Sure! Here is a test case generator for the given problem statement:

```python
import random

def tcgen():
    # Define the constraints
    max_n = 10**15
    max_m = 10**15
    
    # Generate random values for n and m within the constraints
    n = random.randint(1, max_n)
    m = random.randint(0, max_m)
    
    return n, m

# Example usage of the test case generator
if __name__ == "__main__":
    n, m = tcgen()
    print(f"{n} {m}")
```

Explanation:
- The generator function `tcgen` creates random test cases within the specified constraints.
- `n` is generated randomly between 1 and \(10^{15}\).
- `m` is generated randomly between 0 and \(10^{15}\).
- The function returns a tuple `(n, m)`.
- The example usage at the end is for demonstration purposes, printing the generated test case in the format expected by the problem.

Since `n` and `m` can be very large and may not fit in a 32-bit integer, Python's `int` type, which can handle arbitrarily large integers, is used.