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

    OpenVMS usage:longword_unsigned
    type:         longword (unsigned)
    access:       write only
    mechanism:    by value

    The relative position of the first character of the substring if
    found, or zero if not found.

    On Alpha systems, if the relative position of the substring can
    exceed 2**32-1, assign the return value to a quadword to ensure
    that you retrieve the correct relative position.