Solidity: Convert hex-string variable into bytes [duplicate]

Question

I am looking for an option to efficiently convert a string passed to a function as a parameter, interpreted as hex, into bytes. In Solidity.

I.e. doing the same that this piece of code would do

bytes memory b = hex"abcdef1234567890";

just with a string passed as a parameter for a function.

contract C {
  function f(string memory s) public pure returns (bytes memory) {
    bytes memory b;
    ... // read hex-string into b
    return b;
  }
}

Ideally, I'd want something that isn't "manually" looping through the characters of the string in order to translate each into a byte individually as described here: Solidity convert hex string to bytes. Unfortunately, I can't do this off-chain.

Is there such a way?