lzx.c 32.6 KB
Newer Older
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
/***************************************************************************
 *                        lzx.c - LZX decompression routines               *
 *                           -------------------                           *
 *                                                                         *
 *  maintainer: Jed Wing <jedwin@ugcs.caltech.edu>                         *
 *  source:     modified lzx.c from cabextract v0.5                        *
 *  notes:      This file was taken from cabextract v0.5, which was,       *
 *              itself, a modified version of the lzx decompression code   *
 *              from unlzx.                                                *
 *                                                                         *
 *  platforms:  In its current incarnation, this file has been tested on   *
 *              two different Linux platforms (one, redhat-based, with a   *
 *              2.1.2 glibc and gcc 2.95.x, and the other, Debian, with    *
 *              2.2.4 glibc and both gcc 2.95.4 and gcc 3.0.2).  Both were *
 *              Intel x86 compatible machines.                             *
 ***************************************************************************/

/***************************************************************************
19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35
 *
 *   Copyright(C) Stuart Caie
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
 *
36 37 38
 ***************************************************************************/

#include "lzx.h"
39
#include <stdarg.h>
40 41 42 43
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

44 45 46
#include "windef.h"
#include "winbase.h"

47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182
/* sized types */
typedef unsigned char  UBYTE; /* 8 bits exactly    */
typedef unsigned short UWORD; /* 16 bits (or more) */

/* some constants defined by the LZX specification */
#define LZX_MIN_MATCH                (2)
#define LZX_MAX_MATCH                (257)
#define LZX_NUM_CHARS                (256)
#define LZX_BLOCKTYPE_INVALID        (0)   /* also blocktypes 4-7 invalid */
#define LZX_BLOCKTYPE_VERBATIM       (1)
#define LZX_BLOCKTYPE_ALIGNED        (2)
#define LZX_BLOCKTYPE_UNCOMPRESSED   (3)
#define LZX_PRETREE_NUM_ELEMENTS     (20)
#define LZX_ALIGNED_NUM_ELEMENTS     (8)   /* aligned offset tree #elements */
#define LZX_NUM_PRIMARY_LENGTHS      (7)   /* this one missing from spec! */
#define LZX_NUM_SECONDARY_LENGTHS    (249) /* length tree #elements */

/* LZX huffman defines: tweak tablebits as desired */
#define LZX_PRETREE_MAXSYMBOLS  (LZX_PRETREE_NUM_ELEMENTS)
#define LZX_PRETREE_TABLEBITS   (6)
#define LZX_MAINTREE_MAXSYMBOLS (LZX_NUM_CHARS + 50*8)
#define LZX_MAINTREE_TABLEBITS  (12)
#define LZX_LENGTH_MAXSYMBOLS   (LZX_NUM_SECONDARY_LENGTHS+1)
#define LZX_LENGTH_TABLEBITS    (12)
#define LZX_ALIGNED_MAXSYMBOLS  (LZX_ALIGNED_NUM_ELEMENTS)
#define LZX_ALIGNED_TABLEBITS   (7)

#define LZX_LENTABLE_SAFETY (64) /* we allow length table decoding overruns */

#define LZX_DECLARE_TABLE(tbl) \
  UWORD tbl##_table[(1<<LZX_##tbl##_TABLEBITS) + (LZX_##tbl##_MAXSYMBOLS<<1)];\
  UBYTE tbl##_len  [LZX_##tbl##_MAXSYMBOLS + LZX_LENTABLE_SAFETY]

struct LZXstate
{
    UBYTE *window;         /* the actual decoding window              */
    ULONG window_size;     /* window size (32Kb through 2Mb)          */
    ULONG actual_size;     /* window size when it was first allocated */
    ULONG window_posn;     /* current offset within the window        */
    ULONG R0, R1, R2;      /* for the LRU offset system               */
    UWORD main_elements;   /* number of main tree elements            */
    int   header_read;     /* have we started decoding at all yet?    */
    UWORD block_type;      /* type of this block                      */
    ULONG block_length;    /* uncompressed length of this block       */
    ULONG block_remaining; /* uncompressed bytes still left to decode */
    ULONG frames_read;     /* the number of CFDATA blocks processed   */
    LONG  intel_filesize;  /* magic header value used for transform   */
    LONG  intel_curpos;    /* current offset in transform space       */
    int   intel_started;   /* have we seen any translatable data yet? */

    LZX_DECLARE_TABLE(PRETREE);
    LZX_DECLARE_TABLE(MAINTREE);
    LZX_DECLARE_TABLE(LENGTH);
    LZX_DECLARE_TABLE(ALIGNED);
};

/* LZX decruncher */

/* Microsoft's LZX document and their implementation of the
 * com.ms.util.cab Java package do not concur.
 *
 * In the LZX document, there is a table showing the correlation between
 * window size and the number of position slots. It states that the 1MB
 * window = 40 slots and the 2MB window = 42 slots. In the implementation,
 * 1MB = 42 slots, 2MB = 50 slots. The actual calculation is 'find the
 * first slot whose position base is equal to or more than the required
 * window size'. This would explain why other tables in the document refer
 * to 50 slots rather than 42.
 *
 * The constant NUM_PRIMARY_LENGTHS used in the decompression pseudocode
 * is not defined in the specification.
 *
 * The LZX document does not state the uncompressed block has an
 * uncompressed length field. Where does this length field come from, so
 * we can know how large the block is? The implementation has it as the 24
 * bits following after the 3 blocktype bits, before the alignment
 * padding.
 *
 * The LZX document states that aligned offset blocks have their aligned
 * offset huffman tree AFTER the main and length trees. The implementation
 * suggests that the aligned offset tree is BEFORE the main and length
 * trees.
 *
 * The LZX document decoding algorithm states that, in an aligned offset
 * block, if an extra_bits value is 1, 2 or 3, then that number of bits
 * should be read and the result added to the match offset. This is
 * correct for 1 and 2, but not 3, where just a huffman symbol (using the
 * aligned tree) should be read.
 *
 * Regarding the E8 preprocessing, the LZX document states 'No translation
 * may be performed on the last 6 bytes of the input block'. This is
 * correct.  However, the pseudocode provided checks for the *E8 leader*
 * up to the last 6 bytes. If the leader appears between -10 and -7 bytes
 * from the end, this would cause the next four bytes to be modified, at
 * least one of which would be in the last 6 bytes, which is not allowed
 * according to the spec.
 *
 * The specification states that the huffman trees must always contain at
 * least one element. However, many CAB files contain blocks where the
 * length tree is completely empty (because there are no matches), and
 * this is expected to succeed.
 */


/* LZX uses what it calls 'position slots' to represent match offsets.
 * What this means is that a small 'position slot' number and a small
 * offset from that slot are encoded instead of one large offset for
 * every match.
 * - position_base is an index to the position slot bases
 * - extra_bits states how many bits of offset-from-base data is needed.
 */
static const UBYTE extra_bits[51] = {
     0,  0,  0,  0,  1,  1,  2,  2,  3,  3,  4,  4,  5,  5,  6,  6,
     7,  7,  8,  8,  9,  9, 10, 10, 11, 11, 12, 12, 13, 13, 14, 14,
    15, 15, 16, 16, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17,
    17, 17, 17
};

static const ULONG position_base[51] = {
          0,       1,       2,      3,      4,      6,      8,     12,     16,     24,     32,       48,      64,      96,     128,     192,
        256,     384,     512,    768,   1024,   1536,   2048,   3072,   4096,   6144,   8192,    12288,   16384,   24576,   32768,   49152,
      65536,   98304,  131072, 196608, 262144, 393216, 524288, 655360, 786432, 917504, 1048576, 1179648, 1310720, 1441792, 1572864, 1703936,
    1835008, 1966080, 2097152
};

struct LZXstate *LZXinit(int window)
{
    struct LZXstate *pState=NULL;
    ULONG wndsize = 1 << window;
    int i, posn_slots;

    /* LZX supports window sizes of 2^15 (32Kb) through 2^21 (2Mb) */
    /* if a previously allocated window is big enough, keep it     */
    if (window < 15 || window > 21) return NULL;

    /* allocate state and associated window */
183 184
    pState = HeapAlloc(GetProcessHeap(), 0, sizeof(struct LZXstate));
    if (!(pState->window = HeapAlloc(GetProcessHeap(), 0, wndsize)))
185
    {
186
        HeapFree(GetProcessHeap(), 0, pState);
187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221
        return NULL;
    }
    pState->actual_size = wndsize;
    pState->window_size = wndsize;

    /* calculate required position slots */
    if (window == 20) posn_slots = 42;
    else if (window == 21) posn_slots = 50;
    else posn_slots = window << 1;

    /** alternatively **/
    /* posn_slots=i=0; while (i < wndsize) i += 1 << extra_bits[posn_slots++]; */

    /* initialize other state */
    pState->R0  =  pState->R1  = pState->R2 = 1;
    pState->main_elements   = LZX_NUM_CHARS + (posn_slots << 3);
    pState->header_read     = 0;
    pState->frames_read     = 0;
    pState->block_remaining = 0;
    pState->block_type      = LZX_BLOCKTYPE_INVALID;
    pState->intel_curpos    = 0;
    pState->intel_started   = 0;
    pState->window_posn     = 0;

    /* initialise tables to 0 (because deltas will be applied to them) */
    for (i = 0; i < LZX_MAINTREE_MAXSYMBOLS; i++) pState->MAINTREE_len[i] = 0;
    for (i = 0; i < LZX_LENGTH_MAXSYMBOLS; i++)   pState->LENGTH_len[i]   = 0;

    return pState;
}

void LZXteardown(struct LZXstate *pState)
{
    if (pState)
    {
222 223
        HeapFree(GetProcessHeap(), 0, pState->window);
        HeapFree(GetProcessHeap(), 0, pState);
224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834
    }
}

int LZXreset(struct LZXstate *pState)
{
    int i;

    pState->R0  =  pState->R1  = pState->R2 = 1;
    pState->header_read     = 0;
    pState->frames_read     = 0;
    pState->block_remaining = 0;
    pState->block_type      = LZX_BLOCKTYPE_INVALID;
    pState->intel_curpos    = 0;
    pState->intel_started   = 0;
    pState->window_posn     = 0;

    for (i = 0; i < LZX_MAINTREE_MAXSYMBOLS + LZX_LENTABLE_SAFETY; i++) pState->MAINTREE_len[i] = 0;
    for (i = 0; i < LZX_LENGTH_MAXSYMBOLS + LZX_LENTABLE_SAFETY; i++)   pState->LENGTH_len[i]   = 0;

    return DECR_OK;
}


/* Bitstream reading macros:
 *
 * INIT_BITSTREAM    should be used first to set up the system
 * READ_BITS(var,n)  takes N bits from the buffer and puts them in var
 *
 * ENSURE_BITS(n)    ensures there are at least N bits in the bit buffer
 * PEEK_BITS(n)      extracts (without removing) N bits from the bit buffer
 * REMOVE_BITS(n)    removes N bits from the bit buffer
 *
 * These bit access routines work by using the area beyond the MSB and the
 * LSB as a free source of zeroes. This avoids having to mask any bits.
 * So we have to know the bit width of the bitbuffer variable. This is
 * sizeof(ULONG) * 8, also defined as ULONG_BITS
 */

/* number of bits in ULONG. Note: This must be at multiple of 16, and at
 * least 32 for the bitbuffer code to work (ie, it must be able to ensure
 * up to 17 bits - that's adding 16 bits when there's one bit left, or
 * adding 32 bits when there are no bits left. The code should work fine
 * for machines where ULONG >= 32 bits.
 */
#define ULONG_BITS (sizeof(ULONG)<<3)

#define INIT_BITSTREAM do { bitsleft = 0; bitbuf = 0; } while (0)

#define ENSURE_BITS(n)							\
  while (bitsleft < (n)) {						\
    bitbuf |= ((inpos[1]<<8)|inpos[0]) << (ULONG_BITS-16 - bitsleft);	\
    bitsleft += 16; inpos+=2;						\
  }

#define PEEK_BITS(n)   (bitbuf >> (ULONG_BITS - (n)))
#define REMOVE_BITS(n) ((bitbuf <<= (n)), (bitsleft -= (n)))

#define READ_BITS(v,n) do {						\
  ENSURE_BITS(n);							\
  (v) = PEEK_BITS(n);							\
  REMOVE_BITS(n);							\
} while (0)


/* Huffman macros */

#define TABLEBITS(tbl)   (LZX_##tbl##_TABLEBITS)
#define MAXSYMBOLS(tbl)  (LZX_##tbl##_MAXSYMBOLS)
#define SYMTABLE(tbl)    (pState->tbl##_table)
#define LENTABLE(tbl)    (pState->tbl##_len)

/* BUILD_TABLE(tablename) builds a huffman lookup table from code lengths.
 * In reality, it just calls make_decode_table() with the appropriate
 * values - they're all fixed by some #defines anyway, so there's no point
 * writing each call out in full by hand.
 */
#define BUILD_TABLE(tbl)						\
  if (make_decode_table(						\
    MAXSYMBOLS(tbl), TABLEBITS(tbl), LENTABLE(tbl), SYMTABLE(tbl)	\
  )) { return DECR_ILLEGALDATA; }


/* READ_HUFFSYM(tablename, var) decodes one huffman symbol from the
 * bitstream using the stated table and puts it in var.
 */
#define READ_HUFFSYM(tbl,var) do {					\
  ENSURE_BITS(16);							\
  hufftbl = SYMTABLE(tbl);						\
  if ((i = hufftbl[PEEK_BITS(TABLEBITS(tbl))]) >= MAXSYMBOLS(tbl)) {	\
    j = 1 << (ULONG_BITS - TABLEBITS(tbl));				\
    do {								\
      j >>= 1; i <<= 1; i |= (bitbuf & j) ? 1 : 0;			\
      if (!j) { return DECR_ILLEGALDATA; }	                        \
    } while ((i = hufftbl[i]) >= MAXSYMBOLS(tbl));			\
  }									\
  j = LENTABLE(tbl)[(var) = i];						\
  REMOVE_BITS(j);							\
} while (0)


/* READ_LENGTHS(tablename, first, last) reads in code lengths for symbols
 * first to last in the given table. The code lengths are stored in their
 * own special LZX way.
 */
#define READ_LENGTHS(tbl,first,last) do { \
  lb.bb = bitbuf; lb.bl = bitsleft; lb.ip = inpos; \
  if (lzx_read_lens(pState, LENTABLE(tbl),(first),(last),&lb)) { \
    return DECR_ILLEGALDATA; \
  } \
  bitbuf = lb.bb; bitsleft = lb.bl; inpos = lb.ip; \
} while (0)


/* make_decode_table(nsyms, nbits, length[], table[])
 *
 * This function was coded by David Tritscher. It builds a fast huffman
 * decoding table out of just a canonical huffman code lengths table.
 *
 * nsyms  = total number of symbols in this huffman tree.
 * nbits  = any symbols with a code length of nbits or less can be decoded
 *          in one lookup of the table.
 * length = A table to get code lengths from [0 to syms-1]
 * table  = The table to fill up with decoded symbols and pointers.
 *
 * Returns 0 for OK or 1 for error
 */

static int make_decode_table(ULONG nsyms, ULONG nbits, UBYTE *length, UWORD *table) {
    register UWORD sym;
    register ULONG leaf;
    register UBYTE bit_num = 1;
    ULONG fill;
    ULONG pos         = 0; /* the current position in the decode table */
    ULONG table_mask  = 1 << nbits;
    ULONG bit_mask    = table_mask >> 1; /* don't do 0 length codes */
    ULONG next_symbol = bit_mask; /* base of allocation for long codes */

    /* fill entries for codes short enough for a direct mapping */
    while (bit_num <= nbits) {
        for (sym = 0; sym < nsyms; sym++) {
            if (length[sym] == bit_num) {
                leaf = pos;

                if((pos += bit_mask) > table_mask) return 1; /* table overrun */

                /* fill all possible lookups of this symbol with the symbol itself */
                fill = bit_mask;
                while (fill-- > 0) table[leaf++] = sym;
            }
        }
        bit_mask >>= 1;
        bit_num++;
    }

    /* if there are any codes longer than nbits */
    if (pos != table_mask) {
        /* clear the remainder of the table */
        for (sym = pos; sym < table_mask; sym++) table[sym] = 0;

        /* give ourselves room for codes to grow by up to 16 more bits */
        pos <<= 16;
        table_mask <<= 16;
        bit_mask = 1 << 15;

        while (bit_num <= 16) {
            for (sym = 0; sym < nsyms; sym++) {
                if (length[sym] == bit_num) {
                    leaf = pos >> 16;
                    for (fill = 0; fill < bit_num - nbits; fill++) {
                        /* if this path hasn't been taken yet, 'allocate' two entries */
                        if (table[leaf] == 0) {
                            table[(next_symbol << 1)] = 0;
                            table[(next_symbol << 1) + 1] = 0;
                            table[leaf] = next_symbol++;
                        }
                        /* follow the path and select either left or right for next bit */
                        leaf = table[leaf] << 1;
                        if ((pos >> (15-fill)) & 1) leaf++;
                    }
                    table[leaf] = sym;

                    if ((pos += bit_mask) > table_mask) return 1; /* table overflow */
                }
            }
            bit_mask >>= 1;
            bit_num++;
        }
    }

    /* full table? */
    if (pos == table_mask) return 0;

    /* either erroneous table, or all elements are 0 - let's find out. */
    for (sym = 0; sym < nsyms; sym++) if (length[sym]) return 1;
    return 0;
}

struct lzx_bits {
  ULONG bb;
  int bl;
  UBYTE *ip;
};

static int lzx_read_lens(struct LZXstate *pState, UBYTE *lens, ULONG first, ULONG last, struct lzx_bits *lb) {
    ULONG i,j, x,y;
    int z;

    register ULONG bitbuf = lb->bb;
    register int bitsleft = lb->bl;
    UBYTE *inpos = lb->ip;
    UWORD *hufftbl;

    for (x = 0; x < 20; x++) {
        READ_BITS(y, 4);
        LENTABLE(PRETREE)[x] = y;
    }
    BUILD_TABLE(PRETREE);

    for (x = first; x < last; ) {
        READ_HUFFSYM(PRETREE, z);
        if (z == 17) {
            READ_BITS(y, 4); y += 4;
            while (y--) lens[x++] = 0;
        }
        else if (z == 18) {
            READ_BITS(y, 5); y += 20;
            while (y--) lens[x++] = 0;
        }
        else if (z == 19) {
            READ_BITS(y, 1); y += 4;
            READ_HUFFSYM(PRETREE, z);
            z = lens[x] - z; if (z < 0) z += 17;
            while (y--) lens[x++] = z;
        }
        else {
            z = lens[x] - z; if (z < 0) z += 17;
            lens[x++] = z;
        }
    }

    lb->bb = bitbuf;
    lb->bl = bitsleft;
    lb->ip = inpos;
    return 0;
}

int LZXdecompress(struct LZXstate *pState, unsigned char *inpos, unsigned char *outpos, int inlen, int outlen) {
    UBYTE *endinp = inpos + inlen;
    UBYTE *window = pState->window;
    UBYTE *runsrc, *rundest;
    UWORD *hufftbl; /* used in READ_HUFFSYM macro as chosen decoding table */

    ULONG window_posn = pState->window_posn;
    ULONG window_size = pState->window_size;
    ULONG R0 = pState->R0;
    ULONG R1 = pState->R1;
    ULONG R2 = pState->R2;

    register ULONG bitbuf;
    register int bitsleft;
    ULONG match_offset, i,j,k; /* ijk used in READ_HUFFSYM macro */
    struct lzx_bits lb; /* used in READ_LENGTHS macro */

    int togo = outlen, this_run, main_element, aligned_bits;
    int match_length, length_footer, extra, verbatim_bits;
    int copy_length;

    INIT_BITSTREAM;

    /* read header if necessary */
    if (!pState->header_read) {
        i = j = 0;
        READ_BITS(k, 1); if (k) { READ_BITS(i,16); READ_BITS(j,16); }
        pState->intel_filesize = (i << 16) | j; /* or 0 if not encoded */
        pState->header_read = 1;
    }

    /* main decoding loop */
    while (togo > 0) {
        /* last block finished, new block expected */
        if (pState->block_remaining == 0) {
            if (pState->block_type == LZX_BLOCKTYPE_UNCOMPRESSED) {
                if (pState->block_length & 1) inpos++; /* realign bitstream to word */
                INIT_BITSTREAM;
            }

            READ_BITS(pState->block_type, 3);
            READ_BITS(i, 16);
            READ_BITS(j, 8);
            pState->block_remaining = pState->block_length = (i << 8) | j;

            switch (pState->block_type) {
                case LZX_BLOCKTYPE_ALIGNED:
                    for (i = 0; i < 8; i++) { READ_BITS(j, 3); LENTABLE(ALIGNED)[i] = j; }
                    BUILD_TABLE(ALIGNED);
                    /* rest of aligned header is same as verbatim */

                case LZX_BLOCKTYPE_VERBATIM:
                    READ_LENGTHS(MAINTREE, 0, 256);
                    READ_LENGTHS(MAINTREE, 256, pState->main_elements);
                    BUILD_TABLE(MAINTREE);
                    if (LENTABLE(MAINTREE)[0xE8] != 0) pState->intel_started = 1;

                    READ_LENGTHS(LENGTH, 0, LZX_NUM_SECONDARY_LENGTHS);
                    BUILD_TABLE(LENGTH);
                    break;

                case LZX_BLOCKTYPE_UNCOMPRESSED:
                    pState->intel_started = 1; /* because we can't assume otherwise */
                    ENSURE_BITS(16); /* get up to 16 pad bits into the buffer */
                    if (bitsleft > 16) inpos -= 2; /* and align the bitstream! */
                    R0 = inpos[0]|(inpos[1]<<8)|(inpos[2]<<16)|(inpos[3]<<24);inpos+=4;
                    R1 = inpos[0]|(inpos[1]<<8)|(inpos[2]<<16)|(inpos[3]<<24);inpos+=4;
                    R2 = inpos[0]|(inpos[1]<<8)|(inpos[2]<<16)|(inpos[3]<<24);inpos+=4;
                    break;

                default:
                    return DECR_ILLEGALDATA;
            }
        }

        /* buffer exhaustion check */
        if (inpos > endinp) {
            /* it's possible to have a file where the next run is less than
             * 16 bits in size. In this case, the READ_HUFFSYM() macro used
             * in building the tables will exhaust the buffer, so we should
             * allow for this, but not allow those accidentally read bits to
             * be used (so we check that there are at least 16 bits
             * remaining - in this boundary case they aren't really part of
             * the compressed data)
             */
            if (inpos > (endinp+2) || bitsleft < 16) return DECR_ILLEGALDATA;
        }

        while ((this_run = pState->block_remaining) > 0 && togo > 0) {
            if (this_run > togo) this_run = togo;
            togo -= this_run;
            pState->block_remaining -= this_run;

            /* apply 2^x-1 mask */
            window_posn &= window_size - 1;
            /* runs can't straddle the window wraparound */
            if ((window_posn + this_run) > window_size)
                return DECR_DATAFORMAT;

            switch (pState->block_type) {

                case LZX_BLOCKTYPE_VERBATIM:
                    while (this_run > 0) {
                        READ_HUFFSYM(MAINTREE, main_element);

                        if (main_element < LZX_NUM_CHARS) {
                            /* literal: 0 to LZX_NUM_CHARS-1 */
                            window[window_posn++] = main_element;
                            this_run--;
                        }
                        else {
                            /* match: LZX_NUM_CHARS + ((slot<<3) | length_header (3 bits)) */
                            main_element -= LZX_NUM_CHARS;

                            match_length = main_element & LZX_NUM_PRIMARY_LENGTHS;
                            if (match_length == LZX_NUM_PRIMARY_LENGTHS) {
                                READ_HUFFSYM(LENGTH, length_footer);
                                match_length += length_footer;
                            }
                            match_length += LZX_MIN_MATCH;

                            match_offset = main_element >> 3;

                            if (match_offset > 2) {
                                /* not repeated offset */
                                if (match_offset != 3) {
                                    extra = extra_bits[match_offset];
                                    READ_BITS(verbatim_bits, extra);
                                    match_offset = position_base[match_offset] - 2 + verbatim_bits;
                                }
                                else {
                                    match_offset = 1;
                                }

                                /* update repeated offset LRU queue */
                                R2 = R1; R1 = R0; R0 = match_offset;
                            }
                            else if (match_offset == 0) {
                                match_offset = R0;
                            }
                            else if (match_offset == 1) {
                                match_offset = R1;
                                R1 = R0; R0 = match_offset;
                            }
                            else /* match_offset == 2 */ {
                                match_offset = R2;
                                R2 = R0; R0 = match_offset;
                            }

                            rundest = window + window_posn;
                            this_run -= match_length;

                            /* copy any wrapped around source data */
                            if (window_posn >= match_offset) {
                                /* no wrap */
                                 runsrc = rundest - match_offset;
                            } else {
                                runsrc = rundest + (window_size - match_offset);
                                copy_length = match_offset - window_posn;
                                if (copy_length < match_length) {
                                     match_length -= copy_length;
                                     window_posn += copy_length;
                                     while (copy_length-- > 0) *rundest++ = *runsrc++;
                                     runsrc = window;
                                }
                            }
                            window_posn += match_length;
 
                            /* copy match data - no worries about destination wraps */
                            while (match_length-- > 0) *rundest++ = *runsrc++;

                        }
                    }
                    break;

                case LZX_BLOCKTYPE_ALIGNED:
                    while (this_run > 0) {
                        READ_HUFFSYM(MAINTREE, main_element);

                        if (main_element < LZX_NUM_CHARS) {
                            /* literal: 0 to LZX_NUM_CHARS-1 */
                            window[window_posn++] = main_element;
                            this_run--;
                        }
                        else {
                            /* match: LZX_NUM_CHARS + ((slot<<3) | length_header (3 bits)) */
                            main_element -= LZX_NUM_CHARS;

                            match_length = main_element & LZX_NUM_PRIMARY_LENGTHS;
                            if (match_length == LZX_NUM_PRIMARY_LENGTHS) {
                                READ_HUFFSYM(LENGTH, length_footer);
                                match_length += length_footer;
                            }
                            match_length += LZX_MIN_MATCH;

                            match_offset = main_element >> 3;

                            if (match_offset > 2) {
                                /* not repeated offset */
                                extra = extra_bits[match_offset];
                                match_offset = position_base[match_offset] - 2;
                                if (extra > 3) {
                                    /* verbatim and aligned bits */
                                    extra -= 3;
                                    READ_BITS(verbatim_bits, extra);
                                    match_offset += (verbatim_bits << 3);
                                    READ_HUFFSYM(ALIGNED, aligned_bits);
                                    match_offset += aligned_bits;
                                }
                                else if (extra == 3) {
                                    /* aligned bits only */
                                    READ_HUFFSYM(ALIGNED, aligned_bits);
                                    match_offset += aligned_bits;
                                }
                                else if (extra > 0) { /* extra==1, extra==2 */
                                    /* verbatim bits only */
                                    READ_BITS(verbatim_bits, extra);
                                    match_offset += verbatim_bits;
                                }
                                else /* extra == 0 */ {
                                    /* ??? */
                                    match_offset = 1;
                                }

                                /* update repeated offset LRU queue */
                                R2 = R1; R1 = R0; R0 = match_offset;
                            }
                            else if (match_offset == 0) {
                                match_offset = R0;
                            }
                            else if (match_offset == 1) {
                                match_offset = R1;
                                R1 = R0; R0 = match_offset;
                            }
                            else /* match_offset == 2 */ {
                                match_offset = R2;
                                R2 = R0; R0 = match_offset;
                            }

                            rundest = window + window_posn;
                            this_run -= match_length;

                            /* copy any wrapped around source data */
                            if (window_posn >= match_offset) {
                                /* no wrap */
                                 runsrc = rundest - match_offset;
                            } else {
                                runsrc = rundest + (window_size - match_offset);
                                copy_length = match_offset - window_posn;
                                if (copy_length < match_length) {
                                     match_length -= copy_length;
                                     window_posn += copy_length;
                                     while (copy_length-- > 0) *rundest++ = *runsrc++;
                                     runsrc = window;
                                }
                            }
                            window_posn += match_length;
 
                            /* copy match data - no worries about destination wraps */
                            while (match_length-- > 0) *rundest++ = *runsrc++;

                        }
                    }
                    break;

                case LZX_BLOCKTYPE_UNCOMPRESSED:
                    if ((inpos + this_run) > endinp) return DECR_ILLEGALDATA;
                    memcpy(window + window_posn, inpos, (size_t) this_run);
                    inpos += this_run; window_posn += this_run;
                    break;

                default:
                    return DECR_ILLEGALDATA; /* might as well */
            }

        }
    }

    if (togo != 0) return DECR_ILLEGALDATA;
    memcpy(outpos, window + ((!window_posn) ? window_size : window_posn) - outlen, (size_t) outlen);

    pState->window_posn = window_posn;
    pState->R0 = R0;
    pState->R1 = R1;
    pState->R2 = R2;

    /* intel E8 decoding */
    if ((pState->frames_read++ < 32768) && pState->intel_filesize != 0) {
        if (outlen <= 6 || !pState->intel_started) {
            pState->intel_curpos += outlen;
        }
        else {
            UBYTE *data    = outpos;
            UBYTE *dataend = data + outlen - 10;
            LONG curpos    = pState->intel_curpos;
            LONG filesize  = pState->intel_filesize;
            LONG abs_off, rel_off;

            pState->intel_curpos = curpos + outlen;

            while (data < dataend) {
                if (*data++ != 0xE8) { curpos++; continue; }
                abs_off = data[0] | (data[1]<<8) | (data[2]<<16) | (data[3]<<24);
                if ((abs_off >= -curpos) && (abs_off < filesize)) {
                    rel_off = (abs_off >= 0) ? abs_off - curpos : abs_off + filesize;
                    data[0] = (UBYTE) rel_off;
                    data[1] = (UBYTE) (rel_off >> 8);
                    data[2] = (UBYTE) (rel_off >> 16);
                    data[3] = (UBYTE) (rel_off >> 24);
                }
                data += 4;
                curpos += 5;
            }
        }
    }
    return DECR_OK;
}

#ifdef LZX_CHM_TESTDRIVER
int main(int c, char **v)
{
    FILE *fin, *fout;
    struct LZXstate state;
    UBYTE ibuf[16384];
    UBYTE obuf[32768];
    int ilen, olen;
    int status;
    int i;
    int count=0;
    int w = atoi(v[1]);
    LZXinit(&state, w);
    fout = fopen(v[2], "wb");
    for (i=3; i<c; i++)
    {
        fin = fopen(v[i], "rb");
        ilen = fread(ibuf, 1, 16384, fin);
        status = LZXdecompress(&state, ibuf, obuf, ilen, 32768);
        switch (status)
        {
            case DECR_OK:
                printf("ok\n");
                fwrite(obuf, 1, 32768, fout);
                break;
            case DECR_DATAFORMAT:
                printf("bad format\n");
                break;
            case DECR_ILLEGALDATA:
                printf("illegal data\n");
                break;
            case DECR_NOMEMORY:
                printf("no memory\n");
                break;
            default:
                break;
        }
        fclose(fin);
        if (++count == 2)
        {
            count = 0;
            LZXreset(&state);
        }
    }
    fclose(fout);
}
#endif