/* void	 AddDaysToDate365( m2, d2, y2, m1, d1, y1, ndays )
 *
 * ARGUMENTS
 *	int  m1,  d1,  y1	- Specify a base date.
 *	int *m2, *d2, *y2	- Specify a date to be calculated
 *	int ndays		- Number of days (+ or -) to be	added to base
 *
 * DESCRIPTION
 *  A signed number of days (ndays) is added to	the base date to form a
 *  second date	which is transferred to	the variables m2,d2,y2.	 If any	of
 *  the	arguments are NULL on input, an	error results.
 *
 *  Years < 100	are taken to be	in 20th	century.
 *
 *  Years are considered to have 365 days.  Leap years are considered here.
 *
 * SIDE	EFFECTS
 *	Modified d2, m2, y2.
 *
 * RETURNS
 *	None.
 *
 * POSSIBLE ERROR CODES
 *
 *	GM_ARGVAL
 *	GM_NULLPOINTER
 *
 * AUTHOR
 *  Don	Killen	 03-Feb-1988  16:27:32
 *   Copyright (C) 1988-1990 Greenleaf Software	Inc.  All rights reserved.
 *
 * MODIFICATIONS
 *
 *
 */

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

void AddDaysToDate365(m2,d2,y2,m1,d1,y1,ndays)
int m1,*m2,d1,*d2,y1,*y2,ndays;
{
	long	n1;
	int	np, x, z, mt, dt=1, dp,	ny, t1,	t2;

	mbool	ly;
	_MacStart(GM_ADATE365);

	if (d2==NULL||m2==NULL||y2==NULL)  {
		_MacErr(GM_NULLPOINTER);
		_MacRetV;
	}

	if ( m1<1 || m1>12 || d1<1 || d1>31 || y1<1 || y1>9999 )  {
		_MacErr(GM_ARGVAL);
		_MacRetV;
	}

	if (m1<=2)  {
		x=0;
		z=y1-1;
	}
	else  {
		x=(4*m1	+ 23) /	10;
		z=y1;
	}

	/* compute day # */
	n1 = (long) y1 * 365L +	(long) (31*(m1-1) + d1 + z/4 - x)
		+(long)	ndays;

	/* estimate year */
	*y2 = (int) ((4L * n1) / 1461L);
	np = (int) (n1 - ((long) (*y2) * 365L +	(long) (((*y2) - 1) / 4)));
	/* correct year	estimate */
	while (np<1)  {		/* year	too large */
		*y2 = (*y2)-1;
		np = (int) (n1 - ((long)(*y2) *	365L +
			(long) (((*y2)-1) / 4)));
	}
	if ( ((*y2) % 4) == 0)
		ny = 366;
	else
		ny = 365;
	while (np > ny )  {	/* year	too small */
		*y2 = (*y2)+1;
		np = (int) (n1 - ((long)(*y2) *	365L +
			(long) (((*y2)-1) / 4)));
	}

/* no leap year	in 1700, 1800, 1900 */
	if ((y1>=1700 && y1<=1900) || (*y2>=1700 && *y2<=1900))	 {
		t1 = (m1<=2) ? y1-1 : y1;
		t2 = (np<60) ? (*y2)-1 : *y2;
		if (np==60 && ndays<0)
			t2--;
/* if y1 and y2	fall on	different centuries, extra leap	year counted */
		np+= ((t2/100) - (t1/100));
		if (np<1)  {
			*y2 = *y2-1;
			*m2 = 12;
			*d2 = 31;
			_MacRetV;
		}
		if (np>366)  {
			*y2 = *y2+1;
			*m2 = 1;
			*d2 = 1;
			_MacRetV;
		}

	}

	/* handle Jan. & Feb. */
	if (np <= 31)  {
		*m2 = 1;
		*d2 = np;
		_MacRetV;
	}

	/* check for leap year */
	ly = ((*y2) % 4	== 0);

	if (np <= 59 + (ly))  {
		*m2 = 2;
		*d2 = np - 31;
		_MacRetV;
	}

	/* handle other	months */
	if (ly)
		np--;
	mt = 2;
	do  {
		mt++;
		dp = dt;
		dt = np	- 31 * (mt - 1)	+ (4 * mt + 23)	/ 10;
	} while	(dt>=1);
	*m2 = mt-1;
	*d2 = dp;

	_MacRetV;
}