Gas Optimizations

[code423n4]

Custom Error Should Be Used For Gas-optimization

Permalinks

• https://github.com/code-423n4/2022-05-cally/blob/1849f9ee12434038aa80753266ce6a2f2b082c59/contracts/src/Cally.sol#L167-L171
• https://github.com/code-423n4/2022-05-cally/blob/1849f9ee12434038aa80753266ce6a2f2b082c59/contracts/src/Cally.sol#L211-L220
• https://github.com/code-423n4/2022-05-cally/blob/1849f9ee12434038aa80753266ce6a2f2b082c59/contracts/src/Cally.sol#L224
• https://github.com/code-423n4/2022-05-cally/blob/1849f9ee12434038aa80753266ce6a2f2b082c59/contracts/src/Cally.sol#L228
• https://github.com/code-423n4/2022-05-cally/blob/1849f9ee12434038aa80753266ce6a2f2b082c59/contracts/src/Cally.sol#L260-L263
• https://github.com/code-423n4/2022-05-cally/blob/1849f9ee12434038aa80753266ce6a2f2b082c59/contracts/src/Cally.sol#L269-L272
• https://github.com/code-423n4/2022-05-cally/blob/1849f9ee12434038aa80753266ce6a2f2b082c59/contracts/src/Cally.sol#L304-L307
• https://github.com/code-423n4/2022-05-cally/blob/1849f9ee12434038aa80753266ce6a2f2b082c59/contracts/src/Cally.sol#L320-L323
• https://github.com/code-423n4/2022-05-cally/blob/1849f9ee12434038aa80753266ce6a2f2b082c59/contracts/src/Cally.sol#L328-L330
• https://github.com/code-423n4/2022-05-cally/blob/1849f9ee12434038aa80753266ce6a2f2b082c59/contracts/src/Cally.sol#L353-L354
• https://github.com/code-423n4/2022-05-cally/blob/1849f9ee12434038aa80753266ce6a2f2b082c59/contracts/src/Cally.sol#L436-L441
• https://github.com/code-423n4/2022-05-cally/blob/1849f9ee12434038aa80753266ce6a2f2b082c59/contracts/src/Cally.sol#L456

Description

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

Mitigation

Consider using custom errors instead if the contract uses solidity version 0.8.4 or above.

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Local Variable Used Only Once

Permalinks

https://github.com/code-423n4/2022-05-cally/blob/1849f9ee12434038aa80753266ce6a2f2b082c59/contracts/src/Cally.sol#L227-L228

Description

It is assumed that auctionStartTimestamp is a locally cached variable in order to reduce gas cost, however, it is only used once after being defined.

Mitigation

auctionStartTimestamp can be replaced at this line to save more gas.

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Update Only Certain Variable in Struct Can Save More Gas

Permalinks

https://github.com/code-423n4/2022-05-cally/blob/1849f9ee12434038aa80753266ce6a2f2b082c59/contracts/src/Cally.sol#L241

Description

As the fact that EVM is a 256-bits stack machine, contract storage will be read and written in a 256 bits stack. All stacks will be read and written on utilizing for the struct variable that used multiple stacks (total size > 256 bits). Therefore, if a contract want to update certain variables which located in the same storage slot or less than the total slot, it is better to read/write only the particular variables rather than the entire struct.

Mitigation

The LoC 231-241 can be replaced as following:

// set new currentStrike
_vaults[vaultId].currentStrike = getDutchAuctionStrike(
    strikeOptions[vault.dutchAuctionStartingStrikeIndex],
    vault.currentExpiration + AUCTION_DURATION,
    vault.dutchAuctionReserveStrike
);

// set new expiration
_vaults[vaultId].currentExpiration = uint32(block.timestamp) + (vault.durationDays * 1 days);

The LoC 278-279 can be replaced as following:

_vaults[vaultId].isExercised = true;

The gas report test from Foundry:
│ Function Name ┆ min ┆ avg ┆ median ┆ max ┆ # calls │
│ buyOption ┆ 1788 ┆ 75271 ┆ 79045 ┆ 99845 ┆ 41 │
│ buyOption (optimized) ┆ 1788 ┆ 74517 ┆ 78186 ┆ 98986 ┆ 41 |
│ exercise ┆ 470 ┆ 50035 ┆ 64223 ┆ 87933 ┆ 18 │
│ exercise (optimized) ┆ 470 ┆ 49258 ┆ 63163 ┆ 86873 ┆ 18 │