Handle dates outside of strtotime()'s range in date_to_int, int_to_date

Close #9

src/MD_STD.php

@@ -939,12 +939,11 @@ public static function split_string_array_into_sized_parts(array $input, int $si
      */
     public static function date_to_int(string $date):int {
 
-        // Edge case: -0000-01-01
-        if (substr($date, 0, 5) === '-0000') {
-            return -1 * intval(str_replace("-", "", ltrim($date, "0-")));
-        }
+        $isNegative = substr($date, 0, 1) === '-';
+        $parts = explode('-', $date);
 
-        return intval(date("Ymd", self::strtotime($date)));
+        if ($isNegative === true) return -1 * intval(implode($parts));
+        else return intval(implode($parts));
 
     }
 
@@ -973,7 +972,7 @@ public static function int_to_date(int $date_int):string {
 
         $day = substr($dateStr, -2, 2);
         $month = substr($dateStr, -4, 2);
-        $year = substr($dateStr, -8, 4);
+        $year = substr($dateStr, 0, -4);
 
         return match($isNegative) {
             true => '-',