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[Bug libc/469] New: mktime bug when INT_MAX - 1900 < tm_year
- From: "eggert at gnu dot org" <sourceware-bugzilla at sources dot redhat dot com>
- To: glibc-bugs at sources dot redhat dot com
- Date: 22 Oct 2004 19:54:06 -0000
- Subject: [Bug libc/469] New: mktime bug when INT_MAX - 1900 < tm_year
- Reply-to: sourceware-bugzilla at sources dot redhat dot com
When the tm_year component is greater than INT_MAX - 1900, mktime
has a problem: it adds 1900 to tm_year and then tests whether the
result is a leap year. Because the addition overflows, the resulting
behavior is undefined.
Here is a patch, imported from gnulib.
2004-10-22 Paul Eggert <eggert@cs.ucla.edu>
Import a fix from gnulib.
* time/mktime.c (__isleap): Remove; all uses replaced by:
(leapyear): New function, which avoids overflow by not adding
1900 to year before testing whether it is a leap year.
--- 1/time/mktime.c 2004-10-22 12:24:21 -0700
+++ 2/time/mktime.c 2004-10-22 12:39:29 -0700
@@ -75,12 +75,17 @@ verify (right_shift_propagates_sign, -1
#define TM_YEAR_BASE 1900
verify (base_year_is_a_multiple_of_100, TM_YEAR_BASE % 100 == 0);
-#ifndef __isleap
-/* Nonzero if YEAR is a leap year (every 4 years,
- except every 100th isn't, and every 400th is). */
-# define __isleap(year) \
- ((year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0))
-#endif
+/* Return 1 if YEAR + TM_YEAR_BASE is a leap year. */
+static inline int
+leapyear (int year)
+{
+ /* Don't add YEAR to TM_YEAR_BASE, as that might overflow.
+ Also, work even if YEAR is negative. */
+ return
+ ((year & 3) == 0
+ && (year % 100 != 0
+ || ((year / 100) & 3) == (- (TM_YEAR_BASE / 100) & 3)));
+}
/* How many days come before each month (0-12). */
#ifndef _LIBC
@@ -234,7 +239,7 @@ __mktime_internal (struct tm *tp,
/* Calculate day of year from year, month, and day of month.
The result need not be in range. */
- int yday = ((__mon_yday[__isleap (year + TM_YEAR_BASE)]
+ int yday = ((__mon_yday[leapyear (year)]
[mon_remainder + 12 * negative_mon_remainder])
+ mday - 1);
--
Summary: mktime bug when INT_MAX - 1900 < tm_year
Product: glibc
Version: 2.3.3
Status: NEW
Severity: normal
Priority: P2
Component: libc
AssignedTo: gotom at debian dot or dot jp
ReportedBy: eggert at gnu dot org
CC: glibc-bugs at sources dot redhat dot com
GCC build triplet: N.A.
GCC host triplet: N.A.
GCC target triplet: N.A.
http://sources.redhat.com/bugzilla/show_bug.cgi?id=469
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