contrib/tcpdump/checksum.c

   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
  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
 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
 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
 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     checksum = 0;
 156
 157     c0 = 0;
 158     c1 = 0;
 159
 160     for (index = 0; index < length; index++) {
 161         /*
 162          * Ignore the contents of the checksum field.
 163          */
 164         if (index == checksum_offset ||
 165             index == checksum_offset+1) {
 166             c1 += c0;
 167             pptr++;
 168         } else {
 169             c0 = c0 + *(pptr++);
 170             c1 += c0;
 171         }
 172     }
 173
 174     c0 = c0 % 255;
 175     c1 = c1 % 255;
 176
 177     mul = (length - checksum_offset)*(c0);
 178
 179     x = mul - c0 - c1;
 180     y = c1 - mul - 1;
 181
 182     if ( y >= 0 ) y++;
 183     if ( x < 0 ) x--;
 184
 185     x %= 255;
 186     y %= 255;
 187
 188
 189     if (x == 0) x = 255;
 190     if (y == 0) y = 255;
 191
 192     y &= 0x00FF;
 193     checksum = ((x << 8) | y);
 194
 195     return checksum;
 196 }