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 unsigned 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) + (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 - (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::game_phase() calculates the game phase interpolating total non-pawn
469 /// material between endgame and midgame limits.
471 Phase Position::game_phase() const {
473 Value npm = st->npMaterial[WHITE] + st->npMaterial[BLACK];
475 npm = std::max(EndgameLimit, std::min(npm, MidgameLimit));
477 return Phase(((npm - EndgameLimit) * 128) / (MidgameLimit - EndgameLimit));
481 /// Position::check_blockers() returns a bitboard of all the pieces with color
482 /// 'c' that are blocking check on the king with color 'kingColor'. A piece
483 /// blocks a check if removing that piece from the board would result in a
484 /// position where the king is in check. A check blocking piece can be either a
485 /// pinned or a discovered check piece, according if its color 'c' is the same
486 /// or the opposite of 'kingColor'.
488 Bitboard Position::check_blockers(Color c, Color kingColor) const {
490 Bitboard b, pinners, result = 0;
491 Square ksq = king_square(kingColor);
493 // Pinners are sliders that give check when a pinned piece is removed
494 pinners = ( (pieces( ROOK, QUEEN) & PseudoAttacks[ROOK ][ksq])
495 | (pieces(BISHOP, QUEEN) & PseudoAttacks[BISHOP][ksq])) & pieces(~kingColor);
499 b = between_bb(ksq, pop_lsb(&pinners)) & pieces();
501 if (!more_than_one(b))
502 result |= b & pieces(c);
508 /// Position::attackers_to() computes a bitboard of all pieces which attack a
509 /// given square. Slider attacks use the occ bitboard to indicate occupancy.
511 Bitboard Position::attackers_to(Square s, Bitboard occ) const {
513 return (attacks_from<PAWN>(s, BLACK) & pieces(WHITE, PAWN))
514 | (attacks_from<PAWN>(s, WHITE) & pieces(BLACK, PAWN))
515 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
516 | (attacks_bb<ROOK>(s, occ) & pieces(ROOK, QUEEN))
517 | (attacks_bb<BISHOP>(s, occ) & pieces(BISHOP, QUEEN))
518 | (attacks_from<KING>(s) & pieces(KING));
522 /// Position::legal() tests whether a pseudo-legal move is legal
524 bool Position::legal(Move m, Bitboard pinned) const {
527 assert(pinned == pinned_pieces(sideToMove));
529 Color us = sideToMove;
530 Square from = from_sq(m);
532 assert(color_of(moved_piece(m)) == us);
533 assert(piece_on(king_square(us)) == make_piece(us, KING));
535 // En passant captures are a tricky special case. Because they are rather
536 // uncommon, we do it simply by testing whether the king is attacked after
538 if (type_of(m) == ENPASSANT)
540 Square ksq = king_square(us);
541 Square to = to_sq(m);
542 Square capsq = to - pawn_push(us);
543 Bitboard occ = (pieces() ^ from ^ capsq) | to;
545 assert(to == ep_square());
546 assert(moved_piece(m) == make_piece(us, PAWN));
547 assert(piece_on(capsq) == make_piece(~us, PAWN));
548 assert(piece_on(to) == NO_PIECE);
550 return !(attacks_bb< ROOK>(ksq, occ) & pieces(~us, QUEEN, ROOK))
551 && !(attacks_bb<BISHOP>(ksq, occ) & pieces(~us, QUEEN, BISHOP));
554 // If the moving piece is a king, check whether the destination
555 // square is attacked by the opponent. Castling moves are checked
556 // for legality during move generation.
557 if (type_of(piece_on(from)) == KING)
558 return type_of(m) == CASTLING || !(attackers_to(to_sq(m)) & pieces(~us));
560 // A non-king move is legal if and only if it is not pinned or it
561 // is moving along the ray towards or away from the king.
564 || aligned(from, to_sq(m), king_square(us));
568 /// Position::pseudo_legal() takes a random move and tests whether the move is
569 /// pseudo legal. It is used to validate moves from TT that can be corrupted
570 /// due to SMP concurrent access or hash position key aliasing.
572 bool Position::pseudo_legal(const Move m) const {
574 Color us = sideToMove;
575 Square from = from_sq(m);
576 Square to = to_sq(m);
577 Piece pc = moved_piece(m);
579 // Use a slower but simpler function for uncommon cases
580 if (type_of(m) != NORMAL)
581 return MoveList<LEGAL>(*this).contains(m);
583 // Is not a promotion, so promotion piece must be empty
584 if (promotion_type(m) - 2 != NO_PIECE_TYPE)
587 // If the 'from' square is not occupied by a piece belonging to the side to
588 // move, the move is obviously not legal.
589 if (pc == NO_PIECE || color_of(pc) != us)
592 // The destination square cannot be occupied by a friendly piece
596 // Handle the special case of a pawn move
597 if (type_of(pc) == PAWN)
599 // We have already handled promotion moves, so destination
600 // cannot be on the 8th/1st rank.
601 if (rank_of(to) == relative_rank(us, RANK_8))
604 if ( !(attacks_from<PAWN>(from, us) & pieces(~us) & to) // Not a capture
606 && !((from + pawn_push(us) == to) && empty(to)) // Not a single push
608 && !( (from + 2 * pawn_push(us) == to) // Not a double push
609 && (rank_of(from) == relative_rank(us, RANK_2))
611 && empty(to - pawn_push(us))))
614 else if (!(attacks_from(pc, from) & to))
617 // Evasions generator already takes care to avoid some kind of illegal moves
618 // and legal() relies on this. We therefore have to take care that the same
619 // kind of moves are filtered out here.
622 if (type_of(pc) != KING)
624 // Double check? In this case a king move is required
625 if (more_than_one(checkers()))
628 // Our move must be a blocking evasion or a capture of the checking piece
629 if (!((between_bb(lsb(checkers()), king_square(us)) | checkers()) & to))
632 // In case of king moves under check we have to remove king so as to catch
633 // invalid moves like b1a1 when opposite queen is on c1.
634 else if (attackers_to(to, pieces() ^ from) & pieces(~us))
642 /// Position::gives_check() tests whether a pseudo-legal move gives a check
644 bool Position::gives_check(Move m, const CheckInfo& ci) const {
647 assert(ci.dcCandidates == discovered_check_candidates());
648 assert(color_of(moved_piece(m)) == sideToMove);
650 Square from = from_sq(m);
651 Square to = to_sq(m);
652 PieceType pt = type_of(piece_on(from));
654 // Is there a direct check?
655 if (ci.checkSq[pt] & to)
658 // Is there a discovered check?
659 if ( unlikely(ci.dcCandidates)
660 && (ci.dcCandidates & from)
661 && !aligned(from, to, ci.ksq))
670 return attacks_bb(Piece(promotion_type(m)), to, pieces() ^ from) & ci.ksq;
672 // En passant capture with check? We have already handled the case
673 // of direct checks and ordinary discovered check, so the only case we
674 // need to handle is the unusual case of a discovered check through
675 // the captured pawn.
678 Square capsq = make_square(file_of(to), rank_of(from));
679 Bitboard b = (pieces() ^ from ^ capsq) | to;
681 return (attacks_bb< ROOK>(ci.ksq, b) & pieces(sideToMove, QUEEN, ROOK))
682 | (attacks_bb<BISHOP>(ci.ksq, b) & pieces(sideToMove, QUEEN, BISHOP));
687 Square rfrom = to; // Castling is encoded as 'King captures the rook'
688 Square kto = relative_square(sideToMove, rfrom > kfrom ? SQ_G1 : SQ_C1);
689 Square rto = relative_square(sideToMove, rfrom > kfrom ? SQ_F1 : SQ_D1);
691 return (PseudoAttacks[ROOK][rto] & ci.ksq)
692 && (attacks_bb<ROOK>(rto, (pieces() ^ kfrom ^ rfrom) | rto | kto) & ci.ksq);
701 /// Position::do_move() makes a move, and saves all information necessary
702 /// to a StateInfo object. The move is assumed to be legal. Pseudo-legal
703 /// moves should be filtered out before this function is called.
705 void Position::do_move(Move m, StateInfo& newSt) {
708 do_move(m, newSt, ci, gives_check(m, ci));
711 void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveIsCheck) {
714 assert(&newSt != st);
719 // Copy some fields of the old state to our new StateInfo object except the
720 // ones which are going to be recalculated from scratch anyway and then switch
721 // our state pointer to point to the new (ready to be updated) state.
722 std::memcpy(&newSt, st, StateCopySize64 * sizeof(uint64_t));
727 // Update side to move
730 // Increment ply counters. In particular, rule50 will be reset to zero later on
731 // in case of a capture or a pawn move.
736 Color us = sideToMove;
738 Square from = from_sq(m);
739 Square to = to_sq(m);
740 Piece pc = piece_on(from);
741 PieceType pt = type_of(pc);
742 PieceType captured = type_of(m) == ENPASSANT ? PAWN : type_of(piece_on(to));
744 assert(color_of(pc) == us);
745 assert(piece_on(to) == NO_PIECE || color_of(piece_on(to)) == them || type_of(m) == CASTLING);
746 assert(captured != KING);
748 if (type_of(m) == CASTLING)
750 assert(pc == make_piece(us, KING));
753 do_castling<true>(from, to, rfrom, rto);
755 captured = NO_PIECE_TYPE;
756 st->psq += psq[us][ROOK][rto] - psq[us][ROOK][rfrom];
757 k ^= Zobrist::psq[us][ROOK][rfrom] ^ Zobrist::psq[us][ROOK][rto];
764 // If the captured piece is a pawn, update pawn hash key, otherwise
765 // update non-pawn material.
766 if (captured == PAWN)
768 if (type_of(m) == ENPASSANT)
770 capsq += pawn_push(them);
773 assert(to == st->epSquare);
774 assert(relative_rank(us, to) == RANK_6);
775 assert(piece_on(to) == NO_PIECE);
776 assert(piece_on(capsq) == make_piece(them, PAWN));
778 board[capsq] = NO_PIECE;
781 st->pawnKey ^= Zobrist::psq[them][PAWN][capsq];
784 st->npMaterial[them] -= PieceValue[MG][captured];
786 // Update board and piece lists
787 remove_piece(capsq, them, captured);
789 // Update material hash key and prefetch access to materialTable
790 k ^= Zobrist::psq[them][captured][capsq];
791 st->materialKey ^= Zobrist::psq[them][captured][pieceCount[them][captured]];
792 prefetch((char*)thisThread->materialTable[st->materialKey]);
794 // Update incremental scores
795 st->psq -= psq[them][captured][capsq];
797 // Reset rule 50 counter
802 k ^= Zobrist::psq[us][pt][from] ^ Zobrist::psq[us][pt][to];
804 // Reset en passant square
805 if (st->epSquare != SQ_NONE)
807 k ^= Zobrist::enpassant[file_of(st->epSquare)];
808 st->epSquare = SQ_NONE;
811 // Update castling rights if needed
812 if (st->castlingRights && (castlingRightsMask[from] | castlingRightsMask[to]))
814 int cr = castlingRightsMask[from] | castlingRightsMask[to];
815 k ^= Zobrist::castling[st->castlingRights & cr];
816 st->castlingRights &= ~cr;
819 // Prefetch TT access as soon as we know the new hash key
820 prefetch((char*)TT.first_entry(k));
822 // Move the piece. The tricky Chess960 castling is handled earlier
823 if (type_of(m) != CASTLING)
824 move_piece(from, to, us, pt);
826 // If the moving piece is a pawn do some special extra work
829 // Set en-passant square if the moved pawn can be captured
830 if ( (int(to) ^ int(from)) == 16
831 && (attacks_from<PAWN>(from + pawn_push(us), us) & pieces(them, PAWN)))
833 st->epSquare = Square((from + to) / 2);
834 k ^= Zobrist::enpassant[file_of(st->epSquare)];
837 else if (type_of(m) == PROMOTION)
839 PieceType promotion = promotion_type(m);
841 assert(relative_rank(us, to) == RANK_8);
842 assert(promotion >= KNIGHT && promotion <= QUEEN);
844 remove_piece(to, us, PAWN);
845 put_piece(to, us, promotion);
848 k ^= Zobrist::psq[us][PAWN][to] ^ Zobrist::psq[us][promotion][to];
849 st->pawnKey ^= Zobrist::psq[us][PAWN][to];
850 st->materialKey ^= Zobrist::psq[us][promotion][pieceCount[us][promotion]-1]
851 ^ Zobrist::psq[us][PAWN][pieceCount[us][PAWN]];
853 // Update incremental score
854 st->psq += psq[us][promotion][to] - psq[us][PAWN][to];
857 st->npMaterial[us] += PieceValue[MG][promotion];
860 // Update pawn hash key and prefetch access to pawnsTable
861 st->pawnKey ^= Zobrist::psq[us][PAWN][from] ^ Zobrist::psq[us][PAWN][to];
862 prefetch((char*)thisThread->pawnsTable[st->pawnKey]);
864 // Reset rule 50 draw counter
868 // Update incremental scores
869 st->psq += psq[us][pt][to] - psq[us][pt][from];
872 st->capturedType = captured;
874 // Update the key with the final value
877 // Update checkers bitboard: piece must be already moved due to attacks_from()
882 if (type_of(m) != NORMAL)
883 st->checkersBB = attackers_to(king_square(them)) & pieces(us);
887 if (ci.checkSq[pt] & to)
888 st->checkersBB |= to;
891 if (unlikely(ci.dcCandidates) && (ci.dcCandidates & from))
894 st->checkersBB |= attacks_from<ROOK>(king_square(them)) & pieces(us, QUEEN, ROOK);
897 st->checkersBB |= attacks_from<BISHOP>(king_square(them)) & pieces(us, QUEEN, BISHOP);
902 sideToMove = ~sideToMove;
908 /// Position::undo_move() unmakes a move. When it returns, the position should
909 /// be restored to exactly the same state as before the move was made.
911 void Position::undo_move(Move m) {
915 sideToMove = ~sideToMove;
917 Color us = sideToMove;
918 Square from = from_sq(m);
919 Square to = to_sq(m);
920 PieceType pt = type_of(piece_on(to));
922 assert(empty(from) || type_of(m) == CASTLING);
923 assert(st->capturedType != KING);
925 if (type_of(m) == PROMOTION)
927 assert(pt == promotion_type(m));
928 assert(relative_rank(us, to) == RANK_8);
929 assert(promotion_type(m) >= KNIGHT && promotion_type(m) <= QUEEN);
931 remove_piece(to, us, promotion_type(m));
932 put_piece(to, us, PAWN);
936 if (type_of(m) == CASTLING)
939 do_castling<false>(from, to, rfrom, rto);
943 move_piece(to, from, us, pt); // Put the piece back at the source square
945 if (st->capturedType)
949 if (type_of(m) == ENPASSANT)
951 capsq -= pawn_push(us);
954 assert(to == st->previous->epSquare);
955 assert(relative_rank(us, to) == RANK_6);
956 assert(piece_on(capsq) == NO_PIECE);
959 put_piece(capsq, ~us, st->capturedType); // Restore the captured piece
963 // Finally point our state pointer back to the previous state
971 /// Position::do_castling() is a helper used to do/undo a castling move. This
972 /// is a bit tricky, especially in Chess960.
974 void Position::do_castling(Square from, Square& to, Square& rfrom, Square& rto) {
976 bool kingSide = to > from;
977 rfrom = to; // Castling is encoded as "king captures friendly rook"
978 rto = relative_square(sideToMove, kingSide ? SQ_F1 : SQ_D1);
979 to = relative_square(sideToMove, kingSide ? SQ_G1 : SQ_C1);
981 // Remove both pieces first since squares could overlap in Chess960
982 remove_piece(Do ? from : to, sideToMove, KING);
983 remove_piece(Do ? rfrom : rto, sideToMove, ROOK);
984 board[Do ? from : to] = board[Do ? rfrom : rto] = NO_PIECE; // Since remove_piece doesn't do it for us
985 put_piece(Do ? to : from, sideToMove, KING);
986 put_piece(Do ? rto : rfrom, sideToMove, ROOK);
990 /// Position::do(undo)_null_move() is used to do(undo) a "null move": It flips
991 /// the side to move without executing any move on the board.
993 void Position::do_null_move(StateInfo& newSt) {
997 std::memcpy(&newSt, st, sizeof(StateInfo)); // Fully copy here
1002 if (st->epSquare != SQ_NONE)
1004 st->key ^= Zobrist::enpassant[file_of(st->epSquare)];
1005 st->epSquare = SQ_NONE;
1008 st->key ^= Zobrist::side;
1009 prefetch((char*)TT.first_entry(st->key));
1012 st->pliesFromNull = 0;
1014 sideToMove = ~sideToMove;
1016 assert(pos_is_ok());
1019 void Position::undo_null_move() {
1021 assert(!checkers());
1024 sideToMove = ~sideToMove;
1028 /// Position::see() is a static exchange evaluator: It tries to estimate the
1029 /// material gain or loss resulting from a move.
1031 Value Position::see_sign(Move m) const {
1035 // Early return if SEE cannot be negative because captured piece value
1036 // is not less then capturing one. Note that king moves always return
1037 // here because king midgame value is set to 0.
1038 if (PieceValue[MG][moved_piece(m)] <= PieceValue[MG][piece_on(to_sq(m))])
1039 return VALUE_KNOWN_WIN;
1044 Value Position::see(Move m) const {
1047 Bitboard occupied, attackers, stmAttackers;
1057 swapList[0] = PieceValue[MG][piece_on(to)];
1058 stm = color_of(piece_on(from));
1059 occupied = pieces() ^ from;
1061 // Castling moves are implemented as king capturing the rook so cannot be
1062 // handled correctly. Simply return 0 that is always the correct value
1063 // unless in the rare case the rook ends up under attack.
1064 if (type_of(m) == CASTLING)
1067 if (type_of(m) == ENPASSANT)
1069 occupied ^= to - pawn_push(stm); // Remove the captured pawn
1070 swapList[0] = PieceValue[MG][PAWN];
1073 // Find all attackers to the destination square, with the moving piece
1074 // removed, but possibly an X-ray attacker added behind it.
1075 attackers = attackers_to(to, occupied) & occupied;
1077 // If the opponent has no attackers we are finished
1079 stmAttackers = attackers & pieces(stm);
1083 // The destination square is defended, which makes things rather more
1084 // difficult to compute. We proceed by building up a "swap list" containing
1085 // the material gain or loss at each stop in a sequence of captures to the
1086 // destination square, where the sides alternately capture, and always
1087 // capture with the least valuable piece. After each capture, we look for
1088 // new X-ray attacks from behind the capturing piece.
1089 captured = type_of(piece_on(from));
1092 assert(slIndex < 32);
1094 // Add the new entry to the swap list
1095 swapList[slIndex] = -swapList[slIndex - 1] + PieceValue[MG][captured];
1097 // Locate and remove the next least valuable attacker
1098 captured = min_attacker<PAWN>(byTypeBB, to, stmAttackers, occupied, attackers);
1100 // Stop before processing a king capture
1101 if (captured == KING)
1103 if (stmAttackers == attackers)
1110 stmAttackers = attackers & pieces(stm);
1113 } while (stmAttackers);
1115 // Having built the swap list, we negamax through it to find the best
1116 // achievable score from the point of view of the side to move.
1118 swapList[slIndex - 1] = std::min(-swapList[slIndex], swapList[slIndex - 1]);
1124 /// Position::is_draw() tests whether the position is drawn by material, 50 moves
1125 /// rule or repetition. It does not detect stalemates.
1127 bool Position::is_draw() const {
1130 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMg))
1133 if (st->rule50 > 99 && (!checkers() || MoveList<LEGAL>(*this).size()))
1136 StateInfo* stp = st;
1137 for (int i = 2, e = std::min(st->rule50, st->pliesFromNull); i <= e; i += 2)
1139 stp = stp->previous->previous;
1141 if (stp->key == st->key)
1142 return true; // Draw at first repetition
1149 /// Position::flip() flips position with the white and black sides reversed. This
1150 /// is only useful for debugging e.g. for finding evaluation symmetry bugs.
1152 static char toggle_case(char c) {
1153 return char(islower(c) ? toupper(c) : tolower(c));
1156 void Position::flip() {
1159 std::stringstream ss(fen());
1161 for (Rank r = RANK_8; r >= RANK_1; --r) // Piece placement
1163 std::getline(ss, token, r > RANK_1 ? '/' : ' ');
1164 f.insert(0, token + (f.empty() ? " " : "/"));
1167 ss >> token; // Active color
1168 f += (token == "w" ? "B " : "W "); // Will be lowercased later
1170 ss >> token; // Castling availability
1173 std::transform(f.begin(), f.end(), f.begin(), toggle_case);
1175 ss >> token; // En passant square
1176 f += (token == "-" ? token : token.replace(1, 1, token[1] == '3' ? "6" : "3"));
1178 std::getline(ss, token); // Half and full moves
1181 set(f, is_chess960(), this_thread());
1183 assert(pos_is_ok());
1187 /// Position::pos_is_ok() performs some consistency checks for the position object.
1188 /// This is meant to be helpful when debugging.
1190 bool Position::pos_is_ok(int* step) const {
1192 // Which parts of the position should be verified?
1193 const bool all = false;
1195 const bool testBitboards = all || false;
1196 const bool testState = all || false;
1197 const bool testKingCount = all || false;
1198 const bool testKingCapture = all || false;
1199 const bool testPieceCounts = all || false;
1200 const bool testPieceList = all || false;
1201 const bool testCastlingSquares = all || false;
1206 if ( (sideToMove != WHITE && sideToMove != BLACK)
1207 || piece_on(king_square(WHITE)) != W_KING
1208 || piece_on(king_square(BLACK)) != B_KING
1209 || ( ep_square() != SQ_NONE
1210 && relative_rank(sideToMove, ep_square()) != RANK_6))
1213 if (step && ++*step, testBitboards)
1215 // The intersection of the white and black pieces must be empty
1216 if (pieces(WHITE) & pieces(BLACK))
1219 // The union of the white and black pieces must be equal to all
1221 if ((pieces(WHITE) | pieces(BLACK)) != pieces())
1224 // Separate piece type bitboards must have empty intersections
1225 for (PieceType p1 = PAWN; p1 <= KING; ++p1)
1226 for (PieceType p2 = PAWN; p2 <= KING; ++p2)
1227 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1231 if (step && ++*step, testState)
1235 if ( st->key != si.key
1236 || st->pawnKey != si.pawnKey
1237 || st->materialKey != si.materialKey
1238 || st->npMaterial[WHITE] != si.npMaterial[WHITE]
1239 || st->npMaterial[BLACK] != si.npMaterial[BLACK]
1240 || st->psq != si.psq
1241 || st->checkersBB != si.checkersBB)
1245 if (step && ++*step, testKingCount)
1246 if ( std::count(board, board + SQUARE_NB, W_KING) != 1
1247 || std::count(board, board + SQUARE_NB, B_KING) != 1)
1250 if (step && ++*step, testKingCapture)
1251 if (attackers_to(king_square(~sideToMove)) & pieces(sideToMove))
1254 if (step && ++*step, testPieceCounts)
1255 for (Color c = WHITE; c <= BLACK; ++c)
1256 for (PieceType pt = PAWN; pt <= KING; ++pt)
1257 if (pieceCount[c][pt] != popcount<Full>(pieces(c, pt)))
1260 if (step && ++*step, testPieceList)
1261 for (Color c = WHITE; c <= BLACK; ++c)
1262 for (PieceType pt = PAWN; pt <= KING; ++pt)
1263 for (int i = 0; i < pieceCount[c][pt]; ++i)
1264 if ( board[pieceList[c][pt][i]] != make_piece(c, pt)
1265 || index[pieceList[c][pt][i]] != i)
1268 if (step && ++*step, testCastlingSquares)
1269 for (Color c = WHITE; c <= BLACK; ++c)
1270 for (CastlingSide s = KING_SIDE; s <= QUEEN_SIDE; s = CastlingSide(s + 1))
1272 if (!can_castle(c | s))
1275 if ( (castlingRightsMask[king_square(c)] & (c | s)) != (c | s)
1276 || piece_on(castlingRookSquare[c | s]) != make_piece(c, ROOK)
1277 || castlingRightsMask[castlingRookSquare[c | s]] != (c | s))