sys/netinet/in4_cksum.c

   1 /*      $NetBSD: in4_cksum.c,v 1.16 2008/02/07 22:45:20 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 1.16 2008/02/07 22:45:20 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 }