Simple Linear Congruential Generator in Javascript

lcg.js

// A simple Linear Congruential Generator

// Establish the parameters of the generator
var m = 25,
    // a - 1 should be divisible by m's prime factors
    a = 11,
    // c and m should be co-prime
    c = 17;
// Setting the seed
var z = 3;
var rand = function() {
  // define the recurrence relationship
  z = (a * z + c) % m;
  // return an integer 
  // Could return a float in (0, 1) by dividing by m
  return z;
};

You could include range specifications. :)

Thanks!

I modified and encapsulated the script a bit. If someone needs a predictable seedable rng, you can use this

function createRand(seed) {
  var m = 25;
  var a = 11;
  var c = 17;

  var z = seed || 3;
  return function() {
    z = (a * z + c) % m;
    return z/m;
  };
}

Usage:

var rand = createRand();
var a = rand() * 100;

With the given parameters, it seems that dividing by m = 25 ensures you'll only ever see values of the form i / 25, where i is in [0, 24]...

Much larger primes are needed in general. See here for some suggestions.