The IEEE754 remainder function even beats C in that it can return a negative value even if both inputs are positive. IIRC the logic that leads to this is:

    remainder(a, b)
    n = round(a/b)
    return a - n * b

Because it rounds to get n, n * b can be greater than a :D

Even more fun as the original x87 implementation preceded IEEE754 its remainder operation (fprem, because it's technically a partial remainder) used truncation rather than rounding as that's the obvious behaviour. To support the IEEE754 specification they had to add fprem1 which performs a rounding operation instead. Hurrah! :D