1/* $NetBSD: ffs.S,v 1.5 2003/04/05 23:08:52 bjh21 Exp $ */
2/*
3 * Copyright (c) 2001 Christopher Gilbert
4 * All rights reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 * 1. Redistributions of source code must retain the above copyright
10 * notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
14 * 3. The name of the company nor the name of the author may be used to
15 * endorse or promote products derived from this software without specific
16 * prior written permission.
17 *
18 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
19 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
20 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
21 * IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
22 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
23 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
24 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
25 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
26 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
27 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
28 * SUCH DAMAGE.
29 */
30
31#include <machine/asm.h>
32
| 1/* $NetBSD: ffs.S,v 1.5 2003/04/05 23:08:52 bjh21 Exp $ */
2/*
3 * Copyright (c) 2001 Christopher Gilbert
4 * All rights reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 * 1. Redistributions of source code must retain the above copyright
10 * notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
14 * 3. The name of the company nor the name of the author may be used to
15 * endorse or promote products derived from this software without specific
16 * prior written permission.
17 *
18 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
19 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
20 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
21 * IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
22 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
23 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
24 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
25 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
26 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
27 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
28 * SUCH DAMAGE.
29 */
30
31#include <machine/asm.h>
32
|
34
35/*
36 * ffs - find first set bit, this algorithm isolates the first set
37 * bit, then multiplies the number by 0x0450fbaf which leaves the top
38 * 6 bits as an index into the table. This algorithm should be a win
39 * over the checking each bit in turn as per the C compiled version.
40 *
41 * under ARMv5 there's an instruction called CLZ (count leading Zero's) that
42 * could be used
43 *
44 * This is the ffs algorithm devised by d.seal and posted to comp.sys.arm on
45 * 16 Feb 1994.
46 */
47
48ENTRY(ffs)
49 /* Standard trick to isolate bottom bit in r0 or 0 if r0 = 0 on entry */
50 rsb r1, r0, #0
51 ands r0, r0, r1
52#ifndef _ARM_ARCH_5
53 /*
54 * now r0 has at most one set bit, call this X
55 * if X = 0, all further instructions are skipped
56 */
57 adrne r2, .L_ffs_table
58 orrne r0, r0, r0, lsl #4 /* r0 = X * 0x11 */
59 orrne r0, r0, r0, lsl #6 /* r0 = X * 0x451 */
60 rsbne r0, r0, r0, lsl #16 /* r0 = X * 0x0450fbaf */
61
62 /* now lookup in table indexed on top 6 bits of r0 */
63 ldrneb r0, [ r2, r0, lsr #26 ]
64
65 RET
66.text;
67.type .L_ffs_table, _ASM_TYPE_OBJECT;
68.L_ffs_table:
69/* 0 1 2 3 4 5 6 7 */
70 .byte 0, 1, 2, 13, 3, 7, 0, 14 /* 0- 7 */
71 .byte 4, 0, 8, 0, 0, 0, 0, 15 /* 8-15 */
72 .byte 11, 5, 0, 0, 9, 0, 0, 26 /* 16-23 */
73 .byte 0, 0, 0, 0, 0, 22, 28, 16 /* 24-31 */
74 .byte 32, 12, 6, 0, 0, 0, 0, 0 /* 32-39 */
75 .byte 10, 0, 0, 25, 0, 0, 21, 27 /* 40-47 */
76 .byte 31, 0, 0, 0, 0, 24, 0, 20 /* 48-55 */
77 .byte 30, 0, 23, 19, 29, 18, 17, 0 /* 56-63 */
78#else
79 clzne r0, r0
80 rsbne r0, r0, #32
81 RET
82#endif
| 34
35/*
36 * ffs - find first set bit, this algorithm isolates the first set
37 * bit, then multiplies the number by 0x0450fbaf which leaves the top
38 * 6 bits as an index into the table. This algorithm should be a win
39 * over the checking each bit in turn as per the C compiled version.
40 *
41 * under ARMv5 there's an instruction called CLZ (count leading Zero's) that
42 * could be used
43 *
44 * This is the ffs algorithm devised by d.seal and posted to comp.sys.arm on
45 * 16 Feb 1994.
46 */
47
48ENTRY(ffs)
49 /* Standard trick to isolate bottom bit in r0 or 0 if r0 = 0 on entry */
50 rsb r1, r0, #0
51 ands r0, r0, r1
52#ifndef _ARM_ARCH_5
53 /*
54 * now r0 has at most one set bit, call this X
55 * if X = 0, all further instructions are skipped
56 */
57 adrne r2, .L_ffs_table
58 orrne r0, r0, r0, lsl #4 /* r0 = X * 0x11 */
59 orrne r0, r0, r0, lsl #6 /* r0 = X * 0x451 */
60 rsbne r0, r0, r0, lsl #16 /* r0 = X * 0x0450fbaf */
61
62 /* now lookup in table indexed on top 6 bits of r0 */
63 ldrneb r0, [ r2, r0, lsr #26 ]
64
65 RET
66.text;
67.type .L_ffs_table, _ASM_TYPE_OBJECT;
68.L_ffs_table:
69/* 0 1 2 3 4 5 6 7 */
70 .byte 0, 1, 2, 13, 3, 7, 0, 14 /* 0- 7 */
71 .byte 4, 0, 8, 0, 0, 0, 0, 15 /* 8-15 */
72 .byte 11, 5, 0, 0, 9, 0, 0, 26 /* 16-23 */
73 .byte 0, 0, 0, 0, 0, 22, 28, 16 /* 24-31 */
74 .byte 32, 12, 6, 0, 0, 0, 0, 0 /* 32-39 */
75 .byte 10, 0, 0, 25, 0, 0, 21, 27 /* 40-47 */
76 .byte 31, 0, 0, 0, 0, 24, 0, 20 /* 48-55 */
77 .byte 30, 0, 23, 19, 29, 18, 17, 0 /* 56-63 */
78#else
79 clzne r0, r0
80 rsbne r0, r0, #32
81 RET
82#endif
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