VMS Help RTL Routines, MTH$, MTH$VxFOLRLy MA V5, Returns  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    OpenVMS usage:longword_signed or floating_point
    type:         longword integer (signed), F_floating, D_floating
                  or G_floating
    access:       write only
    mechanism:    by value

    The function value is the result of the last iteration of the
    linear recurrence relation. The function value is returned in R0
    or R0 and R1.