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annotate libs/libjpeg/jdatasrc.c @ 9:64e15874f3bd

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author John Tsiombikas <nuclear@member.fsf.org>
date Sat, 26 Sep 2015 02:56:07 +0300
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nuclear@2 1 /*
nuclear@2 2 * jdatasrc.c
nuclear@2 3 *
nuclear@2 4 * Copyright (C) 1994-1996, Thomas G. Lane.
nuclear@2 5 * This file is part of the Independent JPEG Group's software.
nuclear@2 6 * For conditions of distribution and use, see the accompanying README file.
nuclear@2 7 *
nuclear@2 8 * This file contains decompression data source routines for the case of
nuclear@2 9 * reading JPEG data from a file (or any stdio stream). While these routines
nuclear@2 10 * are sufficient for most applications, some will want to use a different
nuclear@2 11 * source manager.
nuclear@2 12 * IMPORTANT: we assume that fread() will correctly transcribe an array of
nuclear@2 13 * JOCTETs from 8-bit-wide elements on external storage. If char is wider
nuclear@2 14 * than 8 bits on your machine, you may need to do some tweaking.
nuclear@2 15 */
nuclear@2 16
nuclear@2 17 /* this is not a core library module, so it doesn't define JPEG_INTERNALS */
nuclear@2 18 #include "jinclude.h"
nuclear@2 19 #include "jpeglib.h"
nuclear@2 20 #include "jerror.h"
nuclear@2 21
nuclear@2 22
nuclear@2 23 /* Expanded data source object for stdio input */
nuclear@2 24
nuclear@2 25 typedef struct {
nuclear@2 26 struct jpeg_source_mgr pub; /* public fields */
nuclear@2 27
nuclear@2 28 FILE * infile; /* source stream */
nuclear@2 29 JOCTET * buffer; /* start of buffer */
nuclear@2 30 boolean start_of_file; /* have we gotten any data yet? */
nuclear@2 31 } my_source_mgr;
nuclear@2 32
nuclear@2 33 typedef my_source_mgr * my_src_ptr;
nuclear@2 34
nuclear@2 35 #define INPUT_BUF_SIZE 4096 /* choose an efficiently fread'able size */
nuclear@2 36
nuclear@2 37
nuclear@2 38 /*
nuclear@2 39 * Initialize source --- called by jpeg_read_header
nuclear@2 40 * before any data is actually read.
nuclear@2 41 */
nuclear@2 42
nuclear@2 43 METHODDEF(void)
nuclear@2 44 init_source (j_decompress_ptr cinfo)
nuclear@2 45 {
nuclear@2 46 my_src_ptr src = (my_src_ptr) cinfo->src;
nuclear@2 47
nuclear@2 48 /* We reset the empty-input-file flag for each image,
nuclear@2 49 * but we don't clear the input buffer.
nuclear@2 50 * This is correct behavior for reading a series of images from one source.
nuclear@2 51 */
nuclear@2 52 src->start_of_file = TRUE;
nuclear@2 53 }
nuclear@2 54
nuclear@2 55
nuclear@2 56 /*
nuclear@2 57 * Fill the input buffer --- called whenever buffer is emptied.
nuclear@2 58 *
nuclear@2 59 * In typical applications, this should read fresh data into the buffer
nuclear@2 60 * (ignoring the current state of next_input_byte & bytes_in_buffer),
nuclear@2 61 * reset the pointer & count to the start of the buffer, and return TRUE
nuclear@2 62 * indicating that the buffer has been reloaded. It is not necessary to
nuclear@2 63 * fill the buffer entirely, only to obtain at least one more byte.
nuclear@2 64 *
nuclear@2 65 * There is no such thing as an EOF return. If the end of the file has been
nuclear@2 66 * reached, the routine has a choice of ERREXIT() or inserting fake data into
nuclear@2 67 * the buffer. In most cases, generating a warning message and inserting a
nuclear@2 68 * fake EOI marker is the best course of action --- this will allow the
nuclear@2 69 * decompressor to output however much of the image is there. However,
nuclear@2 70 * the resulting error message is misleading if the real problem is an empty
nuclear@2 71 * input file, so we handle that case specially.
nuclear@2 72 *
nuclear@2 73 * In applications that need to be able to suspend compression due to input
nuclear@2 74 * not being available yet, a FALSE return indicates that no more data can be
nuclear@2 75 * obtained right now, but more may be forthcoming later. In this situation,
nuclear@2 76 * the decompressor will return to its caller (with an indication of the
nuclear@2 77 * number of scanlines it has read, if any). The application should resume
nuclear@2 78 * decompression after it has loaded more data into the input buffer. Note
nuclear@2 79 * that there are substantial restrictions on the use of suspension --- see
nuclear@2 80 * the documentation.
nuclear@2 81 *
nuclear@2 82 * When suspending, the decompressor will back up to a convenient restart point
nuclear@2 83 * (typically the start of the current MCU). next_input_byte & bytes_in_buffer
nuclear@2 84 * indicate where the restart point will be if the current call returns FALSE.
nuclear@2 85 * Data beyond this point must be rescanned after resumption, so move it to
nuclear@2 86 * the front of the buffer rather than discarding it.
nuclear@2 87 */
nuclear@2 88
nuclear@2 89 METHODDEF(boolean)
nuclear@2 90 fill_input_buffer (j_decompress_ptr cinfo)
nuclear@2 91 {
nuclear@2 92 my_src_ptr src = (my_src_ptr) cinfo->src;
nuclear@2 93 size_t nbytes;
nuclear@2 94
nuclear@2 95 nbytes = JFREAD(src->infile, src->buffer, INPUT_BUF_SIZE);
nuclear@2 96
nuclear@2 97 if (nbytes <= 0) {
nuclear@2 98 if (src->start_of_file) /* Treat empty input file as fatal error */
nuclear@2 99 ERREXIT(cinfo, JERR_INPUT_EMPTY);
nuclear@2 100 WARNMS(cinfo, JWRN_JPEG_EOF);
nuclear@2 101 /* Insert a fake EOI marker */
nuclear@2 102 src->buffer[0] = (JOCTET) 0xFF;
nuclear@2 103 src->buffer[1] = (JOCTET) JPEG_EOI;
nuclear@2 104 nbytes = 2;
nuclear@2 105 }
nuclear@2 106
nuclear@2 107 src->pub.next_input_byte = src->buffer;
nuclear@2 108 src->pub.bytes_in_buffer = nbytes;
nuclear@2 109 src->start_of_file = FALSE;
nuclear@2 110
nuclear@2 111 return TRUE;
nuclear@2 112 }
nuclear@2 113
nuclear@2 114
nuclear@2 115 /*
nuclear@2 116 * Skip data --- used to skip over a potentially large amount of
nuclear@2 117 * uninteresting data (such as an APPn marker).
nuclear@2 118 *
nuclear@2 119 * Writers of suspendable-input applications must note that skip_input_data
nuclear@2 120 * is not granted the right to give a suspension return. If the skip extends
nuclear@2 121 * beyond the data currently in the buffer, the buffer can be marked empty so
nuclear@2 122 * that the next read will cause a fill_input_buffer call that can suspend.
nuclear@2 123 * Arranging for additional bytes to be discarded before reloading the input
nuclear@2 124 * buffer is the application writer's problem.
nuclear@2 125 */
nuclear@2 126
nuclear@2 127 METHODDEF(void)
nuclear@2 128 skip_input_data (j_decompress_ptr cinfo, long num_bytes)
nuclear@2 129 {
nuclear@2 130 my_src_ptr src = (my_src_ptr) cinfo->src;
nuclear@2 131
nuclear@2 132 /* Just a dumb implementation for now. Could use fseek() except
nuclear@2 133 * it doesn't work on pipes. Not clear that being smart is worth
nuclear@2 134 * any trouble anyway --- large skips are infrequent.
nuclear@2 135 */
nuclear@2 136 if (num_bytes > 0) {
nuclear@2 137 while (num_bytes > (long) src->pub.bytes_in_buffer) {
nuclear@2 138 num_bytes -= (long) src->pub.bytes_in_buffer;
nuclear@2 139 (void) fill_input_buffer(cinfo);
nuclear@2 140 /* note we assume that fill_input_buffer will never return FALSE,
nuclear@2 141 * so suspension need not be handled.
nuclear@2 142 */
nuclear@2 143 }
nuclear@2 144 src->pub.next_input_byte += (size_t) num_bytes;
nuclear@2 145 src->pub.bytes_in_buffer -= (size_t) num_bytes;
nuclear@2 146 }
nuclear@2 147 }
nuclear@2 148
nuclear@2 149
nuclear@2 150 /*
nuclear@2 151 * An additional method that can be provided by data source modules is the
nuclear@2 152 * resync_to_restart method for error recovery in the presence of RST markers.
nuclear@2 153 * For the moment, this source module just uses the default resync method
nuclear@2 154 * provided by the JPEG library. That method assumes that no backtracking
nuclear@2 155 * is possible.
nuclear@2 156 */
nuclear@2 157
nuclear@2 158
nuclear@2 159 /*
nuclear@2 160 * Terminate source --- called by jpeg_finish_decompress
nuclear@2 161 * after all data has been read. Often a no-op.
nuclear@2 162 *
nuclear@2 163 * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
nuclear@2 164 * application must deal with any cleanup that should happen even
nuclear@2 165 * for error exit.
nuclear@2 166 */
nuclear@2 167
nuclear@2 168 METHODDEF(void)
nuclear@2 169 term_source (j_decompress_ptr cinfo)
nuclear@2 170 {
nuclear@2 171 /* no work necessary here */
nuclear@2 172 }
nuclear@2 173
nuclear@2 174
nuclear@2 175 /*
nuclear@2 176 * Prepare for input from a stdio stream.
nuclear@2 177 * The caller must have already opened the stream, and is responsible
nuclear@2 178 * for closing it after finishing decompression.
nuclear@2 179 */
nuclear@2 180
nuclear@2 181 GLOBAL(void)
nuclear@2 182 jpeg_stdio_src (j_decompress_ptr cinfo, FILE * infile)
nuclear@2 183 {
nuclear@2 184 my_src_ptr src;
nuclear@2 185
nuclear@2 186 /* The source object and input buffer are made permanent so that a series
nuclear@2 187 * of JPEG images can be read from the same file by calling jpeg_stdio_src
nuclear@2 188 * only before the first one. (If we discarded the buffer at the end of
nuclear@2 189 * one image, we'd likely lose the start of the next one.)
nuclear@2 190 * This makes it unsafe to use this manager and a different source
nuclear@2 191 * manager serially with the same JPEG object. Caveat programmer.
nuclear@2 192 */
nuclear@2 193 if (cinfo->src == NULL) { /* first time for this JPEG object? */
nuclear@2 194 cinfo->src = (struct jpeg_source_mgr *)
nuclear@2 195 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
nuclear@2 196 SIZEOF(my_source_mgr));
nuclear@2 197 src = (my_src_ptr) cinfo->src;
nuclear@2 198 src->buffer = (JOCTET *)
nuclear@2 199 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
nuclear@2 200 INPUT_BUF_SIZE * SIZEOF(JOCTET));
nuclear@2 201 }
nuclear@2 202
nuclear@2 203 src = (my_src_ptr) cinfo->src;
nuclear@2 204 src->pub.init_source = init_source;
nuclear@2 205 src->pub.fill_input_buffer = fill_input_buffer;
nuclear@2 206 src->pub.skip_input_data = skip_input_data;
nuclear@2 207 src->pub.resync_to_restart = jpeg_resync_to_restart; /* use default method */
nuclear@2 208 src->pub.term_source = term_source;
nuclear@2 209 src->infile = infile;
nuclear@2 210 src->pub.bytes_in_buffer = 0; /* forces fill_input_buffer on first read */
nuclear@2 211 src->pub.next_input_byte = NULL; /* until buffer loaded */
nuclear@2 212 }