1 files changed, 114 insertions, 0 deletions
diff --git a/rand/rand_xoshiro/src/xoshiro128plus.rs b/rand/rand_xoshiro/src/xoshiro128plus.rs
new file mode 100644
index 0000000..b0c7cc7
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+++ b/rand/rand_xoshiro/src/xoshiro128plus.rs
@@ -0,0 +1,114 @@
+// 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::{next_u64_via_u32, fill_bytes_via_next};
+use rand_core::le::read_u32_into;
+use rand_core::{SeedableRng, RngCore, Error};
+
+/// A xoshiro128+ random number generator.
+///
+/// The xoshiro128+ 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 `xoshiro128starstar.c`
+/// reference source code](http://xoshiro.di.unimi.it/xoshiro128starstar.c) by
+/// David Blackman and Sebastiano Vigna.
+#[derive(Debug, Clone)]
+pub struct Xoshiro128Plus {
+    s: [u32; 4],
+}
+
+impl Xoshiro128Plus {
+    /// Jump forward, equivalently to 2^64 calls to `next_u32()`.
+    ///
+    /// This can be used to generate 2^64 non-overlapping subsequences for
+    /// parallel computations.
+    ///
+    /// ```
+    /// # extern crate rand;
+    /// # extern crate rand_xoshiro;
+    /// # fn main() {
+    /// use rand::SeedableRng;
+    /// use rand_xoshiro::Xoroshiro128StarStar;
+    ///
+    /// let rng1 = Xoroshiro128StarStar::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!(u32, self, [0x8764000b, 0xf542d2d3, 0x6fa035c3, 0x77f2db5b]);
+    }
+}
+
+impl SeedableRng for Xoshiro128Plus {
+    type Seed = [u8; 16];
+
+    /// Create a new `Xoshiro128Plus`.  If `seed` is entirely 0, it will be
+    /// mapped to a different seed.
+    #[inline]
+    fn from_seed(seed: [u8; 16]) -> Xoshiro128Plus {
+        deal_with_zero_seed!(seed, Self);
+        let mut state = [0; 4];
+        read_u32_into(&seed, &mut state);
+        Xoshiro128Plus { s: state }
+    }
+
+    /// Seed a `Xoshiro128Plus` from a `u64` using `SplitMix64`.
+    fn seed_from_u64(seed: u64) -> Xoshiro128Plus {
+        from_splitmix!(seed)
+    }
+}
+
+impl RngCore for Xoshiro128Plus {
+    #[inline]
+    fn next_u32(&mut self) -> u32 {
+        let result_plus = self.s[0].wrapping_add(self.s[3]);
+        impl_xoshiro_u32!(self);
+        result_plus
+    }
+
+    #[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<(), Error> {
+        self.fill_bytes(dest);
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn reference() {
+        let mut rng = Xoshiro128Plus::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/xoshiro128plus.c
+        let expected = [
+            5, 12295, 25178119, 27286542, 39879690, 1140358681, 3276312097,
+            4110231701, 399823256, 2144435200,
+        ];
+        for &e in &expected {
+            assert_eq!(rng.next_u32(), e);
+        }
+    }
+}