xorshift64star

src/lib.rs

@@ -9,6 +9,7 @@ extern crate std;
 pub mod cachepadded;
 pub mod drop_guard;
 pub mod ptr;
+pub mod rand;
 #[cfg(feature = "alloc")]
 pub mod smallbox;
 pub mod util;

src/rand.rs

@@ -0,0 +1,32 @@
+use core::cell::Cell;
+
+/// A simple implementation of the XorShift64* pseudorandom number generator (PRNG).
+/// Based on the algorithm described by George Marsaglia.
+pub struct XorShift64Star {
+    state: Cell<u64>,
+}
+
+impl XorShift64Star {
+    /// Initializes the prng with a seed. Provided seed must be nonzero.
+    pub fn new(seed: u64) -> Self {
+        XorShift64Star {
+            state: Cell::new(seed),
+        }
+    }
+
+    /// Returns a pseudorandom number.
+    pub fn next(&self) -> u64 {
+        let mut x = self.state.get();
+        debug_assert_ne!(x, 0);
+        x ^= x >> 12;
+        x ^= x << 25;
+        x ^= x >> 27;
+        self.state.set(x);
+        x.wrapping_mul(0x2545_f491_4f6c_dd1d)
+    }
+
+    /// Return a pseudorandom number from `0..n`.
+    pub fn next_usize(&self, n: usize) -> usize {
+        (self.next() % n as u64) as usize
+    }
+}