lukris02 data for issue #223

data/lukris02-G.md

@@ -0,0 +1,71 @@
+# Gas Optimizations Report for Non Fungible Trading contest
+## Overview
+During the audit, 3 gas issues were found.  
+Total savings ~20,245.
+№ | Title | Instance Count | Saved
+--- | --- | --- | ---
+G-1 | Optimization for ```isOpen``` | 1 | 20,000
+G-2 | Use unchecked blocks for incrementing i | 3 | 105
+G-3 | Use unchecked blocks for subtractions where underflow is impossible | 4 | 140
+
+## Gas Optimizations Findings(3)
+### G-1. Optimization for ```isOpen```
+##### Description
+For state variable [```isOpen```](https://github.com/code-423n4/2022-11-non-fungible/blob/main/contracts/Exchange.sol#L33), 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](https://github.com/code-423n4/2022-11-non-fungible/blob/main/contracts/Exchange.sol#L56-L63):
+```
+    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](https://docs.soliditylang.org/en/v0.8.17/control-structures.html#checked-or-unchecked-arithmetic).
+##### 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
+#