expm1(), expm1f(), expm1l()
Compute the exponential of a number, then subtract 1
Synopsis:
#include <math.h>
double expm1 ( double x );
float expm1f ( float x );
long double expm1l ( long double x );
Arguments:
- x
- The number for which you want to calculate the exponential minus one.
Library:
- libm
- The general-purpose math library.
- libm-sve
- 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.
Description:
The expm1(), expm1f(), and expm1l() functions compute the exponential of x, minus 1 (ex - 1).
The value of expm1( x ) may be more accurate than
exp( x ) - 1.0 for small values of x.
The expm1() and
log1p() functions are useful for
financial calculations of (((1+x)**n)-1)/x, namely:
expm1(n * log1p(x))/x
when x is very small (for example, when performing calculations with a small daily interest rate). These functions also simplify writing accurate inverse hyperbolic functions.
To check for error situations, use feclearexcept() and fetestexcept(). For example:
- Call
feclearexcept(FE_ALL_EXCEPT)before calling expm1(), expm1f(), or expm1l(). - On return, if
fetestexcept(FE_ALL_EXCEPT)is nonzero, then an error has occurred.
Returns:
The exponential value of x, minus 1.
| If x is: | These functions return: | Errors: |
|---|---|---|
| ±0.0 | 0.0, with the same sign as x | — |
| A value that would cause overflow | Inf | FE_OVERFLOW |
| -Inf | -1 | — |
| 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;
double a, b;
feclearexcept(FE_ALL_EXCEPT);
a = 2;
b = expm1(a);
printf("(e ^ %f) -1 is %f \n", a, b);
except_flags = fetestexcept(FE_ALL_EXCEPT);
if(except_flags) {
/* An error occurred; handle it appropriately. */
}
return EXIT_SUCCESS;
}
produces the output:
(e ^ 2.000000) -1 is 6.389056
Classification:
| Safety: | |
|---|---|
| Cancellation point | No |
| Signal handler | Yes |
| Thread | Yes |