/* DEC	*AntiLog10Decimal(pDst,pSrc)
 *
 * ARGUMENT
 *	pDst is	a DEC pointer to the destination.
 *	pSrc is	a DEC pointer to the source.
 *
 * DESCRIPTION
 *	Takes the base 10 anti-logarithm (power) of pSrc,
 *  ie.	10**x, storing result in pDst.
 *
 * RETURNS
 *	pDst if	successful, GM_NULL otherwise.
 *
 * ALGORITHM
 *	Set e**x = 10 ** y, then x*ln(e) = y*ln10. Then, ln(e)=1 by
 *  definition,	so x = y*ln(10), or y times a constant.	 Therefore, we
 *  set	z=y*ln(10), and	10**y =	e**z.
 *
 *
 * POSSIBLE ERROR CODES
 *
 *	GM_NULLPOINTER
 *	GM_OVERFLOW
 *	GM_UNDERFLOW
 *
 * AUTHOR
 *	Andy Anderson	8-18-87		13:51
 *   Copyright (C) 1987-1990 Greenleaf Software	Inc.  All rights reserved.
 *
 * MODIFICATIONS
 *
 */

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

DEC	*AntiLog10Decimal(pDst,pSrc)
DEC	*pDst;
DEC	*pSrc;
{
	int	i;
	DEC	dtemp, *temp=&dtemp, *pt, t1;

	_MacStart(GM_DALOG);

	_MacInVar(pSrc,GM_NULL);
	_MacOutVar(pDst,GM_NULL);

	/* 10**0 is a one by definition	*/
	if(_MacIsDecZ(pSrc)) {
		pt=&decOne;
		_MacDCopy(pDst,pt);
		_MacRet(pDst);
	}

	pt=&t1;
	_MacDZero(pt);

	/* if the power	is integer and small enough, use int power rtn */
	if((IsDecimalInt(pSrc))	&& ((pSrc->dc.msd == 0)	&&
		(pSrc->ls.lsl[1] == 0L)	&& (pSrc->dc.sl[1] == 0))
		&& (!(pSrc->dc.sl[0] & 0x8000))) {
		pt->dc.id = 0;
		pt->dc.sl[0] = 10;
		i = _IntPwrDec80Bit(pt,pt,ConvDecimalToInt(pSrc));
		if(i !=	GM_SUCCESS) {
			_MacErr(i);
			_MacRet(GM_NULL);
		}
	}
	else {

		/* first create	z = y*ln10, overflow impossible	*/
		 (void)	_MulDec80Bit(temp,pSrc,&decLn10);

		/* then	e**(yln10) = 10**y */
		i = _ExpDec80Bit(pt, temp);
		if(i==GM_OVERFLOW) {
			_MacErr(i);
			_MacRet(GM_NULL);
		}

	}

	i = _Sq5UnsTo4Uns(pt);		/* reduce to 18-digit */
	if(i!=GM_SUCCESS) {
		_MacErr(GM_OVERFLOW);
		_MacRet(GM_NULL);
	}

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

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