4 * Copyright (C) 1994-1996, Thomas G. Lane.
5 * This file is part of the Independent JPEG Group's software.
6 * For conditions of distribution and use, see the accompanying README file.
8 * This file contains decompression data source routines for the case of
9 * reading JPEG data from a file (or any stdio stream). While these routines
10 * are sufficient for most applications, some will want to use a different
12 * IMPORTANT: we assume that fread() will correctly transcribe an array of
13 * JOCTETs from 8-bit-wide elements on external storage. If char is wider
14 * than 8 bits on your machine, you may need to do some tweaking.
17 /* -------------------------------------------------------------------------- */
22 /* -------------------------------------------------------------------------- */
24 /* this is not a core library module, so it doesn't define JPEG_INTERNALS */
28 /* Expanded data source object for stdio input */
31 struct jpeg_source_mgr pub; /* public fields */
33 fs_file infile; /* source stream */
34 JOCTET * buffer; /* start of buffer */
35 boolean start_of_file; /* have we gotten any data yet? */
38 typedef my_source_mgr * my_src_ptr;
40 #define INPUT_BUF_SIZE 4096 /* choose an efficiently fread'able size */
44 * Initialize source --- called by jpeg_read_header
45 * before any data is actually read.
49 init_source (j_decompress_ptr cinfo)
51 my_src_ptr src = (my_src_ptr) cinfo->src;
53 /* We reset the empty-input-file flag for each image,
54 * but we don't clear the input buffer.
55 * This is correct behavior for reading a series of images from one source.
57 src->start_of_file = TRUE;
62 * Fill the input buffer --- called whenever buffer is emptied.
64 * In typical applications, this should read fresh data into the buffer
65 * (ignoring the current state of next_input_byte & bytes_in_buffer),
66 * reset the pointer & count to the start of the buffer, and return TRUE
67 * indicating that the buffer has been reloaded. It is not necessary to
68 * fill the buffer entirely, only to obtain at least one more byte.
70 * There is no such thing as an EOF return. If the end of the file has been
71 * reached, the routine has a choice of ERREXIT() or inserting fake data into
72 * the buffer. In most cases, generating a warning message and inserting a
73 * fake EOI marker is the best course of action --- this will allow the
74 * decompressor to output however much of the image is there. However,
75 * the resulting error message is misleading if the real problem is an empty
76 * input file, so we handle that case specially.
78 * In applications that need to be able to suspend compression due to input
79 * not being available yet, a FALSE return indicates that no more data can be
80 * obtained right now, but more may be forthcoming later. In this situation,
81 * the decompressor will return to its caller (with an indication of the
82 * number of scanlines it has read, if any). The application should resume
83 * decompression after it has loaded more data into the input buffer. Note
84 * that there are substantial restrictions on the use of suspension --- see
87 * When suspending, the decompressor will back up to a convenient restart point
88 * (typically the start of the current MCU). next_input_byte & bytes_in_buffer
89 * indicate where the restart point will be if the current call returns FALSE.
90 * Data beyond this point must be rescanned after resumption, so move it to
91 * the front of the buffer rather than discarding it.
95 fill_input_buffer (j_decompress_ptr cinfo)
97 my_src_ptr src = (my_src_ptr) cinfo->src;
100 nbytes = fs_read(src->buffer, 1, INPUT_BUF_SIZE, src->infile);
103 if (src->start_of_file) /* Treat empty input file as fatal error */
104 ERREXIT(cinfo, JERR_INPUT_EMPTY);
105 WARNMS(cinfo, JWRN_JPEG_EOF);
106 /* Insert a fake EOI marker */
107 src->buffer[0] = (JOCTET) 0xFF;
108 src->buffer[1] = (JOCTET) JPEG_EOI;
112 src->pub.next_input_byte = src->buffer;
113 src->pub.bytes_in_buffer = nbytes;
114 src->start_of_file = FALSE;
121 * Skip data --- used to skip over a potentially large amount of
122 * uninteresting data (such as an APPn marker).
124 * Writers of suspendable-input applications must note that skip_input_data
125 * is not granted the right to give a suspension return. If the skip extends
126 * beyond the data currently in the buffer, the buffer can be marked empty so
127 * that the next read will cause a fill_input_buffer call that can suspend.
128 * Arranging for additional bytes to be discarded before reloading the input
129 * buffer is the application writer's problem.
133 skip_input_data (j_decompress_ptr cinfo, long num_bytes)
135 my_src_ptr src = (my_src_ptr) cinfo->src;
137 /* Just a dumb implementation for now. Could use fseek() except
138 * it doesn't work on pipes. Not clear that being smart is worth
139 * any trouble anyway --- large skips are infrequent.
142 while (num_bytes > (long) src->pub.bytes_in_buffer) {
143 num_bytes -= (long) src->pub.bytes_in_buffer;
144 (void) fill_input_buffer(cinfo);
145 /* note we assume that fill_input_buffer will never return FALSE,
146 * so suspension need not be handled.
149 src->pub.next_input_byte += (size_t) num_bytes;
150 src->pub.bytes_in_buffer -= (size_t) num_bytes;
156 * An additional method that can be provided by data source modules is the
157 * resync_to_restart method for error recovery in the presence of RST markers.
158 * For the moment, this source module just uses the default resync method
159 * provided by the JPEG library. That method assumes that no backtracking
165 * Terminate source --- called by jpeg_finish_decompress
166 * after all data has been read. Often a no-op.
168 * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
169 * application must deal with any cleanup that should happen even
174 term_source (j_decompress_ptr cinfo)
176 /* no work necessary here */
181 * Prepare for input from a stdio stream.
182 * The caller must have already opened the stream, and is responsible
183 * for closing it after finishing decompression.
187 fs_jpg_src (j_decompress_ptr cinfo, fs_file infile)
191 /* The source object and input buffer are made permanent so that a series
192 * of JPEG images can be read from the same file by calling jpeg_stdio_src
193 * only before the first one. (If we discarded the buffer at the end of
194 * one image, we'd likely lose the start of the next one.)
195 * This makes it unsafe to use this manager and a different source
196 * manager serially with the same JPEG object. Caveat programmer.
198 if (cinfo->src == NULL) { /* first time for this JPEG object? */
199 cinfo->src = (struct jpeg_source_mgr *)
200 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
201 sizeof (my_source_mgr));
202 src = (my_src_ptr) cinfo->src;
203 src->buffer = (JOCTET *)
204 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
205 INPUT_BUF_SIZE * sizeof (JOCTET));
208 src = (my_src_ptr) cinfo->src;
209 src->pub.init_source = init_source;
210 src->pub.fill_input_buffer = fill_input_buffer;
211 src->pub.skip_input_data = skip_input_data;
212 src->pub.resync_to_restart = jpeg_resync_to_restart; /* use default method */
213 src->pub.term_source = term_source;
214 src->infile = infile;
215 src->pub.bytes_in_buffer = 0; /* forces fill_input_buffer on first read */
216 src->pub.next_input_byte = NULL; /* until buffer loaded */