From 3f5890be70e093760d85066f9102d9e2b48cf84b Mon Sep 17 00:00:00 2001
From: Stepan Koltsov <stepan.koltsov@gmail.com>
Date: Mon, 22 May 2017 23:15:08 +0300
Subject: [PATCH] Optimize Bytes::slice(n, n) (#123)
Return empty `Bytes` object
Bench for `slice_empty` difference is
```
55 ns/iter (+/- 1) # before this patch
17 ns/iter (+/- 5) # with this patch
```
Bench for `slice_not_empty` is
```
25,058 ns/iter (+/- 1,099) # before this patch
25,072 ns/iter (+/- 1,593) # with this patch
```
---
benches/bytes.rs | 22 +++++++++++++++++++++-
src/bytes.rs | 5 +++++
tests/test_bytes.rs | 9 +++++++++
3 files changed, 35 insertions(+), 1 deletion(-)
diff --git a/benches/bytes.rs b/benches/bytes.rs
index 4232ced..ff07395 100644
--- a/benches/bytes.rs
+++ b/benches/bytes.rs
@@ -4,7 +4,7 @@ extern crate bytes;
extern crate test;
use test::Bencher;
-use bytes::{BytesMut, BufMut};
+use bytes::{Bytes, BytesMut, BufMut};
#[bench]
fn alloc_small(b: &mut Bencher) {
@@ -126,3 +126,23 @@ fn drain_write_drain(b: &mut Bencher) {
test::black_box(parts);
})
}
+
+#[bench]
+fn slice_empty(b: &mut Bencher) {
+ b.iter(|| {
+ // Use empty vec to avoid measure of allocation/deallocation
+ let bytes = Bytes::from(Vec::new());
+ (bytes.slice(0, 0), bytes)
+ })
+}
+
+#[bench]
+fn slice_not_empty(b: &mut Bencher) {
+ b.iter(|| {
+ let b = Bytes::from(b"aabbccddeeffgghh".to_vec());
+ for _ in 0..1024 {
+ test::black_box(b.slice(3, 5));
+ test::black_box(&b);
+ }
+ })
+}
diff --git a/src/bytes.rs b/src/bytes.rs
index 6246509..4b0ef42 100644
--- a/src/bytes.rs
+++ b/src/bytes.rs
@@ -464,6 +464,11 @@ impl Bytes {
/// Requires that `begin <= end` and `end <= self.len()`, otherwise slicing
/// will panic.
pub fn slice(&self, begin: usize, end: usize) -> Bytes {
+ if begin == end {
+ assert!(begin <= self.len());
+ return Bytes::new();
+ }
+
let mut ret = self.clone();
unsafe {
diff --git a/tests/test_bytes.rs b/tests/test_bytes.rs
index af481a2..c8d23d3 100644
--- a/tests/test_bytes.rs
+++ b/tests/test_bytes.rs
@@ -79,6 +79,15 @@ fn slice() {
let b = a.slice(3, 5);
assert_eq!(b, b"lo"[..]);
+ let b = a.slice(0, 0);
+ assert_eq!(b, b""[..]);
+
+ let b = a.slice(3, 3);
+ assert_eq!(b, b""[..]);
+
+ let b = a.slice(a.len(), a.len());
+ assert_eq!(b, b""[..]);
+
let b = a.slice_to(5);
assert_eq!(b, b"hello"[..]);
--
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