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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.
#[cfg(feature="serde1")] use serde::{Serialize, Deserialize};
use rand_core::impls::fill_bytes_via_next;
use rand_core::le::read_u64_into;
use rand_core::{SeedableRng, RngCore, Error};
/// A xoshiro256+ random number generator.
///
/// The xoshiro256+ 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 `xoshiro256plus.c`
/// reference source code](http://xoshiro.di.unimi.it/xoshiro256plus.c) by
/// David Blackman and Sebastiano Vigna.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature="serde1", derive(Serialize, Deserialize))]
pub struct Xoshiro256Plus {
s: [u64; 4],
}
impl Xoshiro256Plus {
/// Jump forward, equivalently to 2^128 calls to `next_u64()`.
///
/// This can be used to generate 2^128 non-overlapping subsequences for
/// parallel computations.
///
/// ```
/// use rand_xoshiro::rand_core::SeedableRng;
/// use rand_xoshiro::Xoshiro256Plus;
///
/// let rng1 = Xoshiro256Plus::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, [
0x180ec6d33cfd0aba, 0xd5a61266f0c9392c,
0xa9582618e03fc9aa, 0x39abdc4529b1661c
]);
}
/// Jump forward, equivalently to 2^192 calls to `next_u64()`.
///
/// This can be used to generate 2^64 starting points, from each of which
/// `jump()` will generate 2^64 non-overlapping subsequences for parallel
/// distributed computations.
pub fn long_jump(&mut self) {
impl_jump!(u64, self, [
0x76e15d3efefdcbbf, 0xc5004e441c522fb3,
0x77710069854ee241, 0x39109bb02acbe635
]);
}
}
impl SeedableRng for Xoshiro256Plus {
type Seed = [u8; 32];
/// Create a new `Xoshiro256Plus`. If `seed` is entirely 0, it will be
/// mapped to a different seed.
#[inline]
fn from_seed(seed: [u8; 32]) -> Xoshiro256Plus {
deal_with_zero_seed!(seed, Self);
let mut state = [0; 4];
read_u64_into(&seed, &mut state);
Xoshiro256Plus { s: state }
}
/// Seed a `Xoshiro256Plus` from a `u64` using `SplitMix64`.
fn seed_from_u64(seed: u64) -> Xoshiro256Plus {
from_splitmix!(seed)
}
}
impl RngCore for Xoshiro256Plus {
#[inline]
fn next_u32(&mut self) -> u32 {
// The 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 result_plus = self.s[0].wrapping_add(self.s[3]);
impl_xoshiro_u64!(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 = Xoshiro256Plus::from_seed(
[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]);
// These values were produced with the reference implementation:
// http://xoshiro.di.unimi.it/xoshiro256plus.c
let expected = [
5, 211106232532999, 211106635186183, 9223759065350669058,
9250833439874351877, 13862484359527728515, 2346507365006083650,
1168864526675804870, 34095955243042024, 3466914240207415127,
];
for &e in &expected {
assert_eq!(rng.next_u64(), e);
}
}
}
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