OpenVMS usage:longword_signed
    type:         longword (signed)
    access:       write only
    mechanism:    by value

    Position in source-string where the first match is found; zero if
    no match is 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.