contract UnlimitedAllowanceToken is ERC827Token {

    uint internal constant MAX_UINT = 2**256 - 1;
    
    /// @dev ERC20 transferFrom, modified such that an allowance of MAX_UINT represents an unlimited allowance.
    /// @param _from Address to transfer from.
    /// @param _to Address to transfer to.
    /// @param _value Amount to transfer.
    /// @return Success of transfer.
    function transferFrom(address _from, address _to, uint _value)
        public
        returns (bool)
    {
        uint allowance = allowed[_from][msg.sender];
        if (balances[_from] >= _value
            && allowance >= _value
            && balances[_to] + _value >= balances[_to]
        ) {
            balances[_to] += _value;
            balances[_from] -= _value;
            if (allowance < MAX_UINT) {
                allowed[_from][msg.sender] -= _value;
            }
            emit Transfer(_from, _to, _value);
            return true;
        } else {
            return false;
        }
    }
}
function transferFrom(address _from, address _to, uint _value)
    public
    returns (bool)
{
    uint allowance = allowed[_from][msg.sender];
    if (balances[_from] >= _value
        && allowance >= _value
        && balances[_to] + _value >= balances[_to]
    ) {
        balances[_to] += _value;
        balances[_from] -= _value;
        if (allowance < MAX_UINT) {
            allowed[_from][msg.sender] -= _value;
        }
        emit Transfer(_from, _to, _value);
        return true;
    } else {
        return false;
    }
}

/// @dev ERC20 transferFrom, modified such that an allowance of MAX_UINT represents an unlimited allowance.
/// @param _from Address to transfer from.
/// @param _to Address to transfer to.
/// @param _value Amount to transfer.
/// @return Success of transfer.