vrd 0.0.10

A lightweight, no_std-friendly random number generator backed by Xoshiro256++ with optional Mersenne Twister support.
Documentation 
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// Copyright © 2023-2026 vrd. All rights reserved.
// SPDX-License-Identifier: Apache-2.0 OR MIT

//! Poisson distribution sampling via Knuth's multiplicative algorithm.
//!
//! Run: `cargo run --example poisson`

#[path = "support.rs"]
mod support;

use vrd::Random;

fn main() {
    support::header("vrd -- poisson");

    support::task_with_output(
        "poisson(3.0) — first 12 samples",
        || {
            let mut rng = Random::from_u64_seed(0xF15);
            (0..12).map(|_| format!("{}", rng.poisson(3.0))).collect()
        },
    );

    support::task_with_output("Mean approaches lambda", || {
        let n = 30_000usize;
        let mut lines = Vec::new();
        for &lambda in &[0.5, 1.0, 3.0, 7.0] {
            let mut rng = Random::from_u64_seed(0xF15);
            let mean: f64 =
                (0..n).map(|_| rng.poisson(lambda) as f64).sum::<f64>()
                    / n as f64;
            lines.push(format!(
                "lambda = {lambda:.1} -> mean = {mean:.4}",
            ));
        }
        lines
    });

    support::task_with_output("Histogram for lambda = 4.0", || {
        let mut rng = Random::from_u64_seed(7);
        let mut bins = [0u64; 16];
        for _ in 0..5_000 {
            let k = rng.poisson(4.0) as usize;
            if k < bins.len() {
                bins[k] += 1;
            }
        }
        let max = *bins.iter().max().unwrap_or(&1);
        bins.iter()
            .enumerate()
            .map(|(k, &c)| {
                let bar = "\u{2588}"
                    .repeat((c as f64 / max as f64 * 40.0) as usize);
                format!("k = {k:>2}: {bar}")
            })
            .collect()
    });

    support::summary(3);
}