chromium/third_party/libjpeg_turbo/jdphuff.c

/*
 * jdphuff.c
 *
 * This file was part of the Independent JPEG Group's software:
 * Copyright (C) 1995-1997, Thomas G. Lane.
 * libjpeg-turbo Modifications:
 * Copyright (C) 2015-2016, 2018-2022, D. R. Commander.
 * For conditions of distribution and use, see the accompanying README.ijg
 * file.
 *
 * This file contains Huffman entropy decoding routines for progressive JPEG.
 *
 * Much of the complexity here has to do with supporting input suspension.
 * If the data source module demands suspension, we want to be able to back
 * up to the start of the current MCU.  To do this, we copy state variables
 * into local working storage, and update them back to the permanent
 * storage only upon successful completion of an MCU.
 *
 * NOTE: All referenced figures are from
 * Recommendation ITU-T T.81 (1992) | ISO/IEC 10918-1:1994.
 */

#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
#include "jdhuff.h"             /* Declarations shared with jdhuff.c */
#include <limits.h>


#ifdef D_PROGRESSIVE_SUPPORTED

/*
 * Expanded entropy decoder object for progressive Huffman decoding.
 *
 * The savable_state subrecord contains fields that change within an MCU,
 * but must not be updated permanently until we complete the MCU.
 */

savable_state;

phuff_entropy_decoder;

phuff_entropy_ptr;

/* Forward declarations */
METHODDEF(boolean) decode_mcu_DC_first(j_decompress_ptr cinfo,
                                       JBLOCKROW *MCU_data);
METHODDEF(boolean) decode_mcu_AC_first(j_decompress_ptr cinfo,
                                       JBLOCKROW *MCU_data);
METHODDEF(boolean) decode_mcu_DC_refine(j_decompress_ptr cinfo,
                                        JBLOCKROW *MCU_data);
METHODDEF(boolean) decode_mcu_AC_refine(j_decompress_ptr cinfo,
                                        JBLOCKROW *MCU_data);


/*
 * Initialize for a Huffman-compressed scan.
 */

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


/*
 * Figure F.12: extend sign bit.
 * On some machines, a shift and add will be faster than a table lookup.
 */

#define AVOID_TABLES
#ifdef AVOID_TABLES

#define NEG_1 …
#define HUFF_EXTEND(x, s) …

#else

#define HUFF_EXTEND …

static const int extend_test[16] = {   /* entry n is 2**(n-1) */
  0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080,
  0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000
};

static const int extend_offset[16] = { /* entry n is (-1 << n) + 1 */
  0, ((-1) << 1) + 1, ((-1) << 2) + 1, ((-1) << 3) + 1, ((-1) << 4) + 1,
  ((-1) << 5) + 1, ((-1) << 6) + 1, ((-1) << 7) + 1, ((-1) << 8) + 1,
  ((-1) << 9) + 1, ((-1) << 10) + 1, ((-1) << 11) + 1, ((-1) << 12) + 1,
  ((-1) << 13) + 1, ((-1) << 14) + 1, ((-1) << 15) + 1
};

#endif /* AVOID_TABLES */


/*
 * Check for a restart marker & resynchronize decoder.
 * Returns FALSE if must suspend.
 */

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


/*
 * Huffman MCU decoding.
 * Each of these routines decodes and returns one MCU's worth of
 * Huffman-compressed coefficients.
 * The coefficients are reordered from zigzag order into natural array order,
 * but are not dequantized.
 *
 * The i'th block of the MCU is stored into the block pointed to by
 * MCU_data[i].  WE ASSUME THIS AREA IS INITIALLY ZEROED BY THE CALLER.
 *
 * We return FALSE if data source requested suspension.  In that case no
 * changes have been made to permanent state.  (Exception: some output
 * coefficients may already have been assigned.  This is harmless for
 * spectral selection, since we'll just re-assign them on the next call.
 * Successive approximation AC refinement has to be more careful, however.)
 */

/*
 * MCU decoding for DC initial scan (either spectral selection,
 * or first pass of successive approximation).
 */

METHODDEF(boolean)
decode_mcu_DC_first(j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
{ … }


/*
 * MCU decoding for AC initial scan (either spectral selection,
 * or first pass of successive approximation).
 */

METHODDEF(boolean)
decode_mcu_AC_first(j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
{ … }


/*
 * MCU decoding for DC successive approximation refinement scan.
 * Note: we assume such scans can be multi-component, although the spec
 * is not very clear on the point.
 */

METHODDEF(boolean)
decode_mcu_DC_refine(j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
{ … }


/*
 * MCU decoding for AC successive approximation refinement scan.
 */

METHODDEF(boolean)
decode_mcu_AC_refine(j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
{ … }


/*
 * Module initialization routine for progressive Huffman entropy decoding.
 */

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

#endif /* D_PROGRESSIVE_SUPPORTED */