atomic.h

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/*
 * Copyright (C) 2006  Internet Systems Consortium, Inc. ("ISC")
 *
 * 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 ISC DISCLAIMS ALL WARRANTIES WITH
 * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
 * AND FITNESS.  IN NO EVENT SHALL ISC 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.
 */

/* $Id: atomic.h,v 1.2.2.1 2006/06/21 03:38:32 marka Exp $ */

#ifndef ISC_ATOMIC_H
#define ISC_ATOMIC_H 1

#include <isc/platform.h>
#include <isc/types.h>

#ifdef ISC_PLATFORM_USEGCCASM
/*
 * This routine atomically increments the value stored in 'p' by 'val', and
 * returns the previous value.
 *
 * Open issue: can 'fetchadd' make the code faster for some particular values
 * (e.g., 1 and -1)?
 */
static inline isc_int32_t
isc_atomic_xadd(isc_int32_t *p, isc_int32_t val) {
	isc_int32_t prev, swapped;

	for (prev = *(volatile isc_int32_t *)p; ; prev = swapped) {
		swapped = prev + val;
		__asm__ volatile(
			"mov ar.ccv=%2;"
			"cmpxchg4.acq %0=%4,%3,ar.ccv"
			: "=r" (swapped), "=m" (*p)
			: "r" (prev), "r" (swapped), "m" (*p)
			: "memory");
		if (swapped == prev)
			break;
	}

	return (prev);
}

/*
 * This routine atomically stores the value 'val' in 'p'.
 */
static inline void
isc_atomic_store(isc_int32_t *p, isc_int32_t val) {
	__asm__ volatile(
		"st4.rel %0=%1"
		: "=m" (*p)
		: "r" (val)
		: "memory"
		);
}

/*
 * This routine atomically replaces the value in 'p' with 'val', if the
 * original value is equal to 'cmpval'.  The original value is returned in any
 * case.
 */
static inline isc_int32_t
isc_atomic_cmpxchg(isc_int32_t *p, isc_int32_t cmpval, isc_int32_t val) {
	isc_int32_t ret;

	__asm__ volatile(
		"mov ar.ccv=%2;"
		"cmpxchg4.acq %0=%4,%3,ar.ccv"
		: "=r" (ret), "=m" (*p)
		: "r" (cmpval), "r" (val), "m" (*p)
		: "memory");

	return (ret);
}
#else /* !ISC_PLATFORM_USEGCCASM */

#error "unsupported compiler.  disable atomic ops by --disable-atomic"

#endif
#endif /* ISC_ATOMIC_H */