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 90 init_crc10_table(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 128 init_checksum(void) { 129 130 init_crc10_table(); 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 } 190