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
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