/* DEC	*DepreciateDeclining(depr, remval, book, salv,dbf,life,partial,time);
 *
 * ARGUMENT
 *	DEC	*depr, *remval,	*book, *salv, *dbf, *partial;
 *	int	life, time;
 *
 * DESCRIPTION
 *	Calculate a specific year's depreciation and remaining depreciable
 *   value according to	declining balance depreciation.
 *   With a declining balance factor of	dbf, the item has book value
 *   book, salvage value salv, and lifetime life (which	may include a partial
 *   period).  At year#	time, the depreciation and remaining value are
 *   computed and stored in depr and remval.  The first	year is	always
 *   the partial year.
 *
 * SIDE	EFFECTS
 *	depr and remval	are changed.
 *
 * RETURNS
 *	depr if	successful, otherwise GM_NULL.
 *
 * POSSIBLE ERRORS
 *	GM_NULLPOINTER
 *	GM_ARGVAL
 *
 * AUTHOR
 *  Jared Levy
 *   Copyright (C) 1988-1990 Greenleaf Software	Inc.  All rights reserved.
 *
 * MODIFICATIONS
 *
 *
 */

#include <stdio.h>
#include "gm.h"
#include "gmsystem.h"

DEC	*DepreciateDeclining(depr, remval, book, salv,dbf,life,	partial, time)
DEC	*depr, *remval,	*book, *salv, *dbf, *partial;
int	life, time;
{
	int	i, plife;
	DEC	drbv, *rbv=&drbv, dfol,	*fol=&dfol;
	DEC	dtemp, *temp=&dtemp, dnsalv, *nsalv=&dnsalv;

	_MacStart(GM_DPDB);

	if (!depr||!remval||!book||!salv||!partial||!dbf)  {
		_MacErr(GM_NULLPOINTER);
		_MacRet(GM_NULL);
	}
	if (_MacBad(salv)||_MacBad(partial)||_MacBad(dbf))  {
		_MacErr(GM_INIT);
		_MacRet(GM_NULL);
	}

	plife=life+(_MacIsDecZ(partial)?0:1);

	if (time<0||life<1||_MacIsDecN(book)||_MacIsDecN(salv)||time>plife
		||_MacIsDecN(dbf)
		||_MacIsDecN(partial)||CompareDecimal(partial,&decOne)==1)  {
		_MacDZero(depr);
		_MacDZero(remval);
		_MacErr(GM_ARGVAL);
		_MacRet(GM_NULL);
	}

	(void) _ScaleDec80Bit(rbv, book, 2);
	(void) _ScaleDec80Bit(nsalv, salv, 2);
	(void) _SubDec80Bit(remval, rbv, nsalv);

	if (time==0)  {
		_MacDZero(depr);
		_MacRet(depr);
	}

	(void) ConvLongToDecimal(temp, (long) life * 100L);
	(void) _DivDec80Bit(fol, dbf, temp);

/* handle partial first	year */
	if (_MacIsDecZ(partial))  {
		i=0;
	}
	else  {
		(void) _MulDec80Bit(temp,rbv,fol);
		(void) _MulDec80Bit(depr, temp,	partial);
		(void) _ScaleDec80Bit(depr,depr,2);
		(void) _SubDec80Bit(remval, remval, depr);
/* remaining value can't be negative */
		if (_MacIsDecN(remval))	 {
			(void) _AddDec80Bit(depr, depr,	remval);
			_MacDZero(remval);
		}
		(void) _SubDec80Bit(rbv, rbv, depr);
		i=1;
	}

/* handle remaining years */

	while (i<time)	{
		i++;
		(void) _MulDec80Bit(depr, rbv, fol);
		(void) _ScaleDec80Bit(depr,depr,2);
		(void) _SubDec80Bit(remval, remval, depr);
/* remaining value can't be negative */
		if (_MacIsDecN(remval))	 {
			(void) _AddDec80Bit(depr, depr,	remval);
			_MacDZero(remval);
		}
		(void) _SubDec80Bit(rbv,rbv,depr);
	}

/* remaining depreciable value after last year should be 0 */
	if (time==plife&&!_MacIsDecZ(remval))  {
		(void) _AddDec80Bit(depr,depr,remval);
		_MacDZero(remval);
	}

	_MacRet(depr);
}