QuickSwap and StellaSwap contest - Saintcode_'s results

USE CALLDATA INSTEAD OF MEMORY

When a function with a memory array is called externally, the abi.decode() step has to use a for-loop to copy each index of the calldata to the memory index. Each iteration of this for-loop costs at least 60 gas (i.e. 60 * <mem_array>.length). Using calldata directly, obliviates the need for such a loop in the contract code and runtime execution.

When arguments are read-only on external functions, the data location should be calldata

3 Instances: -DataStorageOperator.sol line 90 -AdaptiveFee.sol line 28 -DataStorage line 280

<ARRAY>.LENGTH SHOULD NOT BE LOOKED UP IN EVERY LOOP OF A FOR-LOOP

Reading array length at each iteration of the loop consumes more gas than necessary. In the best case scenario (length read on a memory variable), caching the array length in the stack saves around 3 gas per iteration. In the worst case scenario (external calls at each iteration), the amount of gas wasted can be massive.

Consider storing the array’s length in a variable before the for-loop, and use this new variable instead

1 Instance: -DataStorage.sol line 307

<X> += <Y> COSTS MORE GAS THAN <X> = <X> + <Y> FOR STATE VARIABLES

4 Instances: -AlgebraPool.sol lines 257, 258, 931, 945

USE MULTIPLE REQUIRE() STATMENTS INSTEAD OF REQUIRE(EXPRESSION && EXPRESSION && ...)

1 Instance: -AlgebraFactory.sol line 110 -AlgebraPool.sol lines 953, 968 -DataStorageOperator.sol line 46

IT COSTS MORE GAS TO INITIALIZE VARIABLES WITH THEIR DEFAULT VALUE THAN LETTING THE DEFAULT VALUE 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) {

1 Instance: -DataStorage.sol line 307

>= COSTS LESS GAS THAN >

The compiler uses opcodes GT and ISZERO for solidity code that uses >, but only requires LT for >=, which saves 3 gas

27 Instances: -AlgebraPool.sol lines 224, 228, 237, 434, 451, 452, 454, 455, 505, 506, 617, 641, 645, 667, 734, 808, 814, 898, 904, 911, 924, 927, 938, 941 -DataStorageOperator.sol line 138

++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

The unchecked keyword is new in solidity version 0.8.0, so this only applies to that version or higher, which these instances are. This saves 30-40 gas per loop for (uint256 i = 0; i < orders.length; /** NOTE: Removed i++ **/ ) { // Do the thing // Unchecked pre-increment is cheapest unchecked { ++i; } } 1 Instance: -DataStorage.sol line 307

USING PRIVATE RATHER THAN PUBLIC FOR CONSTANTS, SAVES GAS

If needed, the value can be read from the verified contract source code. Savings are due to the compiler not having to create non-payable getter functions for deployment calldata, and not adding another entry to the method ID table

1 Instance: -DataStorage.sol line 12

USE A MORE RECENT VERSION OF SOLIDITY

Use a solidity version above 0.8.0