fabs()

SYNOPSIS
#include <math.h>

   double fabs(double x);
   float fabsf(float x);
   long double fabsl(long double x);

   Link with -lm.

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

   fabsf(), fabsl():
       _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 ||
       _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
       or cc -std=c99

DESCRIPTION
The fabs() functions return the absolute value of the floating-point
number x.

RETURN VALUE
These functions return the absolute value of x.

   If x is a NaN, a NaN is returned.

   If x is -0, +0 is returned.

   If  x  is  negative infinity or positive infinity, positive infinity is
   returned.