2012-11-15 12:06:41 +01:00
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/* $NetBSD: ffs.S,v 1.3 2011/07/04 12:18:05 mrg Exp $ */
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2011-02-14 20:36:03 +01:00
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/*-
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* Copyright (c) 2002 The NetBSD Foundation, Inc.
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* All rights reserved.
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*
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* This code is derived from software contributed to The NetBSD Foundation
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* by ITOH Yasufumi.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*/
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#include <machine/asm.h>
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#if defined(LIBC_SCCS) && !defined(lint)
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2012-11-15 12:06:41 +01:00
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RCSID("$NetBSD: ffs.S,v 1.3 2011/07/04 12:18:05 mrg Exp $")
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2011-02-14 20:36:03 +01:00
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#endif
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/*
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* ffs - find first bit set
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*
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* This code makes use of ``test 8bit'' and ``shift 8bit'' instructions.
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* The remaining 8bit is tested in every 2bit.
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*/
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2012-11-15 12:06:41 +01:00
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WEAK_ALIAS(__ffssi2,ffs)
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2011-02-14 20:36:03 +01:00
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ENTRY(ffs)
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mov r4,r0 ! using r0 specific instructions
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tst #0xff,r0
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bf/s L8bit
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mov #0+1,r1 ! ret = 1..8
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tst r0,r0 ! ffs(0) is 0
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bt Lzero ! testing here to accelerate ret=1..8 cases
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shlr8 r0
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tst #0xff,r0
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bf/s L8bit
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mov #8+1,r1 ! ret = 9..16
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shlr8 r0
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tst #0xff,r0
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bf/s L8bit
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mov #16+1,r1 ! ret = 17..24
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shlr8 r0
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mov #24+1,r1 ! ret = 25..32
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L8bit:
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tst #0x0f,r0
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bt 4f
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tst #0x03,r0
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bt 2f
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tst #0x01,r0 ! not bit 0 -> T
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mov #0,r0
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rts
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addc r1,r0 ! 0 + r1 + T -> r0
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2: tst #0x04,r0
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mov #2,r0
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rts
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addc r1,r0
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4: tst #0x30,r0
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bt 6f
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tst #0x10,r0
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mov #4,r0
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rts
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addc r1,r0
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6: tst #0x40,r0
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mov #6,r0
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rts
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addc r1,r0
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Lzero: rts
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nop
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