android/guava/src/com/google/common/primitives/UnsignedLong.java
public UnsignedLong mod(UnsignedLong val) {
    return fromLongBits(UnsignedLongs.remainder(value, checkNotNull(val).value));
  }
public UnsignedLong mod(UnsignedLong val) {
    return fromLongBits(UnsignedLongs.remainder(value, checkNotNull(val).value));
  }
Returns this modulo {@code val}.

@since 14.0