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      1 /*
      2  * jdtrans.c
      3  *
      4  * Copyright (C) 1995-1997, Thomas G. Lane.
      5  * This file is part of the Independent JPEG Group's software.
      6  * For conditions of distribution and use, see the accompanying README file.
      7  *
      8  * This file contains library routines for transcoding decompression,
      9  * that is, reading raw DCT coefficient arrays from an input JPEG file.
     10  * The routines in jdapimin.c will also be needed by a transcoder.
     11  */
     12 
     13 #define JPEG_INTERNALS
     14 #include "jinclude.h"
     15 #include "jpeglib.h"
     16 
     17 
     18 /* Forward declarations */
     19 LOCAL(void) transdecode_master_selection JPP((j_decompress_ptr cinfo));
     20 
     21 
     22 /*
     23  * Read the coefficient arrays from a JPEG file.
     24  * jpeg_read_header must be completed before calling this.
     25  *
     26  * The entire image is read into a set of virtual coefficient-block arrays,
     27  * one per component.  The return value is a pointer to the array of
     28  * virtual-array descriptors.  These can be manipulated directly via the
     29  * JPEG memory manager, or handed off to jpeg_write_coefficients().
     30  * To release the memory occupied by the virtual arrays, call
     31  * jpeg_finish_decompress() when done with the data.
     32  *
     33  * An alternative usage is to simply obtain access to the coefficient arrays
     34  * during a buffered-image-mode decompression operation.  This is allowed
     35  * after any jpeg_finish_output() call.  The arrays can be accessed until
     36  * jpeg_finish_decompress() is called.  (Note that any call to the library
     37  * may reposition the arrays, so don't rely on access_virt_barray() results
     38  * to stay valid across library calls.)
     39  *
     40  * Returns NULL if suspended.  This case need be checked only if
     41  * a suspending data source is used.
     42  */
     43 
     44 GLOBAL(jvirt_barray_ptr *)
     45 jpeg_read_coefficients (j_decompress_ptr cinfo)
     46 {
     47   if (cinfo->global_state == DSTATE_READY) {
     48     /* First call: initialize active modules */
     49     transdecode_master_selection(cinfo);
     50     cinfo->global_state = DSTATE_RDCOEFS;
     51   }
     52   if (cinfo->global_state == DSTATE_RDCOEFS) {
     53     /* Absorb whole file into the coef buffer */
     54     for (;;) {
     55       int retcode;
     56       /* Call progress monitor hook if present */
     57       if (cinfo->progress != NULL)
     58 	(*cinfo->progress->progress_monitor) ((j_common_ptr) cinfo);
     59       /* Absorb some more input */
     60       retcode = (*cinfo->inputctl->consume_input) (cinfo);
     61       if (retcode == JPEG_SUSPENDED)
     62 	return NULL;
     63       if (retcode == JPEG_REACHED_EOI)
     64 	break;
     65       /* Advance progress counter if appropriate */
     66       if (cinfo->progress != NULL &&
     67 	  (retcode == JPEG_ROW_COMPLETED || retcode == JPEG_REACHED_SOS)) {
     68 	if (++cinfo->progress->pass_counter >= cinfo->progress->pass_limit) {
     69 	  /* startup underestimated number of scans; ratchet up one scan */
     70 	  cinfo->progress->pass_limit += (long) cinfo->total_iMCU_rows;
     71 	}
     72       }
     73     }
     74     /* Set state so that jpeg_finish_decompress does the right thing */
     75     cinfo->global_state = DSTATE_STOPPING;
     76   }
     77   /* At this point we should be in state DSTATE_STOPPING if being used
     78    * standalone, or in state DSTATE_BUFIMAGE if being invoked to get access
     79    * to the coefficients during a full buffered-image-mode decompression.
     80    */
     81   if ((cinfo->global_state == DSTATE_STOPPING ||
     82        cinfo->global_state == DSTATE_BUFIMAGE) && cinfo->buffered_image) {
     83     return cinfo->coef->coef_arrays;
     84   }
     85   /* Oops, improper usage */
     86   ERREXIT1(cinfo, JERR_BAD_STATE, cinfo->global_state);
     87   return NULL;			/* keep compiler happy */
     88 }
     89 
     90 
     91 /*
     92  * Master selection of decompression modules for transcoding.
     93  * This substitutes for jdmaster.c's initialization of the full decompressor.
     94  */
     95 
     96 LOCAL(void)
     97 transdecode_master_selection (j_decompress_ptr cinfo)
     98 {
     99   /* This is effectively a buffered-image operation. */
    100   cinfo->buffered_image = TRUE;
    101 
    102   /* Entropy decoding: either Huffman or arithmetic coding. */
    103   if (cinfo->arith_code) {
    104     ERREXIT(cinfo, JERR_ARITH_NOTIMPL);
    105   } else {
    106     if (cinfo->progressive_mode) {
    107 #ifdef D_PROGRESSIVE_SUPPORTED
    108       jinit_phuff_decoder(cinfo);
    109 #else
    110       ERREXIT(cinfo, JERR_NOT_COMPILED);
    111 #endif
    112     } else
    113       jinit_huff_decoder(cinfo);
    114   }
    115 
    116   /* Always get a full-image coefficient buffer. */
    117   jinit_d_coef_controller(cinfo, TRUE);
    118 
    119   /* We can now tell the memory manager to allocate virtual arrays. */
    120   (*cinfo->mem->realize_virt_arrays) ((j_common_ptr) cinfo);
    121 
    122   /* Initialize input side of decompressor to consume first scan. */
    123   (*cinfo->inputctl->start_input_pass) (cinfo);
    124 
    125   /* Initialize progress monitoring. */
    126   if (cinfo->progress != NULL) {
    127     int nscans;
    128     /* Estimate number of scans to set pass_limit. */
    129     if (cinfo->progressive_mode) {
    130       /* Arbitrarily estimate 2 interleaved DC scans + 3 AC scans/component. */
    131       nscans = 2 + 3 * cinfo->num_components;
    132     } else if (cinfo->inputctl->has_multiple_scans) {
    133       /* For a nonprogressive multiscan file, estimate 1 scan per component. */
    134       nscans = cinfo->num_components;
    135     } else {
    136       nscans = 1;
    137     }
    138     cinfo->progress->pass_counter = 0L;
    139     cinfo->progress->pass_limit = (long) cinfo->total_iMCU_rows * nscans;
    140     cinfo->progress->completed_passes = 0;
    141     cinfo->progress->total_passes = 1;
    142   }
    143 }
    144