tcpdump  4.99.1
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checksum.c
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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@gredler.at)
18  */
19 
20 #ifdef HAVE_CONFIG_H
21 #include <config.h>
22 #endif
23 
24 #include "netdissect-stdinc.h"
25 
26 #include <stdio.h>
27 #include <stdlib.h>
28 #include <string.h>
29 #include <assert.h>
30 
31 #include "netdissect.h"
32 
33 /*
34  * CRC-10 table generated using the following Python snippet:
35 
36 import sys
37 
38 crc_table = []
39 for i in range(256):
40  accum = i << 2
41  for j in range(8):
42  accum <<= 1
43  if accum & 0x400:
44  accum ^= 0x633
45  crc_table.append(accum)
46 
47 for i in range(len(crc_table)/8):
48  for j in range(8):
49  sys.stdout.write("0x%04x, " % crc_table[i*8+j])
50  sys.stdout.write("\n")
51 
52  */
53 static const uint16_t crc10_table[256] =
54 {
55  0x0000, 0x0233, 0x0255, 0x0066, 0x0299, 0x00aa, 0x00cc, 0x02ff,
56  0x0301, 0x0132, 0x0154, 0x0367, 0x0198, 0x03ab, 0x03cd, 0x01fe,
57  0x0031, 0x0202, 0x0264, 0x0057, 0x02a8, 0x009b, 0x00fd, 0x02ce,
58  0x0330, 0x0103, 0x0165, 0x0356, 0x01a9, 0x039a, 0x03fc, 0x01cf,
59  0x0062, 0x0251, 0x0237, 0x0004, 0x02fb, 0x00c8, 0x00ae, 0x029d,
60  0x0363, 0x0150, 0x0136, 0x0305, 0x01fa, 0x03c9, 0x03af, 0x019c,
61  0x0053, 0x0260, 0x0206, 0x0035, 0x02ca, 0x00f9, 0x009f, 0x02ac,
62  0x0352, 0x0161, 0x0107, 0x0334, 0x01cb, 0x03f8, 0x039e, 0x01ad,
63  0x00c4, 0x02f7, 0x0291, 0x00a2, 0x025d, 0x006e, 0x0008, 0x023b,
64  0x03c5, 0x01f6, 0x0190, 0x03a3, 0x015c, 0x036f, 0x0309, 0x013a,
65  0x00f5, 0x02c6, 0x02a0, 0x0093, 0x026c, 0x005f, 0x0039, 0x020a,
66  0x03f4, 0x01c7, 0x01a1, 0x0392, 0x016d, 0x035e, 0x0338, 0x010b,
67  0x00a6, 0x0295, 0x02f3, 0x00c0, 0x023f, 0x000c, 0x006a, 0x0259,
68  0x03a7, 0x0194, 0x01f2, 0x03c1, 0x013e, 0x030d, 0x036b, 0x0158,
69  0x0097, 0x02a4, 0x02c2, 0x00f1, 0x020e, 0x003d, 0x005b, 0x0268,
70  0x0396, 0x01a5, 0x01c3, 0x03f0, 0x010f, 0x033c, 0x035a, 0x0169,
71  0x0188, 0x03bb, 0x03dd, 0x01ee, 0x0311, 0x0122, 0x0144, 0x0377,
72  0x0289, 0x00ba, 0x00dc, 0x02ef, 0x0010, 0x0223, 0x0245, 0x0076,
73  0x01b9, 0x038a, 0x03ec, 0x01df, 0x0320, 0x0113, 0x0175, 0x0346,
74  0x02b8, 0x008b, 0x00ed, 0x02de, 0x0021, 0x0212, 0x0274, 0x0047,
75  0x01ea, 0x03d9, 0x03bf, 0x018c, 0x0373, 0x0140, 0x0126, 0x0315,
76  0x02eb, 0x00d8, 0x00be, 0x028d, 0x0072, 0x0241, 0x0227, 0x0014,
77  0x01db, 0x03e8, 0x038e, 0x01bd, 0x0342, 0x0171, 0x0117, 0x0324,
78  0x02da, 0x00e9, 0x008f, 0x02bc, 0x0043, 0x0270, 0x0216, 0x0025,
79  0x014c, 0x037f, 0x0319, 0x012a, 0x03d5, 0x01e6, 0x0180, 0x03b3,
80  0x024d, 0x007e, 0x0018, 0x022b, 0x00d4, 0x02e7, 0x0281, 0x00b2,
81  0x017d, 0x034e, 0x0328, 0x011b, 0x03e4, 0x01d7, 0x01b1, 0x0382,
82  0x027c, 0x004f, 0x0029, 0x021a, 0x00e5, 0x02d6, 0x02b0, 0x0083,
83  0x012e, 0x031d, 0x037b, 0x0148, 0x03b7, 0x0184, 0x01e2, 0x03d1,
84  0x022f, 0x001c, 0x007a, 0x0249, 0x00b6, 0x0285, 0x02e3, 0x00d0,
85  0x011f, 0x032c, 0x034a, 0x0179, 0x0386, 0x01b5, 0x01d3, 0x03e0,
86  0x021e, 0x002d, 0x004b, 0x0278, 0x0087, 0x02b4, 0x02d2, 0x00e1
87 };
88 
89 static void
91 {
92 #define CRC10_POLYNOMIAL 0x633
93  int i, j;
94  uint16_t accum;
95  uint16_t verify_crc10_table[256];
96 
97  for ( i = 0; i < 256; i++ )
98  {
99  accum = ((unsigned short) i << 2);
100  for ( j = 0; j < 8; j++ )
101  {
102  if ((accum <<= 1) & 0x400) accum ^= CRC10_POLYNOMIAL;
103  }
104  verify_crc10_table[i] = accum;
105  }
106  assert(memcmp(verify_crc10_table,
107  crc10_table,
108  sizeof(verify_crc10_table)) == 0);
109 #undef CRC10_POLYNOMIAL
110 }
111 
112 uint16_t
113 verify_crc10_cksum(uint16_t accum, const u_char *p, int length)
114 {
115  int i;
116 
117  for ( i = 0; i < length; i++ )
118  {
119  accum = ((accum << 8) & 0x3ff)
120  ^ crc10_table[( accum >> 2) & 0xff]
121  ^ *p++;
122  }
123  return accum;
124 }
125 
126 /* precompute checksum tables */
127 void
129 
131 
132 }
133 
134 /*
135  * Creates the OSI Fletcher checksum. See 8473-1, Appendix C, section C.3.
136  * The checksum field of the passed PDU does not need to be reset to zero.
137  */
138 uint16_t
139 create_osi_cksum (const uint8_t *pptr, int checksum_offset, int length)
140 {
141 
142  int x;
143  int y;
144  uint32_t mul;
145  uint32_t c0;
146  uint32_t c1;
147  uint16_t checksum;
148  int idx;
149 
150  c0 = 0;
151  c1 = 0;
152 
153  for (idx = 0; idx < length; idx++) {
154  /*
155  * Ignore the contents of the checksum field.
156  */
157  if (idx == checksum_offset ||
158  idx == checksum_offset+1) {
159  c1 += c0;
160  pptr++;
161  } else {
162  c0 = c0 + *(pptr++);
163  c1 += c0;
164  }
165  }
166 
167  c0 = c0 % 255;
168  c1 = c1 % 255;
169 
170  mul = (length - checksum_offset)*(c0);
171 
172  x = mul - c0 - c1;
173  y = c1 - mul - 1;
174 
175  if ( y >= 0 ) y++;
176  if ( x < 0 ) x--;
177 
178  x %= 255;
179  y %= 255;
180 
181 
182  if (x == 0) x = 255;
183  if (y == 0) y = 255;
184 
185  y &= 0x00FF;
186  checksum = ((x << 8) | y);
187 
188  return checksum;
189 }
uint16_t create_osi_cksum(const uint8_t *pptr, int checksum_offset, int length)
Definition: checksum.c:139
uint16_t verify_crc10_cksum(uint16_t accum, const u_char *p, int length)
Definition: checksum.c:113
#define CRC10_POLYNOMIAL
static void init_crc10_table(void)
Definition: checksum.c:90
void init_checksum(void)
Definition: checksum.c:128
static const uint16_t crc10_table[256]
Definition: checksum.c:53