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 1.4 2004/01/17 05:47:55 carlsonj Exp $
  42  */
  43
  44 #include <sys/types.h>
  45 #include <stdio.h>
  46 #include <stddef.h>
  47 #include <stdlib.h>
  48 #include <string.h>
  49 #include "ppp_defs.h"
  50 #include "ppp-comp.h"
  51
  52 #if DO_BSD_COMPRESS
  53
  54 /*
  55  * PPP "BSD compress" compression
  56  *  The differences between this compression and the classic BSD LZW
  57  *  source are obvious from the requirement that the classic code worked
  58  *  with files while this handles arbitrarily long streams that
  59  *  are broken into packets.  They are:
  60  *
  61  *      When the code size expands, a block of junk is not emitted by
  62  *          the compressor and not expected by the decompressor.
  63  *
  64  *      New codes are not necessarily assigned every time an old
  65  *          code is output by the compressor.  This is because a packet
  66  *          end forces a code to be emitted, but does not imply that a
  67  *          new sequence has been seen.
  68  *
  69  *      The compression ratio is checked at the first end of a packet
  70  *          after the appropriate gap.  Besides simplifying and speeding
  71  *          things up, this makes it more likely that the transmitter
  72  *          and receiver will agree when the dictionary is cleared when
  73  *          compression is not going well.
  74  */
  75
  76 /*
  77  * A dictionary for doing BSD compress.
  78  */
  79 struct bsd_db {
  80     int     totlen;                     /* length of this structure */
  81     u_int   hsize;                      /* size of the hash table */
  82     u_char  hshift;                     /* used in hash function */
  83     u_char  n_bits;                     /* current bits/code */
  84     u_char  maxbits;
  85     u_char  debug;
  86     u_char  unit;
  87     u_short seqno;                      /* sequence number of next packet */
  88     u_int   hdrlen;                     /* header length to preallocate */
  89     u_int   mru;
  90     u_int   maxmaxcode;                 /* largest valid code */
  91     u_int   max_ent;                    /* largest code in use */
  92     u_int   in_count;                   /* uncompressed bytes, aged */
  93     u_int   bytes_out;                  /* compressed bytes, aged */
  94     u_int   ratio;                      /* recent compression ratio */
  95     u_int   checkpoint;                 /* when to next check the ratio */
  96     u_int   clear_count;                /* times dictionary cleared */
  97     u_int   incomp_count;               /* incompressible packets */
  98     u_int   incomp_bytes;               /* incompressible bytes */
  99     u_int   uncomp_count;               /* uncompressed packets */
 100     u_int   uncomp_bytes;               /* uncompressed bytes */
 101     u_int   comp_count;                 /* compressed packets */
 102     u_int   comp_bytes;                 /* compressed bytes */
 103     u_short *lens;                      /* array of lengths of codes */
 104     struct bsd_dict {
 105         union {                         /* hash value */
 106             u_int32_t   fcode;
 107             struct {
 108 #ifdef BSD_LITTLE_ENDIAN
 109                 u_short prefix;         /* preceding code */
 110                 u_char  suffix;         /* last character of new code */
 111                 u_char  pad;
 112 #else
 113                 u_char  pad;
 114                 u_char  suffix;         /* last character of new code */
 115                 u_short prefix;         /* preceding code */
 116 #endif
 117             } hs;
 118         } f;
 119         u_short codem1;                 /* output of hash table -1 */
 120         u_short cptr;                   /* map code to hash table entry */
 121     } dict[1];
 122 };
 123
 124 #define BSD_OVHD        2               /* BSD compress overhead/packet */
 125 #define BSD_INIT_BITS   BSD_MIN_BITS
 126
 127 static void     *bsd_decomp_alloc __P((u_char *options, int opt_len));
 128 static void     bsd_free __P((void *state));
 129 static int      bsd_decomp_init __P((void *state, u_char *options, int opt_len,
 130                                      int unit, int hdrlen, int mru, int debug));
 131 static void     bsd_incomp __P((void *state, u_char *dmsg, int len));
 132 static int      bsd_decompress __P((void *state, u_char *cmp, int inlen,
 133                                     u_char *dmp, int *outlen));
 134 static void     bsd_reset __P((void *state));
 135 static void     bsd_comp_stats __P((void *state, struct compstat *stats));
 136
 137 /*
 138  * Exported procedures.
 139  */
 140 struct compressor ppp_bsd_compress = {
 141     CI_BSD_COMPRESS,            /* compress_proto */
 142     bsd_decomp_alloc,           /* decomp_alloc */
 143     bsd_free,                   /* decomp_free */
 144     bsd_decomp_init,            /* decomp_init */
 145     bsd_reset,                  /* decomp_reset */
 146     bsd_decompress,             /* decompress */
 147     bsd_incomp,                 /* incomp */
 148     bsd_comp_stats,             /* decomp_stat */
 149 };
 150
 151 /*
 152  * the next two codes should not be changed lightly, as they must not
 153  * lie within the contiguous general code space.
 154  */
 155 #define CLEAR   256                     /* table clear output code */
 156 #define FIRST   257                     /* first free entry */
 157 #define LAST    255
 158
 159 #define MAXCODE(b)      ((1 << (b)) - 1)
 160 #define BADCODEM1       MAXCODE(BSD_MAX_BITS)
 161
 162 #define BSD_HASH(prefix,suffix,hshift)  ((((u_int32_t)(suffix)) << (hshift)) \
 163                                          ^ (u_int32_t)(prefix))
 164 #define BSD_KEY(prefix,suffix)          ((((u_int32_t)(suffix)) << 16) \
 165                                          + (u_int32_t)(prefix))
 166
 167 #define CHECK_GAP       10000           /* Ratio check interval */
 168
 169 #define RATIO_SCALE_LOG 8
 170 #define RATIO_SCALE     (1<<RATIO_SCALE_LOG)
 171 #define RATIO_MAX       (0x7fffffff>>RATIO_SCALE_LOG)
 172
 173 /*
 174  * clear the dictionary
 175  */
 176 static void
 177 bsd_clear(db)
 178     struct bsd_db *db;
 179 {
 180     db->clear_count++;
 181     db->max_ent = FIRST-1;
 182     db->n_bits = BSD_INIT_BITS;
 183     db->ratio = 0;
 184     db->bytes_out = 0;
 185     db->in_count = 0;
 186     db->checkpoint = CHECK_GAP;
 187 }
 188
 189 /*
 190  * If the dictionary is full, then see if it is time to reset it.
 191  *
 192  * Compute the compression ratio using fixed-point arithmetic
 193  * with 8 fractional bits.
 194  *
 195  * Since we have an infinite stream instead of a single file,
 196  * watch only the local compression ratio.
 197  *
 198  * Since both peers must reset the dictionary at the same time even in
 199  * the absence of CLEAR codes (while packets are incompressible), they
 200  * must compute the same ratio.
 201  */
 202 static int                              /* 1=output CLEAR */
 203 bsd_check(db)
 204     struct bsd_db *db;
 205 {
 206     u_int new_ratio;
 207
 208     if (db->in_count >= db->checkpoint) {
 209         /* age the ratio by limiting the size of the counts */
 210         if (db->in_count >= RATIO_MAX
 211             || db->bytes_out >= RATIO_MAX) {
 212             db->in_count -= db->in_count/4;
 213             db->bytes_out -= db->bytes_out/4;
 214         }
 215
 216         db->checkpoint = db->in_count + CHECK_GAP;
 217
 218         if (db->max_ent >= db->maxmaxcode) {
 219             /* Reset the dictionary only if the ratio is worse,
 220              * or if it looks as if it has been poisoned
 221              * by incompressible data.
 222              *
 223              * This does not overflow, because
 224              *  db->in_count <= RATIO_MAX.
 225              */
 226             new_ratio = db->in_count << RATIO_SCALE_LOG;
 227             if (db->bytes_out != 0)
 228                 new_ratio /= db->bytes_out;
 229
 230             if (new_ratio < db->ratio || new_ratio < 1 * RATIO_SCALE) {
 231                 bsd_clear(db);
 232                 return 1;
 233             }
 234             db->ratio = new_ratio;
 235         }
 236     }
 237     return 0;
 238 }
 239
 240 /*
 241  * Return statistics.
 242  */
 243 static void
 244 bsd_comp_stats(state, stats)
 245     void *state;
 246     struct compstat *stats;
 247 {
 248     struct bsd_db *db = (struct bsd_db *) state;
 249     u_int out;
 250
 251     stats->unc_bytes = db->uncomp_bytes;
 252     stats->unc_packets = db->uncomp_count;
 253     stats->comp_bytes = db->comp_bytes;
 254     stats->comp_packets = db->comp_count;
 255     stats->inc_bytes = db->incomp_bytes;
 256     stats->inc_packets = db->incomp_count;
 257     stats->ratio = db->in_count;
 258     out = db->bytes_out;
 259     if (stats->ratio <= 0x7fffff)
 260         stats->ratio <<= 8;
 261     else
 262         out >>= 8;
 263     if (out != 0)
 264         stats->ratio /= out;
 265 }
 266
 267 /*
 268  * Reset state, as on a CCP ResetReq.
 269  */
 270 static void
 271 bsd_reset(state)
 272     void *state;
 273 {
 274     struct bsd_db *db = (struct bsd_db *) state;
 275
 276     db->seqno = 0;
 277     bsd_clear(db);
 278     db->clear_count = 0;
 279 }
 280
 281 /*
 282  * Allocate space for a (de) compressor.
 283  */
 284 static void *
 285 bsd_alloc(options, opt_len, decomp)
 286     u_char *options;
 287     int opt_len, decomp;
 288 {
 289     int bits;
 290     u_int newlen, hsize, hshift, maxmaxcode;
 291     struct bsd_db *db;
 292
 293     if (opt_len != 3 || options[0] != CI_BSD_COMPRESS || options[1] != 3
 294         || BSD_VERSION(options[2]) != BSD_CURRENT_VERSION)
 295         return NULL;
 296
 297     bits = BSD_NBITS(options[2]);
 298     switch (bits) {
 299     case 9:                     /* needs 82152 for both directions */
 300     case 10:                    /* needs 84144 */
 301     case 11:                    /* needs 88240 */
 302     case 12:                    /* needs 96432 */
 303         hsize = 5003;
 304         hshift = 4;
 305         break;
 306     case 13:                    /* needs 176784 */
 307         hsize = 9001;
 308         hshift = 5;
 309         break;
 310     case 14:                    /* needs 353744 */
 311         hsize = 18013;
 312         hshift = 6;
 313         break;
 314     case 15:                    /* needs 691440 */
 315         hsize = 35023;
 316         hshift = 7;
 317         break;
 318     case 16:                    /* needs 1366160--far too much, */
 319         /* hsize = 69001; */    /* and 69001 is too big for cptr */
 320         /* hshift = 8; */       /* in struct bsd_db */
 321         /* break; */
 322     default:
 323         return NULL;
 324     }
 325
 326     maxmaxcode = MAXCODE(bits);
 327     newlen = sizeof(*db) + (hsize-1) * (sizeof(db->dict[0]));
 328     db = (struct bsd_db *) malloc(newlen);
 329     if (!db)
 330         return NULL;
 331     memset(db, 0, sizeof(*db) - sizeof(db->dict));
 332
 333     if (!decomp) {
 334         db->lens = NULL;
 335     } else {
 336         db->lens = (u_short *) malloc((maxmaxcode+1) * sizeof(db->lens[0]));
 337         if (!db->lens) {
 338             free(db);
 339             return NULL;
 340         }
 341     }
 342
 343     db->totlen = newlen;
 344     db->hsize = hsize;
 345     db->hshift = hshift;
 346     db->maxmaxcode = maxmaxcode;
 347     db->maxbits = bits;
 348
 349     return (void *) db;
 350 }
 351
 352 static void
 353 bsd_free(state)
 354     void *state;
 355 {
 356     struct bsd_db *db = (struct bsd_db *) state;
 357
 358     if (db->lens)
 359         free(db->lens);
 360     free(db);
 361 }
 362
 363 static void *
 364 bsd_decomp_alloc(options, opt_len)
 365     u_char *options;
 366     int opt_len;
 367 {
 368     return bsd_alloc(options, opt_len, 1);
 369 }
 370
 371 /*
 372  * Initialize the database.
 373  */
 374 static int
 375 bsd_init(db, options, opt_len, unit, hdrlen, mru, debug, decomp)
 376     struct bsd_db *db;
 377     u_char *options;
 378     int opt_len, unit, hdrlen, mru, debug, decomp;
 379 {
 380     int i;
 381
 382     if (opt_len < CILEN_BSD_COMPRESS
 383         || options[0] != CI_BSD_COMPRESS || options[1] != CILEN_BSD_COMPRESS
 384         || BSD_VERSION(options[2]) != BSD_CURRENT_VERSION
 385         || BSD_NBITS(options[2]) != db->maxbits
 386         || decomp && db->lens == NULL)
 387         return 0;
 388
 389     if (decomp) {
 390         i = LAST+1;
 391         while (i != 0)
 392             db->lens[--i] = 1;
 393     }
 394     i = db->hsize;
 395     while (i != 0) {
 396         db->dict[--i].codem1 = BADCODEM1;
 397         db->dict[i].cptr = 0;
 398     }
 399
 400     db->unit = unit;
 401     db->hdrlen = hdrlen;
 402     db->mru = mru;
 403     if (debug)
 404         db->debug = 1;
 405
 406     bsd_reset(db);
 407
 408     return 1;
 409 }
 410
 411 static int
 412 bsd_decomp_init(state, options, opt_len, unit, hdrlen, mru, debug)
 413     void *state;
 414     u_char *options;
 415     int opt_len, unit, hdrlen, mru, debug;
 416 {
 417     return bsd_init((struct bsd_db *) state, options, opt_len,
 418                     unit, hdrlen, mru, debug, 1);
 419 }
 420
 421
 422 /*
 423  * Update the "BSD Compress" dictionary on the receiver for
 424  * incompressible data by pretending to compress the incoming data.
 425  */
 426 static void
 427 bsd_incomp(state, dmsg, mlen)
 428     void *state;
 429     u_char *dmsg;
 430     int mlen;
 431 {
 432     struct bsd_db *db = (struct bsd_db *) state;
 433     u_int hshift = db->hshift;
 434     u_int max_ent = db->max_ent;
 435     u_int n_bits = db->n_bits;
 436     struct bsd_dict *dictp;
 437     u_int32_t fcode;
 438     u_char c;
 439     long hval, disp;
 440     int slen, ilen;
 441     u_int bitno = 7;
 442     u_char *rptr;
 443     u_int ent;
 444
 445     rptr = dmsg;
 446     ent = rptr[0];              /* get the protocol */
 447     if (ent == 0) {
 448         ++rptr;
 449         --mlen;
 450         ent = rptr[0];
 451     }
 452     if ((ent & 1) == 0 || ent < 0x21 || ent > 0xf9)
 453         return;
 454
 455     db->seqno++;
 456     ilen = 1;           /* count the protocol as 1 byte */
 457     ++rptr;
 458     slen = dmsg + mlen - rptr;
 459     ilen += slen;
 460     for (; slen > 0; --slen) {
 461         c = *rptr++;
 462         fcode = BSD_KEY(ent, c);
 463         hval = BSD_HASH(ent, c, hshift);
 464         dictp = &db->dict[hval];
 465
 466         /* validate and then check the entry */
 467         if (dictp->codem1 >= max_ent)
 468             goto nomatch;
 469         if (dictp->f.fcode == fcode) {
 470             ent = dictp->codem1+1;
 471             continue;   /* found (prefix,suffix) */
 472         }
 473
 474         /* continue probing until a match or invalid entry */
 475         disp = (hval == 0) ? 1 : hval;
 476         do {
 477             hval += disp;
 478             if (hval >= db->hsize)
 479                 hval -= db->hsize;
 480             dictp = &db->dict[hval];
 481             if (dictp->codem1 >= max_ent)
 482                 goto nomatch;
 483         } while (dictp->f.fcode != fcode);
 484         ent = dictp->codem1+1;
 485         continue;       /* finally found (prefix,suffix) */
 486
 487     nomatch:            /* output (count) the prefix */
 488         bitno += n_bits;
 489
 490         /* code -> hashtable */
 491         if (max_ent < db->maxmaxcode) {
 492             struct bsd_dict *dictp2;
 493             /* expand code size if needed */
 494             if (max_ent >= MAXCODE(n_bits))
 495                 db->n_bits = ++n_bits;
 496
 497             /* Invalidate previous hash table entry
 498              * assigned this code, and then take it over.
 499              */
 500             dictp2 = &db->dict[max_ent+1];
 501             if (db->dict[dictp2->cptr].codem1 == max_ent)
 502                 db->dict[dictp2->cptr].codem1 = BADCODEM1;
 503             dictp2->cptr = hval;
 504             dictp->codem1 = max_ent;
 505             dictp->f.fcode = fcode;
 506
 507             db->max_ent = ++max_ent;
 508             db->lens[max_ent] = db->lens[ent]+1;
 509         }
 510         ent = c;
 511     }
 512     bitno += n_bits;            /* output (count) the last code */
 513     db->bytes_out += bitno/8;
 514     db->in_count += ilen;
 515     (void)bsd_check(db);
 516
 517     ++db->incomp_count;
 518     db->incomp_bytes += ilen;
 519     ++db->uncomp_count;
 520     db->uncomp_bytes += ilen;
 521
 522     /* Increase code size if we would have without the packet
 523      * boundary and as the decompressor will.
 524      */
 525     if (max_ent >= MAXCODE(n_bits) && max_ent < db->maxmaxcode)
 526         db->n_bits++;
 527 }
 528
 529
 530 /*
 531  * Decompress "BSD Compress"
 532  *
 533  * Because of patent problems, we return DECOMP_ERROR for errors
 534  * found by inspecting the input data and for system problems, but
 535  * DECOMP_FATALERROR for any errors which could possibly be said to
 536  * be being detected "after" decompression.  For DECOMP_ERROR,
 537  * we can issue a CCP reset-request; for DECOMP_FATALERROR, we may be
 538  * infringing a patent of Motorola's if we do, so we take CCP down
 539  * instead.
 540  *
 541  * Given that the frame has the correct sequence number and a good FCS,
 542  * errors such as invalid codes in the input most likely indicate a
 543  * bug, so we return DECOMP_FATALERROR for them in order to turn off
 544  * compression, even though they are detected by inspecting the input.
 545  */
 546 static int
 547 bsd_decompress(state, cmsg, inlen, dmp, outlenp)
 548     void *state;
 549     u_char *cmsg, *dmp;
 550     int inlen, *outlenp;
 551 {
 552     struct bsd_db *db = (struct bsd_db *) state;
 553     u_int max_ent = db->max_ent;
 554     u_int32_t accm = 0;
 555     u_int bitno = 32;           /* 1st valid bit in accm */
 556     u_int n_bits = db->n_bits;
 557     u_int tgtbitno = 32-n_bits; /* bitno when we have a code */
 558     struct bsd_dict *dictp;
 559     int explen, i, seq, len;
 560     u_int incode, oldcode, finchar;
 561     u_char *p, *rptr, *wptr;
 562     int ilen;
 563     int dlen, space, codelen, extra;
 564
 565     rptr = cmsg;
 566     if (*rptr == 0)
 567         ++rptr;
 568     ++rptr;                     /* skip protocol (assumed 0xfd) */
 569     seq = (rptr[0] << 8) + rptr[1];
 570     rptr += BSD_OVHD;
 571     ilen = len = cmsg + inlen - rptr;
 572
 573     /*
 574      * Check the sequence number and give up if it is not what we expect.
 575      */
 576     if (seq != db->seqno++) {
 577         if (db->debug)
 578             printf("bsd_decomp%d: bad sequence # %d, expected %d\n",
 579                    db->unit, seq, db->seqno - 1);
 580         return DECOMP_ERROR;
 581     }
 582
 583     wptr = dmp + db->hdrlen;
 584
 585     oldcode = CLEAR;
 586     explen = 0;
 587     while (len > 0) {
 588         /*
 589          * Accumulate bytes until we have a complete code.
 590          * Then get the next code, relying on the 32-bit,
 591          * unsigned accm to mask the result.
 592          */
 593         bitno -= 8;
 594         accm |= *rptr++ << bitno;
 595         --len;
 596         if (tgtbitno < bitno)
 597             continue;
 598         incode = accm >> tgtbitno;
 599         accm <<= n_bits;
 600         bitno += n_bits;
 601
 602         if (incode == CLEAR) {
 603             /*
 604              * The dictionary must only be cleared at
 605              * the end of a packet.  But there could be an
 606              * empty message block at the end.
 607              */
 608             if (len > 0) {
 609                 if (db->debug)
 610                     printf("bsd_decomp%d: bad CLEAR\n", db->unit);
 611                 return DECOMP_FATALERROR;
 612             }
 613             bsd_clear(db);
 614             explen = ilen = 0;
 615             break;
 616         }
 617
 618         if (incode > max_ent + 2 || incode > db->maxmaxcode
 619             || incode > max_ent && oldcode == CLEAR) {
 620             if (db->debug) {
 621                 printf("bsd_decomp%d: bad code 0x%x oldcode=0x%x ",
 622                        db->unit, incode, oldcode);
 623                 printf("max_ent=0x%x dlen=%d seqno=%d\n",
 624                        max_ent, dlen, db->seqno);
 625             }
 626             return DECOMP_FATALERROR;   /* probably a bug */
 627         }
 628
 629         /* Special case for KwKwK string. */
 630         if (incode > max_ent) {
 631             finchar = oldcode;
 632             extra = 1;
 633         } else {
 634             finchar = incode;
 635             extra = 0;
 636         }
 637
 638         codelen = db->lens[finchar];
 639         explen += codelen + extra;
 640         if (explen > db->mru + 1) {
 641             if (db->debug)
 642                 printf("bsd_decomp%d: ran out of mru\n", db->unit);
 643             return DECOMP_FATALERROR;
 644         }
 645
 646         /*
 647          * Decode this code and install it in the decompressed buffer.
 648          */
 649         p = (wptr += codelen);
 650         while (finchar > LAST) {
 651             dictp = &db->dict[db->dict[finchar].cptr];
 652 #ifdef DEBUG
 653             --codelen;
 654             if (codelen <= 0) {
 655                 printf("bsd_decomp%d: fell off end of chain ", db->unit);
 656                 printf("0x%x at 0x%x by 0x%x, max_ent=0x%x\n",
 657                        incode, finchar, db->dict[finchar].cptr, max_ent);
 658                 return DECOMP_FATALERROR;
 659             }
 660             if (dictp->codem1 != finchar-1) {
 661                 printf("bsd_decomp%d: bad code chain 0x%x finchar=0x%x ",
 662                        db->unit, incode, finchar);
 663                 printf("oldcode=0x%x cptr=0x%x codem1=0x%x\n", oldcode,
 664                        db->dict[finchar].cptr, dictp->codem1);
 665                 return DECOMP_FATALERROR;
 666             }
 667 #endif
 668             *--p = dictp->f.hs.suffix;
 669             finchar = dictp->f.hs.prefix;
 670         }
 671         *--p = finchar;
 672
 673 #ifdef DEBUG
 674         if (--codelen != 0)
 675             printf("bsd_decomp%d: short by %d after code 0x%x, max_ent=0x%x\n",
 676                    db->unit, codelen, incode, max_ent);
 677 #endif
 678
 679         if (extra)              /* the KwKwK case again */
 680             *wptr++ = finchar;
 681
 682         /*
 683          * If not first code in a packet, and
 684          * if not out of code space, then allocate a new code.
 685          *
 686          * Keep the hash table correct so it can be used
 687          * with uncompressed packets.
 688          */
 689         if (oldcode != CLEAR && max_ent < db->maxmaxcode) {
 690             struct bsd_dict *dictp2;
 691             u_int32_t fcode;
 692             int hval, disp;
 693
 694             fcode = BSD_KEY(oldcode,finchar);
 695             hval = BSD_HASH(oldcode,finchar,db->hshift);
 696             dictp = &db->dict[hval];
 697
 698             /* look for a free hash table entry */
 699             if (dictp->codem1 < max_ent) {
 700                 disp = (hval == 0) ? 1 : hval;
 701                 do {
 702                     hval += disp;
 703                     if (hval >= db->hsize)
 704                         hval -= db->hsize;
 705                     dictp = &db->dict[hval];
 706                 } while (dictp->codem1 < max_ent);
 707             }
 708
 709             /*
 710              * Invalidate previous hash table entry
 711              * assigned this code, and then take it over
 712              */
 713             dictp2 = &db->dict[max_ent+1];
 714             if (db->dict[dictp2->cptr].codem1 == max_ent) {
 715                 db->dict[dictp2->cptr].codem1 = BADCODEM1;
 716             }
 717             dictp2->cptr = hval;
 718             dictp->codem1 = max_ent;
 719             dictp->f.fcode = fcode;
 720
 721             db->max_ent = ++max_ent;
 722             db->lens[max_ent] = db->lens[oldcode]+1;
 723
 724             /* Expand code size if needed. */
 725             if (max_ent >= MAXCODE(n_bits) && max_ent < db->maxmaxcode) {
 726                 db->n_bits = ++n_bits;
 727                 tgtbitno = 32-n_bits;
 728             }
 729         }
 730         oldcode = incode;
 731     }
 732     *outlenp = wptr - (dmp + db->hdrlen);
 733
 734     /*
 735      * Keep the checkpoint right so that incompressible packets
 736      * clear the dictionary at the right times.
 737      */
 738     db->bytes_out += ilen;
 739     db->in_count += explen;
 740     if (bsd_check(db) && db->debug) {
 741         printf("bsd_decomp%d: peer should have cleared dictionary\n",
 742                db->unit);
 743     }
 744
 745     ++db->comp_count;
 746     db->comp_bytes += ilen + BSD_OVHD;
 747     ++db->uncomp_count;
 748     db->uncomp_bytes += explen;
 749
 750     return DECOMP_OK;
 751 }
 752 #endif /* DO_BSD_COMPRESS */