| // 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 good statistical properties, besides a low linear |
| /// complexity in the lowest bits. |
| /// |
| /// 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 Xoshiro128Plus { |
| s: [u32; 4], |
| } |
| |
| impl Xoshiro128Plus { |
| /// 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 Xoshiro128Plus { |
| type Seed = [u8; 16]; |
| |
| /// Create a new `Xoshiro128Plus`. If `seed` is entirely 0, it will be |
| /// mapped to a different seed. |
| #[inline] |
| fn from_seed(seed: [u8; 16]) -> Xoshiro128Plus { |
| deal_with_zero_seed!(seed, Self); |
| let mut state = [0; 4]; |
| read_u32_into(&seed, &mut state); |
| Xoshiro128Plus { s: state } |
| } |
| |
| /// Seed a `Xoshiro128Plus` from a `u64` using `SplitMix64`. |
| fn seed_from_u64(seed: u64) -> Xoshiro128Plus { |
| from_splitmix!(seed) |
| } |
| } |
| |
| impl RngCore for Xoshiro128Plus { |
| #[inline] |
| fn next_u32(&mut self) -> u32 { |
| let result_plus = self.s[0].wrapping_add(self.s[3]); |
| impl_xoshiro_u32!(self); |
| result_plus |
| } |
| |
| #[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 = Xoshiro128Plus::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/xoshiro128plus.c |
| let expected = [ |
| 5, 12295, 25178119, 27286542, 39879690, 1140358681, 3276312097, |
| 4110231701, 399823256, 2144435200, |
| ]; |
| for &e in &expected { |
| assert_eq!(rng.next_u32(), e); |
| } |
| } |
| } |