Add BitAnd impl for BooleanBitfield

eth2/utils/boolean-bitfield/src/lib.rs

@@ -114,6 +114,28 @@ impl cmp::PartialEq for BooleanBitfield {
     }
 }
 
+/// Create a new bitfield that is a union of two other bitfields.
+///
+/// For example `union(0101, 1000) == 1101`
+impl std::ops::BitAnd for BooleanBitfield {
+    type Output = Self;
+
+    fn bitand(self, other: Self) -> Self {
+        let (biggest, smallest) = if self.len() > other.len() {
+            (&self, &other)
+        } else {
+            (&other, &self)
+        };
+        let mut new = biggest.clone();
+        for i in 0..smallest.len() {
+            if let Ok(true) = smallest.get(i) {
+                new.set(i, true);
+            }
+        }
+        new
+    }
+}
+
 impl ssz::Encodable for BooleanBitfield {
     // ssz_append encodes Self according to the `ssz` spec.
     fn ssz_append(&self, s: &mut ssz::SszStream) {
@@ -375,4 +397,12 @@ mod tests {
         let (decoded, _) = BooleanBitfield::ssz_decode(&ssz, 0).unwrap();
         assert_eq!(original, decoded);
     }
+
+    #[test]
+    fn test_bitand() {
+        let a = BooleanBitfield::from_bytes(&vec![2, 8, 1][..]);
+        let b = BooleanBitfield::from_bytes(&vec![4, 8, 16][..]);
+        let c = BooleanBitfield::from_bytes(&vec![6, 8, 17][..]);
+        assert_eq!(c, a & b);
+    }
 }