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erf(), erff(), erfl()
Compute the error function of a number

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erf(), erff(), erfl()

QNX SDP8.0C Library ReferenceAPIDeveloper

Compute the error function of a number

Synopsis:

#include <math.h>

double erf ( double x );

float erff ( float x );

long double erfl ( long double x );

Arguments:

x: The number for which you want to compute the error function.

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.

Note:

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

Description:

The erf(), erff(), and erfl() functions compute the following:
erf(x) = 2/sqrt(pi)*integral from 0 to x of exp(-t*t) dt

erf(x) = 2/sqrt(pi)*integral from 0 to x of exp(-t*t) dt

If x is large and the result of erf() is subtracted from 1.0, the results aren't very accurate; use erfc() instead.

This equality is true: erf(-x) = -erf(x)

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

Call feclearexcept(FE_ALL_EXCEPT) before calling erf(), erff(), or erfl().
On return, if fetestexcept(FE_ALL_EXCEPT) is nonzero, then an error has occurred.

Returns:

The value of the error function.


If `x` is:	These functions return:	Errors:
±0.0	0.0, with the same sign as `x`	—
A value that would cause underflow	`x`	FE_UNDERFLOW
±Inf	1.0, with the same sign as `x`	—
NaN	NaN	—

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

Classification:

C11, POSIX 1003.1


Safety:
Cancellation point	No
Signal handler	Yes
Thread	Yes

Page updated: August 09, 2024