Code shared from the Rust Playground

playground.rs

#[macro_use]
extern crate criterion;

// Don't run this on Playground!
// Run it locally using `cargo bench`

use criterion::Criterion;
use ndarray::Array1;

fn midpoints(n: u32, a: f32, b: f32) -> Array1<f32> {
    assert!(a < b);
    assert!(n > 0);
    let length = (b - a) / (n as f32);
    let start = a + length;
    let end = b + length;
    Array1::range(start, end, length)
}

fn rectangle_rule<F>(n: u32, a: f32, b: f32, f: F) -> f32
    where
        F: FnMut(&f32) -> f32
{
    let points = midpoints(n, a, b);
    let f_values = points.map(f);
    let length = (b - a) / (n as f32);
    let integral_estimate = f_values.sum() * length;
    integral_estimate
}

fn criterion_benchmark(c: &mut Criterion) {
    c.bench_function(
        "rectangle",
        move |b| b.iter(
            || rectangle_rule(50000, 0., 1., |x| x.sin())
        )
    );
}

criterion_group!(benches, criterion_benchmark);
criterion_main!(benches);