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#include <string.h>
36
37#include "utils.h"
38
39/*
40 * in_cksum --
41 *	Checksum routine for Internet Protocol family headers (C Version)
42 */
43u_short
44in_cksum(u_char *addr, int len)
45{
46	int nleft, sum;
47	u_char *w;
48	union {
49		u_short	us;
50		u_char	uc[2];
51	} last;
52	u_short answer;
53
54	nleft = len;
55	sum = 0;
56	w = addr;
57
58	/*
59	 * Our algorithm is simple, using a 32 bit accumulator (sum), we add
60	 * sequential 16 bit words to it, and at the end, fold back all the
61	 * carry bits from the top 16 bits into the lower 16 bits.
62	 */
63	while (nleft > 1)  {
64		u_short data;
65
66		memcpy(&data, w, sizeof(data));
67		sum += data;
68		w += sizeof(data);
69		nleft -= sizeof(data);
70	}
71
72	/* mop up an odd byte, if necessary */
73	if (nleft == 1) {
74		last.uc[0] = *w;
75		last.uc[1] = 0;
76		sum += last.us;
77	}
78
79	/* add back carry outs from top 16 bits to low 16 bits */
80	sum = (sum >> 16) + (sum & 0xffff);	/* add hi 16 to low 16 */
81	sum += (sum >> 16);			/* add carry */
82	answer = ~sum;				/* truncate to 16 bits */
83	return(answer);
84}
85