1 /* license:BSD-3-Clause
2 * copyright-holders:Aaron Giles
3 ****************************************************************************
4
5 huffman.c
6
7 Static Huffman compression and decompression helpers.
8
9 ****************************************************************************
10
11 Maximum codelength is officially (alphabetsize - 1). This would be 255 bits
12 (since we use 1 byte values). However, it is also dependent upon the number
13 of samples used, as follows:
14
15 2 bits -> 3..4 samples
16 3 bits -> 5..7 samples
17 4 bits -> 8..12 samples
18 5 bits -> 13..20 samples
19 6 bits -> 21..33 samples
20 7 bits -> 34..54 samples
21 8 bits -> 55..88 samples
22 9 bits -> 89..143 samples
23 10 bits -> 144..232 samples
24 11 bits -> 233..376 samples
25 12 bits -> 377..609 samples
26 13 bits -> 610..986 samples
27 14 bits -> 987..1596 samples
28 15 bits -> 1597..2583 samples
29 16 bits -> 2584..4180 samples -> note that a 4k data size guarantees codelength <= 16 bits
30 17 bits -> 4181..6764 samples
31 18 bits -> 6765..10945 samples
32 19 bits -> 10946..17710 samples
33 20 bits -> 17711..28656 samples
34 21 bits -> 28657..46367 samples
35 22 bits -> 46368..75024 samples
36 23 bits -> 75025..121392 samples
37 24 bits -> 121393..196417 samples
38 25 bits -> 196418..317810 samples
39 26 bits -> 317811..514228 samples
40 27 bits -> 514229..832039 samples
41 28 bits -> 832040..1346268 samples
42 29 bits -> 1346269..2178308 samples
43 30 bits -> 2178309..3524577 samples
44 31 bits -> 3524578..5702886 samples
45 32 bits -> 5702887..9227464 samples
46
47 Looking at it differently, here is where powers of 2 fall into these buckets:
48
49 256 samples -> 11 bits max
50 512 samples -> 12 bits max
51 1k samples -> 14 bits max
52 2k samples -> 15 bits max
53 4k samples -> 16 bits max
54 8k samples -> 18 bits max
55 16k samples -> 19 bits max
56 32k samples -> 21 bits max
57 64k samples -> 22 bits max
58 128k samples -> 24 bits max
59 256k samples -> 25 bits max
60 512k samples -> 27 bits max
61 1M samples -> 28 bits max
62 2M samples -> 29 bits max
63 4M samples -> 31 bits max
64 8M samples -> 32 bits max
65
66 ****************************************************************************
67
68 Delta-RLE encoding works as follows:
69
70 Starting value is assumed to be 0. All data is encoded as a delta
71 from the previous value, such that final[i] = final[i - 1] + delta.
72 Long runs of 0s are RLE-encoded as follows:
73
74 0x100 = repeat count of 8
75 0x101 = repeat count of 9
76 0x102 = repeat count of 10
77 0x103 = repeat count of 11
78 0x104 = repeat count of 12
79 0x105 = repeat count of 13
80 0x106 = repeat count of 14
81 0x107 = repeat count of 15
82 0x108 = repeat count of 16
83 0x109 = repeat count of 32
84 0x10a = repeat count of 64
85 0x10b = repeat count of 128
86 0x10c = repeat count of 256
87 0x10d = repeat count of 512
88 0x10e = repeat count of 1024
89 0x10f = repeat count of 2048
90
91 Note that repeat counts are reset at the end of a row, so if a 0 run
92 extends to the end of a row, a large repeat count may be used.
93
94 The reason for starting the run counts at 8 is that 0 is expected to
95 be the most common symbol, and is typically encoded in 1 or 2 bits.
96
97 ***************************************************************************/
98
99 #include <stdlib.h>
100 #include <assert.h>
101 #include <stdio.h>
102 #include <string.h>
103
104 #include "huffman.h"
105
106 #define MAX(x,y) ((x) > (y) ? (x) : (y))
107
108 /***************************************************************************
109 * MACROS
110 ***************************************************************************
111 */
112
113 #define MAKE_LOOKUP(code,bits) (((code) << 5) | ((bits) & 0x1f))
114
115 /***************************************************************************
116 * IMPLEMENTATION
117 ***************************************************************************
118 */
119
120 /*-------------------------------------------------
121 * huffman_context_base - create an encoding/
122 * decoding context
123 *-------------------------------------------------
124 */
125
create_huffman_decoder(int numcodes,int maxbits)126 struct huffman_decoder* create_huffman_decoder(int numcodes, int maxbits)
127 {
128 /* limit to 24 bits */
129 if (maxbits > 24)
130 return NULL;
131
132 struct huffman_decoder* decoder = (struct huffman_decoder*)malloc(sizeof(struct huffman_decoder));
133 decoder->numcodes = numcodes;
134 decoder->maxbits = maxbits;
135 decoder->lookup = (lookup_value*)malloc(sizeof(lookup_value) * (1 << maxbits));
136 decoder->huffnode = (struct node_t*)malloc(sizeof(struct node_t) * numcodes);
137 decoder->datahisto = NULL;
138 decoder->prevdata = 0;
139 decoder->rleremaining = 0;
140 return decoder;
141 }
142
143 /*-------------------------------------------------
144 * decode_one - decode a single code from the
145 * huffman stream
146 *-------------------------------------------------
147 */
148
huffman_decode_one(struct huffman_decoder * decoder,struct bitstream * bitbuf)149 uint32_t huffman_decode_one(struct huffman_decoder* decoder, struct bitstream* bitbuf)
150 {
151 /* peek ahead to get maxbits worth of data */
152 uint32_t bits = bitstream_peek(bitbuf, decoder->maxbits);
153
154 /* look it up, then remove the actual number of bits for this code */
155 lookup_value lookup = decoder->lookup[bits];
156 bitstream_remove(bitbuf, lookup & 0x1f);
157
158 /* return the value */
159 return lookup >> 5;
160 }
161
162 /*-------------------------------------------------
163 * import_tree_rle - import an RLE-encoded
164 * huffman tree from a source data stream
165 *-------------------------------------------------
166 */
167
huffman_import_tree_rle(struct huffman_decoder * decoder,struct bitstream * bitbuf)168 enum huffman_error huffman_import_tree_rle(struct huffman_decoder* decoder, struct bitstream* bitbuf)
169 {
170 /* bits per entry depends on the maxbits */
171 int numbits;
172 if (decoder->maxbits >= 16)
173 numbits = 5;
174 else if (decoder->maxbits >= 8)
175 numbits = 4;
176 else
177 numbits = 3;
178
179 /* loop until we read all the nodes */
180 int curnode;
181 for (curnode = 0; curnode < decoder->numcodes; )
182 {
183 /* a non-one value is just raw */
184 int nodebits = bitstream_read(bitbuf, numbits);
185 if (nodebits != 1)
186 decoder->huffnode[curnode++].numbits = nodebits;
187
188 /* a one value is an escape code */
189 else
190 {
191 /* a double 1 is just a single 1 */
192 nodebits = bitstream_read(bitbuf, numbits);
193 if (nodebits == 1)
194 decoder->huffnode[curnode++].numbits = nodebits;
195
196 /* otherwise, we need one for value for the repeat count */
197 else
198 {
199 int repcount = bitstream_read(bitbuf, numbits) + 3;
200 while (repcount--)
201 decoder->huffnode[curnode++].numbits = nodebits;
202 }
203 }
204 }
205
206 /* make sure we ended up with the right number */
207 if (curnode != decoder->numcodes)
208 return HUFFERR_INVALID_DATA;
209
210 /* assign canonical codes for all nodes based on their code lengths */
211 enum huffman_error error = huffman_assign_canonical_codes(decoder);
212 if (error != HUFFERR_NONE)
213 return error;
214
215 /* build the lookup table */
216 huffman_build_lookup_table(decoder);
217
218 /* determine final input length and report errors */
219 return bitstream_overflow(bitbuf) ? HUFFERR_INPUT_BUFFER_TOO_SMALL : HUFFERR_NONE;
220 }
221
222
223 /*-------------------------------------------------
224 * import_tree_huffman - import a huffman-encoded
225 * huffman tree from a source data stream
226 *-------------------------------------------------
227 */
228
huffman_import_tree_huffman(struct huffman_decoder * decoder,struct bitstream * bitbuf)229 enum huffman_error huffman_import_tree_huffman(struct huffman_decoder* decoder, struct bitstream* bitbuf)
230 {
231 /* start by parsing the lengths for the small tree */
232 struct huffman_decoder* smallhuff = create_huffman_decoder(24, 6);
233 smallhuff->huffnode[0].numbits = bitstream_read(bitbuf, 3);
234 int start = bitstream_read(bitbuf, 3) + 1;
235 int count = 0;
236 for (int index = 1; index < 24; index++)
237 {
238 if (index < start || count == 7)
239 smallhuff->huffnode[index].numbits = 0;
240 else
241 {
242 count = bitstream_read(bitbuf, 3);
243 smallhuff->huffnode[index].numbits = (count == 7) ? 0 : count;
244 }
245 }
246
247 /* then regenerate the tree */
248 enum huffman_error error = huffman_assign_canonical_codes(smallhuff);
249 if (error != HUFFERR_NONE)
250 return error;
251 huffman_build_lookup_table(smallhuff);
252
253 /* determine the maximum length of an RLE count */
254 uint32_t temp = decoder->numcodes - 9;
255 uint8_t rlefullbits = 0;
256 while (temp != 0)
257 temp >>= 1, rlefullbits++;
258
259 /* now process the rest of the data */
260 int last = 0;
261 int curcode;
262 for (curcode = 0; curcode < decoder->numcodes; )
263 {
264 int value = huffman_decode_one(smallhuff, bitbuf);
265 if (value != 0)
266 decoder->huffnode[curcode++].numbits = last = value - 1;
267 else
268 {
269 int count = bitstream_read(bitbuf, 3) + 2;
270 if (count == 7+2)
271 count += bitstream_read(bitbuf, rlefullbits);
272 for ( ; count != 0 && curcode < decoder->numcodes; count--)
273 decoder->huffnode[curcode++].numbits = last;
274 }
275 }
276
277 /* make sure we ended up with the right number */
278 if (curcode != decoder->numcodes)
279 return HUFFERR_INVALID_DATA;
280
281 /* assign canonical codes for all nodes based on their code lengths */
282 error = huffman_assign_canonical_codes(decoder);
283 if (error != HUFFERR_NONE)
284 return error;
285
286 /* build the lookup table */
287 huffman_build_lookup_table(decoder);
288
289 /* determine final input length and report errors */
290 return bitstream_overflow(bitbuf) ? HUFFERR_INPUT_BUFFER_TOO_SMALL : HUFFERR_NONE;
291 }
292
293 /*-------------------------------------------------
294 * compute_tree_from_histo - common backend for
295 * computing a tree based on the data histogram
296 *-------------------------------------------------
297 */
298
huffman_compute_tree_from_histo(struct huffman_decoder * decoder)299 enum huffman_error huffman_compute_tree_from_histo(struct huffman_decoder* decoder)
300 {
301 /* compute the number of data items in the histogram */
302 uint32_t sdatacount = 0;
303 for (int i = 0; i < decoder->numcodes; i++)
304 sdatacount += decoder->datahisto[i];
305
306 /* binary search to achieve the optimum encoding */
307 uint32_t lowerweight = 0;
308 uint32_t upperweight = sdatacount * 2;
309 while (1)
310 {
311 /* build a tree using the current weight */
312 uint32_t curweight = (upperweight + lowerweight) / 2;
313 int curmaxbits = huffman_build_tree(decoder, sdatacount, curweight);
314
315 /* apply binary search here */
316 if (curmaxbits <= decoder->maxbits)
317 {
318 lowerweight = curweight;
319
320 /* early out if it worked with the raw weights, or if we're done searching */
321 if (curweight == sdatacount || (upperweight - lowerweight) <= 1)
322 break;
323 }
324 else
325 upperweight = curweight;
326 }
327
328 /* assign canonical codes for all nodes based on their code lengths */
329 return huffman_assign_canonical_codes(decoder);
330 }
331
332 /***************************************************************************
333 * INTERNAL FUNCTIONS
334 ***************************************************************************
335 */
336
337 /*-------------------------------------------------
338 * tree_node_compare - compare two tree nodes
339 * by weight
340 *-------------------------------------------------
341 */
342
huffman_tree_node_compare(const void * item1,const void * item2)343 static int huffman_tree_node_compare(const void *item1, const void *item2)
344 {
345 const struct node_t *node1 = *(const struct node_t **)item1;
346 const struct node_t *node2 = *(const struct node_t **)item2;
347 if (node2->weight != node1->weight)
348 return node2->weight - node1->weight;
349 if (node2->bits - node1->bits == 0)
350 fprintf(stderr, "identical node sort keys, should not happen!\n");
351 return (int)node1->bits - (int)node2->bits;
352 }
353
354 /*-------------------------------------------------
355 * build_tree - build a huffman tree based on the
356 * data distribution
357 *-------------------------------------------------
358 */
359
huffman_build_tree(struct huffman_decoder * decoder,uint32_t totaldata,uint32_t totalweight)360 int huffman_build_tree(struct huffman_decoder* decoder, uint32_t totaldata, uint32_t totalweight)
361 {
362 /* make a list of all non-zero nodes */
363 struct node_t** list = (struct node_t**)malloc(sizeof(struct node_t*) * decoder->numcodes * 2);
364 int listitems = 0;
365 memset(decoder->huffnode, 0, decoder->numcodes * sizeof(decoder->huffnode[0]));
366 for (int curcode = 0; curcode < decoder->numcodes; curcode++)
367 if (decoder->datahisto[curcode] != 0)
368 {
369 list[listitems++] = &decoder->huffnode[curcode];
370 decoder->huffnode[curcode].count = decoder->datahisto[curcode];
371 decoder->huffnode[curcode].bits = curcode;
372
373 /* scale the weight by the current effective length, ensuring we don't go to 0 */
374 decoder->huffnode[curcode].weight = ((uint64_t)decoder->datahisto[curcode]) * ((uint64_t)totalweight) / ((uint64_t)totaldata);
375 if (decoder->huffnode[curcode].weight == 0)
376 decoder->huffnode[curcode].weight = 1;
377 }
378
379 #if 0
380 fprintf(stderr, "Pre-sort:\n");
381 for (int i = 0; i < listitems; i++) {
382 fprintf(stderr, "weight: %d code: %d\n", list[i]->m_weight, list[i]->m_bits);
383 }
384 #endif
385
386 /* sort the list by weight, largest weight first */
387 qsort(&list[0], listitems, sizeof(list[0]), huffman_tree_node_compare);
388
389 #if 0
390 fprintf(stderr, "Post-sort:\n");
391 for (int i = 0; i < listitems; i++) {
392 fprintf(stderr, "weight: %d code: %d\n", list[i]->m_weight, list[i]->m_bits);
393 }
394 fprintf(stderr, "===================\n");
395 #endif
396
397 /* now build the tree */
398 int nextalloc = decoder->numcodes;
399 while (listitems > 1)
400 {
401 /* remove lowest two items */
402 struct node_t* node1 = &(*list[--listitems]);
403 struct node_t* node0 = &(*list[--listitems]);
404
405 /* create new node */
406 struct node_t* newnode = &decoder->huffnode[nextalloc++];
407 newnode->parent = NULL;
408 node0->parent = node1->parent = newnode;
409 newnode->weight = node0->weight + node1->weight;
410
411 /* insert into list at appropriate location */
412 int curitem;
413 for (curitem = 0; curitem < listitems; curitem++)
414 if (newnode->weight > list[curitem]->weight)
415 {
416 memmove(&list[curitem+1], &list[curitem], (listitems - curitem) * sizeof(list[0]));
417 break;
418 }
419 list[curitem] = newnode;
420 listitems++;
421 }
422
423 /* compute the number of bits in each code, and fill in another histogram */
424 int maxbits = 0;
425 for (int curcode = 0; curcode < decoder->numcodes; curcode++)
426 {
427 struct node_t* node = &decoder->huffnode[curcode];
428 node->numbits = 0;
429 node->bits = 0;
430
431 /* if we have a non-zero weight, compute the number of bits */
432 if (node->weight > 0)
433 {
434 /* determine the number of bits for this node */
435 for (struct node_t *curnode = node; curnode->parent != NULL; curnode = curnode->parent)
436 node->numbits++;
437 if (node->numbits == 0)
438 node->numbits = 1;
439
440 /* keep track of the max */
441 maxbits = MAX(maxbits, ((int)node->numbits));
442 }
443 }
444 return maxbits;
445 }
446
447 /*-------------------------------------------------
448 * assign_canonical_codes - assign canonical codes
449 * to all the nodes based on the number of bits
450 * in each
451 *-------------------------------------------------
452 */
453
huffman_assign_canonical_codes(struct huffman_decoder * decoder)454 enum huffman_error huffman_assign_canonical_codes(struct huffman_decoder* decoder)
455 {
456 /* build up a histogram of bit lengths */
457 uint32_t bithisto[33] = { 0 };
458 for (int curcode = 0; curcode < decoder->numcodes; curcode++)
459 {
460 struct node_t* node = &decoder->huffnode[curcode];
461 if (node->numbits > decoder->maxbits)
462 return HUFFERR_INTERNAL_INCONSISTENCY;
463 if (node->numbits <= 32)
464 bithisto[node->numbits]++;
465 }
466
467 /* for each code length, determine the starting code number */
468 uint32_t curstart = 0;
469 for (int codelen = 32; codelen > 0; codelen--)
470 {
471 uint32_t nextstart = (curstart + bithisto[codelen]) >> 1;
472 if (codelen != 1 && nextstart * 2 != (curstart + bithisto[codelen]))
473 return HUFFERR_INTERNAL_INCONSISTENCY;
474 bithisto[codelen] = curstart;
475 curstart = nextstart;
476 }
477
478 /* now assign canonical codes */
479 for (int curcode = 0; curcode < decoder->numcodes; curcode++)
480 {
481 struct node_t* node = &decoder->huffnode[curcode];
482 if (node->numbits > 0)
483 node->bits = bithisto[node->numbits]++;
484 }
485 return HUFFERR_NONE;
486 }
487
488 /*-------------------------------------------------
489 * build_lookup_table - build a lookup table for
490 * fast decoding
491 *-------------------------------------------------
492 */
493
huffman_build_lookup_table(struct huffman_decoder * decoder)494 void huffman_build_lookup_table(struct huffman_decoder* decoder)
495 {
496 /* iterate over all codes */
497 for (int curcode = 0; curcode < decoder->numcodes; curcode++)
498 {
499 /* process all nodes which have non-zero bits */
500 struct node_t* node = &decoder->huffnode[curcode];
501 if (node->numbits > 0)
502 {
503 /* set up the entry */
504 lookup_value value = MAKE_LOOKUP(curcode, node->numbits);
505
506 /* fill all matching entries */
507 int shift = decoder->maxbits - node->numbits;
508 lookup_value *dest = &decoder->lookup[node->bits << shift];
509 lookup_value *destend = &decoder->lookup[((node->bits + 1) << shift) - 1];
510 while (dest <= destend)
511 *dest++ = value;
512 }
513 }
514 }
515