gwid 0.0.5

RFC 9562-compliant UUIDs
Documentation 
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// Although the logic is the same, this is a vastly simplified port of the Math.random
// implementation in V8 15.4.80.20, which is used in Chrome 154.0.8037.98 (Official Build) (x86_64).
#![allow(dead_code)]

use std::time::SystemTime;
use std::time::UNIX_EPOCH;

#[derive(Default, Debug)]
pub struct State {
    pub s0: u64,
    pub s1: u64,
}

// https://source.chromium.org/chromium/_/chromium/v8/v8/+/c4bf0d1b36dca14d5eaec1ed83ccd77518d2d01a:src/numbers/math-random.cc;drc=99f606174481f6e2f4809c4262122a30a25583af;bpv=0;bpt=0
#[derive(Debug)]
pub struct MathRandom {
    state: State,
    cache_index: usize,
    cache: [u64; Self::K_CACHE_SIZE as usize],
}

impl MathRandom {
    const K_INT64_SIZE: i64 = std::mem::size_of::<i64>() as i64;
    const K_CACHE_SIZE: i64 = 64;
    const K_STATE_SIZE: i64 = 2 * Self::K_INT64_SIZE;

    pub fn initialize(seed: Option<u64>) -> Self {
        let seed = match seed {
            Some(s) => s,
            None => SystemTime::now()
                .duration_since(UNIX_EPOCH)
                .unwrap_or_default()
                .as_secs(),
        };

        let mut this = Self {
            state: State {
                s0: RandomNumberGenerator::murmurhash3(seed),
                s1: RandomNumberGenerator::murmurhash3(!seed),
            },
            cache_index: 0,
            cache: [0; Self::K_CACHE_SIZE as usize],
        };

        this.refill_cache();
        this
    }

    pub fn random_double(&mut self) -> f64 {
        RandomNumberGenerator::to_double(self.current_cached())
    }

    pub fn random_u64(&mut self) -> u64 {
        self.current_cached()
    }

    fn refill_cache(&mut self) {
        for i in (0usize..=(Self::K_CACHE_SIZE - 1) as usize).rev() {
            let s = &mut self.state;
            let random = RandomNumberGenerator::xorshift128(&mut s.s0, &mut s.s1);
            self.cache[i] = random;
        }
        self.cache_index = Self::K_CACHE_SIZE as usize;
    }

    /// Gets element from cache via current cache index
    fn current_cached(&mut self) -> u64 {
        if self.cache_index == 0 {
            self.refill_cache();
        }
        self.cache_index -= 1;
        self.cache[self.cache_index]
    }

    fn reverse_to_double(dbl: f64) -> u64 {
        ((dbl * (1_u64 << 53) as f64) as u64) << 11
    }
}

#[cfg(test)]
mod test {
    use super::*;

    #[test]
    fn matches_chrome() {
        let mut math = MathRandom::initialize(Some(1337));

        // During startup Chrome seems to call Math.random 8 times, so we also need to call it 8 times.
        for _ in 0..8 {
            math.random_double();
        }

        let expected = [
            0.1623809348128048,
            0.803143096276664,
            0.6202810541608373,
            0.4509504712894983,
            0.44412613159342396,
            0.7323221103230801,
            0.7364364137826004,
            0.35209346258118945,
            0.9414014356908873,
            0.6226657071438221,
        ];

        let rands: [f64; 10] = std::array::from_fn(|_| math.random_double());

        assert_eq!(expected, rands);
    }
}

// https://source.chromium.org/chromium/_/chromium/v8/v8/+/main:src/base/utils/random-number-generator.h;drc=99f606174481f6e2f4809c4262122a30a25583af;bpv=0;bpt=0
#[derive(Default, Debug)]
pub struct RandomNumberGenerator {
    state0: u64,
    state1: u64,
}

impl RandomNumberGenerator {
    pub fn new(seed: u64) -> Self {
        let mut this = Self::default();
        this.set_seed(seed);
        this
    }

    pub fn set_seed(&mut self, seed: u64) {
        let initial_seed = seed;
        self.state0 = Self::murmurhash3(initial_seed);
        self.state1 = Self::murmurhash3(!initial_seed);
    }

    pub fn next_u64(&mut self) -> u64 {
        Self::xorshift128(&mut self.state0, &mut self.state1)
    }

    pub fn next_double(&mut self) -> f64 {
        Self::to_double(Self::xorshift128(&mut self.state0, &mut self.state1))
    }

    pub(crate) fn state0(&self) -> u64 {
        self.state0
    }

    pub(crate) fn state1(&self) -> u64 {
        self.state1
    }

    pub fn to_double(random: u64) -> f64 {
        // Get a random [0,2**53) by dropping 11 bits of the state.
        let random_0_to_2_53: f64 = (random >> 11) as f64;
        // Map this to [0, 1) by division with 2**53
        let k2_53: f64 = (1_u64 << 53) as f64;
        random_0_to_2_53 / k2_53
    }

    pub fn xorshift128(state0: &mut u64, state1: &mut u64) -> u64 {
        let mut s1 = *state0;
        let s0 = *state1;
        *state0 = s0;
        s1 ^= s1 << 23;
        s1 ^= s1 >> 17;
        s1 ^= s0;
        s1 ^= s0 >> 26;
        *state1 = s1;
        s0.wrapping_add(s1)
    }

    pub fn murmurhash3(mut h: u64) -> u64 {
        h ^= h >> 33;
        h = h.wrapping_mul(0xFF51AFD7ED558CCDu64);
        h ^= h >> 33;
        h = h.wrapping_mul(0xC4CEB9FE1A85EC53u64);
        h ^= h >> 33;
        h
    }
}