https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=4478
Summary: Implement little endian support for
tvb_get_bits[16|32|64]
Product: Wireshark
Version: SVN
Platform: All
OS/Version: All
Status: NEW
Severity: Enhancement
Priority: Low
Component: Wireshark
AssignedTo: wireshark-bugs@xxxxxxxxxxxxx
ReportedBy: plr.vincent@xxxxxxxxx
Created an attachment (id=4285)
--> (https://bugs.wireshark.org/bugzilla/attachment.cgi?id=4285)
For wireshark/epan/tvbuff.c, as of r31822
Build Information:
Version 1.3.3 (SVN Rev 31822 from /trunk)
Copyright 1998-2010 Gerald Combs <gerald@xxxxxxxxxxxxx> and contributors.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
Compiled with GTK+ 2.18.6, with GLib 2.22.4, with libpcap 1.0.0, with libz
1.2.3.4, without POSIX capabilities, with libpcre 7.8, without SMI, without
c-ares, without ADNS, without Lua, without Python, with GnuTLS 2.8.5, with
Gcrypt 1.4.5, with MIT Kerberos, without GeoIP, without PortAudio, without
AirPcap, with new_packet_list.
Running on Linux 2.6.32-trunk-amd64, with libpcap version 1.0.0, GnuTLS 2.8.5,
Gcrypt 1.4.5.
Built using gcc 4.4.3.
Wireshark is Open Source Software released under the GNU General Public
License.
Check the man page and http://www.wireshark.org for more information.
--
Attached patch adds support for fetching a list of bits, starting at given bit
offset and for given length (nothing new here), allowing little-endian byte
ordering (this is new).
I believe the best to do to describe the implementation is to provide examples,
focusing on tvb_get_bits32:
- file data
0x12 0x34 0x56 0x78 0x9A
- bit_offset, no_of_bits = result // comment
0, 32 = 0x78563412 // regular conversion of 4 first bytes
4, 24 = 0x7856342 // 4 (=bit_offset) MSbs of 1st byte are stripped
4, 32 = 0xA7856342 // 4 (=32 - (bit_offset + no_of_bits)) LSbs of 5th byte
are added to result
And so on for bit_offsets which are not multiple of 4 (it's much less visually
obvious).
As it's my first submission to wireshark, and as it has been quite some months
since I last used C, please review for stupid constructs and bad coding style.
--
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