I wanted to actually use the functionality which multiplies two u64 and only obtain the lowest 64 bits of the result, like so

```
let a: u64 = 1u64 << 2;
let b: u64 = 1u64 << 63;
let c: u64 = a*b;
```

But I got an error saying "thread 'main' panicked at 'attempt to multiply with overflow'" -- how do I disable this?