/* $XConsortium: bits.h /main/6 1995/12/02 16:50:22 dpw $ */
/* AGE Logic - Oct 15 1995 - Larry Hare */
/**** module fax/bits.h ****/
/******************************************************************************

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*****************************************************************************
  
	fax/bits.h -- DDXIE G4 fax bitstream management macros
  
	Ben Fahy -- AGE Logic, Inc. May, 1993
  
*****************************************************************************/

#include "gbits.h"

/* ------------------------------------------------------------------- */
/*
 *	get_white_run_length(next_goal)
 *	get_black_run_length(next_goal)
 *
 * 	These macros try to determine run lengths in horizonal mode.
 *	All possible bit combinations have been previously coded in
 *	a lookup table, so it's not a very big deal.  The only real
 *	complication arises from the fact I may run out of strip data
 *	before finishing.  In this case I want to save my length
 * 	accumulator and read it back in again.  If I have finished
 *	with this length,  I want to move on to the next goal specified
 *	by 'next_goal'.  Otherwise my goal remains to accumulate the
 *	current desired run length.
 */

#define get_white_run_length(next_goal)					\
	{ 								\
	register int code=0,nbits,makeup;				\
	  rl = 0;							\
	  while (1) {							\
 	    code = get_wcode(byteptr,bitpos,endptr);			\
	    rl     = _WhiteFaxTable[code].run_length;			\
	    nbits  = _WhiteFaxTable[code].n_bits;			\
	    makeup = _WhiteFaxTable[code].makeup;			\
	    if (rl == BAD_RUN_LENGTH) {					\
	      length_acc = 0;						\
	      if (!code) {						\
		/* could just be fill bits, try to recover */		\
		goal = FAX_GOAL_RecoverZero;				\
	        break;							\
	      }								\
	      else {							\
		goal = FAX_GOAL_FallOnSword;				\
	        break;							\
	      }								\
	    }								\
	    if (rl != EOL_RUN_LENGTH)					\
	      length_acc += rl;						\
	    if (!makeup)						\
	      goal = next_goal;						\
	      /* just in case adjust_bitstream returns for more data */	\
	    adjust_bitstream(nbits,byteptr,bitpos,endptr);		\
	    if (!makeup)						\
	      break;							\
	  }								\
	}

#define get_black_run_length(next_goal)					\
	{ 								\
	register int code=0,nbits,makeup;				\
	  rl = 0;							\
	  while (1) {							\
 	    code = get_bcode(byteptr,bitpos,endptr);			\
	    rl     = _BlackFaxTable[code].run_length;			\
	    nbits  = _BlackFaxTable[code].n_bits;			\
	    makeup = _BlackFaxTable[code].makeup;			\
	    if (rl == BAD_RUN_LENGTH) {					\
	      length_acc = 0;						\
	      if (!code) {						\
		/* could just be fill bits, will try to recover */	\
		goal = FAX_GOAL_RecoverZero;				\
	        break;							\
	      }								\
	      else {							\
		goal = FAX_GOAL_FallOnSword;				\
	        break;							\
	      }								\
	    }								\
	    if (rl != EOL_RUN_LENGTH)					\
	      length_acc += rl;						\
	    /* if this is an EOL of terminating code, go to next goal */\
	    if (!makeup)						\
	      goal = next_goal;						\
	      /* (set in case adjust_bitstream returns for more data) */\
	    adjust_bitstream(nbits,byteptr,bitpos,endptr);		\
	    if (!makeup)						\
	      break;							\
	  }								\
	}

/* ------------------------------------------------------------------- */
/*
 *	get_a0a1(next_goal)
 *	get_a1a2(next_goal)
 *
 * 	These macros try to determine run lengths in horizonal mode.
 *	They just leverage off of lower-level macros, so they're easy
 */
#define get_a0a1(next_goal)						\
	{								\
	   if (a0_color == WHITE)					\
	      get_white_run_length(next_goal) /* ; */			\
	   else								\
	      get_black_run_length(next_goal);				\
	}
#define get_a1a2(next_goal)						\
	{								\
	   if (a0_color == WHITE)					\
	      get_black_run_length(next_goal) /* ; */			\
	   else								\
	      get_white_run_length(next_goal);				\
	}
/* ------------------------------------------------------------------- */
/*
 *	save_state_and_return(state);
 *	localize_state(state);
 *
 * 	These macros transfer state variables back and forth between
 *	the reentrant data structure 'state' and register variables.
 *	Hopefully neither will be called often,  so we don't have to
 *	spend energy analyzing what is 'dirty' versus what hasn't been
 *	touched since the last save, etc.
 *
 * 	Strategy:
 *		brute force.
 *
 */
#if defined(_G32D)
#define save_state_and_return(state) 					\
	{								\
	    state->a0_color 	= a0_color;				\
	    state->a0_pos   	= a0_pos;				\
	    state->a0a1   	= a0a1;					\
	    state->bits.bitpos  = bitpos;				\
	    state->bits.byteptr = byteptr;				\
	    state->bits.endptr  = endptr;				\
	    state->goal     	= goal;					\
	    state->n_old_trans	= n_old_trans;				\
	    state->old_trans	= old_trans;				\
	    state->n_new_trans	= n_new_trans;				\
	    state->new_trans	= new_trans;				\
	    state->length_acc	= length_acc;				\
	    state->last_b1_idx	= last_b1_idx;				\
	    state->width	= width;				\
	    state->rl  		= rl;					\
	    state->g32d_horiz	= g32d_horiz;				\
	    return(lines_found);					\
	}

#define	localize_state(state)						\
	    a0_color  		= state->a0_color;			\
	    a0_pos	  	= state->a0_pos;			\
	    a0a1		= state->a0a1;   			\
	    bitpos 	  	= state->bits.bitpos;			\
	    byteptr	  	= state->bits.byteptr;			\
	    endptr    		= state->bits.endptr;			\
	    goal	  	= state->goal;				\
	    n_old_trans		= state->n_old_trans;			\
	    old_trans		= state->old_trans;			\
	    n_new_trans		= state->n_new_trans;			\
	    new_trans		= state->new_trans;			\
	    length_acc		= state->length_acc;			\
	    last_b1_idx		= state->last_b1_idx;			\
	    width		= state->width;				\
	    rl			= state->rl;				\
	    g32d_horiz		= state->g32d_horiz;
#endif  /* if defined(_G32D) */

#if defined(_G31D) || defined(_G4)
#define save_state_and_return(state) 					\
	{								\
	    state->a0_color 	= a0_color;				\
	    state->a0_pos   	= a0_pos;				\
	    state->a0a1   	= a0a1;					\
	    state->bits.bitpos  = bitpos;				\
	    state->bits.byteptr = byteptr;				\
	    state->bits.endptr  = endptr;				\
	    state->goal     	= goal;					\
	    state->n_old_trans	= n_old_trans;				\
	    state->old_trans	= old_trans;				\
	    state->n_new_trans	= n_new_trans;				\
	    state->new_trans	= new_trans;				\
	    state->length_acc	= length_acc;				\
	    state->last_b1_idx	= last_b1_idx;				\
	    state->width	= width;				\
	    state->rl		= rl;					\
	    return(lines_found);					\
	}

#define	localize_state(state)						\
	    a0_color  		= state->a0_color;			\
	    a0_pos	  	= state->a0_pos;			\
	    a0a1		= state->a0a1;   			\
	    bitpos 	  	= state->bits.bitpos;			\
	    byteptr	  	= state->bits.byteptr;			\
	    endptr    		= state->bits.endptr;			\
	    goal	  	= state->goal;				\
	    n_old_trans		= state->n_old_trans;			\
	    old_trans		= state->old_trans;			\
	    n_new_trans		= state->n_new_trans;			\
	    new_trans		= state->new_trans;			\
	    length_acc		= state->length_acc;			\
	    last_b1_idx		= state->last_b1_idx;			\
	    width		= state->width;				\
	    rl			= state->rl;
#endif  /* defined(_G31D) */

#if defined(_PBits)
#define save_state_and_return(state) 					\
	{								\
	    state->a0_color 	= a0_color;				\
	    state->a0_pos   	= a0_pos;				\
	    state->bits.byteptr = byteptr;				\
	    state->bits.endptr  = endptr;				\
	    state->goal     	= goal;					\
	    state->length_acc	= length_acc;				\
	    state->width	= width;				\
	    state->rl		= rl;					\
	    return(lines_found);					\
	}

#define	localize_state(state)						\
	    a0_color  		= state->a0_color;			\
	    a0_pos	  	= state->a0_pos;			\
	    byteptr	  	= state->bits.byteptr;			\
	    endptr    		= state->bits.endptr;			\
	    goal	  	= state->goal;				\
	    length_acc		= state->length_acc;			\
	    width		= state->width;				\
	    rl			= state->rl;
#endif  /* defined(_Pbits) */

/* ------------------------------------------------------------------- */
/*
 *	reset_transitions();
 *
 * 	Macro to trade old and new transition buffers
 *
 * 	Strategy:
 *		Do the obvious
 */
#define	reset_transitions()						\
	    {								\
	    register int *tmp = old_trans;				\
	    old_trans   = new_trans;					\
	    new_trans   = tmp;						\
	    n_old_trans = n_new_trans;					\
	    n_new_trans = 0;						\
	    last_b1_idx	= 0;						\
	    }

/* ------------------------------------------------------------------- */
/*
 * 	get_mode_and_length(mode,length,byteptr,bitpos,endptr);
 *
 * 	Macro to get next coding mode (vertical or horizontal or ...)
 * 
 *	Strategy:  the modes are encoded with 8 bits or less except
 *		for EOL,  which is 001 (12 bits).  However, none of 
 *		the other modes use 00, so there's no conflict.
 *
 *		We have precomputed a lookup table that tells us for
 *		any sequence of 8 bits, what mode and length goes
 *		along with that sequence.  So all we have to do is 
 *		get the 8 bits and run them through the lookup table 
 *		and we're done.
 *
 *	Note:	I'm trying to write this so a decent compiler will only
 *		do one load to get both mode and length.  Hopefully, your
 *		compiler will fetch '*entry' all at once, then shift and
 *		mask to get components.
 *
 *		Very old compilers may have troubles with the struct =
 *		construction.  You'll have to change entry to *entry
 *		and the entry.mode to entry->mode, etc.
 */

#define get_mode_and_length(mode,length,byteptr,bitpos,endptr) 		\
	{ register unsigned char bits=get_byte(byteptr,bitpos,endptr);	\
	  register TwoDTable entry;					\
	  entry = _TwoDFaxTable[bits];					\
	  mode   = entry.mode;						\
	  length = entry.n_bits;					\
	}

/* ------------------------------------------------------------------- */

/*
 * 	find_b1pos(a0_pos,a0_color,n_old_trans,old_trans);
 *
 * 	Macro to find pixel of opposite color of a0, to right of a0,
 *	on the previous line.
 * 
 *	Strategy:  b1 is more or less monotonically increasing. The
 *		only possible exception is during vertical coding when
 *		a1 is left of b1 by 2 or 3:
 *
 *	 0   1   2   3   4   5   6   7   8   9  10  11  12  13  14
 *                       b1'     b1
 *       B   B   B   B   W   W   B   B   B   B   
 *       B   B   W   B   W   B   W
 *		a0  a1  
 *
 *	In the diagram above, b1 is the first changing element to the
 *	right of a0 which goes from white to black.  a1 is three to the
 *	left of b1.  
 *
 *	When we set a0'=a1 and proceed decoding, since the new a0' is 
 *	black,  we want the first changing element to the right of a0'
 *	which goes from black to white.  This is b1', as pictured. Note
 *	that b1' < b1!  So the b1 sequence is not monotically increasing,
 *	though it is close.  
 *
 *	At most we have to back up one transition to get the right 
 *	changing element for a0'.  This is because b1 is W->B, while
 *	the transition before is B-W, the one before that W->B, and
 *	so on. The transition before b1 is a candidate for b1', but
 *	not the one before that (it's the wrong color). The third
 *	transition before b1 must be at a position <= a0'.  But the
 *	definition of b1' requires that b1' be to the right of a0'.
 *	Therefore,  only the transition immediately before b1 could
 *	possibly server as b1'.
 *
 *	Moral:  If the last b1 we found was index last_b1_idx, then
 *	we can start searching for b1' at last_b1_idx-1,  with complete
 *	assurance that we'll find it.  (if it exists :)
 *
 *	One more thing:  WHITE is defined as 0. BLACK is 1.  The 1st
 *	transition (last_b1_idx=0) is W->B,  the 2nd (last_b1_idx=1)
 *	is B->W, etc.  So an even transition is black, and odd is white.
 *
 *			   BLACK    WHITE
 *			 |   0   |   1   |  bit1 of transition idx
 *             ----------|-------|-------|
 *	  a0   WHITE(0)  |  ok   |  bad  |
 *	color  BLACK(1)  |  bad  |  ok   |
 *             ----------|-------|-------|
 *
 *	We need a transition which is opposite in color to a0_color.  
 *	From the table above, if a0_color ^ (idx & 1), the colors
 *	match and we need to choose the next transition to the right.
 */
#define find_b1pos(a0_pos,a0_color,n_old,old)				\
	{  								\
	  if (last_b1_idx > 0) 						\
		--last_b1_idx;	/* avoid gotcha from above evil case */	\
									\
	  /* search for first changing element to right of a0_pos */	\
	  while (old[last_b1_idx] <= a0_pos) 				\
		if (++last_b1_idx >= n_old)				\
			break;	/* if out of transitions, give up */	\
									\
	  /* check out color - if matching, use next transition	*/	\
	  if (a0_color ^ (last_b1_idx & 1))				\
		++last_b1_idx;						\
	 	    							\
	  if (last_b1_idx < n_old)  					\
		b1_pos = old[last_b1_idx];				\
	  else {							\
		last_b1_idx = 0;					\
		b1_pos = -1;						\
	  }								\
	}

/* ------------------------------------------------------------------- */
/*
 * 	find_b2pos(a0_pos,a0_color,n_old_trans,old_trans);
 *
 * 	Macro to find the end of a chunk of pixels in the previous line,
 *	which we passed by because they are uncorrelated with this line.
 * 
 *	Strategy:  teeny tiny modification to find_b1pos.
 *
 */
#define find_b2pos(a0_pos,a0_color,n_old,old)				\
	{  								\
	  if (last_b1_idx > 0) 						\
		--last_b1_idx;	/* avoid gotcha from above evil case */	\
									\
	  /* search for first changing element to right of a0_pos */	\
	  while (old[last_b1_idx] <= a0_pos) 				\
		if (++last_b1_idx >= (n_old-1))	/* CHANGE */		\
			break;	/* if out of transitions, give up */	\
									\
	  /* check out color - if matching, use next transition	*/	\
	  if (a0_color ^ (last_b1_idx & 1))				\
		++last_b1_idx;						\
	 	    							\
	  if (last_b1_idx < n_old-1)  		/* CHANGE */		\
		b2_pos = old[last_b1_idx+1];    /* CHANGE */		\
	  else {							\
		last_b1_idx = 0;					\
		b2_pos = -1;						\
	  }								\
	}

/* ------------------------------------------------------------------- */
/**** module fax/bits.h ****/
