Librsync is a library for calculating and applying network deltas,
with an interface designed to ease integration into diverse network
applications.  Librsync encapsulates the core algorithms of the rsync
protocol, which help with efficient calculation of the differences
between two files.  The rsync algorithm is different from most
differencing algorithms because it does not require the presence of
the two files to calculate the delta.  Instead, it requires a set of
checksums of each block of one file, which together form a signature
for that file.  Blocks at any point in the other file which have the
same checksum are likely to be identical, and whatever remains is the
difference.

Homepage:
http://librsync.sourcefrog.net/
