2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2009 Marco Costalba
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/>.
38 #include "ucioption.h"
47 int Position::castleRightsMask[64];
49 Key Position::zobrist[2][8][64];
50 Key Position::zobEp[64];
51 Key Position::zobCastle[16];
52 Key Position::zobMaterial[2][8][16];
53 Key Position::zobSideToMove;
55 Score Position::PieceSquareTable[16][64];
57 static bool RequestPending = false;
62 CheckInfo::CheckInfo(const Position& pos) {
64 Color us = pos.side_to_move();
65 Color them = opposite_color(us);
67 ksq = pos.king_square(them);
68 dc = pos.discovered_check_candidates(us);
70 checkSq[PAWN] = pos.attacks_from<PAWN>(ksq, them);
71 checkSq[KNIGHT] = pos.attacks_from<KNIGHT>(ksq);
72 checkSq[BISHOP] = pos.attacks_from<BISHOP>(ksq);
73 checkSq[ROOK] = pos.attacks_from<ROOK>(ksq);
74 checkSq[QUEEN] = checkSq[BISHOP] | checkSq[ROOK];
75 checkSq[KING] = EmptyBoardBB;
78 Position::Position(const Position& pos) {
82 Position::Position(const string& fen) {
87 /// Position::from_fen() initializes the position object with the given FEN
88 /// string. This function is not very robust - make sure that input FENs are
89 /// correct (this is assumed to be the responsibility of the GUI).
91 void Position::from_fen(const string& fen) {
93 static const string pieceLetters = "KQRBNPkqrbnp";
94 static const Piece pieces[] = { WK, WQ, WR, WB, WN, WP, BK, BQ, BR, BB, BN, BP };
102 for ( ; fen[i] != ' '; i++)
106 // Skip the given number of files
107 file += (fen[i] - '1' + 1);
110 else if (fen[i] == '/')
116 size_t idx = pieceLetters.find(fen[i]);
117 if (idx == string::npos)
119 std::cout << "Error in FEN at character " << i << std::endl;
122 Square square = make_square(file, rank);
123 put_piece(pieces[idx], square);
129 if (fen[i] != 'w' && fen[i] != 'b')
131 std::cout << "Error in FEN at character " << i << std::endl;
134 sideToMove = (fen[i] == 'w' ? WHITE : BLACK);
140 std::cout << "Error in FEN at character " << i << std::endl;
145 while(strchr("KQkqabcdefghABCDEFGH-", fen[i])) {
151 else if(fen[i] == 'K') allow_oo(WHITE);
152 else if(fen[i] == 'Q') allow_ooo(WHITE);
153 else if(fen[i] == 'k') allow_oo(BLACK);
154 else if(fen[i] == 'q') allow_ooo(BLACK);
155 else if(fen[i] >= 'A' && fen[i] <= 'H') {
156 File rookFile, kingFile = FILE_NONE;
157 for(Square square = SQ_B1; square <= SQ_G1; square++)
158 if(piece_on(square) == WK)
159 kingFile = square_file(square);
160 if(kingFile == FILE_NONE) {
161 std::cout << "Error in FEN at character " << i << std::endl;
164 initialKFile = kingFile;
165 rookFile = File(fen[i] - 'A') + FILE_A;
166 if(rookFile < initialKFile) {
168 initialQRFile = rookFile;
172 initialKRFile = rookFile;
175 else if(fen[i] >= 'a' && fen[i] <= 'h') {
176 File rookFile, kingFile = FILE_NONE;
177 for(Square square = SQ_B8; square <= SQ_G8; square++)
178 if(piece_on(square) == BK)
179 kingFile = square_file(square);
180 if(kingFile == FILE_NONE) {
181 std::cout << "Error in FEN at character " << i << std::endl;
184 initialKFile = kingFile;
185 rookFile = File(fen[i] - 'a') + FILE_A;
186 if(rookFile < initialKFile) {
188 initialQRFile = rookFile;
192 initialKRFile = rookFile;
196 std::cout << "Error in FEN at character " << i << std::endl;
203 while (fen[i] == ' ')
207 if ( i <= fen.length() - 2
208 && (fen[i] >= 'a' && fen[i] <= 'h')
209 && (fen[i+1] == '3' || fen[i+1] == '6'))
210 st->epSquare = square_from_string(fen.substr(i, 2));
212 // Various initialisation
213 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
214 castleRightsMask[sq] = ALL_CASTLES;
216 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO|WHITE_OOO);
217 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO|BLACK_OOO);
218 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
219 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
220 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
221 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
225 st->key = compute_key();
226 st->pawnKey = compute_pawn_key();
227 st->materialKey = compute_material_key();
228 st->value = compute_value();
229 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
230 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
234 /// Position::to_fen() converts the position object to a FEN string. This is
235 /// probably only useful for debugging.
237 const string Position::to_fen() const {
239 static const string pieceLetters = " PNBRQK pnbrqk";
243 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
246 for (File file = FILE_A; file <= FILE_H; file++)
248 Square sq = make_square(file, rank);
249 if (!square_is_occupied(sq))
255 fen += (char)skip + '0';
258 fen += pieceLetters[piece_on(sq)];
261 fen += (char)skip + '0';
263 fen += (rank > RANK_1 ? '/' : ' ');
265 fen += (sideToMove == WHITE ? "w " : "b ");
266 if (st->castleRights != NO_CASTLES)
268 if (can_castle_kingside(WHITE)) fen += 'K';
269 if (can_castle_queenside(WHITE)) fen += 'Q';
270 if (can_castle_kingside(BLACK)) fen += 'k';
271 if (can_castle_queenside(BLACK)) fen += 'q';
276 if (ep_square() != SQ_NONE)
277 fen += square_to_string(ep_square());
285 /// Position::print() prints an ASCII representation of the position to
286 /// the standard output. If a move is given then also the san is print.
288 void Position::print(Move m) const {
290 static const string pieceLetters = " PNBRQK PNBRQK .";
292 // Check for reentrancy, as example when called from inside
293 // MovePicker that is used also here in move_to_san()
297 RequestPending = true;
299 std::cout << std::endl;
302 string col = (color_of_piece_on(move_from(m)) == BLACK ? ".." : "");
303 std::cout << "Move is: " << col << move_to_san(*this, m) << std::endl;
305 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
307 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl;
308 for (File file = FILE_A; file <= FILE_H; file++)
310 Square sq = make_square(file, rank);
311 Piece piece = piece_on(sq);
312 if (piece == EMPTY && square_color(sq) == WHITE)
315 char col = (color_of_piece_on(sq) == BLACK ? '=' : ' ');
316 std::cout << '|' << col << pieceLetters[piece] << col;
318 std::cout << '|' << std::endl;
320 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl
321 << "Fen is: " << to_fen() << std::endl
322 << "Key is: " << st->key << std::endl;
324 RequestPending = false;
328 /// Position::copy() creates a copy of the input position.
330 void Position::copy(const Position& pos) {
332 memcpy(this, &pos, sizeof(Position));
333 saveState(); // detach and copy state info
337 /// Position:hidden_checkers<>() returns a bitboard of all pinned (against the
338 /// king) pieces for the given color and for the given pinner type. Or, when
339 /// template parameter FindPinned is false, the pieces of the given color
340 /// candidate for a discovery check against the enemy king.
341 /// Note that checkersBB bitboard must be already updated.
343 template<bool FindPinned>
344 Bitboard Position::hidden_checkers(Color c) const {
346 Bitboard pinners, result = EmptyBoardBB;
348 // Pinned pieces protect our king, dicovery checks attack
350 Square ksq = king_square(FindPinned ? c : opposite_color(c));
352 // Pinners are sliders, not checkers, that give check when
353 // candidate pinned is removed.
354 pinners = (pieces(ROOK, QUEEN, FindPinned ? opposite_color(c) : c) & RookPseudoAttacks[ksq])
355 | (pieces(BISHOP, QUEEN, FindPinned ? opposite_color(c) : c) & BishopPseudoAttacks[ksq]);
357 if (FindPinned && pinners)
358 pinners &= ~st->checkersBB;
362 Square s = pop_1st_bit(&pinners);
363 Bitboard b = squares_between(s, ksq) & occupied_squares();
367 if ( !(b & (b - 1)) // Only one bit set?
368 && (b & pieces_of_color(c))) // Is an our piece?
375 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
376 /// king) pieces for the given color.
378 Bitboard Position::pinned_pieces(Color c) const {
380 return hidden_checkers<true>(c);
384 /// Position:discovered_check_candidates() returns a bitboard containing all
385 /// pieces for the given side which are candidates for giving a discovered
388 Bitboard Position::discovered_check_candidates(Color c) const {
390 return hidden_checkers<false>(c);
393 /// Position::attackers_to() computes a bitboard containing all pieces which
394 /// attacks a given square.
396 Bitboard Position::attackers_to(Square s) const {
398 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
399 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
400 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
401 | (attacks_from<ROOK>(s) & pieces(ROOK, QUEEN))
402 | (attacks_from<BISHOP>(s) & pieces(BISHOP, QUEEN))
403 | (attacks_from<KING>(s) & pieces(KING));
406 /// Position::attacks_from() computes a bitboard of all attacks
407 /// of a given piece put in a given square.
409 Bitboard Position::attacks_from(Piece p, Square s) const {
411 assert(square_is_ok(s));
415 case WP: return attacks_from<PAWN>(s, WHITE);
416 case BP: return attacks_from<PAWN>(s, BLACK);
417 case WN: case BN: return attacks_from<KNIGHT>(s);
418 case WB: case BB: return attacks_from<BISHOP>(s);
419 case WR: case BR: return attacks_from<ROOK>(s);
420 case WQ: case BQ: return attacks_from<QUEEN>(s);
421 case WK: case BK: return attacks_from<KING>(s);
428 /// Position::move_attacks_square() tests whether a move from the current
429 /// position attacks a given square.
431 bool Position::move_attacks_square(Move m, Square s) const {
433 assert(move_is_ok(m));
434 assert(square_is_ok(s));
436 Square f = move_from(m), t = move_to(m);
438 assert(square_is_occupied(f));
440 if (bit_is_set(attacks_from(piece_on(f), t), s))
443 // Move the piece and scan for X-ray attacks behind it
444 Bitboard occ = occupied_squares();
445 Color us = color_of_piece_on(f);
448 Bitboard xray = ( (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
449 |(bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN))) & pieces_of_color(us);
451 // If we have attacks we need to verify that are caused by our move
452 // and are not already existent ones.
453 return xray && (xray ^ (xray & attacks_from<QUEEN>(s)));
457 /// Position::find_checkers() computes the checkersBB bitboard, which
458 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
459 /// currently works by calling Position::attackers_to, which is probably
460 /// inefficient. Consider rewriting this function to use the last move
461 /// played, like in non-bitboard versions of Glaurung.
463 void Position::find_checkers() {
465 Color us = side_to_move();
466 st->checkersBB = attackers_to(king_square(us)) & pieces_of_color(opposite_color(us));
470 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
472 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
475 assert(move_is_ok(m));
476 assert(pinned == pinned_pieces(side_to_move()));
478 // Castling moves are checked for legality during move generation.
479 if (move_is_castle(m))
482 Color us = side_to_move();
483 Square from = move_from(m);
485 assert(color_of_piece_on(from) == us);
486 assert(piece_on(king_square(us)) == piece_of_color_and_type(us, KING));
488 // En passant captures are a tricky special case. Because they are
489 // rather uncommon, we do it simply by testing whether the king is attacked
490 // after the move is made
493 Color them = opposite_color(us);
494 Square to = move_to(m);
495 Square capsq = make_square(square_file(to), square_rank(from));
496 Bitboard b = occupied_squares();
497 Square ksq = king_square(us);
499 assert(to == ep_square());
500 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
501 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
502 assert(piece_on(to) == EMPTY);
505 clear_bit(&b, capsq);
508 return !(rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, them))
509 && !(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, them));
512 // If the moving piece is a king, check whether the destination
513 // square is attacked by the opponent.
514 if (type_of_piece_on(from) == KING)
515 return !(attackers_to(move_to(m)) & pieces_of_color(opposite_color(us)));
517 // A non-king move is legal if and only if it is not pinned or it
518 // is moving along the ray towards or away from the king.
520 || !bit_is_set(pinned, from)
521 || (direction_between_squares(from, king_square(us)) == direction_between_squares(move_to(m), king_square(us))));
525 /// Position::pl_move_is_evasion() tests whether a pseudo-legal move is a legal evasion
527 bool Position::pl_move_is_evasion(Move m, Bitboard pinned) const
531 Color us = side_to_move();
532 Square from = move_from(m);
533 Square to = move_to(m);
535 // King moves and en-passant captures are verified in pl_move_is_legal()
536 if (type_of_piece_on(from) == KING || move_is_ep(m))
537 return pl_move_is_legal(m, pinned);
539 Bitboard target = checkers();
540 Square checksq = pop_1st_bit(&target);
542 if (target) // double check ?
545 // Our move must be a blocking evasion or a capture of the checking piece
546 target = squares_between(checksq, king_square(us)) | checkers();
547 return bit_is_set(target, to) && pl_move_is_legal(m, pinned);
551 /// Position::move_is_check() tests whether a pseudo-legal move is a check
553 bool Position::move_is_check(Move m) const {
555 Bitboard dc = discovered_check_candidates(side_to_move());
556 return move_is_check(m, dc);
559 bool Position::move_is_check(Move m, Bitboard dcCandidates) const {
562 assert(move_is_ok(m));
563 assert(dcCandidates == discovered_check_candidates(side_to_move()));
565 Color us = side_to_move();
566 Color them = opposite_color(us);
567 Square from = move_from(m);
568 Square to = move_to(m);
569 Square ksq = king_square(them);
571 assert(color_of_piece_on(from) == us);
572 assert(piece_on(ksq) == piece_of_color_and_type(them, KING));
574 // Proceed according to the type of the moving piece
575 switch (type_of_piece_on(from))
579 if (bit_is_set(attacks_from<PAWN>(ksq, them), to)) // Normal check?
582 if ( dcCandidates // Discovered check?
583 && bit_is_set(dcCandidates, from)
584 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
587 if (move_is_promotion(m)) // Promotion with check?
589 Bitboard b = occupied_squares();
592 switch (move_promotion_piece(m))
595 return bit_is_set(attacks_from<KNIGHT>(to), ksq);
597 return bit_is_set(bishop_attacks_bb(to, b), ksq);
599 return bit_is_set(rook_attacks_bb(to, b), ksq);
601 return bit_is_set(queen_attacks_bb(to, b), ksq);
606 // En passant capture with check? We have already handled the case
607 // of direct checks and ordinary discovered check, the only case we
608 // need to handle is the unusual case of a discovered check through the
610 else if (move_is_ep(m))
612 Square capsq = make_square(square_file(to), square_rank(from));
613 Bitboard b = occupied_squares();
615 clear_bit(&b, capsq);
617 return (rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, us))
618 ||(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, us));
622 // Test discovered check and normal check according to piece type
624 return (dcCandidates && bit_is_set(dcCandidates, from))
625 || bit_is_set(attacks_from<KNIGHT>(ksq), to);
628 return (dcCandidates && bit_is_set(dcCandidates, from))
629 || (direction_is_diagonal(ksq, to) && bit_is_set(attacks_from<BISHOP>(ksq), to));
632 return (dcCandidates && bit_is_set(dcCandidates, from))
633 || (direction_is_straight(ksq, to) && bit_is_set(attacks_from<ROOK>(ksq), to));
636 // Discovered checks are impossible!
637 assert(!bit_is_set(dcCandidates, from));
638 return ( (direction_is_straight(ksq, to) && bit_is_set(attacks_from<ROOK>(ksq), to))
639 || (direction_is_diagonal(ksq, to) && bit_is_set(attacks_from<BISHOP>(ksq), to)));
643 if ( bit_is_set(dcCandidates, from)
644 && (direction_between_squares(from, ksq) != direction_between_squares(to, ksq)))
647 // Castling with check?
648 if (move_is_castle(m))
650 Square kfrom, kto, rfrom, rto;
651 Bitboard b = occupied_squares();
657 kto = relative_square(us, SQ_G1);
658 rto = relative_square(us, SQ_F1);
660 kto = relative_square(us, SQ_C1);
661 rto = relative_square(us, SQ_D1);
663 clear_bit(&b, kfrom);
664 clear_bit(&b, rfrom);
667 return bit_is_set(rook_attacks_bb(rto, b), ksq);
671 default: // NO_PIECE_TYPE
679 /// Position::update_checkers() udpates chekers info given the move. It is called
680 /// in do_move() and is faster then find_checkers().
682 template<PieceType Piece>
683 inline void Position::update_checkers(Bitboard* pCheckersBB, Square ksq, Square from,
684 Square to, Bitboard dcCandidates) {
686 const bool Bishop = (Piece == QUEEN || Piece == BISHOP);
687 const bool Rook = (Piece == QUEEN || Piece == ROOK);
688 const bool Slider = Bishop || Rook;
691 if ( ( (Bishop && bit_is_set(BishopPseudoAttacks[ksq], to))
692 || (Rook && bit_is_set(RookPseudoAttacks[ksq], to)))
693 && bit_is_set(attacks_from<Piece>(ksq), to)) // slow, try to early skip
694 set_bit(pCheckersBB, to);
696 else if ( Piece != KING
698 && bit_is_set(Piece == PAWN ? attacks_from<PAWN>(ksq, opposite_color(sideToMove))
699 : attacks_from<Piece>(ksq), to))
700 set_bit(pCheckersBB, to);
703 if (Piece != QUEEN && bit_is_set(dcCandidates, from))
706 (*pCheckersBB) |= (attacks_from<ROOK>(ksq) & pieces(ROOK, QUEEN, side_to_move()));
709 (*pCheckersBB) |= (attacks_from<BISHOP>(ksq) & pieces(BISHOP, QUEEN, side_to_move()));
714 /// Position::do_move() makes a move, and saves all information necessary
715 /// to a StateInfo object. The move is assumed to be legal.
716 /// Pseudo-legal moves should be filtered out before this function is called.
718 void Position::do_move(Move m, StateInfo& newSt) {
720 do_move(m, newSt, discovered_check_candidates(side_to_move()));
723 void Position::do_move(Move m, StateInfo& newSt, Bitboard dcCandidates) {
726 assert(move_is_ok(m));
728 Bitboard key = st->key;
730 // Copy some fields of old state to our new StateInfo object except the
731 // ones which are recalculated from scratch anyway, then switch our state
732 // pointer to point to the new, ready to be updated, state.
733 struct ReducedStateInfo {
734 Key pawnKey, materialKey;
735 int castleRights, rule50, pliesFromNull;
741 memcpy(&newSt, st, sizeof(ReducedStateInfo));
745 // Save the current key to the history[] array, in order to be able to
746 // detect repetition draws.
747 history[gamePly] = key;
750 // Update side to move
751 key ^= zobSideToMove;
753 // Increment the 50 moves rule draw counter. Resetting it to zero in the
754 // case of non-reversible moves is taken care of later.
758 if (move_is_castle(m))
765 Color us = side_to_move();
766 Color them = opposite_color(us);
767 Square from = move_from(m);
768 Square to = move_to(m);
769 bool ep = move_is_ep(m);
770 bool pm = move_is_promotion(m);
772 Piece piece = piece_on(from);
773 PieceType pt = type_of_piece(piece);
774 PieceType capture = ep ? PAWN : type_of_piece_on(to);
776 assert(color_of_piece_on(from) == us);
777 assert(color_of_piece_on(to) == them || square_is_empty(to));
778 assert(!(ep || pm) || piece == piece_of_color_and_type(us, PAWN));
779 assert(!pm || relative_rank(us, to) == RANK_8);
782 do_capture_move(key, capture, them, to, ep);
785 key ^= zobrist[us][pt][from] ^ zobrist[us][pt][to];
787 // Reset en passant square
788 if (st->epSquare != SQ_NONE)
790 key ^= zobEp[st->epSquare];
791 st->epSquare = SQ_NONE;
794 // Update castle rights, try to shortcut a common case
795 int cm = castleRightsMask[from] & castleRightsMask[to];
796 if (cm != ALL_CASTLES && ((cm & st->castleRights) != st->castleRights))
798 key ^= zobCastle[st->castleRights];
799 st->castleRights &= castleRightsMask[from];
800 st->castleRights &= castleRightsMask[to];
801 key ^= zobCastle[st->castleRights];
804 // Prefetch TT access as soon as we know key is updated
808 Bitboard move_bb = make_move_bb(from, to);
809 do_move_bb(&(byColorBB[us]), move_bb);
810 do_move_bb(&(byTypeBB[pt]), move_bb);
811 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
813 board[to] = board[from];
816 // Update piece lists, note that index[from] is not updated and
817 // becomes stale. This works as long as index[] is accessed just
818 // by known occupied squares.
819 index[to] = index[from];
820 pieceList[us][pt][index[to]] = to;
822 // If the moving piece was a pawn do some special extra work
825 // Reset rule 50 draw counter
828 // Update pawn hash key
829 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
831 // Set en passant square, only if moved pawn can be captured
832 if ((to ^ from) == 16)
834 if (attacks_from<PAWN>(from + (us == WHITE ? DELTA_N : DELTA_S), us) & pieces(PAWN, them))
836 st->epSquare = Square((int(from) + int(to)) / 2);
837 key ^= zobEp[st->epSquare];
842 // Update incremental scores
843 st->value += pst_delta(piece, from, to);
846 st->capture = capture;
848 if (pm) // promotion ?
850 PieceType promotion = move_promotion_piece(m);
852 assert(promotion >= KNIGHT && promotion <= QUEEN);
854 // Insert promoted piece instead of pawn
855 clear_bit(&(byTypeBB[PAWN]), to);
856 set_bit(&(byTypeBB[promotion]), to);
857 board[to] = piece_of_color_and_type(us, promotion);
859 // Update material key
860 st->materialKey ^= zobMaterial[us][PAWN][pieceCount[us][PAWN]];
861 st->materialKey ^= zobMaterial[us][promotion][pieceCount[us][promotion]+1];
863 // Update piece counts
864 pieceCount[us][PAWN]--;
865 pieceCount[us][promotion]++;
867 // Update piece lists, move the last pawn at index[to] position
868 // and shrink the list. Add a new promotion piece to the list.
869 Square lastPawnSquare = pieceList[us][PAWN][pieceCount[us][PAWN]];
870 index[lastPawnSquare] = index[to];
871 pieceList[us][PAWN][index[lastPawnSquare]] = lastPawnSquare;
872 pieceList[us][PAWN][pieceCount[us][PAWN]] = SQ_NONE;
873 index[to] = pieceCount[us][promotion] - 1;
874 pieceList[us][promotion][index[to]] = to;
876 // Partially revert hash keys update
877 key ^= zobrist[us][PAWN][to] ^ zobrist[us][promotion][to];
878 st->pawnKey ^= zobrist[us][PAWN][to];
880 // Partially revert and update incremental scores
881 st->value -= pst(us, PAWN, to);
882 st->value += pst(us, promotion, to);
885 st->npMaterial[us] += piece_value_midgame(promotion);
888 // Update the key with the final value
891 // Update checkers bitboard, piece must be already moved
893 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
896 st->checkersBB = EmptyBoardBB;
897 Square ksq = king_square(them);
900 case PAWN: update_checkers<PAWN>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
901 case KNIGHT: update_checkers<KNIGHT>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
902 case BISHOP: update_checkers<BISHOP>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
903 case ROOK: update_checkers<ROOK>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
904 case QUEEN: update_checkers<QUEEN>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
905 case KING: update_checkers<KING>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
906 default: assert(false); break;
911 sideToMove = opposite_color(sideToMove);
912 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
918 /// Position::do_capture_move() is a private method used to update captured
919 /// piece info. It is called from the main Position::do_move function.
921 void Position::do_capture_move(Bitboard& key, PieceType capture, Color them, Square to, bool ep) {
923 assert(capture != KING);
927 if (ep) // en passant ?
929 capsq = (them == BLACK)? (to - DELTA_N) : (to - DELTA_S);
931 assert(to == st->epSquare);
932 assert(relative_rank(opposite_color(them), to) == RANK_6);
933 assert(piece_on(to) == EMPTY);
934 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
936 board[capsq] = EMPTY;
939 // Remove captured piece
940 clear_bit(&(byColorBB[them]), capsq);
941 clear_bit(&(byTypeBB[capture]), capsq);
942 clear_bit(&(byTypeBB[0]), capsq);
945 key ^= zobrist[them][capture][capsq];
947 // Update incremental scores
948 st->value -= pst(them, capture, capsq);
950 // If the captured piece was a pawn, update pawn hash key,
951 // otherwise update non-pawn material.
953 st->pawnKey ^= zobrist[them][PAWN][capsq];
955 st->npMaterial[them] -= piece_value_midgame(capture);
957 // Update material hash key
958 st->materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];
960 // Update piece count
961 pieceCount[them][capture]--;
963 // Update piece list, move the last piece at index[capsq] position
965 // WARNING: This is a not perfectly revresible operation. When we
966 // will reinsert the captured piece in undo_move() we will put it
967 // at the end of the list and not in its original place, it means
968 // index[] and pieceList[] are not guaranteed to be invariant to a
969 // do_move() + undo_move() sequence.
970 Square lastPieceSquare = pieceList[them][capture][pieceCount[them][capture]];
971 index[lastPieceSquare] = index[capsq];
972 pieceList[them][capture][index[lastPieceSquare]] = lastPieceSquare;
973 pieceList[them][capture][pieceCount[them][capture]] = SQ_NONE;
975 // Reset rule 50 counter
980 /// Position::do_castle_move() is a private method used to make a castling
981 /// move. It is called from the main Position::do_move function. Note that
982 /// castling moves are encoded as "king captures friendly rook" moves, for
983 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
985 void Position::do_castle_move(Move m) {
987 assert(move_is_ok(m));
988 assert(move_is_castle(m));
990 Color us = side_to_move();
991 Color them = opposite_color(us);
993 // Reset capture field
994 st->capture = NO_PIECE_TYPE;
996 // Find source squares for king and rook
997 Square kfrom = move_from(m);
998 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1001 assert(piece_on(kfrom) == piece_of_color_and_type(us, KING));
1002 assert(piece_on(rfrom) == piece_of_color_and_type(us, ROOK));
1004 // Find destination squares for king and rook
1005 if (rfrom > kfrom) // O-O
1007 kto = relative_square(us, SQ_G1);
1008 rto = relative_square(us, SQ_F1);
1010 kto = relative_square(us, SQ_C1);
1011 rto = relative_square(us, SQ_D1);
1014 // Remove pieces from source squares:
1015 clear_bit(&(byColorBB[us]), kfrom);
1016 clear_bit(&(byTypeBB[KING]), kfrom);
1017 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1018 clear_bit(&(byColorBB[us]), rfrom);
1019 clear_bit(&(byTypeBB[ROOK]), rfrom);
1020 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1022 // Put pieces on destination squares:
1023 set_bit(&(byColorBB[us]), kto);
1024 set_bit(&(byTypeBB[KING]), kto);
1025 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1026 set_bit(&(byColorBB[us]), rto);
1027 set_bit(&(byTypeBB[ROOK]), rto);
1028 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1030 // Update board array
1031 Piece king = piece_of_color_and_type(us, KING);
1032 Piece rook = piece_of_color_and_type(us, ROOK);
1033 board[kfrom] = board[rfrom] = EMPTY;
1037 // Update piece lists
1038 pieceList[us][KING][index[kfrom]] = kto;
1039 pieceList[us][ROOK][index[rfrom]] = rto;
1040 int tmp = index[rfrom]; // In Chess960 could be rto == kfrom
1041 index[kto] = index[kfrom];
1044 // Update incremental scores
1045 st->value += pst_delta(king, kfrom, kto);
1046 st->value += pst_delta(rook, rfrom, rto);
1049 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1050 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1052 // Clear en passant square
1053 if (st->epSquare != SQ_NONE)
1055 st->key ^= zobEp[st->epSquare];
1056 st->epSquare = SQ_NONE;
1059 // Update castling rights
1060 st->key ^= zobCastle[st->castleRights];
1061 st->castleRights &= castleRightsMask[kfrom];
1062 st->key ^= zobCastle[st->castleRights];
1064 // Reset rule 50 counter
1067 // Update checkers BB
1068 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
1071 sideToMove = opposite_color(sideToMove);
1072 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1078 /// Position::undo_move() unmakes a move. When it returns, the position should
1079 /// be restored to exactly the same state as before the move was made.
1081 void Position::undo_move(Move m) {
1084 assert(move_is_ok(m));
1087 sideToMove = opposite_color(sideToMove);
1089 if (move_is_castle(m))
1091 undo_castle_move(m);
1095 Color us = side_to_move();
1096 Color them = opposite_color(us);
1097 Square from = move_from(m);
1098 Square to = move_to(m);
1099 bool ep = move_is_ep(m);
1100 bool pm = move_is_promotion(m);
1102 PieceType pt = type_of_piece_on(to);
1104 assert(square_is_empty(from));
1105 assert(color_of_piece_on(to) == us);
1106 assert(!pm || relative_rank(us, to) == RANK_8);
1107 assert(!ep || to == st->previous->epSquare);
1108 assert(!ep || relative_rank(us, to) == RANK_6);
1109 assert(!ep || piece_on(to) == piece_of_color_and_type(us, PAWN));
1111 if (pm) // promotion ?
1113 PieceType promotion = move_promotion_piece(m);
1116 assert(promotion >= KNIGHT && promotion <= QUEEN);
1117 assert(piece_on(to) == piece_of_color_and_type(us, promotion));
1119 // Replace promoted piece with a pawn
1120 clear_bit(&(byTypeBB[promotion]), to);
1121 set_bit(&(byTypeBB[PAWN]), to);
1123 // Update piece counts
1124 pieceCount[us][promotion]--;
1125 pieceCount[us][PAWN]++;
1127 // Update piece list replacing promotion piece with a pawn
1128 Square lastPromotionSquare = pieceList[us][promotion][pieceCount[us][promotion]];
1129 index[lastPromotionSquare] = index[to];
1130 pieceList[us][promotion][index[lastPromotionSquare]] = lastPromotionSquare;
1131 pieceList[us][promotion][pieceCount[us][promotion]] = SQ_NONE;
1132 index[to] = pieceCount[us][PAWN] - 1;
1133 pieceList[us][PAWN][index[to]] = to;
1137 // Put the piece back at the source square
1138 Bitboard move_bb = make_move_bb(to, from);
1139 do_move_bb(&(byColorBB[us]), move_bb);
1140 do_move_bb(&(byTypeBB[pt]), move_bb);
1141 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
1143 board[from] = piece_of_color_and_type(us, pt);
1146 // Update piece list
1147 index[from] = index[to];
1148 pieceList[us][pt][index[from]] = from;
1155 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1157 assert(st->capture != KING);
1158 assert(!ep || square_is_empty(capsq));
1160 // Restore the captured piece
1161 set_bit(&(byColorBB[them]), capsq);
1162 set_bit(&(byTypeBB[st->capture]), capsq);
1163 set_bit(&(byTypeBB[0]), capsq);
1165 board[capsq] = piece_of_color_and_type(them, st->capture);
1167 // Update piece count
1168 pieceCount[them][st->capture]++;
1170 // Update piece list, add a new captured piece in capsq square
1171 index[capsq] = pieceCount[them][st->capture] - 1;
1172 pieceList[them][st->capture][index[capsq]] = capsq;
1175 // Finally point our state pointer back to the previous state
1182 /// Position::undo_castle_move() is a private method used to unmake a castling
1183 /// move. It is called from the main Position::undo_move function. Note that
1184 /// castling moves are encoded as "king captures friendly rook" moves, for
1185 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1187 void Position::undo_castle_move(Move m) {
1189 assert(move_is_ok(m));
1190 assert(move_is_castle(m));
1192 // When we have arrived here, some work has already been done by
1193 // Position::undo_move. In particular, the side to move has been switched,
1194 // so the code below is correct.
1195 Color us = side_to_move();
1197 // Find source squares for king and rook
1198 Square kfrom = move_from(m);
1199 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1202 // Find destination squares for king and rook
1203 if (rfrom > kfrom) // O-O
1205 kto = relative_square(us, SQ_G1);
1206 rto = relative_square(us, SQ_F1);
1208 kto = relative_square(us, SQ_C1);
1209 rto = relative_square(us, SQ_D1);
1212 assert(piece_on(kto) == piece_of_color_and_type(us, KING));
1213 assert(piece_on(rto) == piece_of_color_and_type(us, ROOK));
1215 // Remove pieces from destination squares:
1216 clear_bit(&(byColorBB[us]), kto);
1217 clear_bit(&(byTypeBB[KING]), kto);
1218 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1219 clear_bit(&(byColorBB[us]), rto);
1220 clear_bit(&(byTypeBB[ROOK]), rto);
1221 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1223 // Put pieces on source squares:
1224 set_bit(&(byColorBB[us]), kfrom);
1225 set_bit(&(byTypeBB[KING]), kfrom);
1226 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1227 set_bit(&(byColorBB[us]), rfrom);
1228 set_bit(&(byTypeBB[ROOK]), rfrom);
1229 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1232 board[rto] = board[kto] = EMPTY;
1233 board[rfrom] = piece_of_color_and_type(us, ROOK);
1234 board[kfrom] = piece_of_color_and_type(us, KING);
1236 // Update piece lists
1237 pieceList[us][KING][index[kto]] = kfrom;
1238 pieceList[us][ROOK][index[rto]] = rfrom;
1239 int tmp = index[rto]; // In Chess960 could be rto == kfrom
1240 index[kfrom] = index[kto];
1243 // Finally point our state pointer back to the previous state
1250 /// Position::do_null_move makes() a "null move": It switches the side to move
1251 /// and updates the hash key without executing any move on the board.
1253 void Position::do_null_move(StateInfo& backupSt) {
1256 assert(!is_check());
1258 // Back up the information necessary to undo the null move to the supplied
1259 // StateInfo object.
1260 // Note that differently from normal case here backupSt is actually used as
1261 // a backup storage not as a new state to be used.
1262 backupSt.key = st->key;
1263 backupSt.epSquare = st->epSquare;
1264 backupSt.value = st->value;
1265 backupSt.previous = st->previous;
1266 backupSt.pliesFromNull = st->pliesFromNull;
1267 st->previous = &backupSt;
1269 // Save the current key to the history[] array, in order to be able to
1270 // detect repetition draws.
1271 history[gamePly] = st->key;
1273 // Update the necessary information
1274 if (st->epSquare != SQ_NONE)
1275 st->key ^= zobEp[st->epSquare];
1277 st->key ^= zobSideToMove;
1278 TT.prefetch(st->key);
1280 sideToMove = opposite_color(sideToMove);
1281 st->epSquare = SQ_NONE;
1283 st->pliesFromNull = 0;
1284 st->value += (sideToMove == WHITE) ? TempoValue : -TempoValue;
1289 /// Position::undo_null_move() unmakes a "null move".
1291 void Position::undo_null_move() {
1294 assert(!is_check());
1296 // Restore information from the our backup StateInfo object
1297 StateInfo* backupSt = st->previous;
1298 st->key = backupSt->key;
1299 st->epSquare = backupSt->epSquare;
1300 st->value = backupSt->value;
1301 st->previous = backupSt->previous;
1302 st->pliesFromNull = backupSt->pliesFromNull;
1304 // Update the necessary information
1305 sideToMove = opposite_color(sideToMove);
1311 /// Position::see() is a static exchange evaluator: It tries to estimate the
1312 /// material gain or loss resulting from a move. There are three versions of
1313 /// this function: One which takes a destination square as input, one takes a
1314 /// move, and one which takes a 'from' and a 'to' square. The function does
1315 /// not yet understand promotions captures.
1317 int Position::see(Square to) const {
1319 assert(square_is_ok(to));
1320 return see(SQ_NONE, to);
1323 int Position::see(Move m) const {
1325 assert(move_is_ok(m));
1326 return see(move_from(m), move_to(m));
1329 int Position::see_sign(Move m) const {
1331 assert(move_is_ok(m));
1333 Square from = move_from(m);
1334 Square to = move_to(m);
1336 // Early return if SEE cannot be negative because capturing piece value
1337 // is not bigger then captured one.
1338 if ( midgame_value_of_piece_on(from) <= midgame_value_of_piece_on(to)
1339 && type_of_piece_on(from) != KING)
1342 return see(from, to);
1345 int Position::see(Square from, Square to) const {
1348 static const int seeValues[18] = {
1349 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1350 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1351 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1352 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1356 Bitboard attackers, stmAttackers, b;
1358 assert(square_is_ok(from) || from == SQ_NONE);
1359 assert(square_is_ok(to));
1361 // Initialize colors
1362 Color us = (from != SQ_NONE ? color_of_piece_on(from) : opposite_color(color_of_piece_on(to)));
1363 Color them = opposite_color(us);
1365 // Initialize pieces
1366 Piece piece = piece_on(from);
1367 Piece capture = piece_on(to);
1368 Bitboard occ = occupied_squares();
1370 // King cannot be recaptured
1371 if (type_of_piece(piece) == KING)
1372 return seeValues[capture];
1374 // Handle en passant moves
1375 if (st->epSquare == to && type_of_piece_on(from) == PAWN)
1377 assert(capture == EMPTY);
1379 Square capQq = (side_to_move() == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1380 capture = piece_on(capQq);
1381 assert(type_of_piece_on(capQq) == PAWN);
1383 // Remove the captured pawn
1384 clear_bit(&occ, capQq);
1389 // Find all attackers to the destination square, with the moving piece
1390 // removed, but possibly an X-ray attacker added behind it.
1391 clear_bit(&occ, from);
1392 attackers = (rook_attacks_bb(to, occ) & pieces(ROOK, QUEEN))
1393 | (bishop_attacks_bb(to, occ) & pieces(BISHOP, QUEEN))
1394 | (attacks_from<KNIGHT>(to) & pieces(KNIGHT))
1395 | (attacks_from<KING>(to) & pieces(KING))
1396 | (attacks_from<PAWN>(to, WHITE) & pieces(PAWN, BLACK))
1397 | (attacks_from<PAWN>(to, BLACK) & pieces(PAWN, WHITE));
1399 if (from != SQ_NONE)
1402 // If we don't have any attacker we are finished
1403 if ((attackers & pieces_of_color(us)) == EmptyBoardBB)
1406 // Locate the least valuable attacker to the destination square
1407 // and use it to initialize from square.
1408 stmAttackers = attackers & pieces_of_color(us);
1410 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1413 from = first_1(stmAttackers & pieces(pt));
1414 piece = piece_on(from);
1417 // If the opponent has no attackers we are finished
1418 stmAttackers = attackers & pieces_of_color(them);
1420 return seeValues[capture];
1422 attackers &= occ; // Remove the moving piece
1424 // The destination square is defended, which makes things rather more
1425 // difficult to compute. We proceed by building up a "swap list" containing
1426 // the material gain or loss at each stop in a sequence of captures to the
1427 // destination square, where the sides alternately capture, and always
1428 // capture with the least valuable piece. After each capture, we look for
1429 // new X-ray attacks from behind the capturing piece.
1430 int lastCapturingPieceValue = seeValues[piece];
1431 int swapList[32], n = 1;
1435 swapList[0] = seeValues[capture];
1438 // Locate the least valuable attacker for the side to move. The loop
1439 // below looks like it is potentially infinite, but it isn't. We know
1440 // that the side to move still has at least one attacker left.
1441 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1444 // Remove the attacker we just found from the 'attackers' bitboard,
1445 // and scan for new X-ray attacks behind the attacker.
1446 b = stmAttackers & pieces(pt);
1447 occ ^= (b & (~b + 1));
1448 attackers |= (rook_attacks_bb(to, occ) & pieces(ROOK, QUEEN))
1449 | (bishop_attacks_bb(to, occ) & pieces(BISHOP, QUEEN));
1453 // Add the new entry to the swap list
1455 swapList[n] = -swapList[n - 1] + lastCapturingPieceValue;
1458 // Remember the value of the capturing piece, and change the side to move
1459 // before beginning the next iteration
1460 lastCapturingPieceValue = seeValues[pt];
1461 c = opposite_color(c);
1462 stmAttackers = attackers & pieces_of_color(c);
1464 // Stop after a king capture
1465 if (pt == KING && stmAttackers)
1468 swapList[n++] = QueenValueMidgame*10;
1471 } while (stmAttackers);
1473 // Having built the swap list, we negamax through it to find the best
1474 // achievable score from the point of view of the side to move
1476 swapList[n-1] = Min(-swapList[n], swapList[n-1]);
1482 /// Position::saveState() copies the content of the current state
1483 /// inside startState and makes st point to it. This is needed
1484 /// when the st pointee could become stale, as example because
1485 /// the caller is about to going out of scope.
1487 void Position::saveState() {
1491 st->previous = NULL; // as a safe guard
1495 /// Position::clear() erases the position object to a pristine state, with an
1496 /// empty board, white to move, and no castling rights.
1498 void Position::clear() {
1501 memset(st, 0, sizeof(StateInfo));
1502 st->epSquare = SQ_NONE;
1504 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1505 memset(byTypeBB, 0, sizeof(Bitboard) * 8);
1506 memset(pieceCount, 0, sizeof(int) * 2 * 8);
1507 memset(index, 0, sizeof(int) * 64);
1509 for (int i = 0; i < 64; i++)
1512 for (int i = 0; i < 8; i++)
1513 for (int j = 0; j < 16; j++)
1514 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1518 initialKFile = FILE_E;
1519 initialKRFile = FILE_H;
1520 initialQRFile = FILE_A;
1524 /// Position::reset_game_ply() simply sets gamePly to 0. It is used from the
1525 /// UCI interface code, whenever a non-reversible move is made in a
1526 /// 'position fen <fen> moves m1 m2 ...' command. This makes it possible
1527 /// for the program to handle games of arbitrary length, as long as the GUI
1528 /// handles draws by the 50 move rule correctly.
1530 void Position::reset_game_ply() {
1536 /// Position::put_piece() puts a piece on the given square of the board,
1537 /// updating the board array, bitboards, and piece counts.
1539 void Position::put_piece(Piece p, Square s) {
1541 Color c = color_of_piece(p);
1542 PieceType pt = type_of_piece(p);
1545 index[s] = pieceCount[c][pt];
1546 pieceList[c][pt][index[s]] = s;
1548 set_bit(&(byTypeBB[pt]), s);
1549 set_bit(&(byColorBB[c]), s);
1550 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1552 pieceCount[c][pt]++;
1556 /// Position::allow_oo() gives the given side the right to castle kingside.
1557 /// Used when setting castling rights during parsing of FEN strings.
1559 void Position::allow_oo(Color c) {
1561 st->castleRights |= (1 + int(c));
1565 /// Position::allow_ooo() gives the given side the right to castle queenside.
1566 /// Used when setting castling rights during parsing of FEN strings.
1568 void Position::allow_ooo(Color c) {
1570 st->castleRights |= (4 + 4*int(c));
1574 /// Position::compute_key() computes the hash key of the position. The hash
1575 /// key is usually updated incrementally as moves are made and unmade, the
1576 /// compute_key() function is only used when a new position is set up, and
1577 /// to verify the correctness of the hash key when running in debug mode.
1579 Key Position::compute_key() const {
1581 Key result = Key(0ULL);
1583 for (Square s = SQ_A1; s <= SQ_H8; s++)
1584 if (square_is_occupied(s))
1585 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1587 if (ep_square() != SQ_NONE)
1588 result ^= zobEp[ep_square()];
1590 result ^= zobCastle[st->castleRights];
1591 if (side_to_move() == BLACK)
1592 result ^= zobSideToMove;
1598 /// Position::compute_pawn_key() computes the hash key of the position. The
1599 /// hash key is usually updated incrementally as moves are made and unmade,
1600 /// the compute_pawn_key() function is only used when a new position is set
1601 /// up, and to verify the correctness of the pawn hash key when running in
1604 Key Position::compute_pawn_key() const {
1606 Key result = Key(0ULL);
1610 for (Color c = WHITE; c <= BLACK; c++)
1612 b = pieces(PAWN, c);
1615 s = pop_1st_bit(&b);
1616 result ^= zobrist[c][PAWN][s];
1623 /// Position::compute_material_key() computes the hash key of the position.
1624 /// The hash key is usually updated incrementally as moves are made and unmade,
1625 /// the compute_material_key() function is only used when a new position is set
1626 /// up, and to verify the correctness of the material hash key when running in
1629 Key Position::compute_material_key() const {
1631 Key result = Key(0ULL);
1632 for (Color c = WHITE; c <= BLACK; c++)
1633 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1635 int count = piece_count(c, pt);
1636 for (int i = 0; i <= count; i++)
1637 result ^= zobMaterial[c][pt][i];
1643 /// Position::compute_value() compute the incremental scores for the middle
1644 /// game and the endgame. These functions are used to initialize the incremental
1645 /// scores when a new position is set up, and to verify that the scores are correctly
1646 /// updated by do_move and undo_move when the program is running in debug mode.
1647 Score Position::compute_value() const {
1649 Score result = make_score(0, 0);
1653 for (Color c = WHITE; c <= BLACK; c++)
1654 for (PieceType pt = PAWN; pt <= KING; pt++)
1659 s = pop_1st_bit(&b);
1660 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1661 result += pst(c, pt, s);
1665 result += (side_to_move() == WHITE ? TempoValue / 2 : -TempoValue / 2);
1670 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1671 /// game material score for the given side. Material scores are updated
1672 /// incrementally during the search, this function is only used while
1673 /// initializing a new Position object.
1675 Value Position::compute_non_pawn_material(Color c) const {
1677 Value result = Value(0);
1679 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1681 Bitboard b = pieces(pt, c);
1684 assert(piece_on(first_1(b)) == piece_of_color_and_type(c, pt));
1686 result += piece_value_midgame(pt);
1693 /// Position::is_draw() tests whether the position is drawn by material,
1694 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1695 /// must be done by the search.
1697 bool Position::is_draw() const {
1699 // Draw by material?
1701 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1704 // Draw by the 50 moves rule?
1705 if (st->rule50 > 100 || (st->rule50 == 100 && !is_check()))
1708 // Draw by repetition?
1709 for (int i = 2; i < Min(Min(gamePly, st->rule50), st->pliesFromNull); i += 2)
1710 if (history[gamePly - i] == st->key)
1717 /// Position::is_mate() returns true or false depending on whether the
1718 /// side to move is checkmated.
1720 bool Position::is_mate() const {
1722 MoveStack moves[256];
1723 return is_check() && (generate_moves(*this, moves, false) == moves);
1727 /// Position::has_mate_threat() tests whether a given color has a mate in one
1728 /// from the current position.
1730 bool Position::has_mate_threat(Color c) {
1733 Color stm = side_to_move();
1738 // If the input color is not equal to the side to move, do a null move
1742 MoveStack mlist[120];
1743 bool result = false;
1744 Bitboard pinned = pinned_pieces(sideToMove);
1746 // Generate pseudo-legal non-capture and capture check moves
1747 MoveStack* last = generate_non_capture_checks(*this, mlist);
1748 last = generate_captures(*this, last);
1750 // Loop through the moves, and see if one of them is mate
1751 for (MoveStack* cur = mlist; cur != last; cur++)
1753 Move move = cur->move;
1754 if (!pl_move_is_legal(move, pinned))
1764 // Undo null move, if necessary
1772 /// Position::init_zobrist() is a static member function which initializes the
1773 /// various arrays used to compute hash keys.
1775 void Position::init_zobrist() {
1777 for (int i = 0; i < 2; i++)
1778 for (int j = 0; j < 8; j++)
1779 for (int k = 0; k < 64; k++)
1780 zobrist[i][j][k] = Key(genrand_int64());
1782 for (int i = 0; i < 64; i++)
1783 zobEp[i] = Key(genrand_int64());
1785 for (int i = 0; i < 16; i++)
1786 zobCastle[i] = genrand_int64();
1788 zobSideToMove = genrand_int64();
1790 for (int i = 0; i < 2; i++)
1791 for (int j = 0; j < 8; j++)
1792 for (int k = 0; k < 16; k++)
1793 zobMaterial[i][j][k] = (k > 0)? Key(genrand_int64()) : Key(0LL);
1795 for (int i = 0; i < 16; i++)
1796 zobMaterial[0][KING][i] = zobMaterial[1][KING][i] = Key(0ULL);
1800 /// Position::init_piece_square_tables() initializes the piece square tables.
1801 /// This is a two-step operation: First, the white halves of the tables are
1802 /// copied from the MgPST[][] and EgPST[][] arrays, with a small random number
1803 /// added to each entry if the "Randomness" UCI parameter is non-zero.
1804 /// Second, the black halves of the tables are initialized by mirroring
1805 /// and changing the sign of the corresponding white scores.
1807 void Position::init_piece_square_tables() {
1809 int r = get_option_value_int("Randomness"), i;
1810 for (Square s = SQ_A1; s <= SQ_H8; s++)
1811 for (Piece p = WP; p <= WK; p++)
1813 i = (r == 0)? 0 : (genrand_int32() % (r*2) - r);
1814 PieceSquareTable[p][s] = make_score(MgPST[p][s] + i, EgPST[p][s] + i);
1817 for (Square s = SQ_A1; s <= SQ_H8; s++)
1818 for (Piece p = BP; p <= BK; p++)
1819 PieceSquareTable[p][s] = -PieceSquareTable[p-8][flip_square(s)];
1823 /// Position::flipped_copy() makes a copy of the input position, but with
1824 /// the white and black sides reversed. This is only useful for debugging,
1825 /// especially for finding evaluation symmetry bugs.
1827 void Position::flipped_copy(const Position& pos) {
1829 assert(pos.is_ok());
1834 for (Square s = SQ_A1; s <= SQ_H8; s++)
1835 if (!pos.square_is_empty(s))
1836 put_piece(Piece(int(pos.piece_on(s)) ^ 8), flip_square(s));
1839 sideToMove = opposite_color(pos.side_to_move());
1842 if (pos.can_castle_kingside(WHITE)) allow_oo(BLACK);
1843 if (pos.can_castle_queenside(WHITE)) allow_ooo(BLACK);
1844 if (pos.can_castle_kingside(BLACK)) allow_oo(WHITE);
1845 if (pos.can_castle_queenside(BLACK)) allow_ooo(WHITE);
1847 initialKFile = pos.initialKFile;
1848 initialKRFile = pos.initialKRFile;
1849 initialQRFile = pos.initialQRFile;
1851 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
1852 castleRightsMask[sq] = ALL_CASTLES;
1854 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
1855 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
1856 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
1857 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
1858 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
1859 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
1861 // En passant square
1862 if (pos.st->epSquare != SQ_NONE)
1863 st->epSquare = flip_square(pos.st->epSquare);
1869 st->key = compute_key();
1870 st->pawnKey = compute_pawn_key();
1871 st->materialKey = compute_material_key();
1873 // Incremental scores
1874 st->value = compute_value();
1877 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
1878 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
1884 /// Position::is_ok() performs some consitency checks for the position object.
1885 /// This is meant to be helpful when debugging.
1887 bool Position::is_ok(int* failedStep) const {
1889 // What features of the position should be verified?
1890 static const bool debugBitboards = false;
1891 static const bool debugKingCount = false;
1892 static const bool debugKingCapture = false;
1893 static const bool debugCheckerCount = false;
1894 static const bool debugKey = false;
1895 static const bool debugMaterialKey = false;
1896 static const bool debugPawnKey = false;
1897 static const bool debugIncrementalEval = false;
1898 static const bool debugNonPawnMaterial = false;
1899 static const bool debugPieceCounts = false;
1900 static const bool debugPieceList = false;
1902 if (failedStep) *failedStep = 1;
1905 if (!color_is_ok(side_to_move()))
1908 // Are the king squares in the position correct?
1909 if (failedStep) (*failedStep)++;
1910 if (piece_on(king_square(WHITE)) != WK)
1913 if (failedStep) (*failedStep)++;
1914 if (piece_on(king_square(BLACK)) != BK)
1918 if (failedStep) (*failedStep)++;
1919 if (!file_is_ok(initialKRFile))
1922 if (!file_is_ok(initialQRFile))
1925 // Do both sides have exactly one king?
1926 if (failedStep) (*failedStep)++;
1929 int kingCount[2] = {0, 0};
1930 for (Square s = SQ_A1; s <= SQ_H8; s++)
1931 if (type_of_piece_on(s) == KING)
1932 kingCount[color_of_piece_on(s)]++;
1934 if (kingCount[0] != 1 || kingCount[1] != 1)
1938 // Can the side to move capture the opponent's king?
1939 if (failedStep) (*failedStep)++;
1940 if (debugKingCapture)
1942 Color us = side_to_move();
1943 Color them = opposite_color(us);
1944 Square ksq = king_square(them);
1945 if (attackers_to(ksq) & pieces_of_color(us))
1949 // Is there more than 2 checkers?
1950 if (failedStep) (*failedStep)++;
1951 if (debugCheckerCount && count_1s(st->checkersBB) > 2)
1955 if (failedStep) (*failedStep)++;
1958 // The intersection of the white and black pieces must be empty
1959 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
1962 // The union of the white and black pieces must be equal to all
1964 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
1967 // Separate piece type bitboards must have empty intersections
1968 for (PieceType p1 = PAWN; p1 <= KING; p1++)
1969 for (PieceType p2 = PAWN; p2 <= KING; p2++)
1970 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1974 // En passant square OK?
1975 if (failedStep) (*failedStep)++;
1976 if (ep_square() != SQ_NONE)
1978 // The en passant square must be on rank 6, from the point of view of the
1980 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
1985 if (failedStep) (*failedStep)++;
1986 if (debugKey && st->key != compute_key())
1989 // Pawn hash key OK?
1990 if (failedStep) (*failedStep)++;
1991 if (debugPawnKey && st->pawnKey != compute_pawn_key())
1994 // Material hash key OK?
1995 if (failedStep) (*failedStep)++;
1996 if (debugMaterialKey && st->materialKey != compute_material_key())
1999 // Incremental eval OK?
2000 if (failedStep) (*failedStep)++;
2001 if (debugIncrementalEval && st->value != compute_value())
2004 // Non-pawn material OK?
2005 if (failedStep) (*failedStep)++;
2006 if (debugNonPawnMaterial)
2008 if (st->npMaterial[WHITE] != compute_non_pawn_material(WHITE))
2011 if (st->npMaterial[BLACK] != compute_non_pawn_material(BLACK))
2016 if (failedStep) (*failedStep)++;
2017 if (debugPieceCounts)
2018 for (Color c = WHITE; c <= BLACK; c++)
2019 for (PieceType pt = PAWN; pt <= KING; pt++)
2020 if (pieceCount[c][pt] != count_1s(pieces(pt, c)))
2023 if (failedStep) (*failedStep)++;
2026 for(Color c = WHITE; c <= BLACK; c++)
2027 for(PieceType pt = PAWN; pt <= KING; pt++)
2028 for(int i = 0; i < pieceCount[c][pt]; i++)
2030 if (piece_on(piece_list(c, pt, i)) != piece_of_color_and_type(c, pt))
2033 if (index[piece_list(c, pt, i)] != i)
2037 if (failedStep) *failedStep = 0;