determinize.js

/**
 * All code is in an anonymous closure to keep the global namespace clean.
 */
(function (
    global, pool, math, width, chunks, digits, module, define, rngname) {

//
// The following constants are related to IEEE 754 limits.
//
var startdenom = math.pow(width, chunks),
    significance = math.pow(2, digits),
    overflow = significance * 2,
    mask = width - 1,

//
// seedrandom()
// This is the seedrandom function described above.
//
impl = math['seed' + rngname] = function(seed, use_entropy, callback) {
  var key = [];

  // Flatten the seed string or build one from local entropy if needed.
  var shortseed = mixkey(flatten(
    use_entropy ? [seed, tostring(pool)] :
    (seed == null) ? autoseed() : seed, 3), key);

  // Use the seed to initialize an ARC4 generator.
  var arc4 = new ARC4(key);

  // Mix the randomness into accumulated entropy.
  mixkey(tostring(arc4.S), pool);

  // Calling convention: what to return as a function of prng, seed, is_math.
  return (callback ||
      // If called as a method of Math (Math.seedrandom()), mutate Math.random
      // because that is how seedrandom.js has worked since v1.0.  Otherwise,
      // it is a newer calling convention, so return the prng directly.
      function(prng, seed, is_math_call) {
        if (is_math_call) { math[rngname] = prng; return seed; }
        else return prng;
      })(

  // This function returns a random double in [0, 1) that contains
  // randomness in every bit of the mantissa of the IEEE 754 value.
  function() {
    var n = arc4.g(chunks),             // Start with a numerator n < 2 ^ 48
        d = startdenom,                 //   and denominator d = 2 ^ 48.
        x = 0;                          //   and no 'extra last byte'.
    while (n < significance) {          // Fill up all significant digits by
      n = (n + x) * width;              //   shifting numerator and
      d *= width;                       //   denominator and generating a
      x = arc4.g(1);                    //   new least-significant-byte.
    }
    while (n >= overflow) {             // To avoid rounding up, before adding
      n /= 2;                           //   last byte, shift everything
      d /= 2;                           //   right using integer math until
      x >>>= 1;                         //   we have exactly the desired bits.
    }
    return (n + x) / d;                 // Form the number within [0, 1).
  }, shortseed, this == math);
};

//
// ARC4
//
// An ARC4 implementation.  The constructor takes a key in the form of
// an array of at most (width) integers that should be 0 <= x < (width).
//
// The g(count) method returns a pseudorandom integer that concatenates
// the next (count) outputs from ARC4.  Its return value is a number x
// that is in the range 0 <= x < (width ^ count).
//
/** @constructor */
function ARC4(key) {
  var t, keylen = key.length,
      me = this, i = 0, j = me.i = me.j = 0, s = me.S = [];

  // The empty key [] is treated as [0].
  if (!keylen) { key = [keylen++]; }

  // Set up S using the standard key scheduling algorithm.
  while (i < width) {
    s[i] = i++;
  }
  for (i = 0; i < width; i++) {
    s[i] = s[j = mask & (j + key[i % keylen] + (t = s[i]))];
    s[j] = t;
  }

  // The "g" method returns the next (count) outputs as one number.
  (me.g = function(count) {
    // Using instance members instead of closure state nearly doubles speed.
    var t, r = 0,
        i = me.i, j = me.j, s = me.S;
    while (count--) {
      t = s[i = mask & (i + 1)];
      r = r * width + s[mask & ((s[i] = s[j = mask & (j + t)]) + (s[j] = t))];
    }
    me.i = i; me.j = j;
    return r;
    // For robust unpredictability discard an initial batch of values.
    // See http://www.rsa.com/rsalabs/node.asp?id=2009
  })(width);
}

//
// flatten()
// Converts an object tree to nested arrays of strings.
//
function flatten(obj, depth) {
  var result = [], typ = (typeof obj), prop;
  if (depth && typ == 'object') {
    for (prop in obj) {
      try { result.push(flatten(obj[prop], depth - 1)); } catch (e) {}
    }
  }
  return (result.length ? result : typ == 'string' ? obj : obj + '\0');
}

//
// mixkey()
// Mixes a string seed into a key that is an array of integers, and
// returns a shortened string seed that is equivalent to the result key.
//
function mixkey(seed, key) {
  var stringseed = seed + '', smear, j = 0;
  while (j < stringseed.length) {
    key[mask & j] =
      mask & ((smear ^= key[mask & j] * 19) + stringseed.charCodeAt(j++));
  }
  return tostring(key);
}

//
// autoseed()
// Returns an object for autoseeding, using window.crypto if available.
//
/** @param {Uint8Array|Navigator=} seed */
function autoseed(seed) {
  try {
    global.crypto.getRandomValues(seed = new Uint8Array(width));
    return tostring(seed);
  } catch (e) {
    return [+new Date, global, (seed = global.navigator) && seed.plugins,
            global.screen, tostring(pool)];
  }
}

//
// tostring()
// Converts an array of charcodes to a string
//
function tostring(a) {
  return String.fromCharCode.apply(0, a);
}

//
// When seedrandom.js is loaded, we immediately mix a few bits
// from the built-in RNG into the entropy pool.  Because we do
// not want to intefere with determinstic PRNG state later,
// seedrandom will not call math.random on its own again after
// initialization.
//
mixkey(math[rngname](), pool);

//
// Nodejs and AMD support: export the implemenation as a module using
// either convention.
//
if (module && module.exports) {
  module.exports = impl;
} else if (define && define.amd) {
  define(function() { return impl; });
}

// End anonymous scope, and pass initial values.
})(
  this,   // global window object
  [],     // pool: entropy pool starts empty
  Math,   // math: package containing random, pow, and seedrandom
  256,    // width: each RC4 output is 0 <= x < 256
  6,      // chunks: at least six RC4 outputs for each double
  52,     // digits: there are 52 significant digits in a double
  (typeof module) == 'object' && module,    // present in node.js
  (typeof define) == 'function' && define,  // present with an AMD loader
  'random'// rngname: name for Math.random and Math.seedrandom
);
		   
function determinize(millis){

    var OrigDate = Date;
    Date = function(){return new OrigDate(millis);};
    
    Math.seedrandom(millis);

    window.performance = {};
 }