diff options
Diffstat (limited to 'src/timezone/pgtz.c')
| -rw-r--r-- | src/timezone/pgtz.c | 64 |
1 files changed, 46 insertions, 18 deletions
diff --git a/src/timezone/pgtz.c b/src/timezone/pgtz.c index 599aaac4efc..6b193f40ab7 100644 --- a/src/timezone/pgtz.c +++ b/src/timezone/pgtz.c @@ -6,7 +6,7 @@ * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group * * IDENTIFICATION - * $PostgreSQL: pgsql/src/timezone/pgtz.c,v 1.29 2004/12/31 22:03:59 pgsql Exp $ + * $PostgreSQL: pgsql/src/timezone/pgtz.c,v 1.29.4.1 2008/07/01 03:41:25 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -74,7 +74,7 @@ pg_TZDIR(void) #define T_WEEK ((time_t) (60*60*24*7)) #define T_MONTH ((time_t) (60*60*24*31)) -#define MAX_TEST_TIMES (52*100) /* 100 years, or 1904..2004 */ +#define MAX_TEST_TIMES (52*100) /* 100 years */ struct tztry { @@ -232,6 +232,7 @@ identify_system_timezone(void) time_t t; struct tztry tt; struct tm *tm; + int thisyear; int bestscore; char tmptzdir[MAXPGPATH]; int std_ofs; @@ -244,24 +245,46 @@ identify_system_timezone(void) /* * Set up the list of dates to be probed to see how well our timezone - * matches the system zone. We first probe January and July of 2004; - * this serves to quickly eliminate the vast majority of the TZ - * database entries. If those dates match, we probe every week from - * 2004 backwards to late 1904. (Weekly resolution is good enough to - * identify DST transition rules, since everybody switches on - * Sundays.) The further back the zone matches, the better we score - * it. This may seem like a rather random way of doing things, but - * experience has shown that system-supplied timezone definitions are - * likely to have DST behavior that is right for the recent past and - * not so accurate further back. Scoring in this way allows us to - * recognize zones that have some commonality with the zic database, - * without insisting on exact match. (Note: we probe Thursdays, not - * Sundays, to avoid triggering DST-transition bugs in localtime - * itself.) + * matches the system zone. We first probe January and July of the + * current year; this serves to quickly eliminate the vast majority of the + * TZ database entries. If those dates match, we probe every week for 100 + * years backwards from the current July. (Weekly resolution is good + * enough to identify DST transition rules, since everybody switches on + * Sundays.) This is sufficient to cover most of the Unix time_t range, + * and we don't want to look further than that since many systems won't + * have sane TZ behavior further back anyway. The further + * back the zone matches, the better we score it. This may seem like a + * rather random way of doing things, but experience has shown that + * system-supplied timezone definitions are likely to have DST behavior + * that is right for the recent past and not so accurate further back. + * Scoring in this way allows us to recognize zones that have some + * commonality with the zic database, without insisting on exact match. + * (Note: we probe Thursdays, not Sundays, to avoid triggering + * DST-transition bugs in localtime itself.) */ + tnow = time(NULL); + tm = localtime(&tnow); + if (!tm) + return NULL; /* give up if localtime is broken... */ + thisyear = tm->tm_year + 1900; + + t = build_time_t(thisyear, 1, 15); + /* + * Round back to GMT midnight Thursday. This depends on the knowledge + * that the time_t origin is Thu Jan 01 1970. (With a different origin + * we'd be probing some other day of the week, but it wouldn't matter + * anyway unless localtime() had DST-transition bugs.) + */ + t -= (t % T_WEEK); + tt.n_test_times = 0; - tt.test_times[tt.n_test_times++] = build_time_t(2004, 1, 15); - tt.test_times[tt.n_test_times++] = t = build_time_t(2004, 7, 15); + tt.test_times[tt.n_test_times++] = t; + + t = build_time_t(thisyear, 7, 15); + t -= (t % T_WEEK); + + tt.test_times[tt.n_test_times++] = t; + while (tt.n_test_times < MAX_TEST_TIMES) { t -= T_WEEK; @@ -276,7 +299,12 @@ identify_system_timezone(void) &tt, &bestscore, resultbuf); if (bestscore > 0) + { + /* Ignore zic's rather silly "Factory" time zone; use GMT instead */ + if (strcmp(resultbuf, "Factory") == 0) + return NULL; return resultbuf; + } /* * Couldn't find a match in the database, so next we try constructed |