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* jdatasrc-tj.c
* This file was part of the Independent JPEG Group's software:
* Copyright (C) 1994-1996, Thomas G. Lane.
* Modified 2009-2011 by Guido Vollbeding.
* libjpeg-turbo Modifications:
* Copyright (C) 2011, 2016, D. R. Commander.
* For conditions of distribution and use, see the accompanying README.ijg
* file.
* This file contains decompression data source routines for the case of
* reading JPEG data from memory or 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"
* Initialize source --- called by jpeg_read_header
* before any data is actually read.
init_mem_source (j_decompress_ptr cinfo)
/* no work necessary here */
* 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.
fill_mem_input_buffer (j_decompress_ptr cinfo)
static const JOCTET mybuffer[4] = {
/* The whole JPEG data is expected to reside in the supplied memory
* buffer, so any request for more data beyond the given buffer size
* is treated as an error.
/* Insert a fake EOI marker */
cinfo->src->next_input_byte = mybuffer;
cinfo->src->bytes_in_buffer = 2;
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.
skip_input_data (j_decompress_ptr cinfo, long num_bytes)
struct jpeg_source_mgr *src = 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->bytes_in_buffer) {
num_bytes -= (long) src->bytes_in_buffer;
(void) (*src->fill_input_buffer) (cinfo);
/* note we assume that fill_input_buffer will never return FALSE,
* so suspension need not be handled.
src->next_input_byte += (size_t) num_bytes;
src->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.
term_source (j_decompress_ptr cinfo)
/* no work necessary here */
* Prepare for input from a supplied memory buffer.
* The buffer must contain the whole JPEG data.
jpeg_mem_src_tj (j_decompress_ptr cinfo,
const unsigned char *inbuffer, unsigned long insize)
struct jpeg_source_mgr *src;
if (inbuffer == NULL || insize == 0) /* Treat empty input as fatal error */
/* The source object is made permanent so that a series of JPEG images
* can be read from the same buffer by calling jpeg_mem_src only before
* the first one.
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(struct jpeg_source_mgr));
} else if (cinfo->src->init_source != init_mem_source) {
/* It is unsafe to reuse the existing source manager unless it was created
* by this function.
src = cinfo->src;
src->init_source = init_mem_source;
src->fill_input_buffer = fill_mem_input_buffer;
src->skip_input_data = skip_input_data;
src->resync_to_restart = jpeg_resync_to_restart; /* use default method */
src->term_source = term_source;
src->bytes_in_buffer = (size_t) insize;
src->next_input_byte = (const JOCTET *) inbuffer;