1/*	$NetBSD: ffs.S,v 1.1 2005/12/20 19:28:50 christos 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 * 3. All advertising materials mentioning features or use of this software
19 *    must display the following acknowledgement:
20 *	This product includes software developed by the NetBSD
21 *	Foundation, Inc. and its contributors.
22 * 4. Neither the name of The NetBSD Foundation nor the names of its
23 *    contributors may be used to endorse or promote products derived
24 *    from this software without specific prior written permission.
25 *
26 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
27 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
28 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
29 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
30 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
31 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
32 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
33 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
34 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
35 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
36 * POSSIBILITY OF SUCH DAMAGE.
37 */
38
39#include <machine/asm.h>
40
41#if defined(LIBC_SCCS) && !defined(lint)
42	RCSID("$NetBSD: ffs.S,v 1.1 2005/12/20 19:28:50 christos Exp $")
43#endif
44
45/*
46 * ffs - find first bit set
47 *
48 * This code makes use of ``test 8bit'' and ``shift 8bit'' instructions.
49 * The remaining 8bit is tested in every 2bit.
50 */
51
52ENTRY(ffs)
53	mov	r4,r0		! using r0 specific instructions
54	tst	#0xff,r0
55	bf/s	L8bit
56	mov	#0+1,r1		! ret = 1..8
57
58	tst	r0,r0		! ffs(0) is 0
59	bt	Lzero		! testing here to accelerate ret=1..8 cases
60
61	shlr8	r0
62	tst	#0xff,r0
63	bf/s	L8bit
64	mov	#8+1,r1		! ret = 9..16
65
66	shlr8	r0
67	tst	#0xff,r0
68	bf/s	L8bit
69	mov	#16+1,r1	! ret = 17..24
70
71	shlr8	r0
72	mov	#24+1,r1	! ret = 25..32
73
74L8bit:
75	tst	#0x0f,r0
76	bt	4f
77
78	tst	#0x03,r0
79	bt	2f
80	tst	#0x01,r0	! not bit 0 -> T
81	mov	#0,r0
82	rts
83	 addc	r1,r0		! 0 + r1 + T -> r0
84
852:	tst	#0x04,r0
86	mov	#2,r0
87	rts
88	 addc	r1,r0
89
904:	tst	#0x30,r0
91	bt	6f
92	tst	#0x10,r0
93	mov	#4,r0
94	rts
95	 addc	r1,r0
96
976:	tst	#0x40,r0
98	mov	#6,r0
99	rts
100	 addc	r1,r0
101
102Lzero:	rts
103	 nop
104