Line data Source code
1 : /* $OpenBSD: slcompress.c,v 1.12 2015/12/03 14:34:48 blambert Exp $ */
2 : /* $NetBSD: slcompress.c,v 1.17 1997/05/17 21:12:10 christos Exp $ */
3 :
4 : /*
5 : * Copyright (c) 1989, 1993, 1994
6 : * The Regents of the University of California. 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 University 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 REGENTS 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 REGENTS 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 : * @(#)slcompress.c 8.2 (Berkeley) 4/16/94
33 : */
34 :
35 : /*
36 : * Routines to compress and uncompess tcp packets (for transmission
37 : * over low speed serial lines.
38 : *
39 : * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
40 : * - Initial distribution.
41 : */
42 :
43 : #include <sys/param.h>
44 : #include <sys/mbuf.h>
45 : #include <sys/systm.h>
46 :
47 : #include <netinet/in.h>
48 : #include <netinet/ip.h>
49 : #include <netinet/tcp.h>
50 :
51 : #include <net/slcompress.h>
52 :
53 : #ifndef SL_NO_STATS
54 : #define INCR(counter) ++comp->counter;
55 : #else
56 : #define INCR(counter)
57 : #endif
58 :
59 : #define BCMP(p1, p2, n) bcmp((char *)(p1), (char *)(p2), (int)(n))
60 : #define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (int)(n))
61 :
62 : void
63 0 : sl_compress_init(struct slcompress *comp)
64 : {
65 : u_int i;
66 0 : struct cstate *tstate = comp->tstate;
67 :
68 0 : bzero((char *)comp, sizeof(*comp));
69 0 : for (i = MAX_STATES - 1; i > 0; --i) {
70 0 : tstate[i].cs_id = i;
71 0 : tstate[i].cs_next = &tstate[i - 1];
72 : }
73 0 : tstate[0].cs_next = &tstate[MAX_STATES - 1];
74 0 : tstate[0].cs_id = 0;
75 0 : comp->last_cs = &tstate[0];
76 0 : comp->last_recv = 255;
77 0 : comp->last_xmit = 255;
78 0 : comp->flags = SLF_TOSS;
79 0 : }
80 :
81 :
82 : /*
83 : * Like sl_compress_init, but we get to specify the maximum connection
84 : * ID to use on transmission.
85 : */
86 : void
87 0 : sl_compress_setup(struct slcompress *comp, int max_state)
88 : {
89 : u_int i;
90 0 : struct cstate *tstate = comp->tstate;
91 :
92 0 : if (max_state == -1) {
93 : max_state = MAX_STATES - 1;
94 0 : bzero((char *)comp, sizeof(*comp));
95 0 : } else {
96 : /* Don't reset statistics */
97 0 : bzero((char *)comp->tstate, sizeof(comp->tstate));
98 0 : bzero((char *)comp->rstate, sizeof(comp->rstate));
99 : }
100 0 : for (i = max_state; i > 0; --i) {
101 0 : tstate[i].cs_id = i;
102 0 : tstate[i].cs_next = &tstate[i - 1];
103 : }
104 0 : tstate[0].cs_next = &tstate[max_state];
105 0 : tstate[0].cs_id = 0;
106 0 : comp->last_cs = &tstate[0];
107 0 : comp->last_recv = 255;
108 0 : comp->last_xmit = 255;
109 0 : comp->flags = SLF_TOSS;
110 0 : }
111 :
112 :
113 : /* ENCODE encodes a number that is known to be non-zero. ENCODEZ
114 : * checks for zero (since zero has to be encoded in the long, 3 byte
115 : * form).
116 : */
117 : #define ENCODE(n) { \
118 : if ((u_int16_t)(n) >= 256) { \
119 : *cp++ = 0; \
120 : cp[1] = (n); \
121 : cp[0] = (n) >> 8; \
122 : cp += 2; \
123 : } else { \
124 : *cp++ = (n); \
125 : } \
126 : }
127 : #define ENCODEZ(n) { \
128 : if ((u_int16_t)(n) >= 256 || (u_int16_t)(n) == 0) { \
129 : *cp++ = 0; \
130 : cp[1] = (n); \
131 : cp[0] = (n) >> 8; \
132 : cp += 2; \
133 : } else { \
134 : *cp++ = (n); \
135 : } \
136 : }
137 :
138 : #define DECODEL(f) { \
139 : if (*cp == 0) {\
140 : (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \
141 : cp += 3; \
142 : } else { \
143 : (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \
144 : } \
145 : }
146 :
147 : #define DECODES(f) { \
148 : if (*cp == 0) {\
149 : (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \
150 : cp += 3; \
151 : } else { \
152 : (f) = htons(ntohs(f) + (u_int32_t)*cp++); \
153 : } \
154 : }
155 :
156 : #define DECODEU(f) { \
157 : if (*cp == 0) {\
158 : (f) = htons((cp[1] << 8) | cp[2]); \
159 : cp += 3; \
160 : } else { \
161 : (f) = htons((u_int32_t)*cp++); \
162 : } \
163 : }
164 :
165 : u_int
166 0 : sl_compress_tcp(struct mbuf *m, struct ip *ip, struct slcompress *comp,
167 : int compress_cid)
168 : {
169 0 : struct cstate *cs = comp->last_cs->cs_next;
170 0 : u_int hlen = ip->ip_hl;
171 : struct tcphdr *oth;
172 : struct tcphdr *th;
173 : u_int deltaS, deltaA;
174 : u_int changes = 0;
175 0 : u_char new_seq[16];
176 0 : u_char *cp = new_seq;
177 :
178 : /*
179 : * Bail if this is an IP fragment or if the TCP packet isn't
180 : * `compressible' (i.e., ACK isn't set or some other control bit is
181 : * set). (We assume that the caller has already made sure the
182 : * packet is IP proto TCP).
183 : */
184 0 : if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40)
185 0 : return (TYPE_IP);
186 :
187 0 : th = (struct tcphdr *)&((int32_t *)ip)[hlen];
188 0 : if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK)
189 0 : return (TYPE_IP);
190 : /*
191 : * Packet is compressible -- we're going to send either a
192 : * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need
193 : * to locate (or create) the connection state. Special case the
194 : * most recently used connection since it's most likely to be used
195 : * again & we don't have to do any reordering if it's used.
196 : */
197 0 : INCR(sls_packets)
198 0 : if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr ||
199 0 : ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr ||
200 0 : *(int32_t *)th != ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) {
201 : /*
202 : * Wasn't the first -- search for it.
203 : *
204 : * States are kept in a circularly linked list with
205 : * last_cs pointing to the end of the list. The
206 : * list is kept in lru order by moving a state to the
207 : * head of the list whenever it is referenced. Since
208 : * the list is short and, empirically, the connection
209 : * we want is almost always near the front, we locate
210 : * states via linear search. If we don't find a state
211 : * for the datagram, the oldest state is (re-)used.
212 : */
213 : struct cstate *lcs;
214 0 : struct cstate *lastcs = comp->last_cs;
215 :
216 0 : do {
217 0 : lcs = cs; cs = cs->cs_next;
218 0 : INCR(sls_searches)
219 0 : if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr
220 0 : && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr
221 0 : && *(int32_t *)th ==
222 0 : ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl])
223 : goto found;
224 0 : } while (cs != lastcs);
225 :
226 : /*
227 : * Didn't find it -- re-use oldest cstate. Send an
228 : * uncompressed packet that tells the other side what
229 : * connection number we're using for this conversation.
230 : * Note that since the state list is circular, the oldest
231 : * state points to the newest and we only need to set
232 : * last_cs to update the lru linkage.
233 : */
234 0 : INCR(sls_misses)
235 0 : comp->last_cs = lcs;
236 0 : hlen += th->th_off;
237 0 : hlen <<= 2;
238 0 : goto uncompressed;
239 :
240 : found:
241 : /*
242 : * Found it -- move to the front on the connection list.
243 : */
244 0 : if (cs == lastcs)
245 0 : comp->last_cs = lcs;
246 : else {
247 0 : lcs->cs_next = cs->cs_next;
248 0 : cs->cs_next = lastcs->cs_next;
249 0 : lastcs->cs_next = cs;
250 : }
251 0 : }
252 :
253 : /*
254 : * Make sure that only what we expect to change changed. The first
255 : * line of the `if' checks the IP protocol version, header length &
256 : * type of service. The 2nd line checks the "Don't fragment" bit.
257 : * The 3rd line checks the time-to-live and protocol (the protocol
258 : * check is unnecessary but costless). The 4th line checks the TCP
259 : * header length. The 5th line checks IP options, if any. The 6th
260 : * line checks TCP options, if any. If any of these things are
261 : * different between the previous & current datagram, we send the
262 : * current datagram `uncompressed'.
263 : */
264 0 : oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen];
265 : deltaS = hlen;
266 0 : hlen += th->th_off;
267 0 : hlen <<= 2;
268 :
269 0 : if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] ||
270 0 : ((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] ||
271 0 : ((u_int16_t *)ip)[4] != ((u_int16_t *)&cs->cs_ip)[4] ||
272 0 : th->th_off != oth->th_off ||
273 0 : (deltaS > 5 &&
274 0 : BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) ||
275 0 : (th->th_off > 5 &&
276 0 : BCMP(th + 1, oth + 1, (th->th_off - 5) << 2)))
277 : goto uncompressed;
278 :
279 : /*
280 : * Figure out which of the changing fields changed. The
281 : * receiver expects changes in the order: urgent, window,
282 : * ack, seq (the order minimizes the number of temporaries
283 : * needed in this section of code).
284 : */
285 0 : if (th->th_flags & TH_URG) {
286 0 : deltaS = ntohs(th->th_urp);
287 0 : ENCODEZ(deltaS);
288 : changes |= NEW_U;
289 0 : } else if (th->th_urp != oth->th_urp)
290 : /* argh! URG not set but urp changed -- a sensible
291 : * implementation should never do this but RFC793
292 : * doesn't prohibit the change so we have to deal
293 : * with it. */
294 : goto uncompressed;
295 :
296 0 : deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win));
297 0 : if (deltaS) {
298 0 : ENCODE(deltaS);
299 0 : changes |= NEW_W;
300 0 : }
301 :
302 0 : deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack);
303 0 : if (deltaA) {
304 0 : if (deltaA > 0xffff)
305 : goto uncompressed;
306 0 : ENCODE(deltaA);
307 0 : changes |= NEW_A;
308 0 : }
309 :
310 0 : deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq);
311 0 : if (deltaS) {
312 0 : if (deltaS > 0xffff)
313 : goto uncompressed;
314 0 : ENCODE(deltaS);
315 0 : changes |= NEW_S;
316 0 : }
317 :
318 0 : switch(changes) {
319 :
320 : case 0:
321 : /*
322 : * Nothing changed. If this packet contains data and the
323 : * last one didn't, this is probably a data packet following
324 : * an ack (normal on an interactive connection) and we send
325 : * it compressed. Otherwise it's probably a retransmit,
326 : * retransmitted ack or window probe. Send it uncompressed
327 : * in case the other side missed the compressed version.
328 : */
329 0 : if (ip->ip_len != cs->cs_ip.ip_len &&
330 0 : ntohs(cs->cs_ip.ip_len) == hlen)
331 : break;
332 :
333 : /* FALLTHROUGH */
334 :
335 : case SPECIAL_I:
336 : case SPECIAL_D:
337 : /*
338 : * actual changes match one of our special case encodings --
339 : * send packet uncompressed.
340 : */
341 : goto uncompressed;
342 :
343 : case NEW_S|NEW_A:
344 0 : if (deltaS == deltaA &&
345 0 : deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
346 : /* special case for echoed terminal traffic */
347 : changes = SPECIAL_I;
348 : cp = new_seq;
349 0 : }
350 : break;
351 :
352 : case NEW_S:
353 0 : if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
354 : /* special case for data xfer */
355 : changes = SPECIAL_D;
356 : cp = new_seq;
357 0 : }
358 : break;
359 : }
360 :
361 0 : deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id);
362 0 : if (deltaS != 1) {
363 0 : ENCODEZ(deltaS);
364 0 : changes |= NEW_I;
365 0 : }
366 0 : if (th->th_flags & TH_PUSH)
367 0 : changes |= TCP_PUSH_BIT;
368 : /*
369 : * Grab the cksum before we overwrite it below. Then update our
370 : * state with this packet's header.
371 : */
372 0 : deltaA = ntohs(th->th_sum);
373 0 : BCOPY(ip, &cs->cs_ip, hlen);
374 :
375 : /*
376 : * We want to use the original packet as our compressed packet.
377 : * (cp - new_seq) is the number of bytes we need for compressed
378 : * sequence numbers. In addition we need one byte for the change
379 : * mask, one for the connection id and two for the tcp checksum.
380 : * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how
381 : * many bytes of the original packet to toss so subtract the two to
382 : * get the new packet size.
383 : */
384 0 : deltaS = cp - new_seq;
385 : cp = (u_char *)ip;
386 0 : if (compress_cid == 0 || comp->last_xmit != cs->cs_id) {
387 0 : comp->last_xmit = cs->cs_id;
388 0 : hlen -= deltaS + 4;
389 0 : cp += hlen;
390 0 : *cp++ = changes | NEW_C;
391 0 : *cp++ = cs->cs_id;
392 0 : } else {
393 0 : hlen -= deltaS + 3;
394 0 : cp += hlen;
395 0 : *cp++ = changes;
396 : }
397 0 : m->m_len -= hlen;
398 0 : m->m_data += hlen;
399 0 : *cp++ = deltaA >> 8;
400 0 : *cp++ = deltaA;
401 0 : BCOPY(new_seq, cp, deltaS);
402 0 : INCR(sls_compressed)
403 0 : return (TYPE_COMPRESSED_TCP);
404 :
405 : /*
406 : * Update connection state cs & send uncompressed packet ('uncompressed'
407 : * means a regular ip/tcp packet but with the 'conversation id' we hope
408 : * to use on future compressed packets in the protocol field).
409 : */
410 : uncompressed:
411 0 : BCOPY(ip, &cs->cs_ip, hlen);
412 0 : ip->ip_p = cs->cs_id;
413 0 : comp->last_xmit = cs->cs_id;
414 0 : return (TYPE_UNCOMPRESSED_TCP);
415 0 : }
416 :
417 :
418 : int
419 0 : sl_uncompress_tcp(u_char **bufp, int len, u_int type, struct slcompress *comp)
420 : {
421 0 : u_char *hdr, *cp;
422 0 : int hlen, vjlen;
423 :
424 0 : cp = bufp? *bufp: NULL;
425 0 : vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen);
426 0 : if (vjlen < 0)
427 0 : return (0); /* error */
428 0 : if (vjlen == 0)
429 0 : return (len); /* was uncompressed already */
430 :
431 0 : cp += vjlen;
432 0 : len -= vjlen;
433 :
434 : /*
435 : * At this point, cp points to the first byte of data in the
436 : * packet. If we're not aligned on a 4-byte boundary, copy the
437 : * data down so the ip & tcp headers will be aligned. Then back up
438 : * cp by the tcp/ip header length to make room for the reconstructed
439 : * header (we assume the packet we were handed has enough space to
440 : * prepend 128 bytes of header).
441 : */
442 0 : if ((long)cp & 3) {
443 0 : if (len > 0)
444 0 : (void) memmove((caddr_t)((long)cp &~ 3), cp, len);
445 0 : cp = (u_char *)((long)cp &~ 3);
446 0 : }
447 0 : cp -= hlen;
448 0 : len += hlen;
449 0 : BCOPY(hdr, cp, hlen);
450 :
451 0 : *bufp = cp;
452 0 : return (len);
453 0 : }
454 :
455 : /*
456 : * Uncompress a packet of total length total_len. The first buflen
457 : * bytes are at buf; this must include the entire (compressed or
458 : * uncompressed) TCP/IP header. This procedure returns the length
459 : * of the VJ header, with a pointer to the uncompressed IP header
460 : * in *hdrp and its length in *hlenp.
461 : */
462 : int
463 0 : sl_uncompress_tcp_core(u_char *buf, int buflen, int total_len, u_int type,
464 : struct slcompress *comp, u_char **hdrp, u_int *hlenp)
465 : {
466 : u_char *cp;
467 : u_int hlen, changes;
468 : struct tcphdr *th;
469 : struct cstate *cs;
470 : struct ip *ip;
471 : u_int16_t *bp;
472 : u_int vjlen;
473 :
474 0 : switch (type) {
475 :
476 : case TYPE_UNCOMPRESSED_TCP:
477 0 : ip = (struct ip *) buf;
478 0 : if (ip->ip_p >= MAX_STATES)
479 : goto bad;
480 0 : cs = &comp->rstate[comp->last_recv = ip->ip_p];
481 0 : comp->flags &=~ SLF_TOSS;
482 0 : ip->ip_p = IPPROTO_TCP;
483 : /*
484 : * Calculate the size of the TCP/IP header and make sure that
485 : * we don't overflow the space we have available for it.
486 : */
487 0 : hlen = ip->ip_hl << 2;
488 0 : if (hlen + sizeof(struct tcphdr) > buflen)
489 : goto bad;
490 0 : hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2;
491 0 : if (hlen > MAX_HDR || hlen > buflen)
492 : goto bad;
493 0 : BCOPY(ip, &cs->cs_ip, hlen);
494 0 : cs->cs_hlen = hlen;
495 0 : INCR(sls_uncompressedin)
496 0 : *hdrp = (u_char *) &cs->cs_ip;
497 0 : *hlenp = hlen;
498 0 : return (0);
499 :
500 : default:
501 : goto bad;
502 :
503 : case TYPE_COMPRESSED_TCP:
504 : break;
505 : }
506 : /* We've got a compressed packet. */
507 0 : INCR(sls_compressedin)
508 : cp = buf;
509 0 : changes = *cp++;
510 0 : if (changes & NEW_C) {
511 : /* Make sure the state index is in range, then grab the state.
512 : * If we have a good state index, clear the 'discard' flag. */
513 0 : if (*cp >= MAX_STATES)
514 : goto bad;
515 :
516 0 : comp->flags &=~ SLF_TOSS;
517 0 : comp->last_recv = *cp++;
518 0 : } else {
519 : /* this packet has an implicit state index. If we've
520 : * had a line error since the last time we got an
521 : * explicit state index, we have to toss the packet. */
522 0 : if (comp->flags & SLF_TOSS) {
523 0 : INCR(sls_tossed)
524 0 : return (-1);
525 : }
526 : }
527 0 : cs = &comp->rstate[comp->last_recv];
528 0 : hlen = cs->cs_ip.ip_hl << 2;
529 0 : th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen];
530 0 : th->th_sum = htons((*cp << 8) | cp[1]);
531 0 : cp += 2;
532 0 : if (changes & TCP_PUSH_BIT)
533 0 : th->th_flags |= TH_PUSH;
534 : else
535 0 : th->th_flags &=~ TH_PUSH;
536 :
537 0 : switch (changes & SPECIALS_MASK) {
538 : case SPECIAL_I:
539 : {
540 0 : u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
541 0 : th->th_ack = htonl(ntohl(th->th_ack) + i);
542 0 : th->th_seq = htonl(ntohl(th->th_seq) + i);
543 : }
544 0 : break;
545 :
546 : case SPECIAL_D:
547 0 : th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len)
548 : - cs->cs_hlen);
549 0 : break;
550 :
551 : default:
552 0 : if (changes & NEW_U) {
553 0 : th->th_flags |= TH_URG;
554 0 : DECODEU(th->th_urp)
555 : } else
556 0 : th->th_flags &=~ TH_URG;
557 0 : if (changes & NEW_W)
558 0 : DECODES(th->th_win)
559 0 : if (changes & NEW_A)
560 0 : DECODEL(th->th_ack)
561 0 : if (changes & NEW_S)
562 0 : DECODEL(th->th_seq)
563 : break;
564 : }
565 0 : if (changes & NEW_I) {
566 0 : DECODES(cs->cs_ip.ip_id)
567 : } else
568 0 : cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1);
569 :
570 : /*
571 : * At this point, cp points to the first byte of data in the
572 : * packet. Fill in the IP total length and update the IP
573 : * header checksum.
574 : */
575 0 : vjlen = cp - buf;
576 0 : buflen -= vjlen;
577 0 : if (buflen < 0)
578 : /* we must have dropped some characters (crc should detect
579 : * this but the old slip framing won't) */
580 : goto bad;
581 :
582 0 : total_len += cs->cs_hlen - vjlen;
583 0 : cs->cs_ip.ip_len = htons(total_len);
584 :
585 : /* recompute the ip header checksum */
586 0 : bp = (u_int16_t *) &cs->cs_ip;
587 0 : cs->cs_ip.ip_sum = 0;
588 0 : for (changes = 0; hlen > 0; hlen -= 2)
589 0 : changes += *bp++;
590 0 : changes = (changes & 0xffff) + (changes >> 16);
591 0 : changes = (changes & 0xffff) + (changes >> 16);
592 0 : cs->cs_ip.ip_sum = ~ changes;
593 :
594 0 : *hdrp = (u_char *) &cs->cs_ip;
595 0 : *hlenp = cs->cs_hlen;
596 0 : return vjlen;
597 :
598 : bad:
599 0 : comp->flags |= SLF_TOSS;
600 0 : INCR(sls_errorin)
601 0 : return (-1);
602 0 : }
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