Base Conversion Routine from C# to C++

I have a base conversion routine currently in C# that uses very large integers, and I need it converting to C++ using the MPIR library. Here's a pastebin of the method in C#: [login to view URL] And here's the library that it'll need to use: [login to view URL] I'll need to be able to call it from C#, handing the function a BigInteger, the new base and the length, as in the example. The goal is to make the function as fast and flexible as possible, by running it in a separate thread, and using MPIR in unmanaged space. If it helps, I can supply some use case examples.