gmtime() oddities for large values

[Edwin Groothuis]

Hello!

With my hat of the tzdata/tzcode maintainer on the FreeBSD system, I sometimes
get the more interesting bugs reported.

For example this piece of code, on 64 bit machines it returns the same values
for values bigger than the initial one:

    #include <errno.h>
    #include <stdint.h>
    #include <stdio.h>
    #include <time.h>

    void t_inspect(time_t t)
    {
        struct tm *tp;
        errno = 0;
        tp = gmtime(&t);
        printf("t: %ld, tp: %p errno: %d\n", t, tp, errno);
        if (tp)
            printf("sec: %d, min: %d, hour: %d, mday: %d, mon: %d, "
                "year: %d, wday: %d, yday: %d, isdst: %d, gmtoff: %ld, "
                "zone: %s\n", tp->tm_sec, tp->tm_min, tp->tm_hour,
                tp->tm_mday, tp->tm_mon, tp->tm_year, tp->tm_wday,
                tp->tm_yday, tp->tm_isdst, tp->tm_gmtoff, tp->tm_zone);
    }

    int main(void)
    {
        // time_t t = INT32_MAX;
        time_t t = 67767976233532799;
        t_inspect(t-1);
        t_inspect(t);
        t_inspect(t+1);
        t_inspect(t+2);
        return 0;
    }

The output on a 64 bit machine is (the interesting part is the sec=59)

t: 67767976233532798, tp: 0x80085b9a0 errno: 2
sec: 58, min: 59, hour: 23, mday: 31, mon: 11, year: 2147481747, wday: 2, yday:
364, isdst: 0, gmtoff: 0, zone: UTC
t: 67767976233532799, tp: 0x80085b9a0 errno: 0
sec: 59, min: 59, hour: 23, mday: 31, mon: 11, year: 2147481747, wday: 2, yday:
364, isdst: 0, gmtoff: 0, zone: UTC
t: 67767976233532800, tp: 0x80085b9a0 errno: 0
sec: 59, min: 59, hour: 23, mday: 31, mon: 11, year: 2147481747, wday: 2, yday:
364, isdst: 0, gmtoff: 0, zone: UTC
t: 67767976233532801, tp: 0x80085b9a0 errno: 0
sec: 59, min: 59, hour: 23, mday: 31, mon: 11, year: 2147481747, wday: 2, yday:
364, isdst: 0, gmtoff: 0, zone: UTC


Right now, I am looking for confirmation from people on the list if this
behaviour is also happening on other 64 bit operating systems or that it is a
FreeBSD specific quirk.

Edwin