PkmnLib_rs/src/utils/random.rs

use rand::distributions::{Distribution, Uniform};
use rand::{Rng, SeedableRng};
use rand_pcg::Pcg32;

/// A random number generator.
#[derive(Clone)]
pub struct Random {
    /// The seed of the random number generator.
    seed: u128,
    /// A float distribution.
    distribution: Uniform<f64>,
    /// The underlying RNG. PCG for fast, hard to predict random number generation.
    random_gen: Pcg32,
}

impl Default for Random {
    /// The default for the RNG uses the nanoseconds since epoch as seed.
    fn default() -> Self {
        let seed = chrono::Utc::now().timestamp_nanos() as u128;
        Random::new(seed)
    }
}

impl Random {
    /// Creates a new RNG with a specific seed.
    pub fn new(seed: u128) -> Self {
        Random {
            seed,
            distribution: Uniform::from(0.0..1.0),
            random_gen: Pcg32::from_seed(seed.to_be_bytes()),
        }
    }

    /// The seed used for the RNG.
    pub fn get_seed(&self) -> u128 {
        self.seed
    }

    /// Get a random 32 bit integer between minimal and maximal 32 bit integer
    pub fn get(&mut self) -> i32 {
        self.random_gen.gen()
    }

    /// Get a random 32 bit signed integer between 0 and max. If max equals 0, always returns 0.
    pub fn get_max(&mut self, max: i32) -> i32 {
        if max <= 0 {
            return 0;
        }
        Uniform::from(0..max).sample(&mut self.random_gen)
    }

    /// Get a random 32 bit signed integer between min and max. If max is equal or less than min,
    /// always returns min.
    pub fn get_between(&mut self, min: i32, max: i32) -> i32 {
        if max <= min {
            return min;
        }
        Uniform::from(min..max).sample(&mut self.random_gen)
    }

    /// Get a random 32 bit integer unsigned between 0 and maximal 32 bit unsigned int.
    pub fn get_unsigned(&mut self) -> u32 {
        self.random_gen.gen()
    }

    /// Get a random 32 bit signed integer between 0 and max. If max equals 0, always returns 0.
    pub fn get_max_unsigned(&mut self, max: u32) -> u32 {
        if max == 0 {
            return 0;
        }
        Uniform::from(0..max).sample(&mut self.random_gen)
    }

    /// Get a random 32 bit unsigned integer between min and max. If max is equal or less than min,
    /// always returns min.
    pub fn get_between_unsigned(&mut self, min: u32, max: u32) -> u32 {
        if max <= min {
            return min;
        }
        Uniform::from(min..max).sample(&mut self.random_gen)
    }

    /// Gets a random 32 bit float between 0.0 and 1.0
    pub fn get_float(&mut self) -> f32 {
        self.get_double() as f32
    }
    /// Gets a random 64 bit float between 0.0 and 1.0
    pub fn get_double(&mut self) -> f64 {
        self.distribution.sample(&mut self.random_gen)
    }
}

#[cfg(test)]
mod tests {
    use std::hint::black_box;
    use test::Bencher;

    use crate::utils::random::Random;

    extern crate test;

    #[test]
    #[cfg_attr(miri, ignore)]
    fn create_random() {
        let _default = Random::default();
        let empty = Random::new(100);
        assert_eq!(empty.get_seed(), 100);
    }

    #[test]
    fn get_random_with_seed() {
        let mut v = Random::new(10);
        assert_eq!(v.get(), 1755576946);
        assert_eq!(v.get(), 1254514019);
        assert_eq!(v.get(), 1735834837);
        assert_eq!(v.get(), 51079449);
        assert_eq!(v.get(), 506997516);
        assert_eq!(v.get(), -173527621);
        assert_eq!(v.get(), 683138464);
        assert_eq!(v.get(), 580236580);
    }

    #[test]
    fn get_random_unsigned_with_seed() {
        let mut v = Random::new(10);
        assert_eq!(v.get_unsigned(), 1755576946);
        assert_eq!(v.get_unsigned(), 1254514019);
        assert_eq!(v.get_unsigned(), 1735834837);
        assert_eq!(v.get_unsigned(), 51079449);
        assert_eq!(v.get_unsigned(), 506997516);
        assert_eq!(v.get_unsigned(), 4121439675);
        assert_eq!(v.get_unsigned(), 683138464);
        assert_eq!(v.get_unsigned(), 580236580);
    }

    #[test]
    fn get_random_with_limit_with_seed() {
        let mut v = Random::new(10);
        assert_eq!(v.get_max(10), 4);
        assert_eq!(v.get_max(10), 2);
        assert_eq!(v.get_max(10), 4);
        assert_eq!(v.get_max(10), 0);
        assert_eq!(v.get_max(10), 1);
        assert_eq!(v.get_max(10), 9);
        assert_eq!(v.get_max(10), 1);
        assert_eq!(v.get_max(10), 1);

        assert_eq!(v.get_max(2), 0);
        assert_eq!(v.get_max(2), 1);
        assert_eq!(v.get_max(2), 1);
        assert_eq!(v.get_max(2), 1);
        assert_eq!(v.get_max(2), 0);
        assert_eq!(v.get_max(2), 1);
        assert_eq!(v.get_max(2), 0);
        assert_eq!(v.get_max(2), 0);
        assert_eq!(v.get_max(2), 1);
    }

    #[test]
    fn get_random_unsigned_with_limit_with_seed() {
        let mut v = Random::new(10);
        assert_eq!(v.get_max_unsigned(4121439675), 1684647164);
    }

    #[test]
    fn get_random_with_limit_with_range() {
        let mut v = Random::new(10);
        assert_eq!(v.get_between(10, 30), 18);
        assert_eq!(v.get_between(10, 30), 15);
        assert_eq!(v.get_between(10, 30), 18);
        assert_eq!(v.get_between(10, 30), 10);
        assert_eq!(v.get_between(10, 30), 12);
        assert_eq!(v.get_between(10, 30), 29);
        assert_eq!(v.get_between(10, 30), 13);
        assert_eq!(v.get_between(10, 30), 12);
    }

    #[test]
    fn get_random_unsigned_with_limit_with_range() {
        let mut v = Random::new(10);
        assert_eq!(v.get_between_unsigned(4121439675, 4121439678), 4121439676);
    }

    #[test]
    fn get_random_float() {
        let mut v = Random::new(10);
        assert_eq!(v.get_float(), 0.2920893);
    }

    #[test]
    fn get_random_double() {
        let mut v = Random::new(10);
        assert_eq!(v.get_double(), 0.2920893066117427);
    }

    #[test]
    fn get_random_clone_then_continue() {
        let mut v = Random::new(10);
        assert_eq!(v.get_unsigned(), 1755576946);
        let mut clone = v.clone();
        assert_eq!(clone.get_unsigned(), 1254514019);
        assert_eq!(v.get_unsigned(), 1254514019);
    }

    #[test]
    #[cfg_attr(miri, ignore)]
    fn check_random_distribution() {
        let mut v = Random::new(10);
        const AMOUNT: usize = 100_000;

        let mut arr: [i32; AMOUNT] = [0; AMOUNT];
        for i in 0..AMOUNT {
            arr[i] = v.get_between(0, 2);
        }

        let mut num_zeros = 0;
        let mut num_ones = 0;
        for v in arr.iter() {
            if *v == 0 {
                num_zeros += 1;
            } else if *v == 1 {
                num_ones += 1;
            }
        }
        let div = num_zeros as f32 / num_ones as f32;
        assert_approx_eq::assert_approx_eq!(div, 1.0, 0.01);
    }

    #[test]
    #[cfg_attr(miri, ignore)]
    fn check_random_distribution_0_to_3() {
        let mut v = Random::new(10);
        const AMOUNT: usize = 100_000;

        let mut arr: [i32; AMOUNT] = [0; AMOUNT];
        for i in 0..AMOUNT {
            arr[i] = v.get_between(0, 3);
        }

        let mut num_zeros = 0;
        let mut num_ones = 0;
        let mut num_twos = 0;
        for v in arr.iter() {
            if *v == 0 {
                num_zeros += 1;
            } else if *v == 1 {
                num_ones += 1;
            } else if *v == 2 {
                num_twos += 1;
            }
        }
        assert_approx_eq::assert_approx_eq!(num_zeros as f32 / num_ones as f32, 1.0, 0.01);
        assert_approx_eq::assert_approx_eq!(num_zeros as f32 / num_twos as f32, 1.0, 0.01);
        assert_approx_eq::assert_approx_eq!(num_ones as f32 / num_twos as f32, 1.0, 0.01);
    }

    #[bench]
    #[cfg_attr(miri, ignore)]
    fn bench_1000_random_ints_between(b: &mut Bencher) {
        b.iter(|| {
            let mut random = Random::new(10);
            for _ in 0..1000 {
                black_box(random.get_between(0, 100));
            }
        });
    }
}