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annotate libs/libjpeg/jdatasrc.c @ 2:334d17aed7de

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author John Tsiombikas <nuclear@member.fsf.org>
date Sun, 02 Feb 2014 18:36:38 +0200
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nuclear@0 1 /*
nuclear@0 2 * jdatasrc.c
nuclear@0 3 *
nuclear@0 4 * Copyright (C) 1994-1996, Thomas G. Lane.
nuclear@0 5 * This file is part of the Independent JPEG Group's software.
nuclear@0 6 * For conditions of distribution and use, see the accompanying README file.
nuclear@0 7 *
nuclear@0 8 * This file contains decompression data source routines for the case of
nuclear@0 9 * reading JPEG data from a file (or any stdio stream). While these routines
nuclear@0 10 * are sufficient for most applications, some will want to use a different
nuclear@0 11 * source manager.
nuclear@0 12 * IMPORTANT: we assume that fread() will correctly transcribe an array of
nuclear@0 13 * JOCTETs from 8-bit-wide elements on external storage. If char is wider
nuclear@0 14 * than 8 bits on your machine, you may need to do some tweaking.
nuclear@0 15 */
nuclear@0 16
nuclear@0 17 /* this is not a core library module, so it doesn't define JPEG_INTERNALS */
nuclear@0 18 #include "jinclude.h"
nuclear@0 19 #include "jpeglib.h"
nuclear@0 20 #include "jerror.h"
nuclear@0 21
nuclear@0 22
nuclear@0 23 /* Expanded data source object for stdio input */
nuclear@0 24
nuclear@0 25 typedef struct {
nuclear@0 26 struct jpeg_source_mgr pub; /* public fields */
nuclear@0 27
nuclear@0 28 FILE * infile; /* source stream */
nuclear@0 29 JOCTET * buffer; /* start of buffer */
nuclear@0 30 boolean start_of_file; /* have we gotten any data yet? */
nuclear@0 31 } my_source_mgr;
nuclear@0 32
nuclear@0 33 typedef my_source_mgr * my_src_ptr;
nuclear@0 34
nuclear@0 35 #define INPUT_BUF_SIZE 4096 /* choose an efficiently fread'able size */
nuclear@0 36
nuclear@0 37
nuclear@0 38 /*
nuclear@0 39 * Initialize source --- called by jpeg_read_header
nuclear@0 40 * before any data is actually read.
nuclear@0 41 */
nuclear@0 42
nuclear@0 43 METHODDEF(void)
nuclear@0 44 init_source (j_decompress_ptr cinfo)
nuclear@0 45 {
nuclear@0 46 my_src_ptr src = (my_src_ptr) cinfo->src;
nuclear@0 47
nuclear@0 48 /* We reset the empty-input-file flag for each image,
nuclear@0 49 * but we don't clear the input buffer.
nuclear@0 50 * This is correct behavior for reading a series of images from one source.
nuclear@0 51 */
nuclear@0 52 src->start_of_file = TRUE;
nuclear@0 53 }
nuclear@0 54
nuclear@0 55
nuclear@0 56 /*
nuclear@0 57 * Fill the input buffer --- called whenever buffer is emptied.
nuclear@0 58 *
nuclear@0 59 * In typical applications, this should read fresh data into the buffer
nuclear@0 60 * (ignoring the current state of next_input_byte & bytes_in_buffer),
nuclear@0 61 * reset the pointer & count to the start of the buffer, and return TRUE
nuclear@0 62 * indicating that the buffer has been reloaded. It is not necessary to
nuclear@0 63 * fill the buffer entirely, only to obtain at least one more byte.
nuclear@0 64 *
nuclear@0 65 * There is no such thing as an EOF return. If the end of the file has been
nuclear@0 66 * reached, the routine has a choice of ERREXIT() or inserting fake data into
nuclear@0 67 * the buffer. In most cases, generating a warning message and inserting a
nuclear@0 68 * fake EOI marker is the best course of action --- this will allow the
nuclear@0 69 * decompressor to output however much of the image is there. However,
nuclear@0 70 * the resulting error message is misleading if the real problem is an empty
nuclear@0 71 * input file, so we handle that case specially.
nuclear@0 72 *
nuclear@0 73 * In applications that need to be able to suspend compression due to input
nuclear@0 74 * not being available yet, a FALSE return indicates that no more data can be
nuclear@0 75 * obtained right now, but more may be forthcoming later. In this situation,
nuclear@0 76 * the decompressor will return to its caller (with an indication of the
nuclear@0 77 * number of scanlines it has read, if any). The application should resume
nuclear@0 78 * decompression after it has loaded more data into the input buffer. Note
nuclear@0 79 * that there are substantial restrictions on the use of suspension --- see
nuclear@0 80 * the documentation.
nuclear@0 81 *
nuclear@0 82 * When suspending, the decompressor will back up to a convenient restart point
nuclear@0 83 * (typically the start of the current MCU). next_input_byte & bytes_in_buffer
nuclear@0 84 * indicate where the restart point will be if the current call returns FALSE.
nuclear@0 85 * Data beyond this point must be rescanned after resumption, so move it to
nuclear@0 86 * the front of the buffer rather than discarding it.
nuclear@0 87 */
nuclear@0 88
nuclear@0 89 METHODDEF(boolean)
nuclear@0 90 fill_input_buffer (j_decompress_ptr cinfo)
nuclear@0 91 {
nuclear@0 92 my_src_ptr src = (my_src_ptr) cinfo->src;
nuclear@0 93 size_t nbytes;
nuclear@0 94
nuclear@0 95 nbytes = JFREAD(src->infile, src->buffer, INPUT_BUF_SIZE);
nuclear@0 96
nuclear@0 97 if (nbytes <= 0) {
nuclear@0 98 if (src->start_of_file) /* Treat empty input file as fatal error */
nuclear@0 99 ERREXIT(cinfo, JERR_INPUT_EMPTY);
nuclear@0 100 WARNMS(cinfo, JWRN_JPEG_EOF);
nuclear@0 101 /* Insert a fake EOI marker */
nuclear@0 102 src->buffer[0] = (JOCTET) 0xFF;
nuclear@0 103 src->buffer[1] = (JOCTET) JPEG_EOI;
nuclear@0 104 nbytes = 2;
nuclear@0 105 }
nuclear@0 106
nuclear@0 107 src->pub.next_input_byte = src->buffer;
nuclear@0 108 src->pub.bytes_in_buffer = nbytes;
nuclear@0 109 src->start_of_file = FALSE;
nuclear@0 110
nuclear@0 111 return TRUE;
nuclear@0 112 }
nuclear@0 113
nuclear@0 114
nuclear@0 115 /*
nuclear@0 116 * Skip data --- used to skip over a potentially large amount of
nuclear@0 117 * uninteresting data (such as an APPn marker).
nuclear@0 118 *
nuclear@0 119 * Writers of suspendable-input applications must note that skip_input_data
nuclear@0 120 * is not granted the right to give a suspension return. If the skip extends
nuclear@0 121 * beyond the data currently in the buffer, the buffer can be marked empty so
nuclear@0 122 * that the next read will cause a fill_input_buffer call that can suspend.
nuclear@0 123 * Arranging for additional bytes to be discarded before reloading the input
nuclear@0 124 * buffer is the application writer's problem.
nuclear@0 125 */
nuclear@0 126
nuclear@0 127 METHODDEF(void)
nuclear@0 128 skip_input_data (j_decompress_ptr cinfo, long num_bytes)
nuclear@0 129 {
nuclear@0 130 my_src_ptr src = (my_src_ptr) cinfo->src;
nuclear@0 131
nuclear@0 132 /* Just a dumb implementation for now. Could use fseek() except
nuclear@0 133 * it doesn't work on pipes. Not clear that being smart is worth
nuclear@0 134 * any trouble anyway --- large skips are infrequent.
nuclear@0 135 */
nuclear@0 136 if (num_bytes > 0) {
nuclear@0 137 while (num_bytes > (long) src->pub.bytes_in_buffer) {
nuclear@0 138 num_bytes -= (long) src->pub.bytes_in_buffer;
nuclear@0 139 (void) fill_input_buffer(cinfo);
nuclear@0 140 /* note we assume that fill_input_buffer will never return FALSE,
nuclear@0 141 * so suspension need not be handled.
nuclear@0 142 */
nuclear@0 143 }
nuclear@0 144 src->pub.next_input_byte += (size_t) num_bytes;
nuclear@0 145 src->pub.bytes_in_buffer -= (size_t) num_bytes;
nuclear@0 146 }
nuclear@0 147 }
nuclear@0 148
nuclear@0 149
nuclear@0 150 /*
nuclear@0 151 * An additional method that can be provided by data source modules is the
nuclear@0 152 * resync_to_restart method for error recovery in the presence of RST markers.
nuclear@0 153 * For the moment, this source module just uses the default resync method
nuclear@0 154 * provided by the JPEG library. That method assumes that no backtracking
nuclear@0 155 * is possible.
nuclear@0 156 */
nuclear@0 157
nuclear@0 158
nuclear@0 159 /*
nuclear@0 160 * Terminate source --- called by jpeg_finish_decompress
nuclear@0 161 * after all data has been read. Often a no-op.
nuclear@0 162 *
nuclear@0 163 * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
nuclear@0 164 * application must deal with any cleanup that should happen even
nuclear@0 165 * for error exit.
nuclear@0 166 */
nuclear@0 167
nuclear@0 168 METHODDEF(void)
nuclear@0 169 term_source (j_decompress_ptr cinfo)
nuclear@0 170 {
nuclear@0 171 /* no work necessary here */
nuclear@0 172 }
nuclear@0 173
nuclear@0 174
nuclear@0 175 /*
nuclear@0 176 * Prepare for input from a stdio stream.
nuclear@0 177 * The caller must have already opened the stream, and is responsible
nuclear@0 178 * for closing it after finishing decompression.
nuclear@0 179 */
nuclear@0 180
nuclear@0 181 GLOBAL(void)
nuclear@0 182 jpeg_stdio_src (j_decompress_ptr cinfo, FILE * infile)
nuclear@0 183 {
nuclear@0 184 my_src_ptr src;
nuclear@0 185
nuclear@0 186 /* The source object and input buffer are made permanent so that a series
nuclear@0 187 * of JPEG images can be read from the same file by calling jpeg_stdio_src
nuclear@0 188 * only before the first one. (If we discarded the buffer at the end of
nuclear@0 189 * one image, we'd likely lose the start of the next one.)
nuclear@0 190 * This makes it unsafe to use this manager and a different source
nuclear@0 191 * manager serially with the same JPEG object. Caveat programmer.
nuclear@0 192 */
nuclear@0 193 if (cinfo->src == NULL) { /* first time for this JPEG object? */
nuclear@0 194 cinfo->src = (struct jpeg_source_mgr *)
nuclear@0 195 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
nuclear@0 196 SIZEOF(my_source_mgr));
nuclear@0 197 src = (my_src_ptr) cinfo->src;
nuclear@0 198 src->buffer = (JOCTET *)
nuclear@0 199 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
nuclear@0 200 INPUT_BUF_SIZE * SIZEOF(JOCTET));
nuclear@0 201 }
nuclear@0 202
nuclear@0 203 src = (my_src_ptr) cinfo->src;
nuclear@0 204 src->pub.init_source = init_source;
nuclear@0 205 src->pub.fill_input_buffer = fill_input_buffer;
nuclear@0 206 src->pub.skip_input_data = skip_input_data;
nuclear@0 207 src->pub.resync_to_restart = jpeg_resync_to_restart; /* use default method */
nuclear@0 208 src->pub.term_source = term_source;
nuclear@0 209 src->infile = infile;
nuclear@0 210 src->pub.bytes_in_buffer = 0; /* forces fill_input_buffer on first read */
nuclear@0 211 src->pub.next_input_byte = NULL; /* until buffer loaded */
nuclear@0 212 }