This is cal_mjd.c in view mode; [Download] [Up]
#include <stdio.h>
#include <math.h>
#include "astro.h"
/* given a date in months, mn, days, dy, years, yr,
* return the modified Julian date (number of days elapsed since 1900 jan 0.5),
* *mjd.
*/
cal_mjd (mn, dy, yr, mjd)
int mn, yr;
double dy;
double *mjd;
{
int b, d, m, y;
long c;
m = mn;
y = (yr < 0) ? yr + 1 : yr;
if (mn < 3) {
m += 12;
y -= 1;
}
if (yr < 1582 || yr == 1582 && (mn < 10 || mn == 10 && dy < 15))
b = 0;
else {
int a;
a = y/100;
b = 2 - a + a/4;
}
if (y < 0)
c = (long)((365.25*y) - 0.75) - 694025L;
else
c = (long)(365.25*y) - 694025L;
d = 30.6001*(m+1);
*mjd = b + c + d + dy - 0.5;
}
/* given the modified Julian date (number of days elapsed since 1900 jan 0.5,),
* mjd, return the calendar date in months, *mn, days, *dy, and years, *yr.
*/
mjd_cal (mjd, mn, dy, yr)
double mjd;
int *mn, *yr;
double *dy;
{
double d, f;
double i, a, b, ce, g;
d = mjd + 0.5;
i = floor(d);
f = d-i;
if (f == 1) {
f = 0;
i += 1;
}
if (i > -115860.0) {
a = floor((i/36524.25)+.9983573)+14;
i += 1 + a - floor(a/4.0);
}
b = floor((i/365.25)+.802601);
ce = i - floor((365.25*b)+.750001)+416;
g = floor(ce/30.6001);
*mn = g - 1;
*dy = ce - floor(30.6001*g)+f;
*yr = b + 1899;
if (g > 13.5)
*mn = g - 13;
if (*mn < 2.5)
*yr = b + 1900;
if (*yr < 1)
*yr -= 1;
}
/* given an mjd, set *dow to 0..6 according to which dayof the week it falls
* on (0=sunday) or set it to -1 if can't figure it out.
*/
mjd_dow (mjd, dow)
double mjd;
int *dow;
{
/* cal_mjd() uses Gregorian dates on or after Oct 15, 1582.
* (Pope Gregory XIII dropped 10 days, Oct 5..14, and improved the leap-
* year algorithm). however, Great Britian and the colonies did not
* adopt it until Sept 14, 1752 (they dropped 11 days, Sept 3-13,
* due to additional accumulated error). leap years before 1752 thus
* can not easily be accounted for from the cal_mjd() number...
*/
if (mjd < -53798.5) {
/* pre sept 14, 1752 too hard to correct */
*dow = -1;
return;
}
*dow = ((long)floor(mjd-.5) + 1) % 7;/* 1/1/1900 (mjd 0.5) is a Monday*/
if (*dow < 0)
*dow += 7;
}
/* given a mjd, return the the number of days in the month. */
mjd_dpm (mjd, ndays)
double mjd;
int *ndays;
{
static short dpm[] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
int m, y;
double d;
mjd_cal (mjd, &m, &d, &y);
*ndays = (m==2 && ((y%4==0 && y%100!=0)||y%400==0)) ? 29 : dpm[m-1];
}
/* given a mjd, return the year as a double. */
mjd_year (mjd, yr)
double mjd;
double *yr;
{
int m, y;
double d;
double e0, e1; /* mjd of start of this year, start of next year */
mjd_cal (mjd, &m, &d, &y);
if (y == -1) y = -2;
cal_mjd (1, 1.0, y, &e0);
cal_mjd (1, 1.0, y+1, &e1);
*yr = y + (mjd - e0)/(e1 - e0);
}
/* given a decimal year, return mjd */
year_mjd (y, mjd)
double y;
double *mjd;
{
double e0, e1; /* mjd of start of this year, start of next year */
int yf = floor (y);
if (yf == -1) yf = -2;
cal_mjd (1, 1.0, yf, &e0);
cal_mjd (1, 1.0, yf+1, &e1);
*mjd = e0 + (y - yf)*(e1-e0);
}
These are the contents of the former NiCE NeXT User Group NeXTSTEP/OpenStep software archive, currently hosted by Netfuture.ch.