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