Ethos Reserve contest - TheSavageTeddy's results

Using bitwise-not ~ instead of -(i+1) saves gas

Calculating -(i+1) instead of ~ costs 9 more gas, because of the extra ADD , SUB and PUSHs that can be replaced by NOT to achieve the same result.

startIdx = uint(-(_startIdx + 1)); => startIdx = uint(~_startIdx);

There is 1 instance of this issue:

File: MultiTroveGetter.sol
44:             startIdx = uint(-(_startIdx + 1));

https://github.com/code-423n4/2023-02-ethos/blob/main/Ethos-Core/contracts/MultiTroveGetter.sol#L44

Check Require() / Revert() statements that use less gas first

Checks that cost less gas, such as checking function parameters, should be placed before more expensive checks such as ones that invoke msg.sender, because the function will be able to revert before checking more expensive statements. In this case, require(msg.sender == vault, "Only vault can withdraw"); should be placed after the other require() statements which use less gas, to prevent wasting around 24680 gas.

There is 1 instance of this issue:

File: ReaperBaseStrategyv4.sol
95:     function withdraw(uint256 _amount) external override returns (uint256 loss) {
96:         require(msg.sender == vault, "Only vault can withdraw");
97:         require(_amount != 0, "Amount cannot be zero");
98:         require(_amount <= balanceOf(), "Ammount must be less than balance");

https://github.com/code-423n4/2023-02-ethos/blob/main/Ethos-Vault/contracts/abstract/ReaperBaseStrategyv4.sol#L95-L98

Expressions for constant values such as calling KECCAK256() should use immutable rather than constant

Constant values for function calls result in increased gas costs as immutables are evaluated at deployment time, in contrast to constants which are executed at runtime for each invocation.

There are 8 instances of this issue:

File: ReaperVaultV2.sol
73:     bytes32 public constant DEPOSITOR = keccak256("DEPOSITOR");
74:     bytes32 public constant STRATEGIST = keccak256("STRATEGIST");
75:     bytes32 public constant GUARDIAN = keccak256("GUARDIAN");
76:     bytes32 public constant ADMIN = keccak256("ADMIN");

https://github.com/code-423n4/2023-02-ethos/blob/main/Ethos-Vault/contracts/ReaperVaultV2.sol#L73-L76

File: ReaperBaseStrategyv4.sol
49:     bytes32 public constant KEEPER = keccak256("KEEPER");
50:     bytes32 public constant STRATEGIST = keccak256("STRATEGIST");
51:     bytes32 public constant GUARDIAN = keccak256("GUARDIAN");
52:     bytes32 public constant ADMIN = keccak256("ADMIN");

https://github.com/code-423n4/2023-02-ethos/blob/main/Ethos-Vault/contracts/abstract/ReaperBaseStrategyv4.sol#L49-L52

Use unchecked{} for subtraction operations where operands cannot underflow because of a previous if statement

Using unchecked{} for operations that cannot underflow because of a previous if statement saves gas as it ignores the overflow/underflow checks.

There are 15 instances of this issue:

File: MultiTroveGetter.sol
50:         if (startIdx >= sortedTrovesSize) {
51:             _troves = new CombinedTroveData[](0);
52:         } else {
53:             uint maxCount = sortedTrovesSize - startIdx; /// @audit use unchecked{} as it cannot underflow because of previous if statement

https://github.com/code-423n4/2023-02-ethos/blob/main/Ethos-Core/contracts/MultiTroveGetter.sol#L50-L53

File: PriceFeed.sol
509:         uint price;
510:         if (_answerDigits >= TARGET_DIGITS) {
511:             // Scale the returned price value down to Liquity's target precision
512:             price = _price.div(10 ** (_answerDigits - TARGET_DIGITS)); /// @audit use unchecked{} as it cannot underflow because of previous if statement
513:         }
514:         else if (_answerDigits < TARGET_DIGITS) {
515:             // Scale the returned price value up to Liquity's target precision
516:             price = _price.mul(10 ** (TARGET_DIGITS - _answerDigits)); /// @audit use unchecked{} as it cannot underflow because of previous if statement

https://github.com/code-423n4/2023-02-ethos/blob/main/Ethos-Core/contracts/PriceFeed.sol#L509-L516

File: PriceFeed.sol
522:         uint256 price = _price;
523:         if (TARGET_DIGITS > TELLOR_DIGITS) {
524:             price = price.mul(10**(TARGET_DIGITS - TELLOR_DIGITS)); /// @audit use unchecked{} as it cannot underflow because of previous if statement
525:         } else if (TARGET_DIGITS < TELLOR_DIGITS) {
526:             price = price.div(10**(TELLOR_DIGITS - TARGET_DIGITS)); /// @audit use unchecked{} as it cannot underflow because of previous if statement

https://github.com/code-423n4/2023-02-ethos/blob/main/Ethos-Core/contracts/PriceFeed.sol#L522-L526

File: TroveManager.sol
492:         uint cappedCollPortion = _entireTroveDebt.mul(_MCR).div(_price);
493:         if (_collDecimals < LiquityMath.CR_CALCULATION_DECIMALS) {
494:             cappedCollPortion = cappedCollPortion.div(10 ** (LiquityMath.CR_CALCULATION_DECIMALS - _collDecimals)); /// @audit use unchecked{} as it cannot underflow because of previous if statement
495:         } else if (_collDecimals > LiquityMath.CR_CALCULATION_DECIMALS) {
496:             cappedCollPortion = cappedCollPortion.mul(10 ** (_collDecimals - LiquityMath.CR_CALCULATION_DECIMALS)); /// @audit use unchecked{} as it cannot underflow because of previous if statement

https://github.com/code-423n4/2023-02-ethos/blob/main/Ethos-Core/contracts/TroveManager.sol#L492-L496

File: ReaperStrategyGranarySupplyOnly.sol
79:         uint256 wantBalance = balanceOfWant();
80:         if (wantBalance > _debt) {
81:             uint256 toReinvest = wantBalance - _debt; /// @audit use unchecked{} as it cannot underflow because of previous if statement

https://github.com/code-423n4/2023-02-ethos/blob/main/Ethos-Vault/contracts/ReaperStrategyGranarySupplyOnly.sol#L79-L81

File: ReaperStrategyGranarySupplyOnly.sol
91:         uint256 wantBal = balanceOfWant();
92:         if (wantBal < _amountNeeded) {
93:             _withdraw(_amountNeeded - wantBal); /// @audit use unchecked{} as it cannot underflow because of previous if statement

https://github.com/code-423n4/2023-02-ethos/blob/main/Ethos-Vault/contracts/ReaperStrategyGranarySupplyOnly.sol#L91-L93

File: ReaperStrategyGranarySupplyOnly.sol
099:         if (_amountNeeded > liquidatedAmount) {
100:             loss = _amountNeeded - liquidatedAmount; /// @audit use unchecked{} as it cannot underflow because of previous if statement

https://github.com/code-423n4/2023-02-ethos/blob/main/Ethos-Vault/contracts/ReaperStrategyGranarySupplyOnly.sol#L099-L100

File: ReaperStrategyGranarySupplyOnly.sol
File: ReaperStrategyGranarySupplyOnly.sol
131:         if (totalAssets > allocated) {
132:             uint256 profit = totalAssets - allocated; /// @audit use unchecked{} as it cannot underflow because of previous if statement
133:             toFree += profit;
134:             roi = int256(profit);
135:         } else if (totalAssets < allocated) {
136:             roi = -int256(allocated - totalAssets); /// @audit use unchecked{} as it cannot underflow because of previous if statement

https://github.com/code-423n4/2023-02-ethos/blob/main/Ethos-Vault/contracts/ReaperStrategyGranarySupplyOnly.sol#L131-L136

File: ReaperVaultV2.sol
234:         if (stratCurrentAllocation > stratMaxAllocation) {
235:             return -int256(stratCurrentAllocation - stratMaxAllocation); /// @audit use unchecked{} as it cannot underflow because of previous if statement
236:         } else if (stratCurrentAllocation < stratMaxAllocation) {
237:             uint256 vaultMaxAllocation = (totalAllocBPS * balance()) / PERCENT_DIVISOR;
238:             uint256 vaultCurrentAllocation = totalAllocated;
239: 
240:             if (vaultCurrentAllocation >= vaultMaxAllocation) {
241:                 return 0;
242:             }
243: 
244:             uint256 available = stratMaxAllocation - stratCurrentAllocation; /// @audit use unchecked{} as it cannot underflow because of previous if statement

https://github.com/code-423n4/2023-02-ethos/blob/main/Ethos-Vault/contracts/ReaperVaultV2.sol#L234-L244

File: ReaperVaultV2.sol
374:                 if (value <= vaultBalance) {
375:                     break;
376:                 }
377: 
378:                 address stratAddr = withdrawalQueue[i];
379:                 uint256 strategyBal = strategies[stratAddr].allocated;
380:                 if (strategyBal == 0) {
381:                     continue;
382:                 }
383: 
384:                 uint256 remaining = value - vaultBalance; /// @audit use unchecked{} as it cannot underflow because of previous if statement

https://github.com/code-423n4/2023-02-ethos/blob/main/Ethos-Vault/contracts/ReaperVaultV2.sol#L374-L384

File: ReaperVaultV2.sol
525:         if (vars.credit > vars.freeWantInStrat) {
526:             token.safeTransfer(vars.stratAddr, vars.credit - vars.freeWantInStrat); /// @audit use unchecked{} as it cannot underflow because of previous if statement
527:         } else if (vars.credit < vars.freeWantInStrat) {
528:             token.safeTransferFrom(vars.stratAddr, address(this), vars.freeWantInStrat - vars.credit); /// @audit use unchecked{} as it cannot underflow because of previous if statement

https://github.com/code-423n4/2023-02-ethos/blob/main/Ethos-Vault/contracts/ReaperVaultV2.sol#L525-L528

File: ReaperVaultV2.sol
534:         if (vars.lockedProfitBeforeLoss > vars.loss) {
535:             lockedProfit = vars.lockedProfitBeforeLoss - vars.loss; /// @audit use unchecked{} as it cannot underflow because of previous if statement

https://github.com/code-423n4/2023-02-ethos/blob/main/Ethos-Vault/contracts/ReaperVaultV2.sol#L534-L535

File: ReaperBaseStrategyv4.sol
119:             uint256 amountFreed = _liquidateAllPositions();
120:             if (amountFreed < debt) {
121:                 roi = -int256(debt - amountFreed); /// @audit use unchecked{} as it cannot underflow because of previous if statement
122:             } else if (amountFreed > debt) {
123:                 roi = int256(amountFreed - debt); /// @audit use unchecked{} as it cannot underflow because of previous if statement

https://github.com/code-423n4/2023-02-ethos/blob/main/Ethos-Vault/contracts/abstract/ReaperBaseStrategyv4.sol#L119-L123

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

This saves around 13 gas for each execution.

There are 8 instances of this issue:

totalAllocBPS += _allocBPS;

https://github.com/code-423n4/2023-02-ethos/blob/main/Ethos-Vault/contracts/ReaperVaultV2.sol#L168

totalAllocBPS -= strategies[_strategy].allocBPS;

https://github.com/code-423n4/2023-02-ethos/blob/main/Ethos-Vault/contracts/ReaperVaultV2.sol#L194

totalAllocBPS += _allocBPS;

https://github.com/code-423n4/2023-02-ethos/blob/main/Ethos-Vault/contracts/ReaperVaultV2.sol#L196

totalAllocBPS -= strategies[_strategy].allocBPS;

https://github.com/code-423n4/2023-02-ethos/blob/main/Ethos-Vault/contracts/ReaperVaultV2.sol#L214

totalAllocBPS -= bpsChange;

https://github.com/code-423n4/2023-02-ethos/blob/main/Ethos-Vault/contracts/ReaperVaultV2.sol#L445

totalAllocated -= loss;

https://github.com/code-423n4/2023-02-ethos/blob/main/Ethos-Vault/contracts/ReaperVaultV2.sol#L452

totalAllocated -= vars.debtPayment;

https://github.com/code-423n4/2023-02-ethos/blob/main/Ethos-Vault/contracts/ReaperVaultV2.sol#L515

totalAllocated += vars.credit;

https://github.com/code-423n4/2023-02-ethos/blob/main/Ethos-Vault/contracts/ReaperVaultV2.sol#L521

Use a more recent version of Solidity

Using ^0.8.0 as opposed to 0.6.11, which is used in many contracts, saves gas as several operations are optimized in the newer versions of Solidity. For example, accessing data in calldata, reduced gas cost when emitting event data and the introduction of immutable state variables save gas.

There are 33 instances of this issue:

File: ActivePool.sol
3: pragma solidity 0.6.11;

File: BorrowerOperations.sol
3: pragma solidity 0.6.11;

File: CollateralConfig.sol
3: pragma solidity 0.6.11;

File: CollSurplusPool.sol
3: pragma solidity 0.6.11;

File: DefaultPool.sol
3: pragma solidity 0.6.11;

File: GasPool.sol
3: pragma solidity 0.6.11;

File: HintHelpers.sol
3: pragma solidity 0.6.11;

File: LUSDToken.sol
3: pragma solidity 0.6.11;

File: Migrations.sol
3: pragma solidity 0.6.11;

File: MultiTroveGetter.sol
3: pragma solidity 0.6.11;

File: PriceFeed.sol
3: pragma solidity 0.6.11;

File: RedemptionHelper.sol
3: pragma solidity 0.6.11;

File: SortedTroves.sol
3: pragma solidity 0.6.11;

File: StabilityPool.sol
3: pragma solidity 0.6.11;

File: TroveManager.sol
3: pragma solidity 0.6.11;

File: LQTYStaking.sol
3: pragma solidity 0.6.11;

File: CommunityIssuance.sol
3: pragma solidity 0.6.11;

File: IActivePool.sol
3: pragma solidity 0.6.11;

File: IBorrowerOperations.sol
3: pragma solidity 0.6.11;

File: ICollateralConfig.sol
3: pragma solidity 0.6.11;

File: ICollSurplusPool.sol
3: pragma solidity 0.6.11;

File: ICommunityIssuance.sol
3: pragma solidity 0.6.11;

File: IDefaultPool.sol
3: pragma solidity 0.6.11;

File: ILiquityBase.sol
3: pragma solidity 0.6.11;

File: ILQTYStaking.sol
3: pragma solidity 0.6.11;

File: ILUSDToken.sol
3: pragma solidity 0.6.11;

File: IPool.sol
3: pragma solidity 0.6.11;

File: IPriceFeed.sol
3: pragma solidity 0.6.11;

File: IRedemptionHelper.sol
3: pragma solidity 0.6.11;

File: ISortedTroves.sol
3: pragma solidity 0.6.11;

File: IStabilityPool.sol
3: pragma solidity 0.6.11;

File: ITellorCaller.sol
3: pragma solidity 0.6.11;

File: ITroveManager.sol
3: pragma solidity 0.6.11;