From 9f5bd5fe81be011b09621090db0a29b5f65bee04 Mon Sep 17 00:00:00 2001
From: Ryo Onodera <ryoqun@gmail.com>
Date: Thu, 25 Jun 2020 18:23:31 +0900
Subject: [PATCH] Expose SlotHistory::oldest() -> Slot (#10799)

---
 sdk/src/slot_history.rs | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/sdk/src/slot_history.rs b/sdk/src/slot_history.rs
index 695669aafd..4765fab704 100644
--- a/sdk/src/slot_history.rs
+++ b/sdk/src/slot_history.rs
@@ -65,7 +65,7 @@ impl SlotHistory {
     pub fn check(&self, slot: Slot) -> Check {
         if slot >= self.next_slot {
             Check::Future
-        } else if self.next_slot - slot > MAX_ENTRIES {
+        } else if slot < self.oldest() {
             Check::TooOld
         } else if self.bits.get(slot % MAX_ENTRIES) {
             Check::Found
@@ -73,6 +73,10 @@ impl SlotHistory {
             Check::NotFound
         }
     }
+
+    pub fn oldest(&self) -> Slot {
+        self.next_slot.saturating_sub(MAX_ENTRIES)
+    }
 }
 
 #[cfg(test)]
@@ -183,4 +187,16 @@ mod tests {
         assert_eq!(slot_history.check(6), Check::Future);
         assert_eq!(slot_history.check(11), Check::Future);
     }
+
+    #[test]
+    fn test_oldest() {
+        let mut slot_history = SlotHistory::default();
+        assert_eq!(slot_history.oldest(), 0);
+        slot_history.add(10);
+        assert_eq!(slot_history.oldest(), 0);
+        slot_history.add(MAX_ENTRIES - 1);
+        assert_eq!(slot_history.oldest(), 0);
+        slot_history.add(MAX_ENTRIES);
+        assert_eq!(slot_history.oldest(), 1);
+    }
 }