/* DEC	*PowerDecimal(pDst,pSrc1,pSrc2)
 *
 * ARGUMENT
 *	DEC	*pDst,*pSrc1,*pSrc2;
 *
 * DESCRIPTION
 *	Calculates pSrc1 to the	power pSrc2 and	returns	the answer in pDst.
 *  This provides an x**y power	function for DEC numbers. Because of
 *  the	way we store DEC numbers, the base can't be very large if the
 *  power is greater than 3 or 4.  A separate function is provided for
 *  integral powers, which uses	a different algorithm and is MUCH FASTER.
 *
 * SIDE	EFFECTS
 *	None.
 *
 * RETURNS
 *	Pointer	to the result if no error, otherwise GM_NULL.
 *
 * ALGORITHM:
 *	x**y = e**(y*ln(x)). Therefore,	call dlnx() to get the natural log
 *  and	then multiply by the power of x.  Finally, call	dexx() to provide
 *  e**z.
 *
 * POSSIBLE ERROR CODES
 *
 *	GM_NULLPOINTER
 *	GM_OVERFLOW
 *	GM_UNDERFLOW
 *	GM_IMAG
 *	GM_PWR0
 *
 * AUTHOR
 *  Andy Anderson   05-JAN-1987	 17:30
 *   Copyright (C) 1987-1990 Greenleaf Software	Inc.  All rights reserved.
 *
 * MODIFICATIONS
 *
 */

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

DEC	*PowerDecimal(pDst,pSrc1,pSrc2)
DEC	*pDst, *pSrc1, *pSrc2;
{
	DEC	temp, *pt;
	int	i;

	_MacStart(GM_DPOW);
	_MacInVarD(pSrc1);
	_MacInVarD(pSrc2);
	_MacOutVarD(pDst);

	if (_MacIsDecN(pSrc1))	{
		_MacErr(GM_IMAG);
		_MacRet(GM_NULL);
	}

	if (_MacIsDecZ(pSrc1))	{
		if (_MacIsDecP(pSrc2))	{
			_MacDZero(pDst);
			_MacRet(pDst);
		}
		else  {
			_MacErr(GM_PWR0);
			_MacRet(GM_NULL);
		}
	}

	pt = &temp;

	/* if the power	is integer and small enough, use int power rtn */
	if((pSrc2->dc.id == 0) && ((pSrc2->dc.msd == 0)	&&
		(pSrc2->ls.lsl[1] == 0L) && (pSrc2->dc.sl[1] ==	0))
		&& (!(pSrc2->dc.sl[0] &	0x8000))) {
		i = _IntPwrDec80Bit(pt,pSrc1,ConvDecimalToInt(pSrc2));
		if(i ==	GM_OVERFLOW) {
			_MacErr(i);
			_MacRet(GM_NULL);
		}
	}
	else {

		(void) _LnDec80Bit(pt, pSrc1);
		i = _MulDec80Bit(pt, pt, pSrc2);
		if(i!=GM_SUCCESS) {
			_MacErr(i);
			_MacRet(GM_NULL);
		}
		i = _ExpDec80Bit(pt, pt);
		if(i==GM_OVERFLOW) {
			_MacErr(i);
			_MacRet(GM_NULL);
		}
	}

	i = _Sq5UnsTo4Uns(pt);
	if(i!=GM_SUCCESS) {
		_MacErr(GM_OVERFLOW);
		_MacRet(GM_NULL);
	}

	if (_MacIsDecZ(pt))  {
		_MacErr(GM_UNDERFLOW);
	}

	_MacDCopy(pDst,pt);
	_MacRet(pDst);
}