1/*
2 * Copyright (c) 1998-2006 The TCPDUMP project
3 *
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.
14 *
15 * miscellaneous checksumming routines
16 *
17 * Original code by Hannes Gredler (hannes@juniper.net)
18 */
19
20#ifndef lint
21static const char rcsid[] _U_ =
22    "@(#) $Header: /tcpdump/master/tcpdump/checksum.c,v 1.4 2006-09-25 09:23:32 hannes Exp $";
23#endif
24
25#ifdef HAVE_CONFIG_H
26#include "config.h"
27#endif
28
29#include <tcpdump-stdinc.h>
30
31#include <stdio.h>
32#include <stdlib.h>
33#include <string.h>
34#include <assert.h>
35
36#include "interface.h"
37
38/*
39 * CRC-10 table generated using the following Python snippet:
40
41import sys
42
43crc_table = []
44for i in range(256):
45	accum = i << 2
46	for j in range(8):
47		accum <<= 1
48		if accum & 0x400:
49			accum ^= 0x633
50	crc_table.append(accum)
51
52for i in range(len(crc_table)/8):
53	for j in range(8):
54		sys.stdout.write("0x%04x, " % crc_table[i*8+j])
55	sys.stdout.write("\n")
56
57 */
58static const u_int16_t crc10_table[256] =
59{
60	0x0000, 0x0233, 0x0255, 0x0066, 0x0299, 0x00aa, 0x00cc, 0x02ff,
61	0x0301, 0x0132, 0x0154, 0x0367, 0x0198, 0x03ab, 0x03cd, 0x01fe,
62	0x0031, 0x0202, 0x0264, 0x0057, 0x02a8, 0x009b, 0x00fd, 0x02ce,
63	0x0330, 0x0103, 0x0165, 0x0356, 0x01a9, 0x039a, 0x03fc, 0x01cf,
64	0x0062, 0x0251, 0x0237, 0x0004, 0x02fb, 0x00c8, 0x00ae, 0x029d,
65	0x0363, 0x0150, 0x0136, 0x0305, 0x01fa, 0x03c9, 0x03af, 0x019c,
66	0x0053, 0x0260, 0x0206, 0x0035, 0x02ca, 0x00f9, 0x009f, 0x02ac,
67	0x0352, 0x0161, 0x0107, 0x0334, 0x01cb, 0x03f8, 0x039e, 0x01ad,
68	0x00c4, 0x02f7, 0x0291, 0x00a2, 0x025d, 0x006e, 0x0008, 0x023b,
69	0x03c5, 0x01f6, 0x0190, 0x03a3, 0x015c, 0x036f, 0x0309, 0x013a,
70	0x00f5, 0x02c6, 0x02a0, 0x0093, 0x026c, 0x005f, 0x0039, 0x020a,
71	0x03f4, 0x01c7, 0x01a1, 0x0392, 0x016d, 0x035e, 0x0338, 0x010b,
72	0x00a6, 0x0295, 0x02f3, 0x00c0, 0x023f, 0x000c, 0x006a, 0x0259,
73	0x03a7, 0x0194, 0x01f2, 0x03c1, 0x013e, 0x030d, 0x036b, 0x0158,
74	0x0097, 0x02a4, 0x02c2, 0x00f1, 0x020e, 0x003d, 0x005b, 0x0268,
75	0x0396, 0x01a5, 0x01c3, 0x03f0, 0x010f, 0x033c, 0x035a, 0x0169,
76	0x0188, 0x03bb, 0x03dd, 0x01ee, 0x0311, 0x0122, 0x0144, 0x0377,
77	0x0289, 0x00ba, 0x00dc, 0x02ef, 0x0010, 0x0223, 0x0245, 0x0076,
78	0x01b9, 0x038a, 0x03ec, 0x01df, 0x0320, 0x0113, 0x0175, 0x0346,
79	0x02b8, 0x008b, 0x00ed, 0x02de, 0x0021, 0x0212, 0x0274, 0x0047,
80	0x01ea, 0x03d9, 0x03bf, 0x018c, 0x0373, 0x0140, 0x0126, 0x0315,
81	0x02eb, 0x00d8, 0x00be, 0x028d, 0x0072, 0x0241, 0x0227, 0x0014,
82	0x01db, 0x03e8, 0x038e, 0x01bd, 0x0342, 0x0171, 0x0117, 0x0324,
83	0x02da, 0x00e9, 0x008f, 0x02bc, 0x0043, 0x0270, 0x0216, 0x0025,
84	0x014c, 0x037f, 0x0319, 0x012a, 0x03d5, 0x01e6, 0x0180, 0x03b3,
85	0x024d, 0x007e, 0x0018, 0x022b, 0x00d4, 0x02e7, 0x0281, 0x00b2,
86	0x017d, 0x034e, 0x0328, 0x011b, 0x03e4, 0x01d7, 0x01b1, 0x0382,
87	0x027c, 0x004f, 0x0029, 0x021a, 0x00e5, 0x02d6, 0x02b0, 0x0083,
88	0x012e, 0x031d, 0x037b, 0x0148, 0x03b7, 0x0184, 0x01e2, 0x03d1,
89	0x022f, 0x001c, 0x007a, 0x0249, 0x00b6, 0x0285, 0x02e3, 0x00d0,
90	0x011f, 0x032c, 0x034a, 0x0179, 0x0386, 0x01b5, 0x01d3, 0x03e0,
91	0x021e, 0x002d, 0x004b, 0x0278, 0x0087, 0x02b4, 0x02d2, 0x00e1
92};
93
94static void
95init_crc10_table(void)
96{
97#define CRC10_POLYNOMIAL 0x633
98    register int i, j;
99    register u_int16_t accum;
100    u_int16_t verify_crc10_table[256];
101
102    for ( i = 0;  i < 256;  i++ )
103    {
104        accum = ((unsigned short) i << 2);
105        for ( j = 0;  j < 8;  j++ )
106        {
107            if ((accum <<= 1) & 0x400) accum ^= CRC10_POLYNOMIAL;
108        }
109        verify_crc10_table[i] = accum;
110    }
111    assert(memcmp(verify_crc10_table,
112				  crc10_table,
113				  sizeof(verify_crc10_table)) == 0);
114#undef CRC10_POLYNOMIAL
115}
116
117u_int16_t
118verify_crc10_cksum(u_int16_t accum, const u_char *p, int length)
119{
120    register int i;
121
122    for ( i = 0;  i < length;  i++ )
123    {
124        accum = ((accum << 8) & 0x3ff)
125            ^ crc10_table[( accum >> 2) & 0xff]
126            ^ *p++;
127    }
128    return accum;
129}
130
131/* precompute checksum tables */
132void
133init_checksum(void) {
134
135    init_crc10_table();
136
137}
138
139/*
140 * Creates the OSI Fletcher checksum. See 8473-1, Appendix C, section C.3.
141 * The checksum field of the passed PDU does not need to be reset to zero.
142 */
143u_int16_t
144create_osi_cksum (const u_int8_t *pptr, int checksum_offset, int length)
145{
146
147    int x;
148    int y;
149    u_int32_t mul;
150    u_int32_t c0;
151    u_int32_t c1;
152    u_int16_t checksum;
153    int index;
154
155    c0 = 0;
156    c1 = 0;
157
158    for (index = 0; index < length; index++) {
159        /*
160         * Ignore the contents of the checksum field.
161         */
162        if (index == checksum_offset ||
163            index == checksum_offset+1) {
164            c1 += c0;
165            pptr++;
166        } else {
167            c0 = c0 + *(pptr++);
168            c1 += c0;
169        }
170    }
171
172    c0 = c0 % 255;
173    c1 = c1 % 255;
174
175    mul = (length - checksum_offset)*(c0);
176
177    x = mul - c0 - c1;
178    y = c1 - mul - 1;
179
180    if ( y >= 0 ) y++;
181    if ( x < 0 ) x--;
182
183    x %= 255;
184    y %= 255;
185
186
187    if (x == 0) x = 255;
188    if (y == 0) y = 255;
189
190    y &= 0x00FF;
191    checksum = ((x << 8) | y);
192
193    return checksum;
194}
195