Fix average time (#202)

* fix: Average Time

* fix: Average time if stats are reset

backend/src/util/num_stats.rs

@@ -22,7 +22,7 @@ impl<T: Saturating + NumOps + Zero + Bounded + Copy + Sum + TryFrom<usize>> NumS
     pub fn push(&mut self, val: T) {
         let slot = &mut self.stack[self.index % self.stack.len()];
 
-        self.sum = (self.sum + val).saturating_sub(*slot);
+        self.sum = (self.sum + val) - *slot;
 
         *slot = val;
 
@@ -31,6 +31,11 @@ impl<T: Saturating + NumOps + Zero + Bounded + Copy + Sum + TryFrom<usize>> NumS
 
     pub fn average(&self) -> T {
         let cap = std::cmp::min(self.index, self.stack.len());
+
+        if cap == 0 {
+            return T::zero();
+        }
+
         let cap = T::try_from(cap).unwrap_or_else(|_| T::max_value());
 
         self.sum / cap
@@ -39,5 +44,61 @@ impl<T: Saturating + NumOps + Zero + Bounded + Copy + Sum + TryFrom<usize>> NumS
     pub fn reset(&mut self) {
         self.index = 0;
         self.sum = T::zero();
+
+        for val in self.stack.iter_mut() {
+            *val = T::zero();
+        }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn calculates_correct_average() {
+        let mut stats: NumStats<u64> = NumStats::new(10);
+
+        stats.push(3);
+        stats.push(7);
+
+        assert_eq!(stats.average(), 5);
+    }
+
+    #[test]
+    fn calculates_correct_average_over_bounds() {
+        let mut stats: NumStats<u64> = NumStats::new(10);
+
+        stats.push(100);
+
+        for _ in 0..9 {
+            stats.push(0);
+        }
+
+        assert_eq!(stats.average(), 10);
+
+        stats.push(0);
+
+        assert_eq!(stats.average(), 0);
+    }
+
+    #[test]
+    fn resets_properly() {
+        let mut stats: NumStats<u64> = NumStats::new(10);
+
+        for _ in 0..10 {
+            stats.push(100);
+        }
+
+        assert_eq!(stats.average(), 100);
+
+        stats.reset();
+
+        assert_eq!(stats.average(), 0);
+
+        stats.push(7);
+        stats.push(3);
+
+        assert_eq!(stats.average(), 5);
+    }
+}