library UInt256Lib {
    uint256 private constant MAX_INT256 = ~(uint256(1) << 255);

    /**
     * @dev Safely converts a uint256 to an int256.
     */
    function toInt256Safe(uint256 a) internal pure returns (int256) {
        require(a <= MAX_INT256);
        return int256(a);
    }
}
/**
 * @title Various utilities useful for uint256.
 */
function toInt256Safe(uint256 a) internal pure returns (int256) {
    require(a <= MAX_INT256);
    return int256(a);
}

/**
 * @dev Safely converts a uint256 to an int256.
 */