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 ( dcCandidates // Discovered check?
556 && bit_is_set(dcCandidates, from)
557 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
560 if (move_promotion(m)) // Promotion with check?
562 Bitboard b = occupied_squares();
565 switch (move_promotion(m))
568 return bit_is_set(piece_attacks<KNIGHT>(to), ksq);
570 return bit_is_set(bishop_attacks_bb(to, b), ksq);
572 return bit_is_set(rook_attacks_bb(to, b), ksq);
574 return bit_is_set(queen_attacks_bb(to, b), ksq);
579 // En passant capture with check? We have already handled the case
580 // of direct checks and ordinary discovered check, the only case we
581 // need to handle is the unusual case of a discovered check through the
583 else if (move_is_ep(m))
585 Square capsq = make_square(square_file(to), square_rank(from));
586 Bitboard b = occupied_squares();
588 clear_bit(&b, capsq);
590 return (rook_attacks_bb(ksq, b) & rooks_and_queens(us))
591 ||(bishop_attacks_bb(ksq, b) & bishops_and_queens(us));
595 // Test discovered check and normal check according to piece type
597 return (dcCandidates && bit_is_set(dcCandidates, from))
598 || bit_is_set(piece_attacks<KNIGHT>(ksq), to);
601 return (dcCandidates && bit_is_set(dcCandidates, from))
602 || ( direction_between_squares(ksq, to) != DIR_NONE
603 && bit_is_set(piece_attacks<BISHOP>(ksq), to));
606 return (dcCandidates && bit_is_set(dcCandidates, from))
607 || ( direction_between_squares(ksq, to) != DIR_NONE
608 && bit_is_set(piece_attacks<ROOK>(ksq), to));
611 // Discovered checks are impossible!
612 assert(!bit_is_set(dcCandidates, from));
613 return ( direction_between_squares(ksq, to) != DIR_NONE
614 && bit_is_set(piece_attacks<QUEEN>(ksq), to));
618 if ( bit_is_set(dcCandidates, from)
619 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
622 // Castling with check?
623 if (move_is_castle(m))
625 Square kfrom, kto, rfrom, rto;
626 Bitboard b = occupied_squares();
632 kto = relative_square(us, SQ_G1);
633 rto = relative_square(us, SQ_F1);
635 kto = relative_square(us, SQ_C1);
636 rto = relative_square(us, SQ_D1);
638 clear_bit(&b, kfrom);
639 clear_bit(&b, rfrom);
642 return bit_is_set(rook_attacks_bb(rto, b), ksq);
646 default: // NO_PIECE_TYPE
654 /// Position::update_checkers() udpates chekers info given the move. It is called
655 /// in do_move() and is faster then find_checkers().
657 template<PieceType Piece>
658 inline void Position::update_checkers(Bitboard* pCheckersBB, Square ksq, Square from,
659 Square to, Bitboard dcCandidates) {
661 const bool Bishop = (Piece == QUEEN || Piece == BISHOP);
662 const bool Rook = (Piece == QUEEN || Piece == ROOK);
663 const bool Slider = Bishop || Rook;
665 if ( ( (Bishop && bit_is_set(BishopPseudoAttacks[ksq], to))
666 || (Rook && bit_is_set(RookPseudoAttacks[ksq], to)))
667 && bit_is_set(piece_attacks<Piece>(ksq), to)) // slow, try to early skip
668 set_bit(pCheckersBB, to);
670 else if ( Piece != KING
672 && bit_is_set(piece_attacks<Piece>(ksq), to))
673 set_bit(pCheckersBB, to);
675 if (Piece != QUEEN && bit_is_set(dcCandidates, from))
678 (*pCheckersBB) |= (piece_attacks<ROOK>(ksq) & rooks_and_queens(side_to_move()));
681 (*pCheckersBB) |= (piece_attacks<BISHOP>(ksq) & bishops_and_queens(side_to_move()));
686 /// Position::do_move() makes a move, and saves all information necessary
687 /// to a StateInfo object. The move is assumed to be legal.
688 /// Pseudo-legal moves should be filtered out before this function is called.
690 void Position::do_move(Move m, StateInfo& newSt) {
692 do_move(m, newSt, discovered_check_candidates(side_to_move()));
695 void Position::do_move(Move m, StateInfo& newSt, Bitboard dcCandidates) {
698 assert(move_is_ok(m));
700 // Copy some fields of old state to our new StateInfo object except the
701 // ones which are recalculated from scratch anyway, then switch our state
702 // pointer to point to the new, ready to be updated, state.
703 struct ReducedStateInfo {
704 Key key, pawnKey, materialKey;
705 int castleRights, rule50;
707 Value mgValue, egValue;
710 memcpy(&newSt, st, sizeof(ReducedStateInfo));
711 newSt.capture = NO_PIECE_TYPE;
715 // Save the current key to the history[] array, in order to be able to
716 // detect repetition draws.
717 history[gamePly] = st->key;
719 // Increment the 50 moves rule draw counter. Resetting it to zero in the
720 // case of non-reversible moves is taken care of later.
723 if (move_is_castle(m))
725 else if (move_promotion(m))
726 do_promotion_move(m);
727 else if (move_is_ep(m))
731 Color us = side_to_move();
732 Color them = opposite_color(us);
733 Square from = move_from(m);
734 Square to = move_to(m);
736 assert(color_of_piece_on(from) == us);
737 assert(color_of_piece_on(to) == them || piece_on(to) == EMPTY);
739 PieceType piece = type_of_piece_on(from);
741 st->capture = type_of_piece_on(to);
744 do_capture_move(st->capture, them, to);
747 clear_bit(&(byColorBB[us]), from);
748 clear_bit(&(byTypeBB[piece]), from);
749 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
750 set_bit(&(byColorBB[us]), to);
751 set_bit(&(byTypeBB[piece]), to);
752 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
753 board[to] = board[from];
757 st->key ^= zobrist[us][piece][from] ^ zobrist[us][piece][to];
759 // Update incremental scores
760 st->mgValue -= pst<MidGame>(us, piece, from);
761 st->mgValue += pst<MidGame>(us, piece, to);
762 st->egValue -= pst<EndGame>(us, piece, from);
763 st->egValue += pst<EndGame>(us, piece, to);
765 // If the moving piece was a king, update the king square
769 // Reset en passant square
770 if (st->epSquare != SQ_NONE)
772 st->key ^= zobEp[st->epSquare];
773 st->epSquare = SQ_NONE;
776 // If the moving piece was a pawn do some special extra work
779 // Reset rule 50 draw counter
782 // Update pawn hash key
783 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
785 // Set en passant square, only if moved pawn can be captured
786 if (abs(int(to) - int(from)) == 16)
788 if ( (us == WHITE && (pawn_attacks(WHITE, from + DELTA_N) & pawns(BLACK)))
789 || (us == BLACK && (pawn_attacks(BLACK, from + DELTA_S) & pawns(WHITE))))
791 st->epSquare = Square((int(from) + int(to)) / 2);
792 st->key ^= zobEp[st->epSquare];
797 // Update piece lists
798 pieceList[us][piece][index[from]] = to;
799 index[to] = index[from];
801 // Update castle rights
802 st->key ^= zobCastle[st->castleRights];
803 st->castleRights &= castleRightsMask[from];
804 st->castleRights &= castleRightsMask[to];
805 st->key ^= zobCastle[st->castleRights];
807 // Update checkers bitboard, piece must be already moved
808 st->checkersBB = EmptyBoardBB;
809 Square ksq = king_square(them);
812 case PAWN: update_checkers<PAWN>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
813 case KNIGHT: update_checkers<KNIGHT>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
814 case BISHOP: update_checkers<BISHOP>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
815 case ROOK: update_checkers<ROOK>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
816 case QUEEN: update_checkers<QUEEN>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
817 case KING: update_checkers<KING>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
818 default: assert(false); break;
823 st->key ^= zobSideToMove;
824 sideToMove = opposite_color(sideToMove);
827 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
828 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
834 /// Position::do_capture_move() is a private method used to update captured
835 /// piece info. It is called from the main Position::do_move function.
837 void Position::do_capture_move(PieceType capture, Color them, Square to) {
839 assert(capture != KING);
841 // Remove captured piece
842 clear_bit(&(byColorBB[them]), to);
843 clear_bit(&(byTypeBB[capture]), to);
846 st->key ^= zobrist[them][capture][to];
848 // If the captured piece was a pawn, update pawn hash key
850 st->pawnKey ^= zobrist[them][PAWN][to];
852 // Update incremental scores
853 st->mgValue -= pst<MidGame>(them, capture, to);
854 st->egValue -= pst<EndGame>(them, capture, to);
858 npMaterial[them] -= piece_value_midgame(capture);
860 // Update material hash key
861 st->materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];
863 // Update piece count
864 pieceCount[them][capture]--;
867 pieceList[them][capture][index[to]] = pieceList[them][capture][pieceCount[them][capture]];
868 index[pieceList[them][capture][index[to]]] = index[to];
870 // Reset rule 50 counter
875 /// Position::do_castle_move() is a private method used to make a castling
876 /// move. It is called from the main Position::do_move function. Note that
877 /// castling moves are encoded as "king captures friendly rook" moves, for
878 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
880 void Position::do_castle_move(Move m) {
883 assert(move_is_ok(m));
884 assert(move_is_castle(m));
886 Color us = side_to_move();
887 Color them = opposite_color(us);
889 // Find source squares for king and rook
890 Square kfrom = move_from(m);
891 Square rfrom = move_to(m); // HACK: See comment at beginning of function
894 assert(piece_on(kfrom) == piece_of_color_and_type(us, KING));
895 assert(piece_on(rfrom) == piece_of_color_and_type(us, ROOK));
897 // Find destination squares for king and rook
898 if (rfrom > kfrom) // O-O
900 kto = relative_square(us, SQ_G1);
901 rto = relative_square(us, SQ_F1);
903 kto = relative_square(us, SQ_C1);
904 rto = relative_square(us, SQ_D1);
907 // Remove pieces from source squares
908 clear_bit(&(byColorBB[us]), kfrom);
909 clear_bit(&(byTypeBB[KING]), kfrom);
910 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
911 clear_bit(&(byColorBB[us]), rfrom);
912 clear_bit(&(byTypeBB[ROOK]), rfrom);
913 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
915 // Put pieces on destination squares
916 set_bit(&(byColorBB[us]), kto);
917 set_bit(&(byTypeBB[KING]), kto);
918 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
919 set_bit(&(byColorBB[us]), rto);
920 set_bit(&(byTypeBB[ROOK]), rto);
921 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
923 // Update board array
924 board[kfrom] = board[rfrom] = EMPTY;
925 board[kto] = piece_of_color_and_type(us, KING);
926 board[rto] = piece_of_color_and_type(us, ROOK);
928 // Update king square
929 kingSquare[us] = kto;
931 // Update piece lists
932 pieceList[us][KING][index[kfrom]] = kto;
933 pieceList[us][ROOK][index[rfrom]] = rto;
934 int tmp = index[rfrom];
935 index[kto] = index[kfrom];
938 // Update incremental scores
939 st->mgValue -= pst<MidGame>(us, KING, kfrom);
940 st->mgValue += pst<MidGame>(us, KING, kto);
941 st->egValue -= pst<EndGame>(us, KING, kfrom);
942 st->egValue += pst<EndGame>(us, KING, kto);
943 st->mgValue -= pst<MidGame>(us, ROOK, rfrom);
944 st->mgValue += pst<MidGame>(us, ROOK, rto);
945 st->egValue -= pst<EndGame>(us, ROOK, rfrom);
946 st->egValue += pst<EndGame>(us, ROOK, rto);
949 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
950 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
952 // Clear en passant square
953 if (st->epSquare != SQ_NONE)
955 st->key ^= zobEp[st->epSquare];
956 st->epSquare = SQ_NONE;
959 // Update castling rights
960 st->key ^= zobCastle[st->castleRights];
961 st->castleRights &= castleRightsMask[kfrom];
962 st->key ^= zobCastle[st->castleRights];
964 // Reset rule 50 counter
967 // Update checkers BB
968 st->checkersBB = attacks_to(king_square(them), us);
972 /// Position::do_promotion_move() is a private method used to make a promotion
973 /// move. It is called from the main Position::do_move function.
975 void Position::do_promotion_move(Move m) {
982 assert(move_is_ok(m));
983 assert(move_promotion(m));
986 them = opposite_color(us);
990 assert(relative_rank(us, to) == RANK_8);
991 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
992 assert(color_of_piece_on(to) == them || square_is_empty(to));
994 st->capture = type_of_piece_on(to);
997 do_capture_move(st->capture, them, to);
1000 clear_bit(&(byColorBB[us]), from);
1001 clear_bit(&(byTypeBB[PAWN]), from);
1002 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1003 board[from] = EMPTY;
1005 // Insert promoted piece
1006 promotion = move_promotion(m);
1007 assert(promotion >= KNIGHT && promotion <= QUEEN);
1008 set_bit(&(byColorBB[us]), to);
1009 set_bit(&(byTypeBB[promotion]), to);
1010 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1011 board[to] = piece_of_color_and_type(us, promotion);
1014 st->key ^= zobrist[us][PAWN][from] ^ zobrist[us][promotion][to];
1016 // Update pawn hash key
1017 st->pawnKey ^= zobrist[us][PAWN][from];
1019 // Update material key
1020 st->materialKey ^= zobMaterial[us][PAWN][pieceCount[us][PAWN]];
1021 st->materialKey ^= zobMaterial[us][promotion][pieceCount[us][promotion]+1];
1023 // Update piece counts
1024 pieceCount[us][PAWN]--;
1025 pieceCount[us][promotion]++;
1027 // Update piece lists
1028 pieceList[us][PAWN][index[from]] = pieceList[us][PAWN][pieceCount[us][PAWN]];
1029 index[pieceList[us][PAWN][index[from]]] = index[from];
1030 pieceList[us][promotion][pieceCount[us][promotion] - 1] = to;
1031 index[to] = pieceCount[us][promotion] - 1;
1033 // Update incremental scores
1034 st->mgValue -= pst<MidGame>(us, PAWN, from);
1035 st->mgValue += pst<MidGame>(us, promotion, to);
1036 st->egValue -= pst<EndGame>(us, PAWN, from);
1037 st->egValue += pst<EndGame>(us, promotion, to);
1040 npMaterial[us] += piece_value_midgame(promotion);
1042 // Clear the en passant square
1043 if (st->epSquare != SQ_NONE)
1045 st->key ^= zobEp[st->epSquare];
1046 st->epSquare = SQ_NONE;
1049 // Update castle rights
1050 st->key ^= zobCastle[st->castleRights];
1051 st->castleRights &= castleRightsMask[to];
1052 st->key ^= zobCastle[st->castleRights];
1054 // Reset rule 50 counter
1057 // Update checkers BB
1058 st->checkersBB = attacks_to(king_square(them), us);
1062 /// Position::do_ep_move() is a private method used to make an en passant
1063 /// capture. It is called from the main Position::do_move function.
1065 void Position::do_ep_move(Move m) {
1068 Square from, to, capsq;
1071 assert(move_is_ok(m));
1072 assert(move_is_ep(m));
1074 us = side_to_move();
1075 them = opposite_color(us);
1076 from = move_from(m);
1078 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1080 assert(to == st->epSquare);
1081 assert(relative_rank(us, to) == RANK_6);
1082 assert(piece_on(to) == EMPTY);
1083 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
1084 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
1086 // Remove captured piece
1087 clear_bit(&(byColorBB[them]), capsq);
1088 clear_bit(&(byTypeBB[PAWN]), capsq);
1089 clear_bit(&(byTypeBB[0]), capsq); // HACK: byTypeBB[0] == occupied squares
1090 board[capsq] = EMPTY;
1092 // Remove moving piece from source square
1093 clear_bit(&(byColorBB[us]), from);
1094 clear_bit(&(byTypeBB[PAWN]), from);
1095 clear_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1097 // Put moving piece on destination square
1098 set_bit(&(byColorBB[us]), to);
1099 set_bit(&(byTypeBB[PAWN]), to);
1100 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1101 board[to] = board[from];
1102 board[from] = EMPTY;
1104 // Update material hash key
1105 st->materialKey ^= zobMaterial[them][PAWN][pieceCount[them][PAWN]];
1107 // Update piece count
1108 pieceCount[them][PAWN]--;
1110 // Update piece list
1111 pieceList[us][PAWN][index[from]] = to;
1112 index[to] = index[from];
1113 pieceList[them][PAWN][index[capsq]] = pieceList[them][PAWN][pieceCount[them][PAWN]];
1114 index[pieceList[them][PAWN][index[capsq]]] = index[capsq];
1117 st->key ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1118 st->key ^= zobrist[them][PAWN][capsq];
1119 st->key ^= zobEp[st->epSquare];
1121 // Update pawn hash key
1122 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
1123 st->pawnKey ^= zobrist[them][PAWN][capsq];
1125 // Update incremental scores
1126 st->mgValue -= pst<MidGame>(them, PAWN, capsq);
1127 st->mgValue -= pst<MidGame>(us, PAWN, from);
1128 st->mgValue += pst<MidGame>(us, PAWN, to);
1129 st->egValue -= pst<EndGame>(them, PAWN, capsq);
1130 st->egValue -= pst<EndGame>(us, PAWN, from);
1131 st->egValue += pst<EndGame>(us, PAWN, to);
1133 // Reset en passant square
1134 st->epSquare = SQ_NONE;
1136 // Reset rule 50 counter
1139 // Update checkers BB
1140 st->checkersBB = attacks_to(king_square(them), us);
1144 /// Position::undo_move() unmakes a move. When it returns, the position should
1145 /// be restored to exactly the same state as before the move was made.
1147 void Position::undo_move(Move m) {
1150 assert(move_is_ok(m));
1153 sideToMove = opposite_color(sideToMove);
1155 if (move_is_castle(m))
1156 undo_castle_move(m);
1157 else if (move_promotion(m))
1158 undo_promotion_move(m);
1159 else if (move_is_ep(m))
1167 us = side_to_move();
1168 them = opposite_color(us);
1169 from = move_from(m);
1172 assert(piece_on(from) == EMPTY);
1173 assert(color_of_piece_on(to) == us);
1175 // Put the piece back at the source square
1176 piece = type_of_piece_on(to);
1177 set_bit(&(byColorBB[us]), from);
1178 set_bit(&(byTypeBB[piece]), from);
1179 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1180 board[from] = piece_of_color_and_type(us, piece);
1182 // Clear the destination square
1183 clear_bit(&(byColorBB[us]), to);
1184 clear_bit(&(byTypeBB[piece]), to);
1185 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1187 // If the moving piece was a king, update the king square
1189 kingSquare[us] = from;
1191 // Update piece list
1192 pieceList[us][piece][index[to]] = from;
1193 index[from] = index[to];
1197 assert(st->capture != KING);
1199 // Replace the captured piece
1200 set_bit(&(byColorBB[them]), to);
1201 set_bit(&(byTypeBB[st->capture]), to);
1202 set_bit(&(byTypeBB[0]), to);
1203 board[to] = piece_of_color_and_type(them, st->capture);
1206 if (st->capture != PAWN)
1207 npMaterial[them] += piece_value_midgame(st->capture);
1209 // Update piece list
1210 pieceList[them][st->capture][pieceCount[them][st->capture]] = to;
1211 index[to] = pieceCount[them][st->capture];
1213 // Update piece count
1214 pieceCount[them][st->capture]++;
1219 // Finally point our state pointer back to the previous state
1226 /// Position::undo_castle_move() is a private method used to unmake a castling
1227 /// move. It is called from the main Position::undo_move function. Note that
1228 /// castling moves are encoded as "king captures friendly rook" moves, for
1229 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1231 void Position::undo_castle_move(Move m) {
1233 assert(move_is_ok(m));
1234 assert(move_is_castle(m));
1236 // When we have arrived here, some work has already been done by
1237 // Position::undo_move. In particular, the side to move has been switched,
1238 // so the code below is correct.
1239 Color us = side_to_move();
1241 // Find source squares for king and rook
1242 Square kfrom = move_from(m);
1243 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1246 // Find destination squares for king and rook
1247 if (rfrom > kfrom) // O-O
1249 kto = relative_square(us, SQ_G1);
1250 rto = relative_square(us, SQ_F1);
1252 kto = relative_square(us, SQ_C1);
1253 rto = relative_square(us, SQ_D1);
1256 assert(piece_on(kto) == piece_of_color_and_type(us, KING));
1257 assert(piece_on(rto) == piece_of_color_and_type(us, ROOK));
1259 // Remove pieces from destination squares
1260 clear_bit(&(byColorBB[us]), kto);
1261 clear_bit(&(byTypeBB[KING]), kto);
1262 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1263 clear_bit(&(byColorBB[us]), rto);
1264 clear_bit(&(byTypeBB[ROOK]), rto);
1265 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1267 // Put pieces on source squares
1268 set_bit(&(byColorBB[us]), kfrom);
1269 set_bit(&(byTypeBB[KING]), kfrom);
1270 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1271 set_bit(&(byColorBB[us]), rfrom);
1272 set_bit(&(byTypeBB[ROOK]), rfrom);
1273 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1276 board[rto] = board[kto] = EMPTY;
1277 board[rfrom] = piece_of_color_and_type(us, ROOK);
1278 board[kfrom] = piece_of_color_and_type(us, KING);
1280 // Update king square
1281 kingSquare[us] = kfrom;
1283 // Update piece lists
1284 pieceList[us][KING][index[kto]] = kfrom;
1285 pieceList[us][ROOK][index[rto]] = rfrom;
1286 int tmp = index[rto]; // Necessary because we may have rto == kfrom in FRC.
1287 index[kfrom] = index[kto];
1292 /// Position::undo_promotion_move() is a private method used to unmake a
1293 /// promotion move. It is called from the main Position::do_move
1296 void Position::undo_promotion_move(Move m) {
1300 PieceType promotion;
1302 assert(move_is_ok(m));
1303 assert(move_promotion(m));
1305 // When we have arrived here, some work has already been done by
1306 // Position::undo_move. In particular, the side to move has been switched,
1307 // so the code below is correct.
1308 us = side_to_move();
1309 them = opposite_color(us);
1310 from = move_from(m);
1313 assert(relative_rank(us, to) == RANK_8);
1314 assert(piece_on(from) == EMPTY);
1316 // Remove promoted piece
1317 promotion = move_promotion(m);
1318 assert(piece_on(to)==piece_of_color_and_type(us, promotion));
1319 assert(promotion >= KNIGHT && promotion <= QUEEN);
1320 clear_bit(&(byColorBB[us]), to);
1321 clear_bit(&(byTypeBB[promotion]), to);
1322 clear_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1324 // Insert pawn at source square
1325 set_bit(&(byColorBB[us]), from);
1326 set_bit(&(byTypeBB[PAWN]), from);
1327 set_bit(&(byTypeBB[0]), from); // HACK: byTypeBB[0] == occupied squares
1328 board[from] = piece_of_color_and_type(us, PAWN);
1331 npMaterial[us] -= piece_value_midgame(promotion);
1333 // Update piece list
1334 pieceList[us][PAWN][pieceCount[us][PAWN]] = from;
1335 index[from] = pieceCount[us][PAWN];
1336 pieceList[us][promotion][index[to]] =
1337 pieceList[us][promotion][pieceCount[us][promotion] - 1];
1338 index[pieceList[us][promotion][index[to]]] = index[to];
1340 // Update piece counts
1341 pieceCount[us][promotion]--;
1342 pieceCount[us][PAWN]++;
1346 assert(st->capture != KING);
1348 // Insert captured piece:
1349 set_bit(&(byColorBB[them]), to);
1350 set_bit(&(byTypeBB[st->capture]), to);
1351 set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
1352 board[to] = piece_of_color_and_type(them, st->capture);
1354 // Update material. Because the move is a promotion move, we know
1355 // that the captured piece cannot be a pawn.
1356 assert(st->capture != PAWN);
1357 npMaterial[them] += piece_value_midgame(st->capture);
1359 // Update piece list
1360 pieceList[them][st->capture][pieceCount[them][st->capture]] = to;
1361 index[to] = pieceCount[them][st->capture];
1363 // Update piece count
1364 pieceCount[them][st->capture]++;
1370 /// Position::undo_ep_move() is a private method used to unmake an en passant
1371 /// capture. It is called from the main Position::undo_move function.
1373 void Position::undo_ep_move(Move m) {
1375 assert(move_is_ok(m));
1376 assert(move_is_ep(m));
1378 // When we have arrived here, some work has already been done by
1379 // Position::undo_move. In particular, the side to move has been switched,
1380 // so the code below is correct.
1381 Color us = side_to_move();
1382 Color them = opposite_color(us);
1383 Square from = move_from(m);
1384 Square to = move_to(m);
1385 Square capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1387 assert(to == st->previous->epSquare);
1388 assert(relative_rank(us, to) == RANK_6);
1389 assert(piece_on(to) == piece_of_color_and_type(us, PAWN));
1390 assert(piece_on(from) == EMPTY);
1391 assert(piece_on(capsq) == EMPTY);
1393 // Replace captured piece
1394 set_bit(&(byColorBB[them]), capsq);
1395 set_bit(&(byTypeBB[PAWN]), capsq);
1396 set_bit(&(byTypeBB[0]), capsq);
1397 board[capsq] = piece_of_color_and_type(them, PAWN);
1399 // Remove moving piece from destination square
1400 clear_bit(&(byColorBB[us]), to);
1401 clear_bit(&(byTypeBB[PAWN]), to);
1402 clear_bit(&(byTypeBB[0]), to);
1405 // Replace moving piece at source square
1406 set_bit(&(byColorBB[us]), from);
1407 set_bit(&(byTypeBB[PAWN]), from);
1408 set_bit(&(byTypeBB[0]), from);
1409 board[from] = piece_of_color_and_type(us, PAWN);
1411 // Update piece list:
1412 pieceList[us][PAWN][index[to]] = from;
1413 index[from] = index[to];
1414 pieceList[them][PAWN][pieceCount[them][PAWN]] = capsq;
1415 index[capsq] = pieceCount[them][PAWN];
1417 // Update piece count:
1418 pieceCount[them][PAWN]++;
1422 /// Position::do_null_move makes() a "null move": It switches the side to move
1423 /// and updates the hash key without executing any move on the board.
1425 void Position::do_null_move(StateInfo& backupSt) {
1428 assert(!is_check());
1430 // Back up the information necessary to undo the null move to the supplied
1431 // StateInfo object. In the case of a null move, the only thing we need to
1432 // remember is the last move made and the en passant square.
1433 // Note that differently from normal case here backupSt is actually used as
1434 // a backup storage not as a new state to be used.
1435 backupSt.lastMove = st->lastMove;
1436 backupSt.epSquare = st->epSquare;
1437 backupSt.previous = st->previous;
1438 st->previous = &backupSt;
1440 // Save the current key to the history[] array, in order to be able to
1441 // detect repetition draws.
1442 history[gamePly] = st->key;
1444 // Update the necessary information
1445 sideToMove = opposite_color(sideToMove);
1446 if (st->epSquare != SQ_NONE)
1447 st->key ^= zobEp[st->epSquare];
1449 st->epSquare = SQ_NONE;
1452 st->key ^= zobSideToMove;
1454 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1455 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1461 /// Position::undo_null_move() unmakes a "null move".
1463 void Position::undo_null_move() {
1466 assert(!is_check());
1468 // Restore information from the our backup StateInfo object
1469 st->lastMove = st->previous->lastMove;
1470 st->epSquare = st->previous->epSquare;
1471 st->previous = st->previous->previous;
1473 if (st->epSquare != SQ_NONE)
1474 st->key ^= zobEp[st->epSquare];
1476 // Update the necessary information
1477 sideToMove = opposite_color(sideToMove);
1480 st->key ^= zobSideToMove;
1482 st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
1483 st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
1489 /// Position::see() is a static exchange evaluator: It tries to estimate the
1490 /// material gain or loss resulting from a move. There are three versions of
1491 /// this function: One which takes a destination square as input, one takes a
1492 /// move, and one which takes a 'from' and a 'to' square. The function does
1493 /// not yet understand promotions captures.
1495 int Position::see(Square to) const {
1497 assert(square_is_ok(to));
1498 return see(SQ_NONE, to);
1501 int Position::see(Move m) const {
1503 assert(move_is_ok(m));
1504 return see(move_from(m), move_to(m));
1507 int Position::see(Square from, Square to) const {
1510 static const int seeValues[18] = {
1511 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1512 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1513 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1514 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1518 Bitboard attackers, occ, b;
1520 assert(square_is_ok(from) || from == SQ_NONE);
1521 assert(square_is_ok(to));
1523 // Initialize colors
1524 Color us = (from != SQ_NONE ? color_of_piece_on(from) : opposite_color(color_of_piece_on(to)));
1525 Color them = opposite_color(us);
1527 // Initialize pieces
1528 Piece piece = piece_on(from);
1529 Piece capture = piece_on(to);
1531 // Find all attackers to the destination square, with the moving piece
1532 // removed, but possibly an X-ray attacker added behind it.
1533 occ = occupied_squares();
1535 // Handle en passant moves
1536 if (st->epSquare == to && type_of_piece_on(from) == PAWN)
1538 assert(capture == EMPTY);
1540 Square capQq = (side_to_move() == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1541 capture = piece_on(capQq);
1543 assert(type_of_piece_on(capQq) == PAWN);
1545 // Remove the captured pawn
1546 clear_bit(&occ, capQq);
1551 clear_bit(&occ, from);
1552 attackers = (rook_attacks_bb(to, occ) & rooks_and_queens())
1553 | (bishop_attacks_bb(to, occ) & bishops_and_queens())
1554 | (piece_attacks<KNIGHT>(to) & knights())
1555 | (piece_attacks<KING>(to) & kings())
1556 | (pawn_attacks(WHITE, to) & pawns(BLACK))
1557 | (pawn_attacks(BLACK, to) & pawns(WHITE));
1559 if (from != SQ_NONE)
1562 // If we don't have any attacker we are finished
1563 if ((attackers & pieces_of_color(us)) == EmptyBoardBB)
1566 // Locate the least valuable attacker to the destination square
1567 // and use it to initialize from square.
1569 for (pt = PAWN; !(attackers & pieces_of_color_and_type(us, pt)); pt++)
1572 from = first_1(attackers & pieces_of_color_and_type(us, pt));
1573 piece = piece_on(from);
1576 // If the opponent has no attackers we are finished
1577 if ((attackers & pieces_of_color(them)) == EmptyBoardBB)
1578 return seeValues[capture];
1580 attackers &= occ; // Remove the moving piece
1582 // The destination square is defended, which makes things rather more
1583 // difficult to compute. We proceed by building up a "swap list" containing
1584 // the material gain or loss at each stop in a sequence of captures to the
1585 // destination square, where the sides alternately capture, and always
1586 // capture with the least valuable piece. After each capture, we look for
1587 // new X-ray attacks from behind the capturing piece.
1588 int lastCapturingPieceValue = seeValues[piece];
1589 int swapList[32], n = 1;
1593 swapList[0] = seeValues[capture];
1596 // Locate the least valuable attacker for the side to move. The loop
1597 // below looks like it is potentially infinite, but it isn't. We know
1598 // that the side to move still has at least one attacker left.
1599 for (pt = PAWN; !(attackers & pieces_of_color_and_type(c, pt)); pt++)
1602 // Remove the attacker we just found from the 'attackers' bitboard,
1603 // and scan for new X-ray attacks behind the attacker.
1604 b = attackers & pieces_of_color_and_type(c, pt);
1605 occ ^= (b & (~b + 1));
1606 attackers |= (rook_attacks_bb(to, occ) & rooks_and_queens())
1607 | (bishop_attacks_bb(to, occ) & bishops_and_queens());
1611 // Add the new entry to the swap list
1613 swapList[n] = -swapList[n - 1] + lastCapturingPieceValue;
1616 // Remember the value of the capturing piece, and change the side to move
1617 // before beginning the next iteration
1618 lastCapturingPieceValue = seeValues[pt];
1619 c = opposite_color(c);
1621 // Stop after a king capture
1622 if (pt == KING && (attackers & pieces_of_color(c)))
1625 swapList[n++] = 100;
1628 } while (attackers & pieces_of_color(c));
1630 // Having built the swap list, we negamax through it to find the best
1631 // achievable score from the point of view of the side to move
1633 swapList[n-1] = Min(-swapList[n], swapList[n-1]);
1639 /// Position::setStartState() copies the content of the argument
1640 /// inside startState and makes st point to it. This is needed
1641 /// when the st pointee could become stale, as example because
1642 /// the caller is about to going out of scope.
1644 void Position::setStartState(const StateInfo& s) {
1651 /// Position::clear() erases the position object to a pristine state, with an
1652 /// empty board, white to move, and no castling rights.
1654 void Position::clear() {
1657 memset(st, 0, sizeof(StateInfo));
1658 st->epSquare = SQ_NONE;
1660 memset(index, 0, sizeof(int) * 64);
1661 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1663 for (int i = 0; i < 64; i++)
1666 for (int i = 0; i < 7; i++)
1668 byTypeBB[i] = EmptyBoardBB;
1669 pieceCount[0][i] = pieceCount[1][i] = 0;
1670 for (int j = 0; j < 8; j++)
1671 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1676 initialKFile = FILE_E;
1677 initialKRFile = FILE_H;
1678 initialQRFile = FILE_A;
1682 /// Position::reset_game_ply() simply sets gamePly to 0. It is used from the
1683 /// UCI interface code, whenever a non-reversible move is made in a
1684 /// 'position fen <fen> moves m1 m2 ...' command. This makes it possible
1685 /// for the program to handle games of arbitrary length, as long as the GUI
1686 /// handles draws by the 50 move rule correctly.
1688 void Position::reset_game_ply() {
1694 /// Position::put_piece() puts a piece on the given square of the board,
1695 /// updating the board array, bitboards, and piece counts.
1697 void Position::put_piece(Piece p, Square s) {
1699 Color c = color_of_piece(p);
1700 PieceType pt = type_of_piece(p);
1703 index[s] = pieceCount[c][pt];
1704 pieceList[c][pt][index[s]] = s;
1706 set_bit(&(byTypeBB[pt]), s);
1707 set_bit(&(byColorBB[c]), s);
1708 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1710 pieceCount[c][pt]++;
1717 /// Position::allow_oo() gives the given side the right to castle kingside.
1718 /// Used when setting castling rights during parsing of FEN strings.
1720 void Position::allow_oo(Color c) {
1722 st->castleRights |= (1 + int(c));
1726 /// Position::allow_ooo() gives the given side the right to castle queenside.
1727 /// Used when setting castling rights during parsing of FEN strings.
1729 void Position::allow_ooo(Color c) {
1731 st->castleRights |= (4 + 4*int(c));
1735 /// Position::compute_key() computes the hash key of the position. The hash
1736 /// key is usually updated incrementally as moves are made and unmade, the
1737 /// compute_key() function is only used when a new position is set up, and
1738 /// to verify the correctness of the hash key when running in debug mode.
1740 Key Position::compute_key() const {
1742 Key result = Key(0ULL);
1744 for (Square s = SQ_A1; s <= SQ_H8; s++)
1745 if (square_is_occupied(s))
1746 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1748 if (ep_square() != SQ_NONE)
1749 result ^= zobEp[ep_square()];
1751 result ^= zobCastle[st->castleRights];
1752 if (side_to_move() == BLACK)
1753 result ^= zobSideToMove;
1759 /// Position::compute_pawn_key() computes the hash key of the position. The
1760 /// hash key is usually updated incrementally as moves are made and unmade,
1761 /// the compute_pawn_key() function is only used when a new position is set
1762 /// up, and to verify the correctness of the pawn hash key when running in
1765 Key Position::compute_pawn_key() const {
1767 Key result = Key(0ULL);
1771 for (Color c = WHITE; c <= BLACK; c++)
1776 s = pop_1st_bit(&b);
1777 result ^= zobrist[c][PAWN][s];
1784 /// Position::compute_material_key() computes the hash key of the position.
1785 /// The hash key is usually updated incrementally as moves are made and unmade,
1786 /// the compute_material_key() function is only used when a new position is set
1787 /// up, and to verify the correctness of the material hash key when running in
1790 Key Position::compute_material_key() const {
1792 Key result = Key(0ULL);
1793 for (Color c = WHITE; c <= BLACK; c++)
1794 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1796 int count = piece_count(c, pt);
1797 for (int i = 0; i <= count; i++)
1798 result ^= zobMaterial[c][pt][i];
1804 /// Position::compute_value() compute the incremental scores for the middle
1805 /// game and the endgame. These functions are used to initialize the incremental
1806 /// scores when a new position is set up, and to verify that the scores are correctly
1807 /// updated by do_move and undo_move when the program is running in debug mode.
1808 template<Position::GamePhase Phase>
1809 Value Position::compute_value() const {
1811 Value result = Value(0);
1815 for (Color c = WHITE; c <= BLACK; c++)
1816 for (PieceType pt = PAWN; pt <= KING; pt++)
1818 b = pieces_of_color_and_type(c, pt);
1821 s = pop_1st_bit(&b);
1822 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1823 result += pst<Phase>(c, pt, s);
1827 const Value TempoValue = (Phase == MidGame ? TempoValueMidgame : TempoValueEndgame);
1828 result += (side_to_move() == WHITE)? TempoValue / 2 : -TempoValue / 2;
1833 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1834 /// game material score for the given side. Material scores are updated
1835 /// incrementally during the search, this function is only used while
1836 /// initializing a new Position object.
1838 Value Position::compute_non_pawn_material(Color c) const {
1840 Value result = Value(0);
1842 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1844 Bitboard b = pieces_of_color_and_type(c, pt);
1847 assert(piece_on(first_1(b)) == piece_of_color_and_type(c, pt));
1849 result += piece_value_midgame(pt);
1856 /// Position::is_draw() tests whether the position is drawn by material,
1857 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1858 /// must be done by the search.
1860 bool Position::is_draw() const {
1862 // Draw by material?
1864 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1867 // Draw by the 50 moves rule?
1868 if (st->rule50 > 100 || (st->rule50 == 100 && !is_check()))
1871 // Draw by repetition?
1872 for (int i = 2; i < Min(gamePly, st->rule50); i += 2)
1873 if (history[gamePly - i] == st->key)
1880 /// Position::is_mate() returns true or false depending on whether the
1881 /// side to move is checkmated.
1883 bool Position::is_mate() const {
1885 MoveStack moves[256];
1887 return is_check() && !generate_evasions(*this, moves, pinned_pieces(sideToMove));
1891 /// Position::has_mate_threat() tests whether a given color has a mate in one
1892 /// from the current position.
1894 bool Position::has_mate_threat(Color c) {
1897 Color stm = side_to_move();
1902 // If the input color is not equal to the side to move, do a null move
1906 MoveStack mlist[120];
1908 bool result = false;
1909 Bitboard dc = discovered_check_candidates(sideToMove);
1910 Bitboard pinned = pinned_pieces(sideToMove);
1912 // Generate pseudo-legal non-capture and capture check moves
1913 count = generate_non_capture_checks(*this, mlist, dc);
1914 count += generate_captures(*this, mlist + count);
1916 // Loop through the moves, and see if one of them is mate
1917 for (int i = 0; i < count; i++)
1919 Move move = mlist[i].move;
1921 if (!pl_move_is_legal(move, pinned))
1931 // Undo null move, if necessary
1939 /// Position::init_zobrist() is a static member function which initializes the
1940 /// various arrays used to compute hash keys.
1942 void Position::init_zobrist() {
1944 for(Piece p = WP; p <= BK; p++)
1945 for(Square s = SQ_A1; s <= SQ_H8; s++)
1946 zobrist[color_of_piece(p)][type_of_piece(p)][s] = genrand_int64();
1949 for(int i = 1; i < 64; i++)
1950 zobEp[i] = genrand_int64();
1952 for(int i = 15; i >= 0; i--)
1953 zobCastle[(i&8) | (i&1) | ((i&2) << 1) | ((i&4) >> 1)] = genrand_int64();
1955 zobSideToMove = genrand_int64();
1957 for (int i = 0; i < 2; i++)
1958 for (int j = 0; j < 8; j++)
1959 for (int k = 0; k < 16; k++)
1960 zobMaterial[i][j][k] = (k > 0)? genrand_int64() : 0LL;
1962 for (int i = 0; i < 16; i++)
1963 zobMaterial[0][KING][i] = zobMaterial[1][KING][i] = 0ULL;
1967 /// Position::init_piece_square_tables() initializes the piece square tables.
1968 /// This is a two-step operation: First, the white halves of the tables are
1969 /// copied from the MgPST[][] and EgPST[][] arrays, with a small random number
1970 /// added to each entry if the "Randomness" UCI parameter is non-zero.
1971 /// Second, the black halves of the tables are initialized by mirroring
1972 /// and changing the sign of the corresponding white scores.
1974 void Position::init_piece_square_tables() {
1976 int r = get_option_value_int("Randomness"), i;
1977 for (Square s = SQ_A1; s <= SQ_H8; s++)
1978 for (Piece p = WP; p <= WK; p++)
1980 i = (r == 0)? 0 : (genrand_int32() % (r*2) - r);
1981 MgPieceSquareTable[p][s] = Value(MgPST[p][s] + i);
1982 EgPieceSquareTable[p][s] = Value(EgPST[p][s] + i);
1985 for (Square s = SQ_A1; s <= SQ_H8; s++)
1986 for (Piece p = BP; p <= BK; p++)
1988 MgPieceSquareTable[p][s] = -MgPieceSquareTable[p-8][flip_square(s)];
1989 EgPieceSquareTable[p][s] = -EgPieceSquareTable[p-8][flip_square(s)];
1994 /// Position::flipped_copy() makes a copy of the input position, but with
1995 /// the white and black sides reversed. This is only useful for debugging,
1996 /// especially for finding evaluation symmetry bugs.
1998 void Position::flipped_copy(const Position &pos) {
2000 assert(pos.is_ok());
2005 for (Square s = SQ_A1; s <= SQ_H8; s++)
2006 if (!pos.square_is_empty(s))
2007 put_piece(Piece(int(pos.piece_on(s)) ^ 8), flip_square(s));
2010 sideToMove = opposite_color(pos.side_to_move());
2013 if (pos.can_castle_kingside(WHITE)) allow_oo(BLACK);
2014 if (pos.can_castle_queenside(WHITE)) allow_ooo(BLACK);
2015 if (pos.can_castle_kingside(BLACK)) allow_oo(WHITE);
2016 if (pos.can_castle_queenside(BLACK)) allow_ooo(WHITE);
2018 initialKFile = pos.initialKFile;
2019 initialKRFile = pos.initialKRFile;
2020 initialQRFile = pos.initialQRFile;
2022 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
2023 castleRightsMask[sq] = ALL_CASTLES;
2025 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
2026 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
2027 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
2028 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
2029 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
2030 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
2032 // En passant square
2033 if (pos.st->epSquare != SQ_NONE)
2034 st->epSquare = flip_square(pos.st->epSquare);
2040 st->key = compute_key();
2041 st->pawnKey = compute_pawn_key();
2042 st->materialKey = compute_material_key();
2044 // Incremental scores
2045 st->mgValue = compute_value<MidGame>();
2046 st->egValue = compute_value<EndGame>();
2049 npMaterial[WHITE] = compute_non_pawn_material(WHITE);
2050 npMaterial[BLACK] = compute_non_pawn_material(BLACK);
2056 /// Position::is_ok() performs some consitency checks for the position object.
2057 /// This is meant to be helpful when debugging.
2059 bool Position::is_ok(int* failedStep) const {
2061 // What features of the position should be verified?
2062 static const bool debugBitboards = false;
2063 static const bool debugKingCount = false;
2064 static const bool debugKingCapture = false;
2065 static const bool debugCheckerCount = false;
2066 static const bool debugKey = false;
2067 static const bool debugMaterialKey = false;
2068 static const bool debugPawnKey = false;
2069 static const bool debugIncrementalEval = false;
2070 static const bool debugNonPawnMaterial = false;
2071 static const bool debugPieceCounts = false;
2072 static const bool debugPieceList = false;
2074 if (failedStep) *failedStep = 1;
2077 if (!color_is_ok(side_to_move()))
2080 // Are the king squares in the position correct?
2081 if (failedStep) (*failedStep)++;
2082 if (piece_on(king_square(WHITE)) != WK)
2085 if (failedStep) (*failedStep)++;
2086 if (piece_on(king_square(BLACK)) != BK)
2090 if (failedStep) (*failedStep)++;
2091 if (!file_is_ok(initialKRFile))
2094 if (!file_is_ok(initialQRFile))
2097 // Do both sides have exactly one king?
2098 if (failedStep) (*failedStep)++;
2101 int kingCount[2] = {0, 0};
2102 for (Square s = SQ_A1; s <= SQ_H8; s++)
2103 if (type_of_piece_on(s) == KING)
2104 kingCount[color_of_piece_on(s)]++;
2106 if (kingCount[0] != 1 || kingCount[1] != 1)
2110 // Can the side to move capture the opponent's king?
2111 if (failedStep) (*failedStep)++;
2112 if (debugKingCapture)
2114 Color us = side_to_move();
2115 Color them = opposite_color(us);
2116 Square ksq = king_square(them);
2117 if (square_is_attacked(ksq, us))
2121 // Is there more than 2 checkers?
2122 if (failedStep) (*failedStep)++;
2123 if (debugCheckerCount && count_1s(st->checkersBB) > 2)
2127 if (failedStep) (*failedStep)++;
2130 // The intersection of the white and black pieces must be empty
2131 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
2134 // The union of the white and black pieces must be equal to all
2136 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
2139 // Separate piece type bitboards must have empty intersections
2140 for (PieceType p1 = PAWN; p1 <= KING; p1++)
2141 for (PieceType p2 = PAWN; p2 <= KING; p2++)
2142 if (p1 != p2 && (pieces_of_type(p1) & pieces_of_type(p2)))
2146 // En passant square OK?
2147 if (failedStep) (*failedStep)++;
2148 if (ep_square() != SQ_NONE)
2150 // The en passant square must be on rank 6, from the point of view of the
2152 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
2157 if (failedStep) (*failedStep)++;
2158 if (debugKey && st->key != compute_key())
2161 // Pawn hash key OK?
2162 if (failedStep) (*failedStep)++;
2163 if (debugPawnKey && st->pawnKey != compute_pawn_key())
2166 // Material hash key OK?
2167 if (failedStep) (*failedStep)++;
2168 if (debugMaterialKey && st->materialKey != compute_material_key())
2171 // Incremental eval OK?
2172 if (failedStep) (*failedStep)++;
2173 if (debugIncrementalEval)
2175 if (st->mgValue != compute_value<MidGame>())
2178 if (st->egValue != compute_value<EndGame>())
2182 // Non-pawn material OK?
2183 if (failedStep) (*failedStep)++;
2184 if (debugNonPawnMaterial)
2186 if (npMaterial[WHITE] != compute_non_pawn_material(WHITE))
2189 if (npMaterial[BLACK] != compute_non_pawn_material(BLACK))
2194 if (failedStep) (*failedStep)++;
2195 if (debugPieceCounts)
2196 for (Color c = WHITE; c <= BLACK; c++)
2197 for (PieceType pt = PAWN; pt <= KING; pt++)
2198 if (pieceCount[c][pt] != count_1s(pieces_of_color_and_type(c, pt)))
2201 if (failedStep) (*failedStep)++;
2204 for(Color c = WHITE; c <= BLACK; c++)
2205 for(PieceType pt = PAWN; pt <= KING; pt++)
2206 for(int i = 0; i < pieceCount[c][pt]; i++)
2208 if (piece_on(piece_list(c, pt, i)) != piece_of_color_and_type(c, pt))
2211 if (index[piece_list(c, pt, i)] != i)
2215 if (failedStep) *failedStep = 0;