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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 (at) 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     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