Initial import of itertools-0.9.0.

Bug: 155309706
Change-Id: Id790c146e836f0eadfb0d8a103cbe2d226a598c3

benches/tuple_combinations.rs

diff --git a/benches/tuple_combinations.rs b/benches/tuple_combinations.rs
new file mode 100644
index 0000000..84411ef
--- /dev/null
+++ b/benches/tuple_combinations.rs
@@ -0,0 +1,113 @@
+use criterion::{black_box, criterion_group, criterion_main, Criterion};
+use itertools::Itertools;
+
+// approximate 100_000 iterations for each combination
+const N1: usize = 100_000;
+const N2: usize = 448;
+const N3: usize = 86;
+const N4: usize = 41;
+
+fn comb_for1(c: &mut Criterion) {
+    c.bench_function("comb for1", move |b| {
+        b.iter(|| {
+            for i in 0..N1 {
+                black_box(i);
+            }
+        })
+    });
+}
+
+fn comb_for2(c: &mut Criterion) {
+    c.bench_function("comb for2", move |b| {
+        b.iter(|| {
+            for i in 0..N2 {
+                for j in (i + 1)..N2 {
+                    black_box(i + j);
+                }
+            }
+        })
+    });
+}
+
+fn comb_for3(c: &mut Criterion) {
+    c.bench_function("comb for3", move |b| {
+        b.iter(|| {
+            for i in 0..N3 {
+                for j in (i + 1)..N3 {
+                    for k in (j + 1)..N3 {
+                        black_box(i + j + k);
+                    }
+                }
+            }
+        })
+    });
+}
+
+fn comb_for4(c: &mut Criterion) {
+    c.bench_function("comb for4", move |b| {
+        b.iter(|| {
+            for i in 0..N4 {
+                for j in (i + 1)..N4 {
+                    for k in (j + 1)..N4 {
+                        for l in (k + 1)..N4 {
+                            black_box(i + j + k + l);
+                        }
+                    }
+                }
+            }
+        })
+    });
+}
+
+fn comb_c1(c: &mut Criterion) {
+    c.bench_function("comb c1", move |b| {
+        b.iter(|| {
+            for (i,) in (0..N1).tuple_combinations() {
+                black_box(i);
+            }
+        })
+    });
+}
+
+fn comb_c2(c: &mut Criterion) {
+    c.bench_function("comb c2", move |b| {
+        b.iter(|| {
+            for (i, j) in (0..N2).tuple_combinations() {
+                black_box(i + j);
+            }
+        })
+    });
+}
+
+fn comb_c3(c: &mut Criterion) {
+    c.bench_function("comb c3", move |b| {
+        b.iter(|| {
+            for (i, j, k) in (0..N3).tuple_combinations() {
+                black_box(i + j + k);
+            }
+        })
+    });
+}
+
+fn comb_c4(c: &mut Criterion) {
+    c.bench_function("comb c4", move |b| {
+        b.iter(|| {
+            for (i, j, k, l) in (0..N4).tuple_combinations() {
+                black_box(i + j + k + l);
+            }
+        })
+    });
+}
+
+criterion_group!(
+    benches,
+    comb_for1,
+    comb_for2,
+    comb_for3,
+    comb_for4,
+    comb_c1,
+    comb_c2,
+    comb_c3,
+    comb_c4,
+);
+criterion_main!(benches);