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      1 /*	$NetBSD: atomic_c11_compare_exchange_cas_8.c,v 1.5 2024/01/29 16:09:45 christos Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2007 The NetBSD Foundation, Inc.
      5  * All rights reserved.
      6  *
      7  * This code is derived from software contributed to The NetBSD Foundation
      8  * by Martin Husemann.
      9  *
     10  * Redistribution and use in source and binary forms, with or without
     11  * modification, are permitted provided that the following conditions
     12  * are met:
     13  * 1. Redistributions of source code must retain the above copyright
     14  *    notice, this list of conditions and the following disclaimer.
     15  * 2. Redistributions in binary form must reproduce the above copyright
     16  *    notice, this list of conditions and the following disclaimer in the
     17  *    documentation and/or other materials provided with the distribution.
     18  *
     19  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     20  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     21  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     22  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     23  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     24  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     25  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     26  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     27  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     28  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     29  * POSSIBILITY OF SUCH DAMAGE.
     30  */
     31 
     32 #include "atomic_op_namespace.h"
     33 
     34 #if !defined(_KERNEL) && !defined(_STANDALONE)
     35 #include <stdbool.h>
     36 #endif
     37 #include <sys/atomic.h>
     38 
     39 bool __atomic_compare_exchange_1(volatile void *, void *, uint8_t,
     40     bool, int, int);
     41 
     42 bool
     43 /*ARGSUSED*/
     44 __atomic_compare_exchange_1(volatile void *mem,
     45     void *expected, uint8_t desired,
     46     bool weak, int success, int failure)
     47 {
     48 	uint8_t * const ep = expected;
     49 	const uint8_t old = *ep;
     50 
     51 	/*
     52 	 * Ignore the details (weak, memory model on success and failure)
     53 	 * and just do the cas. If we get here the compiler couldn't
     54 	 * do better and it mostly will not matter at all.
     55 	 */
     56 	const uint8_t prev = atomic_cas_8(mem, old, desired);
     57 	if (prev == old)
     58 		return true;
     59 	*ep = prev;
     60 	return false;
     61 }
     62