chromium/third_party/libjpeg_turbo/jdhuff.c

/*
 * jdhuff.c
 *
 * This file was part of the Independent JPEG Group's software:
 * Copyright (C) 1991-1997, Thomas G. Lane.
 * libjpeg-turbo Modifications:
 * Copyright (C) 2009-2011, 2016, 2018-2019, D. R. Commander.
 * Copyright (C) 2018, Matthias Räncker.
 * For conditions of distribution and use, see the accompanying README.ijg
 * file.
 *
 * This file contains Huffman entropy decoding routines.
 *
 * 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 jdphuff.c */
#include "jpegcomp.h"
#include "jstdhuff.c"


/*
 * Expanded entropy decoder object for 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;

huff_entropy_decoder;

huff_entropy_ptr;


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

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


/*
 * Compute the derived values for a Huffman table.
 * This routine also performs some validation checks on the table.
 *
 * Note this is also used by jdphuff.c.
 */

GLOBAL(void)
jpeg_make_d_derived_tbl(j_decompress_ptr cinfo, boolean isDC, int tblno,
                        d_derived_tbl **pdtbl)
{ … }


/*
 * Out-of-line code for bit fetching (shared with jdphuff.c).
 * See jdhuff.h for info about usage.
 * Note: current values of get_buffer and bits_left are passed as parameters,
 * but are returned in the corresponding fields of the state struct.
 *
 * On most machines MIN_GET_BITS should be 25 to allow the full 32-bit width
 * of get_buffer to be used.  (On machines with wider words, an even larger
 * buffer could be used.)  However, on some machines 32-bit shifts are
 * quite slow and take time proportional to the number of places shifted.
 * (This is true with most PC compilers, for instance.)  In this case it may
 * be a win to set MIN_GET_BITS to the minimum value of 15.  This reduces the
 * average shift distance at the cost of more calls to jpeg_fill_bit_buffer.
 */

#ifdef SLOW_SHIFT_32
#define MIN_GET_BITS …
#else
#define MIN_GET_BITS …
#endif


GLOBAL(boolean)
jpeg_fill_bit_buffer(bitread_working_state *state,
                     register bit_buf_type get_buffer, register int bits_left,
                     int nbits)
/* Load up the bit buffer to a depth of at least nbits */
{ … }


/* Macro version of the above, which performs much better but does not
   handle markers.  We have to hand off any blocks with markers to the
   slower routines. */

#define GET_BYTE …

#if SIZEOF_SIZE_T == 8 || defined(_WIN64) || (defined(__x86_64__) && defined(__ILP32__))

/* Pre-fetch 48 bytes, because the holding register is 64-bit */
#define FILL_BIT_BUFFER_FAST …

#else

/* Pre-fetch 16 bytes, because the holding register is 32-bit */
#define FILL_BIT_BUFFER_FAST …

#endif


/*
 * Out-of-line code for Huffman code decoding.
 * See jdhuff.h for info about usage.
 */

GLOBAL(int)
jpeg_huff_decode(bitread_working_state *state,
                 register bit_buf_type get_buffer, register int bits_left,
                 d_derived_tbl *htbl, int min_bits)
{ … }


/*
 * 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)
{ … }


#if defined(__has_feature)
#if __has_feature(undefined_behavior_sanitizer)
__attribute__((no_sanitize("signed-integer-overflow"),
               no_sanitize("unsigned-integer-overflow")))
#endif
#endif
LOCAL(boolean)
decode_mcu_slow(j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
{ … }


#if defined(__has_feature)
#if __has_feature(undefined_behavior_sanitizer)
__attribute__((no_sanitize("signed-integer-overflow"),
               no_sanitize("unsigned-integer-overflow")))
#endif
#endif
LOCAL(boolean)
decode_mcu_fast(j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
{ … }


/*
 * Decode and return 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 HAS BEEN ZEROED BY THE CALLER.
 * (Wholesale zeroing is usually a little faster than retail...)
 *
 * Returns 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
 * this module, since we'll just re-assign them on the next call.)
 */

#define BUFSIZE …

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


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

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