Canto contest - rfa's results

GAS

Title: Using calldata to store read only string and array arguments

Occurrences: https://github.com/Plex-Engineer/manifest/blob/cf88a30070689b71c2678642dc0fdfa1740f666c/contracts/Proposal-Store.sol#L46-L47 https://github.com/Plex-Engineer/manifest/blob/cf88a30070689b71c2678642dc0fdfa1740f666c/contracts/Proposal-Store.sol#L39-L40

Using calldata can save execution gas fee:

    function AddProposal(uint propId, string calldata title, string calldata desc, address[] memory targets, 
                        uint[] calldata values, string[] calldata signatures, bytes[] calldata calldatas) public 

Title: Function visibility can set to external

Occurrences: https://github.com/Plex-Engineer/manifest/blob/cf88a30070689b71c2678642dc0fdfa1740f666c/contracts/Proposal-Store.sol#L47 https://github.com/Plex-Engineer/manifest/blob/cf88a30070689b71c2678642dc0fdfa1740f666c/contracts/Proposal-Store.sol#L52

The function is never called in the same contract. Changing the visibility to external is more effective

Title: Returning default value

https://github.com/Plex-Engineer/manifest/blob/688e9b4e7835854c22ef44b045d6d226b784b4b8/contracts/Proposal-Store.sol#L56

Returning default value is unnecessary, we can just remove L56 and let the function returning the 0 value by default. It can save 614 gas in case propId is not exist (and the function called from other contract)

Title: Use uint8 for _unlocked

https://github.com/Plex-Engineer/stableswap/blob/489d010eb99a0885139b2d5ed5a2d826838cc5f9/contracts/BaseV1-core.sol#L123

Max value of _unlocked is 2. We can change uint (uint256) with just smaller size uint (uint8)

Title: Using prefix increment and unchecked for i inside for()

Using prefix increment and unchecked for i is the most effective way for doing iteration:

for (uint i = 0; i < _prices.length;) {
            priceAverageCumulative += _prices[i];
	    unchecked{++i;}
        }

Title: Effective way to return in sample() function

https://github.com/Plex-Engineer/stableswap/blob/489d010eb99a0885139b2d5ed5a2d826838cc5f9/contracts/BaseV1-core.sol#L218-L234

By naming the returns() var with _prices, we don't need to return _prices in the last of function (which quite expensive because beside we declare new var at L219, we MSTORE all the _prices value into returns var).

Change to:

    function sample(address tokenIn, uint amountIn, uint points, uint window) public view returns (uint[] memory _prices) { //@audit-info: Give the returns() name
 // @audit-info: remove L219

        uint length = observations.length-1;
        uint i = length - (points * window);
        uint nextIndex = 0;
        uint index = 0;

        for (; i < length; i+=window) {
            nextIndex = i + window;
            uint timeElapsed = observations[nextIndex].timestamp - observations[i].timestamp;
            uint _reserve0 = (observations[nextIndex].reserve0Cumulative - observations[i].reserve0Cumulative) / timeElapsed;
            uint _reserve1 = (observations[nextIndex].reserve1Cumulative - observations[i].reserve1Cumulative) / timeElapsed;
            _prices[index] = _getAmountOut(amountIn, tokenIn, _reserve0, _reserve1);
            index = index + 1;
        }
	//@audit-info: remove return statement
    }

By doing this way, we can save 119 gas (if length == 1)

Title: Reading block.timestamp

https://github.com/Plex-Engineer/stableswap/blob/489d010eb99a0885139b2d5ed5a2d826838cc5f9/contracts/BaseV1-core.sol#L181-L185

blockTimestamp var is used to return the value of current block.timestamp in currentCumulativePrices function. We can just use block.timestamp to get current timestamp instead of calling blockTimestamp var. it can save 2 gas

Change to:

        if (_blockTimestampLast != block.timestamp) {
            // subtraction overflow is desired
            uint timeElapsed = block.timestamp - _blockTimestampLast;
            reserve0Cumulative += _reserve0 * timeElapsed;
            reserve1Cumulative += _reserve1 * timeElapsed;
        }

Title: Use ++index to do increment

https://github.com/Plex-Engineer/stableswap/blob/489d010eb99a0885139b2d5ed5a2d826838cc5f9/contracts/BaseV1-core.sol#L232

By using ++index compared to the current implementation can save 65 gas per loop

Title: Using && in require()

https://github.com/Plex-Engineer/stableswap/blob/489d010eb99a0885139b2d5ed5a2d826838cc5f9/contracts/BaseV1-core.sol#L272 https://github.com/Plex-Engineer/stableswap/blob/489d010eb99a0885139b2d5ed5a2d826838cc5f9/contracts/BaseV1-core.sol#L294

For every function which will be called quite often times, we can use multiple require() than && operator. Despite it will increase deployment gas fee. It will reduce execution gas fee by 15 Change to:

        require(amount0 > 0, 'ILB');
        require(amount1 > 0, 'ILB');