/*
   * 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
  ", 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
  ", 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
  ", 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
  ", 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
  ", 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
  ");
  
  	if (!skb_in || !skb_out) {
  		printk(KERN_ERR "bsd_decompress called with NULL parameter
  ");
  		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
  ",
  			       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
  ", 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
  ",
  				       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
  ", db->unit);
  #ifdef DEBUG
  				printk(KERN_DEBUG "  len=%d, finchar=0x%x, codelen=%d,skblen=%d
  ",
  				       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
  ", 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
  ", 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
  ", 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
  ",
  			       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
  ");
  	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);