@Override
    protected void onSerialize(Serializer buf) {
        super.onSerialize(buf);
        buf.putInt(null, numBits);
    }
Sets the number of bits to operate on.

@param numBits The number of bits.
@return This, to allow chaining.
searchlib/src/main/java/com/yahoo/searchlib/expression/UnaryBitFunctionNode.java