code: function checksum(str) {
      crcTbl = crcTbl || makeCRCTable();
  
      /* jslint bitwise: true */
      var crc = 0 ^ (-1);
  
      for (var i = 0; i < str.length; i++) {
          crc = (crc >>> 8) ^ crcTbl[(crc ^ str.charCodeAt(i)) & 0xFF];
      }
  
      return (crc ^ (-1)) >>> 0;
  }
docs: Generate a checkum for a string
  @param str
  @returns {number}