Gas Optimizations

[code423n4]

• [S]: Suggested optimation, save a decent amount of gas without compromising readability;
• [M]: Minor optimation, the amount of gas saved is minor, change when you see fit;
• [N]: Non-preferred, the amount of gas saved is at cost of readability, only apply when gas saving is a top priority.

[M] Adding unchecked directive can save gas

For the arithmetic operations that will never over/underflow, using the unchecked directive (Solidity v0.8 has default overflow/underflow checks) can save some gas from the unnecessary internal over/underflow checks.

For example:

https://github.com/code-423n4/2022-02-nested/blob/fe6f9ef7783c3c84798c8ab5fc58085a55cebcfc/contracts/NestedFactory.sol#L337-L339

require(amountSpent <= _inputTokenAmount - feesAmount, "NF: OVERSPENT");

uint256 underSpentAmount = _inputTokenAmount - feesAmount - amountSpent;

_inputTokenAmount - feesAmount - amountSpent; will never underflow.

[M] ++i is more efficient than i++

Using ++i is more gas efficient than i++, especially in a loop.

For example:

https://github.com/code-423n4/2022-02-nested/blob/fe6f9ef7783c3c84798c8ab5fc58085a55cebcfc/contracts/FeeSplitter.sol#L148-L148

https://github.com/code-423n4/2022-02-nested/blob/fe6f9ef7783c3c84798c8ab5fc58085a55cebcfc/contracts/FeeSplitter.sol#L165-L165

https://github.com/code-423n4/2022-02-nested/blob/fe6f9ef7783c3c84798c8ab5fc58085a55cebcfc/contracts/FeeSplitter.sol#L165-L165

https://github.com/code-423n4/2022-02-nested/blob/fe6f9ef7783c3c84798c8ab5fc58085a55cebcfc/contracts/FeeSplitter.sol#L261-L261

https://github.com/code-423n4/2022-02-nested/blob/fe6f9ef7783c3c84798c8ab5fc58085a55cebcfc/contracts/FeeSplitter.sol#L280-L280

https://github.com/code-423n4/2022-02-nested/blob/fe6f9ef7783c3c84798c8ab5fc58085a55cebcfc/contracts/FeeSplitter.sol#L318-L318

https://github.com/code-423n4/2022-02-nested/blob/fe6f9ef7783c3c84798c8ab5fc58085a55cebcfc/contracts/NestedFactory.sol#L103-L103

https://github.com/code-423n4/2022-02-nested/blob/fe6f9ef7783c3c84798c8ab5fc58085a55cebcfc/contracts/NestedFactory.sol#L113-L113

https://github.com/code-423n4/2022-02-nested/blob/fe6f9ef7783c3c84798c8ab5fc58085a55cebcfc/contracts/NestedRecords.sol#L196-L196

https://github.com/code-423n4/2022-02-nested/blob/fe6f9ef7783c3c84798c8ab5fc58085a55cebcfc/contracts/OperatorResolver.sol#L60-L60

[N] Unnecessary checked arithmetic in for loops

There is no risk of overflow caused by increamenting the iteration index in for loops (the i++ in for for (uint256 i = 0; i < tokensCount; i++)).

Increments perform overflow checks that are not necessary in this case.

Recommendation

Surround the increment expressions with an unchecked { ... } block to avoid the default overflow checks. For example, change the for loop:

https://github.com/code-423n4/2022-02-nested/blob/fe6f9ef7783c3c84798c8ab5fc58085a55cebcfc/contracts/NestedRecords.sol#L196-L198

for (uint256 i = 0; i < tokensCount; i++) {
        amounts[i] = getAssetHolding(_nftId, tokens[i]);
}

to:

for (uint256 i = 0; i < tokensCount;) {
        amounts[i] = getAssetHolding(_nftId, tokens[i]);
        unchecked { ++i; }
}

[adrien-supizet]

[M] Adding unchecked directive can save gas

This suggestion requires wrapping all the following statements of the function in the unchecked directive. Looking at solidity docs this "should" be safe, but the small gas optimization is not worth taking a risk and making readers of the code doubtful of what it does.

[M] ++i is more efficient than i++

disputed, already acknowledged during the first audit

[N] Unnecessary checked arithmetic in for loops

disputed. the optimization suggested makes the code hard to read for very very little gas saving

[harleythedogC4]

Even though the changes will not be adopted, some of these are technically valid submissions so I am removing the dispute tag and will assign an appropriate score.

EDIT: Nevermind, see below. All have been judged invalid.

[harleythedogC4]

My personal judgements:

1. "Adding unchecked directive can save gas". This issue (or at least something similar enough to be considered a duplicate) appeared in the first audit Adding unchecked directive can save gas 2021-11-nested-findings#173 Invalid.
2. "++i is more efficient than i++". Already from last contest. Invalid.
3. "Unnecessary checked arithmetic in for loops". Already from last contest (unchecked { ++i } is more gas efficient than i++ for loops 2021-11-nested-findings#25). Invalid.