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isdn_bsdcomp.c

/*
 * 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/system.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 && 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);

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