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;
54 Key Position::zobExclusion;
56 Score Position::PieceSquareTable[16][64];
58 static bool RequestPending = false;
63 CheckInfo::CheckInfo(const Position& pos) {
65 Color us = pos.side_to_move();
66 Color them = opposite_color(us);
68 ksq = pos.king_square(them);
69 dcCandidates = pos.discovered_check_candidates(us);
71 checkSq[PAWN] = pos.attacks_from<PAWN>(ksq, them);
72 checkSq[KNIGHT] = pos.attacks_from<KNIGHT>(ksq);
73 checkSq[BISHOP] = pos.attacks_from<BISHOP>(ksq);
74 checkSq[ROOK] = pos.attacks_from<ROOK>(ksq);
75 checkSq[QUEEN] = checkSq[BISHOP] | checkSq[ROOK];
76 checkSq[KING] = EmptyBoardBB;
79 Position::Position(const Position& pos) {
83 Position::Position(const string& fen) {
88 /// Position::from_fen() initializes the position object with the given FEN
89 /// string. This function is not very robust - make sure that input FENs are
90 /// correct (this is assumed to be the responsibility of the GUI).
92 void Position::from_fen(const string& fen) {
94 static const string pieceLetters = "KQRBNPkqrbnp";
95 static const Piece pieces[] = { WK, WQ, WR, WB, WN, WP, BK, BQ, BR, BB, BN, BP };
103 for ( ; fen[i] != ' '; i++)
107 // Skip the given number of files
108 file += (fen[i] - '1' + 1);
111 else if (fen[i] == '/')
117 size_t idx = pieceLetters.find(fen[i]);
118 if (idx == string::npos)
120 std::cout << "Error in FEN at character " << i << std::endl;
123 Square square = make_square(file, rank);
124 put_piece(pieces[idx], square);
130 if (fen[i] != 'w' && fen[i] != 'b')
132 std::cout << "Error in FEN at character " << i << std::endl;
135 sideToMove = (fen[i] == 'w' ? WHITE : BLACK);
141 std::cout << "Error in FEN at character " << i << std::endl;
146 while(strchr("KQkqabcdefghABCDEFGH-", fen[i])) {
152 else if(fen[i] == 'K') allow_oo(WHITE);
153 else if(fen[i] == 'Q') allow_ooo(WHITE);
154 else if(fen[i] == 'k') allow_oo(BLACK);
155 else if(fen[i] == 'q') allow_ooo(BLACK);
156 else if(fen[i] >= 'A' && fen[i] <= 'H') {
157 File rookFile, kingFile = FILE_NONE;
158 for(Square square = SQ_B1; square <= SQ_G1; square++)
159 if(piece_on(square) == WK)
160 kingFile = square_file(square);
161 if(kingFile == FILE_NONE) {
162 std::cout << "Error in FEN at character " << i << std::endl;
165 initialKFile = kingFile;
166 rookFile = File(fen[i] - 'A') + FILE_A;
167 if(rookFile < initialKFile) {
169 initialQRFile = rookFile;
173 initialKRFile = rookFile;
176 else if(fen[i] >= 'a' && fen[i] <= 'h') {
177 File rookFile, kingFile = FILE_NONE;
178 for(Square square = SQ_B8; square <= SQ_G8; square++)
179 if(piece_on(square) == BK)
180 kingFile = square_file(square);
181 if(kingFile == FILE_NONE) {
182 std::cout << "Error in FEN at character " << i << std::endl;
185 initialKFile = kingFile;
186 rookFile = File(fen[i] - 'a') + FILE_A;
187 if(rookFile < initialKFile) {
189 initialQRFile = rookFile;
193 initialKRFile = rookFile;
197 std::cout << "Error in FEN at character " << i << std::endl;
204 while (fen[i] == ' ')
207 // En passant square -- ignore if no capture is possible
208 if ( i <= fen.length() - 2
209 && (fen[i] >= 'a' && fen[i] <= 'h')
210 && (fen[i+1] == '3' || fen[i+1] == '6'))
212 Square fenEpSquare = square_from_string(fen.substr(i, 2));
213 Color them = opposite_color(sideToMove);
214 if (attacks_from<PAWN>(fenEpSquare, them) & this->pieces(PAWN, sideToMove))
215 st->epSquare = square_from_string(fen.substr(i, 2));
218 // Various initialisation
219 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
220 castleRightsMask[sq] = ALL_CASTLES;
222 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO|WHITE_OOO);
223 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO|BLACK_OOO);
224 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
225 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
226 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
227 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
231 st->key = compute_key();
232 st->pawnKey = compute_pawn_key();
233 st->materialKey = compute_material_key();
234 st->value = compute_value();
235 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
236 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
240 /// Position::to_fen() converts the position object to a FEN string. This is
241 /// probably only useful for debugging.
243 const string Position::to_fen() const {
245 static const string pieceLetters = " PNBRQK pnbrqk";
249 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
252 for (File file = FILE_A; file <= FILE_H; file++)
254 Square sq = make_square(file, rank);
255 if (!square_is_occupied(sq))
261 fen += (char)skip + '0';
264 fen += pieceLetters[piece_on(sq)];
267 fen += (char)skip + '0';
269 fen += (rank > RANK_1 ? '/' : ' ');
271 fen += (sideToMove == WHITE ? "w " : "b ");
272 if (st->castleRights != NO_CASTLES)
274 if (initialKFile == FILE_E && initialQRFile == FILE_A && initialKRFile == FILE_H)
276 if (can_castle_kingside(WHITE)) fen += 'K';
277 if (can_castle_queenside(WHITE)) fen += 'Q';
278 if (can_castle_kingside(BLACK)) fen += 'k';
279 if (can_castle_queenside(BLACK)) fen += 'q';
283 if (can_castle_kingside(WHITE))
284 fen += toupper(file_to_char(initialKRFile));
285 if (can_castle_queenside(WHITE))
286 fen += toupper(file_to_char(initialQRFile));
287 if (can_castle_kingside(BLACK))
288 fen += file_to_char(initialKRFile);
289 if (can_castle_queenside(BLACK))
290 fen += file_to_char(initialQRFile);
296 if (ep_square() != SQ_NONE)
297 fen += square_to_string(ep_square());
305 /// Position::print() prints an ASCII representation of the position to
306 /// the standard output. If a move is given then also the san is print.
308 void Position::print(Move m) const {
310 static const string pieceLetters = " PNBRQK PNBRQK .";
312 // Check for reentrancy, as example when called from inside
313 // MovePicker that is used also here in move_to_san()
317 RequestPending = true;
319 std::cout << std::endl;
322 string col = (color_of_piece_on(move_from(m)) == BLACK ? ".." : "");
323 std::cout << "Move is: " << col << move_to_san(*this, m) << std::endl;
325 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
327 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl;
328 for (File file = FILE_A; file <= FILE_H; file++)
330 Square sq = make_square(file, rank);
331 Piece piece = piece_on(sq);
332 if (piece == EMPTY && square_color(sq) == WHITE)
335 char col = (color_of_piece_on(sq) == BLACK ? '=' : ' ');
336 std::cout << '|' << col << pieceLetters[piece] << col;
338 std::cout << '|' << std::endl;
340 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl
341 << "Fen is: " << to_fen() << std::endl
342 << "Key is: " << st->key << std::endl;
344 RequestPending = false;
348 /// Position::copy() creates a copy of the input position.
350 void Position::copy(const Position& pos) {
352 memcpy(this, &pos, sizeof(Position));
353 saveState(); // detach and copy state info
357 /// Position:hidden_checkers<>() returns a bitboard of all pinned (against the
358 /// king) pieces for the given color and for the given pinner type. Or, when
359 /// template parameter FindPinned is false, the pieces of the given color
360 /// candidate for a discovery check against the enemy king.
361 /// Bitboard checkersBB must be already updated when looking for pinners.
363 template<bool FindPinned>
364 Bitboard Position::hidden_checkers(Color c) const {
366 Bitboard result = EmptyBoardBB;
367 Bitboard pinners = pieces_of_color(FindPinned ? opposite_color(c) : c);
369 // Pinned pieces protect our king, dicovery checks attack
371 Square ksq = king_square(FindPinned ? c : opposite_color(c));
373 // Pinners are sliders, not checkers, that give check when candidate pinned is removed
374 pinners &= (pieces(ROOK, QUEEN) & RookPseudoAttacks[ksq]) | (pieces(BISHOP, QUEEN) & BishopPseudoAttacks[ksq]);
376 if (FindPinned && pinners)
377 pinners &= ~st->checkersBB;
381 Square s = pop_1st_bit(&pinners);
382 Bitboard b = squares_between(s, ksq) & occupied_squares();
386 if ( !(b & (b - 1)) // Only one bit set?
387 && (b & pieces_of_color(c))) // Is an our piece?
394 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
395 /// king) pieces for the given color. Note that checkersBB bitboard must
396 /// be already updated.
398 Bitboard Position::pinned_pieces(Color c) const {
400 return hidden_checkers<true>(c);
404 /// Position:discovered_check_candidates() returns a bitboard containing all
405 /// pieces for the given side which are candidates for giving a discovered
406 /// check. Contrary to pinned_pieces() here there is no need of checkersBB
407 /// to be already updated.
409 Bitboard Position::discovered_check_candidates(Color c) const {
411 return hidden_checkers<false>(c);
414 /// Position::attackers_to() computes a bitboard containing all pieces which
415 /// attacks a given square.
417 Bitboard Position::attackers_to(Square s) const {
419 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
420 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
421 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
422 | (attacks_from<ROOK>(s) & pieces(ROOK, QUEEN))
423 | (attacks_from<BISHOP>(s) & pieces(BISHOP, QUEEN))
424 | (attacks_from<KING>(s) & pieces(KING));
427 /// Position::attacks_from() computes a bitboard of all attacks
428 /// of a given piece put in a given square.
430 Bitboard Position::attacks_from(Piece p, Square s) const {
432 assert(square_is_ok(s));
436 case WP: return attacks_from<PAWN>(s, WHITE);
437 case BP: return attacks_from<PAWN>(s, BLACK);
438 case WN: case BN: return attacks_from<KNIGHT>(s);
439 case WB: case BB: return attacks_from<BISHOP>(s);
440 case WR: case BR: return attacks_from<ROOK>(s);
441 case WQ: case BQ: return attacks_from<QUEEN>(s);
442 case WK: case BK: return attacks_from<KING>(s);
449 /// Position::move_attacks_square() tests whether a move from the current
450 /// position attacks a given square.
452 bool Position::move_attacks_square(Move m, Square s) const {
454 assert(move_is_ok(m));
455 assert(square_is_ok(s));
457 Square f = move_from(m), t = move_to(m);
459 assert(square_is_occupied(f));
461 if (bit_is_set(attacks_from(piece_on(f), t), s))
464 // Move the piece and scan for X-ray attacks behind it
465 Bitboard occ = occupied_squares();
466 Color us = color_of_piece_on(f);
469 Bitboard xray = ( (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
470 |(bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN))) & pieces_of_color(us);
472 // If we have attacks we need to verify that are caused by our move
473 // and are not already existent ones.
474 return xray && (xray ^ (xray & attacks_from<QUEEN>(s)));
478 /// Position::find_checkers() computes the checkersBB bitboard, which
479 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
480 /// currently works by calling Position::attackers_to, which is probably
481 /// inefficient. Consider rewriting this function to use the last move
482 /// played, like in non-bitboard versions of Glaurung.
484 void Position::find_checkers() {
486 Color us = side_to_move();
487 st->checkersBB = attackers_to(king_square(us)) & pieces_of_color(opposite_color(us));
491 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
493 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
496 assert(move_is_ok(m));
497 assert(pinned == pinned_pieces(side_to_move()));
499 // Castling moves are checked for legality during move generation.
500 if (move_is_castle(m))
503 Color us = side_to_move();
504 Square from = move_from(m);
506 assert(color_of_piece_on(from) == us);
507 assert(piece_on(king_square(us)) == piece_of_color_and_type(us, KING));
509 // En passant captures are a tricky special case. Because they are
510 // rather uncommon, we do it simply by testing whether the king is attacked
511 // after the move is made
514 Color them = opposite_color(us);
515 Square to = move_to(m);
516 Square capsq = make_square(square_file(to), square_rank(from));
517 Bitboard b = occupied_squares();
518 Square ksq = king_square(us);
520 assert(to == ep_square());
521 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
522 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
523 assert(piece_on(to) == EMPTY);
526 clear_bit(&b, capsq);
529 return !(rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, them))
530 && !(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, them));
533 // If the moving piece is a king, check whether the destination
534 // square is attacked by the opponent.
535 if (type_of_piece_on(from) == KING)
536 return !(attackers_to(move_to(m)) & pieces_of_color(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 || (direction_between_squares(from, king_square(us)) == direction_between_squares(move_to(m), king_square(us))));
546 /// Position::pl_move_is_evasion() tests whether a pseudo-legal move is a legal evasion
548 bool Position::pl_move_is_evasion(Move m, Bitboard pinned) const
552 Color us = side_to_move();
553 Square from = move_from(m);
554 Square to = move_to(m);
556 // King moves and en-passant captures are verified in pl_move_is_legal()
557 if (type_of_piece_on(from) == KING || move_is_ep(m))
558 return pl_move_is_legal(m, pinned);
560 Bitboard target = checkers();
561 Square checksq = pop_1st_bit(&target);
563 if (target) // double check ?
566 // Our move must be a blocking evasion or a capture of the checking piece
567 target = squares_between(checksq, king_square(us)) | checkers();
568 return bit_is_set(target, to) && pl_move_is_legal(m, pinned);
572 /// Position::move_is_check() tests whether a pseudo-legal move is a check
574 bool Position::move_is_check(Move m) const {
576 return move_is_check(m, CheckInfo(*this));
579 bool Position::move_is_check(Move m, const CheckInfo& ci) const {
582 assert(move_is_ok(m));
583 assert(ci.dcCandidates == discovered_check_candidates(side_to_move()));
584 assert(color_of_piece_on(move_from(m)) == side_to_move());
585 assert(piece_on(ci.ksq) == piece_of_color_and_type(opposite_color(side_to_move()), KING));
587 Square from = move_from(m);
588 Square to = move_to(m);
589 PieceType pt = type_of_piece_on(from);
592 if (bit_is_set(ci.checkSq[pt], to))
596 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
598 // For pawn and king moves we need to verify also direction
599 if ( (pt != PAWN && pt != KING)
600 ||(direction_between_squares(from, ci.ksq) != direction_between_squares(to, ci.ksq)))
604 // Can we skip the ugly special cases ?
605 if (!move_is_special(m))
608 Color us = side_to_move();
609 Bitboard b = occupied_squares();
611 // Promotion with check ?
612 if (move_is_promotion(m))
616 switch (move_promotion_piece(m))
619 return bit_is_set(attacks_from<KNIGHT>(to), ci.ksq);
621 return bit_is_set(bishop_attacks_bb(to, b), ci.ksq);
623 return bit_is_set(rook_attacks_bb(to, b), ci.ksq);
625 return bit_is_set(queen_attacks_bb(to, b), ci.ksq);
631 // En passant capture with check? We have already handled the case
632 // of direct checks and ordinary discovered check, the only case we
633 // need to handle is the unusual case of a discovered check through the
637 Square capsq = make_square(square_file(to), square_rank(from));
639 clear_bit(&b, capsq);
641 return (rook_attacks_bb(ci.ksq, b) & pieces(ROOK, QUEEN, us))
642 ||(bishop_attacks_bb(ci.ksq, b) & pieces(BISHOP, QUEEN, us));
645 // Castling with check ?
646 if (move_is_castle(m))
648 Square kfrom, kto, rfrom, rto;
654 kto = relative_square(us, SQ_G1);
655 rto = relative_square(us, SQ_F1);
657 kto = relative_square(us, SQ_C1);
658 rto = relative_square(us, SQ_D1);
660 clear_bit(&b, kfrom);
661 clear_bit(&b, rfrom);
664 return bit_is_set(rook_attacks_bb(rto, b), ci.ksq);
671 /// Position::do_move() makes a move, and saves all information necessary
672 /// to a StateInfo object. The move is assumed to be legal.
673 /// Pseudo-legal moves should be filtered out before this function is called.
675 void Position::do_move(Move m, StateInfo& newSt) {
678 do_move(m, newSt, ci, move_is_check(m, ci));
681 void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveIsCheck) {
684 assert(move_is_ok(m));
686 Bitboard key = st->key;
688 // Copy some fields of old state to our new StateInfo object except the
689 // ones which are recalculated from scratch anyway, then switch our state
690 // pointer to point to the new, ready to be updated, state.
691 struct ReducedStateInfo {
692 Key pawnKey, materialKey;
693 int castleRights, rule50, pliesFromNull;
699 memcpy(&newSt, st, sizeof(ReducedStateInfo));
703 // Save the current key to the history[] array, in order to be able to
704 // detect repetition draws.
705 history[gamePly] = key;
708 // Update side to move
709 key ^= zobSideToMove;
711 // Increment the 50 moves rule draw counter. Resetting it to zero in the
712 // case of non-reversible moves is taken care of later.
716 if (move_is_castle(m))
723 Color us = side_to_move();
724 Color them = opposite_color(us);
725 Square from = move_from(m);
726 Square to = move_to(m);
727 bool ep = move_is_ep(m);
728 bool pm = move_is_promotion(m);
730 Piece piece = piece_on(from);
731 PieceType pt = type_of_piece(piece);
732 PieceType capture = ep ? PAWN : type_of_piece_on(to);
734 assert(color_of_piece_on(from) == us);
735 assert(color_of_piece_on(to) == them || square_is_empty(to));
736 assert(!(ep || pm) || piece == piece_of_color_and_type(us, PAWN));
737 assert(!pm || relative_rank(us, to) == RANK_8);
740 do_capture_move(key, capture, them, to, ep);
743 key ^= zobrist[us][pt][from] ^ zobrist[us][pt][to];
745 // Reset en passant square
746 if (st->epSquare != SQ_NONE)
748 key ^= zobEp[st->epSquare];
749 st->epSquare = SQ_NONE;
752 // Update castle rights, try to shortcut a common case
753 int cm = castleRightsMask[from] & castleRightsMask[to];
754 if (cm != ALL_CASTLES && ((cm & st->castleRights) != st->castleRights))
756 key ^= zobCastle[st->castleRights];
757 st->castleRights &= castleRightsMask[from];
758 st->castleRights &= castleRightsMask[to];
759 key ^= zobCastle[st->castleRights];
762 // Prefetch TT access as soon as we know key is updated
766 Bitboard move_bb = make_move_bb(from, to);
767 do_move_bb(&(byColorBB[us]), move_bb);
768 do_move_bb(&(byTypeBB[pt]), move_bb);
769 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
771 board[to] = board[from];
774 // Update piece lists, note that index[from] is not updated and
775 // becomes stale. This works as long as index[] is accessed just
776 // by known occupied squares.
777 index[to] = index[from];
778 pieceList[us][pt][index[to]] = to;
780 // If the moving piece was a pawn do some special extra work
783 // Reset rule 50 draw counter
786 // Update pawn hash key
787 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
789 // Set en passant square, only if moved pawn can be captured
790 if ((to ^ from) == 16)
792 if (attacks_from<PAWN>(from + (us == WHITE ? DELTA_N : DELTA_S), us) & pieces(PAWN, them))
794 st->epSquare = Square((int(from) + int(to)) / 2);
795 key ^= zobEp[st->epSquare];
800 // Update incremental scores
801 st->value += pst_delta(piece, from, to);
804 st->capture = capture;
806 if (pm) // promotion ?
808 PieceType promotion = move_promotion_piece(m);
810 assert(promotion >= KNIGHT && promotion <= QUEEN);
812 // Insert promoted piece instead of pawn
813 clear_bit(&(byTypeBB[PAWN]), to);
814 set_bit(&(byTypeBB[promotion]), to);
815 board[to] = piece_of_color_and_type(us, promotion);
817 // Update material key
818 st->materialKey ^= zobMaterial[us][PAWN][pieceCount[us][PAWN]];
819 st->materialKey ^= zobMaterial[us][promotion][pieceCount[us][promotion]+1];
821 // Update piece counts
822 pieceCount[us][PAWN]--;
823 pieceCount[us][promotion]++;
825 // Update piece lists, move the last pawn at index[to] position
826 // and shrink the list. Add a new promotion piece to the list.
827 Square lastPawnSquare = pieceList[us][PAWN][pieceCount[us][PAWN]];
828 index[lastPawnSquare] = index[to];
829 pieceList[us][PAWN][index[lastPawnSquare]] = lastPawnSquare;
830 pieceList[us][PAWN][pieceCount[us][PAWN]] = SQ_NONE;
831 index[to] = pieceCount[us][promotion] - 1;
832 pieceList[us][promotion][index[to]] = to;
834 // Partially revert hash keys update
835 key ^= zobrist[us][PAWN][to] ^ zobrist[us][promotion][to];
836 st->pawnKey ^= zobrist[us][PAWN][to];
838 // Partially revert and update incremental scores
839 st->value -= pst(us, PAWN, to);
840 st->value += pst(us, promotion, to);
843 st->npMaterial[us] += piece_value_midgame(promotion);
846 // Update the key with the final value
849 // Update checkers bitboard, piece must be already moved
850 st->checkersBB = EmptyBoardBB;
855 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
859 if (bit_is_set(ci.checkSq[pt], to))
860 st->checkersBB = SetMaskBB[to];
863 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
866 st->checkersBB |= (attacks_from<ROOK>(ci.ksq) & pieces(ROOK, QUEEN, us));
869 st->checkersBB |= (attacks_from<BISHOP>(ci.ksq) & pieces(BISHOP, QUEEN, us));
875 sideToMove = opposite_color(sideToMove);
876 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
882 /// Position::do_capture_move() is a private method used to update captured
883 /// piece info. It is called from the main Position::do_move function.
885 void Position::do_capture_move(Bitboard& key, PieceType capture, Color them, Square to, bool ep) {
887 assert(capture != KING);
891 if (ep) // en passant ?
893 capsq = (them == BLACK)? (to - DELTA_N) : (to - DELTA_S);
895 assert(to == st->epSquare);
896 assert(relative_rank(opposite_color(them), to) == RANK_6);
897 assert(piece_on(to) == EMPTY);
898 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
900 board[capsq] = EMPTY;
903 // Remove captured piece
904 clear_bit(&(byColorBB[them]), capsq);
905 clear_bit(&(byTypeBB[capture]), capsq);
906 clear_bit(&(byTypeBB[0]), capsq);
909 key ^= zobrist[them][capture][capsq];
911 // Update incremental scores
912 st->value -= pst(them, capture, capsq);
914 // If the captured piece was a pawn, update pawn hash key,
915 // otherwise update non-pawn material.
917 st->pawnKey ^= zobrist[them][PAWN][capsq];
919 st->npMaterial[them] -= piece_value_midgame(capture);
921 // Update material hash key
922 st->materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];
924 // Update piece count
925 pieceCount[them][capture]--;
927 // Update piece list, move the last piece at index[capsq] position
929 // WARNING: This is a not perfectly revresible operation. When we
930 // will reinsert the captured piece in undo_move() we will put it
931 // at the end of the list and not in its original place, it means
932 // index[] and pieceList[] are not guaranteed to be invariant to a
933 // do_move() + undo_move() sequence.
934 Square lastPieceSquare = pieceList[them][capture][pieceCount[them][capture]];
935 index[lastPieceSquare] = index[capsq];
936 pieceList[them][capture][index[lastPieceSquare]] = lastPieceSquare;
937 pieceList[them][capture][pieceCount[them][capture]] = SQ_NONE;
939 // Reset rule 50 counter
944 /// Position::do_castle_move() is a private method used to make a castling
945 /// move. It is called from the main Position::do_move function. Note that
946 /// castling moves are encoded as "king captures friendly rook" moves, for
947 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
949 void Position::do_castle_move(Move m) {
951 assert(move_is_ok(m));
952 assert(move_is_castle(m));
954 Color us = side_to_move();
955 Color them = opposite_color(us);
957 // Reset capture field
958 st->capture = NO_PIECE_TYPE;
960 // Find source squares for king and rook
961 Square kfrom = move_from(m);
962 Square rfrom = move_to(m); // HACK: See comment at beginning of function
965 assert(piece_on(kfrom) == piece_of_color_and_type(us, KING));
966 assert(piece_on(rfrom) == piece_of_color_and_type(us, ROOK));
968 // Find destination squares for king and rook
969 if (rfrom > kfrom) // O-O
971 kto = relative_square(us, SQ_G1);
972 rto = relative_square(us, SQ_F1);
974 kto = relative_square(us, SQ_C1);
975 rto = relative_square(us, SQ_D1);
978 // Remove pieces from source squares:
979 clear_bit(&(byColorBB[us]), kfrom);
980 clear_bit(&(byTypeBB[KING]), kfrom);
981 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
982 clear_bit(&(byColorBB[us]), rfrom);
983 clear_bit(&(byTypeBB[ROOK]), rfrom);
984 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
986 // Put pieces on destination squares:
987 set_bit(&(byColorBB[us]), kto);
988 set_bit(&(byTypeBB[KING]), kto);
989 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
990 set_bit(&(byColorBB[us]), rto);
991 set_bit(&(byTypeBB[ROOK]), rto);
992 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
994 // Update board array
995 Piece king = piece_of_color_and_type(us, KING);
996 Piece rook = piece_of_color_and_type(us, ROOK);
997 board[kfrom] = board[rfrom] = EMPTY;
1001 // Update piece lists
1002 pieceList[us][KING][index[kfrom]] = kto;
1003 pieceList[us][ROOK][index[rfrom]] = rto;
1004 int tmp = index[rfrom]; // In Chess960 could be rto == kfrom
1005 index[kto] = index[kfrom];
1008 // Update incremental scores
1009 st->value += pst_delta(king, kfrom, kto);
1010 st->value += pst_delta(rook, rfrom, rto);
1013 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1014 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1016 // Clear en passant square
1017 if (st->epSquare != SQ_NONE)
1019 st->key ^= zobEp[st->epSquare];
1020 st->epSquare = SQ_NONE;
1023 // Update castling rights
1024 st->key ^= zobCastle[st->castleRights];
1025 st->castleRights &= castleRightsMask[kfrom];
1026 st->key ^= zobCastle[st->castleRights];
1028 // Reset rule 50 counter
1031 // Update checkers BB
1032 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
1035 sideToMove = opposite_color(sideToMove);
1036 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1042 /// Position::undo_move() unmakes a move. When it returns, the position should
1043 /// be restored to exactly the same state as before the move was made.
1045 void Position::undo_move(Move m) {
1048 assert(move_is_ok(m));
1051 sideToMove = opposite_color(sideToMove);
1053 if (move_is_castle(m))
1055 undo_castle_move(m);
1059 Color us = side_to_move();
1060 Color them = opposite_color(us);
1061 Square from = move_from(m);
1062 Square to = move_to(m);
1063 bool ep = move_is_ep(m);
1064 bool pm = move_is_promotion(m);
1066 PieceType pt = type_of_piece_on(to);
1068 assert(square_is_empty(from));
1069 assert(color_of_piece_on(to) == us);
1070 assert(!pm || relative_rank(us, to) == RANK_8);
1071 assert(!ep || to == st->previous->epSquare);
1072 assert(!ep || relative_rank(us, to) == RANK_6);
1073 assert(!ep || piece_on(to) == piece_of_color_and_type(us, PAWN));
1075 if (pm) // promotion ?
1077 PieceType promotion = move_promotion_piece(m);
1080 assert(promotion >= KNIGHT && promotion <= QUEEN);
1081 assert(piece_on(to) == piece_of_color_and_type(us, promotion));
1083 // Replace promoted piece with a pawn
1084 clear_bit(&(byTypeBB[promotion]), to);
1085 set_bit(&(byTypeBB[PAWN]), to);
1087 // Update piece counts
1088 pieceCount[us][promotion]--;
1089 pieceCount[us][PAWN]++;
1091 // Update piece list replacing promotion piece with a pawn
1092 Square lastPromotionSquare = pieceList[us][promotion][pieceCount[us][promotion]];
1093 index[lastPromotionSquare] = index[to];
1094 pieceList[us][promotion][index[lastPromotionSquare]] = lastPromotionSquare;
1095 pieceList[us][promotion][pieceCount[us][promotion]] = SQ_NONE;
1096 index[to] = pieceCount[us][PAWN] - 1;
1097 pieceList[us][PAWN][index[to]] = to;
1101 // Put the piece back at the source square
1102 Bitboard move_bb = make_move_bb(to, from);
1103 do_move_bb(&(byColorBB[us]), move_bb);
1104 do_move_bb(&(byTypeBB[pt]), move_bb);
1105 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
1107 board[from] = piece_of_color_and_type(us, pt);
1110 // Update piece list
1111 index[from] = index[to];
1112 pieceList[us][pt][index[from]] = from;
1119 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1121 assert(st->capture != KING);
1122 assert(!ep || square_is_empty(capsq));
1124 // Restore the captured piece
1125 set_bit(&(byColorBB[them]), capsq);
1126 set_bit(&(byTypeBB[st->capture]), capsq);
1127 set_bit(&(byTypeBB[0]), capsq);
1129 board[capsq] = piece_of_color_and_type(them, st->capture);
1131 // Update piece count
1132 pieceCount[them][st->capture]++;
1134 // Update piece list, add a new captured piece in capsq square
1135 index[capsq] = pieceCount[them][st->capture] - 1;
1136 pieceList[them][st->capture][index[capsq]] = capsq;
1139 // Finally point our state pointer back to the previous state
1146 /// Position::undo_castle_move() is a private method used to unmake a castling
1147 /// move. It is called from the main Position::undo_move function. Note that
1148 /// castling moves are encoded as "king captures friendly rook" moves, for
1149 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1151 void Position::undo_castle_move(Move m) {
1153 assert(move_is_ok(m));
1154 assert(move_is_castle(m));
1156 // When we have arrived here, some work has already been done by
1157 // Position::undo_move. In particular, the side to move has been switched,
1158 // so the code below is correct.
1159 Color us = side_to_move();
1161 // Find source squares for king and rook
1162 Square kfrom = move_from(m);
1163 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1166 // Find destination squares for king and rook
1167 if (rfrom > kfrom) // O-O
1169 kto = relative_square(us, SQ_G1);
1170 rto = relative_square(us, SQ_F1);
1172 kto = relative_square(us, SQ_C1);
1173 rto = relative_square(us, SQ_D1);
1176 assert(piece_on(kto) == piece_of_color_and_type(us, KING));
1177 assert(piece_on(rto) == piece_of_color_and_type(us, ROOK));
1179 // Remove pieces from destination squares:
1180 clear_bit(&(byColorBB[us]), kto);
1181 clear_bit(&(byTypeBB[KING]), kto);
1182 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1183 clear_bit(&(byColorBB[us]), rto);
1184 clear_bit(&(byTypeBB[ROOK]), rto);
1185 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1187 // Put pieces on source squares:
1188 set_bit(&(byColorBB[us]), kfrom);
1189 set_bit(&(byTypeBB[KING]), kfrom);
1190 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1191 set_bit(&(byColorBB[us]), rfrom);
1192 set_bit(&(byTypeBB[ROOK]), rfrom);
1193 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1196 board[rto] = board[kto] = EMPTY;
1197 board[rfrom] = piece_of_color_and_type(us, ROOK);
1198 board[kfrom] = piece_of_color_and_type(us, KING);
1200 // Update piece lists
1201 pieceList[us][KING][index[kto]] = kfrom;
1202 pieceList[us][ROOK][index[rto]] = rfrom;
1203 int tmp = index[rto]; // In Chess960 could be rto == kfrom
1204 index[kfrom] = index[kto];
1207 // Finally point our state pointer back to the previous state
1214 /// Position::do_null_move makes() a "null move": It switches the side to move
1215 /// and updates the hash key without executing any move on the board.
1217 void Position::do_null_move(StateInfo& backupSt) {
1220 assert(!is_check());
1222 // Back up the information necessary to undo the null move to the supplied
1223 // StateInfo object.
1224 // Note that differently from normal case here backupSt is actually used as
1225 // a backup storage not as a new state to be used.
1226 backupSt.key = st->key;
1227 backupSt.epSquare = st->epSquare;
1228 backupSt.value = st->value;
1229 backupSt.previous = st->previous;
1230 backupSt.pliesFromNull = st->pliesFromNull;
1231 st->previous = &backupSt;
1233 // Save the current key to the history[] array, in order to be able to
1234 // detect repetition draws.
1235 history[gamePly] = st->key;
1237 // Update the necessary information
1238 if (st->epSquare != SQ_NONE)
1239 st->key ^= zobEp[st->epSquare];
1241 st->key ^= zobSideToMove;
1242 TT.prefetch(st->key);
1244 sideToMove = opposite_color(sideToMove);
1245 st->epSquare = SQ_NONE;
1247 st->pliesFromNull = 0;
1248 st->value += (sideToMove == WHITE) ? TempoValue : -TempoValue;
1253 /// Position::undo_null_move() unmakes a "null move".
1255 void Position::undo_null_move() {
1258 assert(!is_check());
1260 // Restore information from the our backup StateInfo object
1261 StateInfo* backupSt = st->previous;
1262 st->key = backupSt->key;
1263 st->epSquare = backupSt->epSquare;
1264 st->value = backupSt->value;
1265 st->previous = backupSt->previous;
1266 st->pliesFromNull = backupSt->pliesFromNull;
1268 // Update the necessary information
1269 sideToMove = opposite_color(sideToMove);
1275 /// Position::see() is a static exchange evaluator: It tries to estimate the
1276 /// material gain or loss resulting from a move. There are three versions of
1277 /// this function: One which takes a destination square as input, one takes a
1278 /// move, and one which takes a 'from' and a 'to' square. The function does
1279 /// not yet understand promotions captures.
1281 int Position::see(Square to) const {
1283 assert(square_is_ok(to));
1284 return see(SQ_NONE, to);
1287 int Position::see(Move m) const {
1289 assert(move_is_ok(m));
1290 return see(move_from(m), move_to(m));
1293 int Position::see_sign(Move m) const {
1295 assert(move_is_ok(m));
1297 Square from = move_from(m);
1298 Square to = move_to(m);
1300 // Early return if SEE cannot be negative because capturing piece value
1301 // is not bigger then captured one.
1302 if ( midgame_value_of_piece_on(from) <= midgame_value_of_piece_on(to)
1303 && type_of_piece_on(from) != KING)
1306 return see(from, to);
1309 int Position::see(Square from, Square to) const {
1312 static const int seeValues[18] = {
1313 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1314 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1315 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1316 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1320 Bitboard attackers, stmAttackers, b;
1322 assert(square_is_ok(from) || from == SQ_NONE);
1323 assert(square_is_ok(to));
1325 // Initialize colors
1326 Color us = (from != SQ_NONE ? color_of_piece_on(from) : opposite_color(color_of_piece_on(to)));
1327 Color them = opposite_color(us);
1329 // Initialize pieces
1330 Piece piece = piece_on(from);
1331 Piece capture = piece_on(to);
1332 Bitboard occ = occupied_squares();
1334 // King cannot be recaptured
1335 if (type_of_piece(piece) == KING)
1336 return seeValues[capture];
1338 // Handle en passant moves
1339 if (st->epSquare == to && type_of_piece_on(from) == PAWN)
1341 assert(capture == EMPTY);
1343 Square capQq = (side_to_move() == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1344 capture = piece_on(capQq);
1345 assert(type_of_piece_on(capQq) == PAWN);
1347 // Remove the captured pawn
1348 clear_bit(&occ, capQq);
1353 // Find all attackers to the destination square, with the moving piece
1354 // removed, but possibly an X-ray attacker added behind it.
1355 clear_bit(&occ, from);
1356 attackers = (rook_attacks_bb(to, occ) & pieces(ROOK, QUEEN))
1357 | (bishop_attacks_bb(to, occ) & pieces(BISHOP, QUEEN))
1358 | (attacks_from<KNIGHT>(to) & pieces(KNIGHT))
1359 | (attacks_from<KING>(to) & pieces(KING))
1360 | (attacks_from<PAWN>(to, WHITE) & pieces(PAWN, BLACK))
1361 | (attacks_from<PAWN>(to, BLACK) & pieces(PAWN, WHITE));
1363 if (from != SQ_NONE)
1366 // If we don't have any attacker we are finished
1367 if ((attackers & pieces_of_color(us)) == EmptyBoardBB)
1370 // Locate the least valuable attacker to the destination square
1371 // and use it to initialize from square.
1372 stmAttackers = attackers & pieces_of_color(us);
1374 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1377 from = first_1(stmAttackers & pieces(pt));
1378 piece = piece_on(from);
1381 // If the opponent has no attackers we are finished
1382 stmAttackers = attackers & pieces_of_color(them);
1384 return seeValues[capture];
1386 attackers &= occ; // Remove the moving piece
1388 // The destination square is defended, which makes things rather more
1389 // difficult to compute. We proceed by building up a "swap list" containing
1390 // the material gain or loss at each stop in a sequence of captures to the
1391 // destination square, where the sides alternately capture, and always
1392 // capture with the least valuable piece. After each capture, we look for
1393 // new X-ray attacks from behind the capturing piece.
1394 int lastCapturingPieceValue = seeValues[piece];
1395 int swapList[32], n = 1;
1399 swapList[0] = seeValues[capture];
1402 // Locate the least valuable attacker for the side to move. The loop
1403 // below looks like it is potentially infinite, but it isn't. We know
1404 // that the side to move still has at least one attacker left.
1405 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1408 // Remove the attacker we just found from the 'attackers' bitboard,
1409 // and scan for new X-ray attacks behind the attacker.
1410 b = stmAttackers & pieces(pt);
1411 occ ^= (b & (~b + 1));
1412 attackers |= (rook_attacks_bb(to, occ) & pieces(ROOK, QUEEN))
1413 | (bishop_attacks_bb(to, occ) & pieces(BISHOP, QUEEN));
1417 // Add the new entry to the swap list
1419 swapList[n] = -swapList[n - 1] + lastCapturingPieceValue;
1422 // Remember the value of the capturing piece, and change the side to move
1423 // before beginning the next iteration
1424 lastCapturingPieceValue = seeValues[pt];
1425 c = opposite_color(c);
1426 stmAttackers = attackers & pieces_of_color(c);
1428 // Stop after a king capture
1429 if (pt == KING && stmAttackers)
1432 swapList[n++] = QueenValueMidgame*10;
1435 } while (stmAttackers);
1437 // Having built the swap list, we negamax through it to find the best
1438 // achievable score from the point of view of the side to move
1440 swapList[n-1] = Min(-swapList[n], swapList[n-1]);
1446 /// Position::saveState() copies the content of the current state
1447 /// inside startState and makes st point to it. This is needed
1448 /// when the st pointee could become stale, as example because
1449 /// the caller is about to going out of scope.
1451 void Position::saveState() {
1455 st->previous = NULL; // as a safe guard
1459 /// Position::clear() erases the position object to a pristine state, with an
1460 /// empty board, white to move, and no castling rights.
1462 void Position::clear() {
1465 memset(st, 0, sizeof(StateInfo));
1466 st->epSquare = SQ_NONE;
1468 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1469 memset(byTypeBB, 0, sizeof(Bitboard) * 8);
1470 memset(pieceCount, 0, sizeof(int) * 2 * 8);
1471 memset(index, 0, sizeof(int) * 64);
1473 for (int i = 0; i < 64; i++)
1476 for (int i = 0; i < 8; i++)
1477 for (int j = 0; j < 16; j++)
1478 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1482 initialKFile = FILE_E;
1483 initialKRFile = FILE_H;
1484 initialQRFile = FILE_A;
1488 /// Position::reset_game_ply() simply sets gamePly to 0. It is used from the
1489 /// UCI interface code, whenever a non-reversible move is made in a
1490 /// 'position fen <fen> moves m1 m2 ...' command. This makes it possible
1491 /// for the program to handle games of arbitrary length, as long as the GUI
1492 /// handles draws by the 50 move rule correctly.
1494 void Position::reset_game_ply() {
1500 /// Position::put_piece() puts a piece on the given square of the board,
1501 /// updating the board array, bitboards, and piece counts.
1503 void Position::put_piece(Piece p, Square s) {
1505 Color c = color_of_piece(p);
1506 PieceType pt = type_of_piece(p);
1509 index[s] = pieceCount[c][pt];
1510 pieceList[c][pt][index[s]] = s;
1512 set_bit(&(byTypeBB[pt]), s);
1513 set_bit(&(byColorBB[c]), s);
1514 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1516 pieceCount[c][pt]++;
1520 /// Position::allow_oo() gives the given side the right to castle kingside.
1521 /// Used when setting castling rights during parsing of FEN strings.
1523 void Position::allow_oo(Color c) {
1525 st->castleRights |= (1 + int(c));
1529 /// Position::allow_ooo() gives the given side the right to castle queenside.
1530 /// Used when setting castling rights during parsing of FEN strings.
1532 void Position::allow_ooo(Color c) {
1534 st->castleRights |= (4 + 4*int(c));
1538 /// Position::compute_key() computes the hash key of the position. The hash
1539 /// key is usually updated incrementally as moves are made and unmade, the
1540 /// compute_key() function is only used when a new position is set up, and
1541 /// to verify the correctness of the hash key when running in debug mode.
1543 Key Position::compute_key() const {
1545 Key result = Key(0ULL);
1547 for (Square s = SQ_A1; s <= SQ_H8; s++)
1548 if (square_is_occupied(s))
1549 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1551 if (ep_square() != SQ_NONE)
1552 result ^= zobEp[ep_square()];
1554 result ^= zobCastle[st->castleRights];
1555 if (side_to_move() == BLACK)
1556 result ^= zobSideToMove;
1562 /// Position::compute_pawn_key() computes the hash key of the position. The
1563 /// hash key is usually updated incrementally as moves are made and unmade,
1564 /// the compute_pawn_key() function is only used when a new position is set
1565 /// up, and to verify the correctness of the pawn hash key when running in
1568 Key Position::compute_pawn_key() const {
1570 Key result = Key(0ULL);
1574 for (Color c = WHITE; c <= BLACK; c++)
1576 b = pieces(PAWN, c);
1579 s = pop_1st_bit(&b);
1580 result ^= zobrist[c][PAWN][s];
1587 /// Position::compute_material_key() computes the hash key of the position.
1588 /// The hash key is usually updated incrementally as moves are made and unmade,
1589 /// the compute_material_key() function is only used when a new position is set
1590 /// up, and to verify the correctness of the material hash key when running in
1593 Key Position::compute_material_key() const {
1595 Key result = Key(0ULL);
1596 for (Color c = WHITE; c <= BLACK; c++)
1597 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1599 int count = piece_count(c, pt);
1600 for (int i = 0; i <= count; i++)
1601 result ^= zobMaterial[c][pt][i];
1607 /// Position::compute_value() compute the incremental scores for the middle
1608 /// game and the endgame. These functions are used to initialize the incremental
1609 /// scores when a new position is set up, and to verify that the scores are correctly
1610 /// updated by do_move and undo_move when the program is running in debug mode.
1611 Score Position::compute_value() const {
1613 Score result = make_score(0, 0);
1617 for (Color c = WHITE; c <= BLACK; c++)
1618 for (PieceType pt = PAWN; pt <= KING; pt++)
1623 s = pop_1st_bit(&b);
1624 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1625 result += pst(c, pt, s);
1629 result += (side_to_move() == WHITE ? TempoValue / 2 : -TempoValue / 2);
1634 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1635 /// game material score for the given side. Material scores are updated
1636 /// incrementally during the search, this function is only used while
1637 /// initializing a new Position object.
1639 Value Position::compute_non_pawn_material(Color c) const {
1641 Value result = Value(0);
1643 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1645 Bitboard b = pieces(pt, c);
1648 assert(piece_on(first_1(b)) == piece_of_color_and_type(c, pt));
1650 result += piece_value_midgame(pt);
1657 /// Position::is_draw() tests whether the position is drawn by material,
1658 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1659 /// must be done by the search.
1661 bool Position::is_draw() const {
1663 // Draw by material?
1665 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1668 // Draw by the 50 moves rule?
1669 if (st->rule50 > 100 || (st->rule50 == 100 && !is_check()))
1672 // Draw by repetition?
1673 for (int i = 2; i < Min(Min(gamePly, st->rule50), st->pliesFromNull); i += 2)
1674 if (history[gamePly - i] == st->key)
1681 /// Position::is_mate() returns true or false depending on whether the
1682 /// side to move is checkmated.
1684 bool Position::is_mate() const {
1686 MoveStack moves[256];
1687 return is_check() && (generate_moves(*this, moves, false) == moves);
1691 /// Position::has_mate_threat() tests whether a given color has a mate in one
1692 /// from the current position.
1694 bool Position::has_mate_threat(Color c) {
1697 Color stm = side_to_move();
1702 // If the input color is not equal to the side to move, do a null move
1706 MoveStack mlist[120];
1707 bool result = false;
1708 Bitboard pinned = pinned_pieces(sideToMove);
1710 // Generate pseudo-legal non-capture and capture check moves
1711 MoveStack* last = generate_non_capture_checks(*this, mlist);
1712 last = generate_captures(*this, last);
1714 // Loop through the moves, and see if one of them is mate
1715 for (MoveStack* cur = mlist; cur != last; cur++)
1717 Move move = cur->move;
1718 if (!pl_move_is_legal(move, pinned))
1728 // Undo null move, if necessary
1736 /// Position::init_zobrist() is a static member function which initializes the
1737 /// various arrays used to compute hash keys.
1739 void Position::init_zobrist() {
1741 for (int i = 0; i < 2; i++)
1742 for (int j = 0; j < 8; j++)
1743 for (int k = 0; k < 64; k++)
1744 zobrist[i][j][k] = Key(genrand_int64());
1746 for (int i = 0; i < 64; i++)
1747 zobEp[i] = Key(genrand_int64());
1749 for (int i = 0; i < 16; i++)
1750 zobCastle[i] = genrand_int64();
1752 zobSideToMove = genrand_int64();
1754 for (int i = 0; i < 2; i++)
1755 for (int j = 0; j < 8; j++)
1756 for (int k = 0; k < 16; k++)
1757 zobMaterial[i][j][k] = (k > 0)? Key(genrand_int64()) : Key(0LL);
1759 for (int i = 0; i < 16; i++)
1760 zobMaterial[0][KING][i] = zobMaterial[1][KING][i] = Key(0ULL);
1762 zobExclusion = genrand_int64();
1766 /// Position::init_piece_square_tables() initializes the piece square tables.
1767 /// This is a two-step operation: First, the white halves of the tables are
1768 /// copied from the MgPST[][] and EgPST[][] arrays, with a small random number
1769 /// added to each entry if the "Randomness" UCI parameter is non-zero.
1770 /// Second, the black halves of the tables are initialized by mirroring
1771 /// and changing the sign of the corresponding white scores.
1773 void Position::init_piece_square_tables() {
1775 int r = get_option_value_int("Randomness"), i;
1776 for (Square s = SQ_A1; s <= SQ_H8; s++)
1777 for (Piece p = WP; p <= WK; p++)
1779 i = (r == 0)? 0 : (genrand_int32() % (r*2) - r);
1780 PieceSquareTable[p][s] = make_score(MgPST[p][s] + i, EgPST[p][s] + i);
1783 for (Square s = SQ_A1; s <= SQ_H8; s++)
1784 for (Piece p = BP; p <= BK; p++)
1785 PieceSquareTable[p][s] = -PieceSquareTable[p-8][flip_square(s)];
1789 /// Position::flipped_copy() makes a copy of the input position, but with
1790 /// the white and black sides reversed. This is only useful for debugging,
1791 /// especially for finding evaluation symmetry bugs.
1793 void Position::flipped_copy(const Position& pos) {
1795 assert(pos.is_ok());
1800 for (Square s = SQ_A1; s <= SQ_H8; s++)
1801 if (!pos.square_is_empty(s))
1802 put_piece(Piece(int(pos.piece_on(s)) ^ 8), flip_square(s));
1805 sideToMove = opposite_color(pos.side_to_move());
1808 if (pos.can_castle_kingside(WHITE)) allow_oo(BLACK);
1809 if (pos.can_castle_queenside(WHITE)) allow_ooo(BLACK);
1810 if (pos.can_castle_kingside(BLACK)) allow_oo(WHITE);
1811 if (pos.can_castle_queenside(BLACK)) allow_ooo(WHITE);
1813 initialKFile = pos.initialKFile;
1814 initialKRFile = pos.initialKRFile;
1815 initialQRFile = pos.initialQRFile;
1817 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
1818 castleRightsMask[sq] = ALL_CASTLES;
1820 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
1821 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
1822 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
1823 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
1824 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
1825 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
1827 // En passant square
1828 if (pos.st->epSquare != SQ_NONE)
1829 st->epSquare = flip_square(pos.st->epSquare);
1835 st->key = compute_key();
1836 st->pawnKey = compute_pawn_key();
1837 st->materialKey = compute_material_key();
1839 // Incremental scores
1840 st->value = compute_value();
1843 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
1844 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
1850 /// Position::is_ok() performs some consitency checks for the position object.
1851 /// This is meant to be helpful when debugging.
1853 bool Position::is_ok(int* failedStep) const {
1855 // What features of the position should be verified?
1856 static const bool debugBitboards = false;
1857 static const bool debugKingCount = false;
1858 static const bool debugKingCapture = false;
1859 static const bool debugCheckerCount = false;
1860 static const bool debugKey = false;
1861 static const bool debugMaterialKey = false;
1862 static const bool debugPawnKey = false;
1863 static const bool debugIncrementalEval = false;
1864 static const bool debugNonPawnMaterial = false;
1865 static const bool debugPieceCounts = false;
1866 static const bool debugPieceList = false;
1867 static const bool debugCastleSquares = false;
1869 if (failedStep) *failedStep = 1;
1872 if (!color_is_ok(side_to_move()))
1875 // Are the king squares in the position correct?
1876 if (failedStep) (*failedStep)++;
1877 if (piece_on(king_square(WHITE)) != WK)
1880 if (failedStep) (*failedStep)++;
1881 if (piece_on(king_square(BLACK)) != BK)
1885 if (failedStep) (*failedStep)++;
1886 if (!file_is_ok(initialKRFile))
1889 if (!file_is_ok(initialQRFile))
1892 // Do both sides have exactly one king?
1893 if (failedStep) (*failedStep)++;
1896 int kingCount[2] = {0, 0};
1897 for (Square s = SQ_A1; s <= SQ_H8; s++)
1898 if (type_of_piece_on(s) == KING)
1899 kingCount[color_of_piece_on(s)]++;
1901 if (kingCount[0] != 1 || kingCount[1] != 1)
1905 // Can the side to move capture the opponent's king?
1906 if (failedStep) (*failedStep)++;
1907 if (debugKingCapture)
1909 Color us = side_to_move();
1910 Color them = opposite_color(us);
1911 Square ksq = king_square(them);
1912 if (attackers_to(ksq) & pieces_of_color(us))
1916 // Is there more than 2 checkers?
1917 if (failedStep) (*failedStep)++;
1918 if (debugCheckerCount && count_1s(st->checkersBB) > 2)
1922 if (failedStep) (*failedStep)++;
1925 // The intersection of the white and black pieces must be empty
1926 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
1929 // The union of the white and black pieces must be equal to all
1931 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
1934 // Separate piece type bitboards must have empty intersections
1935 for (PieceType p1 = PAWN; p1 <= KING; p1++)
1936 for (PieceType p2 = PAWN; p2 <= KING; p2++)
1937 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1941 // En passant square OK?
1942 if (failedStep) (*failedStep)++;
1943 if (ep_square() != SQ_NONE)
1945 // The en passant square must be on rank 6, from the point of view of the
1947 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
1952 if (failedStep) (*failedStep)++;
1953 if (debugKey && st->key != compute_key())
1956 // Pawn hash key OK?
1957 if (failedStep) (*failedStep)++;
1958 if (debugPawnKey && st->pawnKey != compute_pawn_key())
1961 // Material hash key OK?
1962 if (failedStep) (*failedStep)++;
1963 if (debugMaterialKey && st->materialKey != compute_material_key())
1966 // Incremental eval OK?
1967 if (failedStep) (*failedStep)++;
1968 if (debugIncrementalEval && st->value != compute_value())
1971 // Non-pawn material OK?
1972 if (failedStep) (*failedStep)++;
1973 if (debugNonPawnMaterial)
1975 if (st->npMaterial[WHITE] != compute_non_pawn_material(WHITE))
1978 if (st->npMaterial[BLACK] != compute_non_pawn_material(BLACK))
1983 if (failedStep) (*failedStep)++;
1984 if (debugPieceCounts)
1985 for (Color c = WHITE; c <= BLACK; c++)
1986 for (PieceType pt = PAWN; pt <= KING; pt++)
1987 if (pieceCount[c][pt] != count_1s(pieces(pt, c)))
1990 if (failedStep) (*failedStep)++;
1993 for(Color c = WHITE; c <= BLACK; c++)
1994 for(PieceType pt = PAWN; pt <= KING; pt++)
1995 for(int i = 0; i < pieceCount[c][pt]; i++)
1997 if (piece_on(piece_list(c, pt, i)) != piece_of_color_and_type(c, pt))
2000 if (index[piece_list(c, pt, i)] != i)
2005 if (failedStep) (*failedStep)++;
2006 if (debugCastleSquares) {
2007 for (Color c = WHITE; c <= BLACK; c++) {
2008 if (can_castle_kingside(c) && piece_on(initial_kr_square(c)) != piece_of_color_and_type(c, ROOK))
2010 if (can_castle_queenside(c) && piece_on(initial_qr_square(c)) != piece_of_color_and_type(c, ROOK))
2013 if (castleRightsMask[initial_kr_square(WHITE)] != (ALL_CASTLES ^ WHITE_OO))
2015 if (castleRightsMask[initial_qr_square(WHITE)] != (ALL_CASTLES ^ WHITE_OOO))
2017 if (castleRightsMask[initial_kr_square(BLACK)] != (ALL_CASTLES ^ BLACK_OO))
2019 if (castleRightsMask[initial_qr_square(BLACK)] != (ALL_CASTLES ^ BLACK_OOO))
2023 if (failedStep) *failedStep = 0;