Zokyo Gas Savings
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    • โœ”๏ธGas Saving Technique 1: Unchecked Arithmetic
    • โ›“๏ธGas Saving Technique 2: Immutable Variable
    • โœจGas Saving Technique 3: Double star ** inefficiency
    • ๐Ÿ’ฐGas Saving Technique 4: Cache Array Length
    • โฌ…๏ธGas Saving Technique 5: ++i costs less gas compared to i++
    • โš–๏ธGas Saving Technique 6: NOT operator ! cheaper than boolean FALSE
    • ๐ŸชกGas Saving Technique 7: Using Short Reason Strings
    • ๐ŸชตGas Saving Technique 8: Use Custom Errors instead of Revert Strings to save Gas
    • โœ’๏ธGas Saving Technique 9: Use Custom Errors instead of Revert Strings to save Gas
    • ๐Ÿ‘พGas Saving Technique 10: Calldata cheaper than memory
    • โ›”Gas Saving Technique 11: > 0 is less efficient than != 0 for unsigned integers
    • โž—Gas Saving Technique 12: SafeMath no longer needed
    • ๐Ÿ˜ฎGas Saving Technique 13: variables default to 0
    • ๐ŸงฑGas Saving Technique 14: struct layout/ variable packing
    • ๐Ÿ“žGas Saving Technique 15: Cache External Call
    • โœ๏ธGas Saving Technique 16: Early Validation before external call
    • ๐Ÿ˜ŽGas Saving Technique 17: Donโ€™t cache value that is used once
    • ๐Ÿ˜งGas Saving Technique 18: Redundant code
    • โœ…Gas Saving Technique 19: Early Validation before external call
    • โ›๏ธGas Saving Technique 20: Storage vs Memory read optimizations
    • โœ’๏ธGas Saving Technique 21: Unneeded If statements
    • ๐ŸŒ—Gas Saving Technique 22: >= is cheaper than >
    • ๐ŸŽ’Gas Saving Technique 23: Public to private constants
    • โน๏ธGas Saving Technique 24: Make unchanged variables constant/immutable
    • โฑ๏ธGas Saving Techniques 25: Redundant Access Control Checks
    • โžก๏ธGas Saving Technique 26: Shift Right instead of Dividing by 2
    • ๐ŸชƒGas Saving Tutorial 27: Efficient Boolean Comparison
    • ๐ŸคGas Saving Technique 28: && operator uses more gas
    • ๐Ÿ‘“Gas Saving Technique 29: x = x + y is cheaper than x += y
    • ๐Ÿ‘‚Gas Saving Technique 30: Using 1 and 2 rather than 0 and 1 saves gas
    • โšฝGas Saving Technique 31: Optimize Storage by Avoiding Booleans
    • ๐Ÿ”™Gas Saving Technique 32: Optimal Use of Named Return Variables in Solidity
    • ๐Ÿ›ข๏ธGas Saving Technique 33: Making Functions Payable for Optimized Gas Costs
    • โœ๏ธGas Saving Technique 34: Optimizing Storage References in Smart Contracts
    • โ›ฐ๏ธGas Saving Technique 35: Usage of uints/ints smaller than 32 bytes (256 bits) incurs overhead
    • ๐ŸŒช๏ธGas Saving Technique 36: Inlining Single Use Internal Functions for Savings
    • โ˜„๏ธGas Saving Technique 37: Switching from Public to External Functions for Savings
    • ๐ŸŽ†Gas Saving Technique 38: Upgrading Solidity Compiler to Improve Gas Efficiency and Security
    • ๐Ÿ•ถ๏ธGas Saving Technique 39: Avoiding Duplicated Code for Gas Savings
    • ๐Ÿ˜„Gas Saving Technique 40: Removal of Unused Internal Functions for Gas Savings
    • ๐Ÿ–‹๏ธGas Saving Tutorial 41: In-lining Single Use Modifiers For Gas Saving
    • โ›๏ธGas Saving Technique 42: `require` vs`assert`
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Gas Saving Technique 1: Unchecked Arithmetic

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Last updated 1 year ago

Introduction

With the introduction of Solidity version 0.8 and above, automatic checks for arithmetic overflow and underflow have been incorporated. While these checks enhance security by preventing unexpected behavior, they also consume additional gas for each operation. In scenarios where overflow or underflow is impossible due to the logic of the contract, these automatic checks become unnecessary gas expenditures. The unchecked directive in Solidity allows developers to bypass these checks, conserving gas.

Vulnerability Details & Impact

Automatically embedded overflow and underflow checks for arithmetic operations in Solidity v0.8+ incur extra gas costs for each transaction. By carefully deploying the unchecked directive in operations where overflow or underflow is improbable, developers can optimize contracts for gas efficiency without sacrificing security.

How to Implement unchecked Directive for Gas Savings

Understanding the unchecked Block

Solidityโ€™s unchecked block is utilized to circumvent automatic overflow and underflow checks on arithmetic operations. Within the unchecked block, arithmetic calculations do not trigger these automatic checks, which results in saved gas.

Hereโ€™s a syntactical demonstration:

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

contract GasSaver {
    uint256 public count;
    
    function increment(uint256 amount) public {
        unchecked {
            // Inside this block, overflow checks are disabled
            count += amount;
        }
    }
}

Practical Example: Loop Increment Optimization

Consider a for loop where you're certain that the loop variable wonโ€™t cause an overflow. By employing the unchecked directive, you can increment the loop variable without incurring the gas costs of overflow checks.

Below is a code snippet demonstrating this:

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

contract LoopGasSaver {
    function saveGasInLoop(uint256 iterations) public pure returns (uint256) {
        uint256 sum = 0;
        unchecked {
            for (uint256 i = 0; i < iterations; i++) {
                // Overflow check is skipped for i++, saving gas per iteration
                sum += i;
            }
        }
        return sum;
    }
}

Recommended Mitigation Steps

  1. Identify Safe Operations: Recognize arithmetic operations where overflow/underflow cannot occur.

  2. Implement unchecked: Surround these safe operations with the unchecked block.

  3. Test Thoroughly: Conduct rigorous testing to ensure that the identified operations are truly safe from overflow and underflow.

Conclusion

While the unchecked directive offers a mechanism for gas optimization, it must be used with caution. Misuse of unchecked can expose contracts to security vulnerabilities. Thorough testing and careful consideration are imperative when deploying this directive to ensure that security is not compromised for the sake of gas efficiency.

References and examples:

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https://docs.soliditylang.org/en/v0.8.10/control-structures.html#checked-or-unchecked-arithmetic
[G-01] Adding unchecked directive can save gas - Unchecked