Add cumulative summation iterator

Cargo.toml

@@ -11,6 +11,7 @@ license = "MIT/Apache-2.0"
 keywords = ["FEC", "ErrorCorrection", "FountainCode"]
 
 [dependencies]
+num-traits = "0.2"
 rand = "0.7.3"
 
 [dev-dependencies]

src/iterext.rs

@@ -0,0 +1,59 @@
+use num_traits::Zero;
+use std::ops;
+
+/// Crate-local iterator extensions.
+pub(crate) trait IterExt: Iterator {
+    fn cumsum<S>(self) -> CumSum<Self, S>
+    where
+        S: Zero,
+        Self: Sized,
+    {
+        CumSum {
+            iter: self,
+            sum: S::zero(),
+        }
+    }
+}
+
+impl<I> IterExt for I where I: Iterator {}
+
+pub(crate) struct CumSum<I, S> {
+    iter: I,
+    sum: S,
+}
+
+impl<I, S> Iterator for CumSum<I, S>
+where
+    I: Iterator,
+    S: ops::AddAssign<I::Item> + Copy,
+{
+    type Item = S;
+    fn next(&mut self) -> Option<S> {
+        self.iter.next().map(|elem| {
+            self.sum += elem;
+            self.sum
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::IterExt;
+
+    #[test]
+    fn cumsum_test_i32() {
+        let input = [1_i32, 1, 1, 1, 1, 1];
+        let csum: Vec<i32> = input.iter().cumsum().collect();
+        let expected = [1_i32, 2, 3, 4, 5, 6];
+        assert_eq!(&csum, &expected);
+    }
+
+    #[test]
+    #[allow(clippy::float_cmp)]
+    fn cumsum_test_f32() {
+        let input = [1.0_f32, 1.0, 1.0, 1.0, 1.0, 1.0];
+        let csum: Vec<f32> = input.iter().cumsum().collect();
+        let expected = [1.0_f32, 2.0, 3.0, 4.0, 5.0, 6.0];
+        assert_eq!(&csum, &expected);
+    }
+}

src/lib.rs

@@ -2,4 +2,5 @@ pub mod block;
 pub mod decoder;
 pub mod droplet;
 pub mod encoder;
+mod iterext;
 pub mod soliton;