exp() computes the value of the exponential function, defined
    as e**x, where e is the constant used as a base for natural
    logarithms.

    expm1() computes exp(x)-1 accurately, even for tiny x.

                           Entry-Point Names

    Generic
    Function   Data Type   OpenVMS        Tru64 UNIX
    Name       Required

    exp        S_FLOAT     math$exp_s     expf
               T_FLOAT     math$exp_t     exp
               X_FLOAT     math$exp_x     expl
               F_FLOAT     math$exp_f
               G_FLOAT     math$exp_g

    expm1      S_FLOAT     math$expm1_s   expm1f
               T_FLOAT     math$expm1_t   expm1
               X_FLOAT     math$expm1_x   expm1l
               F_FLOAT     math$expm1_f
               G_FLOAT     math$expm1_g