/*
 * jdtrans.c
 *
 * This file was part of the Independent JPEG Group's software:
 * Copyright (C) 1995-1997, Thomas G. Lane.
 * It was modified by The libjpeg-turbo Project to include only code relevant
 * to libjpeg-turbo.
 * For conditions of distribution and use, see the accompanying README.ijg
 * 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(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;

#if JPEG_LIB_VERSION >= 80
	/* Compute output image dimensions and related values. */
	jpeg_core_output_dimensions(cinfo);
#endif

	/* Entropy decoding: either Huffman or arithmetic coding. */
	if (cinfo->arith_code) {
#ifdef D_ARITH_CODING_SUPPORTED
		jinit_arith_decoder(cinfo);
#else
		ERREXIT(cinfo, JERR_ARITH_NOTIMPL);
#endif
	} else {
		if (cinfo->progressive_mode) {
#ifdef D_PROGRESSIVE_SUPPORTED
			jinit_phuff_decoder(cinfo);
#else
			ERREXIT(cinfo, JERR_NOT_COMPILED);
#endif
		} 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;
	}
}
