Description

   The exp functions compute the value of the exponential function,
   defined as e**x, where e is the constant used as a base for
   natural logarithms.

   The expm1 functions compute exp(x) - 1 accurately, even for tiny
   x.

   If an overflow occurs, the exp functions return the largest
   possible floating-point value and set errno to ERANGE. The
   constant HUGE_VAL is defined in the <math.h> header file to be
   the largest possible floating-point value.