/**
* Returns a day count for the specified years, months and days. All values must be specified in
* their internal representation (undefined values are supported, too). Algorithm is derived from
* J R Stockton (http://www.merlyn.demon.co.uk/daycount.htm).
*
* @param year year
* @param month month
* @param day days
* @return days
*/
private static BigDecimal days(final long year, final int month, final int day) {
final long y = year - (month < 2 ? 1 : 0);
final int m = month + (month < 2 ? 13 : 1);
final int d = day + 1;
return BD365
.multiply(BigDecimal.valueOf(y))
.add(BigDecimal.valueOf(y / 4 - y / 100 + y / 400 - 92 + d + (153 * m - 2) / 5));
}
/**
* Converts a day count into year, month and day components. Algorithm is derived from J R
* Stockton (http://www.merlyn.demon.co.uk/daycount.htm).
*
* @param days day count
* @return result array
*/
private static long[] ymd(final BigDecimal days) {
BigDecimal d = days;
BigDecimal t =
d.add(BD36525).multiply(BD4).divideToIntegralValue(BD146097).subtract(BigDecimal.ONE);
BigDecimal y = BD100.multiply(t);
d = d.subtract(BD36524.multiply(t).add(t.divideToIntegralValue(BD4)));
t = d.add(BD366).multiply(BD4).divideToIntegralValue(BD1461).subtract(BigDecimal.ONE);
y = y.add(t);
d = d.subtract(BD365.multiply(t).add(t.divideToIntegralValue(BD4)));
final BigDecimal m = BD5.multiply(d).add(BD2).divideToIntegralValue(BD153);
d = d.subtract(BD153.multiply(m).add(BD2).divideToIntegralValue(BD5));
long mm = m.longValue();
if (mm > 9) {
mm -= 12;
y = y.add(BigDecimal.ONE);
}
return new long[] {y.subtract(BigDecimal.valueOf(ADD_NEG)).longValue(), mm + 2, d.longValue()};
}