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

/*	$KAME: in6_cksum.c,v 1.5 2000/02/22 14:04:17 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);}

static union {
	u_int16_t phs[4];
	struct {
		u_int32_t	ph_len;
		u_int8_t	ph_zero[3];
		u_int8_t	ph_nxt;
	} ph;
} uph;

/*
 * 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)
	register struct mbuf *m;
	u_int8_t nxt;
	u_int32_t off, len;
{
	register u_int16_t *w;
	register int sum = 0;
	register int mlen = 0;
	int byte_swapped = 0;
#if 0
	int srcifid = 0, dstifid = 0;
#endif
	struct ip6_hdr *ip6;	
	
	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);
	}

	/*
	 * 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
1c79356b A	1	/* $KAME: in6_cksum.c,v 1.5 2000/02/22 14:04:17 itojun Exp $ */
	2
	3	/*
	4	* Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project.
	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	* 1. Redistributions of source code must retain the above copyright
	11	* notice, this list of conditions and the following disclaimer.
	12	* 2. Redistributions in binary form must reproduce the above copyright
	13	* notice, this list of conditions and the following disclaimer in the
	14	* documentation and/or other materials provided with the distribution.
	15	* 3. Neither the name of the project nor the names of its contributors
	16	* may be used to endorse or promote products derived from this software
	17	* without specific prior written permission.
	18	*
	19	* THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
	20	* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	21	* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	22	* ARE DISCLAIMED. IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
	23	* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	24	* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	25	* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	26	* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	27	* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	28	* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	29	* SUCH DAMAGE.
	30	*/
	31
	32	/*
	33	* Copyright (c) 1988, 1992, 1993
	34	* The Regents of the University of California. All rights reserved.
	35	*
	36	* Redistribution and use in source and binary forms, with or without
	37	* modification, are permitted provided that the following conditions
	38	* are met:
	39	* 1. Redistributions of source code must retain the above copyright
	40	* notice, this list of conditions and the following disclaimer.
	41	* 2. Redistributions in binary form must reproduce the above copyright
	42	* notice, this list of conditions and the following disclaimer in the
	43	* documentation and/or other materials provided with the distribution.
	44	* 3. All advertising materials mentioning features or use of this software
	45	* must display the following acknowledgement:
	46	* This product includes software developed by the University of
	47	* California, Berkeley and its contributors.
	48	* 4. Neither the name of the University nor the names of its contributors
	49	* may be used to endorse or promote products derived from this software
	50	* without specific prior written permission.
	51	*
	52	* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
	53	* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	54	* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	55	* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
	56	* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	57	* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	58	* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	59	* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	60	* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	61	* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	62	* SUCH DAMAGE.
	63	*
	64	* @(#)in_cksum.c 8.1 (Berkeley) 6/10/93
65	*/
66
67	#include <sys/param.h>
68	#include <sys/mbuf.h>
69	#include <sys/systm.h>
70	#include <netinet/in.h>
71	#include <netinet/ip6.h>
72
73	#include <net/net_osdep.h>
74
75	/*
76	* Checksum routine for Internet Protocol family headers (Portable Version).
77	*
78	* This routine is very heavily used in the network
79	* code and should be modified for each CPU to be as fast as possible.
80	*/
81
82	#define ADDCARRY(x) (x > 65535 ? x -= 65535 : x)
83	#define REDUCE {l_util.l = sum; sum = l_util.s[0] + l_util.s[1]; ADDCARRY(sum);}
84
85	static union {
86	u_int16_t phs[4];
87	struct {
88	u_int32_t ph_len;
89	u_int8_t ph_zero[3];
90	u_int8_t ph_nxt;
91	} ph;
92	} uph;
93
94	/*
95	* m MUST contain a continuous IP6 header.
96	* off is a offset where TCP/UDP/ICMP6 header starts.
97	* len is a total length of a transport segment.
98	* (e.g. TCP header + TCP payload)
99	*/
100
101	int
102	in6_cksum(m, nxt, off, len)
103	register struct mbuf *m;
104	u_int8_t nxt;
105	u_int32_t off, len;
106	{
107	register u_int16_t *w;
108	register int sum = 0;
109	register int mlen = 0;
110	int byte_swapped = 0;
111	#if 0
112	int srcifid = 0, dstifid = 0;
113	#endif
114	struct ip6_hdr *ip6;
115
116	union {
117	u_int8_t c[2];
118	u_int16_t s;
119	} s_util;
120	union {
121	u_int16_t s[2];
122	u_int32_t l;
123	} l_util;
124
125	/* sanity check */
126	if (m->m_pkthdr.len < off + len) {
127	panic("in6_cksum: mbuf len (%d) < off+len (%d+%d)\n",
128	m->m_pkthdr.len, off, len);
129	}
130
131	/*
132	* First create IP6 pseudo header and calculate a summary.
133	*/
134	ip6 = mtod(m, struct ip6_hdr *);
135	#if 0
136	if (IN6_IS_SCOPE_LINKLOCAL(&ip6->ip6_src)) {
137	srcifid = ip6->ip6_src.s6_addr16[1];
138	ip6->ip6_src.s6_addr16[1] = 0;
139	}
140	if (IN6_IS_SCOPE_LINKLOCAL(&ip6->ip6_dst)) {
141	dstifid = ip6->ip6_dst.s6_addr16[1];
142	ip6->ip6_dst.s6_addr16[1] = 0;
143	}
144	#endif
145	w = (u_int16_t *)&ip6->ip6_src;
146	uph.ph.ph_len = htonl(len);
147	uph.ph.ph_nxt = nxt;
148
149	/* IPv6 source address */
150	sum += w[0];
151	if (!IN6_IS_SCOPE_LINKLOCAL(&ip6->ip6_src))
152	sum += w[1];
153	sum += w[2]; sum += w[3]; sum += w[4]; sum += w[5];
154	sum += w[6]; sum += w[7];
155	/* IPv6 destination address */
156	sum += w[8];
157	if (!IN6_IS_SCOPE_LINKLOCAL(&ip6->ip6_dst))
158	sum += w[9];
159	sum += w[10]; sum += w[11]; sum += w[12]; sum += w[13];
160	sum += w[14]; sum += w[15];
161	/* Payload length and upper layer identifier */
162	sum += uph.phs[0]; sum += uph.phs[1];
163	sum += uph.phs[2]; sum += uph.phs[3];
164
165	#if 0
166	if (srcifid)
167	ip6->ip6_src.s6_addr16[1] = srcifid;
168	if (dstifid)
169	ip6->ip6_dst.s6_addr16[1] = dstifid;
170	#endif
171	/*
172	* Secondly calculate a summary of the first mbuf excluding offset.
173	*/
174	while (m != NULL && off > 0) {
175	if (m->m_len <= off)
176	off -= m->m_len;
177	else
178	break;
179	m = m->m_next;
180	}
181	w = (u_int16_t )(mtod(m, u_char ) + off);
182	mlen = m->m_len - off;
183	if (len < mlen)
184	mlen = len;
185	len -= mlen;
186	/*
187	* Force to even boundary.
188	*/
189	if ((1 & (long) w) && (mlen > 0)) {
190	REDUCE;
191	sum <<= 8;
192	s_util.c[0] = (u_char )w;
193	w = (u_int16_t )((char )w + 1);
194	mlen--;
195	byte_swapped = 1;
196	}
197	/*
198	* Unroll the loop to make overhead from
199	* branches &c small.
200	*/
201	while ((mlen -= 32) >= 0) {
202	sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
203	sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7];
204	sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11];
205	sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15];
206	w += 16;
207	}
208	mlen += 32;
209	while ((mlen -= 8) >= 0) {
210	sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
211	w += 4;
212	}
213	mlen += 8;
214	if (mlen == 0 && byte_swapped == 0)
215	goto next;
216	REDUCE;
217	while ((mlen -= 2) >= 0) {
218	sum += *w++;
219	}
220	if (byte_swapped) {
221	REDUCE;
222	sum <<= 8;
223	byte_swapped = 0;
224	if (mlen == -1) {
225	s_util.c[1] = (char )w;
226	sum += s_util.s;
227	mlen = 0;
228	} else
229	mlen = -1;
230	} else if (mlen == -1)
231	s_util.c[0] = (char )w;
232	next:
233	m = m->m_next;
234
235	/*
236	* Lastly calculate a summary of the rest of mbufs.
237	*/
238
239	for (;m && len; m = m->m_next) {
240	if (m->m_len == 0)
241	continue;
242	w = mtod(m, u_int16_t *);
243	if (mlen == -1) {
244	/*
245	* The first byte of this mbuf is the continuation
246	* of a word spanning between this mbuf and the
247	* last mbuf.
248	*
249	* s_util.c[0] is already saved when scanning previous
250	* mbuf.
251	*/
252	s_util.c[1] = (char )w;
253	sum += s_util.s;
254	w = (u_int16_t )((char )w + 1);
255	mlen = m->m_len - 1;
256	len--;
257	} else
258	mlen = m->m_len;
259	if (len < mlen)
260	mlen = len;
261	len -= mlen;
262	/*
263	* Force to even boundary.
264	*/
265	if ((1 & (long) w) && (mlen > 0)) {
266	REDUCE;
267	sum <<= 8;
268	s_util.c[0] = (u_char )w;
269	w = (u_int16_t )((char )w + 1);
270	mlen--;
271	byte_swapped = 1;
272	}
273	/*
274	* Unroll the loop to make overhead from
275	* branches &c small.
276	*/
277	while ((mlen -= 32) >= 0) {
278	sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
279	sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7];
280	sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11];
281	sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15];
282	w += 16;
283	}
284	mlen += 32;
285	while ((mlen -= 8) >= 0) {
286	sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
287	w += 4;
288	}
289	mlen += 8;
290	if (mlen == 0 && byte_swapped == 0)
291	continue;
292	REDUCE;
293	while ((mlen -= 2) >= 0) {
294	sum += *w++;
295	}
296	if (byte_swapped) {
297	REDUCE;
298	sum <<= 8;
299	byte_swapped = 0;
300	if (mlen == -1) {
301	s_util.c[1] = (char )w;
302	sum += s_util.s;
303	mlen = 0;
304	} else
305	mlen = -1;
306	} else if (mlen == -1)
307	s_util.c[0] = (char )w;
308	}
309	if (len)
310	panic("in6_cksum: out of data\n");
311	if (mlen == -1) {
312	/* The last mbuf has odd # of bytes. Follow the
313	standard (the odd byte may be shifted left by 8 bits
314	or not as determined by endian-ness of the machine) */
315	s_util.c[1] = 0;
316	sum += s_util.s;
317	}
318	REDUCE;
319	return (~sum & 0xffff);
320	}