Javascript repeatable random number based on multiple inputs

I am trying to create a function that takes 4 parameters and spits out a random number. But I want it so if the same 4 parameters are input, you will always get the same answer. The number should be between 0 and the max argument.

function random (x,y,z,max) {
    output = ;
    return Math.floor(output * max); 
}

Is there any simple forumala I can use to get this? I tried to create one but it didn't look random at all, and would look very similar if you changed one parameter very slightly. I want it to be completely different, but repeatable.

hash function:

function hash (input){
    input = 'random'+input;
    var hash = 0;
    if (input.length == 0) return hash;
    for (i = 0; i < input.length; i++) {
        char = input.charCodeAt(i);
        hash = ((hash<<5)-hash)+char;
        hash = hash & hash; // Convert to 32bit integer
    }
    return Math.abs(hash);
}