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  * Copyright (c) 1999-2003 Apple Computer, Inc.  All Rights Reserved.
   7  *
   8  * This file contains Original Code and/or Modifications of Original Code
   9  * as defined in and that are subject to the Apple Public Source License
  10  * Version 2.0 (the 'License'). You may not use this file except in
  11  * compliance with the License. Please obtain a copy of the License at
  12  * http://www.opensource.apple.com/apsl/ and read it before using this
  13  * file.
  14  *
  15  * The Original Code and all software distributed under the License are
  16  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  17  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  18  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  19  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  20  * Please see the License for the specific language governing rights and
  21  * limitations under the License.
  22  *
  23  * @APPLE_LICENSE_HEADER_END@
  24  */
  25 /*-
  26  * Copyright (c) 1985, 1993
  27  *      The Regents of the University of California.  All rights reserved.
  28  *
  29  * Redistribution and use in source and binary forms, with or without
  30  * modification, are permitted provided that the following conditions
  31  * are met:
  32  * 1. Redistributions of source code must retain the above copyright
  33  *    notice, this list of conditions and the following disclaimer.
  34  * 2. Redistributions in binary form must reproduce the above copyright
  35  *    notice, this list of conditions and the following disclaimer in the
  36  *    documentation and/or other materials provided with the distribution.
  37  * 3. All advertising materials mentioning features or use of this software
  38  *    must display the following acknowledgement:
  39  *      This product includes software developed by the University of
  40  *      California, Berkeley and its contributors.
  41  * 4. Neither the name of the University nor the names of its contributors
  42  *    may be used to endorse or promote products derived from this software
  43  *    without specific prior written permission.
  44  *
  45  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  46  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  47  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  48  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  49  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  50  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  51  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  52  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  53  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  54  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  55  * SUCH DAMAGE.
  56  */
  57
  58 #ifndef lint
  59 static char sccsid[] = "@(#)cksum.c     8.1 (Berkeley) 6/6/93";
  60 #endif /* not lint */
  61
  62 #ifdef sgi
  63 #ident "$Revision: 1.1.1.1 $"
  64 #endif
  65
  66 #include <sys/types.h>
  67
  68 /*
  69  *                      I N _ C K S U M
  70  *
  71  * Checksum routine for Internet Protocol family headers (C Version)
  72  *
  73  * There is no profit in a specialized version of the checksum
  74  * function for any machine where int's are 32 bits and shorts are 16.
  75  *
  76  * All timed packets are smaller than 32K shorts, so there is no need to
  77  * worry about carries except at the end.
  78  */
  79 int
  80 in_cksum(addr, len)
  81         u_short *addr;
  82         int len;
  83 {
  84         register int nleft = len;
  85         register u_short *w = addr;
  86         register u_short answer;
  87         register int sum = 0;
  88
  89         /*
  90          *  Our algorithm is simple, using a 32 bit accumulator (sum),
  91          *  we add sequential 16 bit words to it, and at the end, fold
  92          *  back all the carry bits from the top 16 bits into the lower
  93          *  16 bits.
  94          */
  95         while( nleft > 1 )  {
  96                 sum += *w++;
  97                 nleft -= 2;
  98         }
  99
 100         /* mop up an odd byte, if necessary */
 101         if( nleft == 1 )
 102                 sum += (*(u_char *)w) << 8;
 103
 104         /*
 105          * add back carry outs from top 16 bits to low 16 bits
 106          */
 107         sum = (sum >> 16) + (sum & 0xffff);     /* add hi 16 to low 16 */
 108         sum += (sum >> 16);                     /* add carry */
 109         answer = ~sum;                          /* truncate to 16 bits */
 110         return (answer);
 111 }