2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2009 Marco Costalba
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
36 #include "ucioption.h"
43 int Position::castleRightsMask[64];
45 Key Position::zobrist[2][8][64];
46 Key Position::zobEp[64];
47 Key Position::zobCastle[16];
48 Key Position::zobMaterial[2][8][16];
49 Key Position::zobSideToMove;
51 Value Position::MgPieceSquareTable[16][64];
52 Value Position::EgPieceSquareTable[16][64];
54 static bool RequestPending = false;
62 Position::Position(const Position& pos) {
66 Position::Position(const std::string& fen) {
71 /// Position::from_fen() initializes the position object with the given FEN
72 /// string. This function is not very robust - make sure that input FENs are
73 /// correct (this is assumed to be the responsibility of the GUI).
75 void Position::from_fen(const std::string& fen) {
77 static const std::string pieceLetters = "KQRBNPkqrbnp";
78 static const Piece pieces[] = { WK, WQ, WR, WB, WN, WP, BK, BQ, BR, BB, BN, BP };
86 for ( ; fen[i] != ' '; i++)
90 // Skip the given number of files
91 file += (fen[i] - '1' + 1);
94 else if (fen[i] == '/')
100 size_t idx = pieceLetters.find(fen[i]);
101 if (idx == std::string::npos)
103 std::cout << "Error in FEN at character " << i << std::endl;
106 Square square = make_square(file, rank);
107 put_piece(pieces[idx], square);
113 if (fen[i] != 'w' && fen[i] != 'b')
115 std::cout << "Error in FEN at character " << i << std::endl;
118 sideToMove = (fen[i] == 'w' ? WHITE : BLACK);
124 std::cout << "Error in FEN at character " << i << std::endl;
129 while(strchr("KQkqabcdefghABCDEFGH-", fen[i])) {
135 else if(fen[i] == 'K') allow_oo(WHITE);
136 else if(fen[i] == 'Q') allow_ooo(WHITE);
137 else if(fen[i] == 'k') allow_oo(BLACK);
138 else if(fen[i] == 'q') allow_ooo(BLACK);
139 else if(fen[i] >= 'A' && fen[i] <= 'H') {
140 File rookFile, kingFile = FILE_NONE;
141 for(Square square = SQ_B1; square <= SQ_G1; square++)
142 if(piece_on(square) == WK)
143 kingFile = square_file(square);
144 if(kingFile == FILE_NONE) {
145 std::cout << "Error in FEN at character " << i << std::endl;
148 initialKFile = kingFile;
149 rookFile = File(fen[i] - 'A') + FILE_A;
150 if(rookFile < initialKFile) {
152 initialQRFile = rookFile;
156 initialKRFile = rookFile;
159 else if(fen[i] >= 'a' && fen[i] <= 'h') {
160 File rookFile, kingFile = FILE_NONE;
161 for(Square square = SQ_B8; square <= SQ_G8; square++)
162 if(piece_on(square) == BK)
163 kingFile = square_file(square);
164 if(kingFile == FILE_NONE) {
165 std::cout << "Error in FEN at character " << i << std::endl;
168 initialKFile = kingFile;
169 rookFile = File(fen[i] - 'a') + FILE_A;
170 if(rookFile < initialKFile) {
172 initialQRFile = rookFile;
176 initialKRFile = rookFile;
180 std::cout << "Error in FEN at character " << i << std::endl;
187 while (fen[i] == ' ')
191 if ( i <= fen.length() - 2
192 && (fen[i] >= 'a' && fen[i] <= 'h')
193 && (fen[i+1] == '3' || fen[i+1] == '6'))
194 st->epSquare = square_from_string(fen.substr(i, 2));
196 // Various initialisation
197 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
198 castleRightsMask[sq] = ALL_CASTLES;
200 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO|WHITE_OOO);
201 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO|BLACK_OOO);
202 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
203 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
204 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
205 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
209 st->key = compute_key();
210 st->pawnKey = compute_pawn_key();
211 st->materialKey = compute_material_key();
212 st->mgValue = compute_value<MidGame>();
213 st->egValue = compute_value<EndGame>();
214 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
215 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
219 /// Position::to_fen() converts the position object to a FEN string. This is
220 /// probably only useful for debugging.
222 const std::string Position::to_fen() const {
224 static const std::string pieceLetters = " PNBRQK pnbrqk";
228 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
231 for (File file = FILE_A; file <= FILE_H; file++)
233 Square sq = make_square(file, rank);
234 if (!square_is_occupied(sq))
240 fen += (char)skip + '0';
243 fen += pieceLetters[piece_on(sq)];
246 fen += (char)skip + '0';
248 fen += (rank > RANK_1 ? '/' : ' ');
250 fen += (sideToMove == WHITE ? "w " : "b ");
251 if (st->castleRights != NO_CASTLES)
253 if (can_castle_kingside(WHITE)) fen += 'K';
254 if (can_castle_queenside(WHITE)) fen += 'Q';
255 if (can_castle_kingside(BLACK)) fen += 'k';
256 if (can_castle_queenside(BLACK)) fen += 'q';
261 if (ep_square() != SQ_NONE)
262 fen += square_to_string(ep_square());
270 /// Position::print() prints an ASCII representation of the position to
271 /// the standard output. If a move is given then also the san is print.
273 void Position::print(Move m) const {
275 static const std::string pieceLetters = " PNBRQK PNBRQK .";
277 // Check for reentrancy, as example when called from inside
278 // MovePicker that is used also here in move_to_san()
282 RequestPending = true;
284 std::cout << std::endl;
287 std::string col = (color_of_piece_on(move_from(m)) == BLACK ? ".." : "");
288 std::cout << "Move is: " << col << move_to_san(*this, m) << std::endl;
290 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
292 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl;
293 for (File file = FILE_A; file <= FILE_H; file++)
295 Square sq = make_square(file, rank);
296 Piece piece = piece_on(sq);
297 if (piece == EMPTY && square_color(sq) == WHITE)
300 char col = (color_of_piece_on(sq) == BLACK ? '=' : ' ');
301 std::cout << '|' << col << pieceLetters[piece] << col;
303 std::cout << '|' << std::endl;
305 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl
306 << "Fen is: " << to_fen() << std::endl
307 << "Key is: " << st->key << std::endl;
309 RequestPending = false;
313 /// Position::copy() creates a copy of the input position.
315 void Position::copy(const Position &pos) {
317 memcpy(this, &pos, sizeof(Position));
321 /// Position:hidden_checkers<>() returns a bitboard of all pinned (against the
322 /// king) pieces for the given color and for the given pinner type. Or, when
323 /// template parameter FindPinned is false, the pieces of the given color
324 /// candidate for a discovery check against the enemy king.
325 /// Note that checkersBB bitboard must be already updated.
327 template<bool FindPinned>
328 Bitboard Position::hidden_checkers(Color c) const {
330 Bitboard pinners, result = EmptyBoardBB;
332 // Pinned pieces protect our king, dicovery checks attack
334 Square ksq = king_square(FindPinned ? c : opposite_color(c));
336 // Pinners are sliders, not checkers, that give check when
337 // candidate pinned is removed.
338 pinners = (rooks_and_queens(FindPinned ? opposite_color(c) : c) & RookPseudoAttacks[ksq])
339 | (bishops_and_queens(FindPinned ? opposite_color(c) : c) & BishopPseudoAttacks[ksq]);
341 if (FindPinned && pinners)
342 pinners &= ~st->checkersBB;
346 Square s = pop_1st_bit(&pinners);
347 Bitboard b = squares_between(s, ksq) & occupied_squares();
351 if ( !(b & (b - 1)) // Only one bit set?
352 && (b & pieces_of_color(c))) // Is an our piece?
359 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
360 /// king) pieces for the given color.
362 Bitboard Position::pinned_pieces(Color c) const {
364 return hidden_checkers<true>(c);
368 /// Position:discovered_check_candidates() returns a bitboard containing all
369 /// pieces for the given side which are candidates for giving a discovered
372 Bitboard Position::discovered_check_candidates(Color c) const {
374 return hidden_checkers<false>(c);
377 /// Position::attacks_to() computes a bitboard containing all pieces which
378 /// attacks a given square. There are two versions of this function: One
379 /// which finds attackers of both colors, and one which only finds the
380 /// attackers for one side.
382 Bitboard Position::attacks_to(Square s) const {
384 return (pawn_attacks(BLACK, s) & pawns(WHITE))
385 | (pawn_attacks(WHITE, s) & pawns(BLACK))
386 | (piece_attacks<KNIGHT>(s) & pieces_of_type(KNIGHT))
387 | (piece_attacks<ROOK>(s) & rooks_and_queens())
388 | (piece_attacks<BISHOP>(s) & bishops_and_queens())
389 | (piece_attacks<KING>(s) & pieces_of_type(KING));
392 /// Position::piece_attacks_square() tests whether the piece on square f
393 /// attacks square t.
395 bool Position::piece_attacks_square(Piece p, Square f, Square t) const {
397 assert(square_is_ok(f));
398 assert(square_is_ok(t));
402 case WP: return pawn_attacks_square(WHITE, f, t);
403 case BP: return pawn_attacks_square(BLACK, f, t);
404 case WN: case BN: return piece_attacks_square<KNIGHT>(f, t);
405 case WB: case BB: return piece_attacks_square<BISHOP>(f, t);
406 case WR: case BR: return piece_attacks_square<ROOK>(f, t);
407 case WQ: case BQ: return piece_attacks_square<QUEEN>(f, t);
408 case WK: case BK: return piece_attacks_square<KING>(f, t);
415 /// Position::move_attacks_square() tests whether a move from the current
416 /// position attacks a given square.
418 bool Position::move_attacks_square(Move m, Square s) const {
420 assert(move_is_ok(m));
421 assert(square_is_ok(s));
423 Square f = move_from(m), t = move_to(m);
425 assert(square_is_occupied(f));
427 if (piece_attacks_square(piece_on(f), t, s))
430 // Move the piece and scan for X-ray attacks behind it
431 Bitboard occ = occupied_squares();
432 Color us = color_of_piece_on(f);
435 Bitboard xray = ( (rook_attacks_bb(s, occ) & rooks_and_queens())
436 |(bishop_attacks_bb(s, occ) & bishops_and_queens())) & pieces_of_color(us);
438 // If we have attacks we need to verify that are caused by our move
439 // and are not already existent ones.
440 return xray && (xray ^ (xray & piece_attacks<QUEEN>(s)));
444 /// Position::find_checkers() computes the checkersBB bitboard, which
445 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
446 /// currently works by calling Position::attacks_to, which is probably
447 /// inefficient. Consider rewriting this function to use the last move
448 /// played, like in non-bitboard versions of Glaurung.
450 void Position::find_checkers() {
452 Color us = side_to_move();
453 st->checkersBB = attacks_to(king_square(us), opposite_color(us));
457 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
459 bool Position::pl_move_is_legal(Move m) const {
461 // If we're in check, all pseudo-legal moves are legal, because our
462 // check evasion generator only generates true legal moves.
463 return is_check() || pl_move_is_legal(m, pinned_pieces(side_to_move()));
466 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
469 assert(move_is_ok(m));
470 assert(pinned == pinned_pieces(side_to_move()));
473 // Castling moves are checked for legality during move generation.
474 if (move_is_castle(m))
477 Color us = side_to_move();
478 Square from = move_from(m);
479 Square ksq = king_square(us);
481 assert(color_of_piece_on(from) == us);
482 assert(piece_on(ksq) == piece_of_color_and_type(us, KING));
484 // En passant captures are a tricky special case. Because they are
485 // rather uncommon, we do it simply by testing whether the king is attacked
486 // after the move is made
489 Color them = opposite_color(us);
490 Square to = move_to(m);
491 Square capsq = make_square(square_file(to), square_rank(from));
492 Bitboard b = occupied_squares();
494 assert(to == ep_square());
495 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
496 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
497 assert(piece_on(to) == EMPTY);
500 clear_bit(&b, capsq);
503 return !(rook_attacks_bb(ksq, b) & rooks_and_queens(them))
504 && !(bishop_attacks_bb(ksq, b) & bishops_and_queens(them));
507 // If the moving piece is a king, check whether the destination
508 // square is attacked by the opponent.
510 return !(square_is_attacked(move_to(m), opposite_color(us)));
512 // A non-king move is legal if and only if it is not pinned or it
513 // is moving along the ray towards or away from the king.
515 || !bit_is_set(pinned, from)
516 || (direction_between_squares(from, ksq) == direction_between_squares(move_to(m), ksq)));
520 /// Position::move_is_check() tests whether a pseudo-legal move is a check
522 bool Position::move_is_check(Move m) const {
524 Bitboard dc = discovered_check_candidates(side_to_move());
525 return move_is_check(m, dc);
528 bool Position::move_is_check(Move m, Bitboard dcCandidates) const {
531 assert(move_is_ok(m));
532 assert(dcCandidates == discovered_check_candidates(side_to_move()));
534 Color us = side_to_move();
535 Color them = opposite_color(us);
536 Square from = move_from(m);
537 Square to = move_to(m);
538 Square ksq = king_square(them);
540 assert(color_of_piece_on(from) == us);
541 assert(piece_on(ksq) == piece_of_color_and_type(them, KING));
543 // Proceed according to the type of the moving piece
544 switch (type_of_piece_on(from))
548 if (bit_is_set(pawn_attacks(them, ksq), to)) // Normal check?
551 if ( dcCandidates // Discovered check?
552 && bit_is_set(dcCandidates, from)
553 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
556 if (move_promotion(m)) // Promotion with check?
558 Bitboard b = occupied_squares();
561 switch (move_promotion(m))
564 return bit_is_set(piece_attacks<KNIGHT>(to), ksq);
566 return bit_is_set(bishop_attacks_bb(to, b), ksq);
568 return bit_is_set(rook_attacks_bb(to, b), ksq);
570 return bit_is_set(queen_attacks_bb(to, b), ksq);
575 // En passant capture with check? We have already handled the case
576 // of direct checks and ordinary discovered check, the only case we
577 // need to handle is the unusual case of a discovered check through the
579 else if (move_is_ep(m))
581 Square capsq = make_square(square_file(to), square_rank(from));
582 Bitboard b = occupied_squares();
584 clear_bit(&b, capsq);
586 return (rook_attacks_bb(ksq, b) & rooks_and_queens(us))
587 ||(bishop_attacks_bb(ksq, b) & bishops_and_queens(us));
591 // Test discovered check and normal check according to piece type
593 return (dcCandidates && bit_is_set(dcCandidates, from))
594 || bit_is_set(piece_attacks<KNIGHT>(ksq), to);
597 return (dcCandidates && bit_is_set(dcCandidates, from))
598 || (direction_is_diagonal(ksq, to) && bit_is_set(piece_attacks<BISHOP>(ksq), to));
601 return (dcCandidates && bit_is_set(dcCandidates, from))
602 || (direction_is_straight(ksq, to) && bit_is_set(piece_attacks<ROOK>(ksq), to));
605 // Discovered checks are impossible!
606 assert(!bit_is_set(dcCandidates, from));
607 return ( (direction_is_straight(ksq, to) && bit_is_set(piece_attacks<ROOK>(ksq), to))
608 || (direction_is_diagonal(ksq, to) && bit_is_set(piece_attacks<BISHOP>(ksq), to)));
612 if ( bit_is_set(dcCandidates, from)
613 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
616 // Castling with check?
617 if (move_is_castle(m))
619 Square kfrom, kto, rfrom, rto;
620 Bitboard b = occupied_squares();
626 kto = relative_square(us, SQ_G1);
627 rto = relative_square(us, SQ_F1);
629 kto = relative_square(us, SQ_C1);
630 rto = relative_square(us, SQ_D1);
632 clear_bit(&b, kfrom);
633 clear_bit(&b, rfrom);
636 return bit_is_set(rook_attacks_bb(rto, b), ksq);
640 default: // NO_PIECE_TYPE
648 /// Position::update_checkers() udpates chekers info given the move. It is called
649 /// in do_move() and is faster then find_checkers().
651 template<PieceType Piece>
652 inline void Position::update_checkers(Bitboard* pCheckersBB, Square ksq, Square from,
653 Square to, Bitboard dcCandidates) {
655 const bool Bishop = (Piece == QUEEN || Piece == BISHOP);
656 const bool Rook = (Piece == QUEEN || Piece == ROOK);
657 const bool Slider = Bishop || Rook;
659 if ( ( (Bishop && bit_is_set(BishopPseudoAttacks[ksq], to))
660 || (Rook && bit_is_set(RookPseudoAttacks[ksq], to)))
661 && bit_is_set(piece_attacks<Piece>(ksq), to)) // slow, try to early skip
662 set_bit(pCheckersBB, to);
664 else if ( Piece != KING
666 && bit_is_set(piece_attacks<Piece>(ksq), to))
667 set_bit(pCheckersBB, to);
669 if (Piece != QUEEN && bit_is_set(dcCandidates, from))
672 (*pCheckersBB) |= (piece_attacks<ROOK>(ksq) & rooks_and_queens(side_to_move()));
675 (*pCheckersBB) |= (piece_attacks<BISHOP>(ksq) & bishops_and_queens(side_to_move()));
680 /// Position::do_move() makes a move, and saves all information necessary
681 /// to a StateInfo object. The move is assumed to be legal.
682 /// Pseudo-legal moves should be filtered out before this function is called.
684 void Position::do_move(Move m, StateInfo& newSt) {
686 do_move(m, newSt, discovered_check_candidates(side_to_move()));
689 void Position::do_move(Move m, StateInfo& newSt, Bitboard dcCandidates) {
692 assert(move_is_ok(m));
694 // Copy some fields of old state to our new StateInfo object except the
695 // ones which are recalculated from scratch anyway, then switch our state
696 // pointer to point to the new, ready to be updated, state.
697 struct ReducedStateInfo {
698 Key key, pawnKey, materialKey;
699 int castleRights, rule50;
701 Value mgValue, egValue;
704 memcpy(&newSt, st, sizeof(ReducedStateInfo));
705 newSt.capture = NO_PIECE_TYPE;
709 // Save the current key to the history[] array, in order to be able to
710 // detect repetition draws.
711 history[gamePly] = st->key;
713 // Increment the 50 moves rule draw counter. Resetting it to zero in the
714 // case of non-reversible moves is taken care of later.
717 if (move_is_castle(m))
719 else if (move_promotion(m))
720 do_promotion_move(m);
721 else if (move_is_ep(m))
725 Color us = side_to_move();
726 Color them = opposite_color(us);
727 Square from = move_from(m);
728 Square to = move_to(m);
730 assert(color_of_piece_on(from) == us);
731 assert(color_of_piece_on(to) == them || piece_on(to) == EMPTY);
733 PieceType piece = type_of_piece_on(from);
735 st->capture = type_of_piece_on(to);
738 do_capture_move(st->capture, them, to);
741 clear_bit(&(byColorBB[us]), from);
742 clear_bit(&(byTypeBB[piece]), from);
743 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
744 set_bit(&(byColorBB[us]), to);
745 set_bit(&(byTypeBB[piece]), to);
746 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
747 board[to] = board[from];
751 st->key ^= zobrist[us][piece][from] ^ zobrist[us][piece][to];
753 // Update incremental scores
754 st->mgValue -= pst<MidGame>(us, piece, from);
755 st->mgValue += pst<MidGame>(us, piece, to);
756 st->egValue -= pst<EndGame>(us, piece, from);
757 st->egValue += pst<EndGame>(us, piece, to);
759 // If the moving piece was a king, update the king square
763 // Reset en passant square
764 if (st->epSquare != SQ_NONE)
766 st->key ^= zobEp[st->epSquare];
767 st->epSquare = SQ_NONE;
770 // If the moving piece was a pawn do some special extra work
773 // Reset rule 50 draw counter
776 // Update pawn hash key
777 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
779 // Set en passant square, only if moved pawn can be captured
780 if (abs(int(to) - int(from)) == 16)
782 if ( (us == WHITE && (pawn_attacks(WHITE, from + DELTA_N) & pawns(BLACK)))
783 || (us == BLACK && (pawn_attacks(BLACK, from + DELTA_S) & pawns(WHITE))))
785 st->epSquare = Square((int(from) + int(to)) / 2);
786 st->key ^= zobEp[st->epSquare];
791 // Update piece lists
792 pieceList[us][piece][index[from]] = to;
793 index[to] = index[from];
795 // Update castle rights
796 st->key ^= zobCastle[st->castleRights];
797 st->castleRights &= castleRightsMask[from];
798 st->castleRights &= castleRightsMask[to];
799 st->key ^= zobCastle[st->castleRights];
801 // Update checkers bitboard, piece must be already moved
802 st->checkersBB = EmptyBoardBB;
803 Square ksq = king_square(them);
806 case PAWN: update_checkers<PAWN>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
807 case KNIGHT: update_checkers<KNIGHT>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
808 case BISHOP: update_checkers<BISHOP>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
809 case ROOK: update_checkers<ROOK>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
810 case QUEEN: update_checkers<QUEEN>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
811 case KING: update_checkers<KING>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
812 default: assert(false); break;
817 st->key ^= zobSideToMove;
818 sideToMove = opposite_color(sideToMove);
821 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
822 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
828 /// Position::do_capture_move() is a private method used to update captured
829 /// piece info. It is called from the main Position::do_move function.
831 void Position::do_capture_move(PieceType capture, Color them, Square to) {
833 assert(capture != KING);
835 // Remove captured piece
836 clear_bit(&(byColorBB[them]), to);
837 clear_bit(&(byTypeBB[capture]), to);
840 st->key ^= zobrist[them][capture][to];
842 // If the captured piece was a pawn, update pawn hash key
844 st->pawnKey ^= zobrist[them][PAWN][to];
846 // Update incremental scores
847 st->mgValue -= pst<MidGame>(them, capture, to);
848 st->egValue -= pst<EndGame>(them, capture, to);
852 npMaterial[them] -= piece_value_midgame(capture);
854 // Update material hash key
855 st->materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];
857 // Update piece count
858 pieceCount[them][capture]--;
861 pieceList[them][capture][index[to]] = pieceList[them][capture][pieceCount[them][capture]];
862 index[pieceList[them][capture][index[to]]] = index[to];
864 // Reset rule 50 counter
869 /// Position::do_castle_move() is a private method used to make a castling
870 /// move. It is called from the main Position::do_move function. Note that
871 /// castling moves are encoded as "king captures friendly rook" moves, for
872 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
874 void Position::do_castle_move(Move m) {
877 assert(move_is_ok(m));
878 assert(move_is_castle(m));
880 Color us = side_to_move();
881 Color them = opposite_color(us);
883 // Find source squares for king and rook
884 Square kfrom = move_from(m);
885 Square rfrom = move_to(m); // HACK: See comment at beginning of function
888 assert(piece_on(kfrom) == piece_of_color_and_type(us, KING));
889 assert(piece_on(rfrom) == piece_of_color_and_type(us, ROOK));
891 // Find destination squares for king and rook
892 if (rfrom > kfrom) // O-O
894 kto = relative_square(us, SQ_G1);
895 rto = relative_square(us, SQ_F1);
897 kto = relative_square(us, SQ_C1);
898 rto = relative_square(us, SQ_D1);
901 // Remove pieces from source squares
902 clear_bit(&(byColorBB[us]), kfrom);
903 clear_bit(&(byTypeBB[KING]), kfrom);
904 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
905 clear_bit(&(byColorBB[us]), rfrom);
906 clear_bit(&(byTypeBB[ROOK]), rfrom);
907 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
909 // Put pieces on destination squares
910 set_bit(&(byColorBB[us]), kto);
911 set_bit(&(byTypeBB[KING]), kto);
912 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
913 set_bit(&(byColorBB[us]), rto);
914 set_bit(&(byTypeBB[ROOK]), rto);
915 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
917 // Update board array
918 board[kfrom] = board[rfrom] = EMPTY;
919 board[kto] = piece_of_color_and_type(us, KING);
920 board[rto] = piece_of_color_and_type(us, ROOK);
922 // Update king square
923 kingSquare[us] = kto;
925 // Update piece lists
926 pieceList[us][KING][index[kfrom]] = kto;
927 pieceList[us][ROOK][index[rfrom]] = rto;
928 int tmp = index[rfrom];
929 index[kto] = index[kfrom];
932 // Update incremental scores
933 st->mgValue -= pst<MidGame>(us, KING, kfrom);
934 st->mgValue += pst<MidGame>(us, KING, kto);
935 st->egValue -= pst<EndGame>(us, KING, kfrom);
936 st->egValue += pst<EndGame>(us, KING, kto);
937 st->mgValue -= pst<MidGame>(us, ROOK, rfrom);
938 st->mgValue += pst<MidGame>(us, ROOK, rto);
939 st->egValue -= pst<EndGame>(us, ROOK, rfrom);
940 st->egValue += pst<EndGame>(us, ROOK, rto);
943 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
944 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
946 // Clear en passant square
947 if (st->epSquare != SQ_NONE)
949 st->key ^= zobEp[st->epSquare];
950 st->epSquare = SQ_NONE;
953 // Update castling rights
954 st->key ^= zobCastle[st->castleRights];
955 st->castleRights &= castleRightsMask[kfrom];
956 st->key ^= zobCastle[st->castleRights];
958 // Reset rule 50 counter
961 // Update checkers BB
962 st->checkersBB = attacks_to(king_square(them), us);
966 /// Position::do_promotion_move() is a private method used to make a promotion
967 /// move. It is called from the main Position::do_move function.
969 void Position::do_promotion_move(Move m) {
976 assert(move_is_ok(m));
977 assert(move_promotion(m));
980 them = opposite_color(us);
984 assert(relative_rank(us, to) == RANK_8);
985 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
986 assert(color_of_piece_on(to) == them || square_is_empty(to));
988 st->capture = type_of_piece_on(to);
991 do_capture_move(st->capture, them, to);
994 clear_bit(&(byColorBB[us]), from);
995 clear_bit(&(byTypeBB[PAWN]), from);
996 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
999 // Insert promoted piece
1000 promotion = move_promotion(m);
1001 assert(promotion >= KNIGHT && promotion <= QUEEN);
1002 set_bit(&(byColorBB[us]), to);
1003 set_bit(&(byTypeBB[promotion]), to);
1004 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1005 board[to] = piece_of_color_and_type(us, promotion);
1008 st->key ^= zobrist[us][PAWN][from] ^ zobrist[us][promotion][to];
1010 // Update pawn hash key
1011 st->pawnKey ^= zobrist[us][PAWN][from];
1013 // Update material key
1014 st->materialKey ^= zobMaterial[us][PAWN][pieceCount[us][PAWN]];
1015 st->materialKey ^= zobMaterial[us][promotion][pieceCount[us][promotion]+1];
1017 // Update piece counts
1018 pieceCount[us][PAWN]--;
1019 pieceCount[us][promotion]++;
1021 // Update piece lists
1022 pieceList[us][PAWN][index[from]] = pieceList[us][PAWN][pieceCount[us][PAWN]];
1023 index[pieceList[us][PAWN][index[from]]] = index[from];
1024 pieceList[us][promotion][pieceCount[us][promotion] - 1] = to;
1025 index[to] = pieceCount[us][promotion] - 1;
1027 // Update incremental scores
1028 st->mgValue -= pst<MidGame>(us, PAWN, from);
1029 st->mgValue += pst<MidGame>(us, promotion, to);
1030 st->egValue -= pst<EndGame>(us, PAWN, from);
1031 st->egValue += pst<EndGame>(us, promotion, to);
1034 npMaterial[us] += piece_value_midgame(promotion);
1036 // Clear the en passant square
1037 if (st->epSquare != SQ_NONE)
1039 st->key ^= zobEp[st->epSquare];
1040 st->epSquare = SQ_NONE;
1043 // Update castle rights
1044 st->key ^= zobCastle[st->castleRights];
1045 st->castleRights &= castleRightsMask[to];
1046 st->key ^= zobCastle[st->castleRights];
1048 // Reset rule 50 counter
1051 // Update checkers BB
1052 st->checkersBB = attacks_to(king_square(them), us);
1056 /// Position::do_ep_move() is a private method used to make an en passant
1057 /// capture. It is called from the main Position::do_move function.
1059 void Position::do_ep_move(Move m) {
1062 Square from, to, capsq;
1065 assert(move_is_ok(m));
1066 assert(move_is_ep(m));
1068 us = side_to_move();
1069 them = opposite_color(us);
1070 from = move_from(m);
1072 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1074 assert(to == st->epSquare);
1075 assert(relative_rank(us, to) == RANK_6);
1076 assert(piece_on(to) == EMPTY);
1077 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
1078 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
1080 // Remove captured piece
1081 clear_bit(&(byColorBB[them]), capsq);
1082 clear_bit(&(byTypeBB[PAWN]), capsq);
1083 clear_bit(&(byTypeBB[0]), capsq); // HACK: byTypeBB[0] == occupied squares
1084 board[capsq] = EMPTY;
1086 // Remove moving piece from source square
1087 clear_bit(&(byColorBB[us]), from);
1088 clear_bit(&(byTypeBB[PAWN]), from);
1089 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1091 // Put moving piece on destination square
1092 set_bit(&(byColorBB[us]), to);
1093 set_bit(&(byTypeBB[PAWN]), to);
1094 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1095 board[to] = board[from];
1096 board[from] = EMPTY;
1098 // Update material hash key
1099 st->materialKey ^= zobMaterial[them][PAWN][pieceCount[them][PAWN]];
1101 // Update piece count
1102 pieceCount[them][PAWN]--;
1104 // Update piece list
1105 pieceList[us][PAWN][index[from]] = to;
1106 index[to] = index[from];
1107 pieceList[them][PAWN][index[capsq]] = pieceList[them][PAWN][pieceCount[them][PAWN]];
1108 index[pieceList[them][PAWN][index[capsq]]] = index[capsq];
1111 st->key ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1112 st->key ^= zobrist[them][PAWN][capsq];
1113 st->key ^= zobEp[st->epSquare];
1115 // Update pawn hash key
1116 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1117 st->pawnKey ^= zobrist[them][PAWN][capsq];
1119 // Update incremental scores
1120 st->mgValue -= pst<MidGame>(them, PAWN, capsq);
1121 st->mgValue -= pst<MidGame>(us, PAWN, from);
1122 st->mgValue += pst<MidGame>(us, PAWN, to);
1123 st->egValue -= pst<EndGame>(them, PAWN, capsq);
1124 st->egValue -= pst<EndGame>(us, PAWN, from);
1125 st->egValue += pst<EndGame>(us, PAWN, to);
1127 // Reset en passant square
1128 st->epSquare = SQ_NONE;
1130 // Reset rule 50 counter
1133 // Update checkers BB
1134 st->checkersBB = attacks_to(king_square(them), us);
1138 /// Position::undo_move() unmakes a move. When it returns, the position should
1139 /// be restored to exactly the same state as before the move was made.
1141 void Position::undo_move(Move m) {
1144 assert(move_is_ok(m));
1147 sideToMove = opposite_color(sideToMove);
1149 if (move_is_castle(m))
1150 undo_castle_move(m);
1151 else if (move_promotion(m))
1152 undo_promotion_move(m);
1153 else if (move_is_ep(m))
1161 us = side_to_move();
1162 them = opposite_color(us);
1163 from = move_from(m);
1166 assert(piece_on(from) == EMPTY);
1167 assert(color_of_piece_on(to) == us);
1169 // Put the piece back at the source square
1170 piece = type_of_piece_on(to);
1171 set_bit(&(byColorBB[us]), from);
1172 set_bit(&(byTypeBB[piece]), from);
1173 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1174 board[from] = piece_of_color_and_type(us, piece);
1176 // Clear the destination square
1177 clear_bit(&(byColorBB[us]), to);
1178 clear_bit(&(byTypeBB[piece]), to);
1179 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1181 // If the moving piece was a king, update the king square
1183 kingSquare[us] = from;
1185 // Update piece list
1186 pieceList[us][piece][index[to]] = from;
1187 index[from] = index[to];
1191 assert(st->capture != KING);
1193 // Replace the captured piece
1194 set_bit(&(byColorBB[them]), to);
1195 set_bit(&(byTypeBB[st->capture]), to);
1196 set_bit(&(byTypeBB[0]), to);
1197 board[to] = piece_of_color_and_type(them, st->capture);
1200 if (st->capture != PAWN)
1201 npMaterial[them] += piece_value_midgame(st->capture);
1203 // Update piece list
1204 pieceList[them][st->capture][pieceCount[them][st->capture]] = to;
1205 index[to] = pieceCount[them][st->capture];
1207 // Update piece count
1208 pieceCount[them][st->capture]++;
1213 // Finally point our state pointer back to the previous state
1220 /// Position::undo_castle_move() is a private method used to unmake a castling
1221 /// move. It is called from the main Position::undo_move function. Note that
1222 /// castling moves are encoded as "king captures friendly rook" moves, for
1223 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1225 void Position::undo_castle_move(Move m) {
1227 assert(move_is_ok(m));
1228 assert(move_is_castle(m));
1230 // When we have arrived here, some work has already been done by
1231 // Position::undo_move. In particular, the side to move has been switched,
1232 // so the code below is correct.
1233 Color us = side_to_move();
1235 // Find source squares for king and rook
1236 Square kfrom = move_from(m);
1237 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1240 // Find destination squares for king and rook
1241 if (rfrom > kfrom) // O-O
1243 kto = relative_square(us, SQ_G1);
1244 rto = relative_square(us, SQ_F1);
1246 kto = relative_square(us, SQ_C1);
1247 rto = relative_square(us, SQ_D1);
1250 assert(piece_on(kto) == piece_of_color_and_type(us, KING));
1251 assert(piece_on(rto) == piece_of_color_and_type(us, ROOK));
1253 // Remove pieces from destination squares
1254 clear_bit(&(byColorBB[us]), kto);
1255 clear_bit(&(byTypeBB[KING]), kto);
1256 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1257 clear_bit(&(byColorBB[us]), rto);
1258 clear_bit(&(byTypeBB[ROOK]), rto);
1259 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1261 // Put pieces on source squares
1262 set_bit(&(byColorBB[us]), kfrom);
1263 set_bit(&(byTypeBB[KING]), kfrom);
1264 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1265 set_bit(&(byColorBB[us]), rfrom);
1266 set_bit(&(byTypeBB[ROOK]), rfrom);
1267 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1270 board[rto] = board[kto] = EMPTY;
1271 board[rfrom] = piece_of_color_and_type(us, ROOK);
1272 board[kfrom] = piece_of_color_and_type(us, KING);
1274 // Update king square
1275 kingSquare[us] = kfrom;
1277 // Update piece lists
1278 pieceList[us][KING][index[kto]] = kfrom;
1279 pieceList[us][ROOK][index[rto]] = rfrom;
1280 int tmp = index[rto]; // Necessary because we may have rto == kfrom in FRC.
1281 index[kfrom] = index[kto];
1286 /// Position::undo_promotion_move() is a private method used to unmake a
1287 /// promotion move. It is called from the main Position::do_move
1290 void Position::undo_promotion_move(Move m) {
1294 PieceType promotion;
1296 assert(move_is_ok(m));
1297 assert(move_promotion(m));
1299 // When we have arrived here, some work has already been done by
1300 // Position::undo_move. In particular, the side to move has been switched,
1301 // so the code below is correct.
1302 us = side_to_move();
1303 them = opposite_color(us);
1304 from = move_from(m);
1307 assert(relative_rank(us, to) == RANK_8);
1308 assert(piece_on(from) == EMPTY);
1310 // Remove promoted piece
1311 promotion = move_promotion(m);
1312 assert(piece_on(to)==piece_of_color_and_type(us, promotion));
1313 assert(promotion >= KNIGHT && promotion <= QUEEN);
1314 clear_bit(&(byColorBB[us]), to);
1315 clear_bit(&(byTypeBB[promotion]), to);
1316 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1318 // Insert pawn at source square
1319 set_bit(&(byColorBB[us]), from);
1320 set_bit(&(byTypeBB[PAWN]), from);
1321 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1322 board[from] = piece_of_color_and_type(us, PAWN);
1325 npMaterial[us] -= piece_value_midgame(promotion);
1327 // Update piece list
1328 pieceList[us][PAWN][pieceCount[us][PAWN]] = from;
1329 index[from] = pieceCount[us][PAWN];
1330 pieceList[us][promotion][index[to]] =
1331 pieceList[us][promotion][pieceCount[us][promotion] - 1];
1332 index[pieceList[us][promotion][index[to]]] = index[to];
1334 // Update piece counts
1335 pieceCount[us][promotion]--;
1336 pieceCount[us][PAWN]++;
1340 assert(st->capture != KING);
1342 // Insert captured piece:
1343 set_bit(&(byColorBB[them]), to);
1344 set_bit(&(byTypeBB[st->capture]), to);
1345 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1346 board[to] = piece_of_color_and_type(them, st->capture);
1348 // Update material. Because the move is a promotion move, we know
1349 // that the captured piece cannot be a pawn.
1350 assert(st->capture != PAWN);
1351 npMaterial[them] += piece_value_midgame(st->capture);
1353 // Update piece list
1354 pieceList[them][st->capture][pieceCount[them][st->capture]] = to;
1355 index[to] = pieceCount[them][st->capture];
1357 // Update piece count
1358 pieceCount[them][st->capture]++;
1364 /// Position::undo_ep_move() is a private method used to unmake an en passant
1365 /// capture. It is called from the main Position::undo_move function.
1367 void Position::undo_ep_move(Move m) {
1369 assert(move_is_ok(m));
1370 assert(move_is_ep(m));
1372 // When we have arrived here, some work has already been done by
1373 // Position::undo_move. In particular, the side to move has been switched,
1374 // so the code below is correct.
1375 Color us = side_to_move();
1376 Color them = opposite_color(us);
1377 Square from = move_from(m);
1378 Square to = move_to(m);
1379 Square capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1381 assert(to == st->previous->epSquare);
1382 assert(relative_rank(us, to) == RANK_6);
1383 assert(piece_on(to) == piece_of_color_and_type(us, PAWN));
1384 assert(piece_on(from) == EMPTY);
1385 assert(piece_on(capsq) == EMPTY);
1387 // Replace captured piece
1388 set_bit(&(byColorBB[them]), capsq);
1389 set_bit(&(byTypeBB[PAWN]), capsq);
1390 set_bit(&(byTypeBB[0]), capsq);
1391 board[capsq] = piece_of_color_and_type(them, PAWN);
1393 // Remove moving piece from destination square
1394 clear_bit(&(byColorBB[us]), to);
1395 clear_bit(&(byTypeBB[PAWN]), to);
1396 clear_bit(&(byTypeBB[0]), to);
1399 // Replace moving piece at source square
1400 set_bit(&(byColorBB[us]), from);
1401 set_bit(&(byTypeBB[PAWN]), from);
1402 set_bit(&(byTypeBB[0]), from);
1403 board[from] = piece_of_color_and_type(us, PAWN);
1405 // Update piece list:
1406 pieceList[us][PAWN][index[to]] = from;
1407 index[from] = index[to];
1408 pieceList[them][PAWN][pieceCount[them][PAWN]] = capsq;
1409 index[capsq] = pieceCount[them][PAWN];
1411 // Update piece count:
1412 pieceCount[them][PAWN]++;
1416 /// Position::do_null_move makes() a "null move": It switches the side to move
1417 /// and updates the hash key without executing any move on the board.
1419 void Position::do_null_move(StateInfo& backupSt) {
1422 assert(!is_check());
1424 // Back up the information necessary to undo the null move to the supplied
1425 // StateInfo object. In the case of a null move, the only thing we need to
1426 // remember is the last move made and the en passant square.
1427 // Note that differently from normal case here backupSt is actually used as
1428 // a backup storage not as a new state to be used.
1429 backupSt.lastMove = st->lastMove;
1430 backupSt.epSquare = st->epSquare;
1431 backupSt.previous = st->previous;
1432 st->previous = &backupSt;
1434 // Save the current key to the history[] array, in order to be able to
1435 // detect repetition draws.
1436 history[gamePly] = st->key;
1438 // Update the necessary information
1439 sideToMove = opposite_color(sideToMove);
1440 if (st->epSquare != SQ_NONE)
1441 st->key ^= zobEp[st->epSquare];
1443 st->epSquare = SQ_NONE;
1446 st->key ^= zobSideToMove;
1448 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1449 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1455 /// Position::undo_null_move() unmakes a "null move".
1457 void Position::undo_null_move() {
1460 assert(!is_check());
1462 // Restore information from the our backup StateInfo object
1463 st->lastMove = st->previous->lastMove;
1464 st->epSquare = st->previous->epSquare;
1465 st->previous = st->previous->previous;
1467 if (st->epSquare != SQ_NONE)
1468 st->key ^= zobEp[st->epSquare];
1470 // Update the necessary information
1471 sideToMove = opposite_color(sideToMove);
1474 st->key ^= zobSideToMove;
1476 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1477 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1483 /// Position::see() is a static exchange evaluator: It tries to estimate the
1484 /// material gain or loss resulting from a move. There are three versions of
1485 /// this function: One which takes a destination square as input, one takes a
1486 /// move, and one which takes a 'from' and a 'to' square. The function does
1487 /// not yet understand promotions captures.
1489 int Position::see(Square to) const {
1491 assert(square_is_ok(to));
1492 return see(SQ_NONE, to);
1495 int Position::see(Move m) const {
1497 assert(move_is_ok(m));
1498 return see(move_from(m), move_to(m));
1501 int Position::see(Square from, Square to) const {
1504 static const int seeValues[18] = {
1505 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1506 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1507 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1508 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1512 Bitboard attackers, stmAttackers, occ, b;
1514 assert(square_is_ok(from) || from == SQ_NONE);
1515 assert(square_is_ok(to));
1517 // Initialize colors
1518 Color us = (from != SQ_NONE ? color_of_piece_on(from) : opposite_color(color_of_piece_on(to)));
1519 Color them = opposite_color(us);
1521 // Initialize pieces
1522 Piece piece = piece_on(from);
1523 Piece capture = piece_on(to);
1525 // Find all attackers to the destination square, with the moving piece
1526 // removed, but possibly an X-ray attacker added behind it.
1527 occ = occupied_squares();
1529 // Handle en passant moves
1530 if (st->epSquare == to && type_of_piece_on(from) == PAWN)
1532 assert(capture == EMPTY);
1534 Square capQq = (side_to_move() == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1535 capture = piece_on(capQq);
1536 assert(type_of_piece_on(capQq) == PAWN);
1538 // Remove the captured pawn
1539 clear_bit(&occ, capQq);
1544 clear_bit(&occ, from);
1545 attackers = (rook_attacks_bb(to, occ) & rooks_and_queens())
1546 | (bishop_attacks_bb(to, occ) & bishops_and_queens())
1547 | (piece_attacks<KNIGHT>(to) & knights())
1548 | (piece_attacks<KING>(to) & kings())
1549 | (pawn_attacks(WHITE, to) & pawns(BLACK))
1550 | (pawn_attacks(BLACK, to) & pawns(WHITE));
1552 if (from != SQ_NONE)
1555 // If we don't have any attacker we are finished
1556 if ((attackers & pieces_of_color(us)) == EmptyBoardBB)
1559 // Locate the least valuable attacker to the destination square
1560 // and use it to initialize from square.
1562 for (pt = PAWN; !(attackers & pieces_of_color_and_type(us, pt)); pt++)
1565 from = first_1(attackers & pieces_of_color_and_type(us, pt));
1566 piece = piece_on(from);
1569 // If the opponent has no attackers we are finished
1570 stmAttackers = attackers & pieces_of_color(them);
1572 return seeValues[capture];
1574 attackers &= occ; // Remove the moving piece
1576 // The destination square is defended, which makes things rather more
1577 // difficult to compute. We proceed by building up a "swap list" containing
1578 // the material gain or loss at each stop in a sequence of captures to the
1579 // destination square, where the sides alternately capture, and always
1580 // capture with the least valuable piece. After each capture, we look for
1581 // new X-ray attacks from behind the capturing piece.
1582 int lastCapturingPieceValue = seeValues[piece];
1583 int swapList[32], n = 1;
1587 swapList[0] = seeValues[capture];
1590 // Locate the least valuable attacker for the side to move. The loop
1591 // below looks like it is potentially infinite, but it isn't. We know
1592 // that the side to move still has at least one attacker left.
1593 for (pt = PAWN; !(stmAttackers & pieces_of_type(pt)); pt++)
1596 // Remove the attacker we just found from the 'attackers' bitboard,
1597 // and scan for new X-ray attacks behind the attacker.
1598 b = stmAttackers & pieces_of_type(pt);
1599 occ ^= (b & (~b + 1));
1600 attackers |= (rook_attacks_bb(to, occ) & rooks_and_queens())
1601 | (bishop_attacks_bb(to, occ) & bishops_and_queens());
1605 // Add the new entry to the swap list
1607 swapList[n] = -swapList[n - 1] + lastCapturingPieceValue;
1610 // Remember the value of the capturing piece, and change the side to move
1611 // before beginning the next iteration
1612 lastCapturingPieceValue = seeValues[pt];
1613 c = opposite_color(c);
1614 stmAttackers = attackers & pieces_of_color(c);
1616 // Stop after a king capture
1617 if (pt == KING && stmAttackers)
1620 swapList[n++] = 100;
1623 } while (stmAttackers);
1625 // Having built the swap list, we negamax through it to find the best
1626 // achievable score from the point of view of the side to move
1628 swapList[n-1] = Min(-swapList[n], swapList[n-1]);
1634 /// Position::setStartState() copies the content of the argument
1635 /// inside startState and makes st point to it. This is needed
1636 /// when the st pointee could become stale, as example because
1637 /// the caller is about to going out of scope.
1639 void Position::setStartState(const StateInfo& s) {
1646 /// Position::clear() erases the position object to a pristine state, with an
1647 /// empty board, white to move, and no castling rights.
1649 void Position::clear() {
1652 memset(st, 0, sizeof(StateInfo));
1653 st->epSquare = SQ_NONE;
1655 memset(index, 0, sizeof(int) * 64);
1656 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1658 for (int i = 0; i < 64; i++)
1661 for (int i = 0; i < 7; i++)
1663 byTypeBB[i] = EmptyBoardBB;
1664 pieceCount[0][i] = pieceCount[1][i] = 0;
1665 for (int j = 0; j < 8; j++)
1666 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1671 initialKFile = FILE_E;
1672 initialKRFile = FILE_H;
1673 initialQRFile = FILE_A;
1677 /// Position::reset_game_ply() simply sets gamePly to 0. It is used from the
1678 /// UCI interface code, whenever a non-reversible move is made in a
1679 /// 'position fen <fen> moves m1 m2 ...' command. This makes it possible
1680 /// for the program to handle games of arbitrary length, as long as the GUI
1681 /// handles draws by the 50 move rule correctly.
1683 void Position::reset_game_ply() {
1689 /// Position::put_piece() puts a piece on the given square of the board,
1690 /// updating the board array, bitboards, and piece counts.
1692 void Position::put_piece(Piece p, Square s) {
1694 Color c = color_of_piece(p);
1695 PieceType pt = type_of_piece(p);
1698 index[s] = pieceCount[c][pt];
1699 pieceList[c][pt][index[s]] = s;
1701 set_bit(&(byTypeBB[pt]), s);
1702 set_bit(&(byColorBB[c]), s);
1703 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1705 pieceCount[c][pt]++;
1712 /// Position::allow_oo() gives the given side the right to castle kingside.
1713 /// Used when setting castling rights during parsing of FEN strings.
1715 void Position::allow_oo(Color c) {
1717 st->castleRights |= (1 + int(c));
1721 /// Position::allow_ooo() gives the given side the right to castle queenside.
1722 /// Used when setting castling rights during parsing of FEN strings.
1724 void Position::allow_ooo(Color c) {
1726 st->castleRights |= (4 + 4*int(c));
1730 /// Position::compute_key() computes the hash key of the position. The hash
1731 /// key is usually updated incrementally as moves are made and unmade, the
1732 /// compute_key() function is only used when a new position is set up, and
1733 /// to verify the correctness of the hash key when running in debug mode.
1735 Key Position::compute_key() const {
1737 Key result = Key(0ULL);
1739 for (Square s = SQ_A1; s <= SQ_H8; s++)
1740 if (square_is_occupied(s))
1741 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1743 if (ep_square() != SQ_NONE)
1744 result ^= zobEp[ep_square()];
1746 result ^= zobCastle[st->castleRights];
1747 if (side_to_move() == BLACK)
1748 result ^= zobSideToMove;
1754 /// Position::compute_pawn_key() computes the hash key of the position. The
1755 /// hash key is usually updated incrementally as moves are made and unmade,
1756 /// the compute_pawn_key() function is only used when a new position is set
1757 /// up, and to verify the correctness of the pawn hash key when running in
1760 Key Position::compute_pawn_key() const {
1762 Key result = Key(0ULL);
1766 for (Color c = WHITE; c <= BLACK; c++)
1771 s = pop_1st_bit(&b);
1772 result ^= zobrist[c][PAWN][s];
1779 /// Position::compute_material_key() computes the hash key of the position.
1780 /// The hash key is usually updated incrementally as moves are made and unmade,
1781 /// the compute_material_key() function is only used when a new position is set
1782 /// up, and to verify the correctness of the material hash key when running in
1785 Key Position::compute_material_key() const {
1787 Key result = Key(0ULL);
1788 for (Color c = WHITE; c <= BLACK; c++)
1789 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1791 int count = piece_count(c, pt);
1792 for (int i = 0; i <= count; i++)
1793 result ^= zobMaterial[c][pt][i];
1799 /// Position::compute_value() compute the incremental scores for the middle
1800 /// game and the endgame. These functions are used to initialize the incremental
1801 /// scores when a new position is set up, and to verify that the scores are correctly
1802 /// updated by do_move and undo_move when the program is running in debug mode.
1803 template<Position::GamePhase Phase>
1804 Value Position::compute_value() const {
1806 Value result = Value(0);
1810 for (Color c = WHITE; c <= BLACK; c++)
1811 for (PieceType pt = PAWN; pt <= KING; pt++)
1813 b = pieces_of_color_and_type(c, pt);
1816 s = pop_1st_bit(&b);
1817 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1818 result += pst<Phase>(c, pt, s);
1822 const Value TempoValue = (Phase == MidGame ? TempoValueMidgame : TempoValueEndgame);
1823 result += (side_to_move() == WHITE)? TempoValue / 2 : -TempoValue / 2;
1828 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1829 /// game material score for the given side. Material scores are updated
1830 /// incrementally during the search, this function is only used while
1831 /// initializing a new Position object.
1833 Value Position::compute_non_pawn_material(Color c) const {
1835 Value result = Value(0);
1837 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1839 Bitboard b = pieces_of_color_and_type(c, pt);
1842 assert(piece_on(first_1(b)) == piece_of_color_and_type(c, pt));
1844 result += piece_value_midgame(pt);
1851 /// Position::is_draw() tests whether the position is drawn by material,
1852 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1853 /// must be done by the search.
1855 bool Position::is_draw() const {
1857 // Draw by material?
1859 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1862 // Draw by the 50 moves rule?
1863 if (st->rule50 > 100 || (st->rule50 == 100 && !is_check()))
1866 // Draw by repetition?
1867 for (int i = 2; i < Min(gamePly, st->rule50); i += 2)
1868 if (history[gamePly - i] == st->key)
1875 /// Position::is_mate() returns true or false depending on whether the
1876 /// side to move is checkmated.
1878 bool Position::is_mate() const {
1880 MoveStack moves[256];
1882 return is_check() && !generate_evasions(*this, moves, pinned_pieces(sideToMove));
1886 /// Position::has_mate_threat() tests whether a given color has a mate in one
1887 /// from the current position.
1889 bool Position::has_mate_threat(Color c) {
1892 Color stm = side_to_move();
1897 // If the input color is not equal to the side to move, do a null move
1901 MoveStack mlist[120];
1903 bool result = false;
1904 Bitboard dc = discovered_check_candidates(sideToMove);
1905 Bitboard pinned = pinned_pieces(sideToMove);
1907 // Generate pseudo-legal non-capture and capture check moves
1908 count = generate_non_capture_checks(*this, mlist, dc);
1909 count += generate_captures(*this, mlist + count);
1911 // Loop through the moves, and see if one of them is mate
1912 for (int i = 0; i < count; i++)
1914 Move move = mlist[i].move;
1916 if (!pl_move_is_legal(move, pinned))
1926 // Undo null move, if necessary
1934 /// Position::init_zobrist() is a static member function which initializes the
1935 /// various arrays used to compute hash keys.
1937 void Position::init_zobrist() {
1939 for (int i = 0; i < 2; i++)
1940 for (int j = 0; j < 8; j++)
1941 for (int k = 0; k < 64; k++)
1942 zobrist[i][j][k] = Key(genrand_int64());
1944 for (int i = 0; i < 64; i++)
1945 zobEp[i] = Key(genrand_int64());
1947 for (int i = 0; i < 16; i++)
1948 zobCastle[i] = genrand_int64();
1950 zobSideToMove = genrand_int64();
1952 for (int i = 0; i < 2; i++)
1953 for (int j = 0; j < 8; j++)
1954 for (int k = 0; k < 16; k++)
1955 zobMaterial[i][j][k] = (k > 0)? Key(genrand_int64()) : Key(0LL);
1957 for (int i = 0; i < 16; i++)
1958 zobMaterial[0][KING][i] = zobMaterial[1][KING][i] = Key(0ULL);
1962 /// Position::init_piece_square_tables() initializes the piece square tables.
1963 /// This is a two-step operation: First, the white halves of the tables are
1964 /// copied from the MgPST[][] and EgPST[][] arrays, with a small random number
1965 /// added to each entry if the "Randomness" UCI parameter is non-zero.
1966 /// Second, the black halves of the tables are initialized by mirroring
1967 /// and changing the sign of the corresponding white scores.
1969 void Position::init_piece_square_tables() {
1971 int r = get_option_value_int("Randomness"), i;
1972 for (Square s = SQ_A1; s <= SQ_H8; s++)
1973 for (Piece p = WP; p <= WK; p++)
1975 i = (r == 0)? 0 : (genrand_int32() % (r*2) - r);
1976 MgPieceSquareTable[p][s] = Value(MgPST[p][s] + i);
1977 EgPieceSquareTable[p][s] = Value(EgPST[p][s] + i);
1980 for (Square s = SQ_A1; s <= SQ_H8; s++)
1981 for (Piece p = BP; p <= BK; p++)
1983 MgPieceSquareTable[p][s] = -MgPieceSquareTable[p-8][flip_square(s)];
1984 EgPieceSquareTable[p][s] = -EgPieceSquareTable[p-8][flip_square(s)];
1989 /// Position::flipped_copy() makes a copy of the input position, but with
1990 /// the white and black sides reversed. This is only useful for debugging,
1991 /// especially for finding evaluation symmetry bugs.
1993 void Position::flipped_copy(const Position &pos) {
1995 assert(pos.is_ok());
2000 for (Square s = SQ_A1; s <= SQ_H8; s++)
2001 if (!pos.square_is_empty(s))
2002 put_piece(Piece(int(pos.piece_on(s)) ^ 8), flip_square(s));
2005 sideToMove = opposite_color(pos.side_to_move());
2008 if (pos.can_castle_kingside(WHITE)) allow_oo(BLACK);
2009 if (pos.can_castle_queenside(WHITE)) allow_ooo(BLACK);
2010 if (pos.can_castle_kingside(BLACK)) allow_oo(WHITE);
2011 if (pos.can_castle_queenside(BLACK)) allow_ooo(WHITE);
2013 initialKFile = pos.initialKFile;
2014 initialKRFile = pos.initialKRFile;
2015 initialQRFile = pos.initialQRFile;
2017 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
2018 castleRightsMask[sq] = ALL_CASTLES;
2020 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
2021 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
2022 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
2023 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
2024 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
2025 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
2027 // En passant square
2028 if (pos.st->epSquare != SQ_NONE)
2029 st->epSquare = flip_square(pos.st->epSquare);
2035 st->key = compute_key();
2036 st->pawnKey = compute_pawn_key();
2037 st->materialKey = compute_material_key();
2039 // Incremental scores
2040 st->mgValue = compute_value<MidGame>();
2041 st->egValue = compute_value<EndGame>();
2044 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
2045 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
2051 /// Position::is_ok() performs some consitency checks for the position object.
2052 /// This is meant to be helpful when debugging.
2054 bool Position::is_ok(int* failedStep) const {
2056 // What features of the position should be verified?
2057 static const bool debugBitboards = false;
2058 static const bool debugKingCount = false;
2059 static const bool debugKingCapture = false;
2060 static const bool debugCheckerCount = false;
2061 static const bool debugKey = false;
2062 static const bool debugMaterialKey = false;
2063 static const bool debugPawnKey = false;
2064 static const bool debugIncrementalEval = false;
2065 static const bool debugNonPawnMaterial = false;
2066 static const bool debugPieceCounts = false;
2067 static const bool debugPieceList = false;
2069 if (failedStep) *failedStep = 1;
2072 if (!color_is_ok(side_to_move()))
2075 // Are the king squares in the position correct?
2076 if (failedStep) (*failedStep)++;
2077 if (piece_on(king_square(WHITE)) != WK)
2080 if (failedStep) (*failedStep)++;
2081 if (piece_on(king_square(BLACK)) != BK)
2085 if (failedStep) (*failedStep)++;
2086 if (!file_is_ok(initialKRFile))
2089 if (!file_is_ok(initialQRFile))
2092 // Do both sides have exactly one king?
2093 if (failedStep) (*failedStep)++;
2096 int kingCount[2] = {0, 0};
2097 for (Square s = SQ_A1; s <= SQ_H8; s++)
2098 if (type_of_piece_on(s) == KING)
2099 kingCount[color_of_piece_on(s)]++;
2101 if (kingCount[0] != 1 || kingCount[1] != 1)
2105 // Can the side to move capture the opponent's king?
2106 if (failedStep) (*failedStep)++;
2107 if (debugKingCapture)
2109 Color us = side_to_move();
2110 Color them = opposite_color(us);
2111 Square ksq = king_square(them);
2112 if (square_is_attacked(ksq, us))
2116 // Is there more than 2 checkers?
2117 if (failedStep) (*failedStep)++;
2118 if (debugCheckerCount && count_1s(st->checkersBB) > 2)
2122 if (failedStep) (*failedStep)++;
2125 // The intersection of the white and black pieces must be empty
2126 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
2129 // The union of the white and black pieces must be equal to all
2131 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
2134 // Separate piece type bitboards must have empty intersections
2135 for (PieceType p1 = PAWN; p1 <= KING; p1++)
2136 for (PieceType p2 = PAWN; p2 <= KING; p2++)
2137 if (p1 != p2 && (pieces_of_type(p1) & pieces_of_type(p2)))
2141 // En passant square OK?
2142 if (failedStep) (*failedStep)++;
2143 if (ep_square() != SQ_NONE)
2145 // The en passant square must be on rank 6, from the point of view of the
2147 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
2152 if (failedStep) (*failedStep)++;
2153 if (debugKey && st->key != compute_key())
2156 // Pawn hash key OK?
2157 if (failedStep) (*failedStep)++;
2158 if (debugPawnKey && st->pawnKey != compute_pawn_key())
2161 // Material hash key OK?
2162 if (failedStep) (*failedStep)++;
2163 if (debugMaterialKey && st->materialKey != compute_material_key())
2166 // Incremental eval OK?
2167 if (failedStep) (*failedStep)++;
2168 if (debugIncrementalEval)
2170 if (st->mgValue != compute_value<MidGame>())
2173 if (st->egValue != compute_value<EndGame>())
2177 // Non-pawn material OK?
2178 if (failedStep) (*failedStep)++;
2179 if (debugNonPawnMaterial)
2181 if (npMaterial[WHITE] != compute_non_pawn_material(WHITE))
2184 if (npMaterial[BLACK] != compute_non_pawn_material(BLACK))
2189 if (failedStep) (*failedStep)++;
2190 if (debugPieceCounts)
2191 for (Color c = WHITE; c <= BLACK; c++)
2192 for (PieceType pt = PAWN; pt <= KING; pt++)
2193 if (pieceCount[c][pt] != count_1s(pieces_of_color_and_type(c, pt)))
2196 if (failedStep) (*failedStep)++;
2199 for(Color c = WHITE; c <= BLACK; c++)
2200 for(PieceType pt = PAWN; pt <= KING; pt++)
2201 for(int i = 0; i < pieceCount[c][pt]; i++)
2203 if (piece_on(piece_list(c, pt, i)) != piece_of_color_and_type(c, pt))
2206 if (index[piece_list(c, pt, i)] != i)
2210 if (failedStep) *failedStep = 0;