[glibc/azanella/y2038] time: Add timegm basic tests

[Adhemerval Zanella <azanella@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=52d7778262fe7bde7c1d9ee5b457fccdde9d9016

commit 52d7778262fe7bde7c1d9ee5b457fccdde9d9016
Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date:   Mon Mar 1 11:36:56 2021 -0300

    time: Add timegm basic tests
    
    Checked i686-linux-gnu and x86_64-linux-gnu.

Diff:
---
 time/Makefile     |  2 +-
 time/tst-timegm.c | 95 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 96 insertions(+), 1 deletion(-)

diff --git a/time/Makefile b/time/Makefile
index ed79f1cdb6..5d865a4054 100644
--- a/time/Makefile
+++ b/time/Makefile
@@ -49,7 +49,7 @@ tests	:= test_time clocktest tst-posixtz tst-strptime tst_wcsftime \
 	   tst-tzname tst-y2039 bug-mktime4 tst-strftime2 tst-strftime3 \
 	   tst-clock tst-clock2 tst-clock_nanosleep tst-cpuclock1 \
 	   tst-adjtime tst-ctime tst-difftime tst-mktime4 tst-clock_settime \
-	   tst-itimer tst-gmtime
+	   tst-itimer tst-gmtime tst-timegm
 
 include ../Rules
 
diff --git a/time/tst-timegm.c b/time/tst-timegm.c
new file mode 100644
index 0000000000..3f4d21951a
--- /dev/null
+++ b/time/tst-timegm.c
@@ -0,0 +1,95 @@
+/* Basic tests for timegm.
+   Copyright (C) 2021 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <time.h>
+#include <stdlib.h>
+#include <support/check.h>
+
+static void
+do_test_func (time_t (*func)(struct tm *))
+{
+  {
+    struct tm tmg =
+      {
+	.tm_sec = 0,
+	.tm_min = 0,
+	.tm_hour = 0,
+	.tm_mday = 1,
+	.tm_mon = 0,
+	.tm_year = 70,
+	.tm_wday = 4,
+	.tm_yday = 0,
+	.tm_isdst = 0
+     };
+     time_t t = func (&tmg);
+     TEST_COMPARE (t, 0);
+  }
+
+  {
+    struct tm tmg =
+      {
+	.tm_sec = 7,
+	.tm_min = 14,
+	.tm_hour = 3,
+	.tm_mday = 19,
+	.tm_mon = 0,
+	.tm_year = 138,
+	.tm_wday = 2,
+	.tm_yday = 18,
+	.tm_isdst = 0
+     };
+     time_t t = func (&tmg);
+     TEST_COMPARE (t, 0x7fffffff);
+  }
+
+  if (sizeof (time_t) < 8)
+    return;
+
+  {
+    struct tm tmg =
+      {
+	.tm_sec = 8,
+	.tm_min = 14,
+	.tm_hour = 3,
+	.tm_mday = 19,
+	.tm_mon = 0,
+	.tm_year = 138,
+	.tm_wday = 2,
+	.tm_yday = 18,
+	.tm_isdst = 0
+     };
+     time_t t = func (&tmg);
+     TEST_COMPARE (t, (time_t) 0x80000000ull);
+  }
+}
+
+static int
+do_test (void)
+{
+  do_test_func (timegm);
+
+  /* timelocal is a alias to timegm with the only difference it takes local
+     timezone into account, while timegm takes the input value to be UTC.  */
+  TEST_VERIFY_EXIT (setenv ("TZ", ":", 1) == 0);
+  tzset ();
+  do_test_func (timelocal);
+
+  return 0;
+}
+
+#include <support/test-driver.c>