フラック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;
fn insertion_sort(a: &mut [usize]) {
    for i in 1..a.len() {
        let mut j = i;
        while j > 0 && a[j - 1] > a[j] {
            a.swap(j - 1, j);
            j -= 1;
        }
    }
}



const FLUX_INSERTION_THRESHOLD: usize = 24;

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

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

fn flux_reverse(a: &mut [usize]) {
    let mut lo = 0;
    let mut hi = a.len();
    while lo + 1 < hi {
        hi -= 1;
        a.swap(lo, hi);
        lo += 1;
    }
}

/// Count ascending adjacent pairs (presortedness measure).
fn flux_ordered_pairs(a: &[usize]) -> usize {
    a.windows(2).filter(|w| w[0] <= w[1]).count()
}

fn flux_median3_idx(a: &[usize], i: usize, j: usize, k: usize) -> usize {
    let (x, y, z) = (a[i], a[j], a[k]);
    if x < y {
        if y < z {
            j
        } else if x < z {
            k
        } else {
            i
        }
    } else if x < z {
        i
    } else if y < z {
        k
    } else {
        j
    }
}

/// Quasimedian of 9: median of three medians-of-three sampled across the range.
fn flux_quasimedian9(a: &[usize]) -> usize {
    let n = a.len();
    if n < 9 {
        return a[n / 2];
    }
    let step = n / 8;
    let i0 = 0;
    let i1 = step;
    let i2 = step * 2;
    let i3 = step * 3;
    let i4 = step * 4;
    let i5 = step * 5;
    let i6 = step * 6;
    let i7 = step * 7;
    let i8 = n - 1;
    let m0 = flux_median3_idx(a, i0, i1, i2);
    let m1 = flux_median3_idx(a, i3, i4, i5);
    let m2 = flux_median3_idx(a, i6, i7, i8);
    a[flux_median3_idx(a, m0, m1, m2)]
}

fn flux_merge(a: &mut [usize], swap: &mut [usize]) {
    let n = a.len();
    if n <= 1 {
        return;
    }
    let mid = n / 2;
    flux_merge(&mut a[..mid], swap);
    flux_merge(&mut a[mid..], swap);
    let (left, right) = a.split_at(mid);
    let mut i = 0;
    let mut j = 0;
    let mut k = 0;
    while i < left.len() && j < right.len() {
        if left[i] <= right[j] {
            swap[k] = left[i];
            i += 1;
        } else {
            swap[k] = right[j];
            j += 1;
        }
        k += 1;
    }
    while i < left.len() {
        swap[k] = left[i];
        i += 1;
        k += 1;
    }
    while j < right.len() {
        swap[k] = right[j];
        j += 1;
        k += 1;
    }
    a.copy_from_slice(&swap[..n]);
}

/// Stable dual-destination partition: `≤ pivot` stay toward the front of `a`,
/// `> pivot` are collected after them (educational stand-in for fluxsort’s
/// main/swap split). Returns the length of the left partition.
fn flux_stable_partition(a: &mut [usize], swap: &mut [usize], pivot: usize) -> usize {
    let n = a.len();
    swap[..n].copy_from_slice(a);
    let mut left = 0usize;
    for i in 0..n {
        if swap[i] <= pivot {
            left += 1;
        }
    }
    let mut l = 0usize;
    let mut r = left;
    for i in 0..n {
        let x = swap[i];
        if x <= pivot {
            a[l] = x;
            l += 1;
        } else {
            a[r] = x;
            r += 1;
        }
    }
    left
}

fn flux_partition_sort(a: &mut [usize], swap: &mut [usize]) {
    let n = a.len();
    if n <= 1 {
        return;
    }
    if n < FLUX_INSERTION_THRESHOLD {
        insertion_sort(a);
        return;
    }

    let pivot = flux_quasimedian9(a);
    let left = flux_stable_partition(a, swap, pivot);
    let right = n - left;

    // All keys ≤ pivot: filter equals out so recursion makes progress
    // (fluxsort’s “second sweep” for generic / low-cardinality data).
    if right == 0 {
        swap[..n].copy_from_slice(a);
        let mut lt = 0usize;
        for i in 0..n {
            if swap[i] < pivot {
                a[lt] = swap[i];
                lt += 1;
            }
        }
        let mut eq = lt;
        for i in 0..n {
            if swap[i] == pivot {
                a[eq] = swap[i];
                eq += 1;
            }
        }
        if lt > 1 {
            flux_partition_sort(&mut a[..lt], swap);
        }
        return;
    }

    // Worst-case guard: one side < 1/16 of the other → mergesort both sides.
    let unbalanced = left > 0 && (left < n / 16 || right < n / 16);

    if unbalanced {
        flux_merge(&mut a[..left], swap);
        flux_merge(&mut a[left..], swap);
        return;
    }

    if left > 1 {
        flux_partition_sort(&mut a[..left], swap);
    }
    if right > 1 {
        flux_partition_sort(&mut a[left..], swap);
    }
}

fn flux_analyze(a: &mut [usize], swap: &mut [usize]) -> bool {
    let n = a.len();
    if n <= 1 {
        return true;
    }
    if flux_is_sorted(a) {
        return true;
    }
    if flux_is_reverse_sorted(a) {
        flux_reverse(a);
        return true;
    }

    // Four-segment presortedness: if more than half the adjacent pairs in a
    // segment are ordered, finish that segment with mergesort (stand-in for
    // quadsort). Remaining disorder is handled by partitioning afterward.
    let q = n / 4;
    if q >= 2 {
        let bounds = [0, q, q * 2, q * 3, n];
        for s in 0..4 {
            let lo = bounds[s];
            let hi = bounds[s + 1];
            if hi - lo < 2 {
                continue;
            }
            let pairs = hi - lo - 1;
            if flux_ordered_pairs(&a[lo..hi]) * 2 > pairs {
                flux_merge(&mut a[lo..hi], swap);
            }
        }
        if flux_is_sorted(a) {
            return true;
        }
    }
    false
}

fn flux_sort(a: &mut [usize]) {
    let n = a.len();
    if n <= 1 {
        return;
    }
    let mut swap = vec![0usize; n];
    if flux_analyze(a, &mut swap) {
        return;
    }
    flux_partition_sort(a, &mut swap);
}


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

    flux_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],
    );
    // Seed 0 is a fixed point of the xorshift below, so it would degenerate into
    // yet another all-equal case instead of a 4-value mix. Start at 1.
    for seed in 1..=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