SAFETY comments

Author: AlexKnauth

src/runtime/timer.rs

@@ -119,6 +119,7 @@ pub fn state() -> TimerState {
 /// So you need to be careful when using this value for indexing.
 /// Same index does not imply same split on undo and then split.
 pub fn current_split_index() -> Option<u64> {
+    // SAFETY: It is always safe to call this function.
     let i = unsafe { sys::timer_current_split_index() };
     if i.is_negative() {
         return None;
@@ -132,6 +133,10 @@ pub fn current_split_index() -> Option<u64> {
 /// If `idx` is greater than or equal to the current split index,
 /// `None` is returned instead.
 pub fn segment_splitted(idx: u64) -> Option<bool> {
+    // SAFETY: It is always safe to call this function.
+    // Even when `idx` is out of bounds,
+    // timer_segment_splitted returns `-1`,
+    // and then segment_splitted returns `None`.
     match unsafe { sys::timer_segment_splitted(idx) } {
         1 => Some(true),
         0 => Some(false),