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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::fill_bytes_via_next;
use rand_core::le::read_u64_into;
use rand_core::{SeedableRng, RngCore, Error};
use Seed512;
/// A xoshiro512+ random number generator.
///
/// The xoshiro512+ 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 `xoshiro512plus.c`
/// reference source code](http://xoshiro.di.unimi.it/xoshiro512plus.c) by
/// David Blackman and Sebastiano Vigna.
#[derive(Debug, Clone)]
pub struct Xoshiro512Plus {
s: [u64; 8],
}
impl Xoshiro512Plus {
/// Jump forward, equivalently to 2^256 calls to `next_u64()`.
///
/// This can be used to generate 2^256 non-overlapping subsequences for
/// parallel computations.
///
/// ```
/// # extern crate rand;
/// # extern crate rand_xoshiro;
/// # fn main() {
/// use rand::SeedableRng;
/// use rand_xoshiro::Xoshiro512Plus;
///
/// let rng1 = Xoshiro512Plus::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, [
0x33ed89b6e7a353f9, 0x760083d7955323be, 0x2837f2fbb5f22fae,
0x4b8c5674d309511c, 0xb11ac47a7ba28c25, 0xf1be7667092bcc1c,
0x53851efdb6df0aaf, 0x1ebbc8b23eaf25db
]);
}
}
impl SeedableRng for Xoshiro512Plus {
type Seed = Seed512;
/// Create a new `Xoshiro512Plus`. If `seed` is entirely 0, it will be
/// mapped to a different seed.
#[inline]
fn from_seed(seed: Seed512) -> Xoshiro512Plus {
deal_with_zero_seed!(seed, Self);
let mut state = [0; 8];
read_u64_into(&seed.0, &mut state);
Xoshiro512Plus { s: state }
}
/// Seed a `Xoshiro512Plus` from a `u64` using `SplitMix64`.
fn seed_from_u64(seed: u64) -> Xoshiro512Plus {
from_splitmix!(seed)
}
}
impl RngCore for Xoshiro512Plus {
#[inline]
fn next_u32(&mut self) -> u32 {
self.next_u64() as u32
}
#[inline]
fn next_u64(&mut self) -> u64 {
let result_plus = self.s[0].wrapping_add(self.s[2]);
impl_xoshiro_large!(self);
result_plus
}
#[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 = Xoshiro512Plus::from_seed(Seed512(
[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,
5, 0, 0, 0, 0, 0, 0, 0, 6, 0, 0, 0, 0, 0, 0, 0,
7, 0, 0, 0, 0, 0, 0, 0, 8, 0, 0, 0, 0, 0, 0, 0]));
// These values were produced with the reference implementation:
// http://xoshiro.di.unimi.it/xoshiro512plus.c
let expected = [
4, 8, 4113, 25169936, 52776585412635, 57174648719367,
9223482039571869716, 9331471677901559830, 9340533895746033672,
14078399799840753678,
];
for &e in &expected {
assert_eq!(rng.next_u64(), e);
}
}
}
|
