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Integer Rollover In Solidity

In this article, we will discuss how the integer rollover happens in Solidity.

How Does Integer Rollover Happen?

Consider an example of a variable of type UInt8. The minimum and the maximum value of the variable are 0 and 255.

If the variable's value is zero and we decrease it to one, the value becomes 255. Similarly, if the variable’s value is 255 and we increase it to 1 then the value becomes zero.

The above scenario is an integer rollover. These scenarios were there in the previous version of Solidity. But now most of the operations in Solidity are checked.

Unchecked Keyword In Solidity

In Solidity, if you want to bypass the checks imposed, you can use the unchecked keyword.

Example

Consider the following code: -

// SPDX-License-Identifier: MIT
pragma solidity 0.8.26;

contract ExampleIntegerRollOver {

    uint8 public myUint8Decrement = 0; 
    uint8 public myUint8Increment = 255;

    function decrementUintUnchecked() public {
        unchecked {
            myUint8Decrement--;
        }
    }

    function decrementUint() public {
        myUint8Increment++;
    }

    function incrementUintUnchecked() public {
        unchecked {
            myUint8Increment++;
        }
    }

    function incrementUint() public {
        myUint8Decrement--;
    }

}

Let us discuss each function.

Decrementuintunchecked Function

The initial value of myUint8Decrement is zero.

Picture showing the initial value of the myUint8Decrement variable

When we click decrementUintUnchecked, the value changes to 255.

Picture showing the value of myUint8Decrement variable when decrementUintUnchecked is clicked

The reason for integer rollover is that we use the unchecked keyword.

Decrementuint Function

In this function, we are not using the unchecked keyword. So, there will be no integer rollover and the value of myUint8Decrement will be zero.

Incrementuintunchecked Function

Like the decrementUintUnchecked function, the IncrementUintUnchecked function increments the value of the myUint8Increment variable. As we are using the unchecked keyword, the value of myUint8Increment becomes zero due to integer rollover.

Picture showing the value of myUint8Increment variable when IncrementUintUnchecked is clicked

Incrementuint Function

There will be no change in the value of myUint8Increment.

Posted By -	Karan Gupta

Posted On -	Tuesday, October 15, 2024

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