docs: def get_index_from_base_index(self, base_index):
          """Get index into this array's data given the index into the base array
          """
          r = self.rawdata
          try:
              index = r.get_reverse_index(base_index)
          except IndexError:
              raise IndexError("index %d not in this segment" % base_index)
          if index < 0:
              raise IndexError("index %d not in this segment" % base_index)
          return int(index)