scalb() = x*(2**y) computed, for integer-valued floating point
    number y.

                           Entry-Point Names

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

    scalb      S_FLOAT     math$scalb_s   scalbf
               T_FLOAT     math$scalb_t   scalb
               X_FLOAT     math$scalb_x   scalbl
               F_FLOAT     math$scalb_f
               G_FLOAT     math$scalb_g