float fmodf(float x,
            float y);

fmodf computes the floating-point remainder of x divided by y. fmodf returns the value xn y, for some integer n such that, if y is nonzero, the result has the same sign as x and magnitude less than the magnitude of y.

fmodf (NaN, y) is NaN. fmodf (x, NaN) is NaN. fmodf (± 0, y) is ± 0 for y not zero.
fmodf (∞, y) is NaN.
fmodf (x, 0) is NaN.
fmodf (x, ± ∞) is x for x not infinite.