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  * SPDX-License-Identifier: BSD-3-Clause
    3  *
    4  * Copyright (c) 1988, 1992, 1993
    5  *      The Regents of the University of California.  All rights reserved.
    6  *
    7  * Redistribution and use in source and binary forms, with or without
    8  * modification, are permitted provided that the following conditions
    9  * are met:
   10  * 1. Redistributions of source code must retain the above copyright
   11  *    notice, this list of conditions and the following disclaimer.
   12  * 2. Redistributions in binary form must reproduce the above copyright
   13  *    notice, this list of conditions and the following disclaimer in the
   14  *    documentation and/or other materials provided with the distribution.
   15  * 3. Neither the name of the University nor the names of its contributors
   16  *    may be used to endorse or promote products derived from this software
   17  *    without specific prior written permission.
   18  *
   19  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   21  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   22  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   23  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   24  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   25  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   26  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   27  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   29  * SUCH DAMAGE.
   30  *
   31  *      @(#)in_cksum.c  8.1 (Berkeley) 6/10/93
   32  */
   33 
   34 #include <sys/cdefs.h>
   35 __FBSDID("$FreeBSD: releng/12.0/sys/netinet/in_cksum.c 326023 2017-11-20 19:43:44Z pfg $");
   36 
   37 #include <sys/param.h>
   38 #include <sys/mbuf.h>
   39 
   40 /*
   41  * Checksum routine for Internet Protocol family headers (Portable Version).
   42  *
   43  * This routine is very heavily used in the network
   44  * code and should be modified for each CPU to be as fast as possible.
   45  */
   46 
   47 #define ADDCARRY(x)  (x > 65535 ? x -= 65535 : x)
   48 #define REDUCE {l_util.l = sum; sum = l_util.s[0] + l_util.s[1]; ADDCARRY(sum);}
   49 
   50 int
   51 in_cksum(struct mbuf *m, int len)
   52 {
   53         u_short *w;
   54         int sum = 0;
   55         int mlen = 0;
   56         int byte_swapped = 0;
   57 
   58         union {
   59                 char    c[2];
   60                 u_short s;
   61         } s_util;
   62         union {
   63                 u_short s[2];
   64                 long    l;
   65         } l_util;
   66 
   67         for (;m && len; m = m->m_next) {
   68                 if (m->m_len == 0)
   69                         continue;
   70                 w = mtod(m, u_short *);
   71                 if (mlen == -1) {
   72                         /*
   73                          * The first byte of this mbuf is the continuation
   74                          * of a word spanning between this mbuf and the
   75                          * last mbuf.
   76                          *
   77                          * s_util.c[0] is already saved when scanning previous
   78                          * mbuf.
   79                          */
   80                         s_util.c[1] = *(char *)w;
   81                         sum += s_util.s;
   82                         w = (u_short *)((char *)w + 1);
   83                         mlen = m->m_len - 1;
   84                         len--;
   85                 } else
   86                         mlen = m->m_len;
   87                 if (len < mlen)
   88                         mlen = len;
   89                 len -= mlen;
   90                 /*
   91                  * Force to even boundary.
   92                  */
   93                 if ((1 & (uintptr_t) w) && (mlen > 0)) {
   94                         REDUCE;
   95                         sum <<= 8;
   96                         s_util.c[0] = *(u_char *)w;
   97                         w = (u_short *)((char *)w + 1);
   98                         mlen--;
   99                         byte_swapped = 1;
  100                 }
  101                 /*
  102                  * Unroll the loop to make overhead from
  103                  * branches &c small.
  104                  */
  105                 while ((mlen -= 32) >= 0) {
  106                         sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
  107                         sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7];
  108                         sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11];
  109                         sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15];
  110                         w += 16;
  111                 }
  112                 mlen += 32;
  113                 while ((mlen -= 8) >= 0) {
  114                         sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
  115                         w += 4;
  116                 }
  117                 mlen += 8;
  118                 if (mlen == 0 && byte_swapped == 0)
  119                         continue;
  120                 REDUCE;
  121                 while ((mlen -= 2) >= 0) {
  122                         sum += *w++;
  123                 }
  124                 if (byte_swapped) {
  125                         REDUCE;
  126                         sum <<= 8;
  127                         byte_swapped = 0;
  128                         if (mlen == -1) {
  129                                 s_util.c[1] = *(char *)w;
  130                                 sum += s_util.s;
  131                                 mlen = 0;
  132                         } else
  133                                 mlen = -1;
  134                 } else if (mlen == -1)
  135                         s_util.c[0] = *(char *)w;
  136         }
  137         if (len)
  138                 printf("cksum: out of data\n");
  139         if (mlen == -1) {
  140                 /* The last mbuf has odd # of bytes. Follow the
  141                    standard (the odd byte may be shifted left by 8 bits
  142                    or not as determined by endian-ness of the machine) */
  143                 s_util.c[1] = 0;
  144                 sum += s_util.s;
  145         }
  146         REDUCE;
  147         return (~sum & 0xffff);
  148 }

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