Sigurd Syr (Halvdansson) - Mother

The About seciton has LOTS of notes, which include:

HALFDAN Sigurdsson. The Historia Norwegie names Halfdan son of "Siwardus Risi…filius Haraldi Comati"[280]. Morkinskinna recites the descent of “Harald Sigurdarson” from “Harald hárfagri”, to “Sigurdr hrisi”, to “Hálfdan, father of Sigurdr sýr, the father of Haraldr”, adding that these ancestors were all “kings of Hringaríki in Norway”[281]. m ---. The name of Halfdan's wife is not known.
Halfdan Sigurdsson & his wife had one child

a) SIGURD Syr (-1018).

which states that the mother of Sigurd Syr is unknown.

So, what is the documentation for his mother being Tora Ranesdatter Rise?

Thanks for any clarification