Add test to validate deduplication of 'tm.tm_zone' string.

Signed-off-by: shamb0 <r.raajey@gmail.com>

Author: shamb0

tests/pass-dep/libc/libc-time.rs

@@ -8,6 +8,8 @@ fn main() {
     test_localtime_r_gmt();
     test_localtime_r_pst();
     test_localtime_r_epoch();
+    test_localtime_r_verify_string_deduplication();
+    test_localtime_r_multiple_calls_deduplication()
     // Architecture-specific tests.
     #[cfg(target_pointer_width = "32")]
     test_localtime_r_future_32b();
@@ -125,7 +127,7 @@ fn test_localtime_r_gmt() {
 fn test_localtime_r_pst() {
     let key = "TZ";
     env::set_var(key, "PST8PDT");
-    const TIME_SINCE_EPOCH: libc::time_t = 1712475836;// 2024-04-07 07:43:56 GMT
+    const TIME_SINCE_EPOCH: libc::time_t = 1712475836; // 2024-04-07 07:43:56 GMT
     let custom_time_ptr = &TIME_SINCE_EPOCH;
     let mut tm = create_empty_tm();
 
@@ -276,3 +278,100 @@ fn test_localtime_r_future_32b() {
     assert!(ptr::eq(res, &mut tm));
     env::remove_var(key);
 }
+
+fn test_localtime_r_verify_string_deduplication() {
+    let key = "TZ";
+    env::set_var(key, "PST8PDT");
+
+    // Two timestamps that are in the same timezone (PST/PDT).
+    const TIME_SINCE_EPOCH_TZ_CONST1: libc::time_t = 1712475836; // 2024-04-07 07:43:56 GMT
+    const TIME_SINCE_EPOCH_TZ_CONST2: libc::time_t = 1712575836; // 2024-04-08 11:23:56 GMT
+    const TIME_SINCE_EPOCH_TZ_CONST3: libc::time_t = 1712675836; // 2024-04-09 11:23:56 GMT
+
+    let mut tm1 = create_empty_tm();
+    let mut tm2 = create_empty_tm();
+    let mut tm3 = create_empty_tm();
+
+    unsafe {
+        let res1 = libc::localtime_r(&TIME_SINCE_EPOCH_TZ_CONST1, &mut tm1);
+        let res2 = libc::localtime_r(&TIME_SINCE_EPOCH_TZ_CONST2, &mut tm2);
+        let res3 = libc::localtime_r(&TIME_SINCE_EPOCH_TZ_CONST3, &mut tm3);
+
+        assert!(res1.is_null() == false, "localtime_r failed for first timestamp");
+        assert!(res2.is_null() == false, "localtime_r failed for second timestamp");
+        assert!(res3.is_null() == false, "localtime_r failed for third timestamp");
+
+        #[cfg(any(
+            target_os = "linux",
+            target_os = "macos",
+            target_os = "freebsd",
+            target_os = "android"
+        ))]
+        {
+            let tm_zone1 = std::ffi::CStr::from_ptr(tm1.tm_zone);
+            let tm_zone2 = std::ffi::CStr::from_ptr(tm2.tm_zone);
+            
+            println!("tz res1 :: {:#?}", tm1.tm_zone);
+            println!("tz res2 :: {:#?}", tm2.tm_zone);
+            println!("tz res3 :: {:#?}", tm3.tm_zone);
+
+            assert_eq!(
+                tm_zone1, tm_zone2,
+                "tm_zone strings are not equal, indicating different values."
+            );
+
+            assert_eq!(
+                tm1.tm_zone, tm2.tm_zone,
+                "tm_zone pointers are not equal, string deduplication is not happening."
+            );
+        }
+    }
+}
+
+fn test_localtime_r_multiple_calls_deduplication() {
+    let key = "TZ";
+    env::set_var(key, "PST8PDT");
+
+    const TIME_SINCE_EPOCH_BASE: libc::time_t = 1712475836; // Base timestamp: 2024-04-07 07:43:56 GMT
+    const NUM_CALLS: usize = 50;
+
+    let mut tm_array: Vec<libc::tm> = vec![create_empty_tm(); NUM_CALLS];
+    let mut unique_pointers = std::collections::HashSet::new();
+
+    unsafe {
+        for i in 0..NUM_CALLS {
+            let timestamp = TIME_SINCE_EPOCH_BASE + (i as libc::time_t * 3600); // Increment by 1 hour for each call
+            let tm_ptr = libc::localtime_r(&timestamp, &mut tm_array[i]);
+
+            assert!(!tm_ptr.is_null(), "localtime_r failed for timestamp {timestamp}");
+
+            #[cfg(any(
+                target_os = "linux",
+                target_os = "macos",
+                target_os = "freebsd",
+                target_os = "android"
+            ))]
+            {
+                let tm_zone_ptr = tm_array[i].tm_zone;
+                unique_pointers.insert(tm_zone_ptr);
+            }
+        }
+
+        #[cfg(any(
+            target_os = "linux",
+            target_os = "macos",
+            target_os = "freebsd",
+            target_os = "android"
+        ))]
+        {
+            let unique_count = unique_pointers.len();
+            println!("Number of unique tm_zone pointers: {}", unique_count);
+
+            assert!(
+                unique_count >= 2 && unique_count <= (NUM_CALLS - 1),
+                "Unexpected number of unique tm_zone pointers: {} (expected between 2 and {})",
+                unique_count, NUM_CALLS - 1
+            );
+        }
+    }
+}