Wireshark · Wireshark-bugs: [Wireshark-bugs] [Bug 6658] New: Improvements to GSM RR dissection of half-octet IEs

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https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=6658

           Summary: Improvements to GSM RR dissection of half-octet IEs
           Product: Wireshark
           Version: SVN
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: Minor
          Priority: Low
         Component: Wireshark
        AssignedTo: bugzilla-admin@xxxxxxxxxxxxx
        ReportedBy: wireshark@xxxxxxxxxxxxxxx


Build Information:
Paste the COMPLETE build information from "Help->About Wireshark", "wireshark
-v", or "tshark -v".
--
It was noticed that Wireshark did not dissect the correct nibble for Cipher
Mode Setting in a GSM handover command (pdu attached).

While sorting that out, it was noted that there were some ugly aspects to the
handling of GSM type 1 (V and TV) IEs in general.

The attached patch eliminates the global variable for tracking which nibble is
to be decoded by taking advantage of the fact that half octet IEs always occur
in pairs, and thus a pair can be grouped together for decoding.

There was probably also some confusion caused by the macros UPPER_NIBBLE and
LOWER_NIBBLE because the GSM bit numbering is opposite to Wireshark internal
numbering, so I have changed these to be LEFT_NIBBLE and RIGHT_NIBBLE, which
corresponds to the display format in Wireshark.

The dissection order of half octet IEs has been adjusted where necessary to
align with the ordering shown in the GSM specifications.

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