Gas Optimizations

[code423n4]

Code instance:

    totalSupply in ERC20Mock.sol

Unused state variables

Unused state variables are gas consuming at deployment (since they are located in storage) and are
a bad code practice. Removing those variables will decrease deployment gas cost and improve code quality.
This is a full list of all the unused storage variables we found in your code base.

Code instances:

    NFTPairWithOracle.sol, USE_VALUE2
    WETH9Mock.sol, decimals
    WETH9Mock.sol, symbol
    WETH9Mock.sol, name
    NFTPair.sol, USE_VALUE2

Unused declared local variables

Unused local variables are gas consuming, since the initial value assignment costs gas. And are
a bad code practice. Removing those variables will decrease the gas cost and improve code quality.
This is a full list of all the unused storage variables we found in your code base.

Code instances:

    NFTPairWithOracle.sol, _bentoDeposit, token
    NFTPair.sol, _bentoDeposit, token

Change transferFrom to transfer

'transferFrom(address(this), , **)' could be replaced by the following more gas efficient 'transfer(, **)'
This replacement is more gas efficient and improves the code quality.

Code instances:

    NFTPair.sol, 266 : collateral.transferFrom(address(this), to, tokenId);
    NFTPairWithOracle.sol, 295 : collateral.transferFrom(address(this), to, tokenId);
    NFTPairWithOracle.sol, 573 : collateral.transferFrom(address(this), loan.borrower, tokenId);
    NFTPair.sol, 540 : collateral.transferFrom(address(this), loan.borrower, tokenId);

Caching array length can save gas

Caching the array length is more gas efficient.
This is because access to a local variable in solidity is more efficient than query storage / calldata / memory.
We recommend to change from:

for (uint256 i=0; i<array.length; i++) { ... }

to:

uint len = array.length  
for (uint256 i=0; i<len; i++) { ... }

Code instances:

    NFTPairWithOracle.sol, actions, 674
    NFTPair.sol, actions, 641

Prefix increments are cheaper than postfix increments

Prefix increments are cheaper than postfix increments.
Further more, using unchecked {++x} is even more gas efficient, and the gas saving accumulates every iteration and can make a real change
There is no risk of overflow caused by increamenting the iteration index in for loops (the ++i in for (uint256 i = 0; i < numIterations; ++i)).
But increments perform overflow checks that are not necessary in this case.
These functions use not using prefix increments (++x) or not using the unchecked keyword:

Code instances:

    change to prefix increment and unchecked: NFTPairWithOracle.sol, i, 674
    change to prefix increment and unchecked: NFTPairWithOracle.sol, k, 527
    change to prefix increment and unchecked: NFTPair.sol, k, 494
    change to prefix increment and unchecked: NFTPair.sol, i, 641

Unnecessary index init

In for loops you initialize the index to start from 0, but it already initialized to 0 in default and this assignment cost gas.
It is more clear and gas efficient to declare without assigning 0 and will have the same meaning:

Code instances:

    NFTPair.sol, 641
    NFTPairWithOracle.sol, 674

Unnecessary default assignment

Unnecessary default assignments, you can just declare and it will save gas and have the same meaning.

Code instances:

    NFTPair.sol (L#96) : uint8 private constant LOAN_INITIAL = 0;
    NFTPairWithOracle.sol (L#113) : uint8 private constant LOAN_INITIAL = 0;

Rearrange state variables

You can change the order of the storage variables to decrease memory uses.

Code instances:

In NFTPair.sol,rearranging the storage fields can optimize to: 15 slots from: 17 slots.
The new order of types (you choose the actual variables):
1. IBentoBoxV1
2. NFTPair
3. IERC721
4. IERC20
5. uint256
6. uint256
7. uint256
8. uint256
9. uint256
10. bytes32
11. bytes32
12. int256
13. int256
14. address
15. uint8
16. uint8
17. uint8
18. uint8
19. uint8
20. uint8
21. uint8
22. uint8
23. uint8
24. uint8
25. uint8
26. uint8
27. uint8
28. uint8
29. uint8
30. uint8

In NFTPairWithOracle.sol,rearranging the storage fields can optimize to: 15 slots from: 17 slots.
The new order of types (you choose the actual variables):
1. IBentoBoxV1
2. NFTPairWithOracle
3. IERC721
4. IERC20
5. uint256
6. uint256
7. uint256
8. uint256
9. uint256
10. bytes32
11. bytes32
12. int256
13. int256
14. address
15. uint8
16. uint8
17. uint8
18. uint8
19. uint8
20. uint8
21. uint8
22. uint8
23. uint8
24. uint8
25. uint8
26. uint8
27. uint8
28. uint8
29. uint8
30. uint8

Use bytes32 instead of string to save gas whenever possible

Use bytes32 instead of string to save gas whenever possible.
String is a dynamic data structure and therefore is more gas consuming then bytes32.

Code instances:

    WETH9Mock.sol (L6), string public symbol = "WETH";
    WETH9Mock.sol (L5), string public name = "Wrapped Ether";

Use != 0 instead of > 0

Using != 0 is slightly cheaper than > 0. (see code-423n4/2021-12-maple-findings#75 for similar issue)

Code instances:

    NFTPair.sol, 297: change 'balance > 0' to 'balance != 0'
    WETH9Mock.sol, 51: change 'balance > 0' to 'balance != 0'
    RevertingERC20Mock.sol, 44: change 'balance > 0' to 'balance != 0'
    RevertingERC20Mock.sol, 30: change 'balance > 0' to 'balance != 0'
    WETH9Mock.sol, 26: change 'balance > 0' to 'balance != 0'

Unnecessary cast

Code instances:

    int256 NFTPair.sol._num - unnecessary casting int256(inNum)
    uint256 SimpleStrategyMock.sol.withdraw - unnecessary casting uint256(amount)
    int256 NFTPairWithOracle.sol._num - unnecessary casting int256(inNum)

Use unchecked to save gas for certain additive calculations that cannot overflow

You can use unchecked in the following calculations since there is no risk to overflow:

Code instances:

    NFTPair.sol (L#511) - uint256(loan.startTime) + loanParams.duration > block.timestamp, "NFTPair: loan expired" ); 
    NFTPair.sol (L#258) - uint256(loan.startTime) + tokenLoanParams[tokenId].duration <= block.timestamp, "NFTPair: not expired" );
    NFTPairWithOracle.sol (L#544) - uint256(loan.startTime) + loanParams.duration > block.timestamp, "NFTPair: loan expired" ); 
    NFTPairWithOracle.sol (L#277) - if (uint256(loan.startTime) + tokenLoanParams[tokenId].duration > block.timestamp) {

Consider inline the following functions to save gas

You can inline the following functions instead of writing a specific function to save gas.
(see https://github.com/code-423n4/2021-11-nested-findings/issues/167 for a similar issue.)


    ERC721Mock.sol, _tokenURI, { return ""; }

Inline one time use functions

The following functions are used exactly once. Therefore you can inline them and save gas and improve code clearness.

Code instances:

    NFTPairWithOracle.sol, _call
    NFTPairWithOracle.sol, _bentoWithdraw
    NFTPair.sol, _bentoDeposit
    NFTPairWithOracle.sol, _bentoDeposit
    NFTPair.sol, _call

Change if -> revert pattern to require

Change if -> revert pattern to 'require' to save gas and improve code quality,
if (some_condition) {
revert(revert_message)
}

to: require(!some_condition, revert_message)

In the following locations:

Code instances:

    NFTPairWithOracle.sol, 534
    NFTPair.sol, 501

Upgrade pragma to at least 0.8.4

Using newer compiler versions and the optimizer gives gas optimizations
and additional safety checks are available for free.

The advantages of versions 0.8.* over <0.8.0 are:

    1. Safemath by default from 0.8.0 (can be more gas efficient than library based safemath.)
    2. Low level inliner : from 0.8.2, leads to cheaper runtime gas. Especially relevant when the contract has small functions. For example, OpenZeppelin libraries typically have a lot of small helper functions and if they are not inlined, they cost an additional 20 to 40 gas because of 2 extra jump instructions and additional stack operations needed for function calls.
    3. Optimizer improvements in packed structs: Before 0.8.3, storing packed structs, in some cases used an additional storage read operation. After EIP-2929, if the slot was already cold, this means unnecessary stack operations and extra deploy time costs. However, if the slot was already warm, this means additional cost of 100 gas alongside the same unnecessary stack operations and extra deploy time costs.
    4. Custom errors from 0.8.4, leads to cheaper deploy time cost and run time cost. Note: the run time cost is only relevant when the revert condition is met. In short, replace revert strings by custom errors.

Code instances:

    SimpleStrategyMock.sol
    NFTPairWithOracle.sol
    SushiSwapPairMock.sol
    ReturnFalseERC20Mock.sol
    ISwapperGeneric.sol

Do not cache msg.sender

We recommend not to cache msg.sender since calling it is 2 gas while reading a variable is more.

Code instances:

    https://github.com/code-423n4/2022-04-abranft/tree/main/contracts/NFTPairWithOracle.sol#L561
    https://github.com/code-423n4/2022-04-abranft/tree/main/contracts/NFTPair.sol#L528

Mult instead div in compares

To improve algorithm precision instead using division in comparison use multiplication in the following scenario:

    Instead a < b / c use a * c < b. 

In all of the big and trusted contracts this rule is maintained.

Code instances:

    NFTPairWithOracle.sol, 322, require(rate.mul(uint256(params.ltvBPS)) / BPS >= params.valuation, "Oracle: price too low.");
    NFTPairWithOracle.sol, 288, require(rate.mul(loanParams.ltvBPS) / BPS < amount, "NFT is still valued");

Missing fee parameter validation

Some fee parameters of functions are not checked for invalid values. Validate the parameters:

Code instances:

    NFTPairWithOracle.setFeeTo (newFeeTo)
    NFTPair.setFeeTo (newFeeTo)

[cryptolyndon]

You suggest "unchecked" and that we update the compiler version to the 0.8.x line. Which is it?

Also, same user as #124, which I flagged suspect along with #121, #122, #123. This one seems more elaborate and more unique, but I don't have the wording fresh in my memory anymore. Leaving that to the judges.