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/thirdparty/jpeg/jdatasrc.c

http://crashrpt.googlecode.com/
C | 274 lines | 112 code | 43 blank | 119 comment | 12 complexity | 2b4d40b1c8672d0744ab489d8da4b434 MD5 | raw file
  1/*
  2 * jdatasrc.c
  3 *
  4 * Copyright (C) 1994-1996, Thomas G. Lane.
  5 * Modified 2009-2010 by Guido Vollbeding.
  6 * This file is part of the Independent JPEG Group's software.
  7 * For conditions of distribution and use, see the accompanying README file.
  8 *
  9 * This file contains decompression data source routines for the case of
 10 * reading JPEG data from memory or from a file (or any stdio stream).
 11 * While these routines are sufficient for most applications,
 12 * some will want to use a different source manager.
 13 * IMPORTANT: we assume that fread() will correctly transcribe an array of
 14 * JOCTETs from 8-bit-wide elements on external storage.  If char is wider
 15 * than 8 bits on your machine, you may need to do some tweaking.
 16 */
 17
 18/* this is not a core library module, so it doesn't define JPEG_INTERNALS */
 19#include "jinclude.h"
 20#include "jpeglib.h"
 21#include "jerror.h"
 22
 23
 24/* Expanded data source object for stdio input */
 25
 26typedef struct {
 27  struct jpeg_source_mgr pub;	/* public fields */
 28
 29  FILE * infile;		/* source stream */
 30  JOCTET * buffer;		/* start of buffer */
 31  boolean start_of_file;	/* have we gotten any data yet? */
 32} my_source_mgr;
 33
 34typedef my_source_mgr * my_src_ptr;
 35
 36#define INPUT_BUF_SIZE  4096	/* choose an efficiently fread'able size */
 37
 38
 39/*
 40 * Initialize source --- called by jpeg_read_header
 41 * before any data is actually read.
 42 */
 43
 44METHODDEF(void)
 45init_source (j_decompress_ptr cinfo)
 46{
 47  my_src_ptr src = (my_src_ptr) cinfo->src;
 48
 49  /* We reset the empty-input-file flag for each image,
 50   * but we don't clear the input buffer.
 51   * This is correct behavior for reading a series of images from one source.
 52   */
 53  src->start_of_file = TRUE;
 54}
 55
 56METHODDEF(void)
 57init_mem_source (j_decompress_ptr cinfo)
 58{
 59  /* no work necessary here */
 60}
 61
 62
 63/*
 64 * Fill the input buffer --- called whenever buffer is emptied.
 65 *
 66 * In typical applications, this should read fresh data into the buffer
 67 * (ignoring the current state of next_input_byte & bytes_in_buffer),
 68 * reset the pointer & count to the start of the buffer, and return TRUE
 69 * indicating that the buffer has been reloaded.  It is not necessary to
 70 * fill the buffer entirely, only to obtain at least one more byte.
 71 *
 72 * There is no such thing as an EOF return.  If the end of the file has been
 73 * reached, the routine has a choice of ERREXIT() or inserting fake data into
 74 * the buffer.  In most cases, generating a warning message and inserting a
 75 * fake EOI marker is the best course of action --- this will allow the
 76 * decompressor to output however much of the image is there.  However,
 77 * the resulting error message is misleading if the real problem is an empty
 78 * input file, so we handle that case specially.
 79 *
 80 * In applications that need to be able to suspend compression due to input
 81 * not being available yet, a FALSE return indicates that no more data can be
 82 * obtained right now, but more may be forthcoming later.  In this situation,
 83 * the decompressor will return to its caller (with an indication of the
 84 * number of scanlines it has read, if any).  The application should resume
 85 * decompression after it has loaded more data into the input buffer.  Note
 86 * that there are substantial restrictions on the use of suspension --- see
 87 * the documentation.
 88 *
 89 * When suspending, the decompressor will back up to a convenient restart point
 90 * (typically the start of the current MCU). next_input_byte & bytes_in_buffer
 91 * indicate where the restart point will be if the current call returns FALSE.
 92 * Data beyond this point must be rescanned after resumption, so move it to
 93 * the front of the buffer rather than discarding it.
 94 */
 95
 96METHODDEF(boolean)
 97fill_input_buffer (j_decompress_ptr cinfo)
 98{
 99  my_src_ptr src = (my_src_ptr) cinfo->src;
100  size_t nbytes;
101
102  nbytes = JFREAD(src->infile, src->buffer, INPUT_BUF_SIZE);
103
104  if (nbytes <= 0) {
105    if (src->start_of_file)	/* Treat empty input file as fatal error */
106      ERREXIT(cinfo, JERR_INPUT_EMPTY);
107    WARNMS(cinfo, JWRN_JPEG_EOF);
108    /* Insert a fake EOI marker */
109    src->buffer[0] = (JOCTET) 0xFF;
110    src->buffer[1] = (JOCTET) JPEG_EOI;
111    nbytes = 2;
112  }
113
114  src->pub.next_input_byte = src->buffer;
115  src->pub.bytes_in_buffer = nbytes;
116  src->start_of_file = FALSE;
117
118  return TRUE;
119}
120
121METHODDEF(boolean)
122fill_mem_input_buffer (j_decompress_ptr cinfo)
123{
124  static JOCTET mybuffer[4];
125
126  /* The whole JPEG data is expected to reside in the supplied memory
127   * buffer, so any request for more data beyond the given buffer size
128   * is treated as an error.
129   */
130  WARNMS(cinfo, JWRN_JPEG_EOF);
131  /* Insert a fake EOI marker */
132  mybuffer[0] = (JOCTET) 0xFF;
133  mybuffer[1] = (JOCTET) JPEG_EOI;
134
135  cinfo->src->next_input_byte = mybuffer;
136  cinfo->src->bytes_in_buffer = 2;
137
138  return TRUE;
139}
140
141
142/*
143 * Skip data --- used to skip over a potentially large amount of
144 * uninteresting data (such as an APPn marker).
145 *
146 * Writers of suspendable-input applications must note that skip_input_data
147 * is not granted the right to give a suspension return.  If the skip extends
148 * beyond the data currently in the buffer, the buffer can be marked empty so
149 * that the next read will cause a fill_input_buffer call that can suspend.
150 * Arranging for additional bytes to be discarded before reloading the input
151 * buffer is the application writer's problem.
152 */
153
154METHODDEF(void)
155skip_input_data (j_decompress_ptr cinfo, long num_bytes)
156{
157  struct jpeg_source_mgr * src = cinfo->src;
158
159  /* Just a dumb implementation for now.  Could use fseek() except
160   * it doesn't work on pipes.  Not clear that being smart is worth
161   * any trouble anyway --- large skips are infrequent.
162   */
163  if (num_bytes > 0) {
164    while (num_bytes > (long) src->bytes_in_buffer) {
165      num_bytes -= (long) src->bytes_in_buffer;
166      (void) (*src->fill_input_buffer) (cinfo);
167      /* note we assume that fill_input_buffer will never return FALSE,
168       * so suspension need not be handled.
169       */
170    }
171    src->next_input_byte += (size_t) num_bytes;
172    src->bytes_in_buffer -= (size_t) num_bytes;
173  }
174}
175
176
177/*
178 * An additional method that can be provided by data source modules is the
179 * resync_to_restart method for error recovery in the presence of RST markers.
180 * For the moment, this source module just uses the default resync method
181 * provided by the JPEG library.  That method assumes that no backtracking
182 * is possible.
183 */
184
185
186/*
187 * Terminate source --- called by jpeg_finish_decompress
188 * after all data has been read.  Often a no-op.
189 *
190 * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
191 * application must deal with any cleanup that should happen even
192 * for error exit.
193 */
194
195METHODDEF(void)
196term_source (j_decompress_ptr cinfo)
197{
198  /* no work necessary here */
199}
200
201
202/*
203 * Prepare for input from a stdio stream.
204 * The caller must have already opened the stream, and is responsible
205 * for closing it after finishing decompression.
206 */
207
208GLOBAL(void)
209jpeg_stdio_src (j_decompress_ptr cinfo, FILE * infile)
210{
211  my_src_ptr src;
212
213  /* The source object and input buffer are made permanent so that a series
214   * of JPEG images can be read from the same file by calling jpeg_stdio_src
215   * only before the first one.  (If we discarded the buffer at the end of
216   * one image, we'd likely lose the start of the next one.)
217   * This makes it unsafe to use this manager and a different source
218   * manager serially with the same JPEG object.  Caveat programmer.
219   */
220  if (cinfo->src == NULL) {	/* first time for this JPEG object? */
221    cinfo->src = (struct jpeg_source_mgr *)
222      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
223				  SIZEOF(my_source_mgr));
224    src = (my_src_ptr) cinfo->src;
225    src->buffer = (JOCTET *)
226      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
227				  INPUT_BUF_SIZE * SIZEOF(JOCTET));
228  }
229
230  src = (my_src_ptr) cinfo->src;
231  src->pub.init_source = init_source;
232  src->pub.fill_input_buffer = fill_input_buffer;
233  src->pub.skip_input_data = skip_input_data;
234  src->pub.resync_to_restart = jpeg_resync_to_restart; /* use default method */
235  src->pub.term_source = term_source;
236  src->infile = infile;
237  src->pub.bytes_in_buffer = 0; /* forces fill_input_buffer on first read */
238  src->pub.next_input_byte = NULL; /* until buffer loaded */
239}
240
241
242/*
243 * Prepare for input from a supplied memory buffer.
244 * The buffer must contain the whole JPEG data.
245 */
246
247GLOBAL(void)
248jpeg_mem_src (j_decompress_ptr cinfo,
249	      unsigned char * inbuffer, unsigned long insize)
250{
251  struct jpeg_source_mgr * src;
252
253  if (inbuffer == NULL || insize == 0)	/* Treat empty input as fatal error */
254    ERREXIT(cinfo, JERR_INPUT_EMPTY);
255
256  /* The source object is made permanent so that a series of JPEG images
257   * can be read from the same buffer by calling jpeg_mem_src only before
258   * the first one.
259   */
260  if (cinfo->src == NULL) {	/* first time for this JPEG object? */
261    cinfo->src = (struct jpeg_source_mgr *)
262      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
263				  SIZEOF(struct jpeg_source_mgr));
264  }
265
266  src = cinfo->src;
267  src->init_source = init_mem_source;
268  src->fill_input_buffer = fill_mem_input_buffer;
269  src->skip_input_data = skip_input_data;
270  src->resync_to_restart = jpeg_resync_to_restart; /* use default method */
271  src->term_source = term_source;
272  src->bytes_in_buffer = (size_t) insize;
273  src->next_input_byte = (JOCTET *) inbuffer;
274}