Solidity gas optimisation example

optimisation.sol

// SPDX-License-Identifier: GPL-3.0
pragma solidity ^0.8.10;

contract Test {
    // Gas used for empy function: 22094
    function blank(uint16) public pure returns (string memory) {}

    // Gas used: 31922 - 22094 = 9828
    function toBinary1(uint16 n) public pure returns (string memory) {
        require(n < 1024);
        bytes memory output = new bytes(10);

        for (uint8 i = 0; i < 10; ++i) {
            output[9 - i] = (n % 2 == 1) ? bytes1("1") : bytes1("0");
            n /= 2;
        }

        return string(output);
    }

    // Gas used: 31638 - 22094 = 9544
    function toBinary2(uint16 n) public pure returns (string memory) {
        require(n < 1024);
        bytes memory output = new bytes(10);

        for (uint256 i = 0; i < 10; ++i) {
            output[9 - i] = (n % 2 == 1) ? bytes1("1") : bytes1("0");
            n /= 2;
        }

        return string(output);
    }

    // Gas used: 30408 - 22094 = 8314
    function toBinary3(uint16 n) public pure returns (string memory) {
        require(n < 1024);
        bytes memory output = new bytes(10);

        uint256 i;
        while (i < 10) {
            output[9 - i] = (n % 2 == 1) ? bytes1("1") : bytes1("0");
            n /= 2;
            unchecked {
                ++i;
            }
        }

        return string(output);
    }

    // Gas used: 24081 - 22094 = 1987
    function toBinary4(uint16 n) public pure returns (string memory) {
        require(n < 1024);
        bytes memory output = new bytes(10);

        uint256 i = 9;
        while (i != 0) {
            output[i] = uint256(n) & (1 << i) == 0 ? bytes1("0") : bytes1("1");
            unchecked {
                --i;
            }
        }

        return string(output);
    }

    // Gas used: 24016- 22094 = 1922
    function toBinary5(uint256 n) public pure returns (string memory) {
        require(n < 1024);
        bytes memory output = new bytes(10);

        uint256 i = 9;
        while (i != 0) {
            output[i] = n & (1 << i) == 0 ? bytes1("0") : bytes1("1");
            unchecked {
                --i;
            }
        }

        return string(output);
    }

    // Gas used: 23552 - 22094 = 1458
    function toBinary6(uint256 n) public pure returns (string memory) {
        require(n < 1024);
        bytes memory output = new bytes(10);

        output[0] = n & 1 == 0 ? bytes1("0") : bytes1("1");
        output[1] = n & 2 == 0 ? bytes1("0") : bytes1("1");
        output[2] = n & 4 == 0 ? bytes1("0") : bytes1("1");
        output[3] = n & 8 == 0 ? bytes1("0") : bytes1("1");
        output[4] = n & 16 == 0 ? bytes1("0") : bytes1("1");
        output[5] = n & 32 == 0 ? bytes1("0") : bytes1("1");
        output[6] = n & 64 == 0 ? bytes1("0") : bytes1("1");
        output[7] = n & 128 == 0 ? bytes1("0") : bytes1("1");
        output[8] = n & 256 == 0 ? bytes1("0") : bytes1("1");
        output[9] = n & 512 == 0 ? bytes1("0") : bytes1("1");

        return string(output);
    }
}