2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
38 #include "ucioption.h"
47 Key Position::zobrist[2][8][64];
48 Key Position::zobEp[64];
49 Key Position::zobCastle[16];
50 Key Position::zobMaterial[2][8][16];
51 Key Position::zobSideToMove;
52 Key Position::zobExclusion;
54 Score Position::PieceSquareTable[16][64];
56 static bool RequestPending = false;
61 CheckInfo::CheckInfo(const Position& pos) {
63 Color us = pos.side_to_move();
64 Color them = opposite_color(us);
66 ksq = pos.king_square(them);
67 dcCandidates = pos.discovered_check_candidates(us);
69 checkSq[PAWN] = pos.attacks_from<PAWN>(ksq, them);
70 checkSq[KNIGHT] = pos.attacks_from<KNIGHT>(ksq);
71 checkSq[BISHOP] = pos.attacks_from<BISHOP>(ksq);
72 checkSq[ROOK] = pos.attacks_from<ROOK>(ksq);
73 checkSq[QUEEN] = checkSq[BISHOP] | checkSq[ROOK];
74 checkSq[KING] = EmptyBoardBB;
78 /// Position c'tors. Here we always create a slower but safer copy of
79 /// the original position or the FEN string, we want the new born Position
80 /// object do not depend on any external data. Instead if we know what we
81 /// are doing and we need speed we can create a position with default
82 /// c'tor Position() and then use just fast_copy().
84 Position::Position() {}
86 Position::Position(const Position& pos) {
88 memcpy(this, &pos, sizeof(Position));
89 detach(); // Always detach() in copy c'tor to avoid surprises
92 Position::Position(const string& fen) {
98 /// Position::detach() copies the content of the current state and castling
99 /// masks inside the position itself. This is needed when the st pointee could
100 /// become stale, as example because the caller is about to going out of scope.
102 void Position::detach() {
106 st->previous = NULL; // as a safe guard
110 /// Position::from_fen() initializes the position object with the given FEN
111 /// string. This function is not very robust - make sure that input FENs are
112 /// correct (this is assumed to be the responsibility of the GUI).
114 void Position::from_fen(const string& fen) {
116 static const string pieceLetters = "KQRBNPkqrbnp";
117 static const Piece pieces[] = { WK, WQ, WR, WB, WN, WP, BK, BQ, BR, BB, BN, BP };
125 for ( ; fen[i] != ' '; i++)
129 // Skip the given number of files
130 file += (fen[i] - '1' + 1);
133 else if (fen[i] == '/')
139 size_t idx = pieceLetters.find(fen[i]);
140 if (idx == string::npos)
142 std::cout << "Error in FEN at character " << i << std::endl;
145 Square square = make_square(file, rank);
146 put_piece(pieces[idx], square);
152 if (fen[i] != 'w' && fen[i] != 'b')
154 std::cout << "Error in FEN at character " << i << std::endl;
157 sideToMove = (fen[i] == 'w' ? WHITE : BLACK);
163 std::cout << "Error in FEN at character " << i << std::endl;
168 while (strchr("KQkqabcdefghABCDEFGH-", fen[i])) {
174 else if (fen[i] == 'K') allow_oo(WHITE);
175 else if (fen[i] == 'Q') allow_ooo(WHITE);
176 else if (fen[i] == 'k') allow_oo(BLACK);
177 else if (fen[i] == 'q') allow_ooo(BLACK);
178 else if (fen[i] >= 'A' && fen[i] <= 'H') {
179 File rookFile, kingFile = FILE_NONE;
180 for (Square square = SQ_B1; square <= SQ_G1; square++)
181 if (piece_on(square) == WK)
182 kingFile = square_file(square);
183 if (kingFile == FILE_NONE) {
184 std::cout << "Error in FEN at character " << i << std::endl;
187 initialKFile = kingFile;
188 rookFile = File(fen[i] - 'A') + FILE_A;
189 if (rookFile < initialKFile) {
191 initialQRFile = rookFile;
195 initialKRFile = rookFile;
198 else if (fen[i] >= 'a' && fen[i] <= 'h') {
199 File rookFile, kingFile = FILE_NONE;
200 for (Square square = SQ_B8; square <= SQ_G8; square++)
201 if (piece_on(square) == BK)
202 kingFile = square_file(square);
203 if (kingFile == FILE_NONE) {
204 std::cout << "Error in FEN at character " << i << std::endl;
207 initialKFile = kingFile;
208 rookFile = File(fen[i] - 'a') + FILE_A;
209 if (rookFile < initialKFile) {
211 initialQRFile = rookFile;
215 initialKRFile = rookFile;
219 std::cout << "Error in FEN at character " << i << std::endl;
226 while (fen[i] == ' ')
229 // En passant square -- ignore if no capture is possible
230 if ( i <= fen.length() - 2
231 && (fen[i] >= 'a' && fen[i] <= 'h')
232 && (fen[i+1] == '3' || fen[i+1] == '6'))
234 Square fenEpSquare = square_from_string(fen.substr(i, 2));
235 Color them = opposite_color(sideToMove);
236 if (attacks_from<PAWN>(fenEpSquare, them) & this->pieces(PAWN, sideToMove))
237 st->epSquare = square_from_string(fen.substr(i, 2));
240 // Various initialisation
241 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
242 castleRightsMask[sq] = ALL_CASTLES;
244 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO|WHITE_OOO);
245 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO|BLACK_OOO);
246 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
247 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
248 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
249 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
253 st->key = compute_key();
254 st->pawnKey = compute_pawn_key();
255 st->materialKey = compute_material_key();
256 st->value = compute_value();
257 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
258 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
262 /// Position::to_fen() converts the position object to a FEN string. This is
263 /// probably only useful for debugging.
265 const string Position::to_fen() const {
267 static const string pieceLetters = " PNBRQK pnbrqk";
271 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
274 for (File file = FILE_A; file <= FILE_H; file++)
276 Square sq = make_square(file, rank);
277 if (!square_is_occupied(sq))
283 fen += (char)skip + '0';
286 fen += pieceLetters[piece_on(sq)];
289 fen += (char)skip + '0';
291 fen += (rank > RANK_1 ? '/' : ' ');
293 fen += (sideToMove == WHITE ? "w " : "b ");
294 if (st->castleRights != NO_CASTLES)
296 if (initialKFile == FILE_E && initialQRFile == FILE_A && initialKRFile == FILE_H)
298 if (can_castle_kingside(WHITE)) fen += 'K';
299 if (can_castle_queenside(WHITE)) fen += 'Q';
300 if (can_castle_kingside(BLACK)) fen += 'k';
301 if (can_castle_queenside(BLACK)) fen += 'q';
305 if (can_castle_kingside(WHITE))
306 fen += char(toupper(file_to_char(initialKRFile)));
307 if (can_castle_queenside(WHITE))
308 fen += char(toupper(file_to_char(initialQRFile)));
309 if (can_castle_kingside(BLACK))
310 fen += file_to_char(initialKRFile);
311 if (can_castle_queenside(BLACK))
312 fen += file_to_char(initialQRFile);
318 if (ep_square() != SQ_NONE)
319 fen += square_to_string(ep_square());
327 /// Position::print() prints an ASCII representation of the position to
328 /// the standard output. If a move is given then also the san is print.
330 void Position::print(Move m) const {
332 static const string pieceLetters = " PNBRQK PNBRQK .";
334 // Check for reentrancy, as example when called from inside
335 // MovePicker that is used also here in move_to_san()
339 RequestPending = true;
341 std::cout << std::endl;
345 string col = (color_of_piece_on(move_from(m)) == BLACK ? ".." : "");
346 std::cout << "Move is: " << col << move_to_san(p, m) << std::endl;
348 for (Rank rank = RANK_8; rank >= RANK_1; rank--)
350 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl;
351 for (File file = FILE_A; file <= FILE_H; file++)
353 Square sq = make_square(file, rank);
354 Piece piece = piece_on(sq);
355 if (piece == EMPTY && square_color(sq) == WHITE)
358 char col = (color_of_piece_on(sq) == BLACK ? '=' : ' ');
359 std::cout << '|' << col << pieceLetters[piece] << col;
361 std::cout << '|' << std::endl;
363 std::cout << "+---+---+---+---+---+---+---+---+" << std::endl
364 << "Fen is: " << to_fen() << std::endl
365 << "Key is: " << st->key << std::endl;
367 RequestPending = false;
371 /// Position:hidden_checkers<>() returns a bitboard of all pinned (against the
372 /// king) pieces for the given color and for the given pinner type. Or, when
373 /// template parameter FindPinned is false, the pieces of the given color
374 /// candidate for a discovery check against the enemy king.
375 /// Bitboard checkersBB must be already updated when looking for pinners.
377 template<bool FindPinned>
378 Bitboard Position::hidden_checkers(Color c) const {
380 Bitboard result = EmptyBoardBB;
381 Bitboard pinners = pieces_of_color(FindPinned ? opposite_color(c) : c);
383 // Pinned pieces protect our king, dicovery checks attack
385 Square ksq = king_square(FindPinned ? c : opposite_color(c));
387 // Pinners are sliders, not checkers, that give check when candidate pinned is removed
388 pinners &= (pieces(ROOK, QUEEN) & RookPseudoAttacks[ksq]) | (pieces(BISHOP, QUEEN) & BishopPseudoAttacks[ksq]);
390 if (FindPinned && pinners)
391 pinners &= ~st->checkersBB;
395 Square s = pop_1st_bit(&pinners);
396 Bitboard b = squares_between(s, ksq) & occupied_squares();
400 if ( !(b & (b - 1)) // Only one bit set?
401 && (b & pieces_of_color(c))) // Is an our piece?
408 /// Position:pinned_pieces() returns a bitboard of all pinned (against the
409 /// king) pieces for the given color. Note that checkersBB bitboard must
410 /// be already updated.
412 Bitboard Position::pinned_pieces(Color c) const {
414 return hidden_checkers<true>(c);
418 /// Position:discovered_check_candidates() returns a bitboard containing all
419 /// pieces for the given side which are candidates for giving a discovered
420 /// check. Contrary to pinned_pieces() here there is no need of checkersBB
421 /// to be already updated.
423 Bitboard Position::discovered_check_candidates(Color c) const {
425 return hidden_checkers<false>(c);
428 /// Position::attackers_to() computes a bitboard containing all pieces which
429 /// attacks a given square.
431 Bitboard Position::attackers_to(Square s) const {
433 return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
434 | (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
435 | (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
436 | (attacks_from<ROOK>(s) & pieces(ROOK, QUEEN))
437 | (attacks_from<BISHOP>(s) & pieces(BISHOP, QUEEN))
438 | (attacks_from<KING>(s) & pieces(KING));
441 /// Position::attacks_from() computes a bitboard of all attacks
442 /// of a given piece put in a given square.
444 Bitboard Position::attacks_from(Piece p, Square s) const {
446 assert(square_is_ok(s));
450 case WP: return attacks_from<PAWN>(s, WHITE);
451 case BP: return attacks_from<PAWN>(s, BLACK);
452 case WN: case BN: return attacks_from<KNIGHT>(s);
453 case WB: case BB: return attacks_from<BISHOP>(s);
454 case WR: case BR: return attacks_from<ROOK>(s);
455 case WQ: case BQ: return attacks_from<QUEEN>(s);
456 case WK: case BK: return attacks_from<KING>(s);
463 /// Position::move_attacks_square() tests whether a move from the current
464 /// position attacks a given square.
466 bool Position::move_attacks_square(Move m, Square s) const {
468 assert(move_is_ok(m));
469 assert(square_is_ok(s));
471 Square f = move_from(m), t = move_to(m);
473 assert(square_is_occupied(f));
475 if (bit_is_set(attacks_from(piece_on(f), t), s))
478 // Move the piece and scan for X-ray attacks behind it
479 Bitboard occ = occupied_squares();
480 Color us = color_of_piece_on(f);
483 Bitboard xray = ( (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
484 |(bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN))) & pieces_of_color(us);
486 // If we have attacks we need to verify that are caused by our move
487 // and are not already existent ones.
488 return xray && (xray ^ (xray & attacks_from<QUEEN>(s)));
492 /// Position::find_checkers() computes the checkersBB bitboard, which
493 /// contains a nonzero bit for each checking piece (0, 1 or 2). It
494 /// currently works by calling Position::attackers_to, which is probably
495 /// inefficient. Consider rewriting this function to use the last move
496 /// played, like in non-bitboard versions of Glaurung.
498 void Position::find_checkers() {
500 Color us = side_to_move();
501 st->checkersBB = attackers_to(king_square(us)) & pieces_of_color(opposite_color(us));
505 /// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
507 bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
510 assert(move_is_ok(m));
511 assert(pinned == pinned_pieces(side_to_move()));
513 // Castling moves are checked for legality during move generation.
514 if (move_is_castle(m))
517 Color us = side_to_move();
518 Square from = move_from(m);
520 assert(color_of_piece_on(from) == us);
521 assert(piece_on(king_square(us)) == piece_of_color_and_type(us, KING));
523 // En passant captures are a tricky special case. Because they are
524 // rather uncommon, we do it simply by testing whether the king is attacked
525 // after the move is made
528 Color them = opposite_color(us);
529 Square to = move_to(m);
530 Square capsq = make_square(square_file(to), square_rank(from));
531 Bitboard b = occupied_squares();
532 Square ksq = king_square(us);
534 assert(to == ep_square());
535 assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
536 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
537 assert(piece_on(to) == EMPTY);
540 clear_bit(&b, capsq);
543 return !(rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, them))
544 && !(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, them));
547 // If the moving piece is a king, check whether the destination
548 // square is attacked by the opponent.
549 if (type_of_piece_on(from) == KING)
550 return !(attackers_to(move_to(m)) & pieces_of_color(opposite_color(us)));
552 // A non-king move is legal if and only if it is not pinned or it
553 // is moving along the ray towards or away from the king.
555 || !bit_is_set(pinned, from)
556 || (direction_between_squares(from, king_square(us)) == direction_between_squares(move_to(m), king_square(us))));
560 /// Position::pl_move_is_evasion() tests whether a pseudo-legal move is a legal evasion
562 bool Position::pl_move_is_evasion(Move m, Bitboard pinned) const
566 Color us = side_to_move();
567 Square from = move_from(m);
568 Square to = move_to(m);
570 // King moves and en-passant captures are verified in pl_move_is_legal()
571 if (type_of_piece_on(from) == KING || move_is_ep(m))
572 return pl_move_is_legal(m, pinned);
574 Bitboard target = checkers();
575 Square checksq = pop_1st_bit(&target);
577 if (target) // double check ?
580 // Our move must be a blocking evasion or a capture of the checking piece
581 target = squares_between(checksq, king_square(us)) | checkers();
582 return bit_is_set(target, to) && pl_move_is_legal(m, pinned);
586 /// Position::move_is_check() tests whether a pseudo-legal move is a check
588 bool Position::move_is_check(Move m) const {
590 return move_is_check(m, CheckInfo(*this));
593 bool Position::move_is_check(Move m, const CheckInfo& ci) const {
596 assert(move_is_ok(m));
597 assert(ci.dcCandidates == discovered_check_candidates(side_to_move()));
598 assert(color_of_piece_on(move_from(m)) == side_to_move());
599 assert(piece_on(ci.ksq) == piece_of_color_and_type(opposite_color(side_to_move()), KING));
601 Square from = move_from(m);
602 Square to = move_to(m);
603 PieceType pt = type_of_piece_on(from);
606 if (bit_is_set(ci.checkSq[pt], to))
610 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
612 // For pawn and king moves we need to verify also direction
613 if ( (pt != PAWN && pt != KING)
614 ||(direction_between_squares(from, ci.ksq) != direction_between_squares(to, ci.ksq)))
618 // Can we skip the ugly special cases ?
619 if (!move_is_special(m))
622 Color us = side_to_move();
623 Bitboard b = occupied_squares();
625 // Promotion with check ?
626 if (move_is_promotion(m))
630 switch (move_promotion_piece(m))
633 return bit_is_set(attacks_from<KNIGHT>(to), ci.ksq);
635 return bit_is_set(bishop_attacks_bb(to, b), ci.ksq);
637 return bit_is_set(rook_attacks_bb(to, b), ci.ksq);
639 return bit_is_set(queen_attacks_bb(to, b), ci.ksq);
645 // En passant capture with check? We have already handled the case
646 // of direct checks and ordinary discovered check, the only case we
647 // need to handle is the unusual case of a discovered check through the
651 Square capsq = make_square(square_file(to), square_rank(from));
653 clear_bit(&b, capsq);
655 return (rook_attacks_bb(ci.ksq, b) & pieces(ROOK, QUEEN, us))
656 ||(bishop_attacks_bb(ci.ksq, b) & pieces(BISHOP, QUEEN, us));
659 // Castling with check ?
660 if (move_is_castle(m))
662 Square kfrom, kto, rfrom, rto;
668 kto = relative_square(us, SQ_G1);
669 rto = relative_square(us, SQ_F1);
671 kto = relative_square(us, SQ_C1);
672 rto = relative_square(us, SQ_D1);
674 clear_bit(&b, kfrom);
675 clear_bit(&b, rfrom);
678 return bit_is_set(rook_attacks_bb(rto, b), ci.ksq);
685 /// Position::do_move() makes a move, and saves all information necessary
686 /// to a StateInfo object. The move is assumed to be legal.
687 /// Pseudo-legal moves should be filtered out before this function is called.
689 void Position::do_move(Move m, StateInfo& newSt) {
692 do_move(m, newSt, ci, move_is_check(m, ci));
695 void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveIsCheck) {
698 assert(move_is_ok(m));
700 Bitboard key = st->key;
702 // Copy some fields of old state to our new StateInfo object except the
703 // ones which are recalculated from scratch anyway, then switch our state
704 // pointer to point to the new, ready to be updated, state.
705 struct ReducedStateInfo {
706 Key pawnKey, materialKey;
707 int castleRights, rule50, pliesFromNull;
713 memcpy(&newSt, st, sizeof(ReducedStateInfo));
717 // Save the current key to the history[] array, in order to be able to
718 // detect repetition draws.
719 history[gamePly] = key;
722 // Update side to move
723 key ^= zobSideToMove;
725 // Increment the 50 moves rule draw counter. Resetting it to zero in the
726 // case of non-reversible moves is taken care of later.
730 if (move_is_castle(m))
737 Color us = side_to_move();
738 Color them = opposite_color(us);
739 Square from = move_from(m);
740 Square to = move_to(m);
741 bool ep = move_is_ep(m);
742 bool pm = move_is_promotion(m);
744 Piece piece = piece_on(from);
745 PieceType pt = type_of_piece(piece);
746 PieceType capture = ep ? PAWN : type_of_piece_on(to);
748 assert(color_of_piece_on(from) == us);
749 assert(color_of_piece_on(to) == them || square_is_empty(to));
750 assert(!(ep || pm) || piece == piece_of_color_and_type(us, PAWN));
751 assert(!pm || relative_rank(us, to) == RANK_8);
754 do_capture_move(key, capture, them, to, ep);
757 key ^= zobrist[us][pt][from] ^ zobrist[us][pt][to];
759 // Reset en passant square
760 if (st->epSquare != SQ_NONE)
762 key ^= zobEp[st->epSquare];
763 st->epSquare = SQ_NONE;
766 // Update castle rights, try to shortcut a common case
767 int cm = castleRightsMask[from] & castleRightsMask[to];
768 if (cm != ALL_CASTLES && ((cm & st->castleRights) != st->castleRights))
770 key ^= zobCastle[st->castleRights];
771 st->castleRights &= castleRightsMask[from];
772 st->castleRights &= castleRightsMask[to];
773 key ^= zobCastle[st->castleRights];
776 // Prefetch TT access as soon as we know key is updated
780 Bitboard move_bb = make_move_bb(from, to);
781 do_move_bb(&(byColorBB[us]), move_bb);
782 do_move_bb(&(byTypeBB[pt]), move_bb);
783 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
785 board[to] = board[from];
788 // Update piece lists, note that index[from] is not updated and
789 // becomes stale. This works as long as index[] is accessed just
790 // by known occupied squares.
791 index[to] = index[from];
792 pieceList[us][pt][index[to]] = to;
794 // If the moving piece was a pawn do some special extra work
797 // Reset rule 50 draw counter
800 // Update pawn hash key
801 st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
803 // Set en passant square, only if moved pawn can be captured
804 if ((to ^ from) == 16)
806 if (attacks_from<PAWN>(from + (us == WHITE ? DELTA_N : DELTA_S), us) & pieces(PAWN, them))
808 st->epSquare = Square((int(from) + int(to)) / 2);
809 key ^= zobEp[st->epSquare];
814 // Update incremental scores
815 st->value += pst_delta(piece, from, to);
818 st->capture = capture;
820 if (pm) // promotion ?
822 PieceType promotion = move_promotion_piece(m);
824 assert(promotion >= KNIGHT && promotion <= QUEEN);
826 // Insert promoted piece instead of pawn
827 clear_bit(&(byTypeBB[PAWN]), to);
828 set_bit(&(byTypeBB[promotion]), to);
829 board[to] = piece_of_color_and_type(us, promotion);
831 // Update material key
832 st->materialKey ^= zobMaterial[us][PAWN][pieceCount[us][PAWN]];
833 st->materialKey ^= zobMaterial[us][promotion][pieceCount[us][promotion]+1];
835 // Update piece counts
836 pieceCount[us][PAWN]--;
837 pieceCount[us][promotion]++;
839 // Update piece lists, move the last pawn at index[to] position
840 // and shrink the list. Add a new promotion piece to the list.
841 Square lastPawnSquare = pieceList[us][PAWN][pieceCount[us][PAWN]];
842 index[lastPawnSquare] = index[to];
843 pieceList[us][PAWN][index[lastPawnSquare]] = lastPawnSquare;
844 pieceList[us][PAWN][pieceCount[us][PAWN]] = SQ_NONE;
845 index[to] = pieceCount[us][promotion] - 1;
846 pieceList[us][promotion][index[to]] = to;
848 // Partially revert hash keys update
849 key ^= zobrist[us][PAWN][to] ^ zobrist[us][promotion][to];
850 st->pawnKey ^= zobrist[us][PAWN][to];
852 // Partially revert and update incremental scores
853 st->value -= pst(us, PAWN, to);
854 st->value += pst(us, promotion, to);
857 st->npMaterial[us] += piece_value_midgame(promotion);
860 // Update the key with the final value
863 // Update checkers bitboard, piece must be already moved
864 st->checkersBB = EmptyBoardBB;
869 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
873 if (bit_is_set(ci.checkSq[pt], to))
874 st->checkersBB = SetMaskBB[to];
877 if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
880 st->checkersBB |= (attacks_from<ROOK>(ci.ksq) & pieces(ROOK, QUEEN, us));
883 st->checkersBB |= (attacks_from<BISHOP>(ci.ksq) & pieces(BISHOP, QUEEN, us));
889 sideToMove = opposite_color(sideToMove);
890 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
896 /// Position::do_capture_move() is a private method used to update captured
897 /// piece info. It is called from the main Position::do_move function.
899 void Position::do_capture_move(Bitboard& key, PieceType capture, Color them, Square to, bool ep) {
901 assert(capture != KING);
905 if (ep) // en passant ?
907 capsq = (them == BLACK)? (to - DELTA_N) : (to - DELTA_S);
909 assert(to == st->epSquare);
910 assert(relative_rank(opposite_color(them), to) == RANK_6);
911 assert(piece_on(to) == EMPTY);
912 assert(piece_on(capsq) == piece_of_color_and_type(them, PAWN));
914 board[capsq] = EMPTY;
917 // Remove captured piece
918 clear_bit(&(byColorBB[them]), capsq);
919 clear_bit(&(byTypeBB[capture]), capsq);
920 clear_bit(&(byTypeBB[0]), capsq);
923 key ^= zobrist[them][capture][capsq];
925 // Update incremental scores
926 st->value -= pst(them, capture, capsq);
928 // If the captured piece was a pawn, update pawn hash key,
929 // otherwise update non-pawn material.
931 st->pawnKey ^= zobrist[them][PAWN][capsq];
933 st->npMaterial[them] -= piece_value_midgame(capture);
935 // Update material hash key
936 st->materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];
938 // Update piece count
939 pieceCount[them][capture]--;
941 // Update piece list, move the last piece at index[capsq] position
943 // WARNING: This is a not perfectly revresible operation. When we
944 // will reinsert the captured piece in undo_move() we will put it
945 // at the end of the list and not in its original place, it means
946 // index[] and pieceList[] are not guaranteed to be invariant to a
947 // do_move() + undo_move() sequence.
948 Square lastPieceSquare = pieceList[them][capture][pieceCount[them][capture]];
949 index[lastPieceSquare] = index[capsq];
950 pieceList[them][capture][index[lastPieceSquare]] = lastPieceSquare;
951 pieceList[them][capture][pieceCount[them][capture]] = SQ_NONE;
953 // Reset rule 50 counter
958 /// Position::do_castle_move() is a private method used to make a castling
959 /// move. It is called from the main Position::do_move function. Note that
960 /// castling moves are encoded as "king captures friendly rook" moves, for
961 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
963 void Position::do_castle_move(Move m) {
965 assert(move_is_ok(m));
966 assert(move_is_castle(m));
968 Color us = side_to_move();
969 Color them = opposite_color(us);
971 // Reset capture field
972 st->capture = NO_PIECE_TYPE;
974 // Find source squares for king and rook
975 Square kfrom = move_from(m);
976 Square rfrom = move_to(m); // HACK: See comment at beginning of function
979 assert(piece_on(kfrom) == piece_of_color_and_type(us, KING));
980 assert(piece_on(rfrom) == piece_of_color_and_type(us, ROOK));
982 // Find destination squares for king and rook
983 if (rfrom > kfrom) // O-O
985 kto = relative_square(us, SQ_G1);
986 rto = relative_square(us, SQ_F1);
988 kto = relative_square(us, SQ_C1);
989 rto = relative_square(us, SQ_D1);
992 // Remove pieces from source squares:
993 clear_bit(&(byColorBB[us]), kfrom);
994 clear_bit(&(byTypeBB[KING]), kfrom);
995 clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
996 clear_bit(&(byColorBB[us]), rfrom);
997 clear_bit(&(byTypeBB[ROOK]), rfrom);
998 clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1000 // Put pieces on destination squares:
1001 set_bit(&(byColorBB[us]), kto);
1002 set_bit(&(byTypeBB[KING]), kto);
1003 set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1004 set_bit(&(byColorBB[us]), rto);
1005 set_bit(&(byTypeBB[ROOK]), rto);
1006 set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1008 // Update board array
1009 Piece king = piece_of_color_and_type(us, KING);
1010 Piece rook = piece_of_color_and_type(us, ROOK);
1011 board[kfrom] = board[rfrom] = EMPTY;
1015 // Update piece lists
1016 pieceList[us][KING][index[kfrom]] = kto;
1017 pieceList[us][ROOK][index[rfrom]] = rto;
1018 int tmp = index[rfrom]; // In Chess960 could be rto == kfrom
1019 index[kto] = index[kfrom];
1022 // Update incremental scores
1023 st->value += pst_delta(king, kfrom, kto);
1024 st->value += pst_delta(rook, rfrom, rto);
1027 st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
1028 st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
1030 // Clear en passant square
1031 if (st->epSquare != SQ_NONE)
1033 st->key ^= zobEp[st->epSquare];
1034 st->epSquare = SQ_NONE;
1037 // Update castling rights
1038 st->key ^= zobCastle[st->castleRights];
1039 st->castleRights &= castleRightsMask[kfrom];
1040 st->key ^= zobCastle[st->castleRights];
1042 // Reset rule 50 counter
1045 // Update checkers BB
1046 st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
1049 sideToMove = opposite_color(sideToMove);
1050 st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
1056 /// Position::undo_move() unmakes a move. When it returns, the position should
1057 /// be restored to exactly the same state as before the move was made.
1059 void Position::undo_move(Move m) {
1062 assert(move_is_ok(m));
1065 sideToMove = opposite_color(sideToMove);
1067 if (move_is_castle(m))
1069 undo_castle_move(m);
1073 Color us = side_to_move();
1074 Color them = opposite_color(us);
1075 Square from = move_from(m);
1076 Square to = move_to(m);
1077 bool ep = move_is_ep(m);
1078 bool pm = move_is_promotion(m);
1080 PieceType pt = type_of_piece_on(to);
1082 assert(square_is_empty(from));
1083 assert(color_of_piece_on(to) == us);
1084 assert(!pm || relative_rank(us, to) == RANK_8);
1085 assert(!ep || to == st->previous->epSquare);
1086 assert(!ep || relative_rank(us, to) == RANK_6);
1087 assert(!ep || piece_on(to) == piece_of_color_and_type(us, PAWN));
1089 if (pm) // promotion ?
1091 PieceType promotion = move_promotion_piece(m);
1094 assert(promotion >= KNIGHT && promotion <= QUEEN);
1095 assert(piece_on(to) == piece_of_color_and_type(us, promotion));
1097 // Replace promoted piece with a pawn
1098 clear_bit(&(byTypeBB[promotion]), to);
1099 set_bit(&(byTypeBB[PAWN]), to);
1101 // Update piece counts
1102 pieceCount[us][promotion]--;
1103 pieceCount[us][PAWN]++;
1105 // Update piece list replacing promotion piece with a pawn
1106 Square lastPromotionSquare = pieceList[us][promotion][pieceCount[us][promotion]];
1107 index[lastPromotionSquare] = index[to];
1108 pieceList[us][promotion][index[lastPromotionSquare]] = lastPromotionSquare;
1109 pieceList[us][promotion][pieceCount[us][promotion]] = SQ_NONE;
1110 index[to] = pieceCount[us][PAWN] - 1;
1111 pieceList[us][PAWN][index[to]] = to;
1115 // Put the piece back at the source square
1116 Bitboard move_bb = make_move_bb(to, from);
1117 do_move_bb(&(byColorBB[us]), move_bb);
1118 do_move_bb(&(byTypeBB[pt]), move_bb);
1119 do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
1121 board[from] = piece_of_color_and_type(us, pt);
1124 // Update piece list
1125 index[from] = index[to];
1126 pieceList[us][pt][index[from]] = from;
1133 capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1135 assert(st->capture != KING);
1136 assert(!ep || square_is_empty(capsq));
1138 // Restore the captured piece
1139 set_bit(&(byColorBB[them]), capsq);
1140 set_bit(&(byTypeBB[st->capture]), capsq);
1141 set_bit(&(byTypeBB[0]), capsq);
1143 board[capsq] = piece_of_color_and_type(them, st->capture);
1145 // Update piece count
1146 pieceCount[them][st->capture]++;
1148 // Update piece list, add a new captured piece in capsq square
1149 index[capsq] = pieceCount[them][st->capture] - 1;
1150 pieceList[them][st->capture][index[capsq]] = capsq;
1153 // Finally point our state pointer back to the previous state
1160 /// Position::undo_castle_move() is a private method used to unmake a castling
1161 /// move. It is called from the main Position::undo_move function. Note that
1162 /// castling moves are encoded as "king captures friendly rook" moves, for
1163 /// instance white short castling in a non-Chess960 game is encoded as e1h1.
1165 void Position::undo_castle_move(Move m) {
1167 assert(move_is_ok(m));
1168 assert(move_is_castle(m));
1170 // When we have arrived here, some work has already been done by
1171 // Position::undo_move. In particular, the side to move has been switched,
1172 // so the code below is correct.
1173 Color us = side_to_move();
1175 // Find source squares for king and rook
1176 Square kfrom = move_from(m);
1177 Square rfrom = move_to(m); // HACK: See comment at beginning of function
1180 // Find destination squares for king and rook
1181 if (rfrom > kfrom) // O-O
1183 kto = relative_square(us, SQ_G1);
1184 rto = relative_square(us, SQ_F1);
1186 kto = relative_square(us, SQ_C1);
1187 rto = relative_square(us, SQ_D1);
1190 assert(piece_on(kto) == piece_of_color_and_type(us, KING));
1191 assert(piece_on(rto) == piece_of_color_and_type(us, ROOK));
1193 // Remove pieces from destination squares:
1194 clear_bit(&(byColorBB[us]), kto);
1195 clear_bit(&(byTypeBB[KING]), kto);
1196 clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
1197 clear_bit(&(byColorBB[us]), rto);
1198 clear_bit(&(byTypeBB[ROOK]), rto);
1199 clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
1201 // Put pieces on source squares:
1202 set_bit(&(byColorBB[us]), kfrom);
1203 set_bit(&(byTypeBB[KING]), kfrom);
1204 set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
1205 set_bit(&(byColorBB[us]), rfrom);
1206 set_bit(&(byTypeBB[ROOK]), rfrom);
1207 set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
1210 board[rto] = board[kto] = EMPTY;
1211 board[rfrom] = piece_of_color_and_type(us, ROOK);
1212 board[kfrom] = piece_of_color_and_type(us, KING);
1214 // Update piece lists
1215 pieceList[us][KING][index[kto]] = kfrom;
1216 pieceList[us][ROOK][index[rto]] = rfrom;
1217 int tmp = index[rto]; // In Chess960 could be rto == kfrom
1218 index[kfrom] = index[kto];
1221 // Finally point our state pointer back to the previous state
1228 /// Position::do_null_move makes() a "null move": It switches the side to move
1229 /// and updates the hash key without executing any move on the board.
1231 void Position::do_null_move(StateInfo& backupSt) {
1234 assert(!is_check());
1236 // Back up the information necessary to undo the null move to the supplied
1237 // StateInfo object.
1238 // Note that differently from normal case here backupSt is actually used as
1239 // a backup storage not as a new state to be used.
1240 backupSt.key = st->key;
1241 backupSt.epSquare = st->epSquare;
1242 backupSt.value = st->value;
1243 backupSt.previous = st->previous;
1244 backupSt.pliesFromNull = st->pliesFromNull;
1245 st->previous = &backupSt;
1247 // Save the current key to the history[] array, in order to be able to
1248 // detect repetition draws.
1249 history[gamePly] = st->key;
1251 // Update the necessary information
1252 if (st->epSquare != SQ_NONE)
1253 st->key ^= zobEp[st->epSquare];
1255 st->key ^= zobSideToMove;
1256 TT.prefetch(st->key);
1258 sideToMove = opposite_color(sideToMove);
1259 st->epSquare = SQ_NONE;
1261 st->pliesFromNull = 0;
1262 st->value += (sideToMove == WHITE) ? TempoValue : -TempoValue;
1267 /// Position::undo_null_move() unmakes a "null move".
1269 void Position::undo_null_move() {
1272 assert(!is_check());
1274 // Restore information from the our backup StateInfo object
1275 StateInfo* backupSt = st->previous;
1276 st->key = backupSt->key;
1277 st->epSquare = backupSt->epSquare;
1278 st->value = backupSt->value;
1279 st->previous = backupSt->previous;
1280 st->pliesFromNull = backupSt->pliesFromNull;
1282 // Update the necessary information
1283 sideToMove = opposite_color(sideToMove);
1289 /// Position::see() is a static exchange evaluator: It tries to estimate the
1290 /// material gain or loss resulting from a move. There are three versions of
1291 /// this function: One which takes a destination square as input, one takes a
1292 /// move, and one which takes a 'from' and a 'to' square. The function does
1293 /// not yet understand promotions captures.
1295 int Position::see(Square to) const {
1297 assert(square_is_ok(to));
1298 return see(SQ_NONE, to);
1301 int Position::see(Move m) const {
1303 assert(move_is_ok(m));
1304 return see(move_from(m), move_to(m));
1307 int Position::see_sign(Move m) const {
1309 assert(move_is_ok(m));
1311 Square from = move_from(m);
1312 Square to = move_to(m);
1314 // Early return if SEE cannot be negative because capturing piece value
1315 // is not bigger then captured one.
1316 if ( midgame_value_of_piece_on(from) <= midgame_value_of_piece_on(to)
1317 && type_of_piece_on(from) != KING)
1320 return see(from, to);
1323 int Position::see(Square from, Square to) const {
1326 static const int seeValues[18] = {
1327 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1328 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1329 0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
1330 RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
1334 Bitboard attackers, stmAttackers, b;
1336 assert(square_is_ok(from) || from == SQ_NONE);
1337 assert(square_is_ok(to));
1339 // Initialize colors
1340 Color us = (from != SQ_NONE ? color_of_piece_on(from) : opposite_color(color_of_piece_on(to)));
1341 Color them = opposite_color(us);
1343 // Initialize pieces
1344 Piece piece = piece_on(from);
1345 Piece capture = piece_on(to);
1346 Bitboard occ = occupied_squares();
1348 // King cannot be recaptured
1349 if (type_of_piece(piece) == KING)
1350 return seeValues[capture];
1352 // Handle en passant moves
1353 if (st->epSquare == to && type_of_piece_on(from) == PAWN)
1355 assert(capture == EMPTY);
1357 Square capQq = (side_to_move() == WHITE)? (to - DELTA_N) : (to - DELTA_S);
1358 capture = piece_on(capQq);
1359 assert(type_of_piece_on(capQq) == PAWN);
1361 // Remove the captured pawn
1362 clear_bit(&occ, capQq);
1367 // Find all attackers to the destination square, with the moving piece
1368 // removed, but possibly an X-ray attacker added behind it.
1369 clear_bit(&occ, from);
1370 attackers = (rook_attacks_bb(to, occ) & pieces(ROOK, QUEEN))
1371 | (bishop_attacks_bb(to, occ) & pieces(BISHOP, QUEEN))
1372 | (attacks_from<KNIGHT>(to) & pieces(KNIGHT))
1373 | (attacks_from<KING>(to) & pieces(KING))
1374 | (attacks_from<PAWN>(to, WHITE) & pieces(PAWN, BLACK))
1375 | (attacks_from<PAWN>(to, BLACK) & pieces(PAWN, WHITE));
1377 if (from != SQ_NONE)
1380 // If we don't have any attacker we are finished
1381 if ((attackers & pieces_of_color(us)) == EmptyBoardBB)
1384 // Locate the least valuable attacker to the destination square
1385 // and use it to initialize from square.
1386 stmAttackers = attackers & pieces_of_color(us);
1388 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1391 from = first_1(stmAttackers & pieces(pt));
1392 piece = piece_on(from);
1395 // If the opponent has no attackers we are finished
1396 stmAttackers = attackers & pieces_of_color(them);
1398 return seeValues[capture];
1400 attackers &= occ; // Remove the moving piece
1402 // The destination square is defended, which makes things rather more
1403 // difficult to compute. We proceed by building up a "swap list" containing
1404 // the material gain or loss at each stop in a sequence of captures to the
1405 // destination square, where the sides alternately capture, and always
1406 // capture with the least valuable piece. After each capture, we look for
1407 // new X-ray attacks from behind the capturing piece.
1408 int lastCapturingPieceValue = seeValues[piece];
1409 int swapList[32], n = 1;
1413 swapList[0] = seeValues[capture];
1416 // Locate the least valuable attacker for the side to move. The loop
1417 // below looks like it is potentially infinite, but it isn't. We know
1418 // that the side to move still has at least one attacker left.
1419 for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
1422 // Remove the attacker we just found from the 'attackers' bitboard,
1423 // and scan for new X-ray attacks behind the attacker.
1424 b = stmAttackers & pieces(pt);
1425 occ ^= (b & (~b + 1));
1426 attackers |= (rook_attacks_bb(to, occ) & pieces(ROOK, QUEEN))
1427 | (bishop_attacks_bb(to, occ) & pieces(BISHOP, QUEEN));
1431 // Add the new entry to the swap list
1433 swapList[n] = -swapList[n - 1] + lastCapturingPieceValue;
1436 // Remember the value of the capturing piece, and change the side to move
1437 // before beginning the next iteration
1438 lastCapturingPieceValue = seeValues[pt];
1439 c = opposite_color(c);
1440 stmAttackers = attackers & pieces_of_color(c);
1442 // Stop after a king capture
1443 if (pt == KING && stmAttackers)
1446 swapList[n++] = QueenValueMidgame*10;
1449 } while (stmAttackers);
1451 // Having built the swap list, we negamax through it to find the best
1452 // achievable score from the point of view of the side to move
1454 swapList[n-1] = Min(-swapList[n], swapList[n-1]);
1460 /// Position::clear() erases the position object to a pristine state, with an
1461 /// empty board, white to move, and no castling rights.
1463 void Position::clear() {
1466 memset(st, 0, sizeof(StateInfo));
1467 st->epSquare = SQ_NONE;
1469 memset(byColorBB, 0, sizeof(Bitboard) * 2);
1470 memset(byTypeBB, 0, sizeof(Bitboard) * 8);
1471 memset(pieceCount, 0, sizeof(int) * 2 * 8);
1472 memset(index, 0, sizeof(int) * 64);
1474 for (int i = 0; i < 64; i++)
1477 for (int i = 0; i < 8; i++)
1478 for (int j = 0; j < 16; j++)
1479 pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
1483 initialKFile = FILE_E;
1484 initialKRFile = FILE_H;
1485 initialQRFile = FILE_A;
1489 /// Position::reset_game_ply() simply sets gamePly to 0. It is used from the
1490 /// UCI interface code, whenever a non-reversible move is made in a
1491 /// 'position fen <fen> moves m1 m2 ...' command. This makes it possible
1492 /// for the program to handle games of arbitrary length, as long as the GUI
1493 /// handles draws by the 50 move rule correctly.
1495 void Position::reset_game_ply() {
1501 /// Position::put_piece() puts a piece on the given square of the board,
1502 /// updating the board array, bitboards, and piece counts.
1504 void Position::put_piece(Piece p, Square s) {
1506 Color c = color_of_piece(p);
1507 PieceType pt = type_of_piece(p);
1510 index[s] = pieceCount[c][pt];
1511 pieceList[c][pt][index[s]] = s;
1513 set_bit(&(byTypeBB[pt]), s);
1514 set_bit(&(byColorBB[c]), s);
1515 set_bit(&byTypeBB[0], s); // HACK: byTypeBB[0] contains all occupied squares.
1517 pieceCount[c][pt]++;
1521 /// Position::allow_oo() gives the given side the right to castle kingside.
1522 /// Used when setting castling rights during parsing of FEN strings.
1524 void Position::allow_oo(Color c) {
1526 st->castleRights |= (1 + int(c));
1530 /// Position::allow_ooo() gives the given side the right to castle queenside.
1531 /// Used when setting castling rights during parsing of FEN strings.
1533 void Position::allow_ooo(Color c) {
1535 st->castleRights |= (4 + 4*int(c));
1539 /// Position::compute_key() computes the hash key of the position. The hash
1540 /// key is usually updated incrementally as moves are made and unmade, the
1541 /// compute_key() function is only used when a new position is set up, and
1542 /// to verify the correctness of the hash key when running in debug mode.
1544 Key Position::compute_key() const {
1546 Key result = Key(0ULL);
1548 for (Square s = SQ_A1; s <= SQ_H8; s++)
1549 if (square_is_occupied(s))
1550 result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
1552 if (ep_square() != SQ_NONE)
1553 result ^= zobEp[ep_square()];
1555 result ^= zobCastle[st->castleRights];
1556 if (side_to_move() == BLACK)
1557 result ^= zobSideToMove;
1563 /// Position::compute_pawn_key() computes the hash key of the position. The
1564 /// hash key is usually updated incrementally as moves are made and unmade,
1565 /// the compute_pawn_key() function is only used when a new position is set
1566 /// up, and to verify the correctness of the pawn hash key when running in
1569 Key Position::compute_pawn_key() const {
1571 Key result = Key(0ULL);
1575 for (Color c = WHITE; c <= BLACK; c++)
1577 b = pieces(PAWN, c);
1580 s = pop_1st_bit(&b);
1581 result ^= zobrist[c][PAWN][s];
1588 /// Position::compute_material_key() computes the hash key of the position.
1589 /// The hash key is usually updated incrementally as moves are made and unmade,
1590 /// the compute_material_key() function is only used when a new position is set
1591 /// up, and to verify the correctness of the material hash key when running in
1594 Key Position::compute_material_key() const {
1596 Key result = Key(0ULL);
1597 for (Color c = WHITE; c <= BLACK; c++)
1598 for (PieceType pt = PAWN; pt <= QUEEN; pt++)
1600 int count = piece_count(c, pt);
1601 for (int i = 0; i <= count; i++)
1602 result ^= zobMaterial[c][pt][i];
1608 /// Position::compute_value() compute the incremental scores for the middle
1609 /// game and the endgame. These functions are used to initialize the incremental
1610 /// scores when a new position is set up, and to verify that the scores are correctly
1611 /// updated by do_move and undo_move when the program is running in debug mode.
1612 Score Position::compute_value() const {
1614 Score result = make_score(0, 0);
1618 for (Color c = WHITE; c <= BLACK; c++)
1619 for (PieceType pt = PAWN; pt <= KING; pt++)
1624 s = pop_1st_bit(&b);
1625 assert(piece_on(s) == piece_of_color_and_type(c, pt));
1626 result += pst(c, pt, s);
1630 result += (side_to_move() == WHITE ? TempoValue / 2 : -TempoValue / 2);
1635 /// Position::compute_non_pawn_material() computes the total non-pawn middle
1636 /// game material score for the given side. Material scores are updated
1637 /// incrementally during the search, this function is only used while
1638 /// initializing a new Position object.
1640 Value Position::compute_non_pawn_material(Color c) const {
1642 Value result = Value(0);
1644 for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
1646 Bitboard b = pieces(pt, c);
1649 assert(piece_on(first_1(b)) == piece_of_color_and_type(c, pt));
1651 result += piece_value_midgame(pt);
1658 /// Position::is_draw() tests whether the position is drawn by material,
1659 /// repetition, or the 50 moves rule. It does not detect stalemates, this
1660 /// must be done by the search.
1661 // FIXME: Currently we are not handling 50 move rule correctly when in check
1663 bool Position::is_draw() const {
1665 // Draw by material?
1667 && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
1670 // Draw by the 50 moves rule?
1671 if (st->rule50 > 100 || (st->rule50 == 100 && !is_check()))
1674 // Draw by repetition?
1675 for (int i = 4; i <= Min(Min(gamePly, st->rule50), st->pliesFromNull); i += 2)
1676 if (history[gamePly - i] == st->key)
1683 /// Position::is_mate() returns true or false depending on whether the
1684 /// side to move is checkmated.
1686 bool Position::is_mate() const {
1688 MoveStack moves[256];
1689 return is_check() && (generate_moves(*this, moves, false) == moves);
1693 /// Position::has_mate_threat() tests whether a given color has a mate in one
1694 /// from the current position.
1696 bool Position::has_mate_threat(Color c) {
1699 Color stm = side_to_move();
1704 // If the input color is not equal to the side to move, do a null move
1708 MoveStack mlist[120];
1709 bool result = false;
1710 Bitboard pinned = pinned_pieces(sideToMove);
1712 // Generate pseudo-legal non-capture and capture check moves
1713 MoveStack* last = generate_non_capture_checks(*this, mlist);
1714 last = generate_captures(*this, last);
1716 // Loop through the moves, and see if one of them is mate
1717 for (MoveStack* cur = mlist; cur != last; cur++)
1719 Move move = cur->move;
1720 if (!pl_move_is_legal(move, pinned))
1730 // Undo null move, if necessary
1738 /// Position::init_zobrist() is a static member function which initializes the
1739 /// various arrays used to compute hash keys.
1741 void Position::init_zobrist() {
1743 for (int i = 0; i < 2; i++)
1744 for (int j = 0; j < 8; j++)
1745 for (int k = 0; k < 64; k++)
1746 zobrist[i][j][k] = Key(genrand_int64());
1748 for (int i = 0; i < 64; i++)
1749 zobEp[i] = Key(genrand_int64());
1751 for (int i = 0; i < 16; i++)
1752 zobCastle[i] = genrand_int64();
1754 zobSideToMove = genrand_int64();
1756 for (int i = 0; i < 2; i++)
1757 for (int j = 0; j < 8; j++)
1758 for (int k = 0; k < 16; k++)
1759 zobMaterial[i][j][k] = (k > 0)? Key(genrand_int64()) : Key(0LL);
1761 for (int i = 0; i < 16; i++)
1762 zobMaterial[0][KING][i] = zobMaterial[1][KING][i] = Key(0ULL);
1764 zobExclusion = genrand_int64();
1768 /// Position::init_piece_square_tables() initializes the piece square tables.
1769 /// This is a two-step operation: First, the white halves of the tables are
1770 /// copied from the MgPST[][] and EgPST[][] arrays, with a small random number
1771 /// added to each entry if the "Randomness" UCI parameter is non-zero.
1772 /// Second, the black halves of the tables are initialized by mirroring
1773 /// and changing the sign of the corresponding white scores.
1775 void Position::init_piece_square_tables() {
1777 int r = get_option_value_int("Randomness"), i;
1778 for (Square s = SQ_A1; s <= SQ_H8; s++)
1779 for (Piece p = WP; p <= WK; p++)
1781 i = (r == 0)? 0 : (genrand_int32() % (r*2) - r);
1782 PieceSquareTable[p][s] = make_score(MgPST[p][s] + i, EgPST[p][s] + i);
1785 for (Square s = SQ_A1; s <= SQ_H8; s++)
1786 for (Piece p = BP; p <= BK; p++)
1787 PieceSquareTable[p][s] = -PieceSquareTable[p-8][flip_square(s)];
1791 /// Position::flipped_copy() makes a copy of the input position, but with
1792 /// the white and black sides reversed. This is only useful for debugging,
1793 /// especially for finding evaluation symmetry bugs.
1795 void Position::flipped_copy(const Position& pos) {
1797 assert(pos.is_ok());
1802 for (Square s = SQ_A1; s <= SQ_H8; s++)
1803 if (!pos.square_is_empty(s))
1804 put_piece(Piece(int(pos.piece_on(s)) ^ 8), flip_square(s));
1807 sideToMove = opposite_color(pos.side_to_move());
1810 if (pos.can_castle_kingside(WHITE)) allow_oo(BLACK);
1811 if (pos.can_castle_queenside(WHITE)) allow_ooo(BLACK);
1812 if (pos.can_castle_kingside(BLACK)) allow_oo(WHITE);
1813 if (pos.can_castle_queenside(BLACK)) allow_ooo(WHITE);
1815 initialKFile = pos.initialKFile;
1816 initialKRFile = pos.initialKRFile;
1817 initialQRFile = pos.initialQRFile;
1819 for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
1820 castleRightsMask[sq] = ALL_CASTLES;
1822 castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
1823 castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
1824 castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
1825 castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
1826 castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
1827 castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
1829 // En passant square
1830 if (pos.st->epSquare != SQ_NONE)
1831 st->epSquare = flip_square(pos.st->epSquare);
1837 st->key = compute_key();
1838 st->pawnKey = compute_pawn_key();
1839 st->materialKey = compute_material_key();
1841 // Incremental scores
1842 st->value = compute_value();
1845 st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
1846 st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
1852 /// Position::is_ok() performs some consitency checks for the position object.
1853 /// This is meant to be helpful when debugging.
1855 bool Position::is_ok(int* failedStep) const {
1857 // What features of the position should be verified?
1858 static const bool debugBitboards = false;
1859 static const bool debugKingCount = false;
1860 static const bool debugKingCapture = false;
1861 static const bool debugCheckerCount = false;
1862 static const bool debugKey = false;
1863 static const bool debugMaterialKey = false;
1864 static const bool debugPawnKey = false;
1865 static const bool debugIncrementalEval = false;
1866 static const bool debugNonPawnMaterial = false;
1867 static const bool debugPieceCounts = false;
1868 static const bool debugPieceList = false;
1869 static const bool debugCastleSquares = false;
1871 if (failedStep) *failedStep = 1;
1874 if (!color_is_ok(side_to_move()))
1877 // Are the king squares in the position correct?
1878 if (failedStep) (*failedStep)++;
1879 if (piece_on(king_square(WHITE)) != WK)
1882 if (failedStep) (*failedStep)++;
1883 if (piece_on(king_square(BLACK)) != BK)
1887 if (failedStep) (*failedStep)++;
1888 if (!file_is_ok(initialKRFile))
1891 if (!file_is_ok(initialQRFile))
1894 // Do both sides have exactly one king?
1895 if (failedStep) (*failedStep)++;
1898 int kingCount[2] = {0, 0};
1899 for (Square s = SQ_A1; s <= SQ_H8; s++)
1900 if (type_of_piece_on(s) == KING)
1901 kingCount[color_of_piece_on(s)]++;
1903 if (kingCount[0] != 1 || kingCount[1] != 1)
1907 // Can the side to move capture the opponent's king?
1908 if (failedStep) (*failedStep)++;
1909 if (debugKingCapture)
1911 Color us = side_to_move();
1912 Color them = opposite_color(us);
1913 Square ksq = king_square(them);
1914 if (attackers_to(ksq) & pieces_of_color(us))
1918 // Is there more than 2 checkers?
1919 if (failedStep) (*failedStep)++;
1920 if (debugCheckerCount && count_1s(st->checkersBB) > 2)
1924 if (failedStep) (*failedStep)++;
1927 // The intersection of the white and black pieces must be empty
1928 if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
1931 // The union of the white and black pieces must be equal to all
1933 if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
1936 // Separate piece type bitboards must have empty intersections
1937 for (PieceType p1 = PAWN; p1 <= KING; p1++)
1938 for (PieceType p2 = PAWN; p2 <= KING; p2++)
1939 if (p1 != p2 && (pieces(p1) & pieces(p2)))
1943 // En passant square OK?
1944 if (failedStep) (*failedStep)++;
1945 if (ep_square() != SQ_NONE)
1947 // The en passant square must be on rank 6, from the point of view of the
1949 if (relative_rank(side_to_move(), ep_square()) != RANK_6)
1954 if (failedStep) (*failedStep)++;
1955 if (debugKey && st->key != compute_key())
1958 // Pawn hash key OK?
1959 if (failedStep) (*failedStep)++;
1960 if (debugPawnKey && st->pawnKey != compute_pawn_key())
1963 // Material hash key OK?
1964 if (failedStep) (*failedStep)++;
1965 if (debugMaterialKey && st->materialKey != compute_material_key())
1968 // Incremental eval OK?
1969 if (failedStep) (*failedStep)++;
1970 if (debugIncrementalEval && st->value != compute_value())
1973 // Non-pawn material OK?
1974 if (failedStep) (*failedStep)++;
1975 if (debugNonPawnMaterial)
1977 if (st->npMaterial[WHITE] != compute_non_pawn_material(WHITE))
1980 if (st->npMaterial[BLACK] != compute_non_pawn_material(BLACK))
1985 if (failedStep) (*failedStep)++;
1986 if (debugPieceCounts)
1987 for (Color c = WHITE; c <= BLACK; c++)
1988 for (PieceType pt = PAWN; pt <= KING; pt++)
1989 if (pieceCount[c][pt] != count_1s(pieces(pt, c)))
1992 if (failedStep) (*failedStep)++;
1995 for (Color c = WHITE; c <= BLACK; c++)
1996 for (PieceType pt = PAWN; pt <= KING; pt++)
1997 for (int i = 0; i < pieceCount[c][pt]; i++)
1999 if (piece_on(piece_list(c, pt, i)) != piece_of_color_and_type(c, pt))
2002 if (index[piece_list(c, pt, i)] != i)
2007 if (failedStep) (*failedStep)++;
2008 if (debugCastleSquares) {
2009 for (Color c = WHITE; c <= BLACK; c++) {
2010 if (can_castle_kingside(c) && piece_on(initial_kr_square(c)) != piece_of_color_and_type(c, ROOK))
2012 if (can_castle_queenside(c) && piece_on(initial_qr_square(c)) != piece_of_color_and_type(c, ROOK))
2015 if (castleRightsMask[initial_kr_square(WHITE)] != (ALL_CASTLES ^ WHITE_OO))
2017 if (castleRightsMask[initial_qr_square(WHITE)] != (ALL_CASTLES ^ WHITE_OOO))
2019 if (castleRightsMask[initial_kr_square(BLACK)] != (ALL_CASTLES ^ BLACK_OO))
2021 if (castleRightsMask[initial_qr_square(BLACK)] != (ALL_CASTLES ^ BLACK_OOO))
2025 if (failedStep) *failedStep = 0;