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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::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);
}
}
}
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