if opposite color) among the candidates.
387 Bitboard p = pinners;
391 result |= (squares_between(s, ksq) & candidate_pinned);
395 pinners = EmptyBoardBB;
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(Piece p, 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.
442 bool Position::move_attacks_square(Move m, Square s) const {
444 assert(move_is_ok(m));
445 assert(square_is_ok(s));
447 Square f = move_from(m), t = move_to(m);
449 assert(square_is_occupied(f));
451 if (piece_attacks_square(piece_on(f), t, s))
454 // Move the piece and scan for X-ray attacks behind it
455 Bitboard occ = occupied_squares();
456 Color us = color_of_piece_on(f);
459 Bitboard xray = ( (rook_attacks_bb(s, occ) & rooks_and_queens())
460 |(bishop_attacks_bb(s, occ) & bishops_and_queens())) & pieces_of_color(us);
462 // If we have attacks we need to verify that are caused by our move
463 // and are not already existent ones.
464 return xray && (xray ^ (xray & piece_attacks<QUEEN>(s)));
468 /// Position::find_checkers() computes the checkersBB bitboard, which
469 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
470 /// currently works by calling Position::attacks_to, which is probably
471 /// inefficient. Consider rewriting this function to use the last move
472 /// played, like in non-bitboard versions of Glaurung.
474 void Position::find_checkers() {
476 Color us = side_to_move();
477 checkersBB = attacks_to(king_square(us), opposite_color(us));
481 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
483 bool Position::pl_move_is_legal(Move m) const {
486 assert(move_is_ok(m));
488 // If we're in check, all pseudo-legal moves are legal, because our
489 // check evasion generator only generates true legal moves.
493 // Castling moves are checked for legality during move generation.
494 if (move_is_castle(m))
497 Color us = side_to_move();
498 Color them = opposite_color(us);
499 Square from = move_from(m);
500 Square ksq = king_square(us);
502 assert(color_of_piece_on(from) == us);
503 assert(piece_on(ksq) == piece_of_color_and_type(us, KING));
505 // En passant captures are a tricky special case. Because they are
506 // rather uncommon, we do it simply by testing whether the king is attacked
507 // after the move is made
510 Square to = move_to(m);
511 Square capsq = make_square(square_file(to), square_rank(from));
512 Bitboard b = occupied_squares();
514 assert(to == ep_square());
515 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
516 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
517 assert(piece_on(to) == EMPTY);
520 clear_bit(&b, capsq);
523 return !(rook_attacks_bb(ksq, b) & rooks_and_queens(them))
524 && !(bishop_attacks_bb(ksq, b) & bishops_and_queens(them));
527 // If the moving piece is a king, check whether the destination
528 // square is attacked by the opponent.
530 return !(square_is_attacked(move_to(m), them));
532 // A non-king move is legal if and only if it is not pinned or it
533 // is moving along the ray towards or away from the king.
534 return ( !bit_is_set(pinned_pieces(us), from)
535 || (direction_between_squares(from, ksq) == direction_between_squares(move_to(m), ksq)));
539 /// Position::move_is_check() tests whether a pseudo-legal move is a check
541 bool Position::move_is_check(Move m) const {
544 assert(move_is_ok(m));
546 Color us = side_to_move();
547 Color them = opposite_color(us);
548 Square from = move_from(m);
549 Square to = move_to(m);
550 Square ksq = king_square(them);
551 Bitboard dcCandidates = discovered_check_candidates(us);
553 assert(color_of_piece_on(from) == us);
554 assert(piece_on(ksq) == piece_of_color_and_type(them, KING));
556 // Proceed according to the type of the moving piece
557 switch (type_of_piece_on(from))
561 if (bit_is_set(pawn_attacks(them, ksq), to)) // Normal check?
564 if ( bit_is_set(dcCandidates, from) // Discovered check?
565 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
568 if (move_promotion(m)) // Promotion with check?
570 Bitboard b = occupied_squares();
573 switch (move_promotion(m))
576 return bit_is_set(piece_attacks<KNIGHT>(to), ksq);
578 return bit_is_set(bishop_attacks_bb(to, b), ksq);
580 return bit_is_set(rook_attacks_bb(to, b), ksq);
582 return bit_is_set(queen_attacks_bb(to, b), ksq);
587 // En passant capture with check? We have already handled the case
588 // of direct checks and ordinary discovered check, the only case we
589 // need to handle is the unusual case of a discovered check through the
591 else if (move_is_ep(m))
593 Square capsq = make_square(square_file(to), square_rank(from));
594 Bitboard b = occupied_squares();
596 clear_bit(&b, capsq);
598 return (rook_attacks_bb(ksq, b) & rooks_and_queens(us))
599 ||(bishop_attacks_bb(ksq, b) & bishops_and_queens(us));
604 return bit_is_set(dcCandidates, from) // Discovered check?
605 || bit_is_set(piece_attacks<KNIGHT>(ksq), to); // Normal check?
608 return bit_is_set(dcCandidates, from) // Discovered check?
609 || bit_is_set(piece_attacks<BISHOP>(ksq), to); // Normal check?
612 return bit_is_set(dcCandidates, from) // Discovered check?
613 || bit_is_set(piece_attacks<ROOK>(ksq), to); // Normal check?
616 // Discovered checks are impossible!
617 assert(!bit_is_set(dcCandidates, from));
618 return bit_is_set(piece_attacks<QUEEN>(ksq), to); // Normal check?
622 if ( bit_is_set(dcCandidates, from)
623 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
626 // Castling with check?
627 if (move_is_castle(m))
629 Square kfrom, kto, rfrom, rto;
630 Bitboard b = occupied_squares();
636 kto = relative_square(us, SQ_G1);
637 rto = relative_square(us, SQ_F1);
639 kto = relative_square(us, SQ_C1);
640 rto = relative_square(us, SQ_D1);
642 clear_bit(&b, kfrom);
643 clear_bit(&b, rfrom);
646 return bit_is_set(rook_attacks_bb(rto, b), ksq);
650 default: // NO_PIECE_TYPE
658 /// Position::move_is_capture() tests whether a move from the current
659 /// position is a capture. Move must not be MOVE_NONE.
661 bool Position::move_is_capture(Move m) const {
663 assert(m != MOVE_NONE);
665 return ( !square_is_empty(move_to(m))
666 && (color_of_piece_on(move_to(m)) != color_of_piece_on(move_from(m)))
672 /// Position::backup() is called when making a move. All information
673 /// necessary to restore the position when the move is later unmade
674 /// is saved to an UndoInfo object. The function Position::restore
675 /// does the reverse operation: When one does a backup followed by
676 /// a restore with the same UndoInfo object, the position is restored
677 /// to the state before backup was called.
679 void Position::backup(UndoInfo& u) const {
681 for (Color c = WHITE; c <= BLACK; c++)
683 u.pinners[c] = pinners[c];
684 u.pinned[c] = pinned[c];
685 u.dcCandidates[c] = dcCandidates[c];
687 u.checkersBB = checkersBB;
690 u.materialKey = materialKey;
691 u.castleRights = castleRights;
693 u.epSquare = epSquare;
694 u.lastMove = lastMove;
697 u.capture = NO_PIECE_TYPE;
701 /// Position::restore() is called when unmaking a move. It copies back
702 /// the information backed up during a previous call to Position::backup.
704 void Position::restore(const UndoInfo& u) {
706 for (Color c = WHITE; c <= BLACK; c++)
708 pinners[c] = u.pinners[c];
709 pinned[c] = u.pinned[c];
710 dcCandidates[c] = u.dcCandidates[c];
712 checkersBB = u.checkersBB;
715 materialKey = u.materialKey;
716 castleRights = u.castleRights;
718 epSquare = u.epSquare;
719 lastMove = u.lastMove;
722 // u.capture is restored in undo_move()
726 /// Position::update_checkers() is a private method to udpate chekers info
728 template<PieceType Piece>
729 inline void Position::update_checkers(Bitboard* pCheckersBB, Square ksq, Square from,
730 Square to, Bitboard dcCandidates) {
732 if (Piece != KING && bit_is_set(piece_attacks<Piece>(ksq), to))
733 set_bit(pCheckersBB, to);
735 if (Piece != QUEEN && bit_is_set(dcCandidates, from))
738 (*pCheckersBB) |= (piece_attacks<ROOK>(ksq) & rooks_and_queens(side_to_move()));
741 (*pCheckersBB) |= (piece_attacks<BISHOP>(ksq) & bishops_and_queens(side_to_move()));
746 /// Position::do_move() makes a move, and backs up all information necessary
747 /// to undo the move to an UndoInfo object. The move is assumed to be legal.
748 /// Pseudo-legal moves should be filtered out before this function is called.
750 void Position::do_move(Move m, UndoInfo& u) {
753 assert(move_is_ok(m));
755 // Get now the current (pre-move) dc candidates that we will use
756 // in update_checkers().
757 Bitboard oldDcCandidates = discovered_check_candidates(side_to_move());
759 // Back up the necessary information to our UndoInfo object (except the
760 // captured piece, which is taken care of later.
763 // Save the current key to the history[] array, in order to be able to
764 // detect repetition draws.
765 history[gamePly] = key;
767 // Increment the 50 moves rule draw counter. Resetting it to zero in the
768 // case of non-reversible moves is taken care of later.
771 // Reset pinned bitboard and its friends
772 for (Color c = WHITE; c <= BLACK; c++)
773 pinners[c] = pinned[c] = dcCandidates[c] = ~EmptyBoardBB;
775 if (move_is_castle(m))
777 else if (move_promotion(m))
778 do_promotion_move(m, u);
779 else if (move_is_ep(m))
783 Color us = side_to_move();
784 Color them = opposite_color(us);
785 Square from = move_from(m);
786 Square to = move_to(m);
788 assert(color_of_piece_on(from) == us);
789 assert(color_of_piece_on(to) == them || piece_on(to) == EMPTY);
791 PieceType piece = type_of_piece_on(from);
792 PieceType capture = type_of_piece_on(to);
797 do_capture_move(m, capture, them, to);
801 clear_bit(&(byColorBB[us]), from);
802 clear_bit(&(byTypeBB[piece]), from);
803 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
804 set_bit(&(byColorBB[us]), to);
805 set_bit(&(byTypeBB[piece]), to);
806 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
807 board[to] = board[from];
811 key ^= zobrist[us][piece][from] ^ zobrist[us][piece][to];
813 // Update incremental scores
814 mgValue -= mg_pst(us, piece, from);
815 mgValue += mg_pst(us, piece, to);
816 egValue -= eg_pst(us, piece, from);
817 egValue += eg_pst(us, piece, to);
819 // If the moving piece was a king, update the king square
823 // Reset en passant square
824 if (epSquare != SQ_NONE)
826 key ^= zobEp[epSquare];
830 // If the moving piece was a pawn do some special extra work
833 // Reset rule 50 draw counter
836 // Update pawn hash key
837 pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
839 // Set en passant square, only if moved pawn can be captured
840 if (abs(int(to) - int(from)) == 16)
842 if ( (us == WHITE && (pawn_attacks(WHITE, from + DELTA_N) & pawns(BLACK)))
843 || (us == BLACK && (pawn_attacks(BLACK, from + DELTA_S) & pawns(WHITE))))
845 epSquare = Square((int(from) + int(to)) / 2);
846 key ^= zobEp[epSquare];
851 // Update piece lists
852 pieceList[us][piece][index[from]] = to;
853 index[to] = index[from];
855 // Update castle rights
856 key ^= zobCastle[castleRights];
857 castleRights &= castleRightsMask[from];
858 castleRights &= castleRightsMask[to];
859 key ^= zobCastle[castleRights];
861 // Update checkers bitboard, piece must be already moved
862 checkersBB = EmptyBoardBB;
863 Square ksq = king_square(them);
866 case PAWN: update_checkers<PAWN>(&checkersBB, ksq, from, to, oldDcCandidates); break;
867 case KNIGHT: update_checkers<KNIGHT>(&checkersBB, ksq, from, to, oldDcCandidates); break;
868 case BISHOP: update_checkers<BISHOP>(&checkersBB, ksq, from, to, oldDcCandidates); break;
869 case ROOK: update_checkers<ROOK>(&checkersBB, ksq, from, to, oldDcCandidates); break;
870 case QUEEN: update_checkers<QUEEN>(&checkersBB, ksq, from, to, oldDcCandidates); break;
871 case KING: update_checkers<KING>(&checkersBB, ksq, from, to, oldDcCandidates); break;
872 default: assert(false); break;
877 key ^= zobSideToMove;
878 sideToMove = opposite_color(sideToMove);
881 mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
882 egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
888 /// Position::do_capture_move() is a private method used to update captured
889 /// piece info. It is called from the main Position::do_move function.
891 void Position::do_capture_move(Move m, PieceType capture, Color them, Square to) {
893 assert(capture != KING);
895 // Remove captured piece
896 clear_bit(&(byColorBB[them]), to);
897 clear_bit(&(byTypeBB[capture]), to);
900 key ^= zobrist[them][capture][to];
902 // If the captured piece was a pawn, update pawn hash key
904 pawnKey ^= zobrist[them][PAWN][to];
906 // Update incremental scores
907 mgValue -= mg_pst(them, capture, to);
908 egValue -= eg_pst(them, capture, to);
910 assert(!move_promotion(m) || capture != PAWN);
914 npMaterial[them] -= piece_value_midgame(capture);
916 // Update material hash key
917 materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];
919 // Update piece count
920 pieceCount[them][capture]--;
923 pieceList[them][capture][index[to]] = pieceList[them][capture][pieceCount[them][capture]];
924 index[pieceList[them][capture][index[to]]] = index[to];
926 // Reset rule 50 counter
931 /// Position::do_castle_move() is a private method used to make a castling
932 /// move. It is called from the main Position::do_move function. Note that
933 /// castling moves are encoded as "king captures friendly rook" moves, for
934 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
936 void Position::do_castle_move(Move m) {
939 assert(move_is_ok(m));
940 assert(move_is_castle(m));
942 Color us = side_to_move();
943 Color them = opposite_color(us);
945 // Find source squares for king and rook
946 Square kfrom = move_from(m);
947 Square rfrom = move_to(m); // HACK: See comment at beginning of function
950 assert(piece_on(kfrom) == piece_of_color_and_type(us, KING));
951 assert(piece_on(rfrom) == piece_of_color_and_type(us, ROOK));
953 // Find destination squares for king and rook
954 if (rfrom > kfrom) // O-O
956 kto = relative_square(us, SQ_G1);
957 rto = relative_square(us, SQ_F1);
959 kto = relative_square(us, SQ_C1);
960 rto = relative_square(us, SQ_D1);
963 // Remove pieces from source squares
964 clear_bit(&(byColorBB[us]), kfrom);
965 clear_bit(&(byTypeBB[KING]), kfrom);
966 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
967 clear_bit(&(byColorBB[us]), rfrom);
968 clear_bit(&(byTypeBB[ROOK]), rfrom);
969 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
971 // Put pieces on destination squares
972 set_bit(&(byColorBB[us]), kto);
973 set_bit(&(byTypeBB[KING]), kto);
974 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
975 set_bit(&(byColorBB[us]), rto);
976 set_bit(&(byTypeBB[ROOK]), rto);
977 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
979 // Update board array
980 board[kfrom] = board[rfrom] = EMPTY;
981 board[kto] = piece_of_color_and_type(us, KING);
982 board[rto] = piece_of_color_and_type(us, ROOK);
984 // Update king square
985 kingSquare[us] = kto;
987 // Update piece lists
988 pieceList[us][KING][index[kfrom]] = kto;
989 pieceList[us][ROOK][index[rfrom]] = rto;
990 int tmp = index[rfrom];
991 index[kto] = index[kfrom];
994 // Update incremental scores
995 mgValue -= mg_pst(us, KING, kfrom);
996 mgValue += mg_pst(us, KING, kto);
997 egValue -= eg_pst(us, KING, kfrom);
998 egValue += eg_pst(us, KING, kto);
999 mgValue -= mg_pst(us, ROOK, rfrom);
1000 mgValue += mg_pst(us, ROOK, rto);
1001 egValue -= eg_pst(us, ROOK, rfrom);
1002 egValue += eg_pst(us, ROOK, rto);
1005 key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1006 key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1008 // Clear en passant square
1009 if (epSquare != SQ_NONE)
1011 key ^= zobEp[epSquare];
1015 // Update castling rights
1016 key ^= zobCastle[castleRights];
1017 castleRights &= castleRightsMask[kfrom];
1018 key ^= zobCastle[castleRights];
1020 // Reset rule 50 counter
1023 // Update checkers BB
1024 checkersBB = attacks_to(king_square(them), us);
1028 /// Position::do_promotion_move() is a private method used to make a promotion
1029 /// move. It is called from the main Position::do_move function. The
1030 /// UndoInfo object, which has been initialized in Position::do_move, is
1031 /// used to store the captured piece (if any).
1033 void Position::do_promotion_move(Move m, UndoInfo &u) {
1037 PieceType capture, promotion;
1040 assert(move_is_ok(m));
1041 assert(move_promotion(m));
1043 us = side_to_move();
1044 them = opposite_color(us);
1045 from = move_from(m);
1048 assert(relative_rank(us, to) == RANK_8);
1049 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
1050 assert(color_of_piece_on(to) == them || square_is_empty(to));
1052 capture = type_of_piece_on(to);
1056 u.capture = capture;
1057 do_capture_move(m, capture, them, to);
1061 clear_bit(&(byColorBB[us]), from);
1062 clear_bit(&(byTypeBB[PAWN]), from);
1063 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1064 board[from] = EMPTY;
1066 // Insert promoted piece
1067 promotion = move_promotion(m);
1068 assert(promotion >= KNIGHT && promotion <= QUEEN);
1069 set_bit(&(byColorBB[us]), to);
1070 set_bit(&(byTypeBB[promotion]), to);
1071 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1072 board[to] = piece_of_color_and_type(us, promotion);
1075 key ^= zobrist[us][PAWN][from] ^ zobrist[us][promotion][to];
1077 // Update pawn hash key
1078 pawnKey ^= zobrist[us][PAWN][from];
1080 // Update material key
1081 materialKey ^= zobMaterial[us][PAWN][pieceCount[us][PAWN]];
1082 materialKey ^= zobMaterial[us][promotion][pieceCount[us][promotion]+1];
1084 // Update piece counts
1085 pieceCount[us][PAWN]--;
1086 pieceCount[us][promotion]++;
1088 // Update piece lists
1089 pieceList[us][PAWN][index[from]] = pieceList[us][PAWN][pieceCount[us][PAWN]];
1090 index[pieceList[us][PAWN][index[from]]] = index[from];
1091 pieceList[us][promotion][pieceCount[us][promotion] - 1] = to;
1092 index[to] = pieceCount[us][promotion] - 1;
1094 // Update incremental scores
1095 mgValue -= mg_pst(us, PAWN, from);
1096 mgValue += mg_pst(us, promotion, to);
1097 egValue -= eg_pst(us, PAWN, from);
1098 egValue += eg_pst(us, promotion, to);
1101 npMaterial[us] += piece_value_midgame(promotion);
1103 // Clear the en passant square
1104 if (epSquare != SQ_NONE)
1106 key ^= zobEp[epSquare];
1110 // Update castle rights
1111 key ^= zobCastle[castleRights];
1112 castleRights &= castleRightsMask[to];
1113 key ^= zobCastle[castleRights];
1115 // Reset rule 50 counter
1118 // Update checkers BB
1119 checkersBB = attacks_to(king_square(them), us);
1123 /// Position::do_ep_move() is a private method used to make an en passant
1124 /// capture. It is called from the main Position::do_move function. Because
1125 /// the captured piece is always a pawn, we don't need to pass an UndoInfo
1126 /// object in which to store the captured piece.
1128 void Position::do_ep_move(Move m) {
1131 Square from, to, capsq;
1134 assert(move_is_ok(m));
1135 assert(move_is_ep(m));
1137 us = side_to_move();
1138 them = opposite_color(us);
1139 from = move_from(m);
1141 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1143 assert(to == epSquare);
1144 assert(relative_rank(us, to) == RANK_6);
1145 assert(piece_on(to) == EMPTY);
1146 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
1147 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
1149 // Remove captured piece
1150 clear_bit(&(byColorBB[them]), capsq);
1151 clear_bit(&(byTypeBB[PAWN]), capsq);
1152 clear_bit(&(byTypeBB[0]), capsq); // HACK: byTypeBB[0] == occupied squares
1153 board[capsq] = EMPTY;
1155 // Remove moving piece from source square
1156 clear_bit(&(byColorBB[us]), from);
1157 clear_bit(&(byTypeBB[PAWN]), from);
1158 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1160 // Put moving piece on destination square
1161 set_bit(&(byColorBB[us]), to);
1162 set_bit(&(byTypeBB[PAWN]), to);
1163 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1164 board[to] = board[from];
1165 board[from] = EMPTY;
1167 // Update material hash key
1168 materialKey ^= zobMaterial[them][PAWN][pieceCount[them][PAWN]];
1170 // Update piece count
1171 pieceCount[them][PAWN]--;
1173 // Update piece list
1174 pieceList[us][PAWN][index[from]] = to;
1175 index[to] = index[from];
1176 pieceList[them][PAWN][index[capsq]] = pieceList[them][PAWN][pieceCount[them][PAWN]];
1177 index[pieceList[them][PAWN][index[capsq]]] = index[capsq];
1180 key ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1181 key ^= zobrist[them][PAWN][capsq];
1182 key ^= zobEp[epSquare];
1184 // Update pawn hash key
1185 pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1186 pawnKey ^= zobrist[them][PAWN][capsq];
1188 // Update incremental scores
1189 mgValue -= mg_pst(them, PAWN, capsq);
1190 mgValue -= mg_pst(us, PAWN, from);
1191 mgValue += mg_pst(us, PAWN, to);
1192 egValue -= eg_pst(them, PAWN, capsq);
1193 egValue -= eg_pst(us, PAWN, from);
1194 egValue += eg_pst(us, PAWN, to);
1196 // Reset en passant square
1199 // Reset rule 50 counter
1202 // Update checkers BB
1203 checkersBB = attacks_to(king_square(them), us);
1207 /// Position::undo_move() unmakes a move. When it returns, the position should
1208 /// be restored to exactly the same state as before the move was made. It is
1209 /// important that Position::undo_move is called with the same move and UndoInfo
1210 /// object as the earlier call to Position::do_move.
1212 void Position::undo_move(Move m, const UndoInfo &u) {
1215 assert(move_is_ok(m));
1218 sideToMove = opposite_color(sideToMove);
1220 // Restore information from our UndoInfo object (except the captured piece,
1221 // which is taken care of later)
1224 if (move_is_castle(m))
1225 undo_castle_move(m);
1226 else if (move_promotion(m))
1227 undo_promotion_move(m, u);
1228 else if (move_is_ep(m))
1234 PieceType piece, capture;
1236 us = side_to_move();
1237 them = opposite_color(us);
1238 from = move_from(m);
1241 assert(piece_on(from) == EMPTY);
1242 assert(color_of_piece_on(to) == us);
1244 // Put the piece back at the source square
1245 piece = type_of_piece_on(to);
1246 set_bit(&(byColorBB[us]), from);
1247 set_bit(&(byTypeBB[piece]), from);
1248 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1249 board[from] = piece_of_color_and_type(us, piece);
1251 // Clear the destination square
1252 clear_bit(&(byColorBB[us]), to);
1253 clear_bit(&(byTypeBB[piece]), to);
1254 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1256 // If the moving piece was a king, update the king square
1258 kingSquare[us] = from;
1260 // Update piece list
1261 pieceList[us][piece][index[to]] = from;
1262 index[from] = index[to];
1264 capture = u.capture;
1268 assert(capture != KING);
1270 // Replace the captured piece
1271 set_bit(&(byColorBB[them]), to);
1272 set_bit(&(byTypeBB[capture]), to);
1273 set_bit(&(byTypeBB[0]), to);
1274 board[to] = piece_of_color_and_type(them, capture);
1277 if (capture != PAWN)
1278 npMaterial[them] += piece_value_midgame(capture);
1280 // Update piece list
1281 pieceList[them][capture][pieceCount[them][capture]] = to;
1282 index[to] = pieceCount[them][capture];
1284 // Update piece count
1285 pieceCount[them][capture]++;
1294 /// Position::undo_castle_move() is a private method used to unmake a castling
1295 /// move. It is called from the main Position::undo_move function. Note that
1296 /// castling moves are encoded as "king captures friendly rook" moves, for
1297 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1299 void Position::undo_castle_move(Move m) {
1301 assert(move_is_ok(m));
1302 assert(move_is_castle(m));
1304 // When we have arrived here, some work has already been done by
1305 // Position::undo_move. In particular, the side to move has been switched,
1306 // so the code below is correct.
1307 Color us = side_to_move();
1309 // Find source squares for king and rook
1310 Square kfrom = move_from(m);
1311 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1314 // Find destination squares for king and rook
1315 if (rfrom > kfrom) // O-O
1317 kto = relative_square(us, SQ_G1);
1318 rto = relative_square(us, SQ_F1);
1320 kto = relative_square(us, SQ_C1);
1321 rto = relative_square(us, SQ_D1);
1324 assert(piece_on(kto) == piece_of_color_and_type(us, KING));
1325 assert(piece_on(rto) == piece_of_color_and_type(us, ROOK));
1327 // Remove pieces from destination squares
1328 clear_bit(&(byColorBB[us]), kto);
1329 clear_bit(&(byTypeBB[KING]), kto);
1330 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1331 clear_bit(&(byColorBB[us]), rto);
1332 clear_bit(&(byTypeBB[ROOK]), rto);
1333 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1335 // Put pieces on source squares
1336 set_bit(&(byColorBB[us]), kfrom);
1337 set_bit(&(byTypeBB[KING]), kfrom);
1338 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1339 set_bit(&(byColorBB[us]), rfrom);
1340 set_bit(&(byTypeBB[ROOK]), rfrom);
1341 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1344 board[rto] = board[kto] = EMPTY;
1345 board[rfrom] = piece_of_color_and_type(us, ROOK);
1346 board[kfrom] = piece_of_color_and_type(us, KING);
1348 // Update king square
1349 kingSquare[us] = kfrom;
1351 // Update piece lists
1352 pieceList[us][KING][index[kto]] = kfrom;
1353 pieceList[us][ROOK][index[rto]] = rfrom;
1354 int tmp = index[rto]; // Necessary because we may have rto == kfrom in FRC.
1355 index[kfrom] = index[kto];
1360 /// Position::undo_promotion_move() is a private method used to unmake a
1361 /// promotion move. It is called from the main Position::do_move
1362 /// function. The UndoInfo object, which has been initialized in
1363 /// Position::do_move, is used to put back the captured piece (if any).
1365 void Position::undo_promotion_move(Move m, const UndoInfo &u) {
1369 PieceType capture, promotion;
1371 assert(move_is_ok(m));
1372 assert(move_promotion(m));
1374 // When we have arrived here, some work has already been done by
1375 // Position::undo_move. In particular, the side to move has been switched,
1376 // so the code below is correct.
1377 us = side_to_move();
1378 them = opposite_color(us);
1379 from = move_from(m);
1382 assert(relative_rank(us, to) == RANK_8);
1383 assert(piece_on(from) == EMPTY);
1385 // Remove promoted piece
1386 promotion = move_promotion(m);
1387 assert(piece_on(to)==piece_of_color_and_type(us, promotion));
1388 assert(promotion >= KNIGHT && promotion <= QUEEN);
1389 clear_bit(&(byColorBB[us]), to);
1390 clear_bit(&(byTypeBB[promotion]), to);
1391 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1393 // Insert pawn at source square
1394 set_bit(&(byColorBB[us]), from);
1395 set_bit(&(byTypeBB[PAWN]), from);
1396 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1397 board[from] = piece_of_color_and_type(us, PAWN);
1400 npMaterial[us] -= piece_value_midgame(promotion);
1402 // Update piece list
1403 pieceList[us][PAWN][pieceCount[us][PAWN]] = from;
1404 index[from] = pieceCount[us][PAWN];
1405 pieceList[us][promotion][index[to]] =
1406 pieceList[us][promotion][pieceCount[us][promotion] - 1];
1407 index[pieceList[us][promotion][index[to]]] = index[to];
1409 // Update piece counts
1410 pieceCount[us][promotion]--;
1411 pieceCount[us][PAWN]++;
1413 capture = u.capture;
1417 assert(capture != KING);
1419 // Insert captured piece:
1420 set_bit(&(byColorBB[them]), to);
1421 set_bit(&(byTypeBB[capture]), to);
1422 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1423 board[to] = piece_of_color_and_type(them, capture);
1425 // Update material. Because the move is a promotion move, we know
1426 // that the captured piece cannot be a pawn.
1427 assert(capture != PAWN);
1428 npMaterial[them] += piece_value_midgame(capture);
1430 // Update piece list
1431 pieceList[them][capture][pieceCount[them][capture]] = to;
1432 index[to] = pieceCount[them][capture];
1434 // Update piece count
1435 pieceCount[them][capture]++;
1441 /// Position::undo_ep_move() is a private method used to unmake an en passant
1442 /// capture. It is called from the main Position::undo_move function. Because
1443 /// the captured piece is always a pawn, we don't need to pass an UndoInfo
1444 /// object from which to retrieve the captured piece.
1446 void Position::undo_ep_move(Move m) {
1448 assert(move_is_ok(m));
1449 assert(move_is_ep(m));
1451 // When we have arrived here, some work has already been done by
1452 // Position::undo_move. In particular, the side to move has been switched,
1453 // so the code below is correct.
1454 Color us = side_to_move();
1455 Color them = opposite_color(us);
1456 Square from = move_from(m);
1457 Square to = move_to(m);
1458 Square capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1460 assert(to == ep_square());
1461 assert(relative_rank(us, to) == RANK_6);
1462 assert(piece_on(to) == piece_of_color_and_type(us, PAWN));
1463 assert(piece_on(from) == EMPTY);
1464 assert(piece_on(capsq) == EMPTY);
1466 // Replace captured piece
1467 set_bit(&(byColorBB[them]), capsq);
1468 set_bit(&(byTypeBB[PAWN]), capsq);
1469 set_bit(&(byTypeBB[0]), capsq);
1470 board[capsq] = piece_of_color_and_type(them, PAWN);
1472 // Remove moving piece from destination square
1473 clear_bit(&(byColorBB[us]), to);
1474 clear_bit(&(byTypeBB[PAWN]), to);
1475 clear_bit(&(byTypeBB[0]), to);
1478 // Replace moving piece at source square
1479 set_bit(&(byColorBB[us]), from);
1480 set_bit(&(byTypeBB[PAWN]), from);
1481 set_bit(&(byTypeBB[0]), from);
1482 board[from] = piece_of_color_and_type(us, PAWN);
1484 // Update piece list:
1485 pieceList[us][PAWN][index[to]] = from;
1486 index[from] = index[to];
1487 pieceList[them][PAWN][pieceCount[them][PAWN]] = capsq;
1488 index[capsq] = pieceCount[them][PAWN];
1490 // Update piece count:
1491 pieceCount[them][PAWN]++;
1495 /// Position::do_null_move makes() a "null move": It switches the side to move
1496 /// and updates the hash key without executing any move on the board.
1498 void Position::do_null_move(UndoInfo& u) {
1501 assert(!is_check());
1503 // Back up the information necessary to undo the null move to the supplied
1504 // UndoInfo object. In the case of a null move, the only thing we need to
1505 // remember is the last move made and the en passant square.
1506 u.lastMove = lastMove;
1507 u.epSquare = epSquare;
1509 // Save the current key to the history[] array, in order to be able to
1510 // detect repetition draws.
1511 history[gamePly] = key;
1513 // Update the necessary information
1514 sideToMove = opposite_color(sideToMove);
1515 if (epSquare != SQ_NONE)
1516 key ^= zobEp[epSquare];
1521 key ^= zobSideToMove;
1523 mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1524 egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1530 /// Position::undo_null_move() unmakes a "null move".
1532 void Position::undo_null_move(const UndoInfo &u) {
1535 assert(!is_check());
1537 // Restore information from the supplied UndoInfo object:
1538 lastMove = u.lastMove;
1539 epSquare = u.epSquare;
1540 if (epSquare != SQ_NONE)
1541 key ^= zobEp[epSquare];
1543 // Update the necessary information.
1544 sideToMove = opposite_color(sideToMove);
1547 key ^= zobSideToMove;
1549 mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1550 egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1556 /// Position::see() is a static exchange evaluator: It tries to estimate the
1557 /// material gain or loss resulting from a move. There are three versions of
1558 /// this function: One which takes a destination square as input, one takes a
1559 /// move, and one which takes a 'from' and a 'to' square. The function does
1560 /// not yet understand promotions captures.
1562 int Position::see(Square to) const {
1564 assert(square_is_ok(to));
1565 return see(SQ_NONE, to);
1568 int Position::see(Move m) const {
1570 assert(move_is_ok(m));
1571 return see(move_from(m), move_to(m));
1574 int Position::see(Square from, Square to) const {
1577 static const int seeValues[18] = {
1578 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1579 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1580 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1581 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1585 Bitboard attackers, occ, b;
1587 assert(square_is_ok(from) || from == SQ_NONE);
1588 assert(square_is_ok(to));
1590 // Initialize colors
1591 Color us = (from != SQ_NONE ? color_of_piece_on(from) : opposite_color(color_of_piece_on(to)));
1592 Color them = opposite_color(us);
1594 // Initialize pieces
1595 Piece piece = piece_on(from);
1596 Piece capture = piece_on(to);
1598 // Find all attackers to the destination square, with the moving piece
1599 // removed, but possibly an X-ray attacker added behind it.
1600 occ = occupied_squares();
1602 // Handle en passant moves
1603 if (epSquare == to && type_of_piece_on(from) == PAWN)
1605 assert(capture == EMPTY);
1607 Square capQq = (side_to_move() == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1608 capture = piece_on(capQq);
1610 assert(type_of_piece_on(capQq) == PAWN);
1612 // Remove the captured pawn
1613 clear_bit(&occ, capQq);
1618 clear_bit(&occ, from);
1619 attackers = (rook_attacks_bb(to, occ) & rooks_and_queens())
1620 | (bishop_attacks_bb(to, occ) & bishops_and_queens())
1621 | (piece_attacks<KNIGHT>(to) & knights())
1622 | (piece_attacks<KING>(to) & kings())
1623 | (pawn_attacks(WHITE, to) & pawns(BLACK))
1624 | (pawn_attacks(BLACK, to) & pawns(WHITE));
1626 if (from != SQ_NONE)
1629 // If we don't have any attacker we are finished
1630 if ((attackers & pieces_of_color(us)) == EmptyBoardBB)
1633 // Locate the least valuable attacker to the destination square
1634 // and use it to initialize from square.
1636 for (pt = PAWN; !(attackers & pieces_of_color_and_type(us, pt)); pt++)
1639 from = first_1(attackers & pieces_of_color_and_type(us, pt));
1640 piece = piece_on(from);
1643 // If the opponent has no attackers we are finished
1644 if ((attackers & pieces_of_color(them)) == EmptyBoardBB)
1645 return seeValues[capture];
1647 attackers &= occ; // Remove the moving piece
1649 // The destination square is defended, which makes things rather more
1650 // difficult to compute. We proceed by building up a "swap list" containing
1651 // the material gain or loss at each stop in a sequence of captures to the
1652 // destination square, where the sides alternately capture, and always
1653 // capture with the least valuable piece. After each capture, we look for
1654 // new X-ray attacks from behind the capturing piece.
1655 int lastCapturingPieceValue = seeValues[piece];
1656 int swapList[32], n = 1;
1660 swapList[0] = seeValues[capture];
1663 // Locate the least valuable attacker for the side to move. The loop
1664 // below looks like it is potentially infinite, but it isn't. We know
1665 // that the side to move still has at least one attacker left.
1666 for (pt = PAWN; !(attackers & pieces_of_color_and_type(c, pt)); pt++)
1669 // Remove the attacker we just found from the 'attackers' bitboard,
1670 // and scan for new X-ray attacks behind the attacker.
1671 b = attackers & pieces_of_color_and_type(c, pt);
1673 attackers |= (rook_attacks_bb(to, occ) & rooks_and_queens())
1674 | (bishop_attacks_bb(to, occ) & bishops_and_queens());
1678 // Add the new entry to the swap list
1680 swapList[n] = -swapList[n - 1] + lastCapturingPieceValue;
1683 // Remember the value of the capturing piece, and change the side to move
1684 // before beginning the next iteration
1685 lastCapturingPieceValue = seeValues[pt];
1686 c = opposite_color(c);
1688 // Stop after a king capture
1689 if (pt == KING && (attackers & pieces_of_color(c)))
1692 swapList[n++] = 100;
1695 } while (attackers & pieces_of_color(c));
1697 // Having built the swap list, we negamax through it to find the best
1698 // achievable score from the point of view of the side to move
1700 swapList[n-1] = Min(-swapList[n], swapList[n-1]);
1706 /// Position::clear() erases the position object to a pristine state, with an
1707 /// empty board, white to move, and no castling rights.
1709 void Position::clear() {
1711 for (int i = 0; i < 64; i++)
1717 for (int i = 0; i < 2; i++)
1718 byColorBB[i] = EmptyBoardBB;
1720 for (int i = 0; i < 7; i++)
1722 byTypeBB[i] = EmptyBoardBB;
1723 pieceCount[0][i] = pieceCount[1][i] = 0;
1724 for (int j = 0; j < 8; j++)
1725 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1728 checkersBB = EmptyBoardBB;
1729 for (Color c = WHITE; c <= BLACK; c++)
1730 pinners[c] = pinned[c] = dcCandidates[c] = ~EmptyBoardBB;
1732 lastMove = MOVE_NONE;
1735 castleRights = NO_CASTLES;
1736 initialKFile = FILE_E;
1737 initialKRFile = FILE_H;
1738 initialQRFile = FILE_A;
1745 /// Position::reset_game_ply() simply sets gamePly to 0. It is used from the
1746 /// UCI interface code, whenever a non-reversible move is made in a
1747 /// 'position fen <fen> moves m1 m2 ...' command. This makes it possible
1748 /// for the program to handle games of arbitrary length, as long as the GUI
1749 /// handles draws by the 50 move rule correctly.
1751 void Position::reset_game_ply() {
1757 /// Position::put_piece() puts a piece on the given square of the board,
1758 /// updating the board array, bitboards, and piece counts.
1760 void Position::put_piece(Piece p, Square s) {
1762 Color c = color_of_piece(p);
1763 PieceType pt = type_of_piece(p);
1766 index[s] = pieceCount[c][pt];
1767 pieceList[c][pt][index[s]] = s;
1769 set_bit(&(byTypeBB[pt]), s);
1770 set_bit(&(byColorBB[c]), s);
1771 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1773 pieceCount[c][pt]++;
1780 /// Position::allow_oo() gives the given side the right to castle kingside.
1781 /// Used when setting castling rights during parsing of FEN strings.
1783 void Position::allow_oo(Color c) {
1785 castleRights |= (1 + int(c));
1789 /// Position::allow_ooo() gives the given side the right to castle queenside.
1790 /// Used when setting castling rights during parsing of FEN strings.
1792 void Position::allow_ooo(Color c) {
1794 castleRights |= (4 + 4*int(c));
1798 /// Position::compute_key() computes the hash key of the position. The hash
1799 /// key is usually updated incrementally as moves are made and unmade, the
1800 /// compute_key() function is only used when a new position is set up, and
1801 /// to verify the correctness of the hash key when running in debug mode.
1803 Key Position::compute_key() const {
1805 Key result = Key(0ULL);
1807 for (Square s = SQ_A1; s <= SQ_H8; s++)
1808 if (square_is_occupied(s))
1809 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1811 if (ep_square() != SQ_NONE)
1812 result ^= zobEp[ep_square()];
1814 result ^= zobCastle[castleRights];
1815 if (side_to_move() == BLACK)
1816 result ^= zobSideToMove;
1822 /// Position::compute_pawn_key() computes the hash key of the position. The
1823 /// hash key is usually updated incrementally as moves are made and unmade,
1824 /// the compute_pawn_key() function is only used when a new position is set
1825 /// up, and to verify the correctness of the pawn hash key when running in
1828 Key Position::compute_pawn_key() const {
1830 Key result = Key(0ULL);
1834 for (Color c = WHITE; c <= BLACK; c++)
1839 s = pop_1st_bit(&b);
1840 result ^= zobrist[c][PAWN][s];
1847 /// Position::compute_material_key() computes the hash key of the position.
1848 /// The hash key is usually updated incrementally as moves are made and unmade,
1849 /// the compute_material_key() function is only used when a new position is set
1850 /// up, and to verify the correctness of the material hash key when running in
1853 Key Position::compute_material_key() const {
1855 Key result = Key(0ULL);
1856 for (Color c = WHITE; c <= BLACK; c++)
1857 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1859 int count = piece_count(c, pt);
1860 for (int i = 0; i <= count; i++)
1861 result ^= zobMaterial[c][pt][i];
1867 /// Position::compute_mg_value() and Position::compute_eg_value() compute the
1868 /// incremental scores for the middle game and the endgame. These functions
1869 /// are used to initialize the incremental scores when a new position is set
1870 /// up, and to verify that the scores are correctly updated by do_move
1871 /// and undo_move when the program is running in debug mode.
1873 Value Position::compute_mg_value() const {
1875 Value result = Value(0);
1879 for (Color c = WHITE; c <= BLACK; c++)
1880 for (PieceType pt = PAWN; pt <= KING; pt++)
1882 b = pieces_of_color_and_type(c, pt);
1885 s = pop_1st_bit(&b);
1886 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1887 result += mg_pst(c, pt, s);
1890 result += (side_to_move() == WHITE)? TempoValueMidgame / 2 : -TempoValueMidgame / 2;
1894 Value Position::compute_eg_value() const {
1896 Value result = Value(0);
1900 for (Color c = WHITE; c <= BLACK; c++)
1901 for (PieceType pt = PAWN; pt <= KING; pt++)
1903 b = pieces_of_color_and_type(c, pt);
1906 s = pop_1st_bit(&b);
1907 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1908 result += eg_pst(c, pt, s);
1911 result += (side_to_move() == WHITE)? TempoValueEndgame / 2 : -TempoValueEndgame / 2;
1916 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1917 /// game material score for the given side. Material scores are updated
1918 /// incrementally during the search, this function is only used while
1919 /// initializing a new Position object.
1921 Value Position::compute_non_pawn_material(Color c) const {
1923 Value result = Value(0);
1926 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1928 Bitboard b = pieces_of_color_and_type(c, pt);
1931 s = pop_1st_bit(&b);
1932 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1933 result += piece_value_midgame(pt);
1940 /// Position::is_mate() returns true or false depending on whether the
1941 /// side to move is checkmated. Note that this function is currently very
1942 /// slow, and shouldn't be used frequently inside the search.
1944 bool Position::is_mate() const {
1948 MovePicker mp = MovePicker(*this, false, MOVE_NONE, EmptySearchStack, Depth(0));
1949 return mp.get_next_move() == MOVE_NONE;
1955 /// Position::is_draw() tests whether the position is drawn by material,
1956 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1957 /// must be done by the search.
1959 bool Position::is_draw() const {
1961 // Draw by material?
1963 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1966 // Draw by the 50 moves rule?
1967 if (rule50 > 100 || (rule50 == 100 && !is_check()))
1970 // Draw by repetition?
1971 for (int i = 2; i < Min(gamePly, rule50); i += 2)
1972 if (history[gamePly - i] == key)
1979 /// Position::has_mate_threat() tests whether a given color has a mate in one
1980 /// from the current position. This function is quite slow, but it doesn't
1981 /// matter, because it is currently only called from PV nodes, which are rare.
1983 bool Position::has_mate_threat(Color c) {
1986 Color stm = side_to_move();
1988 // The following lines are useless and silly, but prevents gcc from
1989 // emitting a stupid warning stating that u1.lastMove and u1.epSquare might
1990 // be used uninitialized.
1991 u1.lastMove = lastMove;
1992 u1.epSquare = epSquare;
1997 // If the input color is not equal to the side to move, do a null move
2001 MoveStack mlist[120];
2003 bool result = false;
2005 // Generate legal moves
2006 count = generate_legal_moves(*this, mlist);
2008 // Loop through the moves, and see if one of them is mate
2009 for (int i = 0; i < count; i++)
2011 do_move(mlist[i].move, u2);
2015 undo_move(mlist[i].move, u2);
2018 // Undo null move, if necessary
2026 /// Position::init_zobrist() is a static member function which initializes the
2027 /// various arrays used to compute hash keys.
2029 void Position::init_zobrist() {
2031 for (int i = 0; i < 2; i++)
2032 for (int j = 0; j < 8; j++)
2033 for (int k = 0; k < 64; k++)
2034 zobrist[i][j][k] = Key(genrand_int64());
2036 for (int i = 0; i < 64; i++)
2037 zobEp[i] = Key(genrand_int64());
2039 for (int i = 0; i < 16; i++)
2040 zobCastle[i] = genrand_int64();
2042 zobSideToMove = genrand_int64();
2044 for (int i = 0; i < 2; i++)
2045 for (int j = 0; j < 8; j++)
2046 for (int k = 0; k < 16; k++)
2047 zobMaterial[i][j][k] = (k > 0)? Key(genrand_int64()) : Key(0LL);
2049 for (int i = 0; i < 16; i++)
2050 zobMaterial[0][KING][i] = zobMaterial[1][KING][i] = Key(0ULL);
2054 /// Position::init_piece_square_tables() initializes the piece square tables.
2055 /// This is a two-step operation: First, the white halves of the tables are
2056 /// copied from the MgPST[][] and EgPST[][] arrays, with a small random number
2057 /// added to each entry if the "Randomness" UCI parameter is non-zero.
2058 /// Second, the black halves of the tables are initialized by mirroring
2059 /// and changing the sign of the corresponding white scores.
2061 void Position::init_piece_square_tables() {
2063 int r = get_option_value_int("Randomness"), i;
2064 for (Square s = SQ_A1; s <= SQ_H8; s++)
2065 for (Piece p = WP; p <= WK; p++)
2067 i = (r == 0)? 0 : (genrand_int32() % (r*2) - r);
2068 MgPieceSquareTable[p][s] = Value(MgPST[p][s] + i);
2069 EgPieceSquareTable[p][s] = Value(EgPST[p][s] + i);
2072 for (Square s = SQ_A1; s <= SQ_H8; s++)
2073 for (Piece p = BP; p <= BK; p++)
2075 MgPieceSquareTable[p][s] = -MgPieceSquareTable[p-8][flip_square(s)];
2076 EgPieceSquareTable[p][s] = -EgPieceSquareTable[p-8][flip_square(s)];
2081 /// Position::flipped_copy() makes a copy of the input position, but with
2082 /// the white and black sides reversed. This is only useful for debugging,
2083 /// especially for finding evaluation symmetry bugs.
2085 void Position::flipped_copy(const Position &pos) {
2087 assert(pos.is_ok());
2092 for (Square s = SQ_A1; s <= SQ_H8; s++)
2093 if (!pos.square_is_empty(s))
2094 put_piece(Piece(int(pos.piece_on(s)) ^ 8), flip_square(s));
2097 sideToMove = opposite_color(pos.side_to_move());
2100 if (pos.can_castle_kingside(WHITE)) allow_oo(BLACK);
2101 if (pos.can_castle_queenside(WHITE)) allow_ooo(BLACK);
2102 if (pos.can_castle_kingside(BLACK)) allow_oo(WHITE);
2103 if (pos.can_castle_queenside(BLACK)) allow_ooo(WHITE);
2105 initialKFile = pos.initialKFile;
2106 initialKRFile = pos.initialKRFile;
2107 initialQRFile = pos.initialQRFile;
2109 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
2110 castleRightsMask[sq] = ALL_CASTLES;
2112 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
2113 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
2114 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
2115 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
2116 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
2117 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
2119 // En passant square
2120 if (pos.epSquare != SQ_NONE)
2121 epSquare = flip_square(pos.epSquare);
2127 key = compute_key();
2128 pawnKey = compute_pawn_key();
2129 materialKey = compute_material_key();
2131 // Incremental scores
2132 mgValue = compute_mg_value();
2133 egValue = compute_eg_value();
2136 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
2137 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
2143 /// Position::is_ok() performs some consitency checks for the position object.
2144 /// This is meant to be helpful when debugging.
2146 bool Position::is_ok(int* failedStep) const {
2148 // What features of the position should be verified?
2149 static const bool debugBitboards = false;
2150 static const bool debugKingCount = false;
2151 static const bool debugKingCapture = false;
2152 static const bool debugCheckerCount = false;
2153 static const bool debugKey = false;
2154 static const bool debugMaterialKey = false;
2155 static const bool debugPawnKey = false;
2156 static const bool debugIncrementalEval = false;
2157 static const bool debugNonPawnMaterial = false;
2158 static const bool debugPieceCounts = false;
2159 static const bool debugPieceList = false;
2161 if (failedStep) *failedStep = 1;
2164 if (!color_is_ok(side_to_move()))
2167 // Are the king squares in the position correct?
2168 if (failedStep) (*failedStep)++;
2169 if (piece_on(king_square(WHITE)) != WK)
2172 if (failedStep) (*failedStep)++;
2173 if (piece_on(king_square(BLACK)) != BK)
2177 if (failedStep) (*failedStep)++;
2178 if (!file_is_ok(initialKRFile))
2181 if (!file_is_ok(initialQRFile))
2184 // Do both sides have exactly one king?
2185 if (failedStep) (*failedStep)++;
2188 int kingCount[2] = {0, 0};
2189 for (Square s = SQ_A1; s <= SQ_H8; s++)
2190 if (type_of_piece_on(s) == KING)
2191 kingCount[color_of_piece_on(s)]++;
2193 if (kingCount[0] != 1 || kingCount[1] != 1)
2197 // Can the side to move capture the opponent's king?
2198 if (failedStep) (*failedStep)++;
2199 if (debugKingCapture)
2201 Color us = side_to_move();
2202 Color them = opposite_color(us);
2203 Square ksq = king_square(them);
2204 if (square_is_attacked(ksq, us))
2208 // Is there more than 2 checkers?
2209 if (failedStep) (*failedStep)++;
2210 if (debugCheckerCount && count_1s(checkersBB) > 2)
2214 if (failedStep) (*failedStep)++;
2217 // The intersection of the white and black pieces must be empty
2218 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
2221 // The union of the white and black pieces must be equal to all
2223 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
2226 // Separate piece type bitboards must have empty intersections
2227 for (PieceType p1 = PAWN; p1 <= KING; p1++)
2228 for (PieceType p2 = PAWN; p2 <= KING; p2++)
2229 if (p1 != p2 && (pieces_of_type(p1) & pieces_of_type(p2)))
2233 // En passant square OK?
2234 if (failedStep) (*failedStep)++;
2235 if (ep_square() != SQ_NONE)
2237 // The en passant square must be on rank 6, from the point of view of the
2239 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
2244 if (failedStep) (*failedStep)++;
2245 if (debugKey && key != compute_key())
2248 // Pawn hash key OK?
2249 if (failedStep) (*failedStep)++;
2250 if (debugPawnKey && pawnKey != compute_pawn_key())
2253 // Material hash key OK?
2254 if (failedStep) (*failedStep)++;
2255 if (debugMaterialKey && materialKey != compute_material_key())
2258 // Incremental eval OK?
2259 if (failedStep) (*failedStep)++;
2260 if (debugIncrementalEval)
2262 if (mgValue != compute_mg_value())
2265 if (egValue != compute_eg_value())
2269 // Non-pawn material OK?
2270 if (failedStep) (*failedStep)++;
2271 if (debugNonPawnMaterial)
2273 if (npMaterial[WHITE] != compute_non_pawn_material(WHITE))
2276 if (npMaterial[BLACK] != compute_non_pawn_material(BLACK))
2281 if (failedStep) (*failedStep)++;
2282 if (debugPieceCounts)
2283 for (Color c = WHITE; c <= BLACK; c++)
2284 for (PieceType pt = PAWN; pt <= KING; pt++)
2285 if (pieceCount[c][pt] != count_1s(pieces_of_color_and_type(c, pt)))
2288 if (failedStep) (*failedStep)++;
2291 for(Color c = WHITE; c <= BLACK; c++)
2292 for(PieceType pt = PAWN; pt <= KING; pt++)
2293 for(int i = 0; i < pieceCount[c][pt]; i++)
2295 if (piece_on(piece_list(c, pt, i)) != piece_of_color_and_type(c, pt))
2298 if (index[piece_list(c, pt, i)] != i)
2302 if (failedStep) *failedStep = 0;