ファンエンデボアスソートで配列を並び替える

set -euo pipefail

WORKDIR="$(mktemp -d)"
trap 'rm -rf "$WORKDIR"' EXIT

cat > "$WORKDIR/Dockerfile" <<'EOF'
FROM rust:1.95.0

WORKDIR /app

RUN mkdir -p src

RUN cat > Cargo.toml <<'CARGO'
[package]
name = "rust-benchmark"
version = "0.1.0"
edition = "2021"

[profile.release]
lto = true
codegen-units = 1
panic = "abort"
CARGO

RUN cat > src/main.rs <<'RUST'
use std::{
    env,
    process::Command,
    time::{Duration, Instant},
};
const MIN_POWER: u32 = 8;
const MAX_POWER: u32 = 18;
const RUNS: usize = 8192;


struct VebTree {
    universe: usize,
    min: Option<usize>,
    max: Option<usize>,
    summary: Option<Box<VebTree>>,
    cluster: Vec<Option<Box<VebTree>>>,
}

fn lower_sqrt(universe: usize) -> usize {
    1usize << (universe.trailing_zeros() / 2)
}

impl VebTree {
    fn new(universe: usize) -> Self {
        debug_assert!(universe.is_power_of_two());
        debug_assert!(universe >= 2);

        if universe == 2 {
            return Self {
                universe,
                min: None,
                max: None,
                summary: None,
                cluster: Vec::new(),
            };
        }

        let lower = lower_sqrt(universe);
        let upper = universe / lower;

        Self {
            universe,
            min: None,
            max: None,
            summary: Some(Box::new(Self::new(upper))),
            cluster: (0..upper).map(|_| None).collect(),
        }
    }

    fn high(&self, x: usize) -> usize {
        x / lower_sqrt(self.universe)
    }

    fn low(&self, x: usize) -> usize {
        x % lower_sqrt(self.universe)
    }

    fn index(&self, high: usize, low: usize) -> usize {
        high * lower_sqrt(self.universe) + low
    }

    fn minimum(&self) -> Option<usize> {
        self.min
    }

    fn maximum(&self) -> Option<usize> {
        self.max
    }

    fn cluster_mut(&mut self, i: usize) -> &mut VebTree {
        let lower = lower_sqrt(self.universe);
        self.cluster[i].get_or_insert_with(|| Box::new(Self::new(lower)))
    }

    fn empty_insert(&mut self, x: usize) {
        self.min = Some(x);
        self.max = Some(x);
    }

    fn insert(&mut self, mut x: usize) {
        if self.min.is_none() {
            self.empty_insert(x);
            return;
        }

        if x < self.min.unwrap() {
            let old_min = self.min.unwrap();
            self.min = Some(x);
            x = old_min;
        }

        if self.universe > 2 {
            let h = self.high(x);
            let l = self.low(x);
            if self.cluster[h]
                .as_ref()
                .and_then(|c| c.minimum())
                .is_none()
            {
                self.summary.as_mut().unwrap().insert(h);
                self.cluster_mut(h).empty_insert(l);
            } else {
                self.cluster_mut(h).insert(l);
            }
        }

        if x > self.max.unwrap() {
            self.max = Some(x);
        }
    }

    fn successor(&self, x: usize) -> Option<usize> {
        if self.universe == 2 {
            return if x == 0 && self.max == Some(1) {
                Some(1)
            } else {
                None
            };
        }

        if let Some(min) = self.min {
            if x < min {
                return Some(min);
            }
        } else {
            return None;
        }

        let h = self.high(x);
        let l = self.low(x);
        let max_low = self.cluster[h].as_ref().and_then(|c| c.maximum());
        if max_low.is_some_and(|m| l < m) {
            let offset = self.cluster[h].as_ref().unwrap().successor(l).unwrap();
            return Some(self.index(h, offset));
        }

        let succ_cluster = self.summary.as_ref().unwrap().successor(h)?;
        let offset = self.cluster[succ_cluster]
            .as_ref()
            .and_then(|c| c.minimum())
            .unwrap();
        Some(self.index(succ_cluster, offset))
    }
}

fn van_emde_boas_sort(a: &mut [usize]) {
    if a.len() <= 1 {
        return;
    }

    let min = *a.iter().min().unwrap();
    let max = *a.iter().max().unwrap();
    let span = max - min + 1;
    let mut count = vec![0usize; span];

    for &x in a.iter() {
        count[x - min] += 1;
    }

    let universe = span.next_power_of_two().max(2);
    let mut tree = VebTree::new(universe);

    for (offset, &c) in count.iter().enumerate() {
        if c > 0 {
            tree.insert(offset);
        }
    }

    let mut idx = 0;
    let mut cur = tree.minimum();
    while let Some(v) = cur {
        let value = min + v;
        for _ in 0..count[v] {
            a[idx] = value;
            idx += 1;
        }
        cur = tree.successor(v);
    }
}


fn benchmark_sort(array: &mut [usize]) {

    van_emde_boas_sort(array);

}

fn is_non_decreasing(a: &[usize]) -> bool {
    a.windows(2).all(|w| w[0] <= w[1])
}

fn same_multiset(a: &[usize], b: &[usize]) -> bool {
    if a.len() != b.len() {
        return false;
    }

    let mut left = a.to_vec();
    let mut right = b.to_vec();
    left.sort_unstable();
    right.sort_unstable();
    left == right
}

fn check_correctness_case(label: &str, mut input: Vec<usize>) {
    let original = input.clone();

    benchmark_sort(&mut input);

    if !is_non_decreasing(&input) {
        panic!("correctness case {}: output is not sorted", label);
    }

    if !same_multiset(&input, &original) {
        panic!("correctness case {}: elements were lost or added", label);
    }
}

fn few_unique_values(size: usize, unique: usize, seed: u64) -> Vec<usize> {
    let mut state = seed;

    (0..size)
        .map(|_| {
            state ^= state << 13;
            state ^= state >> 7;
            state ^= state << 17;
            (state as usize % unique) + 1
        })
        .collect()
}

fn run_correctness_checks() {
    check_correctness_case("empty", vec![]);
    check_correctness_case("single", vec![42]);
    check_correctness_case("duplicates", vec![3, 1, 3, 2, 1, 2]);
    check_correctness_case("sorted", vec![1, 2, 3, 4, 5]);
    check_correctness_case("reverse", vec![5, 4, 3, 2, 1]);
    check_correctness_case("all_equal", vec![7, 7, 7, 7]);
    check_correctness_case("skewed_range", vec![1_000_000, 2, 1_000_001, 1, 999_999]);
    // Static-buffer Grail skips the in-buffer build when key collection is sparse
    // (ideal_buffer = false). Exercising that path catches regressions in buffer gating.
    check_correctness_case(
        "few_keys_len16",
        vec![2, 2, 2, 2, 2, 2, 2, 2, 4, 3, 1, 2, 3, 4, 1, 4],
    );
    for seed in 0..32 {
        check_correctness_case(
            &format!("few_keys_len32_seed_{seed}"),
            few_unique_values(32, 4, seed),
        );
    }
}


fn shuffled(size: usize, seed: u64) -> Vec<usize> {
    let mut v: Vec<usize> = (1..=size).collect();

    let mut state = seed;

    for i in (1..size).rev() {
        state ^= state << 13;
        state ^= state >> 7;
        state ^= state << 17;

        let j = (state as usize) % (i + 1);

        v.swap(i, j);
    }

    v
}

fn memory_usage_kb() -> usize {
    // VmHWM (peak RSS, KiB). Reported memory subtracts a per-size baseline that only
    // holds the input array, so the table reflects auxiliary space during sorting.
    let contents = std::fs::read_to_string("/proc/self/status")
        .unwrap_or_default();

    for line in contents.lines() {
        if let Some(rest) = line.strip_prefix("VmHWM:") {
            let kb = rest
                .split_whitespace()
                .next()
                .unwrap_or("0")
                .parse::<usize>()
                .unwrap_or(0);

            return kb;
        }
    }

    0
}

fn micros(d: Duration) -> u128 {
    d.as_micros()
}

fn input_array(size: usize, seed: u64) -> Vec<usize> {
    shuffled(size, seed)
}

fn run_baseline(size: usize) -> usize {
    let _hold = input_array(size, 1);
    memory_usage_kb()
}

fn run_once(size: usize, seed: usize) -> (u128, usize) {
    let mut array = input_array(size, seed as u64);

    let start = Instant::now();

    benchmark_sort(&mut array);

    let elapsed = start.elapsed();
    let mem = memory_usage_kb();

    let expected: Vec<usize> = (1..=size).collect();
    if array != expected {
        panic!(
            "sort failed with seed {} for size {}",
            seed,
            size
        );
    }

    (micros(elapsed), mem)
}

fn run_baseline_child(args: &[String]) {
    let size = args[2].parse::<usize>().expect("invalid size");
    let mem = run_baseline(size);
    println!("{}", mem);
}

fn run_child(args: &[String]) {
    let size = args[2].parse::<usize>().expect("invalid size");
    let seed = args[3].parse::<usize>().expect("invalid seed");
    let (elapsed_us, mem) = run_once(size, seed);
    println!("{} {}", elapsed_us, mem);
}

fn main() {
    let args: Vec<String> = env::args().collect();
    if args.get(1).is_some_and(|arg| arg == "--baseline-once") {
        run_baseline_child(&args);
        return;
    }
    if args.get(1).is_some_and(|arg| arg == "--run-once") {
        run_child(&args);
        return;
    }

    run_correctness_checks();

    println!(
        "| {:>10} | {:>15} | {:>15} | {:>15} | {:>15} |",
        "Size",
        "Average time",
        "Maximum time",
        "Average memory",
        "Maximum memory"
    );

    println!(
        "|{:-<11}:|{:-<16}:|{:-<16}:|{:-<16}:|{:-<16}:|",
        "",
        "",
        "",
        "",
        ""
    );

    for power in MIN_POWER..=MAX_POWER {
        let size = 1usize << power;

        let baseline_output = Command::new(env::current_exe().expect("failed to find current executable"))
            .arg("--baseline-once")
            .arg(size.to_string())
            .output()
            .expect("failed to run benchmark baseline process");

        if !baseline_output.status.success() {
            panic!(
                "benchmark baseline process failed: {}",
                String::from_utf8_lossy(&baseline_output.stderr)
            );
        }

        let baseline_stdout = String::from_utf8(baseline_output.stdout)
            .expect("baseline process returned non-UTF-8 output");
        let baseline_mem = baseline_stdout
            .split_whitespace()
            .next()
            .expect("missing baseline memory usage")
            .parse::<usize>()
            .expect("invalid baseline memory usage");

        let mut total_time: u128 = 0;
        let mut max_time: u128 = 0;

        let mut total_mem: usize = 0;
        let mut max_mem: usize = 0;

        for seed in 1..=RUNS {
            let output = Command::new(env::current_exe().expect("failed to find current executable"))
                .arg("--run-once")
                .arg(size.to_string())
                .arg(seed.to_string())
                .output()
                .expect("failed to run benchmark child process");

            if !output.status.success() {
                panic!(
                    "benchmark child process failed: {}",
                    String::from_utf8_lossy(&output.stderr)
                );
            }

            let stdout = String::from_utf8(output.stdout)
                .expect("child process returned non-UTF-8 output");
            let mut fields = stdout.split_whitespace();
            let elapsed_us = fields
                .next()
                .expect("missing elapsed time")
                .parse::<u128>()
                .expect("invalid elapsed time");
            let mem = fields
                .next()
                .expect("missing memory usage")
                .parse::<usize>()
                .expect("invalid memory usage");

            total_time += elapsed_us;

            if elapsed_us > max_time {
                max_time = elapsed_us;
            }

            let aux_mem = mem.saturating_sub(baseline_mem);

            total_mem += aux_mem;

            if aux_mem > max_mem {
                max_mem = aux_mem;
            }
        }

        let avg_time = total_time / RUNS as u128;
        let avg_mem = total_mem / RUNS;

        println!(
            "| {:>10} | {:>15} | {:>15} | {:>15} | {:>15} |",
            size,
            format!("{}.{:06}", avg_time / 1_000_000, avg_time % 1_000_000),
            format!("{}.{:06}", max_time / 1_000_000, max_time % 1_000_000),
            avg_mem,
            max_mem
        );
    }
}
RUST

RUN cargo build --release

CMD ["./target/release/rust-benchmark"]
EOF

docker build -t rust-benchmark "$WORKDIR"
docker run --rm --init rust-benchmark