exp(), expf(), expl()

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:

If you want only selected processes to run with the SVE version, you can include both libraries in your OS image and use the -l m or -l m-sve option to qcc to link explicitly against the appropriate one.
If you want all processes to use the SVE version, include libm-sve.so in your OS image and set up a symbolic link from libm.so to libm-sve.so. Use the -l m option to qcc to link against the library.

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., e^x).

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

Call feclearexcept(FE_ALL_EXCEPT) before calling exp(), expf(), or expl().
On return, if fetestexcept(FE_ALL_EXCEPT) is nonzero, then an error has occurred.

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.