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;
211 st->key = compute_key();
212 st->pawnKey = compute_pawn_key();
213 st->materialKey = compute_material_key();
214 st->mgValue = compute_value<MidGame>();
215 st->egValue = compute_value<EndGame>();
216 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
217 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
221 /// Position::to_fen() converts the position object to a FEN string. This is
222 /// probably only useful for debugging.
224 const std::string Position::to_fen() const {
226 static const std::string pieceLetters = " PNBRQK pnbrqk";
230 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
233 for (File file = FILE_A; file <= FILE_H; file++)
235 Square sq = make_square(file, rank);
236 if (!square_is_occupied(sq))
242 fen += (char)skip + '0';
245 fen += pieceLetters[piece_on(sq)];
248 fen += (char)skip + '0';
250 fen += (rank > RANK_1 ? '/' : ' ');
252 fen += (sideToMove == WHITE ? "w " : "b ");
253 if (st->castleRights != NO_CASTLES)
255 if (can_castle_kingside(WHITE)) fen += 'K';
256 if (can_castle_queenside(WHITE)) fen += 'Q';
257 if (can_castle_kingside(BLACK)) fen += 'k';
258 if (can_castle_queenside(BLACK)) fen += 'q';
263 if (ep_square() != SQ_NONE)
264 fen += square_to_string(ep_square());
272 /// Position::print() prints an ASCII representation of the position to
273 /// the standard output. If a move is given then also the san is print.
275 void Position::print(Move m) const {
277 static const std::string pieceLetters = " PNBRQK PNBRQK .";
279 // Check for reentrancy, as example when called from inside
280 // MovePicker that is used also here in move_to_san()
284 RequestPending = true;
286 std::cout << std::endl;
289 std::string col = (color_of_piece_on(move_from(m)) == BLACK ? ".." : "");
290 std::cout << "Move is: " << col << move_to_san(*this, m) << std::endl;
292 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
294 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl;
295 for (File file = FILE_A; file <= FILE_H; file++)
297 Square sq = make_square(file, rank);
298 Piece piece = piece_on(sq);
299 if (piece == EMPTY && square_color(sq) == WHITE)
302 char col = (color_of_piece_on(sq) == BLACK ? '=' : ' ');
303 std::cout << '|' << col << pieceLetters[piece] << col;
305 std::cout << '|' << std::endl;
307 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl
308 << "Fen is: " << to_fen() << std::endl
309 << "Key is: " << st->key << std::endl;
311 RequestPending = false;
315 /// Position::copy() creates a copy of the input position.
317 void Position::copy(const Position &pos) {
319 memcpy(this, &pos, sizeof(Position));
323 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
324 /// king) pieces for the given color.
325 Bitboard Position::pinned_pieces(Color c) const {
328 Square ksq = king_square(c);
329 return hidden_checks<ROOK, true>(c, ksq, p) | hidden_checks<BISHOP, true>(c, ksq, p);
333 /// Position:discovered_check_candidates() returns a bitboard containing all
334 /// pieces for the given side which are candidates for giving a discovered
335 /// check. The code is almost the same as the function for finding pinned
338 Bitboard Position::discovered_check_candidates(Color c) const {
341 Square ksq = king_square(opposite_color(c));
342 return hidden_checks<ROOK, false>(c, ksq, p) | hidden_checks<BISHOP, false>(c, ksq, p);
346 /// Position:hidden_checks<>() returns a bitboard of all pinned (against the
347 /// king) pieces for the given color and for the given pinner type. Or, when
348 /// template parameter FindPinned is false, the pinned pieces of opposite color
349 /// that are, indeed, the pieces candidate for a discovery check.
350 /// Note that checkersBB bitboard must be already updated.
351 template<PieceType Piece, bool FindPinned>
352 Bitboard Position::hidden_checks(Color c, Square ksq, Bitboard& pinners) const {
355 Bitboard sliders, result = EmptyBoardBB;
357 if (Piece == ROOK) // Resolved at compile time
358 sliders = rooks_and_queens(FindPinned ? opposite_color(c) : c) & RookPseudoAttacks[ksq];
360 sliders = bishops_and_queens(FindPinned ? opposite_color(c) : c) & BishopPseudoAttacks[ksq];
362 if (sliders && (!FindPinned || (sliders & ~st->checkersBB)))
364 // King blockers are candidate pinned pieces
365 Bitboard candidate_pinned = piece_attacks<Piece>(ksq) & pieces_of_color(c);
367 // Pinners are sliders, not checkers, that give check when
368 // candidate pinned are removed.
369 pinners = (FindPinned ? sliders & ~st->checkersBB : sliders);
372 pinners &= rook_attacks_bb(ksq, occupied_squares() ^ candidate_pinned);
374 pinners &= bishop_attacks_bb(ksq, occupied_squares() ^ candidate_pinned);
376 // Finally for each pinner find the corresponding pinned piece (if same color of king)
377 // or discovery checker (if opposite color) among the candidates.
378 Bitboard p = pinners;
382 result |= (squares_between(s, ksq) & candidate_pinned);
386 pinners = EmptyBoardBB;
392 /// Position::attacks_to() computes a bitboard containing all pieces which
393 /// attacks a given square. There are two versions of this function: One
394 /// which finds attackers of both colors, and one which only finds the
395 /// attackers for one side.
397 Bitboard Position::attacks_to(Square s) const {
399 return (pawn_attacks(BLACK, s) & pawns(WHITE))
400 | (pawn_attacks(WHITE, s) & pawns(BLACK))
401 | (piece_attacks<KNIGHT>(s) & pieces_of_type(KNIGHT))
402 | (piece_attacks<ROOK>(s) & rooks_and_queens())
403 | (piece_attacks<BISHOP>(s) & bishops_and_queens())
404 | (piece_attacks<KING>(s) & pieces_of_type(KING));
407 /// Position::piece_attacks_square() tests whether the piece on square f
408 /// attacks square t.
410 bool Position::piece_attacks_square(Piece p, Square f, Square t) const {
412 assert(square_is_ok(f));
413 assert(square_is_ok(t));
417 case WP: return pawn_attacks_square(WHITE, f, t);
418 case BP: return pawn_attacks_square(BLACK, f, t);
419 case WN: case BN: return piece_attacks_square<KNIGHT>(f, t);
420 case WB: case BB: return piece_attacks_square<BISHOP>(f, t);
421 case WR: case BR: return piece_attacks_square<ROOK>(f, t);
422 case WQ: case BQ: return piece_attacks_square<QUEEN>(f, t);
423 case WK: case BK: return piece_attacks_square<KING>(f, t);
430 /// Position::move_attacks_square() tests whether a move from the current
431 /// position attacks a given square.
433 bool Position::move_attacks_square(Move m, Square s) const {
435 assert(move_is_ok(m));
436 assert(square_is_ok(s));
438 Square f = move_from(m), t = move_to(m);
440 assert(square_is_occupied(f));
442 if (piece_attacks_square(piece_on(f), t, s))
445 // Move the piece and scan for X-ray attacks behind it
446 Bitboard occ = occupied_squares();
447 Color us = color_of_piece_on(f);
450 Bitboard xray = ( (rook_attacks_bb(s, occ) & rooks_and_queens())
451 |(bishop_attacks_bb(s, occ) & bishops_and_queens())) & pieces_of_color(us);
453 // If we have attacks we need to verify that are caused by our move
454 // and are not already existent ones.
455 return xray && (xray ^ (xray & piece_attacks<QUEEN>(s)));
459 /// Position::find_checkers() computes the checkersBB bitboard, which
460 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
461 /// currently works by calling Position::attacks_to, which is probably
462 /// inefficient. Consider rewriting this function to use the last move
463 /// played, like in non-bitboard versions of Glaurung.
465 void Position::find_checkers() {
467 Color us = side_to_move();
468 st->checkersBB = attacks_to(king_square(us), opposite_color(us));
472 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
474 bool Position::pl_move_is_legal(Move m) const {
476 return pl_move_is_legal(m, pinned_pieces(side_to_move()));
479 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
482 assert(move_is_ok(m));
483 assert(pinned == pinned_pieces(side_to_move()));
485 // If we're in check, all pseudo-legal moves are legal, because our
486 // check evasion generator only generates true legal moves.
490 // Castling moves are checked for legality during move generation.
491 if (move_is_castle(m))
494 Color us = side_to_move();
495 Color them = opposite_color(us);
496 Square from = move_from(m);
497 Square ksq = king_square(us);
499 assert(color_of_piece_on(from) == us);
500 assert(piece_on(ksq) == piece_of_color_and_type(us, KING));
502 // En passant captures are a tricky special case. Because they are
503 // rather uncommon, we do it simply by testing whether the king is attacked
504 // after the move is made
507 Square to = move_to(m);
508 Square capsq = make_square(square_file(to), square_rank(from));
509 Bitboard b = occupied_squares();
511 assert(to == ep_square());
512 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
513 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
514 assert(piece_on(to) == EMPTY);
517 clear_bit(&b, capsq);
520 return !(rook_attacks_bb(ksq, b) & rooks_and_queens(them))
521 && !(bishop_attacks_bb(ksq, b) & bishops_and_queens(them));
524 // If the moving piece is a king, check whether the destination
525 // square is attacked by the opponent.
527 return !(square_is_attacked(move_to(m), them));
529 // A non-king move is legal if and only if it is not pinned or it
530 // is moving along the ray towards or away from the king.
531 return ( !bit_is_set(pinned, from)
532 || (direction_between_squares(from, ksq) == direction_between_squares(move_to(m), ksq)));
536 /// Position::move_is_check() tests whether a pseudo-legal move is a check
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 assert(move_is_ok(m));
548 assert(dcCandidates == discovered_check_candidates(side_to_move()));
550 Color us = side_to_move();
551 Color them = opposite_color(us);
552 Square from = move_from(m);
553 Square to = move_to(m);
554 Square ksq = king_square(them);
556 assert(color_of_piece_on(from) == us);
557 assert(piece_on(ksq) == piece_of_color_and_type(them, KING));
559 // Proceed according to the type of the moving piece
560 switch (type_of_piece_on(from))
564 if (bit_is_set(pawn_attacks(them, ksq), to)) // Normal check?
567 if ( bit_is_set(dcCandidates, from) // Discovered check?
568 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
571 if (move_promotion(m)) // Promotion with check?
573 Bitboard b = occupied_squares();
576 switch (move_promotion(m))
579 return bit_is_set(piece_attacks<KNIGHT>(to), ksq);
581 return bit_is_set(bishop_attacks_bb(to, b), ksq);
583 return bit_is_set(rook_attacks_bb(to, b), ksq);
585 return bit_is_set(queen_attacks_bb(to, b), ksq);
590 // En passant capture with check? We have already handled the case
591 // of direct checks and ordinary discovered check, the only case we
592 // need to handle is the unusual case of a discovered check through the
594 else if (move_is_ep(m))
596 Square capsq = make_square(square_file(to), square_rank(from));
597 Bitboard b = occupied_squares();
599 clear_bit(&b, capsq);
601 return (rook_attacks_bb(ksq, b) & rooks_and_queens(us))
602 ||(bishop_attacks_bb(ksq, b) & bishops_and_queens(us));
607 return bit_is_set(dcCandidates, from) // Discovered check?
608 || bit_is_set(piece_attacks<KNIGHT>(ksq), to); // Normal check?
611 return bit_is_set(dcCandidates, from) // Discovered check?
612 || bit_is_set(piece_attacks<BISHOP>(ksq), to); // Normal check?
615 return bit_is_set(dcCandidates, from) // Discovered check?
616 || bit_is_set(piece_attacks<ROOK>(ksq), to); // Normal check?
619 // Discovered checks are impossible!
620 assert(!bit_is_set(dcCandidates, from));
621 return bit_is_set(piece_attacks<QUEEN>(ksq), to); // Normal check?
625 if ( bit_is_set(dcCandidates, from)
626 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
629 // Castling with check?
630 if (move_is_castle(m))
632 Square kfrom, kto, rfrom, rto;
633 Bitboard b = occupied_squares();
639 kto = relative_square(us, SQ_G1);
640 rto = relative_square(us, SQ_F1);
642 kto = relative_square(us, SQ_C1);
643 rto = relative_square(us, SQ_D1);
645 clear_bit(&b, kfrom);
646 clear_bit(&b, rfrom);
649 return bit_is_set(rook_attacks_bb(rto, b), ksq);
653 default: // NO_PIECE_TYPE
661 /// Position::move_is_capture() tests whether a move from the current
662 /// position is a capture. Move must not be MOVE_NONE.
664 bool Position::move_is_capture(Move m) const {
666 assert(m != MOVE_NONE);
668 return ( !square_is_empty(move_to(m))
669 && (color_of_piece_on(move_to(m)) != color_of_piece_on(move_from(m)))
675 /// Position::update_checkers() udpates chekers info given the move. It is called
676 /// in do_move() and is faster then find_checkers().
678 template<PieceType Piece>
679 inline void Position::update_checkers(Bitboard* pCheckersBB, Square ksq, Square from,
680 Square to, Bitboard dcCandidates) {
682 if (Piece != KING && bit_is_set(piece_attacks<Piece>(ksq), to))
683 set_bit(pCheckersBB, to);
685 if (Piece != QUEEN && bit_is_set(dcCandidates, from))
688 (*pCheckersBB) |= (piece_attacks<ROOK>(ksq) & rooks_and_queens(side_to_move()));
691 (*pCheckersBB) |= (piece_attacks<BISHOP>(ksq) & bishops_and_queens(side_to_move()));
696 /// Position::do_move() makes a move, and saves all information necessary
697 /// to a StateInfo object. The move is assumed to be legal.
698 /// Pseudo-legal moves should be filtered out before this function is called.
700 void Position::do_move(Move m, StateInfo& newSt) {
702 do_move(m, newSt, discovered_check_candidates(side_to_move()));
705 void Position::do_move(Move m, StateInfo& newSt, Bitboard dcCandidates) {
708 assert(move_is_ok(m));
710 // Copy some fields of old state to our new StateInfo object except the
711 // ones which are recalculated from scratch anyway, then switch our state
712 // pointer to point to the new, ready to be updated, state.
713 struct ReducedStateInfo {
714 Key key, pawnKey, materialKey;
715 int castleRights, rule50;
717 Value mgValue, egValue;
720 memcpy(&newSt, st, sizeof(ReducedStateInfo));
721 newSt.capture = NO_PIECE_TYPE;
725 // Save the current key to the history[] array, in order to be able to
726 // detect repetition draws.
727 history[gamePly] = st->key;
729 // Increment the 50 moves rule draw counter. Resetting it to zero in the
730 // case of non-reversible moves is taken care of later.
733 if (move_is_castle(m))
735 else if (move_promotion(m))
736 do_promotion_move(m);
737 else if (move_is_ep(m))
741 Color us = side_to_move();
742 Color them = opposite_color(us);
743 Square from = move_from(m);
744 Square to = move_to(m);
746 assert(color_of_piece_on(from) == us);
747 assert(color_of_piece_on(to) == them || piece_on(to) == EMPTY);
749 PieceType piece = type_of_piece_on(from);
751 st->capture = type_of_piece_on(to);
754 do_capture_move(m, st->capture, them, to);
757 clear_bit(&(byColorBB[us]), from);
758 clear_bit(&(byTypeBB[piece]), from);
759 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
760 set_bit(&(byColorBB[us]), to);
761 set_bit(&(byTypeBB[piece]), to);
762 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
763 board[to] = board[from];
767 st->key ^= zobrist[us][piece][from] ^ zobrist[us][piece][to];
769 // Update incremental scores
770 st->mgValue -= pst<MidGame>(us, piece, from);
771 st->mgValue += pst<MidGame>(us, piece, to);
772 st->egValue -= pst<EndGame>(us, piece, from);
773 st->egValue += pst<EndGame>(us, piece, to);
775 // If the moving piece was a king, update the king square
779 // Reset en passant square
780 if (st->epSquare != SQ_NONE)
782 st->key ^= zobEp[st->epSquare];
783 st->epSquare = SQ_NONE;
786 // If the moving piece was a pawn do some special extra work
789 // Reset rule 50 draw counter
792 // Update pawn hash key
793 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
795 // Set en passant square, only if moved pawn can be captured
796 if (abs(int(to) - int(from)) == 16)
798 if ( (us == WHITE && (pawn_attacks(WHITE, from + DELTA_N) & pawns(BLACK)))
799 || (us == BLACK && (pawn_attacks(BLACK, from + DELTA_S) & pawns(WHITE))))
801 st->epSquare = Square((int(from) + int(to)) / 2);
802 st->key ^= zobEp[st->epSquare];
807 // Update piece lists
808 pieceList[us][piece][index[from]] = to;
809 index[to] = index[from];
811 // Update castle rights
812 st->key ^= zobCastle[st->castleRights];
813 st->castleRights &= castleRightsMask[from];
814 st->castleRights &= castleRightsMask[to];
815 st->key ^= zobCastle[st->castleRights];
817 // Update checkers bitboard, piece must be already moved
818 st->checkersBB = EmptyBoardBB;
819 Square ksq = king_square(them);
822 case PAWN: update_checkers<PAWN>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
823 case KNIGHT: update_checkers<KNIGHT>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
824 case BISHOP: update_checkers<BISHOP>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
825 case ROOK: update_checkers<ROOK>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
826 case QUEEN: update_checkers<QUEEN>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
827 case KING: update_checkers<KING>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
828 default: assert(false); break;
833 st->key ^= zobSideToMove;
834 sideToMove = opposite_color(sideToMove);
837 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
838 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
844 /// Position::do_capture_move() is a private method used to update captured
845 /// piece info. It is called from the main Position::do_move function.
847 void Position::do_capture_move(Move m, PieceType capture, Color them, Square to) {
849 assert(capture != KING);
851 // Remove captured piece
852 clear_bit(&(byColorBB[them]), to);
853 clear_bit(&(byTypeBB[capture]), to);
856 st->key ^= zobrist[them][capture][to];
858 // If the captured piece was a pawn, update pawn hash key
860 st->pawnKey ^= zobrist[them][PAWN][to];
862 // Update incremental scores
863 st->mgValue -= pst<MidGame>(them, capture, to);
864 st->egValue -= pst<EndGame>(them, capture, to);
866 assert(!move_promotion(m) || capture != PAWN);
870 npMaterial[them] -= piece_value_midgame(capture);
872 // Update material hash key
873 st->materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];
875 // Update piece count
876 pieceCount[them][capture]--;
879 pieceList[them][capture][index[to]] = pieceList[them][capture][pieceCount[them][capture]];
880 index[pieceList[them][capture][index[to]]] = index[to];
882 // Reset rule 50 counter
887 /// Position::do_castle_move() is a private method used to make a castling
888 /// move. It is called from the main Position::do_move function. Note that
889 /// castling moves are encoded as "king captures friendly rook" moves, for
890 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
892 void Position::do_castle_move(Move m) {
895 assert(move_is_ok(m));
896 assert(move_is_castle(m));
898 Color us = side_to_move();
899 Color them = opposite_color(us);
901 // Find source squares for king and rook
902 Square kfrom = move_from(m);
903 Square rfrom = move_to(m); // HACK: See comment at beginning of function
906 assert(piece_on(kfrom) == piece_of_color_and_type(us, KING));
907 assert(piece_on(rfrom) == piece_of_color_and_type(us, ROOK));
909 // Find destination squares for king and rook
910 if (rfrom > kfrom) // O-O
912 kto = relative_square(us, SQ_G1);
913 rto = relative_square(us, SQ_F1);
915 kto = relative_square(us, SQ_C1);
916 rto = relative_square(us, SQ_D1);
919 // Remove pieces from source squares
920 clear_bit(&(byColorBB[us]), kfrom);
921 clear_bit(&(byTypeBB[KING]), kfrom);
922 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
923 clear_bit(&(byColorBB[us]), rfrom);
924 clear_bit(&(byTypeBB[ROOK]), rfrom);
925 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
927 // Put pieces on destination squares
928 set_bit(&(byColorBB[us]), kto);
929 set_bit(&(byTypeBB[KING]), kto);
930 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
931 set_bit(&(byColorBB[us]), rto);
932 set_bit(&(byTypeBB[ROOK]), rto);
933 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
935 // Update board array
936 board[kfrom] = board[rfrom] = EMPTY;
937 board[kto] = piece_of_color_and_type(us, KING);
938 board[rto] = piece_of_color_and_type(us, ROOK);
940 // Update king square
941 kingSquare[us] = kto;
943 // Update piece lists
944 pieceList[us][KING][index[kfrom]] = kto;
945 pieceList[us][ROOK][index[rfrom]] = rto;
946 int tmp = index[rfrom];
947 index[kto] = index[kfrom];
950 // Update incremental scores
951 st->mgValue -= pst<MidGame>(us, KING, kfrom);
952 st->mgValue += pst<MidGame>(us, KING, kto);
953 st->egValue -= pst<EndGame>(us, KING, kfrom);
954 st->egValue += pst<EndGame>(us, KING, kto);
955 st->mgValue -= pst<MidGame>(us, ROOK, rfrom);
956 st->mgValue += pst<MidGame>(us, ROOK, rto);
957 st->egValue -= pst<EndGame>(us, ROOK, rfrom);
958 st->egValue += pst<EndGame>(us, ROOK, rto);
961 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
962 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
964 // Clear en passant square
965 if (st->epSquare != SQ_NONE)
967 st->key ^= zobEp[st->epSquare];
968 st->epSquare = SQ_NONE;
971 // Update castling rights
972 st->key ^= zobCastle[st->castleRights];
973 st->castleRights &= castleRightsMask[kfrom];
974 st->key ^= zobCastle[st->castleRights];
976 // Reset rule 50 counter
979 // Update checkers BB
980 st->checkersBB = attacks_to(king_square(them), us);
984 /// Position::do_promotion_move() is a private method used to make a promotion
985 /// move. It is called from the main Position::do_move function.
987 void Position::do_promotion_move(Move m) {
994 assert(move_is_ok(m));
995 assert(move_promotion(m));
998 them = opposite_color(us);
1002 assert(relative_rank(us, to) == RANK_8);
1003 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
1004 assert(color_of_piece_on(to) == them || square_is_empty(to));
1006 st->capture = type_of_piece_on(to);
1009 do_capture_move(m, st->capture, them, to);
1012 clear_bit(&(byColorBB[us]), from);
1013 clear_bit(&(byTypeBB[PAWN]), from);
1014 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1015 board[from] = EMPTY;
1017 // Insert promoted piece
1018 promotion = move_promotion(m);
1019 assert(promotion >= KNIGHT && promotion <= QUEEN);
1020 set_bit(&(byColorBB[us]), to);
1021 set_bit(&(byTypeBB[promotion]), to);
1022 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1023 board[to] = piece_of_color_and_type(us, promotion);
1026 st->key ^= zobrist[us][PAWN][from] ^ zobrist[us][promotion][to];
1028 // Update pawn hash key
1029 st->pawnKey ^= zobrist[us][PAWN][from];
1031 // Update material key
1032 st->materialKey ^= zobMaterial[us][PAWN][pieceCount[us][PAWN]];
1033 st->materialKey ^= zobMaterial[us][promotion][pieceCount[us][promotion]+1];
1035 // Update piece counts
1036 pieceCount[us][PAWN]--;
1037 pieceCount[us][promotion]++;
1039 // Update piece lists
1040 pieceList[us][PAWN][index[from]] = pieceList[us][PAWN][pieceCount[us][PAWN]];
1041 index[pieceList[us][PAWN][index[from]]] = index[from];
1042 pieceList[us][promotion][pieceCount[us][promotion] - 1] = to;
1043 index[to] = pieceCount[us][promotion] - 1;
1045 // Update incremental scores
1046 st->mgValue -= pst<MidGame>(us, PAWN, from);
1047 st->mgValue += pst<MidGame>(us, promotion, to);
1048 st->egValue -= pst<EndGame>(us, PAWN, from);
1049 st->egValue += pst<EndGame>(us, promotion, to);
1052 npMaterial[us] += piece_value_midgame(promotion);
1054 // Clear the en passant square
1055 if (st->epSquare != SQ_NONE)
1057 st->key ^= zobEp[st->epSquare];
1058 st->epSquare = SQ_NONE;
1061 // Update castle rights
1062 st->key ^= zobCastle[st->castleRights];
1063 st->castleRights &= castleRightsMask[to];
1064 st->key ^= zobCastle[st->castleRights];
1066 // Reset rule 50 counter
1069 // Update checkers BB
1070 st->checkersBB = attacks_to(king_square(them), us);
1074 /// Position::do_ep_move() is a private method used to make an en passant
1075 /// capture. It is called from the main Position::do_move function.
1077 void Position::do_ep_move(Move m) {
1080 Square from, to, capsq;
1083 assert(move_is_ok(m));
1084 assert(move_is_ep(m));
1086 us = side_to_move();
1087 them = opposite_color(us);
1088 from = move_from(m);
1090 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1092 assert(to == st->epSquare);
1093 assert(relative_rank(us, to) == RANK_6);
1094 assert(piece_on(to) == EMPTY);
1095 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
1096 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
1098 // Remove captured piece
1099 clear_bit(&(byColorBB[them]), capsq);
1100 clear_bit(&(byTypeBB[PAWN]), capsq);
1101 clear_bit(&(byTypeBB[0]), capsq); // HACK: byTypeBB[0] == occupied squares
1102 board[capsq] = EMPTY;
1104 // Remove moving piece from source square
1105 clear_bit(&(byColorBB[us]), from);
1106 clear_bit(&(byTypeBB[PAWN]), from);
1107 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1109 // Put moving piece on destination square
1110 set_bit(&(byColorBB[us]), to);
1111 set_bit(&(byTypeBB[PAWN]), to);
1112 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1113 board[to] = board[from];
1114 board[from] = EMPTY;
1116 // Update material hash key
1117 st->materialKey ^= zobMaterial[them][PAWN][pieceCount[them][PAWN]];
1119 // Update piece count
1120 pieceCount[them][PAWN]--;
1122 // Update piece list
1123 pieceList[us][PAWN][index[from]] = to;
1124 index[to] = index[from];
1125 pieceList[them][PAWN][index[capsq]] = pieceList[them][PAWN][pieceCount[them][PAWN]];
1126 index[pieceList[them][PAWN][index[capsq]]] = index[capsq];
1129 st->key ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1130 st->key ^= zobrist[them][PAWN][capsq];
1131 st->key ^= zobEp[st->epSquare];
1133 // Update pawn hash key
1134 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1135 st->pawnKey ^= zobrist[them][PAWN][capsq];
1137 // Update incremental scores
1138 st->mgValue -= pst<MidGame>(them, PAWN, capsq);
1139 st->mgValue -= pst<MidGame>(us, PAWN, from);
1140 st->mgValue += pst<MidGame>(us, PAWN, to);
1141 st->egValue -= pst<EndGame>(them, PAWN, capsq);
1142 st->egValue -= pst<EndGame>(us, PAWN, from);
1143 st->egValue += pst<EndGame>(us, PAWN, to);
1145 // Reset en passant square
1146 st->epSquare = SQ_NONE;
1148 // Reset rule 50 counter
1151 // Update checkers BB
1152 st->checkersBB = attacks_to(king_square(them), us);
1156 /// Position::undo_move() unmakes a move. When it returns, the position should
1157 /// be restored to exactly the same state as before the move was made.
1159 void Position::undo_move(Move m) {
1162 assert(move_is_ok(m));
1165 sideToMove = opposite_color(sideToMove);
1167 if (move_is_castle(m))
1168 undo_castle_move(m);
1169 else if (move_promotion(m))
1170 undo_promotion_move(m);
1171 else if (move_is_ep(m))
1179 us = side_to_move();
1180 them = opposite_color(us);
1181 from = move_from(m);
1184 assert(piece_on(from) == EMPTY);
1185 assert(color_of_piece_on(to) == us);
1187 // Put the piece back at the source square
1188 piece = type_of_piece_on(to);
1189 set_bit(&(byColorBB[us]), from);
1190 set_bit(&(byTypeBB[piece]), from);
1191 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1192 board[from] = piece_of_color_and_type(us, piece);
1194 // Clear the destination square
1195 clear_bit(&(byColorBB[us]), to);
1196 clear_bit(&(byTypeBB[piece]), to);
1197 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1199 // If the moving piece was a king, update the king square
1201 kingSquare[us] = from;
1203 // Update piece list
1204 pieceList[us][piece][index[to]] = from;
1205 index[from] = index[to];
1209 assert(st->capture != KING);
1211 // Replace the captured piece
1212 set_bit(&(byColorBB[them]), to);
1213 set_bit(&(byTypeBB[st->capture]), to);
1214 set_bit(&(byTypeBB[0]), to);
1215 board[to] = piece_of_color_and_type(them, st->capture);
1218 if (st->capture != PAWN)
1219 npMaterial[them] += piece_value_midgame(st->capture);
1221 // Update piece list
1222 pieceList[them][st->capture][pieceCount[them][st->capture]] = to;
1223 index[to] = pieceCount[them][st->capture];
1225 // Update piece count
1226 pieceCount[them][st->capture]++;
1231 // Finally point out state pointer back to the previous state
1238 /// Position::undo_castle_move() is a private method used to unmake a castling
1239 /// move. It is called from the main Position::undo_move function. Note that
1240 /// castling moves are encoded as "king captures friendly rook" moves, for
1241 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1243 void Position::undo_castle_move(Move m) {
1245 assert(move_is_ok(m));
1246 assert(move_is_castle(m));
1248 // When we have arrived here, some work has already been done by
1249 // Position::undo_move. In particular, the side to move has been switched,
1250 // so the code below is correct.
1251 Color us = side_to_move();
1253 // Find source squares for king and rook
1254 Square kfrom = move_from(m);
1255 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1258 // Find destination squares for king and rook
1259 if (rfrom > kfrom) // O-O
1261 kto = relative_square(us, SQ_G1);
1262 rto = relative_square(us, SQ_F1);
1264 kto = relative_square(us, SQ_C1);
1265 rto = relative_square(us, SQ_D1);
1268 assert(piece_on(kto) == piece_of_color_and_type(us, KING));
1269 assert(piece_on(rto) == piece_of_color_and_type(us, ROOK));
1271 // Remove pieces from destination squares
1272 clear_bit(&(byColorBB[us]), kto);
1273 clear_bit(&(byTypeBB[KING]), kto);
1274 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1275 clear_bit(&(byColorBB[us]), rto);
1276 clear_bit(&(byTypeBB[ROOK]), rto);
1277 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1279 // Put pieces on source squares
1280 set_bit(&(byColorBB[us]), kfrom);
1281 set_bit(&(byTypeBB[KING]), kfrom);
1282 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1283 set_bit(&(byColorBB[us]), rfrom);
1284 set_bit(&(byTypeBB[ROOK]), rfrom);
1285 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1288 board[rto] = board[kto] = EMPTY;
1289 board[rfrom] = piece_of_color_and_type(us, ROOK);
1290 board[kfrom] = piece_of_color_and_type(us, KING);
1292 // Update king square
1293 kingSquare[us] = kfrom;
1295 // Update piece lists
1296 pieceList[us][KING][index[kto]] = kfrom;
1297 pieceList[us][ROOK][index[rto]] = rfrom;
1298 int tmp = index[rto]; // Necessary because we may have rto == kfrom in FRC.
1299 index[kfrom] = index[kto];
1304 /// Position::undo_promotion_move() is a private method used to unmake a
1305 /// promotion move. It is called from the main Position::do_move
1308 void Position::undo_promotion_move(Move m) {
1312 PieceType promotion;
1314 assert(move_is_ok(m));
1315 assert(move_promotion(m));
1317 // When we have arrived here, some work has already been done by
1318 // Position::undo_move. In particular, the side to move has been switched,
1319 // so the code below is correct.
1320 us = side_to_move();
1321 them = opposite_color(us);
1322 from = move_from(m);
1325 assert(relative_rank(us, to) == RANK_8);
1326 assert(piece_on(from) == EMPTY);
1328 // Remove promoted piece
1329 promotion = move_promotion(m);
1330 assert(piece_on(to)==piece_of_color_and_type(us, promotion));
1331 assert(promotion >= KNIGHT && promotion <= QUEEN);
1332 clear_bit(&(byColorBB[us]), to);
1333 clear_bit(&(byTypeBB[promotion]), to);
1334 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1336 // Insert pawn at source square
1337 set_bit(&(byColorBB[us]), from);
1338 set_bit(&(byTypeBB[PAWN]), from);
1339 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1340 board[from] = piece_of_color_and_type(us, PAWN);
1343 npMaterial[us] -= piece_value_midgame(promotion);
1345 // Update piece list
1346 pieceList[us][PAWN][pieceCount[us][PAWN]] = from;
1347 index[from] = pieceCount[us][PAWN];
1348 pieceList[us][promotion][index[to]] =
1349 pieceList[us][promotion][pieceCount[us][promotion] - 1];
1350 index[pieceList[us][promotion][index[to]]] = index[to];
1352 // Update piece counts
1353 pieceCount[us][promotion]--;
1354 pieceCount[us][PAWN]++;
1358 assert(st->capture != KING);
1360 // Insert captured piece:
1361 set_bit(&(byColorBB[them]), to);
1362 set_bit(&(byTypeBB[st->capture]), to);
1363 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1364 board[to] = piece_of_color_and_type(them, st->capture);
1366 // Update material. Because the move is a promotion move, we know
1367 // that the captured piece cannot be a pawn.
1368 assert(st->capture != PAWN);
1369 npMaterial[them] += piece_value_midgame(st->capture);
1371 // Update piece list
1372 pieceList[them][st->capture][pieceCount[them][st->capture]] = to;
1373 index[to] = pieceCount[them][st->capture];
1375 // Update piece count
1376 pieceCount[them][st->capture]++;
1382 /// Position::undo_ep_move() is a private method used to unmake an en passant
1383 /// capture. It is called from the main Position::undo_move function.
1385 void Position::undo_ep_move(Move m) {
1387 assert(move_is_ok(m));
1388 assert(move_is_ep(m));
1390 // When we have arrived here, some work has already been done by
1391 // Position::undo_move. In particular, the side to move has been switched,
1392 // so the code below is correct.
1393 Color us = side_to_move();
1394 Color them = opposite_color(us);
1395 Square from = move_from(m);
1396 Square to = move_to(m);
1397 Square capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1399 assert(to == st->previous->epSquare);
1400 assert(relative_rank(us, to) == RANK_6);
1401 assert(piece_on(to) == piece_of_color_and_type(us, PAWN));
1402 assert(piece_on(from) == EMPTY);
1403 assert(piece_on(capsq) == EMPTY);
1405 // Replace captured piece
1406 set_bit(&(byColorBB[them]), capsq);
1407 set_bit(&(byTypeBB[PAWN]), capsq);
1408 set_bit(&(byTypeBB[0]), capsq);
1409 board[capsq] = piece_of_color_and_type(them, PAWN);
1411 // Remove moving piece from destination square
1412 clear_bit(&(byColorBB[us]), to);
1413 clear_bit(&(byTypeBB[PAWN]), to);
1414 clear_bit(&(byTypeBB[0]), to);
1417 // Replace moving piece at source square
1418 set_bit(&(byColorBB[us]), from);
1419 set_bit(&(byTypeBB[PAWN]), from);
1420 set_bit(&(byTypeBB[0]), from);
1421 board[from] = piece_of_color_and_type(us, PAWN);
1423 // Update piece list:
1424 pieceList[us][PAWN][index[to]] = from;
1425 index[from] = index[to];
1426 pieceList[them][PAWN][pieceCount[them][PAWN]] = capsq;
1427 index[capsq] = pieceCount[them][PAWN];
1429 // Update piece count:
1430 pieceCount[them][PAWN]++;
1434 /// Position::do_null_move makes() a "null move": It switches the side to move
1435 /// and updates the hash key without executing any move on the board.
1437 void Position::do_null_move(StateInfo& newSt) {
1440 assert(!is_check());
1442 // Back up the information necessary to undo the null move to the supplied
1443 // StateInfo object. In the case of a null move, the only thing we need to
1444 // remember is the last move made and the en passant square.
1445 newSt.lastMove = st->lastMove;
1446 newSt.epSquare = st->epSquare;
1447 newSt.previous = st->previous;
1448 st->previous = &newSt;
1450 // Save the current key to the history[] array, in order to be able to
1451 // detect repetition draws.
1452 history[gamePly] = st->key;
1454 // Update the necessary information
1455 sideToMove = opposite_color(sideToMove);
1456 if (st->epSquare != SQ_NONE)
1457 st->key ^= zobEp[st->epSquare];
1459 st->epSquare = SQ_NONE;
1462 st->key ^= zobSideToMove;
1464 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1465 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1471 /// Position::undo_null_move() unmakes a "null move".
1473 void Position::undo_null_move() {
1476 assert(!is_check());
1478 // Restore information from the our StateInfo object
1479 st->lastMove = st->previous->lastMove;
1480 st->epSquare = st->previous->epSquare;
1481 st->previous = st->previous->previous;
1483 if (st->epSquare != SQ_NONE)
1484 st->key ^= zobEp[st->epSquare];
1486 // Update the necessary information
1487 sideToMove = opposite_color(sideToMove);
1490 st->key ^= zobSideToMove;
1492 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1493 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1499 /// Position::see() is a static exchange evaluator: It tries to estimate the
1500 /// material gain or loss resulting from a move. There are three versions of
1501 /// this function: One which takes a destination square as input, one takes a
1502 /// move, and one which takes a 'from' and a 'to' square. The function does
1503 /// not yet understand promotions captures.
1505 int Position::see(Square to) const {
1507 assert(square_is_ok(to));
1508 return see(SQ_NONE, to);
1511 int Position::see(Move m) const {
1513 assert(move_is_ok(m));
1514 return see(move_from(m), move_to(m));
1517 int Position::see(Square from, Square to) const {
1520 static const int seeValues[18] = {
1521 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1522 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1523 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1524 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1528 Bitboard attackers, occ, b;
1530 assert(square_is_ok(from) || from == SQ_NONE);
1531 assert(square_is_ok(to));
1533 // Initialize colors
1534 Color us = (from != SQ_NONE ? color_of_piece_on(from) : opposite_color(color_of_piece_on(to)));
1535 Color them = opposite_color(us);
1537 // Initialize pieces
1538 Piece piece = piece_on(from);
1539 Piece capture = piece_on(to);
1541 // Find all attackers to the destination square, with the moving piece
1542 // removed, but possibly an X-ray attacker added behind it.
1543 occ = occupied_squares();
1545 // Handle en passant moves
1546 if (st->epSquare == to && type_of_piece_on(from) == PAWN)
1548 assert(capture == EMPTY);
1550 Square capQq = (side_to_move() == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1551 capture = piece_on(capQq);
1553 assert(type_of_piece_on(capQq) == PAWN);
1555 // Remove the captured pawn
1556 clear_bit(&occ, capQq);
1561 clear_bit(&occ, from);
1562 attackers = (rook_attacks_bb(to, occ) & rooks_and_queens())
1563 | (bishop_attacks_bb(to, occ) & bishops_and_queens())
1564 | (piece_attacks<KNIGHT>(to) & knights())
1565 | (piece_attacks<KING>(to) & kings())
1566 | (pawn_attacks(WHITE, to) & pawns(BLACK))
1567 | (pawn_attacks(BLACK, to) & pawns(WHITE));
1569 if (from != SQ_NONE)
1572 // If we don't have any attacker we are finished
1573 if ((attackers & pieces_of_color(us)) == EmptyBoardBB)
1576 // Locate the least valuable attacker to the destination square
1577 // and use it to initialize from square.
1579 for (pt = PAWN; !(attackers & pieces_of_color_and_type(us, pt)); pt++)
1582 from = first_1(attackers & pieces_of_color_and_type(us, pt));
1583 piece = piece_on(from);
1586 // If the opponent has no attackers we are finished
1587 if ((attackers & pieces_of_color(them)) == EmptyBoardBB)
1588 return seeValues[capture];
1590 attackers &= occ; // Remove the moving piece
1592 // The destination square is defended, which makes things rather more
1593 // difficult to compute. We proceed by building up a "swap list" containing
1594 // the material gain or loss at each stop in a sequence of captures to the
1595 // destination square, where the sides alternately capture, and always
1596 // capture with the least valuable piece. After each capture, we look for
1597 // new X-ray attacks from behind the capturing piece.
1598 int lastCapturingPieceValue = seeValues[piece];
1599 int swapList[32], n = 1;
1603 swapList[0] = seeValues[capture];
1606 // Locate the least valuable attacker for the side to move. The loop
1607 // below looks like it is potentially infinite, but it isn't. We know
1608 // that the side to move still has at least one attacker left.
1609 for (pt = PAWN; !(attackers & pieces_of_color_and_type(c, pt)); pt++)
1612 // Remove the attacker we just found from the 'attackers' bitboard,
1613 // and scan for new X-ray attacks behind the attacker.
1614 b = attackers & pieces_of_color_and_type(c, pt);
1616 attackers |= (rook_attacks_bb(to, occ) & rooks_and_queens())
1617 | (bishop_attacks_bb(to, occ) & bishops_and_queens());
1621 // Add the new entry to the swap list
1623 swapList[n] = -swapList[n - 1] + lastCapturingPieceValue;
1626 // Remember the value of the capturing piece, and change the side to move
1627 // before beginning the next iteration
1628 lastCapturingPieceValue = seeValues[pt];
1629 c = opposite_color(c);
1631 // Stop after a king capture
1632 if (pt == KING && (attackers & pieces_of_color(c)))
1635 swapList[n++] = 100;
1638 } while (attackers & pieces_of_color(c));
1640 // Having built the swap list, we negamax through it to find the best
1641 // achievable score from the point of view of the side to move
1643 swapList[n-1] = Min(-swapList[n], swapList[n-1]);
1649 /// Position::setStartState() copies the content of the argument
1650 /// inside startState and makes st point to it. This is needed
1651 /// when the st pointee could become stale, as example because
1652 /// the caller is about to going out of scope.
1654 void Position::setStartState(const StateInfo& s) {
1661 /// Position::clear() erases the position object to a pristine state, with an
1662 /// empty board, white to move, and no castling rights.
1664 void Position::clear() {
1667 memset(st, 0, sizeof(StateInfo));
1668 st->epSquare = SQ_NONE;
1670 memset(index, 0, sizeof(int) * 64);
1671 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1673 for (int i = 0; i < 64; i++)
1676 for (int i = 0; i < 7; i++)
1678 byTypeBB[i] = EmptyBoardBB;
1679 pieceCount[0][i] = pieceCount[1][i] = 0;
1680 for (int j = 0; j < 8; j++)
1681 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1686 initialKFile = FILE_E;
1687 initialKRFile = FILE_H;
1688 initialQRFile = FILE_A;
1692 /// Position::reset_game_ply() simply sets gamePly to 0. It is used from the
1693 /// UCI interface code, whenever a non-reversible move is made in a
1694 /// 'position fen <fen> moves m1 m2 ...' command. This makes it possible
1695 /// for the program to handle games of arbitrary length, as long as the GUI
1696 /// handles draws by the 50 move rule correctly.
1698 void Position::reset_game_ply() {
1704 /// Position::put_piece() puts a piece on the given square of the board,
1705 /// updating the board array, bitboards, and piece counts.
1707 void Position::put_piece(Piece p, Square s) {
1709 Color c = color_of_piece(p);
1710 PieceType pt = type_of_piece(p);
1713 index[s] = pieceCount[c][pt];
1714 pieceList[c][pt][index[s]] = s;
1716 set_bit(&(byTypeBB[pt]), s);
1717 set_bit(&(byColorBB[c]), s);
1718 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1720 pieceCount[c][pt]++;
1727 /// Position::allow_oo() gives the given side the right to castle kingside.
1728 /// Used when setting castling rights during parsing of FEN strings.
1730 void Position::allow_oo(Color c) {
1732 st->castleRights |= (1 + int(c));
1736 /// Position::allow_ooo() gives the given side the right to castle queenside.
1737 /// Used when setting castling rights during parsing of FEN strings.
1739 void Position::allow_ooo(Color c) {
1741 st->castleRights |= (4 + 4*int(c));
1745 /// Position::compute_key() computes the hash key of the position. The hash
1746 /// key is usually updated incrementally as moves are made and unmade, the
1747 /// compute_key() function is only used when a new position is set up, and
1748 /// to verify the correctness of the hash key when running in debug mode.
1750 Key Position::compute_key() const {
1752 Key result = Key(0ULL);
1754 for (Square s = SQ_A1; s <= SQ_H8; s++)
1755 if (square_is_occupied(s))
1756 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1758 if (ep_square() != SQ_NONE)
1759 result ^= zobEp[ep_square()];
1761 result ^= zobCastle[st->castleRights];
1762 if (side_to_move() == BLACK)
1763 result ^= zobSideToMove;
1769 /// Position::compute_pawn_key() computes the hash key of the position. The
1770 /// hash key is usually updated incrementally as moves are made and unmade,
1771 /// the compute_pawn_key() function is only used when a new position is set
1772 /// up, and to verify the correctness of the pawn hash key when running in
1775 Key Position::compute_pawn_key() const {
1777 Key result = Key(0ULL);
1781 for (Color c = WHITE; c <= BLACK; c++)
1786 s = pop_1st_bit(&b);
1787 result ^= zobrist[c][PAWN][s];
1794 /// Position::compute_material_key() computes the hash key of the position.
1795 /// The hash key is usually updated incrementally as moves are made and unmade,
1796 /// the compute_material_key() function is only used when a new position is set
1797 /// up, and to verify the correctness of the material hash key when running in
1800 Key Position::compute_material_key() const {
1802 Key result = Key(0ULL);
1803 for (Color c = WHITE; c <= BLACK; c++)
1804 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1806 int count = piece_count(c, pt);
1807 for (int i = 0; i <= count; i++)
1808 result ^= zobMaterial[c][pt][i];
1814 /// Position::compute_value() compute the incremental scores for the middle
1815 /// game and the endgame. These functions are used to initialize the incremental
1816 /// scores when a new position is set up, and to verify that the scores are correctly
1817 /// updated by do_move and undo_move when the program is running in debug mode.
1818 template<Position::GamePhase Phase>
1819 Value Position::compute_value() const {
1821 Value result = Value(0);
1825 for (Color c = WHITE; c <= BLACK; c++)
1826 for (PieceType pt = PAWN; pt <= KING; pt++)
1828 b = pieces_of_color_and_type(c, pt);
1831 s = pop_1st_bit(&b);
1832 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1833 result += pst<Phase>(c, pt, s);
1837 const Value TempoValue = (Phase == MidGame ? TempoValueMidgame : TempoValueEndgame);
1838 result += (side_to_move() == WHITE)? TempoValue / 2 : -TempoValue / 2;
1843 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1844 /// game material score for the given side. Material scores are updated
1845 /// incrementally during the search, this function is only used while
1846 /// initializing a new Position object.
1848 Value Position::compute_non_pawn_material(Color c) const {
1850 Value result = Value(0);
1853 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1855 Bitboard b = pieces_of_color_and_type(c, pt);
1858 s = pop_1st_bit(&b);
1859 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1860 result += piece_value_midgame(pt);
1867 /// Position::is_mate() returns true or false depending on whether the
1868 /// side to move is checkmated. Note that this function is currently very
1869 /// slow, and shouldn't be used frequently inside the search.
1871 bool Position::is_mate() const {
1875 MovePicker mp = MovePicker(*this, false, MOVE_NONE, EmptySearchStack, Depth(0));
1876 return mp.get_next_move() == MOVE_NONE;
1882 /// Position::is_draw() tests whether the position is drawn by material,
1883 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1884 /// must be done by the search.
1886 bool Position::is_draw() const {
1888 // Draw by material?
1890 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1893 // Draw by the 50 moves rule?
1894 if (st->rule50 > 100 || (st->rule50 == 100 && !is_check()))
1897 // Draw by repetition?
1898 for (int i = 2; i < Min(gamePly, st->rule50); i += 2)
1899 if (history[gamePly - i] == st->key)
1906 /// Position::has_mate_threat() tests whether a given color has a mate in one
1907 /// from the current position. This function is quite slow, but it doesn't
1908 /// matter, because it is currently only called from PV nodes, which are rare.
1910 bool Position::has_mate_threat(Color c) {
1913 Color stm = side_to_move();
1915 // The following lines are useless and silly, but prevents gcc from
1916 // emitting a stupid warning stating that u1.lastMove and u1.epSquare might
1917 // be used uninitialized.
1918 st1.lastMove = st->lastMove;
1919 st1.epSquare = st->epSquare;
1924 // If the input color is not equal to the side to move, do a null move
1928 MoveStack mlist[120];
1930 bool result = false;
1932 // Generate legal moves
1933 count = generate_legal_moves(*this, mlist);
1935 // Loop through the moves, and see if one of them is mate
1936 for (int i = 0; i < count; i++)
1938 do_move(mlist[i].move, st2);
1942 undo_move(mlist[i].move);
1945 // Undo null move, if necessary
1953 /// Position::init_zobrist() is a static member function which initializes the
1954 /// various arrays used to compute hash keys.
1956 void Position::init_zobrist() {
1958 for (int i = 0; i < 2; i++)
1959 for (int j = 0; j < 8; j++)
1960 for (int k = 0; k < 64; k++)
1961 zobrist[i][j][k] = Key(genrand_int64());
1963 for (int i = 0; i < 64; i++)
1964 zobEp[i] = Key(genrand_int64());
1966 for (int i = 0; i < 16; i++)
1967 zobCastle[i] = genrand_int64();
1969 zobSideToMove = genrand_int64();
1971 for (int i = 0; i < 2; i++)
1972 for (int j = 0; j < 8; j++)
1973 for (int k = 0; k < 16; k++)
1974 zobMaterial[i][j][k] = (k > 0)? Key(genrand_int64()) : Key(0LL);
1976 for (int i = 0; i < 16; i++)
1977 zobMaterial[0][KING][i] = zobMaterial[1][KING][i] = Key(0ULL);
1981 /// Position::init_piece_square_tables() initializes the piece square tables.
1982 /// This is a two-step operation: First, the white halves of the tables are
1983 /// copied from the MgPST[][] and EgPST[][] arrays, with a small random number
1984 /// added to each entry if the "Randomness" UCI parameter is non-zero.
1985 /// Second, the black halves of the tables are initialized by mirroring
1986 /// and changing the sign of the corresponding white scores.
1988 void Position::init_piece_square_tables() {
1990 int r = get_option_value_int("Randomness"), i;
1991 for (Square s = SQ_A1; s <= SQ_H8; s++)
1992 for (Piece p = WP; p <= WK; p++)
1994 i = (r == 0)? 0 : (genrand_int32() % (r*2) - r);
1995 MgPieceSquareTable[p][s] = Value(MgPST[p][s] + i);
1996 EgPieceSquareTable[p][s] = Value(EgPST[p][s] + i);
1999 for (Square s = SQ_A1; s <= SQ_H8; s++)
2000 for (Piece p = BP; p <= BK; p++)
2002 MgPieceSquareTable[p][s] = -MgPieceSquareTable[p-8][flip_square(s)];
2003 EgPieceSquareTable[p][s] = -EgPieceSquareTable[p-8][flip_square(s)];
2008 /// Position::flipped_copy() makes a copy of the input position, but with
2009 /// the white and black sides reversed. This is only useful for debugging,
2010 /// especially for finding evaluation symmetry bugs.
2012 void Position::flipped_copy(const Position &pos) {
2014 assert(pos.is_ok());
2019 for (Square s = SQ_A1; s <= SQ_H8; s++)
2020 if (!pos.square_is_empty(s))
2021 put_piece(Piece(int(pos.piece_on(s)) ^ 8), flip_square(s));
2024 sideToMove = opposite_color(pos.side_to_move());
2027 if (pos.can_castle_kingside(WHITE)) allow_oo(BLACK);
2028 if (pos.can_castle_queenside(WHITE)) allow_ooo(BLACK);
2029 if (pos.can_castle_kingside(BLACK)) allow_oo(WHITE);
2030 if (pos.can_castle_queenside(BLACK)) allow_ooo(WHITE);
2032 initialKFile = pos.initialKFile;
2033 initialKRFile = pos.initialKRFile;
2034 initialQRFile = pos.initialQRFile;
2036 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
2037 castleRightsMask[sq] = ALL_CASTLES;
2039 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
2040 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
2041 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
2042 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
2043 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
2044 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
2046 // En passant square
2047 if (pos.st->epSquare != SQ_NONE)
2048 st->epSquare = flip_square(pos.st->epSquare);
2054 st->key = compute_key();
2055 st->pawnKey = compute_pawn_key();
2056 st->materialKey = compute_material_key();
2058 // Incremental scores
2059 st->mgValue = compute_value<MidGame>();
2060 st->egValue = compute_value<EndGame>();
2063 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
2064 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
2070 /// Position::is_ok() performs some consitency checks for the position object.
2071 /// This is meant to be helpful when debugging.
2073 bool Position::is_ok(int* failedStep) const {
2075 // What features of the position should be verified?
2076 static const bool debugBitboards = false;
2077 static const bool debugKingCount = false;
2078 static const bool debugKingCapture = false;
2079 static const bool debugCheckerCount = false;
2080 static const bool debugKey = false;
2081 static const bool debugMaterialKey = false;
2082 static const bool debugPawnKey = false;
2083 static const bool debugIncrementalEval = false;
2084 static const bool debugNonPawnMaterial = false;
2085 static const bool debugPieceCounts = false;
2086 static const bool debugPieceList = false;
2088 if (failedStep) *failedStep = 1;
2091 if (!color_is_ok(side_to_move()))
2094 // Are the king squares in the position correct?
2095 if (failedStep) (*failedStep)++;
2096 if (piece_on(king_square(WHITE)) != WK)
2099 if (failedStep) (*failedStep)++;
2100 if (piece_on(king_square(BLACK)) != BK)
2104 if (failedStep) (*failedStep)++;
2105 if (!file_is_ok(initialKRFile))
2108 if (!file_is_ok(initialQRFile))
2111 // Do both sides have exactly one king?
2112 if (failedStep) (*failedStep)++;
2115 int kingCount[2] = {0, 0};
2116 for (Square s = SQ_A1; s <= SQ_H8; s++)
2117 if (type_of_piece_on(s) == KING)
2118 kingCount[color_of_piece_on(s)]++;
2120 if (kingCount[0] != 1 || kingCount[1] != 1)
2124 // Can the side to move capture the opponent's king?
2125 if (failedStep) (*failedStep)++;
2126 if (debugKingCapture)
2128 Color us = side_to_move();
2129 Color them = opposite_color(us);
2130 Square ksq = king_square(them);
2131 if (square_is_attacked(ksq, us))
2135 // Is there more than 2 checkers?
2136 if (failedStep) (*failedStep)++;
2137 if (debugCheckerCount && count_1s(st->checkersBB) > 2)
2141 if (failedStep) (*failedStep)++;
2144 // The intersection of the white and black pieces must be empty
2145 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
2148 // The union of the white and black pieces must be equal to all
2150 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
2153 // Separate piece type bitboards must have empty intersections
2154 for (PieceType p1 = PAWN; p1 <= KING; p1++)
2155 for (PieceType p2 = PAWN; p2 <= KING; p2++)
2156 if (p1 != p2 && (pieces_of_type(p1) & pieces_of_type(p2)))
2160 // En passant square OK?
2161 if (failedStep) (*failedStep)++;
2162 if (ep_square() != SQ_NONE)
2164 // The en passant square must be on rank 6, from the point of view of the
2166 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
2171 if (failedStep) (*failedStep)++;
2172 if (debugKey && st->key != compute_key())
2175 // Pawn hash key OK?
2176 if (failedStep) (*failedStep)++;
2177 if (debugPawnKey && st->pawnKey != compute_pawn_key())
2180 // Material hash key OK?
2181 if (failedStep) (*failedStep)++;
2182 if (debugMaterialKey && st->materialKey != compute_material_key())
2185 // Incremental eval OK?
2186 if (failedStep) (*failedStep)++;
2187 if (debugIncrementalEval)
2189 if (st->mgValue != compute_value<MidGame>())
2192 if (st->egValue != compute_value<EndGame>())
2196 // Non-pawn material OK?
2197 if (failedStep) (*failedStep)++;
2198 if (debugNonPawnMaterial)
2200 if (npMaterial[WHITE] != compute_non_pawn_material(WHITE))
2203 if (npMaterial[BLACK] != compute_non_pawn_material(BLACK))
2208 if (failedStep) (*failedStep)++;
2209 if (debugPieceCounts)
2210 for (Color c = WHITE; c <= BLACK; c++)
2211 for (PieceType pt = PAWN; pt <= KING; pt++)
2212 if (pieceCount[c][pt] != count_1s(pieces_of_color_and_type(c, pt)))
2215 if (failedStep) (*failedStep)++;
2218 for(Color c = WHITE; c <= BLACK; c++)
2219 for(PieceType pt = PAWN; pt <= KING; pt++)
2220 for(int i = 0; i < pieceCount[c][pt]; i++)
2222 if (piece_on(piece_list(c, pt, i)) != piece_of_color_and_type(c, pt))
2225 if (index[piece_list(c, pt, i)] != i)
2229 if (failedStep) *failedStep = 0;