2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2014 Marco Costalba, Joona Kiiski, Tord Romstad
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/>.
37 static const string PieceToChar(" PNBRQK pnbrqk");
41 Value PieceValue[PHASE_NB][PIECE_NB] = {
42 { VALUE_ZERO, PawnValueMg, KnightValueMg, BishopValueMg, RookValueMg, QueenValueMg },
43 { VALUE_ZERO, PawnValueEg, KnightValueEg, BishopValueEg, RookValueEg, QueenValueEg } };
45 static Score psq[COLOR_NB][PIECE_TYPE_NB][SQUARE_NB];
49 Key psq[COLOR_NB][PIECE_TYPE_NB][SQUARE_NB];
50 Key enpassant[FILE_NB];
51 Key castling[CASTLING_RIGHT_NB];
56 Key Position::exclusion_key() const { return st->key ^ Zobrist::exclusion;}
60 // min_attacker() is a helper function used by see() to locate the least
61 // valuable attacker for the side to move, remove the attacker we just found
62 // from the bitboards and scan for new X-ray attacks behind it.
64 template<int Pt> FORCE_INLINE
65 PieceType min_attacker(const Bitboard* bb, const Square& to, const Bitboard& stmAttackers,
66 Bitboard& occupied, Bitboard& attackers) {
68 Bitboard b = stmAttackers & bb[Pt];
70 return min_attacker<Pt+1>(bb, to, stmAttackers, occupied, attackers);
72 occupied ^= b & ~(b - 1);
74 if (Pt == PAWN || Pt == BISHOP || Pt == QUEEN)
75 attackers |= attacks_bb<BISHOP>(to, occupied) & (bb[BISHOP] | bb[QUEEN]);
77 if (Pt == ROOK || Pt == QUEEN)
78 attackers |= attacks_bb<ROOK>(to, occupied) & (bb[ROOK] | bb[QUEEN]);
80 attackers &= occupied; // After X-ray that may add already processed pieces
84 template<> FORCE_INLINE
85 PieceType min_attacker<KING>(const Bitboard*, const Square&, const Bitboard&, Bitboard&, Bitboard&) {
86 return KING; // No need to update bitboards: it is the last cycle
94 CheckInfo::CheckInfo(const Position& pos) {
96 Color them = ~pos.side_to_move();
97 ksq = pos.king_square(them);
99 pinned = pos.pinned_pieces(pos.side_to_move());
100 dcCandidates = pos.discovered_check_candidates();
102 checkSq[PAWN] = pos.attacks_from<PAWN>(ksq, them);
103 checkSq[KNIGHT] = pos.attacks_from<KNIGHT>(ksq);
104 checkSq[BISHOP] = pos.attacks_from<BISHOP>(ksq);
105 checkSq[ROOK] = pos.attacks_from<ROOK>(ksq);
106 checkSq[QUEEN] = checkSq[BISHOP] | checkSq[ROOK];
111 /// Position::init() initializes at startup the various arrays used to compute
112 /// hash keys and the piece square tables. The latter is a two-step operation:
113 /// Firstly, the white halves of the tables are copied from PSQT[] tables.
114 /// Secondly, the black halves of the tables are initialized by flipping and
115 /// changing the sign of the white scores.
117 void Position::init() {
121 for (Color c = WHITE; c <= BLACK; ++c)
122 for (PieceType pt = PAWN; pt <= KING; ++pt)
123 for (Square s = SQ_A1; s <= SQ_H8; ++s)
124 Zobrist::psq[c][pt][s] = rk.rand<Key>();
126 for (File f = FILE_A; f <= FILE_H; ++f)
127 Zobrist::enpassant[f] = rk.rand<Key>();
129 for (int cf = NO_CASTLING; cf <= ANY_CASTLING; ++cf)
134 Key k = Zobrist::castling[1ULL << pop_lsb(&b)];
135 Zobrist::castling[cf] ^= k ? k : rk.rand<Key>();
139 Zobrist::side = rk.rand<Key>();
140 Zobrist::exclusion = rk.rand<Key>();
142 for (PieceType pt = PAWN; pt <= KING; ++pt)
144 PieceValue[MG][make_piece(BLACK, pt)] = PieceValue[MG][pt];
145 PieceValue[EG][make_piece(BLACK, pt)] = PieceValue[EG][pt];
147 Score v = make_score(PieceValue[MG][pt], PieceValue[EG][pt]);
149 for (Square s = SQ_A1; s <= SQ_H8; ++s)
151 psq[WHITE][pt][ s] = (v + PSQT[pt][s]);
152 psq[BLACK][pt][~s] = -(v + PSQT[pt][s]);
158 /// Position::operator=() creates a copy of 'pos'. We want the new born Position
159 /// object to not depend on any external data so we detach state pointer from
162 Position& Position::operator=(const Position& pos) {
164 std::memcpy(this, &pos, sizeof(Position));
175 /// Position::clear() erases the position object to a pristine state, with an
176 /// empty board, white to move, and no castling rights.
178 void Position::clear() {
180 std::memset(this, 0, sizeof(Position));
181 startState.epSquare = SQ_NONE;
184 for (int i = 0; i < PIECE_TYPE_NB; ++i)
185 for (int j = 0; j < 16; ++j)
186 pieceList[WHITE][i][j] = pieceList[BLACK][i][j] = SQ_NONE;
190 /// Position::set() initializes the position object with the given FEN string.
191 /// This function is not very robust - make sure that input FENs are correct,
192 /// this is assumed to be the responsibility of the GUI.
194 void Position::set(const string& fenStr, bool isChess960, Thread* th) {
196 A FEN string defines a particular position using only the ASCII character set.
198 A FEN string contains six fields separated by a space. The fields are:
200 1) Piece placement (from white's perspective). Each rank is described, starting
201 with rank 8 and ending with rank 1. Within each rank, the contents of each
202 square are described from file A through file H. Following the Standard
203 Algebraic Notation (SAN), each piece is identified by a single letter taken
204 from the standard English names. White pieces are designated using upper-case
205 letters ("PNBRQK") whilst Black uses lowercase ("pnbrqk"). Blank squares are
206 noted using digits 1 through 8 (the number of blank squares), and "/"
209 2) Active color. "w" means white moves next, "b" means black.
211 3) Castling availability. If neither side can castle, this is "-". Otherwise,
212 this has one or more letters: "K" (White can castle kingside), "Q" (White
213 can castle queenside), "k" (Black can castle kingside), and/or "q" (Black
214 can castle queenside).
216 4) En passant target square (in algebraic notation). If there's no en passant
217 target square, this is "-". If a pawn has just made a 2-square move, this
218 is the position "behind" the pawn. This is recorded regardless of whether
219 there is a pawn in position to make an en passant capture.
221 5) Halfmove clock. This is the number of halfmoves since the last pawn advance
222 or capture. This is used to determine if a draw can be claimed under the
225 6) Fullmove number. The number of the full move. It starts at 1, and is
226 incremented after Black's move.
229 char col, row, token;
232 std::istringstream ss(fenStr);
237 // 1. Piece placement
238 while ((ss >> token) && !isspace(token))
241 sq += Square(token - '0'); // Advance the given number of files
243 else if (token == '/')
246 else if ((idx = PieceToChar.find(token)) != string::npos)
248 put_piece(sq, color_of(Piece(idx)), type_of(Piece(idx)));
255 sideToMove = (token == 'w' ? WHITE : BLACK);
258 // 3. Castling availability. Compatible with 3 standards: Normal FEN standard,
259 // Shredder-FEN that uses the letters of the columns on which the rooks began
260 // the game instead of KQkq and also X-FEN standard that, in case of Chess960,
261 // if an inner rook is associated with the castling right, the castling tag is
262 // replaced by the file letter of the involved rook, as for the Shredder-FEN.
263 while ((ss >> token) && !isspace(token))
266 Color c = islower(token) ? BLACK : WHITE;
268 token = char(toupper(token));
271 for (rsq = relative_square(c, SQ_H1); type_of(piece_on(rsq)) != ROOK; --rsq) {}
273 else if (token == 'Q')
274 for (rsq = relative_square(c, SQ_A1); type_of(piece_on(rsq)) != ROOK; ++rsq) {}
276 else if (token >= 'A' && token <= 'H')
277 rsq = make_square(File(token - 'A'), relative_rank(c, RANK_1));
282 set_castling_right(c, rsq);
285 // 4. En passant square. Ignore if no pawn capture is possible
286 if ( ((ss >> col) && (col >= 'a' && col <= 'h'))
287 && ((ss >> row) && (row == '3' || row == '6')))
289 st->epSquare = make_square(File(col - 'a'), Rank(row - '1'));
291 if (!(attackers_to(st->epSquare) & pieces(sideToMove, PAWN)))
292 st->epSquare = SQ_NONE;
295 // 5-6. Halfmove clock and fullmove number
296 ss >> std::skipws >> st->rule50 >> gamePly;
298 // Convert from fullmove starting from 1 to ply starting from 0,
299 // handle also common incorrect FEN with fullmove = 0.
300 gamePly = std::max(2 * (gamePly - 1), 0) + int(sideToMove == BLACK);
302 chess960 = isChess960;
310 /// Position::set_castling_right() is a helper function used to set castling
311 /// rights given the corresponding color and the rook starting square.
313 void Position::set_castling_right(Color c, Square rfrom) {
315 Square kfrom = king_square(c);
316 CastlingSide cs = kfrom < rfrom ? KING_SIDE : QUEEN_SIDE;
317 CastlingRight cr = (c | cs);
319 st->castlingRights |= cr;
320 castlingRightsMask[kfrom] |= cr;
321 castlingRightsMask[rfrom] |= cr;
322 castlingRookSquare[cr] = rfrom;
324 Square kto = relative_square(c, cs == KING_SIDE ? SQ_G1 : SQ_C1);
325 Square rto = relative_square(c, cs == KING_SIDE ? SQ_F1 : SQ_D1);
327 for (Square s = std::min(rfrom, rto); s <= std::max(rfrom, rto); ++s)
328 if (s != kfrom && s != rfrom)
329 castlingPath[cr] |= s;
331 for (Square s = std::min(kfrom, kto); s <= std::max(kfrom, kto); ++s)
332 if (s != kfrom && s != rfrom)
333 castlingPath[cr] |= s;
337 /// Position::set_state() computes the hash keys of the position, and other
338 /// data that once computed is updated incrementally as moves are made.
339 /// The function is only used when a new position is set up, and to verify
340 /// the correctness of the StateInfo data when running in debug mode.
342 void Position::set_state(StateInfo* si) const {
344 si->key = si->pawnKey = si->materialKey = 0;
345 si->npMaterial[WHITE] = si->npMaterial[BLACK] = VALUE_ZERO;
346 si->psq = SCORE_ZERO;
348 si->checkersBB = attackers_to(king_square(sideToMove)) & pieces(~sideToMove);
350 for (Bitboard b = pieces(); b; )
352 Square s = pop_lsb(&b);
353 Piece pc = piece_on(s);
354 si->key ^= Zobrist::psq[color_of(pc)][type_of(pc)][s];
355 si->psq += psq[color_of(pc)][type_of(pc)][s];
358 if (ep_square() != SQ_NONE)
359 si->key ^= Zobrist::enpassant[file_of(ep_square())];
361 if (sideToMove == BLACK)
362 si->key ^= Zobrist::side;
364 si->key ^= Zobrist::castling[st->castlingRights];
366 for (Bitboard b = pieces(PAWN); b; )
368 Square s = pop_lsb(&b);
369 si->pawnKey ^= Zobrist::psq[color_of(piece_on(s))][PAWN][s];
372 for (Color c = WHITE; c <= BLACK; ++c)
373 for (PieceType pt = PAWN; pt <= KING; ++pt)
374 for (int cnt = 0; cnt < pieceCount[c][pt]; ++cnt)
375 si->materialKey ^= Zobrist::psq[c][pt][cnt];
377 for (Color c = WHITE; c <= BLACK; ++c)
378 for (PieceType pt = KNIGHT; pt <= QUEEN; ++pt)
379 si->npMaterial[c] += pieceCount[c][pt] * PieceValue[MG][pt];
383 /// Position::fen() returns a FEN representation of the position. In case of
384 /// Chess960 the Shredder-FEN notation is used. This is mainly a debugging function.
386 const string Position::fen() const {
389 std::ostringstream ss;
391 for (Rank r = RANK_8; r >= RANK_1; --r)
393 for (File f = FILE_A; f <= FILE_H; ++f)
395 for (emptyCnt = 0; f <= FILE_H && empty(make_square(f, r)); ++f)
402 ss << PieceToChar[piece_on(make_square(f, r))];
409 ss << (sideToMove == WHITE ? " w " : " b ");
411 if (can_castle(WHITE_OO))
412 ss << (chess960 ? to_char(file_of(castling_rook_square(WHITE | KING_SIDE)), false) : 'K');
414 if (can_castle(WHITE_OOO))
415 ss << (chess960 ? to_char(file_of(castling_rook_square(WHITE | QUEEN_SIDE)), false) : 'Q');
417 if (can_castle(BLACK_OO))
418 ss << (chess960 ? to_char(file_of(castling_rook_square(BLACK | KING_SIDE)), true) : 'k');
420 if (can_castle(BLACK_OOO))
421 ss << (chess960 ? to_char(file_of(castling_rook_square(BLACK | QUEEN_SIDE)), true) : 'q');
423 if (!can_castle(WHITE) && !can_castle(BLACK))
426 ss << (ep_square() == SQ_NONE ? " - " : " " + to_string(ep_square()) + " ")
427 << st->rule50 << " " << 1 + (gamePly - int(sideToMove == BLACK)) / 2;
433 /// Position::pretty() returns an ASCII representation of the position to be
434 /// printed to the standard output together with the move's san notation.
436 const string Position::pretty(Move m) const {
438 std::ostringstream ss;
441 ss << "\nMove: " << (sideToMove == BLACK ? ".." : "")
442 << move_to_san(*const_cast<Position*>(this), m);
444 ss << "\n +---+---+---+---+---+---+---+---+\n";
446 for (Rank r = RANK_8; r >= RANK_1; --r)
448 for (File f = FILE_A; f <= FILE_H; ++f)
449 ss << " | " << PieceToChar[piece_on(make_square(f, r))];
451 ss << " |\n +---+---+---+---+---+---+---+---+\n";
454 ss << "\nFen: " << fen() << "\nKey: " << std::hex << std::uppercase
455 << std::setfill('0') << std::setw(16) << st->key << "\nCheckers: ";
457 for (Bitboard b = checkers(); b; )
458 ss << to_string(pop_lsb(&b)) << " ";
460 ss << "\nLegal moves: ";
461 for (MoveList<LEGAL> it(*this); *it; ++it)
462 ss << move_to_san(*const_cast<Position*>(this), *it) << " ";
468 /// Position::check_blockers() returns a bitboard of all the pieces with color
469 /// 'c' that are blocking check on the king with color 'kingColor'. A piece
470 /// blocks a check if removing that piece from the board would result in a
471 /// position where the king is in check. A check blocking piece can be either a
472 /// pinned or a discovered check piece, according if its color 'c' is the same
473 /// or the opposite of 'kingColor'.
475 Bitboard Position::check_blockers(Color c, Color kingColor) const {
477 Bitboard b, pinners, result = 0;
478 Square ksq = king_square(kingColor);
480 // Pinners are sliders that give check when a pinned piece is removed
481 pinners = ( (pieces( ROOK, QUEEN) & PseudoAttacks[ROOK ][ksq])
482 | (pieces(BISHOP, QUEEN) & PseudoAttacks[BISHOP][ksq])) & pieces(~kingColor);
486 b = between_bb(ksq, pop_lsb(&pinners)) & pieces();
488 if (!more_than_one(b))
489 result |= b & pieces(c);
495 /// Position::attackers_to() computes a bitboard of all pieces which attack a
496 /// given square. Slider attacks use the occ bitboard to indicate occupancy.
498 Bitboard Position::attackers_to(Square s, Bitboard occ) const {
500 return (attacks_from<PAWN>(s, BLACK) & pieces(WHITE, PAWN))
501 | (attacks_from<PAWN>(s, WHITE) & pieces(BLACK, PAWN))
502 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
503 | (attacks_bb<ROOK>(s, occ) & pieces(ROOK, QUEEN))
504 | (attacks_bb<BISHOP>(s, occ) & pieces(BISHOP, QUEEN))
505 | (attacks_from<KING>(s) & pieces(KING));
509 /// Position::legal() tests whether a pseudo-legal move is legal
511 bool Position::legal(Move m, Bitboard pinned) const {
514 assert(pinned == pinned_pieces(sideToMove));
516 Color us = sideToMove;
517 Square from = from_sq(m);
519 assert(color_of(moved_piece(m)) == us);
520 assert(piece_on(king_square(us)) == make_piece(us, KING));
522 // En passant captures are a tricky special case. Because they are rather
523 // uncommon, we do it simply by testing whether the king is attacked after
525 if (type_of(m) == ENPASSANT)
527 Square ksq = king_square(us);
528 Square to = to_sq(m);
529 Square capsq = to - pawn_push(us);
530 Bitboard occ = (pieces() ^ from ^ capsq) | to;
532 assert(to == ep_square());
533 assert(moved_piece(m) == make_piece(us, PAWN));
534 assert(piece_on(capsq) == make_piece(~us, PAWN));
535 assert(piece_on(to) == NO_PIECE);
537 return !(attacks_bb< ROOK>(ksq, occ) & pieces(~us, QUEEN, ROOK))
538 && !(attacks_bb<BISHOP>(ksq, occ) & pieces(~us, QUEEN, BISHOP));
541 // If the moving piece is a king, check whether the destination
542 // square is attacked by the opponent. Castling moves are checked
543 // for legality during move generation.
544 if (type_of(piece_on(from)) == KING)
545 return type_of(m) == CASTLING || !(attackers_to(to_sq(m)) & pieces(~us));
547 // A non-king move is legal if and only if it is not pinned or it
548 // is moving along the ray towards or away from the king.
551 || aligned(from, to_sq(m), king_square(us));
555 /// Position::pseudo_legal() takes a random move and tests whether the move is
556 /// pseudo legal. It is used to validate moves from TT that can be corrupted
557 /// due to SMP concurrent access or hash position key aliasing.
559 bool Position::pseudo_legal(const Move m) const {
561 Color us = sideToMove;
562 Square from = from_sq(m);
563 Square to = to_sq(m);
564 Piece pc = moved_piece(m);
566 // Use a slower but simpler function for uncommon cases
567 if (type_of(m) != NORMAL)
568 return MoveList<LEGAL>(*this).contains(m);
570 // Is not a promotion, so promotion piece must be empty
571 if (promotion_type(m) - 2 != NO_PIECE_TYPE)
574 // If the 'from' square is not occupied by a piece belonging to the side to
575 // move, the move is obviously not legal.
576 if (pc == NO_PIECE || color_of(pc) != us)
579 // The destination square cannot be occupied by a friendly piece
583 // Handle the special case of a pawn move
584 if (type_of(pc) == PAWN)
586 // We have already handled promotion moves, so destination
587 // cannot be on the 8th/1st rank.
588 if (rank_of(to) == relative_rank(us, RANK_8))
591 if ( !(attacks_from<PAWN>(from, us) & pieces(~us) & to) // Not a capture
593 && !((from + pawn_push(us) == to) && empty(to)) // Not a single push
595 && !( (from + 2 * pawn_push(us) == to) // Not a double push
596 && (rank_of(from) == relative_rank(us, RANK_2))
598 && empty(to - pawn_push(us))))
601 else if (!(attacks_from(pc, from) & to))
604 // Evasions generator already takes care to avoid some kind of illegal moves
605 // and legal() relies on this. We therefore have to take care that the same
606 // kind of moves are filtered out here.
609 if (type_of(pc) != KING)
611 // Double check? In this case a king move is required
612 if (more_than_one(checkers()))
615 // Our move must be a blocking evasion or a capture of the checking piece
616 if (!((between_bb(lsb(checkers()), king_square(us)) | checkers()) & to))
619 // In case of king moves under check we have to remove king so as to catch
620 // invalid moves like b1a1 when opposite queen is on c1.
621 else if (attackers_to(to, pieces() ^ from) & pieces(~us))
629 /// Position::gives_check() tests whether a pseudo-legal move gives a check
631 bool Position::gives_check(Move m, const CheckInfo& ci) const {
634 assert(ci.dcCandidates == discovered_check_candidates());
635 assert(color_of(moved_piece(m)) == sideToMove);
637 Square from = from_sq(m);
638 Square to = to_sq(m);
639 PieceType pt = type_of(piece_on(from));
641 // Is there a direct check?
642 if (ci.checkSq[pt] & to)
645 // Is there a discovered check?
646 if ( unlikely(ci.dcCandidates)
647 && (ci.dcCandidates & from)
648 && !aligned(from, to, ci.ksq))
657 return attacks_bb(Piece(promotion_type(m)), to, pieces() ^ from) & ci.ksq;
659 // En passant capture with check? We have already handled the case
660 // of direct checks and ordinary discovered check, so the only case we
661 // need to handle is the unusual case of a discovered check through
662 // the captured pawn.
665 Square capsq = make_square(file_of(to), rank_of(from));
666 Bitboard b = (pieces() ^ from ^ capsq) | to;
668 return (attacks_bb< ROOK>(ci.ksq, b) & pieces(sideToMove, QUEEN, ROOK))
669 | (attacks_bb<BISHOP>(ci.ksq, b) & pieces(sideToMove, QUEEN, BISHOP));
674 Square rfrom = to; // Castling is encoded as 'King captures the rook'
675 Square kto = relative_square(sideToMove, rfrom > kfrom ? SQ_G1 : SQ_C1);
676 Square rto = relative_square(sideToMove, rfrom > kfrom ? SQ_F1 : SQ_D1);
678 return (PseudoAttacks[ROOK][rto] & ci.ksq)
679 && (attacks_bb<ROOK>(rto, (pieces() ^ kfrom ^ rfrom) | rto | kto) & ci.ksq);
688 /// Position::do_move() makes a move, and saves all information necessary
689 /// to a StateInfo object. The move is assumed to be legal. Pseudo-legal
690 /// moves should be filtered out before this function is called.
692 void Position::do_move(Move m, StateInfo& newSt) {
695 do_move(m, newSt, ci, gives_check(m, ci));
698 void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveIsCheck) {
701 assert(&newSt != st);
706 // Copy some fields of the old state to our new StateInfo object except the
707 // ones which are going to be recalculated from scratch anyway and then switch
708 // our state pointer to point to the new (ready to be updated) state.
709 std::memcpy(&newSt, st, StateCopySize64 * sizeof(uint64_t));
714 // Update side to move
717 // Increment ply counters. In particular, rule50 will be reset to zero later on
718 // in case of a capture or a pawn move.
723 Color us = sideToMove;
725 Square from = from_sq(m);
726 Square to = to_sq(m);
727 Piece pc = piece_on(from);
728 PieceType pt = type_of(pc);
729 PieceType captured = type_of(m) == ENPASSANT ? PAWN : type_of(piece_on(to));
731 assert(color_of(pc) == us);
732 assert(piece_on(to) == NO_PIECE || color_of(piece_on(to)) == them || type_of(m) == CASTLING);
733 assert(captured != KING);
735 if (type_of(m) == CASTLING)
737 assert(pc == make_piece(us, KING));
740 do_castling<true>(from, to, rfrom, rto);
742 captured = NO_PIECE_TYPE;
743 st->psq += psq[us][ROOK][rto] - psq[us][ROOK][rfrom];
744 k ^= Zobrist::psq[us][ROOK][rfrom] ^ Zobrist::psq[us][ROOK][rto];
751 // If the captured piece is a pawn, update pawn hash key, otherwise
752 // update non-pawn material.
753 if (captured == PAWN)
755 if (type_of(m) == ENPASSANT)
757 capsq += pawn_push(them);
760 assert(to == st->epSquare);
761 assert(relative_rank(us, to) == RANK_6);
762 assert(piece_on(to) == NO_PIECE);
763 assert(piece_on(capsq) == make_piece(them, PAWN));
765 board[capsq] = NO_PIECE;
768 st->pawnKey ^= Zobrist::psq[them][PAWN][capsq];
771 st->npMaterial[them] -= PieceValue[MG][captured];
773 // Update board and piece lists
774 remove_piece(capsq, them, captured);
776 // Update material hash key and prefetch access to materialTable
777 k ^= Zobrist::psq[them][captured][capsq];
778 st->materialKey ^= Zobrist::psq[them][captured][pieceCount[them][captured]];
779 prefetch((char*)thisThread->materialTable[st->materialKey]);
781 // Update incremental scores
782 st->psq -= psq[them][captured][capsq];
784 // Reset rule 50 counter
789 k ^= Zobrist::psq[us][pt][from] ^ Zobrist::psq[us][pt][to];
791 // Reset en passant square
792 if (st->epSquare != SQ_NONE)
794 k ^= Zobrist::enpassant[file_of(st->epSquare)];
795 st->epSquare = SQ_NONE;
798 // Update castling rights if needed
799 if (st->castlingRights && (castlingRightsMask[from] | castlingRightsMask[to]))
801 int cr = castlingRightsMask[from] | castlingRightsMask[to];
802 k ^= Zobrist::castling[st->castlingRights & cr];
803 st->castlingRights &= ~cr;
806 // Prefetch TT access as soon as we know the new hash key
807 prefetch((char*)TT.first_entry(k));
809 // Move the piece. The tricky Chess960 castling is handled earlier
810 if (type_of(m) != CASTLING)
811 move_piece(from, to, us, pt);
813 // If the moving piece is a pawn do some special extra work
816 // Set en-passant square if the moved pawn can be captured
817 if ( (int(to) ^ int(from)) == 16
818 && (attacks_from<PAWN>(from + pawn_push(us), us) & pieces(them, PAWN)))
820 st->epSquare = Square((from + to) / 2);
821 k ^= Zobrist::enpassant[file_of(st->epSquare)];
824 else if (type_of(m) == PROMOTION)
826 PieceType promotion = promotion_type(m);
828 assert(relative_rank(us, to) == RANK_8);
829 assert(promotion >= KNIGHT && promotion <= QUEEN);
831 remove_piece(to, us, PAWN);
832 put_piece(to, us, promotion);
835 k ^= Zobrist::psq[us][PAWN][to] ^ Zobrist::psq[us][promotion][to];
836 st->pawnKey ^= Zobrist::psq[us][PAWN][to];
837 st->materialKey ^= Zobrist::psq[us][promotion][pieceCount[us][promotion]-1]
838 ^ Zobrist::psq[us][PAWN][pieceCount[us][PAWN]];
840 // Update incremental score
841 st->psq += psq[us][promotion][to] - psq[us][PAWN][to];
844 st->npMaterial[us] += PieceValue[MG][promotion];
847 // Update pawn hash key and prefetch access to pawnsTable
848 st->pawnKey ^= Zobrist::psq[us][PAWN][from] ^ Zobrist::psq[us][PAWN][to];
849 prefetch((char*)thisThread->pawnsTable[st->pawnKey]);
851 // Reset rule 50 draw counter
855 // Update incremental scores
856 st->psq += psq[us][pt][to] - psq[us][pt][from];
859 st->capturedType = captured;
861 // Update the key with the final value
864 // Update checkers bitboard: piece must be already moved due to attacks_from()
869 if (type_of(m) != NORMAL)
870 st->checkersBB = attackers_to(king_square(them)) & pieces(us);
874 if (ci.checkSq[pt] & to)
875 st->checkersBB |= to;
878 if (unlikely(ci.dcCandidates) && (ci.dcCandidates & from))
881 st->checkersBB |= attacks_from<ROOK>(king_square(them)) & pieces(us, QUEEN, ROOK);
884 st->checkersBB |= attacks_from<BISHOP>(king_square(them)) & pieces(us, QUEEN, BISHOP);
889 sideToMove = ~sideToMove;
895 /// Position::undo_move() unmakes a move. When it returns, the position should
896 /// be restored to exactly the same state as before the move was made.
898 void Position::undo_move(Move m) {
902 sideToMove = ~sideToMove;
904 Color us = sideToMove;
905 Square from = from_sq(m);
906 Square to = to_sq(m);
907 PieceType pt = type_of(piece_on(to));
909 assert(empty(from) || type_of(m) == CASTLING);
910 assert(st->capturedType != KING);
912 if (type_of(m) == PROMOTION)
914 assert(pt == promotion_type(m));
915 assert(relative_rank(us, to) == RANK_8);
916 assert(promotion_type(m) >= KNIGHT && promotion_type(m) <= QUEEN);
918 remove_piece(to, us, promotion_type(m));
919 put_piece(to, us, PAWN);
923 if (type_of(m) == CASTLING)
926 do_castling<false>(from, to, rfrom, rto);
930 move_piece(to, from, us, pt); // Put the piece back at the source square
932 if (st->capturedType)
936 if (type_of(m) == ENPASSANT)
938 capsq -= pawn_push(us);
941 assert(to == st->previous->epSquare);
942 assert(relative_rank(us, to) == RANK_6);
943 assert(piece_on(capsq) == NO_PIECE);
946 put_piece(capsq, ~us, st->capturedType); // Restore the captured piece
950 // Finally point our state pointer back to the previous state
958 /// Position::do_castling() is a helper used to do/undo a castling move. This
959 /// is a bit tricky, especially in Chess960.
961 void Position::do_castling(Square from, Square& to, Square& rfrom, Square& rto) {
963 bool kingSide = to > from;
964 rfrom = to; // Castling is encoded as "king captures friendly rook"
965 rto = relative_square(sideToMove, kingSide ? SQ_F1 : SQ_D1);
966 to = relative_square(sideToMove, kingSide ? SQ_G1 : SQ_C1);
968 // Remove both pieces first since squares could overlap in Chess960
969 remove_piece(Do ? from : to, sideToMove, KING);
970 remove_piece(Do ? rfrom : rto, sideToMove, ROOK);
971 board[Do ? from : to] = board[Do ? rfrom : rto] = NO_PIECE; // Since remove_piece doesn't do it for us
972 put_piece(Do ? to : from, sideToMove, KING);
973 put_piece(Do ? rto : rfrom, sideToMove, ROOK);
977 /// Position::do(undo)_null_move() is used to do(undo) a "null move": It flips
978 /// the side to move without executing any move on the board.
980 void Position::do_null_move(StateInfo& newSt) {
984 std::memcpy(&newSt, st, sizeof(StateInfo)); // Fully copy here
989 if (st->epSquare != SQ_NONE)
991 st->key ^= Zobrist::enpassant[file_of(st->epSquare)];
992 st->epSquare = SQ_NONE;
995 st->key ^= Zobrist::side;
996 prefetch((char*)TT.first_entry(st->key));
999 st->pliesFromNull = 0;
1001 sideToMove = ~sideToMove;
1003 assert(pos_is_ok());
1006 void Position::undo_null_move() {
1008 assert(!checkers());
1011 sideToMove = ~sideToMove;
1015 /// Position::see() is a static exchange evaluator: It tries to estimate the
1016 /// material gain or loss resulting from a move.
1018 Value Position::see_sign(Move m) const {
1022 // Early return if SEE cannot be negative because captured piece value
1023 // is not less then capturing one. Note that king moves always return
1024 // here because king midgame value is set to 0.
1025 if (PieceValue[MG][moved_piece(m)] <= PieceValue[MG][piece_on(to_sq(m))])
1026 return VALUE_KNOWN_WIN;
1031 Value Position::see(Move m) const {
1034 Bitboard occupied, attackers, stmAttackers;
1044 swapList[0] = PieceValue[MG][piece_on(to)];
1045 stm = color_of(piece_on(from));
1046 occupied = pieces() ^ from;
1048 // Castling moves are implemented as king capturing the rook so cannot be
1049 // handled correctly. Simply return 0 that is always the correct value
1050 // unless in the rare case the rook ends up under attack.
1051 if (type_of(m) == CASTLING)
1054 if (type_of(m) == ENPASSANT)
1056 occupied ^= to - pawn_push(stm); // Remove the captured pawn
1057 swapList[0] = PieceValue[MG][PAWN];
1060 // Find all attackers to the destination square, with the moving piece
1061 // removed, but possibly an X-ray attacker added behind it.
1062 attackers = attackers_to(to, occupied) & occupied;
1064 // If the opponent has no attackers we are finished
1066 stmAttackers = attackers & pieces(stm);
1070 // The destination square is defended, which makes things rather more
1071 // difficult to compute. We proceed by building up a "swap list" containing
1072 // the material gain or loss at each stop in a sequence of captures to the
1073 // destination square, where the sides alternately capture, and always
1074 // capture with the least valuable piece. After each capture, we look for
1075 // new X-ray attacks from behind the capturing piece.
1076 captured = type_of(piece_on(from));
1079 assert(slIndex < 32);
1081 // Add the new entry to the swap list
1082 swapList[slIndex] = -swapList[slIndex - 1] + PieceValue[MG][captured];
1084 // Locate and remove the next least valuable attacker
1085 captured = min_attacker<PAWN>(byTypeBB, to, stmAttackers, occupied, attackers);
1087 // Stop before processing a king capture
1088 if (captured == KING)
1090 if (stmAttackers == attackers)
1097 stmAttackers = attackers & pieces(stm);
1100 } while (stmAttackers);
1102 // Having built the swap list, we negamax through it to find the best
1103 // achievable score from the point of view of the side to move.
1105 swapList[slIndex - 1] = std::min(-swapList[slIndex], swapList[slIndex - 1]);
1111 /// Position::is_draw() tests whether the position is drawn by material, 50 moves
1112 /// rule or repetition. It does not detect stalemates.
1114 bool Position::is_draw() const {
1117 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMg))
1120 if (st->rule50 > 99 && (!checkers() || MoveList<LEGAL>(*this).size()))
1123 StateInfo* stp = st;
1124 for (int i = 2, e = std::min(st->rule50, st->pliesFromNull); i <= e; i += 2)
1126 stp = stp->previous->previous;
1128 if (stp->key == st->key)
1129 return true; // Draw at first repetition
1136 /// Position::flip() flips position with the white and black sides reversed. This
1137 /// is only useful for debugging e.g. for finding evaluation symmetry bugs.
1139 static char toggle_case(char c) {
1140 return char(islower(c) ? toupper(c) : tolower(c));
1143 void Position::flip() {
1146 std::stringstream ss(fen());
1148 for (Rank r = RANK_8; r >= RANK_1; --r) // Piece placement
1150 std::getline(ss, token, r > RANK_1 ? '/' : ' ');
1151 f.insert(0, token + (f.empty() ? " " : "/"));
1154 ss >> token; // Active color
1155 f += (token == "w" ? "B " : "W "); // Will be lowercased later
1157 ss >> token; // Castling availability
1160 std::transform(f.begin(), f.end(), f.begin(), toggle_case);
1162 ss >> token; // En passant square
1163 f += (token == "-" ? token : token.replace(1, 1, token[1] == '3' ? "6" : "3"));
1165 std::getline(ss, token); // Half and full moves
1168 set(f, is_chess960(), this_thread());
1170 assert(pos_is_ok());
1174 /// Position::pos_is_ok() performs some consistency checks for the position object.
1175 /// This is meant to be helpful when debugging.
1177 bool Position::pos_is_ok(int* step) const {
1179 // Which parts of the position should be verified?
1180 const bool all = false;
1182 const bool testBitboards = all || false;
1183 const bool testState = all || false;
1184 const bool testKingCount = all || false;
1185 const bool testKingCapture = all || false;
1186 const bool testPieceCounts = all || false;
1187 const bool testPieceList = all || false;
1188 const bool testCastlingSquares = all || false;
1193 if ( (sideToMove != WHITE && sideToMove != BLACK)
1194 || piece_on(king_square(WHITE)) != W_KING
1195 || piece_on(king_square(BLACK)) != B_KING
1196 || ( ep_square() != SQ_NONE
1197 && relative_rank(sideToMove, ep_square()) != RANK_6))
1200 if (step && ++*step, testBitboards)
1202 // The intersection of the white and black pieces must be empty
1203 if (pieces(WHITE) & pieces(BLACK))
1206 // The union of the white and black pieces must be equal to all
1208 if ((pieces(WHITE) | pieces(BLACK)) != pieces())
1211 // Separate piece type bitboards must have empty intersections
1212 for (PieceType p1 = PAWN; p1 <= KING; ++p1)
1213 for (PieceType p2 = PAWN; p2 <= KING; ++p2)
1214 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1218 if (step && ++*step, testState)
1222 if ( st->key != si.key
1223 || st->pawnKey != si.pawnKey
1224 || st->materialKey != si.materialKey
1225 || st->npMaterial[WHITE] != si.npMaterial[WHITE]
1226 || st->npMaterial[BLACK] != si.npMaterial[BLACK]
1227 || st->psq != si.psq
1228 || st->checkersBB != si.checkersBB)
1232 if (step && ++*step, testKingCount)
1233 if ( std::count(board, board + SQUARE_NB, W_KING) != 1
1234 || std::count(board, board + SQUARE_NB, B_KING) != 1)
1237 if (step && ++*step, testKingCapture)
1238 if (attackers_to(king_square(~sideToMove)) & pieces(sideToMove))
1241 if (step && ++*step, testPieceCounts)
1242 for (Color c = WHITE; c <= BLACK; ++c)
1243 for (PieceType pt = PAWN; pt <= KING; ++pt)
1244 if (pieceCount[c][pt] != popcount<Full>(pieces(c, pt)))
1247 if (step && ++*step, testPieceList)
1248 for (Color c = WHITE; c <= BLACK; ++c)
1249 for (PieceType pt = PAWN; pt <= KING; ++pt)
1250 for (int i = 0; i < pieceCount[c][pt]; ++i)
1251 if ( board[pieceList[c][pt][i]] != make_piece(c, pt)
1252 || index[pieceList[c][pt][i]] != i)
1255 if (step && ++*step, testCastlingSquares)
1256 for (Color c = WHITE; c <= BLACK; ++c)
1257 for (CastlingSide s = KING_SIDE; s <= QUEEN_SIDE; s = CastlingSide(s + 1))
1259 if (!can_castle(c | s))
1262 if ( (castlingRightsMask[king_square(c)] & (c | s)) != (c | s)
1263 || piece_on(castlingRookSquare[c | s]) != make_piece(c, ROOK)
1264 || castlingRightsMask[castlingRookSquare[c | s]] != (c | s))