2 * Copyright (c) 2001 Charles Mott <cm@linktel.net>
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * $FreeBSD: src/lib/libalias/alias_util.c,v 1.4.2.3 2001/11/03 11:34:33 brian Exp $
27 * $DragonFly: src/lib/libalias/alias_util.c,v 1.3 2004/08/20 00:08:17 joerg Exp $
31 Alias_util.c contains general utilities used by other functions
32 in the packet aliasing module. At the moment, there are functions
33 for computing IP header and TCP packet checksums.
35 The checksum routines are based upon example code in a Unix networking
36 text written by Stevens (sorry, I can't remember the title -- but
37 at least this is a good author).
39 Initial Version: August, 1996 (cjm)
41 Version 1.7: January 9, 1997
42 Added differential checksum update function.
46 Note: the checksum routines assume that the actual checksum word has
47 been zeroed out. If the checksum word is filled with the proper value,
48 then these routines will give a result of zero (useful for testing
52 #include <sys/param.h>
53 #include <netinet/in_systm.h>
54 #include <netinet/in.h>
55 #include <netinet/ip.h>
56 #include <netinet/tcp.h>
59 #include "alias_local.h"
62 PacketAliasInternetChecksum(u_short
*ptr
, int nbytes
)
75 ((u_char
*) &oddbyte
)[0] = *(u_char
*) ptr
;
76 ((u_char
*) &oddbyte
)[1] = 0;
79 sum
= (sum
>> 16) + (sum
& 0xffff);
85 IpChecksum(struct ip
*pip
)
87 return( PacketAliasInternetChecksum((u_short
*) pip
,
93 TcpChecksum(struct ip
*pip
)
97 int nhdr
, ntcp
, nbytes
;
100 nhdr
= pip
->ip_hl
<< 2;
101 ntcp
= ntohs(pip
->ip_len
) - nhdr
;
103 tc
= (struct tcphdr
*) ((char *) pip
+ nhdr
);
104 ptr
= (u_short
*) tc
;
106 /* Add up TCP header and data */
117 ((u_char
*) &oddbyte
)[0] = *(u_char
*) ptr
;
118 ((u_char
*) &oddbyte
)[1] = 0;
122 /* "Pseudo-header" data */
123 ptr
= (u_short
*) &(pip
->ip_dst
);
126 ptr
= (u_short
*) &(pip
->ip_src
);
129 sum
+= htons((u_short
) ntcp
);
130 sum
+= htons((u_short
) pip
->ip_p
);
132 /* Roll over carry bits */
133 sum
= (sum
>> 16) + (sum
& 0xffff);
136 /* Return checksum */
137 return((u_short
) ~sum
);
142 DifferentialChecksum(u_short
*cksum
, u_short
*new, u_short
*old
, int n
)
150 accumulate
-= *new++;
151 accumulate
+= *old
++;
156 accumulate
= -accumulate
;
157 accumulate
= (accumulate
>> 16) + (accumulate
& 0xffff);
158 accumulate
+= accumulate
>> 16;
159 *cksum
= (u_short
) ~accumulate
;
163 accumulate
= (accumulate
>> 16) + (accumulate
& 0xffff);
164 accumulate
+= accumulate
>> 16;
165 *cksum
= (u_short
) accumulate
;