Add Rust implementation of two-stacks (TwoStacks)

Author: segeljakt

rust/src/lib.rs

@@ -46,3 +46,6 @@ pub mod recalc;
 
 /// Subtract-On-Evict
 pub mod soe;
+
+/// Two-Stacks
+pub mod two_stacks;

rust/src/two_stacks/mod.rs

@@ -0,0 +1,73 @@
+use crate::FifoWindow;
+use alga::general::AbstractMonoid;
+use alga::general::Operator;
+use std::marker::PhantomData;
+
+#[derive(Debug)]
+struct Item<Value>
+where
+    Value: Clone,
+{
+    agg: Value,
+    val: Value,
+}
+
+#[derive(Debug)]
+pub struct TwoStacks<Value, BinOp>
+where
+    Value: AbstractMonoid<BinOp> + Clone,
+    BinOp: Operator,
+{
+    front: Vec<Item<Value>>,
+    back: Vec<Item<Value>>,
+    op: PhantomData<BinOp>,
+}
+
+impl<Value, BinOp> FifoWindow<Value, BinOp> for TwoStacks<Value, BinOp>
+where
+    Value: AbstractMonoid<BinOp> + Clone,
+    BinOp: Operator,
+{
+    fn new() -> TwoStacks<Value, BinOp> {
+        TwoStacks {
+            front: Vec::new(),
+            back: Vec::new(),
+            op: PhantomData,
+        }
+    }
+    fn push(&mut self, v: Value) {
+        self.back.push(Item {
+            agg: Self::agg(&self.back).operate(&v),
+            val: v,
+        });
+    }
+    fn pop(&mut self) {
+        if self.front.is_empty() {
+            while let Some(top) = self.back.pop() {
+                self.front.push(Item {
+                    agg: top.val.operate(&Self::agg(&self.front)),
+                    val: top.val,
+                })
+            }
+        }
+        self.front.pop();
+    }
+    fn query(&self) -> Value {
+        Self::agg(&self.front).operate(&Self::agg(&self.back))
+    }
+}
+
+impl<Value, BinOp> TwoStacks<Value, BinOp>
+where
+    Value: AbstractMonoid<BinOp> + Clone,
+    BinOp: Operator,
+{
+    #[inline(always)]
+    fn agg(stack: &Vec<Item<Value>>) -> Value {
+        if let Some(top) = stack.last() {
+            top.agg.clone()
+        } else {
+            Value::identity()
+        }
+    }
+}

rust/tests/fifo-window.rs

@@ -10,6 +10,7 @@ use alga::general::TwoSidedInverse;
 use rand::Rng;
 use swag::recalc::*;
 use swag::soe::*;
+use swag::two_stacks::*;
 use swag::*;
 
 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
@@ -111,3 +112,13 @@ fn test1_soe() {
 fn test2_soe() {
     test2::<SoE<Value, Sum>>();
 }
+
+#[test]
+fn test1_two_stacks() {
+    test1::<TwoStacks<Value, Sum>>();
+}
+
+#[test]
+fn test2_two_stacks() {
+    test2::<TwoStacks<Value, Sum>>();
+}