Random float using coordinate as seed

The Mathf.PerlinNoise(float x, float y) function returns a float that I use. I want a more completely random function that can use coordinates as it's seed.

My ideal would have the exact same input and output as the aforementioned Mathf.PerlinNoise function, . The point is that it can be switched out with the Perlin Noise function to return completely random floats that return the same float for any given coordinate each and every time.