2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008 Marco Costalba
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
36 #include "ucioption.h"
43 extern SearchStack EmptySearchStack;
45 int Position::castleRightsMask[64];
47 Key Position::zobrist[2][8][64];
48 Key Position::zobEp[64];
49 Key Position::zobCastle[16];
50 Key Position::zobMaterial[2][8][16];
51 Key Position::zobSideToMove;
53 Value Position::MgPieceSquareTable[16][64];
54 Value Position::EgPieceSquareTable[16][64];
56 static bool RequestPending = false;
64 Position::Position(const Position& pos) {
68 Position::Position(const std::string& fen) {
73 /// Position::from_fen() initializes the position object with the given FEN
74 /// string. This function is not very robust - make sure that input FENs are
75 /// correct (this is assumed to be the responsibility of the GUI).
77 void Position::from_fen(const std::string& fen) {
79 static const std::string pieceLetters = "KQRBNPkqrbnp";
80 static const Piece pieces[] = { WK, WQ, WR, WB, WN, WP, BK, BQ, BR, BB, BN, BP };
88 for ( ; fen[i] != ' '; i++)
92 // Skip the given number of files
93 file += (fen[i] - '1' + 1);
96 else if (fen[i] == '/')
102 size_t idx = pieceLetters.find(fen[i]);
103 if (idx == std::string::npos)
105 std::cout << "Error in FEN at character " << i << std::endl;
108 Square square = make_square(file, rank);
109 put_piece(pieces[idx], square);
115 if (fen[i] != 'w' && fen[i] != 'b')
117 std::cout << "Error in FEN at character " << i << std::endl;
120 sideToMove = (fen[i] == 'w' ? WHITE : BLACK);
126 std::cout << "Error in FEN at character " << i << std::endl;
131 while(strchr("KQkqabcdefghABCDEFGH-", fen[i])) {
137 else if(fen[i] == 'K') allow_oo(WHITE);
138 else if(fen[i] == 'Q') allow_ooo(WHITE);
139 else if(fen[i] == 'k') allow_oo(BLACK);
140 else if(fen[i] == 'q') allow_ooo(BLACK);
141 else if(fen[i] >= 'A' && fen[i] <= 'H') {
142 File rookFile, kingFile = FILE_NONE;
143 for(Square square = SQ_B1; square <= SQ_G1; square++)
144 if(piece_on(square) == WK)
145 kingFile = square_file(square);
146 if(kingFile == FILE_NONE) {
147 std::cout << "Error in FEN at character " << i << std::endl;
150 initialKFile = kingFile;
151 rookFile = File(fen[i] - 'A') + FILE_A;
152 if(rookFile < initialKFile) {
154 initialQRFile = rookFile;
158 initialKRFile = rookFile;
161 else if(fen[i] >= 'a' && fen[i] <= 'h') {
162 File rookFile, kingFile = FILE_NONE;
163 for(Square square = SQ_B8; square <= SQ_G8; square++)
164 if(piece_on(square) == BK)
165 kingFile = square_file(square);
166 if(kingFile == FILE_NONE) {
167 std::cout << "Error in FEN at character " << i << std::endl;
170 initialKFile = kingFile;
171 rookFile = File(fen[i] - 'a') + FILE_A;
172 if(rookFile < initialKFile) {
174 initialQRFile = rookFile;
178 initialKRFile = rookFile;
182 std::cout << "Error in FEN at character " << i << std::endl;
189 while (fen[i] == ' ')
193 if ( i < fen.length() - 2
194 && (fen[i] >= 'a' && fen[i] <= 'h')
195 && (fen[i+1] == '3' || fen[i+1] == '6'))
196 st->epSquare = square_from_string(fen.substr(i, 2));
198 // Various initialisation
199 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
200 castleRightsMask[sq] = ALL_CASTLES;
202 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO|WHITE_OOO);
203 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO|BLACK_OOO);
204 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
205 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
206 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
207 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
211 st->key = compute_key();
212 st->pawnKey = compute_pawn_key();
213 st->materialKey = compute_material_key();
214 st->mgValue = compute_value<MidGame>();
215 st->egValue = compute_value<EndGame>();
216 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
217 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
221 /// Position::to_fen() converts the position object to a FEN string. This is
222 /// probably only useful for debugging.
224 const std::string Position::to_fen() const {
226 static const std::string pieceLetters = " PNBRQK pnbrqk";
230 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
233 for (File file = FILE_A; file <= FILE_H; file++)
235 Square sq = make_square(file, rank);
236 if (!square_is_occupied(sq))
242 fen += (char)skip + '0';
245 fen += pieceLetters[piece_on(sq)];
248 fen += (char)skip + '0';
250 fen += (rank > RANK_1 ? '/' : ' ');
252 fen += (sideToMove == WHITE ? "w " : "b ");
253 if (st->castleRights != NO_CASTLES)
255 if (can_castle_kingside(WHITE)) fen += 'K';
256 if (can_castle_queenside(WHITE)) fen += 'Q';
257 if (can_castle_kingside(BLACK)) fen += 'k';
258 if (can_castle_queenside(BLACK)) fen += 'q';
263 if (ep_square() != SQ_NONE)
264 fen += square_to_string(ep_square());
272 /// Position::print() prints an ASCII representation of the position to
273 /// the standard output. If a move is given then also the san is print.
275 void Position::print(Move m) const {
277 static const std::string pieceLetters = " PNBRQK PNBRQK .";
279 // Check for reentrancy, as example when called from inside
280 // MovePicker that is used also here in move_to_san()
284 RequestPending = true;
286 std::cout << std::endl;
289 std::string col = (color_of_piece_on(move_from(m)) == BLACK ? ".." : "");
290 std::cout << "Move is: " << col << move_to_san(*this, m) << std::endl;
292 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
294 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl;
295 for (File file = FILE_A; file <= FILE_H; file++)
297 Square sq = make_square(file, rank);
298 Piece piece = piece_on(sq);
299 if (piece == EMPTY && square_color(sq) == WHITE)
302 char col = (color_of_piece_on(sq) == BLACK ? '=' : ' ');
303 std::cout << '|' << col << pieceLetters[piece] << col;
305 std::cout << '|' << std::endl;
307 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl
308 << "Fen is: " << to_fen() << std::endl
309 << "Key is: " << st->key << std::endl;
311 RequestPending = false;
315 /// Position::copy() creates a copy of the input position.
317 void Position::copy(const Position &pos) {
319 memcpy(this, &pos, sizeof(Position));
323 /// Position:hidden_checkers<>() returns a bitboard of all pinned (against the
324 /// king) pieces for the given color and for the given pinner type. Or, when
325 /// template parameter FindPinned is false, the pieces of the given color
326 /// candidate for a discovery check against the enemy king.
327 /// Note that checkersBB bitboard must be already updated.
329 template<bool FindPinned>
330 Bitboard Position::hidden_checkers(Color c) const {
332 Bitboard pinners, result = EmptyBoardBB;
334 // Pinned pieces protect our king, dicovery checks attack
336 Square ksq = king_square(FindPinned ? c : opposite_color(c));
338 // Pinners are sliders, not checkers, that give check when
339 // candidate pinned is removed.
340 pinners = (rooks_and_queens(FindPinned ? opposite_color(c) : c) & RookPseudoAttacks[ksq])
341 | (bishops_and_queens(FindPinned ? opposite_color(c) : c) & BishopPseudoAttacks[ksq]);
343 if (FindPinned && pinners)
344 pinners &= ~st->checkersBB;
348 Square s = pop_1st_bit(&pinners);
349 Bitboard b = squares_between(s, ksq) & occupied_squares();
353 if ( !(b & (b - 1)) // Only one bit set?
354 && (b & pieces_of_color(c))) // Is an our piece?
361 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
362 /// king) pieces for the given color.
364 Bitboard Position::pinned_pieces(Color c) const {
366 return hidden_checkers<true>(c);
370 /// Position:discovered_check_candidates() returns a bitboard containing all
371 /// pieces for the given side which are candidates for giving a discovered
374 Bitboard Position::discovered_check_candidates(Color c) const {
376 return hidden_checkers<false>(c);
379 /// Position::attacks_to() computes a bitboard containing all pieces which
380 /// attacks a given square. There are two versions of this function: One
381 /// which finds attackers of both colors, and one which only finds the
382 /// attackers for one side.
384 Bitboard Position::attacks_to(Square s) const {
386 return (pawn_attacks(BLACK, s) & pawns(WHITE))
387 | (pawn_attacks(WHITE, s) & pawns(BLACK))
388 | (piece_attacks<KNIGHT>(s) & pieces_of_type(KNIGHT))
389 | (piece_attacks<ROOK>(s) & rooks_and_queens())
390 | (piece_attacks<BISHOP>(s) & bishops_and_queens())
391 | (piece_attacks<KING>(s) & pieces_of_type(KING));
394 /// Position::piece_attacks_square() tests whether the piece on square f
395 /// attacks square t.
397 bool Position::piece_attacks_square(Piece p, Square f, Square t) const {
399 assert(square_is_ok(f));
400 assert(square_is_ok(t));
404 case WP: return pawn_attacks_square(WHITE, f, t);
405 case BP: return pawn_attacks_square(BLACK, f, t);
406 case WN: case BN: return piece_attacks_square<KNIGHT>(f, t);
407 case WB: case BB: return piece_attacks_square<BISHOP>(f, t);
408 case WR: case BR: return piece_attacks_square<ROOK>(f, t);
409 case WQ: case BQ: return piece_attacks_square<QUEEN>(f, t);
410 case WK: case BK: return piece_attacks_square<KING>(f, t);
417 /// Position::move_attacks_square() tests whether a move from the current
418 /// position attacks a given square.
420 bool Position::move_attacks_square(Move m, Square s) const {
422 assert(move_is_ok(m));
423 assert(square_is_ok(s));
425 Square f = move_from(m), t = move_to(m);
427 assert(square_is_occupied(f));
429 if (piece_attacks_square(piece_on(f), t, s))
432 // Move the piece and scan for X-ray attacks behind it
433 Bitboard occ = occupied_squares();
434 Color us = color_of_piece_on(f);
437 Bitboard xray = ( (rook_attacks_bb(s, occ) & rooks_and_queens())
438 |(bishop_attacks_bb(s, occ) & bishops_and_queens())) & pieces_of_color(us);
440 // If we have attacks we need to verify that are caused by our move
441 // and are not already existent ones.
442 return xray && (xray ^ (xray & piece_attacks<QUEEN>(s)));
446 /// Position::find_checkers() computes the checkersBB bitboard, which
447 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
448 /// currently works by calling Position::attacks_to, which is probably
449 /// inefficient. Consider rewriting this function to use the last move
450 /// played, like in non-bitboard versions of Glaurung.
452 void Position::find_checkers() {
454 Color us = side_to_move();
455 st->checkersBB = attacks_to(king_square(us), opposite_color(us));
459 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
461 bool Position::pl_move_is_legal(Move m) const {
463 return 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()));
472 // If we're in check, all pseudo-legal moves are legal, because our
473 // check evasion generator only generates true legal moves.
477 // Castling moves are checked for legality during move generation.
478 if (move_is_castle(m))
481 Color us = side_to_move();
482 Square from = move_from(m);
483 Square ksq = king_square(us);
485 assert(color_of_piece_on(from) == us);
486 assert(piece_on(ksq) == piece_of_color_and_type(us, KING));
488 // En passant captures are a tricky special case. Because they are
489 // rather uncommon, we do it simply by testing whether the king is attacked
490 // after the move is made
493 Color them = opposite_color(us);
494 Square to = move_to(m);
495 Square capsq = make_square(square_file(to), square_rank(from));
496 Bitboard b = occupied_squares();
498 assert(to == ep_square());
499 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
500 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
501 assert(piece_on(to) == EMPTY);
504 clear_bit(&b, capsq);
507 return !(rook_attacks_bb(ksq, b) & rooks_and_queens(them))
508 && !(bishop_attacks_bb(ksq, b) & bishops_and_queens(them));
511 // If the moving piece is a king, check whether the destination
512 // square is attacked by the opponent.
514 return !(square_is_attacked(move_to(m), opposite_color(us)));
516 // A non-king move is legal if and only if it is not pinned or it
517 // is moving along the ray towards or away from the king.
519 || !bit_is_set(pinned, from)
520 || (direction_between_squares(from, ksq) == direction_between_squares(move_to(m), ksq)));
524 /// Position::move_is_check() tests whether a pseudo-legal move is a check
526 bool Position::move_is_check(Move m) const {
528 Bitboard dc = discovered_check_candidates(side_to_move());
529 return move_is_check(m, dc);
532 bool Position::move_is_check(Move m, Bitboard dcCandidates) const {
535 assert(move_is_ok(m));
536 assert(dcCandidates == discovered_check_candidates(side_to_move()));
538 Color us = side_to_move();
539 Color them = opposite_color(us);
540 Square from = move_from(m);
541 Square to = move_to(m);
542 Square ksq = king_square(them);
544 assert(color_of_piece_on(from) == us);
545 assert(piece_on(ksq) == piece_of_color_and_type(them, KING));
547 // Proceed according to the type of the moving piece
548 switch (type_of_piece_on(from))
552 if (bit_is_set(pawn_attacks(them, ksq), to)) // Normal check?
555 if ( bit_is_set(dcCandidates, from) // Discovered check?
556 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
559 if (move_promotion(m)) // Promotion with check?
561 Bitboard b = occupied_squares();
564 switch (move_promotion(m))
567 return bit_is_set(piece_attacks<KNIGHT>(to), ksq);
569 return bit_is_set(bishop_attacks_bb(to, b), ksq);
571 return bit_is_set(rook_attacks_bb(to, b), ksq);
573 return bit_is_set(queen_attacks_bb(to, b), ksq);
578 // En passant capture with check? We have already handled the case
579 // of direct checks and ordinary discovered check, the only case we
580 // need to handle is the unusual case of a discovered check through the
582 else if (move_is_ep(m))
584 Square capsq = make_square(square_file(to), square_rank(from));
585 Bitboard b = occupied_squares();
587 clear_bit(&b, capsq);
589 return (rook_attacks_bb(ksq, b) & rooks_and_queens(us))
590 ||(bishop_attacks_bb(ksq, b) & bishops_and_queens(us));
595 return bit_is_set(dcCandidates, from) // Discovered check?
596 || bit_is_set(piece_attacks<KNIGHT>(ksq), to); // Normal check?
599 return bit_is_set(dcCandidates, from) // Discovered check?
600 || bit_is_set(piece_attacks<BISHOP>(ksq), to); // Normal check?
603 return bit_is_set(dcCandidates, from) // Discovered check?
604 || bit_is_set(piece_attacks<ROOK>(ksq), to); // Normal check?
607 // Discovered checks are impossible!
608 assert(!bit_is_set(dcCandidates, from));
609 return bit_is_set(piece_attacks<QUEEN>(ksq), to); // Normal check?
613 if ( bit_is_set(dcCandidates, from)
614 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
617 // Castling with check?
618 if (move_is_castle(m))
620 Square kfrom, kto, rfrom, rto;
621 Bitboard b = occupied_squares();
627 kto = relative_square(us, SQ_G1);
628 rto = relative_square(us, SQ_F1);
630 kto = relative_square(us, SQ_C1);
631 rto = relative_square(us, SQ_D1);
633 clear_bit(&b, kfrom);
634 clear_bit(&b, rfrom);
637 return bit_is_set(rook_attacks_bb(rto, b), ksq);
641 default: // NO_PIECE_TYPE
649 /// Position::move_is_capture() tests whether a move from the current
650 /// position is a capture. Move must not be MOVE_NONE.
652 bool Position::move_is_capture(Move m) const {
654 assert(m != MOVE_NONE);
656 return ( !square_is_empty(move_to(m))
657 && (color_of_piece_on(move_to(m)) != color_of_piece_on(move_from(m)))
663 /// Position::update_checkers() udpates chekers info given the move. It is called
664 /// in do_move() and is faster then find_checkers().
666 template<PieceType Piece>
667 inline void Position::update_checkers(Bitboard* pCheckersBB, Square ksq, Square from,
668 Square to, Bitboard dcCandidates) {
670 const bool Bishop = (Piece == QUEEN || Piece == BISHOP);
671 const bool Rook = (Piece == QUEEN || Piece == ROOK);
672 const bool Slider = Bishop || Rook;
674 if ( ( (Bishop && bit_is_set(BishopPseudoAttacks[ksq], to))
675 || (Rook && bit_is_set(RookPseudoAttacks[ksq], to)))
676 && bit_is_set(piece_attacks<Piece>(ksq), to)) // slow, try to early skip
677 set_bit(pCheckersBB, to);
679 else if ( Piece != KING
681 && bit_is_set(piece_attacks<Piece>(ksq), to))
682 set_bit(pCheckersBB, to);
684 if (Piece != QUEEN && bit_is_set(dcCandidates, from))
687 (*pCheckersBB) |= (piece_attacks<ROOK>(ksq) & rooks_and_queens(side_to_move()));
690 (*pCheckersBB) |= (piece_attacks<BISHOP>(ksq) & bishops_and_queens(side_to_move()));
695 /// Position::do_move() makes a move, and saves all information necessary
696 /// to a StateInfo object. The move is assumed to be legal.
697 /// Pseudo-legal moves should be filtered out before this function is called.
699 void Position::do_move(Move m, StateInfo& newSt) {
701 do_move(m, newSt, discovered_check_candidates(side_to_move()));
704 void Position::do_move(Move m, StateInfo& newSt, Bitboard dcCandidates) {
707 assert(move_is_ok(m));
709 // Copy some fields of old state to our new StateInfo object except the
710 // ones which are recalculated from scratch anyway, then switch our state
711 // pointer to point to the new, ready to be updated, state.
712 struct ReducedStateInfo {
713 Key key, pawnKey, materialKey;
714 int castleRights, rule50;
716 Value mgValue, egValue;
719 memcpy(&newSt, st, sizeof(ReducedStateInfo));
720 newSt.capture = NO_PIECE_TYPE;
724 // Save the current key to the history[] array, in order to be able to
725 // detect repetition draws.
726 history[gamePly] = st->key;
728 // Increment the 50 moves rule draw counter. Resetting it to zero in the
729 // case of non-reversible moves is taken care of later.
732 if (move_is_castle(m))
734 else if (move_promotion(m))
735 do_promotion_move(m);
736 else if (move_is_ep(m))
740 Color us = side_to_move();
741 Color them = opposite_color(us);
742 Square from = move_from(m);
743 Square to = move_to(m);
745 assert(color_of_piece_on(from) == us);
746 assert(color_of_piece_on(to) == them || piece_on(to) == EMPTY);
748 PieceType piece = type_of_piece_on(from);
750 st->capture = type_of_piece_on(to);
753 do_capture_move(m, st->capture, them, to);
756 clear_bit(&(byColorBB[us]), from);
757 clear_bit(&(byTypeBB[piece]), from);
758 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
759 set_bit(&(byColorBB[us]), to);
760 set_bit(&(byTypeBB[piece]), to);
761 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
762 board[to] = board[from];
766 st->key ^= zobrist[us][piece][from] ^ zobrist[us][piece][to];
768 // Update incremental scores
769 st->mgValue -= pst<MidGame>(us, piece, from);
770 st->mgValue += pst<MidGame>(us, piece, to);
771 st->egValue -= pst<EndGame>(us, piece, from);
772 st->egValue += pst<EndGame>(us, piece, to);
774 // If the moving piece was a king, update the king square
778 // Reset en passant square
779 if (st->epSquare != SQ_NONE)
781 st->key ^= zobEp[st->epSquare];
782 st->epSquare = SQ_NONE;
785 // If the moving piece was a pawn do some special extra work
788 // Reset rule 50 draw counter
791 // Update pawn hash key
792 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
794 // Set en passant square, only if moved pawn can be captured
795 if (abs(int(to) - int(from)) == 16)
797 if ( (us == WHITE && (pawn_attacks(WHITE, from + DELTA_N) & pawns(BLACK)))
798 || (us == BLACK && (pawn_attacks(BLACK, from + DELTA_S) & pawns(WHITE))))
800 st->epSquare = Square((int(from) + int(to)) / 2);
801 st->key ^= zobEp[st->epSquare];
806 // Update piece lists
807 pieceList[us][piece][index[from]] = to;
808 index[to] = index[from];
810 // Update castle rights
811 st->key ^= zobCastle[st->castleRights];
812 st->castleRights &= castleRightsMask[from];
813 st->castleRights &= castleRightsMask[to];
814 st->key ^= zobCastle[st->castleRights];
816 // Update checkers bitboard, piece must be already moved
817 st->checkersBB = EmptyBoardBB;
818 Square ksq = king_square(them);
821 case PAWN: update_checkers<PAWN>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
822 case KNIGHT: update_checkers<KNIGHT>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
823 case BISHOP: update_checkers<BISHOP>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
824 case ROOK: update_checkers<ROOK>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
825 case QUEEN: update_checkers<QUEEN>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
826 case KING: update_checkers<KING>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
827 default: assert(false); break;
832 st->key ^= zobSideToMove;
833 sideToMove = opposite_color(sideToMove);
836 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
837 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
843 /// Position::do_capture_move() is a private method used to update captured
844 /// piece info. It is called from the main Position::do_move function.
846 void Position::do_capture_move(Move m, PieceType capture, Color them, Square to) {
848 assert(capture != KING);
850 // Remove captured piece
851 clear_bit(&(byColorBB[them]), to);
852 clear_bit(&(byTypeBB[capture]), to);
855 st->key ^= zobrist[them][capture][to];
857 // If the captured piece was a pawn, update pawn hash key
859 st->pawnKey ^= zobrist[them][PAWN][to];
861 // Update incremental scores
862 st->mgValue -= pst<MidGame>(them, capture, to);
863 st->egValue -= pst<EndGame>(them, capture, to);
865 assert(!move_promotion(m) || capture != PAWN);
869 npMaterial[them] -= piece_value_midgame(capture);
871 // Update material hash key
872 st->materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];
874 // Update piece count
875 pieceCount[them][capture]--;
878 pieceList[them][capture][index[to]] = pieceList[them][capture][pieceCount[them][capture]];
879 index[pieceList[them][capture][index[to]]] = index[to];
881 // Reset rule 50 counter
886 /// Position::do_castle_move() is a private method used to make a castling
887 /// move. It is called from the main Position::do_move function. Note that
888 /// castling moves are encoded as "king captures friendly rook" moves, for
889 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
891 void Position::do_castle_move(Move m) {
894 assert(move_is_ok(m));
895 assert(move_is_castle(m));
897 Color us = side_to_move();
898 Color them = opposite_color(us);
900 // Find source squares for king and rook
901 Square kfrom = move_from(m);
902 Square rfrom = move_to(m); // HACK: See comment at beginning of function
905 assert(piece_on(kfrom) == piece_of_color_and_type(us, KING));
906 assert(piece_on(rfrom) == piece_of_color_and_type(us, ROOK));
908 // Find destination squares for king and rook
909 if (rfrom > kfrom) // O-O
911 kto = relative_square(us, SQ_G1);
912 rto = relative_square(us, SQ_F1);
914 kto = relative_square(us, SQ_C1);
915 rto = relative_square(us, SQ_D1);
918 // Remove pieces from source squares
919 clear_bit(&(byColorBB[us]), kfrom);
920 clear_bit(&(byTypeBB[KING]), kfrom);
921 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
922 clear_bit(&(byColorBB[us]), rfrom);
923 clear_bit(&(byTypeBB[ROOK]), rfrom);
924 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
926 // Put pieces on destination squares
927 set_bit(&(byColorBB[us]), kto);
928 set_bit(&(byTypeBB[KING]), kto);
929 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
930 set_bit(&(byColorBB[us]), rto);
931 set_bit(&(byTypeBB[ROOK]), rto);
932 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
934 // Update board array
935 board[kfrom] = board[rfrom] = EMPTY;
936 board[kto] = piece_of_color_and_type(us, KING);
937 board[rto] = piece_of_color_and_type(us, ROOK);
939 // Update king square
940 kingSquare[us] = kto;
942 // Update piece lists
943 pieceList[us][KING][index[kfrom]] = kto;
944 pieceList[us][ROOK][index[rfrom]] = rto;
945 int tmp = index[rfrom];
946 index[kto] = index[kfrom];
949 // Update incremental scores
950 st->mgValue -= pst<MidGame>(us, KING, kfrom);
951 st->mgValue += pst<MidGame>(us, KING, kto);
952 st->egValue -= pst<EndGame>(us, KING, kfrom);
953 st->egValue += pst<EndGame>(us, KING, kto);
954 st->mgValue -= pst<MidGame>(us, ROOK, rfrom);
955 st->mgValue += pst<MidGame>(us, ROOK, rto);
956 st->egValue -= pst<EndGame>(us, ROOK, rfrom);
957 st->egValue += pst<EndGame>(us, ROOK, rto);
960 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
961 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
963 // Clear en passant square
964 if (st->epSquare != SQ_NONE)
966 st->key ^= zobEp[st->epSquare];
967 st->epSquare = SQ_NONE;
970 // Update castling rights
971 st->key ^= zobCastle[st->castleRights];
972 st->castleRights &= castleRightsMask[kfrom];
973 st->key ^= zobCastle[st->castleRights];
975 // Reset rule 50 counter
978 // Update checkers BB
979 st->checkersBB = attacks_to(king_square(them), us);
983 /// Position::do_promotion_move() is a private method used to make a promotion
984 /// move. It is called from the main Position::do_move function.
986 void Position::do_promotion_move(Move m) {
993 assert(move_is_ok(m));
994 assert(move_promotion(m));
997 them = opposite_color(us);
1001 assert(relative_rank(us, to) == RANK_8);
1002 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
1003 assert(color_of_piece_on(to) == them || square_is_empty(to));
1005 st->capture = type_of_piece_on(to);
1008 do_capture_move(m, st->capture, them, to);
1011 clear_bit(&(byColorBB[us]), from);
1012 clear_bit(&(byTypeBB[PAWN]), from);
1013 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1014 board[from] = EMPTY;
1016 // Insert promoted piece
1017 promotion = move_promotion(m);
1018 assert(promotion >= KNIGHT && promotion <= QUEEN);
1019 set_bit(&(byColorBB[us]), to);
1020 set_bit(&(byTypeBB[promotion]), to);
1021 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1022 board[to] = piece_of_color_and_type(us, promotion);
1025 st->key ^= zobrist[us][PAWN][from] ^ zobrist[us][promotion][to];
1027 // Update pawn hash key
1028 st->pawnKey ^= zobrist[us][PAWN][from];
1030 // Update material key
1031 st->materialKey ^= zobMaterial[us][PAWN][pieceCount[us][PAWN]];
1032 st->materialKey ^= zobMaterial[us][promotion][pieceCount[us][promotion]+1];
1034 // Update piece counts
1035 pieceCount[us][PAWN]--;
1036 pieceCount[us][promotion]++;
1038 // Update piece lists
1039 pieceList[us][PAWN][index[from]] = pieceList[us][PAWN][pieceCount[us][PAWN]];
1040 index[pieceList[us][PAWN][index[from]]] = index[from];
1041 pieceList[us][promotion][pieceCount[us][promotion] - 1] = to;
1042 index[to] = pieceCount[us][promotion] - 1;
1044 // Update incremental scores
1045 st->mgValue -= pst<MidGame>(us, PAWN, from);
1046 st->mgValue += pst<MidGame>(us, promotion, to);
1047 st->egValue -= pst<EndGame>(us, PAWN, from);
1048 st->egValue += pst<EndGame>(us, promotion, to);
1051 npMaterial[us] += piece_value_midgame(promotion);
1053 // Clear the en passant square
1054 if (st->epSquare != SQ_NONE)
1056 st->key ^= zobEp[st->epSquare];
1057 st->epSquare = SQ_NONE;
1060 // Update castle rights
1061 st->key ^= zobCastle[st->castleRights];
1062 st->castleRights &= castleRightsMask[to];
1063 st->key ^= zobCastle[st->castleRights];
1065 // Reset rule 50 counter
1068 // Update checkers BB
1069 st->checkersBB = attacks_to(king_square(them), us);
1073 /// Position::do_ep_move() is a private method used to make an en passant
1074 /// capture. It is called from the main Position::do_move function.
1076 void Position::do_ep_move(Move m) {
1079 Square from, to, capsq;
1082 assert(move_is_ok(m));
1083 assert(move_is_ep(m));
1085 us = side_to_move();
1086 them = opposite_color(us);
1087 from = move_from(m);
1089 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1091 assert(to == st->epSquare);
1092 assert(relative_rank(us, to) == RANK_6);
1093 assert(piece_on(to) == EMPTY);
1094 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
1095 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
1097 // Remove captured piece
1098 clear_bit(&(byColorBB[them]), capsq);
1099 clear_bit(&(byTypeBB[PAWN]), capsq);
1100 clear_bit(&(byTypeBB[0]), capsq); // HACK: byTypeBB[0] == occupied squares
1101 board[capsq] = EMPTY;
1103 // Remove moving piece from source square
1104 clear_bit(&(byColorBB[us]), from);
1105 clear_bit(&(byTypeBB[PAWN]), from);
1106 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1108 // Put moving piece on destination square
1109 set_bit(&(byColorBB[us]), to);
1110 set_bit(&(byTypeBB[PAWN]), to);
1111 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1112 board[to] = board[from];
1113 board[from] = EMPTY;
1115 // Update material hash key
1116 st->materialKey ^= zobMaterial[them][PAWN][pieceCount[them][PAWN]];
1118 // Update piece count
1119 pieceCount[them][PAWN]--;
1121 // Update piece list
1122 pieceList[us][PAWN][index[from]] = to;
1123 index[to] = index[from];
1124 pieceList[them][PAWN][index[capsq]] = pieceList[them][PAWN][pieceCount[them][PAWN]];
1125 index[pieceList[them][PAWN][index[capsq]]] = index[capsq];
1128 st->key ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1129 st->key ^= zobrist[them][PAWN][capsq];
1130 st->key ^= zobEp[st->epSquare];
1132 // Update pawn hash key
1133 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1134 st->pawnKey ^= zobrist[them][PAWN][capsq];
1136 // Update incremental scores
1137 st->mgValue -= pst<MidGame>(them, PAWN, capsq);
1138 st->mgValue -= pst<MidGame>(us, PAWN, from);
1139 st->mgValue += pst<MidGame>(us, PAWN, to);
1140 st->egValue -= pst<EndGame>(them, PAWN, capsq);
1141 st->egValue -= pst<EndGame>(us, PAWN, from);
1142 st->egValue += pst<EndGame>(us, PAWN, to);
1144 // Reset en passant square
1145 st->epSquare = SQ_NONE;
1147 // Reset rule 50 counter
1150 // Update checkers BB
1151 st->checkersBB = attacks_to(king_square(them), us);
1155 /// Position::undo_move() unmakes a move. When it returns, the position should
1156 /// be restored to exactly the same state as before the move was made.
1158 void Position::undo_move(Move m) {
1161 assert(move_is_ok(m));
1164 sideToMove = opposite_color(sideToMove);
1166 if (move_is_castle(m))
1167 undo_castle_move(m);
1168 else if (move_promotion(m))
1169 undo_promotion_move(m);
1170 else if (move_is_ep(m))
1178 us = side_to_move();
1179 them = opposite_color(us);
1180 from = move_from(m);
1183 assert(piece_on(from) == EMPTY);
1184 assert(color_of_piece_on(to) == us);
1186 // Put the piece back at the source square
1187 piece = type_of_piece_on(to);
1188 set_bit(&(byColorBB[us]), from);
1189 set_bit(&(byTypeBB[piece]), from);
1190 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1191 board[from] = piece_of_color_and_type(us, piece);
1193 // Clear the destination square
1194 clear_bit(&(byColorBB[us]), to);
1195 clear_bit(&(byTypeBB[piece]), to);
1196 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1198 // If the moving piece was a king, update the king square
1200 kingSquare[us] = from;
1202 // Update piece list
1203 pieceList[us][piece][index[to]] = from;
1204 index[from] = index[to];
1208 assert(st->capture != KING);
1210 // Replace the captured piece
1211 set_bit(&(byColorBB[them]), to);
1212 set_bit(&(byTypeBB[st->capture]), to);
1213 set_bit(&(byTypeBB[0]), to);
1214 board[to] = piece_of_color_and_type(them, st->capture);
1217 if (st->capture != PAWN)
1218 npMaterial[them] += piece_value_midgame(st->capture);
1220 // Update piece list
1221 pieceList[them][st->capture][pieceCount[them][st->capture]] = to;
1222 index[to] = pieceCount[them][st->capture];
1224 // Update piece count
1225 pieceCount[them][st->capture]++;
1230 // Finally point our state pointer back to the previous state
1237 /// Position::undo_castle_move() is a private method used to unmake a castling
1238 /// move. It is called from the main Position::undo_move function. Note that
1239 /// castling moves are encoded as "king captures friendly rook" moves, for
1240 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1242 void Position::undo_castle_move(Move m) {
1244 assert(move_is_ok(m));
1245 assert(move_is_castle(m));
1247 // When we have arrived here, some work has already been done by
1248 // Position::undo_move. In particular, the side to move has been switched,
1249 // so the code below is correct.
1250 Color us = side_to_move();
1252 // Find source squares for king and rook
1253 Square kfrom = move_from(m);
1254 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1257 // Find destination squares for king and rook
1258 if (rfrom > kfrom) // O-O
1260 kto = relative_square(us, SQ_G1);
1261 rto = relative_square(us, SQ_F1);
1263 kto = relative_square(us, SQ_C1);
1264 rto = relative_square(us, SQ_D1);
1267 assert(piece_on(kto) == piece_of_color_and_type(us, KING));
1268 assert(piece_on(rto) == piece_of_color_and_type(us, ROOK));
1270 // Remove pieces from destination squares
1271 clear_bit(&(byColorBB[us]), kto);
1272 clear_bit(&(byTypeBB[KING]), kto);
1273 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1274 clear_bit(&(byColorBB[us]), rto);
1275 clear_bit(&(byTypeBB[ROOK]), rto);
1276 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1278 // Put pieces on source squares
1279 set_bit(&(byColorBB[us]), kfrom);
1280 set_bit(&(byTypeBB[KING]), kfrom);
1281 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1282 set_bit(&(byColorBB[us]), rfrom);
1283 set_bit(&(byTypeBB[ROOK]), rfrom);
1284 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1287 board[rto] = board[kto] = EMPTY;
1288 board[rfrom] = piece_of_color_and_type(us, ROOK);
1289 board[kfrom] = piece_of_color_and_type(us, KING);
1291 // Update king square
1292 kingSquare[us] = kfrom;
1294 // Update piece lists
1295 pieceList[us][KING][index[kto]] = kfrom;
1296 pieceList[us][ROOK][index[rto]] = rfrom;
1297 int tmp = index[rto]; // Necessary because we may have rto == kfrom in FRC.
1298 index[kfrom] = index[kto];
1303 /// Position::undo_promotion_move() is a private method used to unmake a
1304 /// promotion move. It is called from the main Position::do_move
1307 void Position::undo_promotion_move(Move m) {
1311 PieceType promotion;
1313 assert(move_is_ok(m));
1314 assert(move_promotion(m));
1316 // When we have arrived here, some work has already been done by
1317 // Position::undo_move. In particular, the side to move has been switched,
1318 // so the code below is correct.
1319 us = side_to_move();
1320 them = opposite_color(us);
1321 from = move_from(m);
1324 assert(relative_rank(us, to) == RANK_8);
1325 assert(piece_on(from) == EMPTY);
1327 // Remove promoted piece
1328 promotion = move_promotion(m);
1329 assert(piece_on(to)==piece_of_color_and_type(us, promotion));
1330 assert(promotion >= KNIGHT && promotion <= QUEEN);
1331 clear_bit(&(byColorBB[us]), to);
1332 clear_bit(&(byTypeBB[promotion]), to);
1333 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1335 // Insert pawn at source square
1336 set_bit(&(byColorBB[us]), from);
1337 set_bit(&(byTypeBB[PAWN]), from);
1338 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1339 board[from] = piece_of_color_and_type(us, PAWN);
1342 npMaterial[us] -= piece_value_midgame(promotion);
1344 // Update piece list
1345 pieceList[us][PAWN][pieceCount[us][PAWN]] = from;
1346 index[from] = pieceCount[us][PAWN];
1347 pieceList[us][promotion][index[to]] =
1348 pieceList[us][promotion][pieceCount[us][promotion] - 1];
1349 index[pieceList[us][promotion][index[to]]] = index[to];
1351 // Update piece counts
1352 pieceCount[us][promotion]--;
1353 pieceCount[us][PAWN]++;
1357 assert(st->capture != KING);
1359 // Insert captured piece:
1360 set_bit(&(byColorBB[them]), to);
1361 set_bit(&(byTypeBB[st->capture]), to);
1362 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1363 board[to] = piece_of_color_and_type(them, st->capture);
1365 // Update material. Because the move is a promotion move, we know
1366 // that the captured piece cannot be a pawn.
1367 assert(st->capture != PAWN);
1368 npMaterial[them] += piece_value_midgame(st->capture);
1370 // Update piece list
1371 pieceList[them][st->capture][pieceCount[them][st->capture]] = to;
1372 index[to] = pieceCount[them][st->capture];
1374 // Update piece count
1375 pieceCount[them][st->capture]++;
1381 /// Position::undo_ep_move() is a private method used to unmake an en passant
1382 /// capture. It is called from the main Position::undo_move function.
1384 void Position::undo_ep_move(Move m) {
1386 assert(move_is_ok(m));
1387 assert(move_is_ep(m));
1389 // When we have arrived here, some work has already been done by
1390 // Position::undo_move. In particular, the side to move has been switched,
1391 // so the code below is correct.
1392 Color us = side_to_move();
1393 Color them = opposite_color(us);
1394 Square from = move_from(m);
1395 Square to = move_to(m);
1396 Square capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1398 assert(to == st->previous->epSquare);
1399 assert(relative_rank(us, to) == RANK_6);
1400 assert(piece_on(to) == piece_of_color_and_type(us, PAWN));
1401 assert(piece_on(from) == EMPTY);
1402 assert(piece_on(capsq) == EMPTY);
1404 // Replace captured piece
1405 set_bit(&(byColorBB[them]), capsq);
1406 set_bit(&(byTypeBB[PAWN]), capsq);
1407 set_bit(&(byTypeBB[0]), capsq);
1408 board[capsq] = piece_of_color_and_type(them, PAWN);
1410 // Remove moving piece from destination square
1411 clear_bit(&(byColorBB[us]), to);
1412 clear_bit(&(byTypeBB[PAWN]), to);
1413 clear_bit(&(byTypeBB[0]), to);
1416 // Replace moving piece at source square
1417 set_bit(&(byColorBB[us]), from);
1418 set_bit(&(byTypeBB[PAWN]), from);
1419 set_bit(&(byTypeBB[0]), from);
1420 board[from] = piece_of_color_and_type(us, PAWN);
1422 // Update piece list:
1423 pieceList[us][PAWN][index[to]] = from;
1424 index[from] = index[to];
1425 pieceList[them][PAWN][pieceCount[them][PAWN]] = capsq;
1426 index[capsq] = pieceCount[them][PAWN];
1428 // Update piece count:
1429 pieceCount[them][PAWN]++;
1433 /// Position::do_null_move makes() a "null move": It switches the side to move
1434 /// and updates the hash key without executing any move on the board.
1436 void Position::do_null_move(StateInfo& backupSt) {
1439 assert(!is_check());
1441 // Back up the information necessary to undo the null move to the supplied
1442 // StateInfo object. In the case of a null move, the only thing we need to
1443 // remember is the last move made and the en passant square.
1444 // Note that differently from normal case here backupSt is actually used as
1445 // a backup storage not as a new state to be used.
1446 backupSt.lastMove = st->lastMove;
1447 backupSt.epSquare = st->epSquare;
1448 backupSt.previous = st->previous;
1449 st->previous = &backupSt;
1451 // Save the current key to the history[] array, in order to be able to
1452 // detect repetition draws.
1453 history[gamePly] = st->key;
1455 // Update the necessary information
1456 sideToMove = opposite_color(sideToMove);
1457 if (st->epSquare != SQ_NONE)
1458 st->key ^= zobEp[st->epSquare];
1460 st->epSquare = SQ_NONE;
1463 st->key ^= zobSideToMove;
1465 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1466 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1472 /// Position::undo_null_move() unmakes a "null move".
1474 void Position::undo_null_move() {
1477 assert(!is_check());
1479 // Restore information from the our backup StateInfo object
1480 st->lastMove = st->previous->lastMove;
1481 st->epSquare = st->previous->epSquare;
1482 st->previous = st->previous->previous;
1484 if (st->epSquare != SQ_NONE)
1485 st->key ^= zobEp[st->epSquare];
1487 // Update the necessary information
1488 sideToMove = opposite_color(sideToMove);
1491 st->key ^= zobSideToMove;
1493 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1494 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1500 /// Position::see() is a static exchange evaluator: It tries to estimate the
1501 /// material gain or loss resulting from a move. There are three versions of
1502 /// this function: One which takes a destination square as input, one takes a
1503 /// move, and one which takes a 'from' and a 'to' square. The function does
1504 /// not yet understand promotions captures.
1506 int Position::see(Square to) const {
1508 assert(square_is_ok(to));
1509 return see(SQ_NONE, to);
1512 int Position::see(Move m) const {
1514 assert(move_is_ok(m));
1515 return see(move_from(m), move_to(m));
1518 int Position::see(Square from, Square to) const {
1521 static const int seeValues[18] = {
1522 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1523 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1524 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1525 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1529 Bitboard attackers, occ, b;
1531 assert(square_is_ok(from) || from == SQ_NONE);
1532 assert(square_is_ok(to));
1534 // Initialize colors
1535 Color us = (from != SQ_NONE ? color_of_piece_on(from) : opposite_color(color_of_piece_on(to)));
1536 Color them = opposite_color(us);
1538 // Initialize pieces
1539 Piece piece = piece_on(from);
1540 Piece capture = piece_on(to);
1542 // Find all attackers to the destination square, with the moving piece
1543 // removed, but possibly an X-ray attacker added behind it.
1544 occ = occupied_squares();
1546 // Handle en passant moves
1547 if (st->epSquare == to && type_of_piece_on(from) == PAWN)
1549 assert(capture == EMPTY);
1551 Square capQq = (side_to_move() == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1552 capture = piece_on(capQq);
1554 assert(type_of_piece_on(capQq) == PAWN);
1556 // Remove the captured pawn
1557 clear_bit(&occ, capQq);
1562 clear_bit(&occ, from);
1563 attackers = (rook_attacks_bb(to, occ) & rooks_and_queens())
1564 | (bishop_attacks_bb(to, occ) & bishops_and_queens())
1565 | (piece_attacks<KNIGHT>(to) & knights())
1566 | (piece_attacks<KING>(to) & kings())
1567 | (pawn_attacks(WHITE, to) & pawns(BLACK))
1568 | (pawn_attacks(BLACK, to) & pawns(WHITE));
1570 if (from != SQ_NONE)
1573 // If we don't have any attacker we are finished
1574 if ((attackers & pieces_of_color(us)) == EmptyBoardBB)
1577 // Locate the least valuable attacker to the destination square
1578 // and use it to initialize from square.
1580 for (pt = PAWN; !(attackers & pieces_of_color_and_type(us, pt)); pt++)
1583 from = first_1(attackers & pieces_of_color_and_type(us, pt));
1584 piece = piece_on(from);
1587 // If the opponent has no attackers we are finished
1588 if ((attackers & pieces_of_color(them)) == EmptyBoardBB)
1589 return seeValues[capture];
1591 attackers &= occ; // Remove the moving piece
1593 // The destination square is defended, which makes things rather more
1594 // difficult to compute. We proceed by building up a "swap list" containing
1595 // the material gain or loss at each stop in a sequence of captures to the
1596 // destination square, where the sides alternately capture, and always
1597 // capture with the least valuable piece. After each capture, we look for
1598 // new X-ray attacks from behind the capturing piece.
1599 int lastCapturingPieceValue = seeValues[piece];
1600 int swapList[32], n = 1;
1604 swapList[0] = seeValues[capture];
1607 // Locate the least valuable attacker for the side to move. The loop
1608 // below looks like it is potentially infinite, but it isn't. We know
1609 // that the side to move still has at least one attacker left.
1610 for (pt = PAWN; !(attackers & pieces_of_color_and_type(c, pt)); pt++)
1613 // Remove the attacker we just found from the 'attackers' bitboard,
1614 // and scan for new X-ray attacks behind the attacker.
1615 b = attackers & pieces_of_color_and_type(c, pt);
1617 attackers |= (rook_attacks_bb(to, occ) & rooks_and_queens())
1618 | (bishop_attacks_bb(to, occ) & bishops_and_queens());
1622 // Add the new entry to the swap list
1624 swapList[n] = -swapList[n - 1] + lastCapturingPieceValue;
1627 // Remember the value of the capturing piece, and change the side to move
1628 // before beginning the next iteration
1629 lastCapturingPieceValue = seeValues[pt];
1630 c = opposite_color(c);
1632 // Stop after a king capture
1633 if (pt == KING && (attackers & pieces_of_color(c)))
1636 swapList[n++] = 100;
1639 } while (attackers & pieces_of_color(c));
1641 // Having built the swap list, we negamax through it to find the best
1642 // achievable score from the point of view of the side to move
1644 swapList[n-1] = Min(-swapList[n], swapList[n-1]);
1650 /// Position::setStartState() copies the content of the argument
1651 /// inside startState and makes st point to it. This is needed
1652 /// when the st pointee could become stale, as example because
1653 /// the caller is about to going out of scope.
1655 void Position::setStartState(const StateInfo& s) {
1662 /// Position::clear() erases the position object to a pristine state, with an
1663 /// empty board, white to move, and no castling rights.
1665 void Position::clear() {
1668 memset(st, 0, sizeof(StateInfo));
1669 st->epSquare = SQ_NONE;
1671 memset(index, 0, sizeof(int) * 64);
1672 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1674 for (int i = 0; i < 64; i++)
1677 for (int i = 0; i < 7; i++)
1679 byTypeBB[i] = EmptyBoardBB;
1680 pieceCount[0][i] = pieceCount[1][i] = 0;
1681 for (int j = 0; j < 8; j++)
1682 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1687 initialKFile = FILE_E;
1688 initialKRFile = FILE_H;
1689 initialQRFile = FILE_A;
1693 /// Position::reset_game_ply() simply sets gamePly to 0. It is used from the
1694 /// UCI interface code, whenever a non-reversible move is made in a
1695 /// 'position fen <fen> moves m1 m2 ...' command. This makes it possible
1696 /// for the program to handle games of arbitrary length, as long as the GUI
1697 /// handles draws by the 50 move rule correctly.
1699 void Position::reset_game_ply() {
1705 /// Position::put_piece() puts a piece on the given square of the board,
1706 /// updating the board array, bitboards, and piece counts.
1708 void Position::put_piece(Piece p, Square s) {
1710 Color c = color_of_piece(p);
1711 PieceType pt = type_of_piece(p);
1714 index[s] = pieceCount[c][pt];
1715 pieceList[c][pt][index[s]] = s;
1717 set_bit(&(byTypeBB[pt]), s);
1718 set_bit(&(byColorBB[c]), s);
1719 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1721 pieceCount[c][pt]++;
1728 /// Position::allow_oo() gives the given side the right to castle kingside.
1729 /// Used when setting castling rights during parsing of FEN strings.
1731 void Position::allow_oo(Color c) {
1733 st->castleRights |= (1 + int(c));
1737 /// Position::allow_ooo() gives the given side the right to castle queenside.
1738 /// Used when setting castling rights during parsing of FEN strings.
1740 void Position::allow_ooo(Color c) {
1742 st->castleRights |= (4 + 4*int(c));
1746 /// Position::compute_key() computes the hash key of the position. The hash
1747 /// key is usually updated incrementally as moves are made and unmade, the
1748 /// compute_key() function is only used when a new position is set up, and
1749 /// to verify the correctness of the hash key when running in debug mode.
1751 Key Position::compute_key() const {
1753 Key result = Key(0ULL);
1755 for (Square s = SQ_A1; s <= SQ_H8; s++)
1756 if (square_is_occupied(s))
1757 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1759 if (ep_square() != SQ_NONE)
1760 result ^= zobEp[ep_square()];
1762 result ^= zobCastle[st->castleRights];
1763 if (side_to_move() == BLACK)
1764 result ^= zobSideToMove;
1770 /// Position::compute_pawn_key() computes the hash key of the position. The
1771 /// hash key is usually updated incrementally as moves are made and unmade,
1772 /// the compute_pawn_key() function is only used when a new position is set
1773 /// up, and to verify the correctness of the pawn hash key when running in
1776 Key Position::compute_pawn_key() const {
1778 Key result = Key(0ULL);
1782 for (Color c = WHITE; c <= BLACK; c++)
1787 s = pop_1st_bit(&b);
1788 result ^= zobrist[c][PAWN][s];
1795 /// Position::compute_material_key() computes the hash key of the position.
1796 /// The hash key is usually updated incrementally as moves are made and unmade,
1797 /// the compute_material_key() function is only used when a new position is set
1798 /// up, and to verify the correctness of the material hash key when running in
1801 Key Position::compute_material_key() const {
1803 Key result = Key(0ULL);
1804 for (Color c = WHITE; c <= BLACK; c++)
1805 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1807 int count = piece_count(c, pt);
1808 for (int i = 0; i <= count; i++)
1809 result ^= zobMaterial[c][pt][i];
1815 /// Position::compute_value() compute the incremental scores for the middle
1816 /// game and the endgame. These functions are used to initialize the incremental
1817 /// scores when a new position is set up, and to verify that the scores are correctly
1818 /// updated by do_move and undo_move when the program is running in debug mode.
1819 template<Position::GamePhase Phase>
1820 Value Position::compute_value() const {
1822 Value result = Value(0);
1826 for (Color c = WHITE; c <= BLACK; c++)
1827 for (PieceType pt = PAWN; pt <= KING; pt++)
1829 b = pieces_of_color_and_type(c, pt);
1832 s = pop_1st_bit(&b);
1833 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1834 result += pst<Phase>(c, pt, s);
1838 const Value TempoValue = (Phase == MidGame ? TempoValueMidgame : TempoValueEndgame);
1839 result += (side_to_move() == WHITE)? TempoValue / 2 : -TempoValue / 2;
1844 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1845 /// game material score for the given side. Material scores are updated
1846 /// incrementally during the search, this function is only used while
1847 /// initializing a new Position object.
1849 Value Position::compute_non_pawn_material(Color c) const {
1851 Value result = Value(0);
1854 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1856 Bitboard b = pieces_of_color_and_type(c, pt);
1859 s = pop_1st_bit(&b);
1860 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1861 result += piece_value_midgame(pt);
1868 /// Position::is_mate() returns true or false depending on whether the
1869 /// side to move is checkmated. Note that this function is currently very
1870 /// slow, and shouldn't be used frequently inside the search.
1872 bool Position::is_mate() const {
1876 MovePicker mp = MovePicker(*this, false, MOVE_NONE, EmptySearchStack, Depth(0));
1877 return mp.get_next_move() == MOVE_NONE;
1883 /// Position::is_draw() tests whether the position is drawn by material,
1884 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1885 /// must be done by the search.
1887 bool Position::is_draw() const {
1889 // Draw by material?
1891 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1894 // Draw by the 50 moves rule?
1895 if (st->rule50 > 100 || (st->rule50 == 100 && !is_check()))
1898 // Draw by repetition?
1899 for (int i = 2; i < Min(gamePly, st->rule50); i += 2)
1900 if (history[gamePly - i] == st->key)
1907 /// Position::has_mate_threat() tests whether a given color has a mate in one
1908 /// from the current position. This function is quite slow, but it doesn't
1909 /// matter, because it is currently only called from PV nodes, which are rare.
1911 bool Position::has_mate_threat(Color c) {
1914 Color stm = side_to_move();
1916 // The following lines are useless and silly, but prevents gcc from
1917 // emitting a stupid warning stating that u1.lastMove and u1.epSquare might
1918 // be used uninitialized.
1919 st1.lastMove = st->lastMove;
1920 st1.epSquare = st->epSquare;
1925 // If the input color is not equal to the side to move, do a null move
1929 MoveStack mlist[120];
1931 bool result = false;
1933 // Generate legal moves
1934 count = generate_legal_moves(*this, mlist);
1936 // Loop through the moves, and see if one of them is mate
1937 for (int i = 0; i < count; i++)
1939 do_move(mlist[i].move, st2);
1943 undo_move(mlist[i].move);
1946 // Undo null move, if necessary
1954 /// Position::init_zobrist() is a static member function which initializes the
1955 /// various arrays used to compute hash keys.
1957 void Position::init_zobrist() {
1959 for (int i = 0; i < 2; i++)
1960 for (int j = 0; j < 8; j++)
1961 for (int k = 0; k < 64; k++)
1962 zobrist[i][j][k] = Key(genrand_int64());
1964 for (int i = 0; i < 64; i++)
1965 zobEp[i] = Key(genrand_int64());
1967 for (int i = 0; i < 16; i++)
1968 zobCastle[i] = genrand_int64();
1970 zobSideToMove = genrand_int64();
1972 for (int i = 0; i < 2; i++)
1973 for (int j = 0; j < 8; j++)
1974 for (int k = 0; k < 16; k++)
1975 zobMaterial[i][j][k] = (k > 0)? Key(genrand_int64()) : Key(0LL);
1977 for (int i = 0; i < 16; i++)
1978 zobMaterial[0][KING][i] = zobMaterial[1][KING][i] = Key(0ULL);
1982 /// Position::init_piece_square_tables() initializes the piece square tables.
1983 /// This is a two-step operation: First, the white halves of the tables are
1984 /// copied from the MgPST[][] and EgPST[][] arrays, with a small random number
1985 /// added to each entry if the "Randomness" UCI parameter is non-zero.
1986 /// Second, the black halves of the tables are initialized by mirroring
1987 /// and changing the sign of the corresponding white scores.
1989 void Position::init_piece_square_tables() {
1991 int r = get_option_value_int("Randomness"), i;
1992 for (Square s = SQ_A1; s <= SQ_H8; s++)
1993 for (Piece p = WP; p <= WK; p++)
1995 i = (r == 0)? 0 : (genrand_int32() % (r*2) - r);
1996 MgPieceSquareTable[p][s] = Value(MgPST[p][s] + i);
1997 EgPieceSquareTable[p][s] = Value(EgPST[p][s] + i);
2000 for (Square s = SQ_A1; s <= SQ_H8; s++)
2001 for (Piece p = BP; p <= BK; p++)
2003 MgPieceSquareTable[p][s] = -MgPieceSquareTable[p-8][flip_square(s)];
2004 EgPieceSquareTable[p][s] = -EgPieceSquareTable[p-8][flip_square(s)];
2009 /// Position::flipped_copy() makes a copy of the input position, but with
2010 /// the white and black sides reversed. This is only useful for debugging,
2011 /// especially for finding evaluation symmetry bugs.
2013 void Position::flipped_copy(const Position &pos) {
2015 assert(pos.is_ok());
2020 for (Square s = SQ_A1; s <= SQ_H8; s++)
2021 if (!pos.square_is_empty(s))
2022 put_piece(Piece(int(pos.piece_on(s)) ^ 8), flip_square(s));
2025 sideToMove = opposite_color(pos.side_to_move());
2028 if (pos.can_castle_kingside(WHITE)) allow_oo(BLACK);
2029 if (pos.can_castle_queenside(WHITE)) allow_ooo(BLACK);
2030 if (pos.can_castle_kingside(BLACK)) allow_oo(WHITE);
2031 if (pos.can_castle_queenside(BLACK)) allow_ooo(WHITE);
2033 initialKFile = pos.initialKFile;
2034 initialKRFile = pos.initialKRFile;
2035 initialQRFile = pos.initialQRFile;
2037 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
2038 castleRightsMask[sq] = ALL_CASTLES;
2040 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
2041 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
2042 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
2043 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
2044 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
2045 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
2047 // En passant square
2048 if (pos.st->epSquare != SQ_NONE)
2049 st->epSquare = flip_square(pos.st->epSquare);
2055 st->key = compute_key();
2056 st->pawnKey = compute_pawn_key();
2057 st->materialKey = compute_material_key();
2059 // Incremental scores
2060 st->mgValue = compute_value<MidGame>();
2061 st->egValue = compute_value<EndGame>();
2064 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
2065 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
2071 /// Position::is_ok() performs some consitency checks for the position object.
2072 /// This is meant to be helpful when debugging.
2074 bool Position::is_ok(int* failedStep) const {
2076 // What features of the position should be verified?
2077 static const bool debugBitboards = false;
2078 static const bool debugKingCount = false;
2079 static const bool debugKingCapture = false;
2080 static const bool debugCheckerCount = false;
2081 static const bool debugKey = false;
2082 static const bool debugMaterialKey = false;
2083 static const bool debugPawnKey = false;
2084 static const bool debugIncrementalEval = false;
2085 static const bool debugNonPawnMaterial = false;
2086 static const bool debugPieceCounts = false;
2087 static const bool debugPieceList = false;
2089 if (failedStep) *failedStep = 1;
2092 if (!color_is_ok(side_to_move()))
2095 // Are the king squares in the position correct?
2096 if (failedStep) (*failedStep)++;
2097 if (piece_on(king_square(WHITE)) != WK)
2100 if (failedStep) (*failedStep)++;
2101 if (piece_on(king_square(BLACK)) != BK)
2105 if (failedStep) (*failedStep)++;
2106 if (!file_is_ok(initialKRFile))
2109 if (!file_is_ok(initialQRFile))
2112 // Do both sides have exactly one king?
2113 if (failedStep) (*failedStep)++;
2116 int kingCount[2] = {0, 0};
2117 for (Square s = SQ_A1; s <= SQ_H8; s++)
2118 if (type_of_piece_on(s) == KING)
2119 kingCount[color_of_piece_on(s)]++;
2121 if (kingCount[0] != 1 || kingCount[1] != 1)
2125 // Can the side to move capture the opponent's king?
2126 if (failedStep) (*failedStep)++;
2127 if (debugKingCapture)
2129 Color us = side_to_move();
2130 Color them = opposite_color(us);
2131 Square ksq = king_square(them);
2132 if (square_is_attacked(ksq, us))
2136 // Is there more than 2 checkers?
2137 if (failedStep) (*failedStep)++;
2138 if (debugCheckerCount && count_1s(st->checkersBB) > 2)
2142 if (failedStep) (*failedStep)++;
2145 // The intersection of the white and black pieces must be empty
2146 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
2149 // The union of the white and black pieces must be equal to all
2151 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
2154 // Separate piece type bitboards must have empty intersections
2155 for (PieceType p1 = PAWN; p1 <= KING; p1++)
2156 for (PieceType p2 = PAWN; p2 <= KING; p2++)
2157 if (p1 != p2 && (pieces_of_type(p1) & pieces_of_type(p2)))
2161 // En passant square OK?
2162 if (failedStep) (*failedStep)++;
2163 if (ep_square() != SQ_NONE)
2165 // The en passant square must be on rank 6, from the point of view of the
2167 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
2172 if (failedStep) (*failedStep)++;
2173 if (debugKey && st->key != compute_key())
2176 // Pawn hash key OK?
2177 if (failedStep) (*failedStep)++;
2178 if (debugPawnKey && st->pawnKey != compute_pawn_key())
2181 // Material hash key OK?
2182 if (failedStep) (*failedStep)++;
2183 if (debugMaterialKey && st->materialKey != compute_material_key())
2186 // Incremental eval OK?
2187 if (failedStep) (*failedStep)++;
2188 if (debugIncrementalEval)
2190 if (st->mgValue != compute_value<MidGame>())
2193 if (st->egValue != compute_value<EndGame>())
2197 // Non-pawn material OK?
2198 if (failedStep) (*failedStep)++;
2199 if (debugNonPawnMaterial)
2201 if (npMaterial[WHITE] != compute_non_pawn_material(WHITE))
2204 if (npMaterial[BLACK] != compute_non_pawn_material(BLACK))
2209 if (failedStep) (*failedStep)++;
2210 if (debugPieceCounts)
2211 for (Color c = WHITE; c <= BLACK; c++)
2212 for (PieceType pt = PAWN; pt <= KING; pt++)
2213 if (pieceCount[c][pt] != count_1s(pieces_of_color_and_type(c, pt)))
2216 if (failedStep) (*failedStep)++;
2219 for(Color c = WHITE; c <= BLACK; c++)
2220 for(PieceType pt = PAWN; pt <= KING; pt++)
2221 for(int i = 0; i < pieceCount[c][pt]; i++)
2223 if (piece_on(piece_list(c, pt, i)) != piece_of_color_and_type(c, pt))
2226 if (index[piece_list(c, pt, i)] != i)
2230 if (failedStep) *failedStep = 0;