Is there anyway to create a TupleDesc with uint32 attribute easily?

Hi, hackers.
I'm working on my gsoc project - improving hash index.
I need to create a TupldeDesc with uint32 attribute.
Here is the reason why I need it -
If we store hash code only in the tuple, then the TupleDesc's
attribute should be uint32.
In this way, we can use index_form_tuple() to create a tuple and
needn't write a function for hash specially.

I've tried lookup_rowtype_tupdesc() with INT4OID, but it dosen't work
since int is not composite type.
Is there any easy way to do it or I should change my design?
Hope to hear from you. Thanks!

--
Best Regards,
Xiao Meng

DKERC, Harbin Institute of Technology, China
Gtalk: mx.cogito@gmail.com
MSN: cnEnder@live.com
http://xiaomeng.yo2.cn