1 files changed, 110 insertions, 0 deletions
diff --git a/src/iter/sum.rs b/src/iter/sum.rs
new file mode 100644
index 0000000..a73e0bf
--- /dev/null
+++ b/src/iter/sum.rs
@@ -0,0 +1,110 @@
+use super::plumbing::*;
+use super::ParallelIterator;
+
+use std::iter::{self, Sum};
+use std::marker::PhantomData;
+
+pub(super) fn sum<PI, S>(pi: PI) -> S
+where
+    PI: ParallelIterator,
+    S: Send + Sum<PI::Item> + Sum,
+{
+    pi.drive_unindexed(SumConsumer::new())
+}
+
+fn add<T: Sum>(left: T, right: T) -> T {
+    iter::once(left).chain(iter::once(right)).sum()
+}
+
+struct SumConsumer<S: Send> {
+    _marker: PhantomData<*const S>,
+}
+
+unsafe impl<S: Send> Send for SumConsumer<S> {}
+
+impl<S: Send> SumConsumer<S> {
+    fn new() -> SumConsumer<S> {
+        SumConsumer {
+            _marker: PhantomData,
+        }
+    }
+}
+
+impl<S, T> Consumer<T> for SumConsumer<S>
+where
+    S: Send + Sum<T> + Sum,
+{
+    type Folder = SumFolder<S>;
+    type Reducer = Self;
+    type Result = S;
+
+    fn split_at(self, _index: usize) -> (Self, Self, Self) {
+        (SumConsumer::new(), SumConsumer::new(), SumConsumer::new())
+    }
+
+    fn into_folder(self) -> Self::Folder {
+        SumFolder {
+            sum: iter::empty::<T>().sum(),
+        }
+    }
+
+    fn full(&self) -> bool {
+        false
+    }
+}
+
+impl<S, T> UnindexedConsumer<T> for SumConsumer<S>
+where
+    S: Send + Sum<T> + Sum,
+{
+    fn split_off_left(&self) -> Self {
+        SumConsumer::new()
+    }
+
+    fn to_reducer(&self) -> Self::Reducer {
+        SumConsumer::new()
+    }
+}
+
+impl<S> Reducer<S> for SumConsumer<S>
+where
+    S: Send + Sum,
+{
+    fn reduce(self, left: S, right: S) -> S {
+        add(left, right)
+    }
+}
+
+struct SumFolder<S> {
+    sum: S,
+}
+
+impl<S, T> Folder<T> for SumFolder<S>
+where
+    S: Sum<T> + Sum,
+{
+    type Result = S;
+
+    fn consume(self, item: T) -> Self {
+        SumFolder {
+            sum: add(self.sum, iter::once(item).sum()),
+        }
+    }
+
+    fn consume_iter<I>(self, iter: I) -> Self
+    where
+        I: IntoIterator<Item = T>,
+    {
+        SumFolder {
+            sum: add(self.sum, iter.into_iter().sum()),
+        }
+    }
+
+    fn complete(self) -> S {
+        self.sum
+    }
+
+    fn full(&self) -> bool {
+        false
+    }
+}