Add XorShift64-based pseudo random number generator implementation

src/random/prng.rs

@@ -0,0 +1,41 @@
+use std::time::{SystemTime, UNIX_EPOCH};
+
+use crate::random::Rng;
+
+/// Simple XorShift64-based pseudo random number generator.
+#[derive(Clone)]
+pub struct Prng {
+    state: u64,
+}
+
+impl Prng {
+    /// Create a new generator from the given seed.
+    pub fn new(seed: u64) -> Self {
+        Self { state: seed }
+    }
+
+    /// Create a generator seeded from the current time.
+    pub fn from_entropy() -> Self {
+        let nanos = SystemTime::now()
+            .duration_since(UNIX_EPOCH)
+            .unwrap()
+            .as_nanos() as u64;
+        Self::new(nanos)
+    }
+}
+
+impl Rng for Prng {
+    fn next_u64(&mut self) -> u64 {
+        let mut x = self.state;
+        x ^= x << 13;
+        x ^= x >> 7;
+        x ^= x << 17;
+        self.state = x;
+        x
+    }
+}
+
+/// Convenience constructor using system entropy.
+pub fn rng() -> Prng {
+    Prng::from_entropy()
+}