chromium/third_party/libjpeg_turbo/jdatasrc.c

/*
 * jdatasrc.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) 2013, 2016, 2022, 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"


/* Expanded data source object for stdio input */

my_source_mgr;

my_src_ptr;

#define INPUT_BUF_SIZE …


/*
 * Initialize source --- called by jpeg_read_header
 * before any data is actually read.
 */

METHODDEF(void)
init_source(j_decompress_ptr cinfo)
{ … }

#if JPEG_LIB_VERSION >= 80 || defined(MEM_SRCDST_SUPPORTED)
METHODDEF(void)
init_mem_source(j_decompress_ptr cinfo)
{ … }
#endif


/*
 * 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)
{ … }

#if JPEG_LIB_VERSION >= 80 || defined(MEM_SRCDST_SUPPORTED)
METHODDEF(boolean)
fill_mem_input_buffer(j_decompress_ptr cinfo)
{ … }
#endif


/*
 * 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)
{ … }


/*
 * 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)
{ … }


/*
 * 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)
{ … }


#if JPEG_LIB_VERSION >= 80 || defined(MEM_SRCDST_SUPPORTED)
/*
 * Prepare for input from a supplied memory buffer.
 * The buffer must contain the whole JPEG data.
 */

GLOBAL(void)
jpeg_mem_src(j_decompress_ptr cinfo, const unsigned char *inbuffer,
             unsigned long insize)
{ … }
#endif