MCL/sf/mw/qt: comparison src/3rdparty/libjpeg/jdatasrc.c

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+/*
+* jdatasrc.c
+*
+* Copyright (C) 1994-1996, Thomas G. Lane.
+* This file is part of the Independent JPEG Group's software.
+* For conditions of distribution and use, see the accompanying README file.
+*
+* This file contains decompression data source routines for the case of
+* reading JPEG data from a file (or any stdio stream).  While these routines
+* are sufficient for most applications, some will want to use a different
+* source manager.
+* IMPORTANT: we assume that fread() will correctly transcribe an array of
+* JOCTETs from 8-bit-wide elements on external storage.  If char is wider
+* than 8 bits on your machine, you may need to do some tweaking.
+*/
+/* this is not a core library module, so it doesn't define JPEG_INTERNALS */
+#include "jinclude.h"
+#include "jpeglib.h"
+#include "jerror.h"
+/* Expanded data source object for stdio input */
+typedef struct {
+struct jpeg_source_mgr pub;	/* public fields */
+FILE * infile;		/* source stream */
+JOCTET * buffer;		/* start of buffer */
+boolean start_of_file;	/* have we gotten any data yet? */
+} my_source_mgr;
+typedef my_source_mgr * my_src_ptr;
+#define INPUT_BUF_SIZE  4096	/* choose an efficiently fread'able size */
+/*
+* Initialize source --- called by jpeg_read_header
+* before any data is actually read.
+*/
+METHODDEF(void)
+init_source (j_decompress_ptr cinfo)
+{
+my_src_ptr src = (my_src_ptr) cinfo->src;
+/* We reset the empty-input-file flag for each image,
+* but we don't clear the input buffer.
+* This is correct behavior for reading a series of images from one source.
+*/
+src->start_of_file = TRUE;
+}
+/*
+* Fill the input buffer --- called whenever buffer is emptied.
+*
+* In typical applications, this should read fresh data into the buffer
+* (ignoring the current state of next_input_byte & bytes_in_buffer),
+* reset the pointer & count to the start of the buffer, and return TRUE
+* indicating that the buffer has been reloaded.  It is not necessary to
+* fill the buffer entirely, only to obtain at least one more byte.
+*
+* There is no such thing as an EOF return.  If the end of the file has been
+* reached, the routine has a choice of ERREXIT() or inserting fake data into
+* the buffer.  In most cases, generating a warning message and inserting a
+* fake EOI marker is the best course of action --- this will allow the
+* decompressor to output however much of the image is there.  However,
+* the resulting error message is misleading if the real problem is an empty
+* input file, so we handle that case specially.
+*
+* In applications that need to be able to suspend compression due to input
+* not being available yet, a FALSE return indicates that no more data can be
+* obtained right now, but more may be forthcoming later.  In this situation,
+* the decompressor will return to its caller (with an indication of the
+* number of scanlines it has read, if any).  The application should resume
+* decompression after it has loaded more data into the input buffer.  Note
+* that there are substantial restrictions on the use of suspension --- see
+* the documentation.
+*
+* When suspending, the decompressor will back up to a convenient restart point
+* (typically the start of the current MCU). next_input_byte & bytes_in_buffer
+* indicate where the restart point will be if the current call returns FALSE.
+* Data beyond this point must be rescanned after resumption, so move it to
+* the front of the buffer rather than discarding it.
+*/
+METHODDEF(boolean)
+fill_input_buffer (j_decompress_ptr cinfo)
+{
+my_src_ptr src = (my_src_ptr) cinfo->src;
+size_t nbytes;
+nbytes = JFREAD(src->infile, src->buffer, INPUT_BUF_SIZE);
+if (nbytes <= 0) {
+if (src->start_of_file)	/* Treat empty input file as fatal error */
+ERREXIT(cinfo, JERR_INPUT_EMPTY);
+WARNMS(cinfo, JWRN_JPEG_EOF);
+/* Insert a fake EOI marker */
+src->buffer[0] = (JOCTET) 0xFF;
+src->buffer[1] = (JOCTET) JPEG_EOI;
+nbytes = 2;
+}
+src->pub.next_input_byte = src->buffer;
+src->pub.bytes_in_buffer = nbytes;
+src->start_of_file = FALSE;
+return TRUE;
+}
+/*
+* Skip data --- used to skip over a potentially large amount of
+* uninteresting data (such as an APPn marker).
+*
+* Writers of suspendable-input applications must note that skip_input_data
+* is not granted the right to give a suspension return.  If the skip extends
+* beyond the data currently in the buffer, the buffer can be marked empty so
+* that the next read will cause a fill_input_buffer call that can suspend.
+* Arranging for additional bytes to be discarded before reloading the input
+* buffer is the application writer's problem.
+*/
+METHODDEF(void)
+skip_input_data (j_decompress_ptr cinfo, long num_bytes)
+{
+my_src_ptr src = (my_src_ptr) cinfo->src;
+/* Just a dumb implementation for now.  Could use fseek() except
+* it doesn't work on pipes.  Not clear that being smart is worth
+* any trouble anyway --- large skips are infrequent.
+*/
+if (num_bytes > 0) {
+while (num_bytes > (long) src->pub.bytes_in_buffer) {
+num_bytes -= (long) src->pub.bytes_in_buffer;
+(void) fill_input_buffer(cinfo);
+/* note we assume that fill_input_buffer will never return FALSE,
+* so suspension need not be handled.
+*/
+}
+src->pub.next_input_byte += (size_t) num_bytes;
+src->pub.bytes_in_buffer -= (size_t) num_bytes;
+}
+}
+/*
+* An additional method that can be provided by data source modules is the
+* resync_to_restart method for error recovery in the presence of RST markers.
+* For the moment, this source module just uses the default resync method
+* provided by the JPEG library.  That method assumes that no backtracking
+* is possible.
+*/
+/*
+* Terminate source --- called by jpeg_finish_decompress
+* after all data has been read.  Often a no-op.
+*
+* NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
+* application must deal with any cleanup that should happen even
+* for error exit.
+*/
+METHODDEF(void)
+term_source (j_decompress_ptr cinfo)
+{
+/* no work necessary here */
+}
+/*
+* Prepare for input from a stdio stream.
+* The caller must have already opened the stream, and is responsible
+* for closing it after finishing decompression.
+*/
+GLOBAL(void)
+jpeg_stdio_src (j_decompress_ptr cinfo, FILE * infile)
+{
+my_src_ptr src;
+/* The source object and input buffer are made permanent so that a series
+* of JPEG images can be read from the same file by calling jpeg_stdio_src
+* only before the first one.  (If we discarded the buffer at the end of
+* one image, we'd likely lose the start of the next one.)
+* This makes it unsafe to use this manager and a different source
+* manager serially with the same JPEG object.  Caveat programmer.
+*/
+if (cinfo->src == NULL) {	/* first time for this JPEG object? */
+cinfo->src = (struct jpeg_source_mgr *)
+(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
+				  SIZEOF(my_source_mgr));
+src = (my_src_ptr) cinfo->src;
+src->buffer = (JOCTET *)
+(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
+				  INPUT_BUF_SIZE * SIZEOF(JOCTET));
+}
+src = (my_src_ptr) cinfo->src;
+src->pub.init_source = init_source;
+src->pub.fill_input_buffer = fill_input_buffer;
+src->pub.skip_input_data = skip_input_data;
+src->pub.resync_to_restart = jpeg_resync_to_restart; /* use default method */
+src->pub.term_source = term_source;
+src->infile = infile;
+src->pub.bytes_in_buffer = 0; /* forces fill_input_buffer on first read */
+src->pub.next_input_byte = NULL; /* until buffer loaded */
+}