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 | /* Utilities for building Huffman decoding tables. */ |
8 | |
9 | #include "./huffman.h" |
10 | |
11 | #include <string.h> /* memcpy, memset */ |
12 | |
13 | #include "../common/constants.h" |
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_REVERSE_BITS_MAX 8 |
22 | |
23 | #if defined(BROTLI_RBIT) |
24 | #define BROTLI_REVERSE_BITS_BASE \ |
25 | ((sizeof(brotli_reg_t) << 3) - BROTLI_REVERSE_BITS_MAX) |
26 | #else |
27 | #define BROTLI_REVERSE_BITS_BASE 0 |
28 | static uint8_t kReverseBits[1 << BROTLI_REVERSE_BITS_MAX] = { |
29 | 0x00, 0x80, 0x40, 0xC0, 0x20, 0xA0, 0x60, 0xE0, |
30 | 0x10, 0x90, 0x50, 0xD0, 0x30, 0xB0, 0x70, 0xF0, |
31 | 0x08, 0x88, 0x48, 0xC8, 0x28, 0xA8, 0x68, 0xE8, |
32 | 0x18, 0x98, 0x58, 0xD8, 0x38, 0xB8, 0x78, 0xF8, |
33 | 0x04, 0x84, 0x44, 0xC4, 0x24, 0xA4, 0x64, 0xE4, |
34 | 0x14, 0x94, 0x54, 0xD4, 0x34, 0xB4, 0x74, 0xF4, |
35 | 0x0C, 0x8C, 0x4C, 0xCC, 0x2C, 0xAC, 0x6C, 0xEC, |
36 | 0x1C, 0x9C, 0x5C, 0xDC, 0x3C, 0xBC, 0x7C, 0xFC, |
37 | 0x02, 0x82, 0x42, 0xC2, 0x22, 0xA2, 0x62, 0xE2, |
38 | 0x12, 0x92, 0x52, 0xD2, 0x32, 0xB2, 0x72, 0xF2, |
39 | 0x0A, 0x8A, 0x4A, 0xCA, 0x2A, 0xAA, 0x6A, 0xEA, |
40 | 0x1A, 0x9A, 0x5A, 0xDA, 0x3A, 0xBA, 0x7A, 0xFA, |
41 | 0x06, 0x86, 0x46, 0xC6, 0x26, 0xA6, 0x66, 0xE6, |
42 | 0x16, 0x96, 0x56, 0xD6, 0x36, 0xB6, 0x76, 0xF6, |
43 | 0x0E, 0x8E, 0x4E, 0xCE, 0x2E, 0xAE, 0x6E, 0xEE, |
44 | 0x1E, 0x9E, 0x5E, 0xDE, 0x3E, 0xBE, 0x7E, 0xFE, |
45 | 0x01, 0x81, 0x41, 0xC1, 0x21, 0xA1, 0x61, 0xE1, |
46 | 0x11, 0x91, 0x51, 0xD1, 0x31, 0xB1, 0x71, 0xF1, |
47 | 0x09, 0x89, 0x49, 0xC9, 0x29, 0xA9, 0x69, 0xE9, |
48 | 0x19, 0x99, 0x59, 0xD9, 0x39, 0xB9, 0x79, 0xF9, |
49 | 0x05, 0x85, 0x45, 0xC5, 0x25, 0xA5, 0x65, 0xE5, |
50 | 0x15, 0x95, 0x55, 0xD5, 0x35, 0xB5, 0x75, 0xF5, |
51 | 0x0D, 0x8D, 0x4D, 0xCD, 0x2D, 0xAD, 0x6D, 0xED, |
52 | 0x1D, 0x9D, 0x5D, 0xDD, 0x3D, 0xBD, 0x7D, 0xFD, |
53 | 0x03, 0x83, 0x43, 0xC3, 0x23, 0xA3, 0x63, 0xE3, |
54 | 0x13, 0x93, 0x53, 0xD3, 0x33, 0xB3, 0x73, 0xF3, |
55 | 0x0B, 0x8B, 0x4B, 0xCB, 0x2B, 0xAB, 0x6B, 0xEB, |
56 | 0x1B, 0x9B, 0x5B, 0xDB, 0x3B, 0xBB, 0x7B, 0xFB, |
57 | 0x07, 0x87, 0x47, 0xC7, 0x27, 0xA7, 0x67, 0xE7, |
58 | 0x17, 0x97, 0x57, 0xD7, 0x37, 0xB7, 0x77, 0xF7, |
59 | 0x0F, 0x8F, 0x4F, 0xCF, 0x2F, 0xAF, 0x6F, 0xEF, |
60 | 0x1F, 0x9F, 0x5F, 0xDF, 0x3F, 0xBF, 0x7F, 0xFF |
61 | }; |
62 | #endif /* BROTLI_RBIT */ |
63 | |
64 | #define BROTLI_REVERSE_BITS_LOWEST \ |
65 | ((brotli_reg_t)1 << (BROTLI_REVERSE_BITS_MAX - 1 + BROTLI_REVERSE_BITS_BASE)) |
66 | |
67 | /* Returns reverse(num >> BROTLI_REVERSE_BITS_BASE, BROTLI_REVERSE_BITS_MAX), |
68 | where reverse(value, len) is the bit-wise reversal of the len least |
69 | significant bits of value. */ |
70 | static BROTLI_INLINE brotli_reg_t BrotliReverseBits(brotli_reg_t num) { |
71 | #if defined(BROTLI_RBIT) |
72 | return BROTLI_RBIT(num); |
73 | #else |
74 | return kReverseBits[num]; |
75 | #endif |
76 | } |
77 | |
78 | /* Stores code in table[0], table[step], table[2*step], ..., table[end] */ |
79 | /* Assumes that end is an integer multiple of step */ |
80 | static BROTLI_INLINE void ReplicateValue(HuffmanCode* table, |
81 | int step, int end, |
82 | HuffmanCode code) { |
83 | do { |
84 | end -= step; |
85 | table[end] = code; |
86 | } while (end > 0); |
87 | } |
88 | |
89 | /* Returns the table width of the next 2nd level table. |count| is the histogram |
90 | of bit lengths for the remaining symbols, |len| is the code length of the |
91 | next processed symbol. */ |
92 | static BROTLI_INLINE int NextTableBitSize(const uint16_t* const count, |
93 | int len, int root_bits) { |
94 | int left = 1 << (len - root_bits); |
95 | while (len < BROTLI_HUFFMAN_MAX_CODE_LENGTH) { |
96 | left -= count[len]; |
97 | if (left <= 0) break; |
98 | ++len; |
99 | left <<= 1; |
100 | } |
101 | return len - root_bits; |
102 | } |
103 | |
104 | void BrotliBuildCodeLengthsHuffmanTable(HuffmanCode* table, |
105 | const uint8_t* const code_lengths, |
106 | uint16_t* count) { |
107 | HuffmanCode code; /* current table entry */ |
108 | int symbol; /* symbol index in original or sorted table */ |
109 | brotli_reg_t key; /* prefix code */ |
110 | brotli_reg_t key_step; /* prefix code addend */ |
111 | int step; /* step size to replicate values in current table */ |
112 | int table_size; /* size of current table */ |
113 | int sorted[BROTLI_CODE_LENGTH_CODES]; /* symbols sorted by code length */ |
114 | /* offsets in sorted table for each length */ |
115 | int offset[BROTLI_HUFFMAN_MAX_CODE_LENGTH_CODE_LENGTH + 1]; |
116 | int bits; |
117 | int bits_count; |
118 | BROTLI_DCHECK(BROTLI_HUFFMAN_MAX_CODE_LENGTH_CODE_LENGTH <= |
119 | BROTLI_REVERSE_BITS_MAX); |
120 | |
121 | /* Generate offsets into sorted symbol table by code length. */ |
122 | symbol = -1; |
123 | bits = 1; |
124 | BROTLI_REPEAT(BROTLI_HUFFMAN_MAX_CODE_LENGTH_CODE_LENGTH, { |
125 | symbol += count[bits]; |
126 | offset[bits] = symbol; |
127 | bits++; |
128 | }); |
129 | /* Symbols with code length 0 are placed after all other symbols. */ |
130 | offset[0] = BROTLI_CODE_LENGTH_CODES - 1; |
131 | |
132 | /* Sort symbols by length, by symbol order within each length. */ |
133 | symbol = BROTLI_CODE_LENGTH_CODES; |
134 | do { |
135 | BROTLI_REPEAT(6, { |
136 | symbol--; |
137 | sorted[offset[code_lengths[symbol]]--] = symbol; |
138 | }); |
139 | } while (symbol != 0); |
140 | |
141 | table_size = 1 << BROTLI_HUFFMAN_MAX_CODE_LENGTH_CODE_LENGTH; |
142 | |
143 | /* Special case: all symbols but one have 0 code length. */ |
144 | if (offset[0] == 0) { |
145 | code = ConstructHuffmanCode(0, (uint16_t)sorted[0]); |
146 | for (key = 0; key < (brotli_reg_t)table_size; ++key) { |
147 | table[key] = code; |
148 | } |
149 | return; |
150 | } |
151 | |
152 | /* Fill in table. */ |
153 | key = 0; |
154 | key_step = BROTLI_REVERSE_BITS_LOWEST; |
155 | symbol = 0; |
156 | bits = 1; |
157 | step = 2; |
158 | do { |
159 | for (bits_count = count[bits]; bits_count != 0; --bits_count) { |
160 | code = ConstructHuffmanCode((uint8_t)bits, (uint16_t)sorted[symbol++]); |
161 | ReplicateValue(&table[BrotliReverseBits(key)], step, table_size, code); |
162 | key += key_step; |
163 | } |
164 | step <<= 1; |
165 | key_step >>= 1; |
166 | } while (++bits <= BROTLI_HUFFMAN_MAX_CODE_LENGTH_CODE_LENGTH); |
167 | } |
168 | |
169 | uint32_t BrotliBuildHuffmanTable(HuffmanCode* root_table, |
170 | int root_bits, |
171 | const uint16_t* const symbol_lists, |
172 | uint16_t* count) { |
173 | HuffmanCode code; /* current table entry */ |
174 | HuffmanCode* table; /* next available space in table */ |
175 | int len; /* current code length */ |
176 | int symbol; /* symbol index in original or sorted table */ |
177 | brotli_reg_t key; /* prefix code */ |
178 | brotli_reg_t key_step; /* prefix code addend */ |
179 | brotli_reg_t sub_key; /* 2nd level table prefix code */ |
180 | brotli_reg_t sub_key_step; /* 2nd level table prefix code addend */ |
181 | int step; /* step size to replicate values in current table */ |
182 | int table_bits; /* key length of current table */ |
183 | int table_size; /* size of current table */ |
184 | int total_size; /* sum of root table size and 2nd level table sizes */ |
185 | int max_length = -1; |
186 | int bits; |
187 | int bits_count; |
188 | |
189 | BROTLI_DCHECK(root_bits <= BROTLI_REVERSE_BITS_MAX); |
190 | BROTLI_DCHECK(BROTLI_HUFFMAN_MAX_CODE_LENGTH - root_bits <= |
191 | BROTLI_REVERSE_BITS_MAX); |
192 | |
193 | while (symbol_lists[max_length] == 0xFFFF) max_length--; |
194 | max_length += BROTLI_HUFFMAN_MAX_CODE_LENGTH + 1; |
195 | |
196 | table = root_table; |
197 | table_bits = root_bits; |
198 | table_size = 1 << table_bits; |
199 | total_size = table_size; |
200 | |
201 | /* Fill in the root table. Reduce the table size to if possible, |
202 | and create the repetitions by memcpy. */ |
203 | if (table_bits > max_length) { |
204 | table_bits = max_length; |
205 | table_size = 1 << table_bits; |
206 | } |
207 | key = 0; |
208 | key_step = BROTLI_REVERSE_BITS_LOWEST; |
209 | bits = 1; |
210 | step = 2; |
211 | do { |
212 | symbol = bits - (BROTLI_HUFFMAN_MAX_CODE_LENGTH + 1); |
213 | for (bits_count = count[bits]; bits_count != 0; --bits_count) { |
214 | symbol = symbol_lists[symbol]; |
215 | code = ConstructHuffmanCode((uint8_t)bits, (uint16_t)symbol); |
216 | ReplicateValue(&table[BrotliReverseBits(key)], step, table_size, code); |
217 | key += key_step; |
218 | } |
219 | step <<= 1; |
220 | key_step >>= 1; |
221 | } while (++bits <= table_bits); |
222 | |
223 | /* If root_bits != table_bits then replicate to fill the remaining slots. */ |
224 | while (total_size != table_size) { |
225 | memcpy(&table[table_size], &table[0], |
226 | (size_t)table_size * sizeof(table[0])); |
227 | table_size <<= 1; |
228 | } |
229 | |
230 | /* Fill in 2nd level tables and add pointers to root table. */ |
231 | key_step = BROTLI_REVERSE_BITS_LOWEST >> (root_bits - 1); |
232 | sub_key = (BROTLI_REVERSE_BITS_LOWEST << 1); |
233 | sub_key_step = BROTLI_REVERSE_BITS_LOWEST; |
234 | for (len = root_bits + 1, step = 2; len <= max_length; ++len) { |
235 | symbol = len - (BROTLI_HUFFMAN_MAX_CODE_LENGTH + 1); |
236 | for (; count[len] != 0; --count[len]) { |
237 | if (sub_key == (BROTLI_REVERSE_BITS_LOWEST << 1U)) { |
238 | table += table_size; |
239 | table_bits = NextTableBitSize(count, len, root_bits); |
240 | table_size = 1 << table_bits; |
241 | total_size += table_size; |
242 | sub_key = BrotliReverseBits(key); |
243 | key += key_step; |
244 | root_table[sub_key] = ConstructHuffmanCode( |
245 | (uint8_t)(table_bits + root_bits), |
246 | (uint16_t)(((size_t)(table - root_table)) - sub_key)); |
247 | sub_key = 0; |
248 | } |
249 | symbol = symbol_lists[symbol]; |
250 | code = ConstructHuffmanCode((uint8_t)(len - root_bits), (uint16_t)symbol); |
251 | ReplicateValue( |
252 | &table[BrotliReverseBits(sub_key)], step, table_size, code); |
253 | sub_key += sub_key_step; |
254 | } |
255 | step <<= 1; |
256 | sub_key_step >>= 1; |
257 | } |
258 | return (uint32_t)total_size; |
259 | } |
260 | |
261 | uint32_t BrotliBuildSimpleHuffmanTable(HuffmanCode* table, |
262 | int root_bits, |
263 | uint16_t* val, |
264 | uint32_t num_symbols) { |
265 | uint32_t table_size = 1; |
266 | const uint32_t goal_size = 1U << root_bits; |
267 | switch (num_symbols) { |
268 | case 0: |
269 | table[0] = ConstructHuffmanCode(0, val[0]); |
270 | break; |
271 | case 1: |
272 | if (val[1] > val[0]) { |
273 | table[0] = ConstructHuffmanCode(1, val[0]); |
274 | table[1] = ConstructHuffmanCode(1, val[1]); |
275 | } else { |
276 | table[0] = ConstructHuffmanCode(1, val[1]); |
277 | table[1] = ConstructHuffmanCode(1, val[0]); |
278 | } |
279 | table_size = 2; |
280 | break; |
281 | case 2: |
282 | table[0] = ConstructHuffmanCode(1, val[0]); |
283 | table[2] = ConstructHuffmanCode(1, val[0]); |
284 | if (val[2] > val[1]) { |
285 | table[1] = ConstructHuffmanCode(2, val[1]); |
286 | table[3] = ConstructHuffmanCode(2, val[2]); |
287 | } else { |
288 | table[1] = ConstructHuffmanCode(2, val[2]); |
289 | table[3] = ConstructHuffmanCode(2, val[1]); |
290 | } |
291 | table_size = 4; |
292 | break; |
293 | case 3: { |
294 | int i, k; |
295 | for (i = 0; i < 3; ++i) { |
296 | for (k = i + 1; k < 4; ++k) { |
297 | if (val[k] < val[i]) { |
298 | uint16_t t = val[k]; |
299 | val[k] = val[i]; |
300 | val[i] = t; |
301 | } |
302 | } |
303 | } |
304 | table[0] = ConstructHuffmanCode(2, val[0]); |
305 | table[2] = ConstructHuffmanCode(2, val[1]); |
306 | table[1] = ConstructHuffmanCode(2, val[2]); |
307 | table[3] = ConstructHuffmanCode(2, val[3]); |
308 | table_size = 4; |
309 | break; |
310 | } |
311 | case 4: { |
312 | if (val[3] < val[2]) { |
313 | uint16_t t = val[3]; |
314 | val[3] = val[2]; |
315 | val[2] = t; |
316 | } |
317 | table[0] = ConstructHuffmanCode(1, val[0]); |
318 | table[1] = ConstructHuffmanCode(2, val[1]); |
319 | table[2] = ConstructHuffmanCode(1, val[0]); |
320 | table[3] = ConstructHuffmanCode(3, val[2]); |
321 | table[4] = ConstructHuffmanCode(1, val[0]); |
322 | table[5] = ConstructHuffmanCode(2, val[1]); |
323 | table[6] = ConstructHuffmanCode(1, val[0]); |
324 | table[7] = ConstructHuffmanCode(3, val[3]); |
325 | table_size = 8; |
326 | break; |
327 | } |
328 | } |
329 | while (table_size != goal_size) { |
330 | memcpy(&table[table_size], &table[0], |
331 | (size_t)table_size * sizeof(table[0])); |
332 | table_size <<= 1; |
333 | } |
334 | return goal_size; |
335 | } |
336 | |
337 | #if defined(__cplusplus) || defined(c_plusplus) |
338 | } /* extern "C" */ |
339 | #endif |
340 | |