Reverse patching

Hello,
I'm trying to apply rdiff (a very impressive program, so far) to a 
certain situation and I have some questions about its use and functioning:
1) Is there anyway to 'reverse-patch'.  If I produce a delta for file1 
to file2, I know I can apply the delta to file1 to obtain file2; can I 
also apply the delta, in some way, to file2 to get file 1? (similar to 
"patch -R")
2) If I create a signature and then a delta for two identical files, 
will rdiff produce a delta of size 0?  If not, under which 
circumstances, if any in particular?
Thank you for your answers,
Afsheen



------------------------------------------------------------------------------
Join us December 9, 2009 for the Red Hat Virtual Experience,
a free event focused on virtualization and cloud computing. 
Attend in-depth sessions from your desk. Your couch. Anywhere.
http://p.sf.net/sfu/redhat-sfdev2dev