/* Because this code is derived from the 4.3BSD compress source:

/* $NetBSD: bsd-comp.c,v 1.23 2024/07/05 04:31:53 rin Exp $ */
/* Id: bsd-comp.c,v 1.6 1996/08/28 06:31:58 paulus Exp */

/* Because this code is derived from the 4.3BSD compress source:
*
*
* 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. 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.
*/

/*
* This version is for use with mbufs on BSD-derived systems.
*/

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: bsd-comp.c,v 1.23 2024/07/05 04:31:53 rin Exp $");

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/mbuf.h>
#include <sys/socket.h>
#include <sys/module.h>
#include <net/if.h>
#include <net/if_types.h>
#include <net/ppp_defs.h>
#include <net/if_ppp.h>

#define PACKETPTR struct mbuf *
#include <net/ppp-comp.h>

#if DO_BSD_COMPRESS
/*
* PPP "BSD compress" compression
* The differences between this compression and the classic BSD LZW
* source are obvious from the requirement that the classic code worked
* with files while this handles arbitrarily long streams that
* are broken into packets. They are:
*
* When the code size expands, a block of junk is not emitted by
* the compressor and not expected by the decompressor.
*
* New codes are not necessarily assigned every time an old
* code is output by the compressor. This is because a packet
* end forces a code to be emitted, but does not imply that a
* new sequence has been seen.
*
* The compression ratio is checked at the first end of a packet
* after the appropriate gap. Besides simplifying and speeding
* things up, this makes it more likely that the transmitter
* and receiver will agree when the dictionary is cleared when
* compression is not going well.
*/

/*
* A dictionary for doing BSD compress.
*/
struct bsd_db {
int totlen; /* length of this structure */
u_int hsize; /* size of the hash table */
u_char hshift; /* used in hash function */
u_char n_bits; /* current bits/code */
u_char maxbits;
u_char debug;
u_char unit;
uint16_t seqno; /* sequence # of next packet */
u_int hdrlen; /* header length to preallocate */
u_int mru;
u_int maxmaxcode; /* largest valid code */
u_int max_ent; /* largest code in use */
u_int in_count; /* uncompressed bytes, aged */
u_int bytes_out; /* compressed bytes, aged */
u_int ratio; /* recent compression ratio */
u_int checkpoint; /* when to next check the ratio */
u_int clear_count; /* times dictionary cleared */
u_int incomp_count; /* incompressible packets */
u_int incomp_bytes; /* incompressible bytes */
u_int uncomp_count; /* uncompressed packets */
u_int uncomp_bytes; /* uncompressed bytes */
u_int comp_count; /* compressed packets */
u_int comp_bytes; /* compressed bytes */
uint16_t *lens; /* array of lengths of codes */
struct bsd_dict {
union { /* hash value */
uint32_t fcode;
struct {
#if BYTE_ORDER == LITTLE_ENDIAN
uint16_t prefix; /* preceding code */
u_char suffix; /* last character of new code */
u_char pad;
#else
u_char pad;
u_char suffix; /* last character of new code */
uint16_t prefix; /* preceding code */
#endif
} hs;
} f;
uint16_t codem1; /* output of hash table -1 */
uint16_t cptr; /* map code to hash table entry */
} dict[1];
};

#define BSD_OVHD 2 /* BSD compress overhead/packet */
#define BSD_INIT_BITS BSD_MIN_BITS

static void *bsd_comp_alloc(u_char *options, int opt_len);
static void *bsd_decomp_alloc(u_char *options, int opt_len);
static void bsd_free(void *state);
static int bsd_comp_init(void *state, u_char *options, int opt_len,
int unit, int hdrlen, int debug);
static int bsd_decomp_init(void *state, u_char *options, int opt_len,
int unit, int hdrlen, int mru, int debug);
static int bsd_compress(void *state, struct mbuf **mret,
struct mbuf *mp, int slen, int maxolen);
static void bsd_incomp(void *state, struct mbuf *dmsg);
static int bsd_decompress(void *state, struct mbuf *cmp,
struct mbuf **dmpp);
static void bsd_reset(void *state);
static void bsd_comp_stats(void *state, struct compstat *stats);

/*
* Procedures exported to if_ppp.c.
*/
static struct compressor ppp_bsd_compress = {
.compress_proto = CI_BSD_COMPRESS,
.comp_alloc = bsd_comp_alloc,
.comp_free = bsd_free,
.comp_init = bsd_comp_init,
.comp_reset = bsd_reset,
.compress = bsd_compress,
.comp_stat = bsd_comp_stats,
.decomp_alloc = bsd_decomp_alloc,
.decomp_free = bsd_free,
.decomp_init = bsd_decomp_init,
.decomp_reset = bsd_reset,
.decompress = bsd_decompress,
.incomp = bsd_incomp,
.decomp_stat = bsd_comp_stats,
};

/*
* 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(BSD_MAX_BITS)

#define BSD_HASH(prefix,suffix,hshift) ((((uint32_t)(suffix)) << (hshift)) \
^ (uint32_t)(prefix))
#define BSD_KEY(prefix,suffix) ((((uint32_t)(suffix)) << 16) \
+ (uint32_t)(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)

static void bsd_clear(struct bsd_db *);
static int bsd_check(struct bsd_db *);
static void *bsd_alloc(u_char *, int, int);
static int bsd_init(struct bsd_db *, u_char *, int, int, int, int,
int, int);

/*
* 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->ratio = 0;
db->bytes_out = 0;
db->in_count = 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 /* 1=output CLEAR */
bsd_check(struct bsd_db *db)
{
u_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/4;
db->bytes_out -= db->bytes_out/4;
}

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_comp_stats(void *state, struct compstat *stats)
{
struct bsd_db *db = (struct bsd_db *) state;
u_int out;

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->ratio = db->in_count;
out = db->bytes_out;
if (stats->ratio <= 0x7fffff)
stats->ratio <<= 8;
else
out >>= 8;
if (out != 0)
stats->ratio /= out;
}

/*
* Reset state, as on a CCP ResetReq.
*/
static void
bsd_reset(void *state)
{
struct bsd_db *db = (struct bsd_db *) state;

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

/*
* Allocate space for a (de) compressor.
*/
static void *
bsd_alloc(u_char *options, int opt_len, int decomp)
{
int bits;
u_int newlen, hsize, hshift, maxmaxcode;
struct bsd_db *db;

if (opt_len < CILEN_BSD_COMPRESS || options[0] != CI_BSD_COMPRESS
|| options[1] != CILEN_BSD_COMPRESS
|| BSD_VERSION(options[2]) != BSD_CURRENT_VERSION)
return NULL;
bits = BSD_NBITS(options[2]);
switch (bits) {
case 9: /* needs 82152 for both directions */
case 10: /* needs 84144 */
case 11: /* needs 88240 */
case 12: /* needs 96432 */
hsize = 5003;
hshift = 4;
break;
case 13: /* needs 176784 */
hsize = 9001;
hshift = 5;
break;
case 14: /* needs 353744 */
hsize = 18013;
hshift = 6;
break;
case 15: /* needs 691440 */
hsize = 35023;
hshift = 7;
break;
case 16: /* needs 1366160--far too much, */
/* hsize = 69001; */ /* and 69001 is too big for cptr */
/* hshift = 8; */ /* in struct bsd_db */
/* break; */
default:
return NULL;
}

maxmaxcode = MAXCODE(bits);
newlen = sizeof(*db) + (hsize-1) * (sizeof(db->dict[0]));
db = malloc(newlen, M_DEVBUF, M_NOWAIT|M_ZERO);
if (!db)
return NULL;

if (!decomp) {
db->lens = NULL;
} else {
db->lens = malloc((maxmaxcode+1) * sizeof(db->lens[0]),
M_DEVBUF, M_NOWAIT);
if (!db->lens) {
free(db, M_DEVBUF);
return NULL;
}
}

db->totlen = newlen;
db->hsize = hsize;
db->hshift = hshift;
db->maxmaxcode = maxmaxcode;
db->maxbits = bits;

return (void *) db;
}

static void
bsd_free(void *state)
{
struct bsd_db *db = (struct bsd_db *) state;

if (db->lens)
free(db->lens, M_DEVBUF);
free(db, M_DEVBUF);
}

static void *
bsd_comp_alloc(u_char *options, int opt_len)
{
return bsd_alloc(options, opt_len, 0);
}

static void *
bsd_decomp_alloc(u_char *options, int opt_len)
{
return bsd_alloc(options, opt_len, 1);
}

/*
* Initialize the database.
*/
static int
bsd_init(struct bsd_db *db, u_char *options, int opt_len, int unit, int hdrlen,
int mru, int debug, int decomp)
{
int i;

if (opt_len < CILEN_BSD_COMPRESS || options[0] != CI_BSD_COMPRESS
|| options[1] != CILEN_BSD_COMPRESS
|| BSD_VERSION(options[2]) != BSD_CURRENT_VERSION
|| BSD_NBITS(options[2]) != db->maxbits
|| (decomp && db->lens == NULL))
return 0;

if (decomp) {
i = LAST+1;
while (i != 0)
db->lens[--i] = 1;
}
i = db->hsize;
while (i != 0) {
db->dict[--i].codem1 = BADCODEM1;
db->dict[i].cptr = 0;
}

db->unit = unit;
db->hdrlen = hdrlen;
db->mru = mru;
#ifndef DEBUG
if (debug)
#endif
db->debug = 1;

bsd_reset(db);

return 1;
}

static int
bsd_comp_init(void *state, u_char *options, int opt_len, int unit, int hdrlen,
int debug)
{
return bsd_init((struct bsd_db *) state, options, opt_len,
unit, hdrlen, 0, debug, 0);
}

static int
bsd_decomp_init(void *state, u_char *options, int opt_len, int unit, int hdrlen,
int mru, int debug)
{
return bsd_init((struct bsd_db *) state, options, opt_len,
unit, hdrlen, mru, debug, 1);
}

/*
* compress a packet
* One change from the BSD compress command is that when the
* code size expands, we do not output a bunch of padding.
*/
int /* new slen */
bsd_compress(void *state,
struct mbuf **mret /* return compressed mbuf chain here */,
struct mbuf *mp /* from here */,
int slen, int maxolen)
{
struct bsd_db *db = (struct bsd_db *) state;
int hshift = db->hshift;
u_int max_ent = db->max_ent;
u_int n_bits = db->n_bits;
u_int bitno = 32;
uint32_t accm = 0, fcode;
struct bsd_dict *dictp;
u_char c;
int hval, disp, ent, ilen;
u_char *rptr, *wptr;
u_char *cp_end;
int olen;
struct mbuf *m;

#define PUTBYTE(v) { \
++olen; \
if (wptr) { \
*wptr++ = (v); \
if (wptr >= cp_end) { \
m->m_len = wptr - mtod(m, u_char *); \
MGET(m->m_next, M_DONTWAIT, MT_DATA); \
m = m->m_next; \
if (m) { \
m->m_len = 0; \
if (maxolen - olen > MLEN) \
MCLGET(m, M_DONTWAIT); \
wptr = mtod(m, u_char *); \
cp_end = wptr + M_TRAILINGSPACE(m); \
} else \
wptr = NULL; \
} \
} \
}

#define OUTPUT(ent) { \
bitno -= n_bits; \
accm |= ((ent) << bitno); \
do { \
PUTBYTE(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.
*/
rptr = mtod(mp, u_char *);
ent = PPP_PROTOCOL(rptr);
if (ent < 0x21 || ent > 0xf9) {
*mret = NULL;
return slen;
}

/* Don't generate compressed packets which are larger than
the uncompressed packet. */
if (maxolen > slen)
maxolen = slen;

/* Allocate one mbuf to start with. */
MGET(m, M_DONTWAIT, MT_DATA);
*mret = m;
if (m != NULL) {
m->m_len = 0;
if (maxolen + db->hdrlen > MLEN)
MCLGET(m, M_DONTWAIT);
m->m_data += db->hdrlen;
wptr = mtod(m, u_char *);
cp_end = wptr + M_TRAILINGSPACE(m);
} else
wptr = cp_end = NULL;

/*
* Copy the PPP header over, changing the protocol,
* and install the 2-byte packet sequence number.
*/
if (wptr) {
*wptr++ = PPP_ADDRESS(rptr); /* assumes the ppp header is */
*wptr++ = PPP_CONTROL(rptr); /* all in one mbuf */
*wptr++ = 0; /* change the protocol */
*wptr++ = PPP_COMP;
*wptr++ = db->seqno >> 8;
*wptr++ = db->seqno;
}
++db->seqno;

olen = 0;
rptr += PPP_HDRLEN;
slen = mp->m_len - PPP_HDRLEN;
ilen = slen + 1;
for (;;) {
if (slen <= 0) {
mp = mp->m_next;
if (!mp)
break;
rptr = mtod(mp, u_char *);
slen = mp->m_len;
if (!slen)
continue; /* handle 0-length buffers */
ilen += slen;
}

slen--;
c = *rptr++;
fcode = BSD_KEY(ent, c);
hval = BSD_HASH(ent, c, hshift);
dictp = &db->dict[hval];

/* Validate and then check the entry. */
if (dictp->codem1 >= max_ent)
goto nomatch;
if (dictp->f.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 = &db->dict[hval];
if (dictp->codem1 >= max_ent)
goto nomatch;
} while (dictp->f.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;
/* expand code size if needed */
if (max_ent >= MAXCODE(n_bits))
db->n_bits = ++n_bits;

/* Invalidate old hash table entry using
* this code, and then take it over.
*/
dictp2 = &db->dict[max_ent+1];
if (db->dict[dictp2->cptr].codem1 == max_ent)
db->dict[dictp2->cptr].codem1 = BADCODEM1;
dictp2->cptr = hval;
dictp->codem1 = max_ent;
dictp->f.fcode = fcode;

db->max_ent = ++max_ent;
}
ent = c;
}

OUTPUT(ent); /* output the last code */
db->bytes_out += olen;
db->in_count += ilen;
if (bitno < 32)
++db->bytes_out; /* count complete bytes */

if (bsd_check(db))
OUTPUT(CLEAR); /* do not count the CLEAR */

/*
* Pad dribble bits of last code with ones.
* Do not emit a completely useless byte of ones.
*/
if (bitno != 32)
PUTBYTE((accm | (0xff << (bitno-8))) >> 24);

if (m != NULL) {
m->m_len = wptr - mtod(m, u_char *);
m->m_next = NULL;
}

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

db->uncomp_bytes += ilen;
++db->uncomp_count;
if (olen + PPP_HDRLEN + BSD_OVHD > maxolen) {
/* throw away the compressed stuff if it is longer than uncompressed */
m_freem(*mret);
*mret = NULL;
++db->incomp_count;
db->incomp_bytes += ilen;
} else {
++db->comp_count;
db->comp_bytes += olen + BSD_OVHD;
}

return olen + PPP_HDRLEN + BSD_OVHD;
#undef OUTPUT
#undef PUTBYTE
}

/*
* 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 mbuf *dmsg)
{
struct bsd_db *db = (struct bsd_db *) state;
u_int hshift = db->hshift;
u_int max_ent = db->max_ent;
u_int n_bits = db->n_bits;
struct bsd_dict *dictp;
uint32_t fcode;
u_char c;
uint32_t hval, disp;
int slen, ilen;
u_int bitno = 7;
u_char *rptr;
u_int ent;

/*
* If the protocol is not in the range we're interested in,
* just return without looking at the packet. If it is,
* the protocol becomes the first byte to "compress".
*/
rptr = mtod(dmsg, u_char *);
ent = PPP_PROTOCOL(rptr);
if (ent < 0x21 || ent > 0xf9)
return;

db->seqno++;
ilen = 1; /* count the protocol as 1 byte */
rptr += PPP_HDRLEN;
slen = dmsg->m_len - PPP_HDRLEN;
for (;;) {
if (slen <= 0) {
dmsg = dmsg->m_next;
if (!dmsg)
break;
rptr = mtod(dmsg, u_char *);
slen = dmsg->m_len;
continue;
}
ilen += slen;

do {
c = *rptr++;
fcode = BSD_KEY(ent, c);
hval = BSD_HASH(ent, c, hshift);
dictp = &db->dict[hval];

/* validate and then check the entry */
if (dictp->codem1 >= max_ent)
goto nomatch;
if (dictp->f.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 = &db->dict[hval];
if (dictp->codem1 >= max_ent)
goto nomatch;
} while (dictp->f.fcode != fcode);
ent = dictp->codem1+1;
continue; /* finally found (prefix,suffix) */

nomatch: /* output (count) the prefix */
bitno += n_bits;

/* code -> hashtable */
if (max_ent < db->maxmaxcode) {
struct bsd_dict *dictp2;
/* expand code size if needed */
if (max_ent >= MAXCODE(n_bits))
db->n_bits = ++n_bits;

/* Invalidate previous hash table entry
* assigned this code, and then take it over.
*/
dictp2 = &db->dict[max_ent+1];
if (db->dict[dictp2->cptr].codem1 == max_ent)
db->dict[dictp2->cptr].codem1 = BADCODEM1;
dictp2->cptr = hval;
dictp->codem1 = max_ent;
dictp->f.fcode = fcode;

db->max_ent = ++max_ent;
db->lens[max_ent] = db->lens[ent]+1;
}
ent = c;
} while (--slen != 0);
}
bitno += n_bits; /* output (count) the last code */
db->bytes_out += bitno/8;
db->in_count += ilen;
(void)bsd_check(db);

++db->incomp_count;
db->incomp_bytes += ilen;
++db->uncomp_count;
db->uncomp_bytes += ilen;

/* Increase code size if we would have without the packet
* boundary and as the decompressor will.
*/
if (max_ent >= MAXCODE(n_bits) && max_ent < db->maxmaxcode)
db->n_bits++;
}

/*
* Decompress "BSD Compress".
*
* Because of patent problems, we return DECOMP_ERROR for errors
* found by inspecting the input data and for system problems, but
* DECOMP_FATALERROR for any errors which could possibly be said to
* be being detected "after" decompression. For DECOMP_ERROR,
* we can issue a CCP reset-request; for DECOMP_FATALERROR, we may be
* infringing a patent of Motorola's if we do, so we take CCP down
* instead.
*
* Given that the frame has the correct sequence number and a good FCS,
* errors such as invalid codes in the input most likely indicate a
* bug, so we return DECOMP_FATALERROR for them in order to turn off
* compression, even though they are detected by inspecting the input.
*/
int
bsd_decompress(void *state, struct mbuf *cmp, struct mbuf **dmpp)
{
struct bsd_db *db = (struct bsd_db *) state;
u_int max_ent = db->max_ent;
uint32_t accm = 0;
u_int bitno = 32; /* 1st valid bit in accm */
u_int n_bits = db->n_bits;
u_int tgtbitno = 32-n_bits; /* bitno when we have a code */
struct bsd_dict *dictp;
int explen, i, seq, len;
u_int incode, oldcode, finchar;
u_char *p, *rptr, *wptr;
struct mbuf *m, *dmp, *mret;
int adrs, ctrl, ilen;
int space, codelen, extra;

/*
* Save the address/control from the PPP header
* and then get the sequence number.
*/
*dmpp = NULL;
rptr = mtod(cmp, u_char *);
adrs = PPP_ADDRESS(rptr);
ctrl = PPP_CONTROL(rptr);
rptr += PPP_HDRLEN;
len = cmp->m_len - PPP_HDRLEN;
seq = 0;
for (i = 0; i < 2; ++i) {
while (len <= 0) {
cmp = cmp->m_next;
if (cmp == NULL)
return DECOMP_ERROR;
rptr = mtod(cmp, u_char *);
len = cmp->m_len;
}
seq = (seq << 8) + *rptr++;
--len;
}

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

/*
* Allocate one mbuf to start with.
*/
MGETHDR(dmp, M_DONTWAIT, MT_DATA);
if (dmp == NULL)
return DECOMP_ERROR;
mret = dmp;
dmp->m_len = 0;
dmp->m_next = NULL;
MCLGET(dmp, M_DONTWAIT);
dmp->m_data += db->hdrlen;
wptr = mtod(dmp, u_char *);
space = M_TRAILINGSPACE(dmp) - PPP_HDRLEN + 1;

/*
* Fill in the ppp header, but not the last byte of the protocol
* (that comes from the decompressed data).
*/
wptr[0] = adrs;
wptr[1] = ctrl;
wptr[2] = 0;
wptr += PPP_HDRLEN - 1;

ilen = len;
oldcode = CLEAR;
explen = 0;
for (;;) {
if (len == 0) {
cmp = cmp->m_next;
if (!cmp) /* quit at end of message */
break;
rptr = mtod(cmp, u_char *);
len = cmp->m_len;
ilen += len;
continue; /* handle 0-length buffers */
}

/*
* 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 |= *rptr++ << bitno;
--len;
if (tgtbitno < bitno)
continue;
incode = accm >> tgtbitno;
accm <<= n_bits;
bitno += n_bits;

if (incode == CLEAR) {
/*
* The dictionary must only be cleared at
* the end of a packet. But there could be an
* empty mbuf at the end.
*/
if (len > 0 || cmp->m_next != NULL) {
while ((cmp = cmp->m_next) != NULL)
len += cmp->m_len;
if (len > 0) {
m_freem(mret);
if (db->debug)
printf("bsd_decomp%d: bad CLEAR\n", db->unit);
return DECOMP_FATALERROR; /* probably a bug */
}
}
bsd_clear(db);
explen = ilen = 0;
break;
}

if (incode > max_ent + 2 || incode > db->maxmaxcode
|| (incode > max_ent && oldcode == CLEAR)) {
m_freem(mret);
if (db->debug) {
printf("bsd_decomp%d: bad code 0x%x oldcode=0x%x ",
db->unit, incode, oldcode);
printf("max_ent=0x%x explen=%d seqno=%d\n",
max_ent, explen, 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 = db->lens[finchar];
explen += codelen + extra;
if (explen > db->mru + 1) {
m_freem(mret);
if (db->debug) {
printf("bsd_decomp%d: ran out of mru\n", db->unit);
#ifdef DEBUG
while ((cmp = cmp->m_next) != NULL)
len += cmp->m_len;
printf(" len=%d, finchar=0x%x, codelen=%d, explen=%d\n",
len, finchar, codelen, explen);
#endif
}
return DECOMP_FATALERROR;
}

/*
* For simplicity, the decoded characters go in a single mbuf,
* so we allocate a single extra cluster mbuf if necessary.
*/
if ((space -= codelen + extra) < 0) {
dmp->m_len = wptr - mtod(dmp, u_char *);
MGET(m, M_DONTWAIT, MT_DATA);
if (m == NULL) {
m_freem(mret);
return DECOMP_ERROR;
}
m->m_len = 0;
m->m_next = NULL;
dmp->m_next = m;
MCLGET(m, M_DONTWAIT);
space = M_TRAILINGSPACE(m) - (codelen + extra);
if (space < 0) {
/* now that's what I call *compression*. */
m_freem(mret);
return DECOMP_ERROR;
}
dmp = m;
wptr = mtod(dmp, u_char *);
}

/*
* Decode this code and install it in the decompressed buffer.
*/
p = (wptr += codelen);
while (finchar > LAST) {
dictp = &db->dict[db->dict[finchar].cptr];
#ifdef DEBUG
if (--codelen <= 0 || dictp->codem1 != finchar-1)
goto bad;
#endif
*--p = dictp->f.hs.suffix;
finchar = dictp->f.hs.prefix;
}
*--p = finchar;

#ifdef DEBUG
if (--codelen != 0)
printf("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 */
*wptr++ = 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;
uint32_t fcode;
uint32_t hval, disp;

fcode = BSD_KEY(oldcode,finchar);
hval = BSD_HASH(oldcode,finchar,db->hshift);
dictp = &db->dict[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 = &db->dict[hval];
} while (dictp->codem1 < max_ent);
}

/*
* Invalidate previous hash table entry
* assigned this code, and then take it over
*/
dictp2 = &db->dict[max_ent+1];
if (db->dict[dictp2->cptr].codem1 == max_ent) {
db->dict[dictp2->cptr].codem1 = BADCODEM1;
}
dictp2->cptr = hval;
dictp->codem1 = max_ent;
dictp->f.fcode = fcode;

db->max_ent = ++max_ent;
db->lens[max_ent] = db->lens[oldcode]+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;
}
dmp->m_len = wptr - mtod(dmp, u_char *);

/*
* Keep the checkpoint right so that incompressible packets
* clear the dictionary at the right times.
*/
db->bytes_out += ilen;
db->in_count += explen;
if (bsd_check(db) && db->debug) {
printf("bsd_decomp%d: peer should have cleared dictionary\n",
db->unit);
}

++db->comp_count;
db->comp_bytes += ilen + BSD_OVHD;
++db->uncomp_count;
db->uncomp_bytes += explen;

*dmpp = mret;
return DECOMP_OK;

#ifdef DEBUG
bad:
if (codelen <= 0) {
printf("bsd_decomp%d: fell off end of chain ", db->unit);
printf("0x%x at 0x%x by 0x%x, max_ent=0x%x\n",
incode, finchar, db->dict[finchar].cptr, max_ent);
} else if (dictp->codem1 != finchar-1) {
printf("bsd_decomp%d: bad code chain 0x%x finchar=0x%x ",
db->unit, incode, finchar);
printf("oldcode=0x%x cptr=0x%x codem1=0x%x\n", oldcode,
db->dict[finchar].cptr, dictp->codem1);
}
m_freem(mret);
return DECOMP_FATALERROR;
#endif /* DEBUG */
}

MODULE(MODULE_CLASS_MISC, ppp_bsdcomp, "if_ppp");

static int
ppp_bsdcomp_modcmd(modcmd_t cmd, void *arg)
{

switch (cmd) {
case MODULE_CMD_INIT:
return ppp_register_compressor(&ppp_bsd_compress, 1);
case MODULE_CMD_FINI:
return ppp_unregister_compressor(&ppp_bsd_compress, 1);
case MODULE_CMD_STAT:
return 0;
default:
return ENOTTY;
}

return ENOTTY;
}
#endif /* DO_BSD_COMPRESS */