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git.proxmox.com Git - mirror_frr.git/blob - isisd/iso_checksum.c
2 * IS-IS Rout(e)ing protocol - iso_checksum.c
3 * ISO checksum related routines
5 * Copyright (C) 2001,2002 Sampo Saaristo
6 * Tampere University of Technology
7 * Institute of Communications Engineering
9 * This program is free software; you can redistribute it and/or modify it
10 * under the terms of the GNU General Public Licenseas published by the Free
11 * Software Foundation; either version 2 of the License, or (at your option)
14 * This program is distributed in the hope that it will be useful,but WITHOUT
15 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
16 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
19 * You should have received a copy of the GNU General Public License along
20 * with this program; see the file COPYING; if not, write to the Free Software
21 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
25 #include "iso_checksum.h"
29 * Calculations of the OSI checksum.
30 * ISO/IEC 8473 defines the sum as
37 * sum (L-i+1)a (mod 255) = 0
43 * Verifies that the checksum is correct.
44 * Return 0 on correct and 1 on invalid checksum.
45 * Based on Annex C.4 of ISO/IEC 8473
48 int iso_csum_verify(uint8_t *buffer
, int len
, uint16_t csum
, int offset
)
58 * If both are zero return correct
60 if (c0
== 0 && c1
== 0)
64 * If either, but not both are zero return incorrect
66 if (c0
== 0 || c1
== 0)
69 checksum
= fletcher_checksum(buffer
, len
, offset
);
70 if (checksum
== htons(csum
))