pragma solidity 0.4.18; library SafeMath { function sub(uint8 a, uint8 b) internal pure returns (uint8) { assert(b <= a); return a - b; } function add(uint8 a, uint8 b) internal pure returns (uint8) { uint8 c = a + b; assert(c >= a); return c; } } contract TestSafeMath { using SafeMath for uint8; function safeAdd(uint8 num) public pure returns (uint8) { uint8 result = 255; return result.add(num); } function safeSub(uint8 num) public pure returns (uint8) { uint8 result = 0; return result.sub(num); } } 0.4.18