/* DEC	*Log10Decimal(pDst,pSrc)
 * ARGUMENT
 *	pDst is	a DEC pointer to the destination.
 *	pSrc is	a DEC pointer to the source.
 *
 * DESCRIPTION
 *	Takes the base 10 logarithm of pSrc, storing result in pDst.
 *
 * SIDE	EFFECTS
 *	None.
 *
 * RETURNS
 *	pDst if	successful, GM_NULL otherwise.
 *
 * ALGORTIHM
 *	log x =	(1/ln10) * ln(x), with ln(x) calculated	as:
 *
 *    pSrc = 10^m * 2^(-d) * x		.7 <= x	< 1.4
 *    z	= (x - 1) / (x + 1)
 *    ln pSrc =	m * ln 10 - d *	ln 2 + ln x
 *    ln x = 2 * SUM [z^(2 * n + 1) / (2 * n + 1)]
 *	n = 0, 1, 2, 3,...
 *
 * POSSIBLE ERROR CODES
 *
 *	GM_NULLPOINTER
 *	GM_IMAG
 *
 * AUTHOR
 *  Jared Levy		4 / 8 /	1987
 *   Copyright (C) 1987-1990 Greenleaf Software	Inc.  All rights reserved.
 *
 * MODIFICATIONS
 *
 *
 */

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

DEC	*Log10Decimal(pDst,pSrc)
DEC	*pDst;
DEC	*pSrc;
{
	DEC	dtemp, *temp=&dtemp;

	_MacStart(GM_DLOG);
	_MacInVarD(pSrc);
	_MacOutVarD(pDst);

	if (!_MacIsDecP(pSrc))	{
		_MacErr(GM_IMAG);
		_MacRet(GM_NULL);
	}

	_MacDZero(temp);
	/* first take ln(pSrc) */
	(void) _LnDec80Bit(temp, pSrc);	/* can't fail if pSrc is positive */
	/* then	(1/ln(10))* ln(pSrc) */
	(void) _MulDec80Bit(pDst, &decReciprocalOfLn10,	temp);
	/* then	back to	64-bit */
	(void) _Sq5UnsTo4Uns(pDst);	/* cannot be unsuccessful */

	_MacRet(pDst);
}