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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::fill_bytes_via_next;
+use rand_core::le::read_u64_into;
+use rand_core::{SeedableRng, RngCore, Error};
+
+/// A xoshiro256** random number generator.
+///
+/// The xoshiro256** algorithm is not suitable for cryptographic purposes, but
+/// is very fast and has excellent statistical properties.
+///
+/// The algorithm used here is translated from [the `xoshiro256starstar.c`
+/// reference source code](http://xoshiro.di.unimi.it/xoshiro256starstar.c) by
+/// David Blackman and Sebastiano Vigna.
+#[derive(Debug, Clone)]
+pub struct Xoshiro256StarStar {
+ s: [u64; 4],
+}
+
+impl Xoshiro256StarStar {
+ /// Jump forward, equivalently to 2^128 calls to `next_u64()`.
+ ///
+ /// This can be used to generate 2^128 non-overlapping subsequences for
+ /// parallel computations.
+ ///
+ /// ```
+ /// # extern crate rand;
+ /// # extern crate rand_xoshiro;
+ /// # fn main() {
+ /// use rand::SeedableRng;
+ /// use rand_xoshiro::Xoshiro256StarStar;
+ ///
+ /// let rng1 = Xoshiro256StarStar::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!(u64, self, [
+ 0x180ec6d33cfd0aba, 0xd5a61266f0c9392c,
+ 0xa9582618e03fc9aa, 0x39abdc4529b1661c
+ ]);
+ }
+
+ /// Jump forward, equivalently to 2^192 calls to `next_u64()`.
+ ///
+ /// This can be used to generate 2^64 starting points, from each of which
+ /// `jump()` will generate 2^64 non-overlapping subsequences for parallel
+ /// distributed computations.
+ pub fn long_jump(&mut self) {
+ impl_jump!(u64, self, [
+ 0x76e15d3efefdcbbf, 0xc5004e441c522fb3,
+ 0x77710069854ee241, 0x39109bb02acbe635
+ ]);
+ }
+}
+
+impl SeedableRng for Xoshiro256StarStar {
+ type Seed = [u8; 32];
+
+ /// Create a new `Xoshiro256StarStar`. If `seed` is entirely 0, it will be
+ /// mapped to a different seed.
+ #[inline]
+ fn from_seed(seed: [u8; 32]) -> Xoshiro256StarStar {
+ deal_with_zero_seed!(seed, Self);
+ let mut state = [0; 4];
+ read_u64_into(&seed, &mut state);
+ Xoshiro256StarStar { s: state }
+ }
+
+ /// Seed a `Xoshiro256StarStar` from a `u64` using `SplitMix64`.
+ fn seed_from_u64(seed: u64) -> Xoshiro256StarStar {
+ from_splitmix!(seed)
+ }
+}
+
+impl RngCore for Xoshiro256StarStar {
+ #[inline]
+ fn next_u32(&mut self) -> u32 {
+ self.next_u64() as u32
+ }
+
+ #[inline]
+ fn next_u64(&mut self) -> u64 {
+ let result_starstar = starstar_u64!(self.s[1]);
+ impl_xoshiro_u64!(self);
+ result_starstar
+ }
+
+ #[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 = Xoshiro256StarStar::from_seed(
+ [1, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0,
+ 3, 0, 0, 0, 0, 0, 0, 0, 4, 0, 0, 0, 0, 0, 0, 0]);
+ // These values were produced with the reference implementation:
+ // http://xoshiro.di.unimi.it/xoshiro128starstar.c
+ let expected = [
+ 11520, 0, 1509978240, 1215971899390074240, 1216172134540287360,
+ 607988272756665600, 16172922978634559625, 8476171486693032832,
+ 10595114339597558777, 2904607092377533576,
+ ];
+ for &e in &expected {
+ assert_eq!(rng.next_u64(), e);
+ }
+ }
+}