copysign (3)
Leading comments
Copyright 1993 David Metcalfe (david@prism.demon.co.uk) %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Sin...
NAME
copysign, copysignf, copysignl  copy sign of a numberSYNOPSIS
#include <math.h> double copysign(double x, double y);
float copysignf(float x, float y);
long double copysignl(long double x, long double y);
Link with lm.
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
copysign(), copysignf(), copysignl():

_SVID_SOURCE  _BSD_SOURCE  _XOPEN_SOURCE >= 600  _ISOC99_SOURCE 
_POSIX_C_SOURCE >= 200112L;
or cc std=c99
DESCRIPTION
These functions return a value whose absolute value matches that of x, but whose sign bit matches that of y.For example, copysign(42.0, 1.0) and copysign(42.0, 1.0) both return 42.0.
RETURN VALUE
On success, these functions return a value whose magnitude is taken from x and whose sign is taken from y.If x is a NaN, a NaN with the sign bit of y is returned.
ERRORS
No errors occur.ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).Interface  Attribute  Value 
copysign(), copysignf(), copysignl()  Thread safety  MTSafe 