2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008 Marco Costalba
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
35 #include "ucioption.h"
42 extern SearchStack EmptySearchStack;
44 int Position::castleRightsMask[64];
46 Key Position::zobrist[2][8][64];
47 Key Position::zobEp[64];
48 Key Position::zobCastle[16];
49 Key Position::zobMaterial[2][8][16];
50 Key Position::zobSideToMove;
52 Value Position::MgPieceSquareTable[16][64];
53 Value Position::EgPieceSquareTable[16][64];
55 static bool RequestPending = false;
63 Position::Position(const Position& pos) {
67 Position::Position(const std::string& fen) {
72 /// Position::from_fen() initializes the position object with the given FEN
73 /// string. This function is not very robust - make sure that input FENs are
74 /// correct (this is assumed to be the responsibility of the GUI).
76 void Position::from_fen(const std::string& fen) {
78 static const std::string pieceLetters = "KQRBNPkqrbnp";
79 static const Piece pieces[] = { WK, WQ, WR, WB, WN, WP, BK, BQ, BR, BB, BN, BP };
87 for ( ; fen[i] != ' '; i++)
91 // Skip the given number of files
92 file += (fen[i] - '1' + 1);
95 else if (fen[i] == '/')
101 size_t idx = pieceLetters.find(fen[i]);
102 if (idx == std::string::npos)
104 std::cout << "Error in FEN at character " << i << std::endl;
107 Square square = make_square(file, rank);
108 put_piece(pieces[idx], square);
114 if (fen[i] != 'w' && fen[i] != 'b')
116 std::cout << "Error in FEN at character " << i << std::endl;
119 sideToMove = (fen[i] == 'w' ? WHITE : BLACK);
125 std::cout << "Error in FEN at character " << i << std::endl;
130 while(strchr("KQkqabcdefghABCDEFGH-", fen[i])) {
136 else if(fen[i] == 'K') allow_oo(WHITE);
137 else if(fen[i] == 'Q') allow_ooo(WHITE);
138 else if(fen[i] == 'k') allow_oo(BLACK);
139 else if(fen[i] == 'q') allow_ooo(BLACK);
140 else if(fen[i] >= 'A' && fen[i] <= 'H') {
141 File rookFile, kingFile = FILE_NONE;
142 for(Square square = SQ_B1; square <= SQ_G1; square++)
143 if(piece_on(square) == WK)
144 kingFile = square_file(square);
145 if(kingFile == FILE_NONE) {
146 std::cout << "Error in FEN at character " << i << std::endl;
149 initialKFile = kingFile;
150 rookFile = File(fen[i] - 'A') + FILE_A;
151 if(rookFile < initialKFile) {
153 initialQRFile = rookFile;
157 initialKRFile = rookFile;
160 else if(fen[i] >= 'a' && fen[i] <= 'h') {
161 File rookFile, kingFile = FILE_NONE;
162 for(Square square = SQ_B8; square <= SQ_G8; square++)
163 if(piece_on(square) == BK)
164 kingFile = square_file(square);
165 if(kingFile == FILE_NONE) {
166 std::cout << "Error in FEN at character " << i << std::endl;
169 initialKFile = kingFile;
170 rookFile = File(fen[i] - 'a') + FILE_A;
171 if(rookFile < initialKFile) {
173 initialQRFile = rookFile;
177 initialKRFile = rookFile;
181 std::cout << "Error in FEN at character " << i << std::endl;
188 while (fen[i] == ' ')
192 if ( i < fen.length() - 2
193 && (fen[i] >= 'a' && fen[i] <= 'h')
194 && (fen[i+1] == '3' || fen[i+1] == '6'))
195 epSquare = square_from_string(fen.substr(i, 2));
197 // Various initialisation
198 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
199 castleRightsMask[sq] = ALL_CASTLES;
201 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO|WHITE_OOO);
202 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO|BLACK_OOO);
203 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
204 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
205 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
206 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
211 pawnKey = compute_pawn_key();
212 materialKey = compute_material_key();
213 mgValue = compute_value<MidGame>();
214 egValue = compute_value<EndGame>();
215 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
216 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
220 /// Position::to_fen() converts the position object to a FEN string. This is
221 /// probably only useful for debugging.
223 const std::string Position::to_fen() const {
225 static const std::string pieceLetters = " PNBRQK pnbrqk";
229 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
232 for (File file = FILE_A; file <= FILE_H; file++)
234 Square sq = make_square(file, rank);
235 if (!square_is_occupied(sq))
241 fen += (char)skip + '0';
244 fen += pieceLetters[piece_on(sq)];
247 fen += (char)skip + '0';
249 fen += (rank > RANK_1 ? '/' : ' ');
251 fen += (sideToMove == WHITE ? "w " : "b ");
252 if (castleRights != NO_CASTLES)
254 if (can_castle_kingside(WHITE)) fen += 'K';
255 if (can_castle_queenside(WHITE)) fen += 'Q';
256 if (can_castle_kingside(BLACK)) fen += 'k';
257 if (can_castle_queenside(BLACK)) fen += 'q';
262 if (ep_square() != SQ_NONE)
263 fen += square_to_string(ep_square());
271 /// Position::print() prints an ASCII representation of the position to
272 /// the standard output. If a move is given then also the san is print.
274 void Position::print(Move m) const {
276 static const std::string pieceLetters = " PNBRQK PNBRQK .";
278 // Check for reentrancy, as example when called from inside
279 // MovePicker that is used also here in move_to_san()
283 RequestPending = true;
285 std::cout << std::endl;
288 std::string col = (color_of_piece_on(move_from(m)) == BLACK ? ".." : "");
289 std::cout << "Move is: " << col << move_to_san(*this, m) << std::endl;
291 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
293 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl;
294 for (File file = FILE_A; file <= FILE_H; file++)
296 Square sq = make_square(file, rank);
297 Piece piece = piece_on(sq);
298 if (piece == EMPTY && square_color(sq) == WHITE)
301 char col = (color_of_piece_on(sq) == BLACK ? '=' : ' ');
302 std::cout << '|' << col << pieceLetters[piece] << col;
304 std::cout << '|' << std::endl;
306 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl
307 << "Fen is: " << to_fen() << std::endl
308 << "Key is: " << key << std::endl;
310 RequestPending = false;
314 /// Position::copy() creates a copy of the input position.
316 void Position::copy(const Position &pos) {
318 memcpy(this, &pos, sizeof(Position));
322 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
323 /// king) pieces for the given color.
324 Bitboard Position::pinned_pieces(Color c) const {
326 if (pinned[c] != ~EmptyBoardBB)
330 Square ksq = king_square(c);
331 pinned[c] = hidden_checks<ROOK, true>(c, ksq, p1) | hidden_checks<BISHOP, true>(c, ksq, p2);
332 pinners[c] = p1 | p2;
336 Bitboard Position::pinned_pieces(Color c, Bitboard& p) const {
338 if (pinned[c] == ~EmptyBoardBB)
345 Bitboard Position::discovered_check_candidates(Color c) const {
347 if (dcCandidates[c] != ~EmptyBoardBB)
348 return dcCandidates[c];
351 Square ksq = king_square(opposite_color(c));
352 dcCandidates[c] = hidden_checks<ROOK, false>(c, ksq, dummy) | hidden_checks<BISHOP, false>(c, ksq, dummy);
353 return dcCandidates[c];
356 /// Position:hidden_checks<>() returns a bitboard of all pinned (against the
357 /// king) pieces for the given color and for the given pinner type. Or, when
358 /// template parameter FindPinned is false, the pinned pieces of opposite color
359 /// that are, indeed, the pieces candidate for a discovery check.
360 template<PieceType Piece, bool FindPinned>
361 Bitboard Position::hidden_checks(Color c, Square ksq, Bitboard& pinners) const {
364 Bitboard sliders, result = EmptyBoardBB;
366 if (Piece == ROOK) // Resolved at compile time
367 sliders = rooks_and_queens(FindPinned ? opposite_color(c) : c) & RookPseudoAttacks[ksq];
369 sliders = bishops_and_queens(FindPinned ? opposite_color(c) : c) & BishopPseudoAttacks[ksq];
371 if (sliders && (!FindPinned || (sliders & ~checkersBB)))
373 // King blockers are candidate pinned pieces
374 Bitboard candidate_pinned = piece_attacks<Piece>(ksq) & pieces_of_color(c);
376 // Pinners are sliders, not checkers, that give check when
377 // candidate pinned are removed.
378 pinners = (FindPinned ? sliders & ~checkersBB : sliders);
381 pinners &= rook_attacks_bb(ksq, occupied_squares() ^ candidate_pinned);
383 pinners &= bishop_attacks_bb(ksq, occupied_squares() ^ candidate_pinned);
385 // Finally for each pinner find the corresponding pinned piece (if same color of king)
386 // or discovery checker (if opposite color) among the candidates.
387 Bitboard p = pinners;
391 result |= (squares_between(s, ksq) & candidate_pinned);
395 pinners = EmptyBoardBB;
401 /// Position::attacks_to() computes a bitboard containing all pieces which
402 /// attacks a given square. There are two versions of this function: One
403 /// which finds attackers of both colors, and one which only finds the
404 /// attackers for one side.
406 Bitboard Position::attacks_to(Square s) const {
408 return (pawn_attacks(BLACK, s) & pawns(WHITE))
409 | (pawn_attacks(WHITE, s) & pawns(BLACK))
410 | (piece_attacks<KNIGHT>(s) & pieces_of_type(KNIGHT))
411 | (piece_attacks<ROOK>(s) & rooks_and_queens())
412 | (piece_attacks<BISHOP>(s) & bishops_and_queens())
413 | (piece_attacks<KING>(s) & pieces_of_type(KING));
416 /// Position::piece_attacks_square() tests whether the piece on square f
417 /// attacks square t.
419 bool Position::piece_attacks_square(Piece p, Square f, Square t) const {
421 assert(square_is_ok(f));
422 assert(square_is_ok(t));
426 case WP: return pawn_attacks_square(WHITE, f, t);
427 case BP: return pawn_attacks_square(BLACK, f, t);
428 case WN: case BN: return piece_attacks_square<KNIGHT>(f, t);
429 case WB: case BB: return piece_attacks_square<BISHOP>(f, t);
430 case WR: case BR: return piece_attacks_square<ROOK>(f, t);
431 case WQ: case BQ: return piece_attacks_square<QUEEN>(f, t);
432 case WK: case BK: return piece_attacks_square<KING>(f, t);
439 /// Position::move_attacks_square() tests whether a move from the current
440 /// position attacks a given square.
442 bool Position::move_attacks_square(Move m, Square s) const {
444 assert(move_is_ok(m));
445 assert(square_is_ok(s));
447 Square f = move_from(m), t = move_to(m);
449 assert(square_is_occupied(f));
451 if (piece_attacks_square(piece_on(f), t, s))
454 // Move the piece and scan for X-ray attacks behind it
455 Bitboard occ = occupied_squares();
456 Color us = color_of_piece_on(f);
459 Bitboard xray = ( (rook_attacks_bb(s, occ) & rooks_and_queens())
460 |(bishop_attacks_bb(s, occ) & bishops_and_queens())) & pieces_of_color(us);
462 // If we have attacks we need to verify that are caused by our move
463 // and are not already existent ones.
464 return xray && (xray ^ (xray & piece_attacks<QUEEN>(s)));
468 /// Position::find_checkers() computes the checkersBB bitboard, which
469 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
470 /// currently works by calling Position::attacks_to, which is probably
471 /// inefficient. Consider rewriting this function to use the last move
472 /// played, like in non-bitboard versions of Glaurung.
474 void Position::find_checkers() {
476 Color us = side_to_move();
477 checkersBB = attacks_to(king_square(us), opposite_color(us));
481 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
483 bool Position::pl_move_is_legal(Move m) const {
486 assert(move_is_ok(m));
488 // If we're in check, all pseudo-legal moves are legal, because our
489 // check evasion generator only generates true legal moves.
493 // Castling moves are checked for legality during move generation.
494 if (move_is_castle(m))
497 Color us = side_to_move();
498 Color them = opposite_color(us);
499 Square from = move_from(m);
500 Square ksq = king_square(us);
502 assert(color_of_piece_on(from) == us);
503 assert(piece_on(ksq) == piece_of_color_and_type(us, KING));
505 // En passant captures are a tricky special case. Because they are
506 // rather uncommon, we do it simply by testing whether the king is attacked
507 // after the move is made
510 Square to = move_to(m);
511 Square capsq = make_square(square_file(to), square_rank(from));
512 Bitboard b = occupied_squares();
514 assert(to == ep_square());
515 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
516 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
517 assert(piece_on(to) == EMPTY);
520 clear_bit(&b, capsq);
523 return !(rook_attacks_bb(ksq, b) & rooks_and_queens(them))
524 && !(bishop_attacks_bb(ksq, b) & bishops_and_queens(them));
527 // If the moving piece is a king, check whether the destination
528 // square is attacked by the opponent.
530 return !(square_is_attacked(move_to(m), them));
532 // A non-king move is legal if and only if it is not pinned or it
533 // is moving along the ray towards or away from the king.
534 return ( !bit_is_set(pinned_pieces(us), from)
535 || (direction_between_squares(from, ksq) == direction_between_squares(move_to(m), ksq)));
539 /// Position::move_is_check() tests whether a pseudo-legal move is a check
541 bool Position::move_is_check(Move m) const {
544 assert(move_is_ok(m));
546 Color us = side_to_move();
547 Color them = opposite_color(us);
548 Square from = move_from(m);
549 Square to = move_to(m);
550 Square ksq = king_square(them);
551 Bitboard dcCandidates = discovered_check_candidates(us);
553 assert(color_of_piece_on(from) == us);
554 assert(piece_on(ksq) == piece_of_color_and_type(them, KING));
556 // Proceed according to the type of the moving piece
557 switch (type_of_piece_on(from))
561 if (bit_is_set(pawn_attacks(them, ksq), to)) // Normal check?
564 if ( bit_is_set(dcCandidates, from) // Discovered check?
565 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
568 if (move_promotion(m)) // Promotion with check?
570 Bitboard b = occupied_squares();
573 switch (move_promotion(m))
576 return bit_is_set(piece_attacks<KNIGHT>(to), ksq);
578 return bit_is_set(bishop_attacks_bb(to, b), ksq);
580 return bit_is_set(rook_attacks_bb(to, b), ksq);
582 return bit_is_set(queen_attacks_bb(to, b), ksq);
587 // En passant capture with check? We have already handled the case
588 // of direct checks and ordinary discovered check, the only case we
589 // need to handle is the unusual case of a discovered check through the
591 else if (move_is_ep(m))
593 Square capsq = make_square(square_file(to), square_rank(from));
594 Bitboard b = occupied_squares();
596 clear_bit(&b, capsq);
598 return (rook_attacks_bb(ksq, b) & rooks_and_queens(us))
599 ||(bishop_attacks_bb(ksq, b) & bishops_and_queens(us));
604 return bit_is_set(dcCandidates, from) // Discovered check?
605 || bit_is_set(piece_attacks<KNIGHT>(ksq), to); // Normal check?
608 return bit_is_set(dcCandidates, from) // Discovered check?
609 || bit_is_set(piece_attacks<BISHOP>(ksq), to); // Normal check?
612 return bit_is_set(dcCandidates, from) // Discovered check?
613 || bit_is_set(piece_attacks<ROOK>(ksq), to); // Normal check?
616 // Discovered checks are impossible!
617 assert(!bit_is_set(dcCandidates, from));
618 return bit_is_set(piece_attacks<QUEEN>(ksq), to); // Normal check?
622 if ( bit_is_set(dcCandidates, from)
623 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
626 // Castling with check?
627 if (move_is_castle(m))
629 Square kfrom, kto, rfrom, rto;
630 Bitboard b = occupied_squares();
636 kto = relative_square(us, SQ_G1);
637 rto = relative_square(us, SQ_F1);
639 kto = relative_square(us, SQ_C1);
640 rto = relative_square(us, SQ_D1);
642 clear_bit(&b, kfrom);
643 clear_bit(&b, rfrom);
646 return bit_is_set(rook_attacks_bb(rto, b), ksq);
650 default: // NO_PIECE_TYPE
658 /// Position::move_is_capture() tests whether a move from the current
659 /// position is a capture. Move must not be MOVE_NONE.
661 bool Position::move_is_capture(Move m) const {
663 assert(m != MOVE_NONE);
665 return ( !square_is_empty(move_to(m))
666 && (color_of_piece_on(move_to(m)) != color_of_piece_on(move_from(m)))
672 /// Position::update_checkers() is a private method to udpate chekers info
674 template<PieceType Piece>
675 inline void Position::update_checkers(Bitboard* pCheckersBB, Square ksq, Square from,
676 Square to, Bitboard dcCandidates) {
678 if (Piece != KING && bit_is_set(piece_attacks<Piece>(ksq), to))
679 set_bit(pCheckersBB, to);
681 if (Piece != QUEEN && bit_is_set(dcCandidates, from))
684 (*pCheckersBB) |= (piece_attacks<ROOK>(ksq) & rooks_and_queens(side_to_move()));
687 (*pCheckersBB) |= (piece_attacks<BISHOP>(ksq) & bishops_and_queens(side_to_move()));
692 /// Position::do_move() makes a move, and backs up all information necessary
693 /// to undo the move to an UndoInfo object. The move is assumed to be legal.
694 /// Pseudo-legal moves should be filtered out before this function is called.
696 void Position::do_move(Move m, UndoInfo& u) {
699 assert(move_is_ok(m));
701 // Get now the current (pre-move) dc candidates that we will use
702 // in update_checkers().
703 Bitboard oldDcCandidates = discovered_check_candidates(side_to_move());
705 // Back up the necessary information to our UndoInfo object (except the
706 // captured piece, which is taken care of later.
708 u.capture = NO_PIECE_TYPE;
711 // Save the current key to the history[] array, in order to be able to
712 // detect repetition draws.
713 history[gamePly] = key;
715 // Increment the 50 moves rule draw counter. Resetting it to zero in the
716 // case of non-reversible moves is taken care of later.
719 // Reset pinned bitboard and its friends
720 for (Color c = WHITE; c <= BLACK; c++)
721 pinners[c] = pinned[c] = dcCandidates[c] = ~EmptyBoardBB;
723 if (move_is_castle(m))
725 else if (move_promotion(m))
726 do_promotion_move(m);
727 else if (move_is_ep(m))
731 Color us = side_to_move();
732 Color them = opposite_color(us);
733 Square from = move_from(m);
734 Square to = move_to(m);
736 assert(color_of_piece_on(from) == us);
737 assert(color_of_piece_on(to) == them || piece_on(to) == EMPTY);
739 PieceType piece = type_of_piece_on(from);
740 PieceType capture = type_of_piece_on(to);
745 do_capture_move(m, capture, them, to);
749 clear_bit(&(byColorBB[us]), from);
750 clear_bit(&(byTypeBB[piece]), from);
751 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
752 set_bit(&(byColorBB[us]), to);
753 set_bit(&(byTypeBB[piece]), to);
754 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
755 board[to] = board[from];
759 key ^= zobrist[us][piece][from] ^ zobrist[us][piece][to];
761 // Update incremental scores
762 mgValue -= pst<MidGame>(us, piece, from);
763 mgValue += pst<MidGame>(us, piece, to);
764 egValue -= pst<EndGame>(us, piece, from);
765 egValue += pst<EndGame>(us, piece, to);
767 // If the moving piece was a king, update the king square
771 // Reset en passant square
772 if (epSquare != SQ_NONE)
774 key ^= zobEp[epSquare];
778 // If the moving piece was a pawn do some special extra work
781 // Reset rule 50 draw counter
784 // Update pawn hash key
785 pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
787 // Set en passant square, only if moved pawn can be captured
788 if (abs(int(to) - int(from)) == 16)
790 if ( (us == WHITE && (pawn_attacks(WHITE, from + DELTA_N) & pawns(BLACK)))
791 || (us == BLACK && (pawn_attacks(BLACK, from + DELTA_S) & pawns(WHITE))))
793 epSquare = Square((int(from) + int(to)) / 2);
794 key ^= zobEp[epSquare];
799 // Update piece lists
800 pieceList[us][piece][index[from]] = to;
801 index[to] = index[from];
803 // Update castle rights
804 key ^= zobCastle[castleRights];
805 castleRights &= castleRightsMask[from];
806 castleRights &= castleRightsMask[to];
807 key ^= zobCastle[castleRights];
809 // Update checkers bitboard, piece must be already moved
810 checkersBB = EmptyBoardBB;
811 Square ksq = king_square(them);
814 case PAWN: update_checkers<PAWN>(&checkersBB, ksq, from, to, oldDcCandidates); break;
815 case KNIGHT: update_checkers<KNIGHT>(&checkersBB, ksq, from, to, oldDcCandidates); break;
816 case BISHOP: update_checkers<BISHOP>(&checkersBB, ksq, from, to, oldDcCandidates); break;
817 case ROOK: update_checkers<ROOK>(&checkersBB, ksq, from, to, oldDcCandidates); break;
818 case QUEEN: update_checkers<QUEEN>(&checkersBB, ksq, from, to, oldDcCandidates); break;
819 case KING: update_checkers<KING>(&checkersBB, ksq, from, to, oldDcCandidates); break;
820 default: assert(false); break;
825 key ^= zobSideToMove;
826 sideToMove = opposite_color(sideToMove);
829 mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
830 egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
836 /// Position::do_capture_move() is a private method used to update captured
837 /// piece info. It is called from the main Position::do_move function.
839 void Position::do_capture_move(Move m, PieceType capture, Color them, Square to) {
841 assert(capture != KING);
843 // Remove captured piece
844 clear_bit(&(byColorBB[them]), to);
845 clear_bit(&(byTypeBB[capture]), to);
848 key ^= zobrist[them][capture][to];
850 // If the captured piece was a pawn, update pawn hash key
852 pawnKey ^= zobrist[them][PAWN][to];
854 // Update incremental scores
855 mgValue -= pst<MidGame>(them, capture, to);
856 egValue -= pst<EndGame>(them, capture, to);
858 assert(!move_promotion(m) || capture != PAWN);
862 npMaterial[them] -= piece_value_midgame(capture);
864 // Update material hash key
865 materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];
867 // Update piece count
868 pieceCount[them][capture]--;
871 pieceList[them][capture][index[to]] = pieceList[them][capture][pieceCount[them][capture]];
872 index[pieceList[them][capture][index[to]]] = index[to];
874 // Reset rule 50 counter
879 /// Position::do_castle_move() is a private method used to make a castling
880 /// move. It is called from the main Position::do_move function. Note that
881 /// castling moves are encoded as "king captures friendly rook" moves, for
882 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
884 void Position::do_castle_move(Move m) {
887 assert(move_is_ok(m));
888 assert(move_is_castle(m));
890 Color us = side_to_move();
891 Color them = opposite_color(us);
893 // Find source squares for king and rook
894 Square kfrom = move_from(m);
895 Square rfrom = move_to(m); // HACK: See comment at beginning of function
898 assert(piece_on(kfrom) == piece_of_color_and_type(us, KING));
899 assert(piece_on(rfrom) == piece_of_color_and_type(us, ROOK));
901 // Find destination squares for king and rook
902 if (rfrom > kfrom) // O-O
904 kto = relative_square(us, SQ_G1);
905 rto = relative_square(us, SQ_F1);
907 kto = relative_square(us, SQ_C1);
908 rto = relative_square(us, SQ_D1);
911 // Remove pieces from source squares
912 clear_bit(&(byColorBB[us]), kfrom);
913 clear_bit(&(byTypeBB[KING]), kfrom);
914 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
915 clear_bit(&(byColorBB[us]), rfrom);
916 clear_bit(&(byTypeBB[ROOK]), rfrom);
917 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
919 // Put pieces on destination squares
920 set_bit(&(byColorBB[us]), kto);
921 set_bit(&(byTypeBB[KING]), kto);
922 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
923 set_bit(&(byColorBB[us]), rto);
924 set_bit(&(byTypeBB[ROOK]), rto);
925 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
927 // Update board array
928 board[kfrom] = board[rfrom] = EMPTY;
929 board[kto] = piece_of_color_and_type(us, KING);
930 board[rto] = piece_of_color_and_type(us, ROOK);
932 // Update king square
933 kingSquare[us] = kto;
935 // Update piece lists
936 pieceList[us][KING][index[kfrom]] = kto;
937 pieceList[us][ROOK][index[rfrom]] = rto;
938 int tmp = index[rfrom];
939 index[kto] = index[kfrom];
942 // Update incremental scores
943 mgValue -= pst<MidGame>(us, KING, kfrom);
944 mgValue += pst<MidGame>(us, KING, kto);
945 egValue -= pst<EndGame>(us, KING, kfrom);
946 egValue += pst<EndGame>(us, KING, kto);
947 mgValue -= pst<MidGame>(us, ROOK, rfrom);
948 mgValue += pst<MidGame>(us, ROOK, rto);
949 egValue -= pst<EndGame>(us, ROOK, rfrom);
950 egValue += pst<EndGame>(us, ROOK, rto);
953 key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
954 key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
956 // Clear en passant square
957 if (epSquare != SQ_NONE)
959 key ^= zobEp[epSquare];
963 // Update castling rights
964 key ^= zobCastle[castleRights];
965 castleRights &= castleRightsMask[kfrom];
966 key ^= zobCastle[castleRights];
968 // Reset rule 50 counter
971 // Update checkers BB
972 checkersBB = attacks_to(king_square(them), us);
976 /// Position::do_promotion_move() is a private method used to make a promotion
977 /// move. It is called from the main Position::do_move function. The
978 /// UndoInfo object, which has been initialized in Position::do_move, is
979 /// used to store the captured piece (if any).
981 void Position::do_promotion_move(Move m) {
985 PieceType capture, promotion;
988 assert(move_is_ok(m));
989 assert(move_promotion(m));
992 them = opposite_color(us);
996 assert(relative_rank(us, to) == RANK_8);
997 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
998 assert(color_of_piece_on(to) == them || square_is_empty(to));
1000 capture = type_of_piece_on(to);
1004 previous->capture = capture;
1005 do_capture_move(m, capture, them, to);
1009 clear_bit(&(byColorBB[us]), from);
1010 clear_bit(&(byTypeBB[PAWN]), from);
1011 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1012 board[from] = EMPTY;
1014 // Insert promoted piece
1015 promotion = move_promotion(m);
1016 assert(promotion >= KNIGHT && promotion <= QUEEN);
1017 set_bit(&(byColorBB[us]), to);
1018 set_bit(&(byTypeBB[promotion]), to);
1019 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1020 board[to] = piece_of_color_and_type(us, promotion);
1023 key ^= zobrist[us][PAWN][from] ^ zobrist[us][promotion][to];
1025 // Update pawn hash key
1026 pawnKey ^= zobrist[us][PAWN][from];
1028 // Update material key
1029 materialKey ^= zobMaterial[us][PAWN][pieceCount[us][PAWN]];
1030 materialKey ^= zobMaterial[us][promotion][pieceCount[us][promotion]+1];
1032 // Update piece counts
1033 pieceCount[us][PAWN]--;
1034 pieceCount[us][promotion]++;
1036 // Update piece lists
1037 pieceList[us][PAWN][index[from]] = pieceList[us][PAWN][pieceCount[us][PAWN]];
1038 index[pieceList[us][PAWN][index[from]]] = index[from];
1039 pieceList[us][promotion][pieceCount[us][promotion] - 1] = to;
1040 index[to] = pieceCount[us][promotion] - 1;
1042 // Update incremental scores
1043 mgValue -= pst<MidGame>(us, PAWN, from);
1044 mgValue += pst<MidGame>(us, promotion, to);
1045 egValue -= pst<EndGame>(us, PAWN, from);
1046 egValue += pst<EndGame>(us, promotion, to);
1049 npMaterial[us] += piece_value_midgame(promotion);
1051 // Clear the en passant square
1052 if (epSquare != SQ_NONE)
1054 key ^= zobEp[epSquare];
1058 // Update castle rights
1059 key ^= zobCastle[castleRights];
1060 castleRights &= castleRightsMask[to];
1061 key ^= zobCastle[castleRights];
1063 // Reset rule 50 counter
1066 // Update checkers BB
1067 checkersBB = attacks_to(king_square(them), us);
1071 /// Position::do_ep_move() is a private method used to make an en passant
1072 /// capture. It is called from the main Position::do_move function. Because
1073 /// the captured piece is always a pawn, we don't need to pass an UndoInfo
1074 /// object in which to store the captured piece.
1076 void Position::do_ep_move(Move m) {
1079 Square from, to, capsq;
1082 assert(move_is_ok(m));
1083 assert(move_is_ep(m));
1085 us = side_to_move();
1086 them = opposite_color(us);
1087 from = move_from(m);
1089 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1091 assert(to == epSquare);
1092 assert(relative_rank(us, to) == RANK_6);
1093 assert(piece_on(to) == EMPTY);
1094 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
1095 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
1097 // Remove captured piece
1098 clear_bit(&(byColorBB[them]), capsq);
1099 clear_bit(&(byTypeBB[PAWN]), capsq);
1100 clear_bit(&(byTypeBB[0]), capsq); // HACK: byTypeBB[0] == occupied squares
1101 board[capsq] = EMPTY;
1103 // Remove moving piece from source square
1104 clear_bit(&(byColorBB[us]), from);
1105 clear_bit(&(byTypeBB[PAWN]), from);
1106 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1108 // Put moving piece on destination square
1109 set_bit(&(byColorBB[us]), to);
1110 set_bit(&(byTypeBB[PAWN]), to);
1111 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1112 board[to] = board[from];
1113 board[from] = EMPTY;
1115 // Update material hash key
1116 materialKey ^= zobMaterial[them][PAWN][pieceCount[them][PAWN]];
1118 // Update piece count
1119 pieceCount[them][PAWN]--;
1121 // Update piece list
1122 pieceList[us][PAWN][index[from]] = to;
1123 index[to] = index[from];
1124 pieceList[them][PAWN][index[capsq]] = pieceList[them][PAWN][pieceCount[them][PAWN]];
1125 index[pieceList[them][PAWN][index[capsq]]] = index[capsq];
1128 key ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1129 key ^= zobrist[them][PAWN][capsq];
1130 key ^= zobEp[epSquare];
1132 // Update pawn hash key
1133 pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1134 pawnKey ^= zobrist[them][PAWN][capsq];
1136 // Update incremental scores
1137 mgValue -= pst<MidGame>(them, PAWN, capsq);
1138 mgValue -= pst<MidGame>(us, PAWN, from);
1139 mgValue += pst<MidGame>(us, PAWN, to);
1140 egValue -= pst<EndGame>(them, PAWN, capsq);
1141 egValue -= pst<EndGame>(us, PAWN, from);
1142 egValue += pst<EndGame>(us, PAWN, to);
1144 // Reset en passant square
1147 // Reset rule 50 counter
1150 // Update checkers BB
1151 checkersBB = attacks_to(king_square(them), us);
1155 /// Position::undo_move() unmakes a move. When it returns, the position should
1156 /// be restored to exactly the same state as before the move was made. It is
1157 /// important that Position::undo_move is called with the same move and UndoInfo
1158 /// object as the earlier call to Position::do_move.
1160 void Position::undo_move(Move m) {
1163 assert(move_is_ok(m));
1166 sideToMove = opposite_color(sideToMove);
1168 // Restore information from our UndoInfo object (except the captured piece,
1169 // which is taken care of later)
1170 undoInfoUnion = *previous;
1172 if (move_is_castle(m))
1173 undo_castle_move(m);
1174 else if (move_promotion(m))
1175 undo_promotion_move(m);
1176 else if (move_is_ep(m))
1184 us = side_to_move();
1185 them = opposite_color(us);
1186 from = move_from(m);
1189 assert(piece_on(from) == EMPTY);
1190 assert(color_of_piece_on(to) == us);
1192 // Put the piece back at the source square
1193 piece = type_of_piece_on(to);
1194 set_bit(&(byColorBB[us]), from);
1195 set_bit(&(byTypeBB[piece]), from);
1196 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1197 board[from] = piece_of_color_and_type(us, piece);
1199 // Clear the destination square
1200 clear_bit(&(byColorBB[us]), to);
1201 clear_bit(&(byTypeBB[piece]), to);
1202 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1204 // If the moving piece was a king, update the king square
1206 kingSquare[us] = from;
1208 // Update piece list
1209 pieceList[us][piece][index[to]] = from;
1210 index[from] = index[to];
1214 assert(capture != KING);
1216 // Replace the captured piece
1217 set_bit(&(byColorBB[them]), to);
1218 set_bit(&(byTypeBB[capture]), to);
1219 set_bit(&(byTypeBB[0]), to);
1220 board[to] = piece_of_color_and_type(them, capture);
1223 if (capture != PAWN)
1224 npMaterial[them] += piece_value_midgame(capture);
1226 // Update piece list
1227 pieceList[them][capture][pieceCount[them][capture]] = to;
1228 index[to] = pieceCount[them][capture];
1230 // Update piece count
1231 pieceCount[them][capture]++;
1240 /// Position::undo_castle_move() is a private method used to unmake a castling
1241 /// move. It is called from the main Position::undo_move function. Note that
1242 /// castling moves are encoded as "king captures friendly rook" moves, for
1243 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1245 void Position::undo_castle_move(Move m) {
1247 assert(move_is_ok(m));
1248 assert(move_is_castle(m));
1250 // When we have arrived here, some work has already been done by
1251 // Position::undo_move. In particular, the side to move has been switched,
1252 // so the code below is correct.
1253 Color us = side_to_move();
1255 // Find source squares for king and rook
1256 Square kfrom = move_from(m);
1257 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1260 // Find destination squares for king and rook
1261 if (rfrom > kfrom) // O-O
1263 kto = relative_square(us, SQ_G1);
1264 rto = relative_square(us, SQ_F1);
1266 kto = relative_square(us, SQ_C1);
1267 rto = relative_square(us, SQ_D1);
1270 assert(piece_on(kto) == piece_of_color_and_type(us, KING));
1271 assert(piece_on(rto) == piece_of_color_and_type(us, ROOK));
1273 // Remove pieces from destination squares
1274 clear_bit(&(byColorBB[us]), kto);
1275 clear_bit(&(byTypeBB[KING]), kto);
1276 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1277 clear_bit(&(byColorBB[us]), rto);
1278 clear_bit(&(byTypeBB[ROOK]), rto);
1279 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1281 // Put pieces on source squares
1282 set_bit(&(byColorBB[us]), kfrom);
1283 set_bit(&(byTypeBB[KING]), kfrom);
1284 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1285 set_bit(&(byColorBB[us]), rfrom);
1286 set_bit(&(byTypeBB[ROOK]), rfrom);
1287 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1290 board[rto] = board[kto] = EMPTY;
1291 board[rfrom] = piece_of_color_and_type(us, ROOK);
1292 board[kfrom] = piece_of_color_and_type(us, KING);
1294 // Update king square
1295 kingSquare[us] = kfrom;
1297 // Update piece lists
1298 pieceList[us][KING][index[kto]] = kfrom;
1299 pieceList[us][ROOK][index[rto]] = rfrom;
1300 int tmp = index[rto]; // Necessary because we may have rto == kfrom in FRC.
1301 index[kfrom] = index[kto];
1306 /// Position::undo_promotion_move() is a private method used to unmake a
1307 /// promotion move. It is called from the main Position::do_move
1308 /// function. The UndoInfo object, which has been initialized in
1309 /// Position::do_move, is used to put back the captured piece (if any).
1311 void Position::undo_promotion_move(Move m) {
1315 PieceType promotion;
1317 assert(move_is_ok(m));
1318 assert(move_promotion(m));
1320 // When we have arrived here, some work has already been done by
1321 // Position::undo_move. In particular, the side to move has been switched,
1322 // so the code below is correct.
1323 us = side_to_move();
1324 them = opposite_color(us);
1325 from = move_from(m);
1328 assert(relative_rank(us, to) == RANK_8);
1329 assert(piece_on(from) == EMPTY);
1331 // Remove promoted piece
1332 promotion = move_promotion(m);
1333 assert(piece_on(to)==piece_of_color_and_type(us, promotion));
1334 assert(promotion >= KNIGHT && promotion <= QUEEN);
1335 clear_bit(&(byColorBB[us]), to);
1336 clear_bit(&(byTypeBB[promotion]), to);
1337 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1339 // Insert pawn at source square
1340 set_bit(&(byColorBB[us]), from);
1341 set_bit(&(byTypeBB[PAWN]), from);
1342 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1343 board[from] = piece_of_color_and_type(us, PAWN);
1346 npMaterial[us] -= piece_value_midgame(promotion);
1348 // Update piece list
1349 pieceList[us][PAWN][pieceCount[us][PAWN]] = from;
1350 index[from] = pieceCount[us][PAWN];
1351 pieceList[us][promotion][index[to]] =
1352 pieceList[us][promotion][pieceCount[us][promotion] - 1];
1353 index[pieceList[us][promotion][index[to]]] = index[to];
1355 // Update piece counts
1356 pieceCount[us][promotion]--;
1357 pieceCount[us][PAWN]++;
1361 assert(capture != KING);
1363 // Insert captured piece:
1364 set_bit(&(byColorBB[them]), to);
1365 set_bit(&(byTypeBB[capture]), to);
1366 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1367 board[to] = piece_of_color_and_type(them, capture);
1369 // Update material. Because the move is a promotion move, we know
1370 // that the captured piece cannot be a pawn.
1371 assert(capture != PAWN);
1372 npMaterial[them] += piece_value_midgame(capture);
1374 // Update piece list
1375 pieceList[them][capture][pieceCount[them][capture]] = to;
1376 index[to] = pieceCount[them][capture];
1378 // Update piece count
1379 pieceCount[them][capture]++;
1385 /// Position::undo_ep_move() is a private method used to unmake an en passant
1386 /// capture. It is called from the main Position::undo_move function. Because
1387 /// the captured piece is always a pawn, we don't need to pass an UndoInfo
1388 /// object from which to retrieve the captured piece.
1390 void Position::undo_ep_move(Move m) {
1392 assert(move_is_ok(m));
1393 assert(move_is_ep(m));
1395 // When we have arrived here, some work has already been done by
1396 // Position::undo_move. In particular, the side to move has been switched,
1397 // so the code below is correct.
1398 Color us = side_to_move();
1399 Color them = opposite_color(us);
1400 Square from = move_from(m);
1401 Square to = move_to(m);
1402 Square capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1404 assert(to == ep_square());
1405 assert(relative_rank(us, to) == RANK_6);
1406 assert(piece_on(to) == piece_of_color_and_type(us, PAWN));
1407 assert(piece_on(from) == EMPTY);
1408 assert(piece_on(capsq) == EMPTY);
1410 // Replace captured piece
1411 set_bit(&(byColorBB[them]), capsq);
1412 set_bit(&(byTypeBB[PAWN]), capsq);
1413 set_bit(&(byTypeBB[0]), capsq);
1414 board[capsq] = piece_of_color_and_type(them, PAWN);
1416 // Remove moving piece from destination square
1417 clear_bit(&(byColorBB[us]), to);
1418 clear_bit(&(byTypeBB[PAWN]), to);
1419 clear_bit(&(byTypeBB[0]), to);
1422 // Replace moving piece at source square
1423 set_bit(&(byColorBB[us]), from);
1424 set_bit(&(byTypeBB[PAWN]), from);
1425 set_bit(&(byTypeBB[0]), from);
1426 board[from] = piece_of_color_and_type(us, PAWN);
1428 // Update piece list:
1429 pieceList[us][PAWN][index[to]] = from;
1430 index[from] = index[to];
1431 pieceList[them][PAWN][pieceCount[them][PAWN]] = capsq;
1432 index[capsq] = pieceCount[them][PAWN];
1434 // Update piece count:
1435 pieceCount[them][PAWN]++;
1439 /// Position::do_null_move makes() a "null move": It switches the side to move
1440 /// and updates the hash key without executing any move on the board.
1442 void Position::do_null_move(UndoInfo& u) {
1445 assert(!is_check());
1447 // Back up the information necessary to undo the null move to the supplied
1448 // UndoInfo object. In the case of a null move, the only thing we need to
1449 // remember is the last move made and the en passant square.
1450 u.lastMove = lastMove;
1451 u.epSquare = epSquare;
1453 // Save the current key to the history[] array, in order to be able to
1454 // detect repetition draws.
1455 history[gamePly] = key;
1457 // Update the necessary information
1458 sideToMove = opposite_color(sideToMove);
1459 if (epSquare != SQ_NONE)
1460 key ^= zobEp[epSquare];
1465 key ^= zobSideToMove;
1467 mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1468 egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1474 /// Position::undo_null_move() unmakes a "null move".
1476 void Position::undo_null_move(const UndoInfo &u) {
1479 assert(!is_check());
1481 // Restore information from the supplied UndoInfo object:
1482 lastMove = u.lastMove;
1483 epSquare = u.epSquare;
1484 if (epSquare != SQ_NONE)
1485 key ^= zobEp[epSquare];
1487 // Update the necessary information.
1488 sideToMove = opposite_color(sideToMove);
1491 key ^= zobSideToMove;
1493 mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1494 egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1500 /// Position::see() is a static exchange evaluator: It tries to estimate the
1501 /// material gain or loss resulting from a move. There are three versions of
1502 /// this function: One which takes a destination square as input, one takes a
1503 /// move, and one which takes a 'from' and a 'to' square. The function does
1504 /// not yet understand promotions captures.
1506 int Position::see(Square to) const {
1508 assert(square_is_ok(to));
1509 return see(SQ_NONE, to);
1512 int Position::see(Move m) const {
1514 assert(move_is_ok(m));
1515 return see(move_from(m), move_to(m));
1518 int Position::see(Square from, Square to) const {
1521 static const int seeValues[18] = {
1522 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1523 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1524 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1525 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1529 Bitboard attackers, occ, b;
1531 assert(square_is_ok(from) || from == SQ_NONE);
1532 assert(square_is_ok(to));
1534 // Initialize colors
1535 Color us = (from != SQ_NONE ? color_of_piece_on(from) : opposite_color(color_of_piece_on(to)));
1536 Color them = opposite_color(us);
1538 // Initialize pieces
1539 Piece piece = piece_on(from);
1540 Piece capture = piece_on(to);
1542 // Find all attackers to the destination square, with the moving piece
1543 // removed, but possibly an X-ray attacker added behind it.
1544 occ = occupied_squares();
1546 // Handle en passant moves
1547 if (epSquare == to && type_of_piece_on(from) == PAWN)
1549 assert(capture == EMPTY);
1551 Square capQq = (side_to_move() == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1552 capture = piece_on(capQq);
1554 assert(type_of_piece_on(capQq) == PAWN);
1556 // Remove the captured pawn
1557 clear_bit(&occ, capQq);
1562 clear_bit(&occ, from);
1563 attackers = (rook_attacks_bb(to, occ) & rooks_and_queens())
1564 | (bishop_attacks_bb(to, occ) & bishops_and_queens())
1565 | (piece_attacks<KNIGHT>(to) & knights())
1566 | (piece_attacks<KING>(to) & kings())
1567 | (pawn_attacks(WHITE, to) & pawns(BLACK))
1568 | (pawn_attacks(BLACK, to) & pawns(WHITE));
1570 if (from != SQ_NONE)
1573 // If we don't have any attacker we are finished
1574 if ((attackers & pieces_of_color(us)) == EmptyBoardBB)
1577 // Locate the least valuable attacker to the destination square
1578 // and use it to initialize from square.
1580 for (pt = PAWN; !(attackers & pieces_of_color_and_type(us, pt)); pt++)
1583 from = first_1(attackers & pieces_of_color_and_type(us, pt));
1584 piece = piece_on(from);
1587 // If the opponent has no attackers we are finished
1588 if ((attackers & pieces_of_color(them)) == EmptyBoardBB)
1589 return seeValues[capture];
1591 attackers &= occ; // Remove the moving piece
1593 // The destination square is defended, which makes things rather more
1594 // difficult to compute. We proceed by building up a "swap list" containing
1595 // the material gain or loss at each stop in a sequence of captures to the
1596 // destination square, where the sides alternately capture, and always
1597 // capture with the least valuable piece. After each capture, we look for
1598 // new X-ray attacks from behind the capturing piece.
1599 int lastCapturingPieceValue = seeValues[piece];
1600 int swapList[32], n = 1;
1604 swapList[0] = seeValues[capture];
1607 // Locate the least valuable attacker for the side to move. The loop
1608 // below looks like it is potentially infinite, but it isn't. We know
1609 // that the side to move still has at least one attacker left.
1610 for (pt = PAWN; !(attackers & pieces_of_color_and_type(c, pt)); pt++)
1613 // Remove the attacker we just found from the 'attackers' bitboard,
1614 // and scan for new X-ray attacks behind the attacker.
1615 b = attackers & pieces_of_color_and_type(c, pt);
1617 attackers |= (rook_attacks_bb(to, occ) & rooks_and_queens())
1618 | (bishop_attacks_bb(to, occ) & bishops_and_queens());
1622 // Add the new entry to the swap list
1624 swapList[n] = -swapList[n - 1] + lastCapturingPieceValue;
1627 // Remember the value of the capturing piece, and change the side to move
1628 // before beginning the next iteration
1629 lastCapturingPieceValue = seeValues[pt];
1630 c = opposite_color(c);
1632 // Stop after a king capture
1633 if (pt == KING && (attackers & pieces_of_color(c)))
1636 swapList[n++] = 100;
1639 } while (attackers & pieces_of_color(c));
1641 // Having built the swap list, we negamax through it to find the best
1642 // achievable score from the point of view of the side to move
1644 swapList[n-1] = Min(-swapList[n], swapList[n-1]);
1650 /// Position::clear() erases the position object to a pristine state, with an
1651 /// empty board, white to move, and no castling rights.
1653 void Position::clear() {
1655 for (int i = 0; i < 64; i++)
1661 for (int i = 0; i < 2; i++)
1662 byColorBB[i] = EmptyBoardBB;
1664 for (int i = 0; i < 7; i++)
1666 byTypeBB[i] = EmptyBoardBB;
1667 pieceCount[0][i] = pieceCount[1][i] = 0;
1668 for (int j = 0; j < 8; j++)
1669 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1672 checkersBB = EmptyBoardBB;
1673 for (Color c = WHITE; c <= BLACK; c++)
1674 pinners[c] = pinned[c] = dcCandidates[c] = ~EmptyBoardBB;
1676 lastMove = MOVE_NONE;
1679 castleRights = NO_CASTLES;
1680 initialKFile = FILE_E;
1681 initialKRFile = FILE_H;
1682 initialQRFile = FILE_A;
1690 /// Position::reset_game_ply() simply sets gamePly to 0. It is used from the
1691 /// UCI interface code, whenever a non-reversible move is made in a
1692 /// 'position fen <fen> moves m1 m2 ...' command. This makes it possible
1693 /// for the program to handle games of arbitrary length, as long as the GUI
1694 /// handles draws by the 50 move rule correctly.
1696 void Position::reset_game_ply() {
1702 /// Position::put_piece() puts a piece on the given square of the board,
1703 /// updating the board array, bitboards, and piece counts.
1705 void Position::put_piece(Piece p, Square s) {
1707 Color c = color_of_piece(p);
1708 PieceType pt = type_of_piece(p);
1711 index[s] = pieceCount[c][pt];
1712 pieceList[c][pt][index[s]] = s;
1714 set_bit(&(byTypeBB[pt]), s);
1715 set_bit(&(byColorBB[c]), s);
1716 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1718 pieceCount[c][pt]++;
1725 /// Position::allow_oo() gives the given side the right to castle kingside.
1726 /// Used when setting castling rights during parsing of FEN strings.
1728 void Position::allow_oo(Color c) {
1730 castleRights |= (1 + int(c));
1734 /// Position::allow_ooo() gives the given side the right to castle queenside.
1735 /// Used when setting castling rights during parsing of FEN strings.
1737 void Position::allow_ooo(Color c) {
1739 castleRights |= (4 + 4*int(c));
1743 /// Position::compute_key() computes the hash key of the position. The hash
1744 /// key is usually updated incrementally as moves are made and unmade, the
1745 /// compute_key() function is only used when a new position is set up, and
1746 /// to verify the correctness of the hash key when running in debug mode.
1748 Key Position::compute_key() const {
1750 Key result = Key(0ULL);
1752 for (Square s = SQ_A1; s <= SQ_H8; s++)
1753 if (square_is_occupied(s))
1754 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1756 if (ep_square() != SQ_NONE)
1757 result ^= zobEp[ep_square()];
1759 result ^= zobCastle[castleRights];
1760 if (side_to_move() == BLACK)
1761 result ^= zobSideToMove;
1767 /// Position::compute_pawn_key() computes the hash key of the position. The
1768 /// hash key is usually updated incrementally as moves are made and unmade,
1769 /// the compute_pawn_key() function is only used when a new position is set
1770 /// up, and to verify the correctness of the pawn hash key when running in
1773 Key Position::compute_pawn_key() const {
1775 Key result = Key(0ULL);
1779 for (Color c = WHITE; c <= BLACK; c++)
1784 s = pop_1st_bit(&b);
1785 result ^= zobrist[c][PAWN][s];
1792 /// Position::compute_material_key() computes the hash key of the position.
1793 /// The hash key is usually updated incrementally as moves are made and unmade,
1794 /// the compute_material_key() function is only used when a new position is set
1795 /// up, and to verify the correctness of the material hash key when running in
1798 Key Position::compute_material_key() const {
1800 Key result = Key(0ULL);
1801 for (Color c = WHITE; c <= BLACK; c++)
1802 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1804 int count = piece_count(c, pt);
1805 for (int i = 0; i <= count; i++)
1806 result ^= zobMaterial[c][pt][i];
1812 /// Position::compute_value() compute the incremental scores for the middle
1813 /// game and the endgame. These functions are used to initialize the incremental
1814 /// scores when a new position is set up, and to verify that the scores are correctly
1815 /// updated by do_move and undo_move when the program is running in debug mode.
1816 template<Position::GamePhase Phase>
1817 Value Position::compute_value() const {
1819 Value result = Value(0);
1823 for (Color c = WHITE; c <= BLACK; c++)
1824 for (PieceType pt = PAWN; pt <= KING; pt++)
1826 b = pieces_of_color_and_type(c, pt);
1829 s = pop_1st_bit(&b);
1830 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1831 result += pst<Phase>(c, pt, s);
1835 const Value TempoValue = (Phase == MidGame ? TempoValueMidgame : TempoValueEndgame);
1836 result += (side_to_move() == WHITE)? TempoValue / 2 : -TempoValue / 2;
1841 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1842 /// game material score for the given side. Material scores are updated
1843 /// incrementally during the search, this function is only used while
1844 /// initializing a new Position object.
1846 Value Position::compute_non_pawn_material(Color c) const {
1848 Value result = Value(0);
1851 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1853 Bitboard b = pieces_of_color_and_type(c, pt);
1856 s = pop_1st_bit(&b);
1857 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1858 result += piece_value_midgame(pt);
1865 /// Position::is_mate() returns true or false depending on whether the
1866 /// side to move is checkmated. Note that this function is currently very
1867 /// slow, and shouldn't be used frequently inside the search.
1869 bool Position::is_mate() const {
1873 MovePicker mp = MovePicker(*this, false, MOVE_NONE, EmptySearchStack, Depth(0));
1874 return mp.get_next_move() == MOVE_NONE;
1880 /// Position::is_draw() tests whether the position is drawn by material,
1881 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1882 /// must be done by the search.
1884 bool Position::is_draw() const {
1886 // Draw by material?
1888 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1891 // Draw by the 50 moves rule?
1892 if (rule50 > 100 || (rule50 == 100 && !is_check()))
1895 // Draw by repetition?
1896 for (int i = 2; i < Min(gamePly, rule50); i += 2)
1897 if (history[gamePly - i] == key)
1904 /// Position::has_mate_threat() tests whether a given color has a mate in one
1905 /// from the current position. This function is quite slow, but it doesn't
1906 /// matter, because it is currently only called from PV nodes, which are rare.
1908 bool Position::has_mate_threat(Color c) {
1911 Color stm = side_to_move();
1913 // The following lines are useless and silly, but prevents gcc from
1914 // emitting a stupid warning stating that u1.lastMove and u1.epSquare might
1915 // be used uninitialized.
1916 u1.lastMove = lastMove;
1917 u1.epSquare = epSquare;
1922 // If the input color is not equal to the side to move, do a null move
1926 MoveStack mlist[120];
1928 bool result = false;
1930 // Generate legal moves
1931 count = generate_legal_moves(*this, mlist);
1933 // Loop through the moves, and see if one of them is mate
1934 for (int i = 0; i < count; i++)
1936 do_move(mlist[i].move, u2);
1940 undo_move(mlist[i].move);
1943 // Undo null move, if necessary
1951 /// Position::init_zobrist() is a static member function which initializes the
1952 /// various arrays used to compute hash keys.
1954 void Position::init_zobrist() {
1956 for (int i = 0; i < 2; i++)
1957 for (int j = 0; j < 8; j++)
1958 for (int k = 0; k < 64; k++)
1959 zobrist[i][j][k] = Key(genrand_int64());
1961 for (int i = 0; i < 64; i++)
1962 zobEp[i] = Key(genrand_int64());
1964 for (int i = 0; i < 16; i++)
1965 zobCastle[i] = genrand_int64();
1967 zobSideToMove = genrand_int64();
1969 for (int i = 0; i < 2; i++)
1970 for (int j = 0; j < 8; j++)
1971 for (int k = 0; k < 16; k++)
1972 zobMaterial[i][j][k] = (k > 0)? Key(genrand_int64()) : Key(0LL);
1974 for (int i = 0; i < 16; i++)
1975 zobMaterial[0][KING][i] = zobMaterial[1][KING][i] = Key(0ULL);
1979 /// Position::init_piece_square_tables() initializes the piece square tables.
1980 /// This is a two-step operation: First, the white halves of the tables are
1981 /// copied from the MgPST[][] and EgPST[][] arrays, with a small random number
1982 /// added to each entry if the "Randomness" UCI parameter is non-zero.
1983 /// Second, the black halves of the tables are initialized by mirroring
1984 /// and changing the sign of the corresponding white scores.
1986 void Position::init_piece_square_tables() {
1988 int r = get_option_value_int("Randomness"), i;
1989 for (Square s = SQ_A1; s <= SQ_H8; s++)
1990 for (Piece p = WP; p <= WK; p++)
1992 i = (r == 0)? 0 : (genrand_int32() % (r*2) - r);
1993 MgPieceSquareTable[p][s] = Value(MgPST[p][s] + i);
1994 EgPieceSquareTable[p][s] = Value(EgPST[p][s] + i);
1997 for (Square s = SQ_A1; s <= SQ_H8; s++)
1998 for (Piece p = BP; p <= BK; p++)
2000 MgPieceSquareTable[p][s] = -MgPieceSquareTable[p-8][flip_square(s)];
2001 EgPieceSquareTable[p][s] = -EgPieceSquareTable[p-8][flip_square(s)];
2006 /// Position::flipped_copy() makes a copy of the input position, but with
2007 /// the white and black sides reversed. This is only useful for debugging,
2008 /// especially for finding evaluation symmetry bugs.
2010 void Position::flipped_copy(const Position &pos) {
2012 assert(pos.is_ok());
2017 for (Square s = SQ_A1; s <= SQ_H8; s++)
2018 if (!pos.square_is_empty(s))
2019 put_piece(Piece(int(pos.piece_on(s)) ^ 8), flip_square(s));
2022 sideToMove = opposite_color(pos.side_to_move());
2025 if (pos.can_castle_kingside(WHITE)) allow_oo(BLACK);
2026 if (pos.can_castle_queenside(WHITE)) allow_ooo(BLACK);
2027 if (pos.can_castle_kingside(BLACK)) allow_oo(WHITE);
2028 if (pos.can_castle_queenside(BLACK)) allow_ooo(WHITE);
2030 initialKFile = pos.initialKFile;
2031 initialKRFile = pos.initialKRFile;
2032 initialQRFile = pos.initialQRFile;
2034 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
2035 castleRightsMask[sq] = ALL_CASTLES;
2037 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
2038 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
2039 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
2040 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
2041 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
2042 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
2044 // En passant square
2045 if (pos.epSquare != SQ_NONE)
2046 epSquare = flip_square(pos.epSquare);
2052 key = compute_key();
2053 pawnKey = compute_pawn_key();
2054 materialKey = compute_material_key();
2056 // Incremental scores
2057 mgValue = compute_value<MidGame>();
2058 egValue = compute_value<EndGame>();
2061 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
2062 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
2068 /// Position::is_ok() performs some consitency checks for the position object.
2069 /// This is meant to be helpful when debugging.
2071 bool Position::is_ok(int* failedStep) const {
2073 // What features of the position should be verified?
2074 static const bool debugBitboards = false;
2075 static const bool debugKingCount = false;
2076 static const bool debugKingCapture = false;
2077 static const bool debugCheckerCount = false;
2078 static const bool debugKey = false;
2079 static const bool debugMaterialKey = false;
2080 static const bool debugPawnKey = false;
2081 static const bool debugIncrementalEval = false;
2082 static const bool debugNonPawnMaterial = false;
2083 static const bool debugPieceCounts = false;
2084 static const bool debugPieceList = false;
2086 if (failedStep) *failedStep = 1;
2089 if (!color_is_ok(side_to_move()))
2092 // Are the king squares in the position correct?
2093 if (failedStep) (*failedStep)++;
2094 if (piece_on(king_square(WHITE)) != WK)
2097 if (failedStep) (*failedStep)++;
2098 if (piece_on(king_square(BLACK)) != BK)
2102 if (failedStep) (*failedStep)++;
2103 if (!file_is_ok(initialKRFile))
2106 if (!file_is_ok(initialQRFile))
2109 // Do both sides have exactly one king?
2110 if (failedStep) (*failedStep)++;
2113 int kingCount[2] = {0, 0};
2114 for (Square s = SQ_A1; s <= SQ_H8; s++)
2115 if (type_of_piece_on(s) == KING)
2116 kingCount[color_of_piece_on(s)]++;
2118 if (kingCount[0] != 1 || kingCount[1] != 1)
2122 // Can the side to move capture the opponent's king?
2123 if (failedStep) (*failedStep)++;
2124 if (debugKingCapture)
2126 Color us = side_to_move();
2127 Color them = opposite_color(us);
2128 Square ksq = king_square(them);
2129 if (square_is_attacked(ksq, us))
2133 // Is there more than 2 checkers?
2134 if (failedStep) (*failedStep)++;
2135 if (debugCheckerCount && count_1s(checkersBB) > 2)
2139 if (failedStep) (*failedStep)++;
2142 // The intersection of the white and black pieces must be empty
2143 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
2146 // The union of the white and black pieces must be equal to all
2148 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
2151 // Separate piece type bitboards must have empty intersections
2152 for (PieceType p1 = PAWN; p1 <= KING; p1++)
2153 for (PieceType p2 = PAWN; p2 <= KING; p2++)
2154 if (p1 != p2 && (pieces_of_type(p1) & pieces_of_type(p2)))
2158 // En passant square OK?
2159 if (failedStep) (*failedStep)++;
2160 if (ep_square() != SQ_NONE)
2162 // The en passant square must be on rank 6, from the point of view of the
2164 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
2169 if (failedStep) (*failedStep)++;
2170 if (debugKey && key != compute_key())
2173 // Pawn hash key OK?
2174 if (failedStep) (*failedStep)++;
2175 if (debugPawnKey && pawnKey != compute_pawn_key())
2178 // Material hash key OK?
2179 if (failedStep) (*failedStep)++;
2180 if (debugMaterialKey && materialKey != compute_material_key())
2183 // Incremental eval OK?
2184 if (failedStep) (*failedStep)++;
2185 if (debugIncrementalEval)
2187 if (mgValue != compute_value<MidGame>())
2190 if (egValue != compute_value<EndGame>())
2194 // Non-pawn material OK?
2195 if (failedStep) (*failedStep)++;
2196 if (debugNonPawnMaterial)
2198 if (npMaterial[WHITE] != compute_non_pawn_material(WHITE))
2201 if (npMaterial[BLACK] != compute_non_pawn_material(BLACK))
2206 if (failedStep) (*failedStep)++;
2207 if (debugPieceCounts)
2208 for (Color c = WHITE; c <= BLACK; c++)
2209 for (PieceType pt = PAWN; pt <= KING; pt++)
2210 if (pieceCount[c][pt] != count_1s(pieces_of_color_and_type(c, pt)))
2213 if (failedStep) (*failedStep)++;
2216 for(Color c = WHITE; c <= BLACK; c++)
2217 for(PieceType pt = PAWN; pt <= KING; pt++)
2218 for(int i = 0; i < pieceCount[c][pt]; i++)
2220 if (piece_on(piece_list(c, pt, i)) != piece_of_color_and_type(c, pt))
2223 if (index[piece_list(c, pt, i)] != i)
2227 if (failedStep) *failedStep = 0;