 
   # Converts year, month, day to count of days since 0000-01-01.
   @doc false
-  @doc since: "1.5.0"
   def date_to_iso_days(0, 1, 1) do
     0
   end

  end

  @doc false
  @doc since: "1.5.0"
  def add_day_fraction_to_iso_days({days, {parts, ppd}}, add, ppd) do
    normalize_iso_days(days, parts + add, ppd)
  end

  end

  @doc false
  def iso_days_to_unit({days, {parts, ppd}}, unit) do
    day_microseconds = days * @parts_per_day
    microseconds = div(parts * @parts_per_day, ppd)
