jdhuff.h

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/* +------------------------------------------------------------------------+
   |                     Mobile Robot Programming Toolkit (MRPT)            |
   |                          http://www.mrpt.org/                          |
   |                                                                        |
   | Copyright (c) 2005-2017, Individual contributors, see AUTHORS file     |
   | See: http://www.mrpt.org/Authors - All rights reserved.                |
   | Released under BSD License. See details in http://www.mrpt.org/License |
   +------------------------------------------------------------------------+ */

/* Short forms of external names for systems with brain-damaged linkers. */

#ifdef NEED_SHORT_EXTERNAL_NAMES
#define jpeg_make_d_derived_tbl jMkDDerived
#define jpeg_fill_bit_buffer jFilBitBuf
#define jpeg_huff_decode jHufDecode
#endif /* NEED_SHORT_EXTERNAL_NAMES */

/* Derived data constructed for each Huffman table */

#define HUFF_LOOKAHEAD 8 /* # of bits of lookahead */

typedef struct
{
        /* Basic tables: (element [0] of each array is unused) */
        INT32 maxcode[18]; /* largest code of length k (-1 if none) */
        /* (maxcode[17] is a sentinel to ensure jpeg_huff_decode terminates) */
        INT32 valoffset[17]; /* huffval[] offset for codes of length k */
        /* valoffset[k] = huffval[] index of 1st symbol of code length k, less
         * the smallest code of length k; so given a code of length k, the
         * corresponding symbol is huffval[code + valoffset[k]]
         */

        /* Link to public Huffman table (needed only in jpeg_huff_decode) */
        JHUFF_TBL* pub;

        /* Lookahead tables: indexed by the next HUFF_LOOKAHEAD bits of
         * the input data stream.  If the next Huffman code is no more
         * than HUFF_LOOKAHEAD bits long, we can obtain its length and
         * the corresponding symbol directly from these tables.
         */
        int look_nbits[1 << HUFF_LOOKAHEAD]; /* # bits, or 0 if too long */
        UINT8 look_sym[1 << HUFF_LOOKAHEAD]; /* symbol, or unused */
} d_derived_tbl;

/* Expand a Huffman table definition into the derived format */
EXTERN(void)
jpeg_make_d_derived_tbl JPP(
        (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.
 */

typedef INT32 bit_buf_type; /* type of bit-extraction buffer */
#define BIT_BUF_SIZE 32 /* size of buffer in bits */

/* 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.
 */

typedef struct
{ /* Bitreading state saved across MCUs */
        bit_buf_type get_buffer; /* current bit-extraction buffer */
        int bits_left; /* # of unused bits in it */
} bitread_perm_state;

typedef struct
{ /* Bitreading working state within an MCU */
        /* Current data source location */
        /* We need a copy, rather than munging the original, in case of suspension
         */
        const JOCTET* next_input_byte; /* => next byte to read from source */
        size_t bytes_in_buffer; /* # of bytes remaining in source buffer */
        /* Bit input buffer --- note these values are kept in variables,
         * not in this struct, inside the inner loops.
         */
        bit_buf_type get_buffer; /* current bit-extraction buffer */
        int bits_left; /* # of unused bits in it */
        /* Pointer needed by jpeg_fill_bit_buffer. */
        j_decompress_ptr cinfo; /* back link to decompress master record */
} bitread_working_state;

/* Macros to declare and load/save bitread local variables. */
#define BITREAD_STATE_VARS   \
        bit_buf_type get_buffer; \
        int bits_left;           \
        bitread_working_state br_state

#define BITREAD_LOAD_STATE(cinfop, permstate)                \
        br_state.cinfo = cinfop;                                 \
        br_state.next_input_byte = cinfop->src->next_input_byte; \
        br_state.bytes_in_buffer = cinfop->src->bytes_in_buffer; \
        get_buffer = permstate.get_buffer;                       \
        bits_left = permstate.bits_left;

#define BITREAD_SAVE_STATE(cinfop, permstate)                \
        cinfop->src->next_input_byte = br_state.next_input_byte; \
        cinfop->src->bytes_in_buffer = br_state.bytes_in_buffer; \
        permstate.get_buffer = get_buffer;                       \
        permstate.bits_left = bits_left

/*
 * 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)                                 \
        {                                                                          \
                if (bits_left < (nbits))                                               \
                {                                                                      \
                        if (!jpeg_fill_bit_buffer(&(state), get_buffer, bits_left, nbits)) \
                        {                                                                  \
                                action;                                                        \
                        }                                                                  \
                        get_buffer = (state).get_buffer;                                   \
                        bits_left = (state).bits_left;                                     \
                }                                                                      \
        }

#define GET_BITS(nbits) \
        (((int)(get_buffer >> (bits_left -= (nbits)))) & ((1 << (nbits)) - 1))

#define PEEK_BITS(nbits) \
        (((int)(get_buffer >> (bits_left - (nbits)))) & ((1 << (nbits)) - 1))

#define DROP_BITS(nbits) (bits_left -= (nbits))

/* Load up the bit buffer to a depth of at least nbits */
EXTERN(boolean)
jpeg_fill_bit_buffer JPP(
        (bitread_working_state * state, bit_buf_type get_buffer, 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)          \
        {                                                                    \
                int nb, look;                                                    \
                if (bits_left < HUFF_LOOKAHEAD)                                  \
                {                                                                \
                        if (!jpeg_fill_bit_buffer(&state, get_buffer, bits_left, 0)) \
                        {                                                            \
                                failaction;                                              \
                        }                                                            \
                        get_buffer = state.get_buffer;                               \
                        bits_left = state.bits_left;                                 \
                        if (bits_left < HUFF_LOOKAHEAD)                              \
                        {                                                            \
                                nb = 1;                                                  \
                                goto slowlabel;                                          \
                        }                                                            \
                }                                                                \
                look = PEEK_BITS(HUFF_LOOKAHEAD);                                \
                if ((nb = htbl->look_nbits[look]) != 0)                          \
                {                                                                \
                        DROP_BITS(nb);                                               \
                        result = htbl->look_sym[look];                               \
                }                                                                \
                else                                                             \
                {                                                                \
                        nb = HUFF_LOOKAHEAD + 1;                                     \
                slowlabel:                                                       \
                        if ((result = jpeg_huff_decode(                              \
                                         &state, get_buffer, bits_left, htbl, nb)) < 0)      \
                        {                                                            \
                                failaction;                                              \
                        }                                                            \
                        get_buffer = state.get_buffer;                               \
                        bits_left = state.bits_left;                                 \
                }                                                                \
        }

/* Out-of-line case for Huffman code fetching */
EXTERN(int)
jpeg_huff_decode JPP(
        (bitread_working_state * state, bit_buf_type get_buffer, int bits_left,
         d_derived_tbl* htbl, int min_bits));