2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 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/>.
41 #include "ucioption.h"
49 //// Position's static data definitions
52 Key Position::zobrist[2][8][64];
53 Key Position::zobEp[64];
54 Key Position::zobCastle[16];
55 Key Position::zobSideToMove;
56 Key Position::zobExclusion;
58 Score Position::PieceSquareTable[16][64];
60 // Material values arrays, indexed by Piece
61 const Value Position::PieceValueMidgame[17] = {
63 PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
64 RookValueMidgame, QueenValueMidgame, VALUE_ZERO,
65 VALUE_ZERO, VALUE_ZERO,
66 PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
67 RookValueMidgame, QueenValueMidgame
70 const Value Position::PieceValueEndgame[17] = {
72 PawnValueEndgame, KnightValueEndgame, BishopValueEndgame,
73 RookValueEndgame, QueenValueEndgame, VALUE_ZERO,
74 VALUE_ZERO, VALUE_ZERO,
75 PawnValueEndgame, KnightValueEndgame, BishopValueEndgame,
76 RookValueEndgame, QueenValueEndgame
79 // Material values array used by SEE, indexed by PieceType
80 const Value Position::seeValues[] = {
82 PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
83 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10
89 // Bonus for having the side to move (modified by Joona Kiiski)
90 const Score TempoValue = make_score(48, 22);
92 bool isZero(char c) { return c == '0'; }
94 struct PieceLetters : public std::map<char, Piece> {
98 operator[]('K') = WK; operator[]('k') = BK;
99 operator[]('Q') = WQ; operator[]('q') = BQ;
100 operator[]('R') = WR; operator[]('r') = BR;
101 operator[]('B') = WB; operator[]('b') = BB;
102 operator[]('N') = WN; operator[]('n') = BN;
103 operator[]('P') = WP; operator[]('p') = BP;
104 operator[](' ') = PIECE_NONE;
105 operator[]('.') = PIECE_NONE_DARK_SQ;
108 char from_piece(Piece p) const {
110 std::map<char, Piece>::const_iterator it;
111 for (it = begin(); it != end(); ++it)
120 PieceLetters pieceLetters;
126 CheckInfo::CheckInfo(const Position& pos) {
128 Color us = pos.side_to_move();
129 Color them = opposite_color(us);
131 ksq = pos.king_square(them);
132 dcCandidates = pos.discovered_check_candidates(us);
134 checkSq[PAWN] = pos.attacks_from<PAWN>(ksq, them);
135 checkSq[KNIGHT] = pos.attacks_from<KNIGHT>(ksq);
136 checkSq[BISHOP] = pos.attacks_from<BISHOP>(ksq);
137 checkSq[ROOK] = pos.attacks_from<ROOK>(ksq);
138 checkSq[QUEEN] = checkSq[BISHOP] | checkSq[ROOK];
139 checkSq[KING] = EmptyBoardBB;
143 /// Position c'tors. Here we always create a copy of the original position
144 /// or the FEN string, we want the new born Position object do not depend
145 /// on any external data so we detach state pointer from the source one.
147 Position::Position(const Position& pos, int th) {
149 memcpy(this, &pos, sizeof(Position));
150 detach(); // Always detach() in copy c'tor to avoid surprises
155 Position::Position(const string& fen, int th) {
162 /// Position::detach() copies the content of the current state and castling
163 /// masks inside the position itself. This is needed when the st pointee could
164 /// become stale, as example because the caller is about to going out of scope.
166 void Position::detach() {
170 st->previous = NULL; // as a safe guard
174 /// Position::from_fen() initializes the position object with the given FEN
175 /// string. This function is not very robust - make sure that input FENs are
176 /// correct (this is assumed to be the responsibility of the GUI).
178 void Position::from_fen(const string& fen) {
180 A FEN string defines a particular position using only the ASCII character set.
182 A FEN string contains six fields. The separator between fields is a space. The fields are:
184 1) Piece placement (from white's perspective). Each rank is described, starting with rank 8 and ending
185 with rank 1; within each rank, the contents of each square are described from file a through file h.
186 Following the Standard Algebraic Notation (SAN), each piece is identified by a single letter taken
187 from the standard English names. White pieces are designated using upper-case letters ("PNBRQK")
188 while Black take lowercase ("pnbrqk"). Blank squares are noted using digits 1 through 8 (the number
189 of blank squares), and "/" separate ranks.
191 2) Active color. "w" means white moves next, "b" means black.
193 3) Castling availability. If neither side can castle, this is "-". Otherwise, this has one or more
194 letters: "K" (White can castle kingside), "Q" (White can castle queenside), "k" (Black can castle
195 kingside), and/or "q" (Black can castle queenside).
197 4) En passant target square in algebraic notation. If there's no en passant target square, this is "-".
198 If a pawn has just made a 2-square move, this is the position "behind" the pawn. This is recorded
199 regardless of whether there is a pawn in position to make an en passant capture.
201 5) Halfmove clock: This is the number of halfmoves since the last pawn advance or capture. This is used
202 to determine if a draw can be claimed under the fifty-move rule.
204 6) Fullmove number: The number of the full move. It starts at 1, and is incremented after Black's move.
208 std::istringstream ss(fen);
214 // 1. Piece placement field
215 while (ss.get(token) && token != ' ')
219 file += File(token - '0'); // Skip the given number of files
222 else if (token == '/')
229 if (pieceLetters.find(token) == pieceLetters.end())
232 put_piece(pieceLetters[token], make_square(file, rank));
237 if (!ss.get(token) || (token != 'w' && token != 'b'))
240 sideToMove = (token == 'w' ? WHITE : BLACK);
242 if (!ss.get(token) || token != ' ')
245 // 3. Castling availability
246 while (ss.get(token) && token != ' ')
251 if (!set_castling_rights(token))
255 // 4. En passant square -- ignore if no capture is possible
257 if ( (ss.get(col) && (col >= 'a' && col <= 'h'))
258 && (ss.get(row) && (row == '3' || row == '6')))
260 Square fenEpSquare = make_square(file_from_char(col), rank_from_char(row));
261 Color them = opposite_color(sideToMove);
263 if (attacks_from<PAWN>(fenEpSquare, them) & pieces(PAWN, sideToMove))
264 st->epSquare = fenEpSquare;
267 // 5-6. Halfmove clock and fullmove number are not parsed
269 // Various initialisations
270 castleRightsMask[make_square(initialKFile, RANK_1)] ^= WHITE_OO | WHITE_OOO;
271 castleRightsMask[make_square(initialKFile, RANK_8)] ^= BLACK_OO | BLACK_OOO;
272 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
273 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
274 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
275 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
279 st->key = compute_key();
280 st->pawnKey = compute_pawn_key();
281 st->materialKey = compute_material_key();
282 st->value = compute_value();
283 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
284 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
288 cout << "Error in FEN string: " << fen << endl;
292 /// Position::set_castling_rights() sets castling parameters castling avaiability.
293 /// This function is compatible with 3 standards: Normal FEN standard, Shredder-FEN
294 /// that uses the letters of the columns on which the rooks began the game instead
295 /// of KQkq and also X-FEN standard that, in case of Chess960, if an inner Rook is
296 /// associated with the castling right, the traditional castling tag will be replaced
297 /// by the file letter of the involved rook as for the Shredder-FEN.
299 bool Position::set_castling_rights(char token) {
301 Color c = token >= 'a' ? BLACK : WHITE;
302 Square sqA = (c == WHITE ? SQ_A1 : SQ_A8);
303 Square sqH = (c == WHITE ? SQ_H1 : SQ_H8);
304 Piece rook = (c == WHITE ? WR : BR);
306 initialKFile = square_file(king_square(c));
307 token = char(toupper(token));
311 for (Square sq = sqH; sq >= sqA; sq--)
312 if (piece_on(sq) == rook)
315 initialKRFile = square_file(sq);
319 else if (token == 'Q')
321 for (Square sq = sqA; sq <= sqH; sq++)
322 if (piece_on(sq) == rook)
325 initialQRFile = square_file(sq);
329 else if (token >= 'A' && token <= 'H')
331 File rookFile = File(token - 'A') + FILE_A;
332 if (rookFile < initialKFile)
335 initialQRFile = rookFile;
340 initialKRFile = rookFile;
349 /// Position::to_fen() returns a FEN representation of the position. In case
350 /// of Chess960 the Shredder-FEN notation is used. Mainly a debugging function.
352 const string Position::to_fen(bool isChess960) const {
358 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
360 for (File file = FILE_A; file <= FILE_H; file++)
362 sq = make_square(file, rank);
364 if (square_is_occupied(sq))
367 fen += pieceLetters.from_piece(piece_on(sq));
377 fen.erase(std::remove_if(fen.begin(), fen.end(), isZero), fen.end());
378 fen.erase(--fen.end());
379 fen += (sideToMove == WHITE ? " w " : " b ");
381 if (st->castleRights != CASTLES_NONE)
383 if (can_castle_kingside(WHITE))
384 fen += isChess960 ? char(toupper(file_to_char(initialKRFile))) : 'K';
386 if (can_castle_queenside(WHITE))
387 fen += isChess960 ? char(toupper(file_to_char(initialQRFile))) : 'Q';
389 if (can_castle_kingside(BLACK))
390 fen += isChess960 ? file_to_char(initialKRFile) : 'k';
392 if (can_castle_queenside(BLACK))
393 fen += isChess960 ? file_to_char(initialQRFile) : 'q';
397 fen += (ep_square() == SQ_NONE ? " -" : " " + square_to_string(ep_square()));
402 /// Position::print() prints an ASCII representation of the position to
403 /// the standard output. If a move is given then also the san is printed.
405 void Position::print(Move move) const {
407 const char* dottedLine = "\n+---+---+---+---+---+---+---+---+\n";
408 static bool requestPending = false;
410 // Check for reentrancy, as example when called from inside
411 // MovePicker that is used also here in move_to_san()
415 requestPending = true;
419 Position p(*this, thread());
420 string dd = (color_of_piece_on(move_from(move)) == BLACK ? ".." : "");
421 cout << "\nMove is: " << dd << move_to_san(p, move);
424 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
426 cout << dottedLine << '|';
427 for (File file = FILE_A; file <= FILE_H; file++)
429 Square sq = make_square(file, rank);
430 char c = (color_of_piece_on(sq) == BLACK ? '=' : ' ');
431 Piece piece = piece_on(sq);
433 if (piece == PIECE_NONE && square_color(sq) == DARK)
434 piece = PIECE_NONE_DARK_SQ;
436 cout << c << pieceLetters.from_piece(piece) << c << '|';
439 bool chess960 = (cout.iword(0) != 0); // See set960()
440 cout << dottedLine << "Fen is: " << to_fen(chess960) << "\nKey is: " << st->key << endl;
441 requestPending = false;
445 /// Position:hidden_checkers<>() returns a bitboard of all pinned (against the
446 /// king) pieces for the given color and for the given pinner type. Or, when
447 /// template parameter FindPinned is false, the pieces of the given color
448 /// candidate for a discovery check against the enemy king.
449 /// Bitboard checkersBB must be already updated when looking for pinners.
451 template<bool FindPinned>
452 Bitboard Position::hidden_checkers(Color c) const {
454 Bitboard result = EmptyBoardBB;
455 Bitboard pinners = pieces_of_color(FindPinned ? opposite_color(c) : c);
457 // Pinned pieces protect our king, dicovery checks attack
459 Square ksq = king_square(FindPinned ? c : opposite_color(c));
461 // Pinners are sliders, not checkers, that give check when candidate pinned is removed
462 pinners &= (pieces(ROOK, QUEEN) & RookPseudoAttacks[ksq]) | (pieces(BISHOP, QUEEN) & BishopPseudoAttacks[ksq]);
464 if (FindPinned && pinners)
465 pinners &= ~st->checkersBB;
469 Square s = pop_1st_bit(&pinners);
470 Bitboard b = squares_between(s, ksq) & occupied_squares();
474 if ( !(b & (b - 1)) // Only one bit set?
475 && (b & pieces_of_color(c))) // Is an our piece?
482 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
483 /// king) pieces for the given color. Note that checkersBB bitboard must
484 /// be already updated.
486 Bitboard Position::pinned_pieces(Color c) const {
488 return hidden_checkers<true>(c);
492 /// Position:discovered_check_candidates() returns a bitboard containing all
493 /// pieces for the given side which are candidates for giving a discovered
494 /// check. Contrary to pinned_pieces() here there is no need of checkersBB
495 /// to be already updated.
497 Bitboard Position::discovered_check_candidates(Color c) const {
499 return hidden_checkers<false>(c);
502 /// Position::attackers_to() computes a bitboard containing all pieces which
503 /// attacks a given square.
505 Bitboard Position::attackers_to(Square s) const {
507 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
508 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
509 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
510 | (attacks_from<ROOK>(s) & pieces(ROOK, QUEEN))
511 | (attacks_from<BISHOP>(s) & pieces(BISHOP, QUEEN))
512 | (attacks_from<KING>(s) & pieces(KING));
515 /// Position::attacks_from() computes a bitboard of all attacks
516 /// of a given piece put in a given square.
518 Bitboard Position::attacks_from(Piece p, Square s) const {
520 assert(square_is_ok(s));
524 case WB: case BB: return attacks_from<BISHOP>(s);
525 case WR: case BR: return attacks_from<ROOK>(s);
526 case WQ: case BQ: return attacks_from<QUEEN>(s);
527 default: return StepAttackBB[p][s];
531 Bitboard Position::attacks_from(Piece p, Square s, Bitboard occ) {
533 assert(square_is_ok(s));
537 case WB: case BB: return bishop_attacks_bb(s, occ);
538 case WR: case BR: return rook_attacks_bb(s, occ);
539 case WQ: case BQ: return bishop_attacks_bb(s, occ) | rook_attacks_bb(s, occ);
540 default: return StepAttackBB[p][s];
545 /// Position::move_attacks_square() tests whether a move from the current
546 /// position attacks a given square.
548 bool Position::move_attacks_square(Move m, Square s) const {
550 assert(move_is_ok(m));
551 assert(square_is_ok(s));
554 Square f = move_from(m), t = move_to(m);
556 assert(square_is_occupied(f));
558 if (bit_is_set(attacks_from(piece_on(f), t), s))
561 // Move the piece and scan for X-ray attacks behind it
562 occ = occupied_squares();
563 do_move_bb(&occ, make_move_bb(f, t));
564 xray = ( (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
565 |(bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN)))
566 & pieces_of_color(color_of_piece_on(f));
568 // If we have attacks we need to verify that are caused by our move
569 // and are not already existent ones.
570 return xray && (xray ^ (xray & attacks_from<QUEEN>(s)));
574 /// Position::find_checkers() computes the checkersBB bitboard, which
575 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
576 /// currently works by calling Position::attackers_to, which is probably
577 /// inefficient. Consider rewriting this function to use the last move
578 /// played, like in non-bitboard versions of Glaurung.
580 void Position::find_checkers() {
582 Color us = side_to_move();
583 st->checkersBB = attackers_to(king_square(us)) & pieces_of_color(opposite_color(us));
587 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
589 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
592 assert(move_is_ok(m));
593 assert(pinned == pinned_pieces(side_to_move()));
595 // Castling moves are checked for legality during move generation.
596 if (move_is_castle(m))
599 // En passant captures are a tricky special case. Because they are
600 // rather uncommon, we do it simply by testing whether the king is attacked
601 // after the move is made
604 Color us = side_to_move();
605 Color them = opposite_color(us);
606 Square from = move_from(m);
607 Square to = move_to(m);
608 Square capsq = make_square(square_file(to), square_rank(from));
609 Square ksq = king_square(us);
610 Bitboard b = occupied_squares();
612 assert(to == ep_square());
613 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
614 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
615 assert(piece_on(to) == PIECE_NONE);
618 clear_bit(&b, capsq);
621 return !(rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, them))
622 && !(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, them));
625 Color us = side_to_move();
626 Square from = move_from(m);
628 assert(color_of_piece_on(from) == us);
629 assert(piece_on(king_square(us)) == piece_of_color_and_type(us, KING));
631 // If the moving piece is a king, check whether the destination
632 // square is attacked by the opponent.
633 if (type_of_piece_on(from) == KING)
634 return !(attackers_to(move_to(m)) & pieces_of_color(opposite_color(us)));
636 // A non-king move is legal if and only if it is not pinned or it
637 // is moving along the ray towards or away from the king.
639 || !bit_is_set(pinned, from)
640 || squares_aligned(from, move_to(m), king_square(us));
644 /// Position::pl_move_is_evasion() tests whether a pseudo-legal move is a legal evasion
646 bool Position::pl_move_is_evasion(Move m, Bitboard pinned) const
650 Color us = side_to_move();
651 Square from = move_from(m);
652 Square to = move_to(m);
654 // King moves and en-passant captures are verified in pl_move_is_legal()
655 if (type_of_piece_on(from) == KING || move_is_ep(m))
656 return pl_move_is_legal(m, pinned);
658 Bitboard target = checkers();
659 Square checksq = pop_1st_bit(&target);
661 if (target) // double check ?
664 // Our move must be a blocking evasion or a capture of the checking piece
665 target = squares_between(checksq, king_square(us)) | checkers();
666 return bit_is_set(target, to) && pl_move_is_legal(m, pinned);
670 /// Position::move_is_check() tests whether a pseudo-legal move is a check
672 bool Position::move_is_check(Move m) const {
674 return move_is_check(m, CheckInfo(*this));
677 bool Position::move_is_check(Move m, const CheckInfo& ci) const {
680 assert(move_is_ok(m));
681 assert(ci.dcCandidates == discovered_check_candidates(side_to_move()));
682 assert(color_of_piece_on(move_from(m)) == side_to_move());
683 assert(piece_on(ci.ksq) == piece_of_color_and_type(opposite_color(side_to_move()), KING));
685 Square from = move_from(m);
686 Square to = move_to(m);
687 PieceType pt = type_of_piece_on(from);
690 if (bit_is_set(ci.checkSq[pt], to))
694 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
696 // For pawn and king moves we need to verify also direction
697 if ( (pt != PAWN && pt != KING)
698 || !squares_aligned(from, to, ci.ksq))
702 // Can we skip the ugly special cases ?
703 if (!move_is_special(m))
706 Color us = side_to_move();
707 Bitboard b = occupied_squares();
709 // Promotion with check ?
710 if (move_is_promotion(m))
714 switch (move_promotion_piece(m))
717 return bit_is_set(attacks_from<KNIGHT>(to), ci.ksq);
719 return bit_is_set(bishop_attacks_bb(to, b), ci.ksq);
721 return bit_is_set(rook_attacks_bb(to, b), ci.ksq);
723 return bit_is_set(queen_attacks_bb(to, b), ci.ksq);
729 // En passant capture with check ? We have already handled the case
730 // of direct checks and ordinary discovered check, the only case we
731 // need to handle is the unusual case of a discovered check through
732 // the captured pawn.
735 Square capsq = make_square(square_file(to), square_rank(from));
737 clear_bit(&b, capsq);
739 return (rook_attacks_bb(ci.ksq, b) & pieces(ROOK, QUEEN, us))
740 ||(bishop_attacks_bb(ci.ksq, b) & pieces(BISHOP, QUEEN, us));
743 // Castling with check ?
744 if (move_is_castle(m))
746 Square kfrom, kto, rfrom, rto;
752 kto = relative_square(us, SQ_G1);
753 rto = relative_square(us, SQ_F1);
755 kto = relative_square(us, SQ_C1);
756 rto = relative_square(us, SQ_D1);
758 clear_bit(&b, kfrom);
759 clear_bit(&b, rfrom);
762 return bit_is_set(rook_attacks_bb(rto, b), ci.ksq);
769 /// Position::do_move() makes a move, and saves all information necessary
770 /// to a StateInfo object. The move is assumed to be legal.
771 /// Pseudo-legal moves should be filtered out before this function is called.
773 void Position::do_move(Move m, StateInfo& newSt) {
776 do_move(m, newSt, ci, move_is_check(m, ci));
779 void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveIsCheck) {
782 assert(move_is_ok(m));
787 // Copy some fields of old state to our new StateInfo object except the
788 // ones which are recalculated from scratch anyway, then switch our state
789 // pointer to point to the new, ready to be updated, state.
790 struct ReducedStateInfo {
791 Key pawnKey, materialKey;
792 int castleRights, rule50, gamePly, pliesFromNull;
799 memcpy(&newSt, st, sizeof(ReducedStateInfo));
804 // Save the current key to the history[] array, in order to be able to
805 // detect repetition draws.
806 history[st->gamePly++] = key;
808 // Update side to move
809 key ^= zobSideToMove;
811 // Increment the 50 moves rule draw counter. Resetting it to zero in the
812 // case of non-reversible moves is taken care of later.
816 if (move_is_castle(m))
823 Color us = side_to_move();
824 Color them = opposite_color(us);
825 Square from = move_from(m);
826 Square to = move_to(m);
827 bool ep = move_is_ep(m);
828 bool pm = move_is_promotion(m);
830 Piece piece = piece_on(from);
831 PieceType pt = type_of_piece(piece);
832 PieceType capture = ep ? PAWN : type_of_piece_on(to);
834 assert(color_of_piece_on(from) == us);
835 assert(color_of_piece_on(to) == them || square_is_empty(to));
836 assert(!(ep || pm) || piece == piece_of_color_and_type(us, PAWN));
837 assert(!pm || relative_rank(us, to) == RANK_8);
840 do_capture_move(key, capture, them, to, ep);
843 key ^= zobrist[us][pt][from] ^ zobrist[us][pt][to];
845 // Reset en passant square
846 if (st->epSquare != SQ_NONE)
848 key ^= zobEp[st->epSquare];
849 st->epSquare = SQ_NONE;
852 // Update castle rights, try to shortcut a common case
853 int cm = castleRightsMask[from] & castleRightsMask[to];
854 if (cm != ALL_CASTLES && ((cm & st->castleRights) != st->castleRights))
856 key ^= zobCastle[st->castleRights];
857 st->castleRights &= castleRightsMask[from];
858 st->castleRights &= castleRightsMask[to];
859 key ^= zobCastle[st->castleRights];
862 // Prefetch TT access as soon as we know key is updated
863 prefetch((char*)TT.first_entry(key));
866 Bitboard move_bb = make_move_bb(from, to);
867 do_move_bb(&(byColorBB[us]), move_bb);
868 do_move_bb(&(byTypeBB[pt]), move_bb);
869 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
871 board[to] = board[from];
872 board[from] = PIECE_NONE;
874 // Update piece lists, note that index[from] is not updated and
875 // becomes stale. This works as long as index[] is accessed just
876 // by known occupied squares.
877 index[to] = index[from];
878 pieceList[us][pt][index[to]] = to;
880 // If the moving piece was a pawn do some special extra work
883 // Reset rule 50 draw counter
886 // Update pawn hash key and prefetch in L1/L2 cache
887 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
888 prefetchPawn(st->pawnKey, threadID);
890 // Set en passant square, only if moved pawn can be captured
891 if ((to ^ from) == 16)
893 if (attacks_from<PAWN>(from + (us == WHITE ? DELTA_N : DELTA_S), us) & pieces(PAWN, them))
895 st->epSquare = Square((int(from) + int(to)) / 2);
896 key ^= zobEp[st->epSquare];
900 if (pm) // promotion ?
902 PieceType promotion = move_promotion_piece(m);
904 assert(promotion >= KNIGHT && promotion <= QUEEN);
906 // Insert promoted piece instead of pawn
907 clear_bit(&(byTypeBB[PAWN]), to);
908 set_bit(&(byTypeBB[promotion]), to);
909 board[to] = piece_of_color_and_type(us, promotion);
911 // Update piece counts
912 pieceCount[us][promotion]++;
913 pieceCount[us][PAWN]--;
915 // Update material key
916 st->materialKey ^= zobrist[us][PAWN][pieceCount[us][PAWN]];
917 st->materialKey ^= zobrist[us][promotion][pieceCount[us][promotion]-1];
919 // Update piece lists, move the last pawn at index[to] position
920 // and shrink the list. Add a new promotion piece to the list.
921 Square lastPawnSquare = pieceList[us][PAWN][pieceCount[us][PAWN]];
922 index[lastPawnSquare] = index[to];
923 pieceList[us][PAWN][index[lastPawnSquare]] = lastPawnSquare;
924 pieceList[us][PAWN][pieceCount[us][PAWN]] = SQ_NONE;
925 index[to] = pieceCount[us][promotion] - 1;
926 pieceList[us][promotion][index[to]] = to;
928 // Partially revert hash keys update
929 key ^= zobrist[us][PAWN][to] ^ zobrist[us][promotion][to];
930 st->pawnKey ^= zobrist[us][PAWN][to];
932 // Partially revert and update incremental scores
933 st->value -= pst(us, PAWN, to);
934 st->value += pst(us, promotion, to);
937 st->npMaterial[us] += PieceValueMidgame[promotion];
941 // Update incremental scores
942 st->value += pst_delta(piece, from, to);
945 st->capturedType = capture;
947 // Update the key with the final value
950 // Update checkers bitboard, piece must be already moved
951 st->checkersBB = EmptyBoardBB;
956 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
960 if (bit_is_set(ci.checkSq[pt], to))
961 st->checkersBB = SetMaskBB[to];
964 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
967 st->checkersBB |= (attacks_from<ROOK>(ci.ksq) & pieces(ROOK, QUEEN, us));
970 st->checkersBB |= (attacks_from<BISHOP>(ci.ksq) & pieces(BISHOP, QUEEN, us));
976 sideToMove = opposite_color(sideToMove);
977 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
983 /// Position::do_capture_move() is a private method used to update captured
984 /// piece info. It is called from the main Position::do_move function.
986 void Position::do_capture_move(Key& key, PieceType capture, Color them, Square to, bool ep) {
988 assert(capture != KING);
992 // If the captured piece was a pawn, update pawn hash key,
993 // otherwise update non-pawn material.
996 if (ep) // en passant ?
998 capsq = (them == BLACK)? (to - DELTA_N) : (to - DELTA_S);
1000 assert(to == st->epSquare);
1001 assert(relative_rank(opposite_color(them), to) == RANK_6);
1002 assert(piece_on(to) == PIECE_NONE);
1003 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
1005 board[capsq] = PIECE_NONE;
1007 st->pawnKey ^= zobrist[them][PAWN][capsq];
1010 st->npMaterial[them] -= PieceValueMidgame[capture];
1012 // Remove captured piece
1013 clear_bit(&(byColorBB[them]), capsq);
1014 clear_bit(&(byTypeBB[capture]), capsq);
1015 clear_bit(&(byTypeBB[0]), capsq);
1018 key ^= zobrist[them][capture][capsq];
1020 // Update incremental scores
1021 st->value -= pst(them, capture, capsq);
1023 // Update piece count
1024 pieceCount[them][capture]--;
1026 // Update material hash key
1027 st->materialKey ^= zobrist[them][capture][pieceCount[them][capture]];
1029 // Update piece list, move the last piece at index[capsq] position
1031 // WARNING: This is a not perfectly revresible operation. When we
1032 // will reinsert the captured piece in undo_move() we will put it
1033 // at the end of the list and not in its original place, it means
1034 // index[] and pieceList[] are not guaranteed to be invariant to a
1035 // do_move() + undo_move() sequence.
1036 Square lastPieceSquare = pieceList[them][capture][pieceCount[them][capture]];
1037 index[lastPieceSquare] = index[capsq];
1038 pieceList[them][capture][index[lastPieceSquare]] = lastPieceSquare;
1039 pieceList[them][capture][pieceCount[them][capture]] = SQ_NONE;
1041 // Reset rule 50 counter
1046 /// Position::do_castle_move() is a private method used to make a castling
1047 /// move. It is called from the main Position::do_move function. Note that
1048 /// castling moves are encoded as "king captures friendly rook" moves, for
1049 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1051 void Position::do_castle_move(Move m) {
1053 assert(move_is_ok(m));
1054 assert(move_is_castle(m));
1056 Color us = side_to_move();
1057 Color them = opposite_color(us);
1059 // Reset capture field
1060 st->capturedType = PIECE_TYPE_NONE;
1062 // Find source squares for king and rook
1063 Square kfrom = move_from(m);
1064 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1067 assert(piece_on(kfrom) == piece_of_color_and_type(us, KING));
1068 assert(piece_on(rfrom) == piece_of_color_and_type(us, ROOK));
1070 // Find destination squares for king and rook
1071 if (rfrom > kfrom) // O-O
1073 kto = relative_square(us, SQ_G1);
1074 rto = relative_square(us, SQ_F1);
1076 kto = relative_square(us, SQ_C1);
1077 rto = relative_square(us, SQ_D1);
1080 // Remove pieces from source squares:
1081 clear_bit(&(byColorBB[us]), kfrom);
1082 clear_bit(&(byTypeBB[KING]), kfrom);
1083 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1084 clear_bit(&(byColorBB[us]), rfrom);
1085 clear_bit(&(byTypeBB[ROOK]), rfrom);
1086 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1088 // Put pieces on destination squares:
1089 set_bit(&(byColorBB[us]), kto);
1090 set_bit(&(byTypeBB[KING]), kto);
1091 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1092 set_bit(&(byColorBB[us]), rto);
1093 set_bit(&(byTypeBB[ROOK]), rto);
1094 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1096 // Update board array
1097 Piece king = piece_of_color_and_type(us, KING);
1098 Piece rook = piece_of_color_and_type(us, ROOK);
1099 board[kfrom] = board[rfrom] = PIECE_NONE;
1103 // Update piece lists
1104 pieceList[us][KING][index[kfrom]] = kto;
1105 pieceList[us][ROOK][index[rfrom]] = rto;
1106 int tmp = index[rfrom]; // In Chess960 could be rto == kfrom
1107 index[kto] = index[kfrom];
1110 // Update incremental scores
1111 st->value += pst_delta(king, kfrom, kto);
1112 st->value += pst_delta(rook, rfrom, rto);
1115 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1116 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1118 // Clear en passant square
1119 if (st->epSquare != SQ_NONE)
1121 st->key ^= zobEp[st->epSquare];
1122 st->epSquare = SQ_NONE;
1125 // Update castling rights
1126 st->key ^= zobCastle[st->castleRights];
1127 st->castleRights &= castleRightsMask[kfrom];
1128 st->key ^= zobCastle[st->castleRights];
1130 // Reset rule 50 counter
1133 // Update checkers BB
1134 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
1137 sideToMove = opposite_color(sideToMove);
1138 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1144 /// Position::undo_move() unmakes a move. When it returns, the position should
1145 /// be restored to exactly the same state as before the move was made.
1147 void Position::undo_move(Move m) {
1150 assert(move_is_ok(m));
1152 sideToMove = opposite_color(sideToMove);
1154 if (move_is_castle(m))
1156 undo_castle_move(m);
1160 Color us = side_to_move();
1161 Color them = opposite_color(us);
1162 Square from = move_from(m);
1163 Square to = move_to(m);
1164 bool ep = move_is_ep(m);
1165 bool pm = move_is_promotion(m);
1167 PieceType pt = type_of_piece_on(to);
1169 assert(square_is_empty(from));
1170 assert(color_of_piece_on(to) == us);
1171 assert(!pm || relative_rank(us, to) == RANK_8);
1172 assert(!ep || to == st->previous->epSquare);
1173 assert(!ep || relative_rank(us, to) == RANK_6);
1174 assert(!ep || piece_on(to) == piece_of_color_and_type(us, PAWN));
1176 if (pm) // promotion ?
1178 PieceType promotion = move_promotion_piece(m);
1181 assert(promotion >= KNIGHT && promotion <= QUEEN);
1182 assert(piece_on(to) == piece_of_color_and_type(us, promotion));
1184 // Replace promoted piece with a pawn
1185 clear_bit(&(byTypeBB[promotion]), to);
1186 set_bit(&(byTypeBB[PAWN]), to);
1188 // Update piece counts
1189 pieceCount[us][promotion]--;
1190 pieceCount[us][PAWN]++;
1192 // Update piece list replacing promotion piece with a pawn
1193 Square lastPromotionSquare = pieceList[us][promotion][pieceCount[us][promotion]];
1194 index[lastPromotionSquare] = index[to];
1195 pieceList[us][promotion][index[lastPromotionSquare]] = lastPromotionSquare;
1196 pieceList[us][promotion][pieceCount[us][promotion]] = SQ_NONE;
1197 index[to] = pieceCount[us][PAWN] - 1;
1198 pieceList[us][PAWN][index[to]] = to;
1201 // Put the piece back at the source square
1202 Bitboard move_bb = make_move_bb(to, from);
1203 do_move_bb(&(byColorBB[us]), move_bb);
1204 do_move_bb(&(byTypeBB[pt]), move_bb);
1205 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
1207 board[from] = piece_of_color_and_type(us, pt);
1208 board[to] = PIECE_NONE;
1210 // Update piece list
1211 index[from] = index[to];
1212 pieceList[us][pt][index[from]] = from;
1214 if (st->capturedType)
1219 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1221 assert(st->capturedType != KING);
1222 assert(!ep || square_is_empty(capsq));
1224 // Restore the captured piece
1225 set_bit(&(byColorBB[them]), capsq);
1226 set_bit(&(byTypeBB[st->capturedType]), capsq);
1227 set_bit(&(byTypeBB[0]), capsq);
1229 board[capsq] = piece_of_color_and_type(them, st->capturedType);
1231 // Update piece count
1232 pieceCount[them][st->capturedType]++;
1234 // Update piece list, add a new captured piece in capsq square
1235 index[capsq] = pieceCount[them][st->capturedType] - 1;
1236 pieceList[them][st->capturedType][index[capsq]] = capsq;
1239 // Finally point our state pointer back to the previous state
1246 /// Position::undo_castle_move() is a private method used to unmake a castling
1247 /// move. It is called from the main Position::undo_move function. Note that
1248 /// castling moves are encoded as "king captures friendly rook" moves, for
1249 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1251 void Position::undo_castle_move(Move m) {
1253 assert(move_is_ok(m));
1254 assert(move_is_castle(m));
1256 // When we have arrived here, some work has already been done by
1257 // Position::undo_move. In particular, the side to move has been switched,
1258 // so the code below is correct.
1259 Color us = side_to_move();
1261 // Find source squares for king and rook
1262 Square kfrom = move_from(m);
1263 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1266 // Find destination squares for king and rook
1267 if (rfrom > kfrom) // O-O
1269 kto = relative_square(us, SQ_G1);
1270 rto = relative_square(us, SQ_F1);
1272 kto = relative_square(us, SQ_C1);
1273 rto = relative_square(us, SQ_D1);
1276 assert(piece_on(kto) == piece_of_color_and_type(us, KING));
1277 assert(piece_on(rto) == piece_of_color_and_type(us, ROOK));
1279 // Remove pieces from destination squares:
1280 clear_bit(&(byColorBB[us]), kto);
1281 clear_bit(&(byTypeBB[KING]), kto);
1282 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1283 clear_bit(&(byColorBB[us]), rto);
1284 clear_bit(&(byTypeBB[ROOK]), rto);
1285 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1287 // Put pieces on source squares:
1288 set_bit(&(byColorBB[us]), kfrom);
1289 set_bit(&(byTypeBB[KING]), kfrom);
1290 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1291 set_bit(&(byColorBB[us]), rfrom);
1292 set_bit(&(byTypeBB[ROOK]), rfrom);
1293 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1296 board[rto] = board[kto] = PIECE_NONE;
1297 board[rfrom] = piece_of_color_and_type(us, ROOK);
1298 board[kfrom] = piece_of_color_and_type(us, KING);
1300 // Update piece lists
1301 pieceList[us][KING][index[kto]] = kfrom;
1302 pieceList[us][ROOK][index[rto]] = rfrom;
1303 int tmp = index[rto]; // In Chess960 could be rto == kfrom
1304 index[kfrom] = index[kto];
1307 // Finally point our state pointer back to the previous state
1314 /// Position::do_null_move makes() a "null move": It switches the side to move
1315 /// and updates the hash key without executing any move on the board.
1317 void Position::do_null_move(StateInfo& backupSt) {
1320 assert(!is_check());
1322 // Back up the information necessary to undo the null move to the supplied
1323 // StateInfo object.
1324 // Note that differently from normal case here backupSt is actually used as
1325 // a backup storage not as a new state to be used.
1326 backupSt.key = st->key;
1327 backupSt.epSquare = st->epSquare;
1328 backupSt.value = st->value;
1329 backupSt.previous = st->previous;
1330 backupSt.pliesFromNull = st->pliesFromNull;
1331 st->previous = &backupSt;
1333 // Save the current key to the history[] array, in order to be able to
1334 // detect repetition draws.
1335 history[st->gamePly++] = st->key;
1337 // Update the necessary information
1338 if (st->epSquare != SQ_NONE)
1339 st->key ^= zobEp[st->epSquare];
1341 st->key ^= zobSideToMove;
1342 prefetch((char*)TT.first_entry(st->key));
1344 sideToMove = opposite_color(sideToMove);
1345 st->epSquare = SQ_NONE;
1347 st->pliesFromNull = 0;
1348 st->value += (sideToMove == WHITE) ? TempoValue : -TempoValue;
1352 /// Position::undo_null_move() unmakes a "null move".
1354 void Position::undo_null_move() {
1357 assert(!is_check());
1359 // Restore information from the our backup StateInfo object
1360 StateInfo* backupSt = st->previous;
1361 st->key = backupSt->key;
1362 st->epSquare = backupSt->epSquare;
1363 st->value = backupSt->value;
1364 st->previous = backupSt->previous;
1365 st->pliesFromNull = backupSt->pliesFromNull;
1367 // Update the necessary information
1368 sideToMove = opposite_color(sideToMove);
1374 /// Position::see() is a static exchange evaluator: It tries to estimate the
1375 /// material gain or loss resulting from a move. There are three versions of
1376 /// this function: One which takes a destination square as input, one takes a
1377 /// move, and one which takes a 'from' and a 'to' square. The function does
1378 /// not yet understand promotions captures.
1380 int Position::see(Move m) const {
1382 assert(move_is_ok(m));
1383 return see(move_from(m), move_to(m));
1386 int Position::see_sign(Move m) const {
1388 assert(move_is_ok(m));
1390 Square from = move_from(m);
1391 Square to = move_to(m);
1393 // Early return if SEE cannot be negative because captured piece value
1394 // is not less then capturing one. Note that king moves always return
1395 // here because king midgame value is set to 0.
1396 if (midgame_value_of_piece_on(to) >= midgame_value_of_piece_on(from))
1399 return see(from, to);
1402 int Position::see(Square from, Square to) const {
1404 Bitboard occupied, attackers, stmAttackers, b;
1405 int swapList[32], slIndex = 1;
1406 PieceType capturedType, pt;
1409 assert(square_is_ok(from));
1410 assert(square_is_ok(to));
1412 capturedType = type_of_piece_on(to);
1414 // King cannot be recaptured
1415 if (capturedType == KING)
1416 return seeValues[capturedType];
1418 occupied = occupied_squares();
1420 // Handle en passant moves
1421 if (st->epSquare == to && type_of_piece_on(from) == PAWN)
1423 Square capQq = (side_to_move() == WHITE ? to - DELTA_N : to - DELTA_S);
1425 assert(capturedType == PIECE_TYPE_NONE);
1426 assert(type_of_piece_on(capQq) == PAWN);
1428 // Remove the captured pawn
1429 clear_bit(&occupied, capQq);
1430 capturedType = PAWN;
1433 // Find all attackers to the destination square, with the moving piece
1434 // removed, but possibly an X-ray attacker added behind it.
1435 clear_bit(&occupied, from);
1436 attackers = (rook_attacks_bb(to, occupied) & pieces(ROOK, QUEEN))
1437 | (bishop_attacks_bb(to, occupied)& pieces(BISHOP, QUEEN))
1438 | (attacks_from<KNIGHT>(to) & pieces(KNIGHT))
1439 | (attacks_from<KING>(to) & pieces(KING))
1440 | (attacks_from<PAWN>(to, WHITE) & pieces(PAWN, BLACK))
1441 | (attacks_from<PAWN>(to, BLACK) & pieces(PAWN, WHITE));
1443 // If the opponent has no attackers we are finished
1444 stm = opposite_color(color_of_piece_on(from));
1445 stmAttackers = attackers & pieces_of_color(stm);
1447 return seeValues[capturedType];
1449 // The destination square is defended, which makes things rather more
1450 // difficult to compute. We proceed by building up a "swap list" containing
1451 // the material gain or loss at each stop in a sequence of captures to the
1452 // destination square, where the sides alternately capture, and always
1453 // capture with the least valuable piece. After each capture, we look for
1454 // new X-ray attacks from behind the capturing piece.
1455 swapList[0] = seeValues[capturedType];
1456 capturedType = type_of_piece_on(from);
1459 // Locate the least valuable attacker for the side to move. The loop
1460 // below looks like it is potentially infinite, but it isn't. We know
1461 // that the side to move still has at least one attacker left.
1462 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1465 // Remove the attacker we just found from the 'occupied' bitboard,
1466 // and scan for new X-ray attacks behind the attacker.
1467 b = stmAttackers & pieces(pt);
1468 occupied ^= (b & (~b + 1));
1469 attackers |= (rook_attacks_bb(to, occupied) & pieces(ROOK, QUEEN))
1470 | (bishop_attacks_bb(to, occupied) & pieces(BISHOP, QUEEN));
1472 attackers &= occupied; // Cut out pieces we've already done
1474 // Add the new entry to the swap list
1475 assert(slIndex < 32);
1476 swapList[slIndex] = -swapList[slIndex - 1] + seeValues[capturedType];
1479 // Remember the value of the capturing piece, and change the side to
1480 // move before beginning the next iteration.
1482 stm = opposite_color(stm);
1483 stmAttackers = attackers & pieces_of_color(stm);
1485 // Stop before processing a king capture
1486 if (capturedType == KING && stmAttackers)
1488 assert(slIndex < 32);
1489 swapList[slIndex++] = QueenValueMidgame*10;
1492 } while (stmAttackers);
1494 // Having built the swap list, we negamax through it to find the best
1495 // achievable score from the point of view of the side to move.
1497 swapList[slIndex-1] = Min(-swapList[slIndex], swapList[slIndex-1]);
1503 /// Position::clear() erases the position object to a pristine state, with an
1504 /// empty board, white to move, and no castling rights.
1506 void Position::clear() {
1509 memset(st, 0, sizeof(StateInfo));
1510 st->epSquare = SQ_NONE;
1511 startPosPlyCounter = 0;
1514 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1515 memset(byTypeBB, 0, sizeof(Bitboard) * 8);
1516 memset(pieceCount, 0, sizeof(int) * 2 * 8);
1517 memset(index, 0, sizeof(int) * 64);
1519 for (int i = 0; i < 64; i++)
1520 board[i] = PIECE_NONE;
1522 for (int i = 0; i < 8; i++)
1523 for (int j = 0; j < 16; j++)
1524 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1526 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
1527 castleRightsMask[sq] = ALL_CASTLES;
1530 initialKFile = FILE_E;
1531 initialKRFile = FILE_H;
1532 initialQRFile = FILE_A;
1536 /// Position::reset_game_ply() simply sets gamePly to 0. It is used from the
1537 /// UCI interface code, whenever a non-reversible move is made in a
1538 /// 'position fen <fen> moves m1 m2 ...' command. This makes it possible
1539 /// for the program to handle games of arbitrary length, as long as the GUI
1540 /// handles draws by the 50 move rule correctly.
1542 void Position::reset_game_ply() {
1547 void Position::inc_startpos_ply_counter() {
1549 startPosPlyCounter++;
1552 /// Position::put_piece() puts a piece on the given square of the board,
1553 /// updating the board array, pieces list, bitboards, and piece counts.
1555 void Position::put_piece(Piece p, Square s) {
1557 Color c = color_of_piece(p);
1558 PieceType pt = type_of_piece(p);
1561 index[s] = pieceCount[c][pt]++;
1562 pieceList[c][pt][index[s]] = s;
1564 set_bit(&(byTypeBB[pt]), s);
1565 set_bit(&(byColorBB[c]), s);
1566 set_bit(&(byTypeBB[0]), s); // HACK: byTypeBB[0] contains all occupied squares.
1570 /// Position::compute_key() computes the hash key of the position. The hash
1571 /// key is usually updated incrementally as moves are made and unmade, the
1572 /// compute_key() function is only used when a new position is set up, and
1573 /// to verify the correctness of the hash key when running in debug mode.
1575 Key Position::compute_key() const {
1577 Key result = zobCastle[st->castleRights];
1579 for (Square s = SQ_A1; s <= SQ_H8; s++)
1580 if (square_is_occupied(s))
1581 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1583 if (ep_square() != SQ_NONE)
1584 result ^= zobEp[ep_square()];
1586 if (side_to_move() == BLACK)
1587 result ^= zobSideToMove;
1593 /// Position::compute_pawn_key() computes the hash key of the position. The
1594 /// hash key is usually updated incrementally as moves are made and unmade,
1595 /// the compute_pawn_key() function is only used when a new position is set
1596 /// up, and to verify the correctness of the pawn hash key when running in
1599 Key Position::compute_pawn_key() const {
1604 for (Color c = WHITE; c <= BLACK; c++)
1606 b = pieces(PAWN, c);
1608 result ^= zobrist[c][PAWN][pop_1st_bit(&b)];
1614 /// Position::compute_material_key() computes the hash key of the position.
1615 /// The hash key is usually updated incrementally as moves are made and unmade,
1616 /// the compute_material_key() function is only used when a new position is set
1617 /// up, and to verify the correctness of the material hash key when running in
1620 Key Position::compute_material_key() const {
1625 for (Color c = WHITE; c <= BLACK; c++)
1626 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1628 count = piece_count(c, pt);
1629 for (int i = 0; i < count; i++)
1630 result ^= zobrist[c][pt][i];
1636 /// Position::compute_value() compute the incremental scores for the middle
1637 /// game and the endgame. These functions are used to initialize the incremental
1638 /// scores when a new position is set up, and to verify that the scores are correctly
1639 /// updated by do_move and undo_move when the program is running in debug mode.
1640 Score Position::compute_value() const {
1643 Score result = SCORE_ZERO;
1645 for (Color c = WHITE; c <= BLACK; c++)
1646 for (PieceType pt = PAWN; pt <= KING; pt++)
1650 result += pst(c, pt, pop_1st_bit(&b));
1653 result += (side_to_move() == WHITE ? TempoValue / 2 : -TempoValue / 2);
1658 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1659 /// game material value for the given side. Material values are updated
1660 /// incrementally during the search, this function is only used while
1661 /// initializing a new Position object.
1663 Value Position::compute_non_pawn_material(Color c) const {
1665 Value result = VALUE_ZERO;
1667 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1668 result += piece_count(c, pt) * PieceValueMidgame[pt];
1674 /// Position::is_draw() tests whether the position is drawn by material,
1675 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1676 /// must be done by the search.
1678 bool Position::is_draw() const {
1680 // Draw by material?
1682 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1685 // Draw by the 50 moves rule?
1686 if (st->rule50 > 99 && (st->rule50 > 100 || !is_mate()))
1689 // Draw by repetition?
1690 for (int i = 4, e = Min(Min(st->gamePly, st->rule50), st->pliesFromNull); i <= e; i += 2)
1691 if (history[st->gamePly - i] == st->key)
1698 /// Position::is_mate() returns true or false depending on whether the
1699 /// side to move is checkmated.
1701 bool Position::is_mate() const {
1703 MoveStack moves[MOVES_MAX];
1704 return is_check() && generate_moves(*this, moves) == moves;
1708 /// Position::has_mate_threat() tests whether the side to move is under
1709 /// a threat of being mated in one from the current position.
1711 bool Position::has_mate_threat() {
1713 MoveStack mlist[MOVES_MAX], *last, *cur;
1715 bool mateFound = false;
1717 // If we are under check it's up to evasions to do the job
1721 // First pass the move to our opponent doing a null move
1724 // Then generate pseudo-legal moves that could give check
1725 last = generate_non_capture_checks(*this, mlist);
1726 last = generate_captures(*this, last);
1728 // Loop through the moves, and see if one of them gives mate
1729 Bitboard pinned = pinned_pieces(sideToMove);
1730 CheckInfo ci(*this);
1731 for (cur = mlist; cur != last && !mateFound; cur++)
1733 Move move = cur->move;
1734 if ( !pl_move_is_legal(move, pinned)
1735 || !move_is_check(move, ci))
1738 do_move(move, st2, ci, true);
1751 /// Position::init_zobrist() is a static member function which initializes at
1752 /// startup the various arrays used to compute hash keys.
1754 void Position::init_zobrist() {
1759 for (i = 0; i < 2; i++) for (j = 0; j < 8; j++) for (k = 0; k < 64; k++)
1760 zobrist[i][j][k] = rk.rand<Key>();
1762 for (i = 0; i < 64; i++)
1763 zobEp[i] = rk.rand<Key>();
1765 for (i = 0; i < 16; i++)
1766 zobCastle[i] = rk.rand<Key>();
1768 zobSideToMove = rk.rand<Key>();
1769 zobExclusion = rk.rand<Key>();
1773 /// Position::init_piece_square_tables() initializes the piece square tables.
1774 /// This is a two-step operation: First, the white halves of the tables are
1775 /// copied from the MgPST[][] and EgPST[][] arrays. Second, the black halves
1776 /// of the tables are initialized by mirroring and changing the sign of the
1777 /// corresponding white scores.
1779 void Position::init_piece_square_tables() {
1781 for (Square s = SQ_A1; s <= SQ_H8; s++)
1782 for (Piece p = WP; p <= WK; p++)
1783 PieceSquareTable[p][s] = make_score(MgPST[p][s], EgPST[p][s]);
1785 for (Square s = SQ_A1; s <= SQ_H8; s++)
1786 for (Piece p = BP; p <= BK; p++)
1787 PieceSquareTable[p][s] = -PieceSquareTable[p-8][flip_square(s)];
1791 /// Position::flipped_copy() makes a copy of the input position, but with
1792 /// the white and black sides reversed. This is only useful for debugging,
1793 /// especially for finding evaluation symmetry bugs.
1795 void Position::flipped_copy(const Position& pos) {
1797 assert(pos.is_ok());
1800 threadID = pos.thread();
1803 for (Square s = SQ_A1; s <= SQ_H8; s++)
1804 if (!pos.square_is_empty(s))
1805 put_piece(Piece(pos.piece_on(s) ^ 8), flip_square(s));
1808 sideToMove = opposite_color(pos.side_to_move());
1811 if (pos.can_castle_kingside(WHITE)) do_allow_oo(BLACK);
1812 if (pos.can_castle_queenside(WHITE)) do_allow_ooo(BLACK);
1813 if (pos.can_castle_kingside(BLACK)) do_allow_oo(WHITE);
1814 if (pos.can_castle_queenside(BLACK)) do_allow_ooo(WHITE);
1816 initialKFile = pos.initialKFile;
1817 initialKRFile = pos.initialKRFile;
1818 initialQRFile = pos.initialQRFile;
1820 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
1821 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
1822 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
1823 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
1824 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
1825 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
1827 // En passant square
1828 if (pos.st->epSquare != SQ_NONE)
1829 st->epSquare = flip_square(pos.st->epSquare);
1835 st->key = compute_key();
1836 st->pawnKey = compute_pawn_key();
1837 st->materialKey = compute_material_key();
1839 // Incremental scores
1840 st->value = compute_value();
1843 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
1844 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
1850 /// Position::is_ok() performs some consitency checks for the position object.
1851 /// This is meant to be helpful when debugging.
1853 bool Position::is_ok(int* failedStep) const {
1855 // What features of the position should be verified?
1856 const bool debugAll = false;
1858 const bool debugBitboards = debugAll || false;
1859 const bool debugKingCount = debugAll || false;
1860 const bool debugKingCapture = debugAll || false;
1861 const bool debugCheckerCount = debugAll || false;
1862 const bool debugKey = debugAll || false;
1863 const bool debugMaterialKey = debugAll || false;
1864 const bool debugPawnKey = debugAll || false;
1865 const bool debugIncrementalEval = debugAll || false;
1866 const bool debugNonPawnMaterial = debugAll || false;
1867 const bool debugPieceCounts = debugAll || false;
1868 const bool debugPieceList = debugAll || false;
1869 const bool debugCastleSquares = debugAll || false;
1871 if (failedStep) *failedStep = 1;
1874 if (!color_is_ok(side_to_move()))
1877 // Are the king squares in the position correct?
1878 if (failedStep) (*failedStep)++;
1879 if (piece_on(king_square(WHITE)) != WK)
1882 if (failedStep) (*failedStep)++;
1883 if (piece_on(king_square(BLACK)) != BK)
1887 if (failedStep) (*failedStep)++;
1888 if (!file_is_ok(initialKRFile))
1891 if (!file_is_ok(initialQRFile))
1894 // Do both sides have exactly one king?
1895 if (failedStep) (*failedStep)++;
1898 int kingCount[2] = {0, 0};
1899 for (Square s = SQ_A1; s <= SQ_H8; s++)
1900 if (type_of_piece_on(s) == KING)
1901 kingCount[color_of_piece_on(s)]++;
1903 if (kingCount[0] != 1 || kingCount[1] != 1)
1907 // Can the side to move capture the opponent's king?
1908 if (failedStep) (*failedStep)++;
1909 if (debugKingCapture)
1911 Color us = side_to_move();
1912 Color them = opposite_color(us);
1913 Square ksq = king_square(them);
1914 if (attackers_to(ksq) & pieces_of_color(us))
1918 // Is there more than 2 checkers?
1919 if (failedStep) (*failedStep)++;
1920 if (debugCheckerCount && count_1s<CNT32>(st->checkersBB) > 2)
1924 if (failedStep) (*failedStep)++;
1927 // The intersection of the white and black pieces must be empty
1928 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
1931 // The union of the white and black pieces must be equal to all
1933 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
1936 // Separate piece type bitboards must have empty intersections
1937 for (PieceType p1 = PAWN; p1 <= KING; p1++)
1938 for (PieceType p2 = PAWN; p2 <= KING; p2++)
1939 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1943 // En passant square OK?
1944 if (failedStep) (*failedStep)++;
1945 if (ep_square() != SQ_NONE)
1947 // The en passant square must be on rank 6, from the point of view of the
1949 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
1954 if (failedStep) (*failedStep)++;
1955 if (debugKey && st->key != compute_key())
1958 // Pawn hash key OK?
1959 if (failedStep) (*failedStep)++;
1960 if (debugPawnKey && st->pawnKey != compute_pawn_key())
1963 // Material hash key OK?
1964 if (failedStep) (*failedStep)++;
1965 if (debugMaterialKey && st->materialKey != compute_material_key())
1968 // Incremental eval OK?
1969 if (failedStep) (*failedStep)++;
1970 if (debugIncrementalEval && st->value != compute_value())
1973 // Non-pawn material OK?
1974 if (failedStep) (*failedStep)++;
1975 if (debugNonPawnMaterial)
1977 if (st->npMaterial[WHITE] != compute_non_pawn_material(WHITE))
1980 if (st->npMaterial[BLACK] != compute_non_pawn_material(BLACK))
1985 if (failedStep) (*failedStep)++;
1986 if (debugPieceCounts)
1987 for (Color c = WHITE; c <= BLACK; c++)
1988 for (PieceType pt = PAWN; pt <= KING; pt++)
1989 if (pieceCount[c][pt] != count_1s<CNT32>(pieces(pt, c)))
1992 if (failedStep) (*failedStep)++;
1995 for (Color c = WHITE; c <= BLACK; c++)
1996 for (PieceType pt = PAWN; pt <= KING; pt++)
1997 for (int i = 0; i < pieceCount[c][pt]; i++)
1999 if (piece_on(piece_list(c, pt, i)) != piece_of_color_and_type(c, pt))
2002 if (index[piece_list(c, pt, i)] != i)
2007 if (failedStep) (*failedStep)++;
2008 if (debugCastleSquares) {
2009 for (Color c = WHITE; c <= BLACK; c++) {
2010 if (can_castle_kingside(c) && piece_on(initial_kr_square(c)) != piece_of_color_and_type(c, ROOK))
2012 if (can_castle_queenside(c) && piece_on(initial_qr_square(c)) != piece_of_color_and_type(c, ROOK))
2015 if (castleRightsMask[initial_kr_square(WHITE)] != (ALL_CASTLES ^ WHITE_OO))
2017 if (castleRightsMask[initial_qr_square(WHITE)] != (ALL_CASTLES ^ WHITE_OOO))
2019 if (castleRightsMask[initial_kr_square(BLACK)] != (ALL_CASTLES ^ BLACK_OO))
2021 if (castleRightsMask[initial_qr_square(BLACK)] != (ALL_CASTLES ^ BLACK_OOO))
2025 if (failedStep) *failedStep = 0;