New function to extend from another bitset.

src/lib.rs

@@ -34,7 +34,7 @@ impl Hasher for BitHasher {
 
 type BitBuildHasher = BuildHasherDefault<BitHasher>;
 type BitHashMap<K, V> = HashMap<K, V, BitBuildHasher>;
-type BitHashSet<T> = HashSet<T, BitBuildHasher>;
+// type BitHashSet<T> = HashSet<T, BitBuildHasher>;
 
 type Block = u64;
 type Storage = BitHashMap<u64, Block>;
@@ -128,6 +128,18 @@ impl BitSet {
             Some(block) => (block & (1 << bit)) != 0,
         }
     }
+
+    #[inline]
+    pub fn extend_from_bitset(&mut self, other: &Self) {
+        for (key, value) in &other.blocks {
+            *self.blocks.entry(*key).or_insert(0) |= value;
+        }
+
+        self.nbits = self.blocks
+            .values()
+            .map(|block| block.count_ones() as usize)
+            .sum();
+    }
 }
 
 impl Default for BitSet {