1/*-
2 * Copyright (c) 1985, 1993
3 *	The Regents of the University of California.  All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
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.
13 * 3. All advertising materials mentioning features or use of this software
14 *    must display the following acknowledgement:
15 *	This product includes software developed by the University of
16 *	California, Berkeley and its contributors.
17 * 4. Neither the name of the University nor the names of its contributors
18 *    may be used to endorse or promote products derived from this software
19 *    without specific prior written permission.
20 *
21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31 * SUCH DAMAGE.
32 */
33
34#ifndef lint
35#if 0
36static char sccsid[] = "@(#)cksum.c	8.1 (Berkeley) 6/6/93";
37#endif
38__attribute__((__used__))
39static const char rcsid[] =
40  "$FreeBSD: src/usr.sbin/timed/timed/cksum.c,v 1.3 1999/08/28 01:20:17 peter Exp $";
41#endif /* not lint */
42#include <sys/cdefs.h>
43
44#include <sys/types.h>
45
46/*
47 *			I N _ C K S U M
48 *
49 * Checksum routine for Internet Protocol family headers (C Version)
50 *
51 * There is no profit in a specialized version of the checksum
52 * function for any machine where int's are 32 bits and shorts are 16.
53 *
54 * All timed packets are smaller than 32K shorts, so there is no need to
55 * worry about carries except at the end.
56 */
57int
58in_cksum(addr, len)
59	u_short *addr;
60	int len;
61{
62	register int nleft = len;
63	register u_short *w = addr;
64	register u_short answer;
65	register int sum = 0;
66
67	/*
68	 *  Our algorithm is simple, using a 32 bit accumulator (sum),
69	 *  we add sequential 16 bit words to it, and at the end, fold
70	 *  back all the carry bits from the top 16 bits into the lower
71	 *  16 bits.
72	 */
73	while( nleft > 1 )  {
74		sum += *w++;
75		nleft -= 2;
76	}
77
78	/* mop up an odd byte, if necessary */
79	if( nleft == 1 )
80		sum += (*(u_char *)w) << 8;
81
82	/*
83	 * add back carry outs from top 16 bits to low 16 bits
84	 */
85	sum = (sum >> 16) + (sum & 0xffff);	/* add hi 16 to low 16 */
86	sum += (sum >> 16);			/* add carry */
87	answer = ~sum;				/* truncate to 16 bits */
88	return (answer);
89}
90