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* Copyright (C) 1994-1996, Thomas G. Lane.
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* This file is part of the Independent JPEG Group's software.
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* For conditions of distribution and use, see the accompanying README file.
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* This file contains decompression data source routines for the case of
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* reading JPEG data from a file (or any stdio stream). While these routines
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* are sufficient for most applications, some will want to use a different
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* IMPORTANT: we assume that fread() will correctly transcribe an array of
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* JOCTETs from 8-bit-wide elements on external storage. If char is wider
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* than 8 bits on your machine, you may need to do some tweaking.
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/* this is not a core library module, so it doesn't define JPEG_INTERNALS */
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/* Expanded data source object for stdio input */
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struct jpeg_source_mgr pub; /* public fields */
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FILE * infile; /* source stream */
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JOCTET * buffer; /* start of buffer */
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boolean start_of_file; /* have we gotten any data yet? */
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typedef my_source_mgr * my_src_ptr;
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#define INPUT_BUF_SIZE 4096 /* choose an efficiently fread'able size */
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* Initialize source --- called by jpeg_read_header
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* before any data is actually read.
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init_source (j_decompress_ptr cinfo)
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my_src_ptr src = (my_src_ptr) cinfo->src;
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/* We reset the empty-input-file flag for each image,
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* but we don't clear the input buffer.
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* This is correct behavior for reading a series of images from one source.
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src->start_of_file = TRUE;
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* Fill the input buffer --- called whenever buffer is emptied.
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* In typical applications, this should read fresh data into the buffer
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* (ignoring the current state of next_input_byte & bytes_in_buffer),
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* reset the pointer & count to the start of the buffer, and return TRUE
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* indicating that the buffer has been reloaded. It is not necessary to
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* fill the buffer entirely, only to obtain at least one more byte.
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* There is no such thing as an EOF return. If the end of the file has been
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* reached, the routine has a choice of ERREXIT() or inserting fake data into
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* the buffer. In most cases, generating a warning message and inserting a
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* fake EOI marker is the best course of action --- this will allow the
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* decompressor to output however much of the image is there. However,
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* the resulting error message is misleading if the real problem is an empty
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* input file, so we handle that case specially.
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* In applications that need to be able to suspend compression due to input
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* not being available yet, a FALSE return indicates that no more data can be
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* obtained right now, but more may be forthcoming later. In this situation,
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* the decompressor will return to its caller (with an indication of the
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* number of scanlines it has read, if any). The application should resume
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* decompression after it has loaded more data into the input buffer. Note
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* that there are substantial restrictions on the use of suspension --- see
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* When suspending, the decompressor will back up to a convenient restart point
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* (typically the start of the current MCU). next_input_byte & bytes_in_buffer
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* indicate where the restart point will be if the current call returns FALSE.
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* Data beyond this point must be rescanned after resumption, so move it to
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* the front of the buffer rather than discarding it.
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fill_input_buffer (j_decompress_ptr cinfo)
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my_src_ptr src = (my_src_ptr) cinfo->src;
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nbytes = JFREAD(src->infile, src->buffer, INPUT_BUF_SIZE);
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if (src->start_of_file) /* Treat empty input file as fatal error */
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ERREXIT(cinfo, JERR_INPUT_EMPTY);
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WARNMS(cinfo, JWRN_JPEG_EOF);
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/* Insert a fake EOI marker */
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src->buffer[0] = (JOCTET) 0xFF;
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src->buffer[1] = (JOCTET) JPEG_EOI;
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src->pub.next_input_byte = src->buffer;
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src->pub.bytes_in_buffer = nbytes;
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src->start_of_file = FALSE;
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* Skip data --- used to skip over a potentially large amount of
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* uninteresting data (such as an APPn marker).
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* Writers of suspendable-input applications must note that skip_input_data
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* is not granted the right to give a suspension return. If the skip extends
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* beyond the data currently in the buffer, the buffer can be marked empty so
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* that the next read will cause a fill_input_buffer call that can suspend.
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* Arranging for additional bytes to be discarded before reloading the input
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* buffer is the application writer's problem.
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skip_input_data (j_decompress_ptr cinfo, long num_bytes)
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my_src_ptr src = (my_src_ptr) cinfo->src;
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/* Just a dumb implementation for now. Could use fseek() except
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* it doesn't work on pipes. Not clear that being smart is worth
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* any trouble anyway --- large skips are infrequent.
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while (num_bytes > (long) src->pub.bytes_in_buffer) {
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num_bytes -= (long) src->pub.bytes_in_buffer;
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(void) fill_input_buffer(cinfo);
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/* note we assume that fill_input_buffer will never return FALSE,
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* so suspension need not be handled.
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src->pub.next_input_byte += (size_t) num_bytes;
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src->pub.bytes_in_buffer -= (size_t) num_bytes;
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* An additional method that can be provided by data source modules is the
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* resync_to_restart method for error recovery in the presence of RST markers.
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* For the moment, this source module just uses the default resync method
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* provided by the JPEG library. That method assumes that no backtracking
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* Terminate source --- called by jpeg_finish_decompress
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* after all data has been read. Often a no-op.
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* NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
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* application must deal with any cleanup that should happen even
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term_source (j_decompress_ptr cinfo)
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/* no work necessary here */
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* Prepare for input from a stdio stream.
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* The caller must have already opened the stream, and is responsible
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* for closing it after finishing decompression.
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jpeg_stdio_src (j_decompress_ptr cinfo, FILE * infile)
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/* The source object and input buffer are made permanent so that a series
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* of JPEG images can be read from the same file by calling jpeg_stdio_src
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* only before the first one. (If we discarded the buffer at the end of
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* one image, we'd likely lose the start of the next one.)
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* This makes it unsafe to use this manager and a different source
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* manager serially with the same JPEG object. Caveat programmer.
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if (cinfo->src == NULL) { /* first time for this JPEG object? */
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cinfo->src = (struct jpeg_source_mgr *)
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(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
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SIZEOF(my_source_mgr));
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src = (my_src_ptr) cinfo->src;
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src->buffer = (JOCTET *)
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(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
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INPUT_BUF_SIZE * SIZEOF(JOCTET));
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src = (my_src_ptr) cinfo->src;
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src->pub.init_source = init_source;
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src->pub.fill_input_buffer = fill_input_buffer;
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src->pub.skip_input_data = skip_input_data;
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src->pub.resync_to_restart = jpeg_resync_to_restart; /* use default method */
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src->pub.term_source = term_source;
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src->infile = infile;
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src->pub.bytes_in_buffer = 0; /* forces fill_input_buffer on first read */
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src->pub.next_input_byte = NULL; /* until buffer loaded */
added
removed
jpeg-6b/jdatasrc.c
