1/*-
2 * SPDX-License-Identifier: BSD-3-Clause
3 *
4 * Copyright (c) 1989, 1993
5 *	The Regents of the University of California.  All rights reserved.
6 *
7 * This code is derived from software contributed to Berkeley by
8 * Mike Muuss.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 *    notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 *    notice, this list of conditions and the following disclaimer in the
17 *    documentation and/or other materials provided with the distribution.
18 * 3. Neither the name of the University nor the names of its contributors
19 *    may be used to endorse or promote products derived from this software
20 *    without specific prior written permission.
21 *
22 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 * SUCH DAMAGE.
33 */
34
35#if 0
36#ifndef lint
37static const char copyright[] =
38"@(#) Copyright (c) 1989, 1993\n\
39	The Regents of the University of California.  All rights reserved.\n";
40#endif /* not lint */
41
42#ifndef lint
43static char sccsid[] = "@(#)ping.c	8.1 (Berkeley) 6/5/93";
44#endif /* not lint */
45#endif
46#include <sys/cdefs.h>
47__FBSDID("$FreeBSD$");
48
49#include <string.h>
50
51#include "utils.h"
52
53/*
54 * in_cksum --
55 *	Checksum routine for Internet Protocol family headers (C Version)
56 */
57u_short
58in_cksum(u_char *addr, int len)
59{
60	int nleft, sum;
61	u_char *w;
62	union {
63		u_short	us;
64		u_char	uc[2];
65	} last;
66	u_short answer;
67
68	nleft = len;
69	sum = 0;
70	w = addr;
71
72	/*
73	 * Our algorithm is simple, using a 32 bit accumulator (sum), we add
74	 * sequential 16 bit words to it, and at the end, fold back all the
75	 * carry bits from the top 16 bits into the lower 16 bits.
76	 */
77	while (nleft > 1)  {
78		u_short data;
79
80		memcpy(&data, w, sizeof(data));
81		sum += data;
82		w += sizeof(data);
83		nleft -= sizeof(data);
84	}
85
86	/* mop up an odd byte, if necessary */
87	if (nleft == 1) {
88		last.uc[0] = *w;
89		last.uc[1] = 0;
90		sum += last.us;
91	}
92
93	/* add back carry outs from top 16 bits to low 16 bits */
94	sum = (sum >> 16) + (sum & 0xffff);	/* add hi 16 to low 16 */
95	sum += (sum >> 16);			/* add carry */
96	answer = ~sum;				/* truncate to 16 bits */
97	return(answer);
98}
99