2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2015 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/>.
22 #include <cstring> // For std::memset, std::memcmp
37 Value PieceValue[PHASE_NB][PIECE_NB] = {
38 { VALUE_ZERO, PawnValueMg, KnightValueMg, BishopValueMg, RookValueMg, QueenValueMg },
39 { VALUE_ZERO, PawnValueEg, KnightValueEg, BishopValueEg, RookValueEg, QueenValueEg } };
43 Key psq[COLOR_NB][PIECE_TYPE_NB][SQUARE_NB];
44 Key enpassant[FILE_NB];
45 Key castling[CASTLING_RIGHT_NB];
50 Key Position::exclusion_key() const { return st->key ^ Zobrist::exclusion; }
54 const string PieceToChar(" PNBRQK pnbrqk");
55 Score psq[COLOR_NB][PIECE_TYPE_NB][SQUARE_NB];
57 // min_attacker() is a helper function used by see() to locate the least
58 // valuable attacker for the side to move, remove the attacker we just found
59 // from the bitboards and scan for new X-ray attacks behind it.
61 template<int Pt> FORCE_INLINE
62 PieceType min_attacker(const Bitboard* bb, const Square& to, const Bitboard& stmAttackers,
63 Bitboard& occupied, Bitboard& attackers) {
65 Bitboard b = stmAttackers & bb[Pt];
67 return min_attacker<Pt+1>(bb, to, stmAttackers, occupied, attackers);
69 occupied ^= b & ~(b - 1);
71 if (Pt == PAWN || Pt == BISHOP || Pt == QUEEN)
72 attackers |= attacks_bb<BISHOP>(to, occupied) & (bb[BISHOP] | bb[QUEEN]);
74 if (Pt == ROOK || Pt == QUEEN)
75 attackers |= attacks_bb<ROOK>(to, occupied) & (bb[ROOK] | bb[QUEEN]);
77 attackers &= occupied; // After X-ray that may add already processed pieces
81 template<> FORCE_INLINE
82 PieceType min_attacker<KING>(const Bitboard*, const Square&, const Bitboard&, Bitboard&, Bitboard&) {
83 return KING; // No need to update bitboards: it is the last cycle
91 CheckInfo::CheckInfo(const Position& pos) {
93 Color them = ~pos.side_to_move();
94 ksq = pos.king_square(them);
96 pinned = pos.pinned_pieces(pos.side_to_move());
97 dcCandidates = pos.discovered_check_candidates();
99 checkSq[PAWN] = pos.attacks_from<PAWN>(ksq, them);
100 checkSq[KNIGHT] = pos.attacks_from<KNIGHT>(ksq);
101 checkSq[BISHOP] = pos.attacks_from<BISHOP>(ksq);
102 checkSq[ROOK] = pos.attacks_from<ROOK>(ksq);
103 checkSq[QUEEN] = checkSq[BISHOP] | checkSq[ROOK];
108 /// operator<<(Position) returns an ASCII representation of the position
110 std::ostream& operator<<(std::ostream& os, const Position& pos) {
112 os << "\n +---+---+---+---+---+---+---+---+\n";
114 for (Rank r = RANK_8; r >= RANK_1; --r)
116 for (File f = FILE_A; f <= FILE_H; ++f)
117 os << " | " << PieceToChar[pos.piece_on(make_square(f, r))];
119 os << " |\n +---+---+---+---+---+---+---+---+\n";
122 os << "\nFen: " << pos.fen() << "\nKey: " << std::hex << std::uppercase
123 << std::setfill('0') << std::setw(16) << pos.st->key << std::dec << "\nCheckers: ";
125 for (Bitboard b = pos.checkers(); b; )
126 os << UCI::square(pop_lsb(&b)) << " ";
132 /// Position::init() initializes at startup the various arrays used to compute
133 /// hash keys and the piece square tables. The latter is a two-step operation:
134 /// Firstly, the white halves of the tables are copied from PSQT[] tables.
135 /// Secondly, the black halves of the tables are initialized by flipping and
136 /// changing the sign of the white scores.
138 void Position::init() {
142 for (Color c = WHITE; c <= BLACK; ++c)
143 for (PieceType pt = PAWN; pt <= KING; ++pt)
144 for (Square s = SQ_A1; s <= SQ_H8; ++s)
145 Zobrist::psq[c][pt][s] = rng.rand<Key>();
147 for (File f = FILE_A; f <= FILE_H; ++f)
148 Zobrist::enpassant[f] = rng.rand<Key>();
150 for (int cr = NO_CASTLING; cr <= ANY_CASTLING; ++cr)
155 Key k = Zobrist::castling[1ULL << pop_lsb(&b)];
156 Zobrist::castling[cr] ^= k ? k : rng.rand<Key>();
160 Zobrist::side = rng.rand<Key>();
161 Zobrist::exclusion = rng.rand<Key>();
163 for (PieceType pt = PAWN; pt <= KING; ++pt)
165 PieceValue[MG][make_piece(BLACK, pt)] = PieceValue[MG][pt];
166 PieceValue[EG][make_piece(BLACK, pt)] = PieceValue[EG][pt];
168 Score v = make_score(PieceValue[MG][pt], PieceValue[EG][pt]);
170 for (Square s = SQ_A1; s <= SQ_H8; ++s)
172 psq[WHITE][pt][ s] = (v + PSQT[pt][s]);
173 psq[BLACK][pt][~s] = -(v + PSQT[pt][s]);
179 /// Position::operator=() creates a copy of 'pos' but detaching the state pointer
180 /// from the source to be self-consistent and not depending on any external data.
182 Position& Position::operator=(const Position& pos) {
184 std::memcpy(this, &pos, sizeof(Position));
195 /// Position::clear() erases the position object to a pristine state, with an
196 /// empty board, white to move, and no castling rights.
198 void Position::clear() {
200 std::memset(this, 0, sizeof(Position));
201 startState.epSquare = SQ_NONE;
204 for (int i = 0; i < PIECE_TYPE_NB; ++i)
205 for (int j = 0; j < 16; ++j)
206 pieceList[WHITE][i][j] = pieceList[BLACK][i][j] = SQ_NONE;
210 /// Position::set() initializes the position object with the given FEN string.
211 /// This function is not very robust - make sure that input FENs are correct,
212 /// this is assumed to be the responsibility of the GUI.
214 void Position::set(const string& fenStr, bool isChess960, Thread* th) {
216 A FEN string defines a particular position using only the ASCII character set.
218 A FEN string contains six fields separated by a space. The fields are:
220 1) Piece placement (from white's perspective). Each rank is described, starting
221 with rank 8 and ending with rank 1. Within each rank, the contents of each
222 square are described from file A through file H. Following the Standard
223 Algebraic Notation (SAN), each piece is identified by a single letter taken
224 from the standard English names. White pieces are designated using upper-case
225 letters ("PNBRQK") whilst Black uses lowercase ("pnbrqk"). Blank squares are
226 noted using digits 1 through 8 (the number of blank squares), and "/"
229 2) Active color. "w" means white moves next, "b" means black.
231 3) Castling availability. If neither side can castle, this is "-". Otherwise,
232 this has one or more letters: "K" (White can castle kingside), "Q" (White
233 can castle queenside), "k" (Black can castle kingside), and/or "q" (Black
234 can castle queenside).
236 4) En passant target square (in algebraic notation). If there's no en passant
237 target square, this is "-". If a pawn has just made a 2-square move, this
238 is the position "behind" the pawn. This is recorded regardless of whether
239 there is a pawn in position to make an en passant capture.
241 5) Halfmove clock. This is the number of halfmoves since the last pawn advance
242 or capture. This is used to determine if a draw can be claimed under the
245 6) Fullmove number. The number of the full move. It starts at 1, and is
246 incremented after Black's move.
249 unsigned char col, row, token;
252 std::istringstream ss(fenStr);
257 // 1. Piece placement
258 while ((ss >> token) && !isspace(token))
261 sq += Square(token - '0'); // Advance the given number of files
263 else if (token == '/')
266 else if ((idx = PieceToChar.find(token)) != string::npos)
268 put_piece(sq, color_of(Piece(idx)), type_of(Piece(idx)));
275 sideToMove = (token == 'w' ? WHITE : BLACK);
278 // 3. Castling availability. Compatible with 3 standards: Normal FEN standard,
279 // Shredder-FEN that uses the letters of the columns on which the rooks began
280 // the game instead of KQkq and also X-FEN standard that, in case of Chess960,
281 // if an inner rook is associated with the castling right, the castling tag is
282 // replaced by the file letter of the involved rook, as for the Shredder-FEN.
283 while ((ss >> token) && !isspace(token))
286 Color c = islower(token) ? BLACK : WHITE;
288 token = char(toupper(token));
291 for (rsq = relative_square(c, SQ_H1); type_of(piece_on(rsq)) != ROOK; --rsq) {}
293 else if (token == 'Q')
294 for (rsq = relative_square(c, SQ_A1); type_of(piece_on(rsq)) != ROOK; ++rsq) {}
296 else if (token >= 'A' && token <= 'H')
297 rsq = make_square(File(token - 'A'), relative_rank(c, RANK_1));
302 set_castling_right(c, rsq);
305 // 4. En passant square. Ignore if no pawn capture is possible
306 if ( ((ss >> col) && (col >= 'a' && col <= 'h'))
307 && ((ss >> row) && (row == '3' || row == '6')))
309 st->epSquare = make_square(File(col - 'a'), Rank(row - '1'));
311 if (!(attackers_to(st->epSquare) & pieces(sideToMove, PAWN)))
312 st->epSquare = SQ_NONE;
315 // 5-6. Halfmove clock and fullmove number
316 ss >> std::skipws >> st->rule50 >> gamePly;
318 // Convert from fullmove starting from 1 to ply starting from 0,
319 // handle also common incorrect FEN with fullmove = 0.
320 gamePly = std::max(2 * (gamePly - 1), 0) + (sideToMove == BLACK);
322 chess960 = isChess960;
330 /// Position::set_castling_right() is a helper function used to set castling
331 /// rights given the corresponding color and the rook starting square.
333 void Position::set_castling_right(Color c, Square rfrom) {
335 Square kfrom = king_square(c);
336 CastlingSide cs = kfrom < rfrom ? KING_SIDE : QUEEN_SIDE;
337 CastlingRight cr = (c | cs);
339 st->castlingRights |= cr;
340 castlingRightsMask[kfrom] |= cr;
341 castlingRightsMask[rfrom] |= cr;
342 castlingRookSquare[cr] = rfrom;
344 Square kto = relative_square(c, cs == KING_SIDE ? SQ_G1 : SQ_C1);
345 Square rto = relative_square(c, cs == KING_SIDE ? SQ_F1 : SQ_D1);
347 for (Square s = std::min(rfrom, rto); s <= std::max(rfrom, rto); ++s)
348 if (s != kfrom && s != rfrom)
349 castlingPath[cr] |= s;
351 for (Square s = std::min(kfrom, kto); s <= std::max(kfrom, kto); ++s)
352 if (s != kfrom && s != rfrom)
353 castlingPath[cr] |= s;
357 /// Position::set_state() computes the hash keys of the position, and other
358 /// data that once computed is updated incrementally as moves are made.
359 /// The function is only used when a new position is set up, and to verify
360 /// the correctness of the StateInfo data when running in debug mode.
362 void Position::set_state(StateInfo* si) const {
364 si->key = si->pawnKey = si->materialKey = 0;
365 si->nonPawnMaterial[WHITE] = si->nonPawnMaterial[BLACK] = VALUE_ZERO;
366 si->psq = SCORE_ZERO;
368 si->checkersBB = attackers_to(king_square(sideToMove)) & pieces(~sideToMove);
370 for (Bitboard b = pieces(); b; )
372 Square s = pop_lsb(&b);
373 Piece pc = piece_on(s);
374 si->key ^= Zobrist::psq[color_of(pc)][type_of(pc)][s];
375 si->psq += psq[color_of(pc)][type_of(pc)][s];
378 if (ep_square() != SQ_NONE)
379 si->key ^= Zobrist::enpassant[file_of(ep_square())];
381 if (sideToMove == BLACK)
382 si->key ^= Zobrist::side;
384 si->key ^= Zobrist::castling[si->castlingRights];
386 for (Bitboard b = pieces(PAWN); b; )
388 Square s = pop_lsb(&b);
389 si->pawnKey ^= Zobrist::psq[color_of(piece_on(s))][PAWN][s];
392 for (Color c = WHITE; c <= BLACK; ++c)
393 for (PieceType pt = PAWN; pt <= KING; ++pt)
394 for (int cnt = 0; cnt < pieceCount[c][pt]; ++cnt)
395 si->materialKey ^= Zobrist::psq[c][pt][cnt];
397 for (Color c = WHITE; c <= BLACK; ++c)
398 for (PieceType pt = KNIGHT; pt <= QUEEN; ++pt)
399 si->nonPawnMaterial[c] += pieceCount[c][pt] * PieceValue[MG][pt];
403 /// Position::fen() returns a FEN representation of the position. In case of
404 /// Chess960 the Shredder-FEN notation is used. This is mainly a debugging function.
406 const string Position::fen() const {
409 std::ostringstream ss;
411 for (Rank r = RANK_8; r >= RANK_1; --r)
413 for (File f = FILE_A; f <= FILE_H; ++f)
415 for (emptyCnt = 0; f <= FILE_H && empty(make_square(f, r)); ++f)
422 ss << PieceToChar[piece_on(make_square(f, r))];
429 ss << (sideToMove == WHITE ? " w " : " b ");
431 if (can_castle(WHITE_OO))
432 ss << (chess960 ? char('A' + file_of(castling_rook_square(WHITE | KING_SIDE))) : 'K');
434 if (can_castle(WHITE_OOO))
435 ss << (chess960 ? char('A' + file_of(castling_rook_square(WHITE | QUEEN_SIDE))) : 'Q');
437 if (can_castle(BLACK_OO))
438 ss << (chess960 ? char('a' + file_of(castling_rook_square(BLACK | KING_SIDE))) : 'k');
440 if (can_castle(BLACK_OOO))
441 ss << (chess960 ? char('a' + file_of(castling_rook_square(BLACK | QUEEN_SIDE))) : 'q');
443 if (!can_castle(WHITE) && !can_castle(BLACK))
446 ss << (ep_square() == SQ_NONE ? " - " : " " + UCI::square(ep_square()) + " ")
447 << st->rule50 << " " << 1 + (gamePly - (sideToMove == BLACK)) / 2;
453 /// Position::game_phase() calculates the game phase interpolating total non-pawn
454 /// material between endgame and midgame limits.
456 Phase Position::game_phase() const {
458 Value npm = st->nonPawnMaterial[WHITE] + st->nonPawnMaterial[BLACK];
460 npm = std::max(EndgameLimit, std::min(npm, MidgameLimit));
462 return Phase(((npm - EndgameLimit) * PHASE_MIDGAME) / (MidgameLimit - EndgameLimit));
466 /// Position::check_blockers() returns a bitboard of all the pieces with color
467 /// 'c' that are blocking check on the king with color 'kingColor'. A piece
468 /// blocks a check if removing that piece from the board would result in a
469 /// position where the king is in check. A check blocking piece can be either a
470 /// pinned or a discovered check piece, according if its color 'c' is the same
471 /// or the opposite of 'kingColor'.
473 Bitboard Position::check_blockers(Color c, Color kingColor) const {
475 Bitboard b, pinners, result = 0;
476 Square ksq = king_square(kingColor);
478 // Pinners are sliders that give check when a pinned piece is removed
479 pinners = ( (pieces( ROOK, QUEEN) & PseudoAttacks[ROOK ][ksq])
480 | (pieces(BISHOP, QUEEN) & PseudoAttacks[BISHOP][ksq])) & pieces(~kingColor);
484 b = between_bb(ksq, pop_lsb(&pinners)) & pieces();
486 if (!more_than_one(b))
487 result |= b & pieces(c);
493 /// Position::attackers_to() computes a bitboard of all pieces which attack a
494 /// given square. Slider attacks use the occupied bitboard to indicate occupancy.
496 Bitboard Position::attackers_to(Square s, Bitboard occupied) const {
498 return (attacks_from<PAWN>(s, BLACK) & pieces(WHITE, PAWN))
499 | (attacks_from<PAWN>(s, WHITE) & pieces(BLACK, PAWN))
500 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
501 | (attacks_bb<ROOK>(s, occupied) & pieces(ROOK, QUEEN))
502 | (attacks_bb<BISHOP>(s, occupied) & pieces(BISHOP, QUEEN))
503 | (attacks_from<KING>(s) & pieces(KING));
507 /// Position::legal() tests whether a pseudo-legal move is legal
509 bool Position::legal(Move m, Bitboard pinned) const {
512 assert(pinned == pinned_pieces(sideToMove));
514 Color us = sideToMove;
515 Square from = from_sq(m);
517 assert(color_of(moved_piece(m)) == us);
518 assert(piece_on(king_square(us)) == make_piece(us, KING));
520 // En passant captures are a tricky special case. Because they are rather
521 // uncommon, we do it simply by testing whether the king is attacked after
523 if (type_of(m) == ENPASSANT)
525 Square ksq = king_square(us);
526 Square to = to_sq(m);
527 Square capsq = to - pawn_push(us);
528 Bitboard occupied = (pieces() ^ from ^ capsq) | to;
530 assert(to == ep_square());
531 assert(moved_piece(m) == make_piece(us, PAWN));
532 assert(piece_on(capsq) == make_piece(~us, PAWN));
533 assert(piece_on(to) == NO_PIECE);
535 return !(attacks_bb< ROOK>(ksq, occupied) & pieces(~us, QUEEN, ROOK))
536 && !(attacks_bb<BISHOP>(ksq, occupied) & pieces(~us, QUEEN, BISHOP));
539 // If the moving piece is a king, check whether the destination
540 // square is attacked by the opponent. Castling moves are checked
541 // for legality during move generation.
542 if (type_of(piece_on(from)) == KING)
543 return type_of(m) == CASTLING || !(attackers_to(to_sq(m)) & pieces(~us));
545 // A non-king move is legal if and only if it is not pinned or it
546 // is moving along the ray towards or away from the king.
549 || aligned(from, to_sq(m), king_square(us));
553 /// Position::pseudo_legal() takes a random move and tests whether the move is
554 /// pseudo legal. It is used to validate moves from TT that can be corrupted
555 /// due to SMP concurrent access or hash position key aliasing.
557 bool Position::pseudo_legal(const Move m) const {
559 Color us = sideToMove;
560 Square from = from_sq(m);
561 Square to = to_sq(m);
562 Piece pc = moved_piece(m);
564 // Use a slower but simpler function for uncommon cases
565 if (type_of(m) != NORMAL)
566 return MoveList<LEGAL>(*this).contains(m);
568 // Is not a promotion, so promotion piece must be empty
569 if (promotion_type(m) - 2 != NO_PIECE_TYPE)
572 // If the 'from' square is not occupied by a piece belonging to the side to
573 // move, the move is obviously not legal.
574 if (pc == NO_PIECE || color_of(pc) != us)
577 // The destination square cannot be occupied by a friendly piece
581 // Handle the special case of a pawn move
582 if (type_of(pc) == PAWN)
584 // We have already handled promotion moves, so destination
585 // cannot be on the 8th/1st rank.
586 if (rank_of(to) == relative_rank(us, RANK_8))
589 if ( !(attacks_from<PAWN>(from, us) & pieces(~us) & to) // Not a capture
591 && !((from + pawn_push(us) == to) && empty(to)) // Not a single push
593 && !( (from + 2 * pawn_push(us) == to) // Not a double push
594 && (rank_of(from) == relative_rank(us, RANK_2))
596 && empty(to - pawn_push(us))))
599 else if (!(attacks_from(pc, from) & to))
602 // Evasions generator already takes care to avoid some kind of illegal moves
603 // and legal() relies on this. We therefore have to take care that the same
604 // kind of moves are filtered out here.
607 if (type_of(pc) != KING)
609 // Double check? In this case a king move is required
610 if (more_than_one(checkers()))
613 // Our move must be a blocking evasion or a capture of the checking piece
614 if (!((between_bb(lsb(checkers()), king_square(us)) | checkers()) & to))
617 // In case of king moves under check we have to remove king so as to catch
618 // invalid moves like b1a1 when opposite queen is on c1.
619 else if (attackers_to(to, pieces() ^ from) & pieces(~us))
627 /// Position::gives_check() tests whether a pseudo-legal move gives a check
629 bool Position::gives_check(Move m, const CheckInfo& ci) const {
632 assert(ci.dcCandidates == discovered_check_candidates());
633 assert(color_of(moved_piece(m)) == sideToMove);
635 Square from = from_sq(m);
636 Square to = to_sq(m);
637 PieceType pt = type_of(piece_on(from));
639 // Is there a direct check?
640 if (ci.checkSq[pt] & to)
643 // Is there a discovered check?
645 && (ci.dcCandidates & from)
646 && !aligned(from, to, ci.ksq))
655 return attacks_bb(Piece(promotion_type(m)), to, pieces() ^ from) & ci.ksq;
657 // En passant capture with check? We have already handled the case
658 // of direct checks and ordinary discovered check, so the only case we
659 // need to handle is the unusual case of a discovered check through
660 // the captured pawn.
663 Square capsq = make_square(file_of(to), rank_of(from));
664 Bitboard b = (pieces() ^ from ^ capsq) | to;
666 return (attacks_bb< ROOK>(ci.ksq, b) & pieces(sideToMove, QUEEN, ROOK))
667 | (attacks_bb<BISHOP>(ci.ksq, b) & pieces(sideToMove, QUEEN, BISHOP));
672 Square rfrom = to; // Castling is encoded as 'King captures the rook'
673 Square kto = relative_square(sideToMove, rfrom > kfrom ? SQ_G1 : SQ_C1);
674 Square rto = relative_square(sideToMove, rfrom > kfrom ? SQ_F1 : SQ_D1);
676 return (PseudoAttacks[ROOK][rto] & ci.ksq)
677 && (attacks_bb<ROOK>(rto, (pieces() ^ kfrom ^ rfrom) | rto | kto) & ci.ksq);
686 /// Position::do_move() makes a move, and saves all information necessary
687 /// to a StateInfo object. The move is assumed to be legal. Pseudo-legal
688 /// moves should be filtered out before this function is called.
690 void Position::do_move(Move m, StateInfo& newSt) {
693 do_move(m, newSt, ci, gives_check(m, ci));
696 void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool givesCheck) {
699 assert(&newSt != st);
702 Key k = st->key ^ Zobrist::side;
704 // Copy some fields of the old state to our new StateInfo object except the
705 // ones which are going to be recalculated from scratch anyway and then switch
706 // our state pointer to point to the new (ready to be updated) state.
707 std::memcpy(&newSt, st, offsetof(StateInfo, key));
711 // Increment ply counters. In particular, rule50 will be reset to zero later on
712 // in case of a capture or a pawn move.
717 Color us = sideToMove;
719 Square from = from_sq(m);
720 Square to = to_sq(m);
721 PieceType pt = type_of(piece_on(from));
722 PieceType captured = type_of(m) == ENPASSANT ? PAWN : type_of(piece_on(to));
724 assert(color_of(piece_on(from)) == us);
725 assert(piece_on(to) == NO_PIECE || color_of(piece_on(to)) == (type_of(m) != CASTLING ? them : us));
726 assert(captured != KING);
728 if (type_of(m) == CASTLING)
733 do_castling<true>(from, to, rfrom, rto);
735 captured = NO_PIECE_TYPE;
736 st->psq += psq[us][ROOK][rto] - psq[us][ROOK][rfrom];
737 k ^= Zobrist::psq[us][ROOK][rfrom] ^ Zobrist::psq[us][ROOK][rto];
744 // If the captured piece is a pawn, update pawn hash key, otherwise
745 // update non-pawn material.
746 if (captured == PAWN)
748 if (type_of(m) == ENPASSANT)
750 capsq -= pawn_push(us);
753 assert(to == st->epSquare);
754 assert(relative_rank(us, to) == RANK_6);
755 assert(piece_on(to) == NO_PIECE);
756 assert(piece_on(capsq) == make_piece(them, PAWN));
758 board[capsq] = NO_PIECE; // Not done by remove_piece()
761 st->pawnKey ^= Zobrist::psq[them][PAWN][capsq];
764 st->nonPawnMaterial[them] -= PieceValue[MG][captured];
766 // Update board and piece lists
767 remove_piece(capsq, them, captured);
769 // Update material hash key and prefetch access to materialTable
770 k ^= Zobrist::psq[them][captured][capsq];
771 st->materialKey ^= Zobrist::psq[them][captured][pieceCount[them][captured]];
772 prefetch(thisThread->materialTable[st->materialKey]);
774 // Update incremental scores
775 st->psq -= psq[them][captured][capsq];
777 // Reset rule 50 counter
782 k ^= Zobrist::psq[us][pt][from] ^ Zobrist::psq[us][pt][to];
784 // Reset en passant square
785 if (st->epSquare != SQ_NONE)
787 k ^= Zobrist::enpassant[file_of(st->epSquare)];
788 st->epSquare = SQ_NONE;
791 // Update castling rights if needed
792 if (st->castlingRights && (castlingRightsMask[from] | castlingRightsMask[to]))
794 int cr = castlingRightsMask[from] | castlingRightsMask[to];
795 k ^= Zobrist::castling[st->castlingRights & cr];
796 st->castlingRights &= ~cr;
799 // Move the piece. The tricky Chess960 castling is handled earlier
800 if (type_of(m) != CASTLING)
801 move_piece(from, to, us, pt);
803 // If the moving piece is a pawn do some special extra work
806 // Set en-passant square if the moved pawn can be captured
807 if ( (int(to) ^ int(from)) == 16
808 && (attacks_from<PAWN>(to - pawn_push(us), us) & pieces(them, PAWN)))
810 st->epSquare = (from + to) / 2;
811 k ^= Zobrist::enpassant[file_of(st->epSquare)];
814 else if (type_of(m) == PROMOTION)
816 PieceType promotion = promotion_type(m);
818 assert(relative_rank(us, to) == RANK_8);
819 assert(promotion >= KNIGHT && promotion <= QUEEN);
821 remove_piece(to, us, PAWN);
822 put_piece(to, us, promotion);
825 k ^= Zobrist::psq[us][PAWN][to] ^ Zobrist::psq[us][promotion][to];
826 st->pawnKey ^= Zobrist::psq[us][PAWN][to];
827 st->materialKey ^= Zobrist::psq[us][promotion][pieceCount[us][promotion]-1]
828 ^ Zobrist::psq[us][PAWN][pieceCount[us][PAWN]];
830 // Update incremental score
831 st->psq += psq[us][promotion][to] - psq[us][PAWN][to];
834 st->nonPawnMaterial[us] += PieceValue[MG][promotion];
837 // Update pawn hash key and prefetch access to pawnsTable
838 st->pawnKey ^= Zobrist::psq[us][PAWN][from] ^ Zobrist::psq[us][PAWN][to];
839 prefetch(thisThread->pawnsTable[st->pawnKey]);
841 // Reset rule 50 draw counter
845 // Update incremental scores
846 st->psq += psq[us][pt][to] - psq[us][pt][from];
849 st->capturedType = captured;
851 // Update the key with the final value
854 // Update checkers bitboard: piece must be already moved due to attacks_from()
859 if (type_of(m) != NORMAL)
860 st->checkersBB = attackers_to(king_square(them)) & pieces(us);
864 if (ci.checkSq[pt] & to)
865 st->checkersBB |= to;
868 if (ci.dcCandidates && (ci.dcCandidates & from))
873 st->checkersBB |= attacks_from<ROOK>(king_square(them)) & pieces(us, QUEEN, ROOK);
876 st->checkersBB |= attacks_from<BISHOP>(king_square(them)) & pieces(us, QUEEN, BISHOP);
881 sideToMove = ~sideToMove;
887 /// Position::undo_move() unmakes a move. When it returns, the position should
888 /// be restored to exactly the same state as before the move was made.
890 void Position::undo_move(Move m) {
894 sideToMove = ~sideToMove;
896 Color us = sideToMove;
897 Square from = from_sq(m);
898 Square to = to_sq(m);
899 PieceType pt = type_of(piece_on(to));
901 assert(empty(from) || type_of(m) == CASTLING);
902 assert(st->capturedType != KING);
904 if (type_of(m) == PROMOTION)
906 assert(relative_rank(us, to) == RANK_8);
907 assert(pt == promotion_type(m));
908 assert(pt >= KNIGHT && pt <= QUEEN);
910 remove_piece(to, us, pt);
911 put_piece(to, us, PAWN);
915 if (type_of(m) == CASTLING)
918 do_castling<false>(from, to, rfrom, rto);
922 move_piece(to, from, us, pt); // Put the piece back at the source square
924 if (st->capturedType)
928 if (type_of(m) == ENPASSANT)
930 capsq -= pawn_push(us);
933 assert(to == st->previous->epSquare);
934 assert(relative_rank(us, to) == RANK_6);
935 assert(piece_on(capsq) == NO_PIECE);
936 assert(st->capturedType == PAWN);
939 put_piece(capsq, ~us, st->capturedType); // Restore the captured piece
943 // Finally point our state pointer back to the previous state
951 /// Position::do_castling() is a helper used to do/undo a castling move. This
952 /// is a bit tricky, especially in Chess960.
954 void Position::do_castling(Square from, Square& to, Square& rfrom, Square& rto) {
956 bool kingSide = to > from;
957 rfrom = to; // Castling is encoded as "king captures friendly rook"
958 rto = relative_square(sideToMove, kingSide ? SQ_F1 : SQ_D1);
959 to = relative_square(sideToMove, kingSide ? SQ_G1 : SQ_C1);
961 // Remove both pieces first since squares could overlap in Chess960
962 remove_piece(Do ? from : to, sideToMove, KING);
963 remove_piece(Do ? rfrom : rto, sideToMove, ROOK);
964 board[Do ? from : to] = board[Do ? rfrom : rto] = NO_PIECE; // Since remove_piece doesn't do it for us
965 put_piece(Do ? to : from, sideToMove, KING);
966 put_piece(Do ? rto : rfrom, sideToMove, ROOK);
970 /// Position::do(undo)_null_move() is used to do(undo) a "null move": It flips
971 /// the side to move without executing any move on the board.
973 void Position::do_null_move(StateInfo& newSt) {
976 assert(&newSt != st);
978 std::memcpy(&newSt, st, sizeof(StateInfo));
982 if (st->epSquare != SQ_NONE)
984 st->key ^= Zobrist::enpassant[file_of(st->epSquare)];
985 st->epSquare = SQ_NONE;
988 st->key ^= Zobrist::side;
989 prefetch(TT.first_entry(st->key));
992 st->pliesFromNull = 0;
994 sideToMove = ~sideToMove;
999 void Position::undo_null_move() {
1001 assert(!checkers());
1004 sideToMove = ~sideToMove;
1008 /// Position::key_after() computes the new hash key after the given move. Needed
1009 /// for speculative prefetch. It doesn't recognize special moves like castling,
1010 /// en-passant and promotions.
1012 Key Position::key_after(Move m) const {
1014 Color us = sideToMove;
1015 Square from = from_sq(m);
1016 Square to = to_sq(m);
1017 PieceType pt = type_of(piece_on(from));
1018 PieceType captured = type_of(piece_on(to));
1019 Key k = st->key ^ Zobrist::side;
1022 k ^= Zobrist::psq[~us][captured][to];
1024 return k ^ Zobrist::psq[us][pt][to] ^ Zobrist::psq[us][pt][from];
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
1062 // be handled correctly. Simply return VALUE_ZERO that is always correct
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 stmAttackers = attackers & pieces(stm);
1103 } while (stmAttackers && (captured != KING || (--slIndex, false))); // Stop before a king capture
1105 // Having built the swap list, we negamax through it to find the best
1106 // achievable score from the point of view of the side to move.
1108 swapList[slIndex - 1] = std::min(-swapList[slIndex], swapList[slIndex - 1]);
1114 /// Position::is_draw() tests whether the position is drawn by material, 50 moves
1115 /// rule or repetition. It does not detect stalemates.
1117 bool Position::is_draw() const {
1119 if (st->rule50 > 99 && (!checkers() || MoveList<LEGAL>(*this).size()))
1122 StateInfo* stp = st;
1123 for (int i = 2, e = std::min(st->rule50, st->pliesFromNull); i <= e; i += 2)
1125 stp = stp->previous->previous;
1127 if (stp->key == st->key)
1128 return true; // Draw at first repetition
1135 /// Position::flip() flips position with the white and black sides reversed. This
1136 /// is only useful for debugging e.g. for finding evaluation symmetry bugs.
1138 void Position::flip() {
1141 std::stringstream ss(fen());
1143 for (Rank r = RANK_8; r >= RANK_1; --r) // Piece placement
1145 std::getline(ss, token, r > RANK_1 ? '/' : ' ');
1146 f.insert(0, token + (f.empty() ? " " : "/"));
1149 ss >> token; // Active color
1150 f += (token == "w" ? "B " : "W "); // Will be lowercased later
1152 ss >> token; // Castling availability
1155 std::transform(f.begin(), f.end(), f.begin(),
1156 [](char c) { return char(islower(c) ? toupper(c) : tolower(c)); });
1158 ss >> token; // En passant square
1159 f += (token == "-" ? token : token.replace(1, 1, token[1] == '3' ? "6" : "3"));
1161 std::getline(ss, token); // Half and full moves
1164 set(f, is_chess960(), this_thread());
1166 assert(pos_is_ok());
1170 /// Position::pos_is_ok() performs some consistency checks for the position object.
1171 /// This is meant to be helpful when debugging.
1173 bool Position::pos_is_ok(int* failedStep) const {
1175 const bool Fast = true; // Quick (default) or full check?
1177 enum { Default, King, Bitboards, State, Lists, Castling };
1179 for (int step = Default; step <= (Fast ? Default : Castling); step++)
1184 if (step == Default)
1185 if ( (sideToMove != WHITE && sideToMove != BLACK)
1186 || piece_on(king_square(WHITE)) != W_KING
1187 || piece_on(king_square(BLACK)) != B_KING
1188 || ( ep_square() != SQ_NONE
1189 && relative_rank(sideToMove, ep_square()) != RANK_6))
1193 if ( std::count(board, board + SQUARE_NB, W_KING) != 1
1194 || std::count(board, board + SQUARE_NB, B_KING) != 1
1195 || attackers_to(king_square(~sideToMove)) & pieces(sideToMove))
1198 if (step == Bitboards)
1200 if ( (pieces(WHITE) & pieces(BLACK))
1201 ||(pieces(WHITE) | pieces(BLACK)) != pieces())
1204 for (PieceType p1 = PAWN; p1 <= KING; ++p1)
1205 for (PieceType p2 = PAWN; p2 <= KING; ++p2)
1206 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1214 if (std::memcmp(&si, st, sizeof(StateInfo)))
1219 for (Color c = WHITE; c <= BLACK; ++c)
1220 for (PieceType pt = PAWN; pt <= KING; ++pt)
1222 if (pieceCount[c][pt] != popcount<Full>(pieces(c, pt)))
1225 for (int i = 0; i < pieceCount[c][pt]; ++i)
1226 if ( board[pieceList[c][pt][i]] != make_piece(c, pt)
1227 || index[pieceList[c][pt][i]] != i)
1231 if (step == Castling)
1232 for (Color c = WHITE; c <= BLACK; ++c)
1233 for (CastlingSide s = KING_SIDE; s <= QUEEN_SIDE; s = CastlingSide(s + 1))
1235 if (!can_castle(c | s))
1238 if ( piece_on(castlingRookSquare[c | s]) != make_piece(c, ROOK)
1239 || castlingRightsMask[castlingRookSquare[c | s]] != (c | s)
1240 ||(castlingRightsMask[king_square(c)] & (c | s)) != (c | s))