GB18030 multi-byte to wchar

[<dleach qnx com>]

Hello Everyone,

I need some insight on converting a GB18030 encoded multi-byte character
to a wchar_t.  The OS I use does not have fully implemented locale support
in the mbtowc routines :(.  Anyhow, this is what I do have:

The GB18030 multi-byte character.
The bytes broken in seperate entities.
The number of bytes that comprise the GB18030 character (1, 2, or 4).

What do I do know with the seperated bytes to make the
wchar value?  I know how to make a conversion to
a Unicode wchar, but not a "calculation" to a GB18030 wchar.
Is it a simple formulae, or are there look up tables involved?

Is there an all encompassing website/document (in English) that describes
all possible desired manipulations for GB18030?

Any insight appreciated.

Regards.