JavaScript lagged Fibonacci pseudo-random number generator

fibgen.js

var primes = [
    2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,
    73,79,83,89,97,101,103,107,109,113,127,131,137,139,149,151,157,163,167,173,
    179,181,191,193,197,199,211,223,227,229,233,239,241,251,257,263,269,271,277,281,
    283,293,307,311,313,317,331,337,347,349,353,359,367,373,379,383,389,397,401,409,
    419,421,431,433,439,443,449,457,461,463,467,479,487,491,499,503,509,521,523,541,
    547,557,563,569,571,577,587,593,599,601,607,613,617,619,631,641,643,647,653,659,
    661,673,677,683,691,701,709,719,727,733,739,743,751,757,761,769,773,787,797,809,
    811,821,823,827,829,839,853,857,859,863,877,881,883,887,907,911,919,929,937,941,
    947,953,967,971,977,983,991,997,1009,1013,1019,1021,1031,1033,1039,1049,1051,1061,1063,1069,
    1087,1091,1093,1097,1103,1109,1117,1123,1129,1151,1153,1163,1171,1181,1187,1193,1201,1213,1217,1223,
    1229,1231,1237,1249,1259,1277,1279,1283,1289,1291,1297,1301,1303,1307,1319,1321,1327,1361,1367,1373,
    1381,1399,1409,1423,1427,1429,1433,1439,1447,1451,1453,1459,1471,1481,1483,1487,1489,1493,1499,1511,
    1523,1531,1543,1549,1553,1559,1567,1571,1579,1583,1597,1601,1607,1609,1613,1619,1621,1627,1637,1657,
    1663,1667,1669,1693,1697,1699,1709,1721,1723,1733,1741,1747,1753,1759,1777,1783,1787,1789,1801,1811,
    1823,1831,1847,1861,1867,1871,1873,1877,1879,1889,1901,1907,1913,1931,1933,1949,1951,1973,1979,1987,
    1993,1997,1999,2003,2011,2017,2027,2029,2039,2053,2063,2069,2081,2083,2087,2089,2099,2111,2113,2129,
    2131,2137,2141,2143,2153,2161,2179,2203,2207,2213,2221,2237,2239,2243,2251,2267,2269,2273,2281,2287,
    2293,2297,2309,2311,2333,2339,2341,2347,2351,2357,2371,2377,2381,2383,2389,2393,2399,2411,2417,2423,
    2437,2441,2447,2459,2467,2473,2477,2503,2521,2531,2539,2543,2549,2551,2557,2579,2591,2593,2609,2617,
    2621,2633,2647,2657,2659,2663,2671,2677,2683,2687,2689,2693,2699,2707,2711,2713,2719,2729,2731,2741,
    2749,2753,2767,2777,2789,2791,2797,2801,2803,2819,2833,2837,2843,2851,2857,2861,2879,2887,2897,2903,
    2909,2917,2927,2939,2953,2957,2963,2969,2971,2999,3001,3011,3019,3023,3037,3041,3049,3061,3067,3079,
    3083,3089,3109,3119,3121,3137,3163,3167,3169,3181,3187,3191,3203,3209,3217,3221,3229,3251,3253,3257,
    3259,3271,3299,3301,3307,3313,3319,3323,3329,3331,3343,3347,3359,3361,3371,3373,3389,3391,3407,3413,
    3433,3449,3457,3461,3463,3467,3469,3491,3499,3511,3517,3527,3529,3533,3539,3541,3547,3557,3559,3571,
    3581,3583,3593,3607,3613,3617,3623,3631,3637,3643,3659,3671
];



var FIBGEN_BITS = 31;
var FIBGEN_MASK = (((1<<FIBGEN_BITS )-1)&0x7fffffff);

function FibGen(seed) {
    //Lagged Fibonacci generator
    var ki = ((seed & 15) + 3);
    this.k = primes[ki];
    this.j = primes[(ki * 2 / 3)|0];
    this.buffer = FIBGEN_BITS  > 16 ? new Uint32Array(this.k) : FIBGEN_BITS  > 8 ? new Uint16Array(this.k) : new Uint8Array(this.k);
    this.i = 0;
    this.buffer[0] = (seed >>> 4) & FIBGEN_MASK;
    this.buffer[1] = primes[(seed >>> 20) & 0x1ff];

    //Discard initial values to seed it
    ki = this.j * this.k;
    do { this.next(); } while (ki-- !== 0);
}

FibGen.prototype.next = function() {
    var n = (this.buffer[this.i] + this.buffer[this.j]) & FIBGEN_MASK;
//      ki <= 0 && console.log("gen from "+i+" & "+j+" -> "+buffer[i]+"+"+buffer[j]+" -> "+n);
    this.buffer[this.i] = n;
    if (this.i === 0) this.i = this.k - 1; else this.i--;
    if (this.j === 0) this.j = this.k - 1; else this.j--;
    return n;
};

FibGen.prototype.nextUpTo = function (limit) {
    var max = 256;
    var val = this.next() & 0xff;
    while ( max < limit ) {
        val = (val * 256) + (this.next() & 0xff);
        max *= 256;
    }
    return (val * limit / max)|0;
};

FibGen.prototype.randomElement = function (array) {
    return array && array.length > 0 ? array[this.nextUpTo(array.length)] : null;
};

FibGen.prototype.shuffle = function(arr) {
    for (var i = arr.length - 1; i > 1; i--) {
        var j = this.nextUpTo(i + 1);
        if (j !== i) {
            var p = arr[i];
            arr[i] = arr[j];
            arr[j] = p;
        }
    }
};

FibGen.prototype.weightedIndex = function(weights, length) {
   
    var i;
   
    if (typeof length === 'undefined') {
        length = weights.length;
    }
   
    //Calculate delivery weightings
    var totalWeight = 0;
    for (i = 0; i < length; i++) {
        totalWeight += weights[i];
    }

    var offset = this.nextUpTo(totalWeight);
//  console.log("weightedIndex: ",weights, "offset:",offset,"/",totalWeight);
    for (i = 0; i < length; i++) {
        offset -= weights[i];
        if (offset < 0) {
            return i;
        }
    }
};