ffs.S revision 50476 
1/*
2 * Copyright (c) 1993 Winning Strategies, Inc.
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in the
12 *    documentation and/or other materials provided with the distribution.
13 * 3. All advertising materials mentioning features or use of this software
14 *    must display the following acknowledgement:
15 *      This product includes software developed by Winning Strategies, Inc.
16 * 4. The name of the author may not be used to endorse or promote products
17 *    derived from this software withough specific prior written permission
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
20 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
21 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
22 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
23 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
24 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
25 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
26 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
27 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
28 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
29 *
30 * $FreeBSD: head/lib/libc/i386/string/ffs.S 50476 1999-08-28 00:22:10Z peter $
31 */
32
33#if defined(LIBC_RCS) && !defined(lint)
34	.text
35        .asciz "$FreeBSD: head/lib/libc/i386/string/ffs.S 50476 1999-08-28 00:22:10Z peter $"
36#endif /* LIBC_RCS and not lint */
37
38#include "DEFS.h"
39
40/*
41 * ffs(value)
42 *	finds the first bit set in value and returns the index of
43 *	that bit.  Bits are numbered starting from 1, starting at the
44 *	rightmost bit.  A return value of 0 means that the argument
45 *	was zero.
46 *
47 * Written by:
48 *	J.T. Conklin (jtc@wimsey.com), Winning Strategies, Inc.
49 */
50
51ENTRY(ffs)
52	bsfl	4(%esp),%eax
53	jz	L1	 		/* ZF is set if all bits are 0 */
54	incl	%eax			/* bits numbered from 1, not 0 */
55	ret
56
57	.align 2
58L1:	xorl	%eax,%eax		/* clear result */
59	ret
60