blockchains-security-toolkit/advanced_expert/vulnerabilities/overflow.md

## overflow of numbers

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### unchecked math

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* overflow and underflow of numbers in solidity 0.8 throw an error. this can be disabled with `unchecked`.
* disabling overflow / underflow check saves gas.

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```
contract UncheckedMath {
    function add(uint x, uint y) external pure returns (uint) {
        // 22291 gas
        // return x + y;

        // 22103 gas
        unchecked {
            return x + y;
        }
    }

    function sub(uint x, uint y) external pure returns (uint) {
        // 22329 gas
        // return x - y;

        // 22147 gas
        unchecked {
            return x - y;
        }
    }

    function sumOfCubes(uint x, uint y) external pure returns (uint) {
        // Wrap complex math logic inside unchecked
        unchecked {
            uint x3 = x * x * x;
            uint y3 = y * y * y;

            return x3 + y3;
        }
    }
}

```

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