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// Copyright 2018 Developers of the Rand project.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
#[cfg(feature="serde1")] use serde::{Serialize, Deserialize};
use rand_core::le::read_u32_into;
use rand_core::impls::{fill_bytes_via_next, next_u64_via_u32};
use rand_core::{RngCore, SeedableRng};
/// A xoroshiro64** random number generator.
///
/// The xoshiro64** algorithm is not suitable for cryptographic purposes, but
/// is very fast and has excellent statistical properties.
///
/// The algorithm used here is translated from [the `xoroshiro64starstar.c`
/// reference source code](http://xoshiro.di.unimi.it/xoroshiro64starstar.c) by
/// David Blackman and Sebastiano Vigna.
#[allow(missing_copy_implementations)]
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature="serde1", derive(Serialize, Deserialize))]
pub struct Xoroshiro64StarStar {
s0: u32,
s1: u32,
}
impl RngCore for Xoroshiro64StarStar {
#[inline]
fn next_u32(&mut self) -> u32 {
let r = starstar_u32!(self.s0);
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 Xoroshiro64StarStar {
type Seed = [u8; 8];
/// Create a new `Xoroshiro64StarStar`. If `seed` is entirely 0, it will be
/// mapped to a different seed.
fn from_seed(seed: [u8; 8]) -> Xoroshiro64StarStar {
deal_with_zero_seed!(seed, Self);
let mut s = [0; 2];
read_u32_into(&seed, &mut s);
Xoroshiro64StarStar {
s0: s[0],
s1: s[1],
}
}
/// Seed a `Xoroshiro64StarStar` from a `u64` using `SplitMix64`.
fn seed_from_u64(seed: u64) -> Xoroshiro64StarStar {
from_splitmix!(seed)
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn reference() {
let mut rng = Xoroshiro64StarStar::from_seed([1, 0, 0, 0, 2, 0, 0, 0]);
// These values were produced with the reference implementation:
// http://xoshiro.di.unimi.it/xoshiro64starstar.c
let expected = [
3802928447, 813792938, 1618621494, 2955957307, 3252880261,
1129983909, 2539651700, 1327610908, 1757650787, 2763843748,
];
for &e in &expected {
assert_eq!(rng.next_u32(), e);
}
}
#[test]
fn zero_seed() {
let mut rng = Xoroshiro64StarStar::seed_from_u64(0);
assert_ne!(rng.next_u64(), 0);
}
}
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