Ethos Reserve contest - Deivitto's results

Gas

Multiple address/ID mappings can be combined into a single mapping of an address/ID to a struct, where appropriate

if both fields are accessed in the same function, can save ~42 gas per access due to not having to recalculate the key’s keccak256 hash (Gkeccak256 - 30 gas) and that calculation’s associated stack operations.

Both mapping being used in the same functions mostly consider making them a struct instead

• StabilityPool.sol#L214 mapping (uint128 => mapping(uint128 => mapping (address => uint))) public epochToScaleToSum;
• StabilityPool.sol#L223 mapping (uint128 => mapping(uint128 => uint)) public epochToScaleToG;

---

• TroveManager.sol#L86 mapping (address => mapping (address => Trove)) public Troves;
• TroveManager.sol#L88 mapping (address => uint) public totalStakes;
• TroveManager.sol#L91 mapping (address => uint) public totalStakesSnapshot;
• TroveManager.sol#L94 mapping (address => uint) public totalCollateralSnapshot;
• TroveManager.sol#L104 mapping (address => uint) public L_Collateral;
• TroveManager.sol#L105 mapping (address => uint) public L_LUSDDebt;
• TroveManager.sol#L109 mapping (address => mapping (address => RewardSnapshot)) public rewardSnapshots;
• TroveManager.sol#L116 mapping (address => address[]) public TroveOwners;
• TroveManager.sol#L119 mapping (address => uint) public lastCollateralError_Redistribution;
• TroveManager.sol#L120 mapping (address => uint) public lastLUSDDebtError_Redistribution;

---

• ActivePool.sol#L41 mapping (address => uint256) internal collAmount; // collateral => amount tracker
• ActivePool.sol#L42 mapping (address => uint256) internal LUSDDebt; // collateral => corresponding debt tracker
• ActivePool.sol#L44 mapping (address => uint256) public yieldingPercentage; // collateral => % to use for yield farming (in BPS, <= 10k)
• ActivePool.sol#L45 mapping (address => uint256) public yieldingAmount; // collateral => actual wei amount being used for yield farming
• ActivePool.sol#L46 mapping (address => address) public yieldGenerator; // collateral => corresponding ERC4626 vault
• ActivePool.sol#L47 mapping (address => uint256) public yieldClaimThreshold; // collateral => minimum wei amount of yield to claim and redistribute

---

• StabilityPool.sol#L167 mapping (address => uint256) internal collAmounts; // deposited collateral tracker
• StabilityPool.sol#L179 mapping (address => uint) S;
• StabilityPool.sol#L186 mapping (address => Deposit) public deposits; // depositor address -> Deposit struct
• StabilityPool.sol#L187 mapping (address => Snapshots) public depositSnapshots; // depositor address -> snapshots struct
• StabilityPool.sol#L228 mapping (address => uint) public lastCollateralError_Offset;

---

• StabilityPool.sol#L214 mapping (uint128 => mapping(uint128 => mapping (address => uint))) public epochToScaleToSum;
• StabilityPool.sol#L223 mapping (uint128 => mapping(uint128 => uint)) public epochToScaleToG;

---

• LQTYStaking.sol#L28 mapping (address => uint) public F_Collateral; // Running sum of collateral fees per-LQTY-staked
• LQTYStaking.sol#L32 mapping (address => Snapshot) public snapshots;
• LQTYStaking.sol#L35 mapping (address => uint) F_Collateral_Snapshot;

---

• LUSDToken.sol#L54 mapping (address => uint256) private _nonces;
• LUSDToken.sol#L57 mapping (address => uint256) private _balances;
• LUSDToken.sol#L58 mapping (address => mapping (address => uint256)) private _allowances;
• LUSDToken.sol#L62 mapping (address => bool) public troveManagers;
• LUSDToken.sol#L63 mapping (address => bool) public stabilityPools;
• LUSDToken.sol#L64 mapping (address => bool) public borrowerOperations;

<x> += <y> costs more gas than <x> = <x> + <y> for state variables

Using the addition operator instead of plus-equals saves gas. Same goes for other operands like -=.

• ReaperVaultV2.sol#L168 totalAllocBPS += _allocBPS;

• ReaperVaultV2.sol#L196 totalAllocBPS += _allocBPS;

• ReaperVaultV2.sol#L450 stratParams.losses += loss;

• ReaperVaultV2.sol#L505 strategy.gains += vars.gain;

• ReaperVaultV2.sol#L520 strategy.allocated += vars.credit;

• ReaperVaultV2.sol#L521 totalAllocated += vars.credit;

• ReaperVaultV2.sol#L194 totalAllocBPS -= strategies[_strategy].allocBPS;

• ReaperVaultV2.sol#L214 totalAllocBPS -= strategies[_strategy].allocBPS;

• ReaperVaultV2.sol#L395 strategies[stratAddr].allocated -= actualWithdrawn;

• ReaperVaultV2.sol#L396 totalAllocated -= actualWithdrawn;

• ReaperVaultV2.sol#L444 stratParams.allocBPS -= bpsChange;

• ReaperVaultV2.sol#L445 totalAllocBPS -= bpsChange;

• ReaperVaultV2.sol#L451 stratParams.allocated -= loss;

• ReaperVaultV2.sol#L452 totalAllocated -= loss;

• ReaperVaultV2.sol#L514 strategy.allocated -= vars.debtPayment;

• ReaperVaultV2.sol#L515 totalAllocated -= vars.debtPayment;

Redeclaring variables each loop iteration consumes extra gas

Rather than re assigning values to the variables each iterations, at for loops it is being redeclared each variable all over again.

-StabilityPool.sol#L352-L353

-StabilityPool.sol#L398-L399

-StabilityPool.sol#L832-L833

-StabilityPool.sol#L860-L864

-TroveManager.sol#L610

-TroveManager.sol#L819

-LQTYStaking.sol#L207-L208

-LQTYStaking.sol#L229

-LQTYStaking.sol#L242

-ReaperStrategyGranarySupplyOnly.sol#L120

-ReaperVaultV2.sol#L265

Increments at loops can be unchecked{++i} 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 without an extra function. This extra function is used in some parts of the code, however in some locations it is not used

• CollateralConfig.sol#L56 for(uint256 i = 0; i < _collaterals.length; i++) {

• ActivePool.sol#L108 for(uint256 i = 0; i < numCollaterals; i++) {

• TroveManager.sol#L608 for (vars.i = 0; vars.i < _n && vars.user != firstUser; vars.i++) {

• TroveManager.sol#L690 for (vars.i = 0; vars.i < _n; vars.i++) {

• TroveManager.sol#L808 for (vars.i = 0; vars.i < _troveArray.length; vars.i++) {

• TroveManager.sol#L882 for (vars.i = 0; vars.i < _troveArray.length; vars.i++) {

• TroveManager.sol#L934

  • The redeemer swaps (debt - liquidation reserve) LUSD for (debt - liquidation reserve) worth of collateral, so the LUSD liquidation reserve left corresponds to the remaining debt.

• StabilityPool.sol#L351 for (uint i = 0; i < numCollaterals; i++) {

• StabilityPool.sol#L397 for (uint i = 0; i < numCollaterals; i++) {

• StabilityPool.sol#L640 for (uint i = 0; i < assets.length; i++) {

• StabilityPool.sol#L810 for (uint i = 0; i < collaterals.length; i++) {

• StabilityPool.sol#L831 for (uint i = 0; i < collaterals.length; i++) {

• StabilityPool.sol#L859 for (uint i = 0; i < numCollaterals; i++) {

• LQTYStaking.sol#L206 for (uint i = 0; i < assets.length; i++) {

• LQTYStaking.sol#L228 for (uint i = 0; i < collaterals.length; i++) {

• LQTYStaking.sol#L240 for (uint i = 0; i < numCollaterals; i++) {

• ReaperVaultV2.sol#L128v4.sol#L77](https://github.com/code-423n4/2023-02-ethos/blob/34ba1e7dd2d259f06f9d5fa13f5d96be7829ff34/Ethos-Vault/contracts/abstract/ReaperBaseStrategyv4.sol#L77) for (uint256 i = 0; i < numStrategists; i = i.uncheckedInc()) {

• ReaperStrategyGranarySupplyOnly.sol#L117 for (uint256 i = 0; i < numSteps; i = i.uncheckedInc()) {

• ReaperStrategyGranarySupplyOnly.sol#L165 for (uint256 i = 0; i < numSteps; i = i.uncheckedInc()) {

    for (uint256 i = 0; i < numStrategists; i = i.uncheckedInc()) {
  

• ReaperVaultV2.sol#L264 for (uint256 i = 0; i < queueLength; i = i.uncheckedInc()) {

• ReaperVaultV2.sol#L372 for (uint256 i = 0; i < queueLength; i = i.uncheckedInc()) {

• [ReaperBaseStrategy

require()/revert() strings longer than 32 bytes cost extra gas

NOTE: None of these findings where found by 4naly3er output - Gas

Each extra memory word of bytes past the original 32 incurs an MSTORE which costs 3 gas

• BorrowerOperations.sol#L563

• ActivePool.sol#L324

• ActivePool.sol#L334

• ActivePool.sol#L341

• LQTYStaking.sol#L257

• LUSDToken.sol#L136

• LUSDToken.sol#L350

• LUSDToken.sol#L371

• LUSDToken.sol#L386

• ReaperBaseStrategyv4.sol#L193

bytes constants are more efficient than string constants

If data can fit into 32 bytes, then you should use bytes32 datatype rather than bytes or strings as it is cheaper in solidity.

• BorrowerOperations.sol#L21 string constant public NAME = "BorrowerOperations";
• ActivePool.sol#L30 string constant public NAME = "ActivePool";
• StabilityPool.sol#L150 string constant public NAME = "StabilityPool";
• CommunityIssuance.sol#L19 string constant public NAME = "CommunityIssuance";
• LQTYStaking.sol#L23 string constant public NAME = "LQTYStaking";
• LUSDToken.sol#L32 string constant internal _NAME = "LUSD Stablecoin";
• LUSDToken.sol#L33 string constant internal _SYMBOL = "LUSD";
• LUSDToken.sol#L34 string constant internal _VERSION = "1";

Should use arguments instead of state variable

This removes an extra SLOAD

• ReaperVaultV2.sol#L581

Superfluous event fields can be omitted

block.timestamp and block.number are added to event information by default so adding them manually wastes extra gas.

• TroveManager.sol#L1505 emit LastFeeOpTimeUpdated(block.timestamp);

abi.encode() is less gas efficient than abi.encodePacked()

Changing the abi.encode function to abi.encodePacked can save gas since the abi.encode function pads extra null bytes at the end of the call data, which is unnecessary. Also, in general, abi.encodePacked is more gas-efficient.

• LUSDToken.sol#L284 domainSeparator(), keccak256(abi.encode(
• LUSDToken.sol#L305 return keccak256(abi.encode(typeHash, name, version, _chainID(), address(this)));

Splitting require() / assert() statements that use && saves gas

Instead of using the && operator in a single require statement to check multiple conditions, consider using multiple require statements with 1 condition per require statement (saving 3 gas per &).

• BorrowerOperations.sol#L301 assert(msg.sender == _borrower || (msg.sender == stabilityPoolAddress && _collTopUp > 0 && _LUSDChange == 0));

• BorrowerOperations.sol#L653 require(_maxFeePercentage >= BORROWING_FEE_FLOOR && _maxFeePercentage <= DECIMAL_PRECISION,

• TroveManager.sol#L1279 assert(closedStatus != Status.nonExistent && closedStatus != Status.active);

• TroveManager.sol#L1342 assert(troveStatus != Status.nonExistent && troveStatus != Status.active);

• TroveManager.sol#L1539 require (TroveOwnersArrayLength > 1 && sortedTroves.getSize(_collateral) > 1);

• LUSDToken.sol#L348 _recipient != address(0) &&

• LUSDToken.sol#L353 !stabilityPools[_recipient] &&

• LUSDToken.sol#L354 !troveManagers[_recipient] &&

Use of safeMath can be avoided to save gas

In other parts of the project solidity version ^0.8 it's being used and has overflow protection by default so it's not needed safeMath.

• ActivePool.sol#L27 using SafeMath for uint256;
• CommunityIssuance.sol#L15 using SafeMath for uint;
• LQTYStaking.sol#L20 using SafeMath for uint;
• LUSDToken.sol#L29 using SafeMath for uint256;

Use Custom Errors consumes less gas than regular require strings

NOTE: None of these findings where found by 4naly3er output - Gas

Source Instead of using error strings, to reduce deployment and runtime cost, you should use Custom Errors. This would save both deployment and runtime cost.

• BorrowerOperations.sol#L561 require(
• ActivePool.sol#L314 require(
• ActivePool.sol#L321 require(
• ActivePool.sol#L329 require(
• ActivePool.sol#L338 require(
• LQTYStaking.sol#L253 require(
• LUSDToken.sol#L134 require(
• LUSDToken.sol#L347 require(
• LUSDToken.sol#L352 require(
• LUSDToken.sol#L367 require(
• LUSDToken.sol#L384 require(
• ReaperVaultV2.sol#L404 require(
• ReaperBaseStrategyv4.sol#L191 require(
• LUSDToken.sol#L280 revert('LUSD: Invalid s value');

Use assembly to check for address(0) for gas saves

NOTE: None of these findings where found by 4naly3er output - Gas

Saves 6 gas per instance

• ReaperVaultV2.sol#L151 require(_strategy != address(0), "Invalid strategy address");
• ReaperVaultV2.sol#L629 require(newTreasury != address(0), "Invalid address");
• ReaperStrategyGranarySupplyOnly.sol#L167 require(step[0] != address(0));
• ReaperStrategyGranarySupplyOnly.sol#L168 require(step[1] != address(0));

Initializing variables with default value wastes extra gas

NOTE: None of these findings where found by 4naly3er output - Gas

• CollateralConfig.sol#L18 bool public initialized = false;
• ActivePool.sol#L32 bool public addressesSet = false;
• CommunityIssuance.sol#L21 bool public initialized = false;
• LUSDToken.sol#L37 bool public mintingPaused = false;

Functions guaranteed to revert when called by normal users can be marked payable

NOTE: None of these findings where found by 4naly3er output - Gas

If a function modifier such as onlyOwner is used, the function will revert if a normal user tries to pay the function. Marking the function as payable will lower the gas cost for legitimate callers because the compiler will not include checks for whether a payment was provided.

The extra opcodes avoided are: CALLVALUE (2), DUP1 (3), ISZERO (3), PUSH2 (3), JUMPI (10), PUSH1 (3), DUP1 (3), REVERT(0), JUMPDEST (1), POP (2), which costs an average of about 21 gas per call to the function, in addition to the extra deployment cost

• TroveManager.sol#L250 require(msg.sender == owner);

unchecked block can be used to save gas

Where is not expected to overflow, unchecked can be used

• ReaperStrategyGranarySupplyOnly.sol#L81
• ReaperStrategyGranarySupplyOnly.sol#L93
• ReaperStrategyGranarySupplyOnly.sol#L100
• ReaperStrategyGranarySupplyOnly.sol#L132
• ReaperStrategyGranarySupplyOnly.sol#L133
• ReaperStrategyGranarySupplyOnly.sol#L136
• ReaperVaultERC4626.sol#L82
• ReaperVaultERC4626.sol#L125
• ReaperVaultERC4626.sol#L273
• ReaperVaultV2.sol#L194
• ReaperVaultV2.sol#L196
• ReaperVaultV2.sol#L214
• ReaperVaultV2.sol#L419

Explicit named return can be removed

• ReaperVaultERC4626.sol#L29
• ReaperVaultERC4626.sol#L37
• ReaperVaultERC4626.sol#L51
• ReaperVaultERC4626.sol#L66
• ReaperVaultERC4626.sol#L79
• ReaperVaultERC4626.sol#L96
• ReaperVaultERC4626.sol#L122
• ReaperVaultERC4626.sol#L220
• ReaperVaultERC4626.sol#L240

decimals can be set as uint8 for convention and to save 1 storage slot

• CollateralConfig.sol#L29

value of distributionPeriod can be set as default value to save gas

• CommunityIssuance.sol#L58

Remove testing libs for gas saves

• LQTYStaking.sol#L9
• LUSDToken.sol#L9
• StabilityPool.sol#L18
• ActivePool.sol#L15
• BorrowerOperations.sol#L15