Do you realise that this is equal to `pow(2.0, 970.0)` becaue the `-` is inside the power?

It would be better to just use `num::pow` or `num::powf` rather than the `f64` one, or just use `f64::MAX_VALUE` directly.

Also, I'm not quite sure what's this is testing: maybe it would be good to have a test like

```rust
// check this doesn't overflow
let n = f64::MAX_VALUE;
[n, -n, n].sum();
```

```rust
// check this does overflow
let n = f64::MAX_VALUE;
[n, -n, n, n / 10.0].sum();
```