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mktime() bug fix

     The mktime() function has an error wherein it does not work
in all cases if the user gives a positive tm_isdst value other than 1.
This is at odds with the 1999 C standard declaring all positive values
mean the same thing.  (There are not problems when it is called with
tm_isdst <= 0.)  The bug only causes an operational error if the user
calls mktime() with tm_isdst > 1 when the final resolved date is
standard time.
     I have attached an updated mktime.c (which started with the
16.0 version) that corrects the problem in the mktime.tgz archive, along
with a ChangeLog.  In the fix I kept a side-effect of mktime() that
any positive tm_isdst value into a 1 when it is done when the result is
daylight time.  In the diff below, you can see that a comment was
to point out that no correction is made for negative values.  There was
change needed in the code for this, but it is only an addition to the
comment to make more clear what is being done.
     Also attached are a test program and its output (run on my embedded
target) for the 16.0 mktime() and my corrected mktime()--test_mktime.c,
test.16.0, and, respectively.  (The test program is intended
my embedded target, and needs minor tweaking to run standalone.)  It can
be seen in the third test case that the Newlib 16.0 mktime() fails to
adjust the user-supplied time by the DST offset when tm_isdst=2.  While
not shown in the test outputs that I have sent, it does when tm_isdst=1.
     Out of curiousity, I ran the test on Cygwin (which appears to be
using Newlib 14.0) and on RHEL3.  The former surprisingly did not
display the problem, although the latter did.
				Craig Howland

$ diff -u -p mktime.c.orig mktime.c
--- mktime.c.orig	2005-02-25 17:31:20.000000000 -0500
+++ mktime.c	2008-08-27 16:36:42.406250000 -0400
@@ -9,6 +9,8 @@
  * the fields of the structure are set to represent the specified
  * time. Returns the specified calendar time. If the calendar time can
not be
  * represented, returns the value (time_t) -1.
+ *
+ * Modifications:	Fixed tm_isdst usage - 27 August 2008 Craig
@@ -157,7 +159,7 @@ mktime (tim_p)
   time_t tim = 0;
   long days = 0;
-  int year, isdst;
+  int year, isdst, tm_isdst;
   __tzinfo_type *tz = __gettzinfo ();
   /* validate structure */
@@ -202,7 +204,9 @@ mktime (tim_p)
   /* compute total seconds */
   tim += (days * _SEC_IN_DAY);
-  isdst = tim_p->tm_isdst;
+  /* Convert user positive into 1 */
+  tm_isdst = tim_p->tm_isdst > 0  ?  1 : tim_p->tm_isdst;
+  isdst = tm_isdst;
   if (_daylight)
@@ -225,8 +229,10 @@ mktime (tim_p)
 	      isdst = (tz->__tznorth
 		       ? (tim >= startdst_dst && tim < startstd_std)
 		       : (tim >= startdst_dst || tim < startstd_std));
-	      /* if user committed and was wrong, perform correction */
-	      if ((isdst ^ tim_p->tm_isdst) == 1)
+	      /* if user committed and was wrong, perform correction,
but no
+	       * correction to make if user has given negative value
+	       * asks mktime() to determine if DST is in effect or not)
+	      if (tm_isdst >= 0  &&  (isdst ^ tm_isdst) == 1)
 		  /* we either subtract or add the difference between
 		     time zone offsets, depending on which way the user
got it

Attachment: mktime.tgz
Description: mktime.tgz

Attachment: test_mktime.c
Description: test_mktime.c

Attachment: test.16.0
Description: test.16.0


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