pragma solidity ^0.4.18;

contract SafeMath {
    function safeMul(uint a, uint b)
        internal
        pure
        returns (uint256)
    {
        uint c = a * b;
        assert(a == 0 || c / a == b);
        return c;
    }

    function safeDiv(uint a, uint b)
        internal
        pure
        returns (uint256)
    {
        uint c = a / b;
        return c;
    }

    function safeSub(uint a, uint b)
        internal
        pure
        returns (uint256)
    {
        assert(b <= a);
        return a - b;
    }

    function safeAdd(uint a, uint b)
        internal
        pure
        returns (uint256)
    {
        uint c = a + b;
        assert(c >= a);
        return c;
    }

    function max64(uint64 a, uint64 b)
        internal
        pure
        returns (uint256)
    {
        return a >= b ? a : b;
    }

    function min64(uint64 a, uint64 b)
        internal
        pure
        returns (uint256)
    {
        return a < b ? a : b;
    }

    function max256(uint256 a, uint256 b)
        internal
        pure
        returns (uint256)
    {
        return a >= b ? a : b;
    }

    function min256(uint256 a, uint256 b)
        internal
        pure
        returns (uint256)
    {
        return a < b ? a : b;
    }
}