code: private static int gregoYearFromIslamicStart(int year) {
          // ad hoc conversion, improve under #10752
          // rough est for now, ok for grego 1846-2138,
          // otherwise occasionally wrong (for 3% of years)
          int cycle, offset, shift = 0;
          if (year >= 1397) {
              cycle = (year - 1397) / 67;
              offset = (year - 1397) % 67;
              shift = 2*cycle + ((offset >= 33)? 1: 0);
          } else {
              cycle = (year - 1396) / 67 - 1;
              offset = -(year - 1396) % 67;
              shift = 2*cycle + ((offset <= 33)? 1: 0);
          }
          return year + 579 - shift;
      }
docs: utility function for getRelatedYear