Annotation of sys/lib/libkern/arch/sh/ffs.S, Revision 1.1.1.1
1.1 nbrk 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:
52: ENTRY(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:
74: L8bit:
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:
85: 2: tst #0x04,r0
86: mov #2,r0
87: rts
88: addc r1,r0
89:
90: 4: tst #0x30,r0
91: bt 6f
92: tst #0x10,r0
93: mov #4,r0
94: rts
95: addc r1,r0
96:
97: 6: tst #0x40,r0
98: mov #6,r0
99: rts
100: addc r1,r0
101:
102: Lzero: rts
103: nop
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