/* * Copyright (c) 1998-2006 The TCPDUMP project * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that: (1) source code * distributions retain the above copyright notice and this paragraph * in its entirety, and (2) distributions including binary code include * the above copyright notice and this paragraph in its entirety in * the documentation or other materials provided with the distribution. * THIS SOFTWARE IS PROVIDED ``AS IS'' AND * WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT * LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS * FOR A PARTICULAR PURPOSE. * * miscellaneous checksumming routines * * Original code by Hannes Gredler (hannes@juniper.net) */#ifndef lintstatic const char rcsid[] _U_ =    "@(#) $Header: /tcpdump/master/tcpdump/checksum.c,v 1.4 2006-09-25 09:23:32 hannes Exp $";#endif#ifdef HAVE_CONFIG_H#include "config.h"#endif#include <tcpdump-stdinc.h>#include <stdio.h>#include <stdlib.h>#include <string.h>#include "interface.h"#define CRC10_POLYNOMIAL 0x633static u_int16_t crc10_table[256];static voidinit_crc10_table(void){       register int i, j;    register u_int16_t accum;        for ( i = 0;  i < 256;  i++ )    {        accum = ((unsigned short) i << 2);        for ( j = 0;  j < 8;  j++ )        {            if ((accum <<= 1) & 0x400) accum ^= CRC10_POLYNOMIAL;        }        crc10_table[i] = accum;    }    return;}u_int16_tverify_crc10_cksum(u_int16_t accum, const u_char *p, int length){    register int i;    for ( i = 0;  i < length;  i++ )    {        accum = ((accum << 8) & 0x3ff)            ^ crc10_table[( accum >> 2) & 0xff]            ^ *p++;    }    return accum;}/* precompute checksum tables */voidinit_checksum(void) {    init_crc10_table();}/* * Creates the OSI Fletcher checksum. See 8473-1, Appendix C, section C.3. * The checksum field of the passed PDU does not need to be reset to zero. */u_int16_tcreate_osi_cksum (const u_int8_t *pptr, int checksum_offset, int length){    int x;    int y;    u_int32_t mul;    u_int32_t c0;    u_int32_t c1;    u_int16_t checksum;    int index;    checksum = 0;    c0 = 0;    c1 = 0;    for (index = 0; index < length; index++) {        /*         * Ignore the contents of the checksum field.         */        if (index == checksum_offset ||            index == checksum_offset+1) {            c1 += c0;            pptr++;        } else {            c0 = c0 + *(pptr++);            c1 += c0;        }     }    c0 = c0 % 255;    c1 = c1 % 255;    mul = (length - checksum_offset)*(c0);      x = mul - c0 - c1;    y = c1 - mul - 1;    if ( y >= 0 ) y++;    if ( x < 0 ) x--;    x %= 255;    y %= 255;    if (x == 0) x = 255;    if (y == 0) y = 255;    y &= 0x00FF;    checksum = ((x << 8) | y);      return checksum;}