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(__mktime_internal): Adopt the traditional (and

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problematic) notion of what to do when tm_isdst doesn't match.
From Paul Eggert.
This commit is contained in:
Jim Meyering
1999-01-19 04:47:24 +00:00
parent 509abea3f1
commit cdc04ccc0e
1 changed files with 25 additions and 21 deletions
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46
lib/mktime.c
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@@ -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 @@ __mktime_internal (struct tm *tp,
/* 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;
}
}
}