# Gas Optimization Solutions

## 1.1 Gas Optimization Overwiew

{% hint style="info" %}
Gas optimization involves refining code to minimize the amount of gas required to execute a function or transaction on the blockchain. In Ethereum, each operation has a cost in gas units, which directly translates into fees. Common optimizations focus on reducing the use of storage, minimizing computational operations, and using efficient data structures.
{% endhint %}

***

## 1.2 Optimization Techniques

### 1.2.1 Use `uint256` Instead of Smaller Integers

While using smaller integers (e.g., `uint8`, `uint16`) might seem like it would reduce gas costs, it can actually increase costs unless multiple variables are packed into a single storage slot. In general, using `uint256` is the most gas-efficient for operations unless explicit storage packing is implemented.

#### Inefficient

```solidity
uint8 smallInt; // Avoid if not packed
uint16 anotherSmallInt;
```

#### Optimized

```solidity
uint256 optimizedInt; // Prefer `uint256` for independent storage variables
```

### 1.2.3 Pack Storage Variables

Storage on Ethereum is divided into 32-byte slots. By combining variables that are smaller than 32 bytes (like `uint8`, `uint16`, `bool`), multiple variables can share a single storage slot, reducing gas costs.

#### Optimized

```solidity
contract StoragePackingExample {
    uint128 var1;    // Takes up half a storage slot
    uint128 var2;    // Packed into the same slot with `var1`
    uint64 var3;     // Fits with `var2` in a new slot
    uint64 var4;
}
```

### 1.2.4 Use `memory` Instead of `storage` for Temporary Variables

When working with temporary data, use `memory` rather than `storage`. `memory` variables are cheaper since they don’t persist on the blockchain.

#### Inefficient

```solidity
function expensiveFunction() public view returns (uint256) {
    uint256[] storage tempArray = longArray; // Using `storage` incurs extra gas costs
    return tempArray.length;
}
```

#### Optimized

```solidity
function cheaperFunction() public view returns (uint256) {
    uint256[] memory tempArray = longArray; // Using `memory` is cheaper
    return tempArray.length;
}
```

### 1.2.4 Minimize `SSTORE` Operations

Each time a value is written to storage (`SSTORE`), it incurs significant gas costs. Where possible, reduce writes to storage by performing calculations in `memory` and only writing the final result.

#### Inefficient

```solidity
function updateValue() public {
    for (uint256 i = 0; i < 100; i++) {
        storageArray[i] = i; // Every assignment is a storage write
    }
}
```

#### Optimized

```solidity
function updateValue() public {
    uint256;
    for (uint256 i = 0; i < 100; i++) {
        tempArray[i] = i; // Uses `memory`, cheaper than `storage`
    }
    storageArray = tempArray; // Single storage assignment
}
```

### 1.2.5 Use `immutable` and `constant` Variables

Constants and immutables are stored in bytecode, saving storage gas costs. Use `constant` for values known at compile time and `immutable` for values set in the constructor.

```solidity
contract Example {
    uint256 public constant FIXED_FEE = 0.01 ether; // Saves gas, hardcoded in bytecode
    address public immutable admin; // Set once in the constructor

    constructor(address _admin) {
        admin = _admin;
    }
}
```

### 1.2.6 Efficient Loops and Data Structures

Avoid unbounded loops and consider more efficient data structures. For instance, avoid looping through large arrays stored on-chain.

```solidity
function getSum(uint256[] memory values) public pure returns (uint256) {
    uint256 sum = 0;
    uint256 length = values.length;
    for (uint256 i = 0; i < length; ++i) {
        sum += values[i];
    }
    return sum;
}
```

***

## 1.3 Code for Gas-Optimized Contracts

#### Gas-Optimized ERC20 Token Contract

```solidity
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract GasOptimizedERC20 {
    string public constant name = "GasOptimizedToken";
    string public constant symbol = "GOT";
    uint8 public constant decimals = 18;
    uint256 public immutable totalSupply;

    mapping(address => uint256) private balances;
    mapping(address => mapping(address => uint256)) private allowances;

    constructor(uint256 _totalSupply) {
        totalSupply = _totalSupply;
        balances[msg.sender] = _totalSupply;
    }

    function balanceOf(address account) public view returns (uint256) {
        return balances[account];
    }

    function transfer(address recipient, uint256 amount) public returns (bool) {
        _transfer(msg.sender, recipient, amount);
        return true;
    }

    function _transfer(address sender, address recipient, uint256 amount) internal {
        require(sender != address(0), "Invalid sender");
        require(recipient != address(0), "Invalid recipient");
        require(balances[sender] >= amount, "Insufficient balance");

        // Use memory variables to minimize storage access
        uint256 senderBalance = balances[sender];
        uint256 recipientBalance = balances[recipient];
        balances[sender] = senderBalance - amount;
        balances[recipient] = recipientBalance + amount;
    }

    function approve(address spender, uint256 amount) public returns (bool) {
        _approve(msg.sender, spender, amount);
        return true;
    }

    function _approve(address owner, address spender, uint256 amount) internal {
        allowances[owner][spender] = amount;
    }
}
```

#### Explanation of Optimizations

1. **Constants**: `name`, `symbol`, and `decimals` are marked as `constant`, saving gas by storing them in bytecode.
2. **Immutable Total Supply**: The `totalSupply` is set as `immutable`, reducing storage cost.
3. **Efficient Transfers**: `balanceOf` and `transfer` methods use memory variables to minimize repeated storage access.


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