Rework time functions a bit

- mktime: Work unsigned as time_t's type implies (shifting Y2K38 bug to 2106)
- mktime: Add unit tests
- gmtime/localtime: factorize
- gmtime/localtime: Add unit tests
- mktime/gmtime/localtime: Size optimisation (-130 bytes wrt master)
- mktime: Speed optimisation (from 23M cycles on the unit test to 2M)

test/val/lib_common_gmtime_localtime.c

@@ -0,0 +1,84 @@
+#include <stdio.h>
+#include <string.h>
+#include <time.h>
+
+int fails = 0;
+
+time_t timestamps[] = {
+  0,
+  0x2FFFFFFF,
+  0x6FFFFFFF,
+  0xF48656FF,
+  0xF4865700,
+  0xFC5A3EFF,
+  0x6D6739FF,
+  0x6D673A00,
+  0xFFFFFFFF,
+};
+
+/* Values checked against glibc 2.37's implementation of ctime() */
+const char *dates_gmt[] = {
+  "Thu Jan  1 00:00:00 1970\n",
+  "Sun Jul  9 16:12:47 1995\n",
+  "Wed Jul 18 05:49:51 2029\n",
+  "Thu Dec 31 23:59:59 2099\n",
+  "Fri Jan  1 00:00:00 2100\n",
+  "Fri Feb 29 23:59:59 2104\n",
+  "Tue Feb 29 23:59:59 2028\n",
+  "Wed Mar  1 00:00:00 2028\n",
+  "Sun Feb  7 06:28:15 2106\n",
+  NULL
+};
+
+const char *dates_gmt_plus_one[] = {
+  "Thu Jan  1 01:00:00 1970\n",
+  "Sun Jul  9 17:12:47 1995\n",
+  "Wed Jul 18 06:49:51 2029\n",
+  "Fri Jan  1 00:59:59 2100\n",
+  "Fri Jan  1 01:00:00 2100\n",
+  "Sat Mar  1 00:59:59 2104\n",
+  "Wed Mar  1 00:59:59 2028\n",
+  "Wed Mar  1 01:00:00 2028\n",
+  "Thu Jan  1 00:59:59 1970\n",
+  NULL
+};
+
+int main (void)
+{
+    int i;
+
+    for (i = 0; dates_gmt[i] != NULL; i++) {
+      struct tm *tm;
+      char *str;
+
+      /* Check gmtime */
+      tm = gmtime(&timestamps[i]);
+      str = asctime(tm);
+      if (strcmp(str, dates_gmt[i])) {
+        fails++;
+        printf("gmtime: Unexpected result for t %lx: Expected \"%s\", got \"%s\"\n",
+               timestamps[i], dates_gmt[i], str);
+      }
+
+      /* Check localtime with UTC timezone */
+      _tz.timezone = 0;
+      tm = localtime(&timestamps[i]);
+      str = asctime(tm);
+      if (strcmp(str, dates_gmt[i])) {
+        fails++;
+        printf("localtime: Unexpected result for t %lx: Expected \"%s\", got \"%s\"\n",
+               timestamps[i], dates_gmt[i], str);
+      }
+
+      /* Check localtime at UTC+1 */
+      _tz.timezone = 3600;
+      tm = localtime(&timestamps[i]);
+      str = asctime(tm);
+      if (strcmp(str, dates_gmt_plus_one[i])) {
+        fails++;
+        printf("localtime: Unexpected result for t %lx: Expected \"%s\", got \"%s\"\n",
+               timestamps[i], dates_gmt_plus_one[i], str);
+      }
+    }
+    return fails;
+}

test/val/lib_common_mktime.c

@@ -0,0 +1,61 @@
+#include <stdio.h>
+#include <string.h>
+#include <time.h>
+
+int fails = 0;
+
+time_t timestamps[] = {
+  0,
+  0x2FFFFFFF,
+  0x6FFFFFFF,
+  0xF48656FF,
+  0xF4865700,
+  0xFC5A3EFF,
+  0x6D6739FF,
+  0x6D673A00,
+  0xFFFFFFFF,
+};
+
+/* Values checked against glibc 2.37's implementation of ctime() */
+const char *dates[] = {
+  "Thu Jan  1 00:00:00 1970\n",
+  "Sun Jul  9 16:12:47 1995\n",
+  "Wed Jul 18 05:49:51 2029\n",
+  "Thu Dec 31 23:59:59 2099\n",
+  "Fri Jan  1 00:00:00 2100\n",
+  "Fri Feb 29 23:59:59 2104\n",
+  "Tue Feb 29 23:59:59 2028\n",
+  "Wed Mar  1 00:00:00 2028\n",
+  "Sun Feb  7 06:28:15 2106\n",
+  NULL
+};
+
+int main (void)
+{
+    struct tm tm;
+    time_t t;
+    int i;
+
+    /* Verify conversion both ways */
+    for (t = 0x0FFFFFFF; ; t += 0x10000000) {
+      struct tm *tm = gmtime(&t);
+      time_t r = mktime(tm);
+      if (t != r) {
+        fails++;
+        printf("Unexpected result for t %lx: %lx\n", t, r);
+      }
+      if (t == 0xFFFFFFFF) {
+        break;
+      }
+    }
+
+    for (i = 0; dates[i] != NULL; i++) {
+      char *str = ctime(&timestamps[i]);
+      if (strcmp(str, dates[i])) {
+        fails++;
+        printf("Unexpected result for t %lx: Expected \"%s\", got \"%s\"\n",
+               timestamps[i], dates[i], str);
+      }
+    }
+    return fails;
+}