| // 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); |
| } |
| } |
| } |