text: /*
   * jdtrans.c
   *
   * Copyright (C) 1995-1997, Thomas G. Lane.
   * Modified 2000-2009 by Guido Vollbeding.
   * This file is part of the Independent JPEG Group's software.
   * For conditions of distribution and use, see the accompanying README file.
   *
   * This file contains library routines for transcoding decompression,
   * that is, reading raw DCT coefficient arrays from an input JPEG file.
   * The routines in jdapimin.c will also be needed by a transcoder.
   */
  
  #define JPEG_INTERNALS
  #include "jinclude.h"
  #include "jpeglib.h"
  
  
  /* Forward declarations */
  LOCAL(void) transdecode_master_selection JPP((j_decompress_ptr cinfo));
  
  
  /*
   * Read the coefficient arrays from a JPEG file.
   * jpeg_read_header must be completed before calling this.
   *
   * The entire image is read into a set of virtual coefficient-block arrays,
   * one per component.  The return value is a pointer to the array of
   * virtual-array descriptors.  These can be manipulated directly via the
   * JPEG memory manager, or handed off to jpeg_write_coefficients().
   * To release the memory occupied by the virtual arrays, call
   * jpeg_finish_decompress() when done with the data.
   *
   * An alternative usage is to simply obtain access to the coefficient arrays
   * during a buffered-image-mode decompression operation.  This is allowed
   * after any jpeg_finish_output() call.  The arrays can be accessed until
   * jpeg_finish_decompress() is called.  (Note that any call to the library
   * may reposition the arrays, so don't rely on access_virt_barray() results
   * to stay valid across library calls.)
   *
   * Returns NULL if suspended.  This case need be checked only if
   * a suspending data source is used.
   */
  
  GLOBAL(jvirt_barray_ptr *)
  jpeg_read_coefficients (j_decompress_ptr cinfo)
  {
    if (cinfo->global_state == DSTATE_READY) {
      /* First call: initialize active modules */
      transdecode_master_selection(cinfo);
      cinfo->global_state = DSTATE_RDCOEFS;
    }
    if (cinfo->global_state == DSTATE_RDCOEFS) {
      /* Absorb whole file into the coef buffer */
      for (;;) {
        int retcode;
        /* Call progress monitor hook if present */
        if (cinfo->progress != NULL)
      (*cinfo->progress->progress_monitor) ((j_common_ptr) cinfo);
        /* Absorb some more input */
        retcode = (*cinfo->inputctl->consume_input) (cinfo);
        if (retcode == JPEG_SUSPENDED)
      return NULL;
        if (retcode == JPEG_REACHED_EOI)
      break;
        /* Advance progress counter if appropriate */
        if (cinfo->progress != NULL &&
        (retcode == JPEG_ROW_COMPLETED || retcode == JPEG_REACHED_SOS)) {
      if (++cinfo->progress->pass_counter >= cinfo->progress->pass_limit) {
        /* startup underestimated number of scans; ratchet up one scan */
        cinfo->progress->pass_limit += (long) cinfo->total_iMCU_rows;
      }
        }
      }
      /* Set state so that jpeg_finish_decompress does the right thing */
      cinfo->global_state = DSTATE_STOPPING;
    }
    /* At this point we should be in state DSTATE_STOPPING if being used
     * standalone, or in state DSTATE_BUFIMAGE if being invoked to get access
     * to the coefficients during a full buffered-image-mode decompression.
     */
    if ((cinfo->global_state == DSTATE_STOPPING ||
         cinfo->global_state == DSTATE_BUFIMAGE) && cinfo->buffered_image) {
      return cinfo->coef->coef_arrays;
    }
    /* Oops, improper usage */
    ERREXIT1(cinfo, JERR_BAD_STATE, cinfo->global_state);
    return NULL;            /* keep compiler happy */
  }
  
  
  /*
   * Master selection of decompression modules for transcoding.
   * This substitutes for jdmaster.c's initialization of the full decompressor.
   */
  
  LOCAL(void)
  transdecode_master_selection (j_decompress_ptr cinfo)
  {
    /* This is effectively a buffered-image operation. */
    cinfo->buffered_image = TRUE;
  
    /* Compute output image dimensions and related values. */
    jpeg_core_output_dimensions(cinfo);
  
    /* Entropy decoding: either Huffman or arithmetic coding. */
    if (cinfo->arith_code)
      jinit_arith_decoder(cinfo);
    else {
      jinit_huff_decoder(cinfo);
    }
  
    /* Always get a full-image coefficient buffer. */
    jinit_d_coef_controller(cinfo, TRUE);
  
    /* We can now tell the memory manager to allocate virtual arrays. */
    (*cinfo->mem->realize_virt_arrays) ((j_common_ptr) cinfo);
  
    /* Initialize input side of decompressor to consume first scan. */
    (*cinfo->inputctl->start_input_pass) (cinfo);
  
    /* Initialize progress monitoring. */
    if (cinfo->progress != NULL) {
      int nscans;
      /* Estimate number of scans to set pass_limit. */
      if (cinfo->progressive_mode) {
        /* Arbitrarily estimate 2 interleaved DC scans + 3 AC scans/component. */
        nscans = 2 + 3 * cinfo->num_components;
      } else if (cinfo->inputctl->has_multiple_scans) {
        /* For a nonprogressive multiscan file, estimate 1 scan per component. */
        nscans = cinfo->num_components;
      } else {
        nscans = 1;
      }
      cinfo->progress->pass_counter = 0L;
      cinfo->progress->pass_limit = (long) cinfo->total_iMCU_rows * nscans;
      cinfo->progress->completed_passes = 0;
      cinfo->progress->total_passes = 1;
    }
  }
  