Fraxlend (Frax Finance) contest - Amithuddar's results

1)++i costs less gas than i++, especially when it’s used in for-loops (--i/i-- too)

Saves 6 gas PER LOOP

File: 2022-08-frax\src\contracts\FraxlendPair.sol 289,50: for (uint256 i = 0; i < _lenders.length; i++) { 308,52: for (uint256 i = 0; i < _borrowers.length; i++) {

File: 2022-08-frax\src\contracts\FraxlendWhitelist.sol 51,52: for (uint256 i = 0; i < _addresses.length; i++) { 66,52: for (uint256 i = 0; i < _addresses.length; i++) { 81,52: for (uint256 i = 0; i < _addresses.length; i++) {

File: 2022-08-frax\src\contracts\libraries\SafeERC20.sol 27,49: for (i = 0; i < 32 && data[i] != 0; i++) {

2)It costs more gas to initialize variables to zero than to let the default of zero 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) {

File: 2022-08-frax\src\contracts\FraxlendPair.sol 289,50: for (uint256 i = 0; i < _lenders.length; i++) { 308,52: for (uint256 i = 0; i < _borrowers.length; i++) {

File: 2022-08-frax\src\contracts\FraxlendPairCore.sol 265,9: for (uint256 i = 0; i < _approvedBorrowers.length; ++i) { 270,9: for (uint256 i = 0; i < _approvedLenders.length; ++i) {

File: 2022-08-frax\src\contracts\FraxlendWhitelist.sol 51,52: for (uint256 i = 0; i < _addresses.length; i++) { 66,52: for (uint256 i = 0; i < _addresses.length; i++) { 81,52: for (uint256 i = 0; i < _addresses.length; i++) {

File: 2022-08-frax\src\contracts\FraxlendPairDeployer.sol 402,9: for (uint256 i = 0; i < _lengthOfArray; ) {

File: 2022-08-frax\src\contracts\libraries\SafeERC20.sol

27,49: for (i = 0; i < 32 && data[i] != 0; i++) {

3)<ARRAY>.LENGTH SHOULD NOT BE LOOKED UP IN EVERY LOOP OF A FOR-LOOP The overheads outlined below are PER LOOP, excluding the first loop

storage arrays incur a Gwarmaccess (100 gas) memory arrays use MLOAD (3 gas) calldata arrays use CALLDATALOAD (3 gas) Caching the length changes each of these to a DUP<N> (3 gas), and gets rid of the extra DUP<N> needed to store the stack offset

File: 2022-08-frax\src\contracts\FraxlendPair.sol 289,50: for (uint256 i = 0; i < _lenders.length; i++) { 308,52: for (uint256 i = 0; i < _borrowers.length; i++) {

File: 2022-08-frax\src\contracts\FraxlendPairCore.sol 265,9: for (uint256 i = 0; i < _approvedBorrowers.length; ++i) { 270,9: for (uint256 i = 0; i < _approvedLenders.length; ++i) {

File: 2022-08-frax\src\contracts\FraxlendWhitelist.sol 51,52: for (uint256 i = 0; i < _addresses.length; i++) { 66,52: for (uint256 i = 0; i < _addresses.length; i++) { 81,52: for (uint256 i = 0; i < _addresses.length; i++) {

4. ++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

File: 2022-08-frax\src\contracts\FraxlendPair.sol 289,50: for (uint256 i = 0; i < _lenders.length; i++) { 308,52: for (uint256 i = 0; i < _borrowers.length; i++) {

File: 2022-08-frax\src\contracts\FraxlendPairCore.sol 265,9: for (uint256 i = 0; i < _approvedBorrowers.length; ++i) { 270,9: for (uint256 i = 0; i < _approvedLenders.length; ++i) {

File: 2022-08-frax\src\contracts\FraxlendWhitelist.sol 51,52: for (uint256 i = 0; i < _addresses.length; i++) { 66,52: for (uint256 i = 0; i < _addresses.length; i++) { 81,52: for (uint256 i = 0; i < _addresses.length; i++) {

File: 2022-08-frax\src\contracts\libraries\SafeERC20.sol

27,49: for (i = 0; i < 32 && data[i] != 0; i++) {

5)Use custom errors rather than revert()/require() strings to save gas

File: 2022-08-frax\src\contracts\FraxlendPairDeployer.sol 205,13: require(deployedPairsBySalt[salt] == address(0), "FraxlendPairDeployer: Pair already deployed"); 228,13: require(_pairAddress != address(0), "FraxlendPairDeployer: create2 failed"); 253,9: require(deployedPairsByName[_name] == address(0), "FraxlendPairDeployer: Pair name must be unique"); 365,9: require(_maxLTV <= GLOBAL_MAX_LTV, "FraxlendPairDeployer: _maxLTV is too large"); 366,9: require( 399,9: require(msg.sender == CIRCUIT_BREAKER_ADDRESS, "Circuit Breaker only");

File: 2022-08-frax\src\contracts\LinearInterestRate.sol 57,9: require(_minInterest < MAX_INT && _minInterest <= _vertexInterest && _minInterest >= MIN_INT, "LinearInterestRate: _minInterest < MAX_INT && _minInterest <= _vertexInterest && _minInterest >= MIN_INT" ); 61,9: require(_maxInterest <= MAX_INT && _vertexInterest <= _maxInterest && _maxInterest > MIN_INT, "LinearInterestRate: _maxInterest <= MAX_INT && _vertexInterest <= _maxInterest && _maxInterest > MIN_INT" ); 65,9: require(_vertexUtilization < MAX_VERTEX_UTIL && _vertexUtilization > 0, "LinearInterestRate: _vertexUtilization < MAX_VERTEX_UTIL && _vertexUtilization > 0" );

6)X = X + Y IS CHEAPER THAN X += Y File: 2022-08-frax\src\contracts\FraxlendPairCore.sol 475,37: _totalBorrow.amount += uint128(_interestEarned); 476,36: _totalAsset.amount += uint128(_interestEarned); 484,40: _totalAsset.shares += uint128(_feesShare); 566,28: _totalAsset.amount += _amount; 567,28: _totalAsset.shares += _shares; 718,29: _totalBorrow.amount += _borrowAmount; 719,29: _totalBorrow.shares += uint128(_sharesAdded); 724,38: userBorrowShares[msg.sender] += _sharesAdded; 772,42: userCollateralBalance[_borrower] += _collateralAmount; 773,25: totalCollateral += _collateralAmount;