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mktime: do not assume signed right shift propagates sign bit

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* time/mktime.c (isdst_differ): New static function.
(__mktime_internal): No need to normalize tm_isdst now.
(__mktime_internal, not_equal_tm): Use isdst_differ to compare
tm_isdst values.
This commit is contained in:
Paul Eggert 2012-03-16 03:14:03 -07:00
parent 72a22e596c
commit ce73d68397
2 changed files with 18 additions and 6 deletions
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6
ChangeLog
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@ -1,5 +1,11 @@
2012-05-23 Paul Eggert <eggert@cs.ucla.edu>
mktime: do not assume signed right shift propagates sign bit
* time/mktime.c (isdst_differ): New static function.
(__mktime_internal): No need to normalize tm_isdst now.
(__mktime_internal, not_equal_tm): Use isdst_differ to compare
tm_isdst values.
mktime: merge another wrapv change from gnulib
* time/mktime.c (TYPE_MAXIMUM): Rework slightly to avoid diagnostics
from some compilers.

18
time/mktime.c
View File

@ -177,6 +177,14 @@ const unsigned short int __mon_yday[2][13] =
# include "mktime-internal.h"
#endif
/* Return 1 if the values A and B differ according to the rules for
tm_isdst: A and B differ if one is zero and the other positive. */
static int
isdst_differ (int a, int b)
{
return (!a != !b) && (0 <= a) && (0 <= b);
}
/* Return an integer value measuring (YEAR1-YDAY1 HOUR1:MIN1:SEC1) -
(YEAR0-YDAY0 HOUR0:MIN0:SEC0) in seconds, assuming that the clocks
were not adjusted between the time stamps.
@ -362,9 +370,7 @@ __mktime_internal (struct tm *tp,
int mday = tp->tm_mday;
int mon = tp->tm_mon;
int year_requested = tp->tm_year;
/* Normalize the value. */
int isdst = ((tp->tm_isdst >> (8 * sizeof (tp->tm_isdst) - 1))
| (tp->tm_isdst != 0));
int isdst = tp->tm_isdst;
/* 1 if the previous probe was DST. */
int dst2;
@ -494,7 +500,7 @@ __mktime_internal (struct tm *tp,
/* We have a match. Check whether tm.tm_isdst has the requested
value, if any. */
if (isdst != tm.tm_isdst && 0 <= isdst && 0 <= tm.tm_isdst)
if (isdst_differ (isdst, tm.tm_isdst))
{
/* tm.tm_isdst has the wrong value. Look for a neighboring
time with the right value, and use its UTC offset.
@ -532,7 +538,7 @@ __mktime_internal (struct tm *tp,
time_t ot = t + delta * direction;
struct tm otm;
ranged_convert (convert, &ot, &otm);
if (otm.tm_isdst == isdst)
if (! isdst_differ (isdst, otm.tm_isdst))
{
/* We found the desired tm_isdst.
Extrapolate back to the desired time. */
@ -608,7 +614,7 @@ not_equal_tm (const struct tm *a, const struct tm *b)
| (a->tm_mon ^ b->tm_mon)
| (a->tm_year ^ b->tm_year)
| (a->tm_yday ^ b->tm_yday)
| (a->tm_isdst ^ b->tm_isdst));
| isdst_differ (a->tm_isdst, b->tm_isdst));
}
static void