IEEE754 float helper. :be keeps the first register as the high word; :le swaps the two words.
:be
:le
@spec from_2_regs([integer()], :be | :le) :: float()
@spec from_2_regs(integer(), integer(), :be | :le) :: float()
@spec from_2n_regs([integer()], :be | :le) :: [float()]
@spec to_2_regs(float(), :be | :le) :: [integer()]
@spec to_2n_regs([float()], :be | :le) :: [integer()]