Hi On Thu, Mar 09, 2006 at 11:09:45AM -0500, Rich Felker wrote:
On Thu, Mar 09, 2006 at 10:39:10AM -0500, Rich Felker wrote:
You mean just placing the checksum at arbitrary byte positions independent of contents? I'm at least mildly against this since it seems to complicate the implementation, requiring the data to be copied around to make up for the checksums inserted at random positions in it before it can be parsed.
yes, it was a bad idea, forget it
IMO the only piece of data that needs to be protected more than the whole-packet checksum is the forward_ptr (otherwise the demuxer may read unboundedly into the future trying to verify the whole-packet and its checksum). What if, instead of a checksum on the first N bytes of a packet when the packet size is >N, we instead do just a checksum on startcode+forward_ptr when the packet size is >N? This would eliminate the need for buffering to write the data, and would get all the benefits of the secondary-checksum (i.e. protecting forward_ptr).
Forget it; Oded just told me that this is what you originally proposed. :) Sorry I misunderstood. I thought the secondary checksum was going to cover all bytes in the first N bytes of the packet, not just the startcode+forward_ptr.
yes, so we are back to the question of what value does N have 4k, 16k? variable and stored in main header and main header has always a 2nd checksum or every header always has a 2nd checksum and syncpoints have some >N rule? somehow all these seem pretty much the same to me, only thing iam strongly against is allowing very large N personally i think a fixed N would be the best solution [...] -- Michael