minusDays method
Returns date in past given number of days
Implementation
HDate minusDays(int numDays) {
if (numDays == 0) return this;
if (numDays < 0) return plusDays(-numDays);
int year = this.year;
int month = this.month;
int day = this.day;
for (; numDays > 0; --numDays) {
day--;
if (day <= 0) {
month--;
if (month < 1) {
month = 12;
year--;
}
day = daysInMonth(year, month);
}
}
return HDate(year, month, day);
}