Closed form cubic root finder implementation

I'm looking for a non-iterative function that finds the real roots开发者_开发百科 of cubic polynomials. So, an implementation of something like this. I could write it myself of course, but if someone already has an implementation and doesn't mind sharing it, that would save me the 1-2 hours I would need to write it, at the cost of that person taking 30 seconds to paste it here, so that would be great.

Thank you.