public func addingReportingOverflow(_ rhs: UInt128) -> (partialValue: UInt128, overflow: Bool) {
        var resultOverflow = false
        let (lowerBits, lowerOverflow) = self.value.lowerBits.addingReportingOverflow(rhs.value.lowerBits)
        var (upperBits, upperOverflow) = self.value.upperBits.addingReportingOverflow(rhs.value.upperBits)