Line data Source code
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 "./port.h"
14 : #include "./types.h"
15 :
16 : #if defined(__cplusplus) || defined(c_plusplus)
17 : extern "C" {
18 : #endif
19 :
20 : #define BROTLI_REVERSE_BITS_MAX 8
21 :
22 : #ifdef BROTLI_RBIT
23 : #define BROTLI_REVERSE_BITS_BASE (32 - BROTLI_REVERSE_BITS_MAX)
24 : #else
25 : #define BROTLI_REVERSE_BITS_BASE 0
26 : static uint8_t kReverseBits[1 << BROTLI_REVERSE_BITS_MAX] = {
27 : 0x00, 0x80, 0x40, 0xC0, 0x20, 0xA0, 0x60, 0xE0,
28 : 0x10, 0x90, 0x50, 0xD0, 0x30, 0xB0, 0x70, 0xF0,
29 : 0x08, 0x88, 0x48, 0xC8, 0x28, 0xA8, 0x68, 0xE8,
30 : 0x18, 0x98, 0x58, 0xD8, 0x38, 0xB8, 0x78, 0xF8,
31 : 0x04, 0x84, 0x44, 0xC4, 0x24, 0xA4, 0x64, 0xE4,
32 : 0x14, 0x94, 0x54, 0xD4, 0x34, 0xB4, 0x74, 0xF4,
33 : 0x0C, 0x8C, 0x4C, 0xCC, 0x2C, 0xAC, 0x6C, 0xEC,
34 : 0x1C, 0x9C, 0x5C, 0xDC, 0x3C, 0xBC, 0x7C, 0xFC,
35 : 0x02, 0x82, 0x42, 0xC2, 0x22, 0xA2, 0x62, 0xE2,
36 : 0x12, 0x92, 0x52, 0xD2, 0x32, 0xB2, 0x72, 0xF2,
37 : 0x0A, 0x8A, 0x4A, 0xCA, 0x2A, 0xAA, 0x6A, 0xEA,
38 : 0x1A, 0x9A, 0x5A, 0xDA, 0x3A, 0xBA, 0x7A, 0xFA,
39 : 0x06, 0x86, 0x46, 0xC6, 0x26, 0xA6, 0x66, 0xE6,
40 : 0x16, 0x96, 0x56, 0xD6, 0x36, 0xB6, 0x76, 0xF6,
41 : 0x0E, 0x8E, 0x4E, 0xCE, 0x2E, 0xAE, 0x6E, 0xEE,
42 : 0x1E, 0x9E, 0x5E, 0xDE, 0x3E, 0xBE, 0x7E, 0xFE,
43 : 0x01, 0x81, 0x41, 0xC1, 0x21, 0xA1, 0x61, 0xE1,
44 : 0x11, 0x91, 0x51, 0xD1, 0x31, 0xB1, 0x71, 0xF1,
45 : 0x09, 0x89, 0x49, 0xC9, 0x29, 0xA9, 0x69, 0xE9,
46 : 0x19, 0x99, 0x59, 0xD9, 0x39, 0xB9, 0x79, 0xF9,
47 : 0x05, 0x85, 0x45, 0xC5, 0x25, 0xA5, 0x65, 0xE5,
48 : 0x15, 0x95, 0x55, 0xD5, 0x35, 0xB5, 0x75, 0xF5,
49 : 0x0D, 0x8D, 0x4D, 0xCD, 0x2D, 0xAD, 0x6D, 0xED,
50 : 0x1D, 0x9D, 0x5D, 0xDD, 0x3D, 0xBD, 0x7D, 0xFD,
51 : 0x03, 0x83, 0x43, 0xC3, 0x23, 0xA3, 0x63, 0xE3,
52 : 0x13, 0x93, 0x53, 0xD3, 0x33, 0xB3, 0x73, 0xF3,
53 : 0x0B, 0x8B, 0x4B, 0xCB, 0x2B, 0xAB, 0x6B, 0xEB,
54 : 0x1B, 0x9B, 0x5B, 0xDB, 0x3B, 0xBB, 0x7B, 0xFB,
55 : 0x07, 0x87, 0x47, 0xC7, 0x27, 0xA7, 0x67, 0xE7,
56 : 0x17, 0x97, 0x57, 0xD7, 0x37, 0xB7, 0x77, 0xF7,
57 : 0x0F, 0x8F, 0x4F, 0xCF, 0x2F, 0xAF, 0x6F, 0xEF,
58 : 0x1F, 0x9F, 0x5F, 0xDF, 0x3F, 0xBF, 0x7F, 0xFF
59 : };
60 : #endif /* BROTLI_RBIT */
61 :
62 : #define BROTLI_REVERSE_BITS_LOWEST \
63 : (1U << (BROTLI_REVERSE_BITS_MAX - 1 + BROTLI_REVERSE_BITS_BASE))
64 :
65 : /* Returns reverse(num >> BROTLI_REVERSE_BITS_BASE, BROTLI_REVERSE_BITS_MAX),
66 : where reverse(value, len) is the bit-wise reversal of the len least
67 : significant bits of value. */
68 : static BROTLI_INLINE uint32_t BrotliReverseBits(uint32_t num) {
69 : #ifdef BROTLI_RBIT
70 : return BROTLI_RBIT(num);
71 : #else
72 0 : return kReverseBits[num];
73 : #endif
74 : }
75 :
76 : /* Stores code in table[0], table[step], table[2*step], ..., table[end] */
77 : /* Assumes that end is an integer multiple of step */
78 : static BROTLI_INLINE void ReplicateValue(HuffmanCode* table,
79 : int step, int end,
80 : HuffmanCode code) {
81 : do {
82 0 : end -= step;
83 0 : table[end] = code;
84 0 : } while (end > 0);
85 : }
86 :
87 : /* Returns the table width of the next 2nd level table. count is the histogram
88 : of bit lengths for the remaining symbols, len is the code length of the next
89 : processed symbol */
90 : static BROTLI_INLINE int NextTableBitSize(const uint16_t* const count,
91 : int len, int root_bits) {
92 0 : int left = 1 << (len - root_bits);
93 0 : while (len < BROTLI_HUFFMAN_MAX_CODE_LENGTH) {
94 0 : left -= count[len];
95 0 : if (left <= 0) break;
96 0 : ++len;
97 0 : left <<= 1;
98 : }
99 0 : return len - root_bits;
100 : }
101 :
102 0 : void BrotliBuildCodeLengthsHuffmanTable(HuffmanCode* table,
103 : const uint8_t* const code_lengths,
104 : uint16_t* count) {
105 : HuffmanCode code; /* current table entry */
106 : int symbol; /* symbol index in original or sorted table */
107 : uint32_t key; /* prefix code */
108 : uint32_t key_step; /* prefix code addend */
109 : int step; /* step size to replicate values in current table */
110 : int table_size; /* size of current table */
111 : int sorted[18]; /* symbols sorted by code length */
112 : /* offsets in sorted table for each length */
113 : int offset[BROTLI_HUFFMAN_MAX_CODE_LENGTH_CODE_LENGTH + 1];
114 : int bits;
115 : int bits_count;
116 : BROTLI_DCHECK(BROTLI_HUFFMAN_MAX_CODE_LENGTH_CODE_LENGTH <=
117 : BROTLI_REVERSE_BITS_MAX);
118 :
119 : /* generate offsets into sorted symbol table by code length */
120 0 : symbol = -1;
121 0 : bits = 1;
122 0 : BROTLI_REPEAT(BROTLI_HUFFMAN_MAX_CODE_LENGTH_CODE_LENGTH, {
123 : symbol += count[bits];
124 : offset[bits] = symbol;
125 : bits++;
126 : });
127 : /* Symbols with code length 0 are placed after all other symbols. */
128 0 : offset[0] = 17;
129 :
130 : /* sort symbols by length, by symbol order within each length */
131 0 : symbol = 18;
132 : do {
133 0 : BROTLI_REPEAT(6, {
134 : symbol--;
135 : sorted[offset[code_lengths[symbol]]--] = symbol;
136 : });
137 0 : } while (symbol != 0);
138 :
139 0 : table_size = 1 << BROTLI_HUFFMAN_MAX_CODE_LENGTH_CODE_LENGTH;
140 :
141 : /* Special case: all symbols but one have 0 code length. */
142 0 : if (offset[0] == 0) {
143 0 : code.bits = 0;
144 0 : code.value = (uint16_t)sorted[0];
145 0 : for (key = 0; key < (uint32_t)table_size; ++key) {
146 0 : table[key] = code;
147 : }
148 0 : return;
149 : }
150 :
151 : /* fill in table */
152 0 : key = 0;
153 0 : key_step = BROTLI_REVERSE_BITS_LOWEST;
154 0 : symbol = 0;
155 0 : bits = 1;
156 0 : step = 2;
157 : do {
158 0 : code.bits = (uint8_t)bits;
159 0 : for (bits_count = count[bits]; bits_count != 0; --bits_count) {
160 0 : code.value = (uint16_t)sorted[symbol++];
161 0 : ReplicateValue(&table[BrotliReverseBits(key)], step, table_size, code);
162 0 : key += key_step;
163 : }
164 0 : step <<= 1;
165 0 : key_step >>= 1;
166 0 : } while (++bits <= BROTLI_HUFFMAN_MAX_CODE_LENGTH_CODE_LENGTH);
167 : }
168 :
169 0 : 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 : uint32_t key; /* prefix code */
178 : uint32_t key_step; /* prefix code addend */
179 : uint32_t sub_key; /* 2nd level table prefix code */
180 : uint32_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 0 : 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 0 : while (symbol_lists[max_length] == 0xFFFF) max_length--;
194 0 : max_length += BROTLI_HUFFMAN_MAX_CODE_LENGTH + 1;
195 :
196 0 : table = root_table;
197 0 : table_bits = root_bits;
198 0 : table_size = 1 << table_bits;
199 0 : total_size = table_size;
200 :
201 : /* fill in root table */
202 : /* let's reduce the table size to a smaller size if possible, and */
203 : /* create the repetitions by memcpy if possible in the coming loop */
204 0 : if (table_bits > max_length) {
205 0 : table_bits = max_length;
206 0 : table_size = 1 << table_bits;
207 : }
208 0 : key = 0;
209 0 : key_step = BROTLI_REVERSE_BITS_LOWEST;
210 0 : bits = 1;
211 0 : step = 2;
212 : do {
213 0 : code.bits = (uint8_t)bits;
214 0 : symbol = bits - (BROTLI_HUFFMAN_MAX_CODE_LENGTH + 1);
215 0 : for (bits_count = count[bits]; bits_count != 0; --bits_count) {
216 0 : symbol = symbol_lists[symbol];
217 0 : code.value = (uint16_t)symbol;
218 0 : ReplicateValue(&table[BrotliReverseBits(key)], step, table_size, code);
219 0 : key += key_step;
220 : }
221 0 : step <<= 1;
222 0 : key_step >>= 1;
223 0 : } while (++bits <= table_bits);
224 :
225 : /* if root_bits != table_bits we only created one fraction of the */
226 : /* table, and we need to replicate it now. */
227 0 : while (total_size != table_size) {
228 0 : memcpy(&table[table_size], &table[0],
229 0 : (size_t)table_size * sizeof(table[0]));
230 0 : table_size <<= 1;
231 : }
232 :
233 : /* fill in 2nd level tables and add pointers to root table */
234 0 : key_step = BROTLI_REVERSE_BITS_LOWEST >> (root_bits - 1);
235 0 : sub_key = (BROTLI_REVERSE_BITS_LOWEST << 1);
236 0 : sub_key_step = BROTLI_REVERSE_BITS_LOWEST;
237 0 : for (len = root_bits + 1, step = 2; len <= max_length; ++len) {
238 0 : symbol = len - (BROTLI_HUFFMAN_MAX_CODE_LENGTH + 1);
239 0 : for (; count[len] != 0; --count[len]) {
240 0 : if (sub_key == (BROTLI_REVERSE_BITS_LOWEST << 1U)) {
241 0 : table += table_size;
242 0 : table_bits = NextTableBitSize(count, len, root_bits);
243 0 : table_size = 1 << table_bits;
244 0 : total_size += table_size;
245 0 : sub_key = BrotliReverseBits(key);
246 0 : key += key_step;
247 0 : root_table[sub_key].bits = (uint8_t)(table_bits + root_bits);
248 0 : root_table[sub_key].value =
249 0 : (uint16_t)(((size_t)(table - root_table)) - sub_key);
250 0 : sub_key = 0;
251 : }
252 0 : code.bits = (uint8_t)(len - root_bits);
253 0 : symbol = symbol_lists[symbol];
254 0 : code.value = (uint16_t)symbol;
255 0 : ReplicateValue(
256 0 : &table[BrotliReverseBits(sub_key)], step, table_size, code);
257 0 : sub_key += sub_key_step;
258 : }
259 0 : step <<= 1;
260 0 : sub_key_step >>= 1;
261 : }
262 0 : return (uint32_t)total_size;
263 : }
264 :
265 0 : uint32_t BrotliBuildSimpleHuffmanTable(HuffmanCode* table,
266 : int root_bits,
267 : uint16_t* val,
268 : uint32_t num_symbols) {
269 0 : uint32_t table_size = 1;
270 0 : const uint32_t goal_size = 1U << root_bits;
271 0 : switch (num_symbols) {
272 : case 0:
273 0 : table[0].bits = 0;
274 0 : table[0].value = val[0];
275 0 : break;
276 : case 1:
277 0 : table[0].bits = 1;
278 0 : table[1].bits = 1;
279 0 : if (val[1] > val[0]) {
280 0 : table[0].value = val[0];
281 0 : table[1].value = val[1];
282 : } else {
283 0 : table[0].value = val[1];
284 0 : table[1].value = val[0];
285 : }
286 0 : table_size = 2;
287 0 : break;
288 : case 2:
289 0 : table[0].bits = 1;
290 0 : table[0].value = val[0];
291 0 : table[2].bits = 1;
292 0 : table[2].value = val[0];
293 0 : if (val[2] > val[1]) {
294 0 : table[1].value = val[1];
295 0 : table[3].value = val[2];
296 : } else {
297 0 : table[1].value = val[2];
298 0 : table[3].value = val[1];
299 : }
300 0 : table[1].bits = 2;
301 0 : table[3].bits = 2;
302 0 : table_size = 4;
303 0 : break;
304 : case 3: {
305 : int i, k;
306 0 : for (i = 0; i < 3; ++i) {
307 0 : for (k = i + 1; k < 4; ++k) {
308 0 : if (val[k] < val[i]) {
309 0 : uint16_t t = val[k];
310 0 : val[k] = val[i];
311 0 : val[i] = t;
312 : }
313 : }
314 : }
315 0 : for (i = 0; i < 4; ++i) {
316 0 : table[i].bits = 2;
317 : }
318 0 : table[0].value = val[0];
319 0 : table[2].value = val[1];
320 0 : table[1].value = val[2];
321 0 : table[3].value = val[3];
322 0 : table_size = 4;
323 0 : break;
324 : }
325 : case 4: {
326 : int i;
327 0 : if (val[3] < val[2]) {
328 0 : uint16_t t = val[3];
329 0 : val[3] = val[2];
330 0 : val[2] = t;
331 : }
332 0 : for (i = 0; i < 7; ++i) {
333 0 : table[i].value = val[0];
334 0 : table[i].bits = (uint8_t)(1 + (i & 1));
335 : }
336 0 : table[1].value = val[1];
337 0 : table[3].value = val[2];
338 0 : table[5].value = val[1];
339 0 : table[7].value = val[3];
340 0 : table[3].bits = 3;
341 0 : table[7].bits = 3;
342 0 : table_size = 8;
343 0 : break;
344 : }
345 : }
346 0 : while (table_size != goal_size) {
347 0 : memcpy(&table[table_size], &table[0],
348 0 : (size_t)table_size * sizeof(table[0]));
349 0 : table_size <<= 1;
350 : }
351 0 : return goal_size;
352 : }
353 :
354 : #if defined(__cplusplus) || defined(c_plusplus)
355 : } /* extern "C" */
356 : #endif
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