operation
    OpenVMS usage:function_code
    type:         longword (unsigned)
    access:       read only
    mechanism:    by reference
    The conversion to be performed. The operation argument is the
    address of an unsigned longword specifying the operation. Valid
    values for operation are the following:
    Operation              Interpretation
    LIB$K_DELTA_WEEKS_F    Fractional weeks
    LIB$K_DELTA_DAYS_F     Fractional days
    LIB$K_DELTA_HOURS_F    Fractional hours
    LIB$K_DELTA_MINUTES_F  Fractional minutes
    LIB$K_DELTA_SECONDS_F  Fractional seconds
 resultant-time
    OpenVMS usage:floating_point
    type:         IEEE S_floating
    access:       write only
    mechanism:    by reference
    The external time that results from the conversion. The
    resultant-time argument is the address of an IEEE S-floating-
    point value containing the result.
 input-time
    OpenVMS usage:date_time
    type:         quadword (unsigned)
    access:       read only
    mechanism:    by reference
    Delta time to be converted. The input-time argument is the
    address of an unsigned quadword containing the time.