Legacy Document

copysign

You can use the copysign function to assign to some real number the sign of a second value.

double_t copysign (double_t x, double_t y);
long double copysignl (long double x, long double y);

x

Any floating-point number.

y

Any floating-point number.

DESCRIPTION

The copysign function copies the sign of the y parameter into the x parameter and returns the resulting number.

copysign(x, 1.0) is always the absolute value of x. The copysign function simply manipulates sign bits and hence raises no exception flags.

EXCEPTIONS

When x and y are finite and nonzero, the result of $copysign(x,y)$ is exact.

SPECIAL CASES

Table 10-5 shows the results when one of the arguments to the copysign function is a zero, a NaN, or an Infinity. In this table, x and y are finite, nonzero floating-point numbers.

Special cases for the copysign function

Operation	Result	Exceptions raised
$copysign(+0,y)$	0 with sign of y	None
$copysign(x,+0)$	|x|	None
$copysign(-0,y)$	0 with sign of y	None
$copysign(x,-0)$	-|x|	None
$copysign(NaN,y)$	NaN with sign of y	None[26]
$copysign(x,NaN)$	x with sign of NaN	None[26]
$copysign(+$ ,y)	with sign of y	None
$copysign(x,+$ )	|x|	None
$copysign(-$ ,y)	with sign of y	None
$copysign(x,-$ )	-|x|	None

EXAMPLES

z = copysign(-1234.567, 1.0);/* z = 1234.567 */
z = copysign(1.0, -1234.567);/* z = -1.0 */

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