chromium/third_party/libjpeg_turbo/jdinput.c

/*
 * jdinput.c
 *
 * This file was part of the Independent JPEG Group's software:
 * Copyright (C) 1991-1997, Thomas G. Lane.
 * libjpeg-turbo Modifications:
 * Copyright (C) 2010, 2016, 2018, 2022, D. R. Commander.
 * Copyright (C) 2015, Google, Inc.
 * For conditions of distribution and use, see the accompanying README.ijg
 * file.
 *
 * This file contains input control logic for the JPEG decompressor.
 * These routines are concerned with controlling the decompressor's input
 * processing (marker reading and coefficient decoding).  The actual input
 * reading is done in jdmarker.c, jdhuff.c, and jdphuff.c.
 */

#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
#include "jpegcomp.h"


/* Private state */

my_input_controller;

my_inputctl_ptr;


/* Forward declarations */
METHODDEF(int) consume_markers(j_decompress_ptr cinfo);


/*
 * Routines to calculate various quantities related to the size of the image.
 */

LOCAL(void)
initial_setup(j_decompress_ptr cinfo)
/* Called once, when first SOS marker is reached */
{ … }


LOCAL(void)
per_scan_setup(j_decompress_ptr cinfo)
/* Do computations that are needed before processing a JPEG scan */
/* cinfo->comps_in_scan and cinfo->cur_comp_info[] were set from SOS marker */
{ … }


/*
 * Save away a copy of the Q-table referenced by each component present
 * in the current scan, unless already saved during a prior scan.
 *
 * In a multiple-scan JPEG file, the encoder could assign different components
 * the same Q-table slot number, but change table definitions between scans
 * so that each component uses a different Q-table.  (The IJG encoder is not
 * currently capable of doing this, but other encoders might.)  Since we want
 * to be able to dequantize all the components at the end of the file, this
 * means that we have to save away the table actually used for each component.
 * We do this by copying the table at the start of the first scan containing
 * the component.
 * Rec. ITU-T T.81 | ISO/IEC 10918-1 prohibits the encoder from changing the
 * contents of a Q-table slot between scans of a component using that slot.  If
 * the encoder does so anyway, this decoder will simply use the Q-table values
 * that were current at the start of the first scan for the component.
 *
 * The decompressor output side looks only at the saved quant tables,
 * not at the current Q-table slots.
 */

LOCAL(void)
latch_quant_tables(j_decompress_ptr cinfo)
{ … }


/*
 * Initialize the input modules to read a scan of compressed data.
 * The first call to this is done by jdmaster.c after initializing
 * the entire decompressor (during jpeg_start_decompress).
 * Subsequent calls come from consume_markers, below.
 */

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


/*
 * Finish up after inputting a compressed-data scan.
 * This is called by the coefficient controller after it's read all
 * the expected data of the scan.
 */

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


/*
 * Read JPEG markers before, between, or after compressed-data scans.
 * Change state as necessary when a new scan is reached.
 * Return value is JPEG_SUSPENDED, JPEG_REACHED_SOS, or JPEG_REACHED_EOI.
 *
 * The consume_input method pointer points either here or to the
 * coefficient controller's consume_data routine, depending on whether
 * we are reading a compressed data segment or inter-segment markers.
 */

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


/*
 * Reset state to begin a fresh datastream.
 */

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


/*
 * Initialize the input controller module.
 * This is called only once, when the decompression object is created.
 */

GLOBAL(void)
jinit_input_controller(j_decompress_ptr cinfo)
{ … }