exp(), expf(), expl()

Updated: April 19, 2023

Compute the exponential function of a number

Synopsis:

#include <math.h>

double exp( double x );

float expf( float x );

long double expl( long double x );

Arguments:

x
The number for which you want to calculate the exponential.

Library:

libm
The general-purpose math library.
libm-sve
(QNX Neutrino 7.1 or later) A library that optimizes the code for ARMv8.2 chips that have Scalable Vector Extension hardware.

Your system requirements will determine how you should work with these libraries:

Note: Compile your program with the -fno-builtin option to prevent the compiler from using a built-in version of the function.

Description:

These functions compute the exponential function of x (i.e., ex).

To check for error situations, use feclearexcept() and fetestexcept(). For example:

Returns:

The exponential value of x.

If x is: These functions return: Errors:
±0.0 1
A value that would cause overflow Inf FE_OVERFLOW
A value that would cause underflow 0.0 FE_UNDERFLOW
-Inf 0.0
Inf Inf
NaN NaN

These functions raise FE_INEXACT if the FPU reports that the result can't be exactly represented as a floating-point number.

Examples:

#include <stdio.h>
#include <math.h>
#include <fenv.h>
#include <stdlib.h>

int main( void )
{
    int except_flags;

    feclearexcept(FE_ALL_EXCEPT);

    printf( "%f\n", exp(.5) );

    except_flags = fetestexcept(FE_ALL_EXCEPT);
    if(except_flags) {
        /* An error occurred; handle it appropriately. */
    }

    return EXIT_SUCCESS;
}

produces the output:

1.648721

Classification:

C11, POSIX 1003.1

Safety:  
Cancellation point No
Interrupt handler Yes
Signal handler Yes
Thread Yes

Caveats:

The value of expm1(x) may be more accurate than exp(x) - 1.0 for small values of x.