##### Synopsis

    #include <math.h>
    double exp(double x);

##### Description

exp computes the base-e exponential of x.

##### Fast math library behavior

If |x| >~ 709.782, errno is set to EDOM and exp returns HUGE_VAL.

##### IEC 60559 math library behavior

If x is NaN, exp returns NaN.
If x is ?, exp returns ?
If x is -?, exp returns 0.

##### Portability

exp conforms to ISO/IEC 9899:1990 (C90) and ISO/IEC 9899:1999 (C99).