CheapDateFormatter returns incorrect and invalid date strings
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Key: DERBY-4752
URL: https://issues.apache.org/jira/browse/DERBY-4752
Project: Derby
Issue Type: Bug
Components: Services
Affects Versions: 10.7.0.0
Reporter: Knut Anders Hatlen
Priority: Minor
CheapDateFormatter has multiple problems. These are the ones I'm aware of:
1) On the boundary between non-leap years and leap years it will return first
day of thirteenth month in previous year (for instance, 2011-13-01 instead of
2012-01-01)
2) It treats all years divisible by four as leap years. Those divisible by 100
and not by 400 are not leap years. It attempts to adjust for that (see the
snippet below) but it always ends up setting leapYear=true if (year%4)==0.
// It's a leap year if divisible by 4, unless divisible by 100,
// unless divisible by 400.
if ((year % 4L) == 0) {
if ((year % 100L) == 0) {
if ((year % 400L) == 0) {
leapYear = true;
}
}
leapYear = true;
}
3) More leap year trouble. To find out which year it is, it calculates the
number of four year periods that have elapsed since 1970-01-01. A four year
period is considered 365*3+366 days. Although most four year periods are of
that length, some are shorter, so we'll get one day off starting from year
2100, two days off from year 2200, and so on.
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