About Halfdan "Gamle" Sveidasson
Halfdan Sveidasson is mentioned in the Orkney saga:

"Heiti, Gorr’s son, was father of Sveiði the sea-king, the father of Halfdan the old, the father of Ivar the Uplanders’ earl, the father of Eystein the noisy, the father of earl Rognvald the mighty and the wise in council."



See also http://en.wikipedia.org/wiki/Halfdan_the_Old

Other saga personalities who are named Halfdan, and should NOT be confused with this one:

Halfdan Eysteinsson, http://www.geni.com/profile/index/6000000006803712071
Halfdan Hringsson, http://www.geni.com/profile/index/6000000006209764570