1/*	$NetBSD: ffs.S,v 1.2 2008/04/28 20:22:52 martin 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 1.2 2008/04/28 20:22:52 martin 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
45WEAK_ALIAS(__ffssi2,ffs)
46ENTRY(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
68L8bit:
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
792:	tst	#0x04,r0
80	mov	#2,r0
81	rts
82	 addc	r1,r0
83
844:	tst	#0x30,r0
85	bt	6f
86	tst	#0x10,r0
87	mov	#4,r0
88	rts
89	 addc	r1,r0
90
916:	tst	#0x40,r0
92	mov	#6,r0
93	rts
94	 addc	r1,r0
95
96Lzero:	rts
97	 nop
98