template<class F, class>
void
number::
assign(F v) noexcept
{
    static exponent_type const bias =
        static_cast<exponent_type>(std::floor(
            std::log10((std::numeric_limits<
                mantissa_type>::max)()))) - 1;
    if(v < 0)
    {
        v = -v;
        neg_ = true;
    }
    else
    {
        neg_ = false;
    }
    exp_ = static_cast<exponent_type>(
        std::floor(std::log10(v))) - bias;
    mant_ = static_cast<mantissa_type>(
        v / std::pow(10, exp_));
}