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/*
* 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 lint
static 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 0x633
static u_int16_t crc10_table[256];
static void
init_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_t
verify_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 */
void
init_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_t
create_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;
}
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