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      1 /*	$NetBSD: ffs.S,v 1.3 2011/07/04 12:18:05 mrg Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2002 The NetBSD Foundation, Inc.
      5  * All rights reserved.
      6  *
      7  * This code is derived from software contributed to The NetBSD Foundation
      8  * by ITOH Yasufumi.
      9  *
     10  * Redistribution and use in source and binary forms, with or without
     11  * modification, are permitted provided that the following conditions
     12  * are met:
     13  * 1. Redistributions of source code must retain the above copyright
     14  *    notice, this list of conditions and the following disclaimer.
     15  * 2. Redistributions in binary form must reproduce the above copyright
     16  *    notice, this list of conditions and the following disclaimer in the
     17  *    documentation and/or other materials provided with the distribution.
     18  *
     19  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     20  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     21  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     22  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     23  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     24  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     25  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     26  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     27  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     28  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     29  * POSSIBILITY OF SUCH DAMAGE.
     30  */
     31 
     32 #include <machine/asm.h>
     33 
     34 #if defined(LIBC_SCCS) && !defined(lint)
     35 	RCSID("$NetBSD: ffs.S,v 1.3 2011/07/04 12:18:05 mrg Exp $")
     36 #endif
     37 
     38 /*
     39  * ffs - find first bit set
     40  *
     41  * This code makes use of ``test 8bit'' and ``shift 8bit'' instructions.
     42  * The remaining 8bit is tested in every 2bit.
     43  */
     44 
     45 WEAK_ALIAS(__ffssi2,ffs)
     46 ENTRY(ffs)
     47 	mov	r4,r0		! using r0 specific instructions
     48 	tst	#0xff,r0
     49 	bf/s	L8bit
     50 	mov	#0+1,r1		! ret = 1..8
     51 
     52 	tst	r0,r0		! ffs(0) is 0
     53 	bt	Lzero		! testing here to accelerate ret=1..8 cases
     54 
     55 	shlr8	r0
     56 	tst	#0xff,r0
     57 	bf/s	L8bit
     58 	mov	#8+1,r1		! ret = 9..16
     59 
     60 	shlr8	r0
     61 	tst	#0xff,r0
     62 	bf/s	L8bit
     63 	mov	#16+1,r1	! ret = 17..24
     64 
     65 	shlr8	r0
     66 	mov	#24+1,r1	! ret = 25..32
     67 
     68 L8bit:
     69 	tst	#0x0f,r0
     70 	bt	4f
     71 
     72 	tst	#0x03,r0
     73 	bt	2f
     74 	tst	#0x01,r0	! not bit 0 -> T
     75 	mov	#0,r0
     76 	rts
     77 	 addc	r1,r0		! 0 + r1 + T -> r0
     78 
     79 2:	tst	#0x04,r0
     80 	mov	#2,r0
     81 	rts
     82 	 addc	r1,r0
     83 
     84 4:	tst	#0x30,r0
     85 	bt	6f
     86 	tst	#0x10,r0
     87 	mov	#4,r0
     88 	rts
     89 	 addc	r1,r0
     90 
     91 6:	tst	#0x40,r0
     92 	mov	#6,r0
     93 	rts
     94 	 addc	r1,r0
     95 
     96 Lzero:	rts
     97 	 nop
     98