To answer your questions:
1. The bit field should not be octet aligned.
2. The encoding is wrong for both cases. Only
2 bits are needed to express the octet count (remember, the offset is from 1 so
the number 3 indicates 4 octets which is the max for the first value).
Consider the following:
TestSeq ::= SEQUENCE {
b
BOOLEAN,
i INTEGER(0..4294967295),
i2
INTEGER (0..16777215)
}
We get the
following encoding when setting all members to zero:
Binary dump:
IntType.b boolean
0-------
-------- -------- -------- --------
----
IntType.i ConsUnsigned length
-00xxxxx --------
-------- -------- 00------ .---
IntType.i ConsUnsigned
-------- 00000000
-------- -------- --00---- -.--
IntType.i2 ConsUnsigned length
-------- --------
00xxxxxx -------- ----00-- --.-
IntType.i2 ConsUnsigned
-------- --------
-------- 00000000 ------00 ---.
This is explained quite nicely in section 17.11.3
of ASN.1 Complete by John Larmouth. It is easier to read than the
standard.
Regards,
Ed Day
Objective Systems, Inc.
----- Original Message -----
Sent: Friday, May 21, 2004 1:08 AM
Subject: [ASN.1] Encoding of an Integer -
Indefinite length case
Hi,
I would like know to more about the encoding of
an Integer (Indefinite length) case.
Actually, the confusion lies in the
Alignment of the octet.
Example :
One ::= INTEGER
(0..4294967295)
Suppose the given value is : 0. In this
case, I presume that the encoded stream in PER Aligned variant is -
000xxxxx 00000000, 'xxxxx' are zero padding bits.
1. Is it
necessary to Align the octet before encoding this Integer? Means, if a byte is
filled upto 4th bit, then should it be octet aligned before appending the
Integer
bitstream.
2. Two ::= INTEGER
(0..16777215).
Suppose in this case also, the value entered is '0',
will the encoding (bitstream) is same as above one?
Please clarify my
doubts.
I am refering ITU-T 691 document.
Thank you very
much.
Regards,
Murali.
--
Muralikrishna N.
SYNERGY INFOTECH PVT. LTD.
Web Site :- http://www.synergy-infotech.com
Phone : 080 6780026/27/28, 6689904 Extn: 51.
My Home page :- http://www.geocities.com/nidugala
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