Blur Exchange contest - aphak5010's results

Non Fungible Trading Gas Optimization Findings

Summary

The Gas savings are calculated using the yarn test command.
The same tests were used that are provided in the contest repository.

[G-00] Use values 1 and 2 for isOpen instead of 0 and 1

isOpen=1 should be used instead of isOpen=0 and isOpen=2 should be used instead of isOpen=1.
This is because setting storage to a non-zero value from a zero value costs 20000 Gas and setting storage to zero from a non-zero value refunds only 4800 Gas.

Leaving isOpen at a non-zero value continously is significantly cheaper.

The exact values of saved Gas depend of course on how often Exchange.open and Exchange.close are called.

There are 5 instances of isOpen that must be adapted accordingly:

https://github.com/code-423n4/2022-11-non-fungible/blob/e9451f78069999cfd8fdd126b87241eb94e93078/contracts/Exchange.sol#L33

https://github.com/code-423n4/2022-11-non-fungible/blob/e9451f78069999cfd8fdd126b87241eb94e93078/contracts/Exchange.sol#L36

https://github.com/code-423n4/2022-11-non-fungible/blob/e9451f78069999cfd8fdd126b87241eb94e93078/contracts/Exchange.sol#L57

https://github.com/code-423n4/2022-11-non-fungible/blob/e9451f78069999cfd8fdd126b87241eb94e93078/contracts/Exchange.sol#L61

https://github.com/code-423n4/2022-11-non-fungible/blob/e9451f78069999cfd8fdd126b87241eb94e93078/contracts/Exchange.sol#L119

[G-01] Don't initialize variables with default value (Not in automated findings)

There is 1 instance of a variable that is initialized with its default value and that is not already mentioned in the C4audit automated findings.

https://github.com/code-423n4/2022-11-non-fungible/blob/e9451f78069999cfd8fdd126b87241eb94e93078/contracts/Exchange.sol#L146

Deployment Gas saved: 2440
Method call Gas saved: 0

[G-02] Use unchecked{++i} in loops

So far the automated C4audit findings only suggest that you should use ++i instead of i++.
However it is also safe to use unchecked{++i} which saves even more Gas since there are no under-/overflow checks.

There are 3 instances of this:
https://github.com/code-423n4/2022-11-non-fungible/blob/e9451f78069999cfd8fdd126b87241eb94e93078/contracts/Exchange.sol#L184-L208
Fix:

for (uint8 i = 0; i < executionsLength;) {
    ...
    unchecked{++i};
}

https://github.com/code-423n4/2022-11-non-fungible/blob/e9451f78069999cfd8fdd126b87241eb94e93078/contracts/Exchange.sol#L307-L309
Fix:

for (uint8 i = 0; i < orders.length;) {
    ...
    unchecked{++i};
}

https://github.com/code-423n4/2022-11-non-fungible/blob/e9451f78069999cfd8fdd126b87241eb94e93078/contracts/Exchange.sol#L598-L602
Fix:

for (uint8 i = 0; i < fees.length;) {
    ...
    unchecked{++i};
}

[G-03] Use functions instead of modifiers

Modifiers make code more elegant and readable but cost more Gas than functions.
Arguably, the additional Gas cost outweighs the readability benefit.

There are 3 instances where modifiers are defined.

https://github.com/code-423n4/2022-11-non-fungible/blob/e9451f78069999cfd8fdd126b87241eb94e93078/contracts/Exchange.sol#L35

https://github.com/code-423n4/2022-11-non-fungible/blob/e9451f78069999cfd8fdd126b87241eb94e93078/contracts/Exchange.sol#L40

https://github.com/code-423n4/2022-11-non-fungible/blob/e9451f78069999cfd8fdd126b87241eb94e93078/contracts/Exchange.sol#L48