1/*-
2 * Copyright (c) 1985, 1993 The Regents of the University of California.
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in the
12 *    documentation and/or other materials provided with the distribution.
13 * 3. Neither the name of the University nor the names of its contributors
14 *    may be used to endorse or promote products derived from this software
15 *    without specific prior written permission.
16 *
17 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
27 * SUCH DAMAGE.
28 */
29
30#include <sys/cdefs.h>
31#ifndef lint
32#if 0
33static char sccsid[] = "@(#)cksum.c	5.2 (Berkeley) 5/11/93";
34#else
35__RCSID("$NetBSD: cksum.c,v 1.6 2007/01/25 23:25:20 cbiere Exp $");
36#endif
37#endif /* not lint */
38
39#include <sys/types.h>
40#include "globals.h"
41
42/*
43 *			I N _ C K S U M
44 *
45 * Checksum routine for Internet Protocol family headers (C Version)
46 *
47 * There is no profit in a specialized version of the checksum
48 * function for any machine where int's are 32 bits and shorts are 16.
49 *
50 * All timed packets are smaller than 32K shorts, so there is no need to
51 * worry about carries except at the end.
52 */
53int
54in_cksum(const void *data, int len)
55{
56	const u_char *addr = data;
57	int nleft = len;
58	uint16_t answer;
59	int sum = 0;
60
61	/*
62	 *  Our algorithm is simple, using a 32 bit accumulator (sum),
63	 *  we add sequential 16 bit words to it, and at the end, fold
64	 *  back all the carry bits from the top 16 bits into the lower
65	 *  16 bits.
66	 */
67	while (nleft > 1) {
68		uint16_t w;
69
70		memcpy(&w, addr, sizeof(w));
71		sum += w;
72		addr += 2;
73		nleft -= 2;
74	}
75
76	/* mop up an odd byte, if necessary */
77	if (nleft == 1)
78		sum += *addr << 8;
79
80	/*
81	 * add back carry outs from top 16 bits to low 16 bits
82	 */
83	sum = (sum >> 16) + (sum & 0xffff);	/* add hi 16 to low 16 */
84	sum += (sum >> 16);			/* add carry */
85	answer = ~sum;				/* truncate to 16 bits */
86	return (answer);
87}
88