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/>.
36 #include "ucioption.h"
43 extern SearchStack EmptySearchStack;
45 int Position::castleRightsMask[64];
47 Key Position::zobrist[2][8][64];
48 Key Position::zobEp[64];
49 Key Position::zobCastle[16];
50 Key Position::zobMaterial[2][8][16];
51 Key Position::zobSideToMove;
53 Value Position::MgPieceSquareTable[16][64];
54 Value Position::EgPieceSquareTable[16][64];
56 static bool RequestPending = false;
64 Position::Position(const Position& pos) {
68 Position::Position(const std::string& fen) {
73 /// Position::from_fen() initializes the position object with the given FEN
74 /// string. This function is not very robust - make sure that input FENs are
75 /// correct (this is assumed to be the responsibility of the GUI).
77 void Position::from_fen(const std::string& fen) {
79 static const std::string pieceLetters = "KQRBNPkqrbnp";
80 static const Piece pieces[] = { WK, WQ, WR, WB, WN, WP, BK, BQ, BR, BB, BN, BP };
88 for ( ; fen[i] != ' '; i++)
92 // Skip the given number of files
93 file += (fen[i] - '1' + 1);
96 else if (fen[i] == '/')
102 size_t idx = pieceLetters.find(fen[i]);
103 if (idx == std::string::npos)
105 std::cout << "Error in FEN at character " << i << std::endl;
108 Square square = make_square(file, rank);
109 put_piece(pieces[idx], square);
115 if (fen[i] != 'w' && fen[i] != 'b')
117 std::cout << "Error in FEN at character " << i << std::endl;
120 sideToMove = (fen[i] == 'w' ? WHITE : BLACK);
126 std::cout << "Error in FEN at character " << i << std::endl;
131 while(strchr("KQkqabcdefghABCDEFGH-", fen[i])) {
137 else if(fen[i] == 'K') allow_oo(WHITE);
138 else if(fen[i] == 'Q') allow_ooo(WHITE);
139 else if(fen[i] == 'k') allow_oo(BLACK);
140 else if(fen[i] == 'q') allow_ooo(BLACK);
141 else if(fen[i] >= 'A' && fen[i] <= 'H') {
142 File rookFile, kingFile = FILE_NONE;
143 for(Square square = SQ_B1; square <= SQ_G1; square++)
144 if(piece_on(square) == WK)
145 kingFile = square_file(square);
146 if(kingFile == FILE_NONE) {
147 std::cout << "Error in FEN at character " << i << std::endl;
150 initialKFile = kingFile;
151 rookFile = File(fen[i] - 'A') + FILE_A;
152 if(rookFile < initialKFile) {
154 initialQRFile = rookFile;
158 initialKRFile = rookFile;
161 else if(fen[i] >= 'a' && fen[i] <= 'h') {
162 File rookFile, kingFile = FILE_NONE;
163 for(Square square = SQ_B8; square <= SQ_G8; square++)
164 if(piece_on(square) == BK)
165 kingFile = square_file(square);
166 if(kingFile == FILE_NONE) {
167 std::cout << "Error in FEN at character " << i << std::endl;
170 initialKFile = kingFile;
171 rookFile = File(fen[i] - 'a') + FILE_A;
172 if(rookFile < initialKFile) {
174 initialQRFile = rookFile;
178 initialKRFile = rookFile;
182 std::cout << "Error in FEN at character " << i << std::endl;
189 while (fen[i] == ' ')
193 if ( i < fen.length() - 2
194 && (fen[i] >= 'a' && fen[i] <= 'h')
195 && (fen[i+1] == '3' || fen[i+1] == '6'))
196 st->epSquare = square_from_string(fen.substr(i, 2));
198 // Various initialisation
199 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
200 castleRightsMask[sq] = ALL_CASTLES;
202 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO|WHITE_OOO);
203 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO|BLACK_OOO);
204 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
205 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
206 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
207 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
210 find_hidden_checks();
212 st->key = compute_key();
213 st->pawnKey = compute_pawn_key();
214 st->materialKey = compute_material_key();
215 st->mgValue = compute_value<MidGame>();
216 st->egValue = compute_value<EndGame>();
217 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
218 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
222 /// Position::to_fen() converts the position object to a FEN string. This is
223 /// probably only useful for debugging.
225 const std::string Position::to_fen() const {
227 static const std::string pieceLetters = " PNBRQK pnbrqk";
231 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
234 for (File file = FILE_A; file <= FILE_H; file++)
236 Square sq = make_square(file, rank);
237 if (!square_is_occupied(sq))
243 fen += (char)skip + '0';
246 fen += pieceLetters[piece_on(sq)];
249 fen += (char)skip + '0';
251 fen += (rank > RANK_1 ? '/' : ' ');
253 fen += (sideToMove == WHITE ? "w " : "b ");
254 if (st->castleRights != NO_CASTLES)
256 if (can_castle_kingside(WHITE)) fen += 'K';
257 if (can_castle_queenside(WHITE)) fen += 'Q';
258 if (can_castle_kingside(BLACK)) fen += 'k';
259 if (can_castle_queenside(BLACK)) fen += 'q';
264 if (ep_square() != SQ_NONE)
265 fen += square_to_string(ep_square());
273 /// Position::print() prints an ASCII representation of the position to
274 /// the standard output. If a move is given then also the san is print.
276 void Position::print(Move m) const {
278 static const std::string pieceLetters = " PNBRQK PNBRQK .";
280 // Check for reentrancy, as example when called from inside
281 // MovePicker that is used also here in move_to_san()
285 RequestPending = true;
287 std::cout << std::endl;
290 std::string col = (color_of_piece_on(move_from(m)) == BLACK ? ".." : "");
291 std::cout << "Move is: " << col << move_to_san(*this, m) << std::endl;
293 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
295 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl;
296 for (File file = FILE_A; file <= FILE_H; file++)
298 Square sq = make_square(file, rank);
299 Piece piece = piece_on(sq);
300 if (piece == EMPTY && square_color(sq) == WHITE)
303 char col = (color_of_piece_on(sq) == BLACK ? '=' : ' ');
304 std::cout << '|' << col << pieceLetters[piece] << col;
306 std::cout << '|' << std::endl;
308 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl
309 << "Fen is: " << to_fen() << std::endl
310 << "Key is: " << st->key << std::endl;
312 RequestPending = false;
316 /// Position::copy() creates a copy of the input position.
318 void Position::copy(const Position &pos) {
320 memcpy(this, &pos, sizeof(Position));
324 /// Position:hidden_checks<>() returns a bitboard of all pinned (against the
325 /// king) pieces for the given color and for the given pinner type. Or, when
326 /// template parameter FindPinned is false, the pinned pieces of opposite color
327 /// that are, indeed, the pieces candidate for a discovery check.
328 /// Note that checkersBB bitboard must be already updated.
329 template<PieceType Piece, bool FindPinned>
330 Bitboard Position::hidden_checks(Color c, Square ksq, Bitboard& pinners) const {
333 Bitboard sliders, result = EmptyBoardBB;
335 if (Piece == ROOK) // Resolved at compile time
336 sliders = rooks_and_queens(FindPinned ? opposite_color(c) : c) & RookPseudoAttacks[ksq];
338 sliders = bishops_and_queens(FindPinned ? opposite_color(c) : c) & BishopPseudoAttacks[ksq];
340 if (sliders && (!FindPinned || (sliders & ~st->checkersBB)))
342 // King blockers are candidate pinned pieces
343 Bitboard candidate_pinned = piece_attacks<Piece>(ksq) & pieces_of_color(c);
345 // Pinners are sliders, not checkers, that give check when
346 // candidate pinned are removed.
347 pinners = (FindPinned ? sliders & ~st->checkersBB : sliders);
350 pinners &= rook_attacks_bb(ksq, occupied_squares() ^ candidate_pinned);
352 pinners &= bishop_attacks_bb(ksq, occupied_squares() ^ candidate_pinned);
354 // Finally for each pinner find the corresponding pinned piece (if same color of king)
355 // or discovery checker (if opposite color) among the candidates.
356 Bitboard p = pinners;
360 result |= (squares_between(s, ksq) & candidate_pinned);
364 pinners = EmptyBoardBB;
370 /// Position::attacks_to() computes a bitboard containing all pieces which
371 /// attacks a given square. There are two versions of this function: One
372 /// which finds attackers of both colors, and one which only finds the
373 /// attackers for one side.
375 Bitboard Position::attacks_to(Square s) const {
377 return (pawn_attacks(BLACK, s) & pawns(WHITE))
378 | (pawn_attacks(WHITE, s) & pawns(BLACK))
379 | (piece_attacks<KNIGHT>(s) & pieces_of_type(KNIGHT))
380 | (piece_attacks<ROOK>(s) & rooks_and_queens())
381 | (piece_attacks<BISHOP>(s) & bishops_and_queens())
382 | (piece_attacks<KING>(s) & pieces_of_type(KING));
385 /// Position::piece_attacks_square() tests whether the piece on square f
386 /// attacks square t.
388 bool Position::piece_attacks_square(Piece p, Square f, Square t) const {
390 assert(square_is_ok(f));
391 assert(square_is_ok(t));
395 case WP: return pawn_attacks_square(WHITE, f, t);
396 case BP: return pawn_attacks_square(BLACK, f, t);
397 case WN: case BN: return piece_attacks_square<KNIGHT>(f, t);
398 case WB: case BB: return piece_attacks_square<BISHOP>(f, t);
399 case WR: case BR: return piece_attacks_square<ROOK>(f, t);
400 case WQ: case BQ: return piece_attacks_square<QUEEN>(f, t);
401 case WK: case BK: return piece_attacks_square<KING>(f, t);
408 /// Position::move_attacks_square() tests whether a move from the current
409 /// position attacks a given square.
411 bool Position::move_attacks_square(Move m, Square s) const {
413 assert(move_is_ok(m));
414 assert(square_is_ok(s));
416 Square f = move_from(m), t = move_to(m);
418 assert(square_is_occupied(f));
420 if (piece_attacks_square(piece_on(f), t, s))
423 // Move the piece and scan for X-ray attacks behind it
424 Bitboard occ = occupied_squares();
425 Color us = color_of_piece_on(f);
428 Bitboard xray = ( (rook_attacks_bb(s, occ) & rooks_and_queens())
429 |(bishop_attacks_bb(s, occ) & bishops_and_queens())) & pieces_of_color(us);
431 // If we have attacks we need to verify that are caused by our move
432 // and are not already existent ones.
433 return xray && (xray ^ (xray & piece_attacks<QUEEN>(s)));
437 /// Position::find_checkers() computes the checkersBB bitboard, which
438 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
439 /// currently works by calling Position::attacks_to, which is probably
440 /// inefficient. Consider rewriting this function to use the last move
441 /// played, like in non-bitboard versions of Glaurung.
443 void Position::find_checkers() {
445 Color us = side_to_move();
446 st->checkersBB = attacks_to(king_square(us), opposite_color(us));
449 /// Position:find_hidden_checks() computes the pinned, pinners and dcCandidates
450 /// bitboards. There are two versions of this function. One takes a color and
451 /// computes bitboards relative to that color only, the other computes both
452 /// colors. Bitboard checkersBB must be already updated.
454 void Position::find_hidden_checks(Color us, unsigned int types) {
457 Color them = opposite_color(us);
458 Square ksq = king_square(them);
461 st->pinned[them] = hidden_checks<ROOK, true>(them, ksq, p1) | hidden_checks<BISHOP, true>(them, ksq, p2);
462 st->pinners[them] = p1 | p2;
464 if (types & DcCandidates)
465 st->dcCandidates[us] = hidden_checks<ROOK, false>(us, ksq, p1) | hidden_checks<BISHOP, false>(us, ksq, p2);
468 void Position::find_hidden_checks() {
470 for (Color c = WHITE; c <= BLACK; c++)
471 find_hidden_checks(c, Pinned | DcCandidates);
475 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
477 bool Position::pl_move_is_legal(Move m) const {
480 assert(move_is_ok(m));
482 // If we're in check, all pseudo-legal moves are legal, because our
483 // check evasion generator only generates true legal moves.
487 // Castling moves are checked for legality during move generation.
488 if (move_is_castle(m))
491 Color us = side_to_move();
492 Color them = opposite_color(us);
493 Square from = move_from(m);
494 Square ksq = king_square(us);
496 assert(color_of_piece_on(from) == us);
497 assert(piece_on(ksq) == piece_of_color_and_type(us, KING));
499 // En passant captures are a tricky special case. Because they are
500 // rather uncommon, we do it simply by testing whether the king is attacked
501 // after the move is made
504 Square to = move_to(m);
505 Square capsq = make_square(square_file(to), square_rank(from));
506 Bitboard b = occupied_squares();
508 assert(to == ep_square());
509 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
510 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
511 assert(piece_on(to) == EMPTY);
514 clear_bit(&b, capsq);
517 return !(rook_attacks_bb(ksq, b) & rooks_and_queens(them))
518 && !(bishop_attacks_bb(ksq, b) & bishops_and_queens(them));
521 // If the moving piece is a king, check whether the destination
522 // square is attacked by the opponent.
524 return !(square_is_attacked(move_to(m), them));
526 // A non-king move is legal if and only if it is not pinned or it
527 // is moving along the ray towards or away from the king.
528 return ( !bit_is_set(pinned_pieces(us), from)
529 || (direction_between_squares(from, ksq) == direction_between_squares(move_to(m), ksq)));
533 /// Position::move_is_check() tests whether a pseudo-legal move is a check
535 bool Position::move_is_check(Move m) const {
538 assert(move_is_ok(m));
540 Color us = side_to_move();
541 Color them = opposite_color(us);
542 Square from = move_from(m);
543 Square to = move_to(m);
544 Square ksq = king_square(them);
545 Bitboard dcCandidates = discovered_check_candidates(us);
547 assert(color_of_piece_on(from) == us);
548 assert(piece_on(ksq) == piece_of_color_and_type(them, KING));
550 // Proceed according to the type of the moving piece
551 switch (type_of_piece_on(from))
555 if (bit_is_set(pawn_attacks(them, ksq), to)) // Normal check?
558 if ( bit_is_set(dcCandidates, from) // Discovered check?
559 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
562 if (move_promotion(m)) // Promotion with check?
564 Bitboard b = occupied_squares();
567 switch (move_promotion(m))
570 return bit_is_set(piece_attacks<KNIGHT>(to), ksq);
572 return bit_is_set(bishop_attacks_bb(to, b), ksq);
574 return bit_is_set(rook_attacks_bb(to, b), ksq);
576 return bit_is_set(queen_attacks_bb(to, b), ksq);
581 // En passant capture with check? We have already handled the case
582 // of direct checks and ordinary discovered check, the only case we
583 // need to handle is the unusual case of a discovered check through the
585 else if (move_is_ep(m))
587 Square capsq = make_square(square_file(to), square_rank(from));
588 Bitboard b = occupied_squares();
590 clear_bit(&b, capsq);
592 return (rook_attacks_bb(ksq, b) & rooks_and_queens(us))
593 ||(bishop_attacks_bb(ksq, b) & bishops_and_queens(us));
598 return bit_is_set(dcCandidates, from) // Discovered check?
599 || bit_is_set(piece_attacks<KNIGHT>(ksq), to); // Normal check?
602 return bit_is_set(dcCandidates, from) // Discovered check?
603 || bit_is_set(piece_attacks<BISHOP>(ksq), to); // Normal check?
606 return bit_is_set(dcCandidates, from) // Discovered check?
607 || bit_is_set(piece_attacks<ROOK>(ksq), to); // Normal check?
610 // Discovered checks are impossible!
611 assert(!bit_is_set(dcCandidates, from));
612 return bit_is_set(piece_attacks<QUEEN>(ksq), to); // Normal check?
616 if ( bit_is_set(dcCandidates, from)
617 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
620 // Castling with check?
621 if (move_is_castle(m))
623 Square kfrom, kto, rfrom, rto;
624 Bitboard b = occupied_squares();
630 kto = relative_square(us, SQ_G1);
631 rto = relative_square(us, SQ_F1);
633 kto = relative_square(us, SQ_C1);
634 rto = relative_square(us, SQ_D1);
636 clear_bit(&b, kfrom);
637 clear_bit(&b, rfrom);
640 return bit_is_set(rook_attacks_bb(rto, b), ksq);
644 default: // NO_PIECE_TYPE
652 /// Position::move_is_capture() tests whether a move from the current
653 /// position is a capture. Move must not be MOVE_NONE.
655 bool Position::move_is_capture(Move m) const {
657 assert(m != MOVE_NONE);
659 return ( !square_is_empty(move_to(m))
660 && (color_of_piece_on(move_to(m)) != color_of_piece_on(move_from(m)))
666 /// Position::update_checkers() udpates chekers info given the move. It is called
667 /// in do_move() and is faster then find_checkers().
669 template<PieceType Piece>
670 inline void Position::update_checkers(Bitboard* pCheckersBB, Square ksq, Square from,
671 Square to, Bitboard dcCandidates) {
673 if (Piece != KING && bit_is_set(piece_attacks<Piece>(ksq), to))
674 set_bit(pCheckersBB, to);
676 if (Piece != QUEEN && bit_is_set(dcCandidates, from))
679 (*pCheckersBB) |= (piece_attacks<ROOK>(ksq) & rooks_and_queens(side_to_move()));
682 (*pCheckersBB) |= (piece_attacks<BISHOP>(ksq) & bishops_and_queens(side_to_move()));
687 /// Position::update_hidden_checks() udpates pinned, pinners and dcCandidates
688 /// bitboards incrementally, given the move. It is called in do_move and is
689 /// faster then find_hidden_checks().
691 void Position::update_hidden_checks(Square from, Square to) {
693 Color us = sideToMove;
694 Color them = opposite_color(us);
695 Square ksq = king_square(opposite_color(us));
697 Bitboard moveSquares = EmptyBoardBB;
698 set_bit(&moveSquares, from);
699 set_bit(&moveSquares, to);
701 // Our moving piece could have been a possible pinner or hidden checker behind a dcCandidates?
702 bool checkerMoved = (st->dcCandidates[us] | st->pinners[them]) && (moveSquares & sliders());
704 // If we are moving from/to an opponent king attack direction and we was a possible hidden checker
705 // or there exsist some possible hidden checker on that line then recalculate the position
706 // otherwise skip because our dcCandidates and opponent pinned pieces are not changed.
707 if ( (moveSquares & RookPseudoAttacks[ksq]) && (checkerMoved || (rooks_and_queens(us) & RookPseudoAttacks[ksq]))
708 || (moveSquares & BishopPseudoAttacks[ksq]) && (checkerMoved || (bishops_and_queens(us) & BishopPseudoAttacks[ksq])))
709 find_hidden_checks(us, Pinned | DcCandidates);
711 ksq = king_square(us);
715 find_hidden_checks(them, Pinned | DcCandidates);
719 // It is possible that we have captured an opponent hidden checker?
720 Bitboard checkerCaptured = st->capture && (st->dcCandidates[them] || bit_is_set(st->pinners[us], to));
722 // If we are moving from/to an our king attack direction and there was/is some possible
723 // opponent hidden checker then calculate the position otherwise skip because opponent
724 // dcCandidates and our pinned pieces are not changed.
725 if ( (moveSquares & RookPseudoAttacks[ksq]) && (checkerCaptured || (rooks_and_queens(them) & RookPseudoAttacks[ksq]))
726 || (moveSquares & BishopPseudoAttacks[ksq]) && (checkerCaptured || (bishops_and_queens(them) & BishopPseudoAttacks[ksq])))
728 find_hidden_checks(them, Pinned);
730 // If we don't have opponent dc candidates and we are moving in the
731 // attack line then won't be any dc candidates also after the move.
732 if ( st->dcCandidates[them]
733 || (bit_is_set(RookPseudoAttacks[ksq], from) && (rooks_and_queens(them) & RookPseudoAttacks[ksq]))
734 || (bit_is_set(BishopPseudoAttacks[ksq], from) && (bishops_and_queens(them) & BishopPseudoAttacks[ksq])))
735 find_hidden_checks(them, DcCandidates);
740 /// Position::do_move() makes a move, and saves all information necessary
741 /// to a StateInfo object. The move is assumed to be legal.
742 /// Pseudo-legal moves should be filtered out before this function is called.
744 void Position::do_move(Move m, StateInfo& newSt) {
747 assert(move_is_ok(m));
749 // Get now the current (before to move) dc candidates that we will use
750 // in update_checkers().
751 Bitboard oldDcCandidates = discovered_check_candidates(side_to_move());
753 // Copy some fields of old state to our new StateInfo object (except the
754 // captured piece, which is taken care of later) and switch state pointer
755 // to point to the new, ready to be updated, state.
757 newSt.capture = NO_PIECE_TYPE;
761 // Save the current key to the history[] array, in order to be able to
762 // detect repetition draws.
763 history[gamePly] = st->key;
765 // Increment the 50 moves rule draw counter. Resetting it to zero in the
766 // case of non-reversible moves is taken care of later.
769 if (move_is_castle(m))
771 else if (move_promotion(m))
772 do_promotion_move(m);
773 else if (move_is_ep(m))
777 Color us = side_to_move();
778 Color them = opposite_color(us);
779 Square from = move_from(m);
780 Square to = move_to(m);
782 assert(color_of_piece_on(from) == us);
783 assert(color_of_piece_on(to) == them || piece_on(to) == EMPTY);
785 PieceType piece = type_of_piece_on(from);
787 st->capture = type_of_piece_on(to);
790 do_capture_move(m, st->capture, them, to);
793 clear_bit(&(byColorBB[us]), from);
794 clear_bit(&(byTypeBB[piece]), from);
795 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
796 set_bit(&(byColorBB[us]), to);
797 set_bit(&(byTypeBB[piece]), to);
798 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
799 board[to] = board[from];
803 st->key ^= zobrist[us][piece][from] ^ zobrist[us][piece][to];
805 // Update incremental scores
806 st->mgValue -= pst<MidGame>(us, piece, from);
807 st->mgValue += pst<MidGame>(us, piece, to);
808 st->egValue -= pst<EndGame>(us, piece, from);
809 st->egValue += pst<EndGame>(us, piece, to);
811 // If the moving piece was a king, update the king square
815 // Reset en passant square
816 if (st->epSquare != SQ_NONE)
818 st->key ^= zobEp[st->epSquare];
819 st->epSquare = SQ_NONE;
822 // If the moving piece was a pawn do some special extra work
825 // Reset rule 50 draw counter
828 // Update pawn hash key
829 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
831 // Set en passant square, only if moved pawn can be captured
832 if (abs(int(to) - int(from)) == 16)
834 if ( (us == WHITE && (pawn_attacks(WHITE, from + DELTA_N) & pawns(BLACK)))
835 || (us == BLACK && (pawn_attacks(BLACK, from + DELTA_S) & pawns(WHITE))))
837 st->epSquare = Square((int(from) + int(to)) / 2);
838 st->key ^= zobEp[st->epSquare];
843 // Update piece lists
844 pieceList[us][piece][index[from]] = to;
845 index[to] = index[from];
847 // Update castle rights
848 st->key ^= zobCastle[st->castleRights];
849 st->castleRights &= castleRightsMask[from];
850 st->castleRights &= castleRightsMask[to];
851 st->key ^= zobCastle[st->castleRights];
853 // Update checkers bitboard, piece must be already moved
854 st->checkersBB = EmptyBoardBB;
855 Square ksq = king_square(them);
858 case PAWN: update_checkers<PAWN>(&st->checkersBB, ksq, from, to, oldDcCandidates); break;
859 case KNIGHT: update_checkers<KNIGHT>(&st->checkersBB, ksq, from, to, oldDcCandidates); break;
860 case BISHOP: update_checkers<BISHOP>(&st->checkersBB, ksq, from, to, oldDcCandidates); break;
861 case ROOK: update_checkers<ROOK>(&st->checkersBB, ksq, from, to, oldDcCandidates); break;
862 case QUEEN: update_checkers<QUEEN>(&st->checkersBB, ksq, from, to, oldDcCandidates); break;
863 case KING: update_checkers<KING>(&st->checkersBB, ksq, from, to, oldDcCandidates); break;
864 default: assert(false); break;
867 update_hidden_checks(from, to);
871 st->key ^= zobSideToMove;
872 sideToMove = opposite_color(sideToMove);
875 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
876 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
882 /// Position::do_capture_move() is a private method used to update captured
883 /// piece info. It is called from the main Position::do_move function.
885 void Position::do_capture_move(Move m, PieceType capture, Color them, Square to) {
887 assert(capture != KING);
889 // Remove captured piece
890 clear_bit(&(byColorBB[them]), to);
891 clear_bit(&(byTypeBB[capture]), to);
894 st->key ^= zobrist[them][capture][to];
896 // If the captured piece was a pawn, update pawn hash key
898 st->pawnKey ^= zobrist[them][PAWN][to];
900 // Update incremental scores
901 st->mgValue -= pst<MidGame>(them, capture, to);
902 st->egValue -= pst<EndGame>(them, capture, to);
904 assert(!move_promotion(m) || capture != PAWN);
908 npMaterial[them] -= piece_value_midgame(capture);
910 // Update material hash key
911 st->materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];
913 // Update piece count
914 pieceCount[them][capture]--;
917 pieceList[them][capture][index[to]] = pieceList[them][capture][pieceCount[them][capture]];
918 index[pieceList[them][capture][index[to]]] = index[to];
920 // Reset rule 50 counter
925 /// Position::do_castle_move() is a private method used to make a castling
926 /// move. It is called from the main Position::do_move function. Note that
927 /// castling moves are encoded as "king captures friendly rook" moves, for
928 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
930 void Position::do_castle_move(Move m) {
933 assert(move_is_ok(m));
934 assert(move_is_castle(m));
936 Color us = side_to_move();
937 Color them = opposite_color(us);
939 // Find source squares for king and rook
940 Square kfrom = move_from(m);
941 Square rfrom = move_to(m); // HACK: See comment at beginning of function
944 assert(piece_on(kfrom) == piece_of_color_and_type(us, KING));
945 assert(piece_on(rfrom) == piece_of_color_and_type(us, ROOK));
947 // Find destination squares for king and rook
948 if (rfrom > kfrom) // O-O
950 kto = relative_square(us, SQ_G1);
951 rto = relative_square(us, SQ_F1);
953 kto = relative_square(us, SQ_C1);
954 rto = relative_square(us, SQ_D1);
957 // Remove pieces from source squares
958 clear_bit(&(byColorBB[us]), kfrom);
959 clear_bit(&(byTypeBB[KING]), kfrom);
960 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
961 clear_bit(&(byColorBB[us]), rfrom);
962 clear_bit(&(byTypeBB[ROOK]), rfrom);
963 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
965 // Put pieces on destination squares
966 set_bit(&(byColorBB[us]), kto);
967 set_bit(&(byTypeBB[KING]), kto);
968 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
969 set_bit(&(byColorBB[us]), rto);
970 set_bit(&(byTypeBB[ROOK]), rto);
971 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
973 // Update board array
974 board[kfrom] = board[rfrom] = EMPTY;
975 board[kto] = piece_of_color_and_type(us, KING);
976 board[rto] = piece_of_color_and_type(us, ROOK);
978 // Update king square
979 kingSquare[us] = kto;
981 // Update piece lists
982 pieceList[us][KING][index[kfrom]] = kto;
983 pieceList[us][ROOK][index[rfrom]] = rto;
984 int tmp = index[rfrom];
985 index[kto] = index[kfrom];
988 // Update incremental scores
989 st->mgValue -= pst<MidGame>(us, KING, kfrom);
990 st->mgValue += pst<MidGame>(us, KING, kto);
991 st->egValue -= pst<EndGame>(us, KING, kfrom);
992 st->egValue += pst<EndGame>(us, KING, kto);
993 st->mgValue -= pst<MidGame>(us, ROOK, rfrom);
994 st->mgValue += pst<MidGame>(us, ROOK, rto);
995 st->egValue -= pst<EndGame>(us, ROOK, rfrom);
996 st->egValue += pst<EndGame>(us, ROOK, rto);
999 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1000 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1002 // Clear en passant square
1003 if (st->epSquare != SQ_NONE)
1005 st->key ^= zobEp[st->epSquare];
1006 st->epSquare = SQ_NONE;
1009 // Update castling rights
1010 st->key ^= zobCastle[st->castleRights];
1011 st->castleRights &= castleRightsMask[kfrom];
1012 st->key ^= zobCastle[st->castleRights];
1014 // Reset rule 50 counter
1017 // Update checkers BB
1018 st->checkersBB = attacks_to(king_square(them), us);
1020 // Update hidden checks
1021 find_hidden_checks();
1025 /// Position::do_promotion_move() is a private method used to make a promotion
1026 /// move. It is called from the main Position::do_move function.
1028 void Position::do_promotion_move(Move m) {
1032 PieceType promotion;
1035 assert(move_is_ok(m));
1036 assert(move_promotion(m));
1038 us = side_to_move();
1039 them = opposite_color(us);
1040 from = move_from(m);
1043 assert(relative_rank(us, to) == RANK_8);
1044 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
1045 assert(color_of_piece_on(to) == them || square_is_empty(to));
1047 st->capture = type_of_piece_on(to);
1050 do_capture_move(m, st->capture, them, to);
1053 clear_bit(&(byColorBB[us]), from);
1054 clear_bit(&(byTypeBB[PAWN]), from);
1055 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1056 board[from] = EMPTY;
1058 // Insert promoted piece
1059 promotion = move_promotion(m);
1060 assert(promotion >= KNIGHT && promotion <= QUEEN);
1061 set_bit(&(byColorBB[us]), to);
1062 set_bit(&(byTypeBB[promotion]), to);
1063 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1064 board[to] = piece_of_color_and_type(us, promotion);
1067 st->key ^= zobrist[us][PAWN][from] ^ zobrist[us][promotion][to];
1069 // Update pawn hash key
1070 st->pawnKey ^= zobrist[us][PAWN][from];
1072 // Update material key
1073 st->materialKey ^= zobMaterial[us][PAWN][pieceCount[us][PAWN]];
1074 st->materialKey ^= zobMaterial[us][promotion][pieceCount[us][promotion]+1];
1076 // Update piece counts
1077 pieceCount[us][PAWN]--;
1078 pieceCount[us][promotion]++;
1080 // Update piece lists
1081 pieceList[us][PAWN][index[from]] = pieceList[us][PAWN][pieceCount[us][PAWN]];
1082 index[pieceList[us][PAWN][index[from]]] = index[from];
1083 pieceList[us][promotion][pieceCount[us][promotion] - 1] = to;
1084 index[to] = pieceCount[us][promotion] - 1;
1086 // Update incremental scores
1087 st->mgValue -= pst<MidGame>(us, PAWN, from);
1088 st->mgValue += pst<MidGame>(us, promotion, to);
1089 st->egValue -= pst<EndGame>(us, PAWN, from);
1090 st->egValue += pst<EndGame>(us, promotion, to);
1093 npMaterial[us] += piece_value_midgame(promotion);
1095 // Clear the en passant square
1096 if (st->epSquare != SQ_NONE)
1098 st->key ^= zobEp[st->epSquare];
1099 st->epSquare = SQ_NONE;
1102 // Update castle rights
1103 st->key ^= zobCastle[st->castleRights];
1104 st->castleRights &= castleRightsMask[to];
1105 st->key ^= zobCastle[st->castleRights];
1107 // Reset rule 50 counter
1110 // Update checkers BB
1111 st->checkersBB = attacks_to(king_square(them), us);
1113 // Update hidden checks
1114 find_hidden_checks();
1118 /// Position::do_ep_move() is a private method used to make an en passant
1119 /// capture. It is called from the main Position::do_move function.
1121 void Position::do_ep_move(Move m) {
1124 Square from, to, capsq;
1127 assert(move_is_ok(m));
1128 assert(move_is_ep(m));
1130 us = side_to_move();
1131 them = opposite_color(us);
1132 from = move_from(m);
1134 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1136 assert(to == st->epSquare);
1137 assert(relative_rank(us, to) == RANK_6);
1138 assert(piece_on(to) == EMPTY);
1139 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
1140 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
1142 // Remove captured piece
1143 clear_bit(&(byColorBB[them]), capsq);
1144 clear_bit(&(byTypeBB[PAWN]), capsq);
1145 clear_bit(&(byTypeBB[0]), capsq); // HACK: byTypeBB[0] == occupied squares
1146 board[capsq] = EMPTY;
1148 // Remove moving piece from source square
1149 clear_bit(&(byColorBB[us]), from);
1150 clear_bit(&(byTypeBB[PAWN]), from);
1151 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1153 // Put moving piece on destination square
1154 set_bit(&(byColorBB[us]), to);
1155 set_bit(&(byTypeBB[PAWN]), to);
1156 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1157 board[to] = board[from];
1158 board[from] = EMPTY;
1160 // Update material hash key
1161 st->materialKey ^= zobMaterial[them][PAWN][pieceCount[them][PAWN]];
1163 // Update piece count
1164 pieceCount[them][PAWN]--;
1166 // Update piece list
1167 pieceList[us][PAWN][index[from]] = to;
1168 index[to] = index[from];
1169 pieceList[them][PAWN][index[capsq]] = pieceList[them][PAWN][pieceCount[them][PAWN]];
1170 index[pieceList[them][PAWN][index[capsq]]] = index[capsq];
1173 st->key ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1174 st->key ^= zobrist[them][PAWN][capsq];
1175 st->key ^= zobEp[st->epSquare];
1177 // Update pawn hash key
1178 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1179 st->pawnKey ^= zobrist[them][PAWN][capsq];
1181 // Update incremental scores
1182 st->mgValue -= pst<MidGame>(them, PAWN, capsq);
1183 st->mgValue -= pst<MidGame>(us, PAWN, from);
1184 st->mgValue += pst<MidGame>(us, PAWN, to);
1185 st->egValue -= pst<EndGame>(them, PAWN, capsq);
1186 st->egValue -= pst<EndGame>(us, PAWN, from);
1187 st->egValue += pst<EndGame>(us, PAWN, to);
1189 // Reset en passant square
1190 st->epSquare = SQ_NONE;
1192 // Reset rule 50 counter
1195 // Update checkers BB
1196 st->checkersBB = attacks_to(king_square(them), us);
1198 // Update hidden checks
1199 find_hidden_checks();
1203 /// Position::undo_move() unmakes a move. When it returns, the position should
1204 /// be restored to exactly the same state as before the move was made.
1206 void Position::undo_move(Move m) {
1209 assert(move_is_ok(m));
1212 sideToMove = opposite_color(sideToMove);
1214 if (move_is_castle(m))
1215 undo_castle_move(m);
1216 else if (move_promotion(m))
1217 undo_promotion_move(m);
1218 else if (move_is_ep(m))
1226 us = side_to_move();
1227 them = opposite_color(us);
1228 from = move_from(m);
1231 assert(piece_on(from) == EMPTY);
1232 assert(color_of_piece_on(to) == us);
1234 // Put the piece back at the source square
1235 piece = type_of_piece_on(to);
1236 set_bit(&(byColorBB[us]), from);
1237 set_bit(&(byTypeBB[piece]), from);
1238 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1239 board[from] = piece_of_color_and_type(us, piece);
1241 // Clear the destination square
1242 clear_bit(&(byColorBB[us]), to);
1243 clear_bit(&(byTypeBB[piece]), to);
1244 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1246 // If the moving piece was a king, update the king square
1248 kingSquare[us] = from;
1250 // Update piece list
1251 pieceList[us][piece][index[to]] = from;
1252 index[from] = index[to];
1256 assert(st->capture != KING);
1258 // Replace the captured piece
1259 set_bit(&(byColorBB[them]), to);
1260 set_bit(&(byTypeBB[st->capture]), to);
1261 set_bit(&(byTypeBB[0]), to);
1262 board[to] = piece_of_color_and_type(them, st->capture);
1265 if (st->capture != PAWN)
1266 npMaterial[them] += piece_value_midgame(st->capture);
1268 // Update piece list
1269 pieceList[them][st->capture][pieceCount[them][st->capture]] = to;
1270 index[to] = pieceCount[them][st->capture];
1272 // Update piece count
1273 pieceCount[them][st->capture]++;
1278 // Finally point out state pointer back to the previous state
1285 /// Position::undo_castle_move() is a private method used to unmake a castling
1286 /// move. It is called from the main Position::undo_move function. Note that
1287 /// castling moves are encoded as "king captures friendly rook" moves, for
1288 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1290 void Position::undo_castle_move(Move m) {
1292 assert(move_is_ok(m));
1293 assert(move_is_castle(m));
1295 // When we have arrived here, some work has already been done by
1296 // Position::undo_move. In particular, the side to move has been switched,
1297 // so the code below is correct.
1298 Color us = side_to_move();
1300 // Find source squares for king and rook
1301 Square kfrom = move_from(m);
1302 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1305 // Find destination squares for king and rook
1306 if (rfrom > kfrom) // O-O
1308 kto = relative_square(us, SQ_G1);
1309 rto = relative_square(us, SQ_F1);
1311 kto = relative_square(us, SQ_C1);
1312 rto = relative_square(us, SQ_D1);
1315 assert(piece_on(kto) == piece_of_color_and_type(us, KING));
1316 assert(piece_on(rto) == piece_of_color_and_type(us, ROOK));
1318 // Remove pieces from destination squares
1319 clear_bit(&(byColorBB[us]), kto);
1320 clear_bit(&(byTypeBB[KING]), kto);
1321 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1322 clear_bit(&(byColorBB[us]), rto);
1323 clear_bit(&(byTypeBB[ROOK]), rto);
1324 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1326 // Put pieces on source squares
1327 set_bit(&(byColorBB[us]), kfrom);
1328 set_bit(&(byTypeBB[KING]), kfrom);
1329 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1330 set_bit(&(byColorBB[us]), rfrom);
1331 set_bit(&(byTypeBB[ROOK]), rfrom);
1332 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1335 board[rto] = board[kto] = EMPTY;
1336 board[rfrom] = piece_of_color_and_type(us, ROOK);
1337 board[kfrom] = piece_of_color_and_type(us, KING);
1339 // Update king square
1340 kingSquare[us] = kfrom;
1342 // Update piece lists
1343 pieceList[us][KING][index[kto]] = kfrom;
1344 pieceList[us][ROOK][index[rto]] = rfrom;
1345 int tmp = index[rto]; // Necessary because we may have rto == kfrom in FRC.
1346 index[kfrom] = index[kto];
1351 /// Position::undo_promotion_move() is a private method used to unmake a
1352 /// promotion move. It is called from the main Position::do_move
1355 void Position::undo_promotion_move(Move m) {
1359 PieceType promotion;
1361 assert(move_is_ok(m));
1362 assert(move_promotion(m));
1364 // When we have arrived here, some work has already been done by
1365 // Position::undo_move. In particular, the side to move has been switched,
1366 // so the code below is correct.
1367 us = side_to_move();
1368 them = opposite_color(us);
1369 from = move_from(m);
1372 assert(relative_rank(us, to) == RANK_8);
1373 assert(piece_on(from) == EMPTY);
1375 // Remove promoted piece
1376 promotion = move_promotion(m);
1377 assert(piece_on(to)==piece_of_color_and_type(us, promotion));
1378 assert(promotion >= KNIGHT && promotion <= QUEEN);
1379 clear_bit(&(byColorBB[us]), to);
1380 clear_bit(&(byTypeBB[promotion]), to);
1381 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1383 // Insert pawn at source square
1384 set_bit(&(byColorBB[us]), from);
1385 set_bit(&(byTypeBB[PAWN]), from);
1386 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1387 board[from] = piece_of_color_and_type(us, PAWN);
1390 npMaterial[us] -= piece_value_midgame(promotion);
1392 // Update piece list
1393 pieceList[us][PAWN][pieceCount[us][PAWN]] = from;
1394 index[from] = pieceCount[us][PAWN];
1395 pieceList[us][promotion][index[to]] =
1396 pieceList[us][promotion][pieceCount[us][promotion] - 1];
1397 index[pieceList[us][promotion][index[to]]] = index[to];
1399 // Update piece counts
1400 pieceCount[us][promotion]--;
1401 pieceCount[us][PAWN]++;
1405 assert(st->capture != KING);
1407 // Insert captured piece:
1408 set_bit(&(byColorBB[them]), to);
1409 set_bit(&(byTypeBB[st->capture]), to);
1410 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1411 board[to] = piece_of_color_and_type(them, st->capture);
1413 // Update material. Because the move is a promotion move, we know
1414 // that the captured piece cannot be a pawn.
1415 assert(st->capture != PAWN);
1416 npMaterial[them] += piece_value_midgame(st->capture);
1418 // Update piece list
1419 pieceList[them][st->capture][pieceCount[them][st->capture]] = to;
1420 index[to] = pieceCount[them][st->capture];
1422 // Update piece count
1423 pieceCount[them][st->capture]++;
1429 /// Position::undo_ep_move() is a private method used to unmake an en passant
1430 /// capture. It is called from the main Position::undo_move function.
1432 void Position::undo_ep_move(Move m) {
1434 assert(move_is_ok(m));
1435 assert(move_is_ep(m));
1437 // When we have arrived here, some work has already been done by
1438 // Position::undo_move. In particular, the side to move has been switched,
1439 // so the code below is correct.
1440 Color us = side_to_move();
1441 Color them = opposite_color(us);
1442 Square from = move_from(m);
1443 Square to = move_to(m);
1444 Square capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1446 assert(to == st->previous->epSquare);
1447 assert(relative_rank(us, to) == RANK_6);
1448 assert(piece_on(to) == piece_of_color_and_type(us, PAWN));
1449 assert(piece_on(from) == EMPTY);
1450 assert(piece_on(capsq) == EMPTY);
1452 // Replace captured piece
1453 set_bit(&(byColorBB[them]), capsq);
1454 set_bit(&(byTypeBB[PAWN]), capsq);
1455 set_bit(&(byTypeBB[0]), capsq);
1456 board[capsq] = piece_of_color_and_type(them, PAWN);
1458 // Remove moving piece from destination square
1459 clear_bit(&(byColorBB[us]), to);
1460 clear_bit(&(byTypeBB[PAWN]), to);
1461 clear_bit(&(byTypeBB[0]), to);
1464 // Replace moving piece at source square
1465 set_bit(&(byColorBB[us]), from);
1466 set_bit(&(byTypeBB[PAWN]), from);
1467 set_bit(&(byTypeBB[0]), from);
1468 board[from] = piece_of_color_and_type(us, PAWN);
1470 // Update piece list:
1471 pieceList[us][PAWN][index[to]] = from;
1472 index[from] = index[to];
1473 pieceList[them][PAWN][pieceCount[them][PAWN]] = capsq;
1474 index[capsq] = pieceCount[them][PAWN];
1476 // Update piece count:
1477 pieceCount[them][PAWN]++;
1481 /// Position::do_null_move makes() a "null move": It switches the side to move
1482 /// and updates the hash key without executing any move on the board.
1484 void Position::do_null_move(StateInfo& newSt) {
1487 assert(!is_check());
1489 // Back up the information necessary to undo the null move to the supplied
1490 // StateInfo object. In the case of a null move, the only thing we need to
1491 // remember is the last move made and the en passant square.
1492 newSt.lastMove = st->lastMove;
1493 newSt.epSquare = st->epSquare;
1494 newSt.previous = st->previous;
1495 st->previous = &newSt;
1497 // Save the current key to the history[] array, in order to be able to
1498 // detect repetition draws.
1499 history[gamePly] = st->key;
1501 // Update the necessary information
1502 sideToMove = opposite_color(sideToMove);
1503 if (st->epSquare != SQ_NONE)
1504 st->key ^= zobEp[st->epSquare];
1506 st->epSquare = SQ_NONE;
1509 st->key ^= zobSideToMove;
1511 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1512 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1518 /// Position::undo_null_move() unmakes a "null move".
1520 void Position::undo_null_move() {
1523 assert(!is_check());
1525 // Restore information from the our StateInfo object
1526 st->lastMove = st->previous->lastMove;
1527 st->epSquare = st->previous->epSquare;
1528 st->previous = st->previous->previous;
1530 if (st->epSquare != SQ_NONE)
1531 st->key ^= zobEp[st->epSquare];
1533 // Update the necessary information
1534 sideToMove = opposite_color(sideToMove);
1537 st->key ^= zobSideToMove;
1539 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1540 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1546 /// Position::see() is a static exchange evaluator: It tries to estimate the
1547 /// material gain or loss resulting from a move. There are three versions of
1548 /// this function: One which takes a destination square as input, one takes a
1549 /// move, and one which takes a 'from' and a 'to' square. The function does
1550 /// not yet understand promotions captures.
1552 int Position::see(Square to) const {
1554 assert(square_is_ok(to));
1555 return see(SQ_NONE, to);
1558 int Position::see(Move m) const {
1560 assert(move_is_ok(m));
1561 return see(move_from(m), move_to(m));
1564 int Position::see(Square from, Square to) const {
1567 static const int seeValues[18] = {
1568 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1569 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1570 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1571 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1575 Bitboard attackers, occ, b;
1577 assert(square_is_ok(from) || from == SQ_NONE);
1578 assert(square_is_ok(to));
1580 // Initialize colors
1581 Color us = (from != SQ_NONE ? color_of_piece_on(from) : opposite_color(color_of_piece_on(to)));
1582 Color them = opposite_color(us);
1584 // Initialize pinned and pinners bitboards
1585 Bitboard pinned[2], pinners[2];
1586 pinned[us] = pinned_pieces(us, pinners[us]);
1587 pinned[them] = pinned_pieces(them, pinners[them]);
1589 // Initialize pieces
1590 Piece piece = piece_on(from);
1591 Piece capture = piece_on(to);
1593 // Find all attackers to the destination square, with the moving piece
1594 // removed, but possibly an X-ray attacker added behind it.
1595 occ = occupied_squares();
1597 // Handle en passant moves
1598 if (st->epSquare == to && type_of_piece_on(from) == PAWN)
1600 assert(capture == EMPTY);
1602 Square capQq = (side_to_move() == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1603 capture = piece_on(capQq);
1605 assert(type_of_piece_on(capQq) == PAWN);
1607 // Remove the captured pawn
1608 clear_bit(&occ, capQq);
1613 clear_bit(&occ, from);
1614 attackers = (rook_attacks_bb(to, occ) & rooks_and_queens())
1615 | (bishop_attacks_bb(to, occ) & bishops_and_queens())
1616 | (piece_attacks<KNIGHT>(to) & knights())
1617 | (piece_attacks<KING>(to) & kings())
1618 | (pawn_attacks(WHITE, to) & pawns(BLACK))
1619 | (pawn_attacks(BLACK, to) & pawns(WHITE));
1621 // Remove our pinned pieces from attacks if the captured piece is not
1622 // a pinner, otherwise we could remove a valid "capture the pinner" attack.
1623 if (pinned[us] != EmptyBoardBB && !bit_is_set(pinners[us], to))
1624 attackers &= ~pinned[us];
1626 // Remove opponent pinned pieces from attacks if the moving piece is not
1627 // a pinner, otherwise we could remove a piece that is no more pinned
1628 // due to our pinner piece is moving away.
1629 if (pinned[them] != EmptyBoardBB && !bit_is_set(pinners[them], from))
1630 attackers &= ~pinned[them];
1632 if (from != SQ_NONE)
1635 // If we don't have any attacker we are finished
1636 if ((attackers & pieces_of_color(us)) == EmptyBoardBB)
1639 // Locate the least valuable attacker to the destination square
1640 // and use it to initialize from square.
1642 for (pt = PAWN; !(attackers & pieces_of_color_and_type(us, pt)); pt++)
1645 from = first_1(attackers & pieces_of_color_and_type(us, pt));
1646 piece = piece_on(from);
1649 // If the opponent has no attackers we are finished
1650 if ((attackers & pieces_of_color(them)) == EmptyBoardBB)
1651 return seeValues[capture];
1653 attackers &= occ; // Remove the moving piece
1655 // The destination square is defended, which makes things rather more
1656 // difficult to compute. We proceed by building up a "swap list" containing
1657 // the material gain or loss at each stop in a sequence of captures to the
1658 // destination square, where the sides alternately capture, and always
1659 // capture with the least valuable piece. After each capture, we look for
1660 // new X-ray attacks from behind the capturing piece.
1661 int lastCapturingPieceValue = seeValues[piece];
1662 int swapList[32], n = 1;
1666 swapList[0] = seeValues[capture];
1669 // Locate the least valuable attacker for the side to move. The loop
1670 // below looks like it is potentially infinite, but it isn't. We know
1671 // that the side to move still has at least one attacker left.
1672 for (pt = PAWN; !(attackers & pieces_of_color_and_type(c, pt)); pt++)
1675 // Remove the attacker we just found from the 'attackers' bitboard,
1676 // and scan for new X-ray attacks behind the attacker.
1677 b = attackers & pieces_of_color_and_type(c, pt);
1679 attackers |= (rook_attacks_bb(to, occ) & rooks_and_queens())
1680 | (bishop_attacks_bb(to, occ) & bishops_and_queens());
1684 // Add the new entry to the swap list
1686 swapList[n] = -swapList[n - 1] + lastCapturingPieceValue;
1689 // Remember the value of the capturing piece, and change the side to move
1690 // before beginning the next iteration
1691 lastCapturingPieceValue = seeValues[pt];
1692 c = opposite_color(c);
1694 // Remove pinned pieces from attackers
1695 if ( pinned[c] != EmptyBoardBB
1696 && !bit_is_set(pinners[c], to)
1697 && !(pinners[c] & attackers))
1698 attackers &= ~pinned[c];
1700 // Stop after a king capture
1701 if (pt == KING && (attackers & pieces_of_color(c)))
1704 swapList[n++] = 100;
1707 } while (attackers & pieces_of_color(c));
1709 // Having built the swap list, we negamax through it to find the best
1710 // achievable score from the point of view of the side to move
1712 swapList[n-1] = Min(-swapList[n], swapList[n-1]);
1718 /// Position::setStartState() copies the content of the argument
1719 /// inside startState and makes st point to it. This is needed
1720 /// when the st pointee could become stale, as example because
1721 /// the caller is about to going out of scope.
1723 void Position::setStartState(const StateInfo& s) {
1730 /// Position::clear() erases the position object to a pristine state, with an
1731 /// empty board, white to move, and no castling rights.
1733 void Position::clear() {
1736 memset(st, 0, sizeof(StateInfo));
1737 st->epSquare = SQ_NONE;
1739 memset(index, 0, sizeof(int) * 64);
1740 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1742 for (int i = 0; i < 64; i++)
1745 for (int i = 0; i < 7; i++)
1747 byTypeBB[i] = EmptyBoardBB;
1748 pieceCount[0][i] = pieceCount[1][i] = 0;
1749 for (int j = 0; j < 8; j++)
1750 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1755 initialKFile = FILE_E;
1756 initialKRFile = FILE_H;
1757 initialQRFile = FILE_A;
1761 /// Position::reset_game_ply() simply sets gamePly to 0. It is used from the
1762 /// UCI interface code, whenever a non-reversible move is made in a
1763 /// 'position fen <fen> moves m1 m2 ...' command. This makes it possible
1764 /// for the program to handle games of arbitrary length, as long as the GUI
1765 /// handles draws by the 50 move rule correctly.
1767 void Position::reset_game_ply() {
1773 /// Position::put_piece() puts a piece on the given square of the board,
1774 /// updating the board array, bitboards, and piece counts.
1776 void Position::put_piece(Piece p, Square s) {
1778 Color c = color_of_piece(p);
1779 PieceType pt = type_of_piece(p);
1782 index[s] = pieceCount[c][pt];
1783 pieceList[c][pt][index[s]] = s;
1785 set_bit(&(byTypeBB[pt]), s);
1786 set_bit(&(byColorBB[c]), s);
1787 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1789 pieceCount[c][pt]++;
1796 /// Position::allow_oo() gives the given side the right to castle kingside.
1797 /// Used when setting castling rights during parsing of FEN strings.
1799 void Position::allow_oo(Color c) {
1801 st->castleRights |= (1 + int(c));
1805 /// Position::allow_ooo() gives the given side the right to castle queenside.
1806 /// Used when setting castling rights during parsing of FEN strings.
1808 void Position::allow_ooo(Color c) {
1810 st->castleRights |= (4 + 4*int(c));
1814 /// Position::compute_key() computes the hash key of the position. The hash
1815 /// key is usually updated incrementally as moves are made and unmade, the
1816 /// compute_key() function is only used when a new position is set up, and
1817 /// to verify the correctness of the hash key when running in debug mode.
1819 Key Position::compute_key() const {
1821 Key result = Key(0ULL);
1823 for (Square s = SQ_A1; s <= SQ_H8; s++)
1824 if (square_is_occupied(s))
1825 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1827 if (ep_square() != SQ_NONE)
1828 result ^= zobEp[ep_square()];
1830 result ^= zobCastle[st->castleRights];
1831 if (side_to_move() == BLACK)
1832 result ^= zobSideToMove;
1838 /// Position::compute_pawn_key() computes the hash key of the position. The
1839 /// hash key is usually updated incrementally as moves are made and unmade,
1840 /// the compute_pawn_key() function is only used when a new position is set
1841 /// up, and to verify the correctness of the pawn hash key when running in
1844 Key Position::compute_pawn_key() const {
1846 Key result = Key(0ULL);
1850 for (Color c = WHITE; c <= BLACK; c++)
1855 s = pop_1st_bit(&b);
1856 result ^= zobrist[c][PAWN][s];
1863 /// Position::compute_material_key() computes the hash key of the position.
1864 /// The hash key is usually updated incrementally as moves are made and unmade,
1865 /// the compute_material_key() function is only used when a new position is set
1866 /// up, and to verify the correctness of the material hash key when running in
1869 Key Position::compute_material_key() const {
1871 Key result = Key(0ULL);
1872 for (Color c = WHITE; c <= BLACK; c++)
1873 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1875 int count = piece_count(c, pt);
1876 for (int i = 0; i <= count; i++)
1877 result ^= zobMaterial[c][pt][i];
1883 /// Position::compute_value() compute the incremental scores for the middle
1884 /// game and the endgame. These functions are used to initialize the incremental
1885 /// scores when a new position is set up, and to verify that the scores are correctly
1886 /// updated by do_move and undo_move when the program is running in debug mode.
1887 template<Position::GamePhase Phase>
1888 Value Position::compute_value() const {
1890 Value result = Value(0);
1894 for (Color c = WHITE; c <= BLACK; c++)
1895 for (PieceType pt = PAWN; pt <= KING; pt++)
1897 b = pieces_of_color_and_type(c, pt);
1900 s = pop_1st_bit(&b);
1901 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1902 result += pst<Phase>(c, pt, s);
1906 const Value TempoValue = (Phase == MidGame ? TempoValueMidgame : TempoValueEndgame);
1907 result += (side_to_move() == WHITE)? TempoValue / 2 : -TempoValue / 2;
1912 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1913 /// game material score for the given side. Material scores are updated
1914 /// incrementally during the search, this function is only used while
1915 /// initializing a new Position object.
1917 Value Position::compute_non_pawn_material(Color c) const {
1919 Value result = Value(0);
1922 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1924 Bitboard b = pieces_of_color_and_type(c, pt);
1927 s = pop_1st_bit(&b);
1928 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1929 result += piece_value_midgame(pt);
1936 /// Position::is_mate() returns true or false depending on whether the
1937 /// side to move is checkmated. Note that this function is currently very
1938 /// slow, and shouldn't be used frequently inside the search.
1940 bool Position::is_mate() const {
1944 MovePicker mp = MovePicker(*this, false, MOVE_NONE, EmptySearchStack, Depth(0));
1945 return mp.get_next_move() == MOVE_NONE;
1951 /// Position::is_draw() tests whether the position is drawn by material,
1952 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1953 /// must be done by the search.
1955 bool Position::is_draw() const {
1957 // Draw by material?
1959 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1962 // Draw by the 50 moves rule?
1963 if (st->rule50 > 100 || (st->rule50 == 100 && !is_check()))
1966 // Draw by repetition?
1967 for (int i = 2; i < Min(gamePly, st->rule50); i += 2)
1968 if (history[gamePly - i] == st->key)
1975 /// Position::has_mate_threat() tests whether a given color has a mate in one
1976 /// from the current position. This function is quite slow, but it doesn't
1977 /// matter, because it is currently only called from PV nodes, which are rare.
1979 bool Position::has_mate_threat(Color c) {
1982 Color stm = side_to_move();
1984 // The following lines are useless and silly, but prevents gcc from
1985 // emitting a stupid warning stating that u1.lastMove and u1.epSquare might
1986 // be used uninitialized.
1987 st1.lastMove = st->lastMove;
1988 st1.epSquare = st->epSquare;
1993 // If the input color is not equal to the side to move, do a null move
1997 MoveStack mlist[120];
1999 bool result = false;
2001 // Generate legal moves
2002 count = generate_legal_moves(*this, mlist);
2004 // Loop through the moves, and see if one of them is mate
2005 for (int i = 0; i < count; i++)
2007 do_move(mlist[i].move, st2);
2011 undo_move(mlist[i].move);
2014 // Undo null move, if necessary
2022 /// Position::init_zobrist() is a static member function which initializes the
2023 /// various arrays used to compute hash keys.
2025 void Position::init_zobrist() {
2027 for (int i = 0; i < 2; i++)
2028 for (int j = 0; j < 8; j++)
2029 for (int k = 0; k < 64; k++)
2030 zobrist[i][j][k] = Key(genrand_int64());
2032 for (int i = 0; i < 64; i++)
2033 zobEp[i] = Key(genrand_int64());
2035 for (int i = 0; i < 16; i++)
2036 zobCastle[i] = genrand_int64();
2038 zobSideToMove = genrand_int64();
2040 for (int i = 0; i < 2; i++)
2041 for (int j = 0; j < 8; j++)
2042 for (int k = 0; k < 16; k++)
2043 zobMaterial[i][j][k] = (k > 0)? Key(genrand_int64()) : Key(0LL);
2045 for (int i = 0; i < 16; i++)
2046 zobMaterial[0][KING][i] = zobMaterial[1][KING][i] = Key(0ULL);
2050 /// Position::init_piece_square_tables() initializes the piece square tables.
2051 /// This is a two-step operation: First, the white halves of the tables are
2052 /// copied from the MgPST[][] and EgPST[][] arrays, with a small random number
2053 /// added to each entry if the "Randomness" UCI parameter is non-zero.
2054 /// Second, the black halves of the tables are initialized by mirroring
2055 /// and changing the sign of the corresponding white scores.
2057 void Position::init_piece_square_tables() {
2059 int r = get_option_value_int("Randomness"), i;
2060 for (Square s = SQ_A1; s <= SQ_H8; s++)
2061 for (Piece p = WP; p <= WK; p++)
2063 i = (r == 0)? 0 : (genrand_int32() % (r*2) - r);
2064 MgPieceSquareTable[p][s] = Value(MgPST[p][s] + i);
2065 EgPieceSquareTable[p][s] = Value(EgPST[p][s] + i);
2068 for (Square s = SQ_A1; s <= SQ_H8; s++)
2069 for (Piece p = BP; p <= BK; p++)
2071 MgPieceSquareTable[p][s] = -MgPieceSquareTable[p-8][flip_square(s)];
2072 EgPieceSquareTable[p][s] = -EgPieceSquareTable[p-8][flip_square(s)];
2077 /// Position::flipped_copy() makes a copy of the input position, but with
2078 /// the white and black sides reversed. This is only useful for debugging,
2079 /// especially for finding evaluation symmetry bugs.
2081 void Position::flipped_copy(const Position &pos) {
2083 assert(pos.is_ok());
2088 for (Square s = SQ_A1; s <= SQ_H8; s++)
2089 if (!pos.square_is_empty(s))
2090 put_piece(Piece(int(pos.piece_on(s)) ^ 8), flip_square(s));
2093 sideToMove = opposite_color(pos.side_to_move());
2096 if (pos.can_castle_kingside(WHITE)) allow_oo(BLACK);
2097 if (pos.can_castle_queenside(WHITE)) allow_ooo(BLACK);
2098 if (pos.can_castle_kingside(BLACK)) allow_oo(WHITE);
2099 if (pos.can_castle_queenside(BLACK)) allow_ooo(WHITE);
2101 initialKFile = pos.initialKFile;
2102 initialKRFile = pos.initialKRFile;
2103 initialQRFile = pos.initialQRFile;
2105 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
2106 castleRightsMask[sq] = ALL_CASTLES;
2108 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
2109 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
2110 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
2111 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
2112 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
2113 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
2115 // En passant square
2116 if (pos.st->epSquare != SQ_NONE)
2117 st->epSquare = flip_square(pos.st->epSquare);
2123 st->key = compute_key();
2124 st->pawnKey = compute_pawn_key();
2125 st->materialKey = compute_material_key();
2127 // Incremental scores
2128 st->mgValue = compute_value<MidGame>();
2129 st->egValue = compute_value<EndGame>();
2132 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
2133 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
2139 /// Position::is_ok() performs some consitency checks for the position object.
2140 /// This is meant to be helpful when debugging.
2142 bool Position::is_ok(int* failedStep) const {
2144 // What features of the position should be verified?
2145 static const bool debugBitboards = false;
2146 static const bool debugKingCount = false;
2147 static const bool debugKingCapture = false;
2148 static const bool debugCheckerCount = false;
2149 static const bool debugKey = false;
2150 static const bool debugMaterialKey = false;
2151 static const bool debugPawnKey = false;
2152 static const bool debugIncrementalEval = false;
2153 static const bool debugNonPawnMaterial = false;
2154 static const bool debugPieceCounts = false;
2155 static const bool debugPieceList = false;
2157 if (failedStep) *failedStep = 1;
2160 if (!color_is_ok(side_to_move()))
2163 // Are the king squares in the position correct?
2164 if (failedStep) (*failedStep)++;
2165 if (piece_on(king_square(WHITE)) != WK)
2168 if (failedStep) (*failedStep)++;
2169 if (piece_on(king_square(BLACK)) != BK)
2173 if (failedStep) (*failedStep)++;
2174 if (!file_is_ok(initialKRFile))
2177 if (!file_is_ok(initialQRFile))
2180 // Do both sides have exactly one king?
2181 if (failedStep) (*failedStep)++;
2184 int kingCount[2] = {0, 0};
2185 for (Square s = SQ_A1; s <= SQ_H8; s++)
2186 if (type_of_piece_on(s) == KING)
2187 kingCount[color_of_piece_on(s)]++;
2189 if (kingCount[0] != 1 || kingCount[1] != 1)
2193 // Can the side to move capture the opponent's king?
2194 if (failedStep) (*failedStep)++;
2195 if (debugKingCapture)
2197 Color us = side_to_move();
2198 Color them = opposite_color(us);
2199 Square ksq = king_square(them);
2200 if (square_is_attacked(ksq, us))
2204 // Is there more than 2 checkers?
2205 if (failedStep) (*failedStep)++;
2206 if (debugCheckerCount && count_1s(st->checkersBB) > 2)
2210 if (failedStep) (*failedStep)++;
2213 // The intersection of the white and black pieces must be empty
2214 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
2217 // The union of the white and black pieces must be equal to all
2219 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
2222 // Separate piece type bitboards must have empty intersections
2223 for (PieceType p1 = PAWN; p1 <= KING; p1++)
2224 for (PieceType p2 = PAWN; p2 <= KING; p2++)
2225 if (p1 != p2 && (pieces_of_type(p1) & pieces_of_type(p2)))
2229 // En passant square OK?
2230 if (failedStep) (*failedStep)++;
2231 if (ep_square() != SQ_NONE)
2233 // The en passant square must be on rank 6, from the point of view of the
2235 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
2240 if (failedStep) (*failedStep)++;
2241 if (debugKey && st->key != compute_key())
2244 // Pawn hash key OK?
2245 if (failedStep) (*failedStep)++;
2246 if (debugPawnKey && st->pawnKey != compute_pawn_key())
2249 // Material hash key OK?
2250 if (failedStep) (*failedStep)++;
2251 if (debugMaterialKey && st->materialKey != compute_material_key())
2254 // Incremental eval OK?
2255 if (failedStep) (*failedStep)++;
2256 if (debugIncrementalEval)
2258 if (st->mgValue != compute_value<MidGame>())
2261 if (st->egValue != compute_value<EndGame>())
2265 // Non-pawn material OK?
2266 if (failedStep) (*failedStep)++;
2267 if (debugNonPawnMaterial)
2269 if (npMaterial[WHITE] != compute_non_pawn_material(WHITE))
2272 if (npMaterial[BLACK] != compute_non_pawn_material(BLACK))
2277 if (failedStep) (*failedStep)++;
2278 if (debugPieceCounts)
2279 for (Color c = WHITE; c <= BLACK; c++)
2280 for (PieceType pt = PAWN; pt <= KING; pt++)
2281 if (pieceCount[c][pt] != count_1s(pieces_of_color_and_type(c, pt)))
2284 if (failedStep) (*failedStep)++;
2287 for(Color c = WHITE; c <= BLACK; c++)
2288 for(PieceType pt = PAWN; pt <= KING; pt++)
2289 for(int i = 0; i < pieceCount[c][pt]; i++)
2291 if (piece_on(piece_list(c, pt, i)) != piece_of_color_and_type(c, pt))
2294 if (index[piece_list(c, pt, i)] != i)
2298 if (failedStep) *failedStep = 0;