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in4_cksum.c revision 1.16 
      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 (at) 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 (off < sizeof(struct ip))
     54 		panic("in4_cksum: offset too short for IP header");
     55 	if (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 }
    105