initial import of NetBSD tree

1 files changed, 1116 insertions, 0 deletions

diff --git a/sys/net/bsd-comp.c b/sys/net/bsd-comp.c
new file mode 100644
index 00000000000..efe0f02df17
--- /dev/null
+++ b/sys/net/bsd-comp.c
@@ -0,0 +1,1116 @@
+/*	$NetBSD: bsd-comp.c,v 1.1 1995/07/04 06:28:17 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. 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.
+ */
+
+/*
+ * This version is for use with mbufs on BSD-derived systems.
+ *
+ * $Id: bsd-comp.c,v 1.1 1995/10/18 08:53:05 deraadt Exp $
+ */
+
+#include <sys/param.h>
+#include <sys/types.h>
+#include <sys/mbuf.h>
+#include <sys/socket.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;
+    u_int16_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 */
+    u_int16_t *lens;			/* array of lengths of codes */
+    struct bsd_dict {
+	union {				/* hash value */
+	    u_int32_t	fcode;
+	    struct {
+#if BYTE_ORDER == LITTLE_ENDIAN
+		u_int16_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 */
+		u_int16_t prefix;	/* preceding code */
+#endif
+	    } hs;
+	} f;
+	u_int16_t codem1;		/* output of hash table -1 */
+	u_int16_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 __P((u_char *options, int opt_len));
+static void	*bsd_decomp_alloc __P((u_char *options, int opt_len));
+static void	bsd_free __P((void *state));
+static int	bsd_comp_init __P((void *state, u_char *options, int opt_len,
+				   int unit, int hdrlen, int debug));
+static int	bsd_decomp_init __P((void *state, u_char *options, int opt_len,
+				     int unit, int hdrlen, int mru, int debug));
+static int	bsd_compress __P((void *state, struct mbuf **mret,
+				  struct mbuf *mp, int slen, int maxolen));
+static void	bsd_incomp __P((void *state, struct mbuf *dmsg));
+static int	bsd_decompress __P((void *state, struct mbuf *cmp,
+				    struct mbuf **dmpp));
+static void	bsd_reset __P((void *state));
+static void	bsd_comp_stats __P((void *state, struct compstat *stats));
+
+/*
+ * Procedures exported to if_ppp.c.
+ */
+struct compressor ppp_bsd_compress = {
+    CI_BSD_COMPRESS,		/* compress_proto */
+    bsd_comp_alloc,		/* comp_alloc */
+    bsd_free,			/* comp_free */
+    bsd_comp_init,		/* comp_init */
+    bsd_reset,			/* comp_reset */
+    bsd_compress,		/* compress */
+    bsd_comp_stats,		/* comp_stat */
+    bsd_decomp_alloc,		/* decomp_alloc */
+    bsd_free,			/* decomp_free */
+    bsd_decomp_init,		/* decomp_init */
+    bsd_reset,			/* decomp_reset */
+    bsd_decompress,		/* decompress */
+    bsd_incomp,			/* incomp */
+    bsd_comp_stats,		/* decomp_stat */
+};
+
+/*
+ * 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)	((((u_int32_t)(suffix)) << (hshift)) \
+					 ^ (u_int32_t)(prefix))
+#define BSD_KEY(prefix,suffix)		((((u_int32_t)(suffix)) << 16) \
+					 + (u_int32_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)
+
+/*
+ * clear the dictionary
+ */
+static void
+bsd_clear(db)
+    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->incomp_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(db)
+    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(state, 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(state)
+    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(options, opt_len, decomp)
+    u_char *options;
+    int opt_len, 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]));
+    MALLOC(db, struct bsd_db *, newlen, M_DEVBUF, M_NOWAIT);
+    if (!db)
+	return NULL;
+    bzero(db, sizeof(*db) - sizeof(db->dict));
+
+    if (!decomp) {
+	db->lens = NULL;
+    } else {
+	MALLOC(db->lens, u_int16_t *, (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(state)
+    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(options, opt_len)
+    u_char *options;
+    int opt_len;
+{
+    return bsd_alloc(options, opt_len, 0);
+}
+
+static void *
+bsd_decomp_alloc(options, opt_len)
+    u_char *options;
+    int opt_len;
+{
+    return bsd_alloc(options, opt_len, 1);
+}
+
+/*
+ * Initialize the database.
+ */
+static int
+bsd_init(db, options, opt_len, unit, hdrlen, mru, debug, decomp)
+    struct bsd_db *db;
+    u_char *options;
+    int opt_len, unit, hdrlen, mru, debug, 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(state, options, opt_len, unit, hdrlen, debug)
+    void *state;
+    u_char *options;
+    int opt_len, unit, hdrlen, debug;
+{
+    return bsd_init((struct bsd_db *) state, options, opt_len,
+		    unit, hdrlen, 0, debug, 0);
+}
+
+static int
+bsd_decomp_init(state, options, opt_len, unit, hdrlen, mru, debug)
+    void *state;
+    u_char *options;
+    int opt_len, unit, hdrlen, mru, 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(state, mret, mp, slen, maxolen)
+    void *state;
+    struct mbuf **mret;		/* return compressed mbuf chain here */
+    struct mbuf *mp;		/* from here */
+    int slen;			/* uncompressed length */
+    int maxolen;		/* max compressed length */
+{
+    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;
+    u_int32_t accm = 0, fcode;
+    struct bsd_dict *dictp;
+    u_char c;
+    int hval, disp, ent, ilen;
+    struct mbuf *np;
+    u_char *rptr, *wptr;
+    u_char *cp_end;
+    int olen;
+    struct mbuf *m, **mnp;
+
+#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 */
+	if (*mret != NULL) {
+	    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(state, dmsg)
+    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;
+    u_int32_t fcode;
+    u_char c;
+    u_int32_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->incomp_count++;
+    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(state, cmp, dmpp)
+    void *state;
+    struct mbuf *cmp, **dmpp;
+{
+    struct bsd_db *db = (struct bsd_db *) state;
+    u_int max_ent = db->max_ent;
+    u_int32_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;
+    struct mbuf *last;
+
+    /*
+     * 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;
+	    u_int32_t fcode;
+	    u_int32_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 */
+}
+#endif /* DO_BSD_COMPRESS */