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1 /*
2  * jdapistd.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, 2015-2016, D. R. Commander.
8  * Copyright (C) 2015, Google, Inc.
9  * For conditions of distribution and use, see the accompanying README.ijg
10  * file.
11  *
12  * This file contains application interface code for the decompression half
13  * of the JPEG library.  These are the "standard" API routines that are
14  * used in the normal full-decompression case.  They are not used by a
15  * transcoding-only application.  Note that if an application links in
16  * jpeg_start_decompress, it will end up linking in the entire decompressor.
17  * We thus must separate this file from jdapimin.c to avoid linking the
18  * whole decompression library into a transcoder.
19  */
20 
21 #include "jinclude.h"
22 #include "jdmainct.h"
23 #include "jdcoefct.h"
24 #include "jdsample.h"
25 #include "jmemsys.h"
26 
27 /* Forward declarations */
28 LOCAL(boolean) output_pass_setup (j_decompress_ptr cinfo);
29 
30 
31 /*
32  * Decompression initialization.
33  * jpeg_read_header must be completed before calling this.
34  *
35  * If a multipass operating mode was selected, this will do all but the
36  * last pass, and thus may take a great deal of time.
37  *
38  * Returns FALSE if suspended.  The return value need be inspected only if
39  * a suspending data source is used.
40  */
41 
42 GLOBAL(boolean)
jpeg_start_decompress(j_decompress_ptr cinfo)43 jpeg_start_decompress (j_decompress_ptr cinfo)
44 {
45   if (cinfo->global_state == DSTATE_READY) {
46     /* First call: initialize master control, select active modules */
47     jinit_master_decompress(cinfo);
48     if (cinfo->buffered_image) {
49       /* No more work here; expecting jpeg_start_output next */
50       cinfo->global_state = DSTATE_BUFIMAGE;
51       return TRUE;
52     }
53     cinfo->global_state = DSTATE_PRELOAD;
54   }
55   if (cinfo->global_state == DSTATE_PRELOAD) {
56     /* If file has multiple scans, absorb them all into the coef buffer */
57     if (cinfo->inputctl->has_multiple_scans) {
58 #ifdef D_MULTISCAN_FILES_SUPPORTED
59       for (;;) {
60         int retcode;
61         /* Call progress monitor hook if present */
62         if (cinfo->progress != NULL)
63           (*cinfo->progress->progress_monitor) ((j_common_ptr) cinfo);
64         /* Absorb some more input */
65         retcode = (*cinfo->inputctl->consume_input) (cinfo);
66         if (retcode == JPEG_SUSPENDED)
67           return FALSE;
68         if (retcode == JPEG_REACHED_EOI)
69           break;
70         /* Advance progress counter if appropriate */
71         if (cinfo->progress != NULL &&
72             (retcode == JPEG_ROW_COMPLETED || retcode == JPEG_REACHED_SOS)) {
73           if (++cinfo->progress->pass_counter >= cinfo->progress->pass_limit) {
74             /* jdmaster underestimated number of scans; ratchet up one scan */
75             cinfo->progress->pass_limit += (long) cinfo->total_iMCU_rows;
76           }
77         }
78       }
79 #else
80       ERREXIT(cinfo, JERR_NOT_COMPILED);
81 #endif /* D_MULTISCAN_FILES_SUPPORTED */
82     }
83     cinfo->output_scan_number = cinfo->input_scan_number;
84   } else if (cinfo->global_state != DSTATE_PRESCAN)
85     ERREXIT1(cinfo, JERR_BAD_STATE, cinfo->global_state);
86   /* Perform any dummy output passes, and set up for the final pass */
87   return output_pass_setup(cinfo);
88 }
89 
90 
91 /*
92  * Set up for an output pass, and perform any dummy pass(es) needed.
93  * Common subroutine for jpeg_start_decompress and jpeg_start_output.
94  * Entry: global_state = DSTATE_PRESCAN only if previously suspended.
95  * Exit: If done, returns TRUE and sets global_state for proper output mode.
96  *       If suspended, returns FALSE and sets global_state = DSTATE_PRESCAN.
97  */
98 
99 LOCAL(boolean)
output_pass_setup(j_decompress_ptr cinfo)100 output_pass_setup (j_decompress_ptr cinfo)
101 {
102   if (cinfo->global_state != DSTATE_PRESCAN) {
103     /* First call: do pass setup */
104     (*cinfo->master->prepare_for_output_pass) (cinfo);
105     cinfo->output_scanline = 0;
106     cinfo->global_state = DSTATE_PRESCAN;
107   }
108   /* Loop over any required dummy passes */
109   while (cinfo->master->is_dummy_pass) {
110 #ifdef QUANT_2PASS_SUPPORTED
111     /* Crank through the dummy pass */
112     while (cinfo->output_scanline < cinfo->output_height) {
113       JDIMENSION last_scanline;
114       /* Call progress monitor hook if present */
115       if (cinfo->progress != NULL) {
116         cinfo->progress->pass_counter = (long) cinfo->output_scanline;
117         cinfo->progress->pass_limit = (long) cinfo->output_height;
118         (*cinfo->progress->progress_monitor) ((j_common_ptr) cinfo);
119       }
120       /* Process some data */
121       last_scanline = cinfo->output_scanline;
122       (*cinfo->main->process_data) (cinfo, (JSAMPARRAY) NULL,
123                                     &cinfo->output_scanline, (JDIMENSION) 0);
124       if (cinfo->output_scanline == last_scanline)
125         return FALSE;           /* No progress made, must suspend */
126     }
127     /* Finish up dummy pass, and set up for another one */
128     (*cinfo->master->finish_output_pass) (cinfo);
129     (*cinfo->master->prepare_for_output_pass) (cinfo);
130     cinfo->output_scanline = 0;
131 #else
132     ERREXIT(cinfo, JERR_NOT_COMPILED);
133 #endif /* QUANT_2PASS_SUPPORTED */
134   }
135   /* Ready for application to drive output pass through
136    * jpeg_read_scanlines or jpeg_read_raw_data.
137    */
138   cinfo->global_state = cinfo->raw_data_out ? DSTATE_RAW_OK : DSTATE_SCANNING;
139   return TRUE;
140 }
141 
142 
143 /*
144  * Enable partial scanline decompression
145  *
146  * Must be called after jpeg_start_decompress() and before any calls to
147  * jpeg_read_scanlines() or jpeg_skip_scanlines().
148  *
149  * Refer to libjpeg.txt for more information.
150  */
151 
152 GLOBAL(void)
jpeg_crop_scanline(j_decompress_ptr cinfo,JDIMENSION * xoffset,JDIMENSION * width)153 jpeg_crop_scanline (j_decompress_ptr cinfo, JDIMENSION *xoffset,
154                     JDIMENSION *width)
155 {
156   int ci, align, orig_downsampled_width;
157   JDIMENSION input_xoffset;
158   boolean reinit_upsampler = FALSE;
159   jpeg_component_info *compptr;
160 
161   if (cinfo->global_state != DSTATE_SCANNING || cinfo->output_scanline != 0)
162     ERREXIT1(cinfo, JERR_BAD_STATE, cinfo->global_state);
163 
164   if (!xoffset || !width)
165     ERREXIT(cinfo, JERR_BAD_CROP_SPEC);
166 
167   /* xoffset and width must fall within the output image dimensions. */
168   if (*width == 0 || *xoffset + *width > cinfo->output_width)
169     ERREXIT(cinfo, JERR_WIDTH_OVERFLOW);
170 
171   /* No need to do anything if the caller wants the entire width. */
172   if (*width == cinfo->output_width)
173     return;
174 
175   /* Ensuring the proper alignment of xoffset is tricky.  At minimum, it
176    * must align with an MCU boundary, because:
177    *
178    *   (1) The IDCT is performed in blocks, and it is not feasible to modify
179    *       the algorithm so that it can transform partial blocks.
180    *   (2) Because of the SIMD extensions, any input buffer passed to the
181    *       upsampling and color conversion routines must be aligned to the
182    *       SIMD word size (for instance, 128-bit in the case of SSE2.)  The
183    *       easiest way to accomplish this without copying data is to ensure
184    *       that upsampling and color conversion begin at the start of the
185    *       first MCU column that will be inverse transformed.
186    *
187    * In practice, we actually impose a stricter alignment requirement.  We
188    * require that xoffset be a multiple of the maximum MCU column width of all
189    * of the components (the "iMCU column width.")  This is to simplify the
190    * single-pass decompression case, allowing us to use the same MCU column
191    * width for all of the components.
192    */
193   align = cinfo->_min_DCT_scaled_size * cinfo->max_h_samp_factor;
194 
195   /* Adjust xoffset to the nearest iMCU boundary <= the requested value */
196   input_xoffset = *xoffset;
197   *xoffset = (input_xoffset / align) * align;
198 
199   /* Adjust the width so that the right edge of the output image is as
200    * requested (only the left edge is altered.)  It is important that calling
201    * programs check this value after this function returns, so that they can
202    * allocate an output buffer with the appropriate size.
203    */
204   *width = *width + input_xoffset - *xoffset;
205   cinfo->output_width = *width;
206 
207   /* Set the first and last iMCU columns that we must decompress.  These values
208    * will be used in single-scan decompressions.
209    */
210   cinfo->master->first_iMCU_col =
211     (JDIMENSION) (long) (*xoffset) / (long) align;
212   cinfo->master->last_iMCU_col =
213     (JDIMENSION) jdiv_round_up((long) (*xoffset + cinfo->output_width),
214                                (long) align) - 1;
215 
216   for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
217        ci++, compptr++) {
218     /* Set downsampled_width to the new output width. */
219     orig_downsampled_width = compptr->downsampled_width;
220     compptr->downsampled_width =
221       (JDIMENSION) jdiv_round_up((long) (cinfo->output_width *
222                                          compptr->h_samp_factor),
223                                  (long) cinfo->max_h_samp_factor);
224     if (compptr->downsampled_width < 2 && orig_downsampled_width >= 2)
225       reinit_upsampler = TRUE;
226 
227     /* Set the first and last iMCU columns that we must decompress.  These
228      * values will be used in multi-scan decompressions.
229      */
230     cinfo->master->first_MCU_col[ci] =
231       (JDIMENSION) (long) (*xoffset * compptr->h_samp_factor) /
232                    (long) align;
233     cinfo->master->last_MCU_col[ci] =
234       (JDIMENSION) jdiv_round_up((long) ((*xoffset + cinfo->output_width) *
235                                          compptr->h_samp_factor),
236                                  (long) align) - 1;
237   }
238 
239   if (reinit_upsampler) {
240     cinfo->master->jinit_upsampler_no_alloc = TRUE;
241     jinit_upsampler(cinfo);
242     cinfo->master->jinit_upsampler_no_alloc = FALSE;
243   }
244 }
245 
246 
247 /*
248  * Read some scanlines of data from the JPEG decompressor.
249  *
250  * The return value will be the number of lines actually read.
251  * This may be less than the number requested in several cases,
252  * including bottom of image, data source suspension, and operating
253  * modes that emit multiple scanlines at a time.
254  *
255  * Note: we warn about excess calls to jpeg_read_scanlines() since
256  * this likely signals an application programmer error.  However,
257  * an oversize buffer (max_lines > scanlines remaining) is not an error.
258  */
259 
260 GLOBAL(JDIMENSION)
jpeg_read_scanlines(j_decompress_ptr cinfo,JSAMPARRAY scanlines,JDIMENSION max_lines)261 jpeg_read_scanlines (j_decompress_ptr cinfo, JSAMPARRAY scanlines,
262                      JDIMENSION max_lines)
263 {
264   JDIMENSION row_ctr;
265 
266   if (cinfo->global_state != DSTATE_SCANNING)
267     ERREXIT1(cinfo, JERR_BAD_STATE, cinfo->global_state);
268   if (cinfo->output_scanline >= cinfo->output_height) {
269     WARNMS(cinfo, JWRN_TOO_MUCH_DATA);
270     return 0;
271   }
272 
273   /* Call progress monitor hook if present */
274   if (cinfo->progress != NULL) {
275     cinfo->progress->pass_counter = (long) cinfo->output_scanline;
276     cinfo->progress->pass_limit = (long) cinfo->output_height;
277     (*cinfo->progress->progress_monitor) ((j_common_ptr) cinfo);
278   }
279 
280   /* Process some data */
281   row_ctr = 0;
282   (*cinfo->main->process_data) (cinfo, scanlines, &row_ctr, max_lines);
283   cinfo->output_scanline += row_ctr;
284   return row_ctr;
285 }
286 
287 
288 /* Dummy color convert function used by jpeg_skip_scanlines() */
289 LOCAL(void)
noop_convert(j_decompress_ptr cinfo,JSAMPIMAGE input_buf,JDIMENSION input_row,JSAMPARRAY output_buf,int num_rows)290 noop_convert (j_decompress_ptr cinfo, JSAMPIMAGE input_buf,
291               JDIMENSION input_row, JSAMPARRAY output_buf, int num_rows)
292 {
293 }
294 
295 
296 /*
297  * In some cases, it is best to call jpeg_read_scanlines() and discard the
298  * output, rather than skipping the scanlines, because this allows us to
299  * maintain the internal state of the context-based upsampler.  In these cases,
300  * we set up and tear down a dummy color converter in order to avoid valgrind
301  * errors and to achieve the best possible performance.
302  */
303 
304 LOCAL(void)
read_and_discard_scanlines(j_decompress_ptr cinfo,JDIMENSION num_lines)305 read_and_discard_scanlines (j_decompress_ptr cinfo, JDIMENSION num_lines)
306 {
307   JDIMENSION n;
308   void (*color_convert) (j_decompress_ptr cinfo, JSAMPIMAGE input_buf,
309                          JDIMENSION input_row, JSAMPARRAY output_buf,
310                          int num_rows);
311 
312   color_convert = cinfo->cconvert->color_convert;
313   cinfo->cconvert->color_convert = noop_convert;
314 
315   for (n = 0; n < num_lines; n++)
316     jpeg_read_scanlines(cinfo, NULL, 1);
317 
318   cinfo->cconvert->color_convert = color_convert;
319 }
320 
321 
322 /*
323  * Called by jpeg_skip_scanlines().  This partially skips a decompress block by
324  * incrementing the rowgroup counter.
325  */
326 
327 LOCAL(void)
increment_simple_rowgroup_ctr(j_decompress_ptr cinfo,JDIMENSION rows)328 increment_simple_rowgroup_ctr (j_decompress_ptr cinfo, JDIMENSION rows)
329 {
330   JDIMENSION rows_left;
331   my_main_ptr main_ptr = (my_main_ptr) cinfo->main;
332 
333   /* Increment the counter to the next row group after the skipped rows. */
334   main_ptr->rowgroup_ctr += rows / cinfo->max_v_samp_factor;
335 
336   /* Partially skipping a row group would involve modifying the internal state
337    * of the upsampler, so read the remaining rows into a dummy buffer instead.
338    */
339   rows_left = rows % cinfo->max_v_samp_factor;
340   cinfo->output_scanline += rows - rows_left;
341 
342   read_and_discard_scanlines(cinfo, rows_left);
343 }
344 
345 /*
346  * Skips some scanlines of data from the JPEG decompressor.
347  *
348  * The return value will be the number of lines actually skipped.  If skipping
349  * num_lines would move beyond the end of the image, then the actual number of
350  * lines remaining in the image is returned.  Otherwise, the return value will
351  * be equal to num_lines.
352  *
353  * Refer to libjpeg.txt for more information.
354  */
355 
356 GLOBAL(JDIMENSION)
jpeg_skip_scanlines(j_decompress_ptr cinfo,JDIMENSION num_lines)357 jpeg_skip_scanlines (j_decompress_ptr cinfo, JDIMENSION num_lines)
358 {
359   my_main_ptr main_ptr = (my_main_ptr) cinfo->main;
360   my_coef_ptr coef = (my_coef_ptr) cinfo->coef;
361   my_upsample_ptr upsample = (my_upsample_ptr) cinfo->upsample;
362   JDIMENSION i, x;
363   int y;
364   JDIMENSION lines_per_iMCU_row, lines_left_in_iMCU_row, lines_after_iMCU_row;
365   JDIMENSION lines_to_skip, lines_to_read;
366 
367   if (cinfo->global_state != DSTATE_SCANNING)
368     ERREXIT1(cinfo, JERR_BAD_STATE, cinfo->global_state);
369 
370   /* Do not skip past the bottom of the image. */
371   if (cinfo->output_scanline + num_lines >= cinfo->output_height) {
372     cinfo->output_scanline = cinfo->output_height;
373     return cinfo->output_height - cinfo->output_scanline;
374   }
375 
376   if (num_lines == 0)
377     return 0;
378 
379   lines_per_iMCU_row = cinfo->_min_DCT_scaled_size * cinfo->max_v_samp_factor;
380   lines_left_in_iMCU_row =
381     (lines_per_iMCU_row - (cinfo->output_scanline % lines_per_iMCU_row)) %
382     lines_per_iMCU_row;
383   lines_after_iMCU_row = num_lines - lines_left_in_iMCU_row;
384 
385   /* Skip the lines remaining in the current iMCU row.  When upsampling
386    * requires context rows, we need the previous and next rows in order to read
387    * the current row.  This adds some complexity.
388    */
389   if (cinfo->upsample->need_context_rows) {
390     /* If the skipped lines would not move us past the current iMCU row, we
391      * read the lines and ignore them.  There might be a faster way of doing
392      * this, but we are facing increasing complexity for diminishing returns.
393      * The increasing complexity would be a by-product of meddling with the
394      * state machine used to skip context rows.  Near the end of an iMCU row,
395      * the next iMCU row may have already been entropy-decoded.  In this unique
396      * case, we will read the next iMCU row if we cannot skip past it as well.
397      */
398     if ((num_lines < lines_left_in_iMCU_row + 1) ||
399         (lines_left_in_iMCU_row <= 1 && main_ptr->buffer_full &&
400          lines_after_iMCU_row < lines_per_iMCU_row + 1)) {
401       read_and_discard_scanlines(cinfo, num_lines);
402       return num_lines;
403     }
404 
405     /* If the next iMCU row has already been entropy-decoded, make sure that
406      * we do not skip too far.
407      */
408     if (lines_left_in_iMCU_row <= 1 && main_ptr->buffer_full) {
409       cinfo->output_scanline += lines_left_in_iMCU_row + lines_per_iMCU_row;
410       lines_after_iMCU_row -= lines_per_iMCU_row;
411     } else {
412       cinfo->output_scanline += lines_left_in_iMCU_row;
413     }
414 
415     /* If we have just completed the first block, adjust the buffer pointers */
416     if (main_ptr->iMCU_row_ctr == 0 ||
417         (main_ptr->iMCU_row_ctr == 1 && lines_left_in_iMCU_row > 2))
418       set_wraparound_pointers(cinfo);
419     main_ptr->buffer_full = FALSE;
420     main_ptr->rowgroup_ctr = 0;
421     main_ptr->context_state = CTX_PREPARE_FOR_IMCU;
422     upsample->next_row_out = cinfo->max_v_samp_factor;
423     upsample->rows_to_go = cinfo->output_height - cinfo->output_scanline;
424   }
425 
426   /* Skipping is much simpler when context rows are not required. */
427   else {
428     if (num_lines < lines_left_in_iMCU_row) {
429       increment_simple_rowgroup_ctr(cinfo, num_lines);
430       return num_lines;
431     } else {
432       cinfo->output_scanline += lines_left_in_iMCU_row;
433       main_ptr->buffer_full = FALSE;
434       main_ptr->rowgroup_ctr = 0;
435       upsample->next_row_out = cinfo->max_v_samp_factor;
436       upsample->rows_to_go = cinfo->output_height - cinfo->output_scanline;
437     }
438   }
439 
440   /* Calculate how many full iMCU rows we can skip. */
441   if (cinfo->upsample->need_context_rows)
442     lines_to_skip = ((lines_after_iMCU_row - 1) / lines_per_iMCU_row) *
443                     lines_per_iMCU_row;
444   else
445     lines_to_skip = (lines_after_iMCU_row / lines_per_iMCU_row) *
446                     lines_per_iMCU_row;
447   /* Calculate the number of lines that remain to be skipped after skipping all
448    * of the full iMCU rows that we can.  We will not read these lines unless we
449    * have to.
450    */
451   lines_to_read = lines_after_iMCU_row - lines_to_skip;
452 
453   /* For images requiring multiple scans (progressive, non-interleaved, etc.),
454    * all of the entropy decoding occurs in jpeg_start_decompress(), assuming
455    * that the input data source is non-suspending.  This makes skipping easy.
456    */
457   if (cinfo->inputctl->has_multiple_scans) {
458     if (cinfo->upsample->need_context_rows) {
459       cinfo->output_scanline += lines_to_skip;
460       cinfo->output_iMCU_row += lines_to_skip / lines_per_iMCU_row;
461       main_ptr->iMCU_row_ctr += lines_after_iMCU_row / lines_per_iMCU_row;
462       /* It is complex to properly move to the middle of a context block, so
463        * read the remaining lines instead of skipping them.
464        */
465       read_and_discard_scanlines(cinfo, lines_to_read);
466     } else {
467       cinfo->output_scanline += lines_to_skip;
468       cinfo->output_iMCU_row += lines_to_skip / lines_per_iMCU_row;
469       increment_simple_rowgroup_ctr(cinfo, lines_to_read);
470     }
471     upsample->rows_to_go = cinfo->output_height - cinfo->output_scanline;
472     return num_lines;
473   }
474 
475   /* Skip the iMCU rows that we can safely skip. */
476   for (i = 0; i < lines_to_skip; i += lines_per_iMCU_row) {
477     for (y = 0; y < coef->MCU_rows_per_iMCU_row; y++) {
478       for (x = 0; x < cinfo->MCUs_per_row; x++) {
479         /* Calling decode_mcu() with a NULL pointer causes it to discard the
480          * decoded coefficients.  This is ~5% faster for large subsets, but
481          * it's tough to tell a difference for smaller images.
482          */
483         (*cinfo->entropy->decode_mcu) (cinfo, NULL);
484       }
485     }
486     cinfo->input_iMCU_row++;
487     cinfo->output_iMCU_row++;
488     if (cinfo->input_iMCU_row < cinfo->total_iMCU_rows)
489       start_iMCU_row(cinfo);
490     else
491       (*cinfo->inputctl->finish_input_pass) (cinfo);
492   }
493   cinfo->output_scanline += lines_to_skip;
494 
495   if (cinfo->upsample->need_context_rows) {
496     /* Context-based upsampling keeps track of iMCU rows. */
497     main_ptr->iMCU_row_ctr += lines_to_skip / lines_per_iMCU_row;
498 
499     /* It is complex to properly move to the middle of a context block, so
500      * read the remaining lines instead of skipping them.
501      */
502     read_and_discard_scanlines(cinfo, lines_to_read);
503   } else {
504     increment_simple_rowgroup_ctr(cinfo, lines_to_read);
505   }
506 
507   /* Since skipping lines involves skipping the upsampling step, the value of
508    * "rows_to_go" will become invalid unless we set it here.  NOTE: This is a
509    * bit odd, since "rows_to_go" seems to be redundantly keeping track of
510    * output_scanline.
511    */
512   upsample->rows_to_go = cinfo->output_height - cinfo->output_scanline;
513 
514   /* Always skip the requested number of lines. */
515   return num_lines;
516 }
517 
518 /*
519  * Alternate entry point to read raw data.
520  * Processes exactly one iMCU row per call, unless suspended.
521  */
522 
523 GLOBAL(JDIMENSION)
jpeg_read_raw_data(j_decompress_ptr cinfo,JSAMPIMAGE data,JDIMENSION max_lines)524 jpeg_read_raw_data (j_decompress_ptr cinfo, JSAMPIMAGE data,
525                     JDIMENSION max_lines)
526 {
527   JDIMENSION lines_per_iMCU_row;
528 
529   if (cinfo->global_state != DSTATE_RAW_OK)
530     ERREXIT1(cinfo, JERR_BAD_STATE, cinfo->global_state);
531   if (cinfo->output_scanline >= cinfo->output_height) {
532     WARNMS(cinfo, JWRN_TOO_MUCH_DATA);
533     return 0;
534   }
535 
536   /* Call progress monitor hook if present */
537   if (cinfo->progress != NULL) {
538     cinfo->progress->pass_counter = (long) cinfo->output_scanline;
539     cinfo->progress->pass_limit = (long) cinfo->output_height;
540     (*cinfo->progress->progress_monitor) ((j_common_ptr) cinfo);
541   }
542 
543   /* Verify that at least one iMCU row can be returned. */
544   lines_per_iMCU_row = cinfo->max_v_samp_factor * cinfo->_min_DCT_scaled_size;
545   if (max_lines < lines_per_iMCU_row)
546     ERREXIT(cinfo, JERR_BUFFER_SIZE);
547 
548   /* Decompress directly into user's buffer. */
549   if (! (*cinfo->coef->decompress_data) (cinfo, data))
550     return 0;                   /* suspension forced, can do nothing more */
551 
552   /* OK, we processed one iMCU row. */
553   cinfo->output_scanline += lines_per_iMCU_row;
554   return lines_per_iMCU_row;
555 }
556 
557 
558 /* Additional entry points for buffered-image mode. */
559 
560 #ifdef D_MULTISCAN_FILES_SUPPORTED
561 
562 /*
563  * Initialize for an output pass in buffered-image mode.
564  */
565 
566 GLOBAL(boolean)
jpeg_start_output(j_decompress_ptr cinfo,int scan_number)567 jpeg_start_output (j_decompress_ptr cinfo, int scan_number)
568 {
569   if (cinfo->global_state != DSTATE_BUFIMAGE &&
570       cinfo->global_state != DSTATE_PRESCAN)
571     ERREXIT1(cinfo, JERR_BAD_STATE, cinfo->global_state);
572   /* Limit scan number to valid range */
573   if (scan_number <= 0)
574     scan_number = 1;
575   if (cinfo->inputctl->eoi_reached &&
576       scan_number > cinfo->input_scan_number)
577     scan_number = cinfo->input_scan_number;
578   cinfo->output_scan_number = scan_number;
579   /* Perform any dummy output passes, and set up for the real pass */
580   return output_pass_setup(cinfo);
581 }
582 
583 
584 /*
585  * Finish up after an output pass in buffered-image mode.
586  *
587  * Returns FALSE if suspended.  The return value need be inspected only if
588  * a suspending data source is used.
589  */
590 
591 GLOBAL(boolean)
jpeg_finish_output(j_decompress_ptr cinfo)592 jpeg_finish_output (j_decompress_ptr cinfo)
593 {
594   if ((cinfo->global_state == DSTATE_SCANNING ||
595        cinfo->global_state == DSTATE_RAW_OK) && cinfo->buffered_image) {
596     /* Terminate this pass. */
597     /* We do not require the whole pass to have been completed. */
598     (*cinfo->master->finish_output_pass) (cinfo);
599     cinfo->global_state = DSTATE_BUFPOST;
600   } else if (cinfo->global_state != DSTATE_BUFPOST) {
601     /* BUFPOST = repeat call after a suspension, anything else is error */
602     ERREXIT1(cinfo, JERR_BAD_STATE, cinfo->global_state);
603   }
604   /* Read markers looking for SOS or EOI */
605   while (cinfo->input_scan_number <= cinfo->output_scan_number &&
606          ! cinfo->inputctl->eoi_reached) {
607     if ((*cinfo->inputctl->consume_input) (cinfo) == JPEG_SUSPENDED)
608       return FALSE;             /* Suspend, come back later */
609   }
610   cinfo->global_state = DSTATE_BUFIMAGE;
611   return TRUE;
612 }
613 
614 #endif /* D_MULTISCAN_FILES_SUPPORTED */
615