Fast inverse square root.js

// http://en.wikipedia.org/wiki/Fast_inverse_square_root
/*
  Discovering old well known algorithm speed in js.
*/

var _invSqrtL = (function()
{
  var u32Array = new Uint32Array(1), f32Array = new Float32Array(u32Array.buffer);
  
  return function(x)
  {
    f32Array[0] = x;
    u32Array[0] = 0x5f3759df - (u32Array[0] >> 1);
    
    var y = f32Array[0];
    
    return y * (1.5 - 0.5 * x * y * y);
  };
})();


_speedTest(
  [
    function(n)
    {
      // _invSqrtL inlined manualy
      var u32Array = new Uint32Array(1), f32Array = new Float32Array(u32Array.buffer);
      var s = 0;
  
      var i = n; while(i--)
      {
        f32Array[0] = i;
        u32Array[0] = 0x5f3759df - (u32Array[0] >> 1);
        
        var y = f32Array[0];
        
        s += y * (1.5 - 0.5 * i * y * y);
      }
    },
    function(n)
    {
      var _sqrt = Math.sqrt; // caching for best speed
      var s = 0;
      var i = n; while(i--)
      {
        s += 1/_sqrt(i);
      }
    }
  ],
  10000
);  

/*
  chrome8
    0: 820 ms
    1: 411 ms
  
  ff4
    0: 132 ms
    1: 284 ms
*/

/*
  Yes it faster in js too, but only in one browser and requires special api.
  Anyway nice.
*/