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# signalingNaN

A signaling NaN (“not a number”).

```
static var signalingNaN: Double { get }
```

## Discussion

The default IEEE 754 behavior of operations involving a signaling NaN is
to raise the Invalid flag in the floating-point environment and return a
quiet NaN.

Operations on types conforming to the `FloatingPoint` protocol should
support this behavior, but they might also support other options. For
example, it would be reasonable to implement alternative operations in
which operating on a signaling NaN triggers a runtime error or results
in a diagnostic for debugging purposes. Types that implement alternative
behaviors for a signaling NaN must document the departure.

Other than these signaling operations, a signaling NaN behaves in the
same manner as a quiet NaN.

---

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