timed.tproj/timed.tproj/cksum.c

   1 /*
   2  * Copyright (c) 1999 Apple Computer, Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * "Portions Copyright (c) 1999 Apple Computer, Inc.  All Rights
   7  * Reserved.  This file contains Original Code and/or Modifications of
   8  * Original Code as defined in and that are subject to the Apple Public
   9  * Source License Version 1.0 (the 'License').  You may not use this file
  10  * except in compliance with the License.  Please obtain a copy of the
  11  * License at http://www.apple.com/publicsource and read it before using
  12  * this file.
  13  *
  14  * The Original Code and all software distributed under the License are
  15  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  16  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  17  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  18  * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
  19  * License for the specific language governing rights and limitations
  20  * under the License."
  21  *
  22  * @APPLE_LICENSE_HEADER_END@
  23  */
  24 /*-
  25  * Copyright (c) 1985, 1993
  26  *      The Regents of the University of California.  All rights reserved.
  27  *
  28  * Redistribution and use in source and binary forms, with or without
  29  * modification, are permitted provided that the following conditions
  30  * are met:
  31  * 1. Redistributions of source code must retain the above copyright
  32  *    notice, this list of conditions and the following disclaimer.
  33  * 2. Redistributions in binary form must reproduce the above copyright
  34  *    notice, this list of conditions and the following disclaimer in the
  35  *    documentation and/or other materials provided with the distribution.
  36  * 3. All advertising materials mentioning features or use of this software
  37  *    must display the following acknowledgement:
  38  *      This product includes software developed by the University of
  39  *      California, Berkeley and its contributors.
  40  * 4. Neither the name of the University nor the names of its contributors
  41  *    may be used to endorse or promote products derived from this software
  42  *    without specific prior written permission.
  43  *
  44  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  45  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  46  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  47  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  48  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  49  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  50  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  51  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  52  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  53  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  54  * SUCH DAMAGE.
  55  */
  56
  57 #ifndef lint
  58 static char sccsid[] = "@(#)cksum.c     8.1 (Berkeley) 6/6/93";
  59 #endif /* not lint */
  60
  61 #ifdef sgi
  62 #ident "$Revision: 1.1.1.1 $"
  63 #endif
  64
  65 #include <sys/types.h>
  66
  67 /*
  68  *                      I N _ C K S U M
  69  *
  70  * Checksum routine for Internet Protocol family headers (C Version)
  71  *
  72  * There is no profit in a specialized version of the checksum
  73  * function for any machine where int's are 32 bits and shorts are 16.
  74  *
  75  * All timed packets are smaller than 32K shorts, so there is no need to
  76  * worry about carries except at the end.
  77  */
  78 int
  79 in_cksum(addr, len)
  80         u_short *addr;
  81         int len;
  82 {
  83         register int nleft = len;
  84         register u_short *w = addr;
  85         register u_short answer;
  86         register int sum = 0;
  87
  88         /*
  89          *  Our algorithm is simple, using a 32 bit accumulator (sum),
  90          *  we add sequential 16 bit words to it, and at the end, fold
  91          *  back all the carry bits from the top 16 bits into the lower
  92          *  16 bits.
  93          */
  94         while( nleft > 1 )  {
  95                 sum += *w++;
  96                 nleft -= 2;
  97         }
  98
  99         /* mop up an odd byte, if necessary */
 100         if( nleft == 1 )
 101                 sum += (*(u_char *)w) << 8;
 102
 103         /*
 104          * add back carry outs from top 16 bits to low 16 bits
 105          */
 106         sum = (sum >> 16) + (sum & 0xffff);     /* add hi 16 to low 16 */
 107         sum += (sum >> 16);                     /* add carry */
 108         answer = ~sum;                          /* truncate to 16 bits */
 109         return (answer);
 110 }