in4_cksum.c

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    1 /*      $NetBSD: in4_cksum.c,v 1.17 2008/02/12 13:05:55 joerg 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 1.17 2008/02/12 13:05:55 joerg 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 
   47 int
   48 in4_cksum(struct mbuf *m, u_int8_t nxt, int off, int len)
   49 {
   50         uint32_t sum;
   51         uint16_t *w;
   52 
   53         if (__predict_false(off < sizeof(struct ip)))
   54                 panic("in4_cksum: offset too short for IP header");
   55         if (__predict_false(m->m_len < sizeof(struct ip)))
   56                 panic("in4_cksum: mbuf too short for IP header");
   57 
   58         if (nxt == 0)
   59                 return cpu_in_cksum(m, len, off, 0);
   60 
   61         /*
   62          * Compute the equivalent of:
   63          * struct ipovly ip;
   64          *
   65          * bzero(sizeof(*ip));
   66          * ip.ih_pr = nxt;
   67          * ip.ip_len = htons(len);
   68          * ip.ih_src = mtod(m, struct ip *)->ip_src;
   69          * ip.ih_dst = mtod(m, struct ip *)->ip_dst;
   70          * sum = one_add(&ip);
   71          */
   72 
   73 #if BYTE_ORDER == LITTLE_ENDIAN
   74         sum = ((len & 0xffff) + nxt) << 8;
   75 #else
   76         sum = (len & 0xffff) + nxt;
   77 #endif
   78         w = (uint16_t *)(mtod(m, char  *) + offsetof(struct ip, ip_src));
   79         if (__predict_true((uintptr_t)w % 2 == 0)) {
   80                 sum += w[0];
   81                 sum += w[1];
   82                 sum += w[2];
   83                 sum += w[3];
   84         } else {
   85                 uint32_t partial;
   86                 w = (void *)((uintptr_t)w - 1);
   87 #if BYTE_ORDER == LITTLE_ENDIAN
   88                 partial = w[0] & 0xff00;
   89 #else
   90                 partial = w[0] & 0x00ff;
   91 #endif
   92                 partial += w[1];
   93                 partial += w[2];
   94                 partial += w[3];
   95 #if BYTE_ORDER == LITTLE_ENDIAN
   96                 partial += w[4] & 0x00ff;
   97 #else
   98                 partial += w[4] & 0xff00;
   99 #endif
  100                 sum += partial << 8;
  101         }
  102 
  103         return cpu_in_cksum(m, len, off, sum);
  104 }

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FreeBSD/Linux Kernel Cross Reference sys/netinet/in4_cksum.c

FreeBSD/Linux Kernel Cross Reference
sys/netinet/in4_cksum.c