uniswap-v2/contracts/libraries/SafeMath128.sol

// https://github.com/OpenZeppelin/openzeppelin-contracts/blob/2f9ae975c8bdc5c7f7fa26204896f6c717f07164/contracts/math/SafeMath.sol
pragma solidity 0.5.12;

library SafeMath128 {
    function add(uint128 a, uint128 b) internal pure returns (uint128) {
        uint128 c = a + b;
        require(c >= a, "SafeMath: addition overflow");
        return c;
    }

    function sub(uint128 a, uint128 b) internal pure returns (uint128) {
        require(b <= a, "SafeMath: subtraction overflow");
        uint128 c = a - b;
        return c;
    }

    function mul(uint128 a, uint128 b) internal pure returns (uint128) {
        if (a == 0) return 0;
        uint128 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");
        return c;
    }

    function div(uint128 a, uint128 b) internal pure returns (uint128) {
        require(b > 0, "SafeMath: division by zero");
        uint128 c = a / b;
        return c;
    }
}