good randomness

good_randomness.js

// small script i wrote to get strong randomness in node
// putting it here so i dont lose it

// copyright (c) 2011, christopher jeffrey, mit license, etc.

// example output:
// urandom: 0.17843490773309834
// Math.random: 0.7067500613629818
// random: 0.3154916005012327

var fs = require('fs');

var random = function(func) {
  fs.open('/dev/random', 'r', function(err, fd) {
    if (err) return func(err);

    var buff = new Buffer(4);

    fs.read(fd, buff, 0, 4, 0, function(err, bytes) {
      if (err || !bytes) {
        return done(err || new Error('Fail.'));
      }

      var num = buff[0];
      num = (num << 8) | buff[1];
      num = (num << 8) | buff[2];
      num = (num << 8) | buff[3];

      done(null, num / 0xFFFFFFFF);
    });

    function done(err, result) {
      fs.close(fd, function() {
        func(err, result);
      });
    }
  });
};

random(function(err, num) {
  if (err) throw err;
  console.log('random: %d', num);
});

var urandom = function() {
  var fd = fs.openSync('/dev/urandom', 'r')
    , buff
    , num;

  try {
    buff = new Buffer(4);
    fs.readSync(fd, buff, 0, 4, 0);
    num = buff[0];
    num = (num << 8) | buff[1];
    num = (num << 8) | buff[2];
    num = (num << 8) | buff[3];
  } catch(e) {
    fs.closeSync(fd);
    throw e;
  }

  fs.closeSync(fd);

  return num / 0xFFFFFFFF;
};

console.log('urandom: %d', urandom());

// seed a deterministic RNG
// v8.googlecode.com/svn/data/benchmarks/v6/run.html
Math.random = (function() {
  var seed = urandom(); //49734321;
  return function() {
    // Robert Jenkins' 32 bit integer hash function.
    seed = ((seed + 0x7ed55d16) + (seed << 12))  & 0xffffffff;
    seed = ((seed ^ 0xc761c23c) ^ (seed >>> 19)) & 0xffffffff;
    seed = ((seed + 0x165667b1) + (seed << 5))   & 0xffffffff;
    seed = ((seed + 0xd3a2646c) ^ (seed << 9))   & 0xffffffff;
    seed = ((seed + 0xfd7046c5) + (seed << 3))   & 0xffffffff;
    seed = ((seed ^ 0xb55a4f09) ^ (seed >>> 16)) & 0xffffffff;
    return (seed & 0xfffffff) / 0x10000000;
  };
})();

console.log('Math.random: %d', Math.random());