nuclear@2: /*
nuclear@2:  * jdatasrc.c
nuclear@2:  *
nuclear@2:  * Copyright (C) 1994-1996, Thomas G. Lane.
nuclear@2:  * This file is part of the Independent JPEG Group's software.
nuclear@2:  * For conditions of distribution and use, see the accompanying README file.
nuclear@2:  *
nuclear@2:  * This file contains decompression data source routines for the case of
nuclear@2:  * reading JPEG data from a file (or any stdio stream).  While these routines
nuclear@2:  * are sufficient for most applications, some will want to use a different
nuclear@2:  * source manager.
nuclear@2:  * IMPORTANT: we assume that fread() will correctly transcribe an array of
nuclear@2:  * JOCTETs from 8-bit-wide elements on external storage.  If char is wider
nuclear@2:  * than 8 bits on your machine, you may need to do some tweaking.
nuclear@2:  */
nuclear@2: 
nuclear@2: /* this is not a core library module, so it doesn't define JPEG_INTERNALS */
nuclear@2: #include "jinclude.h"
nuclear@2: #include "jpeglib.h"
nuclear@2: #include "jerror.h"
nuclear@2: 
nuclear@2: 
nuclear@2: /* Expanded data source object for stdio input */
nuclear@2: 
nuclear@2: typedef struct {
nuclear@2:   struct jpeg_source_mgr pub;	/* public fields */
nuclear@2: 
nuclear@2:   FILE * infile;		/* source stream */
nuclear@2:   JOCTET * buffer;		/* start of buffer */
nuclear@2:   boolean start_of_file;	/* have we gotten any data yet? */
nuclear@2: } my_source_mgr;
nuclear@2: 
nuclear@2: typedef my_source_mgr * my_src_ptr;
nuclear@2: 
nuclear@2: #define INPUT_BUF_SIZE  4096	/* choose an efficiently fread'able size */
nuclear@2: 
nuclear@2: 
nuclear@2: /*
nuclear@2:  * Initialize source --- called by jpeg_read_header
nuclear@2:  * before any data is actually read.
nuclear@2:  */
nuclear@2: 
nuclear@2: METHODDEF(void)
nuclear@2: init_source (j_decompress_ptr cinfo)
nuclear@2: {
nuclear@2:   my_src_ptr src = (my_src_ptr) cinfo->src;
nuclear@2: 
nuclear@2:   /* We reset the empty-input-file flag for each image,
nuclear@2:    * but we don't clear the input buffer.
nuclear@2:    * This is correct behavior for reading a series of images from one source.
nuclear@2:    */
nuclear@2:   src->start_of_file = TRUE;
nuclear@2: }
nuclear@2: 
nuclear@2: 
nuclear@2: /*
nuclear@2:  * Fill the input buffer --- called whenever buffer is emptied.
nuclear@2:  *
nuclear@2:  * In typical applications, this should read fresh data into the buffer
nuclear@2:  * (ignoring the current state of next_input_byte & bytes_in_buffer),
nuclear@2:  * reset the pointer & count to the start of the buffer, and return TRUE
nuclear@2:  * indicating that the buffer has been reloaded.  It is not necessary to
nuclear@2:  * fill the buffer entirely, only to obtain at least one more byte.
nuclear@2:  *
nuclear@2:  * There is no such thing as an EOF return.  If the end of the file has been
nuclear@2:  * reached, the routine has a choice of ERREXIT() or inserting fake data into
nuclear@2:  * the buffer.  In most cases, generating a warning message and inserting a
nuclear@2:  * fake EOI marker is the best course of action --- this will allow the
nuclear@2:  * decompressor to output however much of the image is there.  However,
nuclear@2:  * the resulting error message is misleading if the real problem is an empty
nuclear@2:  * input file, so we handle that case specially.
nuclear@2:  *
nuclear@2:  * In applications that need to be able to suspend compression due to input
nuclear@2:  * not being available yet, a FALSE return indicates that no more data can be
nuclear@2:  * obtained right now, but more may be forthcoming later.  In this situation,
nuclear@2:  * the decompressor will return to its caller (with an indication of the
nuclear@2:  * number of scanlines it has read, if any).  The application should resume
nuclear@2:  * decompression after it has loaded more data into the input buffer.  Note
nuclear@2:  * that there are substantial restrictions on the use of suspension --- see
nuclear@2:  * the documentation.
nuclear@2:  *
nuclear@2:  * When suspending, the decompressor will back up to a convenient restart point
nuclear@2:  * (typically the start of the current MCU). next_input_byte & bytes_in_buffer
nuclear@2:  * indicate where the restart point will be if the current call returns FALSE.
nuclear@2:  * Data beyond this point must be rescanned after resumption, so move it to
nuclear@2:  * the front of the buffer rather than discarding it.
nuclear@2:  */
nuclear@2: 
nuclear@2: METHODDEF(boolean)
nuclear@2: fill_input_buffer (j_decompress_ptr cinfo)
nuclear@2: {
nuclear@2:   my_src_ptr src = (my_src_ptr) cinfo->src;
nuclear@2:   size_t nbytes;
nuclear@2: 
nuclear@2:   nbytes = JFREAD(src->infile, src->buffer, INPUT_BUF_SIZE);
nuclear@2: 
nuclear@2:   if (nbytes <= 0) {
nuclear@2:     if (src->start_of_file)	/* Treat empty input file as fatal error */
nuclear@2:       ERREXIT(cinfo, JERR_INPUT_EMPTY);
nuclear@2:     WARNMS(cinfo, JWRN_JPEG_EOF);
nuclear@2:     /* Insert a fake EOI marker */
nuclear@2:     src->buffer[0] = (JOCTET) 0xFF;
nuclear@2:     src->buffer[1] = (JOCTET) JPEG_EOI;
nuclear@2:     nbytes = 2;
nuclear@2:   }
nuclear@2: 
nuclear@2:   src->pub.next_input_byte = src->buffer;
nuclear@2:   src->pub.bytes_in_buffer = nbytes;
nuclear@2:   src->start_of_file = FALSE;
nuclear@2: 
nuclear@2:   return TRUE;
nuclear@2: }
nuclear@2: 
nuclear@2: 
nuclear@2: /*
nuclear@2:  * Skip data --- used to skip over a potentially large amount of
nuclear@2:  * uninteresting data (such as an APPn marker).
nuclear@2:  *
nuclear@2:  * Writers of suspendable-input applications must note that skip_input_data
nuclear@2:  * is not granted the right to give a suspension return.  If the skip extends
nuclear@2:  * beyond the data currently in the buffer, the buffer can be marked empty so
nuclear@2:  * that the next read will cause a fill_input_buffer call that can suspend.
nuclear@2:  * Arranging for additional bytes to be discarded before reloading the input
nuclear@2:  * buffer is the application writer's problem.
nuclear@2:  */
nuclear@2: 
nuclear@2: METHODDEF(void)
nuclear@2: skip_input_data (j_decompress_ptr cinfo, long num_bytes)
nuclear@2: {
nuclear@2:   my_src_ptr src = (my_src_ptr) cinfo->src;
nuclear@2: 
nuclear@2:   /* Just a dumb implementation for now.  Could use fseek() except
nuclear@2:    * it doesn't work on pipes.  Not clear that being smart is worth
nuclear@2:    * any trouble anyway --- large skips are infrequent.
nuclear@2:    */
nuclear@2:   if (num_bytes > 0) {
nuclear@2:     while (num_bytes > (long) src->pub.bytes_in_buffer) {
nuclear@2:       num_bytes -= (long) src->pub.bytes_in_buffer;
nuclear@2:       (void) fill_input_buffer(cinfo);
nuclear@2:       /* note we assume that fill_input_buffer will never return FALSE,
nuclear@2:        * so suspension need not be handled.
nuclear@2:        */
nuclear@2:     }
nuclear@2:     src->pub.next_input_byte += (size_t) num_bytes;
nuclear@2:     src->pub.bytes_in_buffer -= (size_t) num_bytes;
nuclear@2:   }
nuclear@2: }
nuclear@2: 
nuclear@2: 
nuclear@2: /*
nuclear@2:  * An additional method that can be provided by data source modules is the
nuclear@2:  * resync_to_restart method for error recovery in the presence of RST markers.
nuclear@2:  * For the moment, this source module just uses the default resync method
nuclear@2:  * provided by the JPEG library.  That method assumes that no backtracking
nuclear@2:  * is possible.
nuclear@2:  */
nuclear@2: 
nuclear@2: 
nuclear@2: /*
nuclear@2:  * Terminate source --- called by jpeg_finish_decompress
nuclear@2:  * after all data has been read.  Often a no-op.
nuclear@2:  *
nuclear@2:  * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
nuclear@2:  * application must deal with any cleanup that should happen even
nuclear@2:  * for error exit.
nuclear@2:  */
nuclear@2: 
nuclear@2: METHODDEF(void)
nuclear@2: term_source (j_decompress_ptr cinfo)
nuclear@2: {
nuclear@2:   /* no work necessary here */
nuclear@2: }
nuclear@2: 
nuclear@2: 
nuclear@2: /*
nuclear@2:  * Prepare for input from a stdio stream.
nuclear@2:  * The caller must have already opened the stream, and is responsible
nuclear@2:  * for closing it after finishing decompression.
nuclear@2:  */
nuclear@2: 
nuclear@2: GLOBAL(void)
nuclear@2: jpeg_stdio_src (j_decompress_ptr cinfo, FILE * infile)
nuclear@2: {
nuclear@2:   my_src_ptr src;
nuclear@2: 
nuclear@2:   /* The source object and input buffer are made permanent so that a series
nuclear@2:    * of JPEG images can be read from the same file by calling jpeg_stdio_src
nuclear@2:    * only before the first one.  (If we discarded the buffer at the end of
nuclear@2:    * one image, we'd likely lose the start of the next one.)
nuclear@2:    * This makes it unsafe to use this manager and a different source
nuclear@2:    * manager serially with the same JPEG object.  Caveat programmer.
nuclear@2:    */
nuclear@2:   if (cinfo->src == NULL) {	/* first time for this JPEG object? */
nuclear@2:     cinfo->src = (struct jpeg_source_mgr *)
nuclear@2:       (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
nuclear@2: 				  SIZEOF(my_source_mgr));
nuclear@2:     src = (my_src_ptr) cinfo->src;
nuclear@2:     src->buffer = (JOCTET *)
nuclear@2:       (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
nuclear@2: 				  INPUT_BUF_SIZE * SIZEOF(JOCTET));
nuclear@2:   }
nuclear@2: 
nuclear@2:   src = (my_src_ptr) cinfo->src;
nuclear@2:   src->pub.init_source = init_source;
nuclear@2:   src->pub.fill_input_buffer = fill_input_buffer;
nuclear@2:   src->pub.skip_input_data = skip_input_data;
nuclear@2:   src->pub.resync_to_restart = jpeg_resync_to_restart; /* use default method */
nuclear@2:   src->pub.term_source = term_source;
nuclear@2:   src->infile = infile;
nuclear@2:   src->pub.bytes_in_buffer = 0; /* forces fill_input_buffer on first read */
nuclear@2:   src->pub.next_input_byte = NULL; /* until buffer loaded */
nuclear@2: }