Ryan Malayter wrote: > On Fri, May 22, 2009 at 9:02 AM, Hasanat Kazmi <hasanatka...@gmail.com> wrote: > > Hello, > > I have previously mailed on list that I am trying to port rsync to NT. I was > > wondering that whether CRC can be used to find check sums rather then > > rolling algorithm. I havnt found any document on web comparing rolling > > algorithm with CRC. > > > > CRC doesn't have the correct properties for rsync, in that you cannot > "subtract" previous bytes from the current hash in an efficent way.
As you sure about this? Each bit of the byte to be subtracted is mixed linearly (i.e. XORs, no ANDs or ORs) into the result even when the result is many bytes away (i.e. block size). It looks, on the face of it, like a small table-driven algorithm, same size table as normal fast CRC but precalculated differently, might work for subtracting previous bytes, as quickly as it adds them on the end. -- Jamie -- Please use reply-all for most replies to avoid omitting the mailing list. To unsubscribe or change options: https://lists.samba.org/mailman/listinfo/rsync Before posting, read: http://www.catb.org/~esr/faqs/smart-questions.html
