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`exp', `expf'--exponential

     #include <math.h>
     double exp(double X);
     float expf(float X);
`exp' and `expf' calculate the exponential of X, that is, e raised to
the power X (where e is the base of the natural system of logarithms,
approximately 2.71828).
   You can use the (non-ANSI) function `matherr' to specify error
handling for these functions.
On success, `exp' and `expf' return the calculated value.  If the
result underflows, the returned value is `0'.  If the result overflows,
the returned value is `HUGE_VAL'.  In either case, `errno' is set to
`exp' is ANSI C.  `expf' is an extension.