A better loop benchmark

loops.rs

#![feature(test)]
#![feature(step_by)]

extern crate test;

fn for_loop() -> usize {
    let mut counter = 1;
	for i in (0..1_000_000) {
	   counter += test::black_box(i);
	}
	counter
}

fn for_step_loop() -> usize {
    let mut counter = 1;
	for i in (0..1_000_000).step_by(1) {
	   counter += test::black_box(i);
	}
	counter
}

fn while_loop() -> usize {
	let mut i=0;
	let mut counter = 1;
	while i < 1_000_000
	{
		counter += test::black_box(i);
		i += 1
	}
	counter
}

#[bench]
fn bench_for(bench:&mut test::Bencher) {
	bench.iter(for_loop);
}

#[bench]
fn bench_for_step(bench:&mut test::Bencher) {
	bench.iter(for_step_loop);
}


#[bench]
fn bench_while(bench:&mut test::Bencher) {
	bench.iter(while_loop);
}

/*
$ rustc -C opt-level=3 loops.rs --test && ./loops --bench

running 3 tests
test bench_for      ... bench:   1,126,115 ns/iter (+/- 1,494)
test bench_for_step ... bench:   1,538,970 ns/iter (+/- 56,400)
test bench_while    ... bench:   1,150,486 ns/iter (+/- 12,384)
 */