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/>.
33 #include "ucioption.h"
39 Key Position::zobrist[2][8][64];
40 Key Position::zobEp[64];
41 Key Position::zobCastle[16];
42 Key Position::zobSideToMove;
43 Key Position::zobExclusion;
45 Score Position::PieceSquareTable[16][64];
47 // Material values arrays, indexed by Piece
48 const Value PieceValueMidgame[17] = {
50 PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
51 RookValueMidgame, QueenValueMidgame,
52 VALUE_ZERO, VALUE_ZERO, VALUE_ZERO,
53 PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
54 RookValueMidgame, QueenValueMidgame
57 const Value PieceValueEndgame[17] = {
59 PawnValueEndgame, KnightValueEndgame, BishopValueEndgame,
60 RookValueEndgame, QueenValueEndgame,
61 VALUE_ZERO, VALUE_ZERO, VALUE_ZERO,
62 PawnValueEndgame, KnightValueEndgame, BishopValueEndgame,
63 RookValueEndgame, QueenValueEndgame
69 // Bonus for having the side to move (modified by Joona Kiiski)
70 const Score TempoValue = make_score(48, 22);
72 // To convert a Piece to and from a FEN char
73 const string PieceToChar(".PNBRQK pnbrqk ");
79 CheckInfo::CheckInfo(const Position& pos) {
81 Color us = pos.side_to_move();
82 Color them = opposite_color(us);
83 Square ksq = pos.king_square(them);
85 dcCandidates = pos.discovered_check_candidates(us);
86 pinned = pos.pinned_pieces(us);
88 checkSq[PAWN] = pos.attacks_from<PAWN>(ksq, them);
89 checkSq[KNIGHT] = pos.attacks_from<KNIGHT>(ksq);
90 checkSq[BISHOP] = pos.attacks_from<BISHOP>(ksq);
91 checkSq[ROOK] = pos.attacks_from<ROOK>(ksq);
92 checkSq[QUEEN] = checkSq[BISHOP] | checkSq[ROOK];
93 checkSq[KING] = EmptyBoardBB;
97 /// Position c'tors. Here we always create a copy of the original position
98 /// or the FEN string, we want the new born Position object do not depend
99 /// on any external data so we detach state pointer from the source one.
101 Position::Position(const Position& pos, int th) {
103 memcpy(this, &pos, sizeof(Position));
104 detach(); // Always detach() in copy c'tor to avoid surprises
109 Position::Position(const string& fen, bool isChess960, int th) {
111 from_fen(fen, isChess960);
116 /// Position::detach() copies the content of the current state and castling
117 /// masks inside the position itself. This is needed when the st pointee could
118 /// become stale, as example because the caller is about to going out of scope.
120 void Position::detach() {
124 st->previous = NULL; // As a safe guard
128 /// Position::from_fen() initializes the position object with the given FEN
129 /// string. This function is not very robust - make sure that input FENs are
130 /// correct (this is assumed to be the responsibility of the GUI).
132 void Position::from_fen(const string& fen, bool isChess960) {
134 A FEN string defines a particular position using only the ASCII character set.
136 A FEN string contains six fields. The separator between fields is a space. The fields are:
138 1) Piece placement (from white's perspective). Each rank is described, starting with rank 8 and ending
139 with rank 1; within each rank, the contents of each square are described from file A through file H.
140 Following the Standard Algebraic Notation (SAN), each piece is identified by a single letter taken
141 from the standard English names. White pieces are designated using upper-case letters ("PNBRQK")
142 while Black take lowercase ("pnbrqk"). Blank squares are noted using digits 1 through 8 (the number
143 of blank squares), and "/" separate ranks.
145 2) Active color. "w" means white moves next, "b" means black.
147 3) Castling availability. If neither side can castle, this is "-". Otherwise, this has one or more
148 letters: "K" (White can castle kingside), "Q" (White can castle queenside), "k" (Black can castle
149 kingside), and/or "q" (Black can castle queenside).
151 4) En passant target square in algebraic notation. If there's no en passant target square, this is "-".
152 If a pawn has just made a 2-square move, this is the position "behind" the pawn. This is recorded
153 regardless of whether there is a pawn in position to make an en passant capture.
155 5) Halfmove clock: This is the number of halfmoves since the last pawn advance or capture. This is used
156 to determine if a draw can be claimed under the fifty-move rule.
158 6) Fullmove number: The number of the full move. It starts at 1, and is incremented after Black's move.
161 char col, row, token;
164 std::istringstream ss(fen);
167 ss >> token >> std::noskipws;
169 // 1. Piece placement
170 while (!isspace(token))
173 sq -= Square(16); // Jump back of 2 rows
175 else if (isdigit(token))
176 sq += Square(token - '0'); // Skip the given number of files
178 else if ((p = PieceToChar.find(token)) != string::npos)
180 put_piece(Piece(p), sq);
189 sideToMove = (token == 'w' ? WHITE : BLACK);
192 // 3. Castling availability
193 while ((ss >> token) && !isspace(token))
194 set_castling_rights(token);
196 // 4. En passant square. Ignore if no pawn capture is possible
197 if ( ((ss >> col) && (col >= 'a' && col <= 'h'))
198 && ((ss >> row) && (row == '3' || row == '6')))
200 st->epSquare = make_square(File(col - 'a'), Rank(row - '1'));
201 Color them = opposite_color(sideToMove);
203 if (!(attacks_from<PAWN>(st->epSquare, them) & pieces(PAWN, sideToMove)))
204 st->epSquare = SQ_NONE;
207 // 5-6. Halfmove clock and fullmove number
208 ss >> std::skipws >> st->rule50 >> fullMoves;
210 // Various initialisations
211 chess960 = isChess960;
214 st->key = compute_key();
215 st->pawnKey = compute_pawn_key();
216 st->materialKey = compute_material_key();
217 st->value = compute_value();
218 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
219 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
223 /// Position::set_castle() is an helper function used to set
224 /// correct castling related flags.
226 void Position::set_castle(int f, Square ksq, Square rsq) {
228 st->castleRights |= f;
229 castleRightsMask[ksq] ^= f;
230 castleRightsMask[rsq] ^= f;
231 castleRookSquare[f] = rsq;
235 /// Position::set_castling_rights() sets castling parameters castling avaiability.
236 /// This function is compatible with 3 standards: Normal FEN standard, Shredder-FEN
237 /// that uses the letters of the columns on which the rooks began the game instead
238 /// of KQkq and also X-FEN standard that, in case of Chess960, if an inner Rook is
239 /// associated with the castling right, the traditional castling tag will be replaced
240 /// by the file letter of the involved rook as for the Shredder-FEN.
242 void Position::set_castling_rights(char token) {
244 Color c = islower(token) ? BLACK : WHITE;
246 Square sqA = relative_square(c, SQ_A1);
247 Square sqH = relative_square(c, SQ_H1);
249 Square rsq, ksq = king_square(c);
250 token = toupper(token);
253 for (rsq = sqH; piece_on(rsq) != make_piece(c, ROOK); rsq--) {}
255 else if (token == 'Q')
256 for (rsq = sqA; piece_on(rsq) != make_piece(c, ROOK); rsq++) {}
258 else if (token >= 'A' && token <= 'H')
259 rsq = make_square(File(token - 'A'), relative_rank(c, RANK_1));
263 if (square_file(rsq) < square_file(ksq))
264 set_castle(WHITE_OOO << c, ksq, rsq);
266 set_castle(WHITE_OO << c, ksq, rsq);
270 /// Position::to_fen() returns a FEN representation of the position. In case
271 /// of Chess960 the Shredder-FEN notation is used. Mainly a debugging function.
273 const string Position::to_fen() const {
279 for (Rank rank = RANK_8; rank >= RANK_1; rank--, fen += '/')
283 for (File file = FILE_A; file <= FILE_H; file++)
285 sq = make_square(file, rank);
287 if (square_is_occupied(sq))
294 fen += PieceToChar[piece_on(sq)];
303 fen += (sideToMove == WHITE ? " w " : " b ");
305 if (st->castleRights != CASTLES_NONE)
307 if (can_castle(WHITE_OO))
308 fen += chess960 ? char(toupper(file_to_char(square_file(castle_rook_square(WHITE_OO))))) : 'K';
310 if (can_castle(WHITE_OOO))
311 fen += chess960 ? char(toupper(file_to_char(square_file(castle_rook_square(WHITE_OOO))))) : 'Q';
313 if (can_castle(BLACK_OO))
314 fen += chess960 ? file_to_char(square_file(castle_rook_square(BLACK_OO))) : 'k';
316 if (can_castle(BLACK_OOO))
317 fen += chess960 ? file_to_char(square_file(castle_rook_square(BLACK_OOO))) : 'q';
321 fen += (ep_square() == SQ_NONE ? " -" : " " + square_to_string(ep_square()));
326 /// Position::print() prints an ASCII representation of the position to
327 /// the standard output. If a move is given then also the san is printed.
329 void Position::print(Move move) const {
331 const char* dottedLine = "\n+---+---+---+---+---+---+---+---+\n";
335 Position p(*this, thread());
336 string dd = (piece_color(piece_on(move_from(move))) == BLACK ? ".." : "");
337 cout << "\nMove is: " << dd << move_to_san(p, move);
340 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
342 cout << dottedLine << '|';
343 for (File file = FILE_A; file <= FILE_H; file++)
345 Square sq = make_square(file, rank);
346 Piece piece = piece_on(sq);
348 if (piece == PIECE_NONE && square_color(sq) == DARK)
349 piece = PIECE_NONE_DARK_SQ;
351 char c = (piece_color(piece_on(sq)) == BLACK ? '=' : ' ');
352 cout << c << PieceToChar[piece] << c << '|';
355 cout << dottedLine << "Fen is: " << to_fen() << "\nKey is: " << st->key << endl;
359 /// Position:hidden_checkers<>() returns a bitboard of all pinned (against the
360 /// king) pieces for the given color and for the given pinner type. Or, when
361 /// template parameter FindPinned is false, the pieces of the given color
362 /// candidate for a discovery check against the enemy king.
363 /// Bitboard checkersBB must be already updated when looking for pinners.
365 template<bool FindPinned>
366 Bitboard Position::hidden_checkers(Color c) const {
368 Bitboard result = EmptyBoardBB;
369 Bitboard pinners = pieces_of_color(FindPinned ? opposite_color(c) : c);
371 // Pinned pieces protect our king, dicovery checks attack
373 Square ksq = king_square(FindPinned ? c : opposite_color(c));
375 // Pinners are sliders, not checkers, that give check when candidate pinned is removed
376 pinners &= (pieces(ROOK, QUEEN) & RookPseudoAttacks[ksq]) | (pieces(BISHOP, QUEEN) & BishopPseudoAttacks[ksq]);
378 if (FindPinned && pinners)
379 pinners &= ~st->checkersBB;
383 Square s = pop_1st_bit(&pinners);
384 Bitboard b = squares_between(s, ksq) & occupied_squares();
388 if ( !(b & (b - 1)) // Only one bit set?
389 && (b & pieces_of_color(c))) // Is an our piece?
396 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
397 /// king) pieces for the given color. Note that checkersBB bitboard must
398 /// be already updated.
400 Bitboard Position::pinned_pieces(Color c) const {
402 return hidden_checkers<true>(c);
406 /// Position:discovered_check_candidates() returns a bitboard containing all
407 /// pieces for the given side which are candidates for giving a discovered
408 /// check. Contrary to pinned_pieces() here there is no need of checkersBB
409 /// to be already updated.
411 Bitboard Position::discovered_check_candidates(Color c) const {
413 return hidden_checkers<false>(c);
416 /// Position::attackers_to() computes a bitboard containing all pieces which
417 /// attacks a given square.
419 Bitboard Position::attackers_to(Square s) const {
421 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
422 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
423 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
424 | (attacks_from<ROOK>(s) & pieces(ROOK, QUEEN))
425 | (attacks_from<BISHOP>(s) & pieces(BISHOP, QUEEN))
426 | (attacks_from<KING>(s) & pieces(KING));
429 Bitboard Position::attackers_to(Square s, Bitboard occ) const {
431 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
432 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
433 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
434 | (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
435 | (bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN))
436 | (attacks_from<KING>(s) & pieces(KING));
439 /// Position::attacks_from() computes a bitboard of all attacks
440 /// of a given piece put in a given square.
442 Bitboard Position::attacks_from(Piece p, Square s) const {
444 assert(square_is_ok(s));
448 case WB: case BB: return attacks_from<BISHOP>(s);
449 case WR: case BR: return attacks_from<ROOK>(s);
450 case WQ: case BQ: return attacks_from<QUEEN>(s);
451 default: return StepAttacksBB[p][s];
455 Bitboard Position::attacks_from(Piece p, Square s, Bitboard occ) {
457 assert(square_is_ok(s));
461 case WB: case BB: return bishop_attacks_bb(s, occ);
462 case WR: case BR: return rook_attacks_bb(s, occ);
463 case WQ: case BQ: return bishop_attacks_bb(s, occ) | rook_attacks_bb(s, occ);
464 default: return StepAttacksBB[p][s];
469 /// Position::move_attacks_square() tests whether a move from the current
470 /// position attacks a given square.
472 bool Position::move_attacks_square(Move m, Square s) const {
474 assert(move_is_ok(m));
475 assert(square_is_ok(s));
478 Square f = move_from(m), t = move_to(m);
480 assert(square_is_occupied(f));
482 if (bit_is_set(attacks_from(piece_on(f), t), s))
485 // Move the piece and scan for X-ray attacks behind it
486 occ = occupied_squares();
487 do_move_bb(&occ, make_move_bb(f, t));
488 xray = ( (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
489 |(bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN)))
490 & pieces_of_color(piece_color(piece_on(f)));
492 // If we have attacks we need to verify that are caused by our move
493 // and are not already existent ones.
494 return xray && (xray ^ (xray & attacks_from<QUEEN>(s)));
498 /// Position::find_checkers() computes the checkersBB bitboard, which
499 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
500 /// currently works by calling Position::attackers_to, which is probably
501 /// inefficient. Consider rewriting this function to use the last move
502 /// played, like in non-bitboard versions of Glaurung.
504 void Position::find_checkers() {
506 Color us = side_to_move();
507 st->checkersBB = attackers_to(king_square(us)) & pieces_of_color(opposite_color(us));
511 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
513 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
516 assert(move_is_ok(m));
517 assert(pinned == pinned_pieces(side_to_move()));
519 Color us = side_to_move();
520 Square from = move_from(m);
522 assert(piece_color(piece_on(from)) == us);
523 assert(piece_on(king_square(us)) == make_piece(us, KING));
525 // En passant captures are a tricky special case. Because they are
526 // rather uncommon, we do it simply by testing whether the king is attacked
527 // after the move is made
530 Color them = opposite_color(us);
531 Square to = move_to(m);
532 Square capsq = make_square(square_file(to), square_rank(from));
533 Square ksq = king_square(us);
534 Bitboard b = occupied_squares();
536 assert(to == ep_square());
537 assert(piece_on(from) == make_piece(us, PAWN));
538 assert(piece_on(capsq) == make_piece(them, PAWN));
539 assert(piece_on(to) == PIECE_NONE);
542 clear_bit(&b, capsq);
545 return !(rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, them))
546 && !(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, them));
549 // If the moving piece is a king, check whether the destination
550 // square is attacked by the opponent. Castling moves are checked
551 // for legality during move generation.
552 if (piece_type(piece_on(from)) == KING)
553 return move_is_castle(m) || !(attackers_to(move_to(m)) & pieces_of_color(opposite_color(us)));
555 // A non-king move is legal if and only if it is not pinned or it
556 // is moving along the ray towards or away from the king.
558 || !bit_is_set(pinned, from)
559 || squares_aligned(from, move_to(m), king_square(us));
563 /// Position::move_is_pl_slow() takes a move and tests whether the move
564 /// is pseudo legal. This version is not very fast and should be used
565 /// only in non time-critical paths.
567 bool Position::move_is_pl_slow(const Move m) const {
569 MoveStack mlist[MAX_MOVES];
570 MoveStack *cur, *last;
572 last = in_check() ? generate<MV_EVASION>(*this, mlist)
573 : generate<MV_NON_EVASION>(*this, mlist);
575 for (cur = mlist; cur != last; cur++)
583 /// Fast version of Position::move_is_pl() that takes a move and a bitboard
584 /// of pinned pieces as input, and tests whether the move is pseudo legal.
586 bool Position::move_is_pl(const Move m) const {
590 Color us = sideToMove;
591 Color them = opposite_color(sideToMove);
592 Square from = move_from(m);
593 Square to = move_to(m);
594 Piece pc = piece_on(from);
596 // Use a slower but simpler function for uncommon cases
597 if (move_is_special(m))
598 return move_is_pl_slow(m);
600 // Is not a promotion, so promotion piece must be empty
601 if (promotion_piece_type(m) - 2 != PIECE_TYPE_NONE)
604 // If the from square is not occupied by a piece belonging to the side to
605 // move, the move is obviously not legal.
606 if (pc == PIECE_NONE || piece_color(pc) != us)
609 // The destination square cannot be occupied by a friendly piece
610 if (piece_color(piece_on(to)) == us)
613 // Handle the special case of a pawn move
614 if (piece_type(pc) == PAWN)
616 // Move direction must be compatible with pawn color
617 int direction = to - from;
618 if ((us == WHITE) != (direction > 0))
621 // We have already handled promotion moves, so destination
622 // cannot be on the 8/1th rank.
623 if (square_rank(to) == RANK_8 || square_rank(to) == RANK_1)
626 // Proceed according to the square delta between the origin and
627 // destination squares.
634 // Capture. The destination square must be occupied by an enemy
635 // piece (en passant captures was handled earlier).
636 if (piece_color(piece_on(to)) != them)
639 // From and to files must be one file apart, avoids a7h5
640 if (abs(square_file(from) - square_file(to)) != 1)
646 // Pawn push. The destination square must be empty.
647 if (!square_is_empty(to))
652 // Double white pawn push. The destination square must be on the fourth
653 // rank, and both the destination square and the square between the
654 // source and destination squares must be empty.
655 if ( square_rank(to) != RANK_4
656 || !square_is_empty(to)
657 || !square_is_empty(from + DELTA_N))
662 // Double black pawn push. The destination square must be on the fifth
663 // rank, and both the destination square and the square between the
664 // source and destination squares must be empty.
665 if ( square_rank(to) != RANK_5
666 || !square_is_empty(to)
667 || !square_is_empty(from + DELTA_S))
675 else if (!bit_is_set(attacks_from(pc, from), to))
680 // In case of king moves under check we have to remove king so to catch
681 // as invalid moves like b1a1 when opposite queen is on c1.
682 if (piece_type(piece_on(from)) == KING)
684 Bitboard b = occupied_squares();
686 if (attackers_to(move_to(m), b) & pieces_of_color(opposite_color(us)))
691 Bitboard target = checkers();
692 Square checksq = pop_1st_bit(&target);
694 if (target) // double check ? In this case a king move is required
697 // Our move must be a blocking evasion or a capture of the checking piece
698 target = squares_between(checksq, king_square(us)) | checkers();
699 if (!bit_is_set(target, move_to(m)))
708 /// Position::move_gives_check() tests whether a pseudo-legal move is a check
710 bool Position::move_gives_check(Move m, const CheckInfo& ci) const {
713 assert(move_is_ok(m));
714 assert(ci.dcCandidates == discovered_check_candidates(side_to_move()));
715 assert(piece_color(piece_on(move_from(m))) == side_to_move());
717 Square from = move_from(m);
718 Square to = move_to(m);
719 PieceType pt = piece_type(piece_on(from));
722 if (bit_is_set(ci.checkSq[pt], to))
726 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
728 // For pawn and king moves we need to verify also direction
729 if ( (pt != PAWN && pt != KING)
730 || !squares_aligned(from, to, king_square(opposite_color(side_to_move()))))
734 // Can we skip the ugly special cases ?
735 if (!move_is_special(m))
738 Color us = side_to_move();
739 Bitboard b = occupied_squares();
740 Square ksq = king_square(opposite_color(us));
742 // Promotion with check ?
743 if (move_is_promotion(m))
747 switch (promotion_piece_type(m))
750 return bit_is_set(attacks_from<KNIGHT>(to), ksq);
752 return bit_is_set(bishop_attacks_bb(to, b), ksq);
754 return bit_is_set(rook_attacks_bb(to, b), ksq);
756 return bit_is_set(queen_attacks_bb(to, b), ksq);
762 // En passant capture with check ? We have already handled the case
763 // of direct checks and ordinary discovered check, the only case we
764 // need to handle is the unusual case of a discovered check through
765 // the captured pawn.
768 Square capsq = make_square(square_file(to), square_rank(from));
770 clear_bit(&b, capsq);
772 return (rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, us))
773 ||(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, us));
776 // Castling with check ?
777 if (move_is_castle(m))
779 Square kfrom, kto, rfrom, rto;
785 kto = relative_square(us, SQ_G1);
786 rto = relative_square(us, SQ_F1);
788 kto = relative_square(us, SQ_C1);
789 rto = relative_square(us, SQ_D1);
791 clear_bit(&b, kfrom);
792 clear_bit(&b, rfrom);
795 return bit_is_set(rook_attacks_bb(rto, b), ksq);
802 /// Position::do_setup_move() makes a permanent move on the board. It should
803 /// be used when setting up a position on board. You can't undo the move.
805 void Position::do_setup_move(Move m) {
809 // Update the number of full moves after black's move
810 if (sideToMove == BLACK)
815 // Reset "game ply" in case we made a non-reversible move.
816 // "game ply" is used for repetition detection.
820 // Our StateInfo newSt is about going out of scope so copy
821 // its content before it disappears.
826 /// Position::do_move() makes a move, and saves all information necessary
827 /// to a StateInfo object. The move is assumed to be legal. Pseudo-legal
828 /// moves should be filtered out before this function is called.
830 void Position::do_move(Move m, StateInfo& newSt) {
833 do_move(m, newSt, ci, move_gives_check(m, ci));
836 void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveIsCheck) {
839 assert(move_is_ok(m));
840 assert(&newSt != st);
845 // Copy some fields of old state to our new StateInfo object except the
846 // ones which are recalculated from scratch anyway, then switch our state
847 // pointer to point to the new, ready to be updated, state.
848 struct ReducedStateInfo {
849 Key pawnKey, materialKey;
850 int castleRights, rule50, gamePly, pliesFromNull;
856 memcpy(&newSt, st, sizeof(ReducedStateInfo));
861 // Save the current key to the history[] array, in order to be able to
862 // detect repetition draws.
863 history[st->gamePly++] = key;
865 // Update side to move
866 key ^= zobSideToMove;
868 // Increment the 50 moves rule draw counter. Resetting it to zero in the
869 // case of non-reversible moves is taken care of later.
873 if (move_is_castle(m))
880 Color us = side_to_move();
881 Color them = opposite_color(us);
882 Square from = move_from(m);
883 Square to = move_to(m);
884 bool ep = move_is_ep(m);
885 bool pm = move_is_promotion(m);
887 Piece piece = piece_on(from);
888 PieceType pt = piece_type(piece);
889 PieceType capture = ep ? PAWN : piece_type(piece_on(to));
891 assert(piece_color(piece_on(from)) == us);
892 assert(piece_color(piece_on(to)) == them || square_is_empty(to));
893 assert(!(ep || pm) || piece == make_piece(us, PAWN));
894 assert(!pm || relative_rank(us, to) == RANK_8);
897 do_capture_move(key, capture, them, to, ep);
900 key ^= zobrist[us][pt][from] ^ zobrist[us][pt][to];
902 // Reset en passant square
903 if (st->epSquare != SQ_NONE)
905 key ^= zobEp[st->epSquare];
906 st->epSquare = SQ_NONE;
909 // Update castle rights if needed
910 if ( st->castleRights != CASTLES_NONE
911 && (castleRightsMask[from] & castleRightsMask[to]) != ALL_CASTLES)
913 key ^= zobCastle[st->castleRights];
914 st->castleRights &= castleRightsMask[from] & castleRightsMask[to];
915 key ^= zobCastle[st->castleRights];
918 // Prefetch TT access as soon as we know key is updated
919 prefetch((char*)TT.first_entry(key));
922 Bitboard move_bb = make_move_bb(from, to);
923 do_move_bb(&(byColorBB[us]), move_bb);
924 do_move_bb(&(byTypeBB[pt]), move_bb);
925 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
927 board[to] = board[from];
928 board[from] = PIECE_NONE;
930 // Update piece lists, note that index[from] is not updated and
931 // becomes stale. This works as long as index[] is accessed just
932 // by known occupied squares.
933 index[to] = index[from];
934 pieceList[us][pt][index[to]] = to;
936 // If the moving piece was a pawn do some special extra work
939 // Reset rule 50 draw counter
942 // Update pawn hash key and prefetch in L1/L2 cache
943 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
945 // Set en passant square, only if moved pawn can be captured
946 if ((to ^ from) == 16)
948 if (attacks_from<PAWN>(from + (us == WHITE ? DELTA_N : DELTA_S), us) & pieces(PAWN, them))
950 st->epSquare = Square((int(from) + int(to)) / 2);
951 key ^= zobEp[st->epSquare];
955 if (pm) // promotion ?
957 PieceType promotion = promotion_piece_type(m);
959 assert(promotion >= KNIGHT && promotion <= QUEEN);
961 // Insert promoted piece instead of pawn
962 clear_bit(&(byTypeBB[PAWN]), to);
963 set_bit(&(byTypeBB[promotion]), to);
964 board[to] = make_piece(us, promotion);
966 // Update piece counts
967 pieceCount[us][promotion]++;
968 pieceCount[us][PAWN]--;
970 // Update material key
971 st->materialKey ^= zobrist[us][PAWN][pieceCount[us][PAWN]];
972 st->materialKey ^= zobrist[us][promotion][pieceCount[us][promotion]-1];
974 // Update piece lists, move the last pawn at index[to] position
975 // and shrink the list. Add a new promotion piece to the list.
976 Square lastPawnSquare = pieceList[us][PAWN][pieceCount[us][PAWN]];
977 index[lastPawnSquare] = index[to];
978 pieceList[us][PAWN][index[lastPawnSquare]] = lastPawnSquare;
979 pieceList[us][PAWN][pieceCount[us][PAWN]] = SQ_NONE;
980 index[to] = pieceCount[us][promotion] - 1;
981 pieceList[us][promotion][index[to]] = to;
983 // Partially revert hash keys update
984 key ^= zobrist[us][PAWN][to] ^ zobrist[us][promotion][to];
985 st->pawnKey ^= zobrist[us][PAWN][to];
987 // Partially revert and update incremental scores
988 st->value -= pst(us, PAWN, to);
989 st->value += pst(us, promotion, to);
992 st->npMaterial[us] += PieceValueMidgame[promotion];
996 // Prefetch pawn and material hash tables
997 Threads[threadID].pawnTable.prefetch(st->pawnKey);
998 Threads[threadID].materialTable.prefetch(st->materialKey);
1000 // Update incremental scores
1001 st->value += pst_delta(piece, from, to);
1003 // Set capture piece
1004 st->capturedType = capture;
1006 // Update the key with the final value
1009 // Update checkers bitboard, piece must be already moved
1010 st->checkersBB = EmptyBoardBB;
1015 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
1019 if (bit_is_set(ci.checkSq[pt], to))
1020 st->checkersBB = SetMaskBB[to];
1023 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
1026 st->checkersBB |= (attacks_from<ROOK>(king_square(them)) & pieces(ROOK, QUEEN, us));
1029 st->checkersBB |= (attacks_from<BISHOP>(king_square(them)) & pieces(BISHOP, QUEEN, us));
1035 sideToMove = opposite_color(sideToMove);
1036 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1042 /// Position::do_capture_move() is a private method used to update captured
1043 /// piece info. It is called from the main Position::do_move function.
1045 void Position::do_capture_move(Key& key, PieceType capture, Color them, Square to, bool ep) {
1047 assert(capture != KING);
1051 // If the captured piece was a pawn, update pawn hash key,
1052 // otherwise update non-pawn material.
1053 if (capture == PAWN)
1055 if (ep) // en passant ?
1057 capsq = (them == BLACK)? (to - DELTA_N) : (to - DELTA_S);
1059 assert(to == st->epSquare);
1060 assert(relative_rank(opposite_color(them), to) == RANK_6);
1061 assert(piece_on(to) == PIECE_NONE);
1062 assert(piece_on(capsq) == make_piece(them, PAWN));
1064 board[capsq] = PIECE_NONE;
1066 st->pawnKey ^= zobrist[them][PAWN][capsq];
1069 st->npMaterial[them] -= PieceValueMidgame[capture];
1071 // Remove captured piece
1072 clear_bit(&(byColorBB[them]), capsq);
1073 clear_bit(&(byTypeBB[capture]), capsq);
1074 clear_bit(&(byTypeBB[0]), capsq);
1077 key ^= zobrist[them][capture][capsq];
1079 // Update incremental scores
1080 st->value -= pst(them, capture, capsq);
1082 // Update piece count
1083 pieceCount[them][capture]--;
1085 // Update material hash key
1086 st->materialKey ^= zobrist[them][capture][pieceCount[them][capture]];
1088 // Update piece list, move the last piece at index[capsq] position
1090 // WARNING: This is a not perfectly revresible operation. When we
1091 // will reinsert the captured piece in undo_move() we will put it
1092 // at the end of the list and not in its original place, it means
1093 // index[] and pieceList[] are not guaranteed to be invariant to a
1094 // do_move() + undo_move() sequence.
1095 Square lastPieceSquare = pieceList[them][capture][pieceCount[them][capture]];
1096 index[lastPieceSquare] = index[capsq];
1097 pieceList[them][capture][index[lastPieceSquare]] = lastPieceSquare;
1098 pieceList[them][capture][pieceCount[them][capture]] = SQ_NONE;
1100 // Reset rule 50 counter
1105 /// Position::do_castle_move() is a private method used to make a castling
1106 /// move. It is called from the main Position::do_move function. Note that
1107 /// castling moves are encoded as "king captures friendly rook" moves, for
1108 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1110 void Position::do_castle_move(Move m) {
1112 assert(move_is_ok(m));
1113 assert(move_is_castle(m));
1115 Color us = side_to_move();
1116 Color them = opposite_color(us);
1118 // Reset capture field
1119 st->capturedType = PIECE_TYPE_NONE;
1121 // Find source squares for king and rook
1122 Square kfrom = move_from(m);
1123 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1126 assert(piece_on(kfrom) == make_piece(us, KING));
1127 assert(piece_on(rfrom) == make_piece(us, ROOK));
1129 // Find destination squares for king and rook
1130 if (rfrom > kfrom) // O-O
1132 kto = relative_square(us, SQ_G1);
1133 rto = relative_square(us, SQ_F1);
1135 kto = relative_square(us, SQ_C1);
1136 rto = relative_square(us, SQ_D1);
1139 // Remove pieces from source squares:
1140 clear_bit(&(byColorBB[us]), kfrom);
1141 clear_bit(&(byTypeBB[KING]), kfrom);
1142 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1143 clear_bit(&(byColorBB[us]), rfrom);
1144 clear_bit(&(byTypeBB[ROOK]), rfrom);
1145 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1147 // Put pieces on destination squares:
1148 set_bit(&(byColorBB[us]), kto);
1149 set_bit(&(byTypeBB[KING]), kto);
1150 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1151 set_bit(&(byColorBB[us]), rto);
1152 set_bit(&(byTypeBB[ROOK]), rto);
1153 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1155 // Update board array
1156 Piece king = make_piece(us, KING);
1157 Piece rook = make_piece(us, ROOK);
1158 board[kfrom] = board[rfrom] = PIECE_NONE;
1162 // Update piece lists
1163 pieceList[us][KING][index[kfrom]] = kto;
1164 pieceList[us][ROOK][index[rfrom]] = rto;
1165 int tmp = index[rfrom]; // In Chess960 could be rto == kfrom
1166 index[kto] = index[kfrom];
1169 // Update incremental scores
1170 st->value += pst_delta(king, kfrom, kto);
1171 st->value += pst_delta(rook, rfrom, rto);
1174 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1175 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1177 // Clear en passant square
1178 if (st->epSquare != SQ_NONE)
1180 st->key ^= zobEp[st->epSquare];
1181 st->epSquare = SQ_NONE;
1184 // Update castling rights
1185 st->key ^= zobCastle[st->castleRights];
1186 st->castleRights &= castleRightsMask[kfrom];
1187 st->key ^= zobCastle[st->castleRights];
1189 // Reset rule 50 counter
1192 // Update checkers BB
1193 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
1196 sideToMove = opposite_color(sideToMove);
1197 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1203 /// Position::undo_move() unmakes a move. When it returns, the position should
1204 /// be restored to exactly the same state as before the move was made.
1206 void Position::undo_move(Move m) {
1209 assert(move_is_ok(m));
1211 sideToMove = opposite_color(sideToMove);
1213 if (move_is_castle(m))
1215 undo_castle_move(m);
1219 Color us = side_to_move();
1220 Color them = opposite_color(us);
1221 Square from = move_from(m);
1222 Square to = move_to(m);
1223 bool ep = move_is_ep(m);
1224 bool pm = move_is_promotion(m);
1226 PieceType pt = piece_type(piece_on(to));
1228 assert(square_is_empty(from));
1229 assert(piece_color(piece_on(to)) == us);
1230 assert(!pm || relative_rank(us, to) == RANK_8);
1231 assert(!ep || to == st->previous->epSquare);
1232 assert(!ep || relative_rank(us, to) == RANK_6);
1233 assert(!ep || piece_on(to) == make_piece(us, PAWN));
1235 if (pm) // promotion ?
1237 PieceType promotion = promotion_piece_type(m);
1240 assert(promotion >= KNIGHT && promotion <= QUEEN);
1241 assert(piece_on(to) == make_piece(us, promotion));
1243 // Replace promoted piece with a pawn
1244 clear_bit(&(byTypeBB[promotion]), to);
1245 set_bit(&(byTypeBB[PAWN]), to);
1247 // Update piece counts
1248 pieceCount[us][promotion]--;
1249 pieceCount[us][PAWN]++;
1251 // Update piece list replacing promotion piece with a pawn
1252 Square lastPromotionSquare = pieceList[us][promotion][pieceCount[us][promotion]];
1253 index[lastPromotionSquare] = index[to];
1254 pieceList[us][promotion][index[lastPromotionSquare]] = lastPromotionSquare;
1255 pieceList[us][promotion][pieceCount[us][promotion]] = SQ_NONE;
1256 index[to] = pieceCount[us][PAWN] - 1;
1257 pieceList[us][PAWN][index[to]] = to;
1260 // Put the piece back at the source square
1261 Bitboard move_bb = make_move_bb(to, from);
1262 do_move_bb(&(byColorBB[us]), move_bb);
1263 do_move_bb(&(byTypeBB[pt]), move_bb);
1264 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
1266 board[from] = make_piece(us, pt);
1267 board[to] = PIECE_NONE;
1269 // Update piece list
1270 index[from] = index[to];
1271 pieceList[us][pt][index[from]] = from;
1273 if (st->capturedType)
1278 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1280 assert(st->capturedType != KING);
1281 assert(!ep || square_is_empty(capsq));
1283 // Restore the captured piece
1284 set_bit(&(byColorBB[them]), capsq);
1285 set_bit(&(byTypeBB[st->capturedType]), capsq);
1286 set_bit(&(byTypeBB[0]), capsq);
1288 board[capsq] = make_piece(them, st->capturedType);
1290 // Update piece count
1291 pieceCount[them][st->capturedType]++;
1293 // Update piece list, add a new captured piece in capsq square
1294 index[capsq] = pieceCount[them][st->capturedType] - 1;
1295 pieceList[them][st->capturedType][index[capsq]] = capsq;
1298 // Finally point our state pointer back to the previous state
1305 /// Position::undo_castle_move() is a private method used to unmake a castling
1306 /// move. It is called from the main Position::undo_move function. Note that
1307 /// castling moves are encoded as "king captures friendly rook" moves, for
1308 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1310 void Position::undo_castle_move(Move m) {
1312 assert(move_is_ok(m));
1313 assert(move_is_castle(m));
1315 // When we have arrived here, some work has already been done by
1316 // Position::undo_move. In particular, the side to move has been switched,
1317 // so the code below is correct.
1318 Color us = side_to_move();
1320 // Find source squares for king and rook
1321 Square kfrom = move_from(m);
1322 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1325 // Find destination squares for king and rook
1326 if (rfrom > kfrom) // O-O
1328 kto = relative_square(us, SQ_G1);
1329 rto = relative_square(us, SQ_F1);
1331 kto = relative_square(us, SQ_C1);
1332 rto = relative_square(us, SQ_D1);
1335 assert(piece_on(kto) == make_piece(us, KING));
1336 assert(piece_on(rto) == make_piece(us, ROOK));
1338 // Remove pieces from destination squares:
1339 clear_bit(&(byColorBB[us]), kto);
1340 clear_bit(&(byTypeBB[KING]), kto);
1341 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1342 clear_bit(&(byColorBB[us]), rto);
1343 clear_bit(&(byTypeBB[ROOK]), rto);
1344 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1346 // Put pieces on source squares:
1347 set_bit(&(byColorBB[us]), kfrom);
1348 set_bit(&(byTypeBB[KING]), kfrom);
1349 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1350 set_bit(&(byColorBB[us]), rfrom);
1351 set_bit(&(byTypeBB[ROOK]), rfrom);
1352 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1355 board[rto] = board[kto] = PIECE_NONE;
1356 board[rfrom] = make_piece(us, ROOK);
1357 board[kfrom] = make_piece(us, KING);
1359 // Update piece lists
1360 pieceList[us][KING][index[kto]] = kfrom;
1361 pieceList[us][ROOK][index[rto]] = rfrom;
1362 int tmp = index[rto]; // In Chess960 could be rto == kfrom
1363 index[kfrom] = index[kto];
1366 // Finally point our state pointer back to the previous state
1373 /// Position::do_null_move makes() a "null move": It switches the side to move
1374 /// and updates the hash key without executing any move on the board.
1376 void Position::do_null_move(StateInfo& backupSt) {
1379 assert(!in_check());
1381 // Back up the information necessary to undo the null move to the supplied
1382 // StateInfo object.
1383 // Note that differently from normal case here backupSt is actually used as
1384 // a backup storage not as a new state to be used.
1385 backupSt.key = st->key;
1386 backupSt.epSquare = st->epSquare;
1387 backupSt.value = st->value;
1388 backupSt.previous = st->previous;
1389 backupSt.pliesFromNull = st->pliesFromNull;
1390 st->previous = &backupSt;
1392 // Save the current key to the history[] array, in order to be able to
1393 // detect repetition draws.
1394 history[st->gamePly++] = st->key;
1396 // Update the necessary information
1397 if (st->epSquare != SQ_NONE)
1398 st->key ^= zobEp[st->epSquare];
1400 st->key ^= zobSideToMove;
1401 prefetch((char*)TT.first_entry(st->key));
1403 sideToMove = opposite_color(sideToMove);
1404 st->epSquare = SQ_NONE;
1406 st->pliesFromNull = 0;
1407 st->value += (sideToMove == WHITE) ? TempoValue : -TempoValue;
1411 /// Position::undo_null_move() unmakes a "null move".
1413 void Position::undo_null_move() {
1416 assert(!in_check());
1418 // Restore information from the our backup StateInfo object
1419 StateInfo* backupSt = st->previous;
1420 st->key = backupSt->key;
1421 st->epSquare = backupSt->epSquare;
1422 st->value = backupSt->value;
1423 st->previous = backupSt->previous;
1424 st->pliesFromNull = backupSt->pliesFromNull;
1426 // Update the necessary information
1427 sideToMove = opposite_color(sideToMove);
1433 /// Position::see() is a static exchange evaluator: It tries to estimate the
1434 /// material gain or loss resulting from a move. There are three versions of
1435 /// this function: One which takes a destination square as input, one takes a
1436 /// move, and one which takes a 'from' and a 'to' square. The function does
1437 /// not yet understand promotions captures.
1439 int Position::see_sign(Move m) const {
1441 assert(move_is_ok(m));
1443 Square from = move_from(m);
1444 Square to = move_to(m);
1446 // Early return if SEE cannot be negative because captured piece value
1447 // is not less then capturing one. Note that king moves always return
1448 // here because king midgame value is set to 0.
1449 if (piece_value_midgame(piece_on(to)) >= piece_value_midgame(piece_on(from)))
1455 int Position::see(Move m) const {
1458 Bitboard occupied, attackers, stmAttackers, b;
1459 int swapList[32], slIndex = 1;
1460 PieceType capturedType, pt;
1463 assert(move_is_ok(m));
1465 // As castle moves are implemented as capturing the rook, they have
1466 // SEE == RookValueMidgame most of the times (unless the rook is under
1468 if (move_is_castle(m))
1471 from = move_from(m);
1473 capturedType = piece_type(piece_on(to));
1474 occupied = occupied_squares();
1476 // Handle en passant moves
1477 if (st->epSquare == to && piece_type(piece_on(from)) == PAWN)
1479 Square capQq = (side_to_move() == WHITE ? to - DELTA_N : to - DELTA_S);
1481 assert(capturedType == PIECE_TYPE_NONE);
1482 assert(piece_type(piece_on(capQq)) == PAWN);
1484 // Remove the captured pawn
1485 clear_bit(&occupied, capQq);
1486 capturedType = PAWN;
1489 // Find all attackers to the destination square, with the moving piece
1490 // removed, but possibly an X-ray attacker added behind it.
1491 clear_bit(&occupied, from);
1492 attackers = attackers_to(to, occupied);
1494 // If the opponent has no attackers we are finished
1495 stm = opposite_color(piece_color(piece_on(from)));
1496 stmAttackers = attackers & pieces_of_color(stm);
1498 return PieceValueMidgame[capturedType];
1500 // The destination square is defended, which makes things rather more
1501 // difficult to compute. We proceed by building up a "swap list" containing
1502 // the material gain or loss at each stop in a sequence of captures to the
1503 // destination square, where the sides alternately capture, and always
1504 // capture with the least valuable piece. After each capture, we look for
1505 // new X-ray attacks from behind the capturing piece.
1506 swapList[0] = PieceValueMidgame[capturedType];
1507 capturedType = piece_type(piece_on(from));
1510 // Locate the least valuable attacker for the side to move. The loop
1511 // below looks like it is potentially infinite, but it isn't. We know
1512 // that the side to move still has at least one attacker left.
1513 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1516 // Remove the attacker we just found from the 'occupied' bitboard,
1517 // and scan for new X-ray attacks behind the attacker.
1518 b = stmAttackers & pieces(pt);
1519 occupied ^= (b & (~b + 1));
1520 attackers |= (rook_attacks_bb(to, occupied) & pieces(ROOK, QUEEN))
1521 | (bishop_attacks_bb(to, occupied) & pieces(BISHOP, QUEEN));
1523 attackers &= occupied; // Cut out pieces we've already done
1525 // Add the new entry to the swap list
1526 assert(slIndex < 32);
1527 swapList[slIndex] = -swapList[slIndex - 1] + PieceValueMidgame[capturedType];
1530 // Remember the value of the capturing piece, and change the side to
1531 // move before beginning the next iteration.
1533 stm = opposite_color(stm);
1534 stmAttackers = attackers & pieces_of_color(stm);
1536 // Stop before processing a king capture
1537 if (capturedType == KING && stmAttackers)
1539 assert(slIndex < 32);
1540 swapList[slIndex++] = QueenValueMidgame*10;
1543 } while (stmAttackers);
1545 // Having built the swap list, we negamax through it to find the best
1546 // achievable score from the point of view of the side to move.
1548 swapList[slIndex-1] = Min(-swapList[slIndex], swapList[slIndex-1]);
1554 /// Position::clear() erases the position object to a pristine state, with an
1555 /// empty board, white to move, and no castling rights.
1557 void Position::clear() {
1560 memset(st, 0, sizeof(StateInfo));
1561 st->epSquare = SQ_NONE;
1565 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1566 memset(byTypeBB, 0, sizeof(Bitboard) * 8);
1567 memset(pieceCount, 0, sizeof(int) * 2 * 8);
1568 memset(index, 0, sizeof(int) * 64);
1570 for (int i = 0; i < 64; i++)
1571 board[i] = PIECE_NONE;
1573 for (int i = 0; i < 8; i++)
1574 for (int j = 0; j < 16; j++)
1575 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1577 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
1578 castleRightsMask[sq] = ALL_CASTLES;
1584 /// Position::put_piece() puts a piece on the given square of the board,
1585 /// updating the board array, pieces list, bitboards, and piece counts.
1587 void Position::put_piece(Piece p, Square s) {
1589 Color c = piece_color(p);
1590 PieceType pt = piece_type(p);
1593 index[s] = pieceCount[c][pt]++;
1594 pieceList[c][pt][index[s]] = s;
1596 set_bit(&(byTypeBB[pt]), s);
1597 set_bit(&(byColorBB[c]), s);
1598 set_bit(&(byTypeBB[0]), s); // HACK: byTypeBB[0] contains all occupied squares.
1602 /// Position::compute_key() computes the hash key of the position. The hash
1603 /// key is usually updated incrementally as moves are made and unmade, the
1604 /// compute_key() function is only used when a new position is set up, and
1605 /// to verify the correctness of the hash key when running in debug mode.
1607 Key Position::compute_key() const {
1609 Key result = zobCastle[st->castleRights];
1611 for (Square s = SQ_A1; s <= SQ_H8; s++)
1612 if (square_is_occupied(s))
1613 result ^= zobrist[piece_color(piece_on(s))][piece_type(piece_on(s))][s];
1615 if (ep_square() != SQ_NONE)
1616 result ^= zobEp[ep_square()];
1618 if (side_to_move() == BLACK)
1619 result ^= zobSideToMove;
1625 /// Position::compute_pawn_key() computes the hash key of the position. The
1626 /// hash key is usually updated incrementally as moves are made and unmade,
1627 /// the compute_pawn_key() function is only used when a new position is set
1628 /// up, and to verify the correctness of the pawn hash key when running in
1631 Key Position::compute_pawn_key() const {
1636 for (Color c = WHITE; c <= BLACK; c++)
1638 b = pieces(PAWN, c);
1640 result ^= zobrist[c][PAWN][pop_1st_bit(&b)];
1646 /// Position::compute_material_key() computes the hash key of the position.
1647 /// The hash key is usually updated incrementally as moves are made and unmade,
1648 /// the compute_material_key() function is only used when a new position is set
1649 /// up, and to verify the correctness of the material hash key when running in
1652 Key Position::compute_material_key() const {
1656 for (Color c = WHITE; c <= BLACK; c++)
1657 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1658 for (int i = 0, cnt = piece_count(c, pt); i < cnt; i++)
1659 result ^= zobrist[c][pt][i];
1665 /// Position::compute_value() compute the incremental scores for the middle
1666 /// game and the endgame. These functions are used to initialize the incremental
1667 /// scores when a new position is set up, and to verify that the scores are correctly
1668 /// updated by do_move and undo_move when the program is running in debug mode.
1669 Score Position::compute_value() const {
1672 Score result = SCORE_ZERO;
1674 for (Color c = WHITE; c <= BLACK; c++)
1675 for (PieceType pt = PAWN; pt <= KING; pt++)
1679 result += pst(c, pt, pop_1st_bit(&b));
1682 result += (side_to_move() == WHITE ? TempoValue / 2 : -TempoValue / 2);
1687 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1688 /// game material value for the given side. Material values are updated
1689 /// incrementally during the search, this function is only used while
1690 /// initializing a new Position object.
1692 Value Position::compute_non_pawn_material(Color c) const {
1694 Value result = VALUE_ZERO;
1696 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1697 result += piece_count(c, pt) * PieceValueMidgame[pt];
1703 /// Position::is_draw() tests whether the position is drawn by material,
1704 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1705 /// must be done by the search.
1706 template<bool SkipRepetition>
1707 bool Position::is_draw() const {
1709 // Draw by material?
1711 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1714 // Draw by the 50 moves rule?
1715 if (st->rule50 > 99 && !is_mate())
1718 // Draw by repetition?
1719 if (!SkipRepetition)
1720 for (int i = 4, e = Min(Min(st->gamePly, st->rule50), st->pliesFromNull); i <= e; i += 2)
1721 if (history[st->gamePly - i] == st->key)
1727 // Explicit template instantiations
1728 template bool Position::is_draw<false>() const;
1729 template bool Position::is_draw<true>() const;
1732 /// Position::is_mate() returns true or false depending on whether the
1733 /// side to move is checkmated.
1735 bool Position::is_mate() const {
1737 MoveStack moves[MAX_MOVES];
1738 return in_check() && generate<MV_LEGAL>(*this, moves) == moves;
1742 /// Position::init() is a static member function which initializes at
1743 /// startup the various arrays used to compute hash keys and the piece
1744 /// square tables. The latter is a two-step operation: First, the white
1745 /// halves of the tables are copied from the MgPST[][] and EgPST[][] arrays.
1746 /// Second, the black halves of the tables are initialized by mirroring
1747 /// and changing the sign of the corresponding white scores.
1749 void Position::init() {
1753 for (Color c = WHITE; c <= BLACK; c++)
1754 for (PieceType pt = PAWN; pt <= KING; pt++)
1755 for (Square s = SQ_A1; s <= SQ_H8; s++)
1756 zobrist[c][pt][s] = rk.rand<Key>();
1758 for (Square s = SQ_A1; s <= SQ_H8; s++)
1759 zobEp[s] = rk.rand<Key>();
1761 for (int i = 0; i < 16; i++)
1762 zobCastle[i] = rk.rand<Key>();
1764 zobSideToMove = rk.rand<Key>();
1765 zobExclusion = rk.rand<Key>();
1767 for (Square s = SQ_A1; s <= SQ_H8; s++)
1768 for (Piece p = WP; p <= WK; p++)
1769 PieceSquareTable[p][s] = make_score(MgPST[p][s], EgPST[p][s]);
1771 for (Square s = SQ_A1; s <= SQ_H8; s++)
1772 for (Piece p = BP; p <= BK; p++)
1773 PieceSquareTable[p][s] = -PieceSquareTable[p-8][flip_square(s)];
1777 /// Position::flip() flips position with the white and black sides reversed. This
1778 /// is only useful for debugging especially for finding evaluation symmetry bugs.
1780 void Position::flip() {
1784 // Make a copy of current position before to start changing
1785 const Position pos(*this, threadID);
1788 threadID = pos.thread();
1791 for (Square s = SQ_A1; s <= SQ_H8; s++)
1792 if (!pos.square_is_empty(s))
1793 put_piece(Piece(pos.piece_on(s) ^ 8), flip_square(s));
1796 sideToMove = opposite_color(pos.side_to_move());
1799 if (pos.can_castle(WHITE_OO))
1800 set_castle(BLACK_OO, king_square(BLACK), flip_square(pos.castle_rook_square(WHITE_OO)));
1801 if (pos.can_castle(WHITE_OOO))
1802 set_castle(BLACK_OOO, king_square(BLACK), flip_square(pos.castle_rook_square(WHITE_OOO)));
1803 if (pos.can_castle(BLACK_OO))
1804 set_castle(WHITE_OO, king_square(WHITE), flip_square(pos.castle_rook_square(BLACK_OO)));
1805 if (pos.can_castle(BLACK_OOO))
1806 set_castle(WHITE_OOO, king_square(WHITE), flip_square(pos.castle_rook_square(BLACK_OOO)));
1808 // En passant square
1809 if (pos.st->epSquare != SQ_NONE)
1810 st->epSquare = flip_square(pos.st->epSquare);
1816 st->key = compute_key();
1817 st->pawnKey = compute_pawn_key();
1818 st->materialKey = compute_material_key();
1820 // Incremental scores
1821 st->value = compute_value();
1824 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
1825 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
1831 /// Position::is_ok() performs some consitency checks for the position object.
1832 /// This is meant to be helpful when debugging.
1834 bool Position::is_ok(int* failedStep) const {
1836 // What features of the position should be verified?
1837 const bool debugAll = false;
1839 const bool debugBitboards = debugAll || false;
1840 const bool debugKingCount = debugAll || false;
1841 const bool debugKingCapture = debugAll || false;
1842 const bool debugCheckerCount = debugAll || false;
1843 const bool debugKey = debugAll || false;
1844 const bool debugMaterialKey = debugAll || false;
1845 const bool debugPawnKey = debugAll || false;
1846 const bool debugIncrementalEval = debugAll || false;
1847 const bool debugNonPawnMaterial = debugAll || false;
1848 const bool debugPieceCounts = debugAll || false;
1849 const bool debugPieceList = debugAll || false;
1850 const bool debugCastleSquares = debugAll || false;
1852 if (failedStep) *failedStep = 1;
1855 if (side_to_move() != WHITE && side_to_move() != BLACK)
1858 // Are the king squares in the position correct?
1859 if (failedStep) (*failedStep)++;
1860 if (piece_on(king_square(WHITE)) != WK)
1863 if (failedStep) (*failedStep)++;
1864 if (piece_on(king_square(BLACK)) != BK)
1867 // Do both sides have exactly one king?
1868 if (failedStep) (*failedStep)++;
1871 int kingCount[2] = {0, 0};
1872 for (Square s = SQ_A1; s <= SQ_H8; s++)
1873 if (piece_type(piece_on(s)) == KING)
1874 kingCount[piece_color(piece_on(s))]++;
1876 if (kingCount[0] != 1 || kingCount[1] != 1)
1880 // Can the side to move capture the opponent's king?
1881 if (failedStep) (*failedStep)++;
1882 if (debugKingCapture)
1884 Color us = side_to_move();
1885 Color them = opposite_color(us);
1886 Square ksq = king_square(them);
1887 if (attackers_to(ksq) & pieces_of_color(us))
1891 // Is there more than 2 checkers?
1892 if (failedStep) (*failedStep)++;
1893 if (debugCheckerCount && count_1s<CNT32>(st->checkersBB) > 2)
1897 if (failedStep) (*failedStep)++;
1900 // The intersection of the white and black pieces must be empty
1901 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
1904 // The union of the white and black pieces must be equal to all
1906 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
1909 // Separate piece type bitboards must have empty intersections
1910 for (PieceType p1 = PAWN; p1 <= KING; p1++)
1911 for (PieceType p2 = PAWN; p2 <= KING; p2++)
1912 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1916 // En passant square OK?
1917 if (failedStep) (*failedStep)++;
1918 if (ep_square() != SQ_NONE)
1920 // The en passant square must be on rank 6, from the point of view of the
1922 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
1927 if (failedStep) (*failedStep)++;
1928 if (debugKey && st->key != compute_key())
1931 // Pawn hash key OK?
1932 if (failedStep) (*failedStep)++;
1933 if (debugPawnKey && st->pawnKey != compute_pawn_key())
1936 // Material hash key OK?
1937 if (failedStep) (*failedStep)++;
1938 if (debugMaterialKey && st->materialKey != compute_material_key())
1941 // Incremental eval OK?
1942 if (failedStep) (*failedStep)++;
1943 if (debugIncrementalEval && st->value != compute_value())
1946 // Non-pawn material OK?
1947 if (failedStep) (*failedStep)++;
1948 if (debugNonPawnMaterial)
1950 if (st->npMaterial[WHITE] != compute_non_pawn_material(WHITE))
1953 if (st->npMaterial[BLACK] != compute_non_pawn_material(BLACK))
1958 if (failedStep) (*failedStep)++;
1959 if (debugPieceCounts)
1960 for (Color c = WHITE; c <= BLACK; c++)
1961 for (PieceType pt = PAWN; pt <= KING; pt++)
1962 if (pieceCount[c][pt] != count_1s<CNT32>(pieces(pt, c)))
1965 if (failedStep) (*failedStep)++;
1967 for (Color c = WHITE; c <= BLACK; c++)
1968 for (PieceType pt = PAWN; pt <= KING; pt++)
1969 for (int i = 0; i < pieceCount[c][pt]; i++)
1971 if (piece_on(piece_list(c, pt, i)) != make_piece(c, pt))
1974 if (index[piece_list(c, pt, i)] != i)
1978 if (failedStep) (*failedStep)++;
1979 if (debugCastleSquares)
1980 for (CastleRight f = WHITE_OO; f <= BLACK_OOO; f = CastleRight(f << 1))
1985 Piece rook = (f & (WHITE_OO | WHITE_OOO) ? WR : BR);
1987 if ( castleRightsMask[castleRookSquare[f]] != (ALL_CASTLES ^ f)
1988 || piece_on(castleRookSquare[f]) != rook)
1992 if (failedStep) *failedStep = 0;