Subject: RE: [rohc] sigcomp issue cabo-12

From: "Price, Richard" <[email-masked]>
Date: Fri, 15 Mar 2002 14:06:50 -0000

> > However, since the circular buffer can now be stored in the lowest UDVM memory
> > addresses (in front of the program code) the above reason is obsolete. So
> > for simplicity byte_copy_right should point to the first byte after the buffer.
> 
> I'd still like to make sure bcr=0x0000 means that the circular buffer ends
> with the byte at 0xFFFF.
>
> I believe this is a natural result of the modulo 2^16 arithmetic rules, but
> maybe it needs to be stated explicitly.

This shouldn't be a problem now that we are using arithmetic modulo 2^16. The old
draft didn't make this assumption; in fact, I'm not sure what the implications of
setting byte_copy_right smaller than byte_copy_left would have been...

Modulo arithmetic closes a lot of potential security holes, so we should make sure
the draft clearly states that *all* arithmetic on 2-byte quantities is carried out
modulo 2^16.

Regards,

Richard