some untested solidity from ChatGPT

function isAlphanumeric(string memory str) public pure returns (bool) {
    bytes memory b = bytes(str); // Convert string to bytes for low-level handling
    uint256 len = b.length; // Store length of string

    // Inline assembly for direct memory access and reduced gas cost
    assembly {
        // Loop over the string, byte by byte
        for { let i := 0 } lt(i, len) { i := add(i, 1) } {
            let char := byte(0, mload(add(add(b, 0x20), i))) // Load the i-th byte of string

            // Check if the character is not alphanumeric
            if or(
                or(
                    lt(char, 0x30), // Less than '0'
                    and(gt(char, 0x39), lt(char, 0x41)) // Greater than '9' and less than 'A'
                ),
                or(
                    gt(char, 0x5A), // Greater than 'Z'
                    and(lt(char, 0x61), gt(char, 0x7A)) // Less than 'a' or greater than 'z'
                )
            ) {
                // If any character is not alphanumeric, return false
                mstore(0x00, 0)
                return(0x00, 0x20)
            }
        }
    }
    // If all characters are alphanumeric, return true
    return true;
}

consider validating namespaces onchain #1991

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