private static @NotNull DfType indexOf(DfaValue qualifier,
                                         DfaMemoryState memState,
                                         DfaValueFactory factory,
                                         SpecialField specialField) {
    DfaValue length = specialField.createValue(factory, qualifier);
    LongRangeSet range = DfIntType.extractRange(memState.getDfType(length));
    return intRange(LongRangeSet.range(-1, range.max() - 1));
  }
private static @NotNull DfType indexOf(DfaValue qualifier,
                                         DfaMemoryState memState,
                                         DfaValueFactory factory,
                                         SpecialField specialField)