Implemented is_subset.

src/lib.rs

@@ -114,6 +114,25 @@ impl BitSet {
             .map(|block| block.count_ones() as usize)
             .sum();
     }
+
+    pub fn is_subset(&self, other: &BitSet) -> bool {
+        if self.len() > other.len() {
+            false
+        } else {
+            self.blocks.iter()
+                .all(|(key, block_a)| {
+                    match other.blocks.get(key) {
+                        Some(block_b) => block_a | block_b == *block_b,
+                        None => false
+                    }
+                })
+        }
+    }
+
+    #[inline]
+    pub fn is_superset(&self, other: &BitSet) -> bool {
+        other.is_subset(self)
+    }
 }
 
 impl Default for BitSet {
@@ -254,4 +273,16 @@ mod tests {
         assert_eq!(set.contains(4), true);
         assert_eq!(set.contains(5), true);
     }
+
+    #[test]
+    fn is_subset() {
+        let sup: BitSet = [1, 2, 3].iter().cloned().collect();
+        let mut set = BitSet::new();
+
+        assert_eq!(set.is_subset(&sup), true);
+        set.insert(2);
+        assert_eq!(set.is_subset(&sup), true);
+        set.insert(4);
+        assert_eq!(set.is_subset(&sup), false);
+    }
 }