source: Dev/trunk/src/client/dojox/math/random/prng4.js

// AMD-ID "dojox/math/random/prng4"
define(["dojo", "dojox"], function(dojo, dojox) {
        
        dojo.getObject("math.random.prng4", true, dojox);

// Copyright (c) 2005  Tom Wu
// All Rights Reserved.
// See "LICENSE-BigInteger" for details.

        // prng4.js - uses Arcfour as a PRNG

        function Arcfour() {
                this.i = 0;
                this.j = 0;
                this.S = new Array(256);
        }

        dojo.extend(Arcfour, {
                init: function(key){
                        // summary:
                        //              Initialize arcfour context
                        // key: int[]
                        //              an array of ints, each from [0..255]
                        var i, j, t, S = this.S, len = key.length;
                        for(i = 0; i < 256; ++i){
                                S[i] = i;
                        }
                        j = 0;
                        for(i = 0; i < 256; ++i){
                                j = (j + S[i] + key[i % len]) & 255;
                                t = S[i];
                                S[i] = S[j];
                                S[j] = t;
                        }
                        this.i = 0;
                        this.j = 0;
                },

                next: function(){
                        var t, i, j, S = this.S;
                        this.i = i = (this.i + 1) & 255;
                        this.j = j = (this.j + S[i]) & 255;
                        t = S[i];
                        S[i] = S[j];
                        S[j] = t;
                        return S[(t + S[i]) & 255];
                }
        });

        dojox.math.random.prng4 = function(){
                return new Arcfour();
        };

        // Pool size must be a multiple of 4 and greater than 32.
        // An array of bytes the size of the pool will be passed to init()
        dojox.math.random.prng4.size = 256;
        
        return dojox.math.random.prng4;
});