/*
 * jdtrans.c
 *
 * Copyright (C) 1995, Thomas G. Lane.
 * 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.
 *
 * 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;
	} else if ( cinfo->global_state != DSTATE_RDCOEFS ) {
		ERREXIT1( cinfo, JERR_BAD_STATE, cinfo->global_state );
	}
	/* 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;
	return cinfo->coef->coef_arrays;
}


/*
 * 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 ) {
	/* Entropy decoding: either Huffman or arithmetic coding. */
	if ( cinfo->arith_code ) {
		ERREXIT( cinfo, JERR_ARITH_NOTIMPL );
	} 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;
	}
}
