1 files changed, 52 insertions, 0 deletions
diff --git a/vendor/varisat/src/schedule/luby.rs b/vendor/varisat/src/schedule/luby.rs
new file mode 100644
index 000000000..9b44f7646
--- /dev/null
+++ b/vendor/varisat/src/schedule/luby.rs
@@ -0,0 +1,52 @@
+//! The reluctant doubling Luby sequence.
+//!
+//! This sequence is [A182105](https://oeis.org/A182105).
+
+/// Infinite iterator yielding the Luby sequence.
+pub struct LubySequence {
+    u: u64,
+    v: u64,
+}
+
+impl Default for LubySequence {
+    fn default() -> LubySequence {
+        LubySequence { u: 1, v: 1 }
+    }
+}
+
+impl LubySequence {
+    /// Yields the next number of hte Luby sequence.
+    pub fn advance(&mut self) -> u64 {
+        let result = self.v;
+
+        // Method by Knuth 2012
+        if (self.u & self.u.wrapping_neg()) == self.v {
+            self.u += 1;
+            self.v = 1;
+        } else {
+            self.v <<= 1;
+        }
+
+        result
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn luby_sequence() {
+        let mut luby = LubySequence::default();
+        let initial_terms: Vec<_> = std::iter::repeat_with(|| luby.advance()).take(64).collect();
+
+        assert_eq!(
+            initial_terms,
+            vec![
+                1, 1, 2, 1, 1, 2, 4, 1, 1, 2, 1, 1, 2, 4, 8, 1, 1, 2, 1, 1, 2, 4, 1, 1, 2, 1, 1, 2,
+                4, 8, 16, 1, 1, 2, 1, 1, 2, 4, 1, 1, 2, 1, 1, 2, 4, 8, 1, 1, 2, 1, 1, 2, 4, 1, 1,
+                2, 1, 1, 2, 4, 8, 16, 32, 1,
+            ]
+        )
+    }
+}