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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.
+
+use rand_core::impls::{next_u64_via_u32, fill_bytes_via_next};
+use rand_core::le::read_u32_into;
+use rand_core::{SeedableRng, RngCore, Error};
+
+/// A xoshiro128** random number generator.
+///
+/// The xoshiro128** algorithm is not suitable for cryptographic purposes, but
+/// is very fast and has excellent statistical properties.
+///
+/// The algorithm used here is translated from [the `xoshiro128starstar.c`
+/// reference source code](http://xoshiro.di.unimi.it/xoshiro128starstar.c) by
+/// David Blackman and Sebastiano Vigna.
+#[derive(Debug, Clone)]
+pub struct Xoshiro128StarStar {
+ s: [u32; 4],
+}
+
+impl Xoshiro128StarStar {
+ /// Jump forward, equivalently to 2^64 calls to `next_u32()`.
+ ///
+ /// This can be used to generate 2^64 non-overlapping subsequences for
+ /// parallel computations.
+ ///
+ /// ```
+ /// # extern crate rand;
+ /// # extern crate rand_xoshiro;
+ /// # fn main() {
+ /// use rand::SeedableRng;
+ /// use rand_xoshiro::Xoroshiro128StarStar;
+ ///
+ /// let rng1 = Xoroshiro128StarStar::seed_from_u64(0);
+ /// let mut rng2 = rng1.clone();
+ /// rng2.jump();
+ /// let mut rng3 = rng2.clone();
+ /// rng3.jump();
+ /// # }
+ /// ```
+ pub fn jump(&mut self) {
+ impl_jump!(u32, self, [0x8764000b, 0xf542d2d3, 0x6fa035c3, 0x77f2db5b]);
+ }
+}
+
+impl SeedableRng for Xoshiro128StarStar {
+ type Seed = [u8; 16];
+
+ /// Create a new `Xoshiro128StarStar`. If `seed` is entirely 0, it will be
+ /// mapped to a different seed.
+ #[inline]
+ fn from_seed(seed: [u8; 16]) -> Xoshiro128StarStar {
+ deal_with_zero_seed!(seed, Self);
+ let mut state = [0; 4];
+ read_u32_into(&seed, &mut state);
+ Xoshiro128StarStar { s: state }
+ }
+
+ /// Seed a `Xoshiro128StarStar` from a `u64` using `SplitMix64`.
+ fn seed_from_u64(seed: u64) -> Xoshiro128StarStar {
+ from_splitmix!(seed)
+ }
+}
+
+impl RngCore for Xoshiro128StarStar {
+ #[inline]
+ fn next_u32(&mut self) -> u32 {
+ let result_starstar = starstar_u64!(self.s[0]);
+ impl_xoshiro_u32!(self);
+ result_starstar
+ }
+
+ #[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<(), Error> {
+ self.fill_bytes(dest);
+ Ok(())
+ }
+}
+
+#[cfg(test)]
+mod tests {
+ use super::*;
+
+ #[test]
+ fn reference() {
+ let mut rng = Xoshiro128StarStar::from_seed(
+ [1, 0, 0, 0, 2, 0, 0, 0, 3, 0, 0, 0, 4, 0, 0, 0]);
+ // These values were produced with the reference implementation:
+ // http://xoshiro.di.unimi.it/xoshiro128starstar.c
+ let expected = [
+ 5760, 40320, 70819200, 3297914139, 2480851620, 1792823698,
+ 4118739149, 1251203317, 1581886583, 1721184582,
+ ];
+ for &e in &expected {
+ assert_eq!(rng.next_u32(), e);
+ }
+ }
+}