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use rand_core::impls::fill_bytes_via_next;
use rand_core::le::read_u64_into;
use rand_core::{Error, RngCore, SeedableRng};
use crate::xoroshiro::Seed512;
/// A xoshiro512** random number generator.
///
/// The xoshiro512** algorithm is not suitable for cryptographic purposes, but
/// is very fast and has excellent statistical properties.
///
/// The algorithm used here is translated from [the `xoshiro512starstar.c`
/// reference source code](http://xoshiro.di.unimi.it/xoshiro512starstar.c) by
/// David Blackman and Sebastiano Vigna.
#[cfg_attr(not(target_os = "cuda"), derive(Copy, cust_core::DeviceCopy))]
#[derive(Debug, Clone, PartialEq, Eq)]
#[repr(C)]
pub struct Xoshiro512StarStar {
s: [u64; 8],
}
impl Xoshiro512StarStar {
/// Jump forward, equivalently to 2^256 calls to `next_u64()`.
///
/// This can be used to generate 2^256 non-overlapping subsequences for
/// parallel computations.
///
/// ```
/// use rand_xoshiro::rand_core::SeedableRng;
/// use rand_xoshiro::Xoshiro512StarStar;
///
/// let rng1 = Xoshiro512StarStar::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
]
);
}
/// Jump forward, equivalently to 2^384 calls to `next_u64()`.
///
/// This can be used to generate 2^128 starting points, from each of which
/// `jump()` will generate 2^128 non-overlapping subsequences for parallel
/// distributed computations.
pub fn long_jump(&mut self) {
impl_jump!(
u64,
self,
[
0x11467fef8f921d28,
0xa2a819f2e79c8ea8,
0xa8299fc284b3959a,
0xb4d347340ca63ee1,
0x1cb0940bedbff6ce,
0xd956c5c4fa1f8e17,
0x915e38fd4eda93bc,
0x5b3ccdfa5d7daca5
]
);
}
/// Initializes multiple RNG states such that each state corresponds to a subsequence
/// separated by `2**256` steps from eachother in the main sequence. This ensures that as long as
/// no state requests more than `2**256` random numbers, the states are guaranteed to be fully independent.
#[cfg(not(target_os = "cuda"))]
pub fn initialize_states(seed: u64, num_states: usize) -> Vec<Self> {
impl_initialize_states!(seed, num_states)
}
}
impl SeedableRng for Xoshiro512StarStar {
type Seed = Seed512;
/// Create a new `Xoshiro512StarStar`. If `seed` is entirely 0, it will be
/// mapped to a different seed.
#[inline]
fn from_seed(seed: Seed512) -> Xoshiro512StarStar {
deal_with_zero_seed!(seed, Self);
let mut state = [0; 8];
read_u64_into(&seed.0, &mut state);
Xoshiro512StarStar { s: state }
}
/// Seed a `Xoshiro512StarStar` from a `u64` using `SplitMix64`.
fn seed_from_u64(seed: u64) -> Xoshiro512StarStar {
from_splitmix!(seed)
}
}
impl RngCore for Xoshiro512StarStar {
#[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_starstar = starstar_u64!(self.s[1]);
impl_xoshiro_large!(self);
result_starstar
}
#[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 = Xoshiro512StarStar::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/xoshiro512starstar.c
let expected = [
11520,
0,
23040,
23667840,
144955163520,
303992986974289920,
25332796375735680,
296904390158016,
13911081092387501979,
15304787717237593024,
];
for &e in &expected {
assert_eq!(rng.next_u64(), e);
}
}
}