Yieldy contest - scaraven's results

Generally, I found the code quite easy to understand and well commented throughout with only a few very minor issues

Use safeTransferFrom instead of transferFrom

https://github.com/code-423n4/2022-06-yieldy/blob/524f3b83522125fb7d4677fa7a7e5ba5a2c0fe67/src/contracts/Migration.sol#L48-L52

In case something unexepected happens, use safeTransferFrom instead of transferFrom.

Use __gap[] after defining storage variables

This applies to all the ...Storage.sol contracts, as they are inherited with other contracts e.g. ERC20PermitUpgradeable, if the developers ever want to add a new storage variable then it will shift all other storage variables causing inconsistencies and potentially break the contracts.

See here for more info

Yieldy.sol

https://github.com/shapeshift/foxy/blob/ff815e5ac85cda363b3979cac78646770759a146/src/contracts/Yieldy.sol#L192 Can be unchecked as a inequality check was already made previously 64 gas diff

https://github.com/shapeshift/foxy/blob/ff815e5ac85cda363b3979cac78646770759a146/src/contracts/Yieldy.sol#L212 Exact same situation as above 64 gas diff

https://github.com/shapeshift/foxy/blob/ff815e5ac85cda363b3979cac78646770759a146/src/contracts/Yieldy.sol#L288-L290

        uint256 creditAmount = _amount * rebasingCreditsPerToken;
        uint256 currentCredits = creditBalances[_address];
        require(currentCredits >= creditAmount, "Not enough balance");


        creditBalances[_address] = creditBalances[_address] - creditAmount;
        rebasingCredits = rebasingCredits - creditAmount;
        _totalSupply = _totalSupply - _amount;

We can place an unchecked expression around this block of code as a require check was made above This also applies to totalSupply because totalSupply = rebasingCredits / rebasingCreditsPerToken so if rebasingCredits >= creditAmount it follows that totalSupply >= amount

64*3 gas diff

Additionally, creditBalances[_address] is cached with currentCredits so reusing that variable will use one less SLOAD operation which costs less gas (even if the slot if warm)

84 gas diff

The block should be:

        uint256 creditAmount = _amount * rebasingCreditsPerToken;
        uint256 currentCredits = creditBalances[_address];
        require(currentCredits >= creditAmount, "Not enough balance");

        unchecked { 
        creditBalances[_address] = currentCredits - creditAmount;
        rebasingCredits = rebasingCredits - creditAmount;
        _totalSupply = _totalSupply - _amount;
        }

https://github.com/shapeshift/foxy/blob/ff815e5ac85cda363b3979cac78646770759a146/src/contracts/Yieldy.sol#L252-L253 As rebasingCredits >= creditBalances[_address]`, we can swap the two lines and the second addition can be unchecked

64 gas diff

Change

        creditBalances[_address] = creditBalances[_address] + creditAmount;
        rebasingCredits = rebasingCredits + creditAmount;

to

        rebasingCredits = rebasingCredits + creditAmount;
        unchecked  { creditBalances[_address] = creditBalances[_address] + creditAmount; }

Staking.sol

https://github.com/shapeshift/foxy/blob/ff815e5ac85cda363b3979cac78646770759a146/src/contracts/Staking.sol#L494 withdrawalAmount is always larger than equal to info.amount therefore this subtraction can be unchecked

64 gas diff

Total Approximate Gas Savings

~ 532 gas should be saved This is estimated using solidity 0.8.9 and optimisations with 200 runs