Function dd_quick_polyeval6 

pub(crate) fn dd_quick_polyeval6(
    x: DoubleDouble,
    a0: DoubleDouble,
    a1: DoubleDouble,
    a2: DoubleDouble,
    a3: DoubleDouble,
    a4: DoubleDouble,
    a5: DoubleDouble,
) -> DoubleDouble