SAMV71 Xplained Ultra Software Package 1.4

memsrc.c

00001 /*
00002  * memsrc.c
00003  *
00004  * Copyright (C) 1994-1996, Thomas G. Lane.
00005  * This file is part of the Independent JPEG Group's software.
00006  * For conditions of distribution and use, see the accompanying README file.
00007  *
00008  * This file contains decompression data source routines for the case of
00009  * reading JPEG data from a memory buffer that is preloaded with the entire
00010  * JPEG file.  This would not seem especially useful at first sight, but
00011  * a number of people have asked for it.
00012  * This is really just a stripped-down version of jdatasrc.c.  Comparison
00013  * of this code with jdatasrc.c may be helpful in seeing how to make
00014  * custom source managers for other purposes.
00015  */
00016 
00017 /* this is not a core library module, so it doesn't define JPEG_INTERNALS */
00018 #include "jinclude.h"
00019 #include "jpeglib.h"
00020 #include "jerror.h"
00021 
00022 
00023 /* Expanded data source object for memory input */
00024 
00025 typedef struct {
00026   struct jpeg_source_mgr pub;   /* public fields */
00027 
00028   JOCTET eoi_buffer[2];     /* a place to put a dummy EOI */
00029 } my_source_mgr;
00030 
00031 typedef my_source_mgr * my_src_ptr;
00032 
00033 
00034 /*
00035  * Initialize source --- called by jpeg_read_header
00036  * before any data is actually read.
00037  */
00038 
00039 METHODDEF(void)
00040 init_source (j_decompress_ptr cinfo)
00041 {
00042   /* No work, since jpeg_memory_src set up the buffer pointer and count.
00043    * Indeed, if we want to read multiple JPEG images from one buffer,
00044    * this *must* not do anything to the pointer.
00045    */
00046 }
00047 
00048 
00049 /*
00050  * Fill the input buffer --- called whenever buffer is emptied.
00051  *
00052  * In this application, this routine should never be called; if it is called,
00053  * the decompressor has overrun the end of the input buffer, implying we
00054  * supplied an incomplete or corrupt JPEG datastream.  A simple error exit
00055  * might be the most appropriate response.
00056  *
00057  * But what we choose to do in this code is to supply dummy EOI markers
00058  * in order to force the decompressor to finish processing and supply
00059  * some sort of output image, no matter how corrupted.
00060  */
00061 
00062 METHODDEF(boolean)
00063 fill_input_buffer (j_decompress_ptr cinfo)
00064 {
00065   my_src_ptr src = (my_src_ptr) cinfo->src;
00066 
00067   WARNMS(cinfo, JWRN_JPEG_EOF);
00068 
00069   /* Create a fake EOI marker */
00070   src->eoi_buffer[0] = (JOCTET) 0xFF;
00071   src->eoi_buffer[1] = (JOCTET) JPEG_EOI;
00072   src->pub.next_input_byte = src->eoi_buffer;
00073   src->pub.bytes_in_buffer = 2;
00074 
00075   return TRUE;
00076 }
00077 
00078 
00079 /*
00080  * Skip data --- used to skip over a potentially large amount of
00081  * uninteresting data (such as an APPn marker).
00082  *
00083  * If we overrun the end of the buffer, we let fill_input_buffer deal with
00084  * it.  An extremely large skip could cause some time-wasting here, but
00085  * it really isn't supposed to happen ... and the decompressor will never
00086  * skip more than 64K anyway.
00087  */
00088 
00089 METHODDEF(void)
00090 skip_input_data (j_decompress_ptr cinfo, long num_bytes)
00091 {
00092   my_src_ptr src = (my_src_ptr) cinfo->src;
00093 
00094   if (num_bytes > 0) {
00095     while (num_bytes > (long) src->pub.bytes_in_buffer) {
00096       num_bytes -= (long) src->pub.bytes_in_buffer;
00097       (void) fill_input_buffer(cinfo);
00098       /* note we assume that fill_input_buffer will never return FALSE,
00099        * so suspension need not be handled.
00100        */
00101     }
00102     src->pub.next_input_byte += (size_t) num_bytes;
00103     src->pub.bytes_in_buffer -= (size_t) num_bytes;
00104   }
00105 }
00106 
00107 
00108 /*
00109  * An additional method that can be provided by data source modules is the
00110  * resync_to_restart method for error recovery in the presence of RST markers.
00111  * For the moment, this source module just uses the default resync method
00112  * provided by the JPEG library.  That method assumes that no backtracking
00113  * is possible.
00114  */
00115 
00116 
00117 /*
00118  * Terminate source --- called by jpeg_finish_decompress
00119  * after all data has been read.  Often a no-op.
00120  *
00121  * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
00122  * application must deal with any cleanup that should happen even
00123  * for error exit.
00124  */
00125 
00126 METHODDEF(void)
00127 term_source (j_decompress_ptr cinfo)
00128 {
00129   /* no work necessary here */
00130 }
00131 
00132 
00133 /*
00134  * Prepare for input from a memory buffer.
00135  */
00136 
00137 GLOBAL(void)
00138 jpeg_memory_src (j_decompress_ptr cinfo, const JOCTET * buffer, size_t bufsize)
00139 {
00140   my_src_ptr src;
00141 
00142   /* The source object is made permanent so that a series of JPEG images
00143    * can be read from a single buffer by calling jpeg_memory_src
00144    * only before the first one.
00145    * This makes it unsafe to use this manager and a different source
00146    * manager serially with the same JPEG object.  Caveat programmer.
00147    */
00148   if (cinfo->src == NULL) { /* first time for this JPEG object? */
00149     cinfo->src = (struct jpeg_source_mgr *)
00150       (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
00151                   SIZEOF(my_source_mgr));
00152   }
00153 
00154   src = (my_src_ptr) cinfo->src;
00155   src->pub.init_source = init_source;
00156   src->pub.fill_input_buffer = fill_input_buffer;
00157   src->pub.skip_input_data = skip_input_data;
00158   src->pub.resync_to_restart = jpeg_resync_to_restart; /* use default method */
00159   src->pub.term_source = term_source;
00160 
00161   src->pub.next_input_byte = buffer;
00162   src->pub.bytes_in_buffer = bufsize;
00163 }
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