4 * A decompressor for the LZX compression format, as used in WIM files.
8 * Copyright (C) 2012, 2013, 2014 Eric Biggers
10 * This file is free software; you can redistribute it and/or modify it under
11 * the terms of the GNU Lesser General Public License as published by the Free
12 * Software Foundation; either version 3 of the License, or (at your option) any
15 * This file is distributed in the hope that it will be useful, but WITHOUT
16 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
17 * FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
20 * You should have received a copy of the GNU Lesser General Public License
21 * along with this file; if not, see http://www.gnu.org/licenses/.
25 * LZX is an LZ77 and Huffman-code based compression format that has many
26 * similarities to DEFLATE (the format used by zlib/gzip). The compression
27 * ratio is as good or better than DEFLATE. See lzx_compress.c for a format
28 * overview, and see https://en.wikipedia.org/wiki/LZX_(algorithm) for a
29 * historical overview. Here I make some pragmatic notes.
31 * The old specification for LZX is the document "Microsoft LZX Data Compression
32 * Format" (1997). It defines the LZX format as used in cabinet files. Allowed
33 * window sizes are 2^n where 15 <= n <= 21. However, this document contains
34 * several errors, so don't read too much into it...
36 * The new specification for LZX is the document "[MS-PATCH]: LZX DELTA
37 * Compression and Decompression" (2014). It defines the LZX format as used by
38 * Microsoft's binary patcher. It corrects several errors in the 1997 document
39 * and extends the format in several ways --- namely, optional reference data,
40 * up to 2^25 byte windows, and longer match lengths.
42 * WIM files use a more restricted form of LZX. No LZX DELTA extensions are
43 * present, the window is not "sliding", E8 preprocessing is done
44 * unconditionally with a fixed file size, and the maximum window size is always
45 * 2^15 bytes (equal to the size of each "chunk" in a compressed WIM resource).
46 * This code is primarily intended to implement this form of LZX. But although
47 * not compatible with WIMGAPI, this code also supports maximum window sizes up
50 * TODO: Add support for window sizes up to 2^25 bytes.
57 #include "wimlib/decompressor_ops.h"
58 #include "wimlib/decompress_common.h"
59 #include "wimlib/error.h"
60 #include "wimlib/lzx_common.h"
61 #include "wimlib/util.h"
65 /* These values are chosen for fast decompression. */
66 #define LZX_MAINCODE_TABLEBITS 11
67 #define LZX_LENCODE_TABLEBITS 10
68 #define LZX_PRECODE_TABLEBITS 6
69 #define LZX_ALIGNEDCODE_TABLEBITS 7
71 #define LZX_READ_LENS_MAX_OVERRUN 50
73 /* Huffman decoding tables, and arrays that map symbols to codeword lengths. */
76 u16 maincode_decode_table[(1 << LZX_MAINCODE_TABLEBITS) +
77 (LZX_MAINCODE_MAX_NUM_SYMBOLS * 2)]
78 _aligned_attribute(DECODE_TABLE_ALIGNMENT);
79 u8 maincode_lens[LZX_MAINCODE_MAX_NUM_SYMBOLS + LZX_READ_LENS_MAX_OVERRUN];
82 u16 lencode_decode_table[(1 << LZX_LENCODE_TABLEBITS) +
83 (LZX_LENCODE_NUM_SYMBOLS * 2)]
84 _aligned_attribute(DECODE_TABLE_ALIGNMENT);
85 u8 lencode_lens[LZX_LENCODE_NUM_SYMBOLS + LZX_READ_LENS_MAX_OVERRUN];
88 u16 alignedcode_decode_table[(1 << LZX_ALIGNEDCODE_TABLEBITS) +
89 (LZX_ALIGNEDCODE_NUM_SYMBOLS * 2)]
90 _aligned_attribute(DECODE_TABLE_ALIGNMENT);
91 u8 alignedcode_lens[LZX_ALIGNEDCODE_NUM_SYMBOLS];
92 } _aligned_attribute(DECODE_TABLE_ALIGNMENT);
94 /* The main LZX decompressor structure.
96 * Note: we keep track of most of the decompression state outside this
97 * structure. This structure only exists so that (1) we can store @window_order
98 * and @num_main_syms for multiple calls to lzx_decompress(); and (2) so that we
99 * don't have to allocate the large 'struct lzx_tables' on the stack. */
100 struct lzx_decompressor {
101 unsigned window_order;
102 unsigned num_main_syms;
103 struct lzx_tables tables;
106 /* Read a Huffman-encoded symbol using the precode. */
108 read_huffsym_using_precode(struct input_bitstream *istream,
109 const u16 precode_decode_table[])
111 return read_huffsym(istream, precode_decode_table,
112 LZX_PRECODE_TABLEBITS, LZX_MAX_PRE_CODEWORD_LEN);
115 /* Read a Huffman-encoded symbol using the main code. */
117 read_huffsym_using_maincode(struct input_bitstream *istream,
118 const struct lzx_tables *tables)
120 return read_huffsym(istream, tables->maincode_decode_table,
121 LZX_MAINCODE_TABLEBITS, LZX_MAX_MAIN_CODEWORD_LEN);
124 /* Read a Huffman-encoded symbol using the length code. */
126 read_huffsym_using_lencode(struct input_bitstream *istream,
127 const struct lzx_tables *tables)
129 return read_huffsym(istream, tables->lencode_decode_table,
130 LZX_LENCODE_TABLEBITS, LZX_MAX_LEN_CODEWORD_LEN);
133 /* Read a Huffman-encoded symbol using the aligned offset code. */
135 read_huffsym_using_alignedcode(struct input_bitstream *istream,
136 const struct lzx_tables *tables)
138 return read_huffsym(istream, tables->alignedcode_decode_table,
139 LZX_ALIGNEDCODE_TABLEBITS, LZX_MAX_ALIGNED_CODEWORD_LEN);
143 * Read the precode from the compressed input bitstream, then use it to decode
144 * @num_lens codeword length values.
147 * The input bitstream.
150 * An array that contains the length values from the previous time the
151 * codeword lengths for this Huffman code were read, or all 0's if this is
152 * the first time. This array must have at least (@num_lens +
153 * LZX_READ_LENS_MAX_OVERRUN) entries.
156 * Number of length values to decode.
158 * Returns 0 on success, or -1 if the data was invalid.
161 lzx_read_codeword_lens(struct input_bitstream *istream, u8 *lens, unsigned num_lens)
163 u16 precode_decode_table[(1 << LZX_PRECODE_TABLEBITS) +
164 (LZX_PRECODE_NUM_SYMBOLS * 2)]
165 _aligned_attribute(DECODE_TABLE_ALIGNMENT);
166 u8 precode_lens[LZX_PRECODE_NUM_SYMBOLS];
168 u8 *lens_end = lens + num_lens;
171 /* Read the lengths of the precode codewords. These are given
173 for (int i = 0; i < LZX_PRECODE_NUM_SYMBOLS; i++) {
174 precode_lens[i] = bitstream_read_bits(istream,
175 LZX_PRECODE_ELEMENT_SIZE);
178 /* Make the decoding table for the precode. */
179 ret = make_huffman_decode_table(precode_decode_table,
180 LZX_PRECODE_NUM_SYMBOLS,
181 LZX_PRECODE_TABLEBITS,
183 LZX_MAX_PRE_CODEWORD_LEN);
187 /* Decode the codeword lengths. */
192 /* Read the next precode symbol. */
193 presym = read_huffsym_using_precode(istream,
194 precode_decode_table);
196 /* Difference from old length */
197 len = *len_ptr - presym;
202 /* Special RLE values */
208 run_len = 4 + bitstream_read_bits(istream, 4);
210 } else if (presym == 18) {
211 /* Longer run of 0's */
212 run_len = 20 + bitstream_read_bits(istream, 5);
215 /* Run of identical lengths */
216 run_len = 4 + bitstream_read_bits(istream, 1);
217 presym = read_huffsym_using_precode(istream,
218 precode_decode_table);
219 len = *len_ptr - presym;
227 /* Worst case overrun is when presym == 18,
228 * run_len == 20 + 31, and only 1 length was remaining.
229 * So LZX_READ_LENS_MAX_OVERRUN == 50.
231 * Overrun while reading the first half of maincode_lens
232 * can corrupt the previous values in the second half.
233 * This doesn't really matter because the resulting
234 * lengths will still be in range, and data that
235 * generates overruns is invalid anyway. */
237 } while (len_ptr < lens_end);
242 * Read the header of an LZX block and save the block type and size in
243 * *block_type_ret and *block_size_ret, respectively.
245 * If the block is compressed, also update the Huffman decode @tables with the
248 * If the block is uncompressed, also update the match offset @queue with the
251 * Return 0 on success, or -1 if the data was invalid.
254 lzx_read_block_header(struct input_bitstream *istream,
255 unsigned num_main_syms,
256 unsigned window_order,
259 struct lzx_tables *tables,
260 struct lzx_lru_queue *queue)
266 bitstream_ensure_bits(istream, 4);
268 /* The first three bits tell us what kind of block it is, and should be
269 * one of the LZX_BLOCKTYPE_* values. */
270 block_type = bitstream_pop_bits(istream, 3);
272 /* Read the block size. This mirrors the behavior of
273 * lzx_write_compressed_block() in lzx_compress.c; see that for more
275 if (bitstream_pop_bits(istream, 1)) {
276 block_size = LZX_DEFAULT_BLOCK_SIZE;
281 tmp = bitstream_read_bits(istream, 8);
283 tmp = bitstream_read_bits(istream, 8);
287 if (window_order >= 16) {
288 tmp = bitstream_read_bits(istream, 8);
294 switch (block_type) {
296 case LZX_BLOCKTYPE_ALIGNED:
298 /* Read the aligned offset code and prepare its decode table.
301 for (int i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++) {
302 tables->alignedcode_lens[i] =
303 bitstream_read_bits(istream,
304 LZX_ALIGNEDCODE_ELEMENT_SIZE);
307 ret = make_huffman_decode_table(tables->alignedcode_decode_table,
308 LZX_ALIGNEDCODE_NUM_SYMBOLS,
309 LZX_ALIGNEDCODE_TABLEBITS,
310 tables->alignedcode_lens,
311 LZX_MAX_ALIGNED_CODEWORD_LEN);
315 /* Fall though, since the rest of the header for aligned offset
316 * blocks is the same as that for verbatim blocks. */
318 case LZX_BLOCKTYPE_VERBATIM:
320 /* Read the main code and prepare its decode table.
322 * Note that the codeword lengths in the main code are encoded
323 * in two parts: one part for literal symbols, and one part for
326 ret = lzx_read_codeword_lens(istream, tables->maincode_lens,
331 ret = lzx_read_codeword_lens(istream,
332 tables->maincode_lens + LZX_NUM_CHARS,
333 num_main_syms - LZX_NUM_CHARS);
337 ret = make_huffman_decode_table(tables->maincode_decode_table,
339 LZX_MAINCODE_TABLEBITS,
340 tables->maincode_lens,
341 LZX_MAX_MAIN_CODEWORD_LEN);
345 /* Read the length code and prepare its decode table. */
347 ret = lzx_read_codeword_lens(istream, tables->lencode_lens,
348 LZX_LENCODE_NUM_SYMBOLS);
352 ret = make_huffman_decode_table(tables->lencode_decode_table,
353 LZX_LENCODE_NUM_SYMBOLS,
354 LZX_LENCODE_TABLEBITS,
355 tables->lencode_lens,
356 LZX_MAX_LEN_CODEWORD_LEN);
362 case LZX_BLOCKTYPE_UNCOMPRESSED:
364 /* Before reading the three LRU match offsets from the
365 * uncompressed block header, the stream must be aligned on a
366 * 16-bit boundary. But, unexpectedly, if the stream is
367 * *already* aligned, the correct thing to do is to throw away
368 * the next 16 bits. */
370 bitstream_ensure_bits(istream, 1);
371 bitstream_align(istream);
372 queue->R[0] = bitstream_read_u32(istream);
373 queue->R[1] = bitstream_read_u32(istream);
374 queue->R[2] = bitstream_read_u32(istream);
376 /* Offsets of 0 are invalid. */
377 if (queue->R[0] == 0 || queue->R[1] == 0 || queue->R[2] == 0)
382 /* Unrecognized block type. */
386 *block_type_ret = block_type;
387 *block_size_ret = block_size;
392 * Decompress an LZX-compressed block of data.
395 * The type of the block (LZX_BLOCKTYPE_VERBATIM or LZX_BLOCKTYPE_ALIGNED).
398 * The size of the block, in bytes.
401 * Pointer to the beginning of the decompression window.
404 * The position in the window at which the block starts.
407 * The Huffman decoding tables for the block.
410 * The least-recently-used queue for match offsets.
413 * The input bitstream, positioned at the start of the block data.
415 * Returns 0 on success, or -1 if the data was invalid.
418 lzx_decompress_block(int block_type, u32 block_size,
419 u8 *window, u32 window_pos,
420 const struct lzx_tables *tables,
421 struct lzx_lru_queue *queue,
422 struct input_bitstream *istream)
424 u8 *window_ptr = &window[window_pos];
425 u8 *window_end = window_ptr + block_size;
428 unsigned offset_slot;
430 unsigned num_extra_bits;
431 unsigned ones_if_aligned = 0U - (block_type == LZX_BLOCKTYPE_ALIGNED);
433 while (window_ptr != window_end) {
435 mainsym = read_huffsym_using_maincode(istream, tables);
436 if (mainsym < LZX_NUM_CHARS) {
438 *window_ptr++ = mainsym;
444 /* Decode the length header and offset slot. */
445 mainsym -= LZX_NUM_CHARS;
446 match_len = mainsym & 0x7;
447 offset_slot = mainsym >> 3;
449 /* If needed, read a length symbol to decode the full length. */
450 if (match_len == 0x7)
451 match_len += read_huffsym_using_lencode(istream, tables);
452 match_len += LZX_MIN_MATCH_LEN;
454 if (offset_slot <= 2) {
457 /* Note: This isn't a real LRU queue, since using the R2
458 * offset doesn't bump the R1 offset down to R2. This
459 * quirk allows all 3 recent offsets to be handled by
460 * the same code. (For R0, the swap is a no-op.) */
461 match_offset = queue->R[offset_slot];
462 queue->R[offset_slot] = queue->R[0];
463 queue->R[0] = match_offset;
465 /* Explicit offset */
467 /* Look up the number of extra bits that need to be read
468 * to decode offsets with this offset slot. */
469 num_extra_bits = lzx_extra_offset_bits[offset_slot];
471 /* Start with the offset slot base value. */
472 match_offset = lzx_offset_slot_base[offset_slot];
474 /* In aligned offset blocks, the low-order 3 bits of
475 * each offset are encoded using the aligned offset
476 * code. Otherwise, all the extra bits are literal. */
478 /*if (block_type == LZX_BLOCKTYPE_ALIGNED && num_extra_bits >= 3) {*/
479 if ((num_extra_bits & ones_if_aligned) >= 3) {
480 match_offset += bitstream_read_bits(istream, num_extra_bits - 3) << 3;
481 match_offset += read_huffsym_using_alignedcode(istream, tables);
483 match_offset += bitstream_read_bits(istream, num_extra_bits);
486 /* Adjust the offset. */
487 match_offset -= LZX_OFFSET_OFFSET;
489 /* Update the match offset LRU queue. */
490 queue->R[2] = queue->R[1];
491 queue->R[1] = queue->R[0];
492 queue->R[0] = match_offset;
495 /* Validate the match, then copy it to the current position. */
497 if (unlikely(match_len > window_end - window_ptr))
500 if (unlikely(match_offset > window_ptr - window))
503 lz_copy(window_ptr, match_len, match_offset, window_end,
506 window_ptr += match_len;
512 lzx_decompress(const void *compressed_data, size_t compressed_size,
513 void *uncompressed_data, size_t uncompressed_size,
516 struct lzx_decompressor *dec = _dec;
517 struct input_bitstream istream;
518 struct lzx_lru_queue queue;
522 bool may_have_e8_byte;
525 init_input_bitstream(&istream, compressed_data, compressed_size);
527 /* Initialize the recent offsets queue. */
528 lzx_lru_queue_init(&queue);
530 /* Codeword lengths begin as all 0's for delta encoding purposes. */
531 memset(dec->tables.maincode_lens, 0, dec->num_main_syms);
532 memset(dec->tables.lencode_lens, 0, LZX_LENCODE_NUM_SYMBOLS);
534 /* Set this to true if there may be 0xe8 bytes in the uncompressed data.
536 may_have_e8_byte = false;
538 /* The compressed data will consist of one or more blocks. The
539 * following loop decompresses one block, and it runs until there all
540 * the compressed data has been decompressed, so there are no more
544 window_pos < uncompressed_size;
545 window_pos += block_size)
547 ret = lzx_read_block_header(&istream, dec->num_main_syms,
548 dec->window_order, &block_type,
549 &block_size, &dec->tables, &queue);
553 if (block_size > uncompressed_size - window_pos)
556 if (block_type != LZX_BLOCKTYPE_UNCOMPRESSED) {
558 /* Compressed block. */
560 ret = lzx_decompress_block(block_type,
570 /* If the first 0xe8 byte was in this block, it must
571 * have been encoded as a literal using mainsym 0xe8. */
572 if (dec->tables.maincode_lens[0xe8] != 0)
573 may_have_e8_byte = true;
576 /* Uncompressed block. */
579 p = bitstream_read_bytes(&istream, block_size);
583 memcpy(&((u8*)uncompressed_data)[window_pos], p, block_size);
585 /* Re-align the bitstream if an odd number of bytes was
588 bitstream_read_byte(&istream);
590 may_have_e8_byte = true;
594 /* Postprocess the data unless it cannot possibly contain 0xe8 bytes */
595 if (may_have_e8_byte)
596 lzx_undo_e8_preprocessing(uncompressed_data, uncompressed_size);
602 lzx_free_decompressor(void *_dec)
604 struct lzx_decompressor *dec = _dec;
610 lzx_create_decompressor(size_t max_block_size, void **dec_ret)
612 struct lzx_decompressor *dec;
613 unsigned window_order;
615 window_order = lzx_get_window_order(max_block_size);
616 if (window_order == 0)
617 return WIMLIB_ERR_INVALID_PARAM;
619 /* The aligned allocation is needed to ensure that the lzx_tables are
620 * aligned properly. */
621 dec = ALIGNED_MALLOC(sizeof(struct lzx_decompressor),
622 DECODE_TABLE_ALIGNMENT);
624 return WIMLIB_ERR_NOMEM;
626 dec->window_order = window_order;
627 dec->num_main_syms = lzx_get_num_main_syms(window_order);
633 const struct decompressor_ops lzx_decompressor_ops = {
634 .create_decompressor = lzx_create_decompressor,
635 .decompress = lzx_decompress,
636 .free_decompressor = lzx_free_decompressor,