chromium/third_party/libjpeg_turbo/jdhuff.h

/*
 * jdhuff.h
 *
 * This file was part of the Independent JPEG Group's software:
 * Copyright (C) 1991-1997, Thomas G. Lane.
 * libjpeg-turbo Modifications:
 * Copyright (C) 2010-2011, 2015-2016, 2021, D. R. Commander.
 * Copyright (C) 2018, Matthias Räncker.
 * For conditions of distribution and use, see the accompanying README.ijg
 * file.
 *
 * This file contains declarations for Huffman entropy decoding routines
 * that are shared between the sequential decoder (jdhuff.c) and the
 * progressive decoder (jdphuff.c).  No other modules need to see these.
 */

#include "jconfigint.h"


/* Derived data constructed for each Huffman table */

#define HUFF_LOOKAHEAD

d_derived_tbl;

/* Expand a Huffman table definition into the derived format */
EXTERN(void) jpeg_make_d_derived_tbl(j_decompress_ptr cinfo, boolean isDC,
                                     int tblno, d_derived_tbl **pdtbl);


/*
 * Fetching the next N bits from the input stream is a time-critical operation
 * for the Huffman decoders.  We implement it with a combination of inline
 * macros and out-of-line subroutines.  Note that N (the number of bits
 * demanded at one time) never exceeds 15 for JPEG use.
 *
 * We read source bytes into get_buffer and dole out bits as needed.
 * If get_buffer already contains enough bits, they are fetched in-line
 * by the macros CHECK_BIT_BUFFER and GET_BITS.  When there aren't enough
 * bits, jpeg_fill_bit_buffer is called; it will attempt to fill get_buffer
 * as full as possible (not just to the number of bits needed; this
 * prefetching reduces the overhead cost of calling jpeg_fill_bit_buffer).
 * Note that jpeg_fill_bit_buffer may return FALSE to indicate suspension.
 * On TRUE return, jpeg_fill_bit_buffer guarantees that get_buffer contains
 * at least the requested number of bits --- dummy zeroes are inserted if
 * necessary.
 */

#if !defined(_WIN32) && !defined(SIZEOF_SIZE_T)
#error Cannot determine word size
#endif

#if SIZEOF_SIZE_T == 8 || defined(_WIN64)

bit_buf_type;            /* type of bit-extraction buffer */
#define BIT_BUF_SIZE

#elif defined(__x86_64__) && defined(__ILP32__)

typedef unsigned long long bit_buf_type; /* type of bit-extraction buffer */
#define BIT_BUF_SIZE

#else

typedef unsigned long bit_buf_type;     /* type of bit-extraction buffer */
#define BIT_BUF_SIZE

#endif

/* If long is > 32 bits on your machine, and shifting/masking longs is
 * reasonably fast, making bit_buf_type be long and setting BIT_BUF_SIZE
 * appropriately should be a win.  Unfortunately we can't define the size
 * with something like  #define BIT_BUF_SIZE (sizeof(bit_buf_type)*8)
 * because not all machines measure sizeof in 8-bit bytes.
 */

bitread_perm_state;

bitread_working_state;

/* Macros to declare and load/save bitread local variables. */
#define BITREAD_STATE_VARS

#define BITREAD_LOAD_STATE(cinfop, permstate)

#define BITREAD_SAVE_STATE(cinfop, permstate)

/*
 * These macros provide the in-line portion of bit fetching.
 * Use CHECK_BIT_BUFFER to ensure there are N bits in get_buffer
 * before using GET_BITS, PEEK_BITS, or DROP_BITS.
 * The variables get_buffer and bits_left are assumed to be locals,
 * but the state struct might not be (jpeg_huff_decode needs this).
 *      CHECK_BIT_BUFFER(state, n, action);
 *              Ensure there are N bits in get_buffer; if suspend, take action.
 *      val = GET_BITS(n);
 *              Fetch next N bits.
 *      val = PEEK_BITS(n);
 *              Fetch next N bits without removing them from the buffer.
 *      DROP_BITS(n);
 *              Discard next N bits.
 * The value N should be a simple variable, not an expression, because it
 * is evaluated multiple times.
 */

#define CHECK_BIT_BUFFER(state, nbits, action)

#define GET_BITS(nbits)

#define PEEK_BITS(nbits)

#define DROP_BITS(nbits)

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


/*
 * Code for extracting next Huffman-coded symbol from input bit stream.
 * Again, this is time-critical and we make the main paths be macros.
 *
 * We use a lookahead table to process codes of up to HUFF_LOOKAHEAD bits
 * without looping.  Usually, more than 95% of the Huffman codes will be 8
 * or fewer bits long.  The few overlength codes are handled with a loop,
 * which need not be inline code.
 *
 * Notes about the HUFF_DECODE macro:
 * 1. Near the end of the data segment, we may fail to get enough bits
 *    for a lookahead.  In that case, we do it the hard way.
 * 2. If the lookahead table contains no entry, the next code must be
 *    more than HUFF_LOOKAHEAD bits long.
 * 3. jpeg_huff_decode returns -1 if forced to suspend.
 */

#define HUFF_DECODE(result, state, htbl, failaction, slowlabel)

#define HUFF_DECODE_FAST(s, nb, htbl)

/* Out-of-line case for Huffman code fetching */
EXTERN(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);