Rolling Checksum Algorithms

Donovan Baarda abo at
Sun Jul 20 23:27:11 EST 2003

On Sun, Jul 20, 2003 at 01:06:11PM +0100, seunosewa at wrote:
> Hi,
> Where can I get good pointers on the rolling checksum algorithm used in rsync? 
> I need an 8-bit or 12-bit rolling checksum too.  Any place where "rolling"
> checksum algorithms are discussed?

You can have a look at the rsync white paper. 

You can also look at pysync for sample implementations in Python;

I think I've posted on this list some comments about various variations on
the rolling checksum. I think the rsync whitepaper credits it as being a
variation on the Adler checksum, but I think it is closer to something I've
seen called a Fletcher checksum.

Pysync has a Python implementation of a rolling adler32 checksum, and has
comments about the variations in rsync, librsync, and xdelta.

Donovan Baarda      

More information about the rsync mailing list