# isdn_bsdcomp.c

    /*
     * BSD compression module
     *
     * Patched version for ISDN syncPPP written 1997/1998 by Michael Hipp
     * The whole module is now SKB based.
     *
     * Compile with:
     *  gcc -O2 -I/usr/src/linux/include -D__KERNEL__ -DMODULE -c isdn_bsdcomp.c
     */

    /*
     * 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.
     */

    #ifndef MODULE
    #error This file must be compiled as a module.
    #endif

    #include <linux/module.h>

    #include <linux/kernel.h>
    #include <linux/sched.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/malloc.h>
    #include <linux/tty.h>
    #include <linux/errno.h>
    #include <linux/sched.h>	/* to get the struct task_struct */
    #include <linux/string.h>	/* used in new tty drivers */
    #include <linux/signal.h>	/* used in new tty drivers */

    #include <asm/system.h>
    #include <asm/bitops.h>
    #include <asm/segment.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/ppp_defs.h>

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

    #include "isdn_ppp.h"

    #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)
    {
    	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
    		 */
    		if (db->dict) {
    			vfree (db->dict);
    			db->dict = NULL;
    		}

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

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

    /*
     * 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 = (struct bsd_db *) kmalloc (sizeof (struct bsd_db),GFP_KERNEL);
    	if (!db)
    		return NULL;

    	memset (db, 0, sizeof(struct bsd_db));

    	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 = (struct bsd_dict *) vmalloc (hsize * sizeof (struct bsd_dict));
    	if (!db->dict) {
    		bsd_free (db);
    		return NULL;
    	}

    	MOD_INC_USE_COUNT;

    	/*
    	 * 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 = (unsigned short *) vmalloc ((maxmaxcode + 1) *
    			sizeof (db->lens[0]));
    		if (!db->lens) {
    			bsd_free (db); /* calls MOD_DEC_USE_COUNT; */
    			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);

    	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 && 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 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 = {
    	NULL,NULL,		/* prev,next: overwritten by isdn_ppp */
    	CI_BSD_COMPRESS,	/* compress_proto */
    	bsd_alloc,		/* alloc */
    	bsd_free,		/* free */
    	bsd_init,		/* init */
    	bsd_reset,		/* reset */
    	bsd_compress,		/* compress */
    	bsd_decompress,		/* decompress */
    	bsd_incomp,		/* incomp */
    	bsd_stats		/* comp_stat */
    };

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

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

    void cleanup_module(void)
    {
    	isdn_ppp_unregister_compressor (&ippp_bsd_compress);
    }