Messages in this thread | | | Date | Wed, 07 Jan 2009 20:16:18 +1030 | From | David Newall <> | Subject | Re: Bug: Status/Summary of slashdot leap-second crash on new years 2008-2009 |
| |
Alan Cox wrote: >> UTC equivalent to conversion on the naive basis that leap seconds are ignored and all >> years divisible by 4 are leap years. This value is not the same as the actual number of >> seconds between the time and the Epoch, because of leap seconds and because clocks are not >> required to be synchronized to a standard reference. >> > > I'm not sure what you are quoting from but it is out of date on the > subject of leap years. >
The range of signed 32-bit times is 1901 through 2039, which has only one century, 2000, which is a leap year. So the caveat for leap years is correct but unnecessary.
So I've discoverd, at least on Ubuntu, something wonderful and reassuring. It already works exactly the way I think is correct. Look: I create a test timezone with no daylight saving and one leap second:
davidn@takauji:~/timetest$ cat tz Zone testzone 0:00 0 XXX/YYY davidn@takauji:~/timetest$ cat leapseconds Leap 2008 Dec 31 23:59:59 + S davidn@takauji:~/timetest$ zic -d . -L leapseconds tz
Then the test program, which makes a time_t (what time() returns) for a few seconds before the leap second, then counts off seconds...
davidn@takauji:~/timetest$ cat timetest.c #include <time.h> #include <stdio.h>
main() {
setenv("TZ", ":/home/davidn/timetest/testzone", 1);
struct tm tm1 = { 55, 59, 23, 31, 11, 108 }; time_t t1 = mktime(&tm1); int i; for (i = 10; --i; t1++) printf("ctime(%ld) = %s", t1, ctime(&t1));
return 0;
}
Observe two 23:59:59's. Apparently it could be better if the second 23:59:59 was 23:59:60, but I prefer it this way.
davidn@takauji:~/timetest$ ./timetest ctime(1230767995) = Wed Dec 31 23:59:55 2008 ctime(1230767996) = Wed Dec 31 23:59:56 2008 ctime(1230767997) = Wed Dec 31 23:59:57 2008 ctime(1230767998) = Wed Dec 31 23:59:58 2008 ctime(1230767999) = Wed Dec 31 23:59:59 2008 ctime(1230768000) = Wed Dec 31 23:59:59 2008 ctime(1230768001) = Thu Jan 1 00:00:00 2009 ctime(1230768002) = Thu Jan 1 00:00:01 2009 ctime(1230768003) = Thu Jan 1 00:00:02 2009
Perhaps this is distribution-dependent, but even so, there's no need for the kernel to drop the second (and it's wrong if it does.)
| |