Add benchmark for VecDeque append

Author: Pazzaz

src/liballoc/Cargo.toml

@@ -23,3 +23,8 @@ path = "../liballoc/tests/lib.rs"
 [[bench]]
 name = "collectionsbenches"
 path = "../liballoc/benches/lib.rs"
+
+[[bench]]
+name = "vec_deque_append_bench"
+path = "../liballoc/benches/vec_deque_append.rs"
+harness = false

src/liballoc/benches/vec_deque_append.rs

@@ -0,0 +1,48 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![feature(duration_as_u128)]
+use std::{collections::VecDeque, time::Instant};
+
+const VECDEQUE_LEN: i32 = 100000;
+const WARMUP_N: usize = 100;
+const BENCH_N: usize = 1000;
+
+fn main() {
+    let a: VecDeque<i32> = (0..VECDEQUE_LEN).collect();
+    let b: VecDeque<i32> = (0..VECDEQUE_LEN).collect();
+
+    for _ in 0..WARMUP_N {
+        let mut c = a.clone();
+        let mut d = b.clone();
+        c.append(&mut d);
+    }
+
+    let mut durations = Vec::with_capacity(BENCH_N);
+
+    for _ in 0..BENCH_N {
+        let mut c = a.clone();
+        let mut d = b.clone();
+        let before = Instant::now();
+        c.append(&mut d);
+        let after = Instant::now();
+        durations.push(after.duration_since(before));
+    }
+
+    let l = durations.len();
+    durations.sort();
+
+    assert!(BENCH_N % 2 == 0);
+    let median = (durations[(l / 2) - 1] + durations[l / 2]) / 2;
+    println!(
+        "\ncustom-bench vec_deque_append {:?} ns/iter\n",
+        median.as_nanos()
+    );
+}