binary_heap.rs

use std::collections::BinaryHeap;

use rand::{seq::SliceRandom, thread_rng};
use test::{black_box, Bencher};

#[bench]
fn bench_find_smallest_1000(b: &mut Bencher) {
    let mut rng = thread_rng();
    let mut vec: Vec<u32> = (0..100_000).collect();
    vec.shuffle(&mut rng);

    b.iter(|| {
        let mut iter = vec.iter().copied();
        let mut heap: BinaryHeap<_> = iter.by_ref().take(1000).collect();

        for x in iter {
            let mut max = heap.peek_mut().unwrap();
            // This comparison should be true only 1% of the time.
            // Unnecessary `sift_down`s will degrade performance
            if x < *max {
                *max = x;
            }
        }

        heap
    })
}

#[bench]
fn bench_peek_mut_deref_mut(b: &mut Bencher) {
    let mut bheap = BinaryHeap::from(vec![42]);
    let vec: Vec<u32> = (0..1_000_000).collect();

    b.iter(|| {
        let vec = black_box(&vec);
        let mut peek_mut = bheap.peek_mut().unwrap();
        // The compiler shouldn't be able to optimize away the `sift_down`
        // assignment in `PeekMut`'s `DerefMut` implementation since
        // the loop might not run.
        for &i in vec.iter() {
            *peek_mut = i;
        }
        // Remove the already minimal overhead of the sift_down
        std::mem::forget(peek_mut);
    })
}

#[bench]
fn bench_from_vec(b: &mut Bencher) {
    let mut rng = thread_rng();
    let mut vec: Vec<u32> = (0..100_000).collect();
    vec.shuffle(&mut rng);

    b.iter(|| BinaryHeap::from(vec.clone()))
}

#[bench]
fn bench_into_sorted_vec(b: &mut Bencher) {
    let bheap: BinaryHeap<i32> = (0..10_000).collect();

    b.iter(|| bheap.clone().into_sorted_vec())
}

#[bench]
fn bench_push(b: &mut Bencher) {
    let mut bheap = BinaryHeap::with_capacity(50_000);
    let mut rng = thread_rng();
    let mut vec: Vec<u32> = (0..50_000).collect();
    vec.shuffle(&mut rng);

    b.iter(|| {
        for &i in vec.iter() {
            bheap.push(i);
        }
        black_box(&mut bheap);
        bheap.clear();
    })
}

#[bench]
fn bench_pop(b: &mut Bencher) {
    let mut bheap = BinaryHeap::with_capacity(10_000);

    b.iter(|| {
        bheap.extend((0..10_000).rev());
        black_box(&mut bheap);
        while let Some(elem) = bheap.pop() {
            black_box(elem);
        }
    })
}