summaryrefslogtreecommitdiff
path: root/rand/rand_xoshiro/src/xoroshiro128starstar.rs
diff options
context:
space:
mode:
Diffstat (limited to 'rand/rand_xoshiro/src/xoroshiro128starstar.rs')
-rw-r--r--rand/rand_xoshiro/src/xoroshiro128starstar.rs129
1 files changed, 129 insertions, 0 deletions
diff --git a/rand/rand_xoshiro/src/xoroshiro128starstar.rs b/rand/rand_xoshiro/src/xoroshiro128starstar.rs
new file mode 100644
index 0000000..2d27850
--- /dev/null
+++ b/rand/rand_xoshiro/src/xoroshiro128starstar.rs
@@ -0,0 +1,129 @@
+// 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;
+use rand_core::le::read_u64_into;
+use rand_core::impls::fill_bytes_via_next;
+use rand_core::{RngCore, SeedableRng};
+
+/// A xoroshiro128** random number generator.
+///
+/// The xoroshiro128** algorithm is not suitable for cryptographic purposes, but
+/// is very fast and has excellent statistical properties.
+///
+/// The algorithm used here is translated from [the `xoroshiro128starstar.c`
+/// reference source code](http://xoshiro.di.unimi.it/xoroshiro128starstar.c) by
+/// David Blackman and Sebastiano Vigna.
+#[allow(missing_copy_implementations)]
+#[derive(Debug, Clone)]
+pub struct Xoroshiro128StarStar {
+ s0: u64,
+ s1: u64,
+}
+
+impl Xoroshiro128StarStar {
+ /// Jump forward, equivalently to 2^64 calls to `next_u64()`.
+ ///
+ /// 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!(u64, self, [0xdf900294d8f554a5, 0x170865df4b3201fc]);
+ }
+
+ /// Jump forward, equivalently to 2^96 calls to `next_u64()`.
+ ///
+ /// This can be used to generate 2^32 starting points, from each of which
+ /// `jump()` will generate 2^32 non-overlapping subsequences for parallel
+ /// distributed computations.
+ pub fn long_jump(&mut self) {
+ impl_jump!(u64, self, [0xd2a98b26625eee7b, 0xdddf9b1090aa7ac1]);
+ }
+}
+
+impl RngCore for Xoroshiro128StarStar {
+ #[inline]
+ fn next_u32(&mut self) -> u32 {
+ self.next_u64() as u32
+ }
+
+ #[inline]
+ fn next_u64(&mut self) -> u64 {
+ let r = starstar_u64!(self.s0);
+ impl_xoroshiro_u64!(self);
+ r
+ }
+
+ #[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 Xoroshiro128StarStar {
+ type Seed = [u8; 16];
+
+ /// Create a new `Xoroshiro128StarStar`. If `seed` is entirely 0, it will be
+ /// mapped to a different seed.
+ fn from_seed(seed: [u8; 16]) -> Xoroshiro128StarStar {
+ deal_with_zero_seed!(seed, Self);
+ let mut s = [0; 2];
+ read_u64_into(&seed, &mut s);
+
+ Xoroshiro128StarStar {
+ s0: s[0],
+ s1: s[1],
+ }
+ }
+
+ /// Seed a `Xoroshiro128StarStar` from a `u64` using `SplitMix64`.
+ fn seed_from_u64(seed: u64) -> Xoroshiro128StarStar {
+ from_splitmix!(seed)
+ }
+}
+
+#[cfg(test)]
+mod tests {
+ use super::*;
+
+ #[test]
+ fn reference() {
+ let mut rng = Xoroshiro128StarStar::from_seed(
+ [1, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0]);
+ // These values were produced with the reference implementation:
+ // http://xoshiro.di.unimi.it/xoshiro128starstar.c
+ let expected = [
+ 5760, 97769243520, 9706862127477703552, 9223447511460779954,
+ 8358291023205304566, 15695619998649302768, 8517900938696309774,
+ 16586480348202605369, 6959129367028440372, 16822147227405758281,
+ ];
+ for &e in &expected {
+ assert_eq!(rng.next_u64(), e);
+ }
+ }
+}