Mercurial > gnulib
changeset 21352:bb97bd6ae54e
(__mktime_internal): Adopt the traditional (and
problematic) notion of what to do when tm_isdst doesn't match.
From Paul Eggert.
| author | Jim Meyering <jim@meyering.net> |
|---|---|
| date | Tue, 19 Jan 1999 04:47:24 +0000 |
| parents | 2b5e629954ca |
| children | 84975cb6531f |
| files | lib/mktime.c |
| diffstat | 1 files changed, 25 insertions(+), 21 deletions(-) [+] |
line wrap: on
line diff
--- a/lib/mktime.c Tue Jan 19 03:24:03 1999 +0000 +++ b/lib/mktime.c Tue Jan 19 04:47:24 1999 +0000 @@ -1,5 +1,5 @@ /* mktime: convert a `struct tm' to a time_t value - Copyright (C) 1993-1997, 1998 Free Software Foundation, Inc. + Copyright (C) 1993-1998, 1999 Free Software Foundation, Inc. Contributed by Paul Eggert (eggert@twinsun.com). NOTE: The canonical source of this file is maintained with the GNU C Library. @@ -57,7 +57,7 @@ #endif /* DEBUG */ #ifndef __P -# if defined (__GNUC__) || (defined (__STDC__) && __STDC__) +# if defined __GNUC__ || (defined __STDC__ && __STDC__) # define __P(args) args # else # define __P(args) () @@ -318,28 +318,32 @@ /* If we have a match, check whether tm.tm_isdst has the requested value, if any. */ - if (dt == 0 && 0 <= isdst && 0 <= tm.tm_isdst) + if (dt == 0 && isdst != tm.tm_isdst && 0 <= isdst && 0 <= tm.tm_isdst) { - int dst_diff = (isdst != 0) - (tm.tm_isdst != 0); - if (dst_diff) + /* tm.tm_isdst has the wrong value. Look for a neighboring + time with the right value, and use its UTC offset. + Heuristic: probe the previous three calendar quarters (approximately), + looking for the desired isdst. This isn't perfect, + but it's good enough in practice. */ + int quarter = 7889238; /* seconds per average 1/4 Gregorian year */ + int i; + + /* If we're too close to the time_t limit, look in future quarters. */ + if (t < TIME_T_MIN + 3 * quarter) + quarter = -quarter; + + for (i = 1; i <= 3; i++) { - /* Move two hours in the direction indicated by the disagreement, - probe some more, and switch to a new time if found. - The largest known fallback due to daylight savings is two hours: - once, in Newfoundland, 1988-10-30 02:00 -> 00:00. */ - time_t ot = t - 2 * 60 * 60 * dst_diff; - while (--remaining_probes != 0) + time_t ot = t - i * quarter; + struct tm otm; + ranged_convert (convert, &ot, &otm); + if (otm.tm_isdst == isdst) { - struct tm otm; - if (! (dt = ydhms_tm_diff (year, yday, hour, min, sec, - ranged_convert (convert, &ot, &otm)))) - { - t = ot; - tm = otm; - break; - } - if ((ot += dt) == t) - break; /* Avoid a redundant probe. */ + /* We found the desired tm_isdst. + Extrapolate back to the desired time. */ + t = ot + ydhms_tm_diff (year, yday, hour, min, sec, &otm); + ranged_convert (convert, &t, &tm); + break; } } }