usr/src/common/net/dhcp/ipv4_sum.c

   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
  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 }