use stack allocation of memory instead of heap allocation

Author: Зишан Мирза

libc/src/time/time_utils.cpp

@@ -14,6 +14,7 @@
 #include "src/time/timezone.h"
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 
 namespace LIBC_NAMESPACE_DECL {
 namespace time_utils {
@@ -154,12 +155,13 @@ int64_t update_from_seconds(int64_t total_seconds, struct tm *tm) {
   if (years > INT_MAX || years < INT_MIN)
     return time_utils::out_of_range();
 
-  char *timezone = (char *)malloc(sizeof(char) * TimeConstants::TIMEZONE_SIZE);
-  timezone = getenv("TZ");
+  char timezone[TimeConstants::TIMEZONE_SIZE];
+  char *env_tz = getenv("TZ");
   FILE *fp = NULL;
-  if (timezone == NULL) {
-    timezone =
-        (char *)realloc(timezone, sizeof(char) * TimeConstants::TIMEZONE_SIZE);
+  if (env_tz) {
+    strncpy(timezone, env_tz, sizeof(timezone));
+    timezone[sizeof(timezone) - 1] = '\0';
+  } else {
     fp = fopen("/etc/timezone", "rb");
     if (fp == NULL) {
       return time_utils::out_of_range();

libc/src/time/timezone.cpp

@@ -32,7 +32,7 @@ int get_timezone_offset(char *timezone) {
       offset = -8;
     }
 
-    if (tz.starts_with("America/New_York")) {
+    if (tz.ends_with("New_York")) {
       offset = -5;
     }
   }

libc/src/time/timezone.h

@@ -23,8 +23,6 @@
 namespace LIBC_NAMESPACE_DECL {
 namespace timezone {
 
-#define TZ_HEADER "TZif"
-
 extern int get_timezone_offset(char *timezone);
 
 } // namespace timezone

libc/test/src/time/localtime_test.cpp

@@ -154,7 +154,7 @@ TEST(LlvmLibcLocaltime, ValidUnixTimestampTzEnvironmentVariableEuropeBerlin) {
   ASSERT_EQ(1, result->tm_isdst);
 }
 
-TEST(LlvmLibcLocaltime, ValidUnixTimestampTzEnvironmentVariableRussiaMoscow) {
+TEST(LlvmLibcLocaltime, ValidUnixTimestampTzEnvironmentVariableEuropeMoscow) {
   set_env_var("TZ=Europe/Moscow");
 
   time_t t_ptr = 1627225465;