Convert DateTime to Julian Date in C# (ToOADate Safe?)

Question

I need to convert from a standard Gregorian date to a Julian day number.

I\'ve seen nothing documented in C# to do this directly,

Answer 1

I use some calculations in microcontrollers but require years only between 2000 and 2255. Here is my code:

typedef struct {
    unsigned int8   seconds;    // 0 to 59
    unsigned int8   minutes;    // 0 to 59
    unsigned int8   hours;      // 0 to 23  (24-hour time)
    unsigned int8   day;        // 1 to 31
    unsigned int8   weekday;    // 0 = Sunday, 1 = Monday, etc.
    unsigned int8   month;      // 1 to 12
    unsigned int8   year;       // (2)000 to (2)255
    unsigned int32  julian;     // Julian date
} date_time_t;

    

// Convert from DD-MM-YY HH:MM:SS to JulianTime

void JulianTime(date_time_t * dt)
{
    unsigned int8   m, y;

    y = dt->year;
    m = dt->month;
    if (m > 2) m -= 3;
    else {
        m +=  9;
        y --;
    }
    dt->julian  = ((1461 * y) / 4) + ((153 * m + 2) / 5) + dt->day;
    dt->weekday = ( dt->julian + 2 ) % 7;
    dt->julian  = (dt->julian * 24) + (dt->hours   ); 
    dt->julian  = (dt->julian * 60) + (dt->minutes );     
    dt->julian  = (dt->julian * 60) + (dt->seconds );     
}

// Reverse from JulianTime to DD-MM-YY HH:MM:SS

void GregorianTime(date_time_t *dt) 
{
    unsigned int32  j = dt->julian;

    dt->seconds = j % 60;
    j /= 60;
    dt->minutes = j % 60;
    j /= 60;
    dt->hours   = j % 24;
    j /= 24;
    dt->weekday = ( j + 2 ) % 7; // Get day of week
    dt->year = (4 * j) / 1461;
    j = j - ((1461 * dt->year) / 4);
    dt->month = (5 * j - 3) / 153;
    dt->day  = j - (((dt->month * 153) + 3) / 5);
    if ( dt->month < 10 )
    {
        dt->month += 3;
    }
    else
    {
        dt->month -= 9;
        dt->year ++;
    }
}

Hope this helps :D