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
435 const string Position::pretty() const {
437 std::ostringstream ss;
439 ss << "\n +---+---+---+---+---+---+---+---+\n";
441 for (Rank r = RANK_8; r >= RANK_1; --r)
443 for (File f = FILE_A; f <= FILE_H; ++f)
444 ss << " | " << PieceToChar[piece_on(make_square(f, r))];
446 ss << " |\n +---+---+---+---+---+---+---+---+\n";
449 ss << "\nFen: " << fen() << "\nKey: " << std::hex << std::uppercase
450 << std::setfill('0') << std::setw(16) << st->key << "\nCheckers: ";
452 for (Bitboard b = checkers(); b; )
453 ss << to_string(pop_lsb(&b)) << " ";
459 /// Position::game_phase() calculates the game phase interpolating total non-pawn
460 /// material between endgame and midgame limits.
462 Phase Position::game_phase() const {
464 Value npm = st->npMaterial[WHITE] + st->npMaterial[BLACK];
466 npm = std::max(EndgameLimit, std::min(npm, MidgameLimit));
468 return Phase(((npm - EndgameLimit) * 128) / (MidgameLimit - EndgameLimit));
472 /// Position::check_blockers() returns a bitboard of all the pieces with color
473 /// 'c' that are blocking check on the king with color 'kingColor'. A piece
474 /// blocks a check if removing that piece from the board would result in a
475 /// position where the king is in check. A check blocking piece can be either a
476 /// pinned or a discovered check piece, according if its color 'c' is the same
477 /// or the opposite of 'kingColor'.
479 Bitboard Position::check_blockers(Color c, Color kingColor) const {
481 Bitboard b, pinners, result = 0;
482 Square ksq = king_square(kingColor);
484 // Pinners are sliders that give check when a pinned piece is removed
485 pinners = ( (pieces( ROOK, QUEEN) & PseudoAttacks[ROOK ][ksq])
486 | (pieces(BISHOP, QUEEN) & PseudoAttacks[BISHOP][ksq])) & pieces(~kingColor);
490 b = between_bb(ksq, pop_lsb(&pinners)) & pieces();
492 if (!more_than_one(b))
493 result |= b & pieces(c);
499 /// Position::attackers_to() computes a bitboard of all pieces which attack a
500 /// given square. Slider attacks use the occ bitboard to indicate occupancy.
502 Bitboard Position::attackers_to(Square s, Bitboard occ) const {
504 return (attacks_from<PAWN>(s, BLACK) & pieces(WHITE, PAWN))
505 | (attacks_from<PAWN>(s, WHITE) & pieces(BLACK, PAWN))
506 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
507 | (attacks_bb<ROOK>(s, occ) & pieces(ROOK, QUEEN))
508 | (attacks_bb<BISHOP>(s, occ) & pieces(BISHOP, QUEEN))
509 | (attacks_from<KING>(s) & pieces(KING));
513 /// Position::legal() tests whether a pseudo-legal move is legal
515 bool Position::legal(Move m, Bitboard pinned) const {
518 assert(pinned == pinned_pieces(sideToMove));
520 Color us = sideToMove;
521 Square from = from_sq(m);
523 assert(color_of(moved_piece(m)) == us);
524 assert(piece_on(king_square(us)) == make_piece(us, KING));
526 // En passant captures are a tricky special case. Because they are rather
527 // uncommon, we do it simply by testing whether the king is attacked after
529 if (type_of(m) == ENPASSANT)
531 Square ksq = king_square(us);
532 Square to = to_sq(m);
533 Square capsq = to - pawn_push(us);
534 Bitboard occ = (pieces() ^ from ^ capsq) | to;
536 assert(to == ep_square());
537 assert(moved_piece(m) == make_piece(us, PAWN));
538 assert(piece_on(capsq) == make_piece(~us, PAWN));
539 assert(piece_on(to) == NO_PIECE);
541 return !(attacks_bb< ROOK>(ksq, occ) & pieces(~us, QUEEN, ROOK))
542 && !(attacks_bb<BISHOP>(ksq, occ) & pieces(~us, QUEEN, BISHOP));
545 // If the moving piece is a king, check whether the destination
546 // square is attacked by the opponent. Castling moves are checked
547 // for legality during move generation.
548 if (type_of(piece_on(from)) == KING)
549 return type_of(m) == CASTLING || !(attackers_to(to_sq(m)) & pieces(~us));
551 // A non-king move is legal if and only if it is not pinned or it
552 // is moving along the ray towards or away from the king.
555 || aligned(from, to_sq(m), king_square(us));
559 /// Position::pseudo_legal() takes a random move and tests whether the move is
560 /// pseudo legal. It is used to validate moves from TT that can be corrupted
561 /// due to SMP concurrent access or hash position key aliasing.
563 bool Position::pseudo_legal(const Move m) const {
565 Color us = sideToMove;
566 Square from = from_sq(m);
567 Square to = to_sq(m);
568 Piece pc = moved_piece(m);
570 // Use a slower but simpler function for uncommon cases
571 if (type_of(m) != NORMAL)
572 return MoveList<LEGAL>(*this).contains(m);
574 // Is not a promotion, so promotion piece must be empty
575 if (promotion_type(m) - 2 != NO_PIECE_TYPE)
578 // If the 'from' square is not occupied by a piece belonging to the side to
579 // move, the move is obviously not legal.
580 if (pc == NO_PIECE || color_of(pc) != us)
583 // The destination square cannot be occupied by a friendly piece
587 // Handle the special case of a pawn move
588 if (type_of(pc) == PAWN)
590 // We have already handled promotion moves, so destination
591 // cannot be on the 8th/1st rank.
592 if (rank_of(to) == relative_rank(us, RANK_8))
595 if ( !(attacks_from<PAWN>(from, us) & pieces(~us) & to) // Not a capture
597 && !((from + pawn_push(us) == to) && empty(to)) // Not a single push
599 && !( (from + 2 * pawn_push(us) == to) // Not a double push
600 && (rank_of(from) == relative_rank(us, RANK_2))
602 && empty(to - pawn_push(us))))
605 else if (!(attacks_from(pc, from) & to))
608 // Evasions generator already takes care to avoid some kind of illegal moves
609 // and legal() relies on this. We therefore have to take care that the same
610 // kind of moves are filtered out here.
613 if (type_of(pc) != KING)
615 // Double check? In this case a king move is required
616 if (more_than_one(checkers()))
619 // Our move must be a blocking evasion or a capture of the checking piece
620 if (!((between_bb(lsb(checkers()), king_square(us)) | checkers()) & to))
623 // In case of king moves under check we have to remove king so as to catch
624 // invalid moves like b1a1 when opposite queen is on c1.
625 else if (attackers_to(to, pieces() ^ from) & pieces(~us))
633 /// Position::gives_check() tests whether a pseudo-legal move gives a check
635 bool Position::gives_check(Move m, const CheckInfo& ci) const {
638 assert(ci.dcCandidates == discovered_check_candidates());
639 assert(color_of(moved_piece(m)) == sideToMove);
641 Square from = from_sq(m);
642 Square to = to_sq(m);
643 PieceType pt = type_of(piece_on(from));
645 // Is there a direct check?
646 if (ci.checkSq[pt] & to)
649 // Is there a discovered check?
650 if ( unlikely(ci.dcCandidates)
651 && (ci.dcCandidates & from)
652 && !aligned(from, to, ci.ksq))
661 return attacks_bb(Piece(promotion_type(m)), to, pieces() ^ from) & ci.ksq;
663 // En passant capture with check? We have already handled the case
664 // of direct checks and ordinary discovered check, so the only case we
665 // need to handle is the unusual case of a discovered check through
666 // the captured pawn.
669 Square capsq = make_square(file_of(to), rank_of(from));
670 Bitboard b = (pieces() ^ from ^ capsq) | to;
672 return (attacks_bb< ROOK>(ci.ksq, b) & pieces(sideToMove, QUEEN, ROOK))
673 | (attacks_bb<BISHOP>(ci.ksq, b) & pieces(sideToMove, QUEEN, BISHOP));
678 Square rfrom = to; // Castling is encoded as 'King captures the rook'
679 Square kto = relative_square(sideToMove, rfrom > kfrom ? SQ_G1 : SQ_C1);
680 Square rto = relative_square(sideToMove, rfrom > kfrom ? SQ_F1 : SQ_D1);
682 return (PseudoAttacks[ROOK][rto] & ci.ksq)
683 && (attacks_bb<ROOK>(rto, (pieces() ^ kfrom ^ rfrom) | rto | kto) & ci.ksq);
692 /// Position::do_move() makes a move, and saves all information necessary
693 /// to a StateInfo object. The move is assumed to be legal. Pseudo-legal
694 /// moves should be filtered out before this function is called.
696 void Position::do_move(Move m, StateInfo& newSt) {
699 do_move(m, newSt, ci, gives_check(m, ci));
702 void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveIsCheck) {
705 assert(&newSt != st);
710 // Copy some fields of the old state to our new StateInfo object except the
711 // ones which are going to be recalculated from scratch anyway and then switch
712 // our state pointer to point to the new (ready to be updated) state.
713 std::memcpy(&newSt, st, StateCopySize64 * sizeof(uint64_t));
718 // Update side to move
721 // Increment ply counters. In particular, rule50 will be reset to zero later on
722 // in case of a capture or a pawn move.
727 Color us = sideToMove;
729 Square from = from_sq(m);
730 Square to = to_sq(m);
731 Piece pc = piece_on(from);
732 PieceType pt = type_of(pc);
733 PieceType captured = type_of(m) == ENPASSANT ? PAWN : type_of(piece_on(to));
735 assert(color_of(pc) == us);
736 assert(piece_on(to) == NO_PIECE || color_of(piece_on(to)) == them || type_of(m) == CASTLING);
737 assert(captured != KING);
739 if (type_of(m) == CASTLING)
741 assert(pc == make_piece(us, KING));
744 do_castling<true>(from, to, rfrom, rto);
746 captured = NO_PIECE_TYPE;
747 st->psq += psq[us][ROOK][rto] - psq[us][ROOK][rfrom];
748 k ^= Zobrist::psq[us][ROOK][rfrom] ^ Zobrist::psq[us][ROOK][rto];
755 // If the captured piece is a pawn, update pawn hash key, otherwise
756 // update non-pawn material.
757 if (captured == PAWN)
759 if (type_of(m) == ENPASSANT)
761 capsq += pawn_push(them);
764 assert(to == st->epSquare);
765 assert(relative_rank(us, to) == RANK_6);
766 assert(piece_on(to) == NO_PIECE);
767 assert(piece_on(capsq) == make_piece(them, PAWN));
769 board[capsq] = NO_PIECE;
772 st->pawnKey ^= Zobrist::psq[them][PAWN][capsq];
775 st->npMaterial[them] -= PieceValue[MG][captured];
777 // Update board and piece lists
778 remove_piece(capsq, them, captured);
780 // Update material hash key and prefetch access to materialTable
781 k ^= Zobrist::psq[them][captured][capsq];
782 st->materialKey ^= Zobrist::psq[them][captured][pieceCount[them][captured]];
783 prefetch((char*)thisThread->materialTable[st->materialKey]);
785 // Update incremental scores
786 st->psq -= psq[them][captured][capsq];
788 // Reset rule 50 counter
793 k ^= Zobrist::psq[us][pt][from] ^ Zobrist::psq[us][pt][to];
795 // Reset en passant square
796 if (st->epSquare != SQ_NONE)
798 k ^= Zobrist::enpassant[file_of(st->epSquare)];
799 st->epSquare = SQ_NONE;
802 // Update castling rights if needed
803 if (st->castlingRights && (castlingRightsMask[from] | castlingRightsMask[to]))
805 int cr = castlingRightsMask[from] | castlingRightsMask[to];
806 k ^= Zobrist::castling[st->castlingRights & cr];
807 st->castlingRights &= ~cr;
810 // Move the piece. The tricky Chess960 castling is handled earlier
811 if (type_of(m) != CASTLING)
812 move_piece(from, to, us, pt);
814 // If the moving piece is a pawn do some special extra work
817 // Set en-passant square if the moved pawn can be captured
818 if ( (int(to) ^ int(from)) == 16
819 && (attacks_from<PAWN>(from + pawn_push(us), us) & pieces(them, PAWN)))
821 st->epSquare = Square((from + to) / 2);
822 k ^= Zobrist::enpassant[file_of(st->epSquare)];
825 else if (type_of(m) == PROMOTION)
827 PieceType promotion = promotion_type(m);
829 assert(relative_rank(us, to) == RANK_8);
830 assert(promotion >= KNIGHT && promotion <= QUEEN);
832 remove_piece(to, us, PAWN);
833 put_piece(to, us, promotion);
836 k ^= Zobrist::psq[us][PAWN][to] ^ Zobrist::psq[us][promotion][to];
837 st->pawnKey ^= Zobrist::psq[us][PAWN][to];
838 st->materialKey ^= Zobrist::psq[us][promotion][pieceCount[us][promotion]-1]
839 ^ Zobrist::psq[us][PAWN][pieceCount[us][PAWN]];
841 // Update incremental score
842 st->psq += psq[us][promotion][to] - psq[us][PAWN][to];
845 st->npMaterial[us] += PieceValue[MG][promotion];
848 // Update pawn hash key and prefetch access to pawnsTable
849 st->pawnKey ^= Zobrist::psq[us][PAWN][from] ^ Zobrist::psq[us][PAWN][to];
850 prefetch((char*)thisThread->pawnsTable[st->pawnKey]);
852 // Reset rule 50 draw counter
856 // Update incremental scores
857 st->psq += psq[us][pt][to] - psq[us][pt][from];
860 st->capturedType = captured;
862 // Update the key with the final value
865 // Update checkers bitboard: piece must be already moved due to attacks_from()
870 if (type_of(m) != NORMAL)
871 st->checkersBB = attackers_to(king_square(them)) & pieces(us);
875 if (ci.checkSq[pt] & to)
876 st->checkersBB |= to;
879 if (unlikely(ci.dcCandidates) && (ci.dcCandidates & from))
882 st->checkersBB |= attacks_from<ROOK>(king_square(them)) & pieces(us, QUEEN, ROOK);
885 st->checkersBB |= attacks_from<BISHOP>(king_square(them)) & pieces(us, QUEEN, BISHOP);
890 sideToMove = ~sideToMove;
896 /// Position::undo_move() unmakes a move. When it returns, the position should
897 /// be restored to exactly the same state as before the move was made.
899 void Position::undo_move(Move m) {
903 sideToMove = ~sideToMove;
905 Color us = sideToMove;
906 Square from = from_sq(m);
907 Square to = to_sq(m);
908 PieceType pt = type_of(piece_on(to));
910 assert(empty(from) || type_of(m) == CASTLING);
911 assert(st->capturedType != KING);
913 if (type_of(m) == PROMOTION)
915 assert(pt == promotion_type(m));
916 assert(relative_rank(us, to) == RANK_8);
917 assert(promotion_type(m) >= KNIGHT && promotion_type(m) <= QUEEN);
919 remove_piece(to, us, promotion_type(m));
920 put_piece(to, us, PAWN);
924 if (type_of(m) == CASTLING)
927 do_castling<false>(from, to, rfrom, rto);
931 move_piece(to, from, us, pt); // Put the piece back at the source square
933 if (st->capturedType)
937 if (type_of(m) == ENPASSANT)
939 capsq -= pawn_push(us);
942 assert(to == st->previous->epSquare);
943 assert(relative_rank(us, to) == RANK_6);
944 assert(piece_on(capsq) == NO_PIECE);
947 put_piece(capsq, ~us, st->capturedType); // Restore the captured piece
951 // Finally point our state pointer back to the previous state
959 /// Position::do_castling() is a helper used to do/undo a castling move. This
960 /// is a bit tricky, especially in Chess960.
962 void Position::do_castling(Square from, Square& to, Square& rfrom, Square& rto) {
964 bool kingSide = to > from;
965 rfrom = to; // Castling is encoded as "king captures friendly rook"
966 rto = relative_square(sideToMove, kingSide ? SQ_F1 : SQ_D1);
967 to = relative_square(sideToMove, kingSide ? SQ_G1 : SQ_C1);
969 // Remove both pieces first since squares could overlap in Chess960
970 remove_piece(Do ? from : to, sideToMove, KING);
971 remove_piece(Do ? rfrom : rto, sideToMove, ROOK);
972 board[Do ? from : to] = board[Do ? rfrom : rto] = NO_PIECE; // Since remove_piece doesn't do it for us
973 put_piece(Do ? to : from, sideToMove, KING);
974 put_piece(Do ? rto : rfrom, sideToMove, ROOK);
978 /// Position::do(undo)_null_move() is used to do(undo) a "null move": It flips
979 /// the side to move without executing any move on the board.
981 void Position::do_null_move(StateInfo& newSt) {
985 std::memcpy(&newSt, st, sizeof(StateInfo)); // Fully copy here
990 if (st->epSquare != SQ_NONE)
992 st->key ^= Zobrist::enpassant[file_of(st->epSquare)];
993 st->epSquare = SQ_NONE;
996 st->key ^= Zobrist::side;
997 prefetch((char*)TT.first_entry(st->key));
1000 st->pliesFromNull = 0;
1002 sideToMove = ~sideToMove;
1004 assert(pos_is_ok());
1007 void Position::undo_null_move() {
1009 assert(!checkers());
1012 sideToMove = ~sideToMove;
1016 /// Position::key_after() computes the new hash key after the given moven. Needed
1017 /// for speculative prefetch. It doesn't recognize special moves like castling,
1018 /// en-passant and promotions.
1020 Key Position::key_after(Move m) const {
1022 Color us = sideToMove;
1023 Square from = from_sq(m);
1024 Square to = to_sq(m);
1025 PieceType pt = type_of(piece_on(from));
1026 PieceType captured = type_of(piece_on(to));
1027 Key k = st->key ^ Zobrist::side;
1030 k ^= Zobrist::psq[~us][captured][to];
1032 return k ^ Zobrist::psq[us][pt][to] ^ Zobrist::psq[us][pt][from];
1036 /// Position::see() is a static exchange evaluator: It tries to estimate the
1037 /// material gain or loss resulting from a move.
1039 Value Position::see_sign(Move m) const {
1043 // Early return if SEE cannot be negative because captured piece value
1044 // is not less then capturing one. Note that king moves always return
1045 // here because king midgame value is set to 0.
1046 if (PieceValue[MG][moved_piece(m)] <= PieceValue[MG][piece_on(to_sq(m))])
1047 return VALUE_KNOWN_WIN;
1052 Value Position::see(Move m) const {
1055 Bitboard occupied, attackers, stmAttackers;
1065 swapList[0] = PieceValue[MG][piece_on(to)];
1066 stm = color_of(piece_on(from));
1067 occupied = pieces() ^ from;
1069 // Castling moves are implemented as king capturing the rook so cannot be
1070 // handled correctly. Simply return 0 that is always the correct value
1071 // unless in the rare case the rook ends up under attack.
1072 if (type_of(m) == CASTLING)
1075 if (type_of(m) == ENPASSANT)
1077 occupied ^= to - pawn_push(stm); // Remove the captured pawn
1078 swapList[0] = PieceValue[MG][PAWN];
1081 // Find all attackers to the destination square, with the moving piece
1082 // removed, but possibly an X-ray attacker added behind it.
1083 attackers = attackers_to(to, occupied) & occupied;
1085 // If the opponent has no attackers we are finished
1087 stmAttackers = attackers & pieces(stm);
1091 // The destination square is defended, which makes things rather more
1092 // difficult to compute. We proceed by building up a "swap list" containing
1093 // the material gain or loss at each stop in a sequence of captures to the
1094 // destination square, where the sides alternately capture, and always
1095 // capture with the least valuable piece. After each capture, we look for
1096 // new X-ray attacks from behind the capturing piece.
1097 captured = type_of(piece_on(from));
1100 assert(slIndex < 32);
1102 // Add the new entry to the swap list
1103 swapList[slIndex] = -swapList[slIndex - 1] + PieceValue[MG][captured];
1105 // Locate and remove the next least valuable attacker
1106 captured = min_attacker<PAWN>(byTypeBB, to, stmAttackers, occupied, attackers);
1108 // Stop before processing a king capture
1109 if (captured == KING)
1111 if (stmAttackers == attackers)
1118 stmAttackers = attackers & pieces(stm);
1121 } while (stmAttackers);
1123 // Having built the swap list, we negamax through it to find the best
1124 // achievable score from the point of view of the side to move.
1126 swapList[slIndex - 1] = std::min(-swapList[slIndex], swapList[slIndex - 1]);
1132 /// Position::is_draw() tests whether the position is drawn by material, 50 moves
1133 /// rule or repetition. It does not detect stalemates.
1135 bool Position::is_draw() const {
1137 if (st->rule50 > 99 && (!checkers() || MoveList<LEGAL>(*this).size()))
1140 StateInfo* stp = st;
1141 for (int i = 2, e = std::min(st->rule50, st->pliesFromNull); i <= e; i += 2)
1143 stp = stp->previous->previous;
1145 if (stp->key == st->key)
1146 return true; // Draw at first repetition
1153 /// Position::flip() flips position with the white and black sides reversed. This
1154 /// is only useful for debugging e.g. for finding evaluation symmetry bugs.
1156 static char toggle_case(char c) {
1157 return char(islower(c) ? toupper(c) : tolower(c));
1160 void Position::flip() {
1163 std::stringstream ss(fen());
1165 for (Rank r = RANK_8; r >= RANK_1; --r) // Piece placement
1167 std::getline(ss, token, r > RANK_1 ? '/' : ' ');
1168 f.insert(0, token + (f.empty() ? " " : "/"));
1171 ss >> token; // Active color
1172 f += (token == "w" ? "B " : "W "); // Will be lowercased later
1174 ss >> token; // Castling availability
1177 std::transform(f.begin(), f.end(), f.begin(), toggle_case);
1179 ss >> token; // En passant square
1180 f += (token == "-" ? token : token.replace(1, 1, token[1] == '3' ? "6" : "3"));
1182 std::getline(ss, token); // Half and full moves
1185 set(f, is_chess960(), this_thread());
1187 assert(pos_is_ok());
1191 /// Position::pos_is_ok() performs some consistency checks for the position object.
1192 /// This is meant to be helpful when debugging.
1194 bool Position::pos_is_ok(int* step) const {
1196 // Which parts of the position should be verified?
1197 const bool all = false;
1199 const bool testBitboards = all || false;
1200 const bool testState = all || false;
1201 const bool testKingCount = all || false;
1202 const bool testKingCapture = all || false;
1203 const bool testPieceCounts = all || false;
1204 const bool testPieceList = all || false;
1205 const bool testCastlingSquares = all || false;
1210 if ( (sideToMove != WHITE && sideToMove != BLACK)
1211 || piece_on(king_square(WHITE)) != W_KING
1212 || piece_on(king_square(BLACK)) != B_KING
1213 || ( ep_square() != SQ_NONE
1214 && relative_rank(sideToMove, ep_square()) != RANK_6))
1217 if (step && ++*step, testBitboards)
1219 // The intersection of the white and black pieces must be empty
1220 if (pieces(WHITE) & pieces(BLACK))
1223 // The union of the white and black pieces must be equal to all
1225 if ((pieces(WHITE) | pieces(BLACK)) != pieces())
1228 // Separate piece type bitboards must have empty intersections
1229 for (PieceType p1 = PAWN; p1 <= KING; ++p1)
1230 for (PieceType p2 = PAWN; p2 <= KING; ++p2)
1231 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1235 if (step && ++*step, testState)
1239 if ( st->key != si.key
1240 || st->pawnKey != si.pawnKey
1241 || st->materialKey != si.materialKey
1242 || st->npMaterial[WHITE] != si.npMaterial[WHITE]
1243 || st->npMaterial[BLACK] != si.npMaterial[BLACK]
1244 || st->psq != si.psq
1245 || st->checkersBB != si.checkersBB)
1249 if (step && ++*step, testKingCount)
1250 if ( std::count(board, board + SQUARE_NB, W_KING) != 1
1251 || std::count(board, board + SQUARE_NB, B_KING) != 1)
1254 if (step && ++*step, testKingCapture)
1255 if (attackers_to(king_square(~sideToMove)) & pieces(sideToMove))
1258 if (step && ++*step, testPieceCounts)
1259 for (Color c = WHITE; c <= BLACK; ++c)
1260 for (PieceType pt = PAWN; pt <= KING; ++pt)
1261 if (pieceCount[c][pt] != popcount<Full>(pieces(c, pt)))
1264 if (step && ++*step, testPieceList)
1265 for (Color c = WHITE; c <= BLACK; ++c)
1266 for (PieceType pt = PAWN; pt <= KING; ++pt)
1267 for (int i = 0; i < pieceCount[c][pt]; ++i)
1268 if ( board[pieceList[c][pt][i]] != make_piece(c, pt)
1269 || index[pieceList[c][pt][i]] != i)
1272 if (step && ++*step, testCastlingSquares)
1273 for (Color c = WHITE; c <= BLACK; ++c)
1274 for (CastlingSide s = KING_SIDE; s <= QUEEN_SIDE; s = CastlingSide(s + 1))
1276 if (!can_castle(c | s))
1279 if ( (castlingRightsMask[king_square(c)] & (c | s)) != (c | s)
1280 || piece_on(castlingRookSquare[c | s]) != make_piece(c, ROOK)
1281 || castlingRightsMask[castlingRookSquare[c | s]] != (c | s))