In what century did Olaf Geirstad-Alf  and Halfdan the Black live in?
Olaf Geirstad-Alf Olaf Gudrødsson, or as he was named after his death Olaf Geirstad-Alf (Old Norse Ólaf Geirstaða Álfr), was a legendary Norwegian king of the House of Yngling from the "Ynglinga saga". He was the son of Gudrød the Hunter and according to the late "Heimskringla", the half-brother of Halfdan the Black. Gudrød and Olaf conquered a large part of Raumarike.
Breidablik In Norse mythology, Breiðablik ("Broad-gleaming") is the home of Baldr. It is briefly described in Snorri Sturluson's "Gylfaginning" as one of the halls of Asgard: