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/netinet/in_cksum.c

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    1 /*-
    2  * Copyright (c) 1988, 1992, 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  * 4. Neither the name of the University nor the names of its contributors
   14  *    may be used to endorse or promote products derived from this software
   15  *    without specific prior written permission.
   16  *
   17  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   27  * SUCH DAMAGE.
   28  *
   29  *      @(#)in_cksum.c  8.1 (Berkeley) 6/10/93
   30  * $FreeBSD: releng/6.0/sys/netinet/in_cksum.c 139823 2005-01-07 01:45:51Z imp $
   31  */
   32 
   33 #include <sys/param.h>
   34 #include <sys/mbuf.h>
   35 
   36 /*
   37  * Checksum routine for Internet Protocol family headers (Portable Version).
   38  *
   39  * This routine is very heavily used in the network
   40  * code and should be modified for each CPU to be as fast as possible.
   41  */
   42 
   43 #define ADDCARRY(x)  (x > 65535 ? x -= 65535 : x)
   44 #define REDUCE {l_util.l = sum; sum = l_util.s[0] + l_util.s[1]; ADDCARRY(sum);}
   45 
   46 int
   47 in_cksum(m, len)
   48         register struct mbuf *m;
   49         register int len;
   50 {
   51         register u_short *w;
   52         register int sum = 0;
   53         register int mlen = 0;
   54         int byte_swapped = 0;
   55 
   56         union {
   57                 char    c[2];
   58                 u_short s;
   59         } s_util;
   60         union {
   61                 u_short s[2];
   62                 long    l;
   63         } l_util;
   64 
   65         for (;m && len; m = m->m_next) {
   66                 if (m->m_len == 0)
   67                         continue;
   68                 w = mtod(m, u_short *);
   69                 if (mlen == -1) {
   70                         /*
   71                          * The first byte of this mbuf is the continuation
   72                          * of a word spanning between this mbuf and the
   73                          * last mbuf.
   74                          *
   75                          * s_util.c[0] is already saved when scanning previous
   76                          * mbuf.
   77                          */
   78                         s_util.c[1] = *(char *)w;
   79                         sum += s_util.s;
   80                         w = (u_short *)((char *)w + 1);
   81                         mlen = m->m_len - 1;
   82                         len--;
   83                 } else
   84                         mlen = m->m_len;
   85                 if (len < mlen)
   86                         mlen = len;
   87                 len -= mlen;
   88                 /*
   89                  * Force to even boundary.
   90                  */
   91                 if ((1 & (int) w) && (mlen > 0)) {
   92                         REDUCE;
   93                         sum <<= 8;
   94                         s_util.c[0] = *(u_char *)w;
   95                         w = (u_short *)((char *)w + 1);
   96                         mlen--;
   97                         byte_swapped = 1;
   98                 }
   99                 /*
  100                  * Unroll the loop to make overhead from
  101                  * branches &c small.
  102                  */
  103                 while ((mlen -= 32) >= 0) {
  104                         sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
  105                         sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7];
  106                         sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11];
  107                         sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15];
  108                         w += 16;
  109                 }
  110                 mlen += 32;
  111                 while ((mlen -= 8) >= 0) {
  112                         sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
  113                         w += 4;
  114                 }
  115                 mlen += 8;
  116                 if (mlen == 0 && byte_swapped == 0)
  117                         continue;
  118                 REDUCE;
  119                 while ((mlen -= 2) >= 0) {
  120                         sum += *w++;
  121                 }
  122                 if (byte_swapped) {
  123                         REDUCE;
  124                         sum <<= 8;
  125                         byte_swapped = 0;
  126                         if (mlen == -1) {
  127                                 s_util.c[1] = *(char *)w;
  128                                 sum += s_util.s;
  129                                 mlen = 0;
  130                         } else
  131                                 mlen = -1;
  132                 } else if (mlen == -1)
  133                         s_util.c[0] = *(char *)w;
  134         }
  135         if (len)
  136                 printf("cksum: out of data\n");
  137         if (mlen == -1) {
  138                 /* The last mbuf has odd # of bytes. Follow the
  139                    standard (the odd byte may be shifted left by 8 bits
  140                    or not as determined by endian-ness of the machine) */
  141                 s_util.c[1] = 0;
  142                 sum += s_util.s;
  143         }
  144         REDUCE;
  145         return (~sum & 0xffff);
  146 }

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