/* DEC	*DepreciateStraightLine(depr, remval, book, salv, life,	partial, time)
 *
 * ARGUMENT
 *	DEC	*depr, *remval,	*book, *salv, *partial;
 *	int	time, life;
 *
 * DESCRIPTION
 *	Calculate a particular year's depreciation and remaining depreciable
 *   value according to	straight line depreciation.  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	*DepreciateStraightLine(depr, remval, book, salv, life,	partial, time)
DEC	*depr, *remval,	*book, *salv, *partial;
int	time, life;
{
	int	i, plife;
	DEC	dtotlif, *totlif=&dtotlif;
	DEC	dydep, *ydep=&dydep;

	_MacStart(GM_DPSL);

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

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

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

/* calculate yearly depreciation */
	(void) _SubDec80Bit(remval,book,salv);
	(void) _ScaleDec80Bit(remval, remval, 2);
	(void) ConvLongToDecimal(totlif, (long)	life);
	(void) _DivRndDec80Bit(ydep, remval, totlif, 2);

	_MacDZero(depr);

	if (time==0)
		_MacRet(depr);

/* handle partial first	year */
	if (_MacIsDecZ(partial))  {
		i=0;
	}
	else  {
		(void) _MulDec80Bit(depr,ydep,partial);
		(void) _ScaleDec80Bit(depr,depr,2);
		(void) _SubDec80Bit(remval, remval, depr);
		i=1;
	}

/* handle remaining years */
	if (time>i)
		_MacDCopy(depr,	ydep);

	while (i<time)	{
		(void) _SubDec80Bit(remval, remval, ydep);
		i++;
	}

/* add balance to last depreciation period */
	if (time==plife)  {
		_AddDec80Bit(depr, depr, remval);
		_MacDZero(remval);
	}

	_MacRet(depr);
}