Blur Exchange contest - halden's results

G-01: USING BOOLS FOR STORAGE INCURS OVERHEAD

Booleans are more expensive than uint256 or any type that takes up a full word because each write operation emits an extra SLOAD to first read the slot's contents, replace the bits taken up by the boolean, and then write back. source Use uint256(1) and uint256(2) for true/false to avoid a Gwarmaccess (100 gas), and to avoid Gsset (20000 gas) when changing from ‘false’ to ‘true’, after having been ‘true’ in the past.

File: ReentrancyGuarded.sol line 10 bool reentrancyLock = false;

File: ExecutionDelegate.sol line 18 mapping(address => bool) public contracts;

File: ExecutionDelegate.sol line 19 mapping(address => bool) public revokedApproval;

File: BlurExchange.sol line 71 mapping(bytes32 => bool) public cancelledOrFilled;

G-02 Cache storage values in memory to minimize SLOADs

The code can be optimized by minimising the number of SLOADs. SLOADs are expensive 100 gas compared to MLOADs/MSTOREs(3gas). Storage value should get cached in memory

PolicyManager.sol.viewWhitelistedPolicies: _whitelistedPolicies.length() should be cached - _whitelistedPolicies is a storage array File: PolicyManager.sol Line 71 _whitelistedPolicies.length()

New value of nonces[msg.sender] should be saved in additional memory variable File: BlurExchange.sol Line 208 nonces[msg.sender] += 1; // Used emit NonceIncremented(msg.sender, nonces[msg.sender]); // Used

G-03 Remove additional memory variable

The size parameter can be used instead of variable length File: PolicyManager.sol Line 69 uint256 length = size;

G-04 ++i costs less gas compared to i++ or i += 1 in for loops (~5 gas per iteration)

++i costs less gas compared to i++ or i += 1 for unsigned integer, as pre-increment is cheaper (about 5 gas per iteration)

File: PolicyManager.sol Line 77 File: EIP712.sol line 77 File: MerkleVerifier.sol line 38 File: BlurExchange.sol line 199

G-05 Using unchecked blocks to save gas - Increments in for loop can be unchecked

The majority of Solidity for loops increment a uint256 variable that starts at 0. These increment operations never need to be checked for over/underflow because the variable will never reach the max number of uint256 (will run out of gas long before that happens). The default over/underflow check wastes gas in every iteration of virtually every for loop . eg.

File: PolicyManager.sol line 77 File: EIP712.sol line 77 File: MerkleVerifier.sol line 38 File: BlurExchange.sol line 199

[G-06] USE CUSTOM ERRORS INSTEAD OF REVERT STRINGS TO SAVE GAS

Custom errors from Solidity 0.8.4 are cheaper than revert strings (cheaper deployment cost and runtime cost when the revert condition is met). Custom errors are defined using the error statement, which can be used inside and outside of contracts (including interfaces and libraries). see source

File: PolicyManager.sol line 26 require(!_whitelistedPolicies.contains(policy), "Already whitelisted");

File: PolicyManager.sol line 37 require(_whitelistedPolicies.contains(policy), "Not whitelisted");

File: ExecutionDelegate.sol line 22 require(contracts[msg.sender], "Contract is not approved to make transfers");

File: ExecutionDelegate.sol line 77 require(revokedApproval[from] == false, "User has revoked approval");

File: ExecutionDelegate.sol line 92 require(revokedApproval[from] == false, "User has revoked approval");

File: ExecutionDelegate.sol line 108 require(revokedApproval[from] == false, "User has revoked approval");

File: ExecutionDelegate.sol line 124 require(revokedApproval[from] == false, "User has revoked approval");

File: BlurExchange.sol line 36 require(isOpen == 1, "Closed");

File: BlurExchange.sol line 139-143 File: BlurExchange.sol line 219 require(address(_executionDelegate) != address(0), "Address cannot be zero");

File: BlurExchange.sol line 228 require(address(_policyManager) != address(0), "Address cannot be zero");

File: BlurExchange.sol line 237 require(_oracle != address(0), "Address cannot be zero");

File: BlurExchange.sol line 318 require(block.number - order.blockNumber < blockRange, "Signed block number out of range");

File: BlurExchange.sol line 407 require(v == 27 || v == 28, "Invalid v parameter");

File: BlurExchange.sol line 424 require(policyManager.isPolicyWhitelisted(sell.matchingPolicy), "Policy is not whitelisted");

File: BlurExchange.sol line 428 require(policyManager.isPolicyWhitelisted(buy.matchingPolicy), "Policy is not whitelisted");

File: BlurExchange.sol line 431 require(canMatch, "Orders cannot be matched");

File: BlurExchange.sol line 482 require(totalFee <= price, "Total amount of fees are more than the price");

File: BlurExchange.sol line 534 require(_exists(collection), "Collection does not exist");

[G-07] Add unchecked {} for subtractions where the operands can not underflow because of a previous

File: PolicyManager.sol line 72 length = _whitelistedPolicies.length() - cursor;

[G-08] X += Y COSTS MORE GAS THAN X = X + Y FOR STATE VARIABLES

File: BlurExchange.sol line 208 nonces[msg.sender] += 1;

[G-09] Use memory variable instead storage to minimize SLOADs

File: BlurExchange.sol line 221 insted of: emit NewExecutionDelegate(executionDelegate); use: emit NewExecutionDelegate(_executionDelegate);

File: BlurExchange.sol line 230 File: BlurExchange.sol line 239 File: BlurExchange.sol line 247