checksum.c revision 190203
1190203Srpaulo/* 2190203Srpaulo * Copyright (c) 1998-2006 The TCPDUMP project 3190203Srpaulo * 4190203Srpaulo * Redistribution and use in source and binary forms, with or without 5190203Srpaulo * modification, are permitted provided that: (1) source code 6190203Srpaulo * distributions retain the above copyright notice and this paragraph 7190203Srpaulo * in its entirety, and (2) distributions including binary code include 8190203Srpaulo * the above copyright notice and this paragraph in its entirety in 9190203Srpaulo * the documentation or other materials provided with the distribution. 10190203Srpaulo * THIS SOFTWARE IS PROVIDED ``AS IS'' AND 11190203Srpaulo * WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT 12190203Srpaulo * LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 13190203Srpaulo * FOR A PARTICULAR PURPOSE. 14190203Srpaulo * 15190203Srpaulo * miscellaneous checksumming routines 16190203Srpaulo * 17190203Srpaulo * Original code by Hannes Gredler (hannes@juniper.net) 18190203Srpaulo */ 19190203Srpaulo 20190203Srpaulo#ifndef lint 21190203Srpaulostatic const char rcsid[] _U_ = 22190203Srpaulo "@(#) $Header: /tcpdump/master/tcpdump/checksum.c,v 1.4 2006-09-25 09:23:32 hannes Exp $"; 23190203Srpaulo#endif 24190203Srpaulo 25190203Srpaulo#ifdef HAVE_CONFIG_H 26190203Srpaulo#include "config.h" 27190203Srpaulo#endif 28190203Srpaulo 29190203Srpaulo#include <tcpdump-stdinc.h> 30190203Srpaulo 31190203Srpaulo#include <stdio.h> 32190203Srpaulo#include <stdlib.h> 33190203Srpaulo#include <string.h> 34190203Srpaulo 35190203Srpaulo#include "interface.h" 36190203Srpaulo 37190203Srpaulo#define CRC10_POLYNOMIAL 0x633 38190203Srpaulostatic u_int16_t crc10_table[256]; 39190203Srpaulo 40190203Srpaulostatic void 41190203Srpauloinit_crc10_table(void) 42190203Srpaulo{ 43190203Srpaulo register int i, j; 44190203Srpaulo register u_int16_t accum; 45190203Srpaulo 46190203Srpaulo for ( i = 0; i < 256; i++ ) 47190203Srpaulo { 48190203Srpaulo accum = ((unsigned short) i << 2); 49190203Srpaulo for ( j = 0; j < 8; j++ ) 50190203Srpaulo { 51190203Srpaulo if ((accum <<= 1) & 0x400) accum ^= CRC10_POLYNOMIAL; 52190203Srpaulo } 53190203Srpaulo crc10_table[i] = accum; 54190203Srpaulo } 55190203Srpaulo return; 56190203Srpaulo} 57190203Srpaulo 58190203Srpaulou_int16_t 59190203Srpauloverify_crc10_cksum(u_int16_t accum, const u_char *p, int length) 60190203Srpaulo{ 61190203Srpaulo register int i; 62190203Srpaulo 63190203Srpaulo for ( i = 0; i < length; i++ ) 64190203Srpaulo { 65190203Srpaulo accum = ((accum << 8) & 0x3ff) 66190203Srpaulo ^ crc10_table[( accum >> 2) & 0xff] 67190203Srpaulo ^ *p++; 68190203Srpaulo } 69190203Srpaulo return accum; 70190203Srpaulo} 71190203Srpaulo 72190203Srpaulo/* precompute checksum tables */ 73190203Srpaulovoid 74190203Srpauloinit_checksum(void) { 75190203Srpaulo 76190203Srpaulo init_crc10_table(); 77190203Srpaulo 78190203Srpaulo} 79190203Srpaulo 80190203Srpaulo/* 81190203Srpaulo * Creates the OSI Fletcher checksum. See 8473-1, Appendix C, section C.3. 82190203Srpaulo * The checksum field of the passed PDU does not need to be reset to zero. 83190203Srpaulo */ 84190203Srpaulou_int16_t 85190203Srpaulocreate_osi_cksum (const u_int8_t *pptr, int checksum_offset, int length) 86190203Srpaulo{ 87190203Srpaulo 88190203Srpaulo int x; 89190203Srpaulo int y; 90190203Srpaulo u_int32_t mul; 91190203Srpaulo u_int32_t c0; 92190203Srpaulo u_int32_t c1; 93190203Srpaulo u_int16_t checksum; 94190203Srpaulo int index; 95190203Srpaulo 96190203Srpaulo checksum = 0; 97190203Srpaulo 98190203Srpaulo c0 = 0; 99190203Srpaulo c1 = 0; 100190203Srpaulo 101190203Srpaulo for (index = 0; index < length; index++) { 102190203Srpaulo /* 103190203Srpaulo * Ignore the contents of the checksum field. 104190203Srpaulo */ 105190203Srpaulo if (index == checksum_offset || 106190203Srpaulo index == checksum_offset+1) { 107190203Srpaulo c1 += c0; 108190203Srpaulo pptr++; 109190203Srpaulo } else { 110190203Srpaulo c0 = c0 + *(pptr++); 111190203Srpaulo c1 += c0; 112190203Srpaulo } 113190203Srpaulo } 114190203Srpaulo 115190203Srpaulo c0 = c0 % 255; 116190203Srpaulo c1 = c1 % 255; 117190203Srpaulo 118190203Srpaulo mul = (length - checksum_offset)*(c0); 119190203Srpaulo 120190203Srpaulo x = mul - c0 - c1; 121190203Srpaulo y = c1 - mul - 1; 122190203Srpaulo 123190203Srpaulo if ( y >= 0 ) y++; 124190203Srpaulo if ( x < 0 ) x--; 125190203Srpaulo 126190203Srpaulo x %= 255; 127190203Srpaulo y %= 255; 128190203Srpaulo 129190203Srpaulo 130190203Srpaulo if (x == 0) x = 255; 131190203Srpaulo if (y == 0) y = 255; 132190203Srpaulo 133190203Srpaulo y &= 0x00FF; 134190203Srpaulo checksum = ((x << 8) | y); 135190203Srpaulo 136190203Srpaulo return checksum; 137190203Srpaulo} 138