Solidity function to check if a string contains only printable ASCII characters and is at most 32 characters long. Branch-free "vectorized" implementation.

ascii.sol

// SPDX-License-Identifier: MIT
pragma solidity 0.8.17;

function isAsciiPrintableShortString(string memory str) pure returns (bool) {
    unchecked {
        uint256 b = uint256(bytes32(hex"0101010101010101010101010101010101010101010101010101010101010101"));

        bytes32 chars = bytes32(bytes(str));
        uint256 len = bytes(str).length;

        bytes32 nonprintable = chars & bytes32(b * 0xe0);
        nonprintable |= nonprintable >> 1;
        nonprintable &= bytes32(b * 0xa0);
        nonprintable ^= bytes32(b * 0x20);
        nonprintable >>= 8 * (32 - len);

        bytes32 del = chars;
        del &= del >> 1;
        del &= del >> 1;
        del &= del >> 2;
        del &= del >> 2;

        return (nonprintable | del) == 0 && len <= 32;
    }
}