The function f(x) appears to be implementing a Caesar cipher with a shift of 7 characters.

[CODE]:
```python
def caesar_cipher_7(s: str) -> str:
    output = []
    for c in s:
        if 'a' <= c <= 'z':
            output.append(chr((ord(c) - ord('a') + 7) % 26 + ord('a')))
        elif 'A' <= c <= 'Z':
            output.append(chr((ord(c) - ord('A') + 7) % 26 + ord('A')))
        else:
            output.append(c)
    return ''.join(output)
```
