| // 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 byteorder::{ByteOrder, LittleEndian}; |
| use rand_core; |
| use rand_core::le::read_u32_into; |
| use rand_core::impls::{fill_bytes_via_next, next_u64_via_u32}; |
| use rand_core::{RngCore, SeedableRng}; |
| |
| /// A xoroshiro64* random number generator. |
| /// |
| /// The xoroshiro64* 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 `xoroshiro64star.c` |
| /// reference source code](http://xoshiro.di.unimi.it/xoroshiro64star.c) by |
| /// David Blackman and Sebastiano Vigna. |
| #[allow(missing_copy_implementations)] |
| #[derive(Debug, Clone)] |
| pub struct Xoroshiro64Star { |
| s0: u32, |
| s1: u32, |
| } |
| |
| impl RngCore for Xoroshiro64Star { |
| #[inline] |
| fn next_u32(&mut self) -> u32 { |
| let r = self.s0.wrapping_mul(0x9E3779BB); |
| impl_xoroshiro_u32!(self); |
| r |
| } |
| |
| #[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<(), rand_core::Error> { |
| self.fill_bytes(dest); |
| Ok(()) |
| } |
| } |
| |
| impl SeedableRng for Xoroshiro64Star { |
| type Seed = [u8; 8]; |
| |
| /// Create a new `Xoroshiro64Star`. If `seed` is entirely 0, it will be |
| /// mapped to a different seed. |
| fn from_seed(seed: [u8; 8]) -> Xoroshiro64Star { |
| deal_with_zero_seed!(seed, Self); |
| let mut s = [0; 2]; |
| read_u32_into(&seed, &mut s); |
| |
| Xoroshiro64Star { |
| s0: s[0], |
| s1: s[1], |
| } |
| } |
| |
| /// Seed a `Xoroshiro64Star` from a `u64` using `SplitMix64`. |
| fn seed_from_u64(seed: u64) -> Xoroshiro64Star { |
| let mut s = [0; 8]; |
| LittleEndian::write_u64(&mut s, seed); |
| Xoroshiro64Star::from_seed(s) |
| } |
| } |
| |
| #[cfg(test)] |
| mod tests { |
| use super::*; |
| |
| #[test] |
| fn reference() { |
| let mut rng = Xoroshiro64Star::from_seed([1, 0, 0, 0, 2, 0, 0, 0]); |
| // These values were produced with the reference implementation: |
| // http://xoshiro.di.unimi.it/xoshiro64star.c |
| let expected = [ |
| 2654435771, 327208753, 4063491769, 4259754937, 261922412, 168123673, |
| 552743735, 1672597395, 1031040050, 2755315674, |
| ]; |
| for &e in &expected { |
| assert_eq!(rng.next_u32(), e); |
| } |
| } |
| } |