1 : /*
2 : * jdmainct.c
3 : *
4 : * Copyright (C) 1994-1996, Thomas G. Lane.
5 : * Copyright (C) 2010, D. R. Commander.
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 : #include "jpegcomp.h"
21 :
22 :
23 : /*
24 : * In the current system design, the main buffer need never be a full-image
25 : * buffer; any full-height buffers will be found inside the coefficient or
26 : * postprocessing controllers. Nonetheless, the main controller is not
27 : * trivial. Its responsibility is to provide context rows for upsampling/
28 : * rescaling, and doing this in an efficient fashion is a bit tricky.
29 : *
30 : * Postprocessor input data is counted in "row groups". A row group
31 : * is defined to be (v_samp_factor * DCT_scaled_size / min_DCT_scaled_size)
32 : * sample rows of each component. (We require DCT_scaled_size values to be
33 : * chosen such that these numbers are integers. In practice DCT_scaled_size
34 : * values will likely be powers of two, so we actually have the stronger
35 : * condition that DCT_scaled_size / min_DCT_scaled_size is an integer.)
36 : * Upsampling will typically produce max_v_samp_factor pixel rows from each
37 : * row group (times any additional scale factor that the upsampler is
38 : * applying).
39 : *
40 : * The coefficient controller will deliver data to us one iMCU row at a time;
41 : * each iMCU row contains v_samp_factor * DCT_scaled_size sample rows, or
42 : * exactly min_DCT_scaled_size row groups. (This amount of data corresponds
43 : * to one row of MCUs when the image is fully interleaved.) Note that the
44 : * number of sample rows varies across components, but the number of row
45 : * groups does not. Some garbage sample rows may be included in the last iMCU
46 : * row at the bottom of the image.
47 : *
48 : * Depending on the vertical scaling algorithm used, the upsampler may need
49 : * access to the sample row(s) above and below its current input row group.
50 : * The upsampler is required to set need_context_rows TRUE at global selection
51 : * time if so. When need_context_rows is FALSE, this controller can simply
52 : * obtain one iMCU row at a time from the coefficient controller and dole it
53 : * out as row groups to the postprocessor.
54 : *
55 : * When need_context_rows is TRUE, this controller guarantees that the buffer
56 : * passed to postprocessing contains at least one row group's worth of samples
57 : * above and below the row group(s) being processed. Note that the context
58 : * rows "above" the first passed row group appear at negative row offsets in
59 : * the passed buffer. At the top and bottom of the image, the required
60 : * context rows are manufactured by duplicating the first or last real sample
61 : * row; this avoids having special cases in the upsampling inner loops.
62 : *
63 : * The amount of context is fixed at one row group just because that's a
64 : * convenient number for this controller to work with. The existing
65 : * upsamplers really only need one sample row of context. An upsampler
66 : * supporting arbitrary output rescaling might wish for more than one row
67 : * group of context when shrinking the image; tough, we don't handle that.
68 : * (This is justified by the assumption that downsizing will be handled mostly
69 : * by adjusting the DCT_scaled_size values, so that the actual scale factor at
70 : * the upsample step needn't be much less than one.)
71 : *
72 : * To provide the desired context, we have to retain the last two row groups
73 : * of one iMCU row while reading in the next iMCU row. (The last row group
74 : * can't be processed until we have another row group for its below-context,
75 : * and so we have to save the next-to-last group too for its above-context.)
76 : * We could do this most simply by copying data around in our buffer, but
77 : * that'd be very slow. We can avoid copying any data by creating a rather
78 : * strange pointer structure. Here's how it works. We allocate a workspace
79 : * consisting of M+2 row groups (where M = min_DCT_scaled_size is the number
80 : * of row groups per iMCU row). We create two sets of redundant pointers to
81 : * the workspace. Labeling the physical row groups 0 to M+1, the synthesized
82 : * pointer lists look like this:
83 : * M+1 M-1
84 : * master pointer --> 0 master pointer --> 0
85 : * 1 1
86 : * ... ...
87 : * M-3 M-3
88 : * M-2 M
89 : * M-1 M+1
90 : * M M-2
91 : * M+1 M-1
92 : * 0 0
93 : * We read alternate iMCU rows using each master pointer; thus the last two
94 : * row groups of the previous iMCU row remain un-overwritten in the workspace.
95 : * The pointer lists are set up so that the required context rows appear to
96 : * be adjacent to the proper places when we pass the pointer lists to the
97 : * upsampler.
98 : *
99 : * The above pictures describe the normal state of the pointer lists.
100 : * At top and bottom of the image, we diddle the pointer lists to duplicate
101 : * the first or last sample row as necessary (this is cheaper than copying
102 : * sample rows around).
103 : *
104 : * This scheme breaks down if M < 2, ie, min_DCT_scaled_size is 1. In that
105 : * situation each iMCU row provides only one row group so the buffering logic
106 : * must be different (eg, we must read two iMCU rows before we can emit the
107 : * first row group). For now, we simply do not support providing context
108 : * rows when min_DCT_scaled_size is 1. That combination seems unlikely to
109 : * be worth providing --- if someone wants a 1/8th-size preview, they probably
110 : * want it quick and dirty, so a context-free upsampler is sufficient.
111 : */
112 :
113 :
114 : /* Private buffer controller object */
115 :
116 : typedef struct {
117 : struct jpeg_d_main_controller pub; /* public fields */
118 :
119 : /* Pointer to allocated workspace (M or M+2 row groups). */
120 : JSAMPARRAY buffer[MAX_COMPONENTS];
121 :
122 : boolean buffer_full; /* Have we gotten an iMCU row from decoder? */
123 : JDIMENSION rowgroup_ctr; /* counts row groups output to postprocessor */
124 :
125 : /* Remaining fields are only used in the context case. */
126 :
127 : /* These are the master pointers to the funny-order pointer lists. */
128 : JSAMPIMAGE xbuffer[2]; /* pointers to weird pointer lists */
129 :
130 : int whichptr; /* indicates which pointer set is now in use */
131 : int context_state; /* process_data state machine status */
132 : JDIMENSION rowgroups_avail; /* row groups available to postprocessor */
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 3 : 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 3 : my_main_ptr main_ptr = (my_main_ptr) cinfo->main;
165 : int ci, rgroup;
166 3 : int M = cinfo->_min_DCT_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 3 : main_ptr->xbuffer[0] = (JSAMPIMAGE)
174 6 : (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
175 3 : cinfo->num_components * 2 * SIZEOF(JSAMPARRAY));
176 3 : main_ptr->xbuffer[1] = main_ptr->xbuffer[0] + cinfo->num_components;
177 :
178 15 : for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
179 9 : ci++, compptr++) {
180 18 : rgroup = (compptr->v_samp_factor * compptr->_DCT_scaled_size) /
181 9 : cinfo->_min_DCT_scaled_size; /* height of a row group of component */
182 : /* Get space for pointer lists --- M+4 row groups in each list.
183 : * We alloc both pointer lists with one call to save a few cycles.
184 : */
185 9 : xbuf = (JSAMPARRAY)
186 9 : (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
187 : 2 * (rgroup * (M + 4)) * SIZEOF(JSAMPROW));
188 9 : xbuf += rgroup; /* want one row group at negative offsets */
189 9 : main_ptr->xbuffer[0][ci] = xbuf;
190 9 : xbuf += rgroup * (M + 4);
191 9 : main_ptr->xbuffer[1][ci] = xbuf;
192 : }
193 3 : }
194 :
195 :
196 : LOCAL(void)
197 3 : make_funny_pointers (j_decompress_ptr cinfo)
198 : /* Create the funny pointer lists discussed in the comments above.
199 : * The actual workspace is already allocated (in main_ptr->buffer),
200 : * and the space for the pointer lists is allocated too.
201 : * This routine just fills in the curiously ordered lists.
202 : * This will be repeated at the beginning of each pass.
203 : */
204 : {
205 3 : my_main_ptr main_ptr = (my_main_ptr) cinfo->main;
206 : int ci, i, rgroup;
207 3 : int M = cinfo->_min_DCT_scaled_size;
208 : jpeg_component_info *compptr;
209 : JSAMPARRAY buf, xbuf0, xbuf1;
210 :
211 15 : for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
212 9 : ci++, compptr++) {
213 18 : rgroup = (compptr->v_samp_factor * compptr->_DCT_scaled_size) /
214 9 : cinfo->_min_DCT_scaled_size; /* height of a row group of component */
215 9 : xbuf0 = main_ptr->xbuffer[0][ci];
216 9 : xbuf1 = main_ptr->xbuffer[1][ci];
217 : /* First copy the workspace pointers as-is */
218 9 : buf = main_ptr->buffer[ci];
219 129 : for (i = 0; i < rgroup * (M + 2); i++) {
220 120 : xbuf0[i] = xbuf1[i] = buf[i];
221 : }
222 : /* In the second list, put the last four row groups in swapped order */
223 33 : for (i = 0; i < rgroup * 2; i++) {
224 24 : xbuf1[rgroup*(M-2) + i] = buf[rgroup*M + i];
225 24 : xbuf1[rgroup*M + i] = buf[rgroup*(M-2) + i];
226 : }
227 : /* The wraparound pointers at top and bottom will be filled later
228 : * (see set_wraparound_pointers, below). Initially we want the "above"
229 : * pointers to duplicate the first actual data line. This only needs
230 : * to happen in xbuffer[0].
231 : */
232 21 : for (i = 0; i < rgroup; i++) {
233 12 : xbuf0[i - rgroup] = xbuf0[0];
234 : }
235 : }
236 3 : }
237 :
238 :
239 : LOCAL(void)
240 2 : set_wraparound_pointers (j_decompress_ptr cinfo)
241 : /* Set up the "wraparound" pointers at top and bottom of the pointer lists.
242 : * This changes the pointer list state from top-of-image to the normal state.
243 : */
244 : {
245 2 : my_main_ptr main_ptr = (my_main_ptr) cinfo->main;
246 : int ci, i, rgroup;
247 2 : int M = cinfo->_min_DCT_scaled_size;
248 : jpeg_component_info *compptr;
249 : JSAMPARRAY xbuf0, xbuf1;
250 :
251 10 : for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
252 6 : ci++, compptr++) {
253 12 : rgroup = (compptr->v_samp_factor * compptr->_DCT_scaled_size) /
254 6 : cinfo->_min_DCT_scaled_size; /* height of a row group of component */
255 6 : xbuf0 = main_ptr->xbuffer[0][ci];
256 6 : xbuf1 = main_ptr->xbuffer[1][ci];
257 14 : for (i = 0; i < rgroup; i++) {
258 8 : xbuf0[i - rgroup] = xbuf0[rgroup*(M+1) + i];
259 8 : xbuf1[i - rgroup] = xbuf1[rgroup*(M+1) + i];
260 8 : xbuf0[rgroup*(M+2) + i] = xbuf0[i];
261 8 : xbuf1[rgroup*(M+2) + i] = xbuf1[i];
262 : }
263 : }
264 2 : }
265 :
266 :
267 : LOCAL(void)
268 3 : set_bottom_pointers (j_decompress_ptr cinfo)
269 : /* Change the pointer lists to duplicate the last sample row at the bottom
270 : * of the image. whichptr indicates which xbuffer holds the final iMCU row.
271 : * Also sets rowgroups_avail to indicate number of nondummy row groups in row.
272 : */
273 : {
274 3 : my_main_ptr main_ptr = (my_main_ptr) cinfo->main;
275 : int ci, i, rgroup, iMCUheight, rows_left;
276 : jpeg_component_info *compptr;
277 : JSAMPARRAY xbuf;
278 :
279 15 : for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
280 9 : ci++, compptr++) {
281 : /* Count sample rows in one iMCU row and in one row group */
282 9 : iMCUheight = compptr->v_samp_factor * compptr->_DCT_scaled_size;
283 9 : rgroup = iMCUheight / cinfo->_min_DCT_scaled_size;
284 : /* Count nondummy sample rows remaining for this component */
285 9 : rows_left = (int) (compptr->downsampled_height % (JDIMENSION) iMCUheight);
286 9 : if (rows_left == 0) rows_left = iMCUheight;
287 : /* Count nondummy row groups. Should get same answer for each component,
288 : * so we need only do it once.
289 : */
290 9 : if (ci == 0) {
291 3 : main_ptr->rowgroups_avail = (JDIMENSION) ((rows_left-1) / rgroup + 1);
292 : }
293 : /* Duplicate the last real sample row rgroup*2 times; this pads out the
294 : * last partial rowgroup and ensures at least one full rowgroup of context.
295 : */
296 9 : xbuf = main_ptr->xbuffer[main_ptr->whichptr][ci];
297 33 : for (i = 0; i < rgroup * 2; i++) {
298 24 : xbuf[rows_left + i] = xbuf[rows_left-1];
299 : }
300 : }
301 3 : }
302 :
303 :
304 : /*
305 : * Initialize for a processing pass.
306 : */
307 :
308 : METHODDEF(void)
309 5 : start_pass_main (j_decompress_ptr cinfo, J_BUF_MODE pass_mode)
310 : {
311 5 : my_main_ptr main_ptr = (my_main_ptr) cinfo->main;
312 :
313 5 : switch (pass_mode) {
314 : case JBUF_PASS_THRU:
315 5 : if (cinfo->upsample->need_context_rows) {
316 3 : main_ptr->pub.process_data = process_data_context_main;
317 3 : make_funny_pointers(cinfo); /* Create the xbuffer[] lists */
318 3 : main_ptr->whichptr = 0; /* Read first iMCU row into xbuffer[0] */
319 3 : main_ptr->context_state = CTX_PREPARE_FOR_IMCU;
320 3 : main_ptr->iMCU_row_ctr = 0;
321 : } else {
322 : /* Simple case with no context needed */
323 2 : main_ptr->pub.process_data = process_data_simple_main;
324 : }
325 5 : main_ptr->buffer_full = FALSE; /* Mark buffer empty */
326 5 : main_ptr->rowgroup_ctr = 0;
327 5 : break;
328 : #ifdef QUANT_2PASS_SUPPORTED
329 : case JBUF_CRANK_DEST:
330 : /* For last pass of 2-pass quantization, just crank the postprocessor */
331 0 : main_ptr->pub.process_data = process_data_crank_post;
332 0 : break;
333 : #endif
334 : default:
335 0 : ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
336 0 : break;
337 : }
338 5 : }
339 :
340 :
341 : /*
342 : * Process some data.
343 : * This handles the simple case where no context is required.
344 : */
345 :
346 : METHODDEF(void)
347 164 : process_data_simple_main (j_decompress_ptr cinfo,
348 : JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
349 : JDIMENSION out_rows_avail)
350 : {
351 164 : my_main_ptr main_ptr = (my_main_ptr) cinfo->main;
352 : JDIMENSION rowgroups_avail;
353 :
354 : /* Read input data if we haven't filled the main buffer yet */
355 164 : if (! main_ptr->buffer_full) {
356 11 : if (! (*cinfo->coef->decompress_data) (cinfo, main_ptr->buffer))
357 0 : return; /* suspension forced, can do nothing more */
358 11 : main_ptr->buffer_full = TRUE; /* OK, we have an iMCU row to work with */
359 : }
360 :
361 : /* There are always min_DCT_scaled_size row groups in an iMCU row. */
362 164 : rowgroups_avail = (JDIMENSION) cinfo->_min_DCT_scaled_size;
363 : /* Note: at the bottom of the image, we may pass extra garbage row groups
364 : * to the postprocessor. The postprocessor has to check for bottom
365 : * of image anyway (at row resolution), so no point in us doing it too.
366 : */
367 :
368 : /* Feed the postprocessor */
369 164 : (*cinfo->post->post_process_data) (cinfo, main_ptr->buffer,
370 : &main_ptr->rowgroup_ctr, rowgroups_avail,
371 : output_buf, out_row_ctr, out_rows_avail);
372 :
373 : /* Has postprocessor consumed all the data yet? If so, mark buffer empty */
374 164 : if (main_ptr->rowgroup_ctr >= rowgroups_avail) {
375 10 : main_ptr->buffer_full = FALSE;
376 10 : main_ptr->rowgroup_ctr = 0;
377 : }
378 : }
379 :
380 :
381 : /*
382 : * Process some data.
383 : * This handles the case where context rows must be provided.
384 : */
385 :
386 : METHODDEF(void)
387 69 : process_data_context_main (j_decompress_ptr cinfo,
388 : JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
389 : JDIMENSION out_rows_avail)
390 : {
391 69 : my_main_ptr main_ptr = (my_main_ptr) cinfo->main;
392 :
393 : /* Read input data if we haven't filled the main buffer yet */
394 69 : if (! main_ptr->buffer_full) {
395 14 : if (! (*cinfo->coef->decompress_data) (cinfo,
396 7 : main_ptr->xbuffer[main_ptr->whichptr]))
397 2 : return; /* suspension forced, can do nothing more */
398 5 : main_ptr->buffer_full = TRUE; /* OK, we have an iMCU row to work with */
399 5 : main_ptr->iMCU_row_ctr++; /* count rows received */
400 : }
401 :
402 : /* Postprocessor typically will not swallow all the input data it is handed
403 : * in one call (due to filling the output buffer first). Must be prepared
404 : * to exit and restart. This switch lets us keep track of how far we got.
405 : * Note that each case falls through to the next on successful completion.
406 : */
407 67 : switch (main_ptr->context_state) {
408 : case CTX_POSTPONED_ROW:
409 : /* Call postprocessor using previously set pointers for postponed row */
410 4 : (*cinfo->post->post_process_data) (cinfo, main_ptr->xbuffer[main_ptr->whichptr],
411 : &main_ptr->rowgroup_ctr, main_ptr->rowgroups_avail,
412 : output_buf, out_row_ctr, out_rows_avail);
413 4 : if (main_ptr->rowgroup_ctr < main_ptr->rowgroups_avail)
414 2 : return; /* Need to suspend */
415 2 : main_ptr->context_state = CTX_PREPARE_FOR_IMCU;
416 2 : if (*out_row_ctr >= out_rows_avail)
417 2 : return; /* Postprocessor exactly filled output buf */
418 : /*FALLTHROUGH*/
419 : case CTX_PREPARE_FOR_IMCU:
420 : /* Prepare to process first M-1 row groups of this iMCU row */
421 5 : main_ptr->rowgroup_ctr = 0;
422 5 : main_ptr->rowgroups_avail = (JDIMENSION) (cinfo->_min_DCT_scaled_size - 1);
423 : /* Check for bottom of image: if so, tweak pointers to "duplicate"
424 : * the last sample row, and adjust rowgroups_avail to ignore padding rows.
425 : */
426 5 : if (main_ptr->iMCU_row_ctr == cinfo->total_iMCU_rows)
427 3 : set_bottom_pointers(cinfo);
428 5 : main_ptr->context_state = CTX_PROCESS_IMCU;
429 : /*FALLTHROUGH*/
430 : case CTX_PROCESS_IMCU:
431 : /* Call postprocessor using previously set pointers */
432 63 : (*cinfo->post->post_process_data) (cinfo, main_ptr->xbuffer[main_ptr->whichptr],
433 : &main_ptr->rowgroup_ctr, main_ptr->rowgroups_avail,
434 : output_buf, out_row_ctr, out_rows_avail);
435 63 : if (main_ptr->rowgroup_ctr < main_ptr->rowgroups_avail)
436 59 : return; /* Need to suspend */
437 : /* After the first iMCU, change wraparound pointers to normal state */
438 4 : if (main_ptr->iMCU_row_ctr == 1)
439 2 : set_wraparound_pointers(cinfo);
440 : /* Prepare to load new iMCU row using other xbuffer list */
441 4 : main_ptr->whichptr ^= 1; /* 0=>1 or 1=>0 */
442 4 : main_ptr->buffer_full = FALSE;
443 : /* Still need to process last row group of this iMCU row, */
444 : /* which is saved at index M+1 of the other xbuffer */
445 4 : main_ptr->rowgroup_ctr = (JDIMENSION) (cinfo->_min_DCT_scaled_size + 1);
446 4 : main_ptr->rowgroups_avail = (JDIMENSION) (cinfo->_min_DCT_scaled_size + 2);
447 4 : main_ptr->context_state = CTX_POSTPONED_ROW;
448 : }
449 : }
450 :
451 :
452 : /*
453 : * Process some data.
454 : * Final pass of two-pass quantization: just call the postprocessor.
455 : * Source data will be the postprocessor controller's internal buffer.
456 : */
457 :
458 : #ifdef QUANT_2PASS_SUPPORTED
459 :
460 : METHODDEF(void)
461 0 : process_data_crank_post (j_decompress_ptr cinfo,
462 : JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
463 : JDIMENSION out_rows_avail)
464 : {
465 0 : (*cinfo->post->post_process_data) (cinfo, (JSAMPIMAGE) NULL,
466 : (JDIMENSION *) NULL, (JDIMENSION) 0,
467 : output_buf, out_row_ctr, out_rows_avail);
468 0 : }
469 :
470 : #endif /* QUANT_2PASS_SUPPORTED */
471 :
472 :
473 : /*
474 : * Initialize main buffer controller.
475 : */
476 :
477 : GLOBAL(void)
478 5 : jinit_d_main_controller (j_decompress_ptr cinfo, boolean need_full_buffer)
479 : {
480 : my_main_ptr main_ptr;
481 : int ci, rgroup, ngroups;
482 : jpeg_component_info *compptr;
483 :
484 5 : main_ptr = (my_main_ptr)
485 5 : (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
486 : SIZEOF(my_main_controller));
487 5 : cinfo->main = (struct jpeg_d_main_controller *) main_ptr;
488 5 : main_ptr->pub.start_pass = start_pass_main;
489 :
490 5 : if (need_full_buffer) /* shouldn't happen */
491 0 : ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
492 :
493 : /* Allocate the workspace.
494 : * ngroups is the number of row groups we need.
495 : */
496 5 : if (cinfo->upsample->need_context_rows) {
497 3 : if (cinfo->_min_DCT_scaled_size < 2) /* unsupported, see comments above */
498 0 : ERREXIT(cinfo, JERR_NOTIMPL);
499 3 : alloc_funny_pointers(cinfo); /* Alloc space for xbuffer[] lists */
500 3 : ngroups = cinfo->_min_DCT_scaled_size + 2;
501 : } else {
502 2 : ngroups = cinfo->_min_DCT_scaled_size;
503 : }
504 :
505 25 : for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
506 15 : ci++, compptr++) {
507 30 : rgroup = (compptr->v_samp_factor * compptr->_DCT_scaled_size) /
508 15 : cinfo->_min_DCT_scaled_size; /* height of a row group of component */
509 30 : main_ptr->buffer[ci] = (*cinfo->mem->alloc_sarray)
510 45 : ((j_common_ptr) cinfo, JPOOL_IMAGE,
511 15 : compptr->width_in_blocks * compptr->_DCT_scaled_size,
512 15 : (JDIMENSION) (rgroup * ngroups));
513 : }
514 5 : }
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