xref: /illumos-gate/usr/src/common/net/dhcp/ipv4_sum.c (revision 7c478bd9)
1 /*
2  * CDDL HEADER START
3  *
4  * The contents of this file are subject to the terms of the
5  * Common Development and Distribution License, Version 1.0 only
6  * (the "License").  You may not use this file except in compliance
7  * with the License.
8  *
9  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
10  * or http://www.opensolaris.org/os/licensing.
11  * See the License for the specific language governing permissions
12  * and limitations under the License.
13  *
14  * When distributing Covered Code, include this CDDL HEADER in each
15  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
16  * If applicable, add the following below this CDDL HEADER, with the
17  * fields enclosed by brackets "[]" replaced with your own identifying
18  * information: Portions Copyright [yyyy] [name of copyright owner]
19  *
20  * CDDL HEADER END
21  */
22 /*
23  * Copyright (c) 1996-2001 by Sun Microsystems, Inc.
24  * All rights reserved.
25  */
26 
27 #pragma ident	"%Z%%M%	%I%	%E% SMI"
28 
29 #include <sys/types.h>
30 #include "v4_sum_impl.h"
31 
32 /*
33  * Compute one's complement checksum for IP packet headers.
34  */
35 uint16_t
ipv4cksum(uint16_t * cp,uint16_t count)36 ipv4cksum(uint16_t *cp, uint16_t count)
37 {
38 	uint_t		sum = 0;
39 	uint_t		oneword = BIT_WRAP;
40 
41 	if (count == 0)
42 		return (0);
43 
44 	count >>= 1;
45 	while (count--) {
46 		sum += (uint_t)*cp++;
47 		if (sum >= oneword) {		/* Wrap carries into low bit */
48 			sum -= oneword;
49 			sum++;
50 		}
51 	}
52 	return ((uint16_t)~sum);
53 }
54