cmp_longtime2.c

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/*===========================================================================*/
/* DMC Interim     |              cmp_longtime             |         utility */
/*===========================================================================*/
/*
	Name:		cmp_longtime
	Purpose:	compare two times in struct input_time format
	Usage:		int cmp_longtime ();
				struct input_time time1;
				struct input_time time2;
				long precision;
				int result;
				result = cmp_longtime (time1, time2, precision);
	Input:		time1 = 1st time in struct input_time format
				time2 = 2nd time in struct input_time format
				precision = comparison precision in sec >= 0
							(ie., 50% of test window)
	Output:		result =  0 if time1 == time2 (diff <= precision)
				       = -1 if time1 < time2
				       =  1 if time1 > time2
	Externals:	none
	Warnings:	none
	Errors:		none
	Called by:	anything
	Calls to:	none
	Algorithm:	Compute dates relative to january 1 of the lesser year and
				compare. If difference greater than 2 days, return appropriate
				inequality.  Otherwise, compute daytimes in sec relative
				to midnite.  Take any difference in date into account and
				compare the times.  If difference <= precision, return an
				equality, else return the appropriate inequality.
	Notes:		The time structure looks like:
					struct input_time
					{
						unsigned short int year;
						unsigned short int day;
						char hour;
						char minute;
						char second;
						unsigned short int fracsec;
					};
	Problems:	Ignores leap seconds
				Ignores fracsecs in comparison (ie., does not round seconds)
				Maximum effective precision is six months.
	Debug:	  	level D_MIN -
				level D_MED -
			  	level D_MAX - print out start, comparison and finish notices
	References:	none
	Language:	ANSI standard C
	Author:		Kevin MacKenzie		28 mar 1989
	Revisions:
*/

#include "output.h"
#define isaleap(year) (((year%100 != 0) && (year%4 == 0)) || (year%400 == 0))
#define ONEDAY 86400L						/* one day in sec */

int cmp_longtime (time1, time2, precision)
struct	input_time	time1;					/* first time to compare */
struct	input_time	time2;					/* second time to compare */
long				precision;              /* comparison precision, e-04 sec */
{
	register long		diff;				/* value difference */
	register long		dtime1 = 0;			/* daytime #1 in e-04 sec */
	register long 		dtime2 = 0;			/* daytime #2 in e-04 sec */
	long				delta;
	unsigned short int 	lenyr;				/* length of year in days */
	int					err;				/* result */

	if (precision < 0) precision = 0;			/* precision must be >= 0 */

/* compare years */
	diff = (long)time1.year - (long)time2.year;	
	if (diff == 0)       ;					/* difference < 1 year */
	else if (diff == 1)
	{										/* difference near year end */
		lenyr = (isaleap (time2.year)) ? 366 : 365;		/* get length of year */
		time1.day += lenyr;
	}
	else if (diff == -1)
	{										/* difference near year end */
		lenyr = (isaleap (time1.year)) ? 366 : 365;	/* get length of year */
		time2.day += lenyr;
	}
	else if (diff >  1)
		return (err = 1);					/* time1 >>> time2 */
	else if (diff < -1)
		return (err = -1);					/* time1 <<< time2 */

/* compare dates */
	diff = (long)time1.day - (long)time2.day;
	delta = 1 + precision / ONEDAY;
	if (diff > delta)
		return (err = 1);					/* time1 >> time2 */
	else if (diff < -delta)
		return (err = -1);					/* time1 << time2 */
	else
	{										/* close--compute daytimes */
		dtime1 += diff * ONEDAY;					/* difference in dates */
		dtime1 += (time1.hour*3600) + (time1.minute*60) + time1.second;	/* sec*/
		dtime2 += (time2.hour*3600) + (time2.minute*60) + time2.second;	/* sec*/
	}

/* compare daytimes */
	if (dtime1 - dtime2 > precision)
		return (err = 1);					/* time1 > time2 */
	else if (dtime2 - dtime1 > precision)
		return (err = -1);					/* time1 < time2 */

	return (err = 0);						/* time1 == time2 */
}