contract Utils {

    uint256 constant MAX_SAFE_UINT256 = 2**256 - 1;

    /// @notice Check if a contract exists
    /// @param contract_address The address to check whether a contract is
    /// deployed or not
    /// @return True if a contract exists, false otherwise
    function contractExists(address contract_address) public view returns (bool) {
        uint size;

        assembly { // solium-disable-line security/no-inline-assembly
            size := extcodesize(contract_address)
        }

        return size > 0;
    }

    string public constant signature_prefix = "\x19Ethereum Signed Message:\n";

    function min(uint256 a, uint256 b) public pure returns (uint256)
    {
        return a > b ? b : a;
    }

    function max(uint256 a, uint256 b) public pure returns (uint256)
    {
        return a > b ? a : b;
    }

    /// @dev Special subtraction function that does not fail when underflowing.
    /// @param a Minuend
    /// @param b Subtrahend
    /// @return Minimum between the result of the subtraction and 0, the maximum
    /// subtrahend for which no underflow occurs
    function failsafe_subtract(uint256 a, uint256 b)
        public
        pure
        returns (uint256, uint256)
    {
        unchecked {
            return a > b ? (a - b, b) : (0, a);
        }
    }

    /// @dev Special addition function that does not fail when overflowing.
    /// @param a Addend
    /// @param b Addend
    /// @return Maximum between the result of the addition or the maximum
    /// uint256 value
    function failsafe_addition(uint256 a, uint256 b)
        public
        pure
        returns (uint256)
    {
        unchecked {
            uint256 sum = a + b;
            return sum >= a ? sum : MAX_SAFE_UINT256;
        }
    }
}
/// @title Utils
/// @notice Utils contract for various helpers used by the Raiden Network smart
/// contracts.
function contractExists(address contract_address) public view returns (bool) {
    uint size;

    assembly { // solium-disable-line security/no-inline-assembly
        size := extcodesize(contract_address)
    }

    return size > 0;
}

/// @notice Check if a contract exists
/// @param contract_address The address to check whether a contract is
/// deployed or not
/// @return True if a contract exists, false otherwise