VTVL contest - Ocean_Sky's results

[G-01] USE CUSTOM ERRORS INSTEAD OF REVERT STRINGS TO SAVE GAS

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. 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/

Additional recommendation: We can add natspec documentation to explain the custom errors in contract.

Instances: https://github.com/code-423n4/2022-09-vtvl/blob/main/contracts/token/FullPremintERC20Token.sol#L11 https://github.com/code-423n4/2022-09-vtvl/blob/main/contracts/token/VariableSupplyERC20Token.sol#L27 https://github.com/code-423n4/2022-09-vtvl/blob/main/contracts/token/VariableSupplyERC20Token.sol#L37 https://github.com/code-423n4/2022-09-vtvl/blob/main/contracts/token/VariableSupplyERC20Token.sol#L41 https://github.com/code-423n4/2022-09-vtvl/blob/main/contracts/AccessProtected.sol#L25 https://github.com/code-423n4/2022-09-vtvl/blob/main/contracts/AccessProtected.sol#L40 https://github.com/code-423n4/2022-09-vtvl/blob/main/contracts/VTVLVesting.sol#L82 https://github.com/code-423n4/2022-09-vtvl/blob/main/contracts/VTVLVesting.sol#L107 https://github.com/code-423n4/2022-09-vtvl/blob/main/contracts/VTVLVesting.sol#L111 https://github.com/code-423n4/2022-09-vtvl/blob/main/contracts/VTVLVesting.sol#L129 https://github.com/code-423n4/2022-09-vtvl/blob/main/contracts/VTVLVesting.sol#L255 https://github.com/code-423n4/2022-09-vtvl/blob/main/contracts/VTVLVesting.sol#L256 https://github.com/code-423n4/2022-09-vtvl/blob/main/contracts/VTVLVesting.sol#L257 https://github.com/code-423n4/2022-09-vtvl/blob/main/contracts/VTVLVesting.sol#L262 https://github.com/code-423n4/2022-09-vtvl/blob/main/contracts/VTVLVesting.sol#L263 https://github.com/code-423n4/2022-09-vtvl/blob/main/contracts/VTVLVesting.sol#L264 https://github.com/code-423n4/2022-09-vtvl/blob/main/contracts/VTVLVesting.sol#L278

[G-02] CACHE STORAGE VALUES IN MEMORY TO MINIMIZE SLOADS The code can be optimized by minimizing the number of SLOADs. SLOADs are expensive 100 gas compared to MLOADs/MSTOREs (3gas) Storage value should get cached in memory

Instance: https://github.com/code-423n4/2022-09-vtvl/blob/main/contracts/token/VariableSupplyERC20Token.sol#L11

Being read two times: https://github.com/code-423n4/2022-09-vtvl/blob/main/contracts/token/VariableSupplyERC20Token.sol#L40 https://github.com/code-423n4/2022-09-vtvl/blob/main/contracts/token/VariableSupplyERC20Token.sol#L43

[G-03] ++I COSTS LESS GAS COMPARED TO I++ OR I += 1 IN FOR LOOPS (~5 GAS PER ITERATION)

Pre-increments are cheaper than post-increments.

For a uint256 i variable, pre-increment ++i costs 5 gas less than i++ with the optimizer enabled.

Note that post-increments (or post-decrements) return the old value before incrementing or decrementing, hence the name post-increment: However, pre-increments (or pre-decrements) return the new value.

Instance: https://github.com/code-423n4/2022-09-vtvl/blob/main/contracts/VTVLVesting.sol#L353

[G-04] USING UNCHECKED FOR INCREMENTS TO SAVE GAS

In Solidity 0.8+, there’s a default overflow check on unsigned integers. It’s possible to uncheck this in for-loops and save some gas at each iteration but at the cost of some code readability, as this uncheck cannot be made inline. Source: https://github.com/ethereum/solidity/issues/10695

Instance https://github.com/code-423n4/2022-09-vtvl/blob/main/contracts/VTVLVesting.sol#L353

Sample affected code at file VTVLVesting.sol#L353:

for (uint256 i = 0; i < length; i++) { _createClaimUnchecked(_recipients[i], _startTimestamps[i], _endTimestamps[i], _cliffReleaseTimestamps[i], _releaseIntervalsSecs[i], _linearVestAmounts[i], _cliffAmounts[i]); } ); }

can be changed to the following:

for (uint256 i = 0; i < length;) { _createClaimUnchecked(_recipients[i], _startTimestamps[i], _endTimestamps[i], _cliffReleaseTimestamps[i], _releaseIntervalsSecs[i], _linearVestAmounts[i], _cliffAmounts[i]); } ); unchecked { ++i; } }

[G-05] IT COSTS MORE GAS TO INITIALIZE VARIABLES WITH THEIR DEFAULT VALUE THAN LETTING THE DEFAULT VALUE BE APPLIED

In Solidity, all variables are set to zeros by default. So, do not explicitly initialize a variable with its default value if it is zero. As an example: for (uint256 i = 0; i < numIterations; ++i) { should be replaced with for (uint256 i; i < numIterations; ++i) {

Instances: https://github.com/code-423n4/2022-09-vtvl/blob/main/contracts/VTVLVesting.sol#L353 https://github.com/code-423n4/2022-09-vtvl/blob/main/contracts/VTVLVesting.sol#L27

[G-06] SPLITTING REQUIRE() STATEMENTS THAT USE && SAVES GAS - (SAVES 8 GAS PER &&)

Instead of using the && operator in a single require statement to check multiple conditions,using multiple require statements with 1 condition per require statement will save 8 GAS per &&.

The gas difference would only be realized if the revert condition is realized(met).

Instances: https://github.com/code-423n4/2022-09-vtvl/blob/main/contracts/VTVLVesting.sol#L344-L348 https://github.com/code-423n4/2022-09-vtvl/blob/main/contracts/VTVLVesting.sol#L272-L276