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
21 static 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
41 import sys
42
43 crc_table = []
44 for 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
52 for 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 */
58 static 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
94 static void
init_crc10_table(void)95 init_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
117 u_int16_t
verify_crc10_cksum(u_int16_t accum,const u_char * p,int length)118 verify_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 */
132 void
init_checksum(void)133 init_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 */
143 u_int16_t
create_osi_cksum(const u_int8_t * pptr,int checksum_offset,int length)144 create_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