## NAME

`atomic_cas_uint`

,
`atomic_cas_ulong`

,
`atomic_cas_ptr`

—
atomic compare-and-swap
operations

## SYNOPSIS

```
#include
<sys/atomic.h>
```

`unsigned int`

`atomic_cas_uint`

(`volatile unsigned int
*p`, `unsigned int expected`,
`unsigned int new`);

`unsigned long`

`atomic_cas_ulong`

(`volatile unsigned
long *p`, `unsigned long expected`,
`unsigned long new`);

`void *`

`atomic_cas_ptr`

(`volatile void *p`,
`void *expected`, `void *new`);

## DESCRIPTION

The atomic_cas set of functions provide an interface for atomically performing compare-and-swap operations with respect to interrupts and multiple processors in the system.

The value referenced by the pointer `p` is
compared against `expected`. If these values are equal
then `new` replaces the value stored at
`p`.

## CONTEXT

`atomic_cas_uint`

(),
`atomic_cas_ulong`

(), and
`atomic_cas_ptr`

() can all be called during autoconf,
from process context, or from interrupt context.

## RETURN VALUES

These functions return the value at `p` as it
was before the attempt to swap it.

## SEE ALSO

## HISTORY

The atomic_cas functions first appeared in NetBSD 5.0 and OpenBSD 5.5.