code: def int_global_to_local_start(self, index, axis=0):
          
          if index >= self.__mask[axis].stop-self.__halos[1][axis]:
              return None
  
          if index < self.__mask[axis].start:
              return 0
  
          return index-self.__mask[axis].start
docs: Calculate local index from global index from start_index
  
          :param index: global index as integer
          :param axis: current axis to process
          :return: