[PATCH] tzfile.c fixes

[PATCH] tzfile.c fixes

[Jakub Jelinek]

Hi!

TZ=Asia/Tokyo date
since last tzfile.c changes shows 1hr more than actually is and JDT
for 32-bit date (and correct time and timezone for 64-bit date).
The difference is that for 32-bit libc we don't read the TZif2 part
of the zoneinfo file nor the POSIX string in it, and after the use_last
label the new code sets i to num_transitions - 1 and at found it
looks at i - 1 (i.e. num_transitions - 2).

The following patch fixes that, as well as assertion failure
on tst-mktime2 on 32-bit - e.g. for America/Sao_Paulo if time is in between
last transition and 0x7fffffff and last transition is dst, then
__tzname[0] == NULL, __tzname[1] = "something" and num_types > 1.
Generally, the forward search doesn't have to find the other __tzname
if i is sufficiently close to num_transitions, so I think it is best to
search backwards if the forward search doesn't help.

2007-10-16  Jakub Jelinek  <jakub@redhat.com>

	* time/tzfile.c (__tzfile_compute): For use_last case set
	i to num_transition rather than num_transitions - 1.  If forward
	search for other __tzname didn't find it, search backwards.

--- libc/time/tzfile.c.jj	2007-10-16 09:50:03.000000000 +0200
+++ libc/time/tzfile.c	2007-10-16 13:10:25.000000000 +0200
@@ -596,7 +596,7 @@ __tzfile_compute (time_t timer, int use_
 	  if (tzspec == NULL)
 	    {
 	    use_last:
-	      i = num_transitions - 1;
+	      i = num_transitions;
 	      goto found;
 	    }
 
@@ -666,7 +666,8 @@ __tzfile_compute (time_t timer, int use_
 	  i = hi;
 
 	found:
-	  /* assert (timer >= transitions[i - 1] && timer < transitions[i]); */
+	  /* assert (timer >= transitions[i - 1]
+		     && (i == num_transitions || timer < transitions[i]));  */
 	  __tzname[types[type_idxs[i - 1]].isdst]
 	    = __tzstring (&zone_names[types[type_idxs[i - 1]].idx]);
 	  size_t j = i;
@@ -681,12 +682,30 @@ __tzfile_compute (time_t timer, int use_
 		  __tzname[dst] = __tzstring (&zone_names[idx]);
 
 		  if (__tzname[1 - dst] != NULL)
-		    break;
+		    goto got_tznames;
 		}
 
 	      ++j;
 	    }
+	  j = i - 1;
+	  while (j > 0)
+	    {
+	      int type = type_idxs[--j];
+	      int dst = types[type].isdst;
+	      int idx = types[type].idx;
+
+	      if (__tzname[dst] == NULL)
+		{
+		  __tzname[dst] = __tzstring (&zone_names[idx]);
+
+		  if (__tzname[1 - dst] != NULL)
+		    goto got_tznames;
+		}
+	    }
+	  __tzname[1 - types[type_idxs[i - 1]].isdst]
+	    = __tzname[types[type_idxs[i - 1]].isdst];
 
+	got_tznames:
 	  i = type_idxs[i - 1];
 	}
 

	Jakub

Re: [PATCH] tzfile.c fixes

[Jakub Jelinek]

Hi!

The second part isn't desirable e.g. in case of Asia/Tokyo and gave
different results between 32-bit and 64-bit libc say on:

#define _GNU_SOURCE
#include <time.h>
#include <stdlib.h>
#include <stdio.h>

int
main (void)
{
  setenv ("TZ", "Europe/Paris", 1);
  tzset ();
  time_t t = 2144000000; /* Dec 9th, 2037 */
  struct tm *tmp = localtime (&t);
  printf ("Paris: is_dst %d %s %s\n", tmp->tm_isdst, tzname[0], tzname[1]);
  setenv ("TZ", "America/Sao_Paulo", 1);
  tzset ();
  tmp = localtime (&t);
  printf ("Sao Paulo: is_dst %d %s %s\n", tmp->tm_isdst, tzname[0], tzname[1]);
  setenv ("TZ", "Asia/Tokyo", 1);
  tzset ();
  tmp = localtime (&t);
  printf ("Tokyo: is_dst %d %s %s\n", tmp->tm_isdst, tzname[0], tzname[1]);
  return 0;
}

which IMHO should print:

Paris: is_dst 0 CET CEST
Sao Paulo: is_dst 1 BRT BRST
Tokyo: is_dst 0 JST JST

(and does in 64-bit libc).  The following patch only does backward
search if timer was past last transition and only considers transitions
at most a year before the last transition, which is IMHO good enough.
Other alternative is to grab POSIX time string even in 32-bit libc
(but even then we'd need to do at least something in __tzfile_compute
for this, like the
	__tzname[1 - types[type_idxs[i - 1]].isdst]
	  = __tzname[types[type_idxs[i - 1]].isdst];
assignment if we haven't found the second __tzname.

--- libc/time/tzfile.c.jj	2007-10-16 17:01:56.000000000 +0200
+++ libc/time/tzfile.c	2007-10-16 17:12:31.000000000 +0200
@@ -671,9 +671,21 @@ __tzfile_compute (time_t timer, int use_
 	  __tzname[types[type_idxs[i - 1]].isdst]
 	    = __tzstring (&zone_names[types[type_idxs[i - 1]].idx]);
 	  size_t j = i;
-	  while (j < num_transitions)
+	  do
 	    {
-	      int type = type_idxs[j];
+	      int type;
+	      if (__builtin_expect (i == num_transitions, 0))
+		{
+		  if (j-- == 0)
+		    break;
+		  /* When doing backward search, only look at recent
+		     transitions (within last year).  */
+		  if (transitions[j] < timer - 31556952)
+		    break;
+		  type = type_idxs[j];
+		}
+	      else
+		type = type_idxs[j++];
 	      int dst = types[type].isdst;
 	      int idx = types[type].idx;
 
@@ -682,12 +694,15 @@ __tzfile_compute (time_t timer, int use_
 		  __tzname[dst] = __tzstring (&zone_names[idx]);
 
 		  if (__tzname[1 - dst] != NULL)
-		    break;
+		    goto got_tznames;
 		}
-
-	      ++j;
 	    }
+	  while (j < num_transitions);
+
+	  __tzname[1 - types[type_idxs[i - 1]].isdst]
+	    = __tzname[types[type_idxs[i - 1]].isdst];
 
+	got_tznames:
 	  i = type_idxs[i - 1];
 	}
 


	Jakub