On Fri, 27 Jul 2001, Benoit POSTE wrote:
>
> Thank you very much Mr. Scott for resending you e-mail.
>
> So, just to get this straight (last question, I promise!), if
> I understood well:
> > Toto ::= SEQUENCE {
> > one BOOLEAN,
> > ...,
> > two BOOLEAN OPTIONAL,
> > three BOOLEAN OPTIONAL,
> > four BOOLEAN OPTIONAL
> > }
> A value with "one" set to true and all other components absent
> will be encoded:
>
> 0 no addition value present
> 1 encoding of "one"
> 0000011 number of additions in the type (small whole number 3)
> 000 additions presence bitmap
>
> Am I correct? If so, it is a good thing I asked, I think I had
> it wrong.
No, not correct. If no extension addition value is present then the
encoding is (produced by OSS ASN-1Step utility):
ossPrintPER output...
value Toto ::=
{
--TYPE INFORMATION: SEQUENCE
--OFFSET: 0,0
--extension flag: <.0>
one TRUE
--TYPE INFORMATION: BOOLEAN
--OFFSET: 0,1; LENGTH: 0,1
--contents: <1>
}
--PDU padding: <000000>
--TOTAL LENGTH: 1,0
Simply put, the encoding is:
0 no addition value present
1 encoding of "one"
000000 PDU padding
Here it shows what X.691 clause 18.6 says - that once the extension
root has been encoded the type is fully encoded.
> Similarly:
> > Toto ::= SEQUENCE {
> > one BOOLEAN,
> > ...
> > }
> Would be encoded:
>
> 0 no addition value present
> 1 encoding of "one"
> 0000000 number of additions in the type (small whole number 0)
> (no additions presence bitmap)
>
> Right?
No. The encoding would be *exactly* as shown above. That is:
0 no addition value present
1 encoding of "one"
000000 PDU padding
Bancroft
> Again, thanks a lot for patience and your time.
>
> Benoit Poste.
>
>
> Bancroft Scott wrote:
> >
> > On Wed, 25 Jul 2001, Benoit POSTE wrote:
> >
> > >
> > > > X.691 clause 18.1 is abundantly clear on this:
> > > >
> > > > ... The bit shall be one if values of extension
> > > > additions are present in this encoding, and zero
> > > > otherwise....
> > > >
> > > > What is the source of your confusion as to how the SEQUENCE
> > > > should be encoded? It is clear to me.
> > >
> > > Oh all right, so "present" of the additions is to be taken in the
> > > OPTIONAL/DEFAULT sense. I only have the French version of X.691 and in
> > > French it either meant "present" as in OPTIONAL/DEFAULT, or "possess"
> > > (from the type's point of view).
> >
> > No, it hasn't anything to do with OPTIONAL/DEFAULT or with anything from
> > the type's point of view. It speaks of *values* of encoding additions.
> > That is, it is a matter of whether the extension addition values are
> > actually present that determines if the extension bit at the front of
> > the SEQUENCE is to 1.
> >
> > > > ... Ce bit doit être mis à 1 si ce codage contient des
> > > > valeurs d'adjonction d'extension ...
> > > Which literally could mean:
> > > > ... The bit shall be one if this encoding contains
> > > > extension additions ...
> > > I guess I am just going to get the English version too.
> > >
> > > However, 18.7 uses the words "number of extension additions to
> > > encode" so ...
> >
> > Look again at 18.7. It says "number of extension additions in the type
> > being encoded". Here it is referring to the type notation, not the actual
> > value.
> >
> > > I was beginning to wonder if it meant "number of
> > > additions, whether present or not". Of course, one could argue
> > > that encoding an all 0 presence bitmap is rather pointless, but
> > > one benefit is that it tells the receiver the encoder's version.
> > > Hence my confusion about the way to encode it.
> > >
> > > > It would be nice if you were to show us which comment you
> > > > are referring to instead of having everyone spend their time
> > > > trying to figure out which of Mr. Andersen's emails you are
> > > > referring to.
> > >
> > <snip>
>
