Re: [Mingw-w64-public] [PATCH 7/7] crt: Extend t_time test for _localtime64 and _mktime64

[Martin Storsjö]

On Wed, 19 Nov 2025, Pali Rohár wrote:

On Monday 17 November 2025 17:43:41 Pali Rohár wrote:
On Monday 17 November 2025 16:18:14 Martin Storsjö wrote:
On Sat, 25 Oct 2025, Pali Rohár wrote:
---
mingw-w64-crt/testcases/t_time.c | 96 ++++++++++++++++++++++++++++++--
1 file changed, 92 insertions(+), 4 deletions(-)

diff --git a/mingw-w64-crt/testcases/t_time.c b/mingw-w64-crt/testcases/t_time.c
index 50b07d0083a7..75a15d816d31 100644
--- a/mingw-w64-crt/testcases/t_time.c
+++ b/mingw-w64-crt/testcases/t_time.c
@@ -10,14 +10,17 @@ int __cdecl ftime64(struct __timeb64 *tb64);

int main()
{
-  time_t t;
-  __time32_t t32;
-  __time64_t t64;
+  time_t t, t_;
+  __time32_t t32, t32_;
+  __time64_t t64, t64_;
  struct timeb tb;
  struct _timeb tb_;
  struct __timeb32 tb32;
  struct __timeb64 tb64;
  struct tm *htm;
+  struct tm tm1;
+  struct tm tm2;
+  struct tm tm3;
  int ret1, ret2, ret3;
  const char *str;
  const wchar_t *wstr;
@@ -95,7 +98,49 @@ int main()
  assert (htm->tm_yday == 74);
  assert (htm->tm_isdst == 0);

-  /* ctime returns time string in local timezone, so set local timezone to UTC 
to have test timezone independent */
+  time_t times[] = {
+    1700000000 /* Tue Nov 14 22:13:20 UTC 2023 */,
+    1600000000 /* Sun Sep 13 12:26:40 UTC 2020 */,
+  };
+  for (size_t i = 0; i < sizeof(times)/sizeof(*times); i++) {
+    t = times[i];
+    htm = localtime (&t);
+    tm1 = *htm;
+    printf ("localtime(%lld):    sec=%d min=%d hour=%d mday=%d mon=%d year=%d 
wday=%d yday=%d isdst=%d\n",
+        (long long)t, htm->tm_sec, htm->tm_min, htm->tm_hour, htm->tm_mday, htm->tm_mon, 
htm->tm_year, htm->tm_wday, htm->tm_yday, htm->tm_isdst);
+    t_ = mktime (htm);
+    printf ("mktime(): %lld      sec=%d min=%d hour=%d mday=%d mon=%d year=%d 
wday=%d yday=%d isdst=%d\n",
+        (long long)t_, htm->tm_sec, htm->tm_min, htm->tm_hour, htm->tm_mday, htm->tm_mon, 
htm->tm_year, htm->tm_wday, htm->tm_yday, htm->tm_isdst);
+    assert (t_ == t);
+    assert (memcmp (htm, &tm1, sizeof(tm1)) == 0);
+
+    t32 = t;
+    htm = _localtime32 (&t32);
+    tm2 = *htm;
+    printf ("_localtime32(%d): sec=%d min=%d hour=%d mday=%d mon=%d year=%d wday=%d 
yday=%d isdst=%d\n",
+        t32, htm->tm_sec, htm->tm_min, htm->tm_hour, htm->tm_mday, htm->tm_mon, 
htm->tm_year, htm->tm_wday, htm->tm_yday, htm->tm_isdst);
+    t32_ = _mktime32 (htm);
+    printf ("_mktime32(): %d   sec=%d min=%d hour=%d mday=%d mon=%d year=%d wday=%d 
yday=%d isdst=%d\n",
+        t32_, htm->tm_sec, htm->tm_min, htm->tm_hour, htm->tm_mday, htm->tm_mon, 
htm->tm_year, htm->tm_wday, htm->tm_yday, htm->tm_isdst);
+    assert (t32_ == t32);
+    assert (memcmp (htm, &tm2, sizeof(tm2)) == 0);
+
+    t64 = t;
+    htm = _localtime64 (&t64);
+    tm3 = *htm;
+    printf ("_localtime64(%lld): sec=%d min=%d hour=%d mday=%d mon=%d year=%d 
wday=%d yday=%d isdst=%d\n",
+        t64, htm->tm_sec, htm->tm_min, htm->tm_hour, htm->tm_mday, htm->tm_mon, 
htm->tm_year, htm->tm_wday, htm->tm_yday, htm->tm_isdst);
+    t64_ = _mktime64 (htm);
+    printf ("_mktime64(): %lld   sec=%d min=%d hour=%d mday=%d mon=%d year=%d 
wday=%d yday=%d isdst=%d\n",
+        t64_, htm->tm_sec, htm->tm_min, htm->tm_hour, htm->tm_mday, htm->tm_mon, 
htm->tm_year, htm->tm_wday, htm->tm_yday, htm->tm_isdst);
+    assert (t64_ == t64);
+    assert (memcmp (htm, &tm3, sizeof(tm3)) == 0);
+
+    assert (memcmp (&tm1, &tm2, sizeof(tm1)) == 0);
+    assert (memcmp (&tm2, &tm3, sizeof(tm2)) == 0);
+  }
+
+  /* ctime, localtime and mktime returns time string in local timezone, so set 
local timezone to UTC to have test timezone independent */
  putenv ("TZ=UTC");

In addition to setting TZ=UTC here, is it possible to set some other
well-known timezone that would be available everywhere, which we could use
for some testcases for cases closer to the DST switchover time? We could do
that for both mktime and localtime IMO.

I could try to add, but I'm not sure if CRT libraries would be able to
process DST support for non-system timezone. Because Windows system and
WinAPI has just one fixed timezone, which provides bunch of timezone and
DST related functions. And CRT library allows to define any timeshift,
so then there can be a mix of WinAPI timezone, CRT timezone, WinAPI DST
and CRT DST... That is why I wrote test below the quoted part in UTC as
it does not have any DST and no offset.

In itself, these test additions probably are fine though - the above would
be nice extras. But given that corner case handling close to DST
switchovers, I think it would be good to actually check such a case.

So this patchset in itself looks ok, except for the one issue I found in
2/7.

// Martin

Here is diff for this 7/7 change which adds those tests which can uncover 
localtime DST issue:

I chose year 2005 because it seems that forced PST8PDT timezone uses
hardcoded DST settings and older libraries do not have 2006 pacific zone
changes. So tests for year 2005 can be run also against older CRT libs.

Yes, that sounds reasonable to test an old date.

Can you resend this patchset, rebased on latest master, with the fix for 
_localtime64 and the updated test? This large diff is messy to extract 
from being pasted inline in a mail.

// Martin

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