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// 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);
}
}
}
|
