lzx_write_compressed_tree(), lzx_read_code_lens(): Specify signed char
[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 WIM_CHUNK_SIZE (= 32768) bytes.  This is quite similar to
42  * the cabinet (.cab) file format, but they are not the same.  According to the
43  * cabinet format documentation, the LZX block size is independent from the
44  * CFDATA blocks, and a LZX block may span several CFDATA blocks.  However, in
45  * WIMs, LZX blocks do not appear to ever span multiple WIM chunks.  Note that
46  * this means any WIM chunk may be decompressed or compressed independently from
47  * any other chunk, 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_MAINTREE_TABLEBITS) +
124                                         (LZX_MAINTREE_NUM_SYMBOLS * 2)]
125                                         _aligned_attribute(DECODE_TABLE_ALIGNMENT);
126         u8 maintree_lens[LZX_MAINTREE_NUM_SYMBOLS];
127
128
129         u16 lentree_decode_table[(1 << LZX_LENTREE_TABLEBITS) +
130                                         (LZX_LENTREE_NUM_SYMBOLS * 2)]
131                                         _aligned_attribute(DECODE_TABLE_ALIGNMENT);
132         u8 lentree_lens[LZX_LENTREE_NUM_SYMBOLS];
133
134
135         u16 alignedtree_decode_table[(1 << LZX_ALIGNEDTREE_TABLEBITS) +
136                                         (LZX_ALIGNEDTREE_NUM_SYMBOLS * 2)]
137                                         _aligned_attribute(DECODE_TABLE_ALIGNMENT);
138         u8 alignedtree_lens[LZX_ALIGNEDTREE_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_PRETREE_NUM_SYMBOLS, LZX_PRETREE_TABLEBITS, n,
152                             LZX_MAX_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 {
161         return read_huffsym(istream, tables->maintree_decode_table,
162                             tables->maintree_lens, LZX_MAINTREE_NUM_SYMBOLS,
163                             LZX_MAINTREE_TABLEBITS, n, LZX_MAX_CODEWORD_LEN);
164 }
165
166 /* Reads a Huffman-encoded symbol using the length tree. */
167 static inline int
168 read_huffsym_using_lentree(struct input_bitstream *istream,
169                            const struct lzx_tables *tables,
170                            unsigned *n)
171 {
172         return read_huffsym(istream, tables->lentree_decode_table,
173                             tables->lentree_lens, LZX_LENTREE_NUM_SYMBOLS,
174                             LZX_LENTREE_TABLEBITS, n, LZX_MAX_CODEWORD_LEN);
175 }
176
177 /* Reads a Huffman-encoded symbol using the aligned offset tree. */
178 static inline int
179 read_huffsym_using_alignedtree(struct input_bitstream *istream,
180                                const struct lzx_tables *tables,
181                                unsigned *n)
182 {
183         return read_huffsym(istream, tables->alignedtree_decode_table,
184                             tables->alignedtree_lens,
185                             LZX_ALIGNEDTREE_NUM_SYMBOLS,
186                             LZX_ALIGNEDTREE_TABLEBITS, n, 8);
187 }
188
189 /*
190  * Reads the pretree from the input, then uses the pretree to decode @num_lens
191  * code length values from the input.
192  *
193  * @istream:    The bit stream for the input.  It is positioned on the beginning
194  *                      of the pretree for the code length values.
195  * @lens:       An array that contains the length values from the previous time
196  *                      the code lengths for this Huffman tree were read, or all
197  *                      0's if this is the first time.
198  * @num_lens:   Number of length values to decode and return.
199  *
200  */
201 static int
202 lzx_read_code_lens(struct input_bitstream *istream, u8 lens[],
203                    unsigned num_lens)
204 {
205         /* Declare the decoding table and length table for the pretree. */
206         u16 pretree_decode_table[(1 << LZX_PRETREE_TABLEBITS) +
207                                         (LZX_PRETREE_NUM_SYMBOLS * 2)];
208         u8 pretree_lens[LZX_PRETREE_NUM_SYMBOLS];
209         unsigned i;
210         unsigned len;
211         int ret;
212
213         /* Read the code lengths of the pretree codes.  There are 20 lengths of
214          * 4 bits each. */
215         for (i = 0; i < LZX_PRETREE_NUM_SYMBOLS; i++) {
216                 ret = bitstream_read_bits(istream, LZX_PRETREE_ELEMENT_SIZE,
217                                           &len);
218                 if (ret != 0)
219                         return ret;
220                 pretree_lens[i] = len;
221         }
222
223         /* Make the decoding table for the pretree. */
224         ret = make_huffman_decode_table(pretree_decode_table,
225                                         LZX_PRETREE_NUM_SYMBOLS,
226                                         LZX_PRETREE_TABLEBITS,
227                                         pretree_lens,
228                                         LZX_MAX_CODEWORD_LEN);
229         if (ret != 0)
230                 return ret;
231
232         /* Pointer past the last length value that needs to be filled in. */
233         u8 *lens_end = lens + num_lens;
234
235         while (1) {
236
237                 /* Decode a symbol from the input.  If the symbol is between 0
238                  * and 16, it is the difference from the old length.  If it is
239                  * between 17 and 19, it is a special code that indicates that
240                  * some number of the next lengths are all 0, or some number of
241                  * the next lengths are all equal to the next symbol in the
242                  * input. */
243                 unsigned tree_code;
244                 unsigned num_zeroes;
245                 unsigned code;
246                 unsigned num_same;
247                 signed char value;
248
249                 ret = read_huffsym_using_pretree(istream, pretree_decode_table,
250                                                  pretree_lens, &tree_code);
251                 if (ret != 0)
252                         return ret;
253                 switch (tree_code) {
254                 case 17: /* Run of 0's */
255                         ret = bitstream_read_bits(istream, 4, &num_zeroes);
256                         if (ret != 0)
257                                 return ret;
258                         num_zeroes += 4;
259                         while (num_zeroes--) {
260                                 *lens = 0;
261                                 if (++lens == lens_end)
262                                         return 0;
263                         }
264                         break;
265                 case 18: /* Longer run of 0's */
266                         ret = bitstream_read_bits(istream, 5, &num_zeroes);
267                         if (ret != 0)
268                                 return ret;
269                         num_zeroes += 20;
270                         while (num_zeroes--) {
271                                 *lens = 0;
272                                 if (++lens == lens_end)
273                                         return 0;
274                         }
275                         break;
276                 case 19: /* Run of identical lengths */
277                         ret = bitstream_read_bits(istream, 1, &num_same);
278                         if (ret != 0)
279                                 return ret;
280                         num_same += 4;
281                         ret = read_huffsym_using_pretree(istream,
282                                                          pretree_decode_table,
283                                                          pretree_lens,
284                                                          &code);
285                         if (ret != 0)
286                                 return ret;
287                         value = (signed char)*lens - (signed char)code;
288                         if (value < 0)
289                                 value += 17;
290                         while (num_same--) {
291                                 *lens = value;
292                                 if (++lens == lens_end)
293                                         return 0;
294                         }
295                         break;
296                 default: /* Difference from old length. */
297                         value = (signed char)*lens - (signed char)tree_code;
298                         if (value < 0)
299                                 value += 17;
300                         *lens = value;
301                         if (++lens == lens_end)
302                                 return 0;
303                         break;
304                 }
305         }
306 }
307
308 /*
309  * Reads the header for an LZX-compressed block.
310  *
311  * @istream:            The input bitstream.
312  * @block_size_ret:     A pointer to an int into which the size of the block,
313  *                              in bytes, will be returned.
314  * @block_type_ret:     A pointer to an int into which the type of the block
315  *                              (LZX_BLOCKTYPE_*) will be returned.
316  * @tables:             A pointer to a lzx_tables structure in which the
317  *                              main tree, the length tree, and possibly the
318  *                              aligned offset tree will be constructed.
319  * @queue:      A pointer to the least-recently-used queue into which
320  *                      R0, R1, and R2 will be written (only for uncompressed
321  *                      blocks, which contain this information in the header)
322  */
323 static int
324 lzx_read_block_header(struct input_bitstream *istream,
325                       unsigned *block_size_ret,
326                       unsigned *block_type_ret,
327                       struct lzx_tables *tables,
328                       struct lru_queue *queue)
329 {
330         int ret;
331         unsigned block_type;
332         unsigned block_size;
333         unsigned s;
334         unsigned i;
335         unsigned len;
336
337         ret = bitstream_ensure_bits(istream, 4);
338         if (ret) {
339                 ERROR("LZX input stream overrun");
340                 return ret;
341         }
342
343         /* The first three bits tell us what kind of block it is, and are one
344          * of the LZX_BLOCKTYPE_* values.  */
345         block_type = bitstream_read_bits_nocheck(istream, 3);
346
347         /* The next bit indicates whether the block size is the default (32768),
348          * indicated by a 1 bit, or whether the block size is given by the next
349          * 16 bits, indicated by a 0 bit. */
350         s = bitstream_read_bits_nocheck(istream, 1);
351
352         if (s) {
353                 block_size = 32768;
354         } else {
355                 ret = bitstream_read_bits(istream, 16, &block_size);
356                 if (ret)
357                         return ret;
358                 block_size = le16_to_cpu(block_size);
359         }
360
361         switch (block_type) {
362         case LZX_BLOCKTYPE_ALIGNED:
363                 /* Read the path lengths for the elements of the aligned tree,
364                  * then build it. */
365
366                 for (i = 0; i < LZX_ALIGNEDTREE_NUM_SYMBOLS; i++) {
367                         ret = bitstream_read_bits(istream,
368                                                   LZX_ALIGNEDTREE_ELEMENT_SIZE,
369                                                   &len);
370                         if (ret)
371                                 return ret;
372                         tables->alignedtree_lens[i] = len;
373                 }
374
375                 LZX_DEBUG("Building the aligned tree.");
376                 ret = make_huffman_decode_table(tables->alignedtree_decode_table,
377                                                 LZX_ALIGNEDTREE_NUM_SYMBOLS,
378                                                 LZX_ALIGNEDTREE_TABLEBITS,
379                                                 tables->alignedtree_lens,
380                                                 8);
381                 if (ret) {
382                         ERROR("lzx_decompress(): Failed to make the decode "
383                               "table for the aligned offset tree");
384                         return ret;
385                 }
386
387                 /* Fall though, since the rest of the header for aligned offset
388                  * blocks is the same as that for verbatim blocks */
389
390         case LZX_BLOCKTYPE_VERBATIM:
391                 if (block_type == LZX_BLOCKTYPE_VERBATIM)
392                         LZX_DEBUG("Found verbatim block.");
393
394                 LZX_DEBUG("Reading path lengths for main tree.");
395                 /* Read the path lengths for the first 256 elements of the main
396                  * tree. */
397                 ret = lzx_read_code_lens(istream, tables->maintree_lens,
398                                          LZX_NUM_CHARS);
399                 if (ret) {
400                         ERROR("lzx_decompress(): Failed to read the code "
401                               "lengths for the first 256 elements of the "
402                               "main tree");
403                         return ret;
404                 }
405
406                 /* Read the path lengths for the remaining elements of the main
407                  * tree. */
408                 LZX_DEBUG("Reading path lengths for remaining elements of "
409                           "main tree (%d elements).",
410                           LZX_MAINTREE_NUM_SYMBOLS - LZX_NUM_CHARS);
411                 ret = lzx_read_code_lens(istream,
412                                          tables->maintree_lens + LZX_NUM_CHARS,
413                                          LZX_MAINTREE_NUM_SYMBOLS - LZX_NUM_CHARS);
414                 if (ret) {
415                         ERROR("lzx_decompress(): Failed to read the path "
416                               "lengths for the remaining elements of the main "
417                               "tree");
418                         return ret;
419                 }
420
421                 LZX_DEBUG("Building the Huffman decoding "
422                           "table for the main tree.");
423
424                 ret = make_huffman_decode_table(tables->maintree_decode_table,
425                                                 LZX_MAINTREE_NUM_SYMBOLS,
426                                                 LZX_MAINTREE_TABLEBITS,
427                                                 tables->maintree_lens,
428                                                 LZX_MAX_CODEWORD_LEN);
429                 if (ret) {
430                         ERROR("lzx_decompress(): Failed to make the decode "
431                               "table for the main tree");
432                         return ret;
433                 }
434
435                 LZX_DEBUG("Reading path lengths for the length tree.");
436                 ret = lzx_read_code_lens(istream, tables->lentree_lens,
437                                          LZX_LENTREE_NUM_SYMBOLS);
438                 if (ret) {
439                         ERROR("lzx_decompress(): Failed to read the path "
440                               "lengths for the length tree");
441                         return ret;
442                 }
443
444                 LZX_DEBUG("Building the length tree.");
445                 ret = make_huffman_decode_table(tables->lentree_decode_table,
446                                                 LZX_LENTREE_NUM_SYMBOLS,
447                                                 LZX_LENTREE_TABLEBITS,
448                                                 tables->lentree_lens,
449                                                 LZX_MAX_CODEWORD_LEN);
450                 if (ret) {
451                         ERROR("lzx_decompress(): Failed to build the length "
452                               "Huffman tree");
453                         return ret;
454                 }
455                 /* The bitstream of compressed literals and matches for this
456                  * block directly follows and will be read in
457                  * lzx_decompress_block(). */
458                 break;
459         case LZX_BLOCKTYPE_UNCOMPRESSED:
460                 LZX_DEBUG("Found uncompressed block.");
461                 /* Before reading the three LRU match offsets from the
462                  * uncompressed block header, the stream needs to be aligned on
463                  * a 16-bit boundary.  But, unexpectedly, if the stream is
464                  * *already* aligned, the correct thing to do is to throw away
465                  * the next 16 bits. */
466                 if (istream->bitsleft == 0) {
467                         if (istream->data_bytes_left < 14) {
468                                 ERROR("lzx_decompress(): Insufficient length in "
469                                       "uncompressed block");
470                                 return -1;
471                         }
472                         istream->data += 2;
473                         istream->data_bytes_left -= 2;
474                 } else {
475                         if (istream->data_bytes_left < 12) {
476                                 ERROR("lzx_decompress(): Insufficient length in "
477                                       "uncompressed block");
478                                 return -1;
479                         }
480                         istream->bitsleft = 0;
481                         istream->bitbuf = 0;
482                 }
483                 queue->R0 = le32_to_cpu(*(u32*)(istream->data + 0));
484                 queue->R1 = le32_to_cpu(*(u32*)(istream->data + 4));
485                 queue->R2 = le32_to_cpu(*(u32*)(istream->data + 8));
486                 istream->data += 12;
487                 istream->data_bytes_left -= 12;
488                 /* The uncompressed data of this block directly follows and will
489                  * be read in lzx_decompress(). */
490                 break;
491         default:
492                 ERROR("lzx_decompress(): Found invalid block");
493                 return -1;
494         }
495         *block_type_ret = block_type;
496         *block_size_ret = block_size;
497         return 0;
498 }
499
500 /*
501  * Decodes a compressed match from a block of LZX-compressed data.  A match
502  * refers to some match_offset to a point earlier in the window as well as some
503  * match_len, for which the data is to be copied to the current position in the
504  * window.
505  *
506  * @main_element:       The start of the match data, as decoded using the main
507  *                      tree.
508  *
509  * @block_type:         The type of the block (LZX_BLOCKTYPE_ALIGNED or
510  *                      LZX_BLOCKTYPE_VERBATIM)
511  *
512  * @bytes_remaining:    The amount of uncompressed data remaining to be
513  *                      uncompressed in this block.  It is an error if the match
514  *                      is longer than this number.
515  *
516  * @window:             A pointer to the window into which the uncompressed
517  *                      data is being written.
518  *
519  * @window_pos:         The current byte offset in the window.
520  *
521  * @tables:             The Huffman decoding tables for this LZX block (main
522  *                      code, length code, and for LZX_BLOCKTYPE_ALIGNED blocks,
523  *                      also the aligned offset code).
524  *
525  * @queue:              The least-recently used queue for match offsets.
526  *
527  * @istream:            The input bitstream.
528  *
529  * Returns the length of the match, or a negative number on error.  The possible
530  * error cases are:
531  *      - Match would exceed the amount of data remaining to be uncompressed.
532  *      - Match refers to data before the window.
533  *      - The input bitstream ended unexpectedly.
534  */
535 static int
536 lzx_decode_match(unsigned main_element, int block_type,
537                  unsigned bytes_remaining, u8 *window,
538                  unsigned window_pos,
539                  const struct lzx_tables *tables,
540                  struct lru_queue *queue,
541                  struct input_bitstream *istream)
542 {
543         unsigned length_header;
544         unsigned position_slot;
545         unsigned match_len;
546         unsigned match_offset;
547         unsigned additional_len;
548         unsigned num_extra_bits;
549         unsigned verbatim_bits;
550         unsigned aligned_bits;
551         unsigned i;
552         int ret;
553         u8 *match_dest;
554         u8 *match_src;
555
556         /* The main element is offset by 256 because values under 256 indicate a
557          * literal value. */
558         main_element -= LZX_NUM_CHARS;
559
560         /* The length header consists of the lower 3 bits of the main element.
561          * The position slot is the rest of it. */
562         length_header = main_element & LZX_NUM_PRIMARY_LENS;
563         position_slot = main_element >> 3;
564
565         /* If the length_header is less than LZX_NUM_PRIMARY_LENS (= 7), it
566          * gives the match length as the offset from LZX_MIN_MATCH.  Otherwise,
567          * the length is given by an additional symbol encoded using the length
568          * tree, offset by 9 (LZX_MIN_MATCH + LZX_NUM_PRIMARY_LENS) */
569         match_len = LZX_MIN_MATCH + length_header;
570         if (length_header == LZX_NUM_PRIMARY_LENS) {
571                 ret = read_huffsym_using_lentree(istream, tables,
572                                                  &additional_len);
573                 if (ret != 0)
574                         return ret;
575                 match_len += additional_len;
576         }
577
578
579         /* If the position_slot is 0, 1, or 2, the match offset is retrieved
580          * from the LRU queue.  Otherwise, the match offset is not in the LRU
581          * queue. */
582         switch (position_slot) {
583         case 0:
584                 match_offset = queue->R0;
585                 break;
586         case 1:
587                 match_offset = queue->R1;
588                 swap(queue->R0, queue->R1);
589                 break;
590         case 2:
591                 /* The queue doesn't work quite the same as a real LRU queue,
592                  * since using the R2 offset doesn't bump the R1 offset down to
593                  * R2. */
594                 match_offset = queue->R2;
595                 swap(queue->R0, queue->R2);
596                 break;
597         default:
598                 /* Otherwise, the offset was not encoded as one the offsets in
599                  * the queue.  Depending on the position slot, there is a
600                  * certain number of extra bits that need to be read to fully
601                  * decode the match offset. */
602
603                 /* Look up the number of extra bits that need to be read. */
604                 num_extra_bits = lzx_get_num_extra_bits(position_slot);
605
606                 /* For aligned blocks, if there are at least 3 extra bits, the
607                  * actual number of extra bits is 3 less, and they encode a
608                  * number of 8-byte words that are added to the offset; there
609                  * is then an additional symbol read using the aligned tree that
610                  * specifies the actual byte alignment. */
611                 if (block_type == LZX_BLOCKTYPE_ALIGNED && num_extra_bits >= 3) {
612
613                         /* There is an error in the LZX "specification" at this
614                          * point; it indicates that a Huffman symbol is to be
615                          * read only if num_extra_bits is greater than 3, but
616                          * actually it is if num_extra_bits is greater than or
617                          * equal to 3.  (Note that in the case with
618                          * num_extra_bits == 3, the assignment to verbatim_bits
619                          * will just set it to 0. ) */
620                         ret = bitstream_read_bits(istream, num_extra_bits - 3,
621                                                   &verbatim_bits);
622                         if (ret != 0)
623                                 return ret;
624
625                         verbatim_bits <<= 3;
626
627                         ret = read_huffsym_using_alignedtree(istream, tables,
628                                                              &aligned_bits);
629                         if (ret != 0)
630                                 return ret;
631                 } else {
632                         /* For non-aligned blocks, or for aligned blocks with
633                          * less than 3 extra bits, the extra bits are added
634                          * directly to the match offset, and the correction for
635                          * the alignment is taken to be 0. */
636                         ret = bitstream_read_bits(istream, num_extra_bits,
637                                                   &verbatim_bits);
638                         if (ret != 0)
639                                 return ret;
640
641                         aligned_bits = 0;
642                 }
643
644                 /* Calculate the match offset. */
645                 match_offset = lzx_position_base[position_slot] +
646                                verbatim_bits + aligned_bits - 2;
647
648                 /* Update the LRU queue. */
649                 queue->R2 = queue->R1;
650                 queue->R1 = queue->R0;
651                 queue->R0 = match_offset;
652                 break;
653         }
654
655         /* Verify that the match is in the bounds of the part of the window
656          * currently in use, then copy the source of the match to the current
657          * position. */
658         match_dest = window + window_pos;
659         match_src = match_dest - match_offset;
660
661         if (match_len > bytes_remaining) {
662                 ERROR("lzx_decode_match(): Match of length %u bytes overflows "
663                       "uncompressed block size", match_len);
664                 return -1;
665         }
666
667         if (match_src < window) {
668                 ERROR("lzx_decode_match(): Match of length %u bytes references "
669                       "data before window (match_offset = %u, window_pos = %u)",
670                       match_len, match_offset, window_pos);
671                 return -1;
672         }
673
674 #if 0
675         printf("Match: src %u, dst %u, len %u\n", match_src - window,
676                                                 match_dest - window,
677                                                 match_len);
678         putchar('|');
679         for (i = 0; i < match_len; i++) {
680                 match_dest[i] = match_src[i];
681                 putchar(match_src[i]);
682         }
683         putchar('|');
684         putchar('\n');
685 #else
686         for (i = 0; i < match_len; i++)
687                 match_dest[i] = match_src[i];
688 #endif
689
690         return match_len;
691 }
692
693 static void
694 undo_call_insn_translation(u32 *call_insn_target, int input_pos,
695                            s32 file_size)
696 {
697         s32 abs_offset;
698         s32 rel_offset;
699
700         abs_offset = le32_to_cpu(*call_insn_target);
701         if (abs_offset >= -input_pos && abs_offset < file_size) {
702                 if (abs_offset >= 0) {
703                         /* "good translation" */
704                         rel_offset = abs_offset - input_pos;
705                 } else {
706                         /* "compensating translation" */
707                         rel_offset = abs_offset + file_size;
708                 }
709                 *call_insn_target = cpu_to_le32(rel_offset);
710         }
711 }
712
713 /* Undo the 'E8' preprocessing, where the targets of x86 CALL instructions were
714  * changed from relative offsets to absolute offsets.
715  *
716  * Note that this call instruction preprocessing can and will be used on any
717  * data even if it is not actually x86 machine code.  In fact, this type of
718  * preprocessing appears to always be used in LZX-compressed resources in WIM
719  * files; there is no bit to indicate whether it is used or not, unlike in the
720  * LZX compressed format as used in cabinet files, where a bit is reserved for
721  * that purpose.
722  *
723  * Call instruction preprocessing is disabled in the last 6 bytes of the
724  * uncompressed data, which really means the 5-byte call instruction cannot
725  * start in the last 10 bytes of the uncompressed data.  This is one of the
726  * errors in the LZX documentation.
727  *
728  * Call instruction preprocessing does not appear to be disabled after the
729  * 32768th chunk of a WIM stream, which is apparently is yet another difference
730  * from the LZX compression used in cabinet files.
731  *
732  * Call instruction processing is supposed to take the file size as a parameter,
733  * as it is used in calculating the translated jump targets.  But in WIM files,
734  * this file size is always the same (LZX_WIM_MAGIC_FILESIZE == 12000000).*/
735 static void
736 undo_call_insn_preprocessing(u8 uncompressed_data[], int uncompressed_data_len)
737 {
738         for (int i = 0; i < uncompressed_data_len - 10; i++) {
739                 if (uncompressed_data[i] == 0xe8) {
740                         undo_call_insn_translation((u32*)&uncompressed_data[i + 1],
741                                                    i,
742                                                    LZX_WIM_MAGIC_FILESIZE);
743                         i += 4;
744                 }
745         }
746 }
747
748 /*
749  * Decompresses a LZX-compressed block of data from which the header has already
750  * been read.
751  *
752  * @block_type: The type of the block (LZX_BLOCKTYPE_VERBATIM or
753  *              LZX_BLOCKTYPE_ALIGNED)
754  * @block_size: The size of the block, in bytes.
755  * @window:     Pointer to the decompression window.
756  * @window_pos: The current position in the window.  Will be 0 for the first
757  *                      block.
758  * @tables:     The Huffman decoding tables for the block (main, length, and
759  *                      aligned offset, the latter only for LZX_BLOCKTYPE_ALIGNED)
760  * @queue:      The least-recently-used queue for match offsets.
761  * @istream:    The input bitstream for the compressed literals.
762  */
763 static int
764 lzx_decompress_block(int block_type, unsigned block_size,
765                      u8 *window,
766                      unsigned window_pos,
767                      const struct lzx_tables *tables,
768                      struct lru_queue *queue,
769                      struct input_bitstream *istream)
770 {
771         unsigned main_element;
772         unsigned end;
773         int ret;
774         int match_len;
775
776         end = window_pos + block_size;
777         while (window_pos < end) {
778                 ret = read_huffsym_using_maintree(istream, tables,
779                                                   &main_element);
780                 if (ret)
781                         return ret;
782
783                 if (main_element < LZX_NUM_CHARS) {
784                         /* literal: 0 to LZX_NUM_CHARS - 1 */
785                         window[window_pos++] = main_element;
786                 } else {
787                         /* match: LZX_NUM_CHARS to LZX_MAINTREE_NUM_SYMBOLS - 1 */
788                         match_len = lzx_decode_match(main_element,
789                                                      block_type,
790                                                      end - window_pos,
791                                                      window,
792                                                      window_pos,
793                                                      tables,
794                                                      queue,
795                                                      istream);
796                         if (match_len < 0)
797                                 return match_len;
798                         window_pos += match_len;
799                 }
800         }
801         return 0;
802 }
803
804 /* Documented in wimlib.h */
805 WIMLIBAPI int
806 wimlib_lzx_decompress(const void *compressed_data, unsigned compressed_len,
807                       void *uncompressed_data, unsigned uncompressed_len)
808 {
809         struct lzx_tables tables;
810         struct input_bitstream istream;
811         struct lru_queue queue;
812         unsigned window_pos;
813         unsigned block_size;
814         unsigned block_type;
815         int ret;
816         bool e8_preprocessing_done;
817
818         LZX_DEBUG("lzx_decompress (compressed_data = %p, compressed_len = %d, "
819                   "uncompressed_data = %p, uncompressed_len = %d).",
820                   compressed_data, compressed_len,
821                   uncompressed_data, uncompressed_len);
822
823         wimlib_assert(uncompressed_len <= 32768);
824
825         memset(tables.maintree_lens, 0, sizeof(tables.maintree_lens));
826         memset(tables.lentree_lens, 0, sizeof(tables.lentree_lens));
827         queue.R0 = 1;
828         queue.R1 = 1;
829         queue.R2 = 1;
830         init_input_bitstream(&istream, compressed_data, compressed_len);
831
832         e8_preprocessing_done = false; /* Set to true if there may be 0xe8 bytes
833                                           in the uncompressed data. */
834
835         /* The compressed data will consist of one or more blocks.  The
836          * following loop decompresses one block, and it runs until there all
837          * the compressed data has been decompressed, so there are no more
838          * blocks.  */
839
840         for (window_pos = 0;
841              window_pos < uncompressed_len;
842              window_pos += block_size)
843         {
844                 LZX_DEBUG("Reading block header.");
845                 ret = lzx_read_block_header(&istream, &block_size,
846                                             &block_type, &tables, &queue);
847                 if (ret)
848                         return ret;
849
850                 LZX_DEBUG("block_size = %u, window_pos = %u",
851                           block_size, window_pos);
852
853                 if (block_size > uncompressed_len - window_pos) {
854                         ERROR("lzx_decompress(): Expected a block size of at "
855                               "most %u bytes (found %u bytes)",
856                               uncompressed_len - window_pos, block_size);
857                         return -1;
858                 }
859
860                 switch (block_type) {
861                 case LZX_BLOCKTYPE_VERBATIM:
862                 case LZX_BLOCKTYPE_ALIGNED:
863                         if (block_type == LZX_BLOCKTYPE_VERBATIM)
864                                 LZX_DEBUG("LZX_BLOCKTYPE_VERBATIM");
865                         else
866                                 LZX_DEBUG("LZX_BLOCKTYPE_ALIGNED");
867                         ret = lzx_decompress_block(block_type,
868                                                    block_size,
869                                                    uncompressed_data,
870                                                    window_pos,
871                                                    &tables,
872                                                    &queue,
873                                                    &istream);
874                         if (ret)
875                                 return ret;
876                         if (tables.maintree_lens[0xe8] != 0)
877                                 e8_preprocessing_done = true;
878                         break;
879                 case LZX_BLOCKTYPE_UNCOMPRESSED:
880                         LZX_DEBUG("LZX_BLOCKTYPE_UNCOMPRESSED");
881                         if (istream.data_bytes_left < block_size) {
882                                 ERROR("Unexpected end of input when "
883                                       "reading %u bytes from LZX bitstream "
884                                       "(only have %u bytes left)",
885                                       block_size, istream.data_bytes_left);
886                                 return -1;
887                         }
888                         memcpy(&((u8*)uncompressed_data)[window_pos], istream.data,
889                                block_size);
890                         istream.data += block_size;
891                         istream.data_bytes_left -= block_size;
892                         /* Re-align bitstream if an odd number of bytes were
893                          * read.  */
894                         if (istream.data_bytes_left && (block_size & 1)) {
895                                 istream.data_bytes_left--;
896                                 istream.data++;
897                         }
898                         e8_preprocessing_done = true;
899                         break;
900                 }
901         }
902         if (e8_preprocessing_done)
903                 undo_call_insn_preprocessing(uncompressed_data, uncompressed_len);
904         return 0;
905 }