VMS Help RTL Routines, LIB$, LIB$FLT_UNDER, Argument  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 new-setting

    OpenVMS usage:longword_unsigned
    type:         longword (unsigned)
    access:       read only
    mechanism:    by reference

    New floating-point underflow enable setting. The new-setting
    argument is the address of an unsigned byte containing the
    new setting. Bit 0 set to 1 means enable; bit 0 set to 0 means
    disable.