4 * Copyright (C) 1994-1996, Thomas G. Lane.
5 * This file is part of the Independent JPEG Group's software.
6 * The conditions of distribution and use are reproduced below.
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.
18 * Permission is hereby granted to use, copy, modify, and distribute
19 * this software (or portions thereof) for any purpose, without fee,
20 * subject to these conditions:
21 * (1) If any part of the source code for this software is
22 * distributed, then this README file must be included, with this
23 * copyright and no-warranty notice unaltered; and any additions,
24 * deletions, or changes to the original files must be clearly
25 * indicated in accompanying documentation.
26 * (2) If only executable code is distributed, then the accompanying
27 * documentation must state that "this software is based in part on
28 * the work of the Independent JPEG Group".
29 * (3) Permission for use of this software is granted only if the user
30 * accepts full responsibility for any undesirable consequences; the
31 * authors accept NO LIABILITY for damages of any kind.
33 * -- Neverball-related changes
35 * Search-and-replace to use with Neverball's custom IO routines:
37 * * Replaced use of FILE * with fs_file.
38 * * Replaced use of JFREAD with fs_read (fread interface).
45 /* -------------------------------------------------------------------------- */
47 /* this is not a core library module, so it doesn't define JPEG_INTERNALS */
51 /* Expanded data source object for stdio input */
54 struct jpeg_source_mgr pub; /* public fields */
56 fs_file infile; /* source stream */
57 JOCTET * buffer; /* start of buffer */
58 boolean start_of_file; /* have we gotten any data yet? */
61 typedef my_source_mgr * my_src_ptr;
63 #define INPUT_BUF_SIZE 4096 /* choose an efficiently fread'able size */
67 * Initialize source --- called by jpeg_read_header
68 * before any data is actually read.
72 init_source (j_decompress_ptr cinfo)
74 my_src_ptr src = (my_src_ptr) cinfo->src;
76 /* We reset the empty-input-file flag for each image,
77 * but we don't clear the input buffer.
78 * This is correct behavior for reading a series of images from one source.
80 src->start_of_file = TRUE;
85 * Fill the input buffer --- called whenever buffer is emptied.
87 * In typical applications, this should read fresh data into the buffer
88 * (ignoring the current state of next_input_byte & bytes_in_buffer),
89 * reset the pointer & count to the start of the buffer, and return TRUE
90 * indicating that the buffer has been reloaded. It is not necessary to
91 * fill the buffer entirely, only to obtain at least one more byte.
93 * There is no such thing as an EOF return. If the end of the file has been
94 * reached, the routine has a choice of ERREXIT() or inserting fake data into
95 * the buffer. In most cases, generating a warning message and inserting a
96 * fake EOI marker is the best course of action --- this will allow the
97 * decompressor to output however much of the image is there. However,
98 * the resulting error message is misleading if the real problem is an empty
99 * input file, so we handle that case specially.
101 * In applications that need to be able to suspend compression due to input
102 * not being available yet, a FALSE return indicates that no more data can be
103 * obtained right now, but more may be forthcoming later. In this situation,
104 * the decompressor will return to its caller (with an indication of the
105 * number of scanlines it has read, if any). The application should resume
106 * decompression after it has loaded more data into the input buffer. Note
107 * that there are substantial restrictions on the use of suspension --- see
110 * When suspending, the decompressor will back up to a convenient restart point
111 * (typically the start of the current MCU). next_input_byte & bytes_in_buffer
112 * indicate where the restart point will be if the current call returns FALSE.
113 * Data beyond this point must be rescanned after resumption, so move it to
114 * the front of the buffer rather than discarding it.
118 fill_input_buffer (j_decompress_ptr cinfo)
120 my_src_ptr src = (my_src_ptr) cinfo->src;
123 nbytes = fs_read(src->buffer, 1, INPUT_BUF_SIZE, src->infile);
126 if (src->start_of_file) /* Treat empty input file as fatal error */
127 ERREXIT(cinfo, JERR_INPUT_EMPTY);
128 WARNMS(cinfo, JWRN_JPEG_EOF);
129 /* Insert a fake EOI marker */
130 src->buffer[0] = (JOCTET) 0xFF;
131 src->buffer[1] = (JOCTET) JPEG_EOI;
135 src->pub.next_input_byte = src->buffer;
136 src->pub.bytes_in_buffer = nbytes;
137 src->start_of_file = FALSE;
144 * Skip data --- used to skip over a potentially large amount of
145 * uninteresting data (such as an APPn marker).
147 * Writers of suspendable-input applications must note that skip_input_data
148 * is not granted the right to give a suspension return. If the skip extends
149 * beyond the data currently in the buffer, the buffer can be marked empty so
150 * that the next read will cause a fill_input_buffer call that can suspend.
151 * Arranging for additional bytes to be discarded before reloading the input
152 * buffer is the application writer's problem.
156 skip_input_data (j_decompress_ptr cinfo, long num_bytes)
158 my_src_ptr src = (my_src_ptr) cinfo->src;
160 /* Just a dumb implementation for now. Could use fseek() except
161 * it doesn't work on pipes. Not clear that being smart is worth
162 * any trouble anyway --- large skips are infrequent.
165 while (num_bytes > (long) src->pub.bytes_in_buffer) {
166 num_bytes -= (long) src->pub.bytes_in_buffer;
167 (void) fill_input_buffer(cinfo);
168 /* note we assume that fill_input_buffer will never return FALSE,
169 * so suspension need not be handled.
172 src->pub.next_input_byte += (size_t) num_bytes;
173 src->pub.bytes_in_buffer -= (size_t) num_bytes;
179 * An additional method that can be provided by data source modules is the
180 * resync_to_restart method for error recovery in the presence of RST markers.
181 * For the moment, this source module just uses the default resync method
182 * provided by the JPEG library. That method assumes that no backtracking
188 * Terminate source --- called by jpeg_finish_decompress
189 * after all data has been read. Often a no-op.
191 * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
192 * application must deal with any cleanup that should happen even
197 term_source (j_decompress_ptr cinfo)
199 /* no work necessary here */
204 * Prepare for input from a stdio stream.
205 * The caller must have already opened the stream, and is responsible
206 * for closing it after finishing decompression.
210 fs_jpg_src (j_decompress_ptr cinfo, fs_file infile)
214 /* The source object and input buffer are made permanent so that a series
215 * of JPEG images can be read from the same file by calling jpeg_stdio_src
216 * only before the first one. (If we discarded the buffer at the end of
217 * one image, we'd likely lose the start of the next one.)
218 * This makes it unsafe to use this manager and a different source
219 * manager serially with the same JPEG object. Caveat programmer.
221 if (cinfo->src == NULL) { /* first time for this JPEG object? */
222 cinfo->src = (struct jpeg_source_mgr *)
223 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
224 sizeof (my_source_mgr));
225 src = (my_src_ptr) cinfo->src;
226 src->buffer = (JOCTET *)
227 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
228 INPUT_BUF_SIZE * sizeof (JOCTET));
231 src = (my_src_ptr) cinfo->src;
232 src->pub.init_source = init_source;
233 src->pub.fill_input_buffer = fill_input_buffer;
234 src->pub.skip_input_data = skip_input_data;
235 src->pub.resync_to_restart = jpeg_resync_to_restart; /* use default method */
236 src->pub.term_source = term_source;
237 src->infile = infile;
238 src->pub.bytes_in_buffer = 0; /* forces fill_input_buffer on first read */
239 src->pub.next_input_byte = NULL; /* until buffer loaded */