jdhuff.h - third_party/libjpeg-turbo - Git at Google

 /*
  * jdhuff.h
  *
  * This file was part of the Independent JPEG Group's software:
  * Copyright (C) 1991-1997, Thomas G. Lane.
  * libjpeg-turbo 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.
  */


 /* 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
         (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 !defined(_WIN32) && !defined(SIZEOF_SIZE_T)
 #error Cannot determine word size
 #endif

 #if SIZEOF_SIZE_T==8 || 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
         (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
         (bitread_working_state * state, register bit_buf_type get_buffer,
          register int bits_left, d_derived_tbl * htbl, int min_bits);
	/*
	* jdhuff.h
	*
	* This file was part of the Independent JPEG Group's software:
	* Copyright (C) 1991-1997, Thomas G. Lane.
	* libjpeg-turbo 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.
	*/


	/* 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
	(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 !defined(_WIN32) && !defined(SIZEOF_SIZE_T)
	#error Cannot determine word size
	#endif

	#if SIZEOF_SIZE_T==8 \|\| 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
	(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
	(bitread_working_state * state, register bit_buf_type get_buffer,
	register int bits_left, d_derived_tbl * htbl, int min_bits);