code: function(paramString, urls) {
          var product = 1;
          for (var i=0, len=paramString.length; i<len; i++) { 
              product *= paramString.charCodeAt(i) * this.URL_HASH_FACTOR; 
              product -= Math.floor(product); 
          }
          return urls[Math.floor(product * urls.length)];
      }
docs: Method: selectUrl
  selectUrl() implements the standard floating-point multiplicative
  hash function described by Knuth, and hashes the contents of the
  given param string into a float between 0 and 1. This float is then
  scaled to the size of the provided urls array, and used to select
  a URL.
  
  Parameters:
  paramString - {String}
  urls - {Array(String)}
  
  Returns:
  {String} An entry from the urls array, deterministically selected based
  on the paramString.