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& fenStr, 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 fen(fenStr);
167 fen >> std::noskipws;
169 // 1. Piece placement
170 while ((fen >> token) && !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);
187 sideToMove = (token == 'w' ? WHITE : BLACK);
190 // 3. Castling availability
191 while ((fen >> token) && !isspace(token))
192 set_castling_rights(token);
194 // 4. En passant square. Ignore if no pawn capture is possible
195 if ( ((fen >> col) && (col >= 'a' && col <= 'h'))
196 && ((fen >> row) && (row == '3' || row == '6')))
198 st->epSquare = make_square(File(col - 'a'), Rank(row - '1'));
199 Color them = opposite_color(sideToMove);
201 if (!(attacks_from<PAWN>(st->epSquare, them) & pieces(PAWN, sideToMove)))
202 st->epSquare = SQ_NONE;
205 // 5-6. Halfmove clock and fullmove number
206 fen >> std::skipws >> st->rule50 >> fullMoves;
208 // Various initialisations
209 chess960 = isChess960;
210 st->checkersBB = attackers_to(king_square(sideToMove)) & pieces(opposite_color(sideToMove));
212 st->key = compute_key();
213 st->pawnKey = compute_pawn_key();
214 st->materialKey = compute_material_key();
215 st->value = compute_value();
216 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
217 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
221 /// Position::set_castle() is an helper function used to set
222 /// correct castling related flags.
224 void Position::set_castle(int f, Square ksq, Square rsq) {
226 st->castleRights |= f;
227 castleRightsMask[ksq] ^= f;
228 castleRightsMask[rsq] ^= f;
229 castleRookSquare[f] = rsq;
233 /// Position::set_castling_rights() sets castling parameters castling avaiability.
234 /// This function is compatible with 3 standards: Normal FEN standard, Shredder-FEN
235 /// that uses the letters of the columns on which the rooks began the game instead
236 /// of KQkq and also X-FEN standard that, in case of Chess960, if an inner Rook is
237 /// associated with the castling right, the traditional castling tag will be replaced
238 /// by the file letter of the involved rook as for the Shredder-FEN.
240 void Position::set_castling_rights(char token) {
242 Color c = islower(token) ? BLACK : WHITE;
244 Square sqA = relative_square(c, SQ_A1);
245 Square sqH = relative_square(c, SQ_H1);
246 Square rsq, ksq = king_square(c);
248 token = char(toupper(token));
251 for (rsq = sqH; piece_on(rsq) != make_piece(c, ROOK); rsq--) {}
253 else if (token == 'Q')
254 for (rsq = sqA; piece_on(rsq) != make_piece(c, ROOK); rsq++) {}
256 else if (token >= 'A' && token <= 'H')
257 rsq = make_square(File(token - 'A'), relative_rank(c, RANK_1));
261 if (square_file(rsq) < square_file(ksq))
262 set_castle(WHITE_OOO << c, ksq, rsq);
264 set_castle(WHITE_OO << c, ksq, rsq);
268 /// Position::to_fen() returns a FEN representation of the position. In case
269 /// of Chess960 the Shredder-FEN notation is used. Mainly a debugging function.
271 const string Position::to_fen() const {
273 std::ostringstream fen;
277 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
281 for (File file = FILE_A; file <= FILE_H; file++)
283 sq = make_square(file, rank);
285 if (!square_is_empty(sq))
292 fen << PieceToChar[piece_on(sq)];
305 fen << (sideToMove == WHITE ? " w " : " b ");
307 if (st->castleRights != CASTLES_NONE)
309 if (can_castle(WHITE_OO))
310 fen << (chess960 ? char(toupper(file_to_char(square_file(castle_rook_square(WHITE_OO))))) : 'K');
312 if (can_castle(WHITE_OOO))
313 fen << (chess960 ? char(toupper(file_to_char(square_file(castle_rook_square(WHITE_OOO))))) : 'Q');
315 if (can_castle(BLACK_OO))
316 fen << (chess960 ? file_to_char(square_file(castle_rook_square(BLACK_OO))) : 'k');
318 if (can_castle(BLACK_OOO))
319 fen << (chess960 ? file_to_char(square_file(castle_rook_square(BLACK_OOO))) : 'q');
323 fen << (ep_square() == SQ_NONE ? " -" : " " + square_to_string(ep_square()))
324 << " " << st->rule50 << " " << fullMoves;
330 /// Position::print() prints an ASCII representation of the position to
331 /// the standard output. If a move is given then also the san is printed.
333 void Position::print(Move move) const {
335 const char* dottedLine = "\n+---+---+---+---+---+---+---+---+\n";
339 Position p(*this, thread());
340 string dd = (sideToMove == BLACK ? ".." : "");
341 cout << "\nMove is: " << dd << move_to_san(p, move);
344 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
346 cout << dottedLine << '|';
347 for (File file = FILE_A; file <= FILE_H; file++)
349 Square sq = make_square(file, rank);
350 Piece piece = piece_on(sq);
352 if (piece == PIECE_NONE && square_color(sq) == DARK)
353 piece = PIECE_NONE_DARK_SQ;
355 char c = (piece_color(piece_on(sq)) == BLACK ? '=' : ' ');
356 cout << c << PieceToChar[piece] << c << '|';
359 cout << dottedLine << "Fen is: " << to_fen() << "\nKey is: " << st->key << endl;
363 /// Position:hidden_checkers<>() returns a bitboard of all pinned (against the
364 /// king) pieces for the given color. Or, when template parameter FindPinned is
365 /// false, the function return the pieces of the given color candidate for a
366 /// discovery check against the enemy king.
368 template<bool FindPinned>
369 Bitboard Position::hidden_checkers(Color c) const {
371 // Pinned pieces protect our king, dicovery checks attack the enemy king
372 Bitboard b, result = EmptyBoardBB;
373 Bitboard pinners = pieces(FindPinned ? opposite_color(c) : c);
374 Square ksq = king_square(FindPinned ? c : opposite_color(c));
376 // Pinners are sliders, that give check when candidate pinned is removed
377 pinners &= (pieces(ROOK, QUEEN) & RookPseudoAttacks[ksq])
378 | (pieces(BISHOP, QUEEN) & BishopPseudoAttacks[ksq]);
382 b = squares_between(ksq, pop_1st_bit(&pinners)) & occupied_squares();
384 // Only one bit set and is an our piece?
385 if (b && !(b & (b - 1)) && (b & pieces(c)))
392 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
393 /// king) pieces for the given color. Note that checkersBB bitboard must
394 /// be already updated.
396 Bitboard Position::pinned_pieces(Color c) const {
398 return hidden_checkers<true>(c);
402 /// Position:discovered_check_candidates() returns a bitboard containing all
403 /// pieces for the given side which are candidates for giving a discovered
404 /// check. Contrary to pinned_pieces() here there is no need of checkersBB
405 /// to be already updated.
407 Bitboard Position::discovered_check_candidates(Color c) const {
409 return hidden_checkers<false>(c);
412 /// Position::attackers_to() computes a bitboard containing all pieces which
413 /// attacks a given square.
415 Bitboard Position::attackers_to(Square s) const {
417 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
418 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
419 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
420 | (attacks_from<ROOK>(s) & pieces(ROOK, QUEEN))
421 | (attacks_from<BISHOP>(s) & pieces(BISHOP, QUEEN))
422 | (attacks_from<KING>(s) & pieces(KING));
425 Bitboard Position::attackers_to(Square s, Bitboard occ) const {
427 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
428 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
429 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
430 | (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
431 | (bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN))
432 | (attacks_from<KING>(s) & pieces(KING));
435 /// Position::attacks_from() computes a bitboard of all attacks
436 /// of a given piece put in a given square.
438 Bitboard Position::attacks_from(Piece p, Square s) const {
440 assert(square_is_ok(s));
444 case WB: case BB: return attacks_from<BISHOP>(s);
445 case WR: case BR: return attacks_from<ROOK>(s);
446 case WQ: case BQ: return attacks_from<QUEEN>(s);
447 default: return StepAttacksBB[p][s];
451 Bitboard Position::attacks_from(Piece p, Square s, Bitboard occ) {
453 assert(square_is_ok(s));
457 case WB: case BB: return bishop_attacks_bb(s, occ);
458 case WR: case BR: return rook_attacks_bb(s, occ);
459 case WQ: case BQ: return bishop_attacks_bb(s, occ) | rook_attacks_bb(s, occ);
460 default: return StepAttacksBB[p][s];
465 /// Position::move_attacks_square() tests whether a move from the current
466 /// position attacks a given square.
468 bool Position::move_attacks_square(Move m, Square s) const {
470 assert(move_is_ok(m));
471 assert(square_is_ok(s));
474 Square f = move_from(m), t = move_to(m);
476 assert(!square_is_empty(f));
478 if (bit_is_set(attacks_from(piece_on(f), t), s))
481 // Move the piece and scan for X-ray attacks behind it
482 occ = occupied_squares();
483 do_move_bb(&occ, make_move_bb(f, t));
484 xray = ( (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
485 |(bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN)))
486 & pieces(piece_color(piece_on(f)));
488 // If we have attacks we need to verify that are caused by our move
489 // and are not already existent ones.
490 return xray && (xray ^ (xray & attacks_from<QUEEN>(s)));
494 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
496 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
499 assert(move_is_ok(m));
500 assert(pinned == pinned_pieces(side_to_move()));
502 Color us = side_to_move();
503 Square from = move_from(m);
505 assert(piece_color(piece_on(from)) == us);
506 assert(piece_on(king_square(us)) == make_piece(us, KING));
508 // En passant captures are a tricky special case. Because they are rather
509 // uncommon, we do it simply by testing whether the king is attacked after
513 Color them = opposite_color(us);
514 Square to = move_to(m);
515 Square capsq = to + pawn_push(them);
516 Square ksq = king_square(us);
517 Bitboard b = occupied_squares();
519 assert(to == ep_square());
520 assert(piece_on(from) == make_piece(us, PAWN));
521 assert(piece_on(capsq) == make_piece(them, PAWN));
522 assert(piece_on(to) == PIECE_NONE);
525 clear_bit(&b, capsq);
528 return !(rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, them))
529 && !(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, them));
532 // If the moving piece is a king, check whether the destination
533 // square is attacked by the opponent. Castling moves are checked
534 // for legality during move generation.
535 if (piece_type(piece_on(from)) == KING)
536 return move_is_castle(m) || !(attackers_to(move_to(m)) & pieces(opposite_color(us)));
538 // A non-king move is legal if and only if it is not pinned or it
539 // is moving along the ray towards or away from the king.
541 || !bit_is_set(pinned, from)
542 || squares_aligned(from, move_to(m), king_square(us));
546 /// Position::move_is_legal() takes a move and tests whether the move
547 /// is legal. This version is not very fast and should be used only
548 /// in non time-critical paths.
550 bool Position::move_is_legal(const Move m) const {
552 for (MoveList<MV_LEGAL> ml(*this); !ml.end(); ++ml)
560 /// Fast version of Position::move_is_pl() that takes a move and a bitboard
561 /// of pinned pieces as input, and tests whether the move is pseudo legal.
563 bool Position::move_is_pl(const Move m) const {
567 Color us = sideToMove;
568 Color them = opposite_color(sideToMove);
569 Square from = move_from(m);
570 Square to = move_to(m);
571 Piece pc = piece_on(from);
573 // Use a slower but simpler function for uncommon cases
574 if (move_is_special(m))
575 return move_is_legal(m);
577 // Is not a promotion, so promotion piece must be empty
578 if (promotion_piece_type(m) - 2 != PIECE_TYPE_NONE)
581 // If the from square is not occupied by a piece belonging to the side to
582 // move, the move is obviously not legal.
583 if (pc == PIECE_NONE || piece_color(pc) != us)
586 // The destination square cannot be occupied by a friendly piece
587 if (piece_color(piece_on(to)) == us)
590 // Handle the special case of a pawn move
591 if (piece_type(pc) == PAWN)
593 // Move direction must be compatible with pawn color
594 int direction = to - from;
595 if ((us == WHITE) != (direction > 0))
598 // We have already handled promotion moves, so destination
599 // cannot be on the 8/1th rank.
600 if (square_rank(to) == RANK_8 || square_rank(to) == RANK_1)
603 // Proceed according to the square delta between the origin and
604 // destination squares.
611 // Capture. The destination square must be occupied by an enemy
612 // piece (en passant captures was handled earlier).
613 if (piece_color(piece_on(to)) != them)
616 // From and to files must be one file apart, avoids a7h5
617 if (abs(square_file(from) - square_file(to)) != 1)
623 // Pawn push. The destination square must be empty.
624 if (!square_is_empty(to))
629 // Double white pawn push. The destination square must be on the fourth
630 // rank, and both the destination square and the square between the
631 // source and destination squares must be empty.
632 if ( square_rank(to) != RANK_4
633 || !square_is_empty(to)
634 || !square_is_empty(from + DELTA_N))
639 // Double black pawn push. The destination square must be on the fifth
640 // rank, and both the destination square and the square between the
641 // source and destination squares must be empty.
642 if ( square_rank(to) != RANK_5
643 || !square_is_empty(to)
644 || !square_is_empty(from + DELTA_S))
652 else if (!bit_is_set(attacks_from(pc, from), to))
657 // In case of king moves under check we have to remove king so to catch
658 // as invalid moves like b1a1 when opposite queen is on c1.
659 if (piece_type(piece_on(from)) == KING)
661 Bitboard b = occupied_squares();
663 if (attackers_to(move_to(m), b) & pieces(opposite_color(us)))
668 Bitboard target = checkers();
669 Square checksq = pop_1st_bit(&target);
671 if (target) // double check ? In this case a king move is required
674 // Our move must be a blocking evasion or a capture of the checking piece
675 target = squares_between(checksq, king_square(us)) | checkers();
676 if (!bit_is_set(target, move_to(m)))
685 /// Position::move_gives_check() tests whether a pseudo-legal move is a check
687 bool Position::move_gives_check(Move m, const CheckInfo& ci) const {
690 assert(move_is_ok(m));
691 assert(ci.dcCandidates == discovered_check_candidates(side_to_move()));
692 assert(piece_color(piece_on(move_from(m))) == side_to_move());
694 Square from = move_from(m);
695 Square to = move_to(m);
696 PieceType pt = piece_type(piece_on(from));
699 if (bit_is_set(ci.checkSq[pt], to))
703 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
705 // For pawn and king moves we need to verify also direction
706 if ( (pt != PAWN && pt != KING)
707 || !squares_aligned(from, to, king_square(opposite_color(side_to_move()))))
711 // Can we skip the ugly special cases ?
712 if (!move_is_special(m))
715 Color us = side_to_move();
716 Bitboard b = occupied_squares();
717 Square ksq = king_square(opposite_color(us));
719 // Promotion with check ?
720 if (move_is_promotion(m))
724 switch (promotion_piece_type(m))
727 return bit_is_set(attacks_from<KNIGHT>(to), ksq);
729 return bit_is_set(bishop_attacks_bb(to, b), ksq);
731 return bit_is_set(rook_attacks_bb(to, b), ksq);
733 return bit_is_set(queen_attacks_bb(to, b), ksq);
739 // En passant capture with check ? We have already handled the case
740 // of direct checks and ordinary discovered check, the only case we
741 // need to handle is the unusual case of a discovered check through
742 // the captured pawn.
745 Square capsq = make_square(square_file(to), square_rank(from));
747 clear_bit(&b, capsq);
749 return (rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, us))
750 ||(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, us));
753 // Castling with check ?
754 if (move_is_castle(m))
756 Square kfrom, kto, rfrom, rto;
762 kto = relative_square(us, SQ_G1);
763 rto = relative_square(us, SQ_F1);
765 kto = relative_square(us, SQ_C1);
766 rto = relative_square(us, SQ_D1);
768 clear_bit(&b, kfrom);
769 clear_bit(&b, rfrom);
772 return bit_is_set(rook_attacks_bb(rto, b), ksq);
779 /// Position::do_setup_move() makes a permanent move on the board. It should
780 /// be used when setting up a position on board. You can't undo the move.
782 void Position::do_setup_move(Move m) {
786 // Update the number of full moves after black's move
787 if (sideToMove == BLACK)
792 // Reset "game ply" in case we made a non-reversible move.
793 // "game ply" is used for repetition detection.
797 // Our StateInfo newSt is about going out of scope so copy
798 // its content before it disappears.
803 /// Position::do_move() makes a move, and saves all information necessary
804 /// to a StateInfo object. The move is assumed to be legal. Pseudo-legal
805 /// moves should be filtered out before this function is called.
807 void Position::do_move(Move m, StateInfo& newSt) {
810 do_move(m, newSt, ci, move_gives_check(m, ci));
813 void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveIsCheck) {
816 assert(move_is_ok(m));
817 assert(&newSt != st);
822 // Copy some fields of old state to our new StateInfo object except the
823 // ones which are recalculated from scratch anyway, then switch our state
824 // pointer to point to the new, ready to be updated, state.
825 struct ReducedStateInfo {
826 Key pawnKey, materialKey;
827 int castleRights, rule50, gamePly, pliesFromNull;
833 memcpy(&newSt, st, sizeof(ReducedStateInfo));
838 // Save the current key to the history[] array, in order to be able to
839 // detect repetition draws.
840 history[st->gamePly++] = key;
842 // Update side to move
843 key ^= zobSideToMove;
845 // Increment the 50 moves rule draw counter. Resetting it to zero in the
846 // case of non-reversible moves is taken care of later.
850 if (move_is_castle(m))
857 Color us = side_to_move();
858 Color them = opposite_color(us);
859 Square from = move_from(m);
860 Square to = move_to(m);
861 bool ep = move_is_ep(m);
862 bool pm = move_is_promotion(m);
864 Piece piece = piece_on(from);
865 PieceType pt = piece_type(piece);
866 PieceType capture = ep ? PAWN : piece_type(piece_on(to));
868 assert(piece_color(piece_on(from)) == us);
869 assert(piece_color(piece_on(to)) == them || square_is_empty(to));
870 assert(!(ep || pm) || piece == make_piece(us, PAWN));
871 assert(!pm || relative_rank(us, to) == RANK_8);
874 do_capture_move(key, capture, them, to, ep);
877 key ^= zobrist[us][pt][from] ^ zobrist[us][pt][to];
879 // Reset en passant square
880 if (st->epSquare != SQ_NONE)
882 key ^= zobEp[st->epSquare];
883 st->epSquare = SQ_NONE;
886 // Update castle rights if needed
887 if ( st->castleRights != CASTLES_NONE
888 && (castleRightsMask[from] & castleRightsMask[to]) != ALL_CASTLES)
890 key ^= zobCastle[st->castleRights];
891 st->castleRights &= castleRightsMask[from] & castleRightsMask[to];
892 key ^= zobCastle[st->castleRights];
895 // Prefetch TT access as soon as we know key is updated
896 prefetch((char*)TT.first_entry(key));
899 Bitboard move_bb = make_move_bb(from, to);
900 do_move_bb(&byColorBB[us], move_bb);
901 do_move_bb(&byTypeBB[pt], move_bb);
902 do_move_bb(&byTypeBB[0], move_bb); // HACK: byTypeBB[0] == occupied squares
904 board[to] = board[from];
905 board[from] = PIECE_NONE;
907 // Update piece lists, note that index[from] is not updated and
908 // becomes stale. This works as long as index[] is accessed just
909 // by known occupied squares.
910 index[to] = index[from];
911 pieceList[us][pt][index[to]] = to;
913 // If the moving piece was a pawn do some special extra work
916 // Reset rule 50 draw counter
919 // Update pawn hash key and prefetch in L1/L2 cache
920 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
922 // Set en passant square, only if moved pawn can be captured
923 if ((to ^ from) == 16)
925 if (attacks_from<PAWN>(from + pawn_push(us), us) & pieces(PAWN, them))
927 st->epSquare = Square((int(from) + int(to)) / 2);
928 key ^= zobEp[st->epSquare];
932 if (pm) // promotion ?
934 PieceType promotion = promotion_piece_type(m);
936 assert(promotion >= KNIGHT && promotion <= QUEEN);
938 // Insert promoted piece instead of pawn
939 clear_bit(&byTypeBB[PAWN], to);
940 set_bit(&byTypeBB[promotion], to);
941 board[to] = make_piece(us, promotion);
943 // Update piece counts
944 pieceCount[us][promotion]++;
945 pieceCount[us][PAWN]--;
947 // Update material key
948 st->materialKey ^= zobrist[us][PAWN][pieceCount[us][PAWN]];
949 st->materialKey ^= zobrist[us][promotion][pieceCount[us][promotion]-1];
951 // Update piece lists, move the last pawn at index[to] position
952 // and shrink the list. Add a new promotion piece to the list.
953 Square lastPawnSquare = pieceList[us][PAWN][pieceCount[us][PAWN]];
954 index[lastPawnSquare] = index[to];
955 pieceList[us][PAWN][index[lastPawnSquare]] = lastPawnSquare;
956 pieceList[us][PAWN][pieceCount[us][PAWN]] = SQ_NONE;
957 index[to] = pieceCount[us][promotion] - 1;
958 pieceList[us][promotion][index[to]] = to;
960 // Partially revert hash keys update
961 key ^= zobrist[us][PAWN][to] ^ zobrist[us][promotion][to];
962 st->pawnKey ^= zobrist[us][PAWN][to];
964 // Partially revert and update incremental scores
965 st->value -= pst(make_piece(us, PAWN), to);
966 st->value += pst(make_piece(us, promotion), to);
969 st->npMaterial[us] += PieceValueMidgame[promotion];
973 // Prefetch pawn and material hash tables
974 Threads[threadID].pawnTable.prefetch(st->pawnKey);
975 Threads[threadID].materialTable.prefetch(st->materialKey);
977 // Update incremental scores
978 st->value += pst_delta(piece, from, to);
981 st->capturedType = capture;
983 // Update the key with the final value
986 // Update checkers bitboard, piece must be already moved
987 st->checkersBB = EmptyBoardBB;
992 st->checkersBB = attackers_to(king_square(them)) & pieces(us);
996 if (bit_is_set(ci.checkSq[pt], to))
997 st->checkersBB = SetMaskBB[to];
1000 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
1003 st->checkersBB |= (attacks_from<ROOK>(king_square(them)) & pieces(ROOK, QUEEN, us));
1006 st->checkersBB |= (attacks_from<BISHOP>(king_square(them)) & pieces(BISHOP, QUEEN, us));
1012 sideToMove = opposite_color(sideToMove);
1013 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1019 /// Position::do_capture_move() is a private method used to update captured
1020 /// piece info. It is called from the main Position::do_move function.
1022 void Position::do_capture_move(Key& key, PieceType capture, Color them, Square to, bool ep) {
1024 assert(capture != KING);
1028 // If the captured piece was a pawn, update pawn hash key,
1029 // otherwise update non-pawn material.
1030 if (capture == PAWN)
1032 if (ep) // en passant ?
1034 capsq = to + pawn_push(them);
1036 assert(to == st->epSquare);
1037 assert(relative_rank(opposite_color(them), to) == RANK_6);
1038 assert(piece_on(to) == PIECE_NONE);
1039 assert(piece_on(capsq) == make_piece(them, PAWN));
1041 board[capsq] = PIECE_NONE;
1043 st->pawnKey ^= zobrist[them][PAWN][capsq];
1046 st->npMaterial[them] -= PieceValueMidgame[capture];
1048 // Remove captured piece
1049 clear_bit(&byColorBB[them], capsq);
1050 clear_bit(&byTypeBB[capture], capsq);
1051 clear_bit(&byTypeBB[0], capsq);
1054 key ^= zobrist[them][capture][capsq];
1056 // Update incremental scores
1057 st->value -= pst(make_piece(them, capture), capsq);
1059 // Update piece count
1060 pieceCount[them][capture]--;
1062 // Update material hash key
1063 st->materialKey ^= zobrist[them][capture][pieceCount[them][capture]];
1065 // Update piece list, move the last piece at index[capsq] position
1067 // WARNING: This is a not perfectly revresible operation. When we
1068 // will reinsert the captured piece in undo_move() we will put it
1069 // at the end of the list and not in its original place, it means
1070 // index[] and pieceList[] are not guaranteed to be invariant to a
1071 // do_move() + undo_move() sequence.
1072 Square lastPieceSquare = pieceList[them][capture][pieceCount[them][capture]];
1073 index[lastPieceSquare] = index[capsq];
1074 pieceList[them][capture][index[lastPieceSquare]] = lastPieceSquare;
1075 pieceList[them][capture][pieceCount[them][capture]] = SQ_NONE;
1077 // Reset rule 50 counter
1082 /// Position::do_castle_move() is a private method used to make a castling
1083 /// move. It is called from the main Position::do_move function. Note that
1084 /// castling moves are encoded as "king captures friendly rook" moves, for
1085 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1087 void Position::do_castle_move(Move m) {
1089 assert(move_is_ok(m));
1090 assert(move_is_castle(m));
1092 Color us = side_to_move();
1093 Color them = opposite_color(us);
1095 // Find source squares for king and rook
1096 Square kfrom = move_from(m);
1097 Square rfrom = move_to(m);
1100 assert(piece_on(kfrom) == make_piece(us, KING));
1101 assert(piece_on(rfrom) == make_piece(us, ROOK));
1103 // Find destination squares for king and rook
1104 if (rfrom > kfrom) // O-O
1106 kto = relative_square(us, SQ_G1);
1107 rto = relative_square(us, SQ_F1);
1111 kto = relative_square(us, SQ_C1);
1112 rto = relative_square(us, SQ_D1);
1115 // Remove pieces from source squares
1116 clear_bit(&byColorBB[us], kfrom);
1117 clear_bit(&byTypeBB[KING], kfrom);
1118 clear_bit(&byTypeBB[0], kfrom);
1119 clear_bit(&byColorBB[us], rfrom);
1120 clear_bit(&byTypeBB[ROOK], rfrom);
1121 clear_bit(&byTypeBB[0], rfrom);
1123 // Put pieces on destination squares
1124 set_bit(&byColorBB[us], kto);
1125 set_bit(&byTypeBB[KING], kto);
1126 set_bit(&byTypeBB[0], kto);
1127 set_bit(&byColorBB[us], rto);
1128 set_bit(&byTypeBB[ROOK], rto);
1129 set_bit(&byTypeBB[0], rto);
1132 Piece king = make_piece(us, KING);
1133 Piece rook = make_piece(us, ROOK);
1134 board[kfrom] = board[rfrom] = PIECE_NONE;
1138 // Update piece lists
1139 pieceList[us][KING][index[kfrom]] = kto;
1140 pieceList[us][ROOK][index[rfrom]] = rto;
1141 int tmp = index[rfrom]; // In Chess960 could be kto == rfrom
1142 index[kto] = index[kfrom];
1145 // Reset capture field
1146 st->capturedType = PIECE_TYPE_NONE;
1148 // Update incremental scores
1149 st->value += pst_delta(king, kfrom, kto);
1150 st->value += pst_delta(rook, rfrom, rto);
1153 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1154 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1156 // Clear en passant square
1157 if (st->epSquare != SQ_NONE)
1159 st->key ^= zobEp[st->epSquare];
1160 st->epSquare = SQ_NONE;
1163 // Update castling rights
1164 st->key ^= zobCastle[st->castleRights];
1165 st->castleRights &= castleRightsMask[kfrom];
1166 st->key ^= zobCastle[st->castleRights];
1168 // Reset rule 50 counter
1171 // Update checkers BB
1172 st->checkersBB = attackers_to(king_square(them)) & pieces(us);
1175 sideToMove = opposite_color(sideToMove);
1176 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1182 /// Position::undo_move() unmakes a move. When it returns, the position should
1183 /// be restored to exactly the same state as before the move was made.
1185 void Position::undo_move(Move m) {
1188 assert(move_is_ok(m));
1190 sideToMove = opposite_color(sideToMove);
1192 if (move_is_castle(m))
1194 undo_castle_move(m);
1198 Color us = side_to_move();
1199 Color them = opposite_color(us);
1200 Square from = move_from(m);
1201 Square to = move_to(m);
1202 bool ep = move_is_ep(m);
1203 bool pm = move_is_promotion(m);
1205 PieceType pt = piece_type(piece_on(to));
1207 assert(square_is_empty(from));
1208 assert(piece_color(piece_on(to)) == us);
1209 assert(!pm || relative_rank(us, to) == RANK_8);
1210 assert(!ep || to == st->previous->epSquare);
1211 assert(!ep || relative_rank(us, to) == RANK_6);
1212 assert(!ep || piece_on(to) == make_piece(us, PAWN));
1214 if (pm) // promotion ?
1216 PieceType promotion = promotion_piece_type(m);
1219 assert(promotion >= KNIGHT && promotion <= QUEEN);
1220 assert(piece_on(to) == make_piece(us, promotion));
1222 // Replace promoted piece with a pawn
1223 clear_bit(&byTypeBB[promotion], to);
1224 set_bit(&byTypeBB[PAWN], to);
1226 // Update piece counts
1227 pieceCount[us][promotion]--;
1228 pieceCount[us][PAWN]++;
1230 // Update piece list replacing promotion piece with a pawn
1231 Square lastPromotionSquare = pieceList[us][promotion][pieceCount[us][promotion]];
1232 index[lastPromotionSquare] = index[to];
1233 pieceList[us][promotion][index[lastPromotionSquare]] = lastPromotionSquare;
1234 pieceList[us][promotion][pieceCount[us][promotion]] = SQ_NONE;
1235 index[to] = pieceCount[us][PAWN] - 1;
1236 pieceList[us][PAWN][index[to]] = to;
1239 // Put the piece back at the source square
1240 Bitboard move_bb = make_move_bb(to, from);
1241 do_move_bb(&byColorBB[us], move_bb);
1242 do_move_bb(&byTypeBB[pt], move_bb);
1243 do_move_bb(&byTypeBB[0], move_bb); // HACK: byTypeBB[0] == occupied squares
1245 board[from] = make_piece(us, pt);
1246 board[to] = PIECE_NONE;
1248 // Update piece list
1249 index[from] = index[to];
1250 pieceList[us][pt][index[from]] = from;
1252 if (st->capturedType)
1257 capsq = to - pawn_push(us);
1259 assert(st->capturedType != KING);
1260 assert(!ep || square_is_empty(capsq));
1262 // Restore the captured piece
1263 set_bit(&byColorBB[them], capsq);
1264 set_bit(&byTypeBB[st->capturedType], capsq);
1265 set_bit(&byTypeBB[0], capsq);
1267 board[capsq] = make_piece(them, st->capturedType);
1269 // Update piece count
1270 pieceCount[them][st->capturedType]++;
1272 // Update piece list, add a new captured piece in capsq square
1273 index[capsq] = pieceCount[them][st->capturedType] - 1;
1274 pieceList[them][st->capturedType][index[capsq]] = capsq;
1277 // Finally point our state pointer back to the previous state
1284 /// Position::undo_castle_move() is a private method used to unmake a castling
1285 /// move. It is called from the main Position::undo_move function. Note that
1286 /// castling moves are encoded as "king captures friendly rook" moves, for
1287 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1289 void Position::undo_castle_move(Move m) {
1291 assert(move_is_ok(m));
1292 assert(move_is_castle(m));
1294 // When we have arrived here, some work has already been done by
1295 // Position::undo_move. In particular, the side to move has been switched,
1296 // so the code below is correct.
1297 Color us = side_to_move();
1299 // Find source squares for king and rook
1300 Square kfrom = move_from(m);
1301 Square rfrom = move_to(m);
1304 // Find destination squares for king and rook
1305 if (rfrom > kfrom) // O-O
1307 kto = relative_square(us, SQ_G1);
1308 rto = relative_square(us, SQ_F1);
1312 kto = relative_square(us, SQ_C1);
1313 rto = relative_square(us, SQ_D1);
1316 assert(piece_on(kto) == make_piece(us, KING));
1317 assert(piece_on(rto) == make_piece(us, ROOK));
1319 // Remove pieces from destination squares
1320 clear_bit(&byColorBB[us], kto);
1321 clear_bit(&byTypeBB[KING], kto);
1322 clear_bit(&byTypeBB[0], kto);
1323 clear_bit(&byColorBB[us], rto);
1324 clear_bit(&byTypeBB[ROOK], rto);
1325 clear_bit(&byTypeBB[0], rto);
1327 // Put pieces on source squares
1328 set_bit(&byColorBB[us], kfrom);
1329 set_bit(&byTypeBB[KING], kfrom);
1330 set_bit(&byTypeBB[0], kfrom);
1331 set_bit(&byColorBB[us], rfrom);
1332 set_bit(&byTypeBB[ROOK], rfrom);
1333 set_bit(&byTypeBB[0], rfrom);
1336 Piece king = make_piece(us, KING);
1337 Piece rook = make_piece(us, ROOK);
1338 board[kto] = board[rto] = PIECE_NONE;
1339 board[kfrom] = king;
1340 board[rfrom] = rook;
1342 // Update piece lists
1343 pieceList[us][KING][index[kto]] = kfrom;
1344 pieceList[us][ROOK][index[rto]] = rfrom;
1345 int tmp = index[rto]; // In Chess960 could be rto == kfrom
1346 index[kfrom] = index[kto];
1349 // Finally point our state pointer back to the previous state
1356 /// Position::do_null_move makes() a "null move": It switches the side to move
1357 /// and updates the hash key without executing any move on the board.
1359 void Position::do_null_move(StateInfo& backupSt) {
1362 assert(!in_check());
1364 // Back up the information necessary to undo the null move to the supplied
1365 // StateInfo object.
1366 // Note that differently from normal case here backupSt is actually used as
1367 // a backup storage not as a new state to be used.
1368 backupSt.key = st->key;
1369 backupSt.epSquare = st->epSquare;
1370 backupSt.value = st->value;
1371 backupSt.previous = st->previous;
1372 backupSt.pliesFromNull = st->pliesFromNull;
1373 st->previous = &backupSt;
1375 // Save the current key to the history[] array, in order to be able to
1376 // detect repetition draws.
1377 history[st->gamePly++] = st->key;
1379 // Update the necessary information
1380 if (st->epSquare != SQ_NONE)
1381 st->key ^= zobEp[st->epSquare];
1383 st->key ^= zobSideToMove;
1384 prefetch((char*)TT.first_entry(st->key));
1386 sideToMove = opposite_color(sideToMove);
1387 st->epSquare = SQ_NONE;
1389 st->pliesFromNull = 0;
1390 st->value += (sideToMove == WHITE) ? TempoValue : -TempoValue;
1394 /// Position::undo_null_move() unmakes a "null move".
1396 void Position::undo_null_move() {
1399 assert(!in_check());
1401 // Restore information from the our backup StateInfo object
1402 StateInfo* backupSt = st->previous;
1403 st->key = backupSt->key;
1404 st->epSquare = backupSt->epSquare;
1405 st->value = backupSt->value;
1406 st->previous = backupSt->previous;
1407 st->pliesFromNull = backupSt->pliesFromNull;
1409 // Update the necessary information
1410 sideToMove = opposite_color(sideToMove);
1416 /// Position::see() is a static exchange evaluator: It tries to estimate the
1417 /// material gain or loss resulting from a move. There are three versions of
1418 /// this function: One which takes a destination square as input, one takes a
1419 /// move, and one which takes a 'from' and a 'to' square. The function does
1420 /// not yet understand promotions captures.
1422 int Position::see_sign(Move m) const {
1424 assert(move_is_ok(m));
1426 Square from = move_from(m);
1427 Square to = move_to(m);
1429 // Early return if SEE cannot be negative because captured piece value
1430 // is not less then capturing one. Note that king moves always return
1431 // here because king midgame value is set to 0.
1432 if (piece_value_midgame(piece_on(to)) >= piece_value_midgame(piece_on(from)))
1438 int Position::see(Move m) const {
1441 Bitboard occupied, attackers, stmAttackers, b;
1442 int swapList[32], slIndex = 1;
1443 PieceType capturedType, pt;
1446 assert(move_is_ok(m));
1448 // As castle moves are implemented as capturing the rook, they have
1449 // SEE == RookValueMidgame most of the times (unless the rook is under
1451 if (move_is_castle(m))
1454 from = move_from(m);
1456 capturedType = piece_type(piece_on(to));
1457 occupied = occupied_squares();
1459 // Handle en passant moves
1460 if (st->epSquare == to && piece_type(piece_on(from)) == PAWN)
1462 Square capQq = to - pawn_push(side_to_move());
1464 assert(capturedType == PIECE_TYPE_NONE);
1465 assert(piece_type(piece_on(capQq)) == PAWN);
1467 // Remove the captured pawn
1468 clear_bit(&occupied, capQq);
1469 capturedType = PAWN;
1472 // Find all attackers to the destination square, with the moving piece
1473 // removed, but possibly an X-ray attacker added behind it.
1474 clear_bit(&occupied, from);
1475 attackers = attackers_to(to, occupied);
1477 // If the opponent has no attackers we are finished
1478 stm = opposite_color(piece_color(piece_on(from)));
1479 stmAttackers = attackers & pieces(stm);
1481 return PieceValueMidgame[capturedType];
1483 // The destination square is defended, which makes things rather more
1484 // difficult to compute. We proceed by building up a "swap list" containing
1485 // the material gain or loss at each stop in a sequence of captures to the
1486 // destination square, where the sides alternately capture, and always
1487 // capture with the least valuable piece. After each capture, we look for
1488 // new X-ray attacks from behind the capturing piece.
1489 swapList[0] = PieceValueMidgame[capturedType];
1490 capturedType = piece_type(piece_on(from));
1493 // Locate the least valuable attacker for the side to move. The loop
1494 // below looks like it is potentially infinite, but it isn't. We know
1495 // that the side to move still has at least one attacker left.
1496 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1499 // Remove the attacker we just found from the 'occupied' bitboard,
1500 // and scan for new X-ray attacks behind the attacker.
1501 b = stmAttackers & pieces(pt);
1502 occupied ^= (b & (~b + 1));
1503 attackers |= (rook_attacks_bb(to, occupied) & pieces(ROOK, QUEEN))
1504 | (bishop_attacks_bb(to, occupied) & pieces(BISHOP, QUEEN));
1506 attackers &= occupied; // Cut out pieces we've already done
1508 // Add the new entry to the swap list
1509 assert(slIndex < 32);
1510 swapList[slIndex] = -swapList[slIndex - 1] + PieceValueMidgame[capturedType];
1513 // Remember the value of the capturing piece, and change the side to
1514 // move before beginning the next iteration.
1516 stm = opposite_color(stm);
1517 stmAttackers = attackers & pieces(stm);
1519 // Stop before processing a king capture
1520 if (capturedType == KING && stmAttackers)
1522 assert(slIndex < 32);
1523 swapList[slIndex++] = QueenValueMidgame*10;
1526 } while (stmAttackers);
1528 // Having built the swap list, we negamax through it to find the best
1529 // achievable score from the point of view of the side to move.
1531 swapList[slIndex-1] = Min(-swapList[slIndex], swapList[slIndex-1]);
1537 /// Position::clear() erases the position object to a pristine state, with an
1538 /// empty board, white to move, and no castling rights.
1540 void Position::clear() {
1543 memset(st, 0, sizeof(StateInfo));
1544 st->epSquare = SQ_NONE;
1546 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1547 memset(byTypeBB, 0, sizeof(Bitboard) * 8);
1548 memset(pieceCount, 0, sizeof(int) * 2 * 8);
1549 memset(index, 0, sizeof(int) * 64);
1551 for (int i = 0; i < 8; i++)
1552 for (int j = 0; j < 16; j++)
1553 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1555 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
1557 board[sq] = PIECE_NONE;
1558 castleRightsMask[sq] = ALL_CASTLES;
1566 /// Position::put_piece() puts a piece on the given square of the board,
1567 /// updating the board array, pieces list, bitboards, and piece counts.
1569 void Position::put_piece(Piece p, Square s) {
1571 Color c = piece_color(p);
1572 PieceType pt = piece_type(p);
1575 index[s] = pieceCount[c][pt]++;
1576 pieceList[c][pt][index[s]] = s;
1578 set_bit(&byTypeBB[pt], s);
1579 set_bit(&byColorBB[c], s);
1580 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1584 /// Position::compute_key() computes the hash key of the position. The hash
1585 /// key is usually updated incrementally as moves are made and unmade, the
1586 /// compute_key() function is only used when a new position is set up, and
1587 /// to verify the correctness of the hash key when running in debug mode.
1589 Key Position::compute_key() const {
1591 Key result = zobCastle[st->castleRights];
1593 for (Square s = SQ_A1; s <= SQ_H8; s++)
1594 if (!square_is_empty(s))
1595 result ^= zobrist[piece_color(piece_on(s))][piece_type(piece_on(s))][s];
1597 if (ep_square() != SQ_NONE)
1598 result ^= zobEp[ep_square()];
1600 if (side_to_move() == BLACK)
1601 result ^= zobSideToMove;
1607 /// Position::compute_pawn_key() computes the hash key of the position. The
1608 /// hash key is usually updated incrementally as moves are made and unmade,
1609 /// the compute_pawn_key() function is only used when a new position is set
1610 /// up, and to verify the correctness of the pawn hash key when running in
1613 Key Position::compute_pawn_key() const {
1618 for (Color c = WHITE; c <= BLACK; c++)
1620 b = pieces(PAWN, c);
1622 result ^= zobrist[c][PAWN][pop_1st_bit(&b)];
1628 /// Position::compute_material_key() computes the hash key of the position.
1629 /// The hash key is usually updated incrementally as moves are made and unmade,
1630 /// the compute_material_key() function is only used when a new position is set
1631 /// up, and to verify the correctness of the material hash key when running in
1634 Key Position::compute_material_key() const {
1638 for (Color c = WHITE; c <= BLACK; c++)
1639 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1640 for (int i = 0, cnt = piece_count(c, pt); i < cnt; i++)
1641 result ^= zobrist[c][pt][i];
1647 /// Position::compute_value() compute the incremental scores for the middle
1648 /// game and the endgame. These functions are used to initialize the incremental
1649 /// scores when a new position is set up, and to verify that the scores are correctly
1650 /// updated by do_move and undo_move when the program is running in debug mode.
1651 Score Position::compute_value() const {
1654 Score result = SCORE_ZERO;
1656 for (Color c = WHITE; c <= BLACK; c++)
1657 for (PieceType pt = PAWN; pt <= KING; pt++)
1661 result += pst(make_piece(c, pt), pop_1st_bit(&b));
1664 result += (side_to_move() == WHITE ? TempoValue / 2 : -TempoValue / 2);
1669 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1670 /// game material value for the given side. Material values are updated
1671 /// incrementally during the search, this function is only used while
1672 /// initializing a new Position object.
1674 Value Position::compute_non_pawn_material(Color c) const {
1676 Value result = VALUE_ZERO;
1678 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1679 result += piece_count(c, pt) * PieceValueMidgame[pt];
1685 /// Position::is_draw() tests whether the position is drawn by material,
1686 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1687 /// must be done by the search.
1688 template<bool SkipRepetition>
1689 bool Position::is_draw() const {
1691 // Draw by material?
1693 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1696 // Draw by the 50 moves rule?
1697 if (st->rule50 > 99 && !is_mate())
1700 // Draw by repetition?
1701 if (!SkipRepetition)
1702 for (int i = 4, e = Min(Min(st->gamePly, st->rule50), st->pliesFromNull); i <= e; i += 2)
1703 if (history[st->gamePly - i] == st->key)
1709 // Explicit template instantiations
1710 template bool Position::is_draw<false>() const;
1711 template bool Position::is_draw<true>() const;
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 return in_check() && !MoveList<MV_LEGAL>(*this).size();
1723 /// Position::init() is a static member function which initializes at
1724 /// startup the various arrays used to compute hash keys and the piece
1725 /// square tables. The latter is a two-step operation: First, the white
1726 /// halves of the tables are copied from the MgPST[][] and EgPST[][] arrays.
1727 /// Second, the black halves of the tables are initialized by mirroring
1728 /// and changing the sign of the corresponding white scores.
1730 void Position::init() {
1734 for (Color c = WHITE; c <= BLACK; c++)
1735 for (PieceType pt = PAWN; pt <= KING; pt++)
1736 for (Square s = SQ_A1; s <= SQ_H8; s++)
1737 zobrist[c][pt][s] = rk.rand<Key>();
1739 for (Square s = SQ_A1; s <= SQ_H8; s++)
1740 zobEp[s] = rk.rand<Key>();
1742 for (int i = 0; i < 16; i++)
1743 zobCastle[i] = rk.rand<Key>();
1745 zobSideToMove = rk.rand<Key>();
1746 zobExclusion = rk.rand<Key>();
1748 for (Square s = SQ_A1; s <= SQ_H8; s++)
1749 for (Piece p = WP; p <= WK; p++)
1750 pieceSquareTable[p][s] = make_score(MgPST[p][s], EgPST[p][s]);
1752 for (Square s = SQ_A1; s <= SQ_H8; s++)
1753 for (Piece p = BP; p <= BK; p++)
1754 pieceSquareTable[p][s] = -pieceSquareTable[p-8][flip_square(s)];
1758 /// Position::flip() flips position with the white and black sides reversed. This
1759 /// is only useful for debugging especially for finding evaluation symmetry bugs.
1761 void Position::flip() {
1765 // Make a copy of current position before to start changing
1766 const Position pos(*this, threadID);
1769 threadID = pos.thread();
1772 for (Square s = SQ_A1; s <= SQ_H8; s++)
1773 if (!pos.square_is_empty(s))
1774 put_piece(Piece(pos.piece_on(s) ^ 8), flip_square(s));
1777 sideToMove = opposite_color(pos.side_to_move());
1780 if (pos.can_castle(WHITE_OO))
1781 set_castle(BLACK_OO, king_square(BLACK), flip_square(pos.castle_rook_square(WHITE_OO)));
1782 if (pos.can_castle(WHITE_OOO))
1783 set_castle(BLACK_OOO, king_square(BLACK), flip_square(pos.castle_rook_square(WHITE_OOO)));
1784 if (pos.can_castle(BLACK_OO))
1785 set_castle(WHITE_OO, king_square(WHITE), flip_square(pos.castle_rook_square(BLACK_OO)));
1786 if (pos.can_castle(BLACK_OOO))
1787 set_castle(WHITE_OOO, king_square(WHITE), flip_square(pos.castle_rook_square(BLACK_OOO)));
1789 // En passant square
1790 if (pos.st->epSquare != SQ_NONE)
1791 st->epSquare = flip_square(pos.st->epSquare);
1794 st->checkersBB = attackers_to(king_square(sideToMove)) & pieces(opposite_color(sideToMove));
1797 st->key = compute_key();
1798 st->pawnKey = compute_pawn_key();
1799 st->materialKey = compute_material_key();
1801 // Incremental scores
1802 st->value = compute_value();
1805 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
1806 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
1812 /// Position::is_ok() performs some consitency checks for the position object.
1813 /// This is meant to be helpful when debugging.
1815 bool Position::is_ok(int* failedStep) const {
1817 // What features of the position should be verified?
1818 const bool debugAll = false;
1820 const bool debugBitboards = debugAll || false;
1821 const bool debugKingCount = debugAll || false;
1822 const bool debugKingCapture = debugAll || false;
1823 const bool debugCheckerCount = debugAll || false;
1824 const bool debugKey = debugAll || false;
1825 const bool debugMaterialKey = debugAll || false;
1826 const bool debugPawnKey = debugAll || false;
1827 const bool debugIncrementalEval = debugAll || false;
1828 const bool debugNonPawnMaterial = debugAll || false;
1829 const bool debugPieceCounts = debugAll || false;
1830 const bool debugPieceList = debugAll || false;
1831 const bool debugCastleSquares = debugAll || false;
1833 if (failedStep) *failedStep = 1;
1836 if (side_to_move() != WHITE && side_to_move() != BLACK)
1839 // Are the king squares in the position correct?
1840 if (failedStep) (*failedStep)++;
1841 if (piece_on(king_square(WHITE)) != WK)
1844 if (failedStep) (*failedStep)++;
1845 if (piece_on(king_square(BLACK)) != BK)
1848 // Do both sides have exactly one king?
1849 if (failedStep) (*failedStep)++;
1852 int kingCount[2] = {0, 0};
1853 for (Square s = SQ_A1; s <= SQ_H8; s++)
1854 if (piece_type(piece_on(s)) == KING)
1855 kingCount[piece_color(piece_on(s))]++;
1857 if (kingCount[0] != 1 || kingCount[1] != 1)
1861 // Can the side to move capture the opponent's king?
1862 if (failedStep) (*failedStep)++;
1863 if (debugKingCapture)
1865 Color us = side_to_move();
1866 Color them = opposite_color(us);
1867 Square ksq = king_square(them);
1868 if (attackers_to(ksq) & pieces(us))
1872 // Is there more than 2 checkers?
1873 if (failedStep) (*failedStep)++;
1874 if (debugCheckerCount && count_1s<CNT32>(st->checkersBB) > 2)
1878 if (failedStep) (*failedStep)++;
1881 // The intersection of the white and black pieces must be empty
1882 if ((pieces(WHITE) & pieces(BLACK)) != EmptyBoardBB)
1885 // The union of the white and black pieces must be equal to all
1887 if ((pieces(WHITE) | pieces(BLACK)) != occupied_squares())
1890 // Separate piece type bitboards must have empty intersections
1891 for (PieceType p1 = PAWN; p1 <= KING; p1++)
1892 for (PieceType p2 = PAWN; p2 <= KING; p2++)
1893 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1897 // En passant square OK?
1898 if (failedStep) (*failedStep)++;
1899 if (ep_square() != SQ_NONE)
1901 // The en passant square must be on rank 6, from the point of view of the
1903 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
1908 if (failedStep) (*failedStep)++;
1909 if (debugKey && st->key != compute_key())
1912 // Pawn hash key OK?
1913 if (failedStep) (*failedStep)++;
1914 if (debugPawnKey && st->pawnKey != compute_pawn_key())
1917 // Material hash key OK?
1918 if (failedStep) (*failedStep)++;
1919 if (debugMaterialKey && st->materialKey != compute_material_key())
1922 // Incremental eval OK?
1923 if (failedStep) (*failedStep)++;
1924 if (debugIncrementalEval && st->value != compute_value())
1927 // Non-pawn material OK?
1928 if (failedStep) (*failedStep)++;
1929 if (debugNonPawnMaterial)
1931 if (st->npMaterial[WHITE] != compute_non_pawn_material(WHITE))
1934 if (st->npMaterial[BLACK] != compute_non_pawn_material(BLACK))
1939 if (failedStep) (*failedStep)++;
1940 if (debugPieceCounts)
1941 for (Color c = WHITE; c <= BLACK; c++)
1942 for (PieceType pt = PAWN; pt <= KING; pt++)
1943 if (pieceCount[c][pt] != count_1s<CNT32>(pieces(pt, c)))
1946 if (failedStep) (*failedStep)++;
1948 for (Color c = WHITE; c <= BLACK; c++)
1949 for (PieceType pt = PAWN; pt <= KING; pt++)
1950 for (int i = 0; i < pieceCount[c][pt]; i++)
1952 if (piece_on(piece_list(c, pt)[i]) != make_piece(c, pt))
1955 if (index[piece_list(c, pt)[i]] != i)
1959 if (failedStep) (*failedStep)++;
1960 if (debugCastleSquares)
1961 for (CastleRight f = WHITE_OO; f <= BLACK_OOO; f = CastleRight(f << 1))
1966 Piece rook = (f & (WHITE_OO | WHITE_OOO) ? WR : BR);
1968 if ( castleRightsMask[castleRookSquare[f]] != (ALL_CASTLES ^ f)
1969 || piece_on(castleRookSquare[f]) != rook)
1973 if (failedStep) *failedStep = 0;