You'll find "Rundtop" and "Rundtup" farms in the 1865 and 1900 Norway censuses. I didn't find a similar sounding farm name in the 1801 census.
Here is the Ulsager farm in 1801. Owner Knud Olsen was probably Ole Olsen's brother, or if Ole died fairly young,Knud's wife, Birgit Olsdatter, could have been Ole's sister?:http://tinyurl.com/bnzavdd
It would help if you state:
1- Your resources for names and dates.
2- In which Norway county you're referring to.