--- /dev/null
+/*
+ * 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 */
+}
projects / opencv / blobdiff