Legacy Document

fabs

You can use the fabs function to determine the absolute value of a real number.

double_t fabs (double_t x);
long double fabsl (long double x);

x

Any floating-point number.

DESCRIPTION

The fabs function returns the absolute value (positive value) of its argument.

$fabs(x)\; =\; |x|$

This function looks only at the sign bit, not the value, of its argument.

EXCEPTIONS

When x is finite and nonzero, the result of $fabs(x)$ is exact.

SPECIAL CASES

Table 10-6 shows the results when the argument to the fabs function is a zero, a NaN, or an Infinity.

Special cases for the fabs function

Operation	Result	Exceptions raised
$fabs(+0)$	+0	None
$fabs(-0)$	+0	None
$fabs(NaN)$	NaN	None[27]
$fabs(+$ )	+	None
$fabs(-$ )	+	None

EXAMPLES

z = fabs(-1.0);   /* z = 1 */
z = fabs(245.0);  /* z = 245 */

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[27] If the NaN is a signaling NaN, the invalid exception is raised.