function transfer(address _to, uint256 _value) onlyPayloadSize(2 * 32) whenNotPaused external returns (bool success) {
         require(_to != address(0));
         require(_value <= balances[msg.sender]);

         balances[msg.sender] = balances[msg.sender].sub(_value);
         balances[_to] = balances[_to].add(_value);
         emit Transfer(msg.sender, _to, _value);
         return true;
    }