The Tcpdump Group git mirrors - tcpdump/blob - checksum.c

   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@juniper.net)
  18  */
  19
  20 #ifndef lint
  21 static const char rcsid[] _U_ =
  22     "@(#) $Header: /tcpdump/master/tcpdump/checksum.c,v 1.1 2006-02-09 20:33:49 hannes Exp $";
  23 #endif
  24
  25 #ifdef HAVE_CONFIG_H
  26 #include "config.h"
  27 #endif
  28
  29 #include <tcpdump-stdinc.h>
  30
  31 #include <stdio.h>
  32 #include <stdlib.h>
  33 #include <string.h>
  34
  35 #include "interface.h"
  36 #include "extract.h"
  37 #include "addrtoname.h"
  38
  39 #define CRC10_POLYNOMIAL 0x633
  40 static u_int16_t crc10_table[256];
  41
  42 static void
  43 gen_crc10_table(void)
  44 {
  45     register int i, j;
  46     register u_int16_t accum;
  47
  48     for ( i = 0;  i < 256;  i++ )
  49     {
  50         accum = ((unsigned short) i << 2);
  51         for ( j = 0;  j < 8;  j++ )
  52         {
  53             if ((accum <<= 1) & 0x400) accum ^= CRC10_POLYNOMIAL;
  54         }
  55         crc10_table[i] = accum;
  56     }
  57     return;
  58 }
  59
  60 u_int16_t
  61 verify_crc10_cksum(u_int16_t accum, const u_char *p, int length)
  62 {
  63     register int i;
  64
  65     for ( i = 0;  i < length;  i++ )
  66     {
  67         accum = ((accum << 8) & 0x3ff)
  68             ^ crc10_table[( accum >> 2) & 0xff]
  69             ^ *p++;
  70     }
  71     return accum;
  72 }
  73
  74 /* precomputed checksum tables */
  75 void
  76 init_checksum(void) {
  77
  78     gen_crc10_table();
  79
  80 }