/* DEC	*TangentDecimal(pDst,pSrc)
 *
 * ARGUMENT
 *	DEC	*pDst;
 *	DEC	*pSrc;
 *
 * DESCRIPTION
 *	Sets pDst = the	tangent	of pSrc	radians.
 *
 * SIDE	EFFECTS
 *	Possible Errors:  GM_NULLPOINTER,
 *			  GM_OVERFLOW if | tan(pSrc) | > 2^63
 *
 * RETURNS
 *	Returns	pointer	to pDst	if successful, otherwise a GM_NULL.
 *
 * POSSIBLE ERROR CODES
 *
 *	GM_NULLPOINTER
 *	GM_OVERFLOW
 *
 * AUTHOR
 *  Jared Levy		Oct 16,	1987
 *   Copyright (C) 1987-1990 Greenleaf Software	Inc.  All rights reserved.
 *
 * ALGORITHM
 *	tan(x) = +/- (1	- cos(x) ^ 2 ) ^ .5 / cos(x)
 *
 * MODIFICATIONS
 *
 */

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

DEC	*TangentDecimal(pDst,pSrc)
DEC	*pDst;
DEC	*pSrc;

{
	int	i, isn=0;
	DEC	*nsrc, dnsrc, *size, dsize, *temp, dtemp;
	DEC	*cosx, dcosx, *sinx, dsinx;

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

	nsrc = &dnsrc;
	_MacDCopy(nsrc,	pSrc);
	if (_MacIsDecN(nsrc))  {
		isn = 1;
		_MacDChgs(nsrc);
		}

	temp = &dtemp;
	if (CompareDecimal(nsrc, &decPiOver2) == 1)  {
		(void) _DivRndDec80Bit(size = &dsize, nsrc, &decPi, 0);
		(void) _MulDec80Bit(temp, &decPi, size);
		(void) _SubDec80Bit(nsrc, nsrc,	temp);
		if (_MacIsDecN(nsrc))  {
			isn = 1	- isn;
			_MacDChgs(nsrc);
			}
		}

	_CosDec80Bit(cosx = &dcosx, nsrc);
	if (_MacIsDecZ(cosx))  {
		_MacErr(GM_OVERFLOW);
		_MacRet(GM_NULL);
		}

	(void) _MulDec80Bit(temp, cosx,	cosx);
	(void) _SubDec80Bit(temp, &decOne, temp);
	       _SqrtDec80Bit(sinx = &dsinx, temp);
	i =    _DivDec80Bit(pDst, sinx,	cosx);

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

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

	if (isn)
		_MacDChgs(pDst);

	_MacRet(pDst);
}