1 files changed, 144 insertions, 0 deletions
diff --git a/third_party/rust/itertools/benches/tree_fold1.rs b/third_party/rust/itertools/benches/tree_fold1.rs
new file mode 100644
index 0000000000..f12995db8e
--- /dev/null
+++ b/third_party/rust/itertools/benches/tree_fold1.rs
@@ -0,0 +1,144 @@
+use criterion::{criterion_group, criterion_main, Criterion};
+use itertools::{Itertools, cloned};
+
+trait IterEx : Iterator {
+    // Another efficient implementation against which to compare,
+    // but needs `std` so is less desirable.
+    fn tree_fold1_vec<F>(self, mut f: F) -> Option<Self::Item>
+        where F: FnMut(Self::Item, Self::Item) -> Self::Item,
+              Self: Sized,
+    {
+        let hint = self.size_hint().0;
+        let cap = std::mem::size_of::<usize>() * 8 - hint.leading_zeros() as usize;
+        let mut stack = Vec::with_capacity(cap);
+        self.enumerate().for_each(|(mut i, mut x)| {
+            while (i & 1) != 0 {
+                x = f(stack.pop().unwrap(), x);
+                i >>= 1;
+            }
+            stack.push(x);
+        });
+        stack.into_iter().fold1(f)
+    }
+}
+impl<T:Iterator> IterEx for T {}
+
+macro_rules! def_benchs {
+    ($N:expr,
+     $FUN:ident,
+     $BENCH_NAME:ident,
+     ) => (
+        mod $BENCH_NAME {
+            use super::*;
+
+            pub fn sum(c: &mut Criterion) {
+                let v: Vec<u32> = (0.. $N).collect();
+
+                c.bench_function(&(stringify!($BENCH_NAME).replace('_', " ") + " sum"), move |b| {
+                    b.iter(|| {
+                        cloned(&v).$FUN(|x, y| x + y)
+                    })
+                });
+            }
+
+            pub fn complex_iter(c: &mut Criterion) {
+                let u = (3..).take($N / 2);
+                let v = (5..).take($N / 2);
+                let it = u.chain(v);
+
+                c.bench_function(&(stringify!($BENCH_NAME).replace('_', " ") + " complex iter"), move |b| {
+                    b.iter(|| {
+                        it.clone().map(|x| x as f32).$FUN(f32::atan2)
+                    })
+                });
+            }
+
+            pub fn string_format(c: &mut Criterion) {
+                // This goes quadratic with linear `fold1`, so use a smaller
+                // size to not waste too much time in travis.  The allocations
+                // in here are so expensive anyway that it'll still take
+                // way longer per iteration than the other two benchmarks.
+                let v: Vec<u32> = (0.. ($N/4)).collect();
+
+                c.bench_function(&(stringify!($BENCH_NAME).replace('_', " ") + " string format"), move |b| {
+                    b.iter(|| {
+                        cloned(&v).map(|x| x.to_string()).$FUN(|x, y| format!("{} + {}", x, y))
+                    })
+                });
+            }
+        }
+
+        criterion_group!(
+            $BENCH_NAME,
+            $BENCH_NAME::sum,
+            $BENCH_NAME::complex_iter,
+            $BENCH_NAME::string_format,
+        );
+    )
+}
+
+def_benchs!{
+    10_000,
+    fold1,
+    fold1_10k,
+}
+
+def_benchs!{
+    10_000,
+    tree_fold1,
+    tree_fold1_stack_10k,
+}
+
+def_benchs!{
+    10_000,
+    tree_fold1_vec,
+    tree_fold1_vec_10k,
+}
+
+def_benchs!{
+    100,
+    fold1,
+    fold1_100,
+}
+
+def_benchs!{
+    100,
+    tree_fold1,
+    tree_fold1_stack_100,
+}
+
+def_benchs!{
+    100,
+    tree_fold1_vec,
+    tree_fold1_vec_100,
+}
+
+def_benchs!{
+    8,
+    fold1,
+    fold1_08,
+}
+
+def_benchs!{
+    8,
+    tree_fold1,
+    tree_fold1_stack_08,
+}
+
+def_benchs!{
+    8,
+    tree_fold1_vec,
+    tree_fold1_vec_08,
+}
+
+criterion_main!(
+    fold1_10k,
+    tree_fold1_stack_10k,
+    tree_fold1_vec_10k,
+    fold1_100,
+    tree_fold1_stack_100,
+    tree_fold1_vec_100,
+    fold1_08,
+    tree_fold1_stack_08,
+    tree_fold1_vec_08,
+);