https://docs.oracle.com/cd/E88353_01/html/E37846/copysignf-3m.html
copysignf - man pages section 3: Extended Library Functions, Volume 2
copysign , copysignf , copysignl - number manipulation function These functions produce a value with the magnitude of x and the sign of y .
man pagesextended librarysectionfunctionsvolume