summaryrefslogtreecommitdiff
path: root/src/vpn/gnunet-vpn-checksum.c
blob: 0e0e24cdc391970fce242f187ee25e8afcdbc481 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
/*
     This file is part of GNUnet.
     (C) 2010 Christian Grothoff

     GNUnet is free software; you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published
     by the Free Software Foundation; either version 3, or (at your
     option) any later version.

     GNUnet is distributed in the hope that it will be useful, but
     WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
     General Public License for more details.

     You should have received a copy of the GNU General Public License
     along with GNUnet; see the file COPYING.  If not, write to the
     Free Software Foundation, Inc., 59 Temple Place - Suite 330,
     Boston, MA 02111-1307, USA.
*/

/**
 * @file vpn/gnunet-vpn-checksum.c
 * @brief
 * @author Philipp Toelke
 */

#include "gnunet-vpn-checksum.h"

uint32_t
calculate_checksum_update (uint32_t sum, uint16_t * hdr, short len)
{
  for (; len >= 2; len -= 2)
    sum += *(hdr++);
  if (len == 1)
    sum += *((unsigned char *) hdr);
  return sum;
}

uint16_t
calculate_checksum_end (uint32_t sum)
{
  while (sum >> 16)
    sum = (sum >> 16) + (sum & 0xFFFF);

  return ~sum;
}

/**
 * Calculate the checksum of an IPv4-Header
 */
uint16_t
calculate_ip_checksum (uint16_t * hdr, short len)
{
  uint32_t sum = calculate_checksum_update (0, hdr, len);

  return calculate_checksum_end (sum);
}