"""Rounds the given integer `x` up to the nearest multiple of 128, without exceeding the specified `limit`.

The function follows these rules:
- If `x` is less than or equal to 128, returns 128.
- If `x` is less than `limit`, returns the smallest multiple of 128 greater than or equal to `x`.
- If `x` is greater than or equal to `limit`, searches for the largest multiple of 128 less than or equal to `limit` (down to 512) that divides `x` evenly, and returns it.
- If no such candidate is found, returns `limit`.

Args:
    x (int): The integer to round up.
    limit (int): The upper bound (must be a multiple of 128 and at least 128).

Returns:
    int: The rounded value according to the rules above.

Raises:
    AssertionError: If `limit` is less than 128 or not a multiple of 128.
"""