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+# Index
+1. Require / Revert strings longer than 32 bytes cost extra gas
+2. I = I + (-) X is cheaper in gas cost than I += (-=) X
+3. Use unchecked in for/while loops when it's not possible to overflow
+4. Modifiers that are used just once waste gas
+5. Use unchecked in operation that can not be overflow/underflow
+6. Remove variables that are used once
+7. Public functions not used inside the contract should be external
+
+# Details
+## 1. Require / Revert strings longer than 32 bytes cost extra gas
+### Description
+Each extra memory word of bytes past the original 32 incurs an MSTORE which costs 3 gas
+
+### Lines in the code
+[Exchange.sol#L49](https://github.com/code-423n4/2022-11-non-fungible/blob/323b7cbf607425dd81da96c0777c8b12e800305d/contracts/Exchange.sol#L49)
+[Exchange.sol#L295](https://github.com/code-423n4/2022-11-non-fungible/blob/323b7cbf607425dd81da96c0777c8b12e800305d/contracts/Exchange.sol#L295)
+[Exchange.sol#L604](https://github.com/code-423n4/2022-11-non-fungible/blob/323b7cbf607425dd81da96c0777c8b12e800305d/contracts/Exchange.sol#L604)
+[Pool.sol#L63](https://github.com/code-423n4/2022-11-non-fungible/blob/323b7cbf607425dd81da96c0777c8b12e800305d/contracts/Pool.sol#L63)
+
+## 2. I = I + (-) X is cheaper in gas cost than I += (-=) X
+### Description
+In the following example (optimizer = 10000) it's possible to demostrate that I = I + X cost less gas than I += X in state variable.
+
+```solidity
+contract Test_Optimization {
+    uint256 a = 1;
+    function Add () external returns (uint256) {
+        a = a + 1;
+        return a;
+    }
+}
+
+contract Test_Without_Optimization {
+    uint256 a = 1;
+    function Add () external returns (uint256) {
+        a += 1;
+        return a;
+    }
+}
+```
+* Test_Optimization cost is 26324 gas
+* Test_Without_Optimization cost is 26440 gas
+
+With this optimization it's possible to **save 116 gas**
+
+### Lines in the code
+[Exchange.sol#L316](https://github.com/code-423n4/2022-11-non-fungible/blob/323b7cbf607425dd81da96c0777c8b12e800305d/contracts/Exchange.sol#L316)
+[Exchange.sol#L574](https://github.com/code-423n4/2022-11-non-fungible/blob/323b7cbf607425dd81da96c0777c8b12e800305d/contracts/Exchange.sol#L574)
+[Exchange.sol#L601](https://github.com/code-423n4/2022-11-non-fungible/blob/323b7cbf607425dd81da96c0777c8b12e800305d/contracts/Exchange.sol#L601)
+[Pool.sol#L36](https://github.com/code-423n4/2022-11-non-fungible/blob/323b7cbf607425dd81da96c0777c8b12e800305d/contracts/Pool.sol#L36)
+[Pool.sol#L46](https://github.com/code-423n4/2022-11-non-fungible/blob/323b7cbf607425dd81da96c0777c8b12e800305d/contracts/Pool.sol#L46)
+[Pool.sol#L73](https://github.com/code-423n4/2022-11-non-fungible/blob/323b7cbf607425dd81da96c0777c8b12e800305d/contracts/Pool.sol#L73)
+[Pool.sol#L74](https://github.com/code-423n4/2022-11-non-fungible/blob/323b7cbf607425dd81da96c0777c8b12e800305d/contracts/Pool.sol#L74)
+
+## 3. Use unchecked in for/while loops when it's not possible to overflow
+### Description
+Use unchecked { i++; } or unchecked{ ++i; } when it's not possible to overflow to save gas.
+
+### Lines in the code
+[Exchange.sol#L177](https://github.com/code-423n4/2022-11-non-fungible/blob/323b7cbf607425dd81da96c0777c8b12e800305d/contracts/Exchange.sol#L177)
+[Exchange.sol#L184](https://github.com/code-423n4/2022-11-non-fungible/blob/323b7cbf607425dd81da96c0777c8b12e800305d/contracts/Exchange.sol#L184)
+[Exchange.sol#L307](https://github.com/code-423n4/2022-11-non-fungible/blob/323b7cbf607425dd81da96c0777c8b12e800305d/contracts/Exchange.sol#L307)
+[Exchange.sol#L598](https://github.com/code-423n4/2022-11-non-fungible/blob/323b7cbf607425dd81da96c0777c8b12e800305d/contracts/Exchange.sol#L598)
+
+## 4. Modifiers that are used just once waste gas
+### Description
+It's possible to save gas (due to JUMP operation) removing the modifier that are used just once in the code and inlined the code.
+
+### Lines in the code
+[Exchange.sol#L48-L51](https://github.com/code-423n4/2022-11-non-fungible/blob/323b7cbf607425dd81da96c0777c8b12e800305d/contracts/Exchange.sol#L48-L51)
+
+## 5. Use unchecked in operation that can not be overflow/underflow
+### Description
+Operations that could not be overflow/underflow due to an if or require could be unchecked to save gas.
+
+### Lines in the code
+[Exchange.sol#L574](https://github.com/code-423n4/2022-11-non-fungible/blob/323b7cbf607425dd81da96c0777c8b12e800305d/contracts/Exchange.sol#L574)
+[Exchange.sol#L607](https://github.com/code-423n4/2022-11-non-fungible/blob/323b7cbf607425dd81da96c0777c8b12e800305d/contracts/Exchange.sol#L607)
+[Pool.sol#L46](https://github.com/code-423n4/2022-11-non-fungible/blob/323b7cbf607425dd81da96c0777c8b12e800305d/contracts/Pool.sol#L46)
+[Pool.sol#L73](https://github.com/code-423n4/2022-11-non-fungible/blob/323b7cbf607425dd81da96c0777c8b12e800305d/contracts/Pool.sol#L73)
+
+## 6. Remove variables that are used once
+### Description
+Local variables that are used once could be removed.
+
+```diff
+-	uint256 receiveAmount = price - totalFee;
+-	return (receiveAmount);
++	return (price - totalFee);
+```
+[Exchange.sol#L607-L608](https://github.com/code-423n4/2022-11-non-fungible/blob/323b7cbf607425dd81da96c0777c8b12e800305d/contracts/Exchange.sol#L607-L608)
+
+```diff
+-	bool success = IPool(POOL).transferFrom(from, to, amount);
+-	require(success, "Pool transfer failed");
++	require(IPool(POOL).transferFrom(from, to, amount), "Pool transfer failed");
+```
+[Exchange.sol#L635-L636](https://github.com/code-423n4/2022-11-non-fungible/blob/323b7cbf607425dd81da96c0777c8b12e800305d/contracts/Exchange.sol#L635-L636)
+
+## 7. Public functions not used inside the contract should be external
+### Description
+Public functions needs to write all of the arguments to memory is that public functions may be called internally, which is an entirely different
+process than external calls. Internal calls are executed via jumps in the code and when the compiler generates the code for an internal function is 
+expected to have its arguments located in memory.
+
+For external functions, the compiler doesn't need to allow internal calls, and so it allows arguments to be read directly from calldata, saving the copying step.
+
+### Lines in the code
+[Pool.sol#L44](https://github.com/code-423n4/2022-11-non-fungible/blob/323b7cbf607425dd81da96c0777c8b12e800305d/contracts/Pool.sol#L44)
+[Pool.sol#L58](https://github.com/code-423n4/2022-11-non-fungible/blob/323b7cbf607425dd81da96c0777c8b12e800305d/contracts/Pool.sol#L58)
+[Pool.sol#L79](https://github.com/code-423n4/2022-11-non-fungible/blob/323b7cbf607425dd81da96c0777c8b12e800305d/contracts/Pool.sol#L79)
+[Pool.sol#L83](https://github.com/code-423n4/2022-11-non-fungible/blob/323b7cbf607425dd81da96c0777c8b12e800305d/contracts/Pool.sol#L83)
+