The Open Group Base Specifications Issue 7
IEEE Std 1003.1, 2013 Edition

#### NAME

fabs, fabsf, fabsl - absolute value function

#### SYNOPSIS

```#include <math.h> double fabs(double x); float fabsf(float x); long double fabsl(long double x); ```

#### DESCRIPTION

[CX] The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1-2008 defers to the ISO C standard. These functions shall compute the absolute value of their argument x,| x|.

#### RETURN VALUE

Upon successful completion, these functions shall return the absolute value of x.

[MX] If x is NaN, a NaN shall be returned.

If x is ±0, +0 shall be returned.

If x is ±Inf, +Inf shall be returned. #### ERRORS

No errors are defined.

The following sections are informative.

#### EXAMPLES

##### Computing the 1-Norm of a Floating-Point Vector

This example shows the use of fabs() to compute the 1-norm of a vector defined as follows:

```norm1(v) = |v| + |v| + ... + |v[n-1]|

```

where |x| denotes the absolute value of x, n denotes the vector's dimension v[i] denotes the i-th component of v (0<=i<n).

```#include <math.h>

double
norm1(const double v[], const int n)
{
int     i;
double  n1_v;  /* 1-norm of v */

n1_v = 0;
for (i=0; i<n; i++) {
n1_v += fabs (v[i]);
}

return n1_v;
}

```

None.

None.

None.

isnan

XBD <math.h>

#### CHANGE HISTORY

First released in Issue 1. Derived from Issue 1 of the SVID.

#### Issue 5

The DESCRIPTION is updated to indicate how an application should check for an error. This text was previously published in the APPLICATION USAGE section.

#### Issue 6

The fabsf() and fabsl() functions are added for alignment with the ISO/IEC 9899:1999 standard.

The DESCRIPTION, RETURN VALUE, ERRORS, and APPLICATION USAGE sections are revised to align with the ISO/IEC 9899:1999 standard.

IEC 60559:1989 standard floating-point extensions over the ISO/IEC 9899:1999 standard are marked.

IEEE Std 1003.1-2001/Cor 2-2004, item XSH/TC2/D6/27 is applied, adding the example to the EXAMPLES section.

End of informative text.