alex/beta-minecraft-rust

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const MULTIPLIER: i64 = 0x5_DEEC_E66D;
const ADDEND: i64 = 0xB;
const MASK: i64 = (1 << 48) - 1;

/// Port of `java.util.Random`, producing identical sequences for identical seeds.
#[derive(Clone, Debug)]
pub struct JavaRandom {
    seed: i64,
    next_gaussian: Option<f64>,
}

impl Default for JavaRandom {
    fn default() -> Self {
        Self::new(0)
    }
}

impl JavaRandom {
    pub fn new(seed: i64) -> Self {
        Self {
            seed: (seed ^ MULTIPLIER) & MASK,
            next_gaussian: None,
        }
    }

    pub fn set_seed(&mut self, seed: i64) {
        *self = Self::new(seed);
    }

    fn next(&mut self, bits: u32) -> i32 {
        self.seed = self.seed.wrapping_mul(MULTIPLIER).wrapping_add(ADDEND) & MASK;
        (self.seed >> (48 - bits)) as i32
    }

    /// Uniform in `0..bound`. Panics if `bound <= 0`, like Java's `IllegalArgumentException`.
    pub fn next_int(&mut self, bound: i32) -> i32 {
        assert!(bound > 0, "bound must be positive");
        if bound & -bound == bound {
            return ((i64::from(bound) * i64::from(self.next(31))) >> 31) as i32;
        }
        loop {
            let bits = self.next(31);
            let value = bits % bound;
            if bits.wrapping_sub(value).wrapping_add(bound - 1) >= 0 {
                return value;
            }
        }
    }

    pub fn next_i32(&mut self) -> i32 {
        self.next(32)
    }

    pub fn next_long(&mut self) -> i64 {
        let high = i64::from(self.next(32)) << 32;
        high.wrapping_add(i64::from(self.next(32)))
    }

    pub fn next_bool(&mut self) -> bool {
        self.next(1) != 0
    }

    pub fn next_float(&mut self) -> f32 {
        self.next(24) as f32 / (1 << 24) as f32
    }

    pub fn next_double(&mut self) -> f64 {
        let high = i64::from(self.next(26)) << 27;
        (high + i64::from(self.next(27))) as f64 * (1.0 / (1_i64 << 53) as f64)
    }

    /// `nextGaussian`: the polar method, which yields values in pairs.
    pub fn next_gaussian(&mut self) -> f64 {
        if let Some(value) = self.next_gaussian.take() {
            return value;
        }
        loop {
            let v1 = 2.0 * self.next_double() - 1.0;
            let v2 = 2.0 * self.next_double() - 1.0;
            let s = v1 * v1 + v2 * v2;
            if s < 1.0 && s != 0.0 {
                let multiplier = (-2.0 * s.ln() / s).sqrt();
                self.next_gaussian = Some(v2 * multiplier);
                return v1 * multiplier;
            }
        }
    }
}