JDHUFF.h
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上传日期:2022-05-11
资源大小:5032k
文件大小:9k
源码类别:
网络截获/分析
开发平台:
Visual C++
- ////////////////////////////////////////////////////////////////////////
- //
- // Note : this file is included as part of the Smaller Animals Software
- // JpegFile package. Though this file has not been modified from it's
- // original IJG 6a form, it is not the responsibility on the Independent
- // JPEG Group to answer questions regarding this code.
- //
- // Any questions you have about this code should be addressed to :
- //
- // CHRISDL@PAGESZ.NET - the distributor of this package.
- //
- // Remember, by including this code in the JpegFile package, Smaller
- // Animals Software assumes all responsibilities for answering questions
- // about it. If we (SA Software) can't answer your questions ourselves, we
- // will direct you to people who can.
- //
- // Thanks, CDL.
- //
- ////////////////////////////////////////////////////////////////////////
- /*
- * jdhuff.h
- *
- * Copyright (C) 1991-1996, 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) */
- long mincode[17]; /* smallest code of length k */
- long maxcode[18]; /* largest code of length k (-1 if none) */
- /* (maxcode[17] is a sentinel to ensure jpeg_huff_decode terminates) */
- int valptr[17]; /* huffval[] index of 1st symbol of length 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,
- JHUFF_TBL * htbl, 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 long 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 do this 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 */
- unsigned int printed_eod; /* flag to suppress multiple warning msgs */
- } bitread_perm_state;
- typedef struct { /* Bitreading working state within an MCU */
- /* current data source state */
- const JOCTET * next_input_byte; /* => next byte to read from source */
- size_t bytes_in_buffer; /* # of bytes remaining in source buffer */
- int unread_marker; /* nonzero if we have hit a marker */
- /* 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 */
- /* pointers needed by jpeg_fill_bit_buffer */
- j_decompress_ptr cinfo; /* back link to decompress master record */
- unsigned int * printed_eod_ptr; /* => flag in permanent state */
- } 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;
- br_state.unread_marker = cinfop->unread_marker;
- get_buffer = permstate.get_buffer;
- bits_left = permstate.bits_left;
- br_state.printed_eod_ptr = & permstate.printed_eod
- #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;
- cinfop->unread_marker = br_state.unread_marker;
- 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(unsigned int) 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));