/* DEC	*SinglePaymentPresentValue(dst,	intr, nper);
 *
 * ARGUMENT
 *	DEC	*dst,*intr;
 *	int	nper;
 *
 * DESCRIPTION
 *	Calculates the present value of	1 dollar at the	future time of
 *   nper periods at an	interest rate of intr percent per period.
 *   dst = (1 +	intr / 100) ^ -nper
 *
 * SIDE	EFFECTS
 *	The result is stored in	dst.
 *
 * RETURNS
 *	dst 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 "gmsystem.h"
DEC	*SinglePaymentPresentValue(dst,	intr, nper)
DEC	*dst,*intr;
int	nper;
{
	DEC	dtemp, *temp=&dtemp;
	int	i;

	_MacStart(GM_SPPV);
	_MacInVarD(intr);
	_MacOutVarD(dst);

/* interest rate must be greater than -100% */
	if (CompareDecimal(intr,&decMinusHundred)<=0)  {
		_MacErr(GM_ARGVAL);
		_MacRet(GM_NULL);
	}

	_MacDCopy(temp,	intr);
	temp->dc.id +=2;
	(void) _AddDec80Bit(temp, temp,	&decOne);
	i =  _IntPwrDec80Bit(temp, temp, -nper);

	if (i==GM_OVERFLOW)  {
		_MacErr(GM_ARGVAL);
		_MacRet(GM_NULL);
	}

	if (_Sq5UnsTo4Uns(temp)!=GM_SUCCESS)  {
		_MacErr(GM_ARGVAL);
		_MacRet(GM_NULL);
	}

	_MacDCopy(dst, temp);

/* can't have zero value */
	if (_MacIsDecZ(temp))
		_MacErr(GM_ARGVAL);

	_MacRet(temp);
}