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/* $OpenBSD: ffs.S,v 1.1 2006/10/10 22:07:10 miod Exp $ */
/* $NetBSD: ffs.S,v 1.1 2005/12/20 19:28:50 christos Exp $ */
/*-
* Copyright (c) 2002 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This code is derived from software contributed to The NetBSD Foundation
* by ITOH Yasufumi.
*
* 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 by the NetBSD
* Foundation, Inc. and its contributors.
* 4. Neither the name of The NetBSD Foundation nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* 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>
/*
* ffs - find first bit set
*
* This code makes use of ``test 8bit'' and ``shift 8bit'' instructions.
* The remaining 8bit is tested in every 2bit.
*/
ENTRY(ffs)
mov r4,r0 ! using r0 specific instructions
tst #0xff,r0
bf/s L8bit
mov #0+1,r1 ! ret = 1..8
tst r0,r0 ! ffs(0) is 0
bt Lzero ! testing here to accelerate ret=1..8 cases
shlr8 r0
tst #0xff,r0
bf/s L8bit
mov #8+1,r1 ! ret = 9..16
shlr8 r0
tst #0xff,r0
bf/s L8bit
mov #16+1,r1 ! ret = 17..24
shlr8 r0
mov #24+1,r1 ! ret = 25..32
L8bit:
tst #0x0f,r0
bt 4f
tst #0x03,r0
bt 2f
tst #0x01,r0 ! not bit 0 -> T
mov #0,r0
rts
addc r1,r0 ! 0 + r1 + T -> r0
2: tst #0x04,r0
mov #2,r0
rts
addc r1,r0
4: tst #0x30,r0
bt 6f
tst #0x10,r0
mov #4,r0
rts
addc r1,r0
6: tst #0x40,r0
mov #6,r0
rts
addc r1,r0
Lzero: rts
nop
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