/*
 * jdhuff.h
 *
 * Copyright (C) 1991-1995, 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) */
	INT32 mincode[17];      /* smallest code of length k */
	INT32 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 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 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 */
	boolean 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 */
	boolean * 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 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 ) );
