lib/libstand/in_cksum.c

   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  * @(#) Header: in_cksum.c,v 1.1 92/09/11 01:15:55 leres Exp  (LBL)
  36  * $FreeBSD: src/lib/libstand/in_cksum.c,v 1.1.1.1.6.1 2002/07/22 09:28:50 peter Exp $
  37  * $DragonFly: src/lib/libstand/in_cksum.c,v 1.3 2005/12/11 02:27:26 swildner Exp $
  38  */
  39
  40 #include <sys/types.h>
  41 #include <machine/endian.h>
  42
  43 #include "stand.h"
  44
  45 /*
  46  * Checksum routine for Internet Protocol family headers.
  47  * This routine is very heavily used in the network
  48  * code and should be modified for each CPU to be as fast as possible.
  49  * In particular, it should not be this one.
  50  */
  51 int
  52 in_cksum(void *p, int len)
  53 {
  54         int sum = 0, oddbyte = 0, v = 0;
  55         u_char *cp = p;
  56
  57         /* we assume < 2^16 bytes being summed */
  58         while (len > 0) {
  59                 if (oddbyte) {
  60                         sum += v + *cp++;
  61                         len--;
  62                 }
  63                 if (((long)cp & 1) == 0) {
  64                         while ((len -= 2) >= 0) {
  65                                 sum += *(u_short *)cp;
  66                                 cp += 2;
  67                         }
  68                 } else {
  69                         while ((len -= 2) >= 0) {
  70 #if BYTE_ORDER == BIG_ENDIAN
  71                                 sum += *cp++ << 8;
  72                                 sum += *cp++;
  73 #else
  74                                 sum += *cp++;
  75                                 sum += *cp++ << 8;
  76 #endif
  77                         }
  78                 }
  79                 if ((oddbyte = len & 1) != 0)
  80 #if BYTE_ORDER == BIG_ENDIAN
  81                         v = *cp << 8;
  82 #else
  83                         v = *cp;
  84 #endif
  85         }
  86         if (oddbyte)
  87                 sum += v;
  88         sum = (sum >> 16) + (sum & 0xffff); /* add in accumulated carries */
  89         sum += sum >> 16;               /* add potential last carry */
  90         return (0xffff & ~sum);
  91 }