2 * lzx_common.c - Common code for LZX compression and decompression.
6 * Copyright (C) 2012-2016 Eric Biggers
8 * This file is free software; you can redistribute it and/or modify it under
9 * the terms of the GNU Lesser General Public License as published by the Free
10 * Software Foundation; either version 3 of the License, or (at your option) any
13 * This file is distributed in the hope that it will be useful, but WITHOUT
14 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
15 * FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
18 * You should have received a copy of the GNU Lesser General Public License
19 * along with this file; if not, see http://www.gnu.org/licenses/.
29 # include <emmintrin.h>
33 # include <immintrin.h>
36 #include "wimlib/bitops.h"
37 #include "wimlib/endianness.h"
38 #include "wimlib/lzx_common.h"
39 #include "wimlib/unaligned.h"
40 #include "wimlib/util.h"
42 /* Mapping: offset slot => first match offset that uses that offset slot.
44 const u32 lzx_offset_slot_base[LZX_MAX_OFFSET_SLOTS + 1] = {
45 0 , 1 , 2 , 3 , 4 , /* 0 --- 4 */
46 6 , 8 , 12 , 16 , 24 , /* 5 --- 9 */
47 32 , 48 , 64 , 96 , 128 , /* 10 --- 14 */
48 192 , 256 , 384 , 512 , 768 , /* 15 --- 19 */
49 1024 , 1536 , 2048 , 3072 , 4096 , /* 20 --- 24 */
50 6144 , 8192 , 12288 , 16384 , 24576 , /* 25 --- 29 */
51 32768 , 49152 , 65536 , 98304 , 131072 , /* 30 --- 34 */
52 196608 , 262144 , 393216 , 524288 , 655360 , /* 35 --- 39 */
53 786432 , 917504 , 1048576, 1179648, 1310720, /* 40 --- 44 */
54 1441792, 1572864, 1703936, 1835008, 1966080, /* 45 --- 49 */
58 /* Mapping: offset slot => how many extra bits must be read and added to the
59 * corresponding offset slot base to decode the match offset. */
60 const u8 lzx_extra_offset_bits[LZX_MAX_OFFSET_SLOTS] = {
73 /* Round the specified buffer size up to the next valid LZX window size, and
74 * return its order (log2). Or, if the buffer size is 0 or greater than the
75 * largest valid LZX window size, return 0. */
77 lzx_get_window_order(size_t max_bufsize)
79 if (max_bufsize == 0 || max_bufsize > LZX_MAX_WINDOW_SIZE)
82 return max(ilog2_ceil(max_bufsize), LZX_MIN_WINDOW_ORDER);
85 /* Given a valid LZX window order, return the number of symbols that will exist
86 * in the main Huffman code. */
88 lzx_get_num_main_syms(unsigned window_order)
90 /* Note: one would expect that the maximum match offset would be
91 * 'window_size - LZX_MIN_MATCH_LEN', which would occur if the first two
92 * bytes were to match the last two bytes. However, the format
93 * disallows this case. This reduces the number of needed offset slots
95 u32 window_size = (u32)1 << window_order;
96 u32 max_adjusted_offset = (window_size - LZX_MIN_MATCH_LEN - 1) +
97 LZX_OFFSET_ADJUSTMENT;
98 unsigned num_offset_slots = 30;
99 while (max_adjusted_offset >= lzx_offset_slot_base[num_offset_slots])
102 return LZX_NUM_CHARS + (num_offset_slots * LZX_NUM_LEN_HEADERS);
106 do_translate_target(void *target, s32 input_pos)
108 s32 abs_offset, rel_offset;
110 rel_offset = get_unaligned_le32(target);
111 if (rel_offset >= -input_pos && rel_offset < LZX_WIM_MAGIC_FILESIZE) {
112 if (rel_offset < LZX_WIM_MAGIC_FILESIZE - input_pos) {
113 /* "good translation" */
114 abs_offset = rel_offset + input_pos;
116 /* "compensating translation" */
117 abs_offset = rel_offset - LZX_WIM_MAGIC_FILESIZE;
119 put_unaligned_le32(abs_offset, target);
124 undo_translate_target(void *target, s32 input_pos)
126 s32 abs_offset, rel_offset;
128 abs_offset = get_unaligned_le32(target);
129 if (abs_offset >= 0) {
130 if (abs_offset < LZX_WIM_MAGIC_FILESIZE) {
131 /* "good translation" */
132 rel_offset = abs_offset - input_pos;
133 put_unaligned_le32(rel_offset, target);
136 if (abs_offset >= -input_pos) {
137 /* "compensating translation" */
138 rel_offset = abs_offset + LZX_WIM_MAGIC_FILESIZE;
139 put_unaligned_le32(rel_offset, target);
145 * Do or undo the 'E8' preprocessing used in LZX. Before compression, the
146 * uncompressed data is preprocessed by changing the targets of x86 CALL
147 * instructions from relative offsets to absolute offsets. After decompression,
148 * the translation is undone by changing the targets of x86 CALL instructions
149 * from absolute offsets to relative offsets.
151 * Note that despite its intent, E8 preprocessing can be done on any data even
152 * if it is not actually x86 machine code. In fact, E8 preprocessing appears to
153 * always be used in LZX-compressed resources in WIM files; there is no bit to
154 * indicate whether it is used or not, unlike in the LZX compressed format as
155 * used in cabinet files, where a bit is reserved for that purpose.
157 * E8 preprocessing is disabled in the last 6 bytes of the uncompressed data,
158 * which really means the 5-byte call instruction cannot start in the last 10
159 * bytes of the uncompressed data. This is one of the errors in the LZX
162 * E8 preprocessing does not appear to be disabled after the 32768th chunk of a
163 * WIM resource, which apparently is another difference from the LZX compression
164 * used in cabinet files.
166 * E8 processing is supposed to take the file size as a parameter, as it is used
167 * in calculating the translated jump targets. But in WIM files, this file size
168 * is always the same (LZX_WIM_MAGIC_FILESIZE == 12000000).
171 lzx_e8_filter(u8 *data, u32 size, void (*process_target)(void *, s32))
174 #if !defined(__SSE2__) && !defined(__AVX2__)
176 * A worthwhile optimization is to push the end-of-buffer check into the
177 * relatively rare E8 case. This is possible if we replace the last six
178 * bytes of data with E8 bytes; then we are guaranteed to hit an E8 byte
179 * before reaching end-of-buffer. In addition, this scheme guarantees
180 * that no translation can begin following an E8 byte in the last 10
181 * bytes because a 4-byte offset containing E8 as its high byte is a
182 * large negative number that is not valid for translation. That is
183 * exactly what we need.
192 tail = &data[size - 6];
193 memcpy(saved_bytes, tail, 6);
194 memset(tail, 0xE8, 6);
201 (*process_target)(p + 1, p - data);
204 memcpy(tail, saved_bytes, 6);
206 /* SSE2 or AVX-2 optimized version for x86_64 */
214 # define ALIGNMENT_REQUIRED 32
216 # define ALIGNMENT_REQUIRED 16
219 /* Process one byte at a time until the pointer is properly aligned. */
220 while ((uintptr_t)p % ALIGNMENT_REQUIRED != 0) {
221 if (p >= data + size - 10)
223 if (*p == 0xE8 && (valid_mask & 1)) {
224 (*process_target)(p + 1, p - data);
229 valid_mask |= (u64)1 << 63;
232 if (data + size - p >= 64) {
234 /* Vectorized processing */
236 /* Note: we use a "trap" E8 byte to eliminate the need to check
237 * for end-of-buffer in the inner loop. This byte is carefully
238 * positioned so that it will never be changed by a previous
239 * translation before it is detected. */
241 u8 *trap = p + ((data + size - p) & ~31) - 32 + 4;
242 u8 saved_byte = *trap;
249 const __m256i e8_bytes = _mm256_set1_epi8(0xE8);
251 __m256i bytes = *(const __m256i *)p;
252 __m256i cmpresult = _mm256_cmpeq_epi8(bytes, e8_bytes);
253 e8_mask = _mm256_movemask_epi8(cmpresult);
259 const __m128i e8_bytes = _mm_set1_epi8(0xE8);
261 /* Read the next 32 bytes of data and test them
263 __m128i bytes1 = *(const __m128i *)p;
264 __m128i bytes2 = *(const __m128i *)(p + 16);
265 __m128i cmpresult1 = _mm_cmpeq_epi8(bytes1, e8_bytes);
266 __m128i cmpresult2 = _mm_cmpeq_epi8(bytes2, e8_bytes);
267 u32 mask1 = _mm_movemask_epi8(cmpresult1);
268 u32 mask2 = _mm_movemask_epi8(cmpresult2);
269 /* The masks have a bit set for each E8 byte.
270 * We stay in this fast inner loop as long as
271 * there are no E8 bytes. */
273 e8_mask = mask1 | (mask2 << 16);
280 /* Did we pass over data with no E8 bytes? */
284 /* Are we nearing end-of-buffer? */
288 /* Process the E8 bytes. However, the AND with
289 * 'valid_mask' ensures we never process an E8 byte that
290 * was itself part of a translation target. */
291 while ((e8_mask &= valid_mask)) {
292 unsigned bit = ffs32(e8_mask);
293 (*process_target)(p + bit + 1, p + bit - data);
294 valid_mask &= ~((u64)0x1F << bit);
298 valid_mask |= 0xFFFFFFFF00000000;
305 /* Approaching the end of the buffer; process one byte a time. */
306 while (p < data + size - 10) {
307 if (*p == 0xE8 && (valid_mask & 1)) {
308 (*process_target)(p + 1, p - data);
313 valid_mask |= (u64)1 << 63;
315 #endif /* __SSE2__ || __AVX2__ */
319 lzx_preprocess(u8 *data, u32 size)
321 lzx_e8_filter(data, size, do_translate_target);
325 lzx_postprocess(u8 *data, u32 size)
327 lzx_e8_filter(data, size, undo_translate_target);