Wireshark mailing list archives

Re: Why tvb_get_bits() assumes Big Endian?


From: Tomasz Moń <desowin () gmail com>
Date: Thu, 30 Jul 2020 09:19:37 +0200

On Thu, Jul 30, 2020 at 8:58 AM Tomasz Moń <desowin () gmail com> wrote:

On Thu, Jul 30, 2020 at 8:30 AM Jaap Keuter <jaap.keuter () xs4all nl> wrote:
Let’s put a hypothetical here, a 7 bit value spanning 2 octets:

 15 14 13 12 11 10  9  8| 7  6  5  4  3  2  1  0
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|  |  |  |  |  |  | 6| 5| 4| 3| 2| 1| 0|  |  |  |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

This would be the typical interpretation, as seen in network protocols.

Your suggestion is that the interpretation can also be:

 15 14 13 12 11 10  9  8| 7  6  5  4  3  2  1  0
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|  |  |  |  |  |  | 1| 0| 6| 5| 4| 3| 2|  |  |  |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

This is not what I wanted to write. Assuming you meant two octets, and
the bitmask on the 16-bit value is 0x1FC0 then the alternative
interpretation would be:
  15 14 13 12 11 10  9  8| 7  6  5  4  3  2  1  0
 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
 |  |  |  |  |  |  | 4| 3| 2| 1| 0| 6| 5|  |  |  |
 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

Sorry, I should have displayed that in a fixed font earlier! It is
perfectly clear then (the bitmask in your example is 0x03F8, and not
0x1FC0 as I was led to believe due to trying to figure it out on font
not suited for the task)
___________________________________________________________________________
Sent via:    Wireshark-dev mailing list <wireshark-dev () wireshark org>
Archives:    https://www.wireshark.org/lists/wireshark-dev
Unsubscribe: https://www.wireshark.org/mailman/options/wireshark-dev
             mailto:wireshark-dev-request () wireshark org?subject=unsubscribe

Current thread: