The domain of the function is the set of real numbers. The interval where the function behaves unexpectedly is (-64, 64).

[CODE]:
```python
def f(x):
    if x <= -64 or x >= 64:
        return -3.3
    else:
        # Use an approximation function here
        # Example: return some_non_linear_function(x)
        pass
```

Please note that without more information about the function's implementation and behavior within the (-64, 64) interval, it's challenging to provide an accurate description or code approximation for that part of the function.