SIZE contest - karanctf's results

1. cache .length in loops

Summary: 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.

SizeSealed.sol:155:        uint256 bidIndex = a.bids.length;
SizeSealed.sol:195:        if (finalizeData.length != 0) {
SizeSealed.sol:227:        if (bidIndices.length != a.bids.length) {
SizeSealed.sol:241:        uint256[] memory seenBidMap = new uint256[]((bidIndices.length/256)+1);
SizeSealed.sol:244:        for (uint256 i; i < bidIndices.length; i++) {
SizeSealed.sol:302:        for (uint256 i; i < seenBidMap.length - 1; i++) {
SizeSealed.sol:309:        if (seenBidMap[seenBidMap.length - 1] != (1 << (bidIndices.length % 256)) - 1) {

2. <x> += <y> costs more gas than <x> = <x> + <y>

SizeSealed.sol:294:            data.filledBase += baseAmount;
SizeSealed.sol:373:        b.baseWithdrawn += baseTokensAvailable;

3. Use calldata instead of memory when used only for reading

util/ECCMath.sol:25:    function ecMul(Point memory point, uint256 scalar) internal view returns (Point memory) {util/ECCMath.sol:37:    function encryptMessage(Point memory encryptToPub, uint256 encryptWithPriv, bytes32 message)
util/ECCMath.sol:51:    function decryptMessage(Point memory sharedPoint, bytes32 encryptedMessage)
util/ECCMath.sol:60:    function hashPoint(Point memory point) internal pure returns (bytes32) {
izeSealed.sol:217:    function finalize(uint256 auctionId, uint256[] memory bidIndices, uint128 SizeSealed.sol:474:    function getTimings(uint256 auctionId) external view returns (Timings memory timings) {
SizeSealed.sol:478:    function getAuctionData(uint256 auctionId) external view returns (AuctionData memory data) {

4. Use preincrement to save gas in loops

Summary: ++i costs less gas than i++, especially when it is used in for-loops (--i/i-- too) Saves 5 gas PER LOOP

SizeSealed.sol:244:        for (uint256 i; i < bidIndices.length; i++) {
SizeSealed.sol:302:        for (uint256 i; i < seenBidMap.length - 1; i++) {

5. Use variable == false|0 -> !variable or variable == true -> variable

util/ECCMath.sol:27:        if (scalar == 0 || (point.x == 0 && point.y == 0)) return Point(1, 1);
SizeSealed.sol:144:        if (quoteAmount == 0 || quoteAmount == type(uint128).max || quoteAmount < a.params.minimumBidQuote) {
SizeSealed.sol:223:        if (sellerPriv == 0) {
SizeSealed.sol:366:        if (baseAmount == 0) {

6. >= COSTS LESS GAS THAN >

Summary: The compiler uses opcodes GT and ISZERO for solidity code that uses >, but only requires LT for >=, which saves 3 gas https://gist.github.com/IllIllI000/3dc79d25acccfa16dee4e83ffdc6ffde

util/CommonTokenMath.sol:54:        if (currentTime > vestingEnd) {
SizeSealed.sol:37:        } else if (block.timestamp > a.timings.endTimestamp + 24 hours) {
SizeSealed.sol:66:        if (timings.endTimestamp > timings.vestingStartTimestamp) {
SizeSealed.sol:69:        if (timings.vestingStartTimestamp > timings.vestingEndTimestamp) {
SizeSealed.sol:72:        if (timings.cliffPercent > 1e18) {
SizeSealed.sol:79:            ) > auctionParams.reserveQuotePerBase
SizeSealed.sol:273:                    if (data.previousIndex > bidIndex) revert InvalidSorting();
SizeSealed.sol:289:            if (data.filledBase + baseAmount > data.totalBaseAmount) {
SizeSealed.sol:313:        if (data.filledBase > data.totalBaseAmount) {

7. Use abi.encodePacked for gas optimization

Summary: 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.

util/ECCMath.sol:26:        bytes memory data = abi.encode(point, scalar);
util/ECCMath.sol:61:        return keccak256(abi.encode(point));
SizeSealed.sol:467:        return keccak256(abi.encode(message));
test/mocks/MockBuyer.sol:34:        salt = bytes16(keccak256(abi.encode("randomsalt")));
test/mocks/MockSeller.sol:97:        auctionContract.reveal(auctionId, SELLER_PRIVATE_KEY, abi.encode(bidIndices, clearingBase, clearingQuote));

8. Use custom errors to save deployment and runtime costs in case of revert

Summary: Instead of using strings for error messages (e.g., require(msg.sender == owner, “unauthorized”)), you can use custom errors to reduce both deployment and runtime gas costs. In addition, they are very convenient as you can easily pass dynamic information to them.

test/mocks/MockBuyer.sol:44:        require(quoteToken.balanceOf(address(this)) >= quoteAmount);
test/mocks/MockBuyer.sol:81:        require(quoteToken.balanceOf(address(this)) >= quoteAmount);