On Alpha and Integrity server systems, modifies IEEE floating-
    point state and, optionally, returns the previous value.

    The service provides the mechanism to set the specified state
    bits, to clear the specified state bits, and to swap one set of
    state bits for another.

    Format

      SYS$IEEE_SET_FP_CONTROL  [clrmsk] ,[setmsk] ,[prvmsk]

    C Prototype

      int sys$ieee_set_fp_control  (struct _ieee *clrmsk, struct

                                   _ieee *setmsk, struct _ieee

                                   *prvmsk);