2 * Copyright (c) 1998-2006 The TCPDUMP project
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that: (1) source code
6 * distributions retain the above copyright notice and this paragraph
7 * in its entirety, and (2) distributions including binary code include
8 * the above copyright notice and this paragraph in its entirety in
9 * the documentation or other materials provided with the distribution.
10 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND
11 * WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT
12 * LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
13 * FOR A PARTICULAR PURPOSE.
15 * miscellaneous checksumming routines
17 * Original code by Hannes Gredler (hannes@juniper.net)
21 static const char rcsid[] _U_ =
22 "@(#) $Header: /tcpdump/master/tcpdump/checksum.c,v 1.4 2006-09-25 09:23:32 hannes Exp $";
29 #include <tcpdump-stdinc.h>
35 #include "interface.h"
37 #define CRC10_POLYNOMIAL 0x633
38 static u_int16_t crc10_table[256];
41 init_crc10_table(void)
44 register u_int16_t accum;
46 for ( i = 0; i < 256; i++ )
48 accum = ((unsigned short) i << 2);
49 for ( j = 0; j < 8; j++ )
51 if ((accum <<= 1) & 0x400) accum ^= CRC10_POLYNOMIAL;
53 crc10_table[i] = accum;
59 verify_crc10_cksum(u_int16_t accum, const u_char *p, int length)
63 for ( i = 0; i < length; i++ )
65 accum = ((accum << 8) & 0x3ff)
66 ^ crc10_table[( accum >> 2) & 0xff]
72 /* precompute checksum tables */
81 * Creates the OSI Fletcher checksum. See 8473-1, Appendix C, section C.3.
82 * The checksum field of the passed PDU does not need to be reset to zero.
85 create_osi_cksum (const u_int8_t *pptr, int checksum_offset, int length)
101 for (index = 0; index < length; index++) {
103 * Ignore the contents of the checksum field.
105 if (index == checksum_offset ||
106 index == checksum_offset+1) {
118 mul = (length - checksum_offset)*(c0);
134 checksum = ((x << 8) | y);