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 #define MAKE_LOOKUP(code,bits) (((code) << 5) | ((bits) & 0x1f))
113
114
115 //**************************************************************************
116 // IMPLEMENTATION
117 //**************************************************************************
118
119 //-------------------------------------------------
120 // huffman_context_base - create an encoding/
121 // decoding context
122 //-------------------------------------------------
123
create_huffman_decoder(int numcodes,int maxbits)124 struct huffman_decoder* create_huffman_decoder(int numcodes, int maxbits)
125 {
126 struct huffman_decoder* decoder;
127
128 /* limit to 24 bits */
129 if (maxbits > 24)
130 return NULL;
131
132 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
huffman_decode_one(struct huffman_decoder * decoder,struct bitstream * bitbuf)148 uint32_t huffman_decode_one(struct huffman_decoder* decoder, struct bitstream* bitbuf)
149 {
150 /* peek ahead to get maxbits worth of data */
151 uint32_t bits = bitstream_peek(bitbuf, decoder->maxbits);
152
153 /* look it up, then remove the actual number of bits for this code */
154 lookup_value lookup = decoder->lookup[bits];
155 bitstream_remove(bitbuf, lookup & 0x1f);
156
157 /* return the value */
158 return lookup >> 5;
159 }
160
161 //-------------------------------------------------
162 // import_tree_rle - import an RLE-encoded
163 // huffman tree from a source data stream
164 //-------------------------------------------------
165
huffman_import_tree_rle(struct huffman_decoder * decoder,struct bitstream * bitbuf)166 enum huffman_error huffman_import_tree_rle(struct huffman_decoder* decoder, struct bitstream* bitbuf)
167 {
168 enum huffman_error error;
169 int curnode;
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 for (curnode = 0; curnode < decoder->numcodes; )
181 {
182 // a non-one value is just raw
183 int nodebits = bitstream_read(bitbuf, numbits);
184 if (nodebits != 1)
185 decoder->huffnode[curnode++].numbits = nodebits;
186
187 // a one value is an escape code
188 else
189 {
190 // a double 1 is just a single 1
191 nodebits = bitstream_read(bitbuf, numbits);
192 if (nodebits == 1)
193 decoder->huffnode[curnode++].numbits = nodebits;
194
195 // otherwise, we need one for value for the repeat count
196 else
197 {
198 int repcount = bitstream_read(bitbuf, numbits) + 3;
199 while (repcount--)
200 decoder->huffnode[curnode++].numbits = nodebits;
201 }
202 }
203 }
204
205 // make sure we ended up with the right number
206 if (curnode != decoder->numcodes)
207 return HUFFERR_INVALID_DATA;
208
209 // assign canonical codes for all nodes based on their code lengths
210 error = huffman_assign_canonical_codes(decoder);
211 if (error != HUFFERR_NONE)
212 return error;
213
214 // build the lookup table
215 huffman_build_lookup_table(decoder);
216
217 // determine final input length and report errors
218 return bitstream_overflow(bitbuf) ? HUFFERR_INPUT_BUFFER_TOO_SMALL : HUFFERR_NONE;
219 }
220
221
222 //-------------------------------------------------
223 // import_tree_huffman - import a huffman-encoded
224 // huffman tree from a source data stream
225 //-------------------------------------------------
226
huffman_import_tree_huffman(struct huffman_decoder * decoder,struct bitstream * bitbuf)227 enum huffman_error huffman_import_tree_huffman(struct huffman_decoder* decoder, struct bitstream* bitbuf)
228 {
229 int index;
230 int start;
231 int count = 0;
232 uint8_t rlefullbits = 0;
233 int last = 0;
234 int curcode;
235 enum huffman_error error;
236 uint32_t temp;
237 // start by parsing the lengths for the small tree
238 struct huffman_decoder* smallhuff = create_huffman_decoder(24, 6);
239
240 smallhuff->huffnode[0].numbits = bitstream_read(bitbuf, 3);
241 start = bitstream_read(bitbuf, 3) + 1;
242
243 for (index = 1; index < 24; index++)
244 {
245 if (index < start || count == 7)
246 smallhuff->huffnode[index].numbits = 0;
247 else
248 {
249 count = bitstream_read(bitbuf, 3);
250 smallhuff->huffnode[index].numbits = (count == 7) ? 0 : count;
251 }
252 }
253
254 // then regenerate the tree
255 error = huffman_assign_canonical_codes(smallhuff);
256 if (error != HUFFERR_NONE)
257 return error;
258 huffman_build_lookup_table(smallhuff);
259
260 // determine the maximum length of an RLE count
261 temp = decoder->numcodes - 9;
262 while (temp != 0)
263 temp >>= 1, rlefullbits++;
264
265 // now process the rest of the data
266 for (curcode = 0; curcode < decoder->numcodes; )
267 {
268 int value = huffman_decode_one(smallhuff, bitbuf);
269 if (value != 0)
270 decoder->huffnode[curcode++].numbits = last = value - 1;
271 else
272 {
273 int count = bitstream_read(bitbuf, 3) + 2;
274 if (count == 7+2)
275 count += bitstream_read(bitbuf, rlefullbits);
276 for ( ; count != 0 && curcode < decoder->numcodes; count--)
277 decoder->huffnode[curcode++].numbits = last;
278 }
279 }
280
281 // make sure we ended up with the right number
282 if (curcode != decoder->numcodes)
283 return HUFFERR_INVALID_DATA;
284
285 // assign canonical codes for all nodes based on their code lengths
286 error = huffman_assign_canonical_codes(decoder);
287 if (error != HUFFERR_NONE)
288 return error;
289
290 // build the lookup table
291 huffman_build_lookup_table(decoder);
292
293 // determine final input length and report errors
294 return bitstream_overflow(bitbuf) ? HUFFERR_INPUT_BUFFER_TOO_SMALL : HUFFERR_NONE;
295 }
296
297
298 //-------------------------------------------------
299 // compute_tree_from_histo - common backend for
300 // computing a tree based on the data histogram
301 //-------------------------------------------------
302
huffman_compute_tree_from_histo(struct huffman_decoder * decoder)303 enum huffman_error huffman_compute_tree_from_histo(struct huffman_decoder* decoder)
304 {
305 int i;
306 uint32_t upperweight;
307 uint32_t lowerweight = 0;
308 // compute the number of data items in the histogram
309 uint32_t sdatacount = 0;
310 for (i = 0; i < decoder->numcodes; i++)
311 sdatacount += decoder->datahisto[i];
312
313 // binary search to achieve the optimum encoding
314 upperweight = sdatacount * 2;
315 while (1)
316 {
317 // build a tree using the current weight
318 uint32_t curweight = (upperweight + lowerweight) / 2;
319 int curmaxbits = huffman_build_tree(decoder, sdatacount, curweight);
320
321 // apply binary search here
322 if (curmaxbits <= decoder->maxbits)
323 {
324 lowerweight = curweight;
325
326 // early out if it worked with the raw weights, or if we're done searching
327 if (curweight == sdatacount || (upperweight - lowerweight) <= 1)
328 break;
329 }
330 else
331 upperweight = curweight;
332 }
333
334 // assign canonical codes for all nodes based on their code lengths
335 return huffman_assign_canonical_codes(decoder);
336 }
337
338
339
340 //**************************************************************************
341 // INTERNAL FUNCTIONS
342 //**************************************************************************
343
344 //-------------------------------------------------
345 // tree_node_compare - compare two tree nodes
346 // by weight
347 //-------------------------------------------------
348
huffman_tree_node_compare(const void * item1,const void * item2)349 static int huffman_tree_node_compare(const void *item1, const void *item2)
350 {
351 const struct node_t *node1 = *(const struct node_t **)item1;
352 const struct node_t *node2 = *(const struct node_t **)item2;
353 if (node2->weight != node1->weight)
354 return node2->weight - node1->weight;
355 if (node2->bits - node1->bits == 0)
356 fprintf(stderr, "identical node sort keys, should not happen!\n");
357 return (int)node1->bits - (int)node2->bits;
358 }
359
360
361 //-------------------------------------------------
362 // build_tree - build a huffman tree based on the
363 // data distribution
364 //-------------------------------------------------
365
huffman_build_tree(struct huffman_decoder * decoder,uint32_t totaldata,uint32_t totalweight)366 int huffman_build_tree(struct huffman_decoder* decoder, uint32_t totaldata, uint32_t totalweight)
367 {
368 int curcode;
369 int nextalloc;
370 int maxbits = 0;
371 // make a list of all non-zero nodes
372 struct node_t** list = (struct node_t**)malloc(sizeof(struct node_t*) * decoder->numcodes * 2);
373 int listitems = 0;
374 memset(decoder->huffnode, 0, decoder->numcodes * sizeof(decoder->huffnode[0]));
375 for (curcode = 0; curcode < decoder->numcodes; curcode++)
376 if (decoder->datahisto[curcode] != 0)
377 {
378 list[listitems++] = &decoder->huffnode[curcode];
379 decoder->huffnode[curcode].count = decoder->datahisto[curcode];
380 decoder->huffnode[curcode].bits = curcode;
381
382 // scale the weight by the current effective length, ensuring we don't go to 0
383 decoder->huffnode[curcode].weight = ((uint64_t)decoder->datahisto[curcode]) * ((uint64_t)totalweight) / ((uint64_t)totaldata);
384 if (decoder->huffnode[curcode].weight == 0)
385 decoder->huffnode[curcode].weight = 1;
386 }
387 /*
388 fprintf(stderr, "Pre-sort:\n");
389 for (int i = 0; i < listitems; i++) {
390 fprintf(stderr, "weight: %d code: %d\n", list[i]->m_weight, list[i]->m_bits);
391 }
392 */
393 // sort the list by weight, largest weight first
394 qsort(&list[0], listitems, sizeof(list[0]), huffman_tree_node_compare);
395 /*
396 fprintf(stderr, "Post-sort:\n");
397 for (int i = 0; i < listitems; i++) {
398 fprintf(stderr, "weight: %d code: %d\n", list[i]->m_weight, list[i]->m_bits);
399 }
400 fprintf(stderr, "===================\n");
401 */
402 // now build the tree
403 nextalloc = decoder->numcodes;
404
405 while (listitems > 1)
406 {
407 int curitem;
408 // remove lowest two items
409 struct node_t* node1 = &(*list[--listitems]);
410 struct node_t* node0 = &(*list[--listitems]);
411
412 // create new node
413 struct node_t* newnode = &decoder->huffnode[nextalloc++];
414 newnode->parent = NULL;
415 node0->parent = node1->parent = newnode;
416 newnode->weight = node0->weight + node1->weight;
417
418 // insert into list at appropriate location
419 for (curitem = 0; curitem < listitems; curitem++)
420 if (newnode->weight > list[curitem]->weight)
421 {
422 memmove(&list[curitem+1], &list[curitem], (listitems - curitem) * sizeof(list[0]));
423 break;
424 }
425 list[curitem] = newnode;
426 listitems++;
427 }
428
429 // compute the number of bits in each code, and fill in another histogram
430 for (curcode = 0; curcode < decoder->numcodes; curcode++)
431 {
432 struct node_t* node = &decoder->huffnode[curcode];
433 node->numbits = 0;
434 node->bits = 0;
435
436 // if we have a non-zero weight, compute the number of bits
437 if (node->weight > 0)
438 {
439 struct node_t *curnode;
440 // determine the number of bits for this node
441 for (curnode = node; curnode->parent != NULL; curnode = curnode->parent)
442 node->numbits++;
443 if (node->numbits == 0)
444 node->numbits = 1;
445
446 // keep track of the max
447 maxbits = MAX(maxbits, ((int)node->numbits));
448 }
449 }
450 return maxbits;
451 }
452
453
454 //-------------------------------------------------
455 // assign_canonical_codes - assign canonical codes
456 // to all the nodes based on the number of bits
457 // in each
458 //-------------------------------------------------
459
huffman_assign_canonical_codes(struct huffman_decoder * decoder)460 enum huffman_error huffman_assign_canonical_codes(struct huffman_decoder* decoder)
461 {
462 int curcode, codelen;
463 uint32_t curstart = 0;
464
465 // build up a histogram of bit lengths
466 uint32_t bithisto[33] = { 0 };
467 for (curcode = 0; curcode < decoder->numcodes; curcode++)
468 {
469 struct node_t* node = &decoder->huffnode[curcode];
470 if (node->numbits > decoder->maxbits)
471 return HUFFERR_INTERNAL_INCONSISTENCY;
472 if (node->numbits <= 32)
473 bithisto[node->numbits]++;
474 }
475
476 // for each code length, determine the starting code number
477 for (codelen = 32; codelen > 0; codelen--)
478 {
479 uint32_t nextstart = (curstart + bithisto[codelen]) >> 1;
480 if (codelen != 1 && nextstart * 2 != (curstart + bithisto[codelen]))
481 return HUFFERR_INTERNAL_INCONSISTENCY;
482 bithisto[codelen] = curstart;
483 curstart = nextstart;
484 }
485
486 // now assign canonical codes
487 for (curcode = 0; curcode < decoder->numcodes; curcode++)
488 {
489 struct node_t* node = &decoder->huffnode[curcode];
490 if (node->numbits > 0)
491 node->bits = bithisto[node->numbits]++;
492 }
493 return HUFFERR_NONE;
494 }
495
496
497 //-------------------------------------------------
498 // build_lookup_table - build a lookup table for
499 // fast decoding
500 //-------------------------------------------------
501
huffman_build_lookup_table(struct huffman_decoder * decoder)502 void huffman_build_lookup_table(struct huffman_decoder* decoder)
503 {
504 int curcode;
505 // iterate over all codes
506 for (curcode = 0; curcode < decoder->numcodes; curcode++)
507 {
508 // process all nodes which have non-zero bits
509 struct node_t* node = &decoder->huffnode[curcode];
510 if (node->numbits > 0)
511 {
512 int shift;
513 lookup_value *dest;
514 lookup_value *destend;
515
516 // set up the entry
517 lookup_value value = MAKE_LOOKUP(curcode, node->numbits);
518
519 // fill all matching entries
520 shift = decoder->maxbits - node->numbits;
521 dest = &decoder->lookup[node->bits << shift];
522 destend = &decoder->lookup[((node->bits + 1) << shift) - 1];
523
524 while (dest <= destend)
525 *dest++ = value;
526 }
527 }
528 }
529