1/*	$NetBSD: in_cksum.c,v 1.6 2000/03/31 19:55:09 castor Exp $	*/
2
3/*
4 * Copyright (c) 1992 Regents of the University of California.
5 * All rights reserved.
6 *
7 * This software was developed by the Computer Systems Engineering group
8 * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and
9 * contributed to Berkeley.
10 *
11 * Redistribution and use in source and binary forms, with or without
12 * modification, are permitted provided that the following conditions
13 * are met:
14 * 1. Redistributions of source code must retain the above copyright
15 *    notice, this list of conditions and the following disclaimer.
16 * 2. Redistributions in binary form must reproduce the above copyright
17 *    notice, this list of conditions and the following disclaimer in the
18 *    documentation and/or other materials provided with the distribution.
19 * 4. Neither the name of the University nor the names of its contributors
20 *    may be used to endorse or promote products derived from this software
21 *    without specific prior written permission.
22 *
23 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
24 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
25 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
26 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
27 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
28 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
29 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
30 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
31 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
32 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
33 * SUCH DAMAGE.
34 *
35 * @(#) Header: in_cksum.c,v 1.1 92/09/11 01:15:55 leres Exp  (LBL)
36 */
37
38#include <sys/cdefs.h>
39__FBSDID("$FreeBSD: stable/11/stand/libsa/in_cksum.c 329132 2018-02-11 19:51:29Z kevans $");
40
41#include <sys/types.h>
42#include <machine/endian.h>
43
44#include "stand.h"
45
46/*
47 * Checksum routine for Internet Protocol family headers.
48 * This routine is very heavily used in the network
49 * code and should be modified for each CPU to be as fast as possible.
50 * In particular, it should not be this one.
51 */
52int
53in_cksum(p, len)
54	void *p;
55	int len;
56{
57	int sum = 0, oddbyte = 0, v = 0;
58	u_char *cp = p;
59
60	/* we assume < 2^16 bytes being summed */
61	while (len > 0) {
62		if (oddbyte) {
63			sum += v + *cp++;
64			len--;
65		}
66		if (((long)cp & 1) == 0) {
67			while ((len -= 2) >= 0) {
68				sum += *(u_short *)cp;
69				cp += 2;
70			}
71		} else {
72			while ((len -= 2) >= 0) {
73#if BYTE_ORDER == BIG_ENDIAN
74				sum += *cp++ << 8;
75				sum += *cp++;
76#else
77				sum += *cp++;
78				sum += *cp++ << 8;
79#endif
80			}
81		}
82		if ((oddbyte = len & 1) != 0)
83#if BYTE_ORDER == BIG_ENDIAN
84			v = *cp << 8;
85#else
86			v = *cp;
87#endif
88	}
89	if (oddbyte)
90		sum += v;
91	sum = (sum >> 16) + (sum & 0xffff); /* add in accumulated carries */
92	sum += sum >> 16;		/* add potential last carry */
93	return (0xffff & ~sum);
94}
95