xref: /freebsd/lib/libc/string/ffs.c (revision dc36d6f9bb1753f3808552f3afd30eda9a7b206a)
158f0484fSRodney W. Grimes /*-
28a16b7a1SPedro F. Giffuni  * SPDX-License-Identifier: BSD-3-Clause
38a16b7a1SPedro F. Giffuni  *
458f0484fSRodney W. Grimes  * Copyright (c) 1990, 1993
558f0484fSRodney W. Grimes  *	The Regents of the University of California.  All rights reserved.
6ee8b0c43SRobert Clausecker  * Copyright (c) 2023 The FreeBSD Foundation
7ee8b0c43SRobert Clausecker  *
8ee8b0c43SRobert Clausecker  * Portions of this software were developed by Robert Clausecker
9ee8b0c43SRobert Clausecker  * <fuz@FreeBSD.org> under sponsorship from the FreeBSD Foundation.
1058f0484fSRodney W. Grimes  *
1158f0484fSRodney W. Grimes  * Redistribution and use in source and binary forms, with or without
1258f0484fSRodney W. Grimes  * modification, are permitted provided that the following conditions
1358f0484fSRodney W. Grimes  * are met:
1458f0484fSRodney W. Grimes  * 1. Redistributions of source code must retain the above copyright
1558f0484fSRodney W. Grimes  *    notice, this list of conditions and the following disclaimer.
1658f0484fSRodney W. Grimes  * 2. Redistributions in binary form must reproduce the above copyright
1758f0484fSRodney W. Grimes  *    notice, this list of conditions and the following disclaimer in the
1858f0484fSRodney W. Grimes  *    documentation and/or other materials provided with the distribution.
193fb3b97cSEd Maste  * 3. Neither the name of the University nor the names of its contributors
2058f0484fSRodney W. Grimes  *    may be used to endorse or promote products derived from this software
2158f0484fSRodney W. Grimes  *    without specific prior written permission.
2258f0484fSRodney W. Grimes  *
2358f0484fSRodney W. Grimes  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
2458f0484fSRodney W. Grimes  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
2558f0484fSRodney W. Grimes  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
2658f0484fSRodney W. Grimes  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
2758f0484fSRodney W. Grimes  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
2858f0484fSRodney W. Grimes  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
2958f0484fSRodney W. Grimes  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
3058f0484fSRodney W. Grimes  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
3158f0484fSRodney W. Grimes  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
3258f0484fSRodney W. Grimes  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
3358f0484fSRodney W. Grimes  * SUCH DAMAGE.
3458f0484fSRodney W. Grimes  */
3558f0484fSRodney W. Grimes 
36554331bbSRobert Drehmel #include <strings.h>
3758f0484fSRodney W. Grimes 
3858f0484fSRodney W. Grimes /*
39f434fe12SDag-Erling Smørgrav  * Find First Set bit
4058f0484fSRodney W. Grimes  */
4158f0484fSRodney W. Grimes int
ffs(int mask)42554331bbSRobert Drehmel ffs(int mask)
4358f0484fSRodney W. Grimes {
44*3f5788e0SRobert Clausecker 	return (mask == 0 ? 0 : __builtin_ctz(mask) + 1);
4558f0484fSRodney W. Grimes }
46