chromium/third_party/libjpeg_turbo/jdapistd.c

/*
 * jdapistd.c
 *
 * This file was part of the Independent JPEG Group's software:
 * Copyright (C) 1994-1996, Thomas G. Lane.
 * libjpeg-turbo Modifications:
 * Copyright (C) 2010, 2015-2020, 2022, D. R. Commander.
 * Copyright (C) 2015, Google, Inc.
 * For conditions of distribution and use, see the accompanying README.ijg
 * file.
 *
 * This file contains application interface code for the decompression half
 * of the JPEG library.  These are the "standard" API routines that are
 * used in the normal full-decompression case.  They are not used by a
 * transcoding-only application.  Note that if an application links in
 * jpeg_start_decompress, it will end up linking in the entire decompressor.
 * We thus must separate this file from jdapimin.c to avoid linking the
 * whole decompression library into a transcoder.
 */

#include "jinclude.h"
#include "jdmainct.h"
#include "jdcoefct.h"
#include "jdmaster.h"
#include "jdmerge.h"
#include "jdsample.h"
#include "jmemsys.h"

/* Forward declarations */
LOCAL(boolean) output_pass_setup(j_decompress_ptr cinfo);


/*
 * Decompression initialization.
 * jpeg_read_header must be completed before calling this.
 *
 * If a multipass operating mode was selected, this will do all but the
 * last pass, and thus may take a great deal of time.
 *
 * Returns FALSE if suspended.  The return value need be inspected only if
 * a suspending data source is used.
 */

GLOBAL(boolean)
jpeg_start_decompress(j_decompress_ptr cinfo)
{ … }


/*
 * Set up for an output pass, and perform any dummy pass(es) needed.
 * Common subroutine for jpeg_start_decompress and jpeg_start_output.
 * Entry: global_state = DSTATE_PRESCAN only if previously suspended.
 * Exit: If done, returns TRUE and sets global_state for proper output mode.
 *       If suspended, returns FALSE and sets global_state = DSTATE_PRESCAN.
 */

LOCAL(boolean)
output_pass_setup(j_decompress_ptr cinfo)
{ … }


/*
 * Enable partial scanline decompression
 *
 * Must be called after jpeg_start_decompress() and before any calls to
 * jpeg_read_scanlines() or jpeg_skip_scanlines().
 *
 * Refer to libjpeg.txt for more information.
 */

GLOBAL(void)
jpeg_crop_scanline(j_decompress_ptr cinfo, JDIMENSION *xoffset,
                   JDIMENSION *width)
{ … }


/*
 * Read some scanlines of data from the JPEG decompressor.
 *
 * The return value will be the number of lines actually read.
 * This may be less than the number requested in several cases,
 * including bottom of image, data source suspension, and operating
 * modes that emit multiple scanlines at a time.
 *
 * Note: we warn about excess calls to jpeg_read_scanlines() since
 * this likely signals an application programmer error.  However,
 * an oversize buffer (max_lines > scanlines remaining) is not an error.
 */

GLOBAL(JDIMENSION)
jpeg_read_scanlines(j_decompress_ptr cinfo, JSAMPARRAY scanlines,
                    JDIMENSION max_lines)
{ … }


/* Dummy color convert function used by jpeg_skip_scanlines() */
LOCAL(void)
noop_convert(j_decompress_ptr cinfo, JSAMPIMAGE input_buf,
             JDIMENSION input_row, JSAMPARRAY output_buf, int num_rows)
{ … }


/* Dummy quantize function used by jpeg_skip_scanlines() */
LOCAL(void)
noop_quantize(j_decompress_ptr cinfo, JSAMPARRAY input_buf,
              JSAMPARRAY output_buf, int num_rows)
{ … }


/*
 * In some cases, it is best to call jpeg_read_scanlines() and discard the
 * output, rather than skipping the scanlines, because this allows us to
 * maintain the internal state of the context-based upsampler.  In these cases,
 * we set up and tear down a dummy color converter in order to avoid valgrind
 * errors and to achieve the best possible performance.
 */

LOCAL(void)
read_and_discard_scanlines(j_decompress_ptr cinfo, JDIMENSION num_lines)
{ … }


/*
 * Called by jpeg_skip_scanlines().  This partially skips a decompress block by
 * incrementing the rowgroup counter.
 */

LOCAL(void)
increment_simple_rowgroup_ctr(j_decompress_ptr cinfo, JDIMENSION rows)
{ … }

/*
 * Skips some scanlines of data from the JPEG decompressor.
 *
 * The return value will be the number of lines actually skipped.  If skipping
 * num_lines would move beyond the end of the image, then the actual number of
 * lines remaining in the image is returned.  Otherwise, the return value will
 * be equal to num_lines.
 *
 * Refer to libjpeg.txt for more information.
 */

GLOBAL(JDIMENSION)
jpeg_skip_scanlines(j_decompress_ptr cinfo, JDIMENSION num_lines)
{ … }

/*
 * Alternate entry point to read raw data.
 * Processes exactly one iMCU row per call, unless suspended.
 */

GLOBAL(JDIMENSION)
jpeg_read_raw_data(j_decompress_ptr cinfo, JSAMPIMAGE data,
                   JDIMENSION max_lines)
{ … }


/* Additional entry points for buffered-image mode. */

#ifdef D_MULTISCAN_FILES_SUPPORTED

/*
 * Initialize for an output pass in buffered-image mode.
 */

GLOBAL(boolean)
jpeg_start_output(j_decompress_ptr cinfo, int scan_number)
{ … }


/*
 * Finish up after an output pass in buffered-image mode.
 *
 * Returns FALSE if suspended.  The return value need be inspected only if
 * a suspending data source is used.
 */

GLOBAL(boolean)
jpeg_finish_output(j_decompress_ptr cinfo)
{ … }

#endif /* D_MULTISCAN_FILES_SUPPORTED */