VTVL contest - Saintcode_'s results

USE CALLDATA INSTEAD OF MEMORY

When a function with a memory array is called externally, the abi.decode() step has to use a for-loop to copy each index of the calldata to the memory index. Each iteration of this for-loop costs at least 60 gas (i.e. 60 * <mem_array>.length). Using calldata directly, obviates the need for such a loop in the contract code and runtime execution.

When arguments are read-only on external functions, the data location should be calldata

8 Instances: -VTVLVesting.sol lines 147, 334, 335, 336, 337, 338, 339, 340

<X> += <Y> COSTS MORE GAS THAN <X> = <X> + <Y> FOR STATE VARIABLES

2 Instances: -VTVLVesting.sol lines 301, 381

ADD UNCHECKED {} FOR SUBTRACTIONS WHERE THE OPERANDS CANNOT UNDERFLOW BECAUSE OF A PREVIOUS REQUIRE() OR IF-STATEMENT

6 Instances: -VTVLVesting.sol lines 167, 170, 264, 337, 429 -VariableSupplyERC20Token.sol line 43

++I INSTEAD OF I++ (OR USE ASSEMBLY WHEN APPLICABLE)

Use ++i instead of i++. This is especially useful in for loops but this optimization can be used anywhere in your code.

1 Instance: -VTVLVesting.sol line 353

USE MULTIPLE REQUIRE() STATMENTS INSTEAD OF REQUIRE(EXPRESSION && EXPRESSION && ...)

1 Instance: -VTVLVesting.sol lines 344

IT COSTS MORE GAS TO INITIALIZE VARIABLES WITH THEIR DEFAULT VALUE THAN LETTING THE DEFAULT VALUE BE APPLIED

If a variable is not set/initialized, it is assumed to have the default value (0 for uint, false for bool, address(0) for address…). Explicitly initializing it with its default value is an anti-pattern and wastes gas.

As an example: for (uint256 i = 0; i < numIterations; ++i) { should be replaced with for (uint256 i; i < numIterations; ++i) {

3 Instances: -VTVLVesting.sol lines 27, 148, 353

>= COSTS LESS GAS THAN >

The compiler uses opcodes GT and ISZERO for solidity code that uses >, but only requires LT for >=, which saves 3 gas Recommended fix example: change variable > 0 to variable >= 1

9 Instances: -VTVLVesting.sol lines 107, 257, 263, 272, 273 -FullPremintERC20Token.sol line 11 -VariableSupplyERC20Token.sol line 27, 31, 40

++I/I++ SHOULD BE UNCHECKED{++I}/UNCHECKED{I++} WHEN IT IS NOT POSSIBLE FOR THEM TO OVERFLOW, AS IS THE CASE WHEN USED IN FOR- AND WHILE-LOOPS

The unchecked keyword is new in solidity version 0.8.0, so this only applies to that version or higher, which these instances are. This saves 30-40 gas per loop for (uint256 i = 0; i < orders.length; /** NOTE: Removed i++ **/ ) { // Do the thing // Unchecked pre-increment is cheapest unchecked { ++i; } }

1 Instance: -VTVLVesting.sol line 353

USE CUSTOM ERRORS RATHER THAN REVERT()/REQUIRE() STRINGS TO SAVE GAS

Custom errors are available from solidity version 0.8.4. Custom errors save ~50 gas each time they’re hitby avoiding having to allocate and store the revert string. Not defining the strings also save deployment gas

24 Instances: -AccessProtected.sol lines 25, 40 -VTVLVested.sol 82, 107, 111, 129, 255, 256, 257, 262, 263, 264, 270, 295, 344, 374, 402, 426, 447, 449 -FullPremintERC20Token.sol line 11 -VariableSupplyERC20Token.sol lines 27, 37, 41