+++ /dev/null
-/*
- * jdhuff.h
- *
- * Copyright (C) 1991-1997, Thomas G. Lane.
- * This file is part of the Independent JPEG Group's software.
- * For conditions of distribution and use, see the accompanying README 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.
- */
-
-/* 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 register 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 \
- register bit_buf_type get_buffer; \
- register 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, 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) \
-{ register 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, register bit_buf_type get_buffer,
- register int bits_left, d_derived_tbl * htbl, int min_bits));
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