vendor/rand/src/rngs/xoshiro256plusplus.rs

   1 // Copyright 2018 Developers of the Rand project.
   2 //
   3 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   4 // https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   5 // <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
   6 // option. This file may not be copied, modified, or distributed
   7 // except according to those terms.
   8
   9 #[cfg(feature="serde1")] use serde::{Serialize, Deserialize};
  10 use rand_core::impls::fill_bytes_via_next;
  11 use rand_core::le::read_u64_into;
  12 use rand_core::{SeedableRng, RngCore, Error};
  13
  14 /// A xoshiro256** random number generator.
  15 ///
  16 /// The xoshiro256** algorithm is not suitable for cryptographic purposes, but
  17 /// is very fast and has excellent statistical properties.
  18 ///
  19 /// The algorithm used here is translated from [the `xoshiro256plusplus.c`
  20 /// reference source code](http://xoshiro.di.unimi.it/xoshiro256plusplus.c) by
  21 /// David Blackman and Sebastiano Vigna.
  22 #[derive(Debug, Clone, PartialEq, Eq)]
  23 #[cfg_attr(feature="serde1", derive(Serialize, Deserialize))]
  24 pub struct Xoshiro256PlusPlus {
  25     s: [u64; 4],
  26 }
  27
  28 impl SeedableRng for Xoshiro256PlusPlus {
  29     type Seed = [u8; 32];
  30
  31     /// Create a new `Xoshiro256PlusPlus`.  If `seed` is entirely 0, it will be
  32     /// mapped to a different seed.
  33     #[inline]
  34     fn from_seed(seed: [u8; 32]) -> Xoshiro256PlusPlus {
  35         if seed.iter().all(|&x| x == 0) {
  36             return Self::seed_from_u64(0);
  37         }
  38         let mut state = [0; 4];
  39         read_u64_into(&seed, &mut state);
  40         Xoshiro256PlusPlus { s: state }
  41     }
  42
  43     /// Create a new `Xoshiro256PlusPlus` from a `u64` seed.
  44     ///
  45     /// This uses the SplitMix64 generator internally.
  46     fn seed_from_u64(mut state: u64) -> Self {
  47         const PHI: u64 = 0x9e3779b97f4a7c15;
  48         let mut seed = Self::Seed::default();
  49         for chunk in seed.as_mut().chunks_mut(8) {
  50             state = state.wrapping_add(PHI);
  51             let mut z = state;
  52             z = (z ^ (z >> 30)).wrapping_mul(0xbf58476d1ce4e5b9);
  53             z = (z ^ (z >> 27)).wrapping_mul(0x94d049bb133111eb);
  54             z = z ^ (z >> 31);
  55             chunk.copy_from_slice(&z.to_le_bytes());
  56         }
  57         Self::from_seed(seed)
  58     }
  59 }
  60
  61 impl RngCore for Xoshiro256PlusPlus {
  62     #[inline]
  63     fn next_u32(&mut self) -> u32 {
  64         // The lowest bits have some linear dependencies, so we use the
  65         // upper bits instead.
  66         (self.next_u64() >> 32) as u32
  67     }
  68
  69     #[inline]
  70     fn next_u64(&mut self) -> u64 {
  71         let result_plusplus = self.s[0]
  72             .wrapping_add(self.s[3])
  73             .rotate_left(23)
  74             .wrapping_add(self.s[0]);
  75
  76         let t = self.s[1] << 17;
  77
  78         self.s[2] ^= self.s[0];
  79         self.s[3] ^= self.s[1];
  80         self.s[1] ^= self.s[2];
  81         self.s[0] ^= self.s[3];
  82
  83         self.s[2] ^= t;
  84
  85         self.s[3] = self.s[3].rotate_left(45);
  86
  87         result_plusplus
  88     }
  89
  90     #[inline]
  91     fn fill_bytes(&mut self, dest: &mut [u8]) {
  92         fill_bytes_via_next(self, dest);
  93     }
  94
  95     #[inline]
  96     fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> {
  97         self.fill_bytes(dest);
  98         Ok(())
  99     }
 100 }
 101
 102 #[cfg(test)]
 103 mod tests {
 104     use super::*;
 105
 106     #[test]
 107     fn reference() {
 108         let mut rng = Xoshiro256PlusPlus::from_seed(
 109             [1, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0,
 110              3, 0, 0, 0, 0, 0, 0, 0, 4, 0, 0, 0, 0, 0, 0, 0]);
 111         // These values were produced with the reference implementation:
 112         // http://xoshiro.di.unimi.it/xoshiro256plusplus.c
 113         let expected = [
 114             41943041, 58720359, 3588806011781223, 3591011842654386,
 115             9228616714210784205, 9973669472204895162, 14011001112246962877,
 116             12406186145184390807, 15849039046786891736, 10450023813501588000,
 117         ];
 118         for &e in &expected {
 119             assert_eq!(rng.next_u64(), e);
 120         }
 121     }
 122 }