cabs(x,y) is defined as the square root of (x**2 + y**2) and
    returns the same value as hypot(x,y).

                           Entry-Point Names

    Generic                               Compaq
    Function   Data Type   OpenVMS        Tru64 UNIX
    Name       Required    Alpha          Alpha

    cabs       S_FLOAT     math$hypot_s   cabsf
               T_FLOAT     math$hypot_t   cabs
               X_FLOAT     math$hypot_x   cabsl
               F_FLOAT     math$hypot_f
               G_FLOAT     math$hypot_g