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Use excb before and after the mt_fpcr/mf_fpcr instructions as specified
in the alpha ARM 4.7.8.1 (Accessing the FPCR):

	Because Alpha floating-point hardware can overlap the execution of
	a number of floating-point instructions, accessing the FPCR must
	be synchronized with other floating-point instructions. An EXCB
	instruction must be issued both prior to and after accessing the
	FPCR to ensure that the FPCR access is synchronized with the
	execution of previous and subsequent floating-point instructions;
	otherwise synchronization is not ensured.

Use unions to convert between double and uint64_t to avoid casting.

/* $NetBSD: fpsetround.c,v 1.11 2011/06/12 05:44:36 matt Exp $ */

/*
 * Copyright (c) 1995 Christopher G. Demetriou
 * All rights reserved.
 * 
 * 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.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *          This product includes software developed for the
 *          NetBSD Project.  See http://www.NetBSD.org/ for
 *          information about NetBSD.
 * 4. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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.
 * 
 * <<Id: LICENSE,v 1.2 2000/06/14 15:57:33 cgd Exp>>
 */

#include <sys/cdefs.h>
#if defined(LIBC_SCCS) && !defined(lint)
__RCSID("$NetBSD: fpsetround.c,v 1.11 2011/06/12 05:44:36 matt Exp $");
#endif /* LIBC_SCCS and not lint */

#include "namespace.h"

#include <sys/types.h>
#include <ieeefp.h>

#ifdef __weak_alias
__weak_alias(fpsetround,_fpsetround)
#endif

fp_rnd
fpsetround(fp_rnd rnd_dir)
{
	union {
		double d;
		uint64_t u64;
	} fpcrval;
	fp_rnd old;

	__asm("excb; mf_fpcr %0; excb" : "=f" (fpcrval.d));
	old = (fpcrval.u64 >> 58) & 0x3;

	rnd_dir ^= old;

	fpcrval.u64 ^= (long)rnd_dir << 58;

	__asm("excb; mt_fpcr %0; excb" : : "f" (fpcrval.d));

	return old;
}