/* $Xorg: zeroeven.c,v 1.3 2000/08/17 19:47:44 cpqbld Exp $ */
/**** module fax/zeroeven.c ****/
/******************************************************************************

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				NOTICE
                              
This software is being provided by AGE Logic, Inc. under the
following license.  By obtaining, using and/or copying this software,
you agree that you have read, understood, and will comply with these
terms and conditions:

     Permission to use, copy, modify, distribute and sell this
     software and its documentation for any purpose and without
     fee or royalty and to grant others any or all rights granted
     herein is hereby granted, provided that you agree to comply
     with the following copyright notice and statements, including
     the disclaimer, and that the same appears on all copies and
     derivative works of the software and documentation you make.
     
     "Copyright 1993, 1994 by AGE Logic, Inc."
     
     THIS SOFTWARE IS PROVIDED "AS IS".  AGE LOGIC MAKES NO
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     Title to this software shall at all times remain with AGE
     Logic, Inc.
*****************************************************************************
  
	fax/zeroeven.c -- DDXIE fax utility
  
	Ben && Larry -- AGE Logic, Inc. May, 1993
  
*****************************************************************************/


/***	zero_even.c - zero out even transitions. 

	The array wbtrans is arranged as a table of positions at which
	the input changes from white to black, then black to white, then
	white to black, and so on.  We assume all output pixels have
	already been set white. Therefore we only have to fill the
	black ranges with zeros...

	W->B   B->W   W->B   B->W   W->B   B->W   W->B   B->W

	12	17     29     30     65    68      90     92

	bit positions 12-16, 29, 65-67, and 90-91 in the above
	example are black.  It should be clear from the example
	that the size of the run length is t[w]-t[b],  where 
	w=b+1 and b  is the index of a transition from white to 
	black.  Note that if the line was only 92 pixels wide,
	setting the imaginary pixel with index = image width
	B->W still gives us the right answer.

***/

#include <xiemd.h>
#include "macro.h"

/**********************************************************************/

void
zero_even(cp,t,nt,w,white)
register LogInt *cp;
register int	*t, nt,w,white;
{
unsigned int	sbit,ebit;
LogInt		*sbyt, *ebyt, black;

#define ONES ~((LogInt)0)
   
    memset(cp, white ? 0xff: 0, (w+7)>>3);
    black = white ? 0 : ONES; 

    for (nt = (nt>>1) - 1; nt >= 0; nt--) {
	sbit = *t++;
	ebit = *t++; /* if (!nt && (ebit > w)) ebit = w; */
	sbyt = cp + (sbit >> LOGSHIFT); sbit &= LOGMASK;
	ebyt = cp + (ebit >> LOGSHIFT); ebit &= LOGMASK;

	if (sbyt < ebyt) {
	    if (sbit)	    	*sbyt++ ^= BitRight(ONES,sbit);
	    while (sbyt < ebyt)	*sbyt++  = black;
	    if (ebit)		*sbyt   ^= ~BitRight(ONES,ebit);
	} else
	    *sbyt ^= BitRight(ONES,sbit) & ~(BitRight(ONES,ebit));
    }
}
/**** module fax/zeroeven.c ****/