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SmallRng: Replace PCG algorithm with xoshiro{128,256}++ #1038
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b41b4fd
SmallRng: Replace PCG algorithm with xoshiro{128,256}++
vks dd95631
SmallRng: Recommend `rand_chacha` for performance
vks 616ea87
Update changelog
vks 25ea6c1
Revise `SmallRng` advise
vks 0c8dc1c
Fix dead links
vks 530cd27
xoshiro256++: Prefer upper bits
vks 02aafbd
Migrate `SmallRng::seed_from_u64` from PCG32 to SplitMix64
vks a260f2c
Improve `SmallRng` advise
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Original file line number | Diff line number | Diff line change |
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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. | ||
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#[cfg(feature="serde1")] use serde::{Serialize, Deserialize}; | ||
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}; | ||
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/// A xoshiro128++ random number generator. | ||
/// | ||
/// The xoshiro128++ algorithm is not suitable for cryptographic purposes, but | ||
/// is very fast and has excellent statistical properties. | ||
/// | ||
/// The algorithm used here is translated from [the `xoshiro128plusplus.c` | ||
/// reference source code](http://xoshiro.di.unimi.it/xoshiro128plusplus.c) by | ||
/// David Blackman and Sebastiano Vigna. | ||
#[derive(Debug, Clone, PartialEq, Eq)] | ||
#[cfg_attr(feature="serde1", derive(Serialize, Deserialize))] | ||
pub struct Xoshiro128PlusPlus { | ||
s: [u32; 4], | ||
} | ||
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impl SeedableRng for Xoshiro128PlusPlus { | ||
type Seed = [u8; 16]; | ||
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/// Create a new `Xoshiro128PlusPlus`. If `seed` is entirely 0, it will be | ||
/// mapped to a different seed. | ||
#[inline] | ||
fn from_seed(seed: [u8; 16]) -> Xoshiro128PlusPlus { | ||
if seed.iter().all(|&x| x == 0) { | ||
return Self::seed_from_u64(0); | ||
} | ||
let mut state = [0; 4]; | ||
read_u32_into(&seed, &mut state); | ||
Xoshiro128PlusPlus { s: state } | ||
} | ||
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/// Create a new `Xoshiro128PlusPlus` from a `u64` seed. | ||
/// | ||
/// This uses the SplitMix64 generator internally. | ||
fn seed_from_u64(mut state: u64) -> Self { | ||
const PHI: u64 = 0x9e3779b97f4a7c15; | ||
let mut seed = Self::Seed::default(); | ||
for chunk in seed.as_mut().chunks_mut(8) { | ||
state = state.wrapping_add(PHI); | ||
let mut z = state; | ||
z = (z ^ (z >> 30)).wrapping_mul(0xbf58476d1ce4e5b9); | ||
z = (z ^ (z >> 27)).wrapping_mul(0x94d049bb133111eb); | ||
z = z ^ (z >> 31); | ||
chunk.copy_from_slice(&z.to_le_bytes()); | ||
} | ||
Self::from_seed(seed) | ||
} | ||
} | ||
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impl RngCore for Xoshiro128PlusPlus { | ||
#[inline] | ||
fn next_u32(&mut self) -> u32 { | ||
let result_starstar = self.s[0] | ||
.wrapping_add(self.s[3]) | ||
.rotate_left(7) | ||
.wrapping_add(self.s[0]); | ||
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let t = self.s[1] << 9; | ||
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self.s[2] ^= self.s[0]; | ||
self.s[3] ^= self.s[1]; | ||
self.s[1] ^= self.s[2]; | ||
self.s[0] ^= self.s[3]; | ||
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self.s[2] ^= t; | ||
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self.s[3] = self.s[3].rotate_left(11); | ||
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result_starstar | ||
} | ||
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#[inline] | ||
fn next_u64(&mut self) -> u64 { | ||
next_u64_via_u32(self) | ||
} | ||
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#[inline] | ||
fn fill_bytes(&mut self, dest: &mut [u8]) { | ||
fill_bytes_via_next(self, dest); | ||
} | ||
|
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#[inline] | ||
fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> { | ||
self.fill_bytes(dest); | ||
Ok(()) | ||
} | ||
} | ||
|
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#[cfg(test)] | ||
mod tests { | ||
use super::*; | ||
|
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#[test] | ||
fn reference() { | ||
let mut rng = Xoshiro128PlusPlus::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/xoshiro128plusplus.c | ||
let expected = [ | ||
641, 1573767, 3222811527, 3517856514, 836907274, 4247214768, | ||
3867114732, 1355841295, 495546011, 621204420, | ||
]; | ||
for &e in &expected { | ||
assert_eq!(rng.next_u32(), e); | ||
} | ||
} | ||
} |
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Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,122 @@ | ||
// 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}; | ||
|
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/// A xoshiro256** random number generator. | ||
/// | ||
/// The xoshiro256** algorithm is not suitable for cryptographic purposes, but | ||
/// is very fast and has excellent statistical properties. | ||
/// | ||
/// The algorithm used here is translated from [the `xoshiro256plusplus.c` | ||
/// reference source code](http://xoshiro.di.unimi.it/xoshiro256plusplus.c) by | ||
/// David Blackman and Sebastiano Vigna. | ||
#[derive(Debug, Clone, PartialEq, Eq)] | ||
#[cfg_attr(feature="serde1", derive(Serialize, Deserialize))] | ||
pub struct Xoshiro256PlusPlus { | ||
s: [u64; 4], | ||
} | ||
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impl SeedableRng for Xoshiro256PlusPlus { | ||
type Seed = [u8; 32]; | ||
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/// Create a new `Xoshiro256PlusPlus`. If `seed` is entirely 0, it will be | ||
/// mapped to a different seed. | ||
#[inline] | ||
fn from_seed(seed: [u8; 32]) -> Xoshiro256PlusPlus { | ||
if seed.iter().all(|&x| x == 0) { | ||
return Self::seed_from_u64(0); | ||
} | ||
let mut state = [0; 4]; | ||
read_u64_into(&seed, &mut state); | ||
Xoshiro256PlusPlus { s: state } | ||
} | ||
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/// Create a new `Xoshiro256PlusPlus` from a `u64` seed. | ||
/// | ||
/// This uses the SplitMix64 generator internally. | ||
fn seed_from_u64(mut state: u64) -> Self { | ||
const PHI: u64 = 0x9e3779b97f4a7c15; | ||
let mut seed = Self::Seed::default(); | ||
for chunk in seed.as_mut().chunks_mut(8) { | ||
state = state.wrapping_add(PHI); | ||
let mut z = state; | ||
z = (z ^ (z >> 30)).wrapping_mul(0xbf58476d1ce4e5b9); | ||
z = (z ^ (z >> 27)).wrapping_mul(0x94d049bb133111eb); | ||
z = z ^ (z >> 31); | ||
chunk.copy_from_slice(&z.to_le_bytes()); | ||
} | ||
Self::from_seed(seed) | ||
} | ||
} | ||
|
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impl RngCore for Xoshiro256PlusPlus { | ||
#[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 | ||
} | ||
|
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#[inline] | ||
fn next_u64(&mut self) -> u64 { | ||
let result_plusplus = self.s[0] | ||
.wrapping_add(self.s[3]) | ||
.rotate_left(23) | ||
.wrapping_add(self.s[0]); | ||
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let t = self.s[1] << 17; | ||
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self.s[2] ^= self.s[0]; | ||
self.s[3] ^= self.s[1]; | ||
self.s[1] ^= self.s[2]; | ||
self.s[0] ^= self.s[3]; | ||
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self.s[2] ^= t; | ||
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self.s[3] = self.s[3].rotate_left(45); | ||
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result_plusplus | ||
} | ||
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#[inline] | ||
fn fill_bytes(&mut self, dest: &mut [u8]) { | ||
fill_bytes_via_next(self, dest); | ||
} | ||
|
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#[inline] | ||
fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> { | ||
self.fill_bytes(dest); | ||
Ok(()) | ||
} | ||
} | ||
|
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#[cfg(test)] | ||
mod tests { | ||
use super::*; | ||
|
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#[test] | ||
fn reference() { | ||
let mut rng = Xoshiro256PlusPlus::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/xoshiro256plusplus.c | ||
let expected = [ | ||
41943041, 58720359, 3588806011781223, 3591011842654386, | ||
9228616714210784205, 9973669472204895162, 14011001112246962877, | ||
12406186145184390807, 15849039046786891736, 10450023813501588000, | ||
]; | ||
for &e in &expected { | ||
assert_eq!(rng.next_u64(), e); | ||
} | ||
} | ||
} |
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