[apple/xnu.git] / bsd / netinet6 / in6_cksum.c

/*	$FreeBSD: src/sys/netinet6/in6_cksum.c,v 1.1.2.3 2001/07/03 11:01:52 ume Exp $	*/
/*	$KAME: in6_cksum.c,v 1.10 2000/12/03 00:53:59 itojun Exp $	*/

/*
 * Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the project nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * Copyright (c) 1988, 1992, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *	@(#)in_cksum.c	8.1 (Berkeley) 6/10/93
 */

#include <sys/param.h>
#include <sys/mbuf.h>
#include <sys/systm.h>
#include <netinet/in.h>
#include <netinet/ip6.h>

#include <net/net_osdep.h>

/*
 * Checksum routine for Internet Protocol family headers (Portable Version).
 *
 * This routine is very heavily used in the network
 * code and should be modified for each CPU to be as fast as possible.
 */

#define ADDCARRY(x)  (x > 65535 ? x -= 65535 : x)
#define REDUCE {l_util.l = sum; sum = l_util.s[0] + l_util.s[1]; ADDCARRY(sum);}

/*
 * m MUST contain a continuous IP6 header.
 * off is a offset where TCP/UDP/ICMP6 header starts.
 * len is a total length of a transport segment.
 * (e.g. TCP header + TCP payload)
 */

int
in6_cksum(m, nxt, off, len)
	struct mbuf *m;
	u_int8_t nxt;
	u_int32_t off, len;
{
	u_int16_t *w;
	int sum = 0;
	int mlen = 0;
	int byte_swapped = 0;
#if 0
	int srcifid = 0, dstifid = 0;
#endif
	struct ip6_hdr *ip6;	
	union {
		u_int16_t phs[4];
		struct {
			u_int32_t	ph_len;
			u_int8_t	ph_zero[3];
			u_int8_t	ph_nxt;
		} ph __attribute__((__packed__));
	} uph;
	union {
		u_int8_t	c[2];
		u_int16_t	s;
	} s_util;
	union {
		u_int16_t s[2];
		u_int32_t l;
	} l_util;

	/* sanity check */
	if (m->m_pkthdr.len < off + len) {
		panic("in6_cksum: mbuf len (%d) < off+len (%d+%d)\n",
			m->m_pkthdr.len, off, len);
	}

	bzero(&uph, sizeof(uph));

	/*
	 * First create IP6 pseudo header and calculate a summary.
	 */
	ip6 = mtod(m, struct ip6_hdr *);
#if 0
	if (IN6_IS_SCOPE_LINKLOCAL(&ip6->ip6_src)) {
		srcifid = ip6->ip6_src.s6_addr16[1];
		ip6->ip6_src.s6_addr16[1] = 0;
	}
	if (IN6_IS_SCOPE_LINKLOCAL(&ip6->ip6_dst)) {
		dstifid = ip6->ip6_dst.s6_addr16[1];
		ip6->ip6_dst.s6_addr16[1] = 0;
	}
#endif
	w = (u_int16_t *)&ip6->ip6_src;
	uph.ph.ph_len = htonl(len);
	uph.ph.ph_nxt = nxt;

	/* IPv6 source address */
	sum += w[0];
	if (!IN6_IS_SCOPE_LINKLOCAL(&ip6->ip6_src))
		sum += w[1];
	sum += w[2]; sum += w[3]; sum += w[4]; sum += w[5];
	sum += w[6]; sum += w[7];
	/* IPv6 destination address */
	sum += w[8];
	if (!IN6_IS_SCOPE_LINKLOCAL(&ip6->ip6_dst))
		sum += w[9];
	sum += w[10]; sum += w[11]; sum += w[12]; sum += w[13];
	sum += w[14]; sum += w[15];
	/* Payload length and upper layer identifier */
	sum += uph.phs[0];  sum += uph.phs[1];
	sum += uph.phs[2];  sum += uph.phs[3];

#if 0
	if (srcifid)
		ip6->ip6_src.s6_addr16[1] = srcifid;
	if (dstifid)
		ip6->ip6_dst.s6_addr16[1] = dstifid;
#endif
	/*
	 * Secondly calculate a summary of the first mbuf excluding offset.
	 */
	while (m != NULL && off > 0) {
		if (m->m_len <= off)
			off -= m->m_len;
		else
			break;
		m = m->m_next;
	}
	w = (u_int16_t *)(mtod(m, u_char *) + off);
	mlen = m->m_len - off;
	if (len < mlen)
		mlen = len;
	len -= mlen;
	/*
	 * Force to even boundary.
	 */
	if ((1 & (long) w) && (mlen > 0)) {
		REDUCE;
		sum <<= 8;
		s_util.c[0] = *(u_char *)w;
		w = (u_int16_t *)((char *)w + 1);
		mlen--;
		byte_swapped = 1;
	}
	/*
	 * Unroll the loop to make overhead from
	 * branches &c small.
	 */
	while ((mlen -= 32) >= 0) {
		sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
		sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7];
		sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11];
		sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15];
		w += 16;
	}
	mlen += 32;
	while ((mlen -= 8) >= 0) {
		sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
		w += 4;
	}
	mlen += 8;
	if (mlen == 0 && byte_swapped == 0)
		goto next;
	REDUCE;
	while ((mlen -= 2) >= 0) {
		sum += *w++;
	}
	if (byte_swapped) {
		REDUCE;
		sum <<= 8;
		byte_swapped = 0;
		if (mlen == -1) {
			s_util.c[1] = *(char *)w;
			sum += s_util.s;
			mlen = 0;
		} else
			mlen = -1;
	} else if (mlen == -1)
		s_util.c[0] = *(char *)w;
 next:
	m = m->m_next;

	/*
	 * Lastly calculate a summary of the rest of mbufs.
	 */
	
	for (;m && len; m = m->m_next) {
		if (m->m_len == 0)
			continue;
		w = mtod(m, u_int16_t *);
		if (mlen == -1) {
			/*
			 * The first byte of this mbuf is the continuation
			 * of a word spanning between this mbuf and the
			 * last mbuf.
			 *
			 * s_util.c[0] is already saved when scanning previous
			 * mbuf.
			 */
			s_util.c[1] = *(char *)w;
			sum += s_util.s;
			w = (u_int16_t *)((char *)w + 1);
			mlen = m->m_len - 1;
			len--;
		} else
			mlen = m->m_len;
		if (len < mlen)
			mlen = len;
		len -= mlen;
		/*
		 * Force to even boundary.
		 */
		if ((1 & (long) w) && (mlen > 0)) {
			REDUCE;
			sum <<= 8;
			s_util.c[0] = *(u_char *)w;
			w = (u_int16_t *)((char *)w + 1);
			mlen--;
			byte_swapped = 1;
		}
		/*
		 * Unroll the loop to make overhead from
		 * branches &c small.
		 */
		while ((mlen -= 32) >= 0) {
			sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
			sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7];
			sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11];
			sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15];
			w += 16;
		}
		mlen += 32;
		while ((mlen -= 8) >= 0) {
			sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
			w += 4;
		}
		mlen += 8;
		if (mlen == 0 && byte_swapped == 0)
			continue;
		REDUCE;
		while ((mlen -= 2) >= 0) {
			sum += *w++;
		}
		if (byte_swapped) {
			REDUCE;
			sum <<= 8;
			byte_swapped = 0;
			if (mlen == -1) {
				s_util.c[1] = *(char *)w;
				sum += s_util.s;
				mlen = 0;
			} else
				mlen = -1;
		} else if (mlen == -1)
			s_util.c[0] = *(char *)w;
	}
	if (len)
		panic("in6_cksum: out of data\n");
	if (mlen == -1) {
		/* The last mbuf has odd # of bytes. Follow the
		   standard (the odd byte may be shifted left by 8 bits
		   or not as determined by endian-ness of the machine) */
		s_util.c[1] = 0;
		sum += s_util.s;
	}
	REDUCE;
	return (~sum & 0xffff);
}
Commit	Line	Data
9bccf70c A	1	/* $FreeBSD: src/sys/netinet6/in6_cksum.c,v 1.1.2.3 2001/07/03 11:01:52 ume Exp $ */
9bccf70c A	2	/* $KAME: in6_cksum.c,v 1.10 2000/12/03 00:53:59 itojun Exp $ */
1c79356b A	3
	4	/*
	5	* Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project.
	6	* All rights reserved.
	7	*
	8	* Redistribution and use in source and binary forms, with or without
	9	* modification, are permitted provided that the following conditions
	10	* are met:
	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 the
	15	* documentation and/or other materials provided with the distribution.
	16	* 3. Neither the name of the project nor the names of its contributors
	17	* may be used to endorse or promote products derived from this software
	18	* without specific prior written permission.
	19	*
	20	* THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
	21	* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	22	* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	23	* ARE DISCLAIMED. IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
	24	* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	25	* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	26	* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	27	* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	28	* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	29	* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	30	* SUCH DAMAGE.
	31	*/
	32
	33	/*
	34	* Copyright (c) 1988, 1992, 1993
	35	* The Regents of the University of California. All rights reserved.
	36	*
	37	* Redistribution and use in source and binary forms, with or without
	38	* modification, are permitted provided that the following conditions
	39	* are met:
	40	* 1. Redistributions of source code must retain the above copyright
	41	* notice, this list of conditions and the following disclaimer.
	42	* 2. Redistributions in binary form must reproduce the above copyright
	43	* notice, this list of conditions and the following disclaimer in the
	44	* documentation and/or other materials provided with the distribution.
	45	* 3. All advertising materials mentioning features or use of this software
	46	* must display the following acknowledgement:
	47	* This product includes software developed by the University of
	48	* California, Berkeley and its contributors.
	49	* 4. Neither the name of the University nor the names of its contributors
	50	* may be used to endorse or promote products derived from this software
	51	* without specific prior written permission.
	52	*
	53	* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
	54	* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	55	* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	56	* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
	57	* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	58	* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	59	* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	60	* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	61	* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	62	* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	63	* SUCH DAMAGE.
	64	*
	65	* @(#)in_cksum.c 8.1 (Berkeley) 6/10/93
	66	*/
67
68	#include <sys/param.h>
69	#include <sys/mbuf.h>
70	#include <sys/systm.h>
71	#include <netinet/in.h>
72	#include <netinet/ip6.h>
73
74	#include <net/net_osdep.h>
75
76	/*
77	* Checksum routine for Internet Protocol family headers (Portable Version).
78	*
79	* This routine is very heavily used in the network
80	* code and should be modified for each CPU to be as fast as possible.
81	*/
82
83	#define ADDCARRY(x) (x > 65535 ? x -= 65535 : x)
84	#define REDUCE {l_util.l = sum; sum = l_util.s[0] + l_util.s[1]; ADDCARRY(sum);}
85
1c79356b A	86	/*
	87	* m MUST contain a continuous IP6 header.
	88	* off is a offset where TCP/UDP/ICMP6 header starts.
	89	* len is a total length of a transport segment.
	90	* (e.g. TCP header + TCP payload)
	91	*/
	92
	93	int
	94	in6_cksum(m, nxt, off, len)
9bccf70c	95	struct mbuf *m;
1c79356b A	96	u_int8_t nxt;
	97	u_int32_t off, len;
	98	{
9bccf70c A	99	u_int16_t *w;
	100	int sum = 0;
	101	int mlen = 0;
1c79356b A	102	int byte_swapped = 0;
	103	#if 0
	104	int srcifid = 0, dstifid = 0;
	105	#endif
	106	struct ip6_hdr *ip6;
9bccf70c A	107	union {
	108	u_int16_t phs[4];
	109	struct {
	110	u_int32_t ph_len;
	111	u_int8_t ph_zero[3];
	112	u_int8_t ph_nxt;
	113	} ph __attribute__((__packed__));
	114	} uph;
1c79356b A	115	union {
	116	u_int8_t c[2];
	117	u_int16_t s;
	118	} s_util;
	119	union {
	120	u_int16_t s[2];
	121	u_int32_t l;
	122	} l_util;
	123
	124	/* sanity check */
	125	if (m->m_pkthdr.len < off + len) {
	126	panic("in6_cksum: mbuf len (%d) < off+len (%d+%d)\n",
	127	m->m_pkthdr.len, off, len);
	128	}
	129
9bccf70c A	130	bzero(&uph, sizeof(uph));
9bccf70c A	131
1c79356b A	132	/*
	133	* First create IP6 pseudo header and calculate a summary.
	134	*/
	135	ip6 = mtod(m, struct ip6_hdr *);
	136	#if 0
	137	if (IN6_IS_SCOPE_LINKLOCAL(&ip6->ip6_src)) {
	138	srcifid = ip6->ip6_src.s6_addr16[1];
	139	ip6->ip6_src.s6_addr16[1] = 0;
	140	}
	141	if (IN6_IS_SCOPE_LINKLOCAL(&ip6->ip6_dst)) {
	142	dstifid = ip6->ip6_dst.s6_addr16[1];
	143	ip6->ip6_dst.s6_addr16[1] = 0;
	144	}
	145	#endif
	146	w = (u_int16_t *)&ip6->ip6_src;
	147	uph.ph.ph_len = htonl(len);
	148	uph.ph.ph_nxt = nxt;
	149
	150	/* IPv6 source address */
	151	sum += w[0];
	152	if (!IN6_IS_SCOPE_LINKLOCAL(&ip6->ip6_src))
	153	sum += w[1];
	154	sum += w[2]; sum += w[3]; sum += w[4]; sum += w[5];
	155	sum += w[6]; sum += w[7];
	156	/* IPv6 destination address */
	157	sum += w[8];
	158	if (!IN6_IS_SCOPE_LINKLOCAL(&ip6->ip6_dst))
	159	sum += w[9];
	160	sum += w[10]; sum += w[11]; sum += w[12]; sum += w[13];
	161	sum += w[14]; sum += w[15];
	162	/* Payload length and upper layer identifier */
	163	sum += uph.phs[0]; sum += uph.phs[1];
	164	sum += uph.phs[2]; sum += uph.phs[3];
	165
	166	#if 0
	167	if (srcifid)
	168	ip6->ip6_src.s6_addr16[1] = srcifid;
	169	if (dstifid)
	170	ip6->ip6_dst.s6_addr16[1] = dstifid;
	171	#endif
	172	/*
	173	* Secondly calculate a summary of the first mbuf excluding offset.
	174	*/
	175	while (m != NULL && off > 0) {
	176	if (m->m_len <= off)
	177	off -= m->m_len;
	178	else
	179	break;
	180	m = m->m_next;
	181	}
	182	w = (u_int16_t )(mtod(m, u_char ) + off);
	183	mlen = m->m_len - off;
	184	if (len < mlen)
	185	mlen = len;
	186	len -= mlen;
	187	/*
	188	* Force to even boundary.
	189	*/
	190	if ((1 & (long) w) && (mlen > 0)) {
	191	REDUCE;
	192	sum <<= 8;
	193	s_util.c[0] = (u_char )w;
	194	w = (u_int16_t )((char )w + 1);
	195	mlen--;
196	byte_swapped = 1;
197	}
198	/*
199	* Unroll the loop to make overhead from
200	* branches &c small.
201	*/
202	while ((mlen -= 32) >= 0) {
203	sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
204	sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7];
205	sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11];
206	sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15];
207	w += 16;
208	}
209	mlen += 32;
210	while ((mlen -= 8) >= 0) {
211	sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
212	w += 4;
213	}
214	mlen += 8;
215	if (mlen == 0 && byte_swapped == 0)
216	goto next;
217	REDUCE;
218	while ((mlen -= 2) >= 0) {
219	sum += *w++;
220	}
221	if (byte_swapped) {
222	REDUCE;
223	sum <<= 8;
224	byte_swapped = 0;
225	if (mlen == -1) {
226	s_util.c[1] = (char )w;
227	sum += s_util.s;
228	mlen = 0;
229	} else
230	mlen = -1;
231	} else if (mlen == -1)
232	s_util.c[0] = (char )w;
233	next:
234	m = m->m_next;
235
236	/*
237	* Lastly calculate a summary of the rest of mbufs.
238	*/
239
240	for (;m && len; m = m->m_next) {
241	if (m->m_len == 0)
242	continue;
243	w = mtod(m, u_int16_t *);
244	if (mlen == -1) {
245	/*
246	* The first byte of this mbuf is the continuation
247	* of a word spanning between this mbuf and the
248	* last mbuf.
249	*
250	* s_util.c[0] is already saved when scanning previous
251	* mbuf.
252	*/
253	s_util.c[1] = (char )w;
254	sum += s_util.s;
255	w = (u_int16_t )((char )w + 1);
256	mlen = m->m_len - 1;
257	len--;
258	} else
259	mlen = m->m_len;
260	if (len < mlen)
261	mlen = len;
262	len -= mlen;
263	/*
264	* Force to even boundary.
265	*/
266	if ((1 & (long) w) && (mlen > 0)) {
267	REDUCE;
268	sum <<= 8;
269	s_util.c[0] = (u_char )w;
270	w = (u_int16_t )((char )w + 1);
271	mlen--;
272	byte_swapped = 1;
273	}
274	/*
275	* Unroll the loop to make overhead from
276	* branches &c small.
277	*/
278	while ((mlen -= 32) >= 0) {
279	sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
280	sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7];
281	sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11];
282	sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15];
283	w += 16;
284	}
285	mlen += 32;
286	while ((mlen -= 8) >= 0) {
287	sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
288	w += 4;
289	}
290	mlen += 8;
291	if (mlen == 0 && byte_swapped == 0)
292	continue;
293	REDUCE;
294	while ((mlen -= 2) >= 0) {
295	sum += *w++;
296	}
297	if (byte_swapped) {
298	REDUCE;
299	sum <<= 8;
300	byte_swapped = 0;
301	if (mlen == -1) {
302	s_util.c[1] = (char )w;
303	sum += s_util.s;
304	mlen = 0;
305	} else
306	mlen = -1;
307	} else if (mlen == -1)
308	s_util.c[0] = (char )w;
309	}
310	if (len)
311	panic("in6_cksum: out of data\n");
312	if (mlen == -1) {
313	/* The last mbuf has odd # of bytes. Follow the
314	standard (the odd byte may be shifted left by 8 bits
315	or not as determined by endian-ness of the machine) */
316	s_util.c[1] = 0;
317	sum += s_util.s;
318	}
319	REDUCE;
320	return (~sum & 0xffff);
321	}