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 /*

  * jdhuff.h

  *

  * This file was part of the Independent JPEG Group's software:

  * Copyright (C) 1991-1997, Thomas G. Lane.

  * Modifications:

  * Copyright (C) 2010-2011, D. R. Commander.

  * 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[18];		/* 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 table: 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 this tables.

    *

    * The lower 8 bits of each table entry contain the number of

    * bits in the corresponding Huffman code, or HUFF_LOOKAHEAD + 1

    * if too long.  The next 8 bits of each entry contain the

    * symbol.

    */

   int lookup[1<<HUFF_LOOKAHEAD];

 } 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.

  */

 #if __WORDSIZE == 64 || defined(_WIN64)

 typedef size_t bit_buf_type;	/* type of bit-extraction buffer */

 #define BIT_BUF_SIZE  64		/* size of buffer in bits */

 #else

 typedef INT32 bit_buf_type;	/* type of bit-extraction buffer */

 #define BIT_BUF_SIZE  32		/* size of buffer in bits */

 #endif

 /* 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->lookup[look] >> HUFF_LOOKAHEAD)) <= HUFF_LOOKAHEAD) { \

     DROP_BITS(nb); \

     result = htbl->lookup[look] & ((1 << HUFF_LOOKAHEAD) - 1); \

   } else { \

 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; \

   } \

 }

 #define HUFF_DECODE_FAST(s,nb,htbl) \

   FILL_BIT_BUFFER_FAST; \

   s = PEEK_BITS(HUFF_LOOKAHEAD); \

   s = htbl->lookup[s]; \

   nb = s >> HUFF_LOOKAHEAD; \

   /* Pre-execute the common case of nb <= HUFF_LOOKAHEAD */ \

   DROP_BITS(nb); \

   s = s & ((1 << HUFF_LOOKAHEAD) - 1); \

   if (nb > HUFF_LOOKAHEAD) { \

     /* Equivalent of jpeg_huff_decode() */ \

     /* Don't use GET_BITS() here because we don't want to modify bits_left */ \

     s = (get_buffer >> bits_left) & ((1 << (nb)) - 1); \

     while (s > htbl->maxcode[nb]) { \

       s <<= 1; \

       s |= GET_BITS(1); \

       nb++; \

     } \

     s = htbl->pub->huffval[ (int) (s + htbl->valoffset[nb]) & 0xFF ]; \

   }

 /* 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));