Move cuckooMove[8192];
-/// Position::init() initializes at startup the various arrays used to compute
-/// hash keys.
+/// Position::init() initializes at startup the various arrays used to compute hash keys
void Position::init() {
Zobrist::enpassant[f] = rng.rand<Key>();
for (int cr = NO_CASTLING; cr <= ANY_CASTLING; ++cr)
- {
- Zobrist::castling[cr] = 0;
- Bitboard b = cr;
- while (b)
- {
- Key k = Zobrist::castling[1ULL << pop_lsb(&b)];
- Zobrist::castling[cr] ^= k ? k : rng.rand<Key>();
- }
- }
+ Zobrist::castling[cr] = rng.rand<Key>();
Zobrist::side = rng.rand<Key>();
Zobrist::noPawns = rng.rand<Key>();
4) En passant target square (in algebraic notation). If there's no en passant
target square, this is "-". If a pawn has just made a 2-square move, this
- is the position "behind" the pawn. This is recorded only if there is a pawn
- in position to make an en passant capture, and if there really is a pawn
- that might have advanced two squares.
+ is the position "behind" the pawn. Following X-FEN standard, this is recorded only
+ if there is a pawn in position to make an en passant capture, and if there really
+ is a pawn that might have advanced two squares.
5) Halfmove clock. This is the number of halfmoves since the last pawn advance
or capture. This is used to determine if a draw can be claimed under the
set_castling_right(c, rsq);
}
- // 4. En passant square. Ignore if no pawn capture is possible
+ // 4. En passant square.
+ // Ignore if square is invalid or not on side to move relative rank 6.
+ bool enpassant = false;
+
if ( ((ss >> col) && (col >= 'a' && col <= 'h'))
- && ((ss >> row) && (row == '3' || row == '6')))
+ && ((ss >> row) && (row == (sideToMove == WHITE ? '6' : '3'))))
{
st->epSquare = make_square(File(col - 'a'), Rank(row - '1'));
- if ( !(attackers_to(st->epSquare) & pieces(sideToMove, PAWN))
- || !(pieces(~sideToMove, PAWN) & (st->epSquare + pawn_push(~sideToMove))))
- st->epSquare = SQ_NONE;
+ // En passant square will be considered only if
+ // a) side to move have a pawn threatening epSquare
+ // b) there is an enemy pawn in front of epSquare
+ // c) there is no piece on epSquare or behind epSquare
+ enpassant = pawn_attacks_bb(~sideToMove, st->epSquare) & pieces(sideToMove, PAWN)
+ && (pieces(~sideToMove, PAWN) & (st->epSquare + pawn_push(~sideToMove)))
+ && !(pieces() & (st->epSquare | (st->epSquare + pawn_push(sideToMove))));
}
- else
+
+ if (!enpassant)
st->epSquare = SQ_NONE;
// 5-6. Halfmove clock and fullmove number
// Update castling rights if needed
if (st->castlingRights && (castlingRightsMask[from] | castlingRightsMask[to]))
{
- int cr = castlingRightsMask[from] | castlingRightsMask[to];
- k ^= Zobrist::castling[st->castlingRights & cr];
- st->castlingRights &= ~cr;
+ k ^= Zobrist::castling[st->castlingRights];
+ st->castlingRights &= ~(castlingRightsMask[from] | castlingRightsMask[to]);
+ k ^= Zobrist::castling[st->castlingRights];
}
// Move the piece. The tricky Chess960 castling is handled earlier
return bool(res);
}
+
/// Position::is_draw() tests whether the position is drawn by 50-move rule
/// or by repetition. It does not detect stalemates.