double fmod(double x, double y);

**fmod** computes the floating-point remainder of **x**
divided by **y**. #b #this returns the value **x** − *n* **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**.

**fmod** (NaN, *y*) is NaN.
**fmod** (*x*, NaN) is NaN.
**fmod** (± 0, **y**) is ± 0 for **y** not zero.

**fmod** (∞, **y**) is NaN.

**fmod** (**x**, 0) is NaN.

**fmod** (x, ± ∞) is **x** for **x** not infinite.