What is exactly approximate RcpPolyXX methods in FixedUtils.cs?

[KichangKim]

Hi. I'm studying fixed point arithmetic and this FixPointCS is excellent material.

My question is, what is RcpPolyXX approximate? 1/x or 1/(x + 1)?

In Div() method, it used with one subtracted value from original value, like int res = FixedUtil.RcpPoly6(n - ONE);, not FixedUtil.RcpPoly(n) so it is quite confusing.