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 * 3. 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
36#include <sys/types.h>
37#include <machine/endian.h>
38
39#include "stand.h"
40
41/*
42 * Checksum routine for Internet Protocol family headers.
43 * This routine is very heavily used in the network
44 * code and should be modified for each CPU to be as fast as possible.
45 * In particular, it should not be this one.
46 */
47int
48in_cksum(void *p, int len)
49{
50	int sum = 0, oddbyte = 0, v = 0;
51	u_char *cp = p;
52
53	/* we assume < 2^16 bytes being summed */
54	while (len > 0) {
55		if (oddbyte) {
56			sum += v + *cp++;
57			len--;
58		}
59		if (((uintptr_t)cp & 1) == 0) {
60			while ((len -= 2) >= 0) {
61				sum += *(u_short *)cp;
62				cp += 2;
63			}
64		} else {
65			while ((len -= 2) >= 0) {
66#if BYTE_ORDER == BIG_ENDIAN
67				sum += *cp++ << 8;
68				sum += *cp++;
69#else
70				sum += *cp++;
71				sum += *cp++ << 8;
72#endif
73			}
74		}
75		if ((oddbyte = len & 1) != 0)
76#if BYTE_ORDER == BIG_ENDIAN
77			v = *cp << 8;
78#else
79			v = *cp;
80#endif
81	}
82	if (oddbyte)
83		sum += v;
84	sum = (sum >> 16) + (sum & 0xffff); /* add in accumulated carries */
85	sum += sum >> 16;		/* add potential last carry */
86	return (0xffff & ~sum);
87}
88