/*
; #defines
*/
#define BOOL int
#define TRUE 1
#define FALSE 0
/*
; Function prototypes
*/
long ToJul( int, int, int );
void FromJul( long, int *, int *, int * );
BOOL IsLeapYear( int );
int DayOfWeek( long );
/*
;
; USAGE: long ToJul( int, int, int );
; int month; Gregorian calendar date month
; int day; Gregorian calendar date day
; int year; Gregorian calendar date year
;
; DESCRIPTION: Converts Gregorian calendar date to a
; julian day number.
;
; ALGORITHM: adaptation of the FORTRAN code used to
; implement the algorithm presented by
; H. Fliegl and T. Van Flanders,
; Communications of the ACM, Vol. 11,
; No. 10, October, 1968, page 657.
;
;RETURNS: long int representing the julian day number
*/
long ToJul( int month, int day, int year )
{
long jul_day, // returned julian day
lmonth = (long)month, // cast them once
lday = (long)day, // instead of
lyear = (long)year; // each usage
jul_day = lday - 32075L + 1461L *
(lyear + 4800 + (lmonth - 14L) / 12L) /
4L + 367L * (lmonth - 2L - (lmonth - 14L) /
12L * 12L) / 12L - 3L * ((lyear + 4900L +
(lmonth - 14L) / 12L) / 100L) / 4L;
return jul_day;
}
/*
;
; USAGE: void FromJul( long, int *, int *, int * );
; long jul_day; Julian Day number to convert
; int *month; Gregorian calendar month (return)
; int *day; Gregorian calendar day (return)
; int *year; Gregorian calendar year (return)
;
; DESCRIPTION: Converts Julian Day number to its
; corresponding Gregorian calendar date
; components.
;
; ALGORITHM: adaptation of the FORTRAN code used to
; implement the algorithm presented by
; H. Fliegl and T. Van Flanders,
; Communications of the ACM, Vol. 11,
; No. 10, October, 1968, page 657.
;
; RETURNS: Nothing, updates variables pointed to by
; year, month and day.
*/
void FromJul( long jul_date,
int *month,
int *day,
int *year )
{
long t1, // temporary work variables
t2,
yr,
mo;
t1 = jul_date + 68569L;
t2 = 4L * t1 / 146097L;
t1 = t1 - (146097L * t2 + 3L) / 4L;
yr = 4000L * (t1 + 1) / 1461001L;
t1 = t1 - 1461L * yr / 4L + 31;
mo = 80L * t1 / 2447L;
*day = (int)(t1 - 2447L * mo / 80L);
t1 = mo / 11L;
*month = (int)(mo + 2L - 12L * t1);
*year = (int){100L * (t2 - 49L) + yr + t1);
}
/*
; USAGE: int IsLeapYear( int );
; int year; year to check
;
; DESCRIPTION: Determines whether a given year is a
; leap year.
;
; RETURNS:
; TRUE (non-zero) year is a leap year
; FALSE (zero) year is not a leap year
*/
BOOL IsLeapYear( int year )
{
return (year % 4 == 0 &&
(year % 100 != 0 || year % 400 == 0))
}
/*
; USAGE: int DayOfWeek( long );
; long jul_day; julian day number
;
; DESCRIPTION: Determine the day of the week a given
; julian day number falls on.
;
; RETURNS: 0 ... 7, where 0 is a Monday, 7 is a Sunday.
*/
int DayOfWeek( long jul_day )
{
return (int)(jul_day % 7L);
}
/* End of File */