Microbenchmark of the fannkuch_redux' rotate method

rot_bench.rs

#![feature(test)]

extern crate test;

use std::mem;
use std::intrinsics::copy;

fn rotate(x: &mut [i32]) {
    let mut prev = x[0];
    for place in x.iter_mut().rev() {
        prev = mem::replace(place, prev)
    }
}

fn rotate_new(x: &mut [i32]) {
	let tmp = x[0];
	let last = x.len() - 1;
	if last <= 0 { return; }
	unsafe { copy(&x[1], &mut x[0], last); }
	x[last] = tmp;
}

fn rotate_bench(data: &mut [i32], bench: &mut test::Bencher) {
	bench.iter(|| {
		rotate(data);
		test::black_box(data[0]);
	});
}

fn rotate_new_bench(data: &mut [i32], bench: &mut test::Bencher) {
	bench.iter(|| {
		rotate_new(data);
		test::black_box(data[0]);
	});
}

fn test_same(old: &mut [i32], new: &mut [i32]) {
	assert_eq!(old, new);
	rotate(old);
	rotate_new(new);
	assert_eq!(old, new);
}

#[test]
fn test_rotate_16() {
	let mut x = [1i32; 16];
	let mut y = [1i32; 16];
	
	for i in (0i32..16) { 
		x[i as usize] = i; 
		y[i as usize] = i; 
	}
	test_same(&mut x, &mut y);
}

#[test]
fn test_rotate_1() {
	let mut x = [1];
	let mut y = [1];
	
	test_same(&mut x, &mut y);
}

#[bench]
fn bench_rotate_16(bench: &mut test::Bencher) {
	let mut x = [1i32; 16];
	for i in (0i32..16) { x[i as usize] = i; }
	rotate_bench(&mut x, bench);
}

#[bench]
fn bench_rotate_16_new(bench: &mut test::Bencher) {
	let mut x = [1i32; 16];
	for i in (0i32..16) { x[i as usize] = i; }
	rotate_new_bench(&mut x, bench);
}