|
1 /* |
|
2 * jdhuff.c |
|
3 * |
|
4 * Copyright (C) 1991-1997, Thomas G. Lane. |
|
5 * This file is part of the Independent JPEG Group's software. |
|
6 * For conditions of distribution and use, see the accompanying README file. |
|
7 * |
|
8 * This file contains Huffman entropy decoding routines. |
|
9 * |
|
10 * Much of the complexity here has to do with supporting input suspension. |
|
11 * If the data source module demands suspension, we want to be able to back |
|
12 * up to the start of the current MCU. To do this, we copy state variables |
|
13 * into local working storage, and update them back to the permanent |
|
14 * storage only upon successful completion of an MCU. |
|
15 */ |
|
16 |
|
17 #define JPEG_INTERNALS |
|
18 #include "jinclude.h" |
|
19 #include "jpeglib.h" |
|
20 #include "jdhuff.h" /* Declarations shared with jdphuff.c */ |
|
21 |
|
22 |
|
23 /* |
|
24 * Expanded entropy decoder object for Huffman decoding. |
|
25 * |
|
26 * The savable_state subrecord contains fields that change within an MCU, |
|
27 * but must not be updated permanently until we complete the MCU. |
|
28 */ |
|
29 |
|
30 typedef struct { |
|
31 int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */ |
|
32 } savable_state; |
|
33 |
|
34 /* This macro is to work around compilers with missing or broken |
|
35 * structure assignment. You'll need to fix this code if you have |
|
36 * such a compiler and you change MAX_COMPS_IN_SCAN. |
|
37 */ |
|
38 |
|
39 #ifndef NO_STRUCT_ASSIGN |
|
40 #define ASSIGN_STATE(dest,src) ((dest) = (src)) |
|
41 #else |
|
42 #if MAX_COMPS_IN_SCAN == 4 |
|
43 #define ASSIGN_STATE(dest,src) \ |
|
44 ((dest).last_dc_val[0] = (src).last_dc_val[0], \ |
|
45 (dest).last_dc_val[1] = (src).last_dc_val[1], \ |
|
46 (dest).last_dc_val[2] = (src).last_dc_val[2], \ |
|
47 (dest).last_dc_val[3] = (src).last_dc_val[3]) |
|
48 #endif |
|
49 #endif |
|
50 |
|
51 |
|
52 typedef struct { |
|
53 struct jpeg_entropy_decoder pub; /* public fields */ |
|
54 |
|
55 /* These fields are loaded into local variables at start of each MCU. |
|
56 * In case of suspension, we exit WITHOUT updating them. |
|
57 */ |
|
58 bitread_perm_state bitstate; /* Bit buffer at start of MCU */ |
|
59 savable_state saved; /* Other state at start of MCU */ |
|
60 |
|
61 /* These fields are NOT loaded into local working state. */ |
|
62 unsigned int restarts_to_go; /* MCUs left in this restart interval */ |
|
63 |
|
64 /* Pointers to derived tables (these workspaces have image lifespan) */ |
|
65 d_derived_tbl * dc_derived_tbls[NUM_HUFF_TBLS]; |
|
66 d_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS]; |
|
67 |
|
68 /* Precalculated info set up by start_pass for use in decode_mcu: */ |
|
69 |
|
70 /* Pointers to derived tables to be used for each block within an MCU */ |
|
71 d_derived_tbl * dc_cur_tbls[D_MAX_BLOCKS_IN_MCU]; |
|
72 d_derived_tbl * ac_cur_tbls[D_MAX_BLOCKS_IN_MCU]; |
|
73 /* Whether we care about the DC and AC coefficient values for each block */ |
|
74 boolean dc_needed[D_MAX_BLOCKS_IN_MCU]; |
|
75 boolean ac_needed[D_MAX_BLOCKS_IN_MCU]; |
|
76 } huff_entropy_decoder; |
|
77 |
|
78 typedef huff_entropy_decoder * huff_entropy_ptr; |
|
79 |
|
80 |
|
81 /* |
|
82 * Initialize for a Huffman-compressed scan. |
|
83 */ |
|
84 |
|
85 METHODDEF(void) |
|
86 start_pass_huff_decoder (j_decompress_ptr cinfo) |
|
87 { |
|
88 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; |
|
89 int ci, blkn, dctbl, actbl; |
|
90 jpeg_component_info * compptr; |
|
91 |
|
92 /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG. |
|
93 * This ought to be an error condition, but we make it a warning because |
|
94 * there are some baseline files out there with all zeroes in these bytes. |
|
95 */ |
|
96 if (cinfo->Ss != 0 || cinfo->Se != DCTSIZE2-1 || |
|
97 cinfo->Ah != 0 || cinfo->Al != 0) |
|
98 WARNMS(cinfo, JWRN_NOT_SEQUENTIAL); |
|
99 |
|
100 for (ci = 0; ci < cinfo->comps_in_scan; ci++) { |
|
101 compptr = cinfo->cur_comp_info[ci]; |
|
102 dctbl = compptr->dc_tbl_no; |
|
103 actbl = compptr->ac_tbl_no; |
|
104 /* Compute derived values for Huffman tables */ |
|
105 /* We may do this more than once for a table, but it's not expensive */ |
|
106 jpeg_make_d_derived_tbl(cinfo, TRUE, dctbl, |
|
107 & entropy->dc_derived_tbls[dctbl]); |
|
108 jpeg_make_d_derived_tbl(cinfo, FALSE, actbl, |
|
109 & entropy->ac_derived_tbls[actbl]); |
|
110 /* Initialize DC predictions to 0 */ |
|
111 entropy->saved.last_dc_val[ci] = 0; |
|
112 } |
|
113 |
|
114 /* Precalculate decoding info for each block in an MCU of this scan */ |
|
115 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { |
|
116 ci = cinfo->MCU_membership[blkn]; |
|
117 compptr = cinfo->cur_comp_info[ci]; |
|
118 /* Precalculate which table to use for each block */ |
|
119 entropy->dc_cur_tbls[blkn] = entropy->dc_derived_tbls[compptr->dc_tbl_no]; |
|
120 entropy->ac_cur_tbls[blkn] = entropy->ac_derived_tbls[compptr->ac_tbl_no]; |
|
121 /* Decide whether we really care about the coefficient values */ |
|
122 if (compptr->component_needed) { |
|
123 entropy->dc_needed[blkn] = TRUE; |
|
124 /* we don't need the ACs if producing a 1/8th-size image */ |
|
125 entropy->ac_needed[blkn] = (compptr->DCT_scaled_size > 1); |
|
126 } else { |
|
127 entropy->dc_needed[blkn] = entropy->ac_needed[blkn] = FALSE; |
|
128 } |
|
129 } |
|
130 |
|
131 /* Initialize bitread state variables */ |
|
132 entropy->bitstate.bits_left = 0; |
|
133 entropy->bitstate.get_buffer = 0; /* unnecessary, but keeps Purify quiet */ |
|
134 entropy->pub.insufficient_data = FALSE; |
|
135 |
|
136 /* Initialize restart counter */ |
|
137 entropy->restarts_to_go = cinfo->restart_interval; |
|
138 } |
|
139 |
|
140 |
|
141 /* |
|
142 * Compute the derived values for a Huffman table. |
|
143 * This routine also performs some validation checks on the table. |
|
144 * |
|
145 * Note this is also used by jdphuff.c. |
|
146 */ |
|
147 |
|
148 GLOBAL(void) |
|
149 jpeg_make_d_derived_tbl (j_decompress_ptr cinfo, boolean isDC, int tblno, |
|
150 d_derived_tbl ** pdtbl) |
|
151 { |
|
152 JHUFF_TBL *htbl; |
|
153 d_derived_tbl *dtbl; |
|
154 int p, i, l, si, numsymbols; |
|
155 int lookbits, ctr; |
|
156 char huffsize[257]; |
|
157 unsigned int huffcode[257]; |
|
158 unsigned int code; |
|
159 |
|
160 /* Note that huffsize[] and huffcode[] are filled in code-length order, |
|
161 * paralleling the order of the symbols themselves in htbl->huffval[]. |
|
162 */ |
|
163 |
|
164 /* Find the input Huffman table */ |
|
165 if (tblno < 0 || tblno >= NUM_HUFF_TBLS) |
|
166 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno); |
|
167 htbl = |
|
168 isDC ? cinfo->dc_huff_tbl_ptrs[tblno] : cinfo->ac_huff_tbl_ptrs[tblno]; |
|
169 if (htbl == NULL) |
|
170 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno); |
|
171 |
|
172 /* Allocate a workspace if we haven't already done so. */ |
|
173 if (*pdtbl == NULL) |
|
174 *pdtbl = (d_derived_tbl *) |
|
175 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, |
|
176 SIZEOF(d_derived_tbl)); |
|
177 dtbl = *pdtbl; |
|
178 dtbl->pub = htbl; /* fill in back link */ |
|
179 |
|
180 /* Figure C.1: make table of Huffman code length for each symbol */ |
|
181 |
|
182 p = 0; |
|
183 for (l = 1; l <= 16; l++) { |
|
184 i = (int) htbl->bits[l]; |
|
185 if (i < 0 || p + i > 256) /* protect against table overrun */ |
|
186 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE); |
|
187 while (i--) |
|
188 huffsize[p++] = (char) l; |
|
189 } |
|
190 huffsize[p] = 0; |
|
191 numsymbols = p; |
|
192 |
|
193 /* Figure C.2: generate the codes themselves */ |
|
194 /* We also validate that the counts represent a legal Huffman code tree. */ |
|
195 |
|
196 code = 0; |
|
197 si = huffsize[0]; |
|
198 p = 0; |
|
199 while (huffsize[p]) { |
|
200 while (((int) huffsize[p]) == si) { |
|
201 huffcode[p++] = code; |
|
202 code++; |
|
203 } |
|
204 /* code is now 1 more than the last code used for codelength si; but |
|
205 * it must still fit in si bits, since no code is allowed to be all ones. |
|
206 */ |
|
207 if (((INT32) code) >= (((INT32) 1) << si)) |
|
208 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE); |
|
209 code <<= 1; |
|
210 si++; |
|
211 } |
|
212 |
|
213 /* Figure F.15: generate decoding tables for bit-sequential decoding */ |
|
214 |
|
215 p = 0; |
|
216 for (l = 1; l <= 16; l++) { |
|
217 if (htbl->bits[l]) { |
|
218 /* valoffset[l] = huffval[] index of 1st symbol of code length l, |
|
219 * minus the minimum code of length l |
|
220 */ |
|
221 dtbl->valoffset[l] = (INT32) p - (INT32) huffcode[p]; |
|
222 p += htbl->bits[l]; |
|
223 dtbl->maxcode[l] = huffcode[p-1]; /* maximum code of length l */ |
|
224 } else { |
|
225 dtbl->maxcode[l] = -1; /* -1 if no codes of this length */ |
|
226 } |
|
227 } |
|
228 dtbl->maxcode[17] = 0xFFFFFL; /* ensures jpeg_huff_decode terminates */ |
|
229 |
|
230 /* Compute lookahead tables to speed up decoding. |
|
231 * First we set all the table entries to 0, indicating "too long"; |
|
232 * then we iterate through the Huffman codes that are short enough and |
|
233 * fill in all the entries that correspond to bit sequences starting |
|
234 * with that code. |
|
235 */ |
|
236 |
|
237 MEMZERO(dtbl->look_nbits, SIZEOF(dtbl->look_nbits)); |
|
238 |
|
239 p = 0; |
|
240 for (l = 1; l <= HUFF_LOOKAHEAD; l++) { |
|
241 for (i = 1; i <= (int) htbl->bits[l]; i++, p++) { |
|
242 /* l = current code's length, p = its index in huffcode[] & huffval[]. */ |
|
243 /* Generate left-justified code followed by all possible bit sequences */ |
|
244 lookbits = huffcode[p] << (HUFF_LOOKAHEAD-l); |
|
245 for (ctr = 1 << (HUFF_LOOKAHEAD-l); ctr > 0; ctr--) { |
|
246 dtbl->look_nbits[lookbits] = l; |
|
247 dtbl->look_sym[lookbits] = htbl->huffval[p]; |
|
248 lookbits++; |
|
249 } |
|
250 } |
|
251 } |
|
252 |
|
253 /* Validate symbols as being reasonable. |
|
254 * For AC tables, we make no check, but accept all byte values 0..255. |
|
255 * For DC tables, we require the symbols to be in range 0..15. |
|
256 * (Tighter bounds could be applied depending on the data depth and mode, |
|
257 * but this is sufficient to ensure safe decoding.) |
|
258 */ |
|
259 if (isDC) { |
|
260 for (i = 0; i < numsymbols; i++) { |
|
261 int sym = htbl->huffval[i]; |
|
262 if (sym < 0 || sym > 15) |
|
263 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE); |
|
264 } |
|
265 } |
|
266 } |
|
267 |
|
268 |
|
269 /* |
|
270 * Out-of-line code for bit fetching (shared with jdphuff.c). |
|
271 * See jdhuff.h for info about usage. |
|
272 * Note: current values of get_buffer and bits_left are passed as parameters, |
|
273 * but are returned in the corresponding fields of the state struct. |
|
274 * |
|
275 * On most machines MIN_GET_BITS should be 25 to allow the full 32-bit width |
|
276 * of get_buffer to be used. (On machines with wider words, an even larger |
|
277 * buffer could be used.) However, on some machines 32-bit shifts are |
|
278 * quite slow and take time proportional to the number of places shifted. |
|
279 * (This is true with most PC compilers, for instance.) In this case it may |
|
280 * be a win to set MIN_GET_BITS to the minimum value of 15. This reduces the |
|
281 * average shift distance at the cost of more calls to jpeg_fill_bit_buffer. |
|
282 */ |
|
283 |
|
284 #ifdef SLOW_SHIFT_32 |
|
285 #define MIN_GET_BITS 15 /* minimum allowable value */ |
|
286 #else |
|
287 #define MIN_GET_BITS (BIT_BUF_SIZE-7) |
|
288 #endif |
|
289 |
|
290 |
|
291 GLOBAL(boolean) |
|
292 jpeg_fill_bit_buffer (bitread_working_state * state, |
|
293 register bit_buf_type get_buffer, register int bits_left, |
|
294 int nbits) |
|
295 /* Load up the bit buffer to a depth of at least nbits */ |
|
296 { |
|
297 /* Copy heavily used state fields into locals (hopefully registers) */ |
|
298 register const JOCTET * next_input_byte = state->next_input_byte; |
|
299 register size_t bytes_in_buffer = state->bytes_in_buffer; |
|
300 j_decompress_ptr cinfo = state->cinfo; |
|
301 |
|
302 /* Attempt to load at least MIN_GET_BITS bits into get_buffer. */ |
|
303 /* (It is assumed that no request will be for more than that many bits.) */ |
|
304 /* We fail to do so only if we hit a marker or are forced to suspend. */ |
|
305 |
|
306 if (cinfo->unread_marker == 0) { /* cannot advance past a marker */ |
|
307 while (bits_left < MIN_GET_BITS) { |
|
308 register int c; |
|
309 |
|
310 /* Attempt to read a byte */ |
|
311 if (bytes_in_buffer == 0) { |
|
312 if (! (*cinfo->src->fill_input_buffer) (cinfo)) |
|
313 return FALSE; |
|
314 next_input_byte = cinfo->src->next_input_byte; |
|
315 bytes_in_buffer = cinfo->src->bytes_in_buffer; |
|
316 } |
|
317 bytes_in_buffer--; |
|
318 c = GETJOCTET(*next_input_byte++); |
|
319 |
|
320 /* If it's 0xFF, check and discard stuffed zero byte */ |
|
321 if (c == 0xFF) { |
|
322 /* Loop here to discard any padding FF's on terminating marker, |
|
323 * so that we can save a valid unread_marker value. NOTE: we will |
|
324 * accept multiple FF's followed by a 0 as meaning a single FF data |
|
325 * byte. This data pattern is not valid according to the standard. |
|
326 */ |
|
327 do { |
|
328 if (bytes_in_buffer == 0) { |
|
329 if (! (*cinfo->src->fill_input_buffer) (cinfo)) |
|
330 return FALSE; |
|
331 next_input_byte = cinfo->src->next_input_byte; |
|
332 bytes_in_buffer = cinfo->src->bytes_in_buffer; |
|
333 } |
|
334 bytes_in_buffer--; |
|
335 c = GETJOCTET(*next_input_byte++); |
|
336 } while (c == 0xFF); |
|
337 |
|
338 if (c == 0) { |
|
339 /* Found FF/00, which represents an FF data byte */ |
|
340 c = 0xFF; |
|
341 } else { |
|
342 /* Oops, it's actually a marker indicating end of compressed data. |
|
343 * Save the marker code for later use. |
|
344 * Fine point: it might appear that we should save the marker into |
|
345 * bitread working state, not straight into permanent state. But |
|
346 * once we have hit a marker, we cannot need to suspend within the |
|
347 * current MCU, because we will read no more bytes from the data |
|
348 * source. So it is OK to update permanent state right away. |
|
349 */ |
|
350 cinfo->unread_marker = c; |
|
351 /* See if we need to insert some fake zero bits. */ |
|
352 goto no_more_bytes; |
|
353 } |
|
354 } |
|
355 |
|
356 /* OK, load c into get_buffer */ |
|
357 get_buffer = (get_buffer << 8) | c; |
|
358 bits_left += 8; |
|
359 } /* end while */ |
|
360 } else { |
|
361 no_more_bytes: |
|
362 /* We get here if we've read the marker that terminates the compressed |
|
363 * data segment. There should be enough bits in the buffer register |
|
364 * to satisfy the request; if so, no problem. |
|
365 */ |
|
366 if (nbits > bits_left) { |
|
367 /* Uh-oh. Report corrupted data to user and stuff zeroes into |
|
368 * the data stream, so that we can produce some kind of image. |
|
369 * We use a nonvolatile flag to ensure that only one warning message |
|
370 * appears per data segment. |
|
371 */ |
|
372 if (! cinfo->entropy->insufficient_data) { |
|
373 WARNMS(cinfo, JWRN_HIT_MARKER); |
|
374 cinfo->entropy->insufficient_data = TRUE; |
|
375 } |
|
376 /* Fill the buffer with zero bits */ |
|
377 get_buffer <<= MIN_GET_BITS - bits_left; |
|
378 bits_left = MIN_GET_BITS; |
|
379 } |
|
380 } |
|
381 |
|
382 /* Unload the local registers */ |
|
383 state->next_input_byte = next_input_byte; |
|
384 state->bytes_in_buffer = bytes_in_buffer; |
|
385 state->get_buffer = get_buffer; |
|
386 state->bits_left = bits_left; |
|
387 |
|
388 return TRUE; |
|
389 } |
|
390 |
|
391 |
|
392 /* |
|
393 * Out-of-line code for Huffman code decoding. |
|
394 * See jdhuff.h for info about usage. |
|
395 */ |
|
396 |
|
397 GLOBAL(int) |
|
398 jpeg_huff_decode (bitread_working_state * state, |
|
399 register bit_buf_type get_buffer, register int bits_left, |
|
400 d_derived_tbl * htbl, int min_bits) |
|
401 { |
|
402 register int l = min_bits; |
|
403 register INT32 code; |
|
404 |
|
405 /* HUFF_DECODE has determined that the code is at least min_bits */ |
|
406 /* bits long, so fetch that many bits in one swoop. */ |
|
407 |
|
408 CHECK_BIT_BUFFER(*state, l, return -1); |
|
409 code = GET_BITS(l); |
|
410 |
|
411 /* Collect the rest of the Huffman code one bit at a time. */ |
|
412 /* This is per Figure F.16 in the JPEG spec. */ |
|
413 |
|
414 while (code > htbl->maxcode[l]) { |
|
415 code <<= 1; |
|
416 CHECK_BIT_BUFFER(*state, 1, return -1); |
|
417 code |= GET_BITS(1); |
|
418 l++; |
|
419 } |
|
420 |
|
421 /* Unload the local registers */ |
|
422 state->get_buffer = get_buffer; |
|
423 state->bits_left = bits_left; |
|
424 |
|
425 /* With garbage input we may reach the sentinel value l = 17. */ |
|
426 |
|
427 if (l > 16) { |
|
428 WARNMS(state->cinfo, JWRN_HUFF_BAD_CODE); |
|
429 return 0; /* fake a zero as the safest result */ |
|
430 } |
|
431 |
|
432 return htbl->pub->huffval[ (int) (code + htbl->valoffset[l]) ]; |
|
433 } |
|
434 |
|
435 |
|
436 /* |
|
437 * Figure F.12: extend sign bit. |
|
438 * On some machines, a shift and add will be faster than a table lookup. |
|
439 */ |
|
440 |
|
441 #ifdef AVOID_TABLES |
|
442 |
|
443 #define HUFF_EXTEND(x,s) ((x) < (1<<((s)-1)) ? (x) + (((-1)<<(s)) + 1) : (x)) |
|
444 |
|
445 #else |
|
446 |
|
447 #define HUFF_EXTEND(x,s) ((x) < extend_test[s] ? (x) + extend_offset[s] : (x)) |
|
448 |
|
449 static const int extend_test[16] = /* entry n is 2**(n-1) */ |
|
450 { 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080, |
|
451 0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000 }; |
|
452 |
|
453 static const int extend_offset[16] = /* entry n is (-1 << n) + 1 */ |
|
454 { 0, ((-1)<<1) + 1, ((-1)<<2) + 1, ((-1)<<3) + 1, ((-1)<<4) + 1, |
|
455 ((-1)<<5) + 1, ((-1)<<6) + 1, ((-1)<<7) + 1, ((-1)<<8) + 1, |
|
456 ((-1)<<9) + 1, ((-1)<<10) + 1, ((-1)<<11) + 1, ((-1)<<12) + 1, |
|
457 ((-1)<<13) + 1, ((-1)<<14) + 1, ((-1)<<15) + 1 }; |
|
458 |
|
459 #endif /* AVOID_TABLES */ |
|
460 |
|
461 |
|
462 /* |
|
463 * Check for a restart marker & resynchronize decoder. |
|
464 * Returns FALSE if must suspend. |
|
465 */ |
|
466 |
|
467 LOCAL(boolean) |
|
468 process_restart (j_decompress_ptr cinfo) |
|
469 { |
|
470 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; |
|
471 int ci; |
|
472 |
|
473 /* Throw away any unused bits remaining in bit buffer; */ |
|
474 /* include any full bytes in next_marker's count of discarded bytes */ |
|
475 cinfo->marker->discarded_bytes += entropy->bitstate.bits_left / 8; |
|
476 entropy->bitstate.bits_left = 0; |
|
477 |
|
478 /* Advance past the RSTn marker */ |
|
479 if (! (*cinfo->marker->read_restart_marker) (cinfo)) |
|
480 return FALSE; |
|
481 |
|
482 /* Re-initialize DC predictions to 0 */ |
|
483 for (ci = 0; ci < cinfo->comps_in_scan; ci++) |
|
484 entropy->saved.last_dc_val[ci] = 0; |
|
485 |
|
486 /* Reset restart counter */ |
|
487 entropy->restarts_to_go = cinfo->restart_interval; |
|
488 |
|
489 /* Reset out-of-data flag, unless read_restart_marker left us smack up |
|
490 * against a marker. In that case we will end up treating the next data |
|
491 * segment as empty, and we can avoid producing bogus output pixels by |
|
492 * leaving the flag set. |
|
493 */ |
|
494 if (cinfo->unread_marker == 0) |
|
495 entropy->pub.insufficient_data = FALSE; |
|
496 |
|
497 return TRUE; |
|
498 } |
|
499 |
|
500 |
|
501 /* |
|
502 * Decode and return one MCU's worth of Huffman-compressed coefficients. |
|
503 * The coefficients are reordered from zigzag order into natural array order, |
|
504 * but are not dequantized. |
|
505 * |
|
506 * The i'th block of the MCU is stored into the block pointed to by |
|
507 * MCU_data[i]. WE ASSUME THIS AREA HAS BEEN ZEROED BY THE CALLER. |
|
508 * (Wholesale zeroing is usually a little faster than retail...) |
|
509 * |
|
510 * Returns FALSE if data source requested suspension. In that case no |
|
511 * changes have been made to permanent state. (Exception: some output |
|
512 * coefficients may already have been assigned. This is harmless for |
|
513 * this module, since we'll just re-assign them on the next call.) |
|
514 */ |
|
515 |
|
516 METHODDEF(boolean) |
|
517 decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) |
|
518 { |
|
519 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; |
|
520 int blkn; |
|
521 BITREAD_STATE_VARS; |
|
522 savable_state state; |
|
523 |
|
524 /* Process restart marker if needed; may have to suspend */ |
|
525 if (cinfo->restart_interval) { |
|
526 if (entropy->restarts_to_go == 0) |
|
527 if (! process_restart(cinfo)) |
|
528 return FALSE; |
|
529 } |
|
530 |
|
531 /* If we've run out of data, just leave the MCU set to zeroes. |
|
532 * This way, we return uniform gray for the remainder of the segment. |
|
533 */ |
|
534 if (! entropy->pub.insufficient_data) { |
|
535 |
|
536 /* Load up working state */ |
|
537 BITREAD_LOAD_STATE(cinfo,entropy->bitstate); |
|
538 ASSIGN_STATE(state, entropy->saved); |
|
539 |
|
540 /* Outer loop handles each block in the MCU */ |
|
541 |
|
542 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { |
|
543 JBLOCKROW block = MCU_data[blkn]; |
|
544 d_derived_tbl * dctbl = entropy->dc_cur_tbls[blkn]; |
|
545 d_derived_tbl * actbl = entropy->ac_cur_tbls[blkn]; |
|
546 register int s, k, r; |
|
547 |
|
548 /* Decode a single block's worth of coefficients */ |
|
549 |
|
550 /* Section F.2.2.1: decode the DC coefficient difference */ |
|
551 HUFF_DECODE(s, br_state, dctbl, return FALSE, label1); |
|
552 if (s) { |
|
553 CHECK_BIT_BUFFER(br_state, s, return FALSE); |
|
554 r = GET_BITS(s); |
|
555 s = HUFF_EXTEND(r, s); |
|
556 } |
|
557 |
|
558 if (entropy->dc_needed[blkn]) { |
|
559 /* Convert DC difference to actual value, update last_dc_val */ |
|
560 int ci = cinfo->MCU_membership[blkn]; |
|
561 s += state.last_dc_val[ci]; |
|
562 state.last_dc_val[ci] = s; |
|
563 /* Output the DC coefficient (assumes jpeg_natural_order[0] = 0) */ |
|
564 (*block)[0] = (JCOEF) s; |
|
565 } |
|
566 |
|
567 if (entropy->ac_needed[blkn]) { |
|
568 |
|
569 /* Section F.2.2.2: decode the AC coefficients */ |
|
570 /* Since zeroes are skipped, output area must be cleared beforehand */ |
|
571 for (k = 1; k < DCTSIZE2; k++) { |
|
572 HUFF_DECODE(s, br_state, actbl, return FALSE, label2); |
|
573 |
|
574 r = s >> 4; |
|
575 s &= 15; |
|
576 |
|
577 if (s) { |
|
578 k += r; |
|
579 CHECK_BIT_BUFFER(br_state, s, return FALSE); |
|
580 r = GET_BITS(s); |
|
581 s = HUFF_EXTEND(r, s); |
|
582 /* Output coefficient in natural (dezigzagged) order. |
|
583 * Note: the extra entries in jpeg_natural_order[] will save us |
|
584 * if k >= DCTSIZE2, which could happen if the data is corrupted. |
|
585 */ |
|
586 (*block)[jpeg_natural_order[k]] = (JCOEF) s; |
|
587 } else { |
|
588 if (r != 15) |
|
589 break; |
|
590 k += 15; |
|
591 } |
|
592 } |
|
593 |
|
594 } else { |
|
595 |
|
596 /* Section F.2.2.2: decode the AC coefficients */ |
|
597 /* In this path we just discard the values */ |
|
598 for (k = 1; k < DCTSIZE2; k++) { |
|
599 HUFF_DECODE(s, br_state, actbl, return FALSE, label3); |
|
600 |
|
601 r = s >> 4; |
|
602 s &= 15; |
|
603 |
|
604 if (s) { |
|
605 k += r; |
|
606 CHECK_BIT_BUFFER(br_state, s, return FALSE); |
|
607 DROP_BITS(s); |
|
608 } else { |
|
609 if (r != 15) |
|
610 break; |
|
611 k += 15; |
|
612 } |
|
613 } |
|
614 |
|
615 } |
|
616 } |
|
617 |
|
618 /* Completed MCU, so update state */ |
|
619 BITREAD_SAVE_STATE(cinfo,entropy->bitstate); |
|
620 ASSIGN_STATE(entropy->saved, state); |
|
621 } |
|
622 |
|
623 /* Account for restart interval (no-op if not using restarts) */ |
|
624 entropy->restarts_to_go--; |
|
625 |
|
626 return TRUE; |
|
627 } |
|
628 |
|
629 |
|
630 /* |
|
631 * Module initialization routine for Huffman entropy decoding. |
|
632 */ |
|
633 |
|
634 GLOBAL(void) |
|
635 jinit_huff_decoder (j_decompress_ptr cinfo) |
|
636 { |
|
637 huff_entropy_ptr entropy; |
|
638 int i; |
|
639 |
|
640 entropy = (huff_entropy_ptr) |
|
641 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, |
|
642 SIZEOF(huff_entropy_decoder)); |
|
643 cinfo->entropy = (struct jpeg_entropy_decoder *) entropy; |
|
644 entropy->pub.start_pass = start_pass_huff_decoder; |
|
645 entropy->pub.decode_mcu = decode_mcu; |
|
646 |
|
647 /* Mark tables unallocated */ |
|
648 for (i = 0; i < NUM_HUFF_TBLS; i++) { |
|
649 entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL; |
|
650 } |
|
651 } |