Re: [PATCH] tzfile.c fixes

[Jakub Jelinek <jakub at redhat dot com>]

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