Function get_datetimestruct_days

numpy/core/src/multiarray/datetime.c:120–177

* Calculates the days offset from the 1970 epoch. */

 * Calculates the days offset from the 1970 epoch.
 */
NPY_NO_EXPORT npy_int64
get_datetimestruct_days(const npy_datetimestruct *dts)
{
    int i, month;
    npy_int64 year, days = 0;
    int *month_lengths;

    year = dts->year - 1970;
    days = year * 365;

    /* Adjust for leap years */
    if (days >= 0) {
        /*
         * 1968 is the closest leap year before 1970.
         * Exclude the current year, so add 1.
         */
        year += 1;
        /* Add one day for each 4 years */
        days += year / 4;
        /* 1900 is the closest previous year divisible by 100 */
        year += 68;
        /* Subtract one day for each 100 years */
        days -= year / 100;
        /* 1600 is the closest previous year divisible by 400 */
        year += 300;
        /* Add one day for each 400 years */
        days += year / 400;
    }
    else {
        /*
         * 1972 is the closest later year after 1970.
         * Include the current year, so subtract 2.
         */
        year -= 2;
        /* Subtract one day for each 4 years */
        days += year / 4;
        /* 2000 is the closest later year divisible by 100 */
        year -= 28;
        /* Add one day for each 100 years */
        days -= year / 100;
        /* 2000 is also the closest later year divisible by 400 */
        /* Subtract one day for each 400 years */
        days += year / 400;
    }

    month_lengths = _days_per_month_table[is_leapyear(dts->year)];
    month = dts->month - 1;

    /* Add the months */
    for (i = 0; i < month; ++i) {
        days += month_lengths[i];
    }

    /* Add the days */
    days += dts->day - 1;

    return days;
}