| // 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 good statistical properties, besides a low linear |
| /// complexity in the lowest bits. |
| /// |
| /// The algorithm used here is translated from [the `xoroshiro128plus.c` |
| /// reference source code](http://xoshiro.di.unimi.it/xoroshiro128plus.c) by |
| /// David Blackman and Sebastiano Vigna. |
| #[allow(missing_copy_implementations)] |
| #[derive(Debug, Clone)] |
| pub struct Xoroshiro128Plus { |
| s0: u64, |
| s1: u64, |
| } |
| |
| impl Xoroshiro128Plus { |
| /// 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::Xoroshiro128Plus; |
| /// |
| /// let rng1 = Xoroshiro128Plus::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 Xoroshiro128Plus { |
| #[inline] |
| fn next_u32(&mut self) -> u32 { |
| // The two lowest bits have some linear dependencies, so we use the |
| // upper bits instead. |
| (self.next_u64() >> 32) as u32 |
| } |
| |
| #[inline] |
| fn next_u64(&mut self) -> u64 { |
| let r = self.s0.wrapping_add(self.s1); |
| 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 Xoroshiro128Plus { |
| type Seed = [u8; 16]; |
| |
| /// Create a new `Xoroshiro128Plus`. If `seed` is entirely 0, it will be |
| /// mapped to a different seed. |
| fn from_seed(seed: [u8; 16]) -> Xoroshiro128Plus { |
| deal_with_zero_seed!(seed, Self); |
| let mut s = [0; 2]; |
| read_u64_into(&seed, &mut s); |
| |
| Xoroshiro128Plus { |
| s0: s[0], |
| s1: s[1], |
| } |
| } |
| |
| /// Seed a `Xoroshiro128Plus` from a `u64` using `SplitMix64`. |
| fn seed_from_u64(seed: u64) -> Xoroshiro128Plus { |
| from_splitmix!(seed) |
| } |
| } |
| |
| #[cfg(test)] |
| mod tests { |
| use super::*; |
| |
| #[test] |
| fn reference() { |
| let mut rng = Xoroshiro128Plus::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 = [ |
| 3, 412333834243, 2360170716294286339, 9295852285959843169, |
| 2797080929874688578, 6019711933173041966, 3076529664176959358, |
| 3521761819100106140, 7493067640054542992, 920801338098114767, |
| ]; |
| for &e in &expected { |
| assert_eq!(rng.next_u64(), e); |
| } |
| } |
| } |