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```
``````// Copyright 2018 Developers of the Rand project.
//
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use byteorder::{ByteOrder, LittleEndian};
use rand_core;
use rand_core::impls::{fill_bytes_via_next, next_u64_via_u32};
use rand_core::{RngCore, SeedableRng};

/// A xoroshiro64* random number generator.
///
/// The xoroshiro64* algorithm is not suitable for cryptographic purposes, but
/// is very fast and has good statistical properties, besides a low linear
/// complexity in the lowest bits.
///
/// The algorithm used here is translated from [the `xoroshiro64star.c`
/// reference source code](http://xoshiro.di.unimi.it/xoroshiro64star.c) by
/// David Blackman and Sebastiano Vigna.
#[allow(missing_copy_implementations)]
#[derive(Debug, Clone)]
pub struct Xoroshiro64Star {
s0: u32,
s1: u32,
}

impl RngCore for Xoroshiro64Star {
#[inline]
fn next_u32(&mut self) -> u32 {
let r = self.s0.wrapping_mul(0x9E3779BB);
impl_xoroshiro_u32!(self);
r
}

#[inline]
fn next_u64(&mut self) -> u64 {
next_u64_via_u32(self)
}

#[inline]
fn fill_bytes(&mut self, dest: &mut [u8]) {
fill_bytes_via_next(self, dest);
}

#[inline]
fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), rand_core::Error> {
self.fill_bytes(dest);
Ok(())
}
}

impl SeedableRng for Xoroshiro64Star {
type Seed = [u8; 8];

/// Create a new `Xoroshiro64Star`.  If `seed` is entirely 0, it will be
/// mapped to a different seed.
fn from_seed(seed: [u8; 8]) -> Xoroshiro64Star {
deal_with_zero_seed!(seed, Self);
let mut s = [0; 2];

Xoroshiro64Star {
s0: s[0],
s1: s[1],
}
}

/// Seed a `Xoroshiro64Star` from a `u64` using `SplitMix64`.
fn seed_from_u64(seed: u64) -> Xoroshiro64Star {
let mut s = [0; 8];
LittleEndian::write_u64(&mut s, seed);
Xoroshiro64Star::from_seed(s)
}
}

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

#[test]
fn reference() {
let mut rng = Xoroshiro64Star::from_seed([1, 0, 0, 0, 2, 0, 0, 0]);
// These values were produced with the reference implementation:
// http://xoshiro.di.unimi.it/xoshiro64star.c
let expected = [
2654435771, 327208753, 4063491769, 4259754937, 261922412, 168123673,
552743735, 1672597395, 1031040050, 2755315674,
];
for &e in &expected {
assert_eq!(rng.next_u32(), e);
}
}
}
``````