Gas Optimizations

[code423n4]

G01 - Comparison > 0 is less gas efficient than != 0 with uint256 in require statement

contracts/Aura.sol:68   require(_amount > 0, "Must mint something");
contracts/AuraBalRewardPool.sol:121    require(_amount > 0, "RewardPool : Cannot stake 0");
contracts/AuraBalRewardPool.sol:139    require(_amount > 0, "RewardPool : Cannot stake 0");
contracts/AuraBalRewardPool.sol:157    require(amount > 0, "RewardPool : Cannot withdraw 0");
contracts/AuraBalRewardPool.sol:210    require(rewardsAvailable > 0, "!balance");
contracts/AuraLocker.sol:210    require(rewardData[_rewardsToken].lastUpdateTime > 0, "Reward does not exist");
contracts/AuraLocker.sol:259    require(_amount > 0, "Cannot stake 0");
contracts/AuraLocker.sol:359    require(amt > 0, "Nothing locked");
contracts/AuraLocker.sol:385    require(length > 0, "no locks");
contracts/AuraLocker.sol:431    require(locked > 0, "no exp locks");
contracts/AuraLocker.sol:471    require(len > 0, "Nothing to delegate");
contracts/AuraLocker.sol:822    require(_rewards > 0, "No reward");
contracts/AuraLocker.sol:851    require(_reward > 0, "No reward");
contracts/AuraMerkleDrop.sol:122    require(_amount > 0, "!amount");
contracts/AuraPenaltyForwarder.sol:52   require(bal > 0, "!empty");
contracts/AuraVestedEscrow.sol:118  require(totalLocked[_recipient] > 0, "!funding");
contracts/BalLiquidityProvider.sol:57   require(bal > 0 && bal == _request.maxAmountsIn[i], "!bal");
contracts/BalLiquidityProvider.sol:70   require(balAfter > 0, "!mint");
contracts/ExtraRewardsDistributor.sol:171   require(_index > 0 && _index < rewardEpochs[_token].length - 1, "!past");
convex-platform/contracts/contracts/BaseRewardPool.sol:211  require(_amount > 0, 'RewardPool : Cannot stake 0');
convex-platform/contracts/contracts/BaseRewardPool.sol:227  require(amount > 0, 'RewardPool : Cannot withdraw 0');
convex-platform/contracts/contracts/CrvDepositor.sol:169    require(_amount > 0,"!>0");  
convex-platform/contracts/contracts/PoolManagerSecondaryProxy.sol:104   require(weight > 0, "must have weight");

G02 - No need to initialize variables with default values

If a variable is not set, it is assumed to have the default value (0, false etc).

contracts/AuraBalRewardPool.sol:35  uint256 public pendingPenalty = 0;
contracts/AuraBalRewardPool.sol:38  uint256 public periodFinish = 0;
contracts/AuraBalRewardPool.sol:39  uint256 public rewardRate = 0;
contracts/AuraLocker.sol:72    uint256 public queuedCvxCrvRewards = 0;
contracts/AuraLocker.sol:114    bool public isShutdown = false;
contracts/AuraMerkleDrop.sol:29   uint256 public pendingPenalty = 0;
contracts/AuraVestedEscrow.sol:33   bool public initialised = false;
convex-platform/contracts/contracts/BaseRewardPool.sol:71   uint256 public periodFinish = 0;
convex-platform/contracts/contracts/BaseRewardPool.sol:72   uint256 public rewardRate = 0;
convex-platform/contracts/contracts/BaseRewardPool.sol:75   uint256 public queuedRewards = 0;
convex-platform/contracts/contracts/BaseRewardPool.sol:76   uint256 public currentRewards = 0;
convex-platform/contracts/contracts/BaseRewardPool.sol:77   uint256 public historicalRewards = 0;
convex-platform/contracts/contracts/Booster.sol:29  uint256 public platformFee = 0; //possible fee to build treasury
convex-platform/contracts/contracts/CrvDepositor.sol:36 uint256 public incentiveCrv = 0;  
convex-platform/contracts/contracts/VirtualBalanceRewardPool.sol:89    uint256 public periodFinish = 0;
convex-platform/contracts/contracts/VirtualBalanceRewardPool.sol:90    uint256 public rewardRate = 0;
convex-platform/contracts/contracts/VirtualBalanceRewardPool.sol:93    uint256 public queuedRewards = 0;
convex-platform/contracts/contracts/VirtualBalanceRewardPool.sol:94    uint256 public currentRewards = 0;
convex-platform/contracts/contracts/VirtualBalanceRewardPool.sol:95    uint256 public historicalRewards = 0;

G03 - Variables that can be changed to immutable

contracts/AuraLocker.sol:117    string private _name;
contracts/AuraLocker.sol:118    string private _symbol;
contracts/ClaimFeesHelper.sol:23    IFeeDistributor public feeDistro;
convex-platform/contracts/contracts/BaseRewardPool4626.sol:26   address public override asset;
convex-platform/contracts/contracts/DepositToken.sol:22   address public operator;  
convex-platform/contracts/contracts/TokenFactory.sol:21   string public namePostfix;  
convex-platform/contracts/contracts/TokenFactory.sol:22   string public symbolPrefix;

G04 - Cache array length before for loop

Optimizing for loops by caching memory array length before loop, instead of calling it every time.

contracts/AuraClaimZap.sol:143    for (uint256 i = 0; i < rewardContracts.length; i++) {
contracts/AuraClaimZap.sol:147    for (uint256 i = 0; i < extraRewardContracts.length; i++) {
contracts/AuraClaimZap.sol:151    for (uint256 i = 0; i < tokenRewardContracts.length; i++) {
contracts/AuraLocker.sol:696    for (uint256 i = nextUnlockIndex; i < locks.length; i++) {
contracts/AuraVestedEscrow.sol:100    for (uint256 i = 0; i < _recipient.length; i++) {
convex-platform/contracts/contracts/ArbitartorVault.sol:49   for(uint256 i = 0; i < _toPids.length; i++){
convex-platform/contracts/contracts/BaseRewardPool.sol:214  for(uint i=0; i < extraRewards.length; i++){  
convex-platform/contracts/contracts/BaseRewardPool.sol:230  for(uint i=0; i < extraRewards.length; i++){  
convex-platform/contracts/contracts/BaseRewardPool.sol:262  for(uint i=0; i < extraRewards.length; i++){
convex-platform/contracts/contracts/BaseRewardPool.sol:296  for(uint i=0; i < extraRewards.length; i++){  
convex-platform/contracts/contracts/Booster.sol:379    for(uint i=0; i < poolInfo.length; i++){
convex-platform/contracts/contracts/Booster.sol:538   for(uint256 i = 0; i < _gauge.length; i++){
convex-platform/contracts/contracts/PoolManagerSecondaryProxy.sol:69    for(uint i=0; i < usedList.length; i++){  

G05 - Using ++i consumes less gas than i++

contracts/AuraClaimZap.sol:143    for (uint256 i = 0; i < rewardContracts.length; i++) {
contracts/AuraClaimZap.sol:147    for (uint256 i = 0; i < extraRewardContracts.length; i++) {
contracts/AuraClaimZap.sol:151    for (uint256 i = 0; i < tokenRewardContracts.length; i++) {
contracts/AuraLocker.sol:696    for (uint256 i = nextUnlockIndex; i < locks.length; i++) {
contracts/AuraVestedEscrow.sol:100    for (uint256 i = 0; i < _recipient.length; i++) {
contracts/AuraLocker.sol:174    for (uint256 i = 0; i < rewardTokensLength; i++) {
contracts/AuraLocker.sol:306    for (uint256 i; i < rewardTokensLength; i++) {
contracts/AuraLocker.sol:410    for (uint256 i = nextUnlockIndex; i < length; i++) {
contracts/AuraLocker.sol:664    for (uint256 i = locksLength; i > 0; i--) {
contracts/AuraLocker.sol:726    for (uint256 i = epochIndex + 1; i > 0; i--) {
contracts/AuraLocker.sol:773    for (uint256 i = 0; i < userRewardsLength; i++) {
contracts/ExtraRewardsDistributor.sol:233   for (uint256 i = epochIndex; i < tokenEpochs; i++) {

G06 - unchecked block can be used for gas efficiency of the expression that can't overflow/underflow

Check comments

contracts/AuraBalRewardPool.sol:185    rewardToken.safeTransfer(msg.sender, reward - penalty); // penalty <= reward due to L183
contracts/AuraLocker.sol:278    if (idx == 0 || userLocks[_account][idx - 1].unlockTime < unlockTime) { // If idx == 0 then first part return true, so here and on L281 can't be underflow
contracts/AuraLocker.sol:334    while (epochs[epochs.length - 1].date != currentEpoch) {  //  If epochs.length == 0 then it will be checked on L332, so here and on L335 can't be underflow
contracts/AuraLocker.sol:402    uint256 epochsover = currentEpoch.sub(uint256(locks[length - 1].unlockTime)).div(rewardsDuration); // length > 0, checked on L385, so here and on L404 can't be underflow
contracts/AuraLocker.sol:484    uint256 i = len - 1; // len > 0, checked on L471
contracts/AuraLocker.sol:497    i--; // i > 0, checked on L496
contracts/AuraLocker.sol:521    DelegateeCheckpoint memory prevCkpt = ckpts[ckpts.length - 1]; // ckpts.length > 0, checked on L520, so here and on L524 can't be underflow
contracts/AuraLocker.sol:640    return high == 0 ? DelegateeCheckpoint(0, 0) : ckpts[high - 1]; // can't be underflow due to statement logic
contracts/AuraLocker.sol:665    uint256 lockEpoch = uint256(locks[i - 1].unlockTime).sub(lockDuration); // i > 0, checked on L664, so here and on 670 can't be underflow
contracts/AuraLocker.sol:699    lockData = new LockedBalance[](locks.length - i); // i < locks.length due to L696
contracts/AuraLocker.sol:722    uint256 lastIndex = epochs.length - 1; // epochs.length > 0 due to L718
contracts/AuraLocker.sol:727    Epoch memory e = epochs[i - 1]; // i > 0 due to L726
contracts/AuraMerkleDrop.sol:138    aura.safeTransfer(msg.sender, _amount - penalty); // penalty < _amount due to L136
contracts/AuraVestedEscrow.sol:162  uint256 elapsed = _time - startTime;  // startTime < _time due to L158
contracts/ExtraRewardsDistributor.sol:74    require(len == 0 || rewardEpochs[_token][len - 1] < _epoch, "Cannot backdate to this epoch"); // if len == 0 then first part return true
contracts/ExtraRewardsDistributor.sol:102   if (len == 0 || rewardEpochs[_token][len - 1] < _epoch) { if len == 0 then first part return true

G07 - Too 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 has been met.

contracts/AuraLocker.sol:197    require(_rewardsToken != address(stakingToken), "Cannot add StakingToken as reward");

G08 - Named return vatiable

Removing unused named return variables can reduce gas usage and improve code clarity.

contracts/AuraLocker.sol:712    function totalSupply() external view returns (uint256 supply) {
contracts/AuraLocker.sol:739    function findEpochId(uint256 _time) public view returns (uint256 epoch) {
convex-platform/contracts/contracts/BaseRewardPool4626.sol:179  function previewWithdraw(uint256 assets) public view virtual override returns(uint256 shares){  

G09 - No needed +=

No need to use += instead of =, since totalLocked[_recipient[i]] always be 0 here:

contracts/AuraVestedEscrow.sol:103  totalLocked[_recipient[i]] += amount;

G10 - Caching storage values in memory

Variables that are read multiple times in a code block can be cached and re-used instead of reading from storage to save gas.

contracts/AuraLocker.sol:812    .div(lockedSupply) // lockedSupply 2 SLOAD
contracts/AuraMerkleDrop.sol:126    require(MerkleProof.verify(_proof, merkleRoot, leaf), "invalid proof"); // merkleRoot 2 SLOAD
contracts/AuraMerkleDrop.sol:132    aura.safeApprove(address(auraLocker), _amount); // auraLocker 2 SLOAD
contracts/AuraStakingProxy.sol:119  owner = pendingOwner; // pendingOwner 2 SLOAD
contracts/AuraStakingProxy.sol:148  IERC20(crv).safeApprove(crvDepositorWrapper, type(uint256).max); // crvDepositorWrapper 2 SLOAD
contracts/AuraStakingProxy.sol:151  IERC20(cvxCrv).safeApprove(rewards, type(uint256).max); // rewards 2 SLOAD
contracts/AuraStakingProxy.sol:172  require(msg.sender == keeper, "!auth"); // keeper 2 SLOAD
contracts/AuraStakingProxy.sol:179  ICrvDepositor(crvDepositorWrapper).deposit(crvBal, minOut, true, address(0)); // crvDepositorWrapper 2 SLOAD
contracts/AuraStakingProxy.sol:219  IAuraLocker(rewards).notifyRewardAmount(address(_token), bal); // rewards 3 SLOAD
contracts/AuraVestedEscrow.sol:186  rewardToken.safeApprove(address(auraLocker), claimable); // auraLocker 2 SLOAD
convex-platform/contracts/contracts/Booster.sol:235    emit FeeInfoUpdated(_feeDistro, lockRewards, crv); // lockRewards 3 SLOAD
convex-platform/contracts/contracts/Booster.sol:606   IERC20(crv).safeTransfer(treasury, _platform); // treasury 3 SLOAD