isdn_bsdcomp.c

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/*
 * BSD compression module
 *
 * Patched version for ISDN syncPPP written 1997/1998 by Michael Hipp
 * The whole module is now SKB based.
 *
 */

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

/*
 * Original copyright notice:
 *
 * Copyright (c) 1985, 1986 The Regents of the University of California.
 * All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * James A. Woods, derived from original work by Spencer Thomas
 * and Joseph Orost.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *  This product includes software developed by the University of
 *  California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

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

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

#include <linux/if.h>

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

#include <linux/ppp_defs.h>

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

#include "isdn_ppp.h"

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

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

#define BSD_CURRENT_VERSION 1

#define DEBUG 1

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

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

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

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

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

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

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

#define CHECK_GAP   10000       /* Ratio check interval */

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

/*
 * clear the dictionary
 */

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

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

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

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

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

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

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

/*
 * Return statistics.
 */

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

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

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

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

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

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

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

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


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

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

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

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

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

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

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

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

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

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

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

    return (void *)db;
}

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

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

    decomp = db->xmit ? 0 : 1;

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

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

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

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

    db->debug = 1;

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

    return 1;
}

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

    /*
     * Generate the clear command if needed
     */

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

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

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

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

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

#undef OUTPUT
}

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

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

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

    printk(KERN_DEBUG "bsd_decompress called\n");

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

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

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

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

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

    oldcode = CLEAR;

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

module_init(isdn_bsdcomp_init);
module_exit(isdn_bsdcomp_exit);