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### 1.12 `copysign`, `copysignf`—sign of y, magnitude of x

Synopsis

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

Description
`copysign` constructs a number with the magnitude (absolute value) of its first argument, x, and the sign of its second argument, y.

`copysignf` does the same thing; the two functions differ only in the type of their arguments and result.

Returns
`copysign` returns a `double` with the magnitude of x and the sign of y. `copysignf` returns a `float` with the magnitude of x and the sign of y.

Portability
`copysign` is not required by either ANSI C or the System V Interface Definition (Issue 2).