Merge remote-tracking branch 'origin/master'

[unleashed/lotheac.git] / usr / src / uts / common / io / ppp / spppcomp / bsd-comp.c

/*
 * Copyright 2007 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 *
 * 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.
 */

#pragma ident   "%Z%%M% %I%     %E% SMI"

/*
 * This version is for use with STREAMS in Solaris 2
 *
 * $Id: bsd-comp.c,v 1.20 1996/08/28 06:31:57 paulus Exp $
 */

#include <sys/param.h>
#include <sys/types.h>
#include <sys/kmem.h>
#include <sys/stream.h>
#include <sys/cmn_err.h>
#include <sys/ddi.h>
#include <sys/sunddi.h>
#include <sys/byteorder.h>
#include <net/ppp_defs.h>

/* Defined for platform-neutral include file */
#define PACKETPTR               mblk_t *
#include <net/ppp-comp.h>

#ifndef _BIG_ENDIAN
#define BSD_LITTLE_ENDIAN
#endif

#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 */
        uint_t          hsize;          /* size of the hash table */
        uint32_t        unit;
        uchar_t         hshift;         /* used in hash function */
        uchar_t         n_bits;         /* current bits/code */
        uchar_t         maxbits;
        uchar_t         flags;
        ushort_t        seqno;          /* sequence number of next packet */
        ushort_t        mru;
        uint_t          hdrlen;         /* header length to preallocate */
        uint_t          maxmaxcode;     /* largest valid code */
        uint_t          max_ent;        /* largest code in use */
        uint_t          in_count;       /* uncompressed bytes, aged */
        uint_t          bytes_out;      /* compressed bytes, aged */
        uint_t          ratio;          /* recent compression ratio */
        uint_t          checkpoint;     /* when to next check the ratio */
        uint_t          clear_count;    /* times dictionary cleared */
        uint_t          incomp_count;   /* incompressible packets */
        uint_t          incomp_bytes;   /* incompressible bytes */
        uint_t          uncomp_count;   /* uncompressed packets */
        uint_t          uncomp_bytes;   /* uncompressed bytes */
        uint_t          comp_count;     /* compressed packets */
        uint_t          comp_bytes;     /* compressed bytes */
        ushort_t        *lens;          /* array of lengths of codes */
        struct bsd_dict {
        union {                         /* hash value */
                uint32_t        fcode;
                struct {
#ifdef BSD_LITTLE_ENDIAN
                        ushort_t        prefix; /* preceding code */
                        uchar_t         suffix; /* last character of new code */
                        uchar_t         pad;
#else
                        uchar_t         pad;
                        uchar_t         suffix; /* last character of new code */
                        ushort_t        prefix; /* preceding code */
#endif
                } hs;
        } f;
                ushort_t        codem1;         /* output of hash table -1 */
                ushort_t        cptr;           /* map code to hash entry */
        } dict[1];
};

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

/* db->flags values */
#define DS_DEBUG        0x01
#define DS_TESTIN       0x02
#define DS_TESTOUT      0x04
#define DS_INITDONE     0x08

static void     *bsd_comp_alloc(uchar_t *options, int opt_len);
static void     *bsd_decomp_alloc(uchar_t *options, int opt_len);
static void     bsd_free(void *state);
static int      bsd_comp_init(void *state, uchar_t *options, int opt_len,
                                int unit, int hdrlen, int debug);
static int      bsd_decomp_init(void *state, uchar_t *options, int opt_len,
                                int unit, int hdrlen, int mru, int debug);
static int      bsd_compress(void *state, mblk_t **mret,
                                mblk_t *mp, int slen, int maxolen);
static int      bsd_incomp(void *state, mblk_t *dmsg);
static int      bsd_decompress(void *state, mblk_t **dmpp);
static void     bsd_reset(void *state);
static void     bsd_comp_stats(void *state, struct compstat *stats);
static int      bsd_set_effort(void *xarg, void *rarg, int effortlevel);

/*
 * Procedures exported to ppp_comp.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 */
        bsd_set_effort,                 /* set_effort */
};

/*
 * 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)

#define DECOMP_CHUNK    256

/*
 * bsd_clear()
 *
 * 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;
}

/*
 * bsd_check()
 *
 * 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)
{
        uint_t  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);
}

/*
 * bsd_comp_stats()
 *
 * Return statistics.
 */
static void
bsd_comp_stats(void *state, struct compstat *stats)
{
        struct bsd_db   *db = (struct bsd_db *)state;
        uint_t          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;
        }
}

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

        if (db->hsize != 0) {
                db->seqno = 0;

                bsd_clear(db);

                db->clear_count = 0;
        }
}

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

        if (opt_len != 3 ||
            options[0] != CI_BSD_COMPRESS ||
            options[1] != 3 ||
            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;

        /* XXX: this falls thru - it was originally commented */
        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);
        ilen = newlen = sizeof (*db) + (hsize-1) * sizeof (db->dict[0]);
        if (decomp)
                newlen += (maxmaxcode+1) * sizeof (db->lens[0]);
        db = kmem_alloc(newlen, KM_NOSLEEP);
        if (!db) {
                return (NULL);
        }

        bzero(db, sizeof (*db) - sizeof (db->dict));

        if (!decomp) {
                db->lens = NULL;
        } else {
                db->lens = (ushort_t *)((caddr_t)db + ilen);
        }

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

        return ((void *)db);
}

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

        if (db->hsize != 0) {
                /* XXX feeble attempt to catch bad references. */
                db->hsize = 0;

                kmem_free(db, db->totlen);
        }
}

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

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

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

        if (db->hsize == 0 || 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 = (ushort_t)mru;

        if (debug) {
                db->flags |= DS_DEBUG;
        }

        bsd_reset(db);

        db->flags |= DS_INITDONE;

        return (1);
}

/*
 * bsd_comp_init()
 */
static int
bsd_comp_init(void *state, uchar_t *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));
}

/*
 * bsd_decomp_init()
 */
static int
bsd_decomp_init(void *state, uchar_t *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));
}


/*
 * bsd_compress()
 *
 * 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.
 *
 * N.B. at present, we ignore the hdrlen specified in the comp_init call.
 */
static int                      /* new slen */
bsd_compress(void *state, mblk_t **mretp, mblk_t *mp, int slen, int maxolen)
{
        struct bsd_db   *db = (struct bsd_db *)state;
        int             hshift = db->hshift;
        uint_t          max_ent = db->max_ent;
        uint_t          n_bits = db->n_bits;
        uint_t          bitno = 32;
        uint32_t        accm = 0;
        uint32_t        fcode;
        struct bsd_dict *dictp;
        uchar_t         c;
        int             hval;
        int             disp;
        int             ent;
        int             ilen = slen - (PPP_HDRLEN-1);
        mblk_t          *mret;
        uchar_t         *rptr, *rmax;
        uchar_t         *wptr;
        uchar_t         *cp_end;
        int             olen;
        mblk_t          *m;
        mblk_t          **mnp;
        int             hdlcaddr, hdlcctl;

        ASSERT(db->flags & DS_INITDONE);

#define PUTBYTE(v) {                                            \
        if (wptr) {                                             \
                *wptr++ = (v);                                  \
                if (wptr >= cp_end) {                           \
                        m->b_wptr = wptr;                       \
                        m = m->b_cont;                          \
                        if (m) {                                \
                                wptr = m->b_wptr;               \
                                cp_end = m->b_datap->db_lim;    \
                        } else {                                \
                                wptr = NULL;                    \
                        }                                       \
                }                                               \
        }                                                       \
        ++olen;                                                 \
}

#define OUTPUT(ent) {                                           \
        bitno -= n_bits;                                        \
        accm |= ((ent) << bitno);                               \
        do {                                                    \
                PUTBYTE(accm >> 24);                            \
                accm <<= 8;                                     \
                bitno += 8;                                     \
        } while (bitno <= 24);                                  \
}

#define ADJRPTR() {                                             \
        if (rptr != NULL) {                                     \
                while (rptr >= rmax) {                          \
                        if ((mp = mp->b_cont) == NULL) {        \
                                rptr = NULL;                    \
                                break;                          \
                        }                                       \
                        rptr = mp->b_rptr;                      \
                        rmax = mp->b_wptr;                      \
                }                                               \
        }                                                       \
}

#define GETBYTE(v) {                                            \
        if (rptr != NULL) {                                     \
                (v) = *rptr++;                                  \
        }                                                       \
}

        if (db->hsize == 0)
                return (-1);

        /*
         * First get the protocol and check that we're
         * interested in this packet.
         */
        *mretp = NULL;
        rptr = mp->b_rptr;
        rmax = mp->b_wptr;

        /* We CANNOT do a pullup here; it's not our buffer to toy with. */
        ADJRPTR();
        GETBYTE(hdlcaddr);
        ADJRPTR();
        GETBYTE(hdlcctl);
        ADJRPTR();
        GETBYTE(ent);
        ADJRPTR();

        /*
         * Per RFC 1977, the protocol field must be compressed using a
         * PFC-like procedure.  Also, all protocols between 0000-3FFF
         * except the two compression protocols must be LZ compressed.
         */
        if (ent == 0) {
                GETBYTE(ent);
                if (rptr == NULL || ent == PPP_COMP || ent == PPP_COMPFRAG)
                        return (0);
        } else {
                if (ent > 0x3F)
                        return (0);
                ilen++;
        }

        /*
         * Don't generate compressed packets that are larger than the
         * source (uncompressed) packet.
         */
        if (maxolen > slen) {
                maxolen = slen;
        }
        if (maxolen < 6)
                maxolen = 6;

        /*
         * Allocate enough message blocks to give maxolen total space
         */
        mnp = &mret;
        for (olen = maxolen; olen > 0; ) {

                m = allocb((olen < 4096? olen: 4096), BPRI_MED);

                *mnp = m;
                if (m == NULL) {
                        if (mnp == &mret)
                                return (0);
                        /* We allocated some; hope for the best. */
                        break;
                }

                mnp = &m->b_cont;
                olen -= m->b_datap->db_lim - m->b_wptr;
        }

        *mnp = NULL;

        m = mret;
        wptr = m->b_wptr;
        cp_end = m->b_datap->db_lim;

        olen = 0;

        /*
         * Copy the PPP header over, changing the protocol,
         * and install the 2-byte sequence number
         */
        *wptr++ = hdlcaddr;
        *wptr++ = hdlcctl;
        *wptr++ = PPP_COMP>>8;          /* change the protocol */
        *wptr++ = PPP_COMP;
        *wptr++ = db->seqno >> 8;
        *wptr++ = db->seqno;

#ifdef DEBUG
        /*
         * If testing output, just garbling the sequence here does the
         * trick.
         */
        if ((db->flags & DS_TESTOUT) && (db->seqno % 100) == 50)
                wptr[-1] ^= 0xAA;
#endif

        ++db->seqno;

        for (;;) {
                ADJRPTR();
                if (rptr == NULL)
                        break;

                GETBYTE(c);

                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;

                        /*
                         * found (prefix,suffix)
                         */
                        continue;
                }

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

                do {
                        hval += disp;
                        if (hval >= db->hsize) {
                                hval -= db->hsize;
                                if (hval >= db->hsize) {
                                        if (db->flags & DS_DEBUG) {
                                                cmn_err(CE_CONT,
                                                    "bsd_comp%d: internal "
                                                    "error\n",
                                                    db->unit);
                                        }
                                        /* Caller will free it all */
                                        return (-1);
                                }
                        }

                        dictp = &db->dict[hval];

                        if (dictp->codem1 >= max_ent) {
                                goto nomatch;
                        }
                } while (dictp->f.fcode != fcode);

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

                continue;

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

                /*
                 * 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 = (ushort_t)hval;
                        dictp->codem1 = max_ent;
                        dictp->f.fcode = fcode;

                        db->max_ent = ++max_ent;
                }

                ent = c;
        }

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

        olen += (32-bitno+7)/8; /* count complete bytes */

        db->bytes_out += olen;
        db->in_count += ilen;

        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);
        }

        /*
         * 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 (wptr == NULL || olen + PPP_HDRLEN + BSD_OVHD >= maxolen) {
                /*
                 * throw away the compressed stuff if it is longer
                 * than uncompressed
                 */
                freemsg(mret);

                mret = NULL;

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

        } else {

                m->b_wptr = wptr;
                if (m->b_cont) {
                        freemsg(m->b_cont);
                        m->b_cont = NULL;
                }

                ++db->comp_count;
                db->comp_bytes += olen + BSD_OVHD;
        }

        *mretp = mret;

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


/*
 * bsd_incomp()
 *
 * Update the "BSD Compress" dictionary on the receiver for
 * incompressible data by pretending to compress the incoming data.
 */
static int
bsd_incomp(void *state, mblk_t *mp)
{
        struct bsd_db   *db = (struct bsd_db *)state;
        uint_t          hshift = db->hshift;
        uint_t          max_ent = db->max_ent;
        uint_t          n_bits = db->n_bits;
        struct bsd_dict *dictp;
        uint32_t        fcode;
        uchar_t         c;
        long            hval;
        long            disp;
        int             slen;
        int             ilen;
        uint_t          bitno = 7;
        uchar_t         *rptr, *rmax;
        uint_t          ent;

        ASSERT(db->flags & DS_INITDONE);

        if (db->hsize == 0)
                return (-1);

        rptr = mp->b_rptr;
        rmax = mp->b_wptr;
        ADJRPTR();
        GETBYTE(ent);   /* address */
        ADJRPTR();
        GETBYTE(ent);   /* control */
        ADJRPTR();
        GETBYTE(ent);   /* protocol high */
        ADJRPTR();

        /*
         * Per RFC 1977, the protocol field must be compressed using a
         * PFC-like procedure.  Also, all protocols between 0000-3FFF
         * except the two compression protocols must be LZ compressed.
         */
        ilen = 1;                       /* count the protocol as 1 byte */
        if (ent == 0) {
                GETBYTE(ent);
                if (rptr == NULL || ent == PPP_COMP || ent == PPP_COMPFRAG)
                        return (0);
        } else {
                if (ent > 0x3F)
                        return (0);
                ilen++;
        }

        db->seqno++;

        for (;;) {

                slen = mp->b_wptr - rptr;
                if (slen <= 0) {
                        mp = mp->b_cont;
                        if (!mp) {
                                break;
                        }

                        rptr = mp->b_rptr;
                        continue;       /* skip zero-length buffers */
                }

                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;
                                        if (hval >= db->hsize) {
                                                if (db->flags & DS_DEBUG) {
                                                        cmn_err(CE_CONT,
                                                            "bsd_incomp%d: "
                                                            "internal error\n",
                                                            db->unit);
                                                }
                                                return (-1);
                                        }
                                }

                                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 = (ushort_t)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++;
        }
        return (0);
#undef ADJRPTR
}


/*
 * bsd_decompress()
 *
 * 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.
 */
static int
bsd_decompress(void *state, mblk_t **dmpp)
{
        mblk_t          *cmsg = *dmpp, *mnext;
        struct bsd_db   *db = (struct bsd_db *)state;
        uint_t          max_ent = db->max_ent;
        uint32_t        accm = 0;
        uint_t          bitno = 32;             /* 1st valid bit in accm */
        uint_t          n_bits = db->n_bits;
        uint_t          tgtbitno = 32 - n_bits; /* bitno when we have a code */
        struct bsd_dict *dictp;
        int             explen;
        int             seq;
        uint_t          incode;
        uint_t          oldcode;
        uint_t          finchar = 0, ofinchar;
        uchar_t         *p;
        uchar_t         *rptr, *rmax;
        uchar_t         *wptr, *prepos;
        mblk_t          *dmsg;
        mblk_t          *mret;
        int             ilen;
        int             dlen;
        int             codelen;
        int             extra;
        int             decode_proto;
        int             blockctr;
        int             outlen;
        int             adrs, ctrl;

        ASSERT(db->flags & DS_INITDONE);

        /* Note: spppcomp already did a pullup to fix the first buffer. */
        *dmpp = NULL;
        rptr = cmsg->b_rptr;
        rmax = cmsg->b_wptr;
        ilen = 0;

        /*
         * Note that we free as we go.  If we fail to decompress,
         * there's nothing good that the caller can do.
         */
#define ADJRPTR()                                       \
        while (rptr >= rmax) {                          \
                mnext = cmsg->b_cont;                   \
                freeb(cmsg);                            \
                if ((cmsg = mnext) == NULL) {           \
                        rptr = NULL;                    \
                        break;                          \
                }                                       \
                rptr = cmsg->b_rptr;                    \
                rmax = cmsg->b_wptr;                    \
                ilen += rmax-rptr;                      \
        }

        /*
         * Save the address/control from the PPP header
         * and then get the sequence number.
         */
        adrs = rptr[0];
        ctrl = rptr[1];
        rptr += 4;
        ADJRPTR();
        seq = rptr == NULL ? 0 : (*rptr++ << 8);
        ADJRPTR();
        if (rptr == NULL) {
                if (db->flags & DS_DEBUG) {
                        cmn_err(CE_CONT, "bsd_decomp%d: bad buffer\n",
                            db->unit);
                }
                return (DECOMP_ERROR);
        }
        seq |= *rptr++;

#ifdef DEBUG
        /*
         * If testing input, just pretending the sequence is bad here
         * does the trick.
         */
        if ((db->flags & DS_TESTIN) && (db->seqno % 300) == 101)
                seq ^= 0x55;
#endif

        /*
         * Check the sequence number and give up if it is not what we expect.
         */
        if (db->hsize == 0 || seq != db->seqno++) {
                freemsg(cmsg);
                if (db->flags & DS_DEBUG) {
                        cmn_err(CE_CONT, "bsd_decomp%d: bad sequence # %d, "
                            "expected %d\n", db->unit, seq, db->seqno - 1);
                }

                return (DECOMP_ERROR);
        }

        /*
         * Allocate one message block to start with.
         */
        if ((dmsg = allocb(DECOMP_CHUNK + db->hdrlen, BPRI_MED)) == NULL) {
                freemsg(cmsg);
                if (db->flags & DS_DEBUG) {
                        cmn_err(CE_CONT,
                            "bsd_decomp%d: can't allocate first buffer\n",
                            db->unit);
                }
                return (DECOMP_ERROR);
        }

        /*
         * Avoid an error that might cause us to allocate all available memory.
         * Enforce a maximum number of blocks to allocate for message. We add
         * a fudge factor of 5 extra blocks, in order to avoid unnecessary
         * DECOMP_ERROR when the code size is small (9).
         */
        blockctr = ((db->mru + 32 + DECOMP_CHUNK - 1) / DECOMP_CHUNK) + 5;

        mret = dmsg;
        dmsg->b_wptr += db->hdrlen;
        dmsg->b_rptr = wptr = dmsg->b_wptr;

        /*
         * Insert PPP header.  This shouldn't be needed!
         */
        *wptr++ = adrs;
        *wptr++ = ctrl;
        prepos = wptr;
        *wptr++ = 0;
        dmsg->b_wptr = wptr;

        explen = dmsg->b_datap->db_lim - wptr;
        oldcode = CLEAR;
        ilen = rmax-rptr;

        outlen = 0;
        decode_proto = 1;
        for (;;) {
                ADJRPTR();
                if (rptr == NULL)
                        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 |= *rptr++ << bitno;

                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 message block at the end.
                         */
                        ADJRPTR();
                        if (rptr != NULL) {
                                freemsg(mret);
                                freemsg(cmsg);
                                if (db->flags & DS_DEBUG) {
                                        cmn_err(CE_CONT,
                                            "bsd_decomp%d: bad CLEAR\n",
                                            db->unit);
                                }

                                return (DECOMP_FATALERROR);
                        }

                        bsd_clear(db);
                        /* Have to keep cleared state variables! */
                        outlen += wptr-dmsg->b_wptr;
                        dmsg->b_wptr = wptr;
                        db->comp_bytes += ilen;
                        ilen = 0;
                        break;
                }

                /*
                 * Special case for KwKwK string
                 */
                ofinchar = finchar;
                if (incode > max_ent) {
                        if (incode > max_ent + 2 ||
                            incode > db->maxmaxcode ||
                            oldcode == CLEAR) {
                                freemsg(cmsg);
                                freemsg(mret);

                                /* probably a bug if we get here */
                                if (db->flags & DS_DEBUG) {
                                        cmn_err(CE_CONT,
                                            "bsd_decomp%d: bad code 0x%x "
                                            "oldcode=0x%x ", db->unit, incode,
                                            oldcode);
                                }

                                return (DECOMP_FATALERROR);
                        }
                        finchar = oldcode;
                        extra = 1;
                } else {
                        finchar = incode;
                        extra = 0;
                }
                codelen = db->lens[finchar];

                /*
                 * Decode this code and install it in the decompressed buffer
                 */
                explen -= codelen + extra;
                if (explen < 0) {
                        /*
                         * Allocate another message block
                         */
                        dlen = wptr - dmsg->b_wptr;
                        outlen += dlen;
                        db->in_count += dlen;
                        dmsg->b_wptr = wptr;
                        dlen = codelen + extra;

                        if (dlen < DECOMP_CHUNK) {
                                dlen = DECOMP_CHUNK;
                        }

                        if ((--blockctr < 0) ||
                            (dmsg->b_cont = allocb(dlen, BPRI_MED)) == NULL) {
                                freemsg(cmsg);
                                freemsg(mret);
                                if (db->flags & DS_DEBUG) {
                                        cmn_err(CE_CONT,
                                            "bsd_decomp%d: %s output "
                                            "buffers; outlen %d+%d\n",
                                            db->unit,
                                            (blockctr < 0 ? "too many" :
                                            "can't allocate"),
                                            outlen, dlen);
                                }
                                return (DECOMP_ERROR);
                        }

                        dmsg = dmsg->b_cont;
                        wptr = dmsg->b_wptr;
                        explen = dmsg->b_datap->db_lim - wptr - codelen -
                            extra;
                }

                p = (wptr += codelen);

                while (finchar > LAST) {
                        dictp = &db->dict[db->dict[finchar].cptr];
                        *--p = dictp->f.hs.suffix;
                        finchar = dictp->f.hs.prefix;
                }

                *--p = finchar;

                if (decode_proto) {
                        decode_proto = 0;
                        /* Wow, is *this* ugly! */
                        if (!(finchar & 1)) {
                                if (p == prepos+1) {
                                        bcopy(p, prepos, wptr-p);
                                        wptr--;
                                        explen++;
                                        db->in_count++;
                                } else {
                                        /* This is safe, but doesn't look it */
                                        *prepos = *p++;
                                        dmsg->b_rptr = p;
                                }
                        }
                }

                if (extra) {    /* the KwKwK case again */
                        *wptr++ = ofinchar;
                }

                /*
                 * 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;
                        int             hval;
                        int             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;
                                                if (hval >= db->hsize) {
                                                        freemsg(cmsg);
                                                        freemsg(mret);
                                                        if (db->flags &
                                                            DS_DEBUG) {
                        cmn_err(CE_CONT, "bsd_decomp%d: internal error\n",
                            db->unit);
                                                        }
                                                        return
                                                            (DECOMP_FATALERROR);
                                                }
                                        }

                                        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 = (ushort_t)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;
        }

        dlen = wptr-dmsg->b_wptr;
        outlen += dlen;
        db->in_count += dlen;
        dmsg->b_wptr = wptr;
        db->bytes_out += ilen;

        /*
         * Keep the checkpoint right so that incompressible packets
         * clear the dictionary at the right times.
         */
        if (bsd_check(db) && (db->flags & DS_DEBUG)) {
                cmn_err(CE_CONT,
                    "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 += outlen;

        *dmpp = mret;

        return (DECOMP_OK);
}

/* ARGSUSED */
static int
bsd_set_effort(void *xarg, void *rarg, int effortlevel)
{
#ifdef DEBUG
        struct bsd_db *xdb = (struct bsd_db *)xarg;
        struct bsd_db *rdb = (struct bsd_db *)rarg;

        if (effortlevel == 42 || effortlevel == 2112) {
                /* corrupt received data. */
                if (rdb != NULL) {
                        rdb->flags |= DS_TESTIN;
                        cmn_err(CE_CONT, "bsd-comp: enabled input testing.");
                }
                if (effortlevel != 2112)
                        return (0);
        }
        if (effortlevel == 2001 || effortlevel == 2112) {
                /* corrupt transmitted data. */
                if (xdb != NULL) {
                        xdb->flags |= DS_TESTOUT;
                        cmn_err(CE_CONT, "bsd-comp: enabled output testing.");
                }
                return (0);
        }
#endif
        return (0);
}
#endif /* DO_BSD_COMPRESS */