Evens contract

Evens.sol

// SPDX-License-Identifier: AGPL-3.0
pragma solidity 0.8.20;

contract Evens {
    function getEvens(uint256 startNum, uint256 endNum) external pure returns (uint256) {
        assembly("memory-safe") {
            // skip first iteration if startNum is 0
            if iszero(startNum) { startNum := add(startNum, 1) }
            endNum := add(endNum, 1)
            let num := 0
            for { let i := startNum } lt (i, endNum) { i := add(i, 1) } {
                // use masking here to save gas
                if iszero(and(0x0000000000000000000000000000000000000000000000000000000000000001, i)) {
                    num := add(num, 1)
                }
            }
            // shave off some gas by skipping typecheck
            mstore(0, num)
            return (0, 32)
        }
    }
}