www.pudn.com > uCOS-uCGUI-FATFs.rar > jdhuff.h, change:2004-08-18,size:8061b


/* 
 * 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. 
 */ 
 
 
/* 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));