Rust backend (#185)

backend/src/util/num_stats.rs

@@ -0,0 +1,43 @@
+use num_traits::{Zero, NumOps, Bounded};
+use std::iter::Sum;
+use std::convert::TryFrom;
+
+/// Keep track of last N numbers pushed onto internal stack.
+/// Provides means to get an average of said numbers.
+pub struct NumStats<T> {
+    stack: Box<[T]>,
+    index: usize,
+    sum: T,
+}
+
+impl<T: NumOps + Zero + Bounded + Copy + Sum + TryFrom<usize>> NumStats<T> {
+    pub fn new(size: usize) -> Self {
+        NumStats {
+            stack: vec![T::zero(); size].into_boxed_slice(),
+            index: 0,
+            sum: T::zero(),
+        }
+    }
+
+    pub fn push(&mut self, val: T) {
+        let slot = &mut self.stack[self.index % self.stack.len()];
+
+        self.sum = self.sum - *slot + val;
+
+        *slot = val;
+
+        self.index += 1;
+    }
+
+    pub fn average(&self) -> T {
+        let cap = std::cmp::min(self.index, self.stack.len());
+        let cap = T::try_from(cap).unwrap_or_else(|_| T::max_value());
+
+        self.sum / cap
+    }
+
+    pub fn reset(&mut self) {
+        self.index = 0;
+        self.sum = T::zero();
+    }
+}