TimeswapPair.sol modifier lock: Switching between 1, 2 instead of 0, 1 is more gas efficient

[code423n4]

Handle

bitbopper

Vulnerability details

Impact

https://github.com/code-423n4/2022-01-timeswap/blob/5960e07d39f2b4a60cfabde1bd51f4b1e62e7e85/Timeswap/Timeswap-V1-Core/contracts/TimeswapPair.sol#L121:L126 could be more gas efficient

Proof of Concept

Version as in Repo

// SPDX-License-Identifier: GPL-3.0-or-later
pragma solidity =0.8.4;

contract LockProofOld {
	uint256 locked = 0;

	modifier lock() {
	    require(locked == 0, 'E211');
	    locked = 1;
	    _;
	    locked = 0;
	}

	function test() public lock {
	}

}

Proposed Version

// SPDX-License-Identifier: GPL-3.0-or-later
pragma solidity =0.8.4;

contract LockProofNew {
	uint256 locked = 1;

	modifier lock() {
	    require(locked == 1, 'E211');
	    locked = 2;
	    _;
	    locked = 1;
	}

	function test() public lock {
	}

}

Comparison

Test harness

// SPDX-License-Identifier: GPL-3.0-or-later
pragma solidity =0.8.4;

import "ds-test/test.sol";

import "./LockProofOld.sol";
import "./LockProofNew.sol";

contract LockProofTest is DSTest {
    LockProofOld lockproofold;
    LockProofNew lockproofnew;

    function setUp() public {
        lockproofold = new LockProofOld();
        lockproofnew = new LockProofNew();
    }

    function test_old() public {
		lockproofold.test();
    }

    function test_new() public {
		lockproofnew.test();
    }
}

Output

dapp test
Running 2 tests for src/LockProof.t.sol:LockProofTest
[PASS] test_old() (gas: 21042)
[PASS] test_new() (gas: 1136)

[Mathepreneur]

Timeswap-Labs/Timeswap-V1-Core#96