pppdump/bsd-comp.c

   1 /* Because this code is derived from the 4.3BSD compress source:
   2  *
   3  *
   4  * Copyright (c) 1985, 1986 The Regents of the University of California.
   5  * All rights reserved.
   6  *
   7  * This code is derived from software contributed to Berkeley by
   8  * James A. Woods, derived from original work by Spencer Thomas
   9  * and Joseph Orost.
  10  *
  11  * Redistribution and use in source and binary forms, with or without
  12  * modification, are permitted provided that the following conditions
  13  * are met:
  14  * 1. Redistributions of source code must retain the above copyright
  15  *    notice, this list of conditions and the following disclaimer.
  16  * 2. Redistributions in binary form must reproduce the above copyright
  17  *    notice, this list of conditions and the following disclaimer in the
  18  *    documentation and/or other materials provided with the distribution.
  19  * 3. All advertising materials mentioning features or use of this software
  20  *    must display the following acknowledgement:
  21  *      This product includes software developed by the University of
  22  *      California, Berkeley and its contributors.
  23  * 4. Neither the name of the University nor the names of its contributors
  24  *    may be used to endorse or promote products derived from this software
  25  *    without specific prior written permission.
  26  *
  27  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  28  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  29  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  30  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  31  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  32  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  33  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  34  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  35  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  36  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  37  * SUCH DAMAGE.
  38  */
  39
  40 /*
  41  * $Id: bsd-comp.c,v 1.3 1999/04/16 11:35:59 paulus Exp $
  42  */
  43
  44 #include <sys/types.h>
  45 #include <stddef.h>
  46 #include <stdlib.h>
  47 #include "ppp_defs.h"
  48 #include "ppp-comp.h"
  49
  50 #if DO_BSD_COMPRESS
  51
  52 /*
  53  * PPP "BSD compress" compression
  54  *  The differences between this compression and the classic BSD LZW
  55  *  source are obvious from the requirement that the classic code worked
  56  *  with files while this handles arbitrarily long streams that
  57  *  are broken into packets.  They are:
  58  *
  59  *      When the code size expands, a block of junk is not emitted by
  60  *          the compressor and not expected by the decompressor.
  61  *
  62  *      New codes are not necessarily assigned every time an old
  63  *          code is output by the compressor.  This is because a packet
  64  *          end forces a code to be emitted, but does not imply that a
  65  *          new sequence has been seen.
  66  *
  67  *      The compression ratio is checked at the first end of a packet
  68  *          after the appropriate gap.  Besides simplifying and speeding
  69  *          things up, this makes it more likely that the transmitter
  70  *          and receiver will agree when the dictionary is cleared when
  71  *          compression is not going well.
  72  */
  73
  74 /*
  75  * A dictionary for doing BSD compress.
  76  */
  77 struct bsd_db {
  78     int     totlen;                     /* length of this structure */
  79     u_int   hsize;                      /* size of the hash table */
  80     u_char  hshift;                     /* used in hash function */
  81     u_char  n_bits;                     /* current bits/code */
  82     u_char  maxbits;
  83     u_char  debug;
  84     u_char  unit;
  85     u_short seqno;                      /* sequence number of next packet */
  86     u_int   hdrlen;                     /* header length to preallocate */
  87     u_int   mru;
  88     u_int   maxmaxcode;                 /* largest valid code */
  89     u_int   max_ent;                    /* largest code in use */
  90     u_int   in_count;                   /* uncompressed bytes, aged */
  91     u_int   bytes_out;                  /* compressed bytes, aged */
  92     u_int   ratio;                      /* recent compression ratio */
  93     u_int   checkpoint;                 /* when to next check the ratio */
  94     u_int   clear_count;                /* times dictionary cleared */
  95     u_int   incomp_count;               /* incompressible packets */
  96     u_int   incomp_bytes;               /* incompressible bytes */
  97     u_int   uncomp_count;               /* uncompressed packets */
  98     u_int   uncomp_bytes;               /* uncompressed bytes */
  99     u_int   comp_count;                 /* compressed packets */
 100     u_int   comp_bytes;                 /* compressed bytes */
 101     u_short *lens;                      /* array of lengths of codes */
 102     struct bsd_dict {
 103         union {                         /* hash value */
 104             u_int32_t   fcode;
 105             struct {
 106 #ifdef BSD_LITTLE_ENDIAN
 107                 u_short prefix;         /* preceding code */
 108                 u_char  suffix;         /* last character of new code */
 109                 u_char  pad;
 110 #else
 111                 u_char  pad;
 112                 u_char  suffix;         /* last character of new code */
 113                 u_short prefix;         /* preceding code */
 114 #endif
 115             } hs;
 116         } f;
 117         u_short codem1;                 /* output of hash table -1 */
 118         u_short cptr;                   /* map code to hash table entry */
 119     } dict[1];
 120 };
 121
 122 #define BSD_OVHD        2               /* BSD compress overhead/packet */
 123 #define BSD_INIT_BITS   BSD_MIN_BITS
 124
 125 static void     *bsd_decomp_alloc __P((u_char *options, int opt_len));
 126 static void     bsd_free __P((void *state));
 127 static int      bsd_decomp_init __P((void *state, u_char *options, int opt_len,
 128                                      int unit, int hdrlen, int mru, int debug));
 129 static void     bsd_incomp __P((void *state, u_char *dmsg, int len));
 130 static int      bsd_decompress __P((void *state, u_char *cmp, int inlen,
 131                                     u_char *dmp, int *outlen));
 132 static void     bsd_reset __P((void *state));
 133 static void     bsd_comp_stats __P((void *state, struct compstat *stats));
 134
 135 /*
 136  * Exported procedures.
 137  */
 138 struct compressor ppp_bsd_compress = {
 139     CI_BSD_COMPRESS,            /* compress_proto */
 140     bsd_decomp_alloc,           /* decomp_alloc */
 141     bsd_free,                   /* decomp_free */
 142     bsd_decomp_init,            /* decomp_init */
 143     bsd_reset,                  /* decomp_reset */
 144     bsd_decompress,             /* decompress */
 145     bsd_incomp,                 /* incomp */
 146     bsd_comp_stats,             /* decomp_stat */
 147 };
 148
 149 /*
 150  * the next two codes should not be changed lightly, as they must not
 151  * lie within the contiguous general code space.
 152  */
 153 #define CLEAR   256                     /* table clear output code */
 154 #define FIRST   257                     /* first free entry */
 155 #define LAST    255
 156
 157 #define MAXCODE(b)      ((1 << (b)) - 1)
 158 #define BADCODEM1       MAXCODE(BSD_MAX_BITS)
 159
 160 #define BSD_HASH(prefix,suffix,hshift)  ((((u_int32_t)(suffix)) << (hshift)) \
 161                                          ^ (u_int32_t)(prefix))
 162 #define BSD_KEY(prefix,suffix)          ((((u_int32_t)(suffix)) << 16) \
 163                                          + (u_int32_t)(prefix))
 164
 165 #define CHECK_GAP       10000           /* Ratio check interval */
 166
 167 #define RATIO_SCALE_LOG 8
 168 #define RATIO_SCALE     (1<<RATIO_SCALE_LOG)
 169 #define RATIO_MAX       (0x7fffffff>>RATIO_SCALE_LOG)
 170
 171 /*
 172  * clear the dictionary
 173  */
 174 static void
 175 bsd_clear(db)
 176     struct bsd_db *db;
 177 {
 178     db->clear_count++;
 179     db->max_ent = FIRST-1;
 180     db->n_bits = BSD_INIT_BITS;
 181     db->ratio = 0;
 182     db->bytes_out = 0;
 183     db->in_count = 0;
 184     db->checkpoint = CHECK_GAP;
 185 }
 186
 187 /*
 188  * If the dictionary is full, then see if it is time to reset it.
 189  *
 190  * Compute the compression ratio using fixed-point arithmetic
 191  * with 8 fractional bits.
 192  *
 193  * Since we have an infinite stream instead of a single file,
 194  * watch only the local compression ratio.
 195  *
 196  * Since both peers must reset the dictionary at the same time even in
 197  * the absence of CLEAR codes (while packets are incompressible), they
 198  * must compute the same ratio.
 199  */
 200 static int                              /* 1=output CLEAR */
 201 bsd_check(db)
 202     struct bsd_db *db;
 203 {
 204     u_int new_ratio;
 205
 206     if (db->in_count >= db->checkpoint) {
 207         /* age the ratio by limiting the size of the counts */
 208         if (db->in_count >= RATIO_MAX
 209             || db->bytes_out >= RATIO_MAX) {
 210             db->in_count -= db->in_count/4;
 211             db->bytes_out -= db->bytes_out/4;
 212         }
 213
 214         db->checkpoint = db->in_count + CHECK_GAP;
 215
 216         if (db->max_ent >= db->maxmaxcode) {
 217             /* Reset the dictionary only if the ratio is worse,
 218              * or if it looks as if it has been poisoned
 219              * by incompressible data.
 220              *
 221              * This does not overflow, because
 222              *  db->in_count <= RATIO_MAX.
 223              */
 224             new_ratio = db->in_count << RATIO_SCALE_LOG;
 225             if (db->bytes_out != 0)
 226                 new_ratio /= db->bytes_out;
 227
 228             if (new_ratio < db->ratio || new_ratio < 1 * RATIO_SCALE) {
 229                 bsd_clear(db);
 230                 return 1;
 231             }
 232             db->ratio = new_ratio;
 233         }
 234     }
 235     return 0;
 236 }
 237
 238 /*
 239  * Return statistics.
 240  */
 241 static void
 242 bsd_comp_stats(state, stats)
 243     void *state;
 244     struct compstat *stats;
 245 {
 246     struct bsd_db *db = (struct bsd_db *) state;
 247     u_int out;
 248
 249     stats->unc_bytes = db->uncomp_bytes;
 250     stats->unc_packets = db->uncomp_count;
 251     stats->comp_bytes = db->comp_bytes;
 252     stats->comp_packets = db->comp_count;
 253     stats->inc_bytes = db->incomp_bytes;
 254     stats->inc_packets = db->incomp_count;
 255     stats->ratio = db->in_count;
 256     out = db->bytes_out;
 257     if (stats->ratio <= 0x7fffff)
 258         stats->ratio <<= 8;
 259     else
 260         out >>= 8;
 261     if (out != 0)
 262         stats->ratio /= out;
 263 }
 264
 265 /*
 266  * Reset state, as on a CCP ResetReq.
 267  */
 268 static void
 269 bsd_reset(state)
 270     void *state;
 271 {
 272     struct bsd_db *db = (struct bsd_db *) state;
 273
 274     db->seqno = 0;
 275     bsd_clear(db);
 276     db->clear_count = 0;
 277 }
 278
 279 /*
 280  * Allocate space for a (de) compressor.
 281  */
 282 static void *
 283 bsd_alloc(options, opt_len, decomp)
 284     u_char *options;
 285     int opt_len, decomp;
 286 {
 287     int bits;
 288     u_int newlen, hsize, hshift, maxmaxcode;
 289     struct bsd_db *db;
 290
 291     if (opt_len != 3 || options[0] != CI_BSD_COMPRESS || options[1] != 3
 292         || BSD_VERSION(options[2]) != BSD_CURRENT_VERSION)
 293         return NULL;
 294
 295     bits = BSD_NBITS(options[2]);
 296     switch (bits) {
 297     case 9:                     /* needs 82152 for both directions */
 298     case 10:                    /* needs 84144 */
 299     case 11:                    /* needs 88240 */
 300     case 12:                    /* needs 96432 */
 301         hsize = 5003;
 302         hshift = 4;
 303         break;
 304     case 13:                    /* needs 176784 */
 305         hsize = 9001;
 306         hshift = 5;
 307         break;
 308     case 14:                    /* needs 353744 */
 309         hsize = 18013;
 310         hshift = 6;
 311         break;
 312     case 15:                    /* needs 691440 */
 313         hsize = 35023;
 314         hshift = 7;
 315         break;
 316     case 16:                    /* needs 1366160--far too much, */
 317         /* hsize = 69001; */    /* and 69001 is too big for cptr */
 318         /* hshift = 8; */       /* in struct bsd_db */
 319         /* break; */
 320     default:
 321         return NULL;
 322     }
 323
 324     maxmaxcode = MAXCODE(bits);
 325     newlen = sizeof(*db) + (hsize-1) * (sizeof(db->dict[0]));
 326     db = (struct bsd_db *) malloc(newlen);
 327     if (!db)
 328         return NULL;
 329     memset(db, 0, sizeof(*db) - sizeof(db->dict));
 330
 331     if (!decomp) {
 332         db->lens = NULL;
 333     } else {
 334         db->lens = (u_short *) malloc((maxmaxcode+1) * sizeof(db->lens[0]));
 335         if (!db->lens) {
 336             free(db);
 337             return NULL;
 338         }
 339     }
 340
 341     db->totlen = newlen;
 342     db->hsize = hsize;
 343     db->hshift = hshift;
 344     db->maxmaxcode = maxmaxcode;
 345     db->maxbits = bits;
 346
 347     return (void *) db;
 348 }
 349
 350 static void
 351 bsd_free(state)
 352     void *state;
 353 {
 354     struct bsd_db *db = (struct bsd_db *) state;
 355
 356     if (db->lens)
 357         free(db->lens);
 358     free(db);
 359 }
 360
 361 static void *
 362 bsd_decomp_alloc(options, opt_len)
 363     u_char *options;
 364     int opt_len;
 365 {
 366     return bsd_alloc(options, opt_len, 1);
 367 }
 368
 369 /*
 370  * Initialize the database.
 371  */
 372 static int
 373 bsd_init(db, options, opt_len, unit, hdrlen, mru, debug, decomp)
 374     struct bsd_db *db;
 375     u_char *options;
 376     int opt_len, unit, hdrlen, mru, debug, decomp;
 377 {
 378     int i;
 379
 380     if (opt_len < CILEN_BSD_COMPRESS
 381         || options[0] != CI_BSD_COMPRESS || options[1] != CILEN_BSD_COMPRESS
 382         || BSD_VERSION(options[2]) != BSD_CURRENT_VERSION
 383         || BSD_NBITS(options[2]) != db->maxbits
 384         || decomp && db->lens == NULL)
 385         return 0;
 386
 387     if (decomp) {
 388         i = LAST+1;
 389         while (i != 0)
 390             db->lens[--i] = 1;
 391     }
 392     i = db->hsize;
 393     while (i != 0) {
 394         db->dict[--i].codem1 = BADCODEM1;
 395         db->dict[i].cptr = 0;
 396     }
 397
 398     db->unit = unit;
 399     db->hdrlen = hdrlen;
 400     db->mru = mru;
 401     if (debug)
 402         db->debug = 1;
 403
 404     bsd_reset(db);
 405
 406     return 1;
 407 }
 408
 409 static int
 410 bsd_decomp_init(state, options, opt_len, unit, hdrlen, mru, debug)
 411     void *state;
 412     u_char *options;
 413     int opt_len, unit, hdrlen, mru, debug;
 414 {
 415     return bsd_init((struct bsd_db *) state, options, opt_len,
 416                     unit, hdrlen, mru, debug, 1);
 417 }
 418
 419
 420 /*
 421  * Update the "BSD Compress" dictionary on the receiver for
 422  * incompressible data by pretending to compress the incoming data.
 423  */
 424 static void
 425 bsd_incomp(state, dmsg, mlen)
 426     void *state;
 427     u_char *dmsg;
 428     int mlen;
 429 {
 430     struct bsd_db *db = (struct bsd_db *) state;
 431     u_int hshift = db->hshift;
 432     u_int max_ent = db->max_ent;
 433     u_int n_bits = db->n_bits;
 434     struct bsd_dict *dictp;
 435     u_int32_t fcode;
 436     u_char c;
 437     long hval, disp;
 438     int slen, ilen;
 439     u_int bitno = 7;
 440     u_char *rptr;
 441     u_int ent;
 442
 443     rptr = dmsg;
 444     ent = rptr[0];              /* get the protocol */
 445     if (ent == 0) {
 446         ++rptr;
 447         --mlen;
 448         ent = rptr[0];
 449     }
 450     if ((ent & 1) == 0 || ent < 0x21 || ent > 0xf9)
 451         return;
 452
 453     db->seqno++;
 454     ilen = 1;           /* count the protocol as 1 byte */
 455     ++rptr;
 456     slen = dmsg + mlen - rptr;
 457     ilen += slen;
 458     for (; slen > 0; --slen) {
 459         c = *rptr++;
 460         fcode = BSD_KEY(ent, c);
 461         hval = BSD_HASH(ent, c, hshift);
 462         dictp = &db->dict[hval];
 463
 464         /* validate and then check the entry */
 465         if (dictp->codem1 >= max_ent)
 466             goto nomatch;
 467         if (dictp->f.fcode == fcode) {
 468             ent = dictp->codem1+1;
 469             continue;   /* found (prefix,suffix) */
 470         }
 471
 472         /* continue probing until a match or invalid entry */
 473         disp = (hval == 0) ? 1 : hval;
 474         do {
 475             hval += disp;
 476             if (hval >= db->hsize)
 477                 hval -= db->hsize;
 478             dictp = &db->dict[hval];
 479             if (dictp->codem1 >= max_ent)
 480                 goto nomatch;
 481         } while (dictp->f.fcode != fcode);
 482         ent = dictp->codem1+1;
 483         continue;       /* finally found (prefix,suffix) */
 484
 485     nomatch:            /* output (count) the prefix */
 486         bitno += n_bits;
 487
 488         /* code -> hashtable */
 489         if (max_ent < db->maxmaxcode) {
 490             struct bsd_dict *dictp2;
 491             /* expand code size if needed */
 492             if (max_ent >= MAXCODE(n_bits))
 493                 db->n_bits = ++n_bits;
 494
 495             /* Invalidate previous hash table entry
 496              * assigned this code, and then take it over.
 497              */
 498             dictp2 = &db->dict[max_ent+1];
 499             if (db->dict[dictp2->cptr].codem1 == max_ent)
 500                 db->dict[dictp2->cptr].codem1 = BADCODEM1;
 501             dictp2->cptr = hval;
 502             dictp->codem1 = max_ent;
 503             dictp->f.fcode = fcode;
 504
 505             db->max_ent = ++max_ent;
 506             db->lens[max_ent] = db->lens[ent]+1;
 507         }
 508         ent = c;
 509     }
 510     bitno += n_bits;            /* output (count) the last code */
 511     db->bytes_out += bitno/8;
 512     db->in_count += ilen;
 513     (void)bsd_check(db);
 514
 515     ++db->incomp_count;
 516     db->incomp_bytes += ilen;
 517     ++db->uncomp_count;
 518     db->uncomp_bytes += ilen;
 519
 520     /* Increase code size if we would have without the packet
 521      * boundary and as the decompressor will.
 522      */
 523     if (max_ent >= MAXCODE(n_bits) && max_ent < db->maxmaxcode)
 524         db->n_bits++;
 525 }
 526
 527
 528 /*
 529  * Decompress "BSD Compress"
 530  *
 531  * Because of patent problems, we return DECOMP_ERROR for errors
 532  * found by inspecting the input data and for system problems, but
 533  * DECOMP_FATALERROR for any errors which could possibly be said to
 534  * be being detected "after" decompression.  For DECOMP_ERROR,
 535  * we can issue a CCP reset-request; for DECOMP_FATALERROR, we may be
 536  * infringing a patent of Motorola's if we do, so we take CCP down
 537  * instead.
 538  *
 539  * Given that the frame has the correct sequence number and a good FCS,
 540  * errors such as invalid codes in the input most likely indicate a
 541  * bug, so we return DECOMP_FATALERROR for them in order to turn off
 542  * compression, even though they are detected by inspecting the input.
 543  */
 544 static int
 545 bsd_decompress(state, cmsg, inlen, dmp, outlenp)
 546     void *state;
 547     u_char *cmsg, *dmp;
 548     int inlen, *outlenp;
 549 {
 550     struct bsd_db *db = (struct bsd_db *) state;
 551     u_int max_ent = db->max_ent;
 552     u_int32_t accm = 0;
 553     u_int bitno = 32;           /* 1st valid bit in accm */
 554     u_int n_bits = db->n_bits;
 555     u_int tgtbitno = 32-n_bits; /* bitno when we have a code */
 556     struct bsd_dict *dictp;
 557     int explen, i, seq, len;
 558     u_int incode, oldcode, finchar;
 559     u_char *p, *rptr, *wptr;
 560     int ilen;
 561     int dlen, space, codelen, extra;
 562
 563     rptr = cmsg;
 564     if (*rptr == 0)
 565         ++rptr;
 566     ++rptr;                     /* skip protocol (assumed 0xfd) */
 567     seq = (rptr[0] << 8) + rptr[1];
 568     rptr += BSD_OVHD;
 569     ilen = len = cmsg + inlen - rptr;
 570
 571     /*
 572      * Check the sequence number and give up if it is not what we expect.
 573      */
 574     if (seq != db->seqno++) {
 575         if (db->debug)
 576             printf("bsd_decomp%d: bad sequence # %d, expected %d\n",
 577                    db->unit, seq, db->seqno - 1);
 578         return DECOMP_ERROR;
 579     }
 580
 581     wptr = dmp + db->hdrlen;
 582
 583     oldcode = CLEAR;
 584     explen = 0;
 585     while (len > 0) {
 586         /*
 587          * Accumulate bytes until we have a complete code.
 588          * Then get the next code, relying on the 32-bit,
 589          * unsigned accm to mask the result.
 590          */
 591         bitno -= 8;
 592         accm |= *rptr++ << bitno;
 593         --len;
 594         if (tgtbitno < bitno)
 595             continue;
 596         incode = accm >> tgtbitno;
 597         accm <<= n_bits;
 598         bitno += n_bits;
 599
 600         if (incode == CLEAR) {
 601             /*
 602              * The dictionary must only be cleared at
 603              * the end of a packet.  But there could be an
 604              * empty message block at the end.
 605              */
 606             if (len > 0) {
 607                 if (db->debug)
 608                     printf("bsd_decomp%d: bad CLEAR\n", db->unit);
 609                 return DECOMP_FATALERROR;
 610             }
 611             bsd_clear(db);
 612             explen = ilen = 0;
 613             break;
 614         }
 615
 616         if (incode > max_ent + 2 || incode > db->maxmaxcode
 617             || incode > max_ent && oldcode == CLEAR) {
 618             if (db->debug) {
 619                 printf("bsd_decomp%d: bad code 0x%x oldcode=0x%x ",
 620                        db->unit, incode, oldcode);
 621                 printf("max_ent=0x%x dlen=%d seqno=%d\n",
 622                        max_ent, dlen, db->seqno);
 623             }
 624             return DECOMP_FATALERROR;   /* probably a bug */
 625         }
 626
 627         /* Special case for KwKwK string. */
 628         if (incode > max_ent) {
 629             finchar = oldcode;
 630             extra = 1;
 631         } else {
 632             finchar = incode;
 633             extra = 0;
 634         }
 635
 636         codelen = db->lens[finchar];
 637         explen += codelen + extra;
 638         if (explen > db->mru + 1) {
 639             if (db->debug)
 640                 printf("bsd_decomp%d: ran out of mru\n", db->unit);
 641             return DECOMP_FATALERROR;
 642         }
 643
 644         /*
 645          * Decode this code and install it in the decompressed buffer.
 646          */
 647         p = (wptr += codelen);
 648         while (finchar > LAST) {
 649             dictp = &db->dict[db->dict[finchar].cptr];
 650 #ifdef DEBUG
 651             --codelen;
 652             if (codelen <= 0) {
 653                 printf("bsd_decomp%d: fell off end of chain ", db->unit);
 654                 printf("0x%x at 0x%x by 0x%x, max_ent=0x%x\n",
 655                        incode, finchar, db->dict[finchar].cptr, max_ent);
 656                 return DECOMP_FATALERROR;
 657             }
 658             if (dictp->codem1 != finchar-1) {
 659                 printf("bsd_decomp%d: bad code chain 0x%x finchar=0x%x ",
 660                        db->unit, incode, finchar);
 661                 printf("oldcode=0x%x cptr=0x%x codem1=0x%x\n", oldcode,
 662                        db->dict[finchar].cptr, dictp->codem1);
 663                 return DECOMP_FATALERROR;
 664             }
 665 #endif
 666             *--p = dictp->f.hs.suffix;
 667             finchar = dictp->f.hs.prefix;
 668         }
 669         *--p = finchar;
 670
 671 #ifdef DEBUG
 672         if (--codelen != 0)
 673             printf("bsd_decomp%d: short by %d after code 0x%x, max_ent=0x%x\n",
 674                    db->unit, codelen, incode, max_ent);
 675 #endif
 676
 677         if (extra)              /* the KwKwK case again */
 678             *wptr++ = finchar;
 679
 680         /*
 681          * If not first code in a packet, and
 682          * if not out of code space, then allocate a new code.
 683          *
 684          * Keep the hash table correct so it can be used
 685          * with uncompressed packets.
 686          */
 687         if (oldcode != CLEAR && max_ent < db->maxmaxcode) {
 688             struct bsd_dict *dictp2;
 689             u_int32_t fcode;
 690             int hval, disp;
 691
 692             fcode = BSD_KEY(oldcode,finchar);
 693             hval = BSD_HASH(oldcode,finchar,db->hshift);
 694             dictp = &db->dict[hval];
 695
 696             /* look for a free hash table entry */
 697             if (dictp->codem1 < max_ent) {
 698                 disp = (hval == 0) ? 1 : hval;
 699                 do {
 700                     hval += disp;
 701                     if (hval >= db->hsize)
 702                         hval -= db->hsize;
 703                     dictp = &db->dict[hval];
 704                 } while (dictp->codem1 < max_ent);
 705             }
 706
 707             /*
 708              * Invalidate previous hash table entry
 709              * assigned this code, and then take it over
 710              */
 711             dictp2 = &db->dict[max_ent+1];
 712             if (db->dict[dictp2->cptr].codem1 == max_ent) {
 713                 db->dict[dictp2->cptr].codem1 = BADCODEM1;
 714             }
 715             dictp2->cptr = hval;
 716             dictp->codem1 = max_ent;
 717             dictp->f.fcode = fcode;
 718
 719             db->max_ent = ++max_ent;
 720             db->lens[max_ent] = db->lens[oldcode]+1;
 721
 722             /* Expand code size if needed. */
 723             if (max_ent >= MAXCODE(n_bits) && max_ent < db->maxmaxcode) {
 724                 db->n_bits = ++n_bits;
 725                 tgtbitno = 32-n_bits;
 726             }
 727         }
 728         oldcode = incode;
 729     }
 730     *outlenp = wptr - (dmp + db->hdrlen);
 731
 732     /*
 733      * Keep the checkpoint right so that incompressible packets
 734      * clear the dictionary at the right times.
 735      */
 736     db->bytes_out += ilen;
 737     db->in_count += explen;
 738     if (bsd_check(db) && db->debug) {
 739         printf("bsd_decomp%d: peer should have cleared dictionary\n",
 740                db->unit);
 741     }
 742
 743     ++db->comp_count;
 744     db->comp_bytes += ilen + BSD_OVHD;
 745     ++db->uncomp_count;
 746     db->uncomp_bytes += explen;
 747
 748     return DECOMP_OK;
 749 }
 750 #endif /* DO_BSD_COMPRESS */