x                  On success, x * FLT_RADIX ** n is returned.
    NaN                If x is NaN.
    +/- 0              If x is +/- 0.
                       If the result underflows, a range error occurs,
                       and the functions return +/- 0 with a sign the
                       same as x.
    +/- Infinity       If x is +/- Infinity.
    +/- HUGE_VAL
    HUGE_VALF
    HUGE_VALL          If the result overflows, a range error occurs, and
                       the functions return +/- HUGE_VAL, HUGE_VALF, or
                       HUGE_VALL, respectively, with a sign the same as x.