The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/lib/libsa/in_cksum.c

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    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. All advertising materials mentioning features or use of this software
   20  *    must display the following acknowledgement:
   21  *      This product includes software developed by the University of
   22  *      California, Lawrence Berkeley Laboratory and its contributors.
   23  * 4. Neither the name of the University nor the names of its contributors
   24  *    may be used to endorse or promote products derived from this software
   25  *    without specific prior written permission.
   26  *
   27  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   28  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   29  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   30  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   31  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   32  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   33  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   34  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   35  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   36  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   37  * SUCH DAMAGE.
   38  *
   39  * @(#) Header: in_cksum.c,v 1.1 92/09/11 01:15:55 leres Exp  (LBL)
   40  */
   41 
   42 #include <sys/types.h>
   43 #include <sys/socket.h>
   44 
   45 #include <net/if.h>
   46 #include <net/if_ether.h>
   47 
   48 #include <netinet/in.h>
   49 #include <netinet/in_systm.h>
   50 #include <netinet/ip.h>
   51 #include <netinet/ip_var.h>
   52 #include <netinet/udp.h>
   53 #include <netinet/udp_var.h>
   54 
   55 #include <machine/endian.h>
   56 
   57 #include "stand.h"
   58 #include "net.h"
   59 
   60 /*
   61  * Checksum routine for Internet Protocol family headers.
   62  * This routine is very heavily used in the network
   63  * code and should be modified for each CPU to be as fast as possible.
   64  * In particular, it should not be this one.
   65  */
   66 int
   67 in_cksum(p, len)
   68         void *p;
   69         int len;
   70 {
   71         int sum = 0, oddbyte = 0, v = 0;
   72         u_char *cp = p;
   73 
   74         /* we assume < 2^16 bytes being summed */
   75         while (len > 0) {
   76                 if (oddbyte) {
   77                         sum += v + *cp++;
   78                         len--;
   79                 }
   80                 if (((long)cp & 1) == 0) {
   81                         while ((len -= 2) >= 0) {
   82                                 sum += *(u_short *)cp;
   83                                 cp += 2;
   84                         }
   85                 } else {
   86                         while ((len -= 2) >= 0) {
   87 #if BYTE_ORDER == BIG_ENDIAN
   88                                 sum += *cp++ << 8;
   89                                 sum += *cp++;
   90 #else
   91                                 sum += *cp++;
   92                                 sum += *cp++ << 8;
   93 #endif
   94                         }
   95                 }
   96                 if ((oddbyte = len & 1) != 0)
   97 #if BYTE_ORDER == BIG_ENDIAN
   98                         v = *cp << 8;
   99 #else
  100                         v = *cp;
  101 #endif
  102         }
  103         if (oddbyte)
  104                 sum += v;
  105         sum = (sum >> 16) + (sum & 0xffff); /* add in accumulated carries */
  106         sum += sum >> 16;               /* add potential last carry */
  107         return (0xffff & ~sum);
  108 }

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