minix/common/lib/libc/arch/arm/atomic/atomic_cas_8.S

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/* $NetBSD: atomic_cas_8.S,v 1.1 2008/11/18 15:22:56 matt Exp $ */
/*-
* Copyright (c) 2008 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This code is derived from software contributed to The NetBSD Foundation
* by Matt Thomas <matt@3am-software.com>
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
#include <machine/asm.h>
RCSID("$NetBSD: atomic_cas_8.S,v 1.1 2008/11/18 15:22:56 matt Exp $")
ENTRY(atomic_cas_8)
XPUSH {r4,r5} /* we need some more registers */
and r3, r0, #3 /* which byte do we replace? */
#if __ARMEB__
eor r3, r3, #3 /* bytes are reversed on BE */
#endif
mov r3, r3, lsl #3 /* multiply by 8 */
mov r1, r1, lsl r3 /* mov old value to correct byte */
eor r2, r1, r2, lsl r3 /* move new value to correct byte */
/* eor r2, r2, r1 */ /* new value is now (old ^ new) */
mov r5, #0xff /* load mask */
mov r5, r5, lsl r3 /* and move to correct byte */
mov r3, r0 /* move pointer */
1: ldrex r4, [r3] /* load 32bit value */
and r0, r4, r5 /* clear other bytes */
teq r0, r1 /* equal old value? */
bne 2f /* nope, bail. */
eor r4, r4, r2 /* new == old ^ (old ^ new) */
strex ip, r4, [r3] /* attempt to store it */
cmp ip, #0 /* succeed? */
bne 1b /* nope, try again. */
2: XPOP {r4,r5} /* don't need these anymore */
and r1, r3, #3
#if __ARMEB__
eor r1, r1, #3
#endif
mov r0, r0, lsr r1 /* shift it back to lsb byte */
RET