IEEE Std 1003.1-2008, 2016 Edition

Copyright © 2001-2016 The IEEE and The Open Group

fabs, fabsf, fabsl - absolute value function

#include <math.h>

double fabs(doublex);

float fabsf(floatx);

long double fabsl(long doublex);

^{[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|.

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

x.

^{[MX]}Ifxis NaN, a NaN shall be returned.If

xis ±0, +0 shall be returned.If

xis ±Inf, +Inf shall be returned.

No errors are defined.

## 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[0]| + |v[1]| + ... + |v[n-1]|where |

x| denotes the absolute value ofx,ndenotes the vector's dimensionv[i] denotes thei-th component ofv(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.

XBD

<math.h>

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

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

The

fabsf() andfabsl() 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.

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