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/>.
39 #include "ucioption.h"
50 Key Position::zobrist[2][8][64];
51 Key Position::zobEp[64];
52 Key Position::zobCastle[16];
53 Key Position::zobSideToMove;
54 Key Position::zobExclusion;
56 Score Position::PieceSquareTable[16][64];
58 static bool RequestPending = false;
63 CheckInfo::CheckInfo(const Position& pos) {
65 Color us = pos.side_to_move();
66 Color them = opposite_color(us);
68 ksq = pos.king_square(them);
69 dcCandidates = pos.discovered_check_candidates(us);
71 checkSq[PAWN] = pos.attacks_from<PAWN>(ksq, them);
72 checkSq[KNIGHT] = pos.attacks_from<KNIGHT>(ksq);
73 checkSq[BISHOP] = pos.attacks_from<BISHOP>(ksq);
74 checkSq[ROOK] = pos.attacks_from<ROOK>(ksq);
75 checkSq[QUEEN] = checkSq[BISHOP] | checkSq[ROOK];
76 checkSq[KING] = EmptyBoardBB;
80 /// Position c'tors. Here we always create a copy of the original position
81 /// or the FEN string, we want the new born Position object do not depend
82 /// on any external data so we detach state pointer from the source one.
84 Position::Position(int th) : threadID(th) {}
86 Position::Position(const Position& pos, int th) {
88 memcpy(this, &pos, sizeof(Position));
89 detach(); // Always detach() in copy c'tor to avoid surprises
93 Position::Position(const string& fen, int th) {
100 /// Position::detach() copies the content of the current state and castling
101 /// masks inside the position itself. This is needed when the st pointee could
102 /// become stale, as example because the caller is about to going out of scope.
104 void Position::detach() {
108 st->previous = NULL; // as a safe guard
112 /// Position::from_fen() initializes the position object with the given FEN
113 /// string. This function is not very robust - make sure that input FENs are
114 /// correct (this is assumed to be the responsibility of the GUI).
116 void Position::from_fen(const string& fen) {
118 A FEN string defines a particular position using only the ASCII character set.
120 A FEN string contains six fields. The separator between fields is a space. The fields are:
122 1) Piece placement (from white's perspective). Each rank is described, starting with rank 8 and ending
123 with rank 1; within each rank, the contents of each square are described from file a through file h.
124 Following the Standard Algebraic Notation (SAN), each piece is identified by a single letter taken
125 from the standard English names. White pieces are designated using upper-case letters ("PNBRQK")
126 while Black take lowercase ("pnbrqk"). Blank squares are noted using digits 1 through 8 (the number
127 of blank squares), and "/" separate ranks.
129 2) Active color. "w" means white moves next, "b" means black.
131 3) Castling availability. If neither side can castle, this is "-". Otherwise, this has one or more
132 letters: "K" (White can castle kingside), "Q" (White can castle queenside), "k" (Black can castle
133 kingside), and/or "q" (Black can castle queenside).
135 4) En passant target square in algebraic notation. If there's no en passant target square, this is "-".
136 If a pawn has just made a 2-square move, this is the position "behind" the pawn. This is recorded
137 regardless of whether there is a pawn in position to make an en passant capture.
139 5) Halfmove clock: This is the number of halfmoves since the last pawn advance or capture. This is used
140 to determine if a draw can be claimed under the fifty-move rule.
142 6) Fullmove number: The number of the full move. It starts at 1, and is incremented after Black's move.
145 static const string pieceLetters = "KQRBNPkqrbnp";
146 static const Piece pieces[] = { WK, WQ, WR, WB, WN, WP, BK, BQ, BR, BB, BN, BP };
152 std::istringstream ss(fen);
157 // 1. Piece placement field
158 while (ss.get(token) && token != ' ')
162 // Skip the given number of files
163 file += token - '1' + 1;
166 else if (token == '/')
173 idx = pieceLetters.find(token);
174 if (idx == string::npos)
177 put_piece(pieces[idx], make_square(file, rank));
182 if (!ss.get(token) || (token != 'w' && token != 'b'))
185 sideToMove = (token == 'w' ? WHITE : BLACK);
187 if (!ss.get(token) || token != ' ')
190 // 3. Castling availability
191 while (ss.get(token) && token != ' ')
196 if (!set_castling_rights(token))
200 // 4. En passant square -- ignore if no capture is possible
202 if ( (ss.get(col) && (col >= 'a' && col <= 'h'))
203 && (ss.get(row) && (row == '3' || row == '6')))
205 Square fenEpSquare = make_square(file_from_char(col), rank_from_char(row));
206 Color them = opposite_color(sideToMove);
208 if (attacks_from<PAWN>(fenEpSquare, them) & this->pieces(PAWN, sideToMove))
209 st->epSquare = fenEpSquare;
212 // 5-6. Halfmove clock and fullmove number are not parsed
214 // Various initialisations
215 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO|WHITE_OOO);
216 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO|BLACK_OOO);
217 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
218 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
219 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
220 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
224 st->key = compute_key();
225 st->pawnKey = compute_pawn_key();
226 st->materialKey = compute_material_key();
227 st->value = compute_value();
228 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
229 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
233 cout << "Error in FEN string: " << fen << endl;
237 /// Position::set_castling_rights() sets castling parameters castling avaiability.
238 /// This function is compatible with 3 standards: Normal FEN standard, Shredder-FEN
239 /// that uses the letters of the columns on which the rooks began the game instead
240 /// of KQkq and also X-FEN standard that, in case of Chess960, if an inner Rook is
241 /// associated with the castling right, the traditional castling tag will be replaced
242 /// by the file letter of the involved rook as for the Shredder-FEN.
244 bool Position::set_castling_rights(char token) {
246 Color c = token >= 'a' ? BLACK : WHITE;
247 Square sqA = (c == WHITE ? SQ_A1 : SQ_A8);
248 Square sqH = (c == WHITE ? SQ_H1 : SQ_H8);
249 Piece rook = (c == WHITE ? WR : BR);
251 initialKFile = square_file(king_square(c));
252 token = char(toupper(token));
256 for (Square sq = sqH; sq >= sqA; sq--)
257 if (piece_on(sq) == rook)
260 initialKRFile = square_file(sq);
264 else if (token == 'Q')
266 for (Square sq = sqA; sq <= sqH; sq++)
267 if (piece_on(sq) == rook)
270 initialQRFile = square_file(sq);
274 else if (token >= 'A' && token <= 'H')
276 File rookFile = File(token - 'A') + FILE_A;
277 if (rookFile < initialKFile)
280 initialQRFile = rookFile;
285 initialKRFile = rookFile;
294 /// Position::to_fen() converts the position object to a FEN string. This is
295 /// probably only useful for debugging.
297 const string Position::to_fen() const {
299 static const string pieceLetters = " PNBRQK pnbrqk";
303 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
306 for (File file = FILE_A; file <= FILE_H; file++)
308 Square sq = make_square(file, rank);
309 if (!square_is_occupied(sq))
315 fen += (char)skip + '0';
318 fen += pieceLetters[piece_on(sq)];
321 fen += (char)skip + '0';
323 fen += (rank > RANK_1 ? '/' : ' ');
325 fen += (sideToMove == WHITE ? "w " : "b ");
326 if (st->castleRights != NO_CASTLES)
328 if (initialKFile == FILE_E && initialQRFile == FILE_A && initialKRFile == FILE_H)
330 if (can_castle_kingside(WHITE)) fen += 'K';
331 if (can_castle_queenside(WHITE)) fen += 'Q';
332 if (can_castle_kingside(BLACK)) fen += 'k';
333 if (can_castle_queenside(BLACK)) fen += 'q';
337 if (can_castle_kingside(WHITE))
338 fen += char(toupper(file_to_char(initialKRFile)));
339 if (can_castle_queenside(WHITE))
340 fen += char(toupper(file_to_char(initialQRFile)));
341 if (can_castle_kingside(BLACK))
342 fen += file_to_char(initialKRFile);
343 if (can_castle_queenside(BLACK))
344 fen += file_to_char(initialQRFile);
350 if (ep_square() != SQ_NONE)
351 fen += square_to_string(ep_square());
359 /// Position::print() prints an ASCII representation of the position to
360 /// the standard output. If a move is given then also the san is print.
362 void Position::print(Move m) const {
364 static const string pieceLetters = " PNBRQK PNBRQK .";
366 // Check for reentrancy, as example when called from inside
367 // MovePicker that is used also here in move_to_san()
371 RequestPending = true;
376 Position p(*this, thread());
377 string col = (color_of_piece_on(move_from(m)) == BLACK ? ".." : "");
378 cout << "Move is: " << col << move_to_san(p, m) << endl;
380 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
382 cout << "+---+---+---+---+---+---+---+---+" << endl;
383 for (File file = FILE_A; file <= FILE_H; file++)
385 Square sq = make_square(file, rank);
386 Piece piece = piece_on(sq);
387 if (piece == EMPTY && square_color(sq) == WHITE)
390 char col = (color_of_piece_on(sq) == BLACK ? '=' : ' ');
391 cout << '|' << col << pieceLetters[piece] << col;
395 cout << "+---+---+---+---+---+---+---+---+" << endl
396 << "Fen is: " << to_fen() << endl
397 << "Key is: " << st->key << endl;
399 RequestPending = false;
403 /// Position:hidden_checkers<>() returns a bitboard of all pinned (against the
404 /// king) pieces for the given color and for the given pinner type. Or, when
405 /// template parameter FindPinned is false, the pieces of the given color
406 /// candidate for a discovery check against the enemy king.
407 /// Bitboard checkersBB must be already updated when looking for pinners.
409 template<bool FindPinned>
410 Bitboard Position::hidden_checkers(Color c) const {
412 Bitboard result = EmptyBoardBB;
413 Bitboard pinners = pieces_of_color(FindPinned ? opposite_color(c) : c);
415 // Pinned pieces protect our king, dicovery checks attack
417 Square ksq = king_square(FindPinned ? c : opposite_color(c));
419 // Pinners are sliders, not checkers, that give check when candidate pinned is removed
420 pinners &= (pieces(ROOK, QUEEN) & RookPseudoAttacks[ksq]) | (pieces(BISHOP, QUEEN) & BishopPseudoAttacks[ksq]);
422 if (FindPinned && pinners)
423 pinners &= ~st->checkersBB;
427 Square s = pop_1st_bit(&pinners);
428 Bitboard b = squares_between(s, ksq) & occupied_squares();
432 if ( !(b & (b - 1)) // Only one bit set?
433 && (b & pieces_of_color(c))) // Is an our piece?
440 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
441 /// king) pieces for the given color. Note that checkersBB bitboard must
442 /// be already updated.
444 Bitboard Position::pinned_pieces(Color c) const {
446 return hidden_checkers<true>(c);
450 /// Position:discovered_check_candidates() returns a bitboard containing all
451 /// pieces for the given side which are candidates for giving a discovered
452 /// check. Contrary to pinned_pieces() here there is no need of checkersBB
453 /// to be already updated.
455 Bitboard Position::discovered_check_candidates(Color c) const {
457 return hidden_checkers<false>(c);
460 /// Position::attackers_to() computes a bitboard containing all pieces which
461 /// attacks a given square.
463 Bitboard Position::attackers_to(Square s) const {
465 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
466 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
467 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
468 | (attacks_from<ROOK>(s) & pieces(ROOK, QUEEN))
469 | (attacks_from<BISHOP>(s) & pieces(BISHOP, QUEEN))
470 | (attacks_from<KING>(s) & pieces(KING));
473 /// Position::attacks_from() computes a bitboard of all attacks
474 /// of a given piece put in a given square.
476 Bitboard Position::attacks_from(Piece p, Square s) const {
478 assert(square_is_ok(s));
482 case WP: return attacks_from<PAWN>(s, WHITE);
483 case BP: return attacks_from<PAWN>(s, BLACK);
484 case WN: case BN: return attacks_from<KNIGHT>(s);
485 case WB: case BB: return attacks_from<BISHOP>(s);
486 case WR: case BR: return attacks_from<ROOK>(s);
487 case WQ: case BQ: return attacks_from<QUEEN>(s);
488 case WK: case BK: return attacks_from<KING>(s);
495 /// Position::move_attacks_square() tests whether a move from the current
496 /// position attacks a given square.
498 bool Position::move_attacks_square(Move m, Square s) const {
500 assert(move_is_ok(m));
501 assert(square_is_ok(s));
503 Square f = move_from(m), t = move_to(m);
505 assert(square_is_occupied(f));
507 if (bit_is_set(attacks_from(piece_on(f), t), s))
510 // Move the piece and scan for X-ray attacks behind it
511 Bitboard occ = occupied_squares();
512 Color us = color_of_piece_on(f);
515 Bitboard xray = ( (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
516 |(bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN))) & pieces_of_color(us);
518 // If we have attacks we need to verify that are caused by our move
519 // and are not already existent ones.
520 return xray && (xray ^ (xray & attacks_from<QUEEN>(s)));
524 /// Position::find_checkers() computes the checkersBB bitboard, which
525 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
526 /// currently works by calling Position::attackers_to, which is probably
527 /// inefficient. Consider rewriting this function to use the last move
528 /// played, like in non-bitboard versions of Glaurung.
530 void Position::find_checkers() {
532 Color us = side_to_move();
533 st->checkersBB = attackers_to(king_square(us)) & pieces_of_color(opposite_color(us));
537 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
539 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
542 assert(move_is_ok(m));
543 assert(pinned == pinned_pieces(side_to_move()));
545 // Castling moves are checked for legality during move generation.
546 if (move_is_castle(m))
549 Color us = side_to_move();
550 Square from = move_from(m);
552 assert(color_of_piece_on(from) == us);
553 assert(piece_on(king_square(us)) == piece_of_color_and_type(us, KING));
555 // En passant captures are a tricky special case. Because they are
556 // rather uncommon, we do it simply by testing whether the king is attacked
557 // after the move is made
560 Color them = opposite_color(us);
561 Square to = move_to(m);
562 Square capsq = make_square(square_file(to), square_rank(from));
563 Bitboard b = occupied_squares();
564 Square ksq = king_square(us);
566 assert(to == ep_square());
567 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
568 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
569 assert(piece_on(to) == EMPTY);
572 clear_bit(&b, capsq);
575 return !(rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, them))
576 && !(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, them));
579 // If the moving piece is a king, check whether the destination
580 // square is attacked by the opponent.
581 if (type_of_piece_on(from) == KING)
582 return !(attackers_to(move_to(m)) & pieces_of_color(opposite_color(us)));
584 // A non-king move is legal if and only if it is not pinned or it
585 // is moving along the ray towards or away from the king.
587 || !bit_is_set(pinned, from)
588 || (direction_between_squares(from, king_square(us)) == direction_between_squares(move_to(m), king_square(us))));
592 /// Position::pl_move_is_evasion() tests whether a pseudo-legal move is a legal evasion
594 bool Position::pl_move_is_evasion(Move m, Bitboard pinned) const
598 Color us = side_to_move();
599 Square from = move_from(m);
600 Square to = move_to(m);
602 // King moves and en-passant captures are verified in pl_move_is_legal()
603 if (type_of_piece_on(from) == KING || move_is_ep(m))
604 return pl_move_is_legal(m, pinned);
606 Bitboard target = checkers();
607 Square checksq = pop_1st_bit(&target);
609 if (target) // double check ?
612 // Our move must be a blocking evasion or a capture of the checking piece
613 target = squares_between(checksq, king_square(us)) | checkers();
614 return bit_is_set(target, to) && pl_move_is_legal(m, pinned);
618 /// Position::move_is_check() tests whether a pseudo-legal move is a check
620 bool Position::move_is_check(Move m) const {
622 return move_is_check(m, CheckInfo(*this));
625 bool Position::move_is_check(Move m, const CheckInfo& ci) const {
628 assert(move_is_ok(m));
629 assert(ci.dcCandidates == discovered_check_candidates(side_to_move()));
630 assert(color_of_piece_on(move_from(m)) == side_to_move());
631 assert(piece_on(ci.ksq) == piece_of_color_and_type(opposite_color(side_to_move()), KING));
633 Square from = move_from(m);
634 Square to = move_to(m);
635 PieceType pt = type_of_piece_on(from);
638 if (bit_is_set(ci.checkSq[pt], to))
642 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
644 // For pawn and king moves we need to verify also direction
645 if ( (pt != PAWN && pt != KING)
646 ||(direction_between_squares(from, ci.ksq) != direction_between_squares(to, ci.ksq)))
650 // Can we skip the ugly special cases ?
651 if (!move_is_special(m))
654 Color us = side_to_move();
655 Bitboard b = occupied_squares();
657 // Promotion with check ?
658 if (move_is_promotion(m))
662 switch (move_promotion_piece(m))
665 return bit_is_set(attacks_from<KNIGHT>(to), ci.ksq);
667 return bit_is_set(bishop_attacks_bb(to, b), ci.ksq);
669 return bit_is_set(rook_attacks_bb(to, b), ci.ksq);
671 return bit_is_set(queen_attacks_bb(to, b), ci.ksq);
677 // En passant capture with check ? We have already handled the case
678 // of direct checks and ordinary discovered check, the only case we
679 // need to handle is the unusual case of a discovered check through
680 // the captured pawn.
683 Square capsq = make_square(square_file(to), square_rank(from));
685 clear_bit(&b, capsq);
687 return (rook_attacks_bb(ci.ksq, b) & pieces(ROOK, QUEEN, us))
688 ||(bishop_attacks_bb(ci.ksq, b) & pieces(BISHOP, QUEEN, us));
691 // Castling with check ?
692 if (move_is_castle(m))
694 Square kfrom, kto, rfrom, rto;
700 kto = relative_square(us, SQ_G1);
701 rto = relative_square(us, SQ_F1);
703 kto = relative_square(us, SQ_C1);
704 rto = relative_square(us, SQ_D1);
706 clear_bit(&b, kfrom);
707 clear_bit(&b, rfrom);
710 return bit_is_set(rook_attacks_bb(rto, b), ci.ksq);
717 /// Position::do_move() makes a move, and saves all information necessary
718 /// to a StateInfo object. The move is assumed to be legal.
719 /// Pseudo-legal moves should be filtered out before this function is called.
721 void Position::do_move(Move m, StateInfo& newSt) {
724 do_move(m, newSt, ci, move_is_check(m, ci));
727 void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveIsCheck) {
730 assert(move_is_ok(m));
734 // Copy some fields of old state to our new StateInfo object except the
735 // ones which are recalculated from scratch anyway, then switch our state
736 // pointer to point to the new, ready to be updated, state.
737 struct ReducedStateInfo {
738 Key pawnKey, materialKey;
739 int castleRights, rule50, gamePly, pliesFromNull;
745 memcpy(&newSt, st, sizeof(ReducedStateInfo));
749 // Save the current key to the history[] array, in order to be able to
750 // detect repetition draws.
751 history[st->gamePly++] = key;
753 // Update side to move
754 key ^= zobSideToMove;
756 // Increment the 50 moves rule draw counter. Resetting it to zero in the
757 // case of non-reversible moves is taken care of later.
761 if (move_is_castle(m))
768 Color us = side_to_move();
769 Color them = opposite_color(us);
770 Square from = move_from(m);
771 Square to = move_to(m);
772 bool ep = move_is_ep(m);
773 bool pm = move_is_promotion(m);
775 Piece piece = piece_on(from);
776 PieceType pt = type_of_piece(piece);
777 PieceType capture = ep ? PAWN : type_of_piece_on(to);
779 assert(color_of_piece_on(from) == us);
780 assert(color_of_piece_on(to) == them || square_is_empty(to));
781 assert(!(ep || pm) || piece == piece_of_color_and_type(us, PAWN));
782 assert(!pm || relative_rank(us, to) == RANK_8);
785 do_capture_move(key, capture, them, to, ep);
788 key ^= zobrist[us][pt][from] ^ zobrist[us][pt][to];
790 // Reset en passant square
791 if (st->epSquare != SQ_NONE)
793 key ^= zobEp[st->epSquare];
794 st->epSquare = SQ_NONE;
797 // Update castle rights, try to shortcut a common case
798 int cm = castleRightsMask[from] & castleRightsMask[to];
799 if (cm != ALL_CASTLES && ((cm & st->castleRights) != st->castleRights))
801 key ^= zobCastle[st->castleRights];
802 st->castleRights &= castleRightsMask[from];
803 st->castleRights &= castleRightsMask[to];
804 key ^= zobCastle[st->castleRights];
807 // Prefetch TT access as soon as we know key is updated
808 prefetch((char*)TT.first_entry(key));
811 Bitboard move_bb = make_move_bb(from, to);
812 do_move_bb(&(byColorBB[us]), move_bb);
813 do_move_bb(&(byTypeBB[pt]), move_bb);
814 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
816 board[to] = board[from];
819 // Update piece lists, note that index[from] is not updated and
820 // becomes stale. This works as long as index[] is accessed just
821 // by known occupied squares.
822 index[to] = index[from];
823 pieceList[us][pt][index[to]] = to;
825 // If the moving piece was a pawn do some special extra work
828 // Reset rule 50 draw counter
831 // Update pawn hash key
832 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
834 // Set en passant square, only if moved pawn can be captured
835 if ((to ^ from) == 16)
837 if (attacks_from<PAWN>(from + (us == WHITE ? DELTA_N : DELTA_S), us) & pieces(PAWN, them))
839 st->epSquare = Square((int(from) + int(to)) / 2);
840 key ^= zobEp[st->epSquare];
844 if (pm) // promotion ?
846 PieceType promotion = move_promotion_piece(m);
848 assert(promotion >= KNIGHT && promotion <= QUEEN);
850 // Insert promoted piece instead of pawn
851 clear_bit(&(byTypeBB[PAWN]), to);
852 set_bit(&(byTypeBB[promotion]), to);
853 board[to] = piece_of_color_and_type(us, promotion);
855 // Update piece counts
856 pieceCount[us][promotion]++;
857 pieceCount[us][PAWN]--;
859 // Update material key
860 st->materialKey ^= zobrist[us][PAWN][pieceCount[us][PAWN]];
861 st->materialKey ^= zobrist[us][promotion][pieceCount[us][promotion]-1];
863 // Update piece lists, move the last pawn at index[to] position
864 // and shrink the list. Add a new promotion piece to the list.
865 Square lastPawnSquare = pieceList[us][PAWN][pieceCount[us][PAWN]];
866 index[lastPawnSquare] = index[to];
867 pieceList[us][PAWN][index[lastPawnSquare]] = lastPawnSquare;
868 pieceList[us][PAWN][pieceCount[us][PAWN]] = SQ_NONE;
869 index[to] = pieceCount[us][promotion] - 1;
870 pieceList[us][promotion][index[to]] = to;
872 // Partially revert hash keys update
873 key ^= zobrist[us][PAWN][to] ^ zobrist[us][promotion][to];
874 st->pawnKey ^= zobrist[us][PAWN][to];
876 // Partially revert and update incremental scores
877 st->value -= pst(us, PAWN, to);
878 st->value += pst(us, promotion, to);
881 st->npMaterial[us] += piece_value_midgame(promotion);
885 // Update incremental scores
886 st->value += pst_delta(piece, from, to);
889 st->capture = capture;
891 // Update the key with the final value
894 // Update checkers bitboard, piece must be already moved
895 st->checkersBB = EmptyBoardBB;
900 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
904 if (bit_is_set(ci.checkSq[pt], to))
905 st->checkersBB = SetMaskBB[to];
908 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
911 st->checkersBB |= (attacks_from<ROOK>(ci.ksq) & pieces(ROOK, QUEEN, us));
914 st->checkersBB |= (attacks_from<BISHOP>(ci.ksq) & pieces(BISHOP, QUEEN, us));
920 sideToMove = opposite_color(sideToMove);
921 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
927 /// Position::do_capture_move() is a private method used to update captured
928 /// piece info. It is called from the main Position::do_move function.
930 void Position::do_capture_move(Key& key, PieceType capture, Color them, Square to, bool ep) {
932 assert(capture != KING);
936 // If the captured piece was a pawn, update pawn hash key,
937 // otherwise update non-pawn material.
940 if (ep) // en passant ?
942 capsq = (them == BLACK)? (to - DELTA_N) : (to - DELTA_S);
944 assert(to == st->epSquare);
945 assert(relative_rank(opposite_color(them), to) == RANK_6);
946 assert(piece_on(to) == EMPTY);
947 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
949 board[capsq] = EMPTY;
951 st->pawnKey ^= zobrist[them][PAWN][capsq];
954 st->npMaterial[them] -= piece_value_midgame(capture);
956 // Remove captured piece
957 clear_bit(&(byColorBB[them]), capsq);
958 clear_bit(&(byTypeBB[capture]), capsq);
959 clear_bit(&(byTypeBB[0]), capsq);
962 key ^= zobrist[them][capture][capsq];
964 // Update incremental scores
965 st->value -= pst(them, capture, capsq);
967 // Update piece count
968 pieceCount[them][capture]--;
970 // Update material hash key
971 st->materialKey ^= zobrist[them][capture][pieceCount[them][capture]];
973 // Update piece list, move the last piece at index[capsq] position
975 // WARNING: This is a not perfectly revresible operation. When we
976 // will reinsert the captured piece in undo_move() we will put it
977 // at the end of the list and not in its original place, it means
978 // index[] and pieceList[] are not guaranteed to be invariant to a
979 // do_move() + undo_move() sequence.
980 Square lastPieceSquare = pieceList[them][capture][pieceCount[them][capture]];
981 index[lastPieceSquare] = index[capsq];
982 pieceList[them][capture][index[lastPieceSquare]] = lastPieceSquare;
983 pieceList[them][capture][pieceCount[them][capture]] = SQ_NONE;
985 // Reset rule 50 counter
990 /// Position::do_castle_move() is a private method used to make a castling
991 /// move. It is called from the main Position::do_move function. Note that
992 /// castling moves are encoded as "king captures friendly rook" moves, for
993 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
995 void Position::do_castle_move(Move m) {
997 assert(move_is_ok(m));
998 assert(move_is_castle(m));
1000 Color us = side_to_move();
1001 Color them = opposite_color(us);
1003 // Reset capture field
1004 st->capture = NO_PIECE_TYPE;
1006 // Find source squares for king and rook
1007 Square kfrom = move_from(m);
1008 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1011 assert(piece_on(kfrom) == piece_of_color_and_type(us, KING));
1012 assert(piece_on(rfrom) == piece_of_color_and_type(us, ROOK));
1014 // Find destination squares for king and rook
1015 if (rfrom > kfrom) // O-O
1017 kto = relative_square(us, SQ_G1);
1018 rto = relative_square(us, SQ_F1);
1020 kto = relative_square(us, SQ_C1);
1021 rto = relative_square(us, SQ_D1);
1024 // Remove pieces from source squares:
1025 clear_bit(&(byColorBB[us]), kfrom);
1026 clear_bit(&(byTypeBB[KING]), kfrom);
1027 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1028 clear_bit(&(byColorBB[us]), rfrom);
1029 clear_bit(&(byTypeBB[ROOK]), rfrom);
1030 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1032 // Put pieces on destination squares:
1033 set_bit(&(byColorBB[us]), kto);
1034 set_bit(&(byTypeBB[KING]), kto);
1035 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1036 set_bit(&(byColorBB[us]), rto);
1037 set_bit(&(byTypeBB[ROOK]), rto);
1038 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1040 // Update board array
1041 Piece king = piece_of_color_and_type(us, KING);
1042 Piece rook = piece_of_color_and_type(us, ROOK);
1043 board[kfrom] = board[rfrom] = EMPTY;
1047 // Update piece lists
1048 pieceList[us][KING][index[kfrom]] = kto;
1049 pieceList[us][ROOK][index[rfrom]] = rto;
1050 int tmp = index[rfrom]; // In Chess960 could be rto == kfrom
1051 index[kto] = index[kfrom];
1054 // Update incremental scores
1055 st->value += pst_delta(king, kfrom, kto);
1056 st->value += pst_delta(rook, rfrom, rto);
1059 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1060 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1062 // Clear en passant square
1063 if (st->epSquare != SQ_NONE)
1065 st->key ^= zobEp[st->epSquare];
1066 st->epSquare = SQ_NONE;
1069 // Update castling rights
1070 st->key ^= zobCastle[st->castleRights];
1071 st->castleRights &= castleRightsMask[kfrom];
1072 st->key ^= zobCastle[st->castleRights];
1074 // Reset rule 50 counter
1077 // Update checkers BB
1078 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
1081 sideToMove = opposite_color(sideToMove);
1082 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1088 /// Position::undo_move() unmakes a move. When it returns, the position should
1089 /// be restored to exactly the same state as before the move was made.
1091 void Position::undo_move(Move m) {
1094 assert(move_is_ok(m));
1096 sideToMove = opposite_color(sideToMove);
1098 if (move_is_castle(m))
1100 undo_castle_move(m);
1104 Color us = side_to_move();
1105 Color them = opposite_color(us);
1106 Square from = move_from(m);
1107 Square to = move_to(m);
1108 bool ep = move_is_ep(m);
1109 bool pm = move_is_promotion(m);
1111 PieceType pt = type_of_piece_on(to);
1113 assert(square_is_empty(from));
1114 assert(color_of_piece_on(to) == us);
1115 assert(!pm || relative_rank(us, to) == RANK_8);
1116 assert(!ep || to == st->previous->epSquare);
1117 assert(!ep || relative_rank(us, to) == RANK_6);
1118 assert(!ep || piece_on(to) == piece_of_color_and_type(us, PAWN));
1120 if (pm) // promotion ?
1122 PieceType promotion = move_promotion_piece(m);
1125 assert(promotion >= KNIGHT && promotion <= QUEEN);
1126 assert(piece_on(to) == piece_of_color_and_type(us, promotion));
1128 // Replace promoted piece with a pawn
1129 clear_bit(&(byTypeBB[promotion]), to);
1130 set_bit(&(byTypeBB[PAWN]), to);
1132 // Update piece counts
1133 pieceCount[us][promotion]--;
1134 pieceCount[us][PAWN]++;
1136 // Update piece list replacing promotion piece with a pawn
1137 Square lastPromotionSquare = pieceList[us][promotion][pieceCount[us][promotion]];
1138 index[lastPromotionSquare] = index[to];
1139 pieceList[us][promotion][index[lastPromotionSquare]] = lastPromotionSquare;
1140 pieceList[us][promotion][pieceCount[us][promotion]] = SQ_NONE;
1141 index[to] = pieceCount[us][PAWN] - 1;
1142 pieceList[us][PAWN][index[to]] = to;
1145 // Put the piece back at the source square
1146 Bitboard move_bb = make_move_bb(to, from);
1147 do_move_bb(&(byColorBB[us]), move_bb);
1148 do_move_bb(&(byTypeBB[pt]), move_bb);
1149 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
1151 board[from] = piece_of_color_and_type(us, pt);
1154 // Update piece list
1155 index[from] = index[to];
1156 pieceList[us][pt][index[from]] = from;
1163 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1165 assert(st->capture != KING);
1166 assert(!ep || square_is_empty(capsq));
1168 // Restore the captured piece
1169 set_bit(&(byColorBB[them]), capsq);
1170 set_bit(&(byTypeBB[st->capture]), capsq);
1171 set_bit(&(byTypeBB[0]), capsq);
1173 board[capsq] = piece_of_color_and_type(them, st->capture);
1175 // Update piece count
1176 pieceCount[them][st->capture]++;
1178 // Update piece list, add a new captured piece in capsq square
1179 index[capsq] = pieceCount[them][st->capture] - 1;
1180 pieceList[them][st->capture][index[capsq]] = capsq;
1183 // Finally point our state pointer back to the previous state
1190 /// Position::undo_castle_move() is a private method used to unmake a castling
1191 /// move. It is called from the main Position::undo_move function. Note that
1192 /// castling moves are encoded as "king captures friendly rook" moves, for
1193 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1195 void Position::undo_castle_move(Move m) {
1197 assert(move_is_ok(m));
1198 assert(move_is_castle(m));
1200 // When we have arrived here, some work has already been done by
1201 // Position::undo_move. In particular, the side to move has been switched,
1202 // so the code below is correct.
1203 Color us = side_to_move();
1205 // Find source squares for king and rook
1206 Square kfrom = move_from(m);
1207 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1210 // Find destination squares for king and rook
1211 if (rfrom > kfrom) // O-O
1213 kto = relative_square(us, SQ_G1);
1214 rto = relative_square(us, SQ_F1);
1216 kto = relative_square(us, SQ_C1);
1217 rto = relative_square(us, SQ_D1);
1220 assert(piece_on(kto) == piece_of_color_and_type(us, KING));
1221 assert(piece_on(rto) == piece_of_color_and_type(us, ROOK));
1223 // Remove pieces from destination squares:
1224 clear_bit(&(byColorBB[us]), kto);
1225 clear_bit(&(byTypeBB[KING]), kto);
1226 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1227 clear_bit(&(byColorBB[us]), rto);
1228 clear_bit(&(byTypeBB[ROOK]), rto);
1229 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1231 // Put pieces on source squares:
1232 set_bit(&(byColorBB[us]), kfrom);
1233 set_bit(&(byTypeBB[KING]), kfrom);
1234 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1235 set_bit(&(byColorBB[us]), rfrom);
1236 set_bit(&(byTypeBB[ROOK]), rfrom);
1237 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1240 board[rto] = board[kto] = EMPTY;
1241 board[rfrom] = piece_of_color_and_type(us, ROOK);
1242 board[kfrom] = piece_of_color_and_type(us, KING);
1244 // Update piece lists
1245 pieceList[us][KING][index[kto]] = kfrom;
1246 pieceList[us][ROOK][index[rto]] = rfrom;
1247 int tmp = index[rto]; // In Chess960 could be rto == kfrom
1248 index[kfrom] = index[kto];
1251 // Finally point our state pointer back to the previous state
1258 /// Position::do_null_move makes() a "null move": It switches the side to move
1259 /// and updates the hash key without executing any move on the board.
1261 void Position::do_null_move(StateInfo& backupSt) {
1264 assert(!is_check());
1266 // Back up the information necessary to undo the null move to the supplied
1267 // StateInfo object.
1268 // Note that differently from normal case here backupSt is actually used as
1269 // a backup storage not as a new state to be used.
1270 backupSt.key = st->key;
1271 backupSt.epSquare = st->epSquare;
1272 backupSt.value = st->value;
1273 backupSt.previous = st->previous;
1274 backupSt.pliesFromNull = st->pliesFromNull;
1275 st->previous = &backupSt;
1277 // Save the current key to the history[] array, in order to be able to
1278 // detect repetition draws.
1279 history[st->gamePly++] = st->key;
1281 // Update the necessary information
1282 if (st->epSquare != SQ_NONE)
1283 st->key ^= zobEp[st->epSquare];
1285 st->key ^= zobSideToMove;
1286 prefetch((char*)TT.first_entry(st->key));
1288 sideToMove = opposite_color(sideToMove);
1289 st->epSquare = SQ_NONE;
1291 st->pliesFromNull = 0;
1292 st->value += (sideToMove == WHITE) ? TempoValue : -TempoValue;
1296 /// Position::undo_null_move() unmakes a "null move".
1298 void Position::undo_null_move() {
1301 assert(!is_check());
1303 // Restore information from the our backup StateInfo object
1304 StateInfo* backupSt = st->previous;
1305 st->key = backupSt->key;
1306 st->epSquare = backupSt->epSquare;
1307 st->value = backupSt->value;
1308 st->previous = backupSt->previous;
1309 st->pliesFromNull = backupSt->pliesFromNull;
1311 // Update the necessary information
1312 sideToMove = opposite_color(sideToMove);
1318 /// Position::see() is a static exchange evaluator: It tries to estimate the
1319 /// material gain or loss resulting from a move. There are three versions of
1320 /// this function: One which takes a destination square as input, one takes a
1321 /// move, and one which takes a 'from' and a 'to' square. The function does
1322 /// not yet understand promotions captures.
1324 int Position::see(Square to) const {
1326 assert(square_is_ok(to));
1327 return see(SQ_NONE, to);
1330 int Position::see(Move m) const {
1332 assert(move_is_ok(m));
1333 return see(move_from(m), move_to(m));
1336 int Position::see_sign(Move m) const {
1338 assert(move_is_ok(m));
1340 Square from = move_from(m);
1341 Square to = move_to(m);
1343 // Early return if SEE cannot be negative because captured piece value
1344 // is not less then capturing one. Note that king moves always return
1345 // here because king midgame value is set to 0.
1346 if (midgame_value_of_piece_on(to) >= midgame_value_of_piece_on(from))
1349 return see(from, to);
1352 int Position::see(Square from, Square to) const {
1355 static const int seeValues[18] = {
1356 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1357 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1358 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1359 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1363 Bitboard attackers, stmAttackers, b;
1365 assert(square_is_ok(from) || from == SQ_NONE);
1366 assert(square_is_ok(to));
1368 // Initialize colors
1369 Color us = (from != SQ_NONE ? color_of_piece_on(from) : opposite_color(color_of_piece_on(to)));
1370 Color them = opposite_color(us);
1372 // Initialize pieces
1373 Piece piece = piece_on(from);
1374 Piece capture = piece_on(to);
1375 Bitboard occ = occupied_squares();
1377 // King cannot be recaptured
1378 if (type_of_piece(piece) == KING)
1379 return seeValues[capture];
1381 // Handle en passant moves
1382 if (st->epSquare == to && type_of_piece_on(from) == PAWN)
1384 assert(capture == EMPTY);
1386 Square capQq = (side_to_move() == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1387 capture = piece_on(capQq);
1388 assert(type_of_piece_on(capQq) == PAWN);
1390 // Remove the captured pawn
1391 clear_bit(&occ, capQq);
1396 // Find all attackers to the destination square, with the moving piece
1397 // removed, but possibly an X-ray attacker added behind it.
1398 clear_bit(&occ, from);
1399 attackers = (rook_attacks_bb(to, occ) & pieces(ROOK, QUEEN))
1400 | (bishop_attacks_bb(to, occ) & pieces(BISHOP, QUEEN))
1401 | (attacks_from<KNIGHT>(to) & pieces(KNIGHT))
1402 | (attacks_from<KING>(to) & pieces(KING))
1403 | (attacks_from<PAWN>(to, WHITE) & pieces(PAWN, BLACK))
1404 | (attacks_from<PAWN>(to, BLACK) & pieces(PAWN, WHITE));
1406 if (from != SQ_NONE)
1409 // If we don't have any attacker we are finished
1410 if ((attackers & pieces_of_color(us)) == EmptyBoardBB)
1413 // Locate the least valuable attacker to the destination square
1414 // and use it to initialize from square.
1415 stmAttackers = attackers & pieces_of_color(us);
1417 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1420 from = first_1(stmAttackers & pieces(pt));
1421 piece = piece_on(from);
1424 // If the opponent has no attackers we are finished
1425 stmAttackers = attackers & pieces_of_color(them);
1427 return seeValues[capture];
1429 attackers &= occ; // Remove the moving piece
1431 // The destination square is defended, which makes things rather more
1432 // difficult to compute. We proceed by building up a "swap list" containing
1433 // the material gain or loss at each stop in a sequence of captures to the
1434 // destination square, where the sides alternately capture, and always
1435 // capture with the least valuable piece. After each capture, we look for
1436 // new X-ray attacks from behind the capturing piece.
1437 int lastCapturingPieceValue = seeValues[piece];
1438 int swapList[32], n = 1;
1442 swapList[0] = seeValues[capture];
1445 // Locate the least valuable attacker for the side to move. The loop
1446 // below looks like it is potentially infinite, but it isn't. We know
1447 // that the side to move still has at least one attacker left.
1448 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1451 // Remove the attacker we just found from the 'attackers' bitboard,
1452 // and scan for new X-ray attacks behind the attacker.
1453 b = stmAttackers & pieces(pt);
1454 occ ^= (b & (~b + 1));
1455 attackers |= (rook_attacks_bb(to, occ) & pieces(ROOK, QUEEN))
1456 | (bishop_attacks_bb(to, occ) & pieces(BISHOP, QUEEN));
1460 // Add the new entry to the swap list
1462 swapList[n] = -swapList[n - 1] + lastCapturingPieceValue;
1465 // Remember the value of the capturing piece, and change the side to move
1466 // before beginning the next iteration
1467 lastCapturingPieceValue = seeValues[pt];
1468 c = opposite_color(c);
1469 stmAttackers = attackers & pieces_of_color(c);
1471 // Stop after a king capture
1472 if (pt == KING && stmAttackers)
1475 swapList[n++] = QueenValueMidgame*10;
1478 } while (stmAttackers);
1480 // Having built the swap list, we negamax through it to find the best
1481 // achievable score from the point of view of the side to move
1483 swapList[n-1] = Min(-swapList[n], swapList[n-1]);
1489 /// Position::clear() erases the position object to a pristine state, with an
1490 /// empty board, white to move, and no castling rights.
1492 void Position::clear() {
1495 memset(st, 0, sizeof(StateInfo));
1496 st->epSquare = SQ_NONE;
1498 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1499 memset(byTypeBB, 0, sizeof(Bitboard) * 8);
1500 memset(pieceCount, 0, sizeof(int) * 2 * 8);
1501 memset(index, 0, sizeof(int) * 64);
1503 for (int i = 0; i < 64; i++)
1506 for (int i = 0; i < 8; i++)
1507 for (int j = 0; j < 16; j++)
1508 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1510 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
1511 castleRightsMask[sq] = ALL_CASTLES;
1514 initialKFile = FILE_E;
1515 initialKRFile = FILE_H;
1516 initialQRFile = FILE_A;
1520 /// Position::reset_game_ply() simply sets gamePly to 0. It is used from the
1521 /// UCI interface code, whenever a non-reversible move is made in a
1522 /// 'position fen <fen> moves m1 m2 ...' command. This makes it possible
1523 /// for the program to handle games of arbitrary length, as long as the GUI
1524 /// handles draws by the 50 move rule correctly.
1526 void Position::reset_game_ply() {
1532 /// Position::put_piece() puts a piece on the given square of the board,
1533 /// updating the board array, bitboards, and piece counts.
1535 void Position::put_piece(Piece p, Square s) {
1537 Color c = color_of_piece(p);
1538 PieceType pt = type_of_piece(p);
1541 index[s] = pieceCount[c][pt];
1542 pieceList[c][pt][index[s]] = s;
1544 set_bit(&(byTypeBB[pt]), s);
1545 set_bit(&(byColorBB[c]), s);
1546 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1548 pieceCount[c][pt]++;
1552 /// Position::allow_oo() gives the given side the right to castle kingside.
1553 /// Used when setting castling rights during parsing of FEN strings.
1555 void Position::allow_oo(Color c) {
1557 st->castleRights |= (1 + int(c));
1561 /// Position::allow_ooo() gives the given side the right to castle queenside.
1562 /// Used when setting castling rights during parsing of FEN strings.
1564 void Position::allow_ooo(Color c) {
1566 st->castleRights |= (4 + 4*int(c));
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 = Key(0ULL);
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 result ^= zobCastle[st->castleRights];
1587 if (side_to_move() == BLACK)
1588 result ^= zobSideToMove;
1594 /// Position::compute_pawn_key() computes the hash key of the position. The
1595 /// hash key is usually updated incrementally as moves are made and unmade,
1596 /// the compute_pawn_key() function is only used when a new position is set
1597 /// up, and to verify the correctness of the pawn hash key when running in
1600 Key Position::compute_pawn_key() const {
1602 Key result = Key(0ULL);
1606 for (Color c = WHITE; c <= BLACK; c++)
1608 b = pieces(PAWN, c);
1611 s = pop_1st_bit(&b);
1612 result ^= zobrist[c][PAWN][s];
1619 /// Position::compute_material_key() computes the hash key of the position.
1620 /// The hash key is usually updated incrementally as moves are made and unmade,
1621 /// the compute_material_key() function is only used when a new position is set
1622 /// up, and to verify the correctness of the material hash key when running in
1625 Key Position::compute_material_key() const {
1627 Key result = Key(0ULL);
1628 for (Color c = WHITE; c <= BLACK; c++)
1629 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1631 int count = piece_count(c, pt);
1632 for (int i = 0; i < count; i++)
1633 result ^= zobrist[c][pt][i];
1639 /// Position::compute_value() compute the incremental scores for the middle
1640 /// game and the endgame. These functions are used to initialize the incremental
1641 /// scores when a new position is set up, and to verify that the scores are correctly
1642 /// updated by do_move and undo_move when the program is running in debug mode.
1643 Score Position::compute_value() const {
1645 Score result = make_score(0, 0);
1649 for (Color c = WHITE; c <= BLACK; c++)
1650 for (PieceType pt = PAWN; pt <= KING; pt++)
1655 s = pop_1st_bit(&b);
1656 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1657 result += pst(c, pt, s);
1661 result += (side_to_move() == WHITE ? TempoValue / 2 : -TempoValue / 2);
1666 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1667 /// game material score for the given side. Material scores are updated
1668 /// incrementally during the search, this function is only used while
1669 /// initializing a new Position object.
1671 Value Position::compute_non_pawn_material(Color c) const {
1673 Value result = Value(0);
1675 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1677 Bitboard b = pieces(pt, c);
1680 assert(piece_on(first_1(b)) == piece_of_color_and_type(c, pt));
1682 result += piece_value_midgame(pt);
1689 /// Position::is_draw() tests whether the position is drawn by material,
1690 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1691 /// must be done by the search.
1692 // FIXME: Currently we are not handling 50 move rule correctly when in check
1694 bool Position::is_draw() const {
1696 // Draw by material?
1698 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1701 // Draw by the 50 moves rule?
1702 if (st->rule50 > 100 || (st->rule50 == 100 && !is_check()))
1705 // Draw by repetition?
1706 for (int i = 4, e = Min(Min(st->gamePly, st->rule50), st->pliesFromNull); i <= e; i += 2)
1707 if (history[st->gamePly - i] == st->key)
1714 /// Position::is_mate() returns true or false depending on whether the
1715 /// side to move is checkmated.
1717 bool Position::is_mate() const {
1719 MoveStack moves[256];
1720 return is_check() && (generate_moves(*this, moves, false) == moves);
1724 /// Position::has_mate_threat() tests whether a given color has a mate in one
1725 /// from the current position.
1727 bool Position::has_mate_threat(Color c) {
1730 Color stm = side_to_move();
1735 // If the input color is not equal to the side to move, do a null move
1739 MoveStack mlist[120];
1740 bool result = false;
1741 Bitboard pinned = pinned_pieces(sideToMove);
1743 // Generate pseudo-legal non-capture and capture check moves
1744 MoveStack* last = generate_non_capture_checks(*this, mlist);
1745 last = generate_captures(*this, last);
1747 // Loop through the moves, and see if one of them is mate
1748 for (MoveStack* cur = mlist; cur != last; cur++)
1750 Move move = cur->move;
1751 if (!pl_move_is_legal(move, pinned))
1761 // Undo null move, if necessary
1769 /// Position::init_zobrist() is a static member function which initializes the
1770 /// various arrays used to compute hash keys.
1772 void Position::init_zobrist() {
1774 for (int i = 0; i < 2; i++)
1775 for (int j = 0; j < 8; j++)
1776 for (int k = 0; k < 64; k++)
1777 zobrist[i][j][k] = Key(genrand_int64());
1779 for (int i = 0; i < 64; i++)
1780 zobEp[i] = Key(genrand_int64());
1782 for (int i = 0; i < 16; i++)
1783 zobCastle[i] = genrand_int64();
1785 zobSideToMove = genrand_int64();
1786 zobExclusion = genrand_int64();
1790 /// Position::init_piece_square_tables() initializes the piece square tables.
1791 /// This is a two-step operation:
1792 /// First, the white halves of the tables are
1793 /// copied from the MgPST[][] and EgPST[][] arrays.
1794 /// Second, the black halves of the tables are initialized by mirroring
1795 /// and changing the sign of the corresponding white scores.
1797 void Position::init_piece_square_tables() {
1799 for (Square s = SQ_A1; s <= SQ_H8; s++)
1800 for (Piece p = WP; p <= WK; p++)
1801 PieceSquareTable[p][s] = make_score(MgPST[p][s], EgPST[p][s]);
1803 for (Square s = SQ_A1; s <= SQ_H8; s++)
1804 for (Piece p = BP; p <= BK; p++)
1805 PieceSquareTable[p][s] = -PieceSquareTable[p-8][flip_square(s)];
1809 /// Position::flipped_copy() makes a copy of the input position, but with
1810 /// the white and black sides reversed. This is only useful for debugging,
1811 /// especially for finding evaluation symmetry bugs.
1813 void Position::flipped_copy(const Position& pos) {
1815 assert(pos.is_ok());
1818 threadID = pos.thread();
1821 for (Square s = SQ_A1; s <= SQ_H8; s++)
1822 if (!pos.square_is_empty(s))
1823 put_piece(Piece(int(pos.piece_on(s)) ^ 8), flip_square(s));
1826 sideToMove = opposite_color(pos.side_to_move());
1829 if (pos.can_castle_kingside(WHITE)) allow_oo(BLACK);
1830 if (pos.can_castle_queenside(WHITE)) allow_ooo(BLACK);
1831 if (pos.can_castle_kingside(BLACK)) allow_oo(WHITE);
1832 if (pos.can_castle_queenside(BLACK)) allow_ooo(WHITE);
1834 initialKFile = pos.initialKFile;
1835 initialKRFile = pos.initialKRFile;
1836 initialQRFile = pos.initialQRFile;
1838 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
1839 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
1840 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
1841 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
1842 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
1843 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
1845 // En passant square
1846 if (pos.st->epSquare != SQ_NONE)
1847 st->epSquare = flip_square(pos.st->epSquare);
1853 st->key = compute_key();
1854 st->pawnKey = compute_pawn_key();
1855 st->materialKey = compute_material_key();
1857 // Incremental scores
1858 st->value = compute_value();
1861 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
1862 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
1868 /// Position::is_ok() performs some consitency checks for the position object.
1869 /// This is meant to be helpful when debugging.
1871 bool Position::is_ok(int* failedStep) const {
1873 // What features of the position should be verified?
1874 static const bool debugBitboards = false;
1875 static const bool debugKingCount = false;
1876 static const bool debugKingCapture = false;
1877 static const bool debugCheckerCount = false;
1878 static const bool debugKey = false;
1879 static const bool debugMaterialKey = false;
1880 static const bool debugPawnKey = false;
1881 static const bool debugIncrementalEval = false;
1882 static const bool debugNonPawnMaterial = false;
1883 static const bool debugPieceCounts = false;
1884 static const bool debugPieceList = false;
1885 static const bool debugCastleSquares = false;
1887 if (failedStep) *failedStep = 1;
1890 if (!color_is_ok(side_to_move()))
1893 // Are the king squares in the position correct?
1894 if (failedStep) (*failedStep)++;
1895 if (piece_on(king_square(WHITE)) != WK)
1898 if (failedStep) (*failedStep)++;
1899 if (piece_on(king_square(BLACK)) != BK)
1903 if (failedStep) (*failedStep)++;
1904 if (!file_is_ok(initialKRFile))
1907 if (!file_is_ok(initialQRFile))
1910 // Do both sides have exactly one king?
1911 if (failedStep) (*failedStep)++;
1914 int kingCount[2] = {0, 0};
1915 for (Square s = SQ_A1; s <= SQ_H8; s++)
1916 if (type_of_piece_on(s) == KING)
1917 kingCount[color_of_piece_on(s)]++;
1919 if (kingCount[0] != 1 || kingCount[1] != 1)
1923 // Can the side to move capture the opponent's king?
1924 if (failedStep) (*failedStep)++;
1925 if (debugKingCapture)
1927 Color us = side_to_move();
1928 Color them = opposite_color(us);
1929 Square ksq = king_square(them);
1930 if (attackers_to(ksq) & pieces_of_color(us))
1934 // Is there more than 2 checkers?
1935 if (failedStep) (*failedStep)++;
1936 if (debugCheckerCount && count_1s(st->checkersBB) > 2)
1940 if (failedStep) (*failedStep)++;
1943 // The intersection of the white and black pieces must be empty
1944 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
1947 // The union of the white and black pieces must be equal to all
1949 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
1952 // Separate piece type bitboards must have empty intersections
1953 for (PieceType p1 = PAWN; p1 <= KING; p1++)
1954 for (PieceType p2 = PAWN; p2 <= KING; p2++)
1955 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1959 // En passant square OK?
1960 if (failedStep) (*failedStep)++;
1961 if (ep_square() != SQ_NONE)
1963 // The en passant square must be on rank 6, from the point of view of the
1965 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
1970 if (failedStep) (*failedStep)++;
1971 if (debugKey && st->key != compute_key())
1974 // Pawn hash key OK?
1975 if (failedStep) (*failedStep)++;
1976 if (debugPawnKey && st->pawnKey != compute_pawn_key())
1979 // Material hash key OK?
1980 if (failedStep) (*failedStep)++;
1981 if (debugMaterialKey && st->materialKey != compute_material_key())
1984 // Incremental eval OK?
1985 if (failedStep) (*failedStep)++;
1986 if (debugIncrementalEval && st->value != compute_value())
1989 // Non-pawn material OK?
1990 if (failedStep) (*failedStep)++;
1991 if (debugNonPawnMaterial)
1993 if (st->npMaterial[WHITE] != compute_non_pawn_material(WHITE))
1996 if (st->npMaterial[BLACK] != compute_non_pawn_material(BLACK))
2001 if (failedStep) (*failedStep)++;
2002 if (debugPieceCounts)
2003 for (Color c = WHITE; c <= BLACK; c++)
2004 for (PieceType pt = PAWN; pt <= KING; pt++)
2005 if (pieceCount[c][pt] != count_1s(pieces(pt, c)))
2008 if (failedStep) (*failedStep)++;
2011 for (Color c = WHITE; c <= BLACK; c++)
2012 for (PieceType pt = PAWN; pt <= KING; pt++)
2013 for (int i = 0; i < pieceCount[c][pt]; i++)
2015 if (piece_on(piece_list(c, pt, i)) != piece_of_color_and_type(c, pt))
2018 if (index[piece_list(c, pt, i)] != i)
2023 if (failedStep) (*failedStep)++;
2024 if (debugCastleSquares) {
2025 for (Color c = WHITE; c <= BLACK; c++) {
2026 if (can_castle_kingside(c) && piece_on(initial_kr_square(c)) != piece_of_color_and_type(c, ROOK))
2028 if (can_castle_queenside(c) && piece_on(initial_qr_square(c)) != piece_of_color_and_type(c, ROOK))
2031 if (castleRightsMask[initial_kr_square(WHITE)] != (ALL_CASTLES ^ WHITE_OO))
2033 if (castleRightsMask[initial_qr_square(WHITE)] != (ALL_CASTLES ^ WHITE_OOO))
2035 if (castleRightsMask[initial_kr_square(BLACK)] != (ALL_CASTLES ^ BLACK_OO))
2037 if (castleRightsMask[initial_qr_square(BLACK)] != (ALL_CASTLES ^ BLACK_OOO))
2041 if (failedStep) *failedStep = 0;