/*
 * 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(array_size(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(array_size(sizeof(db->lens[0]),
                                              maxmaxcode + 1));
                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_u8(skb_out, (u8)(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_u8(skb_out,
                           (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_u8(skb_out, 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_u8(skb_out, 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);