1 /* SPDX-License-Identifier: GPL-2.0-or-later */
2 /*
3 * decompress_common.h - Code shared by the XPRESS and LZX decompressors
4 *
5 * Copyright (C) 2015 Eric Biggers
6 */
7
8 #ifndef _LINUX_NTFS3_LIB_DECOMPRESS_COMMON_H
9 #define _LINUX_NTFS3_LIB_DECOMPRESS_COMMON_H
10
11 #include <linux/string.h>
12 #include <linux/compiler.h>
13 #include <linux/types.h>
14 #include <linux/slab.h>
15 #include <asm/unaligned.h>
16
17
18 /* "Force inline" macro (not required, but helpful for performance) */
19 #define forceinline __always_inline
20
21 /* Enable whole-word match copying on selected architectures */
22 #if defined(__i386__) || defined(__x86_64__) || defined(__ARM_FEATURE_UNALIGNED)
23 # define FAST_UNALIGNED_ACCESS
24 #endif
25
26 /* Size of a machine word */
27 #define WORDBYTES (sizeof(size_t))
28
29 static forceinline void
30 copy_unaligned_word(const void *src, void *dst)
31 {
32 put_unaligned(get_unaligned((const size_t *)src), (size_t *)dst);
33 }
34
35
36 /* Generate a "word" with platform-dependent size whose bytes all contain the
37 * value 'b'.
38 */
39 static forceinline size_t repeat_byte(u8 b)
40 {
41 size_t v;
42
43 v = b;
44 v |= v << 8;
45 v |= v << 16;
46 v |= v << ((WORDBYTES == 8) ? 32 : 0);
47 return v;
48 }
49
50 /* Structure that encapsulates a block of in-memory data being interpreted as a
51 * stream of bits, optionally with interwoven literal bytes. Bits are assumed
52 * to be stored in little endian 16-bit coding units, with the bits ordered high
53 * to low.
54 */
55 struct input_bitstream {
56
57 /* Bits that have been read from the input buffer. The bits are
58 * left-justified; the next bit is always bit 31.
59 */
60 u32 bitbuf;
61
62 /* Number of bits currently held in @bitbuf. */
63 u32 bitsleft;
64
65 /* Pointer to the next byte to be retrieved from the input buffer. */
66 const u8 *next;
67
68 /* Pointer to just past the end of the input buffer. */
69 const u8 *end;
70 };
71
72 /* Initialize a bitstream to read from the specified input buffer. */
73 static forceinline void init_input_bitstream(struct input_bitstream *is,
74 const void *buffer, u32 size)
75 {
76 is->bitbuf = 0;
77 is->bitsleft = 0;
78 is->next = buffer;
79 is->end = is->next + size;
80 }
81
82 /* Ensure the bit buffer variable for the bitstream contains at least @num_bits
83 * bits. Following this, bitstream_peek_bits() and/or bitstream_remove_bits()
84 * may be called on the bitstream to peek or remove up to @num_bits bits. Note
85 * that @num_bits must be <= 16.
86 */
87 static forceinline void bitstream_ensure_bits(struct input_bitstream *is,
88 u32 num_bits)
89 {
90 if (is->bitsleft < num_bits) {
91 if (is->end - is->next >= 2) {
92 is->bitbuf |= (u32)get_unaligned_le16(is->next)
93 << (16 - is->bitsleft);
94 is->next += 2;
95 }
96 is->bitsleft += 16;
97 }
98 }
99
100 /* Return the next @num_bits bits from the bitstream, without removing them.
101 * There must be at least @num_bits remaining in the buffer variable, from a
102 * previous call to bitstream_ensure_bits().
103 */
104 static forceinline u32
105 bitstream_peek_bits(const struct input_bitstream *is, const u32 num_bits)
106 {
107 return (is->bitbuf >> 1) >> (sizeof(is->bitbuf) * 8 - num_bits - 1);
108 }
109
110 /* Remove @num_bits from the bitstream. There must be at least @num_bits
111 * remaining in the buffer variable, from a previous call to
112 * bitstream_ensure_bits().
113 */
114 static forceinline void
115 bitstream_remove_bits(struct input_bitstream *is, u32 num_bits)
116 {
117 is->bitbuf <<= num_bits;
118 is->bitsleft -= num_bits;
119 }
120
121 /* Remove and return @num_bits bits from the bitstream. There must be at least
122 * @num_bits remaining in the buffer variable, from a previous call to
123 * bitstream_ensure_bits().
124 */
125 static forceinline u32
126 bitstream_pop_bits(struct input_bitstream *is, u32 num_bits)
127 {
128 u32 bits = bitstream_peek_bits(is, num_bits);
129
130 bitstream_remove_bits(is, num_bits);
131 return bits;
132 }
133
134 /* Read and return the next @num_bits bits from the bitstream. */
135 static forceinline u32
136 bitstream_read_bits(struct input_bitstream *is, u32 num_bits)
137 {
138 bitstream_ensure_bits(is, num_bits);
139 return bitstream_pop_bits(is, num_bits);
140 }
141
142 /* Read and return the next literal byte embedded in the bitstream. */
143 static forceinline u8
144 bitstream_read_byte(struct input_bitstream *is)
145 {
146 if (unlikely(is->end == is->next))
147 return 0;
148 return *is->next++;
149 }
150
151 /* Read and return the next 16-bit integer embedded in the bitstream. */
152 static forceinline u16
153 bitstream_read_u16(struct input_bitstream *is)
154 {
155 u16 v;
156
157 if (unlikely(is->end - is->next < 2))
158 return 0;
159 v = get_unaligned_le16(is->next);
160 is->next += 2;
161 return v;
162 }
163
164 /* Read and return the next 32-bit integer embedded in the bitstream. */
165 static forceinline u32
166 bitstream_read_u32(struct input_bitstream *is)
167 {
168 u32 v;
169
170 if (unlikely(is->end - is->next < 4))
171 return 0;
172 v = get_unaligned_le32(is->next);
173 is->next += 4;
174 return v;
175 }
176
177 /* Read into @dst_buffer an array of literal bytes embedded in the bitstream.
178 * Return either a pointer to the byte past the last written, or NULL if the
179 * read overflows the input buffer.
180 */
181 static forceinline void *bitstream_read_bytes(struct input_bitstream *is,
182 void *dst_buffer, size_t count)
183 {
184 if ((size_t)(is->end - is->next) < count)
185 return NULL;
186 memcpy(dst_buffer, is->next, count);
187 is->next += count;
188 return (u8 *)dst_buffer + count;
189 }
190
191 /* Align the input bitstream on a coding-unit boundary. */
192 static forceinline void bitstream_align(struct input_bitstream *is)
193 {
194 is->bitsleft = 0;
195 is->bitbuf = 0;
196 }
197
198 extern int make_huffman_decode_table(u16 decode_table[], const u32 num_syms,
199 const u32 num_bits, const u8 lens[],
200 const u32 max_codeword_len,
201 u16 working_space[]);
202
203
204 /* Reads and returns the next Huffman-encoded symbol from a bitstream. If the
205 * input data is exhausted, the Huffman symbol is decoded as if the missing bits
206 * are all zeroes.
207 */
208 static forceinline u32 read_huffsym(struct input_bitstream *istream,
209 const u16 decode_table[],
210 u32 table_bits,
211 u32 max_codeword_len)
212 {
213 u32 entry;
214 u32 key_bits;
215
216 bitstream_ensure_bits(istream, max_codeword_len);
217
218 /* Index the decode table by the next table_bits bits of the input. */
219 key_bits = bitstream_peek_bits(istream, table_bits);
220 entry = decode_table[key_bits];
221 if (entry < 0xC000) {
222 /* Fast case: The decode table directly provided the
223 * symbol and codeword length. The low 11 bits are the
224 * symbol, and the high 5 bits are the codeword length.
225 */
226 bitstream_remove_bits(istream, entry >> 11);
227 return entry & 0x7FF;
228 }
229 /* Slow case: The codeword for the symbol is longer than
230 * table_bits, so the symbol does not have an entry
231 * directly in the first (1 << table_bits) entries of the
232 * decode table. Traverse the appropriate binary tree
233 * bit-by-bit to decode the symbol.
234 */
235 bitstream_remove_bits(istream, table_bits);
236 do {
237 key_bits = (entry & 0x3FFF) + bitstream_pop_bits(istream, 1);
238 } while ((entry = decode_table[key_bits]) >= 0xC000);
239 return entry;
240 }
241
242 /*
243 * Copy an LZ77 match at (dst - offset) to dst.
244 *
245 * The length and offset must be already validated --- that is, (dst - offset)
246 * can't underrun the output buffer, and (dst + length) can't overrun the output
247 * buffer. Also, the length cannot be 0.
248 *
249 * @bufend points to the byte past the end of the output buffer. This function
250 * won't write any data beyond this position.
251 *
252 * Returns dst + length.
253 */
254 static forceinline u8 *lz_copy(u8 *dst, u32 length, u32 offset, const u8 *bufend,
255 u32 min_length)
256 {
257 const u8 *src = dst - offset;
258
259 /*
260 * Try to copy one machine word at a time. On i386 and x86_64 this is
261 * faster than copying one byte at a time, unless the data is
262 * near-random and all the matches have very short lengths. Note that
263 * since this requires unaligned memory accesses, it won't necessarily
264 * be faster on every architecture.
265 *
266 * Also note that we might copy more than the length of the match. For
267 * example, if a word is 8 bytes and the match is of length 5, then
268 * we'll simply copy 8 bytes. This is okay as long as we don't write
269 * beyond the end of the output buffer, hence the check for (bufend -
270 * end >= WORDBYTES - 1).
271 */
272 #ifdef FAST_UNALIGNED_ACCESS
273 u8 * const end = dst + length;
274
275 if (bufend - end >= (ptrdiff_t)(WORDBYTES - 1)) {
276
277 if (offset >= WORDBYTES) {
278 /* The source and destination words don't overlap. */
279
280 /* To improve branch prediction, one iteration of this
281 * loop is unrolled. Most matches are short and will
282 * fail the first check. But if that check passes, then
283 * it becomes increasing likely that the match is long
284 * and we'll need to continue copying.
285 */
286
287 copy_unaligned_word(src, dst);
288 src += WORDBYTES;
289 dst += WORDBYTES;
290
291 if (dst < end) {
292 do {
293 copy_unaligned_word(src, dst);
294 src += WORDBYTES;
295 dst += WORDBYTES;
296 } while (dst < end);
297 }
298 return end;
299 } else if (offset == 1) {
300
301 /* Offset 1 matches are equivalent to run-length
302 * encoding of the previous byte. This case is common
303 * if the data contains many repeated bytes.
304 */
305 size_t v = repeat_byte(*(dst - 1));
306
307 do {
308 put_unaligned(v, (size_t *)dst);
309 src += WORDBYTES;
310 dst += WORDBYTES;
311 } while (dst < end);
312 return end;
313 }
314 /*
315 * We don't bother with special cases for other 'offset <
316 * WORDBYTES', which are usually rarer than 'offset == 1'. Extra
317 * checks will just slow things down. Actually, it's possible
318 * to handle all the 'offset < WORDBYTES' cases using the same
319 * code, but it still becomes more complicated doesn't seem any
320 * faster overall; it definitely slows down the more common
321 * 'offset == 1' case.
322 */
323 }
324 #endif /* FAST_UNALIGNED_ACCESS */
325
326 /* Fall back to a bytewise copy. */
327
328 if (min_length >= 2) {
329 *dst++ = *src++;
330 length--;
331 }
332 if (min_length >= 3) {
333 *dst++ = *src++;
334 length--;
335 }
336 do {
337 *dst++ = *src++;
338 } while (--length);
339
340 return dst;
341 }
342
343 #endif /* _LINUX_NTFS3_LIB_DECOMPRESS_COMMON_H */
344
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