usr.sbin/timed/timed/cksum.c

   1 /*-
   2  * Copyright (c) 1985, 1993
   3  *      The Regents of the University of California.  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. All advertising materials mentioning features or use of this software
  14  *    must display the following acknowledgement:
  15  *      This product includes software developed by the University of
  16  *      California, Berkeley and its contributors.
  17  * 4. Neither the name of the University nor the names of its contributors
  18  *    may be used to endorse or promote products derived from this software
  19  *    without specific prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  31  * SUCH DAMAGE.
  32  *
  33  * @(#)cksum.c  8.1 (Berkeley) 6/6/93
  34  * $FreeBSD: src/usr.sbin/timed/timed/cksum.c,v 1.3 1999/08/28 01:20:17 peter Exp $
  35  * $DragonFly: src/usr.sbin/timed/timed/cksum.c,v 1.4 2004/09/05 02:09:24 dillon Exp $
  36  */
  37
  38 #include <sys/types.h>
  39 #include "extern.h"
  40
  41 /*
  42  *                      I N _ C K S U M
  43  *
  44  * Checksum routine for Internet Protocol family headers (C Version)
  45  *
  46  * There is no profit in a specialized version of the checksum
  47  * function for any machine where int's are 32 bits and shorts are 16.
  48  *
  49  * All timed packets are smaller than 32K shorts, so there is no need to
  50  * worry about carries except at the end.
  51  */
  52 int
  53 in_cksum(u_short *addr, int len)
  54 {
  55         int nleft = len;
  56         u_short *w = addr;
  57         u_short answer;
  58         int sum = 0;
  59
  60         /*
  61          *  Our algorithm is simple, using a 32 bit accumulator (sum),
  62          *  we add sequential 16 bit words to it, and at the end, fold
  63          *  back all the carry bits from the top 16 bits into the lower
  64          *  16 bits.
  65          */
  66         while( nleft > 1 )  {
  67                 sum += *w++;
  68                 nleft -= 2;
  69         }
  70
  71         /* mop up an odd byte, if necessary */
  72         if( nleft == 1 )
  73                 sum += (*(u_char *)w) << 8;
  74
  75         /*
  76          * add back carry outs from top 16 bits to low 16 bits
  77          */
  78         sum = (sum >> 16) + (sum & 0xffff);     /* add hi 16 to low 16 */
  79         sum += (sum >> 16);                     /* add carry */
  80         answer = ~sum;                          /* truncate to 16 bits */
  81         return (answer);
  82 }