The function calculates the difference between the number of 'a' and 'b' characters in the input string and reports the result with the word "zero" repeated that many times, followed by the total length of the input string.

[CODE]:
```python
def f(x):
    difference = x.count('a') - x.count('b')
    output = "zero " * difference
    return output + str(len(x))
```
Keep in mind this is an approximation of the behavior observed so far, as it's hard to tell the exact implementation without trying all string inputs.

Please, let me know if you'd like me to test more input cases or provide additional explanation.