n                  2**x.
    HUGE_VAL           Overflow occurred; errno is set to ERANGE.
    1                  x is +0 or -0; errno is set to ERANGE.
    0                  x is -Inf or underflow occurred; errno is set
                       to ERANGE.
    x                  x is +Inf; errno is set to ERANGE.
    NaN                x is NaN; errno is set to EDOM.