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Diffstat (limited to 'rand/rand_xoshiro/src/xoshiro512plus.rs')
-rw-r--r-- | rand/rand_xoshiro/src/xoshiro512plus.rs | 124 |
1 files changed, 124 insertions, 0 deletions
diff --git a/rand/rand_xoshiro/src/xoshiro512plus.rs b/rand/rand_xoshiro/src/xoshiro512plus.rs new file mode 100644 index 0000000..fe982e4 --- /dev/null +++ b/rand/rand_xoshiro/src/xoshiro512plus.rs @@ -0,0 +1,124 @@ +// 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); + } + } +} |