aboutsummaryrefslogtreecommitdiffstats
path: root/drivers/isdn/i4l/isdn_bsdcomp.c
blob: 8837ac5a492dd14eb79b392ba0d1d0907bd463dc (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
/*
 * BSD compression module
 *
 * Patched version for ISDN syncPPP written 1997/1998 by Michael Hipp
 * The whole module is now SKB based.
 *
 */

/*
 * Update: The Berkeley copyright was changed, and the change
 * is retroactive to all "true" BSD software (ie everything
 * from UCB as opposed to other peoples code that just carried
 * the same license). The new copyright doesn't clash with the
 * GPL, so the module-only restriction has been removed..
 */

/*
 * Original copyright notice:
 *
 * Copyright (c) 1985, 1986 The Regents of the University of California.
 * All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * James A. Woods, derived from original work by Spencer Thomas
 * and Joseph Orost.
 *
 * 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.
 */

#include <linux/module.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/fcntl.h>
#include <linux/interrupt.h>
#include <linux/ptrace.h>
#include <linux/ioport.h>
#include <linux/in.h>
#include <linux/slab.h>
#include <linux/tty.h>
#include <linux/errno.h>
#include <linux/string.h>	/* used in new tty drivers */
#include <linux/signal.h>	/* used in new tty drivers */
#include <linux/bitops.h>

#include <asm/byteorder.h>
#include <asm/types.h>

#include <linux/if.h>

#include <linux/if_ether.h>
#include <linux/netdevice.h>
#include <linux/skbuff.h>
#include <linux/inet.h>
#include <linux/ioctl.h>
#include <linux/vmalloc.h>

#include <linux/ppp_defs.h>

#include <linux/isdn.h>
#include <linux/isdn_ppp.h>
#include <linux/ip.h>
#include <linux/tcp.h>
#include <linux/if_arp.h>
#include <linux/ppp-comp.h>

#include "isdn_ppp.h"

MODULE_DESCRIPTION("ISDN4Linux: BSD Compression for PPP over ISDN");
MODULE_LICENSE("Dual BSD/GPL");

#define BSD_VERSION(x)	((x) >> 5)
#define BSD_NBITS(x)	((x) & 0x1F)

#define BSD_CURRENT_VERSION	1

#define DEBUG 1

/*
 * A dictionary for doing BSD compress.
 */

struct bsd_dict {
	u32 fcode;
	u16 codem1;		/* output of hash table -1 */
	u16 cptr;		/* map code to hash table entry */
};

struct bsd_db {
	int            totlen;		/* length of this structure */
	unsigned int   hsize;		/* size of the hash table */
	unsigned char  hshift;		/* used in hash function */
	unsigned char  n_bits;		/* current bits/code */
	unsigned char  maxbits;		/* maximum bits/code */
	unsigned char  debug;		/* non-zero if debug desired */
	unsigned char  unit;		/* ppp unit number */
	u16 seqno;			/* sequence # of next packet */
	unsigned int   mru;		/* size of receive (decompress) bufr */
	unsigned int   maxmaxcode;	/* largest valid code */
	unsigned int   max_ent;		/* largest code in use */
	unsigned int   in_count;	/* uncompressed bytes, aged */
	unsigned int   bytes_out;	/* compressed bytes, aged */
	unsigned int   ratio;		/* recent compression ratio */
	unsigned int   checkpoint;	/* when to next check the ratio */
	unsigned int   clear_count;	/* times dictionary cleared */
	unsigned int   incomp_count;	/* incompressible packets */
	unsigned int   incomp_bytes;	/* incompressible bytes */
	unsigned int   uncomp_count;	/* uncompressed packets */
	unsigned int   uncomp_bytes;	/* uncompressed bytes */
	unsigned int   comp_count;	/* compressed packets */
	unsigned int   comp_bytes;	/* compressed bytes */
	unsigned short  *lens;		/* array of lengths of codes */
	struct bsd_dict *dict;		/* dictionary */
	int xmit;
};

#define BSD_OVHD	2		/* BSD compress overhead/packet */
#define MIN_BSD_BITS	9
#define BSD_INIT_BITS	MIN_BSD_BITS
#define MAX_BSD_BITS	15

/*
 * the next two codes should not be changed lightly, as they must not
 * lie within the contiguous general code space.
 */
#define CLEAR	256			/* table clear output code */
#define FIRST	257			/* first free entry */
#define LAST	255

#define MAXCODE(b)	((1 << (b)) - 1)
#define BADCODEM1	MAXCODE(MAX_BSD_BITS)

#define BSD_HASH(prefix, suffix, hshift) ((((unsigned long)(suffix)) << (hshift)) \
					  ^ (unsigned long)(prefix))
#define BSD_KEY(prefix, suffix)		((((unsigned long)(suffix)) << 16) \
					 + (unsigned long)(prefix))

#define CHECK_GAP	10000		/* Ratio check interval */

#define RATIO_SCALE_LOG	8
#define RATIO_SCALE	(1 << RATIO_SCALE_LOG)
#define RATIO_MAX	(0x7fffffff >> RATIO_SCALE_LOG)

/*
 * clear the dictionary
 */

static void bsd_clear(struct bsd_db *db)
{
	db->clear_count++;
	db->max_ent      = FIRST - 1;
	db->n_bits       = BSD_INIT_BITS;
	db->bytes_out    = 0;
	db->in_count     = 0;
	db->incomp_count = 0;
	db->ratio	     = 0;
	db->checkpoint   = CHECK_GAP;
}

/*
 * If the dictionary is full, then see if it is time to reset it.
 *
 * Compute the compression ratio using fixed-point arithmetic
 * with 8 fractional bits.
 *
 * Since we have an infinite stream instead of a single file,
 * watch only the local compression ratio.
 *
 * Since both peers must reset the dictionary at the same time even in
 * the absence of CLEAR codes (while packets are incompressible), they
 * must compute the same ratio.
 */
static int bsd_check(struct bsd_db *db)	/* 1=output CLEAR */
{
	unsigned int new_ratio;

	if (db->in_count >= db->checkpoint)
	{
		/* age the ratio by limiting the size of the counts */
		if (db->in_count >= RATIO_MAX || db->bytes_out >= RATIO_MAX)
		{
			db->in_count  -= (db->in_count  >> 2);
			db->bytes_out -= (db->bytes_out >> 2);
		}

		db->checkpoint = db->in_count + CHECK_GAP;

		if (db->max_ent >= db->maxmaxcode)
		{
			/* Reset the dictionary only if the ratio is worse,
			 * or if it looks as if it has been poisoned
			 * by incompressible data.
			 *
			 * This does not overflow, because
			 *	db->in_count <= RATIO_MAX.
			 */

			new_ratio = db->in_count << RATIO_SCALE_LOG;
			if (db->bytes_out != 0)
			{
				new_ratio /= db->bytes_out;
			}

			if (new_ratio < db->ratio || new_ratio < 1 * RATIO_SCALE)
			{
				bsd_clear(db);
				return 1;
			}
			db->ratio = new_ratio;
		}
	}
	return 0;
}

/*
 * Return statistics.
 */

static void bsd_stats(void *state, struct compstat *stats)
{
	struct bsd_db *db = (struct bsd_db *) state;

	stats->unc_bytes    = db->uncomp_bytes;
	stats->unc_packets  = db->uncomp_count;
	stats->comp_bytes   = db->comp_bytes;
	stats->comp_packets = db->comp_count;
	stats->inc_bytes    = db->incomp_bytes;
	stats->inc_packets  = db->incomp_count;
	stats->in_count     = db->in_count;
	stats->bytes_out    = db->bytes_out;
}

/*
 * Reset state, as on a CCP ResetReq.
 */
static void bsd_reset(void *state, unsigned char code, unsigned char id,
		      unsigned char *data, unsigned len,
		      struct isdn_ppp_resetparams *rsparm)
{
	struct bsd_db *db = (struct bsd_db *) state;

	bsd_clear(db);
	db->seqno       = 0;
	db->clear_count = 0;
}

/*
 * Release the compression structure
 */
static void bsd_free(void *state)
{
	struct bsd_db *db = (struct bsd_db *) state;

	if (db) {
		/*
		 * Release the dictionary
		 */
		vfree(db->dict);
		db->dict = NULL;

		/*
		 * Release the string buffer
		 */
		vfree(db->lens);
		db->lens = NULL;

		/*
		 * Finally release the structure itself.
		 */
		kfree(db);
	}
}


/*
 * Allocate space for a (de) compressor.
 */
static void *bsd_alloc(struct isdn_ppp_comp_data *data)
{
	int bits;
	unsigned int hsize, hshift, maxmaxcode;
	struct bsd_db *db;
	int decomp;

	static unsigned int htab[][2] = {
		{ 5003 , 4 } , { 5003 , 4 } , { 5003 , 4 } , { 5003 , 4 } ,
		{ 9001 , 5 } , { 18013 , 6 } , { 35023 , 7 } , { 69001 , 8 }
	};

	if (data->optlen != 1 || data->num != CI_BSD_COMPRESS
	    || BSD_VERSION(data->options[0]) != BSD_CURRENT_VERSION)
		return NULL;

	bits = BSD_NBITS(data->options[0]);

	if (bits < 9 || bits > 15)
		return NULL;

	hsize = htab[bits - 9][0];
	hshift = htab[bits - 9][1];

	/*
	 * Allocate the main control structure for this instance.
	 */
	maxmaxcode = MAXCODE(bits);
	db = kzalloc(sizeof(struct bsd_db), GFP_KERNEL);
	if (!db)
		return NULL;

	db->xmit = data->flags & IPPP_COMP_FLAG_XMIT;
	decomp = db->xmit ? 0 : 1;

	/*
	 * Allocate space for the dictionary. This may be more than one page in
	 * length.
	 */
	db->dict = vmalloc(hsize * sizeof(struct bsd_dict));
	if (!db->dict) {
		bsd_free(db);
		return NULL;
	}

	/*
	 * If this is the compression buffer then there is no length data.
	 * For decompression, the length information is needed as well.
	 */
	if (!decomp)
		db->lens = NULL;
	else {
		db->lens = vmalloc((maxmaxcode + 1) * sizeof(db->lens[0]));
		if (!db->lens) {
			bsd_free(db);
			return (NULL);
		}
	}

	/*
	 * Initialize the data information for the compression code
	 */
	db->totlen = sizeof(struct bsd_db) + (sizeof(struct bsd_dict) * hsize);
	db->hsize = hsize;
	db->hshift = hshift;
	db->maxmaxcode = maxmaxcode;
	db->maxbits = bits;

	return (void *)db;
}

/*
 * Initialize the database.
 */
static int bsd_init(void *state, struct isdn_ppp_comp_data *data, int unit, int debug)
{
	struct bsd_db *db = state;
	int indx;
	int decomp;

	if (!state || !data) {
		printk(KERN_ERR "isdn_bsd_init: [%d] ERR, state %lx data %lx\n", unit, (long)state, (long)data);
		return 0;
	}

	decomp = db->xmit ? 0 : 1;

	if (data->optlen != 1 || data->num != CI_BSD_COMPRESS
	    || (BSD_VERSION(data->options[0]) != BSD_CURRENT_VERSION)
	    || (BSD_NBITS(data->options[0]) != db->maxbits)
	    || (decomp && db->lens == NULL)) {
		printk(KERN_ERR "isdn_bsd: %d %d %d %d %lx\n", data->optlen, data->num, data->options[0], decomp, (unsigned long)db->lens);
		return 0;
	}

	if (decomp)
		for (indx = LAST; indx >= 0; indx--)
			db->lens[indx] = 1;

	indx = db->hsize;
	while (indx-- != 0) {
		db->dict[indx].codem1 = BADCODEM1;
		db->dict[indx].cptr   = 0;
	}

	db->unit = unit;
	db->mru  = 0;

	db->debug = 1;

	bsd_reset(db, 0, 0, NULL, 0, NULL);

	return 1;
}

/*
 * Obtain pointers to the various structures in the compression tables
 */

#define dict_ptrx(p, idx) &(p->dict[idx])
#define lens_ptrx(p, idx) &(p->lens[idx])

#ifdef DEBUG
static unsigned short *lens_ptr(struct bsd_db *db, int idx)
{
	if ((unsigned int) idx > (unsigned int) db->maxmaxcode) {
		printk(KERN_DEBUG "<9>ppp: lens_ptr(%d) > max\n", idx);
		idx = 0;
	}
	return lens_ptrx(db, idx);
}

static struct bsd_dict *dict_ptr(struct bsd_db *db, int idx)
{
	if ((unsigned int) idx >= (unsigned int) db->hsize) {
		printk(KERN_DEBUG "<9>ppp: dict_ptr(%d) > max\n", idx);
		idx = 0;
	}
	return dict_ptrx(db, idx);
}

#else
#define lens_ptr(db, idx) lens_ptrx(db, idx)
#define dict_ptr(db, idx) dict_ptrx(db, idx)
#endif

/*
 * compress a packet
 */
static int bsd_compress(void *state, struct sk_buff *skb_in, struct sk_buff *skb_out, int proto)
{
	struct bsd_db *db;
	int hshift;
	unsigned int max_ent;
	unsigned int n_bits;
	unsigned int bitno;
	unsigned long accm;
	int ent;
	unsigned long fcode;
	struct bsd_dict *dictp;
	unsigned char c;
	int hval, disp, ilen, mxcode;
	unsigned char *rptr = skb_in->data;
	int isize = skb_in->len;

#define OUTPUT(ent)							\
	{								\
		bitno -= n_bits;					\
		accm |= ((ent) << bitno);				\
		do	{						\
			if (skb_out && skb_tailroom(skb_out) > 0)	\
				*(skb_put(skb_out, 1)) = (unsigned char)(accm >> 24); \
			accm <<= 8;					\
			bitno += 8;					\
		} while (bitno <= 24);					\
	}

	/*
	 * If the protocol is not in the range we're interested in,
	 * just return without compressing the packet.  If it is,
	 * the protocol becomes the first byte to compress.
	 */
	printk(KERN_DEBUG "bsd_compress called with %x\n", proto);

	ent = proto;
	if (proto < 0x21 || proto > 0xf9 || !(proto & 0x1))
		return 0;

	db      = (struct bsd_db *) state;
	hshift  = db->hshift;
	max_ent = db->max_ent;
	n_bits  = db->n_bits;
	bitno   = 32;
	accm    = 0;
	mxcode  = MAXCODE(n_bits);

	/* This is the PPP header information */
	if (skb_out && skb_tailroom(skb_out) >= 2) {
		char *v = skb_put(skb_out, 2);
		/* we only push our own data on the header,
		   AC,PC and protos is pushed by caller  */
		v[0] = db->seqno >> 8;
		v[1] = db->seqno;
	}

	ilen = ++isize; /* This is off by one, but that is what is in draft! */

	while (--ilen > 0) {
		c = *rptr++;
		fcode = BSD_KEY(ent, c);
		hval = BSD_HASH(ent, c, hshift);
		dictp = dict_ptr(db, hval);

		/* Validate and then check the entry. */
		if (dictp->codem1 >= max_ent)
			goto nomatch;

		if (dictp->fcode == fcode) {
			ent = dictp->codem1 + 1;
			continue;	/* found (prefix,suffix) */
		}

		/* continue probing until a match or invalid entry */
		disp = (hval == 0) ? 1 : hval;

		do {
			hval += disp;
			if (hval >= db->hsize)
				hval -= db->hsize;
			dictp = dict_ptr(db, hval);
			if (dictp->codem1 >= max_ent)
				goto nomatch;
		} while (dictp->fcode != fcode);

		ent = dictp->codem1 + 1;	/* finally found (prefix,suffix) */
		continue;

	nomatch:
		OUTPUT(ent);		/* output the prefix */

		/* code -> hashtable */
		if (max_ent < db->maxmaxcode) {
			struct bsd_dict *dictp2;
			struct bsd_dict *dictp3;
			int indx;

			/* expand code size if needed */
			if (max_ent >= mxcode) {
				db->n_bits = ++n_bits;
				mxcode = MAXCODE(n_bits);
			}

			/*
			 * Invalidate old hash table entry using
			 * this code, and then take it over.
			 */
			dictp2 = dict_ptr(db, max_ent + 1);
			indx   = dictp2->cptr;
			dictp3 = dict_ptr(db, indx);

			if (dictp3->codem1 == max_ent)
				dictp3->codem1 = BADCODEM1;

			dictp2->cptr   = hval;
			dictp->codem1  = max_ent;
			dictp->fcode = fcode;
			db->max_ent    = ++max_ent;

			if (db->lens) {
				unsigned short *len1 = lens_ptr(db, max_ent);
				unsigned short *len2 = lens_ptr(db, ent);
				*len1 = *len2 + 1;
			}
		}
		ent = c;
	}

	OUTPUT(ent);		/* output the last code */

	if (skb_out)
		db->bytes_out    += skb_out->len; /* Do not count bytes from here */
	db->uncomp_bytes += isize;
	db->in_count     += isize;
	++db->uncomp_count;
	++db->seqno;

	if (bitno < 32)
		++db->bytes_out; /* must be set before calling bsd_check */

	/*
	 * Generate the clear command if needed
	 */

	if (bsd_check(db))
		OUTPUT(CLEAR);

	/*
	 * Pad dribble bits of last code with ones.
	 * Do not emit a completely useless byte of ones.
	 */
	if (bitno < 32 && skb_out && skb_tailroom(skb_out) > 0)
		*(skb_put(skb_out, 1)) = (unsigned char)((accm | (0xff << (bitno - 8))) >> 24);

	/*
	 * Increase code size if we would have without the packet
	 * boundary because the decompressor will do so.
	 */
	if (max_ent >= mxcode && max_ent < db->maxmaxcode)
		db->n_bits++;

	/* If output length is too large then this is an incompressible frame. */
	if (!skb_out || skb_out->len >= skb_in->len) {
		++db->incomp_count;
		db->incomp_bytes += isize;
		return 0;
	}

	/* Count the number of compressed frames */
	++db->comp_count;
	db->comp_bytes += skb_out->len;
	return skb_out->len;

#undef OUTPUT
}

/*
 * Update the "BSD Compress" dictionary on the receiver for
 * incompressible data by pretending to compress the incoming data.
 */
static void bsd_incomp(void *state, struct sk_buff *skb_in, int proto)
{
	bsd_compress(state, skb_in, NULL, proto);
}

/*
 * Decompress "BSD Compress".
 */
static int bsd_decompress(void *state, struct sk_buff *skb_in, struct sk_buff *skb_out,
			  struct isdn_ppp_resetparams *rsparm)
{
	struct bsd_db *db;
	unsigned int max_ent;
	unsigned long accm;
	unsigned int bitno;		/* 1st valid bit in accm */
	unsigned int n_bits;
	unsigned int tgtbitno;	/* bitno when we have a code */
	struct bsd_dict *dictp;
	int seq;
	unsigned int incode;
	unsigned int oldcode;
	unsigned int finchar;
	unsigned char *p, *ibuf;
	int ilen;
	int codelen;
	int extra;

	db       = (struct bsd_db *) state;
	max_ent  = db->max_ent;
	accm     = 0;
	bitno    = 32;		/* 1st valid bit in accm */
	n_bits   = db->n_bits;
	tgtbitno = 32 - n_bits;	/* bitno when we have a code */

	printk(KERN_DEBUG "bsd_decompress called\n");

	if (!skb_in || !skb_out) {
		printk(KERN_ERR "bsd_decompress called with NULL parameter\n");
		return DECOMP_ERROR;
	}

	/*
	 * Get the sequence number.
	 */
	if ((p = skb_pull(skb_in, 2)) == NULL) {
		return DECOMP_ERROR;
	}
	p -= 2;
	seq = (p[0] << 8) + p[1];
	ilen = skb_in->len;
	ibuf = skb_in->data;

	/*
	 * Check the sequence number and give up if it differs from
	 * the value we're expecting.
	 */
	if (seq != db->seqno) {
		if (db->debug) {
			printk(KERN_DEBUG "bsd_decomp%d: bad sequence # %d, expected %d\n",
			       db->unit, seq, db->seqno - 1);
		}
		return DECOMP_ERROR;
	}

	++db->seqno;
	db->bytes_out += ilen;

	if (skb_tailroom(skb_out) > 0)
		*(skb_put(skb_out, 1)) = 0;
	else
		return DECOMP_ERR_NOMEM;

	oldcode = CLEAR;

	/*
	 * Keep the checkpoint correctly so that incompressible packets
	 * clear the dictionary at the proper times.
	 */

	for (;;) {
		if (ilen-- <= 0) {
			db->in_count += (skb_out->len - 1); /* don't count the header */
			break;
		}

		/*
		 * Accumulate bytes until we have a complete code.
		 * Then get the next code, relying on the 32-bit,
		 * unsigned accm to mask the result.
		 */

		bitno -= 8;
		accm  |= *ibuf++ << bitno;
		if (tgtbitno < bitno)
			continue;

		incode = accm >> tgtbitno;
		accm <<= n_bits;
		bitno += n_bits;

		/*
		 * The dictionary must only be cleared at the end of a packet.
		 */

		if (incode == CLEAR) {
			if (ilen > 0) {
				if (db->debug)
					printk(KERN_DEBUG "bsd_decomp%d: bad CLEAR\n", db->unit);
				return DECOMP_FATALERROR;	/* probably a bug */
			}
			bsd_clear(db);
			break;
		}

		if ((incode > max_ent + 2) || (incode > db->maxmaxcode)
		    || (incode > max_ent && oldcode == CLEAR)) {
			if (db->debug) {
				printk(KERN_DEBUG "bsd_decomp%d: bad code 0x%x oldcode=0x%x ",
				       db->unit, incode, oldcode);
				printk(KERN_DEBUG "max_ent=0x%x skb->Len=%d seqno=%d\n",
				       max_ent, skb_out->len, db->seqno);
			}
			return DECOMP_FATALERROR;	/* probably a bug */
		}

		/* Special case for KwKwK string. */
		if (incode > max_ent) {
			finchar = oldcode;
			extra   = 1;
		} else {
			finchar = incode;
			extra   = 0;
		}

		codelen = *(lens_ptr(db, finchar));
		if (skb_tailroom(skb_out) < codelen + extra) {
			if (db->debug) {
				printk(KERN_DEBUG "bsd_decomp%d: ran out of mru\n", db->unit);
#ifdef DEBUG
				printk(KERN_DEBUG "  len=%d, finchar=0x%x, codelen=%d,skblen=%d\n",
				       ilen, finchar, codelen, skb_out->len);
#endif
			}
			return DECOMP_FATALERROR;
		}

		/*
		 * Decode this code and install it in the decompressed buffer.
		 */

		p = skb_put(skb_out, codelen);
		p += codelen;
		while (finchar > LAST) {
			struct bsd_dict *dictp2 = dict_ptr(db, finchar);

			dictp = dict_ptr(db, dictp2->cptr);

#ifdef DEBUG
			if (--codelen <= 0 || dictp->codem1 != finchar - 1) {
				if (codelen <= 0) {
					printk(KERN_ERR "bsd_decomp%d: fell off end of chain ", db->unit);
					printk(KERN_ERR "0x%x at 0x%x by 0x%x, max_ent=0x%x\n", incode, finchar, dictp2->cptr, max_ent);
				} else {
					if (dictp->codem1 != finchar - 1) {
						printk(KERN_ERR "bsd_decomp%d: bad code chain 0x%x finchar=0x%x ", db->unit, incode, finchar);
						printk(KERN_ERR "oldcode=0x%x cptr=0x%x codem1=0x%x\n", oldcode, dictp2->cptr, dictp->codem1);
					}
				}
				return DECOMP_FATALERROR;
			}
#endif

			{
				u32 fcode = dictp->fcode;
				*--p    = (fcode >> 16) & 0xff;
				finchar = fcode & 0xffff;
			}
		}
		*--p = finchar;

#ifdef DEBUG
		if (--codelen != 0)
			printk(KERN_ERR "bsd_decomp%d: short by %d after code 0x%x, max_ent=0x%x\n", db->unit, codelen, incode, max_ent);
#endif

		if (extra)		/* the KwKwK case again */
			*(skb_put(skb_out, 1)) = finchar;

		/*
		 * If not first code in a packet, and
		 * if not out of code space, then allocate a new code.
		 *
		 * Keep the hash table correct so it can be used
		 * with uncompressed packets.
		 */
		if (oldcode != CLEAR && max_ent < db->maxmaxcode) {
			struct bsd_dict *dictp2, *dictp3;
			u16 *lens1, *lens2;
			unsigned long fcode;
			int hval, disp, indx;

			fcode = BSD_KEY(oldcode, finchar);
			hval  = BSD_HASH(oldcode, finchar, db->hshift);
			dictp = dict_ptr(db, hval);

			/* look for a free hash table entry */
			if (dictp->codem1 < max_ent) {
				disp = (hval == 0) ? 1 : hval;
				do {
					hval += disp;
					if (hval >= db->hsize)
						hval -= db->hsize;
					dictp = dict_ptr(db, hval);
				} while (dictp->codem1 < max_ent);
			}

			/*
			 * Invalidate previous hash table entry
			 * assigned this code, and then take it over
			 */

			dictp2 = dict_ptr(db, max_ent + 1);
			indx   = dictp2->cptr;
			dictp3 = dict_ptr(db, indx);

			if (dictp3->codem1 == max_ent)
				dictp3->codem1 = BADCODEM1;

			dictp2->cptr   = hval;
			dictp->codem1  = max_ent;
			dictp->fcode = fcode;
			db->max_ent    = ++max_ent;

			/* Update the length of this string. */
			lens1  = lens_ptr(db, max_ent);
			lens2  = lens_ptr(db, oldcode);
			*lens1 = *lens2 + 1;

			/* Expand code size if needed. */
			if (max_ent >= MAXCODE(n_bits) && max_ent < db->maxmaxcode) {
				db->n_bits = ++n_bits;
				tgtbitno   = 32-n_bits;
			}
		}
		oldcode = incode;
	}

	++db->comp_count;
	++db->uncomp_count;
	db->comp_bytes   += skb_in->len - BSD_OVHD;
	db->uncomp_bytes += skb_out->len;

	if (bsd_check(db)) {
		if (db->debug)
			printk(KERN_DEBUG "bsd_decomp%d: peer should have cleared dictionary on %d\n",
			       db->unit, db->seqno - 1);
	}
	return skb_out->len;
}

/*************************************************************
 * Table of addresses for the BSD compression module
 *************************************************************/

static struct isdn_ppp_compressor ippp_bsd_compress = {
	.owner          = THIS_MODULE,
	.num            = CI_BSD_COMPRESS,
	.alloc          = bsd_alloc,
	.free           = bsd_free,
	.init           = bsd_init,
	.reset          = bsd_reset,
	.compress       = bsd_compress,
	.decompress     = bsd_decompress,
	.incomp         = bsd_incomp,
	.stat           = bsd_stats,
};

/*************************************************************
 * Module support routines
 *************************************************************/

static int __init isdn_bsdcomp_init(void)
{
	int answer = isdn_ppp_register_compressor(&ippp_bsd_compress);
	if (answer == 0)
		printk(KERN_INFO "PPP BSD Compression module registered\n");
	return answer;
}

static void __exit isdn_bsdcomp_exit(void)
{
	isdn_ppp_unregister_compressor(&ippp_bsd_compress);
}

module_init(isdn_bsdcomp_init);
module_exit(isdn_bsdcomp_exit);