def _from_ordinalf(x, tz=None):
    """                                                                                                                                                         
    Convert Gregorian float of the date, preserving hours, minutes,                                                                                             
    seconds and microseconds.  Return value is a :class:`datetime`.                                                                                             

    The input date `x` is a float in ordinal days at UTC, and the output will                                                                                   
    be the specified :class:`datetime` object corresponding to that time in                                                                                     
    timezone `tz`, or if `tz` is `None`, in the timezone specified in                                                                                           
    `rcParams['timezone']`.                                                                                                                                     
    """
    if tz is None:
        tz = _get_rc_timezone()

    ix = int(x)
    dt = datetime.datetime.fromordinal(ix).replace(tzinfo=UTC)

    remainder = float(x) - ix

    # Round down to the nearest microsecond.                                                                                                                    
    dt += datetime.timedelta(microseconds=int(remainder * MUSECONDS_PER_DAY))

    # Compensate for rounding errors                                                                                                                            
    if dt.microsecond < 10:
        dt = dt.replace(microsecond=0)
    elif dt.microsecond > 999990:
        dt += datetime.timedelta(microseconds=1e6 - dt.microsecond)

    return dt