Yield Witch v2 contest - Sm4rty's results

1. Use !=0 instead of >0 for UINT

0 is less efficient than != 0 for unsigned integers (with proof) != 0 costs less gas compared to > 0 for unsigned integers in require statements with the optimizer enabled (6 gas) Proof: While it may seem that > 0 is cheaper than !=, this is only true without the optimizer enabled and outside a require statement. If you enable the optimizer at 10k AND you’re in a require statement, this will save gas. You can see this tweet for more proofs: https://twitter.com/gzeon/status/1485428085885640706

Instances

contracts/Witch.sol:255 contracts/Witch.sol:300 contracts/Witch.sol:358 contracts/Witch.sol:416

contracts/Witch.sol:255:        require(auction_.start > 0, "Vault not under auction");
contracts/Witch.sol:300:        require(auction_.start > 0, "Vault not under auction");
contracts/Witch.sol:358:        require(auction_.start > 0, "Vault not under auction");
contracts/Witch.sol:416:        require(auction_.start > 0, "Vault not under auction");

Reference:

https://twitter.com/gzeon/status/1485428085885640706

Remediation:

I suggest changing > 0 with != 0. Also, please enable the Optimizer.

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2. Custom Errors instead of Revert Strings to save Gas

Custom errors from Solidity 0.8.4 are cheaper than revert strings (cheaper deployment cost and runtime cost when the revert condition is met)

Starting from Solidity v0.8.4,there is a convenient and gas-efficient way to explain to users why an operation failed through the use of custom errors. Until now, you could already use strings to give more information about failures (e.g., revert("Insufficient funds.");),but they are rather expensive, especially when it comes to deploy cost, and it is difficult to use dynamic information in them.

Custom errors are defined using the error statement, which can be used inside and outside of contracts (including interfaces and libraries).

Instances Includes:

Links: Witch.sol:84: Witch.sol:102-108: Witch.sol:189: Witch.sol:200: Witch.sol:255-256: Witch.sol:300: Witch.sol:313: Witch.sol:328: Witch.sol:358: Witch.sol:365: Witch.sol:395: Witch.sol:416: Witch.sol:437:

Witch.sol:84:         require(param == "ladle", "Unrecognized");
Witch.sol:102:        require(initialOffer <= 1e18, "InitialOffer above 100%");
Witch.sol:103:        require(proportion <= 1e18, "Proportion above 100%");
Witch.sol:104:        require( initialOffer == 0 || initialOffer >= 0.01e18, "InitialOffer below 1%");
Witch.sol:108:        require(proportion >= 0.01e18, "Proportion below 1%");
Witch.sol:189:        require(cauldron.level(vaultId) < 0, "Not undercollateralized");
Witch.sol:200:        require(limits_.sum <= limits_.max, "Collateral limit reached");
Witch.sol:255:        require(auction_.start > 0, "Vault not under auction");
Witch.sol:256:        require(cauldron.level(vaultId) >= 0, "Undercollateralized");
Witch.sol:300:        require(auction_.start > 0, "Vault not under auction");
Witch.sol:313:        require(liquidatorCut >= minInkOut, "Not enough bought");
Witch.sol:328:        require(baseJoin != IJoin(address(0)), "Join not found");
Witch.sol:358:        require(auction_.start > 0, "Vault not under auction");
Witch.sol:365:        require(liquidatorCut >= minInkOut, "Not enough bought");
Witch.sol:395:        require(ilkJoin != IJoin(address(0)), "Join not found");
Witch.sol:416:        require(auction_.start > 0, "Vault not under auction");
Witch.sol:437:        require(auction_.art - artIn >= debt.min * (10**debt.dec),"Leaves dust");

References:

https://blog.soliditylang.org/2021/04/21/custom-errors/

Remediation:

I suggest replacing revert strings with custom errors.

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