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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
The copysign(), copysignf(), and copysignl() functions return a value
whose absolute value matches that of x, but whose sign bit matches that
For example, copysign(42.0, -1.0) and copysign(-42.0, -1.0) both return
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.
No errors occur.
Multithreading (see pthreads(7))
The copysign(), copysignf(), and copysignl() functions are thread-safe.
C99, POSIX.1-2001. This function is defined in IEC 559 (and the
appendix with recommended functions in IEEE 754/IEEE 854).
On architectures where the floating-point formats are not IEEE 754 com-
pliant, these functions may treat a negative zero as positive.
GNU 2013-10-14 COPYSIGN(3)