fabs (original) (raw)

The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition
Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.

A newer edition of this document exists here

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] [Option Start] 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 IEEE Std 1003.1-2001 defers to the ISO C standard. [Option End]

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] [Option Start] 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. [Option End]

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[0]| + |v[1]| + ... + |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; }

APPLICATION USAGE

None.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

isnan(), the Base Definitions volume of IEEE Std 1003.1-2001, <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.

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