calculating an md4 and a signature at the same time?

I have an application sending a bunch of deltas to a server. Before 
actually sending any data, I want to send an md4 sum over to see if the 
files actually differ (taking my chances of hash-collisions), and if so 
send the signature to the server.

 From browsing the librsync (0.9.6) source code, I have the impression 
that it is possible to calculate these at the same time, but can't 
quite get a hold on how. Is this actually possible? Or could I use some 
part of the signature (the last few bytes or sth like that) as a 
good-enough hash?


[standard, but sincere open-source flattery ahead:] I think it's very 
exciting to have library access to the very elegant rsync algorithm. 
Beautiful work. I am wondering if I should be working off the 0.9.6 or 
the CVS-current. I noticed some documentation glitches and suchlike, 
and could try to send patches if you are interested.


d.



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