populate_vec.rs

#![feature(test)]

extern crate test;

use test::{Bencher, black_box};
use std::iter;

const TOTAL_SIZE: usize = 1024;

const TAIL_DATA: [u8; 24] = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24];

#[bench]
fn populate_vec_with_iter(b: &mut Bencher) {
	let mut tail_size = 0usize;

	b.iter(|| {
		let mut buffer = Vec::with_capacity(TOTAL_SIZE);
		buffer.extend(iter::repeat(0).take(TOTAL_SIZE - tail_size));
		buffer.extend_from_slice(&TAIL_DATA[0..tail_size]);
		black_box(buffer);
		tail_size = (tail_size + 23) / 19;
	});

}

#[bench]
fn populate_vec_with_slice(b: &mut Bencher) {
	let mut tail_size = 0usize;

	b.iter(|| {
		let mut buffer = Vec::with_capacity(TOTAL_SIZE);
		buffer.extend_from_slice(&vec![0; TOTAL_SIZE - tail_size]);
		buffer.extend_from_slice(&TAIL_DATA[0..tail_size]);
		black_box(buffer);
		tail_size = (tail_size + 23) / 19;
	});
}

#[bench]
fn populate_vec_with_split_at_mut(b: &mut Bencher) {
	let mut tail_size = 0usize;

	b.iter(|| {
		let mut buffer = vec![0; TOTAL_SIZE];
		{
			let (_head, tail) = buffer.split_at_mut(TOTAL_SIZE - tail_size);
			tail.copy_from_slice(&TAIL_DATA[0..tail_size])
		}
		black_box(buffer);
		tail_size = (tail_size + 23) / 19;
	});

}

     Running target/release/deps/populate_vec-77ce8e8662cf94dc

running 3 tests
test populate_vec_with_iter         ... bench:       1,277 ns/iter (+/- 85)
test populate_vec_with_slice        ... bench:         188 ns/iter (+/- 15)
test populate_vec_with_split_at_mut ... bench:          63 ns/iter (+/- 5)