2 Glaurung, a UCI chess playing engine.
3 Copyright (C) 2004-2008 Tord Romstad
5 Glaurung is free software: you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation, either version 3 of the License, or
8 (at your option) any later version.
10 Glaurung is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
15 You should have received a copy of the GNU General Public License
16 along with this program. If not, see <http://www.gnu.org/licenses/>.
33 #include "ucioption.h"
40 int Position::castleRightsMask[64];
42 Key Position::zobrist[2][8][64];
43 Key Position::zobEp[64];
44 Key Position::zobCastle[16];
45 Key Position::zobMaterial[2][8][16];
46 Key Position::zobSideToMove;
48 Value Position::MgPieceSquareTable[16][64];
49 Value Position::EgPieceSquareTable[16][64];
58 Position::Position(const Position &pos) {
62 Position::Position(const std::string &fen) {
67 /// Position::from_fen() initializes the position object with the given FEN
68 /// string. This function is not very robust - make sure that input FENs are
69 /// correct (this is assumed to be the responsibility of the GUI).
71 void Position::from_fen(const std::string &fen) {
73 static const std::string piecesStr = "KQRBNPkqrbnp";
74 static const Piece pieces[] = { WK, WQ, WR, WB, WN, WP, BK, BQ, BR, BB, BN, BP };
82 for ( ; fen[i] != ' '; i++)
86 // Skip the given number of files
87 file += (fen[i] - '1' + 1);
90 else if (fen[i] == '/')
96 size_t idx = piecesStr.find(fen[i]);
97 if (idx == std::string::npos)
99 std::cout << "Error in FEN at character " << i << std::endl;
102 Square square = make_square(file, rank);
103 put_piece(pieces[idx], square);
109 if (fen[i] != 'w' && fen[i] == 'b')
111 std::cout << "Error in FEN at character " << i << std::endl;
114 sideToMove = (fen[i] == 'w' ? WHITE : BLACK);
120 std::cout << "Error in FEN at character " << i << std::endl;
125 while(strchr("KQkqabcdefghABCDEFGH-", fen[i])) {
129 else if(fen[i] == 'K') allow_oo(WHITE);
130 else if(fen[i] == 'Q') allow_ooo(WHITE);
131 else if(fen[i] == 'k') allow_oo(BLACK);
132 else if(fen[i] == 'q') allow_ooo(BLACK);
133 else if(fen[i] >= 'A' && fen[i] <= 'H') {
134 File rookFile, kingFile = FILE_NONE;
135 for(Square square = SQ_B1; square <= SQ_G1; square++)
136 if(piece_on(square) == WK)
137 kingFile = square_file(square);
138 if(kingFile == FILE_NONE) {
139 std::cout << "Error in FEN at character " << i << std::endl;
142 initialKFile = kingFile;
143 rookFile = File(fen[i] - 'A') + FILE_A;
144 if(rookFile < initialKFile) {
146 initialQRFile = rookFile;
150 initialKRFile = rookFile;
153 else if(fen[i] >= 'a' && fen[i] <= 'h') {
154 File rookFile, kingFile = FILE_NONE;
155 for(Square square = SQ_B8; square <= SQ_G8; square++)
156 if(piece_on(square) == BK)
157 kingFile = square_file(square);
158 if(kingFile == FILE_NONE) {
159 std::cout << "Error in FEN at character " << i << std::endl;
162 initialKFile = kingFile;
163 rookFile = File(fen[i] - 'a') + FILE_A;
164 if(rookFile < initialKFile) {
166 initialQRFile = rookFile;
170 initialKRFile = rookFile;
174 std::cout << "Error in FEN at character " << i << std::endl;
181 while (fen[i] == ' ')
185 if ( i < fen.length() - 2
186 && (fen[i] >= 'a' && fen[i] <= 'h')
187 && (fen[i+1] == '3' || fen[i+1] == '6'))
188 epSquare = square_from_string(fen.substr(i, 2));
190 // Various initialisation
191 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
192 castleRightsMask[sq] = ALL_CASTLES;
194 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO|WHITE_OOO);
195 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO|BLACK_OOO);
196 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
197 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
198 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
199 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
204 pawnKey = compute_pawn_key();
205 materialKey = compute_material_key();
206 mgValue = compute_mg_value();
207 egValue = compute_eg_value();
208 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
209 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
213 /// Position::to_fen() converts the position object to a FEN string. This is
214 /// probably only useful for debugging.
216 const std::string Position::to_fen() const {
217 char pieceLetters[] = " PNBRQK pnbrqk";
221 for(Rank rank = RANK_8; rank >= RANK_1; rank--) {
223 for(File file = FILE_A; file <= FILE_H; file++) {
224 Square square = make_square(file, rank);
225 if(square_is_occupied(square)) {
226 if(skip > 0) result += (char)skip + '0';
227 result += pieceLetters[piece_on(square)];
232 if(skip > 0) result += (char)skip + '0';
233 result += (rank > RANK_1)? '/' : ' ';
236 result += (sideToMove == WHITE)? 'w' : 'b';
238 if(castleRights == NO_CASTLES) result += '-';
240 if(can_castle_kingside(WHITE)) result += 'K';
241 if(can_castle_queenside(WHITE)) result += 'Q';
242 if(can_castle_kingside(BLACK)) result += 'k';
243 if(can_castle_queenside(BLACK)) result += 'q';
247 if(ep_square() == SQ_NONE) result += '-';
248 else result += square_to_string(ep_square());
254 /// Position::print() prints an ASCII representation of the position to
255 /// the standard output.
257 void Position::print() const {
258 char pieceStrings[][8] =
259 {"| ? ", "| P ", "| N ", "| B ", "| R ", "| Q ", "| K ", "| ? ",
260 "| ? ", "|=P=", "|=N=", "|=B=", "|=R=", "|=Q=", "|=K="
263 for(Rank rank = RANK_8; rank >= RANK_1; rank--) {
264 std::cout << "+---+---+---+---+---+---+---+---+\n";
265 for(File file = FILE_A; file <= FILE_H; file++) {
266 Square sq = make_square(file, rank);
267 Piece piece = piece_on(sq);
269 std::cout << ((square_color(sq) == WHITE)? "| " : "| . ");
271 std::cout << pieceStrings[piece];
275 std::cout << "+---+---+---+---+---+---+---+---+\n";
276 std::cout << to_fen() << std::endl;
277 std::cout << key << std::endl;
281 /// Position::copy() creates a copy of the input position.
283 void Position::copy(const Position &pos) {
284 memcpy(this, &pos, sizeof(Position));
288 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
289 /// king) pieces for the given color.
291 Bitboard Position::pinned_pieces(Color c) const {
292 Bitboard b1, b2, pinned, pinners, sliders;
293 Square ksq = king_square(c), s;
294 Color them = opposite_color(c);
296 pinned = EmptyBoardBB;
297 b1 = occupied_squares();
299 sliders = rooks_and_queens(them) & ~checkers();
300 if(sliders & RookPseudoAttacks[ksq]) {
301 b2 = rook_attacks(ksq) & pieces_of_color(c);
302 pinners = rook_attacks_bb(ksq, b1 ^ b2) & sliders;
304 s = pop_1st_bit(&pinners);
305 pinned |= (squares_between(s, ksq) & b2);
309 sliders = bishops_and_queens(them) & ~checkers();
310 if(sliders & BishopPseudoAttacks[ksq]) {
311 b2 = bishop_attacks(ksq) & pieces_of_color(c);
312 pinners = bishop_attacks_bb(ksq, b1 ^ b2) & sliders;
314 s = pop_1st_bit(&pinners);
315 pinned |= (squares_between(s, ksq) & b2);
322 /// Position:discovered_check_candidates() returns a bitboard containing all
323 /// pieces for the given side which are candidates for giving a discovered
324 /// check. The code is almost the same as the function for finding pinned
327 Bitboard Position::discovered_check_candidates(Color c) const {
328 Bitboard b1, b2, dc, checkers, sliders;
329 Square ksq = king_square(opposite_color(c)), s;
332 b1 = occupied_squares();
334 sliders = rooks_and_queens(c);
335 if(sliders & RookPseudoAttacks[ksq]) {
336 b2 = rook_attacks(ksq) & pieces_of_color(c);
337 checkers = rook_attacks_bb(ksq, b1 ^ b2) & sliders;
339 s = pop_1st_bit(&checkers);
340 dc |= (squares_between(s, ksq) & b2);
344 sliders = bishops_and_queens(c);
345 if(sliders & BishopPseudoAttacks[ksq]) {
346 b2 = bishop_attacks(ksq) & pieces_of_color(c);
347 checkers = bishop_attacks_bb(ksq, b1 ^ b2) & sliders;
349 s = pop_1st_bit(&checkers);
350 dc |= (squares_between(s, ksq) & b2);
358 /// Position::square_is_attacked() checks whether the given side attacks the
361 bool Position::square_is_attacked(Square s, Color c) const {
363 (pawn_attacks(opposite_color(c), s) & pawns(c)) ||
364 (knight_attacks(s) & knights(c)) ||
365 (king_attacks(s) & kings(c)) ||
366 (rook_attacks(s) & rooks_and_queens(c)) ||
367 (bishop_attacks(s) & bishops_and_queens(c));
371 /// Position::attacks_to() computes a bitboard containing all pieces which
372 /// attacks a given square. There are two versions of this function: One
373 /// which finds attackers of both colors, and one which only finds the
374 /// attackers for one side.
376 Bitboard Position::attacks_to(Square s) const {
378 (black_pawn_attacks(s) & pawns(WHITE)) |
379 (white_pawn_attacks(s) & pawns(BLACK)) |
380 (knight_attacks(s) & pieces_of_type(KNIGHT)) |
381 (rook_attacks(s) & rooks_and_queens()) |
382 (bishop_attacks(s) & bishops_and_queens()) |
383 (king_attacks(s) & pieces_of_type(KING));
386 Bitboard Position::attacks_to(Square s, Color c) const {
387 return attacks_to(s) & pieces_of_color(c);
391 /// Position::piece_attacks_square() tests whether the piece on square f
392 /// attacks square t.
394 bool Position::piece_attacks_square(Square f, Square t) const {
395 assert(square_is_ok(f));
396 assert(square_is_ok(t));
398 switch(piece_on(f)) {
399 case WP: return white_pawn_attacks_square(f, t);
400 case BP: return black_pawn_attacks_square(f, t);
401 case WN: case BN: return knight_attacks_square(f, t);
402 case WB: case BB: return bishop_attacks_square(f, t);
403 case WR: case BR: return rook_attacks_square(f, t);
404 case WQ: case BQ: return queen_attacks_square(f, t);
405 case WK: case BK: return king_attacks_square(f, t);
406 default: return false;
413 /// Position::find_checkers() computes the checkersBB bitboard, which
414 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
415 /// currently works by calling Position::attacks_to, which is probably
416 /// inefficient. Consider rewriting this function to use the last move
417 /// played, like in non-bitboard versions of Glaurung.
419 void Position::find_checkers() {
420 checkersBB = attacks_to(king_square(side_to_move()),
421 opposite_color(side_to_move()));
425 /// Position::move_is_legal() tests whether a pseudo-legal move is legal.
426 /// There are two versions of this function: One which takes only a
427 /// move as input, and one which takes a move and a bitboard of pinned
428 /// pieces. The latter function is faster, and should always be preferred
429 /// when a pinned piece bitboard has already been computed.
431 bool Position::move_is_legal(Move m) const {
432 return move_is_legal(m, pinned_pieces(side_to_move()));
436 bool Position::move_is_legal(Move m, Bitboard pinned) const {
441 assert(move_is_ok(m));
442 assert(pinned == pinned_pieces(side_to_move()));
444 // If we're in check, all pseudo-legal moves are legal, because our
445 // check evasion generator only generates true legal moves.
446 if(is_check()) return true;
448 // Castling moves are checked for legality during move generation.
449 if(move_is_castle(m)) return true;
452 them = opposite_color(us);
455 ksq = king_square(us);
457 assert(color_of_piece_on(from) == us);
458 assert(piece_on(ksq) == king_of_color(us));
460 // En passant captures are a tricky special case. Because they are
461 // rather uncommon, we do it simply by testing whether the king is attacked
462 // after the move is made:
464 Square to = move_to(m);
465 Square capsq = make_square(square_file(to), square_rank(from));
466 Bitboard b = occupied_squares();
468 assert(to == ep_square());
469 assert(piece_on(from) == pawn_of_color(us));
470 assert(piece_on(capsq) == pawn_of_color(them));
471 assert(piece_on(to) == EMPTY);
473 clear_bit(&b, from); clear_bit(&b, capsq); set_bit(&b, to);
475 (!(rook_attacks_bb(ksq, b) & rooks_and_queens(them)) &&
476 !(bishop_attacks_bb(ksq, b) & bishops_and_queens(them)));
479 // If the moving piece is a king, check whether the destination
480 // square is attacked by the opponent.
481 if(from == ksq) return !(square_is_attacked(move_to(m), them));
483 // A non-king move is legal if and only if it is not pinned or it
484 // is moving along the ray towards or away from the king.
485 if(!bit_is_set(pinned, from)) return true;
486 if(direction_between_squares(from, ksq) ==
487 direction_between_squares(move_to(m), ksq))
494 /// Position::move_is_check() tests whether a pseudo-legal move is a check.
495 /// There are two versions of this function: One which takes only a move as
496 /// input, and one which takes a move and a bitboard of discovered check
497 /// candidates. The latter function is faster, and should always be preferred
498 /// when a discovered check candidates bitboard has already been computed.
500 bool Position::move_is_check(Move m) const {
501 Bitboard dc = discovered_check_candidates(side_to_move());
502 return move_is_check(m, dc);
506 bool Position::move_is_check(Move m, Bitboard dcCandidates) const {
508 Square ksq, from, to;
511 assert(move_is_ok(m));
512 assert(dcCandidates ==
513 discovered_check_candidates(side_to_move()));
516 them = opposite_color(us);
520 ksq = king_square(them);
521 assert(color_of_piece_on(from) == us);
522 assert(piece_on(ksq) == king_of_color(them));
524 // Proceed according to the type of the moving piece:
525 switch(type_of_piece_on(from)) {
528 if(bit_is_set(pawn_attacks(them, ksq), to))
531 else if(bit_is_set(dcCandidates, from) &&
532 direction_between_squares(from, ksq) !=
533 direction_between_squares(to, ksq))
535 // Promotion with check?
536 else if(move_promotion(m)) {
537 Bitboard b = occupied_squares();
540 switch(move_promotion(m)) {
542 return knight_attacks_square(to, ksq);
544 return bit_is_set(bishop_attacks_bb(to, b), ksq);
546 return bit_is_set(rook_attacks_bb(to, b), ksq);
548 return bit_is_set(queen_attacks_bb(to, b), ksq);
553 // En passant capture with check? We have already handled the case
554 // of direct checks and ordinary discovered check, the only case we
555 // need to handle is the unusual case of a discovered check through the
557 else if(move_is_ep(m)) {
558 Square capsq = make_square(square_file(to), square_rank(from));
559 Bitboard b = occupied_squares();
561 clear_bit(&b, from); clear_bit(&b, capsq); set_bit(&b, to);
563 ((rook_attacks_bb(ksq, b) & rooks_and_queens(us)) ||
564 (bishop_attacks_bb(ksq, b) & bishops_and_queens(us)));
570 if(bit_is_set(dcCandidates, from))
574 return bit_is_set(knight_attacks(ksq), to);
578 if(bit_is_set(dcCandidates, from))
582 return bit_is_set(bishop_attacks(ksq), to);
586 if(bit_is_set(dcCandidates, from))
590 return bit_is_set(rook_attacks(ksq), to);
593 // Discovered checks are impossible!
594 assert(!bit_is_set(dcCandidates, from));
596 return bit_is_set(queen_attacks(ksq), to);
600 if(bit_is_set(dcCandidates, from) &&
601 direction_between_squares(from, ksq) !=
602 direction_between_squares(to, ksq))
604 // Castling with check?
605 if(move_is_castle(m)) {
606 Square kfrom, kto, rfrom, rto;
607 Bitboard b = occupied_squares();
612 kto = relative_square(us, SQ_G1);
613 rto = relative_square(us, SQ_F1);
616 kto = relative_square(us, SQ_C1);
617 rto = relative_square(us, SQ_D1);
620 clear_bit(&b, kfrom); clear_bit(&b, rfrom);
621 set_bit(&b, rto); set_bit(&b, kto);
623 return bit_is_set(rook_attacks_bb(rto, b), ksq);
638 /// Position::move_is_capture() tests whether a move from the current
639 /// position is a capture.
641 bool Position::move_is_capture(Move m) const {
643 color_of_piece_on(move_to(m)) == opposite_color(side_to_move())
648 /// Position::move_attacks_square() tests whether a move from the current
649 /// position attacks a given square. Only attacks by the moving piece are
650 /// considered; the function does not handle X-ray attacks.
652 bool Position::move_attacks_square(Move m, Square s) const {
653 assert(move_is_ok(m));
654 assert(square_is_ok(s));
656 Square f = move_from(m), t = move_to(m);
658 assert(square_is_occupied(f));
660 switch(piece_on(f)) {
661 case WP: return white_pawn_attacks_square(t, s);
662 case BP: return black_pawn_attacks_square(t, s);
663 case WN: case BN: return knight_attacks_square(t, s);
664 case WB: case BB: return bishop_attacks_square(t, s);
665 case WR: case BR: return rook_attacks_square(t, s);
666 case WQ: case BQ: return queen_attacks_square(t, s);
667 case WK: case BK: return king_attacks_square(t, s);
668 default: assert(false);
676 /// Position::backup() is called when making a move. All information
677 /// necessary to restore the position when the move is later unmade
678 /// is saved to an UndoInfo object. The function Position::restore
679 /// does the reverse operation: When one does a backup followed by
680 /// a restore with the same UndoInfo object, the position is restored
681 /// to the state before backup was called.
683 void Position::backup(UndoInfo &u) const {
684 u.castleRights = castleRights;
685 u.epSquare = epSquare;
686 u.checkersBB = checkersBB;
689 u.materialKey = materialKey;
691 u.lastMove = lastMove;
692 u.capture = NO_PIECE_TYPE;
698 /// Position::restore() is called when unmaking a move. It copies back
699 /// the information backed up during a previous call to Position::backup.
701 void Position::restore(const UndoInfo &u) {
702 castleRights = u.castleRights;
703 epSquare = u.epSquare;
704 checkersBB = u.checkersBB;
707 materialKey = u.materialKey;
709 lastMove = u.lastMove;
715 /// Position::do_move() makes a move, and backs up all information necessary
716 /// to undo the move to an UndoInfo object. The move is assumed to be legal.
717 /// Pseudo-legal moves should be filtered out before this function is called.
718 /// There are two versions of this function, one which takes only the move and
719 /// the UndoInfo as input, and one which takes a third parameter, a bitboard of
720 /// discovered check candidates. The second version is faster, because knowing
721 /// the discovered check candidates makes it easier to update the checkersBB
722 /// member variable in the position object.
724 void Position::do_move(Move m, UndoInfo &u) {
725 do_move(m, u, discovered_check_candidates(side_to_move()));
728 void Position::do_move(Move m, UndoInfo &u, Bitboard dcCandidates) {
730 assert(move_is_ok(m));
732 // Back up the necessary information to our UndoInfo object (except the
733 // captured piece, which is taken care of later:
736 // Save the current key to the history[] array, in order to be able to
737 // detect repetition draws:
738 history[gamePly] = key;
740 // Increment the 50 moves rule draw counter. Resetting it to zero in the
741 // case of non-reversible moves is taken care of later.
744 if(move_is_castle(m))
746 else if(move_promotion(m))
747 do_promotion_move(m, u);
748 else if(move_is_ep(m))
753 PieceType piece, capture;
756 them = opposite_color(us);
761 assert(color_of_piece_on(from) == us);
762 assert(color_of_piece_on(to) == them || piece_on(to) == EMPTY);
764 piece = type_of_piece_on(from);
765 capture = type_of_piece_on(to);
768 assert(capture != KING);
770 // Remove captured piece:
771 clear_bit(&(byColorBB[them]), to);
772 clear_bit(&(byTypeBB[capture]), to);
775 key ^= zobrist[them][capture][to];
777 // If the captured piece was a pawn, update pawn hash key:
779 pawnKey ^= zobrist[them][PAWN][to];
781 // Update incremental scores:
782 mgValue -= mg_pst(them, capture, to);
783 egValue -= eg_pst(them, capture, to);
787 npMaterial[them] -= piece_value_midgame(capture);
789 // Update material hash key:
790 materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];
792 // Update piece count:
793 pieceCount[them][capture]--;
795 // Update piece list:
796 pieceList[them][capture][index[to]] =
797 pieceList[them][capture][pieceCount[them][capture]];
798 index[pieceList[them][capture][index[to]]] = index[to];
800 // Remember the captured piece, in order to be able to undo the move
804 // Reset rule 50 counter:
809 clear_bit(&(byColorBB[us]), from);
810 clear_bit(&(byTypeBB[piece]), from);
811 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
812 set_bit(&(byColorBB[us]), to);
813 set_bit(&(byTypeBB[piece]), to);
814 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
815 board[to] = board[from];
819 key ^= zobrist[us][piece][from] ^ zobrist[us][piece][to];
821 // Update incremental scores:
822 mgValue -= mg_pst(us, piece, from);
823 mgValue += mg_pst(us, piece, to);
824 egValue -= eg_pst(us, piece, from);
825 egValue += eg_pst(us, piece, to);
827 // If the moving piece was a king, update the king square:
831 // If the move was a double pawn push, set the en passant square.
832 // This code is a bit ugly right now, and should be cleaned up later.
834 if(epSquare != SQ_NONE) {
835 key ^= zobEp[epSquare];
839 if(abs(int(to) - int(from)) == 16) {
840 if((us == WHITE && (white_pawn_attacks(from + DELTA_N) &
842 (us == BLACK && (black_pawn_attacks(from + DELTA_S) &
844 epSquare = Square((int(from) + int(to)) / 2);
845 key ^= zobEp[epSquare];
848 // Reset rule 50 draw counter.
850 // Update pawn hash key:
851 pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
854 // Update piece lists:
855 pieceList[us][piece][index[from]] = to;
856 index[to] = index[from];
858 // Update castle rights:
859 key ^= zobCastle[castleRights];
860 castleRights &= castleRightsMask[from];
861 castleRights &= castleRightsMask[to];
862 key ^= zobCastle[castleRights];
864 // Update checkers bitboard:
865 checkersBB = EmptyBoardBB;
866 Square ksq = king_square(them);
871 if(bit_is_set(pawn_attacks(them, ksq), to))
872 set_bit(&checkersBB, to);
873 if(bit_is_set(dcCandidates, from))
875 ((rook_attacks(ksq) & rooks_and_queens(us)) |
876 (bishop_attacks(ksq) & bishops_and_queens(us)));
880 if(bit_is_set(knight_attacks(ksq), to))
881 set_bit(&checkersBB, to);
882 if(bit_is_set(dcCandidates, from))
884 ((rook_attacks(ksq) & rooks_and_queens(us)) |
885 (bishop_attacks(ksq) & bishops_and_queens(us)));
889 if(bit_is_set(bishop_attacks(ksq), to))
890 set_bit(&checkersBB, to);
891 if(bit_is_set(dcCandidates, from))
893 (rook_attacks(ksq) & rooks_and_queens(us));
897 if(bit_is_set(rook_attacks(ksq), to))
898 set_bit(&checkersBB, to);
899 if(bit_is_set(dcCandidates, from))
901 (bishop_attacks(ksq) & bishops_and_queens(us));
905 if(bit_is_set(queen_attacks(ksq), to))
906 set_bit(&checkersBB, to);
910 if(bit_is_set(dcCandidates, from))
912 ((rook_attacks(ksq) & rooks_and_queens(us)) |
913 (bishop_attacks(ksq) & bishops_and_queens(us)));
923 key ^= zobSideToMove;
924 sideToMove = opposite_color(sideToMove);
927 mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
928 egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
934 /// Position::do_castle_move() is a private method used to make a castling
935 /// move. It is called from the main Position::do_move function. Note that
936 /// castling moves are encoded as "king captures friendly rook" moves, for
937 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
939 void Position::do_castle_move(Move m) {
941 Square kfrom, kto, rfrom, rto;
944 assert(move_is_ok(m));
945 assert(move_is_castle(m));
948 them = opposite_color(us);
950 // Find source squares for king and rook:
951 kfrom = move_from(m);
952 rfrom = move_to(m); // HACK: See comment at beginning of function.
954 assert(piece_on(kfrom) == king_of_color(us));
955 assert(piece_on(rfrom) == rook_of_color(us));
957 // Find destination squares for king and rook:
958 if(rfrom > kfrom) { // O-O
959 kto = relative_square(us, SQ_G1);
960 rto = relative_square(us, SQ_F1);
963 kto = relative_square(us, SQ_C1);
964 rto = relative_square(us, SQ_D1);
967 // Remove pieces from source squares:
968 clear_bit(&(byColorBB[us]), kfrom);
969 clear_bit(&(byTypeBB[KING]), kfrom);
970 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
971 clear_bit(&(byColorBB[us]), rfrom);
972 clear_bit(&(byTypeBB[ROOK]), rfrom);
973 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
975 // Put pieces on destination squares:
976 set_bit(&(byColorBB[us]), kto);
977 set_bit(&(byTypeBB[KING]), kto);
978 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
979 set_bit(&(byColorBB[us]), rto);
980 set_bit(&(byTypeBB[ROOK]), rto);
981 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
983 // Update board array:
984 board[kfrom] = board[rfrom] = EMPTY;
985 board[kto] = king_of_color(us);
986 board[rto] = rook_of_color(us);
988 // Update king square:
989 kingSquare[us] = kto;
991 // Update piece lists:
992 pieceList[us][KING][index[kfrom]] = kto;
993 pieceList[us][ROOK][index[rfrom]] = rto;
994 int tmp = index[rfrom];
995 index[kto] = index[kfrom];
998 // Update incremental scores:
999 mgValue -= mg_pst(us, KING, kfrom);
1000 mgValue += mg_pst(us, KING, kto);
1001 egValue -= eg_pst(us, KING, kfrom);
1002 egValue += eg_pst(us, KING, kto);
1003 mgValue -= mg_pst(us, ROOK, rfrom);
1004 mgValue += mg_pst(us, ROOK, rto);
1005 egValue -= eg_pst(us, ROOK, rfrom);
1006 egValue += eg_pst(us, ROOK, rto);
1009 key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1010 key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1012 // Clear en passant square:
1013 if(epSquare != SQ_NONE) {
1014 key ^= zobEp[epSquare];
1018 // Update castling rights:
1019 key ^= zobCastle[castleRights];
1020 castleRights &= castleRightsMask[kfrom];
1021 key ^= zobCastle[castleRights];
1023 // Reset rule 50 counter:
1026 // Update checkers BB:
1027 checkersBB = attacks_to(king_square(them), us);
1031 /// Position::do_promotion_move() is a private method used to make a promotion
1032 /// move. It is called from the main Position::do_move function. The
1033 /// UndoInfo object, which has been initialized in Position::do_move, is
1034 /// used to store the captured piece (if any).
1036 void Position::do_promotion_move(Move m, UndoInfo &u) {
1039 PieceType capture, promotion;
1042 assert(move_is_ok(m));
1043 assert(move_promotion(m));
1045 us = side_to_move();
1046 them = opposite_color(us);
1048 from = move_from(m);
1051 assert(relative_rank(us, to) == RANK_8);
1052 assert(piece_on(from) == pawn_of_color(us));
1053 assert(color_of_piece_on(to) == them || square_is_empty(to));
1055 capture = type_of_piece_on(to);
1058 assert(capture != KING);
1060 // Remove captured piece:
1061 clear_bit(&(byColorBB[them]), to);
1062 clear_bit(&(byTypeBB[capture]), to);
1065 key ^= zobrist[them][capture][to];
1067 // Update incremental scores:
1068 mgValue -= mg_pst(them, capture, to);
1069 egValue -= eg_pst(them, capture, to);
1071 // Update material. Because our move is a promotion, we know that the
1072 // captured piece is not a pawn.
1073 assert(capture != PAWN);
1074 npMaterial[them] -= piece_value_midgame(capture);
1076 // Update material hash key:
1077 materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];
1079 // Update piece count:
1080 pieceCount[them][capture]--;
1082 // Update piece list:
1083 pieceList[them][capture][index[to]] =
1084 pieceList[them][capture][pieceCount[them][capture]];
1085 index[pieceList[them][capture][index[to]]] = index[to];
1087 // Remember the captured piece, in order to be able to undo the move
1089 u.capture = capture;
1093 clear_bit(&(byColorBB[us]), from);
1094 clear_bit(&(byTypeBB[PAWN]), from);
1095 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1096 board[from] = EMPTY;
1098 // Insert promoted piece:
1099 promotion = move_promotion(m);
1100 assert(promotion >= KNIGHT && promotion <= QUEEN);
1101 set_bit(&(byColorBB[us]), to);
1102 set_bit(&(byTypeBB[promotion]), to);
1103 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1104 board[to] = piece_of_color_and_type(us, promotion);
1107 key ^= zobrist[us][PAWN][from] ^ zobrist[us][promotion][to];
1109 // Update pawn hash key:
1110 pawnKey ^= zobrist[us][PAWN][from];
1112 // Update material key:
1113 materialKey ^= zobMaterial[us][PAWN][pieceCount[us][PAWN]];
1114 materialKey ^= zobMaterial[us][promotion][pieceCount[us][promotion]+1];
1116 // Update piece counts:
1117 pieceCount[us][PAWN]--;
1118 pieceCount[us][promotion]++;
1120 // Update piece lists:
1121 pieceList[us][PAWN][index[from]] =
1122 pieceList[us][PAWN][pieceCount[us][PAWN]];
1123 index[pieceList[us][PAWN][index[from]]] = index[from];
1124 pieceList[us][promotion][pieceCount[us][promotion] - 1] = to;
1125 index[to] = pieceCount[us][promotion] - 1;
1127 // Update incremental scores:
1128 mgValue -= mg_pst(us, PAWN, from);
1129 mgValue += mg_pst(us, promotion, to);
1130 egValue -= eg_pst(us, PAWN, from);
1131 egValue += eg_pst(us, promotion, to);
1134 npMaterial[us] += piece_value_midgame(promotion);
1136 // Clear the en passant square:
1137 if(epSquare != SQ_NONE) {
1138 key ^= zobEp[epSquare];
1142 // Update castle rights:
1143 key ^= zobCastle[castleRights];
1144 castleRights &= castleRightsMask[to];
1145 key ^= zobCastle[castleRights];
1147 // Reset rule 50 counter:
1150 // Update checkers BB:
1151 checkersBB = attacks_to(king_square(them), us);
1155 /// Position::do_ep_move() is a private method used to make an en passant
1156 /// capture. It is called from the main Position::do_move function. Because
1157 /// the captured piece is always a pawn, we don't need to pass an UndoInfo
1158 /// object in which to store the captured piece.
1160 void Position::do_ep_move(Move m) {
1162 Square from, to, capsq;
1165 assert(move_is_ok(m));
1166 assert(move_is_ep(m));
1168 us = side_to_move();
1169 them = opposite_color(us);
1171 // Find from, to and capture squares:
1172 from = move_from(m);
1174 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1176 assert(to == epSquare);
1177 assert(relative_rank(us, to) == RANK_6);
1178 assert(piece_on(to) == EMPTY);
1179 assert(piece_on(from) == pawn_of_color(us));
1180 assert(piece_on(capsq) == pawn_of_color(them));
1182 // Remove captured piece:
1183 clear_bit(&(byColorBB[them]), capsq);
1184 clear_bit(&(byTypeBB[PAWN]), capsq);
1185 clear_bit(&(byTypeBB[0]), capsq); // HACK: byTypeBB[0] == occupied squares
1186 board[capsq] = EMPTY;
1188 // Remove moving piece from source square:
1189 clear_bit(&(byColorBB[us]), from);
1190 clear_bit(&(byTypeBB[PAWN]), from);
1191 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1193 // Put moving piece on destination square:
1194 set_bit(&(byColorBB[us]), to);
1195 set_bit(&(byTypeBB[PAWN]), to);
1196 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1197 board[to] = board[from];
1198 board[from] = EMPTY;
1200 // Update material hash key:
1201 materialKey ^= zobMaterial[them][PAWN][pieceCount[them][PAWN]];
1203 // Update piece count:
1204 pieceCount[them][PAWN]--;
1206 // Update piece list:
1207 pieceList[us][PAWN][index[from]] = to;
1208 index[to] = index[from];
1209 pieceList[them][PAWN][index[capsq]] =
1210 pieceList[them][PAWN][pieceCount[them][PAWN]];
1211 index[pieceList[them][PAWN][index[capsq]]] = index[capsq];
1214 key ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1215 key ^= zobrist[them][PAWN][capsq];
1216 key ^= zobEp[epSquare];
1218 // Update pawn hash key:
1219 pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1220 pawnKey ^= zobrist[them][PAWN][capsq];
1222 // Update incremental scores:
1223 mgValue -= mg_pst(them, PAWN, capsq);
1224 mgValue -= mg_pst(us, PAWN, from);
1225 mgValue += mg_pst(us, PAWN, to);
1226 egValue -= eg_pst(them, PAWN, capsq);
1227 egValue -= eg_pst(us, PAWN, from);
1228 egValue += eg_pst(us, PAWN, to);
1230 // Reset en passant square:
1233 // Reset rule 50 counter:
1236 // Update checkers BB:
1237 checkersBB = attacks_to(king_square(them), us);
1241 /// Position::undo_move() unmakes a move. When it returns, the position should
1242 /// be restored to exactly the same state as before the move was made. It is
1243 /// important that Position::undo_move is called with the same move and UndoInfo
1244 /// object as the earlier call to Position::do_move.
1246 void Position::undo_move(Move m, const UndoInfo &u) {
1248 assert(move_is_ok(m));
1251 sideToMove = opposite_color(sideToMove);
1253 // Restore information from our UndoInfo object (except the captured piece,
1254 // which is taken care of later):
1257 if(move_is_castle(m))
1258 undo_castle_move(m);
1259 else if(move_promotion(m))
1260 undo_promotion_move(m, u);
1261 else if(move_is_ep(m))
1266 PieceType piece, capture;
1268 us = side_to_move();
1269 them = opposite_color(us);
1271 from = move_from(m);
1274 assert(piece_on(from) == EMPTY);
1275 assert(color_of_piece_on(to) == us);
1277 // Put the piece back at the source square:
1278 piece = type_of_piece_on(to);
1279 set_bit(&(byColorBB[us]), from);
1280 set_bit(&(byTypeBB[piece]), from);
1281 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1282 board[from] = piece_of_color_and_type(us, piece);
1284 // Clear the destination square
1285 clear_bit(&(byColorBB[us]), to);
1286 clear_bit(&(byTypeBB[piece]), to);
1287 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1289 // If the moving piece was a king, update the king square:
1291 kingSquare[us] = from;
1293 // Update piece list:
1294 pieceList[us][piece][index[to]] = from;
1295 index[from] = index[to];
1297 capture = u.capture;
1300 assert(capture != KING);
1301 // Replace the captured piece:
1302 set_bit(&(byColorBB[them]), to);
1303 set_bit(&(byTypeBB[capture]), to);
1304 set_bit(&(byTypeBB[0]), to);
1305 board[to] = piece_of_color_and_type(them, capture);
1309 npMaterial[them] += piece_value_midgame(capture);
1311 // Update piece list:
1312 pieceList[them][capture][pieceCount[them][capture]] = to;
1313 index[to] = pieceCount[them][capture];
1315 // Update piece count:
1316 pieceCount[them][capture]++;
1326 /// Position::undo_castle_move() is a private method used to unmake a castling
1327 /// move. It is called from the main Position::undo_move function. Note that
1328 /// castling moves are encoded as "king captures friendly rook" moves, for
1329 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1331 void Position::undo_castle_move(Move m) {
1333 Square kfrom, kto, rfrom, rto;
1335 assert(move_is_ok(m));
1336 assert(move_is_castle(m));
1338 // When we have arrived here, some work has already been done by
1339 // Position::undo_move. In particular, the side to move has been switched,
1340 // so the code below is correct.
1341 us = side_to_move();
1342 them = opposite_color(us);
1344 // Find source squares for king and rook:
1345 kfrom = move_from(m);
1346 rfrom = move_to(m); // HACK: See comment at beginning of function.
1348 // Find destination squares for king and rook:
1349 if(rfrom > kfrom) { // O-O
1350 kto = relative_square(us, SQ_G1);
1351 rto = relative_square(us, SQ_F1);
1354 kto = relative_square(us, SQ_C1);
1355 rto = relative_square(us, SQ_D1);
1358 assert(piece_on(kto) == king_of_color(us));
1359 assert(piece_on(rto) == rook_of_color(us));
1361 // Remove pieces from destination squares:
1362 clear_bit(&(byColorBB[us]), kto);
1363 clear_bit(&(byTypeBB[KING]), kto);
1364 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1365 clear_bit(&(byColorBB[us]), rto);
1366 clear_bit(&(byTypeBB[ROOK]), rto);
1367 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1369 // Put pieces on source squares:
1370 set_bit(&(byColorBB[us]), kfrom);
1371 set_bit(&(byTypeBB[KING]), kfrom);
1372 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1373 set_bit(&(byColorBB[us]), rfrom);
1374 set_bit(&(byTypeBB[ROOK]), rfrom);
1375 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1378 board[rto] = board[kto] = EMPTY;
1379 board[rfrom] = rook_of_color(us);
1380 board[kfrom] = king_of_color(us);
1382 // Update king square:
1383 kingSquare[us] = kfrom;
1385 // Update piece lists:
1386 pieceList[us][KING][index[kto]] = kfrom;
1387 pieceList[us][ROOK][index[rto]] = rfrom;
1388 int tmp = index[rto]; // Necessary because we may have rto == kfrom in FRC.
1389 index[kfrom] = index[kto];
1394 /// Position::undo_promotion_move() is a private method used to unmake a
1395 /// promotion move. It is called from the main Position::do_move
1396 /// function. The UndoInfo object, which has been initialized in
1397 /// Position::do_move, is used to put back the captured piece (if any).
1399 void Position::undo_promotion_move(Move m, const UndoInfo &u) {
1402 PieceType capture, promotion;
1404 assert(move_is_ok(m));
1405 assert(move_promotion(m));
1407 // When we have arrived here, some work has already been done by
1408 // Position::undo_move. In particular, the side to move has been switched,
1409 // so the code below is correct.
1410 us = side_to_move();
1411 them = opposite_color(us);
1413 from = move_from(m);
1416 assert(relative_rank(us, to) == RANK_8);
1417 assert(piece_on(from) == EMPTY);
1419 // Remove promoted piece:
1420 promotion = move_promotion(m);
1421 assert(piece_on(to)==piece_of_color_and_type(us, promotion));
1422 assert(promotion >= KNIGHT && promotion <= QUEEN);
1423 clear_bit(&(byColorBB[us]), to);
1424 clear_bit(&(byTypeBB[promotion]), to);
1425 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1427 // Insert pawn at source square:
1428 set_bit(&(byColorBB[us]), from);
1429 set_bit(&(byTypeBB[PAWN]), from);
1430 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1431 board[from] = pawn_of_color(us);
1434 npMaterial[us] -= piece_value_midgame(promotion);
1436 // Update piece list:
1437 pieceList[us][PAWN][pieceCount[us][PAWN]] = from;
1438 index[from] = pieceCount[us][PAWN];
1439 pieceList[us][promotion][index[to]] =
1440 pieceList[us][promotion][pieceCount[us][promotion] - 1];
1441 index[pieceList[us][promotion][index[to]]] = index[to];
1443 // Update piece counts:
1444 pieceCount[us][promotion]--;
1445 pieceCount[us][PAWN]++;
1447 capture = u.capture;
1449 assert(capture != KING);
1451 // Insert captured piece:
1452 set_bit(&(byColorBB[them]), to);
1453 set_bit(&(byTypeBB[capture]), to);
1454 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1455 board[to] = piece_of_color_and_type(them, capture);
1457 // Update material. Because the move is a promotion move, we know
1458 // that the captured piece cannot be a pawn.
1459 assert(capture != PAWN);
1460 npMaterial[them] += piece_value_midgame(capture);
1462 // Update piece list:
1463 pieceList[them][capture][pieceCount[them][capture]] = to;
1464 index[to] = pieceCount[them][capture];
1466 // Update piece count:
1467 pieceCount[them][capture]++;
1474 /// Position::undo_ep_move() is a private method used to unmake an en passant
1475 /// capture. It is called from the main Position::undo_move function. Because
1476 /// the captured piece is always a pawn, we don't need to pass an UndoInfo
1477 /// object from which to retrieve the captured piece.
1479 void Position::undo_ep_move(Move m) {
1481 Square from, to, capsq;
1483 assert(move_is_ok(m));
1484 assert(move_is_ep(m));
1486 // When we have arrived here, some work has already been done by
1487 // Position::undo_move. In particular, the side to move has been switched,
1488 // so the code below is correct.
1489 us = side_to_move();
1490 them = opposite_color(us);
1492 // Find from, to and captures squares:
1493 from = move_from(m);
1495 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1497 assert(to == ep_square());
1498 assert(relative_rank(us, to) == RANK_6);
1499 assert(piece_on(to) == pawn_of_color(us));
1500 assert(piece_on(from) == EMPTY);
1501 assert(piece_on(capsq) == EMPTY);
1503 // Replace captured piece:
1504 set_bit(&(byColorBB[them]), capsq);
1505 set_bit(&(byTypeBB[PAWN]), capsq);
1506 set_bit(&(byTypeBB[0]), capsq);
1507 board[capsq] = pawn_of_color(them);
1509 // Remove moving piece from destination square:
1510 clear_bit(&(byColorBB[us]), to);
1511 clear_bit(&(byTypeBB[PAWN]), to);
1512 clear_bit(&(byTypeBB[0]), to);
1515 // Replace moving piece at source square:
1516 set_bit(&(byColorBB[us]), from);
1517 set_bit(&(byTypeBB[PAWN]), from);
1518 set_bit(&(byTypeBB[0]), from);
1519 board[from] = pawn_of_color(us);
1521 // Update piece list:
1522 pieceList[us][PAWN][index[to]] = from;
1523 index[from] = index[to];
1524 pieceList[them][PAWN][pieceCount[them][PAWN]] = capsq;
1525 index[capsq] = pieceCount[them][PAWN];
1527 // Update piece count:
1528 pieceCount[them][PAWN]++;
1532 /// Position::do_null_move makes() a "null move": It switches the side to move
1533 /// and updates the hash key without executing any move on the board.
1535 void Position::do_null_move(UndoInfo &u) {
1537 assert(!is_check());
1539 // Back up the information necessary to undo the null move to the supplied
1540 // UndoInfo object. In the case of a null move, the only thing we need to
1541 // remember is the last move made and the en passant square.
1542 u.lastMove = lastMove;
1543 u.epSquare = epSquare;
1545 // Save the current key to the history[] array, in order to be able to
1546 // detect repetition draws:
1547 history[gamePly] = key;
1549 // Update the necessary information.
1550 sideToMove = opposite_color(sideToMove);
1551 if(epSquare != SQ_NONE)
1552 key ^= zobEp[epSquare];
1556 key ^= zobSideToMove;
1558 mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1559 egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1565 /// Position::undo_null_move() unmakes a "null move".
1567 void Position::undo_null_move(const UndoInfo &u) {
1569 assert(!is_check());
1571 // Restore information from the supplied UndoInfo object:
1572 lastMove = u.lastMove;
1573 epSquare = u.epSquare;
1574 if(epSquare != SQ_NONE)
1575 key ^= zobEp[epSquare];
1577 // Update the necessary information.
1578 sideToMove = opposite_color(sideToMove);
1581 key ^= zobSideToMove;
1583 mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1584 egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1590 /// Position::see() is a static exchange evaluator: It tries to estimate the
1591 /// material gain or loss resulting from a move. There are two versions of
1592 /// this function: One which takes a move as input, and one which takes a
1593 /// 'from' and a 'to' square. The function does not yet understand promotions
1594 /// or en passant captures.
1596 int Position::see(Square from, Square to) const {
1597 // Approximate material values, with pawn = 1:
1598 static const int seeValues[18] = {
1599 0, 1, 3, 3, 5, 10, 100, 0, 0, 1, 3, 3, 5, 10, 100, 0, 0, 0
1602 Piece piece, capture;
1603 Bitboard attackers, occ, b;
1605 assert(square_is_ok(from));
1606 assert(square_is_ok(to));
1608 // Initialize colors:
1609 us = color_of_piece_on(from);
1610 them = opposite_color(us);
1612 // Initialize pieces:
1613 piece = piece_on(from);
1614 capture = piece_on(to);
1616 // Find all attackers to the destination square, with the moving piece
1617 // removed, but possibly an X-ray attacker added behind it:
1618 occ = occupied_squares();
1619 clear_bit(&occ, from);
1621 (rook_attacks_bb(to, occ) & rooks_and_queens()) |
1622 (bishop_attacks_bb(to, occ) & bishops_and_queens()) |
1623 (knight_attacks(to) & knights()) |
1624 (king_attacks(to) & kings()) |
1625 (white_pawn_attacks(to) & pawns(BLACK)) |
1626 (black_pawn_attacks(to) & pawns(WHITE));
1629 // If the opponent has no attackers, we are finished:
1630 if((attackers & pieces_of_color(them)) == EmptyBoardBB)
1631 return seeValues[capture];
1633 // The destination square is defended, which makes things rather more
1634 // difficult to compute. We proceed by building up a "swap list" containing
1635 // the material gain or loss at each stop in a sequence of captures to the
1636 // destianation square, where the sides alternately capture, and always
1637 // capture with the least valuable piece. After each capture, we look for
1638 // new X-ray attacks from behind the capturing piece.
1639 int lastCapturingPieceValue = seeValues[piece];
1640 int swapList[32], n = 1;
1644 swapList[0] = seeValues[capture];
1647 // Locate the least valuable attacker for the side to move. The loop
1648 // below looks like it is potentially infinite, but it isn't. We know
1649 // that the side to move still has at least one attacker left.
1650 for(pt = PAWN; !(attackers&pieces_of_color_and_type(c, pt)); pt++)
1653 // Remove the attacker we just found from the 'attackers' bitboard,
1654 // and scan for new X-ray attacks behind the attacker:
1655 b = attackers & pieces_of_color_and_type(c, pt);
1658 (rook_attacks_bb(to, occ) & rooks_and_queens()) |
1659 (bishop_attacks_bb(to, occ) & bishops_and_queens());
1662 // Add the new entry to the swap list:
1664 swapList[n] = -swapList[n - 1] + lastCapturingPieceValue;
1667 // Remember the value of the capturing piece, and change the side to move
1668 // before beginning the next iteration:
1669 lastCapturingPieceValue = seeValues[pt];
1670 c = opposite_color(c);
1672 // Stop after a king capture:
1673 if(pt == KING && (attackers & pieces_of_color(c))) {
1675 swapList[n++] = 100;
1678 } while(attackers & pieces_of_color(c));
1680 // Having built the swap list, we negamax through it to find the best
1681 // achievable score from the point of view of the side to move:
1682 while(--n) swapList[n-1] = Min(-swapList[n], swapList[n-1]);
1688 int Position::see(Move m) const {
1689 assert(move_is_ok(m));
1690 return see(move_from(m), move_to(m));
1694 /// Position::clear() erases the position object to a pristine state, with an
1695 /// empty board, white to move, and no castling rights.
1697 void Position::clear() {
1700 for(i = 0; i < 64; i++) {
1705 for(i = 0; i < 2; i++)
1706 byColorBB[i] = EmptyBoardBB;
1708 for(i = 0; i < 7; i++) {
1709 byTypeBB[i] = EmptyBoardBB;
1710 pieceCount[0][i] = pieceCount[1][i] = 0;
1711 for(j = 0; j < 8; j++)
1712 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1715 checkersBB = EmptyBoardBB;
1717 lastMove = MOVE_NONE;
1720 castleRights = NO_CASTLES;
1721 initialKFile = FILE_E;
1722 initialKRFile = FILE_H;
1723 initialQRFile = FILE_A;
1730 /// Position::reset_game_ply() simply sets gamePly to 0. It is used from the
1731 /// UCI interface code, whenever a non-reversible move is made in a
1732 /// 'position fen <fen> moves m1 m2 ...' command. This makes it possible
1733 /// for the program to handle games of arbitrary length, as long as the GUI
1734 /// handles draws by the 50 move rule correctly.
1736 void Position::reset_game_ply() {
1741 /// Position::put_piece() puts a piece on the given square of the board,
1742 /// updating the board array, bitboards, and piece counts.
1744 void Position::put_piece(Piece p, Square s) {
1745 Color c = color_of_piece(p);
1746 PieceType pt = type_of_piece(p);
1749 index[s] = pieceCount[c][pt];
1750 pieceList[c][pt][index[s]] = s;
1752 set_bit(&(byTypeBB[pt]), s);
1753 set_bit(&(byColorBB[c]), s);
1754 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1756 pieceCount[c][pt]++;
1763 /// Position::allow_oo() gives the given side the right to castle kingside.
1764 /// Used when setting castling rights during parsing of FEN strings.
1766 void Position::allow_oo(Color c) {
1767 castleRights |= (1 + int(c));
1771 /// Position::allow_ooo() gives the given side the right to castle queenside.
1772 /// Used when setting castling rights during parsing of FEN strings.
1774 void Position::allow_ooo(Color c) {
1775 castleRights |= (4 + 4*int(c));
1779 /// Position::compute_key() computes the hash key of the position. The hash
1780 /// key is usually updated incrementally as moves are made and unmade, the
1781 /// compute_key() function is only used when a new position is set up, and
1782 /// to verify the correctness of the hash key when running in debug mode.
1784 Key Position::compute_key() const {
1785 Key result = Key(0ULL);
1787 for(Square s = SQ_A1; s <= SQ_H8; s++)
1788 if(square_is_occupied(s))
1790 zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1792 if(ep_square() != SQ_NONE)
1793 result ^= zobEp[ep_square()];
1794 result ^= zobCastle[castleRights];
1795 if(side_to_move() == BLACK) result ^= zobSideToMove;
1801 /// Position::compute_pawn_key() computes the hash key of the position. The
1802 /// hash key is usually updated incrementally as moves are made and unmade,
1803 /// the compute_pawn_key() function is only used when a new position is set
1804 /// up, and to verify the correctness of the pawn hash key when running in
1807 Key Position::compute_pawn_key() const {
1808 Key result = Key(0ULL);
1812 for(Color c = WHITE; c <= BLACK; c++) {
1815 s = pop_1st_bit(&b);
1816 result ^= zobrist[c][PAWN][s];
1823 /// Position::compute_material_key() computes the hash key of the position.
1824 /// The hash key is usually updated incrementally as moves are made and unmade,
1825 /// the compute_material_key() function is only used when a new position is set
1826 /// up, and to verify the correctness of the material hash key when running in
1829 Key Position::compute_material_key() const {
1830 Key result = Key(0ULL);
1831 for(Color c = WHITE; c <= BLACK; c++)
1832 for(PieceType pt = PAWN; pt <= QUEEN; pt++) {
1833 int count = piece_count(c, pt);
1834 for(int i = 0; i <= count; i++)
1835 result ^= zobMaterial[c][pt][i];
1841 /// Position::compute_mg_value() and Position::compute_eg_value() compute the
1842 /// incremental scores for the middle game and the endgame. These functions
1843 /// are used to initialize the incremental scores when a new position is set
1844 /// up, and to verify that the scores are correctly updated by do_move
1845 /// and undo_move when the program is running in debug mode.
1847 Value Position::compute_mg_value() const {
1848 Value result = Value(0);
1852 for(Color c = WHITE; c <= BLACK; c++)
1853 for(PieceType pt = PAWN; pt <= KING; pt++) {
1854 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 += mg_pst(c, pt, s);
1861 result += (side_to_move() == WHITE)?
1862 (TempoValueMidgame / 2) : -(TempoValueMidgame / 2);
1866 Value Position::compute_eg_value() const {
1867 Value result = Value(0);
1871 for(Color c = WHITE; c <= BLACK; c++)
1872 for(PieceType pt = PAWN; pt <= KING; pt++) {
1873 b = pieces_of_color_and_type(c, pt);
1875 s = pop_1st_bit(&b);
1876 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1877 result += eg_pst(c, pt, s);
1880 result += (side_to_move() == WHITE)?
1881 (TempoValueEndgame / 2) : -(TempoValueEndgame / 2);
1886 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1887 /// game material score for the given side. Material scores are updated
1888 /// incrementally during the search, this function is only used while
1889 /// initializing a new Position object.
1891 Value Position::compute_non_pawn_material(Color c) const {
1892 Value result = Value(0);
1895 for(PieceType pt = KNIGHT; pt <= QUEEN; pt++) {
1896 Bitboard b = pieces_of_color_and_type(c, pt);
1898 s = pop_1st_bit(&b);
1899 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1900 result += piece_value_midgame(pt);
1907 /// Position::is_mate() returns true or false depending on whether the
1908 /// side to move is checkmated. Note that this function is currently very
1909 /// slow, and shouldn't be used frequently inside the search.
1911 bool Position::is_mate() {
1913 MovePicker mp = MovePicker(*this, false, MOVE_NONE, MOVE_NONE, MOVE_NONE,
1914 MOVE_NONE, Depth(0));
1915 return mp.get_next_move() == MOVE_NONE;
1922 /// Position::is_draw() tests whether the position is drawn by material,
1923 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1924 /// must be done by the search.
1926 bool Position::is_draw() const {
1927 // Draw by material?
1929 non_pawn_material(WHITE) + non_pawn_material(BLACK)
1930 <= BishopValueMidgame)
1933 // Draw by the 50 moves rule?
1934 if(rule50 > 100 || (rule50 == 100 && !is_check()))
1937 // Draw by repetition?
1938 for(int i = 2; i < Min(gamePly, rule50); i += 2)
1939 if(history[gamePly - i] == key)
1946 /// Position::has_mate_threat() tests whether a given color has a mate in one
1947 /// from the current position. This function is quite slow, but it doesn't
1948 /// matter, because it is currently only called from PV nodes, which are rare.
1950 bool Position::has_mate_threat(Color c) {
1952 Color stm = side_to_move();
1954 // The following lines are useless and silly, but prevents gcc from
1955 // emitting a stupid warning stating that u1.lastMove and u1.epSquare might
1956 // be used uninitialized.
1957 u1.lastMove = lastMove;
1958 u1.epSquare = epSquare;
1963 // If the input color is not equal to the side to move, do a null move
1964 if(c != stm) do_null_move(u1);
1966 MoveStack mlist[120];
1968 bool result = false;
1970 // Generate legal moves
1971 count = generate_legal_moves(*this, mlist);
1973 // Loop through the moves, and see if one of them is mate.
1974 for(int i = 0; i < count; i++) {
1975 do_move(mlist[i].move, u2);
1976 if(is_mate()) result = true;
1977 undo_move(mlist[i].move, u2);
1980 // Undo null move, if necessary
1981 if(c != stm) undo_null_move(u1);
1987 /// Position::init_zobrist() is a static member function which initializes the
1988 /// various arrays used to compute hash keys.
1990 void Position::init_zobrist() {
1992 for(int i = 0; i < 2; i++)
1993 for(int j = 0; j < 8; j++)
1994 for(int k = 0; k < 64; k++)
1995 zobrist[i][j][k] = Key(genrand_int64());
1997 for(int i = 0; i < 64; i++)
1998 zobEp[i] = Key(genrand_int64());
2000 for(int i = 0; i < 16; i++)
2001 zobCastle[i] = genrand_int64();
2003 zobSideToMove = genrand_int64();
2005 for(int i = 0; i < 2; i++)
2006 for(int j = 0; j < 8; j++)
2007 for(int k = 0; k < 16; k++)
2008 zobMaterial[i][j][k] = (k > 0)? Key(genrand_int64()) : Key(0LL);
2010 for(int i = 0; i < 16; i++)
2011 zobMaterial[0][KING][i] = zobMaterial[1][KING][i] = Key(0ULL);
2015 /// Position::init_piece_square_tables() initializes the piece square tables.
2016 /// This is a two-step operation: First, the white halves of the tables are
2017 /// copied from the MgPST[][] and EgPST[][] arrays, with a small random number
2018 /// added to each entry if the "Randomness" UCI parameter is non-zero.
2019 /// Second, the black halves of the tables are initialized by mirroring
2020 /// and changing the sign of the corresponding white scores.
2022 void Position::init_piece_square_tables() {
2023 int r = get_option_value_int("Randomness"), i;
2024 for(Square s = SQ_A1; s <= SQ_H8; s++) {
2025 for(Piece p = WP; p <= WK; p++) {
2026 i = (r == 0)? 0 : (genrand_int32() % (r*2) - r);
2027 MgPieceSquareTable[p][s] = Value(MgPST[p][s] + i);
2028 EgPieceSquareTable[p][s] = Value(EgPST[p][s] + i);
2031 for(Square s = SQ_A1; s <= SQ_H8; s++)
2032 for(Piece p = BP; p <= BK; p++) {
2033 MgPieceSquareTable[p][s] = -MgPieceSquareTable[p-8][flip_square(s)];
2034 EgPieceSquareTable[p][s] = -EgPieceSquareTable[p-8][flip_square(s)];
2039 /// Position::flipped_copy() makes a copy of the input position, but with
2040 /// the white and black sides reversed. This is only useful for debugging,
2041 /// especially for finding evaluation symmetry bugs.
2043 void Position::flipped_copy(const Position &pos) {
2044 assert(pos.is_ok());
2049 for(Square s = SQ_A1; s <= SQ_H8; s++)
2050 if(!pos.square_is_empty(s))
2051 put_piece(Piece(int(pos.piece_on(s)) ^ 8), flip_square(s));
2054 sideToMove = opposite_color(pos.side_to_move());
2057 if(pos.can_castle_kingside(WHITE)) allow_oo(BLACK);
2058 if(pos.can_castle_queenside(WHITE)) allow_ooo(BLACK);
2059 if(pos.can_castle_kingside(BLACK)) allow_oo(WHITE);
2060 if(pos.can_castle_queenside(BLACK)) allow_ooo(WHITE);
2062 initialKFile = pos.initialKFile;
2063 initialKRFile = pos.initialKRFile;
2064 initialQRFile = pos.initialQRFile;
2066 for(Square sq = SQ_A1; sq <= SQ_H8; sq++)
2067 castleRightsMask[sq] = ALL_CASTLES;
2068 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO|WHITE_OOO);
2069 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO|BLACK_OOO);
2070 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
2071 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
2072 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
2073 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
2075 // En passant square
2076 if(pos.epSquare != SQ_NONE)
2077 epSquare = flip_square(pos.epSquare);
2083 key = compute_key();
2084 pawnKey = compute_pawn_key();
2085 materialKey = compute_material_key();
2087 // Incremental scores
2088 mgValue = compute_mg_value();
2089 egValue = compute_eg_value();
2092 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
2093 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
2099 /// Position::is_ok() performs some consitency checks for the position object.
2100 /// This is meant to be helpful when debugging.
2102 bool Position::is_ok() const {
2104 // What features of the position should be verified?
2105 static const bool debugBitboards = false;
2106 static const bool debugKingCount = false;
2107 static const bool debugKingCapture = false;
2108 static const bool debugCheckerCount = false;
2109 static const bool debugKey = false;
2110 static const bool debugMaterialKey = false;
2111 static const bool debugPawnKey = false;
2112 static const bool debugIncrementalEval = false;
2113 static const bool debugNonPawnMaterial = false;
2114 static const bool debugPieceCounts = false;
2115 static const bool debugPieceList = false;
2118 if(!color_is_ok(side_to_move()))
2121 // Are the king squares in the position correct?
2122 if(piece_on(king_square(WHITE)) != WK)
2124 if(piece_on(king_square(BLACK)) != BK)
2128 if(!file_is_ok(initialKRFile))
2130 if(!file_is_ok(initialQRFile))
2133 // Do both sides have exactly one king?
2134 if(debugKingCount) {
2135 int kingCount[2] = {0, 0};
2136 for(Square s = SQ_A1; s <= SQ_H8; s++)
2137 if(type_of_piece_on(s) == KING)
2138 kingCount[color_of_piece_on(s)]++;
2139 if(kingCount[0] != 1 || kingCount[1] != 1)
2143 // Can the side to move capture the opponent's king?
2144 if(debugKingCapture) {
2145 Color us = side_to_move();
2146 Color them = opposite_color(us);
2147 Square ksq = king_square(them);
2148 if(square_is_attacked(ksq, us))
2152 // Is there more than 2 checkers?
2153 if(debugCheckerCount && count_1s(checkersBB) > 2)
2157 if(debugBitboards) {
2158 // The intersection of the white and black pieces must be empty:
2159 if((pieces_of_color(WHITE) & pieces_of_color(BLACK))
2163 // The union of the white and black pieces must be equal to all
2164 // occupied squares:
2165 if((pieces_of_color(WHITE) | pieces_of_color(BLACK))
2166 != occupied_squares())
2169 // Separate piece type bitboards must have empty intersections:
2170 for(PieceType p1 = PAWN; p1 <= KING; p1++)
2171 for(PieceType p2 = PAWN; p2 <= KING; p2++)
2172 if(p1 != p2 && (pieces_of_type(p1) & pieces_of_type(p2)))
2176 // En passant square OK?
2177 if(ep_square() != SQ_NONE) {
2178 // The en passant square must be on rank 6, from the point of view of the
2180 if(relative_rank(side_to_move(), ep_square()) != RANK_6)
2185 if(debugKey && key != compute_key())
2188 // Pawn hash key OK?
2189 if(debugPawnKey && pawnKey != compute_pawn_key())
2192 // Material hash key OK?
2193 if(debugMaterialKey && materialKey != compute_material_key())
2196 // Incremental eval OK?
2197 if(debugIncrementalEval) {
2198 if(mgValue != compute_mg_value())
2200 if(egValue != compute_eg_value())
2204 // Non-pawn material OK?
2205 if(debugNonPawnMaterial) {
2206 if(npMaterial[WHITE] != compute_non_pawn_material(WHITE))
2208 if(npMaterial[BLACK] != compute_non_pawn_material(BLACK))
2213 if(debugPieceCounts)
2214 for(Color c = WHITE; c <= BLACK; c++)
2215 for(PieceType pt = PAWN; pt <= KING; pt++)
2216 if(pieceCount[c][pt] != count_1s(pieces_of_color_and_type(c, pt)))
2219 if(debugPieceList) {
2220 for(Color c = WHITE; c <= BLACK; c++)
2221 for(PieceType pt = PAWN; pt <= KING; pt++)
2222 for(int i = 0; i < pieceCount[c][pt]; i++) {
2223 if(piece_on(piece_list(c, pt, i)) !=
2224 piece_of_color_and_type(c, pt))
2226 if(index[piece_list(c, pt, i)] != i)