in_cksum.c revision 84221 
1/*	$NetBSD: in_cksum.c,v 1.3 1995/04/22 13:53:48 cgd 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 * 3. All advertising materials mentioning features or use of this software
20 *    must display the following acknowledgement:
21 *	This product includes software developed by the University of
22 *	California, Lawrence Berkeley Laboratory and its contributors.
23 * 4. Neither the name of the University nor the names of its contributors
24 *    may be used to endorse or promote products derived from this software
25 *    without specific prior written permission.
26 *
27 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
28 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
29 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
30 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
31 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
32 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
33 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
34 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
35 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
36 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
37 * SUCH DAMAGE.
38 *
39 * @(#) Header: in_cksum.c,v 1.1 92/09/11 01:15:55 leres Exp  (LBL)
40 */
41
42#include <sys/cdefs.h>
43__FBSDID("$FreeBSD: head/lib/libstand/in_cksum.c 84221 2001-09-30 22:28:01Z dillon $");
44
45#include <sys/types.h>
46
47/*
48 * Checksum routine for Internet Protocol family headers.
49 * This routine is very heavily used in the network
50 * code and should be modified for each CPU to be as fast as possible.
51 * In particular, it should not be this one.
52 */
53int
54in_cksum(p, len)
55	register void *p;
56	register int len;
57{
58	register int sum = 0, oddbyte = 0, v = 0;
59	register u_char *cp = p;
60
61	/* we assume < 2^16 bytes being summed */
62	while (len > 0) {
63		if (oddbyte) {
64			sum += v + *cp++;
65			len--;
66		}
67		if (((long)cp & 1) == 0) {
68			while ((len -= 2) >= 0) {
69				sum += *(u_short *)cp;
70				cp += 2;
71			}
72		} else {
73			while ((len -= 2) >= 0) {
74				sum += *cp++ << 8;
75				sum += *cp++;
76			}
77		}
78		if ((oddbyte = len & 1) != 0)
79			v = *cp << 8;
80	}
81	if (oddbyte)
82		sum += v;
83	sum = (sum >> 16) + (sum & 0xffff); /* add in accumulated carries */
84	sum += sum >> 16;		/* add potential last carry */
85	return (0xffff & ~sum);
86}
87