64-bit random numbers in Node

Program

var bignum = require('bignum');
var crypto = require('crypto');

var randomBignum = function() { return bignum.fromBuffer(crypto.pseudoRandomBytes(8)); }

var avg = randomBignum();
var avg_len = avg.bitLength();
var lengths = {};

for (var i = 0; i < 1e6; i++) {
    var big = randomBignum();
    avg = avg.add(big).div(2);
    var length = big.bitLength();
    if (typeof lengths[length] === 'undefined') { lengths[length] = 0; }
    lengths[length] += 1;
    avg_len = (avg_len + length) / 2;
}
console.log('avg %s', avg);
console.log('avg len %s', avg_len);
console.info('lens %s', require('util').inspect(lengths));

Result1

dmitry@airosol /private/tmp $ time node big.js 
avg 8386866841744540769
avg len 63.11672078688376
lens { '45': 1,
  '47': 2,
  '48': 7,
  '49': 15,
  '50': 23,
  '51': 66,
  '52': 114,
  '53': 248,
  '54': 521,
  '55': 955,
  '56': 1905,
  '57': 4019,
  '58': 7742,
  '59': 15552,
  '60': 31396,
  '61': 63048,
  '62': 125182,
  '63': 249271,
  '64': 499933 }

real    0m50.670s
user    0m48.681s
sys     0m0.690s

Result2

dmitry@airosol /private/tmp $ time node big.js 
avg 12648992876624866288
avg len 63.93897900578206
lens { '44': 2,
  '46': 1,
  '47': 3,
  '48': 12,
  '49': 10,
  '50': 40,
  '51': 56,
  '52': 127,
  '53': 245,
  '54': 503,
  '55': 931,
  '56': 1928,
  '57': 3817,
  '58': 7845,
  '59': 15665,
  '60': 31260,
  '61': 62168,
  '62': 125822,
  '63': 250385,
  '64': 499180 }

real    0m51.208s
user    0m49.258s
sys     0m0.698s

Result3

dmitry@airosol /private/tmp $ time node big.js 
avg 11604449224001379105
avg len 63.694875686108915
lens { '43': 1,
  '44': 1,
  '45': 1,
  '46': 1,
  '47': 5,
  '48': 5,
  '49': 14,
  '50': 25,
  '51': 69,
  '52': 116,
  '53': 242,
  '54': 478,
  '55': 938,
  '56': 1992,
  '57': 4013,
  '58': 7845,
  '59': 15558,
  '60': 31338,
  '61': 62557,
  '62': 125616,
  '63': 250079,
  '64': 499106 }

real    0m50.762s
user    0m48.705s
sys     0m0.716s