reverse xdelta patch

Question

Is there way to make reversing xdelta patch?
For example:
A - version 1 of file.
B - version 2 of file.
P - patch.
File B we can renew by appliing patch P to file A.
Is there way to renew file A if I have file B and patch P ?

Answer 1

It's a requested feature, but currently you have to generate two patches:

xdelta3 -e -s A B P1
xdelta3 -e -s B A P2