Reverse factorial

Question

Well, we all know that if N is given it\'s easy to calculate N!. But what about the inverse?

N! is given and you are about to find N - Is that possible ? I\'m curio

Answer 1

In C from my app Advanced Trigonometry Calculator v1.6.8

    double arcfact(double f) {
        double i=1,result=f;
        while((result/(i+1))>=1) {
            result=result/i;
            i++;
        }
        return result;
    }

What you think about that? Works correctly for factorials integers.