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