dll/3rdparty/libjpeg/jdmaster.c

   1 /*
   2  * jdmaster.c
   3  *
   4  * Copyright (C) 1991-1997, Thomas G. Lane.
   5  * Modified 2002-2013 by Guido Vollbeding.
   6  * This file is part of the Independent JPEG Group's software.
   7  * For conditions of distribution and use, see the accompanying README file.
   8  *
   9  * This file contains master control logic for the JPEG decompressor.
  10  * These routines are concerned with selecting the modules to be executed
  11  * and with determining the number of passes and the work to be done in each
  12  * pass.
  13  */
  14
  15 #define JPEG_INTERNALS
  16 #include "jinclude.h"
  17 #include "jpeglib.h"
  18
  19
  20 /* Private state */
  21
  22 typedef struct {
  23   struct jpeg_decomp_master pub; /* public fields */
  24
  25   int pass_number;              /* # of passes completed */
  26
  27   boolean using_merged_upsample; /* TRUE if using merged upsample/cconvert */
  28
  29   /* Saved references to initialized quantizer modules,
  30    * in case we need to switch modes.
  31    */
  32   struct jpeg_color_quantizer * quantizer_1pass;
  33   struct jpeg_color_quantizer * quantizer_2pass;
  34 } my_decomp_master;
  35
  36 typedef my_decomp_master * my_master_ptr;
  37
  38
  39 /*
  40  * Determine whether merged upsample/color conversion should be used.
  41  * CRUCIAL: this must match the actual capabilities of jdmerge.c!
  42  */
  43
  44 LOCAL(boolean)
  45 use_merged_upsample (j_decompress_ptr cinfo)
  46 {
  47 #ifdef UPSAMPLE_MERGING_SUPPORTED
  48   /* Merging is the equivalent of plain box-filter upsampling */
  49   if (cinfo->do_fancy_upsampling || cinfo->CCIR601_sampling)
  50     return FALSE;
  51   /* jdmerge.c only supports YCC=>RGB color conversion */
  52   if (cinfo->jpeg_color_space != JCS_YCbCr || cinfo->num_components != 3 ||
  53       cinfo->out_color_space != JCS_RGB ||
  54       cinfo->out_color_components != RGB_PIXELSIZE ||
  55       cinfo->color_transform)
  56     return FALSE;
  57   /* and it only handles 2h1v or 2h2v sampling ratios */
  58   if (cinfo->comp_info[0].h_samp_factor != 2 ||
  59       cinfo->comp_info[1].h_samp_factor != 1 ||
  60       cinfo->comp_info[2].h_samp_factor != 1 ||
  61       cinfo->comp_info[0].v_samp_factor >  2 ||
  62       cinfo->comp_info[1].v_samp_factor != 1 ||
  63       cinfo->comp_info[2].v_samp_factor != 1)
  64     return FALSE;
  65   /* furthermore, it doesn't work if we've scaled the IDCTs differently */
  66   if (cinfo->comp_info[0].DCT_h_scaled_size != cinfo->min_DCT_h_scaled_size ||
  67       cinfo->comp_info[1].DCT_h_scaled_size != cinfo->min_DCT_h_scaled_size ||
  68       cinfo->comp_info[2].DCT_h_scaled_size != cinfo->min_DCT_h_scaled_size ||
  69       cinfo->comp_info[0].DCT_v_scaled_size != cinfo->min_DCT_v_scaled_size ||
  70       cinfo->comp_info[1].DCT_v_scaled_size != cinfo->min_DCT_v_scaled_size ||
  71       cinfo->comp_info[2].DCT_v_scaled_size != cinfo->min_DCT_v_scaled_size)
  72     return FALSE;
  73   /* ??? also need to test for upsample-time rescaling, when & if supported */
  74   return TRUE;                  /* by golly, it'll work... */
  75 #else
  76   return FALSE;
  77 #endif
  78 }
  79
  80
  81 /*
  82  * Compute output image dimensions and related values.
  83  * NOTE: this is exported for possible use by application.
  84  * Hence it mustn't do anything that can't be done twice.
  85  * Also note that it may be called before the master module is initialized!
  86  */
  87
  88 GLOBAL(void)
  89 jpeg_calc_output_dimensions (j_decompress_ptr cinfo)
  90 /* Do computations that are needed before master selection phase.
  91  * This function is used for full decompression.
  92  */
  93 {
  94 #ifdef IDCT_SCALING_SUPPORTED
  95   int ci;
  96   jpeg_component_info *compptr;
  97 #endif
  98
  99   /* Prevent application from calling me at wrong times */
 100   if (cinfo->global_state != DSTATE_READY)
 101     ERREXIT1(cinfo, JERR_BAD_STATE, cinfo->global_state);
 102
 103   /* Compute core output image dimensions and DCT scaling choices. */
 104   jpeg_core_output_dimensions(cinfo);
 105
 106 #ifdef IDCT_SCALING_SUPPORTED
 107
 108   /* In selecting the actual DCT scaling for each component, we try to
 109    * scale up the chroma components via IDCT scaling rather than upsampling.
 110    * This saves time if the upsampler gets to use 1:1 scaling.
 111    * Note this code adapts subsampling ratios which are powers of 2.
 112    */
 113   for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
 114        ci++, compptr++) {
 115     int ssize = 1;
 116     while (cinfo->min_DCT_h_scaled_size * ssize <=
 117            (cinfo->do_fancy_upsampling ? DCTSIZE : DCTSIZE / 2) &&
 118            (cinfo->max_h_samp_factor % (compptr->h_samp_factor * ssize * 2)) == 0) {
 119       ssize = ssize * 2;
 120     }
 121     compptr->DCT_h_scaled_size = cinfo->min_DCT_h_scaled_size * ssize;
 122     ssize = 1;
 123     while (cinfo->min_DCT_v_scaled_size * ssize <=
 124            (cinfo->do_fancy_upsampling ? DCTSIZE : DCTSIZE / 2) &&
 125            (cinfo->max_v_samp_factor % (compptr->v_samp_factor * ssize * 2)) == 0) {
 126       ssize = ssize * 2;
 127     }
 128     compptr->DCT_v_scaled_size = cinfo->min_DCT_v_scaled_size * ssize;
 129
 130     /* We don't support IDCT ratios larger than 2. */
 131     if (compptr->DCT_h_scaled_size > compptr->DCT_v_scaled_size * 2)
 132         compptr->DCT_h_scaled_size = compptr->DCT_v_scaled_size * 2;
 133     else if (compptr->DCT_v_scaled_size > compptr->DCT_h_scaled_size * 2)
 134         compptr->DCT_v_scaled_size = compptr->DCT_h_scaled_size * 2;
 135   }
 136
 137   /* Recompute downsampled dimensions of components;
 138    * application needs to know these if using raw downsampled data.
 139    */
 140   for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
 141        ci++, compptr++) {
 142     /* Size in samples, after IDCT scaling */
 143     compptr->downsampled_width = (JDIMENSION)
 144       jdiv_round_up((long) cinfo->image_width *
 145                     (long) (compptr->h_samp_factor * compptr->DCT_h_scaled_size),
 146                     (long) (cinfo->max_h_samp_factor * cinfo->block_size));
 147     compptr->downsampled_height = (JDIMENSION)
 148       jdiv_round_up((long) cinfo->image_height *
 149                     (long) (compptr->v_samp_factor * compptr->DCT_v_scaled_size),
 150                     (long) (cinfo->max_v_samp_factor * cinfo->block_size));
 151   }
 152
 153 #endif /* IDCT_SCALING_SUPPORTED */
 154
 155   /* Report number of components in selected colorspace. */
 156   /* Probably this should be in the color conversion module... */
 157   switch (cinfo->out_color_space) {
 158   case JCS_GRAYSCALE:
 159     cinfo->out_color_components = 1;
 160     break;
 161   case JCS_RGB:
 162   case JCS_BG_RGB:
 163     cinfo->out_color_components = RGB_PIXELSIZE;
 164     break;
 165   case JCS_YCbCr:
 166   case JCS_BG_YCC:
 167     cinfo->out_color_components = 3;
 168     break;
 169   case JCS_CMYK:
 170   case JCS_YCCK:
 171     cinfo->out_color_components = 4;
 172     break;
 173   default:                      /* else must be same colorspace as in file */
 174     cinfo->out_color_components = cinfo->num_components;
 175     break;
 176   }
 177   cinfo->output_components = (cinfo->quantize_colors ? 1 :
 178                               cinfo->out_color_components);
 179
 180   /* See if upsampler will want to emit more than one row at a time */
 181   if (use_merged_upsample(cinfo))
 182     cinfo->rec_outbuf_height = cinfo->max_v_samp_factor;
 183   else
 184     cinfo->rec_outbuf_height = 1;
 185 }
 186
 187
 188 /*
 189  * Several decompression processes need to range-limit values to the range
 190  * 0..MAXJSAMPLE; the input value may fall somewhat outside this range
 191  * due to noise introduced by quantization, roundoff error, etc.  These
 192  * processes are inner loops and need to be as fast as possible.  On most
 193  * machines, particularly CPUs with pipelines or instruction prefetch,
 194  * a (subscript-check-less) C table lookup
 195  *              x = sample_range_limit[x];
 196  * is faster than explicit tests
 197  *              if (x < 0)  x = 0;
 198  *              else if (x > MAXJSAMPLE)  x = MAXJSAMPLE;
 199  * These processes all use a common table prepared by the routine below.
 200  *
 201  * For most steps we can mathematically guarantee that the initial value
 202  * of x is within MAXJSAMPLE+1 of the legal range, so a table running from
 203  * -(MAXJSAMPLE+1) to 2*MAXJSAMPLE+1 is sufficient.  But for the initial
 204  * limiting step (just after the IDCT), a wildly out-of-range value is
 205  * possible if the input data is corrupt.  To avoid any chance of indexing
 206  * off the end of memory and getting a bad-pointer trap, we perform the
 207  * post-IDCT limiting thus:
 208  *              x = range_limit[x & MASK];
 209  * where MASK is 2 bits wider than legal sample data, ie 10 bits for 8-bit
 210  * samples.  Under normal circumstances this is more than enough range and
 211  * a correct output will be generated; with bogus input data the mask will
 212  * cause wraparound, and we will safely generate a bogus-but-in-range output.
 213  * For the post-IDCT step, we want to convert the data from signed to unsigned
 214  * representation by adding CENTERJSAMPLE at the same time that we limit it.
 215  * So the post-IDCT limiting table ends up looking like this:
 216  *   CENTERJSAMPLE,CENTERJSAMPLE+1,...,MAXJSAMPLE,
 217  *   MAXJSAMPLE (repeat 2*(MAXJSAMPLE+1)-CENTERJSAMPLE times),
 218  *   0          (repeat 2*(MAXJSAMPLE+1)-CENTERJSAMPLE times),
 219  *   0,1,...,CENTERJSAMPLE-1
 220  * Negative inputs select values from the upper half of the table after
 221  * masking.
 222  *
 223  * We can save some space by overlapping the start of the post-IDCT table
 224  * with the simpler range limiting table.  The post-IDCT table begins at
 225  * sample_range_limit + CENTERJSAMPLE.
 226  *
 227  * Note that the table is allocated in near data space on PCs; it's small
 228  * enough and used often enough to justify this.
 229  */
 230
 231 LOCAL(void)
 232 prepare_range_limit_table (j_decompress_ptr cinfo)
 233 /* Allocate and fill in the sample_range_limit table */
 234 {
 235   JSAMPLE * table;
 236   int i;
 237
 238   table = (JSAMPLE *)
 239     (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
 240                 (5 * (MAXJSAMPLE+1) + CENTERJSAMPLE) * SIZEOF(JSAMPLE));
 241   table += (MAXJSAMPLE+1);      /* allow negative subscripts of simple table */
 242   cinfo->sample_range_limit = table;
 243   /* First segment of "simple" table: limit[x] = 0 for x < 0 */
 244   MEMZERO(table - (MAXJSAMPLE+1), (MAXJSAMPLE+1) * SIZEOF(JSAMPLE));
 245   /* Main part of "simple" table: limit[x] = x */
 246   for (i = 0; i <= MAXJSAMPLE; i++)
 247     table[i] = (JSAMPLE) i;
 248   table += CENTERJSAMPLE;       /* Point to where post-IDCT table starts */
 249   /* End of simple table, rest of first half of post-IDCT table */
 250   for (i = CENTERJSAMPLE; i < 2*(MAXJSAMPLE+1); i++)
 251     table[i] = MAXJSAMPLE;
 252   /* Second half of post-IDCT table */
 253   MEMZERO(table + (2 * (MAXJSAMPLE+1)),
 254           (2 * (MAXJSAMPLE+1) - CENTERJSAMPLE) * SIZEOF(JSAMPLE));
 255   MEMCOPY(table + (4 * (MAXJSAMPLE+1) - CENTERJSAMPLE),
 256           cinfo->sample_range_limit, CENTERJSAMPLE * SIZEOF(JSAMPLE));
 257 }
 258
 259
 260 /*
 261  * Master selection of decompression modules.
 262  * This is done once at jpeg_start_decompress time.  We determine
 263  * which modules will be used and give them appropriate initialization calls.
 264  * We also initialize the decompressor input side to begin consuming data.
 265  *
 266  * Since jpeg_read_header has finished, we know what is in the SOF
 267  * and (first) SOS markers.  We also have all the application parameter
 268  * settings.
 269  */
 270
 271 LOCAL(void)
 272 master_selection (j_decompress_ptr cinfo)
 273 {
 274   my_master_ptr master = (my_master_ptr) cinfo->master;
 275   boolean use_c_buffer;
 276   long samplesperrow;
 277   JDIMENSION jd_samplesperrow;
 278
 279   /* For now, precision must match compiled-in value... */
 280   if (cinfo->data_precision != BITS_IN_JSAMPLE)
 281     ERREXIT1(cinfo, JERR_BAD_PRECISION, cinfo->data_precision);
 282
 283   /* Initialize dimensions and other stuff */
 284   jpeg_calc_output_dimensions(cinfo);
 285   prepare_range_limit_table(cinfo);
 286
 287   /* Sanity check on image dimensions */
 288   if (cinfo->output_height <= 0 || cinfo->output_width <= 0 ||
 289       cinfo->out_color_components <= 0)
 290     ERREXIT(cinfo, JERR_EMPTY_IMAGE);
 291
 292   /* Width of an output scanline must be representable as JDIMENSION. */
 293   samplesperrow = (long) cinfo->output_width * (long) cinfo->out_color_components;
 294   jd_samplesperrow = (JDIMENSION) samplesperrow;
 295   if ((long) jd_samplesperrow != samplesperrow)
 296     ERREXIT(cinfo, JERR_WIDTH_OVERFLOW);
 297
 298   /* Initialize my private state */
 299   master->pass_number = 0;
 300   master->using_merged_upsample = use_merged_upsample(cinfo);
 301
 302   /* Color quantizer selection */
 303   master->quantizer_1pass = NULL;
 304   master->quantizer_2pass = NULL;
 305   /* No mode changes if not using buffered-image mode. */
 306   if (! cinfo->quantize_colors || ! cinfo->buffered_image) {
 307     cinfo->enable_1pass_quant = FALSE;
 308     cinfo->enable_external_quant = FALSE;
 309     cinfo->enable_2pass_quant = FALSE;
 310   }
 311   if (cinfo->quantize_colors) {
 312     if (cinfo->raw_data_out)
 313       ERREXIT(cinfo, JERR_NOTIMPL);
 314     /* 2-pass quantizer only works in 3-component color space. */
 315     if (cinfo->out_color_components != 3) {
 316       cinfo->enable_1pass_quant = TRUE;
 317       cinfo->enable_external_quant = FALSE;
 318       cinfo->enable_2pass_quant = FALSE;
 319       cinfo->colormap = NULL;
 320     } else if (cinfo->colormap != NULL) {
 321       cinfo->enable_external_quant = TRUE;
 322     } else if (cinfo->two_pass_quantize) {
 323       cinfo->enable_2pass_quant = TRUE;
 324     } else {
 325       cinfo->enable_1pass_quant = TRUE;
 326     }
 327
 328     if (cinfo->enable_1pass_quant) {
 329 #ifdef QUANT_1PASS_SUPPORTED
 330       jinit_1pass_quantizer(cinfo);
 331       master->quantizer_1pass = cinfo->cquantize;
 332 #else
 333       ERREXIT(cinfo, JERR_NOT_COMPILED);
 334 #endif
 335     }
 336
 337     /* We use the 2-pass code to map to external colormaps. */
 338     if (cinfo->enable_2pass_quant || cinfo->enable_external_quant) {
 339 #ifdef QUANT_2PASS_SUPPORTED
 340       jinit_2pass_quantizer(cinfo);
 341       master->quantizer_2pass = cinfo->cquantize;
 342 #else
 343       ERREXIT(cinfo, JERR_NOT_COMPILED);
 344 #endif
 345     }
 346     /* If both quantizers are initialized, the 2-pass one is left active;
 347      * this is necessary for starting with quantization to an external map.
 348      */
 349   }
 350
 351   /* Post-processing: in particular, color conversion first */
 352   if (! cinfo->raw_data_out) {
 353     if (master->using_merged_upsample) {
 354 #ifdef UPSAMPLE_MERGING_SUPPORTED
 355       jinit_merged_upsampler(cinfo); /* does color conversion too */
 356 #else
 357       ERREXIT(cinfo, JERR_NOT_COMPILED);
 358 #endif
 359     } else {
 360       jinit_color_deconverter(cinfo);
 361       jinit_upsampler(cinfo);
 362     }
 363     jinit_d_post_controller(cinfo, cinfo->enable_2pass_quant);
 364   }
 365   /* Inverse DCT */
 366   jinit_inverse_dct(cinfo);
 367   /* Entropy decoding: either Huffman or arithmetic coding. */
 368   if (cinfo->arith_code)
 369     jinit_arith_decoder(cinfo);
 370   else {
 371     jinit_huff_decoder(cinfo);
 372   }
 373
 374   /* Initialize principal buffer controllers. */
 375   use_c_buffer = cinfo->inputctl->has_multiple_scans || cinfo->buffered_image;
 376   jinit_d_coef_controller(cinfo, use_c_buffer);
 377
 378   if (! cinfo->raw_data_out)
 379     jinit_d_main_controller(cinfo, FALSE /* never need full buffer here */);
 380
 381   /* We can now tell the memory manager to allocate virtual arrays. */
 382   (*cinfo->mem->realize_virt_arrays) ((j_common_ptr) cinfo);
 383
 384   /* Initialize input side of decompressor to consume first scan. */
 385   (*cinfo->inputctl->start_input_pass) (cinfo);
 386
 387 #ifdef D_MULTISCAN_FILES_SUPPORTED
 388   /* If jpeg_start_decompress will read the whole file, initialize
 389    * progress monitoring appropriately.  The input step is counted
 390    * as one pass.
 391    */
 392   if (cinfo->progress != NULL && ! cinfo->buffered_image &&
 393       cinfo->inputctl->has_multiple_scans) {
 394     int nscans;
 395     /* Estimate number of scans to set pass_limit. */
 396     if (cinfo->progressive_mode) {
 397       /* Arbitrarily estimate 2 interleaved DC scans + 3 AC scans/component. */
 398       nscans = 2 + 3 * cinfo->num_components;
 399     } else {
 400       /* For a nonprogressive multiscan file, estimate 1 scan per component. */
 401       nscans = cinfo->num_components;
 402     }
 403     cinfo->progress->pass_counter = 0L;
 404     cinfo->progress->pass_limit = (long) cinfo->total_iMCU_rows * nscans;
 405     cinfo->progress->completed_passes = 0;
 406     cinfo->progress->total_passes = (cinfo->enable_2pass_quant ? 3 : 2);
 407     /* Count the input pass as done */
 408     master->pass_number++;
 409   }
 410 #endif /* D_MULTISCAN_FILES_SUPPORTED */
 411 }
 412
 413
 414 /*
 415  * Per-pass setup.
 416  * This is called at the beginning of each output pass.  We determine which
 417  * modules will be active during this pass and give them appropriate
 418  * start_pass calls.  We also set is_dummy_pass to indicate whether this
 419  * is a "real" output pass or a dummy pass for color quantization.
 420  * (In the latter case, jdapistd.c will crank the pass to completion.)
 421  */
 422
 423 METHODDEF(void)
 424 prepare_for_output_pass (j_decompress_ptr cinfo)
 425 {
 426   my_master_ptr master = (my_master_ptr) cinfo->master;
 427
 428   if (master->pub.is_dummy_pass) {
 429 #ifdef QUANT_2PASS_SUPPORTED
 430     /* Final pass of 2-pass quantization */
 431     master->pub.is_dummy_pass = FALSE;
 432     (*cinfo->cquantize->start_pass) (cinfo, FALSE);
 433     (*cinfo->post->start_pass) (cinfo, JBUF_CRANK_DEST);
 434     (*cinfo->main->start_pass) (cinfo, JBUF_CRANK_DEST);
 435 #else
 436     ERREXIT(cinfo, JERR_NOT_COMPILED);
 437 #endif /* QUANT_2PASS_SUPPORTED */
 438   } else {
 439     if (cinfo->quantize_colors && cinfo->colormap == NULL) {
 440       /* Select new quantization method */
 441       if (cinfo->two_pass_quantize && cinfo->enable_2pass_quant) {
 442         cinfo->cquantize = master->quantizer_2pass;
 443         master->pub.is_dummy_pass = TRUE;
 444       } else if (cinfo->enable_1pass_quant) {
 445         cinfo->cquantize = master->quantizer_1pass;
 446       } else {
 447         ERREXIT(cinfo, JERR_MODE_CHANGE);
 448       }
 449     }
 450     (*cinfo->idct->start_pass) (cinfo);
 451     (*cinfo->coef->start_output_pass) (cinfo);
 452     if (! cinfo->raw_data_out) {
 453       if (! master->using_merged_upsample)
 454         (*cinfo->cconvert->start_pass) (cinfo);
 455       (*cinfo->upsample->start_pass) (cinfo);
 456       if (cinfo->quantize_colors)
 457         (*cinfo->cquantize->start_pass) (cinfo, master->pub.is_dummy_pass);
 458       (*cinfo->post->start_pass) (cinfo,
 459             (master->pub.is_dummy_pass ? JBUF_SAVE_AND_PASS : JBUF_PASS_THRU));
 460       (*cinfo->main->start_pass) (cinfo, JBUF_PASS_THRU);
 461     }
 462   }
 463
 464   /* Set up progress monitor's pass info if present */
 465   if (cinfo->progress != NULL) {
 466     cinfo->progress->completed_passes = master->pass_number;
 467     cinfo->progress->total_passes = master->pass_number +
 468                                     (master->pub.is_dummy_pass ? 2 : 1);
 469     /* In buffered-image mode, we assume one more output pass if EOI not
 470      * yet reached, but no more passes if EOI has been reached.
 471      */
 472     if (cinfo->buffered_image && ! cinfo->inputctl->eoi_reached) {
 473       cinfo->progress->total_passes += (cinfo->enable_2pass_quant ? 2 : 1);
 474     }
 475   }
 476 }
 477
 478
 479 /*
 480  * Finish up at end of an output pass.
 481  */
 482
 483 METHODDEF(void)
 484 finish_output_pass (j_decompress_ptr cinfo)
 485 {
 486   my_master_ptr master = (my_master_ptr) cinfo->master;
 487
 488   if (cinfo->quantize_colors)
 489     (*cinfo->cquantize->finish_pass) (cinfo);
 490   master->pass_number++;
 491 }
 492
 493
 494 #ifdef D_MULTISCAN_FILES_SUPPORTED
 495
 496 /*
 497  * Switch to a new external colormap between output passes.
 498  */
 499
 500 GLOBAL(void)
 501 jpeg_new_colormap (j_decompress_ptr cinfo)
 502 {
 503   my_master_ptr master = (my_master_ptr) cinfo->master;
 504
 505   /* Prevent application from calling me at wrong times */
 506   if (cinfo->global_state != DSTATE_BUFIMAGE)
 507     ERREXIT1(cinfo, JERR_BAD_STATE, cinfo->global_state);
 508
 509   if (cinfo->quantize_colors && cinfo->enable_external_quant &&
 510       cinfo->colormap != NULL) {
 511     /* Select 2-pass quantizer for external colormap use */
 512     cinfo->cquantize = master->quantizer_2pass;
 513     /* Notify quantizer of colormap change */
 514     (*cinfo->cquantize->new_color_map) (cinfo);
 515     master->pub.is_dummy_pass = FALSE; /* just in case */
 516   } else
 517     ERREXIT(cinfo, JERR_MODE_CHANGE);
 518 }
 519
 520 #endif /* D_MULTISCAN_FILES_SUPPORTED */
 521
 522
 523 /*
 524  * Initialize master decompression control and select active modules.
 525  * This is performed at the start of jpeg_start_decompress.
 526  */
 527
 528 GLOBAL(void)
 529 jinit_master_decompress (j_decompress_ptr cinfo)
 530 {
 531   my_master_ptr master;
 532
 533   master = (my_master_ptr)
 534       (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
 535                                   SIZEOF(my_decomp_master));
 536   cinfo->master = &master->pub;
 537   master->pub.prepare_for_output_pass = prepare_for_output_pass;
 538   master->pub.finish_output_pass = finish_output_pass;
 539
 540   master->pub.is_dummy_pass = FALSE;
 541
 542   master_selection(cinfo);
 543 }