FIAT DAO veFDT contest - saian's results

Variable can be immutable

Variables that are initialized in constructor and not updated later can be converted to immutable to save gas on storage read

Proof of concept

https://github.com/code-423n4/2022-08-fiatdao/blob/fece3bdb79ccacb501099c24b60312cd0b2e4bb2/contracts/VotingEscrow.sol#L45

    IERC20 public token;

    string public name;
    string public symbol;
    uint256 public decimals = 18; 

Avoid initialising variables with default values

If a variables is not initialized, it is assumed to contain default values (0, address(0), false), explicitly intialising with default values is not necessary

Proof of concept

https://github.com/code-423n4/2022-08-fiatdao/blob/fece3bdb79ccacb501099c24b60312cd0b2e4bb2/contracts/VotingEscrow.sol#L229-L230

        int128 oldSlopeDelta = 0;   
        int128 newSlopeDelta = 0;

https://github.com/code-423n4/2022-08-fiatdao/blob/fece3bdb79ccacb501099c24b60312cd0b2e4bb2/contracts/VotingEscrow.sol#L298

        uint256 blockSlope = 0; // dblock/dt    

https://github.com/code-423n4/2022-08-fiatdao/blob/fece3bdb79ccacb501099c24b60312cd0b2e4bb2/contracts/VotingEscrow.sol#L714

        uint256 min = 0;

https://github.com/code-423n4/2022-08-fiatdao/blob/fece3bdb79ccacb501099c24b60312cd0b2e4bb2/contracts/VotingEscrow.sol#L737

        uint256 min = 0;

https://github.com/code-423n4/2022-08-fiatdao/blob/fece3bdb79ccacb501099c24b60312cd0b2e4bb2/contracts/VotingEscrow.sol#L793

        uint256 dBlock = 0;
        uint256 dTime = 0; 

https://github.com/code-423n4/2022-08-fiatdao/blob/fece3bdb79ccacb501099c24b60312cd0b2e4bb2/contracts/VotingEscrow.sol#L889

        uint256 dTime = 0; 

Avoid addition if uEpoch is 0

Proof of concept

Use index value of 1

https://github.com/code-423n4/2022-08-fiatdao/blob/fece3bdb79ccacb501099c24b60312cd0b2e4bb2/contracts/VotingEscrow.sol#L258

    if (uEpoch == 0) {
        userPointHistory[_addr][uEpoch + 1] = userOldPoint; 
    }

Use custom errors instead of revert strings

Custom errors from solidity 0.8.4 are more efficient than revert strings with cheaper deployment and runtime time costs when revert condition is met

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

Replace i++ with ++i

Pre-increment saves a small amount of gas than postfix increment because it doesnt have to store the previous value. This can be more significant in loops where this operation is done multiple times.

Proof of concept

https://github.com/code-423n4/2022-08-fiatdao/blob/fece3bdb79ccacb501099c24b60312cd0b2e4bb2/contracts/VotingEscrow.sol#L309

        for (uint256 i = 0; i < 255; i++)

https://github.com/code-423n4/2022-08-fiatdao/blob/fece3bdb79ccacb501099c24b60312cd0b2e4bb2/contracts/VotingEscrow.sol#L717

        for (uint256 i = 0; i < 128; i++)

https://github.com/code-423n4/2022-08-fiatdao/blob/fece3bdb79ccacb501099c24b60312cd0b2e4bb2/contracts/VotingEscrow.sol#L739

        for (uint256 i = 0; i < 128; i++)

https://github.com/code-423n4/2022-08-fiatdao/blob/fece3bdb79ccacb501099c24b60312cd0b2e4bb2/contracts/VotingEscrow.sol#L834

        for (uint256 i = 0; i < 255; i++)

Use != 0 instead of > 0 for unsigned integers

Unsigned integers will never have value less than 0, so checking != 0 than > 0 costs less gas

Proof of concept

https://github.com/code-423n4/2022-08-fiatdao/blob/fece3bdb79ccacb501099c24b60312cd0b2e4bb2/contracts/VotingEscrow.sol#L412

    require(_value > 0, "Only non zero amount");

https://github.com/code-423n4/2022-08-fiatdao/blob/fece3bdb79ccacb501099c24b60312cd0b2e4bb2/contracts/VotingEscrow.sol#L448

    require(_value > 0, "Only non zero amount"); 

Assign value instead of addition

Proof of concept

https://github.com/code-423n4/2022-08-fiatdao/blob/fece3bdb79ccacb501099c24b60312cd0b2e4bb2/contracts/VotingEscrow.sol#L418

L413    require(locked_.amount == 0, "Lock exists");

L418    locked_.amount += int128(int256(_value)); 

Cache storage variables

Storage variables that are read multiple times in the same function can be cached and re-used to avoid expensive SLOAD and save gas

Proof of concept

penaltyRecipient in

https://github.com/code-423n4/2022-08-fiatdao/blob/fece3bdb79ccacb501099c24b60312cd0b2e4bb2/contracts/VotingEscrow.sol#L677

    require(token.transfer(penaltyRecipient, amount), "Transfer failed");
    emit CollectPenalty(amount, penaltyRecipient);