Variable LZX window sizes
[wimlib] / src / lzx-decompress.c
1 /*
2  * lzx-decompress.c
3  *
4  * LZX decompression routines, originally based on code taken from cabextract
5  * v0.5, which was, itself, a modified version of the lzx decompression code
6  * from unlzx.
7  */
8
9 /*
10  * Copyright (C) 2012, 2013 Eric Biggers
11  *
12  * This file is part of wimlib, a library for working with WIM files.
13  *
14  * wimlib is free software; you can redistribute it and/or modify it under the
15  * terms of the GNU General Public License as published by the Free
16  * Software Foundation; either version 3 of the License, or (at your option)
17  * any later version.
18  *
19  * wimlib is distributed in the hope that it will be useful, but WITHOUT ANY
20  * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
21  * A PARTICULAR PURPOSE. See the GNU General Public License for more
22  * details.
23  *
24  * You should have received a copy of the GNU General Public License
25  * along with wimlib; if not, see http://www.gnu.org/licenses/.
26  */
27
28 /*
29  * LZX is a LZ77 and Huffman-code based compression format that has many
30  * similarities to the DEFLATE format used in zlib.  The compression ratio is as
31  * good or better than DEFLATE.  However, in WIM files only up to 32768 bytes of
32  * data can ever compressed be in the same LZX block, so a .tar.gz file could
33  * potentially be smaller than a WIM file that uses LZX compression because it
34  * can use a larger LZ77 window size.
35  *
36  * Some notes on the LZX compression format as used in Windows Imaging (WIM)
37  * files:
38  *
39  * A compressed WIM resource consists of a table of chunk offsets followed by
40  * the compressed chunks themselves.  All compressed chunks except possibly the
41  * last decompress to 32768 bytes.  This is quite similar to the cabinet (.cab)
42  * file format, but they are not the same.  According to the cabinet format
43  * documentation, the LZX block size is independent from the CFDATA blocks, and
44  * a LZX block may span several CFDATA blocks.  However, in WIMs, LZX blocks do
45  * not appear to ever span multiple WIM chunks.  Note that this means any WIM
46  * chunk may be decompressed or compressed independently from any other chunk,
47  * which is convenient.
48  *
49  * A LZX compressed WIM chunk contains one or more LZX blocks of the aligned,
50  * verbatim, or uncompressed block types.  For aligned and verbatim blocks, the
51  * size of the block in uncompressed bytes is specified by a bit following the 3
52  * bits that specify the block type, possibly followed by an additional 16 bits.
53  * '1' means to use the default block size (equal to 32768, the size of a WIM
54  * chunk--- and this seems to only be valid for the first LZX block in a WIM
55  * chunk), while '0' means that the block size is provided by the next 16 bits.
56  *
57  * The cabinet format, as documented, allows for the possibility that a
58  * compressed CFDATA chunk is up to 6144 bytes larger than the data it
59  * uncompresses to.  However, in the WIM format it appears that every chunk that
60  * would be 32768 bytes or more when compressed is actually stored fully
61  * uncompressed.
62  *
63  * The 'e8' preprocessing step that changes x86 call instructions to use
64  * absolute offsets instead of relative offsets relies on a filesize parameter.
65  * There is no such parameter for this in the WIM files (even though the size of
66  * the file resource could be used for this purpose), and instead a magic file
67  * size of 12000000 is used.  The 'e8' preprocessing is always done, and there
68  * is no bit to indicate whether it is done or not.
69  */
70
71 /*
72  * Some more notes about errors in Microsoft's LZX documentation:
73  *
74  * Microsoft's LZX document and their implementation of the com.ms.util.cab Java
75  * package do not concur.
76  *
77  * In the LZX document, there is a table showing the correlation between window
78  * size and the number of position slots. It states that the 1MB window = 40
79  * slots and the 2MB window = 42 slots. In the implementation, 1MB = 42 slots,
80  * 2MB = 50 slots. The actual calculation is 'find the first slot whose position
81  * base is equal to or more than the required window size'. This would explain
82  * why other tables in the document refer to 50 slots rather than 42.
83  *
84  * The constant NUM_PRIMARY_LENS used in the decompression pseudocode is not
85  * defined in the specification.
86  *
87  * The LZX document states that aligned offset blocks have their aligned offset
88  * huffman tree AFTER the main and length trees. The implementation suggests
89  * that the aligned offset tree is BEFORE the main and length trees.
90  *
91  * The LZX document decoding algorithm states that, in an aligned offset block,
92  * if an extra_bits value is 1, 2 or 3, then that number of bits should be read
93  * and the result added to the match offset. This is correct for 1 and 2, but
94  * not 3, where just a huffman symbol (using the aligned tree) should be read.
95  *
96  * Regarding the E8 preprocessing, the LZX document states 'No translation may
97  * be performed on the last 6 bytes of the input block'. This is correct.
98  * However, the pseudocode provided checks for the *E8 leader* up to the last 6
99  * bytes. If the leader appears between -10 and -7 bytes from the end, this
100  * would cause the next four bytes to be modified, at least one of which would
101  * be in the last 6 bytes, which is not allowed according to the spec.
102  *
103  * The specification states that the huffman trees must always contain at least
104  * one element. However, many CAB files contain blocks where the length tree is
105  * completely empty (because there are no matches), and this is expected to
106  * succeed.
107  */
108
109 #ifdef HAVE_CONFIG_H
110 #  include "config.h"
111 #endif
112
113 #include "wimlib.h"
114 #include "wimlib/decompress.h"
115 #include "wimlib/lzx.h"
116 #include "wimlib/util.h"
117
118 #include <string.h>
119
120 /* Huffman decoding tables and maps from symbols to code lengths. */
121 struct lzx_tables {
122
123         u16 maintree_decode_table[(1 << LZX_MAINCODE_TABLEBITS) +
124                                         (LZX_MAINCODE_MAX_NUM_SYMBOLS * 2)]
125                                         _aligned_attribute(DECODE_TABLE_ALIGNMENT);
126         u8 maintree_lens[LZX_MAINCODE_MAX_NUM_SYMBOLS];
127
128
129         u16 lentree_decode_table[(1 << LZX_LENCODE_TABLEBITS) +
130                                         (LZX_LENCODE_NUM_SYMBOLS * 2)]
131                                         _aligned_attribute(DECODE_TABLE_ALIGNMENT);
132         u8 lentree_lens[LZX_LENCODE_NUM_SYMBOLS];
133
134
135         u16 alignedtree_decode_table[(1 << LZX_ALIGNEDCODE_TABLEBITS) +
136                                         (LZX_ALIGNEDCODE_NUM_SYMBOLS * 2)]
137                                         _aligned_attribute(DECODE_TABLE_ALIGNMENT);
138         u8 alignedtree_lens[LZX_ALIGNEDCODE_NUM_SYMBOLS];
139 } _aligned_attribute(DECODE_TABLE_ALIGNMENT);
140
141
142 /*
143  * Reads a Huffman-encoded symbol using the pre-tree.
144  */
145 static inline int
146 read_huffsym_using_pretree(struct input_bitstream *istream,
147                            const u16 pretree_decode_table[],
148                            const u8 pretree_lens[], unsigned *n)
149 {
150         return read_huffsym(istream, pretree_decode_table, pretree_lens,
151                             LZX_PRECODE_NUM_SYMBOLS, LZX_PRECODE_TABLEBITS, n,
152                             LZX_MAX_PRE_CODEWORD_LEN);
153 }
154
155 /* Reads a Huffman-encoded symbol using the main tree. */
156 static inline int
157 read_huffsym_using_maintree(struct input_bitstream *istream,
158                             const struct lzx_tables *tables,
159                             unsigned *n,
160                             unsigned num_main_syms)
161 {
162         return read_huffsym(istream, tables->maintree_decode_table,
163                             tables->maintree_lens, num_main_syms,
164                             LZX_MAINCODE_TABLEBITS, n, LZX_MAX_MAIN_CODEWORD_LEN);
165 }
166
167 /* Reads a Huffman-encoded symbol using the length tree. */
168 static inline int
169 read_huffsym_using_lentree(struct input_bitstream *istream,
170                            const struct lzx_tables *tables,
171                            unsigned *n)
172 {
173         return read_huffsym(istream, tables->lentree_decode_table,
174                             tables->lentree_lens, LZX_LENCODE_NUM_SYMBOLS,
175                             LZX_LENCODE_TABLEBITS, n, LZX_MAX_LEN_CODEWORD_LEN);
176 }
177
178 /* Reads a Huffman-encoded symbol using the aligned offset tree. */
179 static inline int
180 read_huffsym_using_alignedtree(struct input_bitstream *istream,
181                                const struct lzx_tables *tables,
182                                unsigned *n)
183 {
184         return read_huffsym(istream, tables->alignedtree_decode_table,
185                             tables->alignedtree_lens,
186                             LZX_ALIGNEDCODE_NUM_SYMBOLS,
187                             LZX_ALIGNEDCODE_TABLEBITS, n,
188                             LZX_MAX_ALIGNED_CODEWORD_LEN);
189 }
190
191 /*
192  * Reads the pretree from the input, then uses the pretree to decode @num_lens
193  * code length values from the input.
194  *
195  * @istream:    The bit stream for the input.  It is positioned on the beginning
196  *                      of the pretree for the code length values.
197  * @lens:       An array that contains the length values from the previous time
198  *                      the code lengths for this Huffman tree were read, or all
199  *                      0's if this is the first time.
200  * @num_lens:   Number of length values to decode and return.
201  *
202  */
203 static int
204 lzx_read_code_lens(struct input_bitstream *istream, u8 lens[],
205                    unsigned num_lens)
206 {
207         /* Declare the decoding table and length table for the pretree. */
208         u16 pretree_decode_table[(1 << LZX_PRECODE_TABLEBITS) +
209                                         (LZX_PRECODE_NUM_SYMBOLS * 2)]
210                                         _aligned_attribute(DECODE_TABLE_ALIGNMENT);
211         u8 pretree_lens[LZX_PRECODE_NUM_SYMBOLS];
212         unsigned i;
213         unsigned len;
214         int ret;
215
216         /* Read the code lengths of the pretree codes.  There are 20 lengths of
217          * 4 bits each. */
218         for (i = 0; i < LZX_PRECODE_NUM_SYMBOLS; i++) {
219                 ret = bitstream_read_bits(istream, LZX_PRECODE_ELEMENT_SIZE,
220                                           &len);
221                 if (ret)
222                         return ret;
223                 pretree_lens[i] = len;
224         }
225
226         /* Make the decoding table for the pretree. */
227         ret = make_huffman_decode_table(pretree_decode_table,
228                                         LZX_PRECODE_NUM_SYMBOLS,
229                                         LZX_PRECODE_TABLEBITS,
230                                         pretree_lens,
231                                         LZX_MAX_PRE_CODEWORD_LEN);
232         if (ret)
233                 return ret;
234
235         /* Pointer past the last length value that needs to be filled in. */
236         u8 *lens_end = lens + num_lens;
237
238         while (1) {
239
240                 /* Decode a symbol from the input.  If the symbol is between 0
241                  * and 16, it is the difference from the old length.  If it is
242                  * between 17 and 19, it is a special code that indicates that
243                  * some number of the next lengths are all 0, or some number of
244                  * the next lengths are all equal to the next symbol in the
245                  * input. */
246                 unsigned tree_code;
247                 unsigned num_zeroes;
248                 unsigned code;
249                 unsigned num_same;
250                 signed char value;
251
252                 ret = read_huffsym_using_pretree(istream, pretree_decode_table,
253                                                  pretree_lens, &tree_code);
254                 if (ret)
255                         return ret;
256                 switch (tree_code) {
257                 case 17: /* Run of 0's */
258                         ret = bitstream_read_bits(istream, 4, &num_zeroes);
259                         if (ret)
260                                 return ret;
261                         num_zeroes += 4;
262                         while (num_zeroes--) {
263                                 *lens = 0;
264                                 if (++lens == lens_end)
265                                         return 0;
266                         }
267                         break;
268                 case 18: /* Longer run of 0's */
269                         ret = bitstream_read_bits(istream, 5, &num_zeroes);
270                         if (ret)
271                                 return ret;
272                         num_zeroes += 20;
273                         while (num_zeroes--) {
274                                 *lens = 0;
275                                 if (++lens == lens_end)
276                                         return 0;
277                         }
278                         break;
279                 case 19: /* Run of identical lengths */
280                         ret = bitstream_read_bits(istream, 1, &num_same);
281                         if (ret)
282                                 return ret;
283                         num_same += 4;
284                         ret = read_huffsym_using_pretree(istream,
285                                                          pretree_decode_table,
286                                                          pretree_lens,
287                                                          &code);
288                         if (ret)
289                                 return ret;
290                         value = (signed char)*lens - (signed char)code;
291                         if (value < 0)
292                                 value += 17;
293                         while (num_same--) {
294                                 *lens = value;
295                                 if (++lens == lens_end)
296                                         return 0;
297                         }
298                         break;
299                 default: /* Difference from old length. */
300                         value = (signed char)*lens - (signed char)tree_code;
301                         if (value < 0)
302                                 value += 17;
303                         *lens = value;
304                         if (++lens == lens_end)
305                                 return 0;
306                         break;
307                 }
308         }
309 }
310
311 /*
312  * Reads the header for an LZX-compressed block.
313  *
314  * @istream:            The input bitstream.
315  * @block_size_ret:     A pointer to an int into which the size of the block,
316  *                              in bytes, will be returned.
317  * @block_type_ret:     A pointer to an int into which the type of the block
318  *                              (LZX_BLOCKTYPE_*) will be returned.
319  * @tables:             A pointer to a lzx_tables structure in which the
320  *                              main tree, the length tree, and possibly the
321  *                              aligned offset tree will be constructed.
322  * @queue:      A pointer to the least-recently-used queue into which
323  *                      R0, R1, and R2 will be written (only for uncompressed
324  *                      blocks, which contain this information in the header)
325  */
326 static int
327 lzx_read_block_header(struct input_bitstream *istream,
328                       unsigned num_main_syms,
329                       unsigned max_window_size,
330                       unsigned *block_size_ret,
331                       unsigned *block_type_ret,
332                       struct lzx_tables *tables,
333                       struct lzx_lru_queue *queue)
334 {
335         int ret;
336         unsigned block_type;
337         unsigned block_size;
338         unsigned s;
339         unsigned i;
340         unsigned len;
341
342         ret = bitstream_ensure_bits(istream, 4);
343         if (ret) {
344                 LZX_DEBUG("LZX input stream overrun");
345                 return ret;
346         }
347
348         /* The first three bits tell us what kind of block it is, and are one
349          * of the LZX_BLOCKTYPE_* values.  */
350         block_type = bitstream_read_bits_nocheck(istream, 3);
351
352         /* Read the block size.  This mirrors the behavior
353          * lzx_write_compressed_block() in lzx-compress.c; see that for more
354          * details.  */
355         s = bitstream_read_bits_nocheck(istream, 1);
356         if (s) {
357                 block_size = LZX_DEFAULT_BLOCK_SIZE;
358         } else {
359                 unsigned tmp;
360                 block_size = 0;
361
362                 ret = bitstream_read_bits(istream, 8, &tmp);
363                 if (ret)
364                         return ret;
365                 block_size |= tmp;
366
367                 ret = bitstream_read_bits(istream, 8, &tmp);
368                 if (ret)
369                         return ret;
370                 block_size <<= 8;
371                 block_size |= tmp;
372
373                 if (max_window_size >= 65536) {
374                         ret = bitstream_read_bits(istream, 8, &tmp);
375                         if (ret)
376                                 return ret;
377                         block_size <<= 8;
378                         block_size |= tmp;
379                 }
380         }
381
382         switch (block_type) {
383         case LZX_BLOCKTYPE_ALIGNED:
384                 /* Read the path lengths for the elements of the aligned tree,
385                  * then build it. */
386
387                 for (i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++) {
388                         ret = bitstream_read_bits(istream,
389                                                   LZX_ALIGNEDCODE_ELEMENT_SIZE,
390                                                   &len);
391                         if (ret)
392                                 return ret;
393                         tables->alignedtree_lens[i] = len;
394                 }
395
396                 LZX_DEBUG("Building the aligned tree.");
397                 ret = make_huffman_decode_table(tables->alignedtree_decode_table,
398                                                 LZX_ALIGNEDCODE_NUM_SYMBOLS,
399                                                 LZX_ALIGNEDCODE_TABLEBITS,
400                                                 tables->alignedtree_lens,
401                                                 LZX_MAX_ALIGNED_CODEWORD_LEN);
402                 if (ret) {
403                         LZX_DEBUG("Failed to make the decode table for the "
404                                   "aligned offset tree");
405                         return ret;
406                 }
407
408                 /* Fall though, since the rest of the header for aligned offset
409                  * blocks is the same as that for verbatim blocks */
410
411         case LZX_BLOCKTYPE_VERBATIM:
412                 if (block_type == LZX_BLOCKTYPE_VERBATIM)
413                         LZX_DEBUG("Found verbatim block.");
414
415                 LZX_DEBUG("Reading path lengths for main tree.");
416                 /* Read the path lengths for the first 256 elements of the main
417                  * tree. */
418                 ret = lzx_read_code_lens(istream, tables->maintree_lens,
419                                          LZX_NUM_CHARS);
420                 if (ret) {
421                         LZX_DEBUG("Failed to read the code lengths for the "
422                                   "first 256 elements of the main tree");
423                         return ret;
424                 }
425
426                 /* Read the path lengths for the remaining elements of the main
427                  * tree. */
428                 LZX_DEBUG("Reading path lengths for remaining elements of "
429                           "main tree (%d elements).",
430                           num_main_syms - LZX_NUM_CHARS);
431                 ret = lzx_read_code_lens(istream,
432                                          tables->maintree_lens + LZX_NUM_CHARS,
433                                          num_main_syms - LZX_NUM_CHARS);
434                 if (ret) {
435                         LZX_DEBUG("Failed to read the path lengths for the "
436                                   "remaining elements of the main tree");
437                         return ret;
438                 }
439
440                 LZX_DEBUG("Building the Huffman decoding "
441                           "table for the main tree.");
442
443                 ret = make_huffman_decode_table(tables->maintree_decode_table,
444                                                 num_main_syms,
445                                                 LZX_MAINCODE_TABLEBITS,
446                                                 tables->maintree_lens,
447                                                 LZX_MAX_MAIN_CODEWORD_LEN);
448                 if (ret) {
449                         LZX_DEBUG("Failed to make the decode "
450                                   "table for the main tree");
451                         return ret;
452                 }
453
454                 LZX_DEBUG("Reading path lengths for the length tree.");
455                 ret = lzx_read_code_lens(istream, tables->lentree_lens,
456                                          LZX_LENCODE_NUM_SYMBOLS);
457                 if (ret) {
458                         LZX_DEBUG("Failed to read the path "
459                                   "lengths for the length tree");
460                         return ret;
461                 }
462
463                 LZX_DEBUG("Building the length tree.");
464                 ret = make_huffman_decode_table(tables->lentree_decode_table,
465                                                 LZX_LENCODE_NUM_SYMBOLS,
466                                                 LZX_LENCODE_TABLEBITS,
467                                                 tables->lentree_lens,
468                                                 LZX_MAX_LEN_CODEWORD_LEN);
469                 if (ret) {
470                         LZX_DEBUG("Failed to build the length Huffman tree");
471                         return ret;
472                 }
473                 /* The bitstream of compressed literals and matches for this
474                  * block directly follows and will be read in
475                  * lzx_decompress_block(). */
476                 break;
477         case LZX_BLOCKTYPE_UNCOMPRESSED:
478                 LZX_DEBUG("Found uncompressed block.");
479                 /* Before reading the three LRU match offsets from the
480                  * uncompressed block header, the stream needs to be aligned on
481                  * a 16-bit boundary.  But, unexpectedly, if the stream is
482                  * *already* aligned, the correct thing to do is to throw away
483                  * the next 16 bits. */
484                 if (istream->bitsleft == 0) {
485                         if (istream->data_bytes_left < 14) {
486                                 LZX_DEBUG("Insufficient length in "
487                                           "uncompressed block");
488                                 return -1;
489                         }
490                         istream->data += 2;
491                         istream->data_bytes_left -= 2;
492                 } else {
493                         if (istream->data_bytes_left < 12) {
494                                 LZX_DEBUG("Insufficient length in "
495                                           "uncompressed block");
496                                 return -1;
497                         }
498                         istream->bitsleft = 0;
499                         istream->bitbuf = 0;
500                 }
501                 queue->R[0] = le32_to_cpu(*(u32*)(istream->data + 0));
502                 queue->R[1] = le32_to_cpu(*(u32*)(istream->data + 4));
503                 queue->R[2] = le32_to_cpu(*(u32*)(istream->data + 8));
504                 istream->data += 12;
505                 istream->data_bytes_left -= 12;
506                 /* The uncompressed data of this block directly follows and will
507                  * be read in lzx_decompress(). */
508                 break;
509         default:
510                 LZX_DEBUG("Found invalid block");
511                 return -1;
512         }
513         *block_type_ret = block_type;
514         *block_size_ret = block_size;
515         return 0;
516 }
517
518 /*
519  * Decodes a compressed match from a block of LZX-compressed data.  A match
520  * refers to some match_offset to a point earlier in the window as well as some
521  * match_len, for which the data is to be copied to the current position in the
522  * window.
523  *
524  * @main_element:       The start of the match data, as decoded using the main
525  *                      tree.
526  *
527  * @block_type:         The type of the block (LZX_BLOCKTYPE_ALIGNED or
528  *                      LZX_BLOCKTYPE_VERBATIM)
529  *
530  * @bytes_remaining:    The amount of uncompressed data remaining to be
531  *                      uncompressed in this block.  It is an error if the match
532  *                      is longer than this number.
533  *
534  * @window:             A pointer to the window into which the uncompressed
535  *                      data is being written.
536  *
537  * @window_pos:         The current byte offset in the window.
538  *
539  * @tables:             The Huffman decoding tables for this LZX block (main
540  *                      code, length code, and for LZX_BLOCKTYPE_ALIGNED blocks,
541  *                      also the aligned offset code).
542  *
543  * @queue:              The least-recently used queue for match offsets.
544  *
545  * @istream:            The input bitstream.
546  *
547  * Returns the length of the match, or a negative number on error.  The possible
548  * error cases are:
549  *      - Match would exceed the amount of data remaining to be uncompressed.
550  *      - Match refers to data before the window.
551  *      - The input bitstream ended unexpectedly.
552  */
553 static int
554 lzx_decode_match(unsigned main_element, int block_type,
555                  unsigned bytes_remaining, u8 *window,
556                  unsigned window_pos,
557                  const struct lzx_tables *tables,
558                  struct lzx_lru_queue *queue,
559                  struct input_bitstream *istream)
560 {
561         unsigned length_header;
562         unsigned position_slot;
563         unsigned match_len;
564         unsigned match_offset;
565         unsigned additional_len;
566         unsigned num_extra_bits;
567         unsigned verbatim_bits;
568         unsigned aligned_bits;
569         unsigned i;
570         int ret;
571         u8 *match_dest;
572         u8 *match_src;
573
574         /* The main element is offset by 256 because values under 256 indicate a
575          * literal value. */
576         main_element -= LZX_NUM_CHARS;
577
578         /* The length header consists of the lower 3 bits of the main element.
579          * The position slot is the rest of it. */
580         length_header = main_element & LZX_NUM_PRIMARY_LENS;
581         position_slot = main_element >> 3;
582
583         /* If the length_header is less than LZX_NUM_PRIMARY_LENS (= 7), it
584          * gives the match length as the offset from LZX_MIN_MATCH_LEN.
585          * Otherwise, the length is given by an additional symbol encoded using
586          * the length tree, offset by 9 (LZX_MIN_MATCH_LEN +
587          * LZX_NUM_PRIMARY_LENS) */
588         match_len = LZX_MIN_MATCH_LEN + length_header;
589         if (length_header == LZX_NUM_PRIMARY_LENS) {
590                 ret = read_huffsym_using_lentree(istream, tables,
591                                                  &additional_len);
592                 if (ret)
593                         return ret;
594                 match_len += additional_len;
595         }
596
597
598         /* If the position_slot is 0, 1, or 2, the match offset is retrieved
599          * from the LRU queue.  Otherwise, the match offset is not in the LRU
600          * queue. */
601         switch (position_slot) {
602         case 0:
603                 match_offset = queue->R[0];
604                 break;
605         case 1:
606                 match_offset = queue->R[1];
607                 swap(queue->R[0], queue->R[1]);
608                 break;
609         case 2:
610                 /* The queue doesn't work quite the same as a real LRU queue,
611                  * since using the R2 offset doesn't bump the R1 offset down to
612                  * R2. */
613                 match_offset = queue->R[2];
614                 swap(queue->R[0], queue->R[2]);
615                 break;
616         default:
617                 /* Otherwise, the offset was not encoded as one the offsets in
618                  * the queue.  Depending on the position slot, there is a
619                  * certain number of extra bits that need to be read to fully
620                  * decode the match offset. */
621
622                 /* Look up the number of extra bits that need to be read. */
623                 num_extra_bits = lzx_get_num_extra_bits(position_slot);
624
625                 /* For aligned blocks, if there are at least 3 extra bits, the
626                  * actual number of extra bits is 3 less, and they encode a
627                  * number of 8-byte words that are added to the offset; there
628                  * is then an additional symbol read using the aligned tree that
629                  * specifies the actual byte alignment. */
630                 if (block_type == LZX_BLOCKTYPE_ALIGNED && num_extra_bits >= 3) {
631
632                         /* There is an error in the LZX "specification" at this
633                          * point; it indicates that a Huffman symbol is to be
634                          * read only if num_extra_bits is greater than 3, but
635                          * actually it is if num_extra_bits is greater than or
636                          * equal to 3.  (Note that in the case with
637                          * num_extra_bits == 3, the assignment to verbatim_bits
638                          * will just set it to 0. ) */
639                         ret = bitstream_read_bits(istream, num_extra_bits - 3,
640                                                   &verbatim_bits);
641                         if (ret)
642                                 return ret;
643
644                         verbatim_bits <<= 3;
645
646                         ret = read_huffsym_using_alignedtree(istream, tables,
647                                                              &aligned_bits);
648                         if (ret)
649                                 return ret;
650                 } else {
651                         /* For non-aligned blocks, or for aligned blocks with
652                          * less than 3 extra bits, the extra bits are added
653                          * directly to the match offset, and the correction for
654                          * the alignment is taken to be 0. */
655                         ret = bitstream_read_bits(istream, num_extra_bits,
656                                                   &verbatim_bits);
657                         if (ret)
658                                 return ret;
659
660                         aligned_bits = 0;
661                 }
662
663                 /* Calculate the match offset. */
664                 match_offset = lzx_position_base[position_slot] +
665                                verbatim_bits + aligned_bits - LZX_OFFSET_OFFSET;
666
667                 /* Update the LRU queue. */
668                 queue->R[2] = queue->R[1];
669                 queue->R[1] = queue->R[0];
670                 queue->R[0] = match_offset;
671                 break;
672         }
673
674         /* Verify that the match is in the bounds of the part of the window
675          * currently in use, then copy the source of the match to the current
676          * position. */
677
678         if (match_len > bytes_remaining) {
679                 LZX_DEBUG("Match of length %u bytes overflows "
680                           "uncompressed block size", match_len);
681                 return -1;
682         }
683
684         if (match_offset > window_pos) {
685                 LZX_DEBUG("Match of length %u bytes references "
686                           "data before window (match_offset = %u, "
687                           "window_pos = %u)",
688                           match_len, match_offset, window_pos);
689                 return -1;
690         }
691
692         match_dest = window + window_pos;
693         match_src = match_dest - match_offset;
694
695 #if 0
696         printf("Match: src %u, dst %u, len %u\n", match_src - window,
697                                                 match_dest - window,
698                                                 match_len);
699         putchar('|');
700         for (i = 0; i < match_len; i++) {
701                 match_dest[i] = match_src[i];
702                 putchar(match_src[i]);
703         }
704         putchar('|');
705         putchar('\n');
706 #else
707         for (i = 0; i < match_len; i++)
708                 match_dest[i] = match_src[i];
709 #endif
710
711         return match_len;
712 }
713
714 static void
715 undo_call_insn_translation(u32 *call_insn_target, int input_pos,
716                            s32 file_size)
717 {
718         s32 abs_offset;
719         s32 rel_offset;
720
721         abs_offset = le32_to_cpu(*call_insn_target);
722         if (abs_offset >= -input_pos && abs_offset < file_size) {
723                 if (abs_offset >= 0) {
724                         /* "good translation" */
725                         rel_offset = abs_offset - input_pos;
726                 } else {
727                         /* "compensating translation" */
728                         rel_offset = abs_offset + file_size;
729                 }
730                 *call_insn_target = cpu_to_le32(rel_offset);
731         }
732 }
733
734 /* Undo the 'E8' preprocessing, where the targets of x86 CALL instructions were
735  * changed from relative offsets to absolute offsets.
736  *
737  * Note that this call instruction preprocessing can and will be used on any
738  * data even if it is not actually x86 machine code.  In fact, this type of
739  * preprocessing appears to always be used in LZX-compressed resources in WIM
740  * files; there is no bit to indicate whether it is used or not, unlike in the
741  * LZX compressed format as used in cabinet files, where a bit is reserved for
742  * that purpose.
743  *
744  * Call instruction preprocessing is disabled in the last 6 bytes of the
745  * uncompressed data, which really means the 5-byte call instruction cannot
746  * start in the last 10 bytes of the uncompressed data.  This is one of the
747  * errors in the LZX documentation.
748  *
749  * Call instruction preprocessing does not appear to be disabled after the
750  * 32768th chunk of a WIM stream, which is apparently is yet another difference
751  * from the LZX compression used in cabinet files.
752  *
753  * Call instruction processing is supposed to take the file size as a parameter,
754  * as it is used in calculating the translated jump targets.  But in WIM files,
755  * this file size is always the same (LZX_WIM_MAGIC_FILESIZE == 12000000).*/
756 static void
757 undo_call_insn_preprocessing(u8 uncompressed_data[], int uncompressed_data_len)
758 {
759         for (int i = 0; i < uncompressed_data_len - 10; i++) {
760                 if (uncompressed_data[i] == 0xe8) {
761                         undo_call_insn_translation((u32*)&uncompressed_data[i + 1],
762                                                    i,
763                                                    LZX_WIM_MAGIC_FILESIZE);
764                         i += 4;
765                 }
766         }
767 }
768
769 /*
770  * Decompresses a LZX-compressed block of data from which the header has already
771  * been read.
772  *
773  * @block_type: The type of the block (LZX_BLOCKTYPE_VERBATIM or
774  *              LZX_BLOCKTYPE_ALIGNED)
775  * @block_size: The size of the block, in bytes.
776  * @num_main_syms:      Number of symbols in the main alphabet.
777  * @window:     Pointer to the decompression window.
778  * @window_pos: The current position in the window.  Will be 0 for the first
779  *                      block.
780  * @tables:     The Huffman decoding tables for the block (main, length, and
781  *                      aligned offset, the latter only for LZX_BLOCKTYPE_ALIGNED)
782  * @queue:      The least-recently-used queue for match offsets.
783  * @istream:    The input bitstream for the compressed literals.
784  */
785 static int
786 lzx_decompress_block(int block_type, unsigned block_size,
787                      unsigned num_main_syms,
788                      u8 *window,
789                      unsigned window_pos,
790                      const struct lzx_tables *tables,
791                      struct lzx_lru_queue *queue,
792                      struct input_bitstream *istream)
793 {
794         unsigned main_element;
795         unsigned end;
796         int ret;
797         int match_len;
798
799         end = window_pos + block_size;
800         while (window_pos < end) {
801                 ret = read_huffsym_using_maintree(istream, tables,
802                                                   &main_element,
803                                                   num_main_syms);
804                 if (ret)
805                         return ret;
806
807                 if (main_element < LZX_NUM_CHARS) {
808                         /* literal: 0 to LZX_NUM_CHARS - 1 */
809                         window[window_pos++] = main_element;
810                 } else {
811                         /* match: LZX_NUM_CHARS to num_main_syms - 1 */
812                         match_len = lzx_decode_match(main_element,
813                                                      block_type,
814                                                      end - window_pos,
815                                                      window,
816                                                      window_pos,
817                                                      tables,
818                                                      queue,
819                                                      istream);
820                         if (match_len < 0)
821                                 return match_len;
822                         window_pos += match_len;
823                 }
824         }
825         return 0;
826 }
827
828 WIMLIBAPI int
829 wimlib_lzx_decompress2(const void *compressed_data, unsigned compressed_len,
830                        void *uncompressed_data, unsigned uncompressed_len,
831                        u32 max_window_size)
832 {
833         struct lzx_tables tables;
834         struct input_bitstream istream;
835         struct lzx_lru_queue queue;
836         unsigned window_pos;
837         unsigned block_size;
838         unsigned block_type;
839         unsigned num_main_syms;
840         int ret;
841         bool e8_preprocessing_done;
842
843         LZX_DEBUG("compressed_data = %p, compressed_len = %u, "
844                   "uncompressed_data = %p, uncompressed_len = %u, "
845                   "max_window_size=%u).",
846                   compressed_data, compressed_len,
847                   uncompressed_data, uncompressed_len, max_window_size);
848
849         if (!lzx_window_size_valid(max_window_size)) {
850                 LZX_DEBUG("Window size of %u is invalid!",
851                           max_window_size);
852                 return -1;
853         }
854
855         num_main_syms = lzx_get_num_main_syms(max_window_size);
856
857         if (uncompressed_len > max_window_size) {
858                 LZX_DEBUG("Uncompressed chunk size of %u exceeds "
859                           "window size of %u!",
860                           uncompressed_len, max_window_size);
861                 return -1;
862         }
863
864         memset(tables.maintree_lens, 0, sizeof(tables.maintree_lens));
865         memset(tables.lentree_lens, 0, sizeof(tables.lentree_lens));
866         lzx_lru_queue_init(&queue);
867         init_input_bitstream(&istream, compressed_data, compressed_len);
868
869         e8_preprocessing_done = false; /* Set to true if there may be 0xe8 bytes
870                                           in the uncompressed data. */
871
872         /* The compressed data will consist of one or more blocks.  The
873          * following loop decompresses one block, and it runs until there all
874          * the compressed data has been decompressed, so there are no more
875          * blocks.  */
876
877         for (window_pos = 0;
878              window_pos < uncompressed_len;
879              window_pos += block_size)
880         {
881                 LZX_DEBUG("Reading block header.");
882                 ret = lzx_read_block_header(&istream, num_main_syms,
883                                             max_window_size, &block_size,
884                                             &block_type, &tables, &queue);
885                 if (ret)
886                         return ret;
887
888                 LZX_DEBUG("block_size = %u, window_pos = %u",
889                           block_size, window_pos);
890
891                 if (block_size > uncompressed_len - window_pos) {
892                         LZX_DEBUG("Expected a block size of at "
893                                   "most %u bytes (found %u bytes)",
894                                   uncompressed_len - window_pos, block_size);
895                         return -1;
896                 }
897
898                 switch (block_type) {
899                 case LZX_BLOCKTYPE_VERBATIM:
900                 case LZX_BLOCKTYPE_ALIGNED:
901                         if (block_type == LZX_BLOCKTYPE_VERBATIM)
902                                 LZX_DEBUG("LZX_BLOCKTYPE_VERBATIM");
903                         else
904                                 LZX_DEBUG("LZX_BLOCKTYPE_ALIGNED");
905                         ret = lzx_decompress_block(block_type,
906                                                    block_size,
907                                                    num_main_syms,
908                                                    uncompressed_data,
909                                                    window_pos,
910                                                    &tables,
911                                                    &queue,
912                                                    &istream);
913                         if (ret)
914                                 return ret;
915
916                         if (tables.maintree_lens[0xe8] != 0)
917                                 e8_preprocessing_done = true;
918                         break;
919                 case LZX_BLOCKTYPE_UNCOMPRESSED:
920                         LZX_DEBUG("LZX_BLOCKTYPE_UNCOMPRESSED");
921                         if (istream.data_bytes_left < block_size) {
922                                 LZX_DEBUG("Unexpected end of input when "
923                                           "reading %u bytes from LZX bitstream "
924                                           "(only have %u bytes left)",
925                                           block_size, istream.data_bytes_left);
926                                 return -1;
927                         }
928                         memcpy(&((u8*)uncompressed_data)[window_pos], istream.data,
929                                block_size);
930                         istream.data += block_size;
931                         istream.data_bytes_left -= block_size;
932                         /* Re-align bitstream if an odd number of bytes were
933                          * read.  */
934                         if (istream.data_bytes_left && (block_size & 1)) {
935                                 istream.data_bytes_left--;
936                                 istream.data++;
937                         }
938                         e8_preprocessing_done = true;
939                         break;
940                 }
941         }
942         if (e8_preprocessing_done)
943                 undo_call_insn_preprocessing(uncompressed_data, uncompressed_len);
944         return 0;
945 }
946
947 /* API function documented in wimlib.h  */
948 WIMLIBAPI int
949 wimlib_lzx_decompress(const void *compressed_data, unsigned compressed_len,
950                       void *uncompressed_data, unsigned uncompressed_len)
951 {
952         return wimlib_lzx_decompress2(compressed_data, compressed_len,
953                                       uncompressed_data, uncompressed_len,
954                                       32768);
955 }