Blur Exchange contest - lukris02's results

Gas Optimizations Report for Non Fungible Trading contest

Overview

During the audit, 3 gas issues were found.
Total savings ~20,245.

Gas Optimizations Findings(3)

G-1. Optimization for isOpen

Description

For state variable isOpen, it is better to use uint256(1) and uint256(2) to avoid spending 20,000 gas when changing from '0' to '1' (when opening after closing).

Link:

    function open() external onlyOwner {
        isOpen = 1;
        emit Opened();
    }
    function close() external onlyOwner {
        isOpen = 0;
        emit Closed();
    }

Saved

This saves ~20,000.

G-2. Use unchecked blocks for incrementing i

Description

In Solidity 0.8+, there’s a default overflow and underflow check on unsigned integers. In the loops, "i" will not overflow because the loop will run out of gas before that.

Instances

• https://github.com/code-423n4/2022-11-non-fungible/blob/main/contracts/Exchange.sol#L184
• https://github.com/code-423n4/2022-11-non-fungible/blob/main/contracts/Exchange.sol#L307
• https://github.com/code-423n4/2022-11-non-fungible/blob/main/contracts/Exchange.sol#L598

Recommendation

Change:

for (uint256 i; i < n; ++i) {
 // ...
}

to:

for (uint256 i; i < n;) { 
 // ...
 unchecked { ++i; }
}

Saved

This saves ~30-40 gas per iteration.
So, ~35*3 = 105

G-3. Use unchecked blocks for subtractions where underflow is impossible

Description

In Solidity 0.8+, there’s a default overflow and underflow check on unsigned integers. When an overflow or underflow isn’t possible (after require or if-statement), some gas can be saved by using unchecked blocks.

Instances

• https://github.com/code-423n4/2022-11-non-fungible/blob/main/contracts/Exchange.sol#L574
• https://github.com/code-423n4/2022-11-non-fungible/blob/main/contracts/Exchange.sol#L607
• https://github.com/code-423n4/2022-11-non-fungible/blob/main/contracts/Pool.sol#L46
• https://github.com/code-423n4/2022-11-non-fungible/blob/main/contracts/Pool.sol#L73

Saved

This saves ~35.
So, ~35*4 = 140