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/in4_cksum.c

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    1 /*      $NetBSD: in4_cksum.c,v 1.20 2014/11/30 18:15:41 christos Exp $  */
    2 
    3 /*-
    4  * Copyright (c) 2008 Joerg Sonnenberger <joerg@NetBSD.org>.
    5  * 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  *
   11  * 1. Redistributions of source code must retain the above copyright
   12  *    notice, this list of conditions and the following disclaimer.
   13  * 2. Redistributions in binary form must reproduce the above copyright
   14  *    notice, this list of conditions and the following disclaimer in
   15  *    the documentation and/or other materials provided with the
   16  *    distribution.
   17  *
   18  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   19  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   20  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   21  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
   22  * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   23  * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
   24  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   25  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
   26  * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
   27  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
   28  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   29  * SUCH DAMAGE.
   30  */
   31 
   32 #include <sys/cdefs.h>
   33 __KERNEL_RCSID(0, "$NetBSD: in4_cksum.c,v 1.20 2014/11/30 18:15:41 christos Exp $");
   34 
   35 #include <sys/param.h>
   36 #include <sys/mbuf.h>
   37 #include <netinet/in.h>
   38 #include <netinet/in_systm.h>
   39 #include <netinet/ip.h>
   40 
   41 /*
   42  * Checksum of the IPv4 pseudo header.
   43  *
   44  * off is supposed to be the skipped IPv4 header, len is the payload size.
   45  */
   46 #ifdef DIAGNOSTIC
   47 #define PANIC(a,...)    panic(a, __VA_ARGS__)
   48 #else
   49 #define PANIC(a,...)    do { \
   50         printf(a, __VA_ARGS__); \
   51         return -1; \
   52 } while (/*CONSTCOND*/0)
   53 #endif
   54 
   55 int
   56 in4_cksum(struct mbuf *m, u_int8_t nxt, int off, int len)
   57 {
   58         uint32_t sum;
   59         uint16_t *w;
   60 
   61         if (__predict_false(m->m_len < sizeof(struct ip)))
   62                 PANIC("%s: mbuf %d too short for IP header %zu", __func__,
   63                     m->m_len, sizeof(struct ip));
   64 
   65         if (nxt == 0)
   66                 return cpu_in_cksum(m, len, off, 0);
   67 
   68         if (__predict_false(off < sizeof(struct ip)))
   69                 PANIC("%s: offset %d too short for IP header %zu", __func__,
   70                     off, sizeof(struct ip));
   71 
   72         /*
   73          * Compute the equivalent of:
   74          * struct ipovly ip;
   75          *
   76          * bzero(sizeof(*ip));
   77          * ip.ih_pr = nxt;
   78          * ip.ip_len = htons(len);
   79          * ip.ih_src = mtod(m, struct ip *)->ip_src;
   80          * ip.ih_dst = mtod(m, struct ip *)->ip_dst;
   81          * sum = one_add(&ip);
   82          */
   83 
   84 #if BYTE_ORDER == LITTLE_ENDIAN
   85         sum = ((len & 0xffff) + nxt) << 8;
   86 #else
   87         sum = (len & 0xffff) + nxt;
   88 #endif
   89         w = (uint16_t *)(mtod(m, char  *) + offsetof(struct ip, ip_src));
   90         if (__predict_true((uintptr_t)w % 2 == 0)) {
   91                 sum += w[0];
   92                 sum += w[1];
   93                 sum += w[2];
   94                 sum += w[3];
   95         } else {
   96                 uint32_t partial;
   97                 w = (void *)((uintptr_t)w - 1);
   98 #if BYTE_ORDER == LITTLE_ENDIAN
   99                 partial = w[0] & 0xff00;
  100 #else
  101                 partial = w[0] & 0x00ff;
  102 #endif
  103                 partial += w[1];
  104                 partial += w[2];
  105                 partial += w[3];
  106 #if BYTE_ORDER == LITTLE_ENDIAN
  107                 partial += w[4] & 0x00ff;
  108 #else
  109                 partial += w[4] & 0xff00;
  110 #endif
  111                 sum += partial << 8;
  112         }
  113 
  114         return cpu_in_cksum(m, len, off, sum);
  115 }

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