chromium/third_party/libjpeg_turbo/jdcoefct.c

/*
 * jdcoefct.c
 *
 * This file was part of the Independent JPEG Group's software:
 * Copyright (C) 1994-1997, Thomas G. Lane.
 * libjpeg-turbo Modifications:
 * Copyright 2009 Pierre Ossman <[email protected]> for Cendio AB
 * Copyright (C) 2010, 2015-2016, 2019-2020, 2022, D. R. Commander.
 * Copyright (C) 2015, 2020, Google, Inc.
 * For conditions of distribution and use, see the accompanying README.ijg
 * file.
 *
 * This file contains the coefficient buffer controller for decompression.
 * This controller is the top level of the JPEG decompressor proper.
 * The coefficient buffer lies between entropy decoding and inverse-DCT steps.
 *
 * In buffered-image mode, this controller is the interface between
 * input-oriented processing and output-oriented processing.
 * Also, the input side (only) is used when reading a file for transcoding.
 */

#include "jinclude.h"
#include "jdcoefct.h"
#include "jpegcomp.h"


/* Forward declarations */
METHODDEF(int) decompress_onepass(j_decompress_ptr cinfo,
                                  JSAMPIMAGE output_buf);
#ifdef D_MULTISCAN_FILES_SUPPORTED
METHODDEF(int) decompress_data(j_decompress_ptr cinfo, JSAMPIMAGE output_buf);
#endif
#ifdef BLOCK_SMOOTHING_SUPPORTED
LOCAL(boolean) smoothing_ok(j_decompress_ptr cinfo);
METHODDEF(int) decompress_smooth_data(j_decompress_ptr cinfo,
                                      JSAMPIMAGE output_buf);
#endif


/*
 * Initialize for an input processing pass.
 */

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


/*
 * Initialize for an output processing pass.
 */

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


/*
 * Decompress and return some data in the single-pass case.
 * Always attempts to emit one fully interleaved MCU row ("iMCU" row).
 * Input and output must run in lockstep since we have only a one-MCU buffer.
 * Return value is JPEG_ROW_COMPLETED, JPEG_SCAN_COMPLETED, or JPEG_SUSPENDED.
 *
 * NB: output_buf contains a plane for each component in image,
 * which we index according to the component's SOF position.
 */

METHODDEF(int)
decompress_onepass(j_decompress_ptr cinfo, JSAMPIMAGE output_buf)
{ … }


/*
 * Dummy consume-input routine for single-pass operation.
 */

METHODDEF(int)
dummy_consume_data(j_decompress_ptr cinfo)
{ … }


#ifdef D_MULTISCAN_FILES_SUPPORTED

/*
 * Consume input data and store it in the full-image coefficient buffer.
 * We read as much as one fully interleaved MCU row ("iMCU" row) per call,
 * ie, v_samp_factor block rows for each component in the scan.
 * Return value is JPEG_ROW_COMPLETED, JPEG_SCAN_COMPLETED, or JPEG_SUSPENDED.
 */

METHODDEF(int)
consume_data(j_decompress_ptr cinfo)
{ … }


/*
 * Decompress and return some data in the multi-pass case.
 * Always attempts to emit one fully interleaved MCU row ("iMCU" row).
 * Return value is JPEG_ROW_COMPLETED, JPEG_SCAN_COMPLETED, or JPEG_SUSPENDED.
 *
 * NB: output_buf contains a plane for each component in image.
 */

METHODDEF(int)
decompress_data(j_decompress_ptr cinfo, JSAMPIMAGE output_buf)
{ … }

#endif /* D_MULTISCAN_FILES_SUPPORTED */


#ifdef BLOCK_SMOOTHING_SUPPORTED

/*
 * This code applies interblock smoothing; the first 9 AC coefficients are
 * estimated from the DC values of a DCT block and its 24 neighboring blocks.
 * We apply smoothing only for progressive JPEG decoding, and only if
 * the coefficients it can estimate are not yet known to full precision.
 */

/* Natural-order array positions of the first 9 zigzag-order coefficients */
#define Q01_POS …
#define Q10_POS …
#define Q20_POS …
#define Q11_POS …
#define Q02_POS …
#define Q03_POS …
#define Q12_POS …
#define Q21_POS …
#define Q30_POS …

/*
 * Determine whether block smoothing is applicable and safe.
 * We also latch the current states of the coef_bits[] entries for the
 * AC coefficients; otherwise, if the input side of the decompressor
 * advances into a new scan, we might think the coefficients are known
 * more accurately than they really are.
 */

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


/*
 * Variant of decompress_data for use when doing block smoothing.
 */

METHODDEF(int)
decompress_smooth_data(j_decompress_ptr cinfo, JSAMPIMAGE output_buf)
{ … }

#endif /* BLOCK_SMOOTHING_SUPPORTED */


/*
 * Initialize coefficient buffer controller.
 */

GLOBAL(void)
jinit_d_coef_controller(j_decompress_ptr cinfo, boolean need_full_buffer)
{ … }