4 * Copyright (C) 1994, 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 /* this is not a core library module, so it doesn't define JPEG_INTERNALS */
19 #include "radiant_jpeglib.h"
21 //extern int leo_buf_size; // FIXME ? merged in from Alpha - replaced by my_source_mgr->src_size
22 /* Expanded data source object for stdio input */
24 struct jpeg_source_mgr pub; /* public fields */
25 int src_size; // FIXME ? merged from Alpha
26 unsigned char *infile; /* source stream */
27 JOCTET * buffer; /* start of buffer */
28 boolean start_of_file; /* have we gotten any data yet? */
30 typedef my_source_mgr * my_src_ptr;
31 #define INPUT_BUF_SIZE 4096 /* choose an efficiently fread'able size */
34 * Initialize source --- called by jpeg_read_header
35 * before any data is actually read.
38 init_source (j_decompress_ptr cinfo)
40 my_src_ptr src = (my_src_ptr) cinfo->src;
41 /* We reset the empty-input-file flag for each image,
42 * but we don't clear the input buffer.
43 * This is correct behavior for reading a series of images from one source.
45 src->start_of_file = TRUE;
49 * Fill the input buffer --- called whenever buffer is emptied.
51 * In typical applications, this should read fresh data into the buffer
52 * (ignoring the current state of next_input_byte & bytes_in_buffer),
53 * reset the pointer & count to the start of the buffer, and return TRUE
54 * indicating that the buffer has been reloaded. It is not necessary to
55 * fill the buffer entirely, only to obtain at least one more byte.
57 * There is no such thing as an EOF return. If the end of the file has been
58 * reached, the routine has a choice of ERREXIT() or inserting fake data into
59 * the buffer. In most cases, generating a warning message and inserting a
60 * fake EOI marker is the best course of action --- this will allow the
61 * decompressor to output however much of the image is there. However,
62 * the resulting error message is misleading if the real problem is an empty
63 * input file, so we handle that case specially.
65 * In applications that need to be able to suspend compression due to input
66 * not being available yet, a FALSE return indicates that no more data can be
67 * obtained right now, but more may be forthcoming later. In this situation,
68 * the decompressor will return to its caller (with an indication of the
69 * number of scanlines it has read, if any). The application should resume
70 * decompression after it has loaded more data into the input buffer. Note
71 * that there are substantial restrictions on the use of suspension --- see
74 * When suspending, the decompressor will back up to a convenient restart point
75 * (typically the start of the current MCU). next_input_byte & bytes_in_buffer
76 * indicate where the restart point will be if the current call returns FALSE.
77 * Data beyond this point must be rescanned after resumption, so move it to
78 * the front of the buffer rather than discarding it.
81 // FIXME ? merged in from Alpha
82 fill_input_buffer (j_decompress_ptr cinfo)
84 my_src_ptr src = (my_src_ptr) cinfo->src;
87 if (src->src_size > INPUT_BUF_SIZE)
88 nbytes = INPUT_BUF_SIZE;
90 nbytes = src->src_size;
91 memcpy (src->buffer, src->infile, nbytes);
92 src->infile += nbytes;
93 src->src_size -= nbytes;
94 src->pub.next_input_byte = src->buffer;
95 src->pub.bytes_in_buffer = nbytes;
96 src->start_of_file = FALSE;
101 * Skip data --- used to skip over a potentially large amount of
102 * uninteresting data (such as an APPn marker).
104 * Writers of suspendable-input applications must note that skip_input_data
105 * is not granted the right to give a suspension return. If the skip extends
106 * beyond the data currently in the buffer, the buffer can be marked empty so
107 * that the next read will cause a fill_input_buffer call that can suspend.
108 * Arranging for additional bytes to be discarded before reloading the input
109 * buffer is the application writer's problem.
112 skip_input_data (j_decompress_ptr cinfo, long num_bytes)
114 my_src_ptr src = (my_src_ptr) cinfo->src;
115 /* Just a dumb implementation for now. Could use fseek() except
116 * it doesn't work on pipes. Not clear that being smart is worth
117 * any trouble anyway --- large skips are infrequent.
120 while (num_bytes > (long) src->pub.bytes_in_buffer) {
121 num_bytes -= (long) src->pub.bytes_in_buffer;
122 (void) fill_input_buffer(cinfo);
123 /* note we assume that fill_input_buffer will never return FALSE,
124 * so suspension need not be handled.
127 src->pub.next_input_byte += (size_t) num_bytes;
128 src->pub.bytes_in_buffer -= (size_t) num_bytes;
133 * An additional method that can be provided by data source modules is the
134 * resync_to_restart method for error recovery in the presence of RST markers.
135 * For the moment, this source module just uses the default resync method
136 * provided by the JPEG library. That method assumes that no backtracking
141 * Terminate source --- called by jpeg_finish_decompress
142 * after all data has been read. Often a no-op.
144 * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
145 * application must deal with any cleanup that should happen even
149 term_source (j_decompress_ptr cinfo)
151 /* no work necessary here */
155 * Prepare for input from a stdio stream.
156 * The caller must have already opened the stream, and is responsible
157 * for closing it after finishing decompression.
160 jpeg_stdio_src (j_decompress_ptr cinfo, unsigned char *infile, int bufsize)
163 /* The source object and input buffer are made permanent so that a series
164 * of JPEG images can be read from the same file by calling jpeg_stdio_src
165 * only before the first one. (If we discarded the buffer at the end of
166 * one image, we'd likely lose the start of the next one.)
167 * This makes it unsafe to use this manager and a different source
168 * manager serially with the same JPEG object. Caveat programmer.
170 if (cinfo->src == NULL) { /* first time for this JPEG object? */
171 cinfo->src = (struct jpeg_source_mgr *)
172 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
173 SIZEOF(my_source_mgr));
174 src = (my_src_ptr) cinfo->src;
175 src->buffer = (JOCTET *)
176 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
177 INPUT_BUF_SIZE * SIZEOF(JOCTET));
179 src = (my_src_ptr) cinfo->src;
180 src->pub.init_source = init_source;
181 src->pub.fill_input_buffer = fill_input_buffer;
182 src->pub.skip_input_data = skip_input_data;
183 src->pub.resync_to_restart = jpeg_resync_to_restart; /* use default method */
184 src->pub.term_source = term_source;
185 src->infile = infile;
186 src->src_size = bufsize; // FIXME ? merged from Alpha
187 src->pub.bytes_in_buffer = 0; /* forces fill_input_buffer on first read */
188 src->pub.next_input_byte = NULL; /* until buffer loaded */