Gas Optimizations

[code423n4]

Gas Report

Table of Contents:

• Gas Report
  • Foreword
  • Findings
    • Version
      • Upgrade pragma to at least 0.8.4
    • Contract size
      • Contract is Ownable but owner capabilites are not used
    • Storage
      • Caching storage values in memory
    • Variables
      • No need to explicitly initialize variables with default values
    • Comparisons
      • Boolean comparisons
      • > 0 is less efficient than != 0 for unsigned integers (with proof)
    • For-Loops
      • An array's length should be cached to save gas in for-loops
      • ++i costs less gas compared to i++ or i += 1
      • Increments can be unchecked
    • Arithmetics
      • Unchecking arithmetics operations that can't underflow/overflow
    • Visibility
      • Consider making some constants as non-public to save gas
    • Errors
      • Reduce the size of error messages (Long revert Strings)
      • Use Custom Errors instead of Revert Strings to save Gas

Foreword

• @audit tags

The code is annotated at multiple places with //@audit comments to pinpoint the issues. Please, pay attention to them for more details.

Findings

Version

Upgrade pragma to at least 0.8.4

Using newer compiler versions and the optimizer give gas optimizations. Also, additional safety checks are available for free.

The advantages here are:

• Low level inliner (>= 0.8.2): Cheaper runtime gas (especially relevant when the contract has small functions).
• Optimizer improvements in packed structs (>= 0.8.3)
• Custom errors (>= 0.8.4): cheaper deployment cost and runtime cost. Note: the runtime cost is only relevant when the revert condition is met. In short, replace revert strings by custom errors.

Consider upgrading pragma to at least 0.8.4:

core-contracts/contracts/CoreCollection.sol:2:pragma solidity ^0.8.0;
core-contracts/contracts/CoreFactory.sol:2:pragma solidity ^0.8.0;
core-contracts/contracts/CoreProxy.sol:2:pragma solidity ^0.8.0;
core-contracts/contracts/ERC721Claimable.sol:2:pragma solidity ^0.8.0;
core-contracts/contracts/ERC721Payable.sol:2:pragma solidity ^0.8.0;

Contract size

Contract is Ownable but owner capabilites are not used

Reduce contract size by removing Ownable given that its functionalities are not used here:

core-contracts/contracts/CoreProxy.sol:4:import {Ownable} from "@openzeppelin/contracts/access/Ownable.sol";
core-contracts/contracts/CoreProxy.sol:8:contract CoreProxy is Ownable {
royalty-vault/contracts/ProxyVault.sol:6:import {Ownable} from "@openzeppelin/contracts/access/Ownable.sol";
royalty-vault/contracts/ProxyVault.sol:8:contract ProxyVault is VaultStorage, Ownable {

Storage

Caching storage values in memory

The code can be optimized by minimising the number of SLOADs. SLOADs are expensive (100 gas) compared to MLOADs/MSTOREs (3 gas). Here, storage values should get cached in memory (see the @audit tags for further details):

core-contracts/contracts/CoreCollection.sol:
  225          startingIndex =
  226              (uint256(
  227                  keccak256(abi.encodePacked("CoreCollection", block.number))
  228              ) % maxSupply) +
  229:             1; //@audit gas: this calculation should be cached and saved in memory before being saved in startingIndex, so that the cached value can be emitted Line L231
  230          startingIndexBlock = uint256(block.number);
  231:         emit StartingIndexSet(startingIndex); //@audit gas: should emit the suggested cached memory variable in comment L229 instead of making a storage read (SLOAD) here

  304:             royaltyVault != address(0) && //@audit gas: royaltyVault should get cached in memory
  305:             IRoyaltyVault(royaltyVault).getVaultBalance() > 0 //@audit gas: should use the suggested cached royaltyVault
  306          ) {
  307:             IRoyaltyVault(royaltyVault).sendToSplitter(); //@audit gas: should use the suggested cached royaltyVault

royalty-vault/contracts/RoyaltyVault.sol:
  38:         require(splitterProxy != address(0), "Splitter is not set"); //@audit gas: splitterProxy should get cached in memory
  
  44:             IERC20(royaltyAsset).transfer(splitterProxy, splitterShare) == true, //@audit gas: should use the suggested cached splitterProxy //@audit gas: royaltyAsset should get cached in memory 
  45              "Failed to transfer royalty Asset to splitter"
  46          );
  47          require(
  48:             ISplitter(splitterProxy).incrementWindow(splitterShare) == true, //@audit gas: should use the suggested cached splitterProxy
  49              "Failed to increment splitter window"
  50          );
  51          require(
  52:             IERC20(royaltyAsset).transfer( //@audit gas: should use the suggested cached royaltyAsset 
  53:                 platformFeeRecipient, //@audit gas: platformFeeRecipient should get cached in memory
  54                  platformShare
  55              ) == true,
  56              "Failed to transfer royalty Asset to platform fee recipient"
  57          );
  58  
  59:         emit RoyaltySentToSplitter(splitterProxy, splitterShare); //@audit gas: should use the suggested cached splitterProxy
  60:         emit FeeSentToPlatform(platformFeeRecipient, platformShare); //@audit gas: should use the suggested cached platformFeeRecipient

Variables

No need to explicitly initialize variables with default values

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) {

Instances include:

core-contracts/contracts/CoreCollection.sol:279:        for (uint256 i = 0; i < _amount; i++) {
splits/contracts/Splitter.sol:49:        uint256 amount = 0;
splits/contracts/Splitter.sol:50:        for (uint256 i = 0; i < currentWindow; i++) {
splits/contracts/Splitter.sol:274:        for (uint256 i = 0; i < proof.length; i++) {

I suggest removing explicit initializations for default values.

Comparisons

Boolean comparisons

Comparing to a constant (true or false) is a bit more expensive than directly checking the returned boolean value.
I suggest using if(directValue) instead of if(directValue == true) and if(!directValue) instead of if(directValue == false) here:

royalty-vault/contracts/RoyaltyVault.sol:44:            IERC20(royaltyAsset).transfer(splitterProxy, splitterShare) == true,
royalty-vault/contracts/RoyaltyVault.sol:48:            ISplitter(splitterProxy).incrementWindow(splitterShare) == true,
royalty-vault/contracts/RoyaltyVault.sol:55:            ) == true,

> 0 is less efficient than != 0 for unsigned integers (with proof)

!= 0 costs less gas compared to > 0 for unsigned integers in require statements with the optimizer enabled (6 gas)

Proof: While it may seem that > 0 is cheaper than !=, this is only true without the optimizer enabled and outside a require statement. If you enable the optimizer at 10k AND you're in a require statement, this will save gas. You can see this tweet for more proofs: https://twitter.com/gzeon/status/1485428085885640706

I suggest changing > 0 with != 0 here:

core-contracts/contracts/CoreCollection.sol:
   52          require(
   53:             _maxSupply > 0,

  146:         require(amount > 0, "CoreCollection: Amount should be greater than 0");

core-contracts/contracts/CoreFactory.sol:
  74      require(
  75:       _collections.length > 0,

royalty-vault/contracts/RoyaltyVault.sol:
  34          require(
  35:             balanceOfVault > 0,

splits/contracts/Splitter.sol:
  164:         require(royaltyAmount > 0, "No additional funds for window");

Also, please enable the Optimizer.

For-Loops

An array's length should be cached to save gas in for-loops

Reading array length at each iteration of the loop takes 6 gas (3 for mload and 3 to place memory_offset) in the stack.

Caching the array length in the stack saves around 3 gas per iteration.

Here, I suggest storing the array's length in a variable before the for-loop, and use it instead:

core-contracts/contracts/CoreFactory.sol:79:    for (uint256 i; i < _collections.length; i++) {
splits/contracts/Splitter.sol:274:        for (uint256 i = 0; i < proof.length; i++) {

++i costs less gas compared to i++ or i += 1

++i costs less gas compared to i++ or i += 1 for unsigned integer, as pre-increment is cheaper (about 5 gas per iteration). This statement is true even with the optimizer enabled.

i++ increments i and returns the initial value of i. Which means:

uint i = 1;  
i++; // == 1 but i == 2  

But ++i returns the actual incremented value:

uint i = 1;  
++i; // == 2 and i == 2 too, so no need for a temporary variable  

In the first case, the compiler has to create a temporary variable (when used) for returning 1 instead of 2

Instances include:

core-contracts/contracts/CoreCollection.sol:279:        for (uint256 i = 0; i < _amount; i++) {
core-contracts/contracts/CoreFactory.sol:79:    for (uint256 i; i < _collections.length; i++) {
splits/contracts/Splitter.sol:50:        for (uint256 i = 0; i < currentWindow; i++) {
splits/contracts/Splitter.sol:166:        currentWindow += 1;
splits/contracts/Splitter.sol:274:        for (uint256 i = 0; i < proof.length; i++) {

I suggest using ++i instead of i++ to increment the value of an uint variable.

Increments can be unchecked

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.

ethereum/solidity#10695

Instances include:

core-contracts/contracts/CoreCollection.sol:279:        for (uint256 i = 0; i < _amount; i++) {
core-contracts/contracts/CoreFactory.sol:79:    for (uint256 i; i < _collections.length; i++) {
splits/contracts/Splitter.sol:50:        for (uint256 i = 0; i < currentWindow; i++) {
splits/contracts/Splitter.sol:274:        for (uint256 i = 0; i < proof.length; i++) {

The code would go from:

for (uint256 i; i < numIterations; i++) {  
 // ...  
}  

to:

for (uint256 i; i < numIterations;) {  
 // ...  
 unchecked { ++i; }  
}  

The risk of overflow is inexistant for a uint256 here.

Arithmetics

Unchecking arithmetics operations that can't underflow/overflow

Solidity version 0.8+ comes with implicit overflow and underflow checks on unsigned integers. When an overflow or an underflow isn't possible (as an example, when a comparison is made before the arithmetic operation), some gas can be saved by using an unchecked block: https://docs.soliditylang.org/en/v0.8.10/control-structures.html#checked-or-unchecked-arithmetic

I suggest wrapping with an unchecked block here (see @audit tags for more details):

File: RoyaltyVault.sol
40:         uint256 platformShare = (balanceOfVault * platformFee) / 10000;
41:         uint256 splitterShare = balanceOfVault - platformShare; //@audit gas: should be unchecked (as L40: platformFee == 500 < 10000 so platformShare < balanceOfVault and I don't believe platformFee would ever be set to >= 10000)

Visibility

Consider making some constants as non-public to save gas

Reducing from public to private or internal can save gas when a constant isn't used outside of its contract.
I suggest changing the visibility from public to internal or private here:

splits/contracts/Splitter.sol:14:    uint256 public constant PERCENTAGE_SCALE = 10e5;
splits/contracts/Splitter.sol:15:    bytes4 public constant IID_IROYALTY = type(IRoyaltyVault).interfaceId;

Errors

Reduce the size of error messages (Long revert Strings)

Shortening revert strings to fit in 32 bytes will decrease deployment time gas and will decrease runtime gas when the revert condition is met.

Revert strings that are longer than 32 bytes require at least one additional mstore, along with additional overhead for computing memory offset, etc.

Revert strings > 32 bytes:

core-contracts/contracts/CoreCollection.sol:47:        require(!initialized, "CoreCollection: Already initialized");
core-contracts/contracts/CoreCollection.sol:54:            "CoreCollection: Max supply should be greater than 0"
core-contracts/contracts/CoreCollection.sol:146:        require(amount > 0, "CoreCollection: Amount should be greater than 0");
core-contracts/contracts/CoreCollection.sol:191:            "CoreCollection: Only Split Factory or owner can initialize vault."
core-contracts/contracts/CoreCollection.sol:206:            "CoreCollection: Hashed Proof is set"
core-contracts/contracts/CoreCollection.sol:222:            "CoreCollection: Starting index is already set"
royalty-vault/contracts/RoyaltyVault.sol:36:            "Vault does not have enough royalty Asset to send"
royalty-vault/contracts/RoyaltyVault.sol:45:            "Failed to transfer royalty Asset to splitter"
royalty-vault/contracts/RoyaltyVault.sol:49:            "Failed to increment splitter window"
royalty-vault/contracts/RoyaltyVault.sol:56:            "Failed to transfer royalty Asset to platform fee recipient"
splits/contracts/Splitter.sol:120:            "NFT has already claimed the given window" 

I suggest shortening the revert strings to fit in 32 bytes, or that using custom errors as described next.

Use Custom Errors instead of Revert Strings to save Gas

Custom errors from Solidity 0.8.4 are cheaper than revert strings (cheaper deployment cost and runtime cost when the revert condition is met)

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

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.

Custom errors are defined using the error statement, which can be used inside and outside of contracts (including interfaces and libraries).

Instances include:

core-contracts/contracts/CoreCollection.sol:42:        require(initialized, "CoreCollection: Not initialized");
core-contracts/contracts/CoreCollection.sol:47:        require(!initialized, "CoreCollection: Already initialized");
core-contracts/contracts/CoreCollection.sol:52:        require(
core-contracts/contracts/CoreCollection.sol:60:        require(_exists(_tokenId), "CoreCollection: Invalid token id");
core-contracts/contracts/CoreCollection.sol:146:        require(amount > 0, "CoreCollection: Amount should be greater than 0");
core-contracts/contracts/CoreCollection.sol:147:        require(
core-contracts/contracts/CoreCollection.sol:153:            require(claimableSet(), "CoreCollection: No claimable");
core-contracts/contracts/CoreCollection.sol:154:            require(
core-contracts/contracts/CoreCollection.sol:160:            require(isForSale, "CoreCollection: Not for sale");
core-contracts/contracts/CoreCollection.sol:189:        require(
core-contracts/contracts/CoreCollection.sol:204:        require(
core-contracts/contracts/CoreCollection.sol:220:        require(
core-contracts/contracts/CoreFactory.sol:35:    require(
core-contracts/contracts/CoreFactory.sol:43:    require(
core-contracts/contracts/CoreFactory.sol:51:    require(
core-contracts/contracts/CoreFactory.sol:74:    require(
core-contracts/contracts/ERC721Claimable.sol:13:    require(root != bytes32(0), 'ERC721Claimable: Not valid root');
core-contracts/contracts/ERC721Claimable.sol:18:    require(claimableSet(), 'ERC721Claimable: No claimable');
core-contracts/contracts/ERC721Claimable.sol:23:    require(!claimableSet(), 'ERC721Claimable: Claimable is already set');
core-contracts/contracts/ERC721Claimable.sol:63:    require(
core-contracts/contracts/ERC721Payable.sol:21:    require(
core-contracts/contracts/ERC721Payable.sol:29:    require(
royalty-vault/contracts/RoyaltyVault.sol:34:        require(
royalty-vault/contracts/RoyaltyVault.sol:38:        require(splitterProxy != address(0), "Splitter is not set");
royalty-vault/contracts/RoyaltyVault.sol:43:        require(
royalty-vault/contracts/RoyaltyVault.sol:47:        require(
royalty-vault/contracts/RoyaltyVault.sol:51:        require(
splits/contracts/SplitFactory.sol:48:    require(
splits/contracts/SplitFactory.sol:81:    require(
splits/contracts/SplitFactory.sol:136:    require(_vault != address(0), 'Invalid vault');
splits/contracts/SplitFactory.sol:137:    require(
splits/contracts/Splitter.sol:40:        require(
splits/contracts/Splitter.sol:117:        require(currentWindow > window, "cannot claim for a future window");
splits/contracts/Splitter.sol:118:        require(
splits/contracts/Splitter.sol:125:        require(
splits/contracts/Splitter.sol:152:        require(
splits/contracts/Splitter.sol:156:        require(
splits/contracts/Splitter.sol:162:        require(wethBalance >= royaltyAmount, "Insufficient funds");
splits/contracts/Splitter.sol:164:        require(royaltyAmount > 0, "No additional funds for window");
splits/contracts/Splitter.sol:237:        require(didSucceed, "Failed to transfer ETH");

I suggest replacing revert strings with custom errors.

[sofianeOuafir]

High quality report

[deluca-mike]

• "Contract is Ownable but owner capabilites are not used" is not valid since storage slot order is important, which is why the other warden mention EIP1967. Better docs are needed to explain or clear this up.