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# add(_:ordering:)

Perform an atomic add operation and return the old and new value,
applying the specified memory ordering.

```
@discardableResult func add(_ operand: UInt8, ordering: AtomicUpdateOrdering) -> (oldValue: UInt8, newValue: UInt8)
```

## Parameters

`operand`

An integer value.

`ordering`

The memory ordering to apply on this operation.

## Return Value

A tuple containing the original value before the operation and
the new value after the operation.

## Discussion> Note: This operation checks for overflow at runtime and will trap if an
> overflow does occur. In `-Ounchecked` builds, overflow checking is not
> performed.
> 
> The need to check for overflow means that this operation is typically
> compiled into a compare-exchange loop. For use cases that require a
> direct atomic addition, see the `wrappingAdd` operation: it avoids the
> loop, but in exchange it allows silent wraps on overflow.

---

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