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 */
43 u_short
in_cksum(u_char * addr,int len)44 in_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