VMS Help RTL Routines, MTH$, BLAS1$VxNRM2, Returns  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    OpenVMS usage:floating_point
    type:         F_floating, D_floating, or G_floating real
    access:       write only
    mechanism:    by value

    The function value, called e_norm, is the Euclidean norm of
    the vector x. The data type of the function value is a real
    number; for the BLAS1$VSCNRM2, BLAS1$VDZNRM2, and BLAS1$VGWNRM2
    routines, the data type of the function value is the real data
    type corresponding to the complex argument data type.