/*+
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 * jdhuff.h+
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 *+
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 * Copyright (C) 1991-1997, Thomas G. Lane.+
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 * This file is part of the Independent JPEG Group's software.+
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 * For conditions of distribution and use, see the accompanying README file.+
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 *+
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 * This file contains declarations for Huffman entropy decoding routines+
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 * that are shared between the sequential decoder (jdhuff.c) and the+
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 * progressive decoder (jdphuff.c).  No other modules need to see these.+
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 */+
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+
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/* Short forms of external names for systems with brain-damaged linkers. */+
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+
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#ifdef NEED_SHORT_EXTERNAL_NAMES+
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#define jpeg_make_d_derived_tbl	jMkDDerived+
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#define jpeg_fill_bit_buffer	jFilBitBuf+
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#define jpeg_huff_decode	jHufDecode+
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#endif /* NEED_SHORT_EXTERNAL_NAMES */+
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+
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+
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/* Derived data constructed for each Huffman table */+
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+
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#define HUFF_LOOKAHEAD	8	/* # of bits of lookahead */+
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+
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typedef struct {+
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  /* Basic tables: (element [0] of each array is unused) */+
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  INT32 maxcode[18];		/* largest code of length k (-1 if none) */+
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  /* (maxcode[17] is a sentinel to ensure jpeg_huff_decode terminates) */+
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  INT32 valoffset[17];		/* huffval[] offset for codes of length k */+
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  /* valoffset[k] = huffval[] index of 1st symbol of code length k, less+
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   * the smallest code of length k; so given a code of length k, the+
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   * corresponding symbol is huffval[code + valoffset[k]]+
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   */+
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+
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  /* Link to public Huffman table (needed only in jpeg_huff_decode) */+
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  JHUFF_TBL *pub;+
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+
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  /* Lookahead tables: indexed by the next HUFF_LOOKAHEAD bits of+
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   * the input data stream.  If the next Huffman code is no more+
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   * than HUFF_LOOKAHEAD bits long, we can obtain its length and+
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   * the corresponding symbol directly from these tables.+
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   */+
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  int look_nbits[1<<HUFF_LOOKAHEAD]; /* # bits, or 0 if too long */+
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  UINT8 look_sym[1<<HUFF_LOOKAHEAD]; /* symbol, or unused */+
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} d_derived_tbl;+
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+
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/* Expand a Huffman table definition into the derived format */+
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EXTERN(void) jpeg_make_d_derived_tbl+
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	JPP((j_decompress_ptr cinfo, boolean isDC, int tblno,+
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	     d_derived_tbl ** pdtbl));+
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+
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+
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/*+
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 * Fetching the next N bits from the input stream is a time-critical operation+
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 * for the Huffman decoders.  We implement it with a combination of inline+
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 * macros and out-of-line subroutines.  Note that N (the number of bits+
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 * demanded at one time) never exceeds 15 for JPEG use.+
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 *+
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 * We read source bytes into get_buffer and dole out bits as needed.+
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 * If get_buffer already contains enough bits, they are fetched in-line+
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 * by the macros CHECK_BIT_BUFFER and GET_BITS.  When there aren't enough+
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 * bits, jpeg_fill_bit_buffer is called; it will attempt to fill get_buffer+
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 * as full as possible (not just to the number of bits needed; this+
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 * prefetching reduces the overhead cost of calling jpeg_fill_bit_buffer).+
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 * Note that jpeg_fill_bit_buffer may return FALSE to indicate suspension.+
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 * On TRUE return, jpeg_fill_bit_buffer guarantees that get_buffer contains+
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 * at least the requested number of bits --- dummy zeroes are inserted if+
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 * necessary.+
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 */+
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+
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typedef INT32 bit_buf_type;	/* type of bit-extraction buffer */+
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#define BIT_BUF_SIZE  32	/* size of buffer in bits */+
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+
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/* If long is > 32 bits on your machine, and shifting/masking longs is+
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 * reasonably fast, making bit_buf_type be long and setting BIT_BUF_SIZE+
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 * appropriately should be a win.  Unfortunately we can't define the size+
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 * with something like  #define BIT_BUF_SIZE (sizeof(bit_buf_type)*8)+
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 * because not all machines measure sizeof in 8-bit bytes.+
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 */+
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+
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typedef struct {		/* Bitreading state saved across MCUs */+
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  bit_buf_type get_buffer;	/* current bit-extraction buffer */+
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  int bits_left;		/* # of unused bits in it */+
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} bitread_perm_state;+
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+
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typedef struct {		/* Bitreading working state within an MCU */+
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  /* Current data source location */+
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  /* We need a copy, rather than munging the original, in case of suspension */+
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  const JOCTET * next_input_byte; /* => next byte to read from source */+
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  size_t bytes_in_buffer;	/* # of bytes remaining in source buffer */+
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  /* Bit input buffer --- note these values are kept in register variables,+
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   * not in this struct, inside the inner loops.+
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   */+
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  bit_buf_type get_buffer;	/* current bit-extraction buffer */+
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  int bits_left;		/* # of unused bits in it */+
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  /* Pointer needed by jpeg_fill_bit_buffer. */+
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  j_decompress_ptr cinfo;	/* back link to decompress master record */+
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} bitread_working_state;+
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+
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/* Macros to declare and load/save bitread local variables. */+
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#define BITREAD_STATE_VARS  \+
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	register bit_buf_type get_buffer;  \+
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	register int bits_left;  \+
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	bitread_working_state br_state+
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+
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#define BITREAD_LOAD_STATE(cinfop,permstate)  \+
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	br_state.cinfo = cinfop; \+
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	br_state.next_input_byte = cinfop->src->next_input_byte; \+
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	br_state.bytes_in_buffer = cinfop->src->bytes_in_buffer; \+
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	get_buffer = permstate.get_buffer; \+
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	bits_left = permstate.bits_left;+
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+
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#define BITREAD_SAVE_STATE(cinfop,permstate)  \+
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	cinfop->src->next_input_byte = br_state.next_input_byte; \+
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	cinfop->src->bytes_in_buffer = br_state.bytes_in_buffer; \+
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	permstate.get_buffer = get_buffer; \+
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	permstate.bits_left = bits_left+
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+
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/*+
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 * These macros provide the in-line portion of bit fetching.+
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 * Use CHECK_BIT_BUFFER to ensure there are N bits in get_buffer+
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 * before using GET_BITS, PEEK_BITS, or DROP_BITS.+
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 * The variables get_buffer and bits_left are assumed to be locals,+
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 * but the state struct might not be (jpeg_huff_decode needs this).+
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 *	CHECK_BIT_BUFFER(state,n,action);+
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 *		Ensure there are N bits in get_buffer; if suspend, take action.+
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 *      val = GET_BITS(n);+
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 *		Fetch next N bits.+
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 *      val = PEEK_BITS(n);+
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 *		Fetch next N bits without removing them from the buffer.+
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 *	DROP_BITS(n);+
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 *		Discard next N bits.+
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 * The value N should be a simple variable, not an expression, because it+
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 * is evaluated multiple times.+
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 */+
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+
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#define CHECK_BIT_BUFFER(state,nbits,action) \+
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	{ if (bits_left < (nbits)) {  \+
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	    if (! jpeg_fill_bit_buffer(&(state),get_buffer,bits_left,nbits))  \+
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	      { action; }  \+
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	    get_buffer = (state).get_buffer; bits_left = (state).bits_left; } }+
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+
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#define GET_BITS(nbits) \+
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	(((int) (get_buffer >> (bits_left -= (nbits)))) & ((1<<(nbits))-1))+
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+
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#define PEEK_BITS(nbits) \+
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	(((int) (get_buffer >> (bits_left -  (nbits)))) & ((1<<(nbits))-1))+
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+
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#define DROP_BITS(nbits) \+
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	(bits_left -= (nbits))+
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+
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/* Load up the bit buffer to a depth of at least nbits */+
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EXTERN(boolean) jpeg_fill_bit_buffer+
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	JPP((bitread_working_state * state, register bit_buf_type get_buffer,+
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	     register int bits_left, int nbits));+
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+
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+
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/*+
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 * Code for extracting next Huffman-coded symbol from input bit stream.+
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 * Again, this is time-critical and we make the main paths be macros.+
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 *+
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 * We use a lookahead table to process codes of up to HUFF_LOOKAHEAD bits+
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 * without looping.  Usually, more than 95% of the Huffman codes will be 8+
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 * or fewer bits long.  The few overlength codes are handled with a loop,+
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 * which need not be inline code.+
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 *+
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 * Notes about the HUFF_DECODE macro:+
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 * 1. Near the end of the data segment, we may fail to get enough bits+
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 *    for a lookahead.  In that case, we do it the hard way.+
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 * 2. If the lookahead table contains no entry, the next code must be+
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 *    more than HUFF_LOOKAHEAD bits long.+
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 * 3. jpeg_huff_decode returns -1 if forced to suspend.+
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 */+
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+
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#define HUFF_DECODE(result,state,htbl,failaction,slowlabel) \+
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{ register int nb, look; \+
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  if (bits_left < HUFF_LOOKAHEAD) { \+
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    if (! jpeg_fill_bit_buffer(&state,get_buffer,bits_left, 0)) {failaction;} \+
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    get_buffer = state.get_buffer; bits_left = state.bits_left; \+
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    if (bits_left < HUFF_LOOKAHEAD) { \+
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      nb = 1; goto slowlabel; \+
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    } \+
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  } \+
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  look = PEEK_BITS(HUFF_LOOKAHEAD); \+
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  if ((nb = htbl->look_nbits[look]) != 0) { \+
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    DROP_BITS(nb); \+
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    result = htbl->look_sym[look]; \+
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  } else { \+
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    nb = HUFF_LOOKAHEAD+1; \+
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slowlabel: \+
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    if ((result=jpeg_huff_decode(&state,get_buffer,bits_left,htbl,nb)) < 0) \+
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	{ failaction; } \+
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    get_buffer = state.get_buffer; bits_left = state.bits_left; \+
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  } \+
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}+
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+
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/* Out-of-line case for Huffman code fetching */+
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EXTERN(int) jpeg_huff_decode+
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	JPP((bitread_working_state * state, register bit_buf_type get_buffer,+
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	     register int bits_left, d_derived_tbl * htbl, int min_bits));+
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