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/>.
34 #include "ucioption.h"
41 int Position::castleRightsMask[64];
43 Key Position::zobrist[2][8][64];
44 Key Position::zobEp[64];
45 Key Position::zobCastle[16];
46 Key Position::zobMaterial[2][8][16];
47 Key Position::zobSideToMove;
49 Value Position::MgPieceSquareTable[16][64];
50 Value Position::EgPieceSquareTable[16][64];
59 Position::Position(const Position &pos) {
63 Position::Position(const std::string &fen) {
68 /// Position::from_fen() initializes the position object with the given FEN
69 /// string. This function is not very robust - make sure that input FENs are
70 /// correct (this is assumed to be the responsibility of the GUI).
72 void Position::from_fen(const std::string &fen) {
74 static const std::string pieceLetters = "KQRBNPkqrbnp";
75 static const Piece pieces[] = { WK, WQ, WR, WB, WN, WP, BK, BQ, BR, BB, BN, BP };
83 for ( ; fen[i] != ' '; i++)
87 // Skip the given number of files
88 file += (fen[i] - '1' + 1);
91 else if (fen[i] == '/')
97 size_t idx = pieceLetters.find(fen[i]);
98 if (idx == std::string::npos)
100 std::cout << "Error in FEN at character " << i << std::endl;
103 Square square = make_square(file, rank);
104 put_piece(pieces[idx], square);
110 if (fen[i] != 'w' && fen[i] != 'b')
112 std::cout << "Error in FEN at character " << i << std::endl;
115 sideToMove = (fen[i] == 'w' ? WHITE : BLACK);
121 std::cout << "Error in FEN at character " << i << std::endl;
126 while(strchr("KQkqabcdefghABCDEFGH-", fen[i])) {
130 else if(fen[i] == 'K') allow_oo(WHITE);
131 else if(fen[i] == 'Q') allow_ooo(WHITE);
132 else if(fen[i] == 'k') allow_oo(BLACK);
133 else if(fen[i] == 'q') allow_ooo(BLACK);
134 else if(fen[i] >= 'A' && fen[i] <= 'H') {
135 File rookFile, kingFile = FILE_NONE;
136 for(Square square = SQ_B1; square <= SQ_G1; square++)
137 if(piece_on(square) == WK)
138 kingFile = square_file(square);
139 if(kingFile == FILE_NONE) {
140 std::cout << "Error in FEN at character " << i << std::endl;
143 initialKFile = kingFile;
144 rookFile = File(fen[i] - 'A') + FILE_A;
145 if(rookFile < initialKFile) {
147 initialQRFile = rookFile;
151 initialKRFile = rookFile;
154 else if(fen[i] >= 'a' && fen[i] <= 'h') {
155 File rookFile, kingFile = FILE_NONE;
156 for(Square square = SQ_B8; square <= SQ_G8; square++)
157 if(piece_on(square) == BK)
158 kingFile = square_file(square);
159 if(kingFile == FILE_NONE) {
160 std::cout << "Error in FEN at character " << i << std::endl;
163 initialKFile = kingFile;
164 rookFile = File(fen[i] - 'a') + FILE_A;
165 if(rookFile < initialKFile) {
167 initialQRFile = rookFile;
171 initialKRFile = rookFile;
175 std::cout << "Error in FEN at character " << i << std::endl;
182 while (fen[i] == ' ')
186 if ( i < fen.length() - 2
187 && (fen[i] >= 'a' && fen[i] <= 'h')
188 && (fen[i+1] == '3' || fen[i+1] == '6'))
189 epSquare = square_from_string(fen.substr(i, 2));
191 // Various initialisation
192 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
193 castleRightsMask[sq] = ALL_CASTLES;
195 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO|WHITE_OOO);
196 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO|BLACK_OOO);
197 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
198 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
199 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
200 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
205 pawnKey = compute_pawn_key();
206 materialKey = compute_material_key();
207 mgValue = compute_mg_value();
208 egValue = compute_eg_value();
209 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
210 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
214 /// Position::to_fen() converts the position object to a FEN string. This is
215 /// probably only useful for debugging.
217 const std::string Position::to_fen() const {
219 static const std::string pieceLetters = " PNBRQK pnbrqk";
223 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
226 for (File file = FILE_A; file <= FILE_H; file++)
228 Square sq = make_square(file, rank);
229 if (!square_is_occupied(sq))
235 fen += (char)skip + '0';
238 fen += pieceLetters[piece_on(sq)];
241 fen += (char)skip + '0';
243 fen += (rank > RANK_1 ? '/' : ' ');
245 fen += (sideToMove == WHITE ? 'w' : 'b') + ' ';
246 if (castleRights != NO_CASTLES)
248 if (can_castle_kingside(WHITE)) fen += 'K';
249 if (can_castle_queenside(WHITE)) fen += 'Q';
250 if (can_castle_kingside(BLACK)) fen += 'k';
251 if (can_castle_queenside(BLACK)) fen += 'q';
256 if (ep_square() != SQ_NONE)
257 fen += square_to_string(ep_square());
265 /// Position::print() prints an ASCII representation of the position to
266 /// the standard output.
268 void Position::print() const {
269 char pieceStrings[][8] =
270 {"| ? ", "| P ", "| N ", "| B ", "| R ", "| Q ", "| K ", "| ? ",
271 "| ? ", "|=P=", "|=N=", "|=B=", "|=R=", "|=Q=", "|=K="
274 for(Rank rank = RANK_8; rank >= RANK_1; rank--) {
275 std::cout << "+---+---+---+---+---+---+---+---+\n";
276 for(File file = FILE_A; file <= FILE_H; file++) {
277 Square sq = make_square(file, rank);
278 Piece piece = piece_on(sq);
280 std::cout << ((square_color(sq) == WHITE)? "| " : "| . ");
282 std::cout << pieceStrings[piece];
286 std::cout << "+---+---+---+---+---+---+---+---+\n";
287 std::cout << to_fen() << std::endl;
288 std::cout << key << std::endl;
292 /// Position::copy() creates a copy of the input position.
294 void Position::copy(const Position &pos) {
296 memcpy(this, &pos, sizeof(Position));
300 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
301 /// king) pieces for the given color.
302 Bitboard Position::pinned_pieces(Color c) const {
304 Square ksq = king_square(c);
305 return hidden_checks<ROOK, true>(c, ksq) | hidden_checks<BISHOP, true>(c, ksq);
309 /// Position:discovered_check_candidates() returns a bitboard containing all
310 /// pieces for the given side which are candidates for giving a discovered
311 /// check. The code is almost the same as the function for finding pinned
314 Bitboard Position::discovered_check_candidates(Color c) const {
316 Square ksq = king_square(opposite_color(c));
317 return hidden_checks<ROOK, false>(c, ksq) | hidden_checks<BISHOP, false>(c, ksq);
321 /// Position:hidden_checks<>() returns a bitboard of all pinned (against the
322 /// king) pieces for the given color and for the given pinner type. Or, when
323 /// template parameter FindPinned is false, the pinned pieces of opposite color
324 /// that are, indeed, the pieces candidate for a discovery check.
325 template<PieceType Piece, bool FindPinned>
326 Bitboard Position::hidden_checks(Color c, Square ksq) const {
329 Bitboard sliders, result = EmptyBoardBB;
331 if (Piece == ROOK) // Resolved at compile time
332 sliders = rooks_and_queens(FindPinned ? opposite_color(c) : c) & RookPseudoAttacks[ksq];
334 sliders = bishops_and_queens(FindPinned ? opposite_color(c) : c) & BishopPseudoAttacks[ksq];
336 if (sliders && (!FindPinned || (sliders & ~checkersBB)))
338 // King blockers are candidate pinned pieces
339 Bitboard candidate_pinned = piece_attacks<Piece>(ksq) & pieces_of_color(c);
341 // Pinners are sliders, not checkers, that give check when
342 // candidate pinned are removed.
343 Bitboard pinners = (FindPinned ? sliders & ~checkersBB : sliders);
346 pinners &= rook_attacks_bb(ksq, occupied_squares() ^ candidate_pinned);
348 pinners &= bishop_attacks_bb(ksq, occupied_squares() ^ candidate_pinned);
350 // Finally for each pinner find the corresponding pinned piece (if same color of king)
351 // or discovery checker (if opposite color) among the candidates.
354 s = pop_1st_bit(&pinners);
355 result |= (squares_between(s, ksq) & candidate_pinned);
362 /// Position::square_is_attacked() checks whether the given side attacks the
365 bool Position::square_is_attacked(Square s, Color c) const {
367 return (pawn_attacks(opposite_color(c), s) & pawns(c))
368 || (piece_attacks<KNIGHT>(s) & knights(c))
369 || (piece_attacks<KING>(s) & kings(c))
370 || (piece_attacks<ROOK>(s) & rooks_and_queens(c))
371 || (piece_attacks<BISHOP>(s) & bishops_and_queens(c));
375 /// Position::attacks_to() computes a bitboard containing all pieces which
376 /// attacks a given square. There are two versions of this function: One
377 /// which finds attackers of both colors, and one which only finds the
378 /// attackers for one side.
380 Bitboard Position::attacks_to(Square s) const {
382 return (pawn_attacks(BLACK, s) & pawns(WHITE))
383 | (pawn_attacks(WHITE, s) & pawns(BLACK))
384 | (piece_attacks<KNIGHT>(s) & pieces_of_type(KNIGHT))
385 | (piece_attacks<ROOK>(s) & rooks_and_queens())
386 | (piece_attacks<BISHOP>(s) & bishops_and_queens())
387 | (piece_attacks<KING>(s) & pieces_of_type(KING));
390 Bitboard Position::attacks_to(Square s, Color c) const {
392 return attacks_to(s) & pieces_of_color(c);
396 /// Position::piece_attacks_square() tests whether the piece on square f
397 /// attacks square t.
399 bool Position::piece_attacks_square(Square f, Square t) const {
401 assert(square_is_ok(f));
402 assert(square_is_ok(t));
406 case WP: return pawn_attacks_square(WHITE, f, t);
407 case BP: return pawn_attacks_square(BLACK, f, t);
408 case WN: case BN: return piece_attacks_square<KNIGHT>(f, t);
409 case WB: case BB: return piece_attacks_square<BISHOP>(f, t);
410 case WR: case BR: return piece_attacks_square<ROOK>(f, t);
411 case WQ: case BQ: return piece_attacks_square<QUEEN>(f, t);
412 case WK: case BK: return piece_attacks_square<KING>(f, t);
418 /// Position::move_attacks_square() tests whether a move from the current
419 /// position attacks a given square. Only attacks by the moving piece are
420 /// considered; the function does not handle X-ray attacks.
422 bool Position::move_attacks_square(Move m, Square s) const {
424 assert(move_is_ok(m));
425 assert(square_is_ok(s));
427 Square f = move_from(m), t = move_to(m);
429 assert(square_is_occupied(f));
433 case WP: return pawn_attacks_square(WHITE, t, s);
434 case BP: return pawn_attacks_square(BLACK, t, s);
435 case WN: case BN: return piece_attacks_square<KNIGHT>(t, s);
436 case WB: case BB: return piece_attacks_square<BISHOP>(t, s);
437 case WR: case BR: return piece_attacks_square<ROOK>(t, s);
438 case WQ: case BQ: return piece_attacks_square<QUEEN>(t, s);
439 case WK: case BK: return piece_attacks_square<KING>(t, s);
440 default: assert(false);
446 /// Position::find_checkers() computes the checkersBB bitboard, which
447 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
448 /// currently works by calling Position::attacks_to, which is probably
449 /// inefficient. Consider rewriting this function to use the last move
450 /// played, like in non-bitboard versions of Glaurung.
452 void Position::find_checkers() {
454 checkersBB = attacks_to(king_square(side_to_move()),opposite_color(side_to_move()));
458 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal.
459 /// There are two versions of this function: One which takes only a
460 /// move as input, and one which takes a move and a bitboard of pinned
461 /// pieces. The latter function is faster, and should always be preferred
462 /// when a pinned piece bitboard has already been computed.
464 bool Position::pl_move_is_legal(Move m) const {
466 return pl_move_is_legal(m, pinned_pieces(side_to_move()));
469 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
475 assert(move_is_ok(m));
476 assert(pinned == pinned_pieces(side_to_move()));
478 // If we're in check, all pseudo-legal moves are legal, because our
479 // check evasion generator only generates true legal moves.
483 // Castling moves are checked for legality during move generation.
484 if (move_is_castle(m))
488 them = opposite_color(us);
490 ksq = king_square(us);
492 assert(color_of_piece_on(from) == us);
493 assert(piece_on(ksq) == king_of_color(us));
495 // En passant captures are a tricky special case. Because they are
496 // rather uncommon, we do it simply by testing whether the king is attacked
497 // after the move is made
500 Square to = move_to(m);
501 Square capsq = make_square(square_file(to), square_rank(from));
502 Bitboard b = occupied_squares();
504 assert(to == ep_square());
505 assert(piece_on(from) == pawn_of_color(us));
506 assert(piece_on(capsq) == pawn_of_color(them));
507 assert(piece_on(to) == EMPTY);
510 clear_bit(&b, capsq);
513 return !(rook_attacks_bb(ksq, b) & rooks_and_queens(them))
514 && !(bishop_attacks_bb(ksq, b) & bishops_and_queens(them));
517 // If the moving piece is a king, check whether the destination
518 // square is attacked by the opponent.
520 return !(square_is_attacked(move_to(m), them));
522 // A non-king move is legal if and only if it is not pinned or it
523 // is moving along the ray towards or away from the king.
524 if ( !bit_is_set(pinned, from)
525 || (direction_between_squares(from, ksq) == direction_between_squares(move_to(m), ksq)))
532 /// Position::move_is_check() tests whether a pseudo-legal move is a check.
533 /// There are two versions of this function: One which takes only a move as
534 /// input, and one which takes a move and a bitboard of discovered check
535 /// candidates. The latter function is faster, and should always be preferred
536 /// when a discovered check candidates bitboard has already been computed.
538 bool Position::move_is_check(Move m) const {
540 Bitboard dc = discovered_check_candidates(side_to_move());
541 return move_is_check(m, dc);
544 bool Position::move_is_check(Move m, Bitboard dcCandidates) const {
547 Square ksq, from, to;
550 assert(move_is_ok(m));
551 assert(dcCandidates == discovered_check_candidates(side_to_move()));
554 them = opposite_color(us);
557 ksq = king_square(them);
559 assert(color_of_piece_on(from) == us);
560 assert(piece_on(ksq) == king_of_color(them));
562 // Proceed according to the type of the moving piece
563 switch (type_of_piece_on(from))
567 if (bit_is_set(pawn_attacks(them, ksq), to)) // Normal check?
570 if ( bit_is_set(dcCandidates, from) // Discovered check?
571 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
574 if (move_promotion(m)) // Promotion with check?
576 Bitboard b = occupied_squares();
579 switch (move_promotion(m))
582 return bit_is_set(piece_attacks<KNIGHT>(to), ksq);
584 return bit_is_set(bishop_attacks_bb(to, b), ksq);
586 return bit_is_set(rook_attacks_bb(to, b), ksq);
588 return bit_is_set(queen_attacks_bb(to, b), ksq);
593 // En passant capture with check? We have already handled the case
594 // of direct checks and ordinary discovered check, the only case we
595 // need to handle is the unusual case of a discovered check through the
597 else if (move_is_ep(m))
599 Square capsq = make_square(square_file(to), square_rank(from));
600 Bitboard b = occupied_squares();
602 clear_bit(&b, capsq);
604 return (rook_attacks_bb(ksq, b) & rooks_and_queens(us))
605 ||(bishop_attacks_bb(ksq, b) & bishops_and_queens(us));
610 return bit_is_set(dcCandidates, from) // Discovered check?
611 || bit_is_set(piece_attacks<KNIGHT>(ksq), to); // Normal check?
614 return bit_is_set(dcCandidates, from) // Discovered check?
615 || bit_is_set(piece_attacks<BISHOP>(ksq), to); // Normal check?
618 return bit_is_set(dcCandidates, from) // Discovered check?
619 || bit_is_set(piece_attacks<ROOK>(ksq), to); // Normal check?
622 // Discovered checks are impossible!
623 assert(!bit_is_set(dcCandidates, from));
624 return bit_is_set(piece_attacks<QUEEN>(ksq), to); // Normal check?
628 if ( bit_is_set(dcCandidates, from)
629 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
632 // Castling with check?
633 if (move_is_castle(m))
635 Square kfrom, kto, rfrom, rto;
636 Bitboard b = occupied_squares();
642 kto = relative_square(us, SQ_G1);
643 rto = relative_square(us, SQ_F1);
645 kto = relative_square(us, SQ_C1);
646 rto = relative_square(us, SQ_D1);
648 clear_bit(&b, kfrom);
649 clear_bit(&b, rfrom);
652 return bit_is_set(rook_attacks_bb(rto, b), ksq);
664 /// Position::move_is_capture() tests whether a move from the current
665 /// position is a capture.
667 bool Position::move_is_capture(Move m) const {
669 return color_of_piece_on(move_to(m)) == opposite_color(side_to_move())
674 /// Position::backup() is called when making a move. All information
675 /// necessary to restore the position when the move is later unmade
676 /// is saved to an UndoInfo object. The function Position::restore
677 /// does the reverse operation: When one does a backup followed by
678 /// a restore with the same UndoInfo object, the position is restored
679 /// to the state before backup was called.
681 void Position::backup(UndoInfo& u) const {
683 u.castleRights = castleRights;
684 u.epSquare = epSquare;
685 u.checkersBB = checkersBB;
688 u.materialKey = materialKey;
690 u.lastMove = lastMove;
691 u.capture = NO_PIECE_TYPE;
697 /// Position::restore() is called when unmaking a move. It copies back
698 /// the information backed up during a previous call to Position::backup.
700 void Position::restore(const UndoInfo& u) {
702 castleRights = u.castleRights;
703 epSquare = u.epSquare;
704 checkersBB = u.checkersBB;
707 materialKey = u.materialKey;
709 lastMove = u.lastMove;
710 // u.capture is restored in undo_move()
716 /// Position::do_move() makes a move, and backs up all information necessary
717 /// to undo the move to an UndoInfo object. The move is assumed to be legal.
718 /// Pseudo-legal moves should be filtered out before this function is called.
719 /// There are two versions of this function, one which takes only the move and
720 /// the UndoInfo as input, and one which takes a third parameter, a bitboard of
721 /// discovered check candidates. The second version is faster, because knowing
722 /// the discovered check candidates makes it easier to update the checkersBB
723 /// member variable in the position object.
725 void Position::do_move(Move m, UndoInfo& u) {
727 do_move(m, u, discovered_check_candidates(side_to_move()));
730 void Position::do_move(Move m, UndoInfo& u, Bitboard dcCandidates) {
733 assert(move_is_ok(m));
735 // Back up the necessary information to our UndoInfo object (except the
736 // captured piece, which is taken care of later.
739 // Save the current key to the history[] array, in order to be able to
740 // detect repetition draws.
741 history[gamePly] = key;
743 // Increment the 50 moves rule draw counter. Resetting it to zero in the
744 // case of non-reversible moves is taken care of later.
747 if (move_is_castle(m))
749 else if (move_promotion(m))
750 do_promotion_move(m, u);
751 else if (move_is_ep(m))
755 Color us = side_to_move();
756 Color them = opposite_color(us);
757 Square from = move_from(m);
758 Square to = move_to(m);
760 assert(color_of_piece_on(from) == us);
761 assert(color_of_piece_on(to) == them || piece_on(to) == EMPTY);
763 PieceType piece = type_of_piece_on(from);
764 PieceType capture = type_of_piece_on(to);
768 assert(capture != KING);
770 // Remove captured piece
771 clear_bit(&(byColorBB[them]), to);
772 clear_bit(&(byTypeBB[capture]), to);
775 key ^= zobrist[them][capture][to];
777 // If the captured piece was a pawn, update pawn hash key
779 pawnKey ^= zobrist[them][PAWN][to];
781 // Update incremental scores
782 mgValue -= mg_pst(them, capture, to);
783 egValue -= eg_pst(them, capture, to);
787 npMaterial[them] -= piece_value_midgame(capture);
789 // Update material hash key
790 materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];
792 // Update piece count
793 pieceCount[them][capture]--;
796 pieceList[them][capture][index[to]] = pieceList[them][capture][pieceCount[them][capture]];
797 index[pieceList[them][capture][index[to]]] = index[to];
799 // Remember the captured piece, in order to be able to undo the move correctly
802 // Reset rule 50 counter
807 clear_bit(&(byColorBB[us]), from);
808 clear_bit(&(byTypeBB[piece]), from);
809 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
810 set_bit(&(byColorBB[us]), to);
811 set_bit(&(byTypeBB[piece]), to);
812 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
813 board[to] = board[from];
817 key ^= zobrist[us][piece][from] ^ zobrist[us][piece][to];
819 // Update incremental scores
820 mgValue -= mg_pst(us, piece, from);
821 mgValue += mg_pst(us, piece, to);
822 egValue -= eg_pst(us, piece, from);
823 egValue += eg_pst(us, piece, to);
825 // If the moving piece was a king, update the king square
829 // If the move was a double pawn push, set the en passant square.
830 // This code is a bit ugly right now, and should be cleaned up later.
832 if (epSquare != SQ_NONE)
834 key ^= zobEp[epSquare];
839 if (abs(int(to) - int(from)) == 16)
842 && (pawn_attacks(WHITE, from + DELTA_N) & pawns(BLACK)))
844 && (pawn_attacks(BLACK, from + DELTA_S) & pawns(WHITE))))
846 epSquare = Square((int(from) + int(to)) / 2);
847 key ^= zobEp[epSquare];
850 // Reset rule 50 draw counter
853 // Update pawn hash key
854 pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
856 // Update piece lists
857 pieceList[us][piece][index[from]] = to;
858 index[to] = index[from];
860 // Update castle rights
861 key ^= zobCastle[castleRights];
862 castleRights &= castleRightsMask[from];
863 castleRights &= castleRightsMask[to];
864 key ^= zobCastle[castleRights];
866 // Update checkers bitboard
867 checkersBB = EmptyBoardBB;
868 Square ksq = king_square(them);
872 if (bit_is_set(pawn_attacks(them, ksq), to))
873 set_bit(&checkersBB, to);
875 if (bit_is_set(dcCandidates, from))
876 checkersBB |= ( (piece_attacks<ROOK>(ksq) & rooks_and_queens(us))
877 |(piece_attacks<BISHOP>(ksq) & bishops_and_queens(us)));
881 if (bit_is_set(piece_attacks<KNIGHT>(ksq), to))
882 set_bit(&checkersBB, to);
884 if (bit_is_set(dcCandidates, from))
885 checkersBB |= ( (piece_attacks<ROOK>(ksq) & rooks_and_queens(us))
886 |(piece_attacks<BISHOP>(ksq) & bishops_and_queens(us)));
890 if (bit_is_set(piece_attacks<BISHOP>(ksq), to))
891 set_bit(&checkersBB, to);
893 if (bit_is_set(dcCandidates, from))
894 checkersBB |= (piece_attacks<ROOK>(ksq) & rooks_and_queens(us));
898 if (bit_is_set(piece_attacks<ROOK>(ksq), to))
899 set_bit(&checkersBB, to);
901 if (bit_is_set(dcCandidates, from))
902 checkersBB |= (piece_attacks<BISHOP>(ksq) & bishops_and_queens(us));
906 if (bit_is_set(piece_attacks<QUEEN>(ksq), to))
907 set_bit(&checkersBB, to);
911 if (bit_is_set(dcCandidates, from))
912 checkersBB |= ( (piece_attacks<ROOK>(ksq) & rooks_and_queens(us))
913 |(piece_attacks<BISHOP>(ksq) & bishops_and_queens(us)));
923 key ^= zobSideToMove;
924 sideToMove = opposite_color(sideToMove);
927 mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
928 egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
934 /// Position::do_castle_move() is a private method used to make a castling
935 /// move. It is called from the main Position::do_move function. Note that
936 /// castling moves are encoded as "king captures friendly rook" moves, for
937 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
939 void Position::do_castle_move(Move m) {
942 assert(move_is_ok(m));
943 assert(move_is_castle(m));
945 Color us = side_to_move();
946 Color them = opposite_color(us);
948 // Find source squares for king and rook
949 Square kfrom = move_from(m);
950 Square rfrom = move_to(m); // HACK: See comment at beginning of function
953 assert(piece_on(kfrom) == king_of_color(us));
954 assert(piece_on(rfrom) == rook_of_color(us));
956 // Find destination squares for king and rook
957 if (rfrom > kfrom) // O-O
959 kto = relative_square(us, SQ_G1);
960 rto = relative_square(us, SQ_F1);
962 kto = relative_square(us, SQ_C1);
963 rto = relative_square(us, SQ_D1);
966 // Remove pieces from source squares
967 clear_bit(&(byColorBB[us]), kfrom);
968 clear_bit(&(byTypeBB[KING]), kfrom);
969 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
970 clear_bit(&(byColorBB[us]), rfrom);
971 clear_bit(&(byTypeBB[ROOK]), rfrom);
972 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
974 // Put pieces on destination squares
975 set_bit(&(byColorBB[us]), kto);
976 set_bit(&(byTypeBB[KING]), kto);
977 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
978 set_bit(&(byColorBB[us]), rto);
979 set_bit(&(byTypeBB[ROOK]), rto);
980 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
982 // Update board array
983 board[kfrom] = board[rfrom] = EMPTY;
984 board[kto] = king_of_color(us);
985 board[rto] = rook_of_color(us);
987 // Update king square
988 kingSquare[us] = kto;
990 // Update piece lists
991 pieceList[us][KING][index[kfrom]] = kto;
992 pieceList[us][ROOK][index[rfrom]] = rto;
993 int tmp = index[rfrom];
994 index[kto] = index[kfrom];
997 // Update incremental scores
998 mgValue -= mg_pst(us, KING, kfrom);
999 mgValue += mg_pst(us, KING, kto);
1000 egValue -= eg_pst(us, KING, kfrom);
1001 egValue += eg_pst(us, KING, kto);
1002 mgValue -= mg_pst(us, ROOK, rfrom);
1003 mgValue += mg_pst(us, ROOK, rto);
1004 egValue -= eg_pst(us, ROOK, rfrom);
1005 egValue += eg_pst(us, ROOK, rto);
1008 key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1009 key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1011 // Clear en passant square
1012 if(epSquare != SQ_NONE)
1014 key ^= zobEp[epSquare];
1018 // Update castling rights
1019 key ^= zobCastle[castleRights];
1020 castleRights &= castleRightsMask[kfrom];
1021 key ^= zobCastle[castleRights];
1023 // Reset rule 50 counter
1026 // Update checkers BB
1027 checkersBB = attacks_to(king_square(them), us);
1031 /// Position::do_promotion_move() is a private method used to make a promotion
1032 /// move. It is called from the main Position::do_move function. The
1033 /// UndoInfo object, which has been initialized in Position::do_move, is
1034 /// used to store the captured piece (if any).
1036 void Position::do_promotion_move(Move m, UndoInfo &u) {
1040 PieceType capture, promotion;
1043 assert(move_is_ok(m));
1044 assert(move_promotion(m));
1046 us = side_to_move();
1047 them = opposite_color(us);
1048 from = move_from(m);
1051 assert(relative_rank(us, to) == RANK_8);
1052 assert(piece_on(from) == pawn_of_color(us));
1053 assert(color_of_piece_on(to) == them || square_is_empty(to));
1055 capture = type_of_piece_on(to);
1059 assert(capture != KING);
1061 // Remove captured piece
1062 clear_bit(&(byColorBB[them]), to);
1063 clear_bit(&(byTypeBB[capture]), to);
1066 key ^= zobrist[them][capture][to];
1068 // Update incremental scores
1069 mgValue -= mg_pst(them, capture, to);
1070 egValue -= eg_pst(them, capture, to);
1072 // Update material. Because our move is a promotion, we know that the
1073 // captured piece is not a pawn.
1074 assert(capture != PAWN);
1075 npMaterial[them] -= piece_value_midgame(capture);
1077 // Update material hash key
1078 materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];
1080 // Update piece count
1081 pieceCount[them][capture]--;
1083 // Update piece list
1084 pieceList[them][capture][index[to]] = pieceList[them][capture][pieceCount[them][capture]];
1085 index[pieceList[them][capture][index[to]]] = index[to];
1087 // Remember the captured piece, in order to be able to undo the move correctly
1088 u.capture = capture;
1092 clear_bit(&(byColorBB[us]), from);
1093 clear_bit(&(byTypeBB[PAWN]), from);
1094 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1095 board[from] = EMPTY;
1097 // Insert promoted piece
1098 promotion = move_promotion(m);
1099 assert(promotion >= KNIGHT && promotion <= QUEEN);
1100 set_bit(&(byColorBB[us]), to);
1101 set_bit(&(byTypeBB[promotion]), to);
1102 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1103 board[to] = piece_of_color_and_type(us, promotion);
1106 key ^= zobrist[us][PAWN][from] ^ zobrist[us][promotion][to];
1108 // Update pawn hash key
1109 pawnKey ^= zobrist[us][PAWN][from];
1111 // Update material key
1112 materialKey ^= zobMaterial[us][PAWN][pieceCount[us][PAWN]];
1113 materialKey ^= zobMaterial[us][promotion][pieceCount[us][promotion]+1];
1115 // Update piece counts
1116 pieceCount[us][PAWN]--;
1117 pieceCount[us][promotion]++;
1119 // Update piece lists
1120 pieceList[us][PAWN][index[from]] = pieceList[us][PAWN][pieceCount[us][PAWN]];
1121 index[pieceList[us][PAWN][index[from]]] = index[from];
1122 pieceList[us][promotion][pieceCount[us][promotion] - 1] = to;
1123 index[to] = pieceCount[us][promotion] - 1;
1125 // Update incremental scores
1126 mgValue -= mg_pst(us, PAWN, from);
1127 mgValue += mg_pst(us, promotion, to);
1128 egValue -= eg_pst(us, PAWN, from);
1129 egValue += eg_pst(us, promotion, to);
1132 npMaterial[us] += piece_value_midgame(promotion);
1134 // Clear the en passant square
1135 if (epSquare != SQ_NONE)
1137 key ^= zobEp[epSquare];
1141 // Update castle rights
1142 key ^= zobCastle[castleRights];
1143 castleRights &= castleRightsMask[to];
1144 key ^= zobCastle[castleRights];
1146 // Reset rule 50 counter
1149 // Update checkers BB
1150 checkersBB = attacks_to(king_square(them), us);
1154 /// Position::do_ep_move() is a private method used to make an en passant
1155 /// capture. It is called from the main Position::do_move function. Because
1156 /// the captured piece is always a pawn, we don't need to pass an UndoInfo
1157 /// object in which to store the captured piece.
1159 void Position::do_ep_move(Move m) {
1162 Square from, to, capsq;
1165 assert(move_is_ok(m));
1166 assert(move_is_ep(m));
1168 us = side_to_move();
1169 them = opposite_color(us);
1170 from = move_from(m);
1172 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1174 assert(to == epSquare);
1175 assert(relative_rank(us, to) == RANK_6);
1176 assert(piece_on(to) == EMPTY);
1177 assert(piece_on(from) == pawn_of_color(us));
1178 assert(piece_on(capsq) == pawn_of_color(them));
1180 // Remove captured piece
1181 clear_bit(&(byColorBB[them]), capsq);
1182 clear_bit(&(byTypeBB[PAWN]), capsq);
1183 clear_bit(&(byTypeBB[0]), capsq); // HACK: byTypeBB[0] == occupied squares
1184 board[capsq] = EMPTY;
1186 // Remove moving piece from source square
1187 clear_bit(&(byColorBB[us]), from);
1188 clear_bit(&(byTypeBB[PAWN]), from);
1189 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1191 // Put moving piece on destination square
1192 set_bit(&(byColorBB[us]), to);
1193 set_bit(&(byTypeBB[PAWN]), to);
1194 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1195 board[to] = board[from];
1196 board[from] = EMPTY;
1198 // Update material hash key
1199 materialKey ^= zobMaterial[them][PAWN][pieceCount[them][PAWN]];
1201 // Update piece count
1202 pieceCount[them][PAWN]--;
1204 // Update piece list
1205 pieceList[us][PAWN][index[from]] = to;
1206 index[to] = index[from];
1207 pieceList[them][PAWN][index[capsq]] = pieceList[them][PAWN][pieceCount[them][PAWN]];
1208 index[pieceList[them][PAWN][index[capsq]]] = index[capsq];
1211 key ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1212 key ^= zobrist[them][PAWN][capsq];
1213 key ^= zobEp[epSquare];
1215 // Update pawn hash key
1216 pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1217 pawnKey ^= zobrist[them][PAWN][capsq];
1219 // Update incremental scores
1220 mgValue -= mg_pst(them, PAWN, capsq);
1221 mgValue -= mg_pst(us, PAWN, from);
1222 mgValue += mg_pst(us, PAWN, to);
1223 egValue -= eg_pst(them, PAWN, capsq);
1224 egValue -= eg_pst(us, PAWN, from);
1225 egValue += eg_pst(us, PAWN, to);
1227 // Reset en passant square
1230 // Reset rule 50 counter
1233 // Update checkers BB
1234 checkersBB = attacks_to(king_square(them), us);
1238 /// Position::undo_move() unmakes a move. When it returns, the position should
1239 /// be restored to exactly the same state as before the move was made. It is
1240 /// important that Position::undo_move is called with the same move and UndoInfo
1241 /// object as the earlier call to Position::do_move.
1243 void Position::undo_move(Move m, const UndoInfo &u) {
1246 assert(move_is_ok(m));
1249 sideToMove = opposite_color(sideToMove);
1251 // Restore information from our UndoInfo object (except the captured piece,
1252 // which is taken care of later)
1255 if (move_is_castle(m))
1256 undo_castle_move(m);
1257 else if (move_promotion(m))
1258 undo_promotion_move(m, u);
1259 else if (move_is_ep(m))
1265 PieceType piece, capture;
1267 us = side_to_move();
1268 them = opposite_color(us);
1269 from = move_from(m);
1272 assert(piece_on(from) == EMPTY);
1273 assert(color_of_piece_on(to) == us);
1275 // Put the piece back at the source square
1276 piece = type_of_piece_on(to);
1277 set_bit(&(byColorBB[us]), from);
1278 set_bit(&(byTypeBB[piece]), from);
1279 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1280 board[from] = piece_of_color_and_type(us, piece);
1282 // Clear the destination square
1283 clear_bit(&(byColorBB[us]), to);
1284 clear_bit(&(byTypeBB[piece]), to);
1285 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1287 // If the moving piece was a king, update the king square
1289 kingSquare[us] = from;
1291 // Update piece list
1292 pieceList[us][piece][index[to]] = from;
1293 index[from] = index[to];
1295 capture = u.capture;
1299 assert(capture != KING);
1301 // Replace the captured piece
1302 set_bit(&(byColorBB[them]), to);
1303 set_bit(&(byTypeBB[capture]), to);
1304 set_bit(&(byTypeBB[0]), to);
1305 board[to] = piece_of_color_and_type(them, capture);
1308 if (capture != PAWN)
1309 npMaterial[them] += piece_value_midgame(capture);
1311 // Update piece list
1312 pieceList[them][capture][pieceCount[them][capture]] = to;
1313 index[to] = pieceCount[them][capture];
1315 // Update piece count
1316 pieceCount[them][capture]++;
1325 /// Position::undo_castle_move() is a private method used to unmake a castling
1326 /// move. It is called from the main Position::undo_move function. Note that
1327 /// castling moves are encoded as "king captures friendly rook" moves, for
1328 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1330 void Position::undo_castle_move(Move m) {
1332 assert(move_is_ok(m));
1333 assert(move_is_castle(m));
1335 // When we have arrived here, some work has already been done by
1336 // Position::undo_move. In particular, the side to move has been switched,
1337 // so the code below is correct.
1338 Color us = side_to_move();
1340 // Find source squares for king and rook
1341 Square kfrom = move_from(m);
1342 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1345 // Find destination squares for king and rook
1346 if (rfrom > kfrom) // O-O
1348 kto = relative_square(us, SQ_G1);
1349 rto = relative_square(us, SQ_F1);
1351 kto = relative_square(us, SQ_C1);
1352 rto = relative_square(us, SQ_D1);
1355 assert(piece_on(kto) == king_of_color(us));
1356 assert(piece_on(rto) == rook_of_color(us));
1358 // Remove pieces from destination squares
1359 clear_bit(&(byColorBB[us]), kto);
1360 clear_bit(&(byTypeBB[KING]), kto);
1361 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1362 clear_bit(&(byColorBB[us]), rto);
1363 clear_bit(&(byTypeBB[ROOK]), rto);
1364 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1366 // Put pieces on source squares
1367 set_bit(&(byColorBB[us]), kfrom);
1368 set_bit(&(byTypeBB[KING]), kfrom);
1369 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1370 set_bit(&(byColorBB[us]), rfrom);
1371 set_bit(&(byTypeBB[ROOK]), rfrom);
1372 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1375 board[rto] = board[kto] = EMPTY;
1376 board[rfrom] = rook_of_color(us);
1377 board[kfrom] = king_of_color(us);
1379 // Update king square
1380 kingSquare[us] = kfrom;
1382 // Update piece lists
1383 pieceList[us][KING][index[kto]] = kfrom;
1384 pieceList[us][ROOK][index[rto]] = rfrom;
1385 int tmp = index[rto]; // Necessary because we may have rto == kfrom in FRC.
1386 index[kfrom] = index[kto];
1391 /// Position::undo_promotion_move() is a private method used to unmake a
1392 /// promotion move. It is called from the main Position::do_move
1393 /// function. The UndoInfo object, which has been initialized in
1394 /// Position::do_move, is used to put back the captured piece (if any).
1396 void Position::undo_promotion_move(Move m, const UndoInfo &u) {
1400 PieceType capture, promotion;
1402 assert(move_is_ok(m));
1403 assert(move_promotion(m));
1405 // When we have arrived here, some work has already been done by
1406 // Position::undo_move. In particular, the side to move has been switched,
1407 // so the code below is correct.
1408 us = side_to_move();
1409 them = opposite_color(us);
1410 from = move_from(m);
1413 assert(relative_rank(us, to) == RANK_8);
1414 assert(piece_on(from) == EMPTY);
1416 // Remove promoted piece
1417 promotion = move_promotion(m);
1418 assert(piece_on(to)==piece_of_color_and_type(us, promotion));
1419 assert(promotion >= KNIGHT && promotion <= QUEEN);
1420 clear_bit(&(byColorBB[us]), to);
1421 clear_bit(&(byTypeBB[promotion]), to);
1422 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1424 // Insert pawn at source square
1425 set_bit(&(byColorBB[us]), from);
1426 set_bit(&(byTypeBB[PAWN]), from);
1427 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1428 board[from] = pawn_of_color(us);
1431 npMaterial[us] -= piece_value_midgame(promotion);
1433 // Update piece list
1434 pieceList[us][PAWN][pieceCount[us][PAWN]] = from;
1435 index[from] = pieceCount[us][PAWN];
1436 pieceList[us][promotion][index[to]] =
1437 pieceList[us][promotion][pieceCount[us][promotion] - 1];
1438 index[pieceList[us][promotion][index[to]]] = index[to];
1440 // Update piece counts
1441 pieceCount[us][promotion]--;
1442 pieceCount[us][PAWN]++;
1444 capture = u.capture;
1448 assert(capture != KING);
1450 // Insert captured piece:
1451 set_bit(&(byColorBB[them]), to);
1452 set_bit(&(byTypeBB[capture]), to);
1453 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1454 board[to] = piece_of_color_and_type(them, capture);
1456 // Update material. Because the move is a promotion move, we know
1457 // that the captured piece cannot be a pawn.
1458 assert(capture != PAWN);
1459 npMaterial[them] += piece_value_midgame(capture);
1461 // Update piece list
1462 pieceList[them][capture][pieceCount[them][capture]] = to;
1463 index[to] = pieceCount[them][capture];
1465 // Update piece count
1466 pieceCount[them][capture]++;
1472 /// Position::undo_ep_move() is a private method used to unmake an en passant
1473 /// capture. It is called from the main Position::undo_move function. Because
1474 /// the captured piece is always a pawn, we don't need to pass an UndoInfo
1475 /// object from which to retrieve the captured piece.
1477 void Position::undo_ep_move(Move m) {
1479 assert(move_is_ok(m));
1480 assert(move_is_ep(m));
1482 // When we have arrived here, some work has already been done by
1483 // Position::undo_move. In particular, the side to move has been switched,
1484 // so the code below is correct.
1485 Color us = side_to_move();
1486 Color them = opposite_color(us);
1487 Square from = move_from(m);
1488 Square to = move_to(m);
1489 Square capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1491 assert(to == ep_square());
1492 assert(relative_rank(us, to) == RANK_6);
1493 assert(piece_on(to) == pawn_of_color(us));
1494 assert(piece_on(from) == EMPTY);
1495 assert(piece_on(capsq) == EMPTY);
1497 // Replace captured piece
1498 set_bit(&(byColorBB[them]), capsq);
1499 set_bit(&(byTypeBB[PAWN]), capsq);
1500 set_bit(&(byTypeBB[0]), capsq);
1501 board[capsq] = pawn_of_color(them);
1503 // Remove moving piece from destination square
1504 clear_bit(&(byColorBB[us]), to);
1505 clear_bit(&(byTypeBB[PAWN]), to);
1506 clear_bit(&(byTypeBB[0]), to);
1509 // Replace moving piece at source square
1510 set_bit(&(byColorBB[us]), from);
1511 set_bit(&(byTypeBB[PAWN]), from);
1512 set_bit(&(byTypeBB[0]), from);
1513 board[from] = pawn_of_color(us);
1515 // Update piece list:
1516 pieceList[us][PAWN][index[to]] = from;
1517 index[from] = index[to];
1518 pieceList[them][PAWN][pieceCount[them][PAWN]] = capsq;
1519 index[capsq] = pieceCount[them][PAWN];
1521 // Update piece count:
1522 pieceCount[them][PAWN]++;
1526 /// Position::do_null_move makes() a "null move": It switches the side to move
1527 /// and updates the hash key without executing any move on the board.
1529 void Position::do_null_move(UndoInfo &u) {
1532 assert(!is_check());
1534 // Back up the information necessary to undo the null move to the supplied
1535 // UndoInfo object. In the case of a null move, the only thing we need to
1536 // remember is the last move made and the en passant square.
1537 u.lastMove = lastMove;
1538 u.epSquare = epSquare;
1540 // Save the current key to the history[] array, in order to be able to
1541 // detect repetition draws.
1542 history[gamePly] = key;
1544 // Update the necessary information
1545 sideToMove = opposite_color(sideToMove);
1546 if (epSquare != SQ_NONE)
1547 key ^= zobEp[epSquare];
1552 key ^= zobSideToMove;
1554 mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1555 egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1561 /// Position::undo_null_move() unmakes a "null move".
1563 void Position::undo_null_move(const UndoInfo &u) {
1566 assert(!is_check());
1568 // Restore information from the supplied UndoInfo object:
1569 lastMove = u.lastMove;
1570 epSquare = u.epSquare;
1571 if (epSquare != SQ_NONE)
1572 key ^= zobEp[epSquare];
1574 // Update the necessary information.
1575 sideToMove = opposite_color(sideToMove);
1578 key ^= zobSideToMove;
1580 mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1581 egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1587 /// Position::see() is a static exchange evaluator: It tries to estimate the
1588 /// material gain or loss resulting from a move. There are two versions of
1589 /// this function: One which takes a move as input, and one which takes a
1590 /// 'from' and a 'to' square. The function does not yet understand promotions
1591 /// or en passant captures.
1593 int Position::see(Move m) const {
1595 assert(move_is_ok(m));
1596 return see(move_from(m), move_to(m));
1599 int Position::see(Square from, Square to) const {
1601 // Approximate material values, with pawn = 1
1602 static const int seeValues[18] = {
1603 0, 1, 3, 3, 5, 10, 100, 0, 0, 1, 3, 3, 5, 10, 100, 0, 0, 0
1606 Bitboard attackers, occ, b;
1608 assert(square_is_ok(from));
1609 assert(square_is_ok(to));
1611 // Initialize colors
1612 Color us = color_of_piece_on(from);
1613 Color them = opposite_color(us);
1615 // Initialize pieces
1616 Piece piece = piece_on(from);
1617 Piece capture = piece_on(to);
1619 // Find all attackers to the destination square, with the moving piece
1620 // removed, but possibly an X-ray attacker added behind it.
1621 occ = occupied_squares();
1622 clear_bit(&occ, from);
1623 attackers = (rook_attacks_bb(to, occ) & rooks_and_queens())
1624 | (bishop_attacks_bb(to, occ) & bishops_and_queens())
1625 | (piece_attacks<KNIGHT>(to) & knights())
1626 | (piece_attacks<KING>(to) & kings())
1627 | (pawn_attacks(WHITE, to) & pawns(BLACK))
1628 | (pawn_attacks(BLACK, to) & pawns(WHITE));
1630 // If the opponent has no attackers, we are finished
1631 if ((attackers & pieces_of_color(them)) == EmptyBoardBB)
1632 return seeValues[capture];
1634 attackers &= occ; // Remove the moving piece
1636 // The destination square is defended, which makes things rather more
1637 // difficult to compute. We proceed by building up a "swap list" containing
1638 // the material gain or loss at each stop in a sequence of captures to the
1639 // destination square, where the sides alternately capture, and always
1640 // capture with the least valuable piece. After each capture, we look for
1641 // new X-ray attacks from behind the capturing piece.
1642 int lastCapturingPieceValue = seeValues[piece];
1643 int swapList[32], n = 1;
1647 swapList[0] = seeValues[capture];
1650 // Locate the least valuable attacker for the side to move. The loop
1651 // below looks like it is potentially infinite, but it isn't. We know
1652 // that the side to move still has at least one attacker left.
1653 for (pt = PAWN; !(attackers & pieces_of_color_and_type(c, pt)); pt++)
1656 // Remove the attacker we just found from the 'attackers' bitboard,
1657 // and scan for new X-ray attacks behind the attacker.
1658 b = attackers & pieces_of_color_and_type(c, pt);
1660 attackers |= (rook_attacks_bb(to, occ) & rooks_and_queens())
1661 | (bishop_attacks_bb(to, occ) & bishops_and_queens());
1665 // Add the new entry to the swap list
1667 swapList[n] = -swapList[n - 1] + lastCapturingPieceValue;
1670 // Remember the value of the capturing piece, and change the side to move
1671 // before beginning the next iteration
1672 lastCapturingPieceValue = seeValues[pt];
1673 c = opposite_color(c);
1675 // Stop after a king capture
1676 if (pt == KING && (attackers & pieces_of_color(c)))
1679 swapList[n++] = 100;
1682 } while (attackers & pieces_of_color(c));
1684 // Having built the swap list, we negamax through it to find the best
1685 // achievable score from the point of view of the side to move
1687 swapList[n-1] = Min(-swapList[n], swapList[n-1]);
1693 /// Position::clear() erases the position object to a pristine state, with an
1694 /// empty board, white to move, and no castling rights.
1696 void Position::clear() {
1698 for (int i = 0; i < 64; i++)
1704 for (int i = 0; i < 2; i++)
1705 byColorBB[i] = EmptyBoardBB;
1707 for (int i = 0; i < 7; i++)
1709 byTypeBB[i] = EmptyBoardBB;
1710 pieceCount[0][i] = pieceCount[1][i] = 0;
1711 for (int j = 0; j < 8; j++)
1712 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1715 checkersBB = EmptyBoardBB;
1717 lastMove = MOVE_NONE;
1720 castleRights = NO_CASTLES;
1721 initialKFile = FILE_E;
1722 initialKRFile = FILE_H;
1723 initialQRFile = FILE_A;
1730 /// Position::reset_game_ply() simply sets gamePly to 0. It is used from the
1731 /// UCI interface code, whenever a non-reversible move is made in a
1732 /// 'position fen <fen> moves m1 m2 ...' command. This makes it possible
1733 /// for the program to handle games of arbitrary length, as long as the GUI
1734 /// handles draws by the 50 move rule correctly.
1736 void Position::reset_game_ply() {
1742 /// Position::put_piece() puts a piece on the given square of the board,
1743 /// updating the board array, bitboards, and piece counts.
1745 void Position::put_piece(Piece p, Square s) {
1747 Color c = color_of_piece(p);
1748 PieceType pt = type_of_piece(p);
1751 index[s] = pieceCount[c][pt];
1752 pieceList[c][pt][index[s]] = s;
1754 set_bit(&(byTypeBB[pt]), s);
1755 set_bit(&(byColorBB[c]), s);
1756 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1758 pieceCount[c][pt]++;
1765 /// Position::allow_oo() gives the given side the right to castle kingside.
1766 /// Used when setting castling rights during parsing of FEN strings.
1768 void Position::allow_oo(Color c) {
1770 castleRights |= (1 + int(c));
1774 /// Position::allow_ooo() gives the given side the right to castle queenside.
1775 /// Used when setting castling rights during parsing of FEN strings.
1777 void Position::allow_ooo(Color c) {
1779 castleRights |= (4 + 4*int(c));
1783 /// Position::compute_key() computes the hash key of the position. The hash
1784 /// key is usually updated incrementally as moves are made and unmade, the
1785 /// compute_key() function is only used when a new position is set up, and
1786 /// to verify the correctness of the hash key when running in debug mode.
1788 Key Position::compute_key() const {
1790 Key result = Key(0ULL);
1792 for (Square s = SQ_A1; s <= SQ_H8; s++)
1793 if (square_is_occupied(s))
1794 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1796 if (ep_square() != SQ_NONE)
1797 result ^= zobEp[ep_square()];
1799 result ^= zobCastle[castleRights];
1800 if (side_to_move() == BLACK)
1801 result ^= zobSideToMove;
1807 /// Position::compute_pawn_key() computes the hash key of the position. The
1808 /// hash key is usually updated incrementally as moves are made and unmade,
1809 /// the compute_pawn_key() function is only used when a new position is set
1810 /// up, and to verify the correctness of the pawn hash key when running in
1813 Key Position::compute_pawn_key() const {
1815 Key result = Key(0ULL);
1819 for (Color c = WHITE; c <= BLACK; c++)
1824 s = pop_1st_bit(&b);
1825 result ^= zobrist[c][PAWN][s];
1832 /// Position::compute_material_key() computes the hash key of the position.
1833 /// The hash key is usually updated incrementally as moves are made and unmade,
1834 /// the compute_material_key() function is only used when a new position is set
1835 /// up, and to verify the correctness of the material hash key when running in
1838 Key Position::compute_material_key() const {
1840 Key result = Key(0ULL);
1841 for (Color c = WHITE; c <= BLACK; c++)
1842 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1844 int count = piece_count(c, pt);
1845 for (int i = 0; i <= count; i++)
1846 result ^= zobMaterial[c][pt][i];
1852 /// Position::compute_mg_value() and Position::compute_eg_value() compute the
1853 /// incremental scores for the middle game and the endgame. These functions
1854 /// are used to initialize the incremental scores when a new position is set
1855 /// up, and to verify that the scores are correctly updated by do_move
1856 /// and undo_move when the program is running in debug mode.
1858 Value Position::compute_mg_value() const {
1860 Value result = Value(0);
1864 for (Color c = WHITE; c <= BLACK; c++)
1865 for (PieceType pt = PAWN; pt <= KING; pt++)
1867 b = pieces_of_color_and_type(c, pt);
1870 s = pop_1st_bit(&b);
1871 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1872 result += mg_pst(c, pt, s);
1875 result += (side_to_move() == WHITE)? TempoValueMidgame / 2 : -TempoValueMidgame / 2;
1879 Value Position::compute_eg_value() const {
1881 Value result = Value(0);
1885 for (Color c = WHITE; c <= BLACK; c++)
1886 for (PieceType pt = PAWN; pt <= KING; pt++)
1888 b = pieces_of_color_and_type(c, pt);
1891 s = pop_1st_bit(&b);
1892 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1893 result += eg_pst(c, pt, s);
1896 result += (side_to_move() == WHITE)? TempoValueEndgame / 2 : -TempoValueEndgame / 2;
1901 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1902 /// game material score for the given side. Material scores are updated
1903 /// incrementally during the search, this function is only used while
1904 /// initializing a new Position object.
1906 Value Position::compute_non_pawn_material(Color c) const {
1908 Value result = Value(0);
1911 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1913 Bitboard b = pieces_of_color_and_type(c, pt);
1916 s = pop_1st_bit(&b);
1917 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1918 result += piece_value_midgame(pt);
1925 /// Position::is_mate() returns true or false depending on whether the
1926 /// side to move is checkmated. Note that this function is currently very
1927 /// slow, and shouldn't be used frequently inside the search.
1929 bool Position::is_mate() {
1933 MovePicker mp = MovePicker(*this, false, MOVE_NONE, MOVE_NONE,
1934 MOVE_NONE, MOVE_NONE, Depth(0));
1935 return mp.get_next_move() == MOVE_NONE;
1941 /// Position::is_draw() tests whether the position is drawn by material,
1942 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1943 /// must be done by the search.
1945 bool Position::is_draw() const {
1947 // Draw by material?
1949 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1952 // Draw by the 50 moves rule?
1953 if (rule50 > 100 || (rule50 == 100 && !is_check()))
1956 // Draw by repetition?
1957 for (int i = 2; i < Min(gamePly, rule50); i += 2)
1958 if (history[gamePly - i] == key)
1965 /// Position::has_mate_threat() tests whether a given color has a mate in one
1966 /// from the current position. This function is quite slow, but it doesn't
1967 /// matter, because it is currently only called from PV nodes, which are rare.
1969 bool Position::has_mate_threat(Color c) {
1972 Color stm = side_to_move();
1974 // The following lines are useless and silly, but prevents gcc from
1975 // emitting a stupid warning stating that u1.lastMove and u1.epSquare might
1976 // be used uninitialized.
1977 u1.lastMove = lastMove;
1978 u1.epSquare = epSquare;
1983 // If the input color is not equal to the side to move, do a null move
1987 MoveStack mlist[120];
1989 bool result = false;
1991 // Generate legal moves
1992 count = generate_legal_moves(*this, mlist);
1994 // Loop through the moves, and see if one of them is mate
1995 for (int i = 0; i < count; i++)
1997 do_move(mlist[i].move, u2);
2001 undo_move(mlist[i].move, u2);
2004 // Undo null move, if necessary
2012 /// Position::init_zobrist() is a static member function which initializes the
2013 /// various arrays used to compute hash keys.
2015 void Position::init_zobrist() {
2017 for (int i = 0; i < 2; i++)
2018 for (int j = 0; j < 8; j++)
2019 for (int k = 0; k < 64; k++)
2020 zobrist[i][j][k] = Key(genrand_int64());
2022 for (int i = 0; i < 64; i++)
2023 zobEp[i] = Key(genrand_int64());
2025 for (int i = 0; i < 16; i++)
2026 zobCastle[i] = genrand_int64();
2028 zobSideToMove = genrand_int64();
2030 for (int i = 0; i < 2; i++)
2031 for (int j = 0; j < 8; j++)
2032 for (int k = 0; k < 16; k++)
2033 zobMaterial[i][j][k] = (k > 0)? Key(genrand_int64()) : Key(0LL);
2035 for (int i = 0; i < 16; i++)
2036 zobMaterial[0][KING][i] = zobMaterial[1][KING][i] = Key(0ULL);
2040 /// Position::init_piece_square_tables() initializes the piece square tables.
2041 /// This is a two-step operation: First, the white halves of the tables are
2042 /// copied from the MgPST[][] and EgPST[][] arrays, with a small random number
2043 /// added to each entry if the "Randomness" UCI parameter is non-zero.
2044 /// Second, the black halves of the tables are initialized by mirroring
2045 /// and changing the sign of the corresponding white scores.
2047 void Position::init_piece_square_tables() {
2049 int r = get_option_value_int("Randomness"), i;
2050 for (Square s = SQ_A1; s <= SQ_H8; s++)
2051 for (Piece p = WP; p <= WK; p++)
2053 i = (r == 0)? 0 : (genrand_int32() % (r*2) - r);
2054 MgPieceSquareTable[p][s] = Value(MgPST[p][s] + i);
2055 EgPieceSquareTable[p][s] = Value(EgPST[p][s] + i);
2058 for (Square s = SQ_A1; s <= SQ_H8; s++)
2059 for (Piece p = BP; p <= BK; p++)
2061 MgPieceSquareTable[p][s] = -MgPieceSquareTable[p-8][flip_square(s)];
2062 EgPieceSquareTable[p][s] = -EgPieceSquareTable[p-8][flip_square(s)];
2067 /// Position::flipped_copy() makes a copy of the input position, but with
2068 /// the white and black sides reversed. This is only useful for debugging,
2069 /// especially for finding evaluation symmetry bugs.
2071 void Position::flipped_copy(const Position &pos) {
2073 assert(pos.is_ok());
2078 for (Square s = SQ_A1; s <= SQ_H8; s++)
2079 if (!pos.square_is_empty(s))
2080 put_piece(Piece(int(pos.piece_on(s)) ^ 8), flip_square(s));
2083 sideToMove = opposite_color(pos.side_to_move());
2086 if (pos.can_castle_kingside(WHITE)) allow_oo(BLACK);
2087 if (pos.can_castle_queenside(WHITE)) allow_ooo(BLACK);
2088 if (pos.can_castle_kingside(BLACK)) allow_oo(WHITE);
2089 if (pos.can_castle_queenside(BLACK)) allow_ooo(WHITE);
2091 initialKFile = pos.initialKFile;
2092 initialKRFile = pos.initialKRFile;
2093 initialQRFile = pos.initialQRFile;
2095 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
2096 castleRightsMask[sq] = ALL_CASTLES;
2098 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
2099 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
2100 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
2101 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
2102 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
2103 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
2105 // En passant square
2106 if (pos.epSquare != SQ_NONE)
2107 epSquare = flip_square(pos.epSquare);
2113 key = compute_key();
2114 pawnKey = compute_pawn_key();
2115 materialKey = compute_material_key();
2117 // Incremental scores
2118 mgValue = compute_mg_value();
2119 egValue = compute_eg_value();
2122 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
2123 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
2129 /// Position::is_ok() performs some consitency checks for the position object.
2130 /// This is meant to be helpful when debugging.
2132 bool Position::is_ok(int* failedStep) const {
2134 // What features of the position should be verified?
2135 static const bool debugBitboards = false;
2136 static const bool debugKingCount = false;
2137 static const bool debugKingCapture = false;
2138 static const bool debugCheckerCount = false;
2139 static const bool debugKey = false;
2140 static const bool debugMaterialKey = false;
2141 static const bool debugPawnKey = false;
2142 static const bool debugIncrementalEval = false;
2143 static const bool debugNonPawnMaterial = false;
2144 static const bool debugPieceCounts = false;
2145 static const bool debugPieceList = false;
2147 if (failedStep) *failedStep = 1;
2150 if (!color_is_ok(side_to_move()))
2153 // Are the king squares in the position correct?
2154 if (failedStep) (*failedStep)++;
2155 if (piece_on(king_square(WHITE)) != WK)
2158 if (failedStep) (*failedStep)++;
2159 if (piece_on(king_square(BLACK)) != BK)
2163 if (failedStep) (*failedStep)++;
2164 if (!file_is_ok(initialKRFile))
2167 if (!file_is_ok(initialQRFile))
2170 // Do both sides have exactly one king?
2171 if (failedStep) (*failedStep)++;
2174 int kingCount[2] = {0, 0};
2175 for (Square s = SQ_A1; s <= SQ_H8; s++)
2176 if (type_of_piece_on(s) == KING)
2177 kingCount[color_of_piece_on(s)]++;
2179 if(kingCount[0] != 1 || kingCount[1] != 1)
2183 // Can the side to move capture the opponent's king?
2184 if (failedStep) (*failedStep)++;
2185 if (debugKingCapture)
2187 Color us = side_to_move();
2188 Color them = opposite_color(us);
2189 Square ksq = king_square(them);
2190 if (square_is_attacked(ksq, us))
2194 // Is there more than 2 checkers?
2195 if (failedStep) (*failedStep)++;
2196 if (debugCheckerCount && count_1s(checkersBB) > 2)
2200 if (failedStep) (*failedStep)++;
2203 // The intersection of the white and black pieces must be empty
2204 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
2207 // The union of the white and black pieces must be equal to all
2209 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
2212 // Separate piece type bitboards must have empty intersections
2213 for (PieceType p1 = PAWN; p1 <= KING; p1++)
2214 for (PieceType p2 = PAWN; p2 <= KING; p2++)
2215 if (p1 != p2 && (pieces_of_type(p1) & pieces_of_type(p2)))
2219 // En passant square OK?
2220 if (failedStep) (*failedStep)++;
2221 if (ep_square() != SQ_NONE)
2223 // The en passant square must be on rank 6, from the point of view of the
2225 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
2230 if (failedStep) (*failedStep)++;
2231 if (debugKey && key != compute_key())
2234 // Pawn hash key OK?
2235 if (failedStep) (*failedStep)++;
2236 if (debugPawnKey && pawnKey != compute_pawn_key())
2239 // Material hash key OK?
2240 if (failedStep) (*failedStep)++;
2241 if (debugMaterialKey && materialKey != compute_material_key())
2244 // Incremental eval OK?
2245 if (failedStep) (*failedStep)++;
2246 if (debugIncrementalEval)
2248 if (mgValue != compute_mg_value())
2251 if (egValue != compute_eg_value())
2255 // Non-pawn material OK?
2256 if (failedStep) (*failedStep)++;
2257 if (debugNonPawnMaterial)
2259 if(npMaterial[WHITE] != compute_non_pawn_material(WHITE))
2262 if(npMaterial[BLACK] != compute_non_pawn_material(BLACK))
2267 if (failedStep) (*failedStep)++;
2268 if (debugPieceCounts)
2269 for (Color c = WHITE; c <= BLACK; c++)
2270 for (PieceType pt = PAWN; pt <= KING; pt++)
2271 if (pieceCount[c][pt] != count_1s(pieces_of_color_and_type(c, pt)))
2274 if (failedStep) (*failedStep)++;
2277 for(Color c = WHITE; c <= BLACK; c++)
2278 for(PieceType pt = PAWN; pt <= KING; pt++)
2279 for(int i = 0; i < pieceCount[c][pt]; i++)
2281 if (piece_on(piece_list(c, pt, i)) != piece_of_color_and_type(c, pt))
2284 if (index[piece_list(c, pt, i)] != i)
2288 if (failedStep) *failedStep = 0;