MD5 sums of large objects

Hello all together,

I have a database containing lots of large objects. Now I'd like to
compare large objects in my database and I thought of having a
function which creates a hashsum (MD5, SHA-1 or whatever) of my large
object, so I can use that in queries:

create function lo_md5(id oid) returns text...

Now I don't know if something like this is already included in the
PostgreSQL distribution, could be found somewhere on pgfoundry or
thirdly how to do it? If I have to program myself I would go for a
C-language function which would use the libpq large-object functions
to create the hashsums.

-- 
---> Dirk Jagdmann
----> http://cubic.org/~doj
-----> http://llg.cubic.org