1/*
2 * Update: The Berkeley copyright was changed, and the change
3 * is retroactive to all "true" BSD software (ie everything
4 * from UCB as opposed to other peoples code that just carried
5 * the same license). The new copyright doesn't clash with the
6 * GPL, so the module-only restriction has been removed..
7 */
8
9/* Because this code is derived from the 4.3BSD compress source:
10 *
11 * Copyright (c) 1985, 1986 The Regents of the University of California.
12 * All rights reserved.
13 *
14 * This code is derived from software contributed to Berkeley by
15 * James A. Woods, derived from original work by Spencer Thomas
16 * and Joseph Orost.
17 *
18 * Redistribution and use in source and binary forms, with or without
19 * modification, are permitted provided that the following conditions
20 * are met:
21 * 1. Redistributions of source code must retain the above copyright
22 *    notice, this list of conditions and the following disclaimer.
23 * 2. Redistributions in binary form must reproduce the above copyright
24 *    notice, this list of conditions and the following disclaimer in the
25 *    documentation and/or other materials provided with the distribution.
26 * 3. All advertising materials mentioning features or use of this software
27 *    must display the following acknowledgement:
28 *	This product includes software developed by the University of
29 *	California, Berkeley and its contributors.
30 * 4. Neither the name of the University nor the names of its contributors
31 *    may be used to endorse or promote products derived from this software
32 *    without specific prior written permission.
33 *
34 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
35 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
36 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
37 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
38 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
39 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
40 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
41 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
42 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
43 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
44 * SUCH DAMAGE.
45 */
46
47/*
48 * This version is for use with contiguous buffers on Linux-derived systems.
49 *
50 *  ==FILEVERSION 20000226==
51 *
52 *  NOTE TO MAINTAINERS:
53 *     If you modify this file at all, please set the number above to the
54 *     date of the modification as YYMMDD (year month day).
55 *     bsd_comp.c is shipped with a PPP distribution as well as with
56 *     the kernel; if everyone increases the FILEVERSION number above,
57 *     then scripts can do the right thing when deciding whether to
58 *     install a new bsd_comp.c file. Don't change the format of that
59 *     line otherwise, so the installation script can recognize it.
60 *
61 * From: bsd_comp.c,v 1.3 1994/12/08 01:59:58 paulus Exp
62 */
63
64#include <linux/module.h>
65#include <linux/init.h>
66#include <linux/slab.h>
67#include <linux/vmalloc.h>
68#include <linux/string.h>
69
70#include <linux/ppp_defs.h>
71
72#undef   PACKETPTR
73#define  PACKETPTR 1
74#include <linux/ppp-comp.h>
75#undef   PACKETPTR
76
77#include <asm/byteorder.h>
78
79/*
80 * PPP "BSD compress" compression
81 *  The differences between this compression and the classic BSD LZW
82 *  source are obvious from the requirement that the classic code worked
83 *  with files while this handles arbitrarily long streams that
84 *  are broken into packets.  They are:
85 *
86 *	When the code size expands, a block of junk is not emitted by
87 *	    the compressor and not expected by the decompressor.
88 *
89 *	New codes are not necessarily assigned every time an old
90 *	    code is output by the compressor.  This is because a packet
91 *	    end forces a code to be emitted, but does not imply that a
92 *	    new sequence has been seen.
93 *
94 *	The compression ratio is checked at the first end of a packet
95 *	    after the appropriate gap.	Besides simplifying and speeding
96 *	    things up, this makes it more likely that the transmitter
97 *	    and receiver will agree when the dictionary is cleared when
98 *	    compression is not going well.
99 */
100
101/*
102 * Macros to extract protocol version and number of bits
103 * from the third byte of the BSD Compress CCP configuration option.
104 */
105
106#define BSD_VERSION(x)	((x) >> 5)
107#define BSD_NBITS(x)	((x) & 0x1F)
108
109#define BSD_CURRENT_VERSION	1
110
111/*
112 * A dictionary for doing BSD compress.
113 */
114
115struct bsd_dict {
116    union {				/* hash value */
117	unsigned long	fcode;
118	struct {
119#if defined(__LITTLE_ENDIAN)		/* Little endian order */
120	    unsigned short	prefix;	/* preceding code */
121	    unsigned char	suffix; /* last character of new code */
122	    unsigned char	pad;
123#elif defined(__BIG_ENDIAN)		/* Big endian order */
124	    unsigned char	pad;
125	    unsigned char	suffix; /* last character of new code */
126	    unsigned short	prefix; /* preceding code */
127#else
128#error Endianness not defined...
129#endif
130	} hs;
131    } f;
132    unsigned short codem1;		/* output of hash table -1 */
133    unsigned short cptr;		/* map code to hash table entry */
134};
135
136struct bsd_db {
137    int	    totlen;			/* length of this structure */
138    unsigned int   hsize;		/* size of the hash table */
139    unsigned char  hshift;		/* used in hash function */
140    unsigned char  n_bits;		/* current bits/code */
141    unsigned char  maxbits;		/* maximum bits/code */
142    unsigned char  debug;		/* non-zero if debug desired */
143    unsigned char  unit;		/* ppp unit number */
144    unsigned short seqno;		/* sequence # of next packet */
145    unsigned int   mru;			/* size of receive (decompress) bufr */
146    unsigned int   maxmaxcode;		/* largest valid code */
147    unsigned int   max_ent;		/* largest code in use */
148    unsigned int   in_count;		/* uncompressed bytes, aged */
149    unsigned int   bytes_out;		/* compressed bytes, aged */
150    unsigned int   ratio;		/* recent compression ratio */
151    unsigned int   checkpoint;		/* when to next check the ratio */
152    unsigned int   clear_count;		/* times dictionary cleared */
153    unsigned int   incomp_count;	/* incompressible packets */
154    unsigned int   incomp_bytes;	/* incompressible bytes */
155    unsigned int   uncomp_count;	/* uncompressed packets */
156    unsigned int   uncomp_bytes;	/* uncompressed bytes */
157    unsigned int   comp_count;		/* compressed packets */
158    unsigned int   comp_bytes;		/* compressed bytes */
159    unsigned short  *lens;		/* array of lengths of codes */
160    struct bsd_dict *dict;		/* dictionary */
161};
162
163#define BSD_OVHD	2		/* BSD compress overhead/packet */
164#define MIN_BSD_BITS	9
165#define BSD_INIT_BITS	MIN_BSD_BITS
166#define MAX_BSD_BITS	15
167
168static void	bsd_free (void *state);
169static void	*bsd_alloc(unsigned char *options, int opt_len, int decomp);
170static void	*bsd_comp_alloc (unsigned char *options, int opt_len);
171static void	*bsd_decomp_alloc (unsigned char *options, int opt_len);
172
173static int	bsd_init        (void *db, unsigned char *options,
174			         int opt_len, int unit, int debug, int decomp);
175static int	bsd_comp_init   (void *state, unsigned char *options,
176			         int opt_len, int unit, int opthdr, int debug);
177static int	bsd_decomp_init (void *state, unsigned char *options,
178				 int opt_len, int unit, int opthdr, int mru,
179				 int debug);
180
181static void	bsd_reset (void *state);
182static void	bsd_comp_stats (void *state, struct compstat *stats);
183
184static int	bsd_compress (void *state, unsigned char *rptr,
185			      unsigned char *obuf, int isize, int osize);
186static void	bsd_incomp (void *state, unsigned char *ibuf, int icnt);
187
188static int	bsd_decompress (void *state, unsigned char *ibuf, int isize,
189				unsigned char *obuf, int osize);
190
191/* These are in ppp_generic.c */
192extern int  ppp_register_compressor   (struct compressor *cp);
193extern void ppp_unregister_compressor (struct compressor *cp);
194
195/*
196 * the next two codes should not be changed lightly, as they must not
197 * lie within the contiguous general code space.
198 */
199#define CLEAR	256			/* table clear output code */
200#define FIRST	257			/* first free entry */
201#define LAST	255
202
203#define MAXCODE(b)	((1 << (b)) - 1)
204#define BADCODEM1	MAXCODE(MAX_BSD_BITS)
205
206#define BSD_HASH(prefix,suffix,hshift) ((((unsigned long)(suffix))<<(hshift)) \
207					 ^ (unsigned long)(prefix))
208#define BSD_KEY(prefix,suffix)		((((unsigned long)(suffix)) << 16) \
209					 + (unsigned long)(prefix))
210
211#define CHECK_GAP	10000		/* Ratio check interval */
212
213#define RATIO_SCALE_LOG	8
214#define RATIO_SCALE	(1<<RATIO_SCALE_LOG)
215#define RATIO_MAX	(0x7fffffff>>RATIO_SCALE_LOG)
216
217/*
218 * clear the dictionary
219 */
220
221static void
222bsd_clear(struct bsd_db *db)
223{
224    db->clear_count++;
225    db->max_ent      = FIRST-1;
226    db->n_bits       = BSD_INIT_BITS;
227    db->bytes_out    = 0;
228    db->in_count     = 0;
229    db->ratio	     = 0;
230    db->checkpoint   = CHECK_GAP;
231}
232
233/*
234 * If the dictionary is full, then see if it is time to reset it.
235 *
236 * Compute the compression ratio using fixed-point arithmetic
237 * with 8 fractional bits.
238 *
239 * Since we have an infinite stream instead of a single file,
240 * watch only the local compression ratio.
241 *
242 * Since both peers must reset the dictionary at the same time even in
243 * the absence of CLEAR codes (while packets are incompressible), they
244 * must compute the same ratio.
245 */
246
247static int bsd_check (struct bsd_db *db)	/* 1=output CLEAR */
248  {
249    unsigned int new_ratio;
250
251    if (db->in_count >= db->checkpoint)
252      {
253	/* age the ratio by limiting the size of the counts */
254	if (db->in_count >= RATIO_MAX || db->bytes_out >= RATIO_MAX)
255	  {
256	    db->in_count  -= (db->in_count  >> 2);
257	    db->bytes_out -= (db->bytes_out >> 2);
258	  }
259
260	db->checkpoint = db->in_count + CHECK_GAP;
261
262	if (db->max_ent >= db->maxmaxcode)
263	  {
264	    /* Reset the dictionary only if the ratio is worse,
265	     * or if it looks as if it has been poisoned
266	     * by incompressible data.
267	     *
268	     * This does not overflow, because
269	     *	db->in_count <= RATIO_MAX.
270	     */
271
272	    new_ratio = db->in_count << RATIO_SCALE_LOG;
273	    if (db->bytes_out != 0)
274	      {
275		new_ratio /= db->bytes_out;
276	      }
277
278	    if (new_ratio < db->ratio || new_ratio < 1 * RATIO_SCALE)
279	      {
280		bsd_clear (db);
281		return 1;
282	      }
283	    db->ratio = new_ratio;
284	  }
285      }
286    return 0;
287  }
288
289/*
290 * Return statistics.
291 */
292
293static void bsd_comp_stats (void *state, struct compstat *stats)
294  {
295    struct bsd_db *db = (struct bsd_db *) state;
296
297    stats->unc_bytes    = db->uncomp_bytes;
298    stats->unc_packets  = db->uncomp_count;
299    stats->comp_bytes   = db->comp_bytes;
300    stats->comp_packets = db->comp_count;
301    stats->inc_bytes    = db->incomp_bytes;
302    stats->inc_packets  = db->incomp_count;
303    stats->in_count     = db->in_count;
304    stats->bytes_out    = db->bytes_out;
305  }
306
307/*
308 * Reset state, as on a CCP ResetReq.
309 */
310
311static void bsd_reset (void *state)
312  {
313    struct bsd_db *db = (struct bsd_db *) state;
314
315    bsd_clear(db);
316
317    db->seqno       = 0;
318    db->clear_count = 0;
319  }
320
321/*
322 * Release the compression structure
323 */
324
325static void bsd_free (void *state)
326{
327	struct bsd_db *db = state;
328
329	if (!db)
330		return;
331
332/*
333 * Release the dictionary
334 */
335	vfree(db->dict);
336	db->dict = NULL;
337/*
338 * Release the string buffer
339 */
340	vfree(db->lens);
341	db->lens = NULL;
342/*
343 * Finally release the structure itself.
344 */
345	kfree(db);
346}
347
348/*
349 * Allocate space for a (de) compressor.
350 */
351
352static void *bsd_alloc (unsigned char *options, int opt_len, int decomp)
353  {
354    int bits;
355    unsigned int hsize, hshift, maxmaxcode;
356    struct bsd_db *db;
357
358    if (opt_len != 3 || options[0] != CI_BSD_COMPRESS || options[1] != 3
359	|| BSD_VERSION(options[2]) != BSD_CURRENT_VERSION)
360      {
361	return NULL;
362      }
363
364    bits = BSD_NBITS(options[2]);
365
366    switch (bits)
367      {
368    case 9:			/* needs 82152 for both directions */
369    case 10:			/* needs 84144 */
370    case 11:			/* needs 88240 */
371    case 12:			/* needs 96432 */
372	hsize = 5003;
373	hshift = 4;
374	break;
375    case 13:			/* needs 176784 */
376	hsize = 9001;
377	hshift = 5;
378	break;
379    case 14:			/* needs 353744 */
380	hsize = 18013;
381	hshift = 6;
382	break;
383    case 15:			/* needs 691440 */
384	hsize = 35023;
385	hshift = 7;
386	break;
387    case 16:			/* needs 1366160--far too much, */
388	/* hsize = 69001; */	/* and 69001 is too big for cptr */
389	/* hshift = 8; */	/* in struct bsd_db */
390	/* break; */
391    default:
392	return NULL;
393      }
394/*
395 * Allocate the main control structure for this instance.
396 */
397    maxmaxcode = MAXCODE(bits);
398    db         = kzalloc(sizeof (struct bsd_db),
399					    GFP_KERNEL);
400    if (!db)
401      {
402	return NULL;
403      }
404
405/*
406 * Allocate space for the dictionary. This may be more than one page in
407 * length.
408 */
409    db->dict = vmalloc(hsize * sizeof(struct bsd_dict));
410    if (!db->dict)
411      {
412	bsd_free (db);
413	return NULL;
414      }
415
416/*
417 * If this is the compression buffer then there is no length data.
418 */
419    if (!decomp)
420      {
421	db->lens = NULL;
422      }
423/*
424 * For decompression, the length information is needed as well.
425 */
426    else
427      {
428        db->lens = vmalloc((maxmaxcode + 1) * sizeof(db->lens[0]));
429	if (!db->lens)
430	  {
431	    bsd_free (db);
432	    return NULL;
433	  }
434      }
435/*
436 * Initialize the data information for the compression code
437 */
438    db->totlen     = sizeof (struct bsd_db)   +
439      		    (sizeof (struct bsd_dict) * hsize);
440
441    db->hsize      = hsize;
442    db->hshift     = hshift;
443    db->maxmaxcode = maxmaxcode;
444    db->maxbits    = bits;
445
446    return (void *) db;
447  }
448
449static void *bsd_comp_alloc (unsigned char *options, int opt_len)
450  {
451    return bsd_alloc (options, opt_len, 0);
452  }
453
454static void *bsd_decomp_alloc (unsigned char *options, int opt_len)
455  {
456    return bsd_alloc (options, opt_len, 1);
457  }
458
459/*
460 * Initialize the database.
461 */
462
463static int bsd_init (void *state, unsigned char *options,
464		     int opt_len, int unit, int debug, int decomp)
465  {
466    struct bsd_db *db = state;
467    int indx;
468
469    if ((opt_len != 3) || (options[0] != CI_BSD_COMPRESS) || (options[1] != 3)
470	|| (BSD_VERSION(options[2]) != BSD_CURRENT_VERSION)
471	|| (BSD_NBITS(options[2]) != db->maxbits)
472	|| (decomp && db->lens == NULL))
473      {
474	return 0;
475      }
476
477    if (decomp)
478      {
479	indx = LAST;
480	do
481	  {
482	    db->lens[indx] = 1;
483	  }
484	while (indx-- > 0);
485      }
486
487    indx = db->hsize;
488    while (indx-- != 0)
489      {
490	db->dict[indx].codem1 = BADCODEM1;
491	db->dict[indx].cptr   = 0;
492      }
493
494    db->unit = unit;
495    db->mru  = 0;
496#ifndef DEBUG
497    if (debug)
498#endif
499      db->debug = 1;
500
501    bsd_reset(db);
502
503    return 1;
504  }
505
506static int bsd_comp_init (void *state, unsigned char *options,
507			  int opt_len, int unit, int opthdr, int debug)
508  {
509    return bsd_init (state, options, opt_len, unit, debug, 0);
510  }
511
512static int bsd_decomp_init (void *state, unsigned char *options,
513			    int opt_len, int unit, int opthdr, int mru,
514			    int debug)
515  {
516    return bsd_init (state, options, opt_len, unit, debug, 1);
517  }
518
519/*
520 * Obtain pointers to the various structures in the compression tables
521 */
522
523#define dict_ptrx(p,idx) &(p->dict[idx])
524#define lens_ptrx(p,idx) &(p->lens[idx])
525
526#ifdef DEBUG
527static unsigned short *lens_ptr(struct bsd_db *db, int idx)
528  {
529    if ((unsigned int) idx > (unsigned int) db->maxmaxcode)
530      {
531	printk ("<9>ppp: lens_ptr(%d) > max\n", idx);
532	idx = 0;
533      }
534    return lens_ptrx (db, idx);
535  }
536
537static struct bsd_dict *dict_ptr(struct bsd_db *db, int idx)
538  {
539    if ((unsigned int) idx >= (unsigned int) db->hsize)
540      {
541	printk ("<9>ppp: dict_ptr(%d) > max\n", idx);
542	idx = 0;
543      }
544    return dict_ptrx (db, idx);
545  }
546
547#else
548#define lens_ptr(db,idx) lens_ptrx(db,idx)
549#define dict_ptr(db,idx) dict_ptrx(db,idx)
550#endif
551
552/*
553 * compress a packet
554 *
555 *	The result of this function is the size of the compressed
556 *	packet. A zero is returned if the packet was not compressed
557 *	for some reason, such as the size being larger than uncompressed.
558 *
559 *	One change from the BSD compress command is that when the
560 *	code size expands, we do not output a bunch of padding.
561 */
562
563static int bsd_compress (void *state, unsigned char *rptr, unsigned char *obuf,
564			 int isize, int osize)
565  {
566    struct bsd_db *db;
567    int hshift;
568    unsigned int max_ent;
569    unsigned int n_bits;
570    unsigned int bitno;
571    unsigned long accm;
572    int ent;
573    unsigned long fcode;
574    struct bsd_dict *dictp;
575    unsigned char c;
576    int hval;
577    int disp;
578    int ilen;
579    int mxcode;
580    unsigned char *wptr;
581    int olen;
582
583#define PUTBYTE(v)			\
584  {					\
585    ++olen;				\
586    if (wptr)				\
587      {					\
588	*wptr++ = (unsigned char) (v);	\
589	if (olen >= osize)		\
590	  {				\
591	    wptr = NULL;		\
592	  }				\
593      }					\
594  }
595
596#define OUTPUT(ent)			\
597  {					\
598    bitno -= n_bits;			\
599    accm |= ((ent) << bitno);		\
600    do					\
601      {					\
602	PUTBYTE(accm >> 24);		\
603	accm <<= 8;			\
604	bitno += 8;			\
605      }					\
606    while (bitno <= 24);		\
607  }
608
609  /*
610   * If the protocol is not in the range we're interested in,
611   * just return without compressing the packet.  If it is,
612   * the protocol becomes the first byte to compress.
613   */
614
615    ent = PPP_PROTOCOL(rptr);
616    if (ent < 0x21 || ent > 0xf9)
617      {
618	return 0;
619      }
620
621    db      = (struct bsd_db *) state;
622    hshift  = db->hshift;
623    max_ent = db->max_ent;
624    n_bits  = db->n_bits;
625    bitno   = 32;
626    accm    = 0;
627    mxcode  = MAXCODE (n_bits);
628
629    /* Initialize the output pointers */
630    wptr  = obuf;
631    olen  = PPP_HDRLEN + BSD_OVHD;
632
633    if (osize > isize)
634      {
635	osize = isize;
636      }
637
638    /* This is the PPP header information */
639    if (wptr)
640      {
641	*wptr++ = PPP_ADDRESS(rptr);
642	*wptr++ = PPP_CONTROL(rptr);
643	*wptr++ = 0;
644	*wptr++ = PPP_COMP;
645	*wptr++ = db->seqno >> 8;
646	*wptr++ = db->seqno;
647      }
648
649    /* Skip the input header */
650    rptr  += PPP_HDRLEN;
651    isize -= PPP_HDRLEN;
652    ilen   = ++isize;	/* Low byte of protocol is counted as input */
653
654    while (--ilen > 0)
655      {
656	c     = *rptr++;
657	fcode = BSD_KEY  (ent, c);
658	hval  = BSD_HASH (ent, c, hshift);
659	dictp = dict_ptr (db, hval);
660
661	/* Validate and then check the entry. */
662	if (dictp->codem1 >= max_ent)
663	  {
664	    goto nomatch;
665	  }
666
667	if (dictp->f.fcode == fcode)
668	  {
669	    ent = dictp->codem1 + 1;
670	    continue;	/* found (prefix,suffix) */
671	  }
672
673	/* continue probing until a match or invalid entry */
674	disp = (hval == 0) ? 1 : hval;
675
676	do
677	  {
678	    hval += disp;
679	    if (hval >= db->hsize)
680	      {
681		hval -= db->hsize;
682	      }
683	    dictp = dict_ptr (db, hval);
684	    if (dictp->codem1 >= max_ent)
685	      {
686		goto nomatch;
687	      }
688	  }
689	while (dictp->f.fcode != fcode);
690
691	ent = dictp->codem1 + 1;	/* finally found (prefix,suffix) */
692	continue;
693
694nomatch:
695	OUTPUT(ent);		/* output the prefix */
696
697	/* code -> hashtable */
698	if (max_ent < db->maxmaxcode)
699	  {
700	    struct bsd_dict *dictp2;
701	    struct bsd_dict *dictp3;
702	    int    indx;
703
704	    /* expand code size if needed */
705	    if (max_ent >= mxcode)
706	      {
707		db->n_bits = ++n_bits;
708		mxcode     = MAXCODE (n_bits);
709	      }
710
711	    /* Invalidate old hash table entry using
712	     * this code, and then take it over.
713	     */
714
715	    dictp2 = dict_ptr (db, max_ent + 1);
716	    indx   = dictp2->cptr;
717	    dictp3 = dict_ptr (db, indx);
718
719	    if (dictp3->codem1 == max_ent)
720	      {
721		dictp3->codem1 = BADCODEM1;
722	      }
723
724	    dictp2->cptr   = hval;
725	    dictp->codem1  = max_ent;
726	    dictp->f.fcode = fcode;
727	    db->max_ent    = ++max_ent;
728
729	    if (db->lens)
730	      {
731		unsigned short *len1 = lens_ptr (db, max_ent);
732		unsigned short *len2 = lens_ptr (db, ent);
733		*len1 = *len2 + 1;
734	      }
735	  }
736	ent = c;
737      }
738
739    OUTPUT(ent);		/* output the last code */
740
741    db->bytes_out    += olen - PPP_HDRLEN - BSD_OVHD;
742    db->uncomp_bytes += isize;
743    db->in_count     += isize;
744    ++db->uncomp_count;
745    ++db->seqno;
746
747    if (bitno < 32)
748      {
749	++db->bytes_out; /* must be set before calling bsd_check */
750      }
751
752    /*
753     * Generate the clear command if needed
754     */
755
756    if (bsd_check(db))
757      {
758	OUTPUT (CLEAR);
759      }
760
761    /*
762     * Pad dribble bits of last code with ones.
763     * Do not emit a completely useless byte of ones.
764     */
765
766    if (bitno != 32)
767      {
768	PUTBYTE((accm | (0xff << (bitno-8))) >> 24);
769      }
770
771    /*
772     * Increase code size if we would have without the packet
773     * boundary because the decompressor will do so.
774     */
775
776    if (max_ent >= mxcode && max_ent < db->maxmaxcode)
777      {
778	db->n_bits++;
779      }
780
781    /* If output length is too large then this is an incomplete frame. */
782    if (wptr == NULL)
783      {
784	++db->incomp_count;
785	db->incomp_bytes += isize;
786	olen              = 0;
787      }
788    else /* Count the number of compressed frames */
789      {
790	++db->comp_count;
791	db->comp_bytes += olen;
792      }
793
794    /* Return the resulting output length */
795    return olen;
796#undef OUTPUT
797#undef PUTBYTE
798  }
799
800/*
801 * Update the "BSD Compress" dictionary on the receiver for
802 * incompressible data by pretending to compress the incoming data.
803 */
804
805static void bsd_incomp (void *state, unsigned char *ibuf, int icnt)
806  {
807    (void) bsd_compress (state, ibuf, (char *) 0, icnt, 0);
808  }
809
810/*
811 * Decompress "BSD Compress".
812 *
813 * Because of patent problems, we return DECOMP_ERROR for errors
814 * found by inspecting the input data and for system problems, but
815 * DECOMP_FATALERROR for any errors which could possibly be said to
816 * be being detected "after" decompression.  For DECOMP_ERROR,
817 * we can issue a CCP reset-request; for DECOMP_FATALERROR, we may be
818 * infringing a patent of Motorola's if we do, so we take CCP down
819 * instead.
820 *
821 * Given that the frame has the correct sequence number and a good FCS,
822 * errors such as invalid codes in the input most likely indicate a
823 * bug, so we return DECOMP_FATALERROR for them in order to turn off
824 * compression, even though they are detected by inspecting the input.
825 */
826
827static int bsd_decompress (void *state, unsigned char *ibuf, int isize,
828			   unsigned char *obuf, int osize)
829  {
830    struct bsd_db *db;
831    unsigned int max_ent;
832    unsigned long accm;
833    unsigned int bitno;		/* 1st valid bit in accm */
834    unsigned int n_bits;
835    unsigned int tgtbitno;	/* bitno when we have a code */
836    struct bsd_dict *dictp;
837    int explen;
838    int seq;
839    unsigned int incode;
840    unsigned int oldcode;
841    unsigned int finchar;
842    unsigned char *p;
843    unsigned char *wptr;
844    int adrs;
845    int ctrl;
846    int ilen;
847    int codelen;
848    int extra;
849
850    db       = (struct bsd_db *) state;
851    max_ent  = db->max_ent;
852    accm     = 0;
853    bitno    = 32;		/* 1st valid bit in accm */
854    n_bits   = db->n_bits;
855    tgtbitno = 32 - n_bits;	/* bitno when we have a code */
856
857    /*
858     * Save the address/control from the PPP header
859     * and then get the sequence number.
860     */
861
862    adrs  = PPP_ADDRESS (ibuf);
863    ctrl  = PPP_CONTROL (ibuf);
864
865    seq   = (ibuf[4] << 8) + ibuf[5];
866
867    ibuf += (PPP_HDRLEN + 2);
868    ilen  = isize - (PPP_HDRLEN + 2);
869
870    /*
871     * Check the sequence number and give up if it differs from
872     * the value we're expecting.
873     */
874
875    if (seq != db->seqno)
876      {
877	if (db->debug)
878	  {
879	    printk("bsd_decomp%d: bad sequence # %d, expected %d\n",
880		   db->unit, seq, db->seqno - 1);
881	  }
882	return DECOMP_ERROR;
883      }
884
885    ++db->seqno;
886    db->bytes_out += ilen;
887
888    /*
889     * Fill in the ppp header, but not the last byte of the protocol
890     * (that comes from the decompressed data).
891     */
892
893    wptr    = obuf;
894    *wptr++ = adrs;
895    *wptr++ = ctrl;
896    *wptr++ = 0;
897
898    oldcode = CLEAR;
899    explen  = 3;
900
901    /*
902     * Keep the checkpoint correctly so that incompressible packets
903     * clear the dictionary at the proper times.
904     */
905
906    for (;;)
907      {
908	if (ilen-- <= 0)
909	  {
910	    db->in_count += (explen - 3); /* don't count the header */
911	    break;
912	  }
913
914	/*
915	 * Accumulate bytes until we have a complete code.
916	 * Then get the next code, relying on the 32-bit,
917	 * unsigned accm to mask the result.
918	 */
919
920	bitno -= 8;
921	accm  |= *ibuf++ << bitno;
922	if (tgtbitno < bitno)
923	  {
924	    continue;
925	  }
926
927	incode = accm >> tgtbitno;
928	accm <<= n_bits;
929	bitno += n_bits;
930
931	/*
932	 * The dictionary must only be cleared at the end of a packet.
933	 */
934
935	if (incode == CLEAR)
936	  {
937	    if (ilen > 0)
938	      {
939		if (db->debug)
940		  {
941		    printk("bsd_decomp%d: bad CLEAR\n", db->unit);
942		  }
943		return DECOMP_FATALERROR;	/* probably a bug */
944	      }
945
946	    bsd_clear(db);
947	    break;
948	  }
949
950	if ((incode > max_ent + 2) || (incode > db->maxmaxcode)
951	    || (incode > max_ent && oldcode == CLEAR))
952	  {
953	    if (db->debug)
954	      {
955		printk("bsd_decomp%d: bad code 0x%x oldcode=0x%x ",
956		       db->unit, incode, oldcode);
957		printk("max_ent=0x%x explen=%d seqno=%d\n",
958		       max_ent, explen, db->seqno);
959	      }
960	    return DECOMP_FATALERROR;	/* probably a bug */
961	  }
962
963	/* Special case for KwKwK string. */
964	if (incode > max_ent)
965	  {
966	    finchar = oldcode;
967	    extra   = 1;
968	  }
969	else
970	  {
971	    finchar = incode;
972	    extra   = 0;
973	  }
974
975	codelen = *(lens_ptr (db, finchar));
976	explen += codelen + extra;
977	if (explen > osize)
978	  {
979	    if (db->debug)
980	      {
981		printk("bsd_decomp%d: ran out of mru\n", db->unit);
982#ifdef DEBUG
983		printk("  len=%d, finchar=0x%x, codelen=%d, explen=%d\n",
984		       ilen, finchar, codelen, explen);
985#endif
986	      }
987	    return DECOMP_FATALERROR;
988	  }
989
990	/*
991	 * Decode this code and install it in the decompressed buffer.
992	 */
993
994	wptr += codelen;
995	p     = wptr;
996	while (finchar > LAST)
997	  {
998	    struct bsd_dict *dictp2 = dict_ptr (db, finchar);
999
1000	    dictp = dict_ptr (db, dictp2->cptr);
1001#ifdef DEBUG
1002	    if (--codelen <= 0 || dictp->codem1 != finchar-1)
1003	      {
1004		if (codelen <= 0)
1005		  {
1006		    printk("bsd_decomp%d: fell off end of chain ", db->unit);
1007		    printk("0x%x at 0x%x by 0x%x, max_ent=0x%x\n",
1008			   incode, finchar, dictp2->cptr, max_ent);
1009		  }
1010		else
1011		  {
1012		    if (dictp->codem1 != finchar-1)
1013		      {
1014			printk("bsd_decomp%d: bad code chain 0x%x "
1015			       "finchar=0x%x ",
1016			       db->unit, incode, finchar);
1017
1018			printk("oldcode=0x%x cptr=0x%x codem1=0x%x\n",
1019			       oldcode, dictp2->cptr, dictp->codem1);
1020		      }
1021		  }
1022		return DECOMP_FATALERROR;
1023	      }
1024#endif
1025	    *--p    = dictp->f.hs.suffix;
1026	    finchar = dictp->f.hs.prefix;
1027	  }
1028	*--p = finchar;
1029
1030#ifdef DEBUG
1031	if (--codelen != 0)
1032	  {
1033	    printk("bsd_decomp%d: short by %d after code 0x%x, max_ent=0x%x\n",
1034		   db->unit, codelen, incode, max_ent);
1035	  }
1036#endif
1037
1038	if (extra)		/* the KwKwK case again */
1039	  {
1040	    *wptr++ = finchar;
1041	  }
1042
1043	/*
1044	 * If not first code in a packet, and
1045	 * if not out of code space, then allocate a new code.
1046	 *
1047	 * Keep the hash table correct so it can be used
1048	 * with uncompressed packets.
1049	 */
1050
1051	if (oldcode != CLEAR && max_ent < db->maxmaxcode)
1052	  {
1053	    struct bsd_dict *dictp2, *dictp3;
1054	    unsigned short  *lens1,  *lens2;
1055	    unsigned long fcode;
1056	    int hval, disp, indx;
1057
1058	    fcode = BSD_KEY(oldcode,finchar);
1059	    hval  = BSD_HASH(oldcode,finchar,db->hshift);
1060	    dictp = dict_ptr (db, hval);
1061
1062	    /* look for a free hash table entry */
1063	    if (dictp->codem1 < max_ent)
1064	      {
1065		disp = (hval == 0) ? 1 : hval;
1066		do
1067		  {
1068		    hval += disp;
1069		    if (hval >= db->hsize)
1070		      {
1071			hval -= db->hsize;
1072		      }
1073		    dictp = dict_ptr (db, hval);
1074		  }
1075		while (dictp->codem1 < max_ent);
1076	      }
1077
1078	    /*
1079	     * Invalidate previous hash table entry
1080	     * assigned this code, and then take it over
1081	     */
1082
1083	    dictp2 = dict_ptr (db, max_ent + 1);
1084	    indx   = dictp2->cptr;
1085	    dictp3 = dict_ptr (db, indx);
1086
1087	    if (dictp3->codem1 == max_ent)
1088	      {
1089		dictp3->codem1 = BADCODEM1;
1090	      }
1091
1092	    dictp2->cptr   = hval;
1093	    dictp->codem1  = max_ent;
1094	    dictp->f.fcode = fcode;
1095	    db->max_ent    = ++max_ent;
1096
1097	    /* Update the length of this string. */
1098	    lens1  = lens_ptr (db, max_ent);
1099	    lens2  = lens_ptr (db, oldcode);
1100	    *lens1 = *lens2 + 1;
1101
1102	    /* Expand code size if needed. */
1103	    if (max_ent >= MAXCODE(n_bits) && max_ent < db->maxmaxcode)
1104	      {
1105		db->n_bits = ++n_bits;
1106		tgtbitno   = 32-n_bits;
1107	      }
1108	  }
1109	oldcode = incode;
1110      }
1111
1112    ++db->comp_count;
1113    ++db->uncomp_count;
1114    db->comp_bytes   += isize - BSD_OVHD - PPP_HDRLEN;
1115    db->uncomp_bytes += explen;
1116
1117    if (bsd_check(db))
1118      {
1119	if (db->debug)
1120	  {
1121	    printk("bsd_decomp%d: peer should have cleared dictionary on %d\n",
1122		   db->unit, db->seqno - 1);
1123	  }
1124      }
1125    return explen;
1126  }
1127
1128/*************************************************************
1129 * Table of addresses for the BSD compression module
1130 *************************************************************/
1131
1132static struct compressor ppp_bsd_compress = {
1133	.compress_proto =	CI_BSD_COMPRESS,
1134	.comp_alloc =		bsd_comp_alloc,
1135	.comp_free =		bsd_free,
1136	.comp_init =		bsd_comp_init,
1137	.comp_reset =		bsd_reset,
1138	.compress =		bsd_compress,
1139	.comp_stat =		bsd_comp_stats,
1140	.decomp_alloc =		bsd_decomp_alloc,
1141	.decomp_free =		bsd_free,
1142	.decomp_init =		bsd_decomp_init,
1143	.decomp_reset =		bsd_reset,
1144	.decompress =		bsd_decompress,
1145	.incomp =		bsd_incomp,
1146	.decomp_stat =		bsd_comp_stats,
1147	.owner =		THIS_MODULE
1148};
1149
1150/*************************************************************
1151 * Module support routines
1152 *************************************************************/
1153
1154static int __init bsdcomp_init(void)
1155{
1156	int answer = ppp_register_compressor(&ppp_bsd_compress);
1157	if (answer == 0)
1158		printk(KERN_INFO "PPP BSD Compression module registered\n");
1159	return answer;
1160}
1161
1162static void __exit bsdcomp_cleanup(void)
1163{
1164	ppp_unregister_compressor(&ppp_bsd_compress);
1165}
1166
1167module_init(bsdcomp_init);
1168module_exit(bsdcomp_cleanup);
1169MODULE_LICENSE("Dual BSD/GPL");
1170MODULE_ALIAS("ppp-compress-" __stringify(CI_BSD_COMPRESS));
1171