copysign

copysign, copysignf, copysignl - copy sign of a number

#include <math.h>
 I double copysign(double  x , double  y );

I float copysignf(float  x , float  y );

I long double copysignl(long double  x , long double  y );

Link with -lm.

The R copysign () functions return a value whose absolute value matches that of x, but whose sign matches that of y. If x is a NaN, then a NaN with the sign of y is returned.

C99, 4.3BSD. 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 compliant, the R copysign () functions may treat a negative zero as positive.

signbit(3)