/*
 * 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;
    }
}