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.\" $OpenBSD: atomic_cas_uint.9,v 1.1 2014/02/03 07:03:04 dlg Exp $
.\"
.\" Copyright (c) 2014 David Gwynne <dlg@openbsd.org>
.\" All rights reserved.
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.Dd $Mdocdate: February 3 2014 $
.Dt ATOMIC_CAS 9
.Os
.Sh NAME
.Nm atomic_cas_uint ,
.Nm atomic_cas_ulong ,
.Nm atomic_cas_ptr
.Nd atomic compare-and-swap operations
.Sh SYNOPSIS
.In sys/atomic.h
.Ft unsigned int
.Fn atomic_cas_uint "volatile unsigned int *p" "unsigned int expected" "unsigned int new"
.Ft unsigned long
.Fn atomic_cas_ulong "volatile unsigned long *p" "unsigned long expected" "unsigned long new"
.Ft void *
.Fn atomic_cas_ptr "volatile void **p" "void *expected" "void *new"
.Sh 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.
.Pp
The value referenced by the pointer
.Fa p
is compared against
.Fa expected .
If these values are equal then
.Fa new
replaces the value stored at
.Fa p .
.Sh RETURN VALUES
These functions return the value at
.Fa p
as it was before the attempt to swap it.
.Sh SEE ALSO
.Xr atomic 9 ,
.Xr atomic_swap_uint 9
.Sh HISTORY
The atomic_cas functions first appeared in
.Ox 5.5 .
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