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Diffstat (limited to 'rand/rand_xoshiro/src/xoroshiro64star.rs')
-rw-r--r-- | rand/rand_xoshiro/src/xoroshiro64star.rs | 97 |
1 files changed, 97 insertions, 0 deletions
diff --git a/rand/rand_xoshiro/src/xoroshiro64star.rs b/rand/rand_xoshiro/src/xoroshiro64star.rs new file mode 100644 index 0000000..86338fd --- /dev/null +++ b/rand/rand_xoshiro/src/xoroshiro64star.rs @@ -0,0 +1,97 @@ +// 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 byteorder::{ByteOrder, LittleEndian}; +use rand_core; +use rand_core::le::read_u32_into; +use rand_core::impls::{fill_bytes_via_next, next_u64_via_u32}; +use rand_core::{RngCore, SeedableRng}; + +/// A xoroshiro64* random number generator. +/// +/// The xoroshiro64* 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 `xoroshiro64star.c` +/// reference source code](http://xoshiro.di.unimi.it/xoroshiro64star.c) by +/// David Blackman and Sebastiano Vigna. +#[allow(missing_copy_implementations)] +#[derive(Debug, Clone)] +pub struct Xoroshiro64Star { + s0: u32, + s1: u32, +} + +impl RngCore for Xoroshiro64Star { + #[inline] + fn next_u32(&mut self) -> u32 { + let r = self.s0.wrapping_mul(0x9E3779BB); + impl_xoroshiro_u32!(self); + r + } + + #[inline] + fn next_u64(&mut self) -> u64 { + next_u64_via_u32(self) + } + + #[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<(), rand_core::Error> { + self.fill_bytes(dest); + Ok(()) + } +} + +impl SeedableRng for Xoroshiro64Star { + type Seed = [u8; 8]; + + /// Create a new `Xoroshiro64Star`. If `seed` is entirely 0, it will be + /// mapped to a different seed. + fn from_seed(seed: [u8; 8]) -> Xoroshiro64Star { + deal_with_zero_seed!(seed, Self); + let mut s = [0; 2]; + read_u32_into(&seed, &mut s); + + Xoroshiro64Star { + s0: s[0], + s1: s[1], + } + } + + /// Seed a `Xoroshiro64Star` from a `u64` using `SplitMix64`. + fn seed_from_u64(seed: u64) -> Xoroshiro64Star { + let mut s = [0; 8]; + LittleEndian::write_u64(&mut s, seed); + Xoroshiro64Star::from_seed(s) + } +} + +#[cfg(test)] +mod tests { + use super::*; + + #[test] + fn reference() { + let mut rng = Xoroshiro64Star::from_seed([1, 0, 0, 0, 2, 0, 0, 0]); + // These values were produced with the reference implementation: + // http://xoshiro.di.unimi.it/xoshiro64star.c + let expected = [ + 2654435771, 327208753, 4063491769, 4259754937, 261922412, 168123673, + 552743735, 1672597395, 1031040050, 2755315674, + ]; + for &e in &expected { + assert_eq!(rng.next_u32(), e); + } + } +} |