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

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

    The absolute value of a complex number. MTH$CABS returns an F-
    floating number. MTH$CDABS returns a D-floating number. MTH$CGABS
    returns a G-floating number.