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::attacks_to() computes a bitboard containing all pieces which
362 /// attacks a given square. There are two versions of this function: One
363 /// which finds attackers of both colors, and one which only finds the
364 /// attackers for one side.
366 Bitboard Position::attacks_to(Square s) const {
368 return (pawn_attacks(BLACK, s) & pawns(WHITE))
369 | (pawn_attacks(WHITE, s) & pawns(BLACK))
370 | (piece_attacks<KNIGHT>(s) & pieces_of_type(KNIGHT))
371 | (piece_attacks<ROOK>(s) & rooks_and_queens())
372 | (piece_attacks<BISHOP>(s) & bishops_and_queens())
373 | (piece_attacks<KING>(s) & pieces_of_type(KING));
376 /// Position::piece_attacks_square() tests whether the piece on square f
377 /// attacks square t.
379 bool Position::piece_attacks_square(Piece p, Square f, Square t) const {
381 assert(square_is_ok(f));
382 assert(square_is_ok(t));
386 case WP: return pawn_attacks_square(WHITE, f, t);
387 case BP: return pawn_attacks_square(BLACK, f, t);
388 case WN: case BN: return piece_attacks_square<KNIGHT>(f, t);
389 case WB: case BB: return piece_attacks_square<BISHOP>(f, t);
390 case WR: case BR: return piece_attacks_square<ROOK>(f, t);
391 case WQ: case BQ: return piece_attacks_square<QUEEN>(f, t);
392 case WK: case BK: return piece_attacks_square<KING>(f, t);
399 /// Position::move_attacks_square() tests whether a move from the current
400 /// position attacks a given square.
402 bool Position::move_attacks_square(Move m, Square s) const {
404 assert(move_is_ok(m));
405 assert(square_is_ok(s));
407 Square f = move_from(m), t = move_to(m);
409 assert(square_is_occupied(f));
411 if (piece_attacks_square(piece_on(f), t, s))
414 // Move the piece and scan for X-ray attacks behind it
415 Bitboard occ = occupied_squares();
416 Color us = color_of_piece_on(f);
419 Bitboard xray = ( (rook_attacks_bb(s, occ) & rooks_and_queens())
420 |(bishop_attacks_bb(s, occ) & bishops_and_queens())) & pieces_of_color(us);
422 // If we have attacks we need to verify that are caused by our move
423 // and are not already existent ones.
424 return xray && (xray ^ (xray & piece_attacks<QUEEN>(s)));
428 /// Position::find_checkers() computes the checkersBB bitboard, which
429 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
430 /// currently works by calling Position::attacks_to, which is probably
431 /// inefficient. Consider rewriting this function to use the last move
432 /// played, like in non-bitboard versions of Glaurung.
434 void Position::find_checkers() {
436 Color us = side_to_move();
437 st->checkersBB = attacks_to(king_square(us), opposite_color(us));
441 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
443 bool Position::pl_move_is_legal(Move m) const {
445 return pl_move_is_legal(m, pinned_pieces(side_to_move()));
448 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
451 assert(move_is_ok(m));
452 assert(pinned == pinned_pieces(side_to_move()));
454 // If we're in check, all pseudo-legal moves are legal, because our
455 // check evasion generator only generates true legal moves.
459 // Castling moves are checked for legality during move generation.
460 if (move_is_castle(m))
463 Color us = side_to_move();
464 Color them = opposite_color(us);
465 Square from = move_from(m);
466 Square ksq = king_square(us);
468 assert(color_of_piece_on(from) == us);
469 assert(piece_on(ksq) == piece_of_color_and_type(us, KING));
471 // En passant captures are a tricky special case. Because they are
472 // rather uncommon, we do it simply by testing whether the king is attacked
473 // after the move is made
476 Square to = move_to(m);
477 Square capsq = make_square(square_file(to), square_rank(from));
478 Bitboard b = occupied_squares();
480 assert(to == ep_square());
481 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
482 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
483 assert(piece_on(to) == EMPTY);
486 clear_bit(&b, capsq);
489 return !(rook_attacks_bb(ksq, b) & rooks_and_queens(them))
490 && !(bishop_attacks_bb(ksq, b) & bishops_and_queens(them));
493 // If the moving piece is a king, check whether the destination
494 // square is attacked by the opponent.
496 return !(square_is_attacked(move_to(m), them));
498 // A non-king move is legal if and only if it is not pinned or it
499 // is moving along the ray towards or away from the king.
500 return ( !bit_is_set(pinned, from)
501 || (direction_between_squares(from, ksq) == direction_between_squares(move_to(m), ksq)));
505 /// Position::move_is_check() tests whether a pseudo-legal move is a check
507 bool Position::move_is_check(Move m) const {
509 Bitboard dc = discovered_check_candidates(side_to_move());
510 return move_is_check(m, dc);
513 bool Position::move_is_check(Move m, Bitboard dcCandidates) const {
516 assert(move_is_ok(m));
517 assert(dcCandidates == discovered_check_candidates(side_to_move()));
519 Color us = side_to_move();
520 Color them = opposite_color(us);
521 Square from = move_from(m);
522 Square to = move_to(m);
523 Square ksq = king_square(them);
525 assert(color_of_piece_on(from) == us);
526 assert(piece_on(ksq) == piece_of_color_and_type(them, KING));
528 // Proceed according to the type of the moving piece
529 switch (type_of_piece_on(from))
533 if (bit_is_set(pawn_attacks(them, ksq), to)) // Normal check?
536 if ( bit_is_set(dcCandidates, from) // Discovered check?
537 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
540 if (move_promotion(m)) // Promotion with check?
542 Bitboard b = occupied_squares();
545 switch (move_promotion(m))
548 return bit_is_set(piece_attacks<KNIGHT>(to), ksq);
550 return bit_is_set(bishop_attacks_bb(to, b), ksq);
552 return bit_is_set(rook_attacks_bb(to, b), ksq);
554 return bit_is_set(queen_attacks_bb(to, b), ksq);
559 // En passant capture with check? We have already handled the case
560 // of direct checks and ordinary discovered check, the only case we
561 // need to handle is the unusual case of a discovered check through the
563 else if (move_is_ep(m))
565 Square capsq = make_square(square_file(to), square_rank(from));
566 Bitboard b = occupied_squares();
568 clear_bit(&b, capsq);
570 return (rook_attacks_bb(ksq, b) & rooks_and_queens(us))
571 ||(bishop_attacks_bb(ksq, b) & bishops_and_queens(us));
576 return bit_is_set(dcCandidates, from) // Discovered check?
577 || bit_is_set(piece_attacks<KNIGHT>(ksq), to); // Normal check?
580 return bit_is_set(dcCandidates, from) // Discovered check?
581 || bit_is_set(piece_attacks<BISHOP>(ksq), to); // Normal check?
584 return bit_is_set(dcCandidates, from) // Discovered check?
585 || bit_is_set(piece_attacks<ROOK>(ksq), to); // Normal check?
588 // Discovered checks are impossible!
589 assert(!bit_is_set(dcCandidates, from));
590 return bit_is_set(piece_attacks<QUEEN>(ksq), to); // Normal check?
594 if ( bit_is_set(dcCandidates, from)
595 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
598 // Castling with check?
599 if (move_is_castle(m))
601 Square kfrom, kto, rfrom, rto;
602 Bitboard b = occupied_squares();
608 kto = relative_square(us, SQ_G1);
609 rto = relative_square(us, SQ_F1);
611 kto = relative_square(us, SQ_C1);
612 rto = relative_square(us, SQ_D1);
614 clear_bit(&b, kfrom);
615 clear_bit(&b, rfrom);
618 return bit_is_set(rook_attacks_bb(rto, b), ksq);
622 default: // NO_PIECE_TYPE
630 /// Position::move_is_capture() tests whether a move from the current
631 /// position is a capture. Move must not be MOVE_NONE.
633 bool Position::move_is_capture(Move m) const {
635 assert(m != MOVE_NONE);
637 return ( !square_is_empty(move_to(m))
638 && (color_of_piece_on(move_to(m)) != color_of_piece_on(move_from(m)))
644 /// Position::update_checkers() udpates chekers info given the move. It is called
645 /// in do_move() and is faster then find_checkers().
647 template<PieceType Piece>
648 inline void Position::update_checkers(Bitboard* pCheckersBB, Square ksq, Square from,
649 Square to, Bitboard dcCandidates) {
651 const bool Bishop = (Piece == QUEEN || Piece == BISHOP);
652 const bool Rook = (Piece == QUEEN || Piece == ROOK);
653 const bool Slider = Bishop || Rook;
655 if ( ( (Bishop && bit_is_set(BishopPseudoAttacks[ksq], to))
656 || (Rook && bit_is_set(RookPseudoAttacks[ksq], to)))
657 && bit_is_set(piece_attacks<Piece>(ksq), to)) // slow, try to early skip
658 set_bit(pCheckersBB, to);
660 else if ( Piece != KING
662 && bit_is_set(piece_attacks<Piece>(ksq), to))
663 set_bit(pCheckersBB, to);
665 if (Piece != QUEEN && bit_is_set(dcCandidates, from))
668 (*pCheckersBB) |= (piece_attacks<ROOK>(ksq) & rooks_and_queens(side_to_move()));
671 (*pCheckersBB) |= (piece_attacks<BISHOP>(ksq) & bishops_and_queens(side_to_move()));
676 /// Position::do_move() makes a move, and saves all information necessary
677 /// to a StateInfo object. The move is assumed to be legal.
678 /// Pseudo-legal moves should be filtered out before this function is called.
680 void Position::do_move(Move m, StateInfo& newSt) {
682 do_move(m, newSt, discovered_check_candidates(side_to_move()));
685 void Position::do_move(Move m, StateInfo& newSt, Bitboard dcCandidates) {
688 assert(move_is_ok(m));
690 // Copy some fields of old state to our new StateInfo object except the
691 // ones which are recalculated from scratch anyway, then switch our state
692 // pointer to point to the new, ready to be updated, state.
693 struct ReducedStateInfo {
694 Key key, pawnKey, materialKey;
695 int castleRights, rule50;
697 Value mgValue, egValue;
700 memcpy(&newSt, st, sizeof(ReducedStateInfo));
701 newSt.capture = NO_PIECE_TYPE;
705 // Save the current key to the history[] array, in order to be able to
706 // detect repetition draws.
707 history[gamePly] = st->key;
709 // Increment the 50 moves rule draw counter. Resetting it to zero in the
710 // case of non-reversible moves is taken care of later.
713 if (move_is_castle(m))
715 else if (move_promotion(m))
716 do_promotion_move(m);
717 else if (move_is_ep(m))
721 Color us = side_to_move();
722 Color them = opposite_color(us);
723 Square from = move_from(m);
724 Square to = move_to(m);
726 assert(color_of_piece_on(from) == us);
727 assert(color_of_piece_on(to) == them || piece_on(to) == EMPTY);
729 PieceType piece = type_of_piece_on(from);
731 st->capture = type_of_piece_on(to);
734 do_capture_move(m, st->capture, them, to);
737 clear_bit(&(byColorBB[us]), from);
738 clear_bit(&(byTypeBB[piece]), from);
739 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
740 set_bit(&(byColorBB[us]), to);
741 set_bit(&(byTypeBB[piece]), to);
742 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
743 board[to] = board[from];
747 st->key ^= zobrist[us][piece][from] ^ zobrist[us][piece][to];
749 // Update incremental scores
750 st->mgValue -= pst<MidGame>(us, piece, from);
751 st->mgValue += pst<MidGame>(us, piece, to);
752 st->egValue -= pst<EndGame>(us, piece, from);
753 st->egValue += pst<EndGame>(us, piece, to);
755 // If the moving piece was a king, update the king square
759 // Reset en passant square
760 if (st->epSquare != SQ_NONE)
762 st->key ^= zobEp[st->epSquare];
763 st->epSquare = SQ_NONE;
766 // If the moving piece was a pawn do some special extra work
769 // Reset rule 50 draw counter
772 // Update pawn hash key
773 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
775 // Set en passant square, only if moved pawn can be captured
776 if (abs(int(to) - int(from)) == 16)
778 if ( (us == WHITE && (pawn_attacks(WHITE, from + DELTA_N) & pawns(BLACK)))
779 || (us == BLACK && (pawn_attacks(BLACK, from + DELTA_S) & pawns(WHITE))))
781 st->epSquare = Square((int(from) + int(to)) / 2);
782 st->key ^= zobEp[st->epSquare];
787 // Update piece lists
788 pieceList[us][piece][index[from]] = to;
789 index[to] = index[from];
791 // Update castle rights
792 st->key ^= zobCastle[st->castleRights];
793 st->castleRights &= castleRightsMask[from];
794 st->castleRights &= castleRightsMask[to];
795 st->key ^= zobCastle[st->castleRights];
797 // Update checkers bitboard, piece must be already moved
798 st->checkersBB = EmptyBoardBB;
799 Square ksq = king_square(them);
802 case PAWN: update_checkers<PAWN>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
803 case KNIGHT: update_checkers<KNIGHT>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
804 case BISHOP: update_checkers<BISHOP>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
805 case ROOK: update_checkers<ROOK>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
806 case QUEEN: update_checkers<QUEEN>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
807 case KING: update_checkers<KING>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
808 default: assert(false); break;
813 st->key ^= zobSideToMove;
814 sideToMove = opposite_color(sideToMove);
817 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
818 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
824 /// Position::do_capture_move() is a private method used to update captured
825 /// piece info. It is called from the main Position::do_move function.
827 void Position::do_capture_move(Move m, PieceType capture, Color them, Square to) {
829 assert(capture != KING);
831 // Remove captured piece
832 clear_bit(&(byColorBB[them]), to);
833 clear_bit(&(byTypeBB[capture]), to);
836 st->key ^= zobrist[them][capture][to];
838 // If the captured piece was a pawn, update pawn hash key
840 st->pawnKey ^= zobrist[them][PAWN][to];
842 // Update incremental scores
843 st->mgValue -= pst<MidGame>(them, capture, to);
844 st->egValue -= pst<EndGame>(them, capture, to);
846 assert(!move_promotion(m) || capture != PAWN);
850 npMaterial[them] -= piece_value_midgame(capture);
852 // Update material hash key
853 st->materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];
855 // Update piece count
856 pieceCount[them][capture]--;
859 pieceList[them][capture][index[to]] = pieceList[them][capture][pieceCount[them][capture]];
860 index[pieceList[them][capture][index[to]]] = index[to];
862 // Reset rule 50 counter
867 /// Position::do_castle_move() is a private method used to make a castling
868 /// move. It is called from the main Position::do_move function. Note that
869 /// castling moves are encoded as "king captures friendly rook" moves, for
870 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
872 void Position::do_castle_move(Move m) {
875 assert(move_is_ok(m));
876 assert(move_is_castle(m));
878 Color us = side_to_move();
879 Color them = opposite_color(us);
881 // Find source squares for king and rook
882 Square kfrom = move_from(m);
883 Square rfrom = move_to(m); // HACK: See comment at beginning of function
886 assert(piece_on(kfrom) == piece_of_color_and_type(us, KING));
887 assert(piece_on(rfrom) == piece_of_color_and_type(us, ROOK));
889 // Find destination squares for king and rook
890 if (rfrom > kfrom) // O-O
892 kto = relative_square(us, SQ_G1);
893 rto = relative_square(us, SQ_F1);
895 kto = relative_square(us, SQ_C1);
896 rto = relative_square(us, SQ_D1);
899 // Remove pieces from source squares
900 clear_bit(&(byColorBB[us]), kfrom);
901 clear_bit(&(byTypeBB[KING]), kfrom);
902 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
903 clear_bit(&(byColorBB[us]), rfrom);
904 clear_bit(&(byTypeBB[ROOK]), rfrom);
905 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
907 // Put pieces on destination squares
908 set_bit(&(byColorBB[us]), kto);
909 set_bit(&(byTypeBB[KING]), kto);
910 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
911 set_bit(&(byColorBB[us]), rto);
912 set_bit(&(byTypeBB[ROOK]), rto);
913 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
915 // Update board array
916 board[kfrom] = board[rfrom] = EMPTY;
917 board[kto] = piece_of_color_and_type(us, KING);
918 board[rto] = piece_of_color_and_type(us, ROOK);
920 // Update king square
921 kingSquare[us] = kto;
923 // Update piece lists
924 pieceList[us][KING][index[kfrom]] = kto;
925 pieceList[us][ROOK][index[rfrom]] = rto;
926 int tmp = index[rfrom];
927 index[kto] = index[kfrom];
930 // Update incremental scores
931 st->mgValue -= pst<MidGame>(us, KING, kfrom);
932 st->mgValue += pst<MidGame>(us, KING, kto);
933 st->egValue -= pst<EndGame>(us, KING, kfrom);
934 st->egValue += pst<EndGame>(us, KING, kto);
935 st->mgValue -= pst<MidGame>(us, ROOK, rfrom);
936 st->mgValue += pst<MidGame>(us, ROOK, rto);
937 st->egValue -= pst<EndGame>(us, ROOK, rfrom);
938 st->egValue += pst<EndGame>(us, ROOK, rto);
941 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
942 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
944 // Clear en passant square
945 if (st->epSquare != SQ_NONE)
947 st->key ^= zobEp[st->epSquare];
948 st->epSquare = SQ_NONE;
951 // Update castling rights
952 st->key ^= zobCastle[st->castleRights];
953 st->castleRights &= castleRightsMask[kfrom];
954 st->key ^= zobCastle[st->castleRights];
956 // Reset rule 50 counter
959 // Update checkers BB
960 st->checkersBB = attacks_to(king_square(them), us);
964 /// Position::do_promotion_move() is a private method used to make a promotion
965 /// move. It is called from the main Position::do_move function.
967 void Position::do_promotion_move(Move m) {
974 assert(move_is_ok(m));
975 assert(move_promotion(m));
978 them = opposite_color(us);
982 assert(relative_rank(us, to) == RANK_8);
983 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
984 assert(color_of_piece_on(to) == them || square_is_empty(to));
986 st->capture = type_of_piece_on(to);
989 do_capture_move(m, st->capture, them, to);
992 clear_bit(&(byColorBB[us]), from);
993 clear_bit(&(byTypeBB[PAWN]), from);
994 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
997 // Insert promoted piece
998 promotion = move_promotion(m);
999 assert(promotion >= KNIGHT && promotion <= QUEEN);
1000 set_bit(&(byColorBB[us]), to);
1001 set_bit(&(byTypeBB[promotion]), to);
1002 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1003 board[to] = piece_of_color_and_type(us, promotion);
1006 st->key ^= zobrist[us][PAWN][from] ^ zobrist[us][promotion][to];
1008 // Update pawn hash key
1009 st->pawnKey ^= zobrist[us][PAWN][from];
1011 // Update material key
1012 st->materialKey ^= zobMaterial[us][PAWN][pieceCount[us][PAWN]];
1013 st->materialKey ^= zobMaterial[us][promotion][pieceCount[us][promotion]+1];
1015 // Update piece counts
1016 pieceCount[us][PAWN]--;
1017 pieceCount[us][promotion]++;
1019 // Update piece lists
1020 pieceList[us][PAWN][index[from]] = pieceList[us][PAWN][pieceCount[us][PAWN]];
1021 index[pieceList[us][PAWN][index[from]]] = index[from];
1022 pieceList[us][promotion][pieceCount[us][promotion] - 1] = to;
1023 index[to] = pieceCount[us][promotion] - 1;
1025 // Update incremental scores
1026 st->mgValue -= pst<MidGame>(us, PAWN, from);
1027 st->mgValue += pst<MidGame>(us, promotion, to);
1028 st->egValue -= pst<EndGame>(us, PAWN, from);
1029 st->egValue += pst<EndGame>(us, promotion, to);
1032 npMaterial[us] += piece_value_midgame(promotion);
1034 // Clear the en passant square
1035 if (st->epSquare != SQ_NONE)
1037 st->key ^= zobEp[st->epSquare];
1038 st->epSquare = SQ_NONE;
1041 // Update castle rights
1042 st->key ^= zobCastle[st->castleRights];
1043 st->castleRights &= castleRightsMask[to];
1044 st->key ^= zobCastle[st->castleRights];
1046 // Reset rule 50 counter
1049 // Update checkers BB
1050 st->checkersBB = attacks_to(king_square(them), us);
1054 /// Position::do_ep_move() is a private method used to make an en passant
1055 /// capture. It is called from the main Position::do_move function.
1057 void Position::do_ep_move(Move m) {
1060 Square from, to, capsq;
1063 assert(move_is_ok(m));
1064 assert(move_is_ep(m));
1066 us = side_to_move();
1067 them = opposite_color(us);
1068 from = move_from(m);
1070 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1072 assert(to == st->epSquare);
1073 assert(relative_rank(us, to) == RANK_6);
1074 assert(piece_on(to) == EMPTY);
1075 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
1076 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
1078 // Remove captured piece
1079 clear_bit(&(byColorBB[them]), capsq);
1080 clear_bit(&(byTypeBB[PAWN]), capsq);
1081 clear_bit(&(byTypeBB[0]), capsq); // HACK: byTypeBB[0] == occupied squares
1082 board[capsq] = EMPTY;
1084 // Remove moving piece from source square
1085 clear_bit(&(byColorBB[us]), from);
1086 clear_bit(&(byTypeBB[PAWN]), from);
1087 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1089 // Put moving piece on destination square
1090 set_bit(&(byColorBB[us]), to);
1091 set_bit(&(byTypeBB[PAWN]), to);
1092 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1093 board[to] = board[from];
1094 board[from] = EMPTY;
1096 // Update material hash key
1097 st->materialKey ^= zobMaterial[them][PAWN][pieceCount[them][PAWN]];
1099 // Update piece count
1100 pieceCount[them][PAWN]--;
1102 // Update piece list
1103 pieceList[us][PAWN][index[from]] = to;
1104 index[to] = index[from];
1105 pieceList[them][PAWN][index[capsq]] = pieceList[them][PAWN][pieceCount[them][PAWN]];
1106 index[pieceList[them][PAWN][index[capsq]]] = index[capsq];
1109 st->key ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1110 st->key ^= zobrist[them][PAWN][capsq];
1111 st->key ^= zobEp[st->epSquare];
1113 // Update pawn hash key
1114 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1115 st->pawnKey ^= zobrist[them][PAWN][capsq];
1117 // Update incremental scores
1118 st->mgValue -= pst<MidGame>(them, PAWN, capsq);
1119 st->mgValue -= pst<MidGame>(us, PAWN, from);
1120 st->mgValue += pst<MidGame>(us, PAWN, to);
1121 st->egValue -= pst<EndGame>(them, PAWN, capsq);
1122 st->egValue -= pst<EndGame>(us, PAWN, from);
1123 st->egValue += pst<EndGame>(us, PAWN, to);
1125 // Reset en passant square
1126 st->epSquare = SQ_NONE;
1128 // Reset rule 50 counter
1131 // Update checkers BB
1132 st->checkersBB = attacks_to(king_square(them), us);
1136 /// Position::undo_move() unmakes a move. When it returns, the position should
1137 /// be restored to exactly the same state as before the move was made.
1139 void Position::undo_move(Move m) {
1142 assert(move_is_ok(m));
1145 sideToMove = opposite_color(sideToMove);
1147 if (move_is_castle(m))
1148 undo_castle_move(m);
1149 else if (move_promotion(m))
1150 undo_promotion_move(m);
1151 else if (move_is_ep(m))
1159 us = side_to_move();
1160 them = opposite_color(us);
1161 from = move_from(m);
1164 assert(piece_on(from) == EMPTY);
1165 assert(color_of_piece_on(to) == us);
1167 // Put the piece back at the source square
1168 piece = type_of_piece_on(to);
1169 set_bit(&(byColorBB[us]), from);
1170 set_bit(&(byTypeBB[piece]), from);
1171 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1172 board[from] = piece_of_color_and_type(us, piece);
1174 // Clear the destination square
1175 clear_bit(&(byColorBB[us]), to);
1176 clear_bit(&(byTypeBB[piece]), to);
1177 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1179 // If the moving piece was a king, update the king square
1181 kingSquare[us] = from;
1183 // Update piece list
1184 pieceList[us][piece][index[to]] = from;
1185 index[from] = index[to];
1189 assert(st->capture != KING);
1191 // Replace the captured piece
1192 set_bit(&(byColorBB[them]), to);
1193 set_bit(&(byTypeBB[st->capture]), to);
1194 set_bit(&(byTypeBB[0]), to);
1195 board[to] = piece_of_color_and_type(them, st->capture);
1198 if (st->capture != PAWN)
1199 npMaterial[them] += piece_value_midgame(st->capture);
1201 // Update piece list
1202 pieceList[them][st->capture][pieceCount[them][st->capture]] = to;
1203 index[to] = pieceCount[them][st->capture];
1205 // Update piece count
1206 pieceCount[them][st->capture]++;
1211 // Finally point our state pointer back to the previous state
1218 /// Position::undo_castle_move() is a private method used to unmake a castling
1219 /// move. It is called from the main Position::undo_move function. Note that
1220 /// castling moves are encoded as "king captures friendly rook" moves, for
1221 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1223 void Position::undo_castle_move(Move m) {
1225 assert(move_is_ok(m));
1226 assert(move_is_castle(m));
1228 // When we have arrived here, some work has already been done by
1229 // Position::undo_move. In particular, the side to move has been switched,
1230 // so the code below is correct.
1231 Color us = side_to_move();
1233 // Find source squares for king and rook
1234 Square kfrom = move_from(m);
1235 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1238 // Find destination squares for king and rook
1239 if (rfrom > kfrom) // O-O
1241 kto = relative_square(us, SQ_G1);
1242 rto = relative_square(us, SQ_F1);
1244 kto = relative_square(us, SQ_C1);
1245 rto = relative_square(us, SQ_D1);
1248 assert(piece_on(kto) == piece_of_color_and_type(us, KING));
1249 assert(piece_on(rto) == piece_of_color_and_type(us, ROOK));
1251 // Remove pieces from destination squares
1252 clear_bit(&(byColorBB[us]), kto);
1253 clear_bit(&(byTypeBB[KING]), kto);
1254 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1255 clear_bit(&(byColorBB[us]), rto);
1256 clear_bit(&(byTypeBB[ROOK]), rto);
1257 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1259 // Put pieces on source squares
1260 set_bit(&(byColorBB[us]), kfrom);
1261 set_bit(&(byTypeBB[KING]), kfrom);
1262 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1263 set_bit(&(byColorBB[us]), rfrom);
1264 set_bit(&(byTypeBB[ROOK]), rfrom);
1265 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1268 board[rto] = board[kto] = EMPTY;
1269 board[rfrom] = piece_of_color_and_type(us, ROOK);
1270 board[kfrom] = piece_of_color_and_type(us, KING);
1272 // Update king square
1273 kingSquare[us] = kfrom;
1275 // Update piece lists
1276 pieceList[us][KING][index[kto]] = kfrom;
1277 pieceList[us][ROOK][index[rto]] = rfrom;
1278 int tmp = index[rto]; // Necessary because we may have rto == kfrom in FRC.
1279 index[kfrom] = index[kto];
1284 /// Position::undo_promotion_move() is a private method used to unmake a
1285 /// promotion move. It is called from the main Position::do_move
1288 void Position::undo_promotion_move(Move m) {
1292 PieceType promotion;
1294 assert(move_is_ok(m));
1295 assert(move_promotion(m));
1297 // When we have arrived here, some work has already been done by
1298 // Position::undo_move. In particular, the side to move has been switched,
1299 // so the code below is correct.
1300 us = side_to_move();
1301 them = opposite_color(us);
1302 from = move_from(m);
1305 assert(relative_rank(us, to) == RANK_8);
1306 assert(piece_on(from) == EMPTY);
1308 // Remove promoted piece
1309 promotion = move_promotion(m);
1310 assert(piece_on(to)==piece_of_color_and_type(us, promotion));
1311 assert(promotion >= KNIGHT && promotion <= QUEEN);
1312 clear_bit(&(byColorBB[us]), to);
1313 clear_bit(&(byTypeBB[promotion]), to);
1314 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1316 // Insert pawn at source square
1317 set_bit(&(byColorBB[us]), from);
1318 set_bit(&(byTypeBB[PAWN]), from);
1319 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1320 board[from] = piece_of_color_and_type(us, PAWN);
1323 npMaterial[us] -= piece_value_midgame(promotion);
1325 // Update piece list
1326 pieceList[us][PAWN][pieceCount[us][PAWN]] = from;
1327 index[from] = pieceCount[us][PAWN];
1328 pieceList[us][promotion][index[to]] =
1329 pieceList[us][promotion][pieceCount[us][promotion] - 1];
1330 index[pieceList[us][promotion][index[to]]] = index[to];
1332 // Update piece counts
1333 pieceCount[us][promotion]--;
1334 pieceCount[us][PAWN]++;
1338 assert(st->capture != KING);
1340 // Insert captured piece:
1341 set_bit(&(byColorBB[them]), to);
1342 set_bit(&(byTypeBB[st->capture]), to);
1343 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1344 board[to] = piece_of_color_and_type(them, st->capture);
1346 // Update material. Because the move is a promotion move, we know
1347 // that the captured piece cannot be a pawn.
1348 assert(st->capture != PAWN);
1349 npMaterial[them] += piece_value_midgame(st->capture);
1351 // Update piece list
1352 pieceList[them][st->capture][pieceCount[them][st->capture]] = to;
1353 index[to] = pieceCount[them][st->capture];
1355 // Update piece count
1356 pieceCount[them][st->capture]++;
1362 /// Position::undo_ep_move() is a private method used to unmake an en passant
1363 /// capture. It is called from the main Position::undo_move function.
1365 void Position::undo_ep_move(Move m) {
1367 assert(move_is_ok(m));
1368 assert(move_is_ep(m));
1370 // When we have arrived here, some work has already been done by
1371 // Position::undo_move. In particular, the side to move has been switched,
1372 // so the code below is correct.
1373 Color us = side_to_move();
1374 Color them = opposite_color(us);
1375 Square from = move_from(m);
1376 Square to = move_to(m);
1377 Square capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1379 assert(to == st->previous->epSquare);
1380 assert(relative_rank(us, to) == RANK_6);
1381 assert(piece_on(to) == piece_of_color_and_type(us, PAWN));
1382 assert(piece_on(from) == EMPTY);
1383 assert(piece_on(capsq) == EMPTY);
1385 // Replace captured piece
1386 set_bit(&(byColorBB[them]), capsq);
1387 set_bit(&(byTypeBB[PAWN]), capsq);
1388 set_bit(&(byTypeBB[0]), capsq);
1389 board[capsq] = piece_of_color_and_type(them, PAWN);
1391 // Remove moving piece from destination square
1392 clear_bit(&(byColorBB[us]), to);
1393 clear_bit(&(byTypeBB[PAWN]), to);
1394 clear_bit(&(byTypeBB[0]), to);
1397 // Replace moving piece at source square
1398 set_bit(&(byColorBB[us]), from);
1399 set_bit(&(byTypeBB[PAWN]), from);
1400 set_bit(&(byTypeBB[0]), from);
1401 board[from] = piece_of_color_and_type(us, PAWN);
1403 // Update piece list:
1404 pieceList[us][PAWN][index[to]] = from;
1405 index[from] = index[to];
1406 pieceList[them][PAWN][pieceCount[them][PAWN]] = capsq;
1407 index[capsq] = pieceCount[them][PAWN];
1409 // Update piece count:
1410 pieceCount[them][PAWN]++;
1414 /// Position::do_null_move makes() a "null move": It switches the side to move
1415 /// and updates the hash key without executing any move on the board.
1417 void Position::do_null_move(StateInfo& backupSt) {
1420 assert(!is_check());
1422 // Back up the information necessary to undo the null move to the supplied
1423 // StateInfo object. In the case of a null move, the only thing we need to
1424 // remember is the last move made and the en passant square.
1425 // Note that differently from normal case here backupSt is actually used as
1426 // a backup storage not as a new state to be used.
1427 backupSt.lastMove = st->lastMove;
1428 backupSt.epSquare = st->epSquare;
1429 backupSt.previous = st->previous;
1430 st->previous = &backupSt;
1432 // Save the current key to the history[] array, in order to be able to
1433 // detect repetition draws.
1434 history[gamePly] = st->key;
1436 // Update the necessary information
1437 sideToMove = opposite_color(sideToMove);
1438 if (st->epSquare != SQ_NONE)
1439 st->key ^= zobEp[st->epSquare];
1441 st->epSquare = SQ_NONE;
1444 st->key ^= zobSideToMove;
1446 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1447 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1453 /// Position::undo_null_move() unmakes a "null move".
1455 void Position::undo_null_move() {
1458 assert(!is_check());
1460 // Restore information from the our backup StateInfo object
1461 st->lastMove = st->previous->lastMove;
1462 st->epSquare = st->previous->epSquare;
1463 st->previous = st->previous->previous;
1465 if (st->epSquare != SQ_NONE)
1466 st->key ^= zobEp[st->epSquare];
1468 // Update the necessary information
1469 sideToMove = opposite_color(sideToMove);
1472 st->key ^= zobSideToMove;
1474 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1475 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1481 /// Position::see() is a static exchange evaluator: It tries to estimate the
1482 /// material gain or loss resulting from a move. There are three versions of
1483 /// this function: One which takes a destination square as input, one takes a
1484 /// move, and one which takes a 'from' and a 'to' square. The function does
1485 /// not yet understand promotions captures.
1487 int Position::see(Square to) const {
1489 assert(square_is_ok(to));
1490 return see(SQ_NONE, to);
1493 int Position::see(Move m) const {
1495 assert(move_is_ok(m));
1496 return see(move_from(m), move_to(m));
1499 int Position::see(Square from, Square to) const {
1502 static const int seeValues[18] = {
1503 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1504 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1505 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1506 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1510 Bitboard attackers, occ, b;
1512 assert(square_is_ok(from) || from == SQ_NONE);
1513 assert(square_is_ok(to));
1515 // Initialize colors
1516 Color us = (from != SQ_NONE ? color_of_piece_on(from) : opposite_color(color_of_piece_on(to)));
1517 Color them = opposite_color(us);
1519 // Initialize pieces
1520 Piece piece = piece_on(from);
1521 Piece capture = piece_on(to);
1523 // Find all attackers to the destination square, with the moving piece
1524 // removed, but possibly an X-ray attacker added behind it.
1525 occ = occupied_squares();
1527 // Handle en passant moves
1528 if (st->epSquare == to && type_of_piece_on(from) == PAWN)
1530 assert(capture == EMPTY);
1532 Square capQq = (side_to_move() == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1533 capture = piece_on(capQq);
1535 assert(type_of_piece_on(capQq) == PAWN);
1537 // Remove the captured pawn
1538 clear_bit(&occ, capQq);
1543 clear_bit(&occ, from);
1544 attackers = (rook_attacks_bb(to, occ) & rooks_and_queens())
1545 | (bishop_attacks_bb(to, occ) & bishops_and_queens())
1546 | (piece_attacks<KNIGHT>(to) & knights())
1547 | (piece_attacks<KING>(to) & kings())
1548 | (pawn_attacks(WHITE, to) & pawns(BLACK))
1549 | (pawn_attacks(BLACK, to) & pawns(WHITE));
1551 if (from != SQ_NONE)
1554 // If we don't have any attacker we are finished
1555 if ((attackers & pieces_of_color(us)) == EmptyBoardBB)
1558 // Locate the least valuable attacker to the destination square
1559 // and use it to initialize from square.
1561 for (pt = PAWN; !(attackers & pieces_of_color_and_type(us, pt)); pt++)
1564 from = first_1(attackers & pieces_of_color_and_type(us, pt));
1565 piece = piece_on(from);
1568 // If the opponent has no attackers we are finished
1569 if ((attackers & pieces_of_color(them)) == EmptyBoardBB)
1570 return seeValues[capture];
1572 attackers &= occ; // Remove the moving piece
1574 // The destination square is defended, which makes things rather more
1575 // difficult to compute. We proceed by building up a "swap list" containing
1576 // the material gain or loss at each stop in a sequence of captures to the
1577 // destination square, where the sides alternately capture, and always
1578 // capture with the least valuable piece. After each capture, we look for
1579 // new X-ray attacks from behind the capturing piece.
1580 int lastCapturingPieceValue = seeValues[piece];
1581 int swapList[32], n = 1;
1585 swapList[0] = seeValues[capture];
1588 // Locate the least valuable attacker for the side to move. The loop
1589 // below looks like it is potentially infinite, but it isn't. We know
1590 // that the side to move still has at least one attacker left.
1591 for (pt = PAWN; !(attackers & pieces_of_color_and_type(c, pt)); pt++)
1594 // Remove the attacker we just found from the 'attackers' bitboard,
1595 // and scan for new X-ray attacks behind the attacker.
1596 b = attackers & pieces_of_color_and_type(c, pt);
1598 attackers |= (rook_attacks_bb(to, occ) & rooks_and_queens())
1599 | (bishop_attacks_bb(to, occ) & bishops_and_queens());
1603 // Add the new entry to the swap list
1605 swapList[n] = -swapList[n - 1] + lastCapturingPieceValue;
1608 // Remember the value of the capturing piece, and change the side to move
1609 // before beginning the next iteration
1610 lastCapturingPieceValue = seeValues[pt];
1611 c = opposite_color(c);
1613 // Stop after a king capture
1614 if (pt == KING && (attackers & pieces_of_color(c)))
1617 swapList[n++] = 100;
1620 } while (attackers & pieces_of_color(c));
1622 // Having built the swap list, we negamax through it to find the best
1623 // achievable score from the point of view of the side to move
1625 swapList[n-1] = Min(-swapList[n], swapList[n-1]);
1631 /// Position::setStartState() copies the content of the argument
1632 /// inside startState and makes st point to it. This is needed
1633 /// when the st pointee could become stale, as example because
1634 /// the caller is about to going out of scope.
1636 void Position::setStartState(const StateInfo& s) {
1643 /// Position::clear() erases the position object to a pristine state, with an
1644 /// empty board, white to move, and no castling rights.
1646 void Position::clear() {
1649 memset(st, 0, sizeof(StateInfo));
1650 st->epSquare = SQ_NONE;
1652 memset(index, 0, sizeof(int) * 64);
1653 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1655 for (int i = 0; i < 64; i++)
1658 for (int i = 0; i < 7; i++)
1660 byTypeBB[i] = EmptyBoardBB;
1661 pieceCount[0][i] = pieceCount[1][i] = 0;
1662 for (int j = 0; j < 8; j++)
1663 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1668 initialKFile = FILE_E;
1669 initialKRFile = FILE_H;
1670 initialQRFile = FILE_A;
1674 /// Position::reset_game_ply() simply sets gamePly to 0. It is used from the
1675 /// UCI interface code, whenever a non-reversible move is made in a
1676 /// 'position fen <fen> moves m1 m2 ...' command. This makes it possible
1677 /// for the program to handle games of arbitrary length, as long as the GUI
1678 /// handles draws by the 50 move rule correctly.
1680 void Position::reset_game_ply() {
1686 /// Position::put_piece() puts a piece on the given square of the board,
1687 /// updating the board array, bitboards, and piece counts.
1689 void Position::put_piece(Piece p, Square s) {
1691 Color c = color_of_piece(p);
1692 PieceType pt = type_of_piece(p);
1695 index[s] = pieceCount[c][pt];
1696 pieceList[c][pt][index[s]] = s;
1698 set_bit(&(byTypeBB[pt]), s);
1699 set_bit(&(byColorBB[c]), s);
1700 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1702 pieceCount[c][pt]++;
1709 /// Position::allow_oo() gives the given side the right to castle kingside.
1710 /// Used when setting castling rights during parsing of FEN strings.
1712 void Position::allow_oo(Color c) {
1714 st->castleRights |= (1 + int(c));
1718 /// Position::allow_ooo() gives the given side the right to castle queenside.
1719 /// Used when setting castling rights during parsing of FEN strings.
1721 void Position::allow_ooo(Color c) {
1723 st->castleRights |= (4 + 4*int(c));
1727 /// Position::compute_key() computes the hash key of the position. The hash
1728 /// key is usually updated incrementally as moves are made and unmade, the
1729 /// compute_key() function is only used when a new position is set up, and
1730 /// to verify the correctness of the hash key when running in debug mode.
1732 Key Position::compute_key() const {
1734 Key result = Key(0ULL);
1736 for (Square s = SQ_A1; s <= SQ_H8; s++)
1737 if (square_is_occupied(s))
1738 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1740 if (ep_square() != SQ_NONE)
1741 result ^= zobEp[ep_square()];
1743 result ^= zobCastle[st->castleRights];
1744 if (side_to_move() == BLACK)
1745 result ^= zobSideToMove;
1751 /// Position::compute_pawn_key() computes the hash key of the position. The
1752 /// hash key is usually updated incrementally as moves are made and unmade,
1753 /// the compute_pawn_key() function is only used when a new position is set
1754 /// up, and to verify the correctness of the pawn hash key when running in
1757 Key Position::compute_pawn_key() const {
1759 Key result = Key(0ULL);
1763 for (Color c = WHITE; c <= BLACK; c++)
1768 s = pop_1st_bit(&b);
1769 result ^= zobrist[c][PAWN][s];
1776 /// Position::compute_material_key() computes the hash key of the position.
1777 /// The hash key is usually updated incrementally as moves are made and unmade,
1778 /// the compute_material_key() function is only used when a new position is set
1779 /// up, and to verify the correctness of the material hash key when running in
1782 Key Position::compute_material_key() const {
1784 Key result = Key(0ULL);
1785 for (Color c = WHITE; c <= BLACK; c++)
1786 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1788 int count = piece_count(c, pt);
1789 for (int i = 0; i <= count; i++)
1790 result ^= zobMaterial[c][pt][i];
1796 /// Position::compute_value() compute the incremental scores for the middle
1797 /// game and the endgame. These functions are used to initialize the incremental
1798 /// scores when a new position is set up, and to verify that the scores are correctly
1799 /// updated by do_move and undo_move when the program is running in debug mode.
1800 template<Position::GamePhase Phase>
1801 Value Position::compute_value() const {
1803 Value result = Value(0);
1807 for (Color c = WHITE; c <= BLACK; c++)
1808 for (PieceType pt = PAWN; pt <= KING; pt++)
1810 b = pieces_of_color_and_type(c, pt);
1813 s = pop_1st_bit(&b);
1814 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1815 result += pst<Phase>(c, pt, s);
1819 const Value TempoValue = (Phase == MidGame ? TempoValueMidgame : TempoValueEndgame);
1820 result += (side_to_move() == WHITE)? TempoValue / 2 : -TempoValue / 2;
1825 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1826 /// game material score for the given side. Material scores are updated
1827 /// incrementally during the search, this function is only used while
1828 /// initializing a new Position object.
1830 Value Position::compute_non_pawn_material(Color c) const {
1832 Value result = Value(0);
1835 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1837 Bitboard b = pieces_of_color_and_type(c, pt);
1840 s = pop_1st_bit(&b);
1841 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1842 result += piece_value_midgame(pt);
1849 /// Position::is_mate() returns true or false depending on whether the
1850 /// side to move is checkmated. Note that this function is currently very
1851 /// slow, and shouldn't be used frequently inside the search.
1853 bool Position::is_mate() const {
1857 MovePicker mp = MovePicker(*this, false, MOVE_NONE, EmptySearchStack, Depth(0));
1858 return mp.get_next_move() == MOVE_NONE;
1864 /// Position::is_draw() tests whether the position is drawn by material,
1865 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1866 /// must be done by the search.
1868 bool Position::is_draw() const {
1870 // Draw by material?
1872 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1875 // Draw by the 50 moves rule?
1876 if (st->rule50 > 100 || (st->rule50 == 100 && !is_check()))
1879 // Draw by repetition?
1880 for (int i = 2; i < Min(gamePly, st->rule50); i += 2)
1881 if (history[gamePly - i] == st->key)
1888 /// Position::has_mate_threat() tests whether a given color has a mate in one
1889 /// from the current position. This function is quite slow, but it doesn't
1890 /// matter, because it is currently only called from PV nodes, which are rare.
1892 bool Position::has_mate_threat(Color c) {
1895 Color stm = side_to_move();
1897 // The following lines are useless and silly, but prevents gcc from
1898 // emitting a stupid warning stating that u1.lastMove and u1.epSquare might
1899 // be used uninitialized.
1900 st1.lastMove = st->lastMove;
1901 st1.epSquare = st->epSquare;
1906 // If the input color is not equal to the side to move, do a null move
1910 MoveStack mlist[120];
1912 bool result = false;
1914 // Generate legal moves
1915 count = generate_legal_moves(*this, mlist);
1917 // Loop through the moves, and see if one of them is mate
1918 for (int i = 0; i < count; i++)
1920 do_move(mlist[i].move, st2);
1924 undo_move(mlist[i].move);
1927 // Undo null move, if necessary
1935 /// Position::init_zobrist() is a static member function which initializes the
1936 /// various arrays used to compute hash keys.
1938 void Position::init_zobrist() {
1940 for (int i = 0; i < 2; i++)
1941 for (int j = 0; j < 8; j++)
1942 for (int k = 0; k < 64; k++)
1943 zobrist[i][j][k] = Key(genrand_int64());
1945 for (int i = 0; i < 64; i++)
1946 zobEp[i] = Key(genrand_int64());
1948 for (int i = 0; i < 16; i++)
1949 zobCastle[i] = genrand_int64();
1951 zobSideToMove = genrand_int64();
1953 for (int i = 0; i < 2; i++)
1954 for (int j = 0; j < 8; j++)
1955 for (int k = 0; k < 16; k++)
1956 zobMaterial[i][j][k] = (k > 0)? Key(genrand_int64()) : Key(0LL);
1958 for (int i = 0; i < 16; i++)
1959 zobMaterial[0][KING][i] = zobMaterial[1][KING][i] = Key(0ULL);
1963 /// Position::init_piece_square_tables() initializes the piece square tables.
1964 /// This is a two-step operation: First, the white halves of the tables are
1965 /// copied from the MgPST[][] and EgPST[][] arrays, with a small random number
1966 /// added to each entry if the "Randomness" UCI parameter is non-zero.
1967 /// Second, the black halves of the tables are initialized by mirroring
1968 /// and changing the sign of the corresponding white scores.
1970 void Position::init_piece_square_tables() {
1972 int r = get_option_value_int("Randomness"), i;
1973 for (Square s = SQ_A1; s <= SQ_H8; s++)
1974 for (Piece p = WP; p <= WK; p++)
1976 i = (r == 0)? 0 : (genrand_int32() % (r*2) - r);
1977 MgPieceSquareTable[p][s] = Value(MgPST[p][s] + i);
1978 EgPieceSquareTable[p][s] = Value(EgPST[p][s] + i);
1981 for (Square s = SQ_A1; s <= SQ_H8; s++)
1982 for (Piece p = BP; p <= BK; p++)
1984 MgPieceSquareTable[p][s] = -MgPieceSquareTable[p-8][flip_square(s)];
1985 EgPieceSquareTable[p][s] = -EgPieceSquareTable[p-8][flip_square(s)];
1990 /// Position::flipped_copy() makes a copy of the input position, but with
1991 /// the white and black sides reversed. This is only useful for debugging,
1992 /// especially for finding evaluation symmetry bugs.
1994 void Position::flipped_copy(const Position &pos) {
1996 assert(pos.is_ok());
2001 for (Square s = SQ_A1; s <= SQ_H8; s++)
2002 if (!pos.square_is_empty(s))
2003 put_piece(Piece(int(pos.piece_on(s)) ^ 8), flip_square(s));
2006 sideToMove = opposite_color(pos.side_to_move());
2009 if (pos.can_castle_kingside(WHITE)) allow_oo(BLACK);
2010 if (pos.can_castle_queenside(WHITE)) allow_ooo(BLACK);
2011 if (pos.can_castle_kingside(BLACK)) allow_oo(WHITE);
2012 if (pos.can_castle_queenside(BLACK)) allow_ooo(WHITE);
2014 initialKFile = pos.initialKFile;
2015 initialKRFile = pos.initialKRFile;
2016 initialQRFile = pos.initialQRFile;
2018 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
2019 castleRightsMask[sq] = ALL_CASTLES;
2021 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
2022 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
2023 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
2024 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
2025 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
2026 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
2028 // En passant square
2029 if (pos.st->epSquare != SQ_NONE)
2030 st->epSquare = flip_square(pos.st->epSquare);
2036 st->key = compute_key();
2037 st->pawnKey = compute_pawn_key();
2038 st->materialKey = compute_material_key();
2040 // Incremental scores
2041 st->mgValue = compute_value<MidGame>();
2042 st->egValue = compute_value<EndGame>();
2045 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
2046 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
2052 /// Position::is_ok() performs some consitency checks for the position object.
2053 /// This is meant to be helpful when debugging.
2055 bool Position::is_ok(int* failedStep) const {
2057 // What features of the position should be verified?
2058 static const bool debugBitboards = false;
2059 static const bool debugKingCount = false;
2060 static const bool debugKingCapture = false;
2061 static const bool debugCheckerCount = false;
2062 static const bool debugKey = false;
2063 static const bool debugMaterialKey = false;
2064 static const bool debugPawnKey = false;
2065 static const bool debugIncrementalEval = false;
2066 static const bool debugNonPawnMaterial = false;
2067 static const bool debugPieceCounts = false;
2068 static const bool debugPieceList = false;
2070 if (failedStep) *failedStep = 1;
2073 if (!color_is_ok(side_to_move()))
2076 // Are the king squares in the position correct?
2077 if (failedStep) (*failedStep)++;
2078 if (piece_on(king_square(WHITE)) != WK)
2081 if (failedStep) (*failedStep)++;
2082 if (piece_on(king_square(BLACK)) != BK)
2086 if (failedStep) (*failedStep)++;
2087 if (!file_is_ok(initialKRFile))
2090 if (!file_is_ok(initialQRFile))
2093 // Do both sides have exactly one king?
2094 if (failedStep) (*failedStep)++;
2097 int kingCount[2] = {0, 0};
2098 for (Square s = SQ_A1; s <= SQ_H8; s++)
2099 if (type_of_piece_on(s) == KING)
2100 kingCount[color_of_piece_on(s)]++;
2102 if (kingCount[0] != 1 || kingCount[1] != 1)
2106 // Can the side to move capture the opponent's king?
2107 if (failedStep) (*failedStep)++;
2108 if (debugKingCapture)
2110 Color us = side_to_move();
2111 Color them = opposite_color(us);
2112 Square ksq = king_square(them);
2113 if (square_is_attacked(ksq, us))
2117 // Is there more than 2 checkers?
2118 if (failedStep) (*failedStep)++;
2119 if (debugCheckerCount && count_1s(st->checkersBB) > 2)
2123 if (failedStep) (*failedStep)++;
2126 // The intersection of the white and black pieces must be empty
2127 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
2130 // The union of the white and black pieces must be equal to all
2132 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
2135 // Separate piece type bitboards must have empty intersections
2136 for (PieceType p1 = PAWN; p1 <= KING; p1++)
2137 for (PieceType p2 = PAWN; p2 <= KING; p2++)
2138 if (p1 != p2 && (pieces_of_type(p1) & pieces_of_type(p2)))
2142 // En passant square OK?
2143 if (failedStep) (*failedStep)++;
2144 if (ep_square() != SQ_NONE)
2146 // The en passant square must be on rank 6, from the point of view of the
2148 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
2153 if (failedStep) (*failedStep)++;
2154 if (debugKey && st->key != compute_key())
2157 // Pawn hash key OK?
2158 if (failedStep) (*failedStep)++;
2159 if (debugPawnKey && st->pawnKey != compute_pawn_key())
2162 // Material hash key OK?
2163 if (failedStep) (*failedStep)++;
2164 if (debugMaterialKey && st->materialKey != compute_material_key())
2167 // Incremental eval OK?
2168 if (failedStep) (*failedStep)++;
2169 if (debugIncrementalEval)
2171 if (st->mgValue != compute_value<MidGame>())
2174 if (st->egValue != compute_value<EndGame>())
2178 // Non-pawn material OK?
2179 if (failedStep) (*failedStep)++;
2180 if (debugNonPawnMaterial)
2182 if (npMaterial[WHITE] != compute_non_pawn_material(WHITE))
2185 if (npMaterial[BLACK] != compute_non_pawn_material(BLACK))
2190 if (failedStep) (*failedStep)++;
2191 if (debugPieceCounts)
2192 for (Color c = WHITE; c <= BLACK; c++)
2193 for (PieceType pt = PAWN; pt <= KING; pt++)
2194 if (pieceCount[c][pt] != count_1s(pieces_of_color_and_type(c, pt)))
2197 if (failedStep) (*failedStep)++;
2200 for(Color c = WHITE; c <= BLACK; c++)
2201 for(PieceType pt = PAWN; pt <= KING; pt++)
2202 for(int i = 0; i < pieceCount[c][pt]; i++)
2204 if (piece_on(piece_list(c, pt, i)) != piece_of_color_and_type(c, pt))
2207 if (index[piece_list(c, pt, i)] != i)
2211 if (failedStep) *failedStep = 0;