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 rank = RANK_8; rank >= RANK_1; --rank)
393 for (File file = FILE_A; file <= FILE_H; ++file)
395 for (emptyCnt = 0; file <= FILE_H && empty(make_square(file, rank)); ++file)
402 ss << PieceToChar[piece_on(make_square(file, rank))];
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 move) const {
438 const string dottedLine = "\n+---+---+---+---+---+---+---+---+";
439 const string twoRows = dottedLine + "\n| | . | | . | | . | | . |"
440 + dottedLine + "\n| . | | . | | . | | . | |";
442 string brd = twoRows + twoRows + twoRows + twoRows + dottedLine;
444 for (Bitboard b = pieces(); b; )
446 Square s = pop_lsb(&b);
447 brd[513 - 68 * rank_of(s) + 4 * file_of(s)] = PieceToChar[piece_on(s)];
450 std::ostringstream ss;
453 ss << "\nMove: " << (sideToMove == BLACK ? ".." : "")
454 << move_to_san(*const_cast<Position*>(this), move);
456 ss << brd << "\nFen: " << fen() << "\nKey: " << std::hex << std::uppercase
457 << std::setfill('0') << std::setw(16) << st->key << "\nCheckers: ";
459 for (Bitboard b = checkers(); b; )
460 ss << to_string(pop_lsb(&b)) << " ";
462 ss << "\nLegal moves: ";
463 for (MoveList<LEGAL> it(*this); *it; ++it)
464 ss << move_to_san(*const_cast<Position*>(this), *it) << " ";
470 /// Position::check_blockers() returns a bitboard of all the pieces with color
471 /// 'c' that are blocking check on the king with color 'kingColor'. A piece
472 /// blocks a check if removing that piece from the board would result in a
473 /// position where the king is in check. A check blocking piece can be either a
474 /// pinned or a discovered check piece, according if its color 'c' is the same
475 /// or the opposite of 'kingColor'.
477 Bitboard Position::check_blockers(Color c, Color kingColor) const {
479 Bitboard b, pinners, result = 0;
480 Square ksq = king_square(kingColor);
482 // Pinners are sliders that give check when a pinned piece is removed
483 pinners = ( (pieces( ROOK, QUEEN) & PseudoAttacks[ROOK ][ksq])
484 | (pieces(BISHOP, QUEEN) & PseudoAttacks[BISHOP][ksq])) & pieces(~kingColor);
488 b = between_bb(ksq, pop_lsb(&pinners)) & pieces();
490 if (!more_than_one(b))
491 result |= b & pieces(c);
497 /// Position::attackers_to() computes a bitboard of all pieces which attack a
498 /// given square. Slider attacks use the occ bitboard to indicate occupancy.
500 Bitboard Position::attackers_to(Square s, Bitboard occ) const {
502 return (attacks_from<PAWN>(s, BLACK) & pieces(WHITE, PAWN))
503 | (attacks_from<PAWN>(s, WHITE) & pieces(BLACK, PAWN))
504 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
505 | (attacks_bb<ROOK>(s, occ) & pieces(ROOK, QUEEN))
506 | (attacks_bb<BISHOP>(s, occ) & pieces(BISHOP, QUEEN))
507 | (attacks_from<KING>(s) & pieces(KING));
511 /// Position::legal() tests whether a pseudo-legal move is legal
513 bool Position::legal(Move m, Bitboard pinned) const {
516 assert(pinned == pinned_pieces(sideToMove));
518 Color us = sideToMove;
519 Square from = from_sq(m);
521 assert(color_of(moved_piece(m)) == us);
522 assert(piece_on(king_square(us)) == make_piece(us, KING));
524 // En passant captures are a tricky special case. Because they are rather
525 // uncommon, we do it simply by testing whether the king is attacked after
527 if (type_of(m) == ENPASSANT)
529 Square ksq = king_square(us);
530 Square to = to_sq(m);
531 Square capsq = to - pawn_push(us);
532 Bitboard occ = (pieces() ^ from ^ capsq) | to;
534 assert(to == ep_square());
535 assert(moved_piece(m) == make_piece(us, PAWN));
536 assert(piece_on(capsq) == make_piece(~us, PAWN));
537 assert(piece_on(to) == NO_PIECE);
539 return !(attacks_bb< ROOK>(ksq, occ) & pieces(~us, QUEEN, ROOK))
540 && !(attacks_bb<BISHOP>(ksq, occ) & pieces(~us, QUEEN, BISHOP));
543 // If the moving piece is a king, check whether the destination
544 // square is attacked by the opponent. Castling moves are checked
545 // for legality during move generation.
546 if (type_of(piece_on(from)) == KING)
547 return type_of(m) == CASTLING || !(attackers_to(to_sq(m)) & pieces(~us));
549 // A non-king move is legal if and only if it is not pinned or it
550 // is moving along the ray towards or away from the king.
553 || aligned(from, to_sq(m), king_square(us));
557 /// Position::pseudo_legal() takes a random move and tests whether the move is
558 /// pseudo legal. It is used to validate moves from TT that can be corrupted
559 /// due to SMP concurrent access or hash position key aliasing.
561 bool Position::pseudo_legal(const Move m) const {
563 Color us = sideToMove;
564 Square from = from_sq(m);
565 Square to = to_sq(m);
566 Piece pc = moved_piece(m);
568 // Use a slower but simpler function for uncommon cases
569 if (type_of(m) != NORMAL)
570 return MoveList<LEGAL>(*this).contains(m);
572 // Is not a promotion, so promotion piece must be empty
573 if (promotion_type(m) - 2 != NO_PIECE_TYPE)
576 // If the 'from' square is not occupied by a piece belonging to the side to
577 // move, the move is obviously not legal.
578 if (pc == NO_PIECE || color_of(pc) != us)
581 // The destination square cannot be occupied by a friendly piece
585 // Handle the special case of a pawn move
586 if (type_of(pc) == PAWN)
588 // We have already handled promotion moves, so destination
589 // cannot be on the 8th/1st rank.
590 if (rank_of(to) == relative_rank(us, RANK_8))
593 if ( !(attacks_from<PAWN>(from, us) & pieces(~us) & to) // Not a capture
595 && !((from + pawn_push(us) == to) && empty(to)) // Not a single push
597 && !( (from + 2 * pawn_push(us) == to) // Not a double push
598 && (rank_of(from) == relative_rank(us, RANK_2))
600 && empty(to - pawn_push(us))))
603 else if (!(attacks_from(pc, from) & to))
606 // Evasions generator already takes care to avoid some kind of illegal moves
607 // and legal() relies on this. We therefore have to take care that the same
608 // kind of moves are filtered out here.
611 if (type_of(pc) != KING)
613 // Double check? In this case a king move is required
614 if (more_than_one(checkers()))
617 // Our move must be a blocking evasion or a capture of the checking piece
618 if (!((between_bb(lsb(checkers()), king_square(us)) | checkers()) & to))
621 // In case of king moves under check we have to remove king so as to catch
622 // invalid moves like b1a1 when opposite queen is on c1.
623 else if (attackers_to(to, pieces() ^ from) & pieces(~us))
631 /// Position::gives_check() tests whether a pseudo-legal move gives a check
633 bool Position::gives_check(Move m, const CheckInfo& ci) const {
636 assert(ci.dcCandidates == discovered_check_candidates());
637 assert(color_of(moved_piece(m)) == sideToMove);
639 Square from = from_sq(m);
640 Square to = to_sq(m);
641 PieceType pt = type_of(piece_on(from));
643 // Is there a direct check?
644 if (ci.checkSq[pt] & to)
647 // Is there a discovered check?
648 if ( unlikely(ci.dcCandidates)
649 && (ci.dcCandidates & from)
650 && !aligned(from, to, ci.ksq))
659 return attacks_bb(Piece(promotion_type(m)), to, pieces() ^ from) & ci.ksq;
661 // En passant capture with check? We have already handled the case
662 // of direct checks and ordinary discovered check, so the only case we
663 // need to handle is the unusual case of a discovered check through
664 // the captured pawn.
667 Square capsq = make_square(file_of(to), rank_of(from));
668 Bitboard b = (pieces() ^ from ^ capsq) | to;
670 return (attacks_bb< ROOK>(ci.ksq, b) & pieces(sideToMove, QUEEN, ROOK))
671 | (attacks_bb<BISHOP>(ci.ksq, b) & pieces(sideToMove, QUEEN, BISHOP));
676 Square rfrom = to; // Castling is encoded as 'King captures the rook'
677 Square kto = relative_square(sideToMove, rfrom > kfrom ? SQ_G1 : SQ_C1);
678 Square rto = relative_square(sideToMove, rfrom > kfrom ? SQ_F1 : SQ_D1);
680 return (PseudoAttacks[ROOK][rto] & ci.ksq)
681 && (attacks_bb<ROOK>(rto, (pieces() ^ kfrom ^ rfrom) | rto | kto) & ci.ksq);
690 /// Position::do_move() makes a move, and saves all information necessary
691 /// to a StateInfo object. The move is assumed to be legal. Pseudo-legal
692 /// moves should be filtered out before this function is called.
694 void Position::do_move(Move m, StateInfo& newSt) {
697 do_move(m, newSt, ci, gives_check(m, ci));
700 void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveIsCheck) {
703 assert(&newSt != st);
708 // Copy some fields of the old state to our new StateInfo object except the
709 // ones which are going to be recalculated from scratch anyway and then switch
710 // our state pointer to point to the new (ready to be updated) state.
711 std::memcpy(&newSt, st, StateCopySize64 * sizeof(uint64_t));
716 // Update side to move
719 // Increment ply counters. In particular, rule50 will be reset to zero later on
720 // in case of a capture or a pawn move.
725 Color us = sideToMove;
727 Square from = from_sq(m);
728 Square to = to_sq(m);
729 Piece pc = piece_on(from);
730 PieceType pt = type_of(pc);
731 PieceType captured = type_of(m) == ENPASSANT ? PAWN : type_of(piece_on(to));
733 assert(color_of(pc) == us);
734 assert(piece_on(to) == NO_PIECE || color_of(piece_on(to)) == them || type_of(m) == CASTLING);
735 assert(captured != KING);
737 if (type_of(m) == CASTLING)
739 assert(pc == make_piece(us, KING));
742 do_castling<true>(from, to, rfrom, rto);
744 captured = NO_PIECE_TYPE;
745 st->psq += psq[us][ROOK][rto] - psq[us][ROOK][rfrom];
746 k ^= Zobrist::psq[us][ROOK][rfrom] ^ Zobrist::psq[us][ROOK][rto];
753 // If the captured piece is a pawn, update pawn hash key, otherwise
754 // update non-pawn material.
755 if (captured == PAWN)
757 if (type_of(m) == ENPASSANT)
759 capsq += pawn_push(them);
762 assert(to == st->epSquare);
763 assert(relative_rank(us, to) == RANK_6);
764 assert(piece_on(to) == NO_PIECE);
765 assert(piece_on(capsq) == make_piece(them, PAWN));
767 board[capsq] = NO_PIECE;
770 st->pawnKey ^= Zobrist::psq[them][PAWN][capsq];
773 st->npMaterial[them] -= PieceValue[MG][captured];
775 // Update board and piece lists
776 remove_piece(capsq, them, captured);
778 // Update material hash key and prefetch access to materialTable
779 k ^= Zobrist::psq[them][captured][capsq];
780 st->materialKey ^= Zobrist::psq[them][captured][pieceCount[them][captured]];
781 prefetch((char*)thisThread->materialTable[st->materialKey]);
783 // Update incremental scores
784 st->psq -= psq[them][captured][capsq];
786 // Reset rule 50 counter
791 k ^= Zobrist::psq[us][pt][from] ^ Zobrist::psq[us][pt][to];
793 // Reset en passant square
794 if (st->epSquare != SQ_NONE)
796 k ^= Zobrist::enpassant[file_of(st->epSquare)];
797 st->epSquare = SQ_NONE;
800 // Update castling rights if needed
801 if (st->castlingRights && (castlingRightsMask[from] | castlingRightsMask[to]))
803 int cr = castlingRightsMask[from] | castlingRightsMask[to];
804 k ^= Zobrist::castling[st->castlingRights & cr];
805 st->castlingRights &= ~cr;
808 // Prefetch TT access as soon as we know the new hash key
809 prefetch((char*)TT.first_entry(k));
811 // Move the piece. The tricky Chess960 castling is handled earlier
812 if (type_of(m) != CASTLING)
813 move_piece(from, to, us, pt);
815 // If the moving piece is a pawn do some special extra work
818 // Set en-passant square if the moved pawn can be captured
819 if ( (int(to) ^ int(from)) == 16
820 && (attacks_from<PAWN>(from + pawn_push(us), us) & pieces(them, PAWN)))
822 st->epSquare = Square((from + to) / 2);
823 k ^= Zobrist::enpassant[file_of(st->epSquare)];
826 if (type_of(m) == PROMOTION)
828 PieceType promotion = promotion_type(m);
830 assert(relative_rank(us, to) == RANK_8);
831 assert(promotion >= KNIGHT && promotion <= QUEEN);
833 remove_piece(to, us, PAWN);
834 put_piece(to, us, promotion);
837 k ^= Zobrist::psq[us][PAWN][to] ^ Zobrist::psq[us][promotion][to];
838 st->pawnKey ^= Zobrist::psq[us][PAWN][to];
839 st->materialKey ^= Zobrist::psq[us][promotion][pieceCount[us][promotion]-1]
840 ^ Zobrist::psq[us][PAWN][pieceCount[us][PAWN]];
842 // Update incremental score
843 st->psq += psq[us][promotion][to] - psq[us][PAWN][to];
846 st->npMaterial[us] += PieceValue[MG][promotion];
849 // Update pawn hash key and prefetch access to pawnsTable
850 st->pawnKey ^= Zobrist::psq[us][PAWN][from] ^ Zobrist::psq[us][PAWN][to];
851 prefetch((char*)thisThread->pawnsTable[st->pawnKey]);
853 // Reset rule 50 draw counter
857 // Update incremental scores
858 st->psq += psq[us][pt][to] - psq[us][pt][from];
861 st->capturedType = captured;
863 // Update the key with the final value
866 // Update checkers bitboard: piece must be already moved due to attacks_from()
871 if (type_of(m) != NORMAL)
872 st->checkersBB = attackers_to(king_square(them)) & pieces(us);
876 if (ci.checkSq[pt] & to)
877 st->checkersBB |= to;
880 if (unlikely(ci.dcCandidates) && (ci.dcCandidates & from))
883 st->checkersBB |= attacks_from<ROOK>(king_square(them)) & pieces(us, QUEEN, ROOK);
886 st->checkersBB |= attacks_from<BISHOP>(king_square(them)) & pieces(us, QUEEN, BISHOP);
891 sideToMove = ~sideToMove;
897 /// Position::undo_move() unmakes a move. When it returns, the position should
898 /// be restored to exactly the same state as before the move was made.
900 void Position::undo_move(Move m) {
904 sideToMove = ~sideToMove;
906 Color us = sideToMove;
907 Square from = from_sq(m);
908 Square to = to_sq(m);
909 PieceType pt = type_of(piece_on(to));
911 assert(empty(from) || type_of(m) == CASTLING);
912 assert(st->capturedType != KING);
914 if (type_of(m) == PROMOTION)
916 assert(pt == promotion_type(m));
917 assert(relative_rank(us, to) == RANK_8);
918 assert(promotion_type(m) >= KNIGHT && promotion_type(m) <= QUEEN);
920 remove_piece(to, us, promotion_type(m));
921 put_piece(to, us, PAWN);
925 if (type_of(m) == CASTLING)
928 do_castling<false>(from, to, rfrom, rto);
932 move_piece(to, from, us, pt); // Put the piece back at the source square
934 if (st->capturedType)
938 if (type_of(m) == ENPASSANT)
940 capsq -= pawn_push(us);
943 assert(to == st->previous->epSquare);
944 assert(relative_rank(us, to) == RANK_6);
945 assert(piece_on(capsq) == NO_PIECE);
948 put_piece(capsq, ~us, st->capturedType); // Restore the captured piece
952 // Finally point our state pointer back to the previous state
960 /// Position::do_castling() is a helper used to do/undo a castling move. This
961 /// is a bit tricky, especially in Chess960.
963 void Position::do_castling(Square from, Square& to, Square& rfrom, Square& rto) {
965 bool kingSide = to > from;
966 rfrom = to; // Castling is encoded as "king captures friendly rook"
967 rto = relative_square(sideToMove, kingSide ? SQ_F1 : SQ_D1);
968 to = relative_square(sideToMove, kingSide ? SQ_G1 : SQ_C1);
970 // Remove both pieces first since squares could overlap in Chess960
971 remove_piece(Do ? from : to, sideToMove, KING);
972 remove_piece(Do ? rfrom : rto, sideToMove, ROOK);
973 board[Do ? from : to] = board[Do ? rfrom : rto] = NO_PIECE; // Since remove_piece doesn't do it for us
974 put_piece(Do ? to : from, sideToMove, KING);
975 put_piece(Do ? rto : rfrom, sideToMove, ROOK);
979 /// Position::do(undo)_null_move() is used to do(undo) a "null move": It flips
980 /// the side to move without executing any move on the board.
982 void Position::do_null_move(StateInfo& newSt) {
986 std::memcpy(&newSt, st, sizeof(StateInfo)); // Fully copy here
991 if (st->epSquare != SQ_NONE)
993 st->key ^= Zobrist::enpassant[file_of(st->epSquare)];
994 st->epSquare = SQ_NONE;
997 st->key ^= Zobrist::side;
998 prefetch((char*)TT.first_entry(st->key));
1001 st->pliesFromNull = 0;
1003 sideToMove = ~sideToMove;
1005 assert(pos_is_ok());
1008 void Position::undo_null_move() {
1010 assert(!checkers());
1013 sideToMove = ~sideToMove;
1017 /// Position::see() is a static exchange evaluator: It tries to estimate the
1018 /// material gain or loss resulting from a move.
1020 Value Position::see_sign(Move m) const {
1024 // Early return if SEE cannot be negative because captured piece value
1025 // is not less then capturing one. Note that king moves always return
1026 // here because king midgame value is set to 0.
1027 if (PieceValue[MG][moved_piece(m)] <= PieceValue[MG][piece_on(to_sq(m))])
1028 return VALUE_KNOWN_WIN;
1033 Value Position::see(Move m) const {
1036 Bitboard occupied, attackers, stmAttackers;
1046 swapList[0] = PieceValue[MG][piece_on(to)];
1047 stm = color_of(piece_on(from));
1048 occupied = pieces() ^ from;
1050 // Castling moves are implemented as king capturing the rook so cannot be
1051 // handled correctly. Simply return 0 that is always the correct value
1052 // unless in the rare case the rook ends up under attack.
1053 if (type_of(m) == CASTLING)
1056 if (type_of(m) == ENPASSANT)
1058 occupied ^= to - pawn_push(stm); // Remove the captured pawn
1059 swapList[0] = PieceValue[MG][PAWN];
1062 // Find all attackers to the destination square, with the moving piece
1063 // removed, but possibly an X-ray attacker added behind it.
1064 attackers = attackers_to(to, occupied) & occupied;
1066 // If the opponent has no attackers we are finished
1068 stmAttackers = attackers & pieces(stm);
1072 // The destination square is defended, which makes things rather more
1073 // difficult to compute. We proceed by building up a "swap list" containing
1074 // the material gain or loss at each stop in a sequence of captures to the
1075 // destination square, where the sides alternately capture, and always
1076 // capture with the least valuable piece. After each capture, we look for
1077 // new X-ray attacks from behind the capturing piece.
1078 captured = type_of(piece_on(from));
1081 assert(slIndex < 32);
1083 // Add the new entry to the swap list
1084 swapList[slIndex] = -swapList[slIndex - 1] + PieceValue[MG][captured];
1086 // Locate and remove the next least valuable attacker
1087 captured = min_attacker<PAWN>(byTypeBB, to, stmAttackers, occupied, attackers);
1089 // Stop before processing a king capture
1090 if (captured == KING)
1092 if (stmAttackers == attackers)
1099 stmAttackers = attackers & pieces(stm);
1102 } while (stmAttackers);
1104 // Having built the swap list, we negamax through it to find the best
1105 // achievable score from the point of view of the side to move.
1107 swapList[slIndex - 1] = std::min(-swapList[slIndex], swapList[slIndex - 1]);
1113 /// Position::is_draw() tests whether the position is drawn by material, 50 moves
1114 /// rule or repetition. It does not detect stalemates.
1116 bool Position::is_draw() const {
1119 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMg))
1122 if (st->rule50 > 99 && (!checkers() || MoveList<LEGAL>(*this).size()))
1125 StateInfo* stp = st;
1126 for (int i = 2, e = std::min(st->rule50, st->pliesFromNull); i <= e; i += 2)
1128 stp = stp->previous->previous;
1130 if (stp->key == st->key)
1131 return true; // Draw at first repetition
1138 /// Position::flip() flips position with the white and black sides reversed. This
1139 /// is only useful for debugging e.g. for finding evaluation symmetry bugs.
1141 static char toggle_case(char c) {
1142 return char(islower(c) ? toupper(c) : tolower(c));
1145 void Position::flip() {
1148 std::stringstream ss(fen());
1150 for (Rank rank = RANK_8; rank >= RANK_1; --rank) // Piece placement
1152 std::getline(ss, token, rank > RANK_1 ? '/' : ' ');
1153 f.insert(0, token + (f.empty() ? " " : "/"));
1156 ss >> token; // Active color
1157 f += (token == "w" ? "B " : "W "); // Will be lowercased later
1159 ss >> token; // Castling availability
1162 std::transform(f.begin(), f.end(), f.begin(), toggle_case);
1164 ss >> token; // En passant square
1165 f += (token == "-" ? token : token.replace(1, 1, token[1] == '3' ? "6" : "3"));
1167 std::getline(ss, token); // Half and full moves
1170 set(f, is_chess960(), this_thread());
1172 assert(pos_is_ok());
1176 /// Position::pos_is_ok() performs some consistency checks for the position object.
1177 /// This is meant to be helpful when debugging.
1179 bool Position::pos_is_ok(int* step) const {
1181 // Which parts of the position should be verified?
1182 const bool all = false;
1184 const bool testBitboards = all || false;
1185 const bool testState = all || false;
1186 const bool testKingCount = all || false;
1187 const bool testKingCapture = all || false;
1188 const bool testPieceCounts = all || false;
1189 const bool testPieceList = all || false;
1190 const bool testCastlingSquares = all || false;
1195 if ( (sideToMove != WHITE && sideToMove != BLACK)
1196 || piece_on(king_square(WHITE)) != W_KING
1197 || piece_on(king_square(BLACK)) != B_KING
1198 || ( ep_square() != SQ_NONE
1199 && relative_rank(sideToMove, ep_square()) != RANK_6))
1202 if (step && ++*step, testBitboards)
1204 // The intersection of the white and black pieces must be empty
1205 if (pieces(WHITE) & pieces(BLACK))
1208 // The union of the white and black pieces must be equal to all
1210 if ((pieces(WHITE) | pieces(BLACK)) != pieces())
1213 // Separate piece type bitboards must have empty intersections
1214 for (PieceType p1 = PAWN; p1 <= KING; ++p1)
1215 for (PieceType p2 = PAWN; p2 <= KING; ++p2)
1216 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1220 if (step && ++*step, testState)
1224 if ( st->key != si.key
1225 || st->pawnKey != si.pawnKey
1226 || st->materialKey != si.materialKey
1227 || st->npMaterial[WHITE] != si.npMaterial[WHITE]
1228 || st->npMaterial[BLACK] != si.npMaterial[BLACK]
1229 || st->psq != si.psq
1230 || st->checkersBB != si.checkersBB)
1234 if (step && ++*step, testKingCount)
1235 if ( std::count(board, board + SQUARE_NB, W_KING) != 1
1236 || std::count(board, board + SQUARE_NB, B_KING) != 1)
1239 if (step && ++*step, testKingCapture)
1240 if (attackers_to(king_square(~sideToMove)) & pieces(sideToMove))
1243 if (step && ++*step, testPieceCounts)
1244 for (Color c = WHITE; c <= BLACK; ++c)
1245 for (PieceType pt = PAWN; pt <= KING; ++pt)
1246 if (pieceCount[c][pt] != popcount<Full>(pieces(c, pt)))
1249 if (step && ++*step, testPieceList)
1250 for (Color c = WHITE; c <= BLACK; ++c)
1251 for (PieceType pt = PAWN; pt <= KING; ++pt)
1252 for (int i = 0; i < pieceCount[c][pt]; ++i)
1253 if ( board[pieceList[c][pt][i]] != make_piece(c, pt)
1254 || index[pieceList[c][pt][i]] != i)
1257 if (step && ++*step, testCastlingSquares)
1258 for (Color c = WHITE; c <= BLACK; ++c)
1259 for (CastlingSide s = KING_SIDE; s <= QUEEN_SIDE; s = CastlingSide(s + 1))
1261 if (!can_castle(c | s))
1264 if ( (castlingRightsMask[king_square(c)] & (c | s)) != (c | s)
1265 || piece_on(castlingRookSquare[c | s]) != make_piece(c, ROOK)
1266 || castlingRightsMask[castlingRookSquare[c | s]] != (c | s))