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ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4. The directory name has changed: no version number in the expanded directory now.
author Franz Glasner <fzglas.hg@dom66.de>
date Mon, 15 Sep 2025 11:43:07 +0200
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1:1d09e1dec1d9 2:b50eed0cc0ef
1 /*
2 * jdmainct.c
3 *
4 * Copyright (C) 1994-1996, Thomas G. Lane.
5 * Modified 2002-2020 by Guido Vollbeding.
6 * This file is part of the Independent JPEG Group's software.
7 * For conditions of distribution and use, see the accompanying README file.
8 *
9 * This file contains the main buffer controller for decompression.
10 * The main buffer lies between the JPEG decompressor proper and the
11 * post-processor; it holds downsampled data in the JPEG colorspace.
12 *
13 * Note that this code is bypassed in raw-data mode, since the application
14 * supplies the equivalent of the main buffer in that case.
15 */
16
17 #define JPEG_INTERNALS
18 #include "jinclude.h"
19 #include "jpeglib.h"
20
21
22 /*
23 * In the current system design, the main buffer need never be a full-image
24 * buffer; any full-height buffers will be found inside the coefficient or
25 * postprocessing controllers. Nonetheless, the main controller is not
26 * trivial. Its responsibility is to provide context rows for upsampling/
27 * rescaling, and doing this in an efficient fashion is a bit tricky.
28 *
29 * Postprocessor input data is counted in "row groups". A row group is
30 * defined to be (v_samp_factor * DCT_v_scaled_size / min_DCT_v_scaled_size)
31 * sample rows of each component. (We require DCT_scaled_size values to be
32 * chosen such that these numbers are integers. In practice DCT_scaled_size
33 * values will likely be powers of two, so we actually have the stronger
34 * condition that DCT_scaled_size / min_DCT_scaled_size is an integer.)
35 * Upsampling will typically produce max_v_samp_factor pixel rows from each
36 * row group (times any additional scale factor that the upsampler is
37 * applying).
38 *
39 * The coefficient controller will deliver data to us one iMCU row at a time;
40 * each iMCU row contains v_samp_factor * DCT_v_scaled_size sample rows, or
41 * exactly min_DCT_v_scaled_size row groups. (This amount of data corresponds
42 * to one row of MCUs when the image is fully interleaved.) Note that the
43 * number of sample rows varies across components, but the number of row
44 * groups does not. Some garbage sample rows may be included in the last iMCU
45 * row at the bottom of the image.
46 *
47 * Depending on the vertical scaling algorithm used, the upsampler may need
48 * access to the sample row(s) above and below its current input row group.
49 * The upsampler is required to set need_context_rows TRUE at global selection
50 * time if so. When need_context_rows is FALSE, this controller can simply
51 * obtain one iMCU row at a time from the coefficient controller and dole it
52 * out as row groups to the postprocessor.
53 *
54 * When need_context_rows is TRUE, this controller guarantees that the buffer
55 * passed to postprocessing contains at least one row group's worth of samples
56 * above and below the row group(s) being processed. Note that the context
57 * rows "above" the first passed row group appear at negative row offsets in
58 * the passed buffer. At the top and bottom of the image, the required
59 * context rows are manufactured by duplicating the first or last real sample
60 * row; this avoids having special cases in the upsampling inner loops.
61 *
62 * The amount of context is fixed at one row group just because that's a
63 * convenient number for this controller to work with. The existing
64 * upsamplers really only need one sample row of context. An upsampler
65 * supporting arbitrary output rescaling might wish for more than one row
66 * group of context when shrinking the image; tough, we don't handle that.
67 * (This is justified by the assumption that downsizing will be handled mostly
68 * by adjusting the DCT_scaled_size values, so that the actual scale factor at
69 * the upsample step needn't be much less than one.)
70 *
71 * To provide the desired context, we have to retain the last two row groups
72 * of one iMCU row while reading in the next iMCU row. (The last row group
73 * can't be processed until we have another row group for its below-context,
74 * and so we have to save the next-to-last group too for its above-context.)
75 * We could do this most simply by copying data around in our buffer, but
76 * that'd be very slow. We can avoid copying any data by creating a rather
77 * strange pointer structure. Here's how it works. We allocate a workspace
78 * consisting of M+2 row groups (where M = min_DCT_v_scaled_size is the number
79 * of row groups per iMCU row). We create two sets of redundant pointers to
80 * the workspace. Labeling the physical row groups 0 to M+1, the synthesized
81 * pointer lists look like this:
82 * M+1 M-1
83 * master pointer --> 0 master pointer --> 0
84 * 1 1
85 * ... ...
86 * M-3 M-3
87 * M-2 M
88 * M-1 M+1
89 * M M-2
90 * M+1 M-1
91 * 0 0
92 * We read alternate iMCU rows using each master pointer; thus the last two
93 * row groups of the previous iMCU row remain un-overwritten in the workspace.
94 * The pointer lists are set up so that the required context rows appear to
95 * be adjacent to the proper places when we pass the pointer lists to the
96 * upsampler.
97 *
98 * The above pictures describe the normal state of the pointer lists.
99 * At top and bottom of the image, we diddle the pointer lists to duplicate
100 * the first or last sample row as necessary (this is cheaper than copying
101 * sample rows around).
102 *
103 * This scheme breaks down if M < 2, ie, min_DCT_v_scaled_size is 1. In that
104 * situation each iMCU row provides only one row group so the buffering logic
105 * must be different (eg, we must read two iMCU rows before we can emit the
106 * first row group). For now, we simply do not support providing context
107 * rows when min_DCT_v_scaled_size is 1. That combination seems unlikely to
108 * be worth providing --- if someone wants a 1/8th-size preview, they probably
109 * want it quick and dirty, so a context-free upsampler is sufficient.
110 */
111
112
113 /* Private buffer controller object */
114
115 typedef struct {
116 struct jpeg_d_main_controller pub; /* public fields */
117
118 /* Pointer to allocated workspace (M or M+2 row groups). */
119 JSAMPARRAY buffer[MAX_COMPONENTS];
120
121 JDIMENSION rowgroup_ctr; /* counts row groups output to postprocessor */
122 JDIMENSION rowgroups_avail; /* row groups available to postprocessor */
123
124 /* Remaining fields are only used in the context case. */
125
126 boolean buffer_full; /* Have we gotten an iMCU row from decoder? */
127
128 /* These are the master pointers to the funny-order pointer lists. */
129 JSAMPIMAGE xbuffer[2]; /* pointers to weird pointer lists */
130
131 int whichptr; /* indicates which pointer set is now in use */
132 int context_state; /* process_data state machine status */
133 JDIMENSION iMCU_row_ctr; /* counts iMCU rows to detect image top/bot */
134 } my_main_controller;
135
136 typedef my_main_controller * my_main_ptr;
137
138 /* context_state values: */
139 #define CTX_PREPARE_FOR_IMCU 0 /* need to prepare for MCU row */
140 #define CTX_PROCESS_IMCU 1 /* feeding iMCU to postprocessor */
141 #define CTX_POSTPONED_ROW 2 /* feeding postponed row group */
142
143
144 /* Forward declarations */
145 METHODDEF(void) process_data_simple_main
146 JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf,
147 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail));
148 METHODDEF(void) process_data_context_main
149 JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf,
150 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail));
151 #ifdef QUANT_2PASS_SUPPORTED
152 METHODDEF(void) process_data_crank_post
153 JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf,
154 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail));
155 #endif
156
157
158 LOCAL(void)
159 alloc_funny_pointers (j_decompress_ptr cinfo)
160 /* Allocate space for the funny pointer lists.
161 * This is done only once, not once per pass.
162 */
163 {
164 my_main_ptr mainp = (my_main_ptr) cinfo->main;
165 int ci, rgroup;
166 int M = cinfo->min_DCT_v_scaled_size;
167 jpeg_component_info *compptr;
168 JSAMPARRAY xbuf;
169
170 /* Get top-level space for component array pointers.
171 * We alloc both arrays with one call to save a few cycles.
172 */
173 mainp->xbuffer[0] = (JSAMPIMAGE) (*cinfo->mem->alloc_small)
174 ((j_common_ptr) cinfo, JPOOL_IMAGE,
175 cinfo->num_components * 2 * SIZEOF(JSAMPARRAY));
176 mainp->xbuffer[1] = mainp->xbuffer[0] + cinfo->num_components;
177
178 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
179 ci++, compptr++) {
180 if (! compptr->component_needed)
181 continue; /* skip uninteresting component */
182 rgroup = (compptr->v_samp_factor * compptr->DCT_v_scaled_size) /
183 cinfo->min_DCT_v_scaled_size; /* height of a row group of component */
184 /* Get space for pointer lists --- M+4 row groups in each list.
185 * We alloc both pointer lists with one call to save a few cycles.
186 */
187 xbuf = (JSAMPARRAY) (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo,
188 JPOOL_IMAGE, 2 * (rgroup * (M + 4)) * SIZEOF(JSAMPROW));
189 xbuf += rgroup; /* want one row group at negative offsets */
190 mainp->xbuffer[0][ci] = xbuf;
191 xbuf += rgroup * (M + 4);
192 mainp->xbuffer[1][ci] = xbuf;
193 }
194 }
195
196
197 LOCAL(void)
198 make_funny_pointers (j_decompress_ptr cinfo)
199 /* Create the funny pointer lists discussed in the comments above.
200 * The actual workspace is already allocated (in mainp->buffer),
201 * and the space for the pointer lists is allocated too.
202 * This routine just fills in the curiously ordered lists.
203 * This will be repeated at the beginning of each pass.
204 */
205 {
206 my_main_ptr mainp = (my_main_ptr) cinfo->main;
207 int ci, i, rgroup;
208 int M = cinfo->min_DCT_v_scaled_size;
209 jpeg_component_info *compptr;
210 JSAMPARRAY buf, xbuf0, xbuf1;
211
212 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
213 ci++, compptr++) {
214 if (! compptr->component_needed)
215 continue; /* skip uninteresting component */
216 rgroup = (compptr->v_samp_factor * compptr->DCT_v_scaled_size) /
217 cinfo->min_DCT_v_scaled_size; /* height of a row group of component */
218 xbuf0 = mainp->xbuffer[0][ci];
219 xbuf1 = mainp->xbuffer[1][ci];
220 /* First copy the workspace pointers as-is */
221 buf = mainp->buffer[ci];
222 for (i = 0; i < rgroup * (M + 2); i++) {
223 xbuf0[i] = xbuf1[i] = buf[i];
224 }
225 /* In the second list, put the last four row groups in swapped order */
226 for (i = 0; i < rgroup * 2; i++) {
227 xbuf1[rgroup*(M-2) + i] = buf[rgroup*M + i];
228 xbuf1[rgroup*M + i] = buf[rgroup*(M-2) + i];
229 }
230 /* The wraparound pointers at top and bottom will be filled later
231 * (see set_wraparound_pointers, below). Initially we want the "above"
232 * pointers to duplicate the first actual data line. This only needs
233 * to happen in xbuffer[0].
234 */
235 for (i = 0; i < rgroup; i++) {
236 xbuf0[i - rgroup] = xbuf0[0];
237 }
238 }
239 }
240
241
242 LOCAL(void)
243 set_wraparound_pointers (j_decompress_ptr cinfo)
244 /* Set up the "wraparound" pointers at top and bottom of the pointer lists.
245 * This changes the pointer list state from top-of-image to the normal state.
246 */
247 {
248 my_main_ptr mainp = (my_main_ptr) cinfo->main;
249 int ci, i, rgroup;
250 int M = cinfo->min_DCT_v_scaled_size;
251 jpeg_component_info *compptr;
252 JSAMPARRAY xbuf0, xbuf1;
253
254 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
255 ci++, compptr++) {
256 if (! compptr->component_needed)
257 continue; /* skip uninteresting component */
258 rgroup = (compptr->v_samp_factor * compptr->DCT_v_scaled_size) /
259 cinfo->min_DCT_v_scaled_size; /* height of a row group of component */
260 xbuf0 = mainp->xbuffer[0][ci];
261 xbuf1 = mainp->xbuffer[1][ci];
262 for (i = 0; i < rgroup; i++) {
263 xbuf0[i - rgroup] = xbuf0[rgroup*(M+1) + i];
264 xbuf1[i - rgroup] = xbuf1[rgroup*(M+1) + i];
265 xbuf0[rgroup*(M+2) + i] = xbuf0[i];
266 xbuf1[rgroup*(M+2) + i] = xbuf1[i];
267 }
268 }
269 }
270
271
272 LOCAL(void)
273 set_bottom_pointers (j_decompress_ptr cinfo)
274 /* Change the pointer lists to duplicate the last sample row at the bottom
275 * of the image. whichptr indicates which xbuffer holds the final iMCU row.
276 * Also sets rowgroups_avail to indicate number of nondummy row groups in row.
277 */
278 {
279 my_main_ptr mainp = (my_main_ptr) cinfo->main;
280 int ci, i, rgroup, iMCUheight, rows_left;
281 jpeg_component_info *compptr;
282 JSAMPARRAY xbuf;
283
284 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
285 ci++, compptr++) {
286 if (! compptr->component_needed)
287 continue; /* skip uninteresting component */
288 /* Count sample rows in one iMCU row and in one row group */
289 iMCUheight = compptr->v_samp_factor * compptr->DCT_v_scaled_size;
290 rgroup = iMCUheight / cinfo->min_DCT_v_scaled_size;
291 /* Count nondummy sample rows remaining for this component */
292 rows_left = (int) (compptr->downsampled_height % (JDIMENSION) iMCUheight);
293 if (rows_left == 0) rows_left = iMCUheight;
294 /* Count nondummy row groups. Should get same answer for each component,
295 * so we need only do it once.
296 */
297 if (ci == 0) {
298 mainp->rowgroups_avail = (JDIMENSION) ((rows_left-1) / rgroup + 1);
299 }
300 /* Duplicate the last real sample row rgroup*2 times; this pads out the
301 * last partial rowgroup and ensures at least one full rowgroup of context.
302 */
303 xbuf = mainp->xbuffer[mainp->whichptr][ci];
304 for (i = 0; i < rgroup * 2; i++) {
305 xbuf[rows_left + i] = xbuf[rows_left-1];
306 }
307 }
308 }
309
310
311 /*
312 * Initialize for a processing pass.
313 */
314
315 METHODDEF(void)
316 start_pass_main (j_decompress_ptr cinfo, J_BUF_MODE pass_mode)
317 {
318 my_main_ptr mainp = (my_main_ptr) cinfo->main;
319
320 switch (pass_mode) {
321 case JBUF_PASS_THRU:
322 if (cinfo->upsample->need_context_rows) {
323 mainp->pub.process_data = process_data_context_main;
324 make_funny_pointers(cinfo); /* Create the xbuffer[] lists */
325 mainp->whichptr = 0; /* Read first iMCU row into xbuffer[0] */
326 mainp->context_state = CTX_PREPARE_FOR_IMCU;
327 mainp->iMCU_row_ctr = 0;
328 mainp->buffer_full = FALSE; /* Mark buffer empty */
329 } else {
330 /* Simple case with no context needed */
331 mainp->pub.process_data = process_data_simple_main;
332 mainp->rowgroup_ctr = mainp->rowgroups_avail; /* Mark buffer empty */
333 }
334 break;
335 #ifdef QUANT_2PASS_SUPPORTED
336 case JBUF_CRANK_DEST:
337 /* For last pass of 2-pass quantization, just crank the postprocessor */
338 mainp->pub.process_data = process_data_crank_post;
339 break;
340 #endif
341 default:
342 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
343 }
344 }
345
346
347 /*
348 * Process some data.
349 * This handles the simple case where no context is required.
350 */
351
352 METHODDEF(void)
353 process_data_simple_main (j_decompress_ptr cinfo, JSAMPARRAY output_buf,
354 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail)
355 {
356 my_main_ptr mainp = (my_main_ptr) cinfo->main;
357
358 /* Read input data if we haven't filled the main buffer yet */
359 if (mainp->rowgroup_ctr >= mainp->rowgroups_avail) {
360 if (! (*cinfo->coef->decompress_data) (cinfo, mainp->buffer))
361 return; /* suspension forced, can do nothing more */
362 mainp->rowgroup_ctr = 0; /* OK, we have an iMCU row to work with */
363 }
364
365 /* Note: at the bottom of the image, we may pass extra garbage row groups
366 * to the postprocessor. The postprocessor has to check for bottom
367 * of image anyway (at row resolution), so no point in us doing it too.
368 */
369
370 /* Feed the postprocessor */
371 (*cinfo->post->post_process_data) (cinfo, mainp->buffer,
372 &mainp->rowgroup_ctr, mainp->rowgroups_avail,
373 output_buf, out_row_ctr, out_rows_avail);
374 }
375
376
377 /*
378 * Process some data.
379 * This handles the case where context rows must be provided.
380 */
381
382 METHODDEF(void)
383 process_data_context_main (j_decompress_ptr cinfo, JSAMPARRAY output_buf,
384 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail)
385 {
386 my_main_ptr mainp = (my_main_ptr) cinfo->main;
387
388 /* Read input data if we haven't filled the main buffer yet */
389 if (! mainp->buffer_full) {
390 if (! (*cinfo->coef->decompress_data) (cinfo,
391 mainp->xbuffer[mainp->whichptr]))
392 return; /* suspension forced, can do nothing more */
393 mainp->buffer_full = TRUE; /* OK, we have an iMCU row to work with */
394 mainp->iMCU_row_ctr++; /* count rows received */
395 }
396
397 /* Postprocessor typically will not swallow all the input data it is handed
398 * in one call (due to filling the output buffer first). Must be prepared
399 * to exit and restart. This switch lets us keep track of how far we got.
400 * Note that each case falls through to the next on successful completion.
401 */
402 switch (mainp->context_state) {
403 case CTX_POSTPONED_ROW:
404 /* Call postprocessor using previously set pointers for postponed row */
405 (*cinfo->post->post_process_data) (cinfo, mainp->xbuffer[mainp->whichptr],
406 &mainp->rowgroup_ctr, mainp->rowgroups_avail,
407 output_buf, out_row_ctr, out_rows_avail);
408 if (mainp->rowgroup_ctr < mainp->rowgroups_avail)
409 return; /* Need to suspend */
410 mainp->context_state = CTX_PREPARE_FOR_IMCU;
411 if (*out_row_ctr >= out_rows_avail)
412 return; /* Postprocessor exactly filled output buf */
413 /*FALLTHROUGH*/
414 case CTX_PREPARE_FOR_IMCU:
415 /* Prepare to process first M-1 row groups of this iMCU row */
416 mainp->rowgroup_ctr = 0;
417 mainp->rowgroups_avail = (JDIMENSION) (cinfo->min_DCT_v_scaled_size - 1);
418 /* Check for bottom of image: if so, tweak pointers to "duplicate"
419 * the last sample row, and adjust rowgroups_avail to ignore padding rows.
420 */
421 if (mainp->iMCU_row_ctr == cinfo->total_iMCU_rows)
422 set_bottom_pointers(cinfo);
423 mainp->context_state = CTX_PROCESS_IMCU;
424 /*FALLTHROUGH*/
425 case CTX_PROCESS_IMCU:
426 /* Call postprocessor using previously set pointers */
427 (*cinfo->post->post_process_data) (cinfo, mainp->xbuffer[mainp->whichptr],
428 &mainp->rowgroup_ctr, mainp->rowgroups_avail,
429 output_buf, out_row_ctr, out_rows_avail);
430 if (mainp->rowgroup_ctr < mainp->rowgroups_avail)
431 return; /* Need to suspend */
432 /* After the first iMCU, change wraparound pointers to normal state */
433 if (mainp->iMCU_row_ctr == 1)
434 set_wraparound_pointers(cinfo);
435 /* Prepare to load new iMCU row using other xbuffer list */
436 mainp->whichptr ^= 1; /* 0=>1 or 1=>0 */
437 mainp->buffer_full = FALSE;
438 /* Still need to process last row group of this iMCU row, */
439 /* which is saved at index M+1 of the other xbuffer */
440 mainp->rowgroup_ctr = (JDIMENSION) (cinfo->min_DCT_v_scaled_size + 1);
441 mainp->rowgroups_avail = (JDIMENSION) (cinfo->min_DCT_v_scaled_size + 2);
442 mainp->context_state = CTX_POSTPONED_ROW;
443 }
444 }
445
446
447 /*
448 * Process some data.
449 * Final pass of two-pass quantization: just call the postprocessor.
450 * Source data will be the postprocessor controller's internal buffer.
451 */
452
453 #ifdef QUANT_2PASS_SUPPORTED
454
455 METHODDEF(void)
456 process_data_crank_post (j_decompress_ptr cinfo, JSAMPARRAY output_buf,
457 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail)
458 {
459 (*cinfo->post->post_process_data) (cinfo, (JSAMPIMAGE) NULL,
460 (JDIMENSION *) NULL, (JDIMENSION) 0,
461 output_buf, out_row_ctr, out_rows_avail);
462 }
463
464 #endif /* QUANT_2PASS_SUPPORTED */
465
466
467 /*
468 * Initialize main buffer controller.
469 */
470
471 GLOBAL(void)
472 jinit_d_main_controller (j_decompress_ptr cinfo, boolean need_full_buffer)
473 {
474 my_main_ptr mainp;
475 int ci, rgroup, ngroups;
476 jpeg_component_info *compptr;
477
478 mainp = (my_main_ptr) (*cinfo->mem->alloc_small)
479 ((j_common_ptr) cinfo, JPOOL_IMAGE, SIZEOF(my_main_controller));
480 cinfo->main = &mainp->pub;
481 mainp->pub.start_pass = start_pass_main;
482
483 if (need_full_buffer) /* shouldn't happen */
484 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
485
486 /* Allocate the workspace.
487 * ngroups is the number of row groups we need.
488 */
489 if (cinfo->upsample->need_context_rows) {
490 if (cinfo->min_DCT_v_scaled_size < 2) /* unsupported, see comments above */
491 ERREXIT(cinfo, JERR_NOTIMPL);
492 alloc_funny_pointers(cinfo); /* Alloc space for xbuffer[] lists */
493 ngroups = cinfo->min_DCT_v_scaled_size + 2;
494 } else {
495 /* There are always min_DCT_v_scaled_size row groups in an iMCU row. */
496 ngroups = cinfo->min_DCT_v_scaled_size;
497 mainp->rowgroups_avail = (JDIMENSION) ngroups;
498 }
499
500 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
501 ci++, compptr++) {
502 if (! compptr->component_needed)
503 continue; /* skip uninteresting component */
504 rgroup = (compptr->v_samp_factor * compptr->DCT_v_scaled_size) /
505 cinfo->min_DCT_v_scaled_size; /* height of a row group of component */
506 mainp->buffer[ci] = (*cinfo->mem->alloc_sarray)
507 ((j_common_ptr) cinfo, JPOOL_IMAGE,
508 compptr->width_in_blocks * ((JDIMENSION) compptr->DCT_h_scaled_size),
509 (JDIMENSION) (rgroup * ngroups));
510 }
511 }