x                  The fractional part of value.
    0                  Both parts of the result are 0.
    NaN                If value is NaN, NaN is returned, errno
                       is set to EDOM, and the value of *eptr is
                       unspecified.
    value              If |value| = Infinity, value is returned,
                       errno is set to EDOM, and the value of *eptr
                       is unspecified.