Creates a generator that returns all allocated entries in the
    bitmap.

    Yields:
        int: The bit index of the allocated entries.

def _allocated_entries_bitmap(self):
    '''Creates a generator that returns all allocated entries in the
    bitmap.

    Yields:
        int: The bit index of the allocated entries.

    '''
    for entry_number in range(len(self._bitmap) * 8):
        if self.entry_allocated(entry_number):
            yield entry_number