138 lines
2.9 KiB
C
138 lines
2.9 KiB
C
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/*
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* Copyright (c) 1998-2006 The TCPDUMP project
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that: (1) source code
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* distributions retain the above copyright notice and this paragraph
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* in its entirety, and (2) distributions including binary code include
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* the above copyright notice and this paragraph in its entirety in
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* the documentation or other materials provided with the distribution.
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* THIS SOFTWARE IS PROVIDED ``AS IS'' AND
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* WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT
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* LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE.
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*
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* miscellaneous checksumming routines
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*
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* Original code by Hannes Gredler (hannes@juniper.net)
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*/
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#ifndef lint
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static const char rcsid[] _U_ =
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"@(#) $Header: /tcpdump/master/tcpdump/checksum.c,v 1.4 2006-09-25 09:23:32 hannes Exp $";
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#endif
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#ifdef HAVE_CONFIG_H
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#include "config.h"
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#endif
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#include <tcpdump-stdinc.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include "interface.h"
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#define CRC10_POLYNOMIAL 0x633
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static u_int16_t crc10_table[256];
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static void
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init_crc10_table(void)
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{
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register int i, j;
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register u_int16_t accum;
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for ( i = 0; i < 256; i++ )
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{
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accum = ((unsigned short) i << 2);
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for ( j = 0; j < 8; j++ )
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{
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if ((accum <<= 1) & 0x400) accum ^= CRC10_POLYNOMIAL;
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}
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crc10_table[i] = accum;
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}
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return;
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}
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u_int16_t
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verify_crc10_cksum(u_int16_t accum, const u_char *p, int length)
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{
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register int i;
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for ( i = 0; i < length; i++ )
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{
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accum = ((accum << 8) & 0x3ff)
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^ crc10_table[( accum >> 2) & 0xff]
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^ *p++;
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}
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return accum;
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}
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/* precompute checksum tables */
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void
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init_checksum(void) {
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init_crc10_table();
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}
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/*
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* Creates the OSI Fletcher checksum. See 8473-1, Appendix C, section C.3.
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* The checksum field of the passed PDU does not need to be reset to zero.
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*/
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u_int16_t
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create_osi_cksum (const u_int8_t *pptr, int checksum_offset, int length)
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{
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int x;
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int y;
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u_int32_t mul;
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u_int32_t c0;
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u_int32_t c1;
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u_int16_t checksum;
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int index;
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checksum = 0;
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c0 = 0;
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c1 = 0;
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for (index = 0; index < length; index++) {
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/*
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* Ignore the contents of the checksum field.
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*/
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if (index == checksum_offset ||
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index == checksum_offset+1) {
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c1 += c0;
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pptr++;
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} else {
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c0 = c0 + *(pptr++);
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c1 += c0;
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}
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}
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c0 = c0 % 255;
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c1 = c1 % 255;
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mul = (length - checksum_offset)*(c0);
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x = mul - c0 - c1;
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y = c1 - mul - 1;
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if ( y >= 0 ) y++;
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if ( x < 0 ) x--;
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x %= 255;
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y %= 255;
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if (x == 0) x = 255;
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if (y == 0) y = 255;
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y &= 0x00FF;
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checksum = ((x << 8) | y);
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return checksum;
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}
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