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code-423n4 / 2022-06-putty-findings

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Gas Optimizations #419

Open code423n4 opened 2 years ago

code423n4 commented 2 years ago

inefficient usage of for loops in PuttyV2.sol Proof of concept https://github.com/code-423n4/2022-06-putty/blob/3b6b844bc39e897bd0bbb69897f2deff12dc3893/contracts/src/PuttyV2.sol#L556 https://github.com/code-423n4/2022-06-putty/blob/3b6b844bc39e897bd0bbb69897f2deff12dc3893/contracts/src/PuttyV2.sol#L594 https://github.com/code-423n4/2022-06-putty/blob/3b6b844bc39e897bd0bbb69897f2deff12dc3893/contracts/src/PuttyV2.sol#L611 https://github.com/code-423n4/2022-06-putty/blob/3b6b844bc39e897bd0bbb69897f2deff12dc3893/contracts/src/PuttyV2.sol#L627 https://github.com/code-423n4/2022-06-putty/blob/3b6b844bc39e897bd0bbb69897f2deff12dc3893/contracts/src/PuttyV2.sol#L637 https://github.com/code-423n4/2022-06-putty/blob/3b6b844bc39e897bd0bbb69897f2deff12dc3893/contracts/src/PuttyV2.sol#L647 https://github.com/code-423n4/2022-06-putty/blob/3b6b844bc39e897bd0bbb69897f2deff12dc3893/contracts/src/PuttyV2.sol#L670 https://github.com/code-423n4/2022-06-putty/blob/3b6b844bc39e897bd0bbb69897f2deff12dc3893/contracts/src/PuttyV2.sol#L728 https://github.com/code-423n4/2022-06-putty/blob/3b6b844bc39e897bd0bbb69897f2deff12dc3893/contracts/src/PuttyV2.sol#L742 contain for loops that are implemented inefficiently in terms of gas for the EVM. Omitting assigning a default-zero type variable to zero, caching array's length, using ++i instead of i++ can save a good chunk of gas, especially if the loop is long running.

Impact Gas savings for protocol interactors

Recommendation Always use uint256 as the type for the index counter, because of EVM's 256 bit word size. Current implementation with uint8 uses more gas than if it used uint256. Don't initialise index counter variable to zero - zero is its default value and reinitialising to zero costs extra gas Use ++i instead of i++ in for loops (small gas saving) You can wrap the ++i in an unchecked block since you have a for loop end check expression anyway Example:


for (uint256 i; i < length;) {
    ...        
    unchecked {
        ++i;
    }
}```