contract StandardToken is ERC20 {

  using SafeMath for uint;

  /* Actual balances of token holders */
  mapping (address => uint) balances;

  /* approve() allowances */
  mapping (address => mapping (address => uint)) allowed;

  /* Interface declaration */
  function isToken() public constant returns (bool) {
    return true;
  }

  /**
   *
   * Fix for the ERC20 short address attack
   *
   * http://vessenes.com/the-erc20-short-address-attack-explained/
   */
  modifier onlyPayloadSize(uint size) {
    assert(msg.data.length >= size + 4);
    _;
  }

  /**
  * @dev transfer token for a specified address
  * @param _to The address to transfer to.
  * @param _value The amount to be transferred.
  */
  function transfer(address _to, uint _value) onlyPayloadSize(2 * 32) returns (bool) {
    require(balances[msg.sender] >= _value);
    balances[msg.sender] = balances[msg.sender].sub(_value);
    balances[_to] = balances[_to].add(_value);
    Transfer(msg.sender, _to, _value);
    return true;
  }

  /**
   * @dev Transfer tokens from one address to another
   * @param _from address The address which you want to send tokens from
   * @param _to address The address which you want to transfer to
   * @param _value uint256 the amount of tokens to be transferred
   */
  function transferFrom(address _from, address _to, uint _value) onlyPayloadSize(2 * 32) returns (bool) {
    require(balances[_from] >= _value && allowed[_from][_to] >= _value);
    allowed[_from][_to] = allowed[_from][_to].sub(_value);
    balances[_from] = balances[_from].sub(_value);
    balances[_to] = balances[_to].add(_value);
    Transfer(_from, _to, _value);
    return true;
  }

  /**
  * @dev Gets the balance of the specified address.
  * @param _owner The address to query the the balance of. 
  * @return An uint256 representing the amount owned by the passed address.
  */
  function balanceOf(address _owner) constant returns (uint balance) {
    return balances[_owner];
  }
  
  /**
   * @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender.
   * @param _spender The address which will spend the funds.
   * @param _value The amount of tokens to be spent.
   */
  function approve(address _spender, uint _value) returns (bool success) {
    // To change the approve amount you first have to reduce the addresses`
    //  allowance to zero by calling `approve(_spender, 0)` if it is not
    //  already 0 to mitigate the race condition described here:
    //  https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
    require((_value == 0) || (allowed[msg.sender][_spender] == 0));

    allowed[msg.sender][_spender] = _value;
    Approval(msg.sender, _spender, _value);
    return true;
  }

  /**
   * @dev Function to check the amount of tokens that an owner allowed to a spender.
   * @param _owner address The address which owns the funds.
   * @param _spender address The address which will spend the funds.
   * @return A uint256 specifying the amount of tokens still available for the spender.
   */
  function allowance(address _owner, address _spender) constant returns (uint remaining) {
    return allowed[_owner][_spender];
  }

}
/**
 * Standard ERC20 token with Short Hand Attack and approve() race condition mitigation.
 *
 * Based on code by FirstBlood:
 * https://github.com/Firstbloodio/token/blob/master/smart_contract/FirstBloodToken.sol
 */
function balanceOf(address _owner) constant returns (uint balance) {
  return balances[_owner];
}

/**
 * @dev Gets the balance of the specified address.
 * @param _owner The address to query the the balance of. 
 * @return An uint256 representing the amount owned by the passed address.
 */