jdate.c

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#include <stdio.h>
#include <stdint.h>
#include <timeutils.h>
 
int jdate(int32_t julian, int32_t *year, int32_t *doy) {
 
    int i;
    int32_t month, day;
 
    int32_t ja, jb, jc, jd, je, jalpha;
 
    jalpha = (int32_t) (((julian - 1867216L) - 0.25) / 36524.25);
    ja = julian + 1 + jalpha - (int32_t) (0.25 * jalpha);
 
    jb = ja + 1524;
    jc = (int32_t) (6680.0 + ((jb - 2439870L) - 122.1) / 365.25);
    jd = 365 * jc + (int32_t) (0.25 * jc);
    je = (int32_t) ((jb - jd) / 30.6001);
 
    day = jb - jd - (int32_t) (30.6001 * je);
    month = je - 1;
    if (month > 12)
        month = month - 12;
    *year = jc - 4715;
 
    if (month > 2) *year = *year - 1;
    if (*year <= 0) *year = *year - 1;
 
    int dmn[24] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31,
        31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
 
    *doy = day;
    for (i = 1; i < month; i++) *doy = *doy + dmn[isleap(*year) * 12 + (i - 1)];
 
    return 0;
}