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Diffstat (limited to 'rand/rand_xoshiro/src/xoshiro256plus.rs')
-rw-r--r-- | rand/rand_xoshiro/src/xoshiro256plus.rs | 133 |
1 files changed, 133 insertions, 0 deletions
diff --git a/rand/rand_xoshiro/src/xoshiro256plus.rs b/rand/rand_xoshiro/src/xoshiro256plus.rs new file mode 100644 index 0000000..08da5a8 --- /dev/null +++ b/rand/rand_xoshiro/src/xoshiro256plus.rs @@ -0,0 +1,133 @@ +// 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}; + +/// 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)] +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. + /// + /// ``` + /// # extern crate rand; + /// # extern crate rand_xoshiro; + /// # fn main() { + /// use rand::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); + } + } +} |