1 | /* Copyright 2013 Google Inc. All Rights Reserved. |
2 | |
3 | Distributed under MIT license. |
4 | See file LICENSE for detail or copy at https://opensource.org/licenses/MIT |
5 | */ |
6 | |
7 | /* Bit reading helpers */ |
8 | |
9 | #ifndef BROTLI_DEC_BIT_READER_H_ |
10 | #define BROTLI_DEC_BIT_READER_H_ |
11 | |
12 | #include <string.h> /* memcpy */ |
13 | |
14 | #include "../common/platform.h" |
15 | #include <brotli/types.h> |
16 | |
17 | #if defined(__cplusplus) || defined(c_plusplus) |
18 | extern "C" { |
19 | #endif |
20 | |
21 | #define BROTLI_SHORT_FILL_BIT_WINDOW_READ (sizeof(brotli_reg_t) >> 1) |
22 | |
23 | static const uint32_t kBitMask[33] = { 0x00000000, |
24 | 0x00000001, 0x00000003, 0x00000007, 0x0000000F, |
25 | 0x0000001F, 0x0000003F, 0x0000007F, 0x000000FF, |
26 | 0x000001FF, 0x000003FF, 0x000007FF, 0x00000FFF, |
27 | 0x00001FFF, 0x00003FFF, 0x00007FFF, 0x0000FFFF, |
28 | 0x0001FFFF, 0x0003FFFF, 0x0007FFFF, 0x000FFFFF, |
29 | 0x001FFFFF, 0x003FFFFF, 0x007FFFFF, 0x00FFFFFF, |
30 | 0x01FFFFFF, 0x03FFFFFF, 0x07FFFFFF, 0x0FFFFFFF, |
31 | 0x1FFFFFFF, 0x3FFFFFFF, 0x7FFFFFFF, 0xFFFFFFFF |
32 | }; |
33 | |
34 | static BROTLI_INLINE uint32_t BitMask(uint32_t n) { |
35 | if (BROTLI_IS_CONSTANT(n) || BROTLI_HAS_UBFX) { |
36 | /* Masking with this expression turns to a single |
37 | "Unsigned Bit Field Extract" UBFX instruction on ARM. */ |
38 | return ~((0xFFFFFFFFu) << n); |
39 | } else { |
40 | return kBitMask[n]; |
41 | } |
42 | } |
43 | |
44 | typedef struct { |
45 | brotli_reg_t val_; /* pre-fetched bits */ |
46 | uint32_t bit_pos_; /* current bit-reading position in val_ */ |
47 | const uint8_t* next_in; /* the byte we're reading from */ |
48 | size_t avail_in; |
49 | } BrotliBitReader; |
50 | |
51 | typedef struct { |
52 | brotli_reg_t val_; |
53 | uint32_t bit_pos_; |
54 | const uint8_t* next_in; |
55 | size_t avail_in; |
56 | } BrotliBitReaderState; |
57 | |
58 | /* Initializes the BrotliBitReader fields. */ |
59 | BROTLI_INTERNAL void BrotliInitBitReader(BrotliBitReader* const br); |
60 | |
61 | /* Ensures that accumulator is not empty. |
62 | May consume up to sizeof(brotli_reg_t) - 1 bytes of input. |
63 | Returns BROTLI_FALSE if data is required but there is no input available. |
64 | For BROTLI_ALIGNED_READ this function also prepares bit reader for aligned |
65 | reading. */ |
66 | BROTLI_INTERNAL BROTLI_BOOL BrotliWarmupBitReader(BrotliBitReader* const br); |
67 | |
68 | static BROTLI_INLINE void BrotliBitReaderSaveState( |
69 | BrotliBitReader* const from, BrotliBitReaderState* to) { |
70 | to->val_ = from->val_; |
71 | to->bit_pos_ = from->bit_pos_; |
72 | to->next_in = from->next_in; |
73 | to->avail_in = from->avail_in; |
74 | } |
75 | |
76 | static BROTLI_INLINE void BrotliBitReaderRestoreState( |
77 | BrotliBitReader* const to, BrotliBitReaderState* from) { |
78 | to->val_ = from->val_; |
79 | to->bit_pos_ = from->bit_pos_; |
80 | to->next_in = from->next_in; |
81 | to->avail_in = from->avail_in; |
82 | } |
83 | |
84 | static BROTLI_INLINE uint32_t BrotliGetAvailableBits( |
85 | const BrotliBitReader* br) { |
86 | return (BROTLI_64_BITS ? 64 : 32) - br->bit_pos_; |
87 | } |
88 | |
89 | /* Returns amount of unread bytes the bit reader still has buffered from the |
90 | BrotliInput, including whole bytes in br->val_. */ |
91 | static BROTLI_INLINE size_t BrotliGetRemainingBytes(BrotliBitReader* br) { |
92 | return br->avail_in + (BrotliGetAvailableBits(br) >> 3); |
93 | } |
94 | |
95 | /* Checks if there is at least |num| bytes left in the input ring-buffer |
96 | (excluding the bits remaining in br->val_). */ |
97 | static BROTLI_INLINE BROTLI_BOOL BrotliCheckInputAmount( |
98 | BrotliBitReader* const br, size_t num) { |
99 | return TO_BROTLI_BOOL(br->avail_in >= num); |
100 | } |
101 | |
102 | /* Guarantees that there are at least |n_bits| + 1 bits in accumulator. |
103 | Precondition: accumulator contains at least 1 bit. |
104 | |n_bits| should be in the range [1..24] for regular build. For portable |
105 | non-64-bit little-endian build only 16 bits are safe to request. */ |
106 | static BROTLI_INLINE void BrotliFillBitWindow( |
107 | BrotliBitReader* const br, uint32_t n_bits) { |
108 | #if (BROTLI_64_BITS) |
109 | if (!BROTLI_ALIGNED_READ && BROTLI_IS_CONSTANT(n_bits) && (n_bits <= 8)) { |
110 | if (br->bit_pos_ >= 56) { |
111 | br->val_ >>= 56; |
112 | br->bit_pos_ ^= 56; /* here same as -= 56 because of the if condition */ |
113 | br->val_ |= BROTLI_UNALIGNED_LOAD64LE(br->next_in) << 8; |
114 | br->avail_in -= 7; |
115 | br->next_in += 7; |
116 | } |
117 | } else if ( |
118 | !BROTLI_ALIGNED_READ && BROTLI_IS_CONSTANT(n_bits) && (n_bits <= 16)) { |
119 | if (br->bit_pos_ >= 48) { |
120 | br->val_ >>= 48; |
121 | br->bit_pos_ ^= 48; /* here same as -= 48 because of the if condition */ |
122 | br->val_ |= BROTLI_UNALIGNED_LOAD64LE(br->next_in) << 16; |
123 | br->avail_in -= 6; |
124 | br->next_in += 6; |
125 | } |
126 | } else { |
127 | if (br->bit_pos_ >= 32) { |
128 | br->val_ >>= 32; |
129 | br->bit_pos_ ^= 32; /* here same as -= 32 because of the if condition */ |
130 | br->val_ |= ((uint64_t)BROTLI_UNALIGNED_LOAD32LE(br->next_in)) << 32; |
131 | br->avail_in -= BROTLI_SHORT_FILL_BIT_WINDOW_READ; |
132 | br->next_in += BROTLI_SHORT_FILL_BIT_WINDOW_READ; |
133 | } |
134 | } |
135 | #else |
136 | if (!BROTLI_ALIGNED_READ && BROTLI_IS_CONSTANT(n_bits) && (n_bits <= 8)) { |
137 | if (br->bit_pos_ >= 24) { |
138 | br->val_ >>= 24; |
139 | br->bit_pos_ ^= 24; /* here same as -= 24 because of the if condition */ |
140 | br->val_ |= BROTLI_UNALIGNED_LOAD32LE(br->next_in) << 8; |
141 | br->avail_in -= 3; |
142 | br->next_in += 3; |
143 | } |
144 | } else { |
145 | if (br->bit_pos_ >= 16) { |
146 | br->val_ >>= 16; |
147 | br->bit_pos_ ^= 16; /* here same as -= 16 because of the if condition */ |
148 | br->val_ |= ((uint32_t)BROTLI_UNALIGNED_LOAD16LE(br->next_in)) << 16; |
149 | br->avail_in -= BROTLI_SHORT_FILL_BIT_WINDOW_READ; |
150 | br->next_in += BROTLI_SHORT_FILL_BIT_WINDOW_READ; |
151 | } |
152 | } |
153 | #endif |
154 | } |
155 | |
156 | /* Mostly like BrotliFillBitWindow, but guarantees only 16 bits and reads no |
157 | more than BROTLI_SHORT_FILL_BIT_WINDOW_READ bytes of input. */ |
158 | static BROTLI_INLINE void BrotliFillBitWindow16(BrotliBitReader* const br) { |
159 | BrotliFillBitWindow(br, 17); |
160 | } |
161 | |
162 | /* Tries to pull one byte of input to accumulator. |
163 | Returns BROTLI_FALSE if there is no input available. */ |
164 | static BROTLI_INLINE BROTLI_BOOL BrotliPullByte(BrotliBitReader* const br) { |
165 | if (br->avail_in == 0) { |
166 | return BROTLI_FALSE; |
167 | } |
168 | br->val_ >>= 8; |
169 | #if (BROTLI_64_BITS) |
170 | br->val_ |= ((uint64_t)*br->next_in) << 56; |
171 | #else |
172 | br->val_ |= ((uint32_t)*br->next_in) << 24; |
173 | #endif |
174 | br->bit_pos_ -= 8; |
175 | --br->avail_in; |
176 | ++br->next_in; |
177 | return BROTLI_TRUE; |
178 | } |
179 | |
180 | /* Returns currently available bits. |
181 | The number of valid bits could be calculated by BrotliGetAvailableBits. */ |
182 | static BROTLI_INLINE brotli_reg_t BrotliGetBitsUnmasked( |
183 | BrotliBitReader* const br) { |
184 | return br->val_ >> br->bit_pos_; |
185 | } |
186 | |
187 | /* Like BrotliGetBits, but does not mask the result. |
188 | The result contains at least 16 valid bits. */ |
189 | static BROTLI_INLINE uint32_t BrotliGet16BitsUnmasked( |
190 | BrotliBitReader* const br) { |
191 | BrotliFillBitWindow(br, 16); |
192 | return (uint32_t)BrotliGetBitsUnmasked(br); |
193 | } |
194 | |
195 | /* Returns the specified number of bits from |br| without advancing bit |
196 | position. */ |
197 | static BROTLI_INLINE uint32_t BrotliGetBits( |
198 | BrotliBitReader* const br, uint32_t n_bits) { |
199 | BrotliFillBitWindow(br, n_bits); |
200 | return (uint32_t)BrotliGetBitsUnmasked(br) & BitMask(n_bits); |
201 | } |
202 | |
203 | /* Tries to peek the specified amount of bits. Returns BROTLI_FALSE, if there |
204 | is not enough input. */ |
205 | static BROTLI_INLINE BROTLI_BOOL BrotliSafeGetBits( |
206 | BrotliBitReader* const br, uint32_t n_bits, uint32_t* val) { |
207 | while (BrotliGetAvailableBits(br) < n_bits) { |
208 | if (!BrotliPullByte(br)) { |
209 | return BROTLI_FALSE; |
210 | } |
211 | } |
212 | *val = (uint32_t)BrotliGetBitsUnmasked(br) & BitMask(n_bits); |
213 | return BROTLI_TRUE; |
214 | } |
215 | |
216 | /* Advances the bit pos by |n_bits|. */ |
217 | static BROTLI_INLINE void BrotliDropBits( |
218 | BrotliBitReader* const br, uint32_t n_bits) { |
219 | br->bit_pos_ += n_bits; |
220 | } |
221 | |
222 | static BROTLI_INLINE void BrotliBitReaderUnload(BrotliBitReader* br) { |
223 | uint32_t unused_bytes = BrotliGetAvailableBits(br) >> 3; |
224 | uint32_t unused_bits = unused_bytes << 3; |
225 | br->avail_in += unused_bytes; |
226 | br->next_in -= unused_bytes; |
227 | if (unused_bits == sizeof(br->val_) << 3) { |
228 | br->val_ = 0; |
229 | } else { |
230 | br->val_ <<= unused_bits; |
231 | } |
232 | br->bit_pos_ += unused_bits; |
233 | } |
234 | |
235 | /* Reads the specified number of bits from |br| and advances the bit pos. |
236 | Precondition: accumulator MUST contain at least |n_bits|. */ |
237 | static BROTLI_INLINE void BrotliTakeBits( |
238 | BrotliBitReader* const br, uint32_t n_bits, uint32_t* val) { |
239 | *val = (uint32_t)BrotliGetBitsUnmasked(br) & BitMask(n_bits); |
240 | BROTLI_LOG(("[BrotliReadBits] %d %d %d val: %6x\n" , |
241 | (int)br->avail_in, (int)br->bit_pos_, (int)n_bits, (int)*val)); |
242 | BrotliDropBits(br, n_bits); |
243 | } |
244 | |
245 | /* Reads the specified number of bits from |br| and advances the bit pos. |
246 | Assumes that there is enough input to perform BrotliFillBitWindow. */ |
247 | static BROTLI_INLINE uint32_t BrotliReadBits( |
248 | BrotliBitReader* const br, uint32_t n_bits) { |
249 | if (BROTLI_64_BITS || (n_bits <= 16)) { |
250 | uint32_t val; |
251 | BrotliFillBitWindow(br, n_bits); |
252 | BrotliTakeBits(br, n_bits, &val); |
253 | return val; |
254 | } else { |
255 | uint32_t low_val; |
256 | uint32_t high_val; |
257 | BrotliFillBitWindow(br, 16); |
258 | BrotliTakeBits(br, 16, &low_val); |
259 | BrotliFillBitWindow(br, 8); |
260 | BrotliTakeBits(br, n_bits - 16, &high_val); |
261 | return low_val | (high_val << 16); |
262 | } |
263 | } |
264 | |
265 | /* Tries to read the specified amount of bits. Returns BROTLI_FALSE, if there |
266 | is not enough input. |n_bits| MUST be positive. */ |
267 | static BROTLI_INLINE BROTLI_BOOL BrotliSafeReadBits( |
268 | BrotliBitReader* const br, uint32_t n_bits, uint32_t* val) { |
269 | while (BrotliGetAvailableBits(br) < n_bits) { |
270 | if (!BrotliPullByte(br)) { |
271 | return BROTLI_FALSE; |
272 | } |
273 | } |
274 | BrotliTakeBits(br, n_bits, val); |
275 | return BROTLI_TRUE; |
276 | } |
277 | |
278 | /* Advances the bit reader position to the next byte boundary and verifies |
279 | that any skipped bits are set to zero. */ |
280 | static BROTLI_INLINE BROTLI_BOOL BrotliJumpToByteBoundary(BrotliBitReader* br) { |
281 | uint32_t pad_bits_count = BrotliGetAvailableBits(br) & 0x7; |
282 | uint32_t pad_bits = 0; |
283 | if (pad_bits_count != 0) { |
284 | BrotliTakeBits(br, pad_bits_count, &pad_bits); |
285 | } |
286 | return TO_BROTLI_BOOL(pad_bits == 0); |
287 | } |
288 | |
289 | /* Copies remaining input bytes stored in the bit reader to the output. Value |
290 | |num| may not be larger than BrotliGetRemainingBytes. The bit reader must be |
291 | warmed up again after this. */ |
292 | static BROTLI_INLINE void BrotliCopyBytes(uint8_t* dest, |
293 | BrotliBitReader* br, size_t num) { |
294 | while (BrotliGetAvailableBits(br) >= 8 && num > 0) { |
295 | *dest = (uint8_t)BrotliGetBitsUnmasked(br); |
296 | BrotliDropBits(br, 8); |
297 | ++dest; |
298 | --num; |
299 | } |
300 | memcpy(dest, br->next_in, num); |
301 | br->avail_in -= num; |
302 | br->next_in += num; |
303 | } |
304 | |
305 | #if defined(__cplusplus) || defined(c_plusplus) |
306 | } /* extern "C" */ |
307 | #endif |
308 | |
309 | #endif /* BROTLI_DEC_BIT_READER_H_ */ |
310 | |