docs: def reverse_index_mapping(self):
          """Get mapping from this segment's indexes to the indexes of
          the base array.
  
          If the index is < 0, the index is out of range, meaning that it doesn't
          exist in this segment and is not mapped to the base array
          """
          if self._reverse_index_mapping is None:
              if self.is_indexed:
                  # Initialize array to out of range
                  r = np.zeros(self.base_length, dtype=np.int32) - 1
                  r[self.order] = np.arange(len(self.order), dtype=np.int32)
              elif self.data.base is None:
                  # Starts at the beginning; produces the identity
                  r = np.arange(self.data_length, dtype=np.int32)
              else:
                  r = np.zeros(self.base_length, dtype=np.int32) - 1
                  r[self.data_start - self.base_start:self.data_end - self.base_start] = np.arange(self.data_length, dtype=np.int32)
              self._reverse_index_mapping = r
          return self._reverse_index_mapping