rawTherapee/rtengine/jpeg_ijg/jpeg_memsrc.cc

/*
 * memsrc.c
 *
 * Copyright (C) 1994-1996, 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 decompression data source routines for the case of
 * reading JPEG data from a memory buffer that is preloaded with the entire
 * JPEG file.  This would not seem especially useful at first sight, but
 * a number of people have asked for it.
 * This is really just a stripped-down version of jdatasrc.c.  Comparison
 * of this code with jdatasrc.c may be helpful in seeing how to make
 * custom source managers for other purposes.
 */

/* this is not a core library module, so it doesn't define JPEG_INTERNALS */
//#include "jinclude.h"
//#include "jmorecfg.h"
//#include "jpeglib.h"
//#include "jerror.h"
#include <cstdio>
#include <jpeglib.h>
#include <jerror.h>
#include "../jpeg.h"


/* Expanded data source object for memory input */
namespace
{

typedef struct {
    struct jpeg_source_mgr pub; /* public fields */
    jmp_buf error_jmp_buf;      /* error handler for this instance */

    JOCTET eoi_buffer[2];     /* a place to put a dummy EOI */
} my_source_mgr;

typedef my_source_mgr * my_src_ptr;

}

/*
 * Initialize source --- called by jpeg_read_header
 * before any data is actually read.
 */

static void
init_source (j_decompress_ptr cinfo)
{
    /* No work, since jpeg_memory_src set up the buffer pointer and count.
     * Indeed, if we want to read multiple JPEG images from one buffer,
     * this *must* not do anything to the pointer.
     */
}


/*
 * Fill the input buffer --- called whenever buffer is emptied.
 *
 * In this application, this routine should never be called; if it is called,
 * the decompressor has overrun the end of the input buffer, implying we
 * supplied an incomplete or corrupt JPEG datastream.  A simple error exit
 * might be the most appropriate response.
 *
 * But what we choose to do in this code is to supply dummy EOI markers
 * in order to force the decompressor to finish processing and supply
 * some sort of output image, no matter how corrupted.
 */

static boolean
fill_input_buffer(j_decompress_ptr cinfo)
{
    my_src_ptr src = (my_src_ptr) cinfo->src;

    WARNMS(cinfo, JWRN_JPEG_EOF);

    /* Create a fake EOI marker */
    src->eoi_buffer[0] = (JOCTET) 0xFF;
    src->eoi_buffer[1] = (JOCTET) JPEG_EOI;
    src->pub.next_input_byte = src->eoi_buffer;
    src->pub.bytes_in_buffer = 2;

    return TRUE;
}


/*
 * Skip data --- used to skip over a potentially large amount of
 * uninteresting data (such as an APPn marker).
 *
 * If we overrun the end of the buffer, we let fill_input_buffer deal with
 * it.  An extremely large skip could cause some time-wasting here, but
 * it really isn't supposed to happen ... and the decompressor will never
 * skip more than 64K anyway.
 */

static void
skip_input_data (j_decompress_ptr cinfo, long num_bytes)
{
    my_src_ptr src = (my_src_ptr) cinfo->src;

    if (num_bytes > 0) {
        while (num_bytes > (long) src->pub.bytes_in_buffer) {
            num_bytes -= (long) src->pub.bytes_in_buffer;
            (void) fill_input_buffer(cinfo);
            /* note we assume that fill_input_buffer will never return FALSE,
             * so suspension need not be handled.
             */
        }

        src->pub.next_input_byte += (size_t) num_bytes;
        src->pub.bytes_in_buffer -= (size_t) num_bytes;
    }
}


/*
 * An additional method that can be provided by data source modules is the
 * resync_to_restart method for error recovery in the presence of RST markers.
 * For the moment, this source module just uses the default resync method
 * provided by the JPEG library.  That method assumes that no backtracking
 * is possible.
 */


/*
 * Terminate source --- called by jpeg_finish_decompress
 * after all data has been read.  Often a no-op.
 *
 * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
 * application must deal with any cleanup that should happen even
 * for error exit.
 */

static void
term_source (j_decompress_ptr cinfo)
{
    /* no work necessary here */
}


/*
 * Prepare for input from a memory buffer.
 */

GLOBAL(void)
jpeg_memory_src (j_decompress_ptr cinfo, const JOCTET * buffer, size_t bufsize)
{
    my_src_ptr src;

    /* The source object is made permanent so that a series of JPEG images
     * can be read from a single buffer by calling jpeg_memory_src
     * only before the first one.
     * This makes it unsafe to use this manager and a different source
     * manager serially with the same JPEG object.  Caveat programmer.
     */
    if (cinfo->src == nullptr) { /* first time for this JPEG object? */
        cinfo->src = (struct jpeg_source_mgr *)
                     (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
                             sizeof(my_source_mgr));
    }

    src = (my_src_ptr) cinfo->src;
    src->pub.init_source = init_source;
    src->pub.fill_input_buffer = fill_input_buffer;
    src->pub.skip_input_data = skip_input_data;
    src->pub.resync_to_restart = jpeg_resync_to_restart; /* use default method */
    src->pub.term_source = term_source;

    src->pub.next_input_byte = buffer;
    src->pub.bytes_in_buffer = bufsize;
}