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1 /*
2  * jdmainct.c
3  *
4  * This file was part of the Independent JPEG Group's software:
5  * Copyright (C) 1994-1996, Thomas G. Lane.
6  * libjpeg-turbo Modifications:
7  * Copyright (C) 2010, 2016, D. R. Commander.
8  * For conditions of distribution and use, see the accompanying README.ijg
9  * file.
10  *
11  * This file contains the main buffer controller for decompression.
12  * The main buffer lies between the JPEG decompressor proper and the
13  * post-processor; it holds downsampled data in the JPEG colorspace.
14  *
15  * Note that this code is bypassed in raw-data mode, since the application
16  * supplies the equivalent of the main buffer in that case.
17  */
18 
19 #include "jinclude.h"
20 #include "jdmainct.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 /* Forward declarations */
115 METHODDEF(void) process_data_simple_main(j_decompress_ptr cinfo,
116                                          JSAMPARRAY output_buf,
117                                          JDIMENSION *out_row_ctr,
118                                          JDIMENSION out_rows_avail);
119 METHODDEF(void) process_data_context_main(j_decompress_ptr cinfo,
120                                           JSAMPARRAY output_buf,
121                                           JDIMENSION *out_row_ctr,
122                                           JDIMENSION out_rows_avail);
123 #ifdef QUANT_2PASS_SUPPORTED
124 METHODDEF(void) process_data_crank_post(j_decompress_ptr cinfo,
125                                         JSAMPARRAY output_buf,
126                                         JDIMENSION *out_row_ctr,
127                                         JDIMENSION out_rows_avail);
128 #endif
129 
130 
131 LOCAL(void)
alloc_funny_pointers(j_decompress_ptr cinfo)132 alloc_funny_pointers(j_decompress_ptr cinfo)
133 /* Allocate space for the funny pointer lists.
134  * This is done only once, not once per pass.
135  */
136 {
137   my_main_ptr main_ptr = (my_main_ptr)cinfo->main;
138   int ci, rgroup;
139   int M = cinfo->_min_DCT_scaled_size;
140   jpeg_component_info *compptr;
141   JSAMPARRAY xbuf;
142 
143   /* Get top-level space for component array pointers.
144    * We alloc both arrays with one call to save a few cycles.
145    */
146   main_ptr->xbuffer[0] = (JSAMPIMAGE)
147     (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE,
148                                 cinfo->num_components * 2 * sizeof(JSAMPARRAY));
149   main_ptr->xbuffer[1] = main_ptr->xbuffer[0] + cinfo->num_components;
150 
151   for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
152        ci++, compptr++) {
153     rgroup = (compptr->v_samp_factor * compptr->_DCT_scaled_size) /
154       cinfo->_min_DCT_scaled_size; /* height of a row group of component */
155     /* Get space for pointer lists --- M+4 row groups in each list.
156      * We alloc both pointer lists with one call to save a few cycles.
157      */
158     xbuf = (JSAMPARRAY)
159       (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE,
160                                   2 * (rgroup * (M + 4)) * sizeof(JSAMPROW));
161     xbuf += rgroup;             /* want one row group at negative offsets */
162     main_ptr->xbuffer[0][ci] = xbuf;
163     xbuf += rgroup * (M + 4);
164     main_ptr->xbuffer[1][ci] = xbuf;
165   }
166 }
167 
168 
169 LOCAL(void)
make_funny_pointers(j_decompress_ptr cinfo)170 make_funny_pointers(j_decompress_ptr cinfo)
171 /* Create the funny pointer lists discussed in the comments above.
172  * The actual workspace is already allocated (in main_ptr->buffer),
173  * and the space for the pointer lists is allocated too.
174  * This routine just fills in the curiously ordered lists.
175  * This will be repeated at the beginning of each pass.
176  */
177 {
178   my_main_ptr main_ptr = (my_main_ptr)cinfo->main;
179   int ci, i, rgroup;
180   int M = cinfo->_min_DCT_scaled_size;
181   jpeg_component_info *compptr;
182   JSAMPARRAY buf, xbuf0, xbuf1;
183 
184   for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
185        ci++, compptr++) {
186     rgroup = (compptr->v_samp_factor * compptr->_DCT_scaled_size) /
187       cinfo->_min_DCT_scaled_size; /* height of a row group of component */
188     xbuf0 = main_ptr->xbuffer[0][ci];
189     xbuf1 = main_ptr->xbuffer[1][ci];
190     /* First copy the workspace pointers as-is */
191     buf = main_ptr->buffer[ci];
192     for (i = 0; i < rgroup * (M + 2); i++) {
193       xbuf0[i] = xbuf1[i] = buf[i];
194     }
195     /* In the second list, put the last four row groups in swapped order */
196     for (i = 0; i < rgroup * 2; i++) {
197       xbuf1[rgroup * (M - 2) + i] = buf[rgroup * M + i];
198       xbuf1[rgroup * M + i] = buf[rgroup * (M - 2) + i];
199     }
200     /* The wraparound pointers at top and bottom will be filled later
201      * (see set_wraparound_pointers, below).  Initially we want the "above"
202      * pointers to duplicate the first actual data line.  This only needs
203      * to happen in xbuffer[0].
204      */
205     for (i = 0; i < rgroup; i++) {
206       xbuf0[i - rgroup] = xbuf0[0];
207     }
208   }
209 }
210 
211 
212 LOCAL(void)
set_bottom_pointers(j_decompress_ptr cinfo)213 set_bottom_pointers(j_decompress_ptr cinfo)
214 /* Change the pointer lists to duplicate the last sample row at the bottom
215  * of the image.  whichptr indicates which xbuffer holds the final iMCU row.
216  * Also sets rowgroups_avail to indicate number of nondummy row groups in row.
217  */
218 {
219   my_main_ptr main_ptr = (my_main_ptr)cinfo->main;
220   int ci, i, rgroup, iMCUheight, rows_left;
221   jpeg_component_info *compptr;
222   JSAMPARRAY xbuf;
223 
224   for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
225        ci++, compptr++) {
226     /* Count sample rows in one iMCU row and in one row group */
227     iMCUheight = compptr->v_samp_factor * compptr->_DCT_scaled_size;
228     rgroup = iMCUheight / cinfo->_min_DCT_scaled_size;
229     /* Count nondummy sample rows remaining for this component */
230     rows_left = (int)(compptr->downsampled_height % (JDIMENSION)iMCUheight);
231     if (rows_left == 0) rows_left = iMCUheight;
232     /* Count nondummy row groups.  Should get same answer for each component,
233      * so we need only do it once.
234      */
235     if (ci == 0) {
236       main_ptr->rowgroups_avail = (JDIMENSION)((rows_left - 1) / rgroup + 1);
237     }
238     /* Duplicate the last real sample row rgroup*2 times; this pads out the
239      * last partial rowgroup and ensures at least one full rowgroup of context.
240      */
241     xbuf = main_ptr->xbuffer[main_ptr->whichptr][ci];
242     for (i = 0; i < rgroup * 2; i++) {
243       xbuf[rows_left + i] = xbuf[rows_left - 1];
244     }
245   }
246 }
247 
248 
249 /*
250  * Initialize for a processing pass.
251  */
252 
253 METHODDEF(void)
start_pass_main(j_decompress_ptr cinfo,J_BUF_MODE pass_mode)254 start_pass_main(j_decompress_ptr cinfo, J_BUF_MODE pass_mode)
255 {
256   my_main_ptr main_ptr = (my_main_ptr)cinfo->main;
257 
258   switch (pass_mode) {
259   case JBUF_PASS_THRU:
260     if (cinfo->upsample->need_context_rows) {
261       main_ptr->pub.process_data = process_data_context_main;
262       make_funny_pointers(cinfo); /* Create the xbuffer[] lists */
263       main_ptr->whichptr = 0;   /* Read first iMCU row into xbuffer[0] */
264       main_ptr->context_state = CTX_PREPARE_FOR_IMCU;
265       main_ptr->iMCU_row_ctr = 0;
266     } else {
267       /* Simple case with no context needed */
268       main_ptr->pub.process_data = process_data_simple_main;
269     }
270     main_ptr->buffer_full = FALSE;      /* Mark buffer empty */
271     main_ptr->rowgroup_ctr = 0;
272     break;
273 #ifdef QUANT_2PASS_SUPPORTED
274   case JBUF_CRANK_DEST:
275     /* For last pass of 2-pass quantization, just crank the postprocessor */
276     main_ptr->pub.process_data = process_data_crank_post;
277     break;
278 #endif
279   default:
280     ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
281     break;
282   }
283 }
284 
285 
286 /*
287  * Process some data.
288  * This handles the simple case where no context is required.
289  */
290 
291 METHODDEF(void)
process_data_simple_main(j_decompress_ptr cinfo,JSAMPARRAY output_buf,JDIMENSION * out_row_ctr,JDIMENSION out_rows_avail)292 process_data_simple_main(j_decompress_ptr cinfo, JSAMPARRAY output_buf,
293                          JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail)
294 {
295   my_main_ptr main_ptr = (my_main_ptr)cinfo->main;
296   JDIMENSION rowgroups_avail;
297 
298   /* Read input data if we haven't filled the main buffer yet */
299   if (!main_ptr->buffer_full) {
300     if (!(*cinfo->coef->decompress_data) (cinfo, main_ptr->buffer))
301       return;                   /* suspension forced, can do nothing more */
302     main_ptr->buffer_full = TRUE;       /* OK, we have an iMCU row to work with */
303   }
304 
305   /* There are always min_DCT_scaled_size row groups in an iMCU row. */
306   rowgroups_avail = (JDIMENSION)cinfo->_min_DCT_scaled_size;
307   /* Note: at the bottom of the image, we may pass extra garbage row groups
308    * to the postprocessor.  The postprocessor has to check for bottom
309    * of image anyway (at row resolution), so no point in us doing it too.
310    */
311 
312   /* Feed the postprocessor */
313   (*cinfo->post->post_process_data) (cinfo, main_ptr->buffer,
314                                      &main_ptr->rowgroup_ctr, rowgroups_avail,
315                                      output_buf, out_row_ctr, out_rows_avail);
316 
317   /* Has postprocessor consumed all the data yet? If so, mark buffer empty */
318   if (main_ptr->rowgroup_ctr >= rowgroups_avail) {
319     main_ptr->buffer_full = FALSE;
320     main_ptr->rowgroup_ctr = 0;
321   }
322 }
323 
324 
325 /*
326  * Process some data.
327  * This handles the case where context rows must be provided.
328  */
329 
330 METHODDEF(void)
process_data_context_main(j_decompress_ptr cinfo,JSAMPARRAY output_buf,JDIMENSION * out_row_ctr,JDIMENSION out_rows_avail)331 process_data_context_main(j_decompress_ptr cinfo, JSAMPARRAY output_buf,
332                           JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail)
333 {
334   my_main_ptr main_ptr = (my_main_ptr)cinfo->main;
335 
336   /* Read input data if we haven't filled the main buffer yet */
337   if (!main_ptr->buffer_full) {
338     if (!(*cinfo->coef->decompress_data) (cinfo,
339                                           main_ptr->xbuffer[main_ptr->whichptr]))
340       return;                   /* suspension forced, can do nothing more */
341     main_ptr->buffer_full = TRUE;       /* OK, we have an iMCU row to work with */
342     main_ptr->iMCU_row_ctr++;   /* count rows received */
343   }
344 
345   /* Postprocessor typically will not swallow all the input data it is handed
346    * in one call (due to filling the output buffer first).  Must be prepared
347    * to exit and restart.  This switch lets us keep track of how far we got.
348    * Note that each case falls through to the next on successful completion.
349    */
350   switch (main_ptr->context_state) {
351   case CTX_POSTPONED_ROW:
352     /* Call postprocessor using previously set pointers for postponed row */
353     (*cinfo->post->post_process_data) (cinfo,
354                                        main_ptr->xbuffer[main_ptr->whichptr],
355                                        &main_ptr->rowgroup_ctr,
356                                        main_ptr->rowgroups_avail, output_buf,
357                                        out_row_ctr, out_rows_avail);
358     if (main_ptr->rowgroup_ctr < main_ptr->rowgroups_avail)
359       return;                   /* Need to suspend */
360     main_ptr->context_state = CTX_PREPARE_FOR_IMCU;
361     if (*out_row_ctr >= out_rows_avail)
362       return;                   /* Postprocessor exactly filled output buf */
363     /*FALLTHROUGH*/
364   case CTX_PREPARE_FOR_IMCU:
365     /* Prepare to process first M-1 row groups of this iMCU row */
366     main_ptr->rowgroup_ctr = 0;
367     main_ptr->rowgroups_avail = (JDIMENSION)(cinfo->_min_DCT_scaled_size - 1);
368     /* Check for bottom of image: if so, tweak pointers to "duplicate"
369      * the last sample row, and adjust rowgroups_avail to ignore padding rows.
370      */
371     if (main_ptr->iMCU_row_ctr == cinfo->total_iMCU_rows)
372       set_bottom_pointers(cinfo);
373     main_ptr->context_state = CTX_PROCESS_IMCU;
374     /*FALLTHROUGH*/
375   case CTX_PROCESS_IMCU:
376     /* Call postprocessor using previously set pointers */
377     (*cinfo->post->post_process_data) (cinfo,
378                                        main_ptr->xbuffer[main_ptr->whichptr],
379                                        &main_ptr->rowgroup_ctr,
380                                        main_ptr->rowgroups_avail, output_buf,
381                                        out_row_ctr, out_rows_avail);
382     if (main_ptr->rowgroup_ctr < main_ptr->rowgroups_avail)
383       return;                   /* Need to suspend */
384     /* After the first iMCU, change wraparound pointers to normal state */
385     if (main_ptr->iMCU_row_ctr == 1)
386       set_wraparound_pointers(cinfo);
387     /* Prepare to load new iMCU row using other xbuffer list */
388     main_ptr->whichptr ^= 1;    /* 0=>1 or 1=>0 */
389     main_ptr->buffer_full = FALSE;
390     /* Still need to process last row group of this iMCU row, */
391     /* which is saved at index M+1 of the other xbuffer */
392     main_ptr->rowgroup_ctr = (JDIMENSION)(cinfo->_min_DCT_scaled_size + 1);
393     main_ptr->rowgroups_avail = (JDIMENSION)(cinfo->_min_DCT_scaled_size + 2);
394     main_ptr->context_state = CTX_POSTPONED_ROW;
395   }
396 }
397 
398 
399 /*
400  * Process some data.
401  * Final pass of two-pass quantization: just call the postprocessor.
402  * Source data will be the postprocessor controller's internal buffer.
403  */
404 
405 #ifdef QUANT_2PASS_SUPPORTED
406 
407 METHODDEF(void)
process_data_crank_post(j_decompress_ptr cinfo,JSAMPARRAY output_buf,JDIMENSION * out_row_ctr,JDIMENSION out_rows_avail)408 process_data_crank_post(j_decompress_ptr cinfo, JSAMPARRAY output_buf,
409                         JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail)
410 {
411   (*cinfo->post->post_process_data) (cinfo, (JSAMPIMAGE)NULL,
412                                      (JDIMENSION *)NULL, (JDIMENSION)0,
413                                      output_buf, out_row_ctr, out_rows_avail);
414 }
415 
416 #endif /* QUANT_2PASS_SUPPORTED */
417 
418 
419 /*
420  * Initialize main buffer controller.
421  */
422 
423 GLOBAL(void)
jinit_d_main_controller(j_decompress_ptr cinfo,boolean need_full_buffer)424 jinit_d_main_controller(j_decompress_ptr cinfo, boolean need_full_buffer)
425 {
426   my_main_ptr main_ptr;
427   int ci, rgroup, ngroups;
428   jpeg_component_info *compptr;
429 
430   main_ptr = (my_main_ptr)
431     (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE,
432                                 sizeof(my_main_controller));
433   cinfo->main = (struct jpeg_d_main_controller *)main_ptr;
434   main_ptr->pub.start_pass = start_pass_main;
435 
436   if (need_full_buffer)         /* shouldn't happen */
437     ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
438 
439   /* Allocate the workspace.
440    * ngroups is the number of row groups we need.
441    */
442   if (cinfo->upsample->need_context_rows) {
443     if (cinfo->_min_DCT_scaled_size < 2) /* unsupported, see comments above */
444       ERREXIT(cinfo, JERR_NOTIMPL);
445     alloc_funny_pointers(cinfo); /* Alloc space for xbuffer[] lists */
446     ngroups = cinfo->_min_DCT_scaled_size + 2;
447   } else {
448     ngroups = cinfo->_min_DCT_scaled_size;
449   }
450 
451   for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
452        ci++, compptr++) {
453     rgroup = (compptr->v_samp_factor * compptr->_DCT_scaled_size) /
454       cinfo->_min_DCT_scaled_size; /* height of a row group of component */
455     main_ptr->buffer[ci] = (*cinfo->mem->alloc_sarray)
456                         ((j_common_ptr)cinfo, JPOOL_IMAGE,
457                          compptr->width_in_blocks * compptr->_DCT_scaled_size,
458                          (JDIMENSION)(rgroup * ngroups));
459   }
460 }
461